Radiation Dose Reduction in Paranasal Sinus CT Using Model-Based Iterative Reconstruction

BACKGROUND AND PURPOSE:CT performed with Veo model-based iterative reconstruction has shown the potential for radiation-dose reduction. This study sought to determine whether Veo could reduce noise and improve the image quality of low-dose sinus CT.MATERIALS AND METHODS:Twenty patients consented to participate and underwent low- and standard-dose sinus CT on the same day. Standard-dose CT was created with filtered back-projection (120 kV[peak], 210 mA, 0.4-second rotation, and 0.531 pitch). For low-dose CT, mA was decreased to 20 (the remaining parameters were unchanged), and images were generated with filtered back-projection and Veo. Standard- and low-dose datasets were reconstructed by using bone and soft-tissue algorithms, while the low-dose Veo reconstruction only had a standard kernel. Two blinded neuroradiologists independently evaluated the image quality of multiple osseous and soft-tissue craniofacial structures. Image noise was measured by using multiple regions of interest.RESULTS:Eight women and 12 men (mean age, 63.3 years) participated. Volume CT dose indices were 2.9 mGy (low dose) and 31.6 mGy (standard dose), and mean dose-length products were 37.4 mGy-cm (low dose) and 406.1 mGy-cm (standard dose). Of all the imaging series, low-dose Veo demonstrated the least noise (P < .001). Compared with filtered back-projection low-dose CT using soft-tissue and bone algorithms, Veo had the best soft-tissue image quality but the poorest bone image quality (P < .001).CONCLUSIONS:Veo significantly reduces noise in low-dose sinus CT. Although this reduction improves soft-tissue evaluation, thin bone becomes less distinct.

A number of radiation dose-reduction strategies have been successfully used for paranasal sinus CT. Because radiation is unavoidably transmitted to the lens of the eye, orbital bismuth shielding has been used to reduce lens radiation exposure with minimal impact on image quality.^1,2 Greater attention has been directed toward adjusting CT parameters, most commonly through the reduction of milliampere-second (mAs) (tube current time product), to allow reduced radiation exposure while maintaining acceptable image quality.^3–13 Recently, high-pitch dual source multidetector CT systems have shown promise of even greater dose reduction.^14,15 Nevertheless, because of progressively decreasing signal-to-noise, a threshold for tube output is invariably reached, below which imaging becomes unacceptable.With the large computational capacities now available on normal workstations, iterative reconstruction techniques have emerged in CT as a viable alternative to the standard algorithm of filtered back-projection. Through increased complexity with more precise modeling of the acquisition process and the incorporation of various physical models, image quality can be maintained even at progressively lower radiation doses.¹⁶ Indeed, one such technique known as iterative reconstruction in image space (IRIS; Siemens, Erlangen, Germany) allows significant radiation-dose reduction in sinus CT without compromising the image quality.¹⁷ More recently, sinogram-affirmed iterative reconstruction (SAFIRE; Siemens) demonstrated effective noise reduction in sinus CT at the expense of some image quality degradation.¹⁸ Unfortunately, because of the proprietary and vendor-specific nature of the iterative reconstruction techniques, results cannot be directly extrapolated across different CT platforms. As a result, the objective of this study was to compare low-radiation-dose sinus CT processed with Veo model-based iterative reconstruction (GE Healthcare, Milwaukee, Wisconsin) with standard and low-dose sinus CT generated with filtered back-projection through the evaluation of image noise and diagnostic image quality in 20 patients.     

Advanced Modeled Iterative Reconstruction in Low-Tube-Voltage Contrast-Enhanced Neck CT: Evaluation of Objective and Subjective Image Quality

BACKGROUND AND PURPOSE:Dose-saving techniques in neck CT cause increased image noise that can be counteracted by iterative reconstruction. Our aim was to evaluate the image quality of advanced modeled iterative reconstruction (ADMIRE) in contrast-enhanced low-tube-voltage neck CT.MATERIALS AND METHODS:Sixty-one patients underwent 90-kV(peak) neck CT by using third-generation 192-section dual-source CT. Image series were reconstructed with standard filtered back-projection and ADMIRE strength levels 1, 3, and 5. Attenuation and noise of the sternocleidomastoid muscle, internal jugular vein, submandibular gland, tongue, subscapularis muscle, and cervical fat were measured. Signal-to-noise and contrast-to-noise ratios were calculated. Two radiologists assessed image noise, image contrast, delineation of smaller structures, and overall diagnostic acceptability. Interobserver agreement was calculated.RESULTS:Image noise was significantly reduced by using ADMIRE compared with filtered back-projection with the lowest noise observed in ADMIRE 5 (filtered back-projection, 9.4 ± 2.4 Hounsfield units [HU]; ADMIRE 1, 8.3 ± 2.8 HU; ADMIRE 3, 6.7 ± 2.0 HU; ADMIRE 5, 5.4 ± 1.7 HU; all, P < .001). Sternocleidomastoid SNR and internal jugular vein–sternocleidomastoid contrast-to-noise ratios were significantly higher for ADMIRE with the best results in ADMIRE 5 (all, P < .001). Subjective image quality and image contrast of ADMIRE 3 and 5 were consistently rated better than those for filtered back-projection and ADMIRE 1 (all, P < .001). Image noise was rated highest for ADMIRE 5 (all, P < .005). Delineation of smaller structures was voted higher in all ADMIRE strength levels compared with filtered back-projection (P < .001). Global interobserver agreement was good (0.75).CONCLUSIONS:Contrast-enhanced 90-kVp neck CT is feasible, and ADMIRE 5 shows superior objective image quality compared with filtered back-projection. ADMIRE 3 and 5 show the best subjective image quality.

Contrast-enhanced CT is a well-established initial cross-sectional imaging technique for examination of the head and neck region.^1–3 Several strategies have been developed for both radiation dose reduction and improvement of image quality. These typically involve adjusting CT acquisition parameters such as tube voltage, tube current, tube rotation time, pitch, and collimation to the patient body and examined body region.^4–6 The interaction of these parameters is complex, and manual adjustments may result in nondiagnostic images. Thus, commercially available techniques, including tube current modulation,⁷ automatic exposure control,^8,9 automated tube voltage adaptation,^10,11 iterative reconstruction,^12–15 and selective in-plane shielding (thyroid, eye lens, breast, and gonads),¹⁶ have been introduced to support the radiologic technologist, physicist, and radiologist team in developing appropriate CT protocols.Reduced tube voltage can increase contrast-to-noise ratio (CNR) of iodine enhancing soft-tissue structures, while the radiation dose is substantially reduced.⁴ The drawback of an increased image noise in low-tube-voltage examinations can be counteracted by iterative reconstruction, which reduces image noise compared with filtered back-projection (FBP).^12,14 Recently introduced advanced modeled iterative reconstruction (ADMIRE) performs detailed modeling in the projection data domain, resulting in less noise and improved artifact suppression.¹⁷ ADMIRE includes a local signal-to-noise relationship analysis and decomposes the image data into information and noise.¹⁸ Further technical details have been described in recent studies.^14,17,18 Thus, neck CT may potentially be performed with a reduced tube voltage and therefore lower radiation dose without impairing image quality.The purpose of our study was to evaluate the impact of ADMIRE on image quality in low-tube-voltage contrast-enhanced neck CT compared with FBP on a 192-section third-generation dual-source CT (DSCT).     

Impact of Model-Based Iterative Reconstruction on Image Quality of Contrast-Enhanced Neck CT

BACKGROUND AND PURPOSE:Improved image quality is clinically desired for contrast-enhanced CT of the neck. We compared 30% adaptive statistical iterative reconstruction and model-based iterative reconstruction algorithms for the assessment of image quality of contrast-enhanced CT of the neck.MATERIALS AND METHODS:Neck contrast-enhanced CT data from 64 consecutive patients were reconstructed retrospectively by using 30% adaptive statistical iterative reconstruction and model-based iterative reconstruction. Objective image quality was assessed by comparing SNR, contrast-to-noise ratio, and background noise at levels 1 (mandible) and 2 (superior mediastinum). Two independent blinded readers subjectively graded the image quality on a scale of 1–5, (grade 5 = excellent image quality without artifacts and grade 1 = nondiagnostic image quality with significant artifacts). The percentage of agreement and disagreement between the 2 readers was assessed.RESULTS:Compared with 30% adaptive statistical iterative reconstruction, model-based iterative reconstruction significantly improved the SNR and contrast-to-noise ratio at levels 1 and 2. Model-based iterative reconstruction also decreased background noise at level 1 (P = .016), though there was no difference at level 2 (P = .61). Model-based iterative reconstruction was scored higher than 30% adaptive statistical iterative reconstruction by both reviewers at the nasopharynx (P < .001) and oropharynx (P < .001) and for overall image quality (P < .001) and was scored lower at the vocal cords (P < .001) and sternoclavicular junction (P < .001), due to artifacts related to thyroid shielding that were specific for model-based iterative reconstruction.CONCLUSIONS:Model-based iterative reconstruction offers improved subjective and objective image quality as evidenced by a higher SNR and contrast-to-noise ratio and lower background noise within the same dataset for contrast-enhanced neck CT. Model-based iterative reconstruction has the potential to reduce the radiation dose while maintaining the image quality, with a minor downside being prominent artifacts related to thyroid shield use on model-based iterative reconstruction.

Since the introduction of CT for medical imaging in the early 1970s, there has been tremendous advancement in overall image quality with concomitant shortening of requisite scan times. Additional major effort has been undertaken to reduce the radiation dose to improve patient safety while maintaining image quality. In particular, image reconstruction algorithms have evolved from the traditional analytic algorithms such as filtered back-projection (FBP) to newer iterative reconstruction methods such as adaptive statistical iterative reconstruction (ASiR; GE Healthcare, Milwaukee, Wisconsin) and most recently model-based iterative reconstruction (MBIR; GE Healthcare), which models system noise statistics and optics.Both phantom and clinical studies have confirmed that the application of the MBIR algorithm results in an improved contrast-to-noise ratio (CNR), lower background noise (BN),^1–4 and reduction of helical conebeam artifacts.^2,4 Clinical studies in the delineation of arteries in the posterior fossa on 3D brain CT angiography,¹ improved liver lesion detection,^3,5 general evaluation of abdominopelvic CT,² and pediatric chest CT⁶ all support the use of MBIR, with or without radiation-dose reduction. In this study, we compared objective and subjective image quality in neck CT images reconstructed with 2 different iterative reconstruction algorithms (MBIR versus 30% adaptive statistical iterative reconstruction [ASiR30]) by using the same raw dataset.     

Pilot Study of Radiation Dose Reduction for Pediatric Head CT in Evaluation of Ventricular Size

BACKGROUND AND PURPOSE:CT is a ubiquitous, efficient, and cost-effective method to evaluate pediatric ventricular size, particularly in patients with CSF shunt diversion who often need emergent imaging. We therefore sought to determine the minimum dose output or CT dose index required to produce clinically acceptable examinations.MATERIALS AND METHODS:Using a validated noise insertion method and CT projection data from 22 patients, standard pediatric head CT images were reconstructed with weighted filtered back-projection and sinogram-affirmed iterative reconstruction corresponding to routine, 25%, and 10% dose. Reconstructed images were then evaluated by 3 neuroradiologists (blinded to dose and reconstruction method) for ventricular size, diagnostic confidence, image quality, evidence of hemorrhage, and shunt tip location, and compared with the reference standard.RESULTS:There was no significant difference in the ventricular size ranking, and the sensitivity for moderate to severe hydrocephalus was 100%. There was no significant difference between the full-dose level and the ventricular size rankings at the 25% or the 10% dose level for either reconstruction kernel (P > .979). Diagnostic confidence was maintained across doses and kernel. Hemorrhage was more difficult to identify as image quality degraded as dose decreased but was still seen in a majority of cases. Shunts were identified by all readers across all doses and reconstruction methods.CONCLUSIONS:CT images having dose reductions of 90% relative to routine head CT examinations provide acceptable image quality to address the specific clinical task of evaluating ventricular size.

Before the advent of ventricular CSF shunt devices for the treatment of hydrocephalus, patients had a poor prognosis with a very high mortality rate. In 1949, Nulsen and Spitz¹ were the first to prove the efficacy of placing a shunt with a 1-way valve into the venous system of a patient with hydrocephalus to free outflow of CSF into the venous system. The eventual introduction of the Spitz-Holter valve in 1956 made ventricular shunting the standard treatment for hydrocephalus.² Since then, significant technical advancements in CSF diversion devices have continued; however, device complications remain fairly common even today. One study estimated that an episode of ventricular shunt failure will occur in 85% of patients within 15 years of device insertion³ with 30%–40% of ventricular shunts failing after the first year of insertion.⁴ Kim et al⁵ reported a ventricular shunt mortality rate of 2.2%. The clinical diagnosis of shunt malfunction is further complicated by nonspecific clinical signs, which can be attributed to other common pediatric ailments.^5,6CT evaluation of ventricular size, in conjunction with clinical symptoms, is the primary means of assessing ventricular CSF shunt failure/malfunction in pediatric patients with closed fontanelles.⁵ However, concerns were expressed regarding the use of CT in children,⁷ primarily because they are more sensitive than adults for some cancers, one of which is radiation-induced brain tumor.⁸ In some cases, these concerns have prevented judicious use of CT imaging.⁹Rapid sequence MR imaging may also be used for evaluation of ventricular size; however, it is not routinely available at large medical centers during off hours, or at small hospitals that do not have MR imaging units. In addition, MR imaging is more time consuming and costly, sometimes requires sedation of young children, and is associated with rare but existing safety risks associated with strong magnetic fields and radiofrequency electromagnetic emissions.^10–12Shunted pediatric patients will require episodic imaging throughout the life of a shunt to ensure proper functionality, and given the wide availability of CT across our large (and often rural) health care network, CT is the principal imaging technique used. However, repeated use of CT in children has recently come into question, with some providers advocating use of MR imaging, despite its associated limitations, because MR imaging does not use ionizing radiation. To allay concerns regarding radiation, we have initiated educational programs for providers and patients that put the very small potential risk associated with a CT examination into proper perspective. In addition, our practice carefully evaluates our scanning protocols to use the lowest doses of radiation necessary to answer the specific diagnostic question.Because assessment of ventricular size does not require the same level of image quality as a routine head CT examination, we hypothesized that the radiation dose could be greatly reduced for this diagnostic task without compromising diagnostic accuracy. Therefore, the purpose of this specific work was to determine the minimum radiation dose required to produce clinically acceptable head CT examinations for the evaluation of ventricular shunt malfunction. As part of this evaluation, we also examined whether the use of newer image reconstruction algorithms designed to facilitate dose reduction, commonly referred to as iterative reconstruction, were required for accurate diagnoses.^11,13     

Influence of Ultra-Low-Dose and Iterative Reconstructions on the Visualization of Orbital Soft Tissues on Maxillofacial CT

BACKGROUND AND PURPOSE:Dose reduction on CT scans for surgical planning and postoperative evaluation of midface and orbital fractures is an important concern. The purpose of this study was to evaluate the variability of various low-dose and iterative reconstruction techniques on the visualization of orbital soft tissues.MATERIALS AND METHODS:Contrast-to-noise ratios of the optic nerve and inferior rectus muscle and subjective scores of a human cadaver were calculated from CT with a reference dose protocol (CT dose index volume = 36.69 mGy) and a subsequent series of low-dose protocols (LDPs I–4: CT dose index volume = 4.18, 2.64, 0.99, and 0.53 mGy) with filtered back-projection (FBP) and adaptive statistical iterative reconstruction (ASIR)-50, ASIR-100, and model-based iterative reconstruction. The Dunn Multiple Comparison Test was used to compare each combination of protocols (α = .05).RESULTS:Compared with the reference dose protocol with FBP, the following statistically significant differences in contrast-to-noise ratios were shown (all, P ≤ .012) for the following: 1) optic nerve: LDP-I with FBP; LDP-II with FBP and ASIR-50; LDP-III with FBP, ASIR-50, and ASIR-100; and LDP-IV with FBP, ASIR-50, and ASIR-100; and 2) inferior rectus muscle: LDP-II with FBP, LDP-III with FBP and ASIR-50, and LDP-IV with FBP, ASIR-50, and ASIR-100. Model-based iterative reconstruction showed the best contrast-to-noise ratio in all images and provided similar subjective scores for LDP-II. ASIR-50 had no remarkable effect, and ASIR-100, a small effect on subjective scores.CONCLUSIONS:Compared with a reference dose protocol with FBP, model-based iterative reconstruction may show similar diagnostic visibility of orbital soft tissues at a CT dose index volume of 2.64 mGy. Low-dose technology and iterative reconstruction technology may redefine current reference dose levels in maxillofacial CT.

The success of modern maxillofacial surgery is undoubtedly related to the increased use of multisection CT. Image data are used for diagnosis and treatment, including software planning, fabrication of rapid prototyping models, customized surgical plate modeling, and computer-guided surgery.However, the increasing use of CT has been cited as a cause for the increasing collective dose of ionizing radiation to populations.¹ The public awareness of cumulative radiation exposure from medical imaging is strongly reflected by legislative authorities and radiologic societies, leading to recent awareness campaigns such as the Image Gently and Image Wisely Campaigns and the American College of Radiology Dose Index Registry Initiatives.²In the field of maxillofacial imaging, the eye lenses and thyroid gland are the most critical organs affected by direct or scattered radiation.³ Available CT technology has to be optimized to assure that the examination adheres to the As Low As Reasonably Achievable (ALARA)/As Low As Diagnostically Achievable (ALADA) principles to reduce the potential risks from ionizing radiation. Protection from ionizing radiation is critical in young and middle-aged patients who frequently have sports-related midface and orbital fractures.⁴ One has to take into account that most patients have already had an initial CT scan during the emergency diagnostic evaluation and may require repeat CT scans for treatment planning, guided surgery, and postoperative evaluation.⁵Modern CT technology is able to substantially reduce the dose.^6–10 Furthermore, dose reduction may not significantly influence registration and navigation accuracy for computer-aided surgery.^11–13 However, the associated increase in noise may significantly influence the diagnostic image quality of soft-tissue structures such as the optical nerve and orbital muscles. The recent implementation of iterative reconstruction techniques such as adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) may improve image quality with reduced radiation doses compared with the traditionally used filtered back-projection (FBP) technique.^14,15The aim of the present study was to evaluate the influence of various low-dose protocols and iterative reconstructions on the visualization of orbital soft tissues.     

Improved Image Quality in Head and Neck CT Using a 3D Iterative Approach to Reduce Metal Artifact

BACKGROUND AND PURPOSE:Metal artifacts from dental fillings and other devices degrade image quality and may compromise the detection and evaluation of lesions in the oral cavity and oropharynx by CT. The aim of this study was to evaluate the effect of iterative metal artifact reduction on CT of the oral cavity and oropharynx.MATERIALS AND METHODS:Data from 50 consecutive patients with metal artifacts from dental hardware were reconstructed with standard filtered back-projection, linear interpolation metal artifact reduction (LIMAR), and iterative metal artifact reduction. The image quality of sections that contained metal was analyzed for the severity of artifacts and diagnostic value.RESULTS:A total of 455 sections (mean ± standard deviation, 9.1 ± 4.1 sections per patient) contained metal and were evaluated with each reconstruction method. Sections without metal were not affected by the algorithms and demonstrated image quality identical to each other. Of these sections, 38% were considered nondiagnostic with filtered back-projection, 31% with LIMAR, and only 7% with iterative metal artifact reduction. Thirty-three percent of the sections had poor image quality with filtered back-projection, 46% with LIMAR, and 10% with iterative metal artifact reduction. Thirteen percent of the sections with filtered back-projection, 17% with LIMAR, and 22% with iterative metal artifact reduction were of moderate image quality, 16% of the sections with filtered back-projection, 5% with LIMAR, and 30% with iterative metal artifact reduction were of good image quality, and 1% of the sections with LIMAR and 31% with iterative metal artifact reduction were of excellent image quality.CONCLUSIONS:Iterative metal artifact reduction yields the highest image quality in comparison with filtered back-projection and linear interpolation metal artifact reduction in patients with metal hardware in the head and neck area.

Imaging plays a crucial role in the staging of oral cancers and is essential for determining tumor resectability, choosing suitable anatomic reconstruction, and planning radiation therapy. The imaging method of choice for evaluating the oral cavity and oropharynx is MR imaging because it provides higher soft-tissue contrast and is less susceptible to artifacts caused by dental hardware. Yet, the limited availability and higher costs of MR imaging, as well as individual patient conditions (breathing or swallowing disorders, claustrophobia, electronic implants such as pacemakers or ferromagnetic foreign bodies), make CT an important alternative option for many patients. Thus, CT is used frequently to stage or follow-up patients because of its wide availability, relatively low cost, and very short scan time. In patients with dental fillings or implants, however, image quality can be degraded by photon starvation and beam hardening.¹ Due to these artifacts, tumors may be only partially visible or completely obscured, making it challenging to define tumor extent. Moreover, streak artifacts may obscure ipsilateral or contralateral lymph node metastases, which can potentially change the therapeutic approach.The use of high-resolution kernels and extended CT-value ranges² improves image quality; evaluating the surrounding soft tissue, however, remains challenging or even impossible in many cases and can lead to missed findings. For metal artifact reduction (MAR),^3,4 sinogram in-painting methods have been proposed. Areas affected by metal artifacts are regarded as missing data and are filled in by different interpolation techniques, such as linear interpolation metal artifact reduction (LIMAR). Because LIMAR is associated with algorithm-induced artifacts, normalized MAR (NMAR) was developed, and it has demonstrated the potential to improve image quality in patients with artifacts from dental hardware and to improve the diagnostic accuracy of head and neck and of pelvic CT^5,6 while minimizing algorithm-induced artifacts.An extension of the MAR methods (ie, LIMAR and NMAR) is a frequency-split technique that also recovers noise texture and anatomic details in close proximity to metal. In a previous study of pelvic CT, this technique delineated adjacent bone and tissue next to metal implants more accurately than NMAR.⁶The aim of this study was to evaluate a novel 3D iterative approach using normalized and frequency split metal artifact reduction in clinical routine head and neck imaging. The resulting image quality was compared with that of filtered back-projection (FBP) reconstructions and LIMAR.     

Temporal Bone CT: Improved Image Quality and Potential for Decreased Radiation Dose Using an Ultra-High-Resolution Scan Mode with an Iterative Reconstruction Algorithm

BACKGROUND AND PURPOSE:Radiation dose in temporal bone CT imaging can be high due to the requirement of high spatial resolution. In this study, we assessed whether CT imaging of the temporal bone by using an ultra-high-resolution scan mode combined with iterative reconstruction provides higher spatial resolution and lower image noise than a z-axis ultra-high-resolution mode.MATERIALS AND METHODS:Patients with baseline temporal bone CT scans acquired by using a z-axis ultra-high-resolution protocol and a follow-up scan by using the ultra-high-resolution–iterative reconstruction technique were identified. Images of left and right temporal bones were reconstructed in the axial, coronal, and Poschl planes. Three neuroradiologists assessed the spatial resolution of the following structures: round and oval windows, incudomallear and incudostapedial joints, basal turn spiral lamina, and scutum. The paired z-axis ultra-high-resolution and ultra-high-resolution–iterative reconstruction images were displayed side by side in random order, with readers blinded to the imaging protocol. Image noise was compared in ROIs over the posterior fossa.RESULTS:We identified 8 patients, yielding 16 sets of temporal bone images (left and right). Three sets were excluded because the patient underwent surgery between the 2 examinations. Spatial resolution was comparable (Poschl) or slightly better (axial and coronal planes) with ultra-high-resolution–iterative reconstruction than with z-axis ultra-high-resolution. A paired t test indicated that noise was significantly lower with ultra-high-resolution–iterative reconstruction than with z-axis ultra-high-resolution (P < .001), with a mean noise reduction of 37% (range, 18%–49%).CONCLUSIONS:The ultra-high-resolution–iterative reconstruction scan mode has similar or slightly better resolution relative to the z-axis ultra-high-resolution mode for CT of the temporal bone but significantly (P < .01) lower image noise, which may enable the dose to be reduced by approximately 50%.

Since the introduction of multidetector techniques, CT has become a major diagnostic technique for temporal bone imaging because its high spatial resolution is well-suited to the task of visualizing the fine anatomic structures of the middle and inner ear.^1–5 To improve spatial resolution, different approaches have been introduced. One of these is the use of an attenuating comb filter to reduce the detector aperture in both fan and cone angle directions, which is referred to as the z-axis ultra-high-resolution (zUHR) technique.⁶ This technique, in combination with a flying focal spot technique, provides nominal image thickness thinner than the detector cell size at the isocenter.^6,7Due to the requirement for high spatial resolution, the radiation dose in temporal CT can be high, especially with the zUHR technique because its dose efficiency is reduced as photons passing through the patient are blocked from the detector by the comb filters in both fan and cone angle directions.⁸ A recent focus of CT imaging has been to reduce patient exposure to ionizing radiation, following the as low as reasonably achievable principle.^9–13 However, the consequent reduction in photons can adversely affect image quality and present a great challenge when imaging small, anatomically complex structures embedded in attenuating bone, such as those of the middle and inner ear. Iterative reconstruction (IR) is a promising reconstruction technique that is superior to standard filtered back-projection reconstructions and theoretically can be used to improve resolution at standard radiation doses or to maintain current resolution by using a reduced radiation dose.^14–17Recently, a new technique combining a deconvolution technique and an IR algorithm, referred to as ultra-high-resolution (UHR)-IR, has been introduced to improve dose efficiency of the zUHR mode. Phantom studies demonstrated that this technique improved dose efficiency by removing the comb filter along the cone (z) direction.⁸ In this study, we retrospectively reviewed temporal bone CT examinations in patients who had baseline studies by using the standard zUHR technique and follow-up examinations by using UHR-IR to determine whether UHR-IR provided improved resolution and lower noise than zUHR in the clinical setting, which could enable reductions in dose.     

Low-Tube-Voltage 80-kVp Neck CT: Evaluation of Diagnostic Accuracy and Interobserver Agreement

BACKGROUND AND PURPOSE:Low-tube-voltage acquisition has been shown to facilitate substantial dose savings for neck CT with similar image contrast compared with standard 120-kVp acquisition. However, its potential for the detection of neck pathologies is uncertain. Our aim was to evaluate the effects of low-tube-voltage 80-kV(peak) acquisitions for neck CT on diagnostic accuracy and interobserver agreement.MATERIALS AND METHODS:Three radiologists individually analyzed 80-kVp and linearly blended 120-kVp image series of 170 patients with a variety of pathologies who underwent dual-energy neck CT. Reviewers were unblinded to the clinical indication for CT but were otherwise blinded to any other data or images and were asked to state a final main diagnosis. Findings were compared with medical record charts, CT reports, and pathology results. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for each observer. Interobserver agreement was evaluated by using intraclass correlation coefficients.RESULTS:Diagnoses were grouped as squamous cell carcinoma–related (n = 107, presence/absence of primary/recurrent squamous cell carcinoma), lymphoma-related (n = 40, presence/absence of primary/recurrent lymphoma), and benign (n = 23, eg, abscess). Cumulative sensitivity, specificity, positive predictive value, and negative predictive value for 80-kVp and blended 120-kVp images were 94.8%, 93.0%, 95.9%, and 91.1%, respectively. Results were also consistently high for squamous cell carcinoma–related (94.8%/95.3%, 89.1%/89.1%, 94.3%/94.4%, 90.1%/91.0%) and lymphoma-related (95.0%, 100.0%, 100.0%, 95.2%) 80-kVp/120-kVp image series. Global interobserver agreement was almost perfect (intraclass correlation coefficient, 0.82, 0.80; 95% CI, 0.76–0.74, 0.86–0.85). Calculated dose-length product was reduced by 48% with 80-kVp acquisitions compared with the standard 120-kVp scans (135.5 versus 282.2 mGy × cm).CONCLUSIONS:Low-tube-voltage 80-kVp CT of the neck provides sufficient image quality with high diagnostic accuracy in routine clinical practice and has the potential to substantially decrease radiation exposure.

CT is a standard imaging technique in routine clinical practice for detection, staging, and follow-up evaluation of various pathologies of the neck, including squamous cell carcinoma (SCC), cervical lymphoma or lymphadenopathy, and parapharyngeal or retropharyngeal abscess.^1–5 CT examinations contribute a substantial amount of cumulative radiation exposure to patients with cervical pathologies, especially if follow-up CT is required.⁶ Thus, various approaches for dose reduction of CT of the neck, brain, paranasal sinus, and the facial skeleton have been proposed, including reduction of tube current and tube potential, high-pitch acquisition, and application of automated exposure-control software.^7–10 The combination of such techniques with an iterative reconstruction algorithm can also provide similar image quality while substantially reducing exposure to ionizing radiation compared with the standard 120-kVp acquisitions.^11,12Several studies have demonstrated that low-tube-voltage acquisitions at 80 kVp can increase iodine attenuation and image contrast of soft-tissue structures and reduce radiation exposure.^13–15 However, only a few studies have investigated low-tube-voltage acquisition CT techniques for imaging of the neck.^16–18 We hypothesized that an 80-kVp acquisition may provide comparable image quality for evaluation of the neck region. To evaluate the efficacy of this technique in simulated routine clinical practice, we retrospectively assessed the diagnostic accuracy of low-tube-voltage 80-kVp image series from dual-energy neck CT (DECT) for evaluation of a variety of cervical pathologies, and the results were compared with linearly blended images representing a standard 120-kVp acquisition. We also assessed interobserver agreement and calculated the potential radiation dose reduction.     

Kimura disease: CT and MR imaging findings

BACKGROUND AND PURPOSE:KD is a rare chronic inflammatory disorder of unknown etiology. The purpose of this study was to evaluate the CT and MR imaging findings of KD in the head and neck.MATERIALS AND METHODS:We retrospectively reviewed the CT (n = 21) and MR (n = 9) images obtained in 28 patients (24 males and 4 females; mean age, 32 years; age range, 10–62 years) with histologically proved KD in the head and neck.RESULTS:In these 28 patients, CT and MR images demonstrated a total of 52 non-nodal lesions, 1–8 cm in greatest diameter, in the head and neck. The lesions were unilateral in 11 patients and bilateral in 17 patients. Eleven patients had a solitary lesion, and 17 patients had 2–4 lesions. The parotid and/or periparotid area was the most frequent location, with 36 lesions in 23 patients. The margin of the lesions was well-defined in 1 and ill-defined in 51 cases. Compared with the adjacent muscle, the MR signal intensity of all lesions was iso- to slightly hyperintense on T1-weighted images and hyperintense on T2-weighted images. Most of the lesions demonstrated mild or moderate enhancement on postcontrast CT scans and moderate or marked enhancement on postcontrast MR images. MR images also showed tubular signal-intensity voids in 7 of 13 lesions. Associated lymphadenopathy was demonstrated in 23 patients, usually bilaterally.CONCLUSIONS:Multiple ill-defined enhancing masses within and around the parotid gland with associated regional lymphadenopathy are characteristic CT and MR imaging findings of KD in the head and neck.

KD is a rare chronic inflammatory disorder of unknown etiology, characterized by angiolymphoid proliferation with peripheral eosinophilia and elevated serum IgE. The disease has a predilection for the head and neck and typically occurs in young Asian males.^1,2 Although it was first described in the Chinese literature in 1937 under the designation of “eosinophilic hyperplastic lymphogranuloma,” it was not until 1948 that the disease to become widely known as KD when Kimura and Ishikawa³ reported it in the Japanese literature.⁴ KD often produces subcutaneous tumorlike nodules with frequently associated involvement of the major salivary gland and regional lymph nodes.⁵Although the clinical and histopathologic findings of KD have been well described in the literature, only a few reports have dealt with its radiologic findings, and generally as case reports or small case series.^6–15 The purpose of this study was to describe the CT and MR imaging findings of histologically proved KD involving the head and neck in 28 patients. To our knowledge, this is the largest imaging study of patients with KD of the head and neck.     

Optimal Virtual Monochromatic Images for Evaluation of Normal Tissues and Head and Neck Cancer Using Dual-Energy CT

BACKGROUND AND PURPOSE:Dual-energy CT is not used routinely for evaluation of the head and neck, and there is no consensus on the optimal virtual monochromatic image energies for evaluating normal tissues or head and neck cancer. We performed a quantitative evaluation to determine the optimal virtual monochromatic images for visualization of normal tissues, head and neck squamous cell carcinoma, and lymphadenopathy.MATERIALS AND METHODS:Dual-energy CT scans from 10 healthy patients and 30 patients with squamous cell carcinoma were evaluated at different virtual monochromatic energy levels ranging from 40 to 140 keV. The signal-to-noise ratios of muscles at 6 different levels, glands (parotid, sublingual, submandibular, and thyroid), 30 tumors, and 17 metastatic lymph nodes were determined as measures of optimal image quality. Lesion attenuation and contrast-to-noise ratios (compared with those of muscle) were evaluated to assess lesion conspicuity.RESULTS:The optimal signal-to-noise ratio for all the tissues was at 65 keV (P < .0001). However, tumor attenuation (P < .0001), attenuation difference between tumor and muscles (P = .03), and lesion contrast-to-noise ratios (P < .0001) were highest at 40 keV.CONCLUSIONS:The optimal image signal-to-noise ratio is at 65 keV, but tumor conspicuity compared with that of muscle is greatest at 40 keV. Optimal evaluation of the neck may be best achieved by a multiparametric approach, with 65-keV virtual monochromatic images providing the best overall image quality and targeted use of 40-keV virtual monochromatic images for tumor evaluation.

There are emerging applications of dual-energy CT (DECT)¹ in all the major subspecialties of radiology.^2–8 Studies have increasingly been demonstrating potential advantages of DECT for the evaluation of head and neck pathologies.^8–18 Extrapolating from abdominal imaging, 70-keV virtual monochromatic image (VMI) reconstructions are believed to be those that most closely resemble a standard single-energy CT acquisition¹⁹ and are usually the default setting for CT of the neck. On the other hand, enhancing tumors have increased attenuation on lower–kiloelectron volt (keV) VMIs, closer to the k edge of iodine,²⁰ albeit at the expense of other factors such as increased image noise. A recent study using a dual-source system (Somatom Definition Flash; Siemens, Erlangen, Germany) evaluated extrapolated monoenergetic datasets at 40, 60, 80, and 100 keV, and the authors concluded that image reconstructions at 60 keV improved lesion enhancement and the contrast-to-noise ratio (CNR), subjective overall image quality, and tumor delineation in head and neck squamous cell carcinoma (HNSCC).¹⁰Most studies that evaluated HNSCC, other than a study that evaluated DECT for the differentiation of benign and malignant tumors,¹⁴ were performed by using dual-source CT. The other major system currently in clinical use is a single-source single-detector DECT system. This system is based on rapid kilovoltage peak (kVp) switching that enables near-simultaneous acquisition of high- and low-energy projection data (GE Discovery CT750HD; GE Healthcare, Milwaukee, Wisconsin). In this system, spectral separation is achieved on the basis of projection-based material decomposition by using the fast sampling capabilities of a proprietary scintillator detector with low afterglow.^5,21 Although the broad principles behind both DECT acquisition systems are similar, there are significant differences in hardware, acquisition, and postprocessing. As a result, any cross-platform application of observations made by using either system requires validation. Furthermore, there is currently no consensus on the optimal VMIs for the evaluation of HNSCC or the approach to incorporate DECT into routine clinical use.The hypothesis behind our investigation was that VMIs acquired at energies other than 70 keV, either alone or in combination, can enhance the conspicuity of HNSCC. The objective of this investigation, therefore, was to determine the optimal VMI that provides the highest image quality and the VMI that enables optimal tumor visualization by using a single-source DECT scan with rapid kVp switching. This determination was made by objectively and quantitatively analyzing normal structures at different levels in the neck and tumors at different primary sites. Spectral evaluation was performed by using different VMI energy levels ranging from 40 to 140 keV in 5-keV increments, and mean attenuation, SNR, and CNR were used as end points for evaluation.     

Dental Flat Panel Conebeam CT in the Evaluation of Patients with Inflammatory Sinonasal Disease: Diagnostic Efficacy and Radiation Dose Savings

BACKGROUND AND PURPOSE:CT is the imaging modality of choice to study the paranasal sinuses; unfortunately, it involves significant radiation dose. Our aim was to assess the diagnostic validity, image quality, and radiation-dose savings of dental conebeam CT in the evaluation of patients with suspected inflammatory disorders of the paranasal sinuses.MATERIAL AND METHODS:We prospectively studied 40 patients with suspected inflammatory disorders of the sinuses with dental conebeam CT and standard CT. Two radiologists analyzed the images independently, blinded to clinical information. The image quality of both techniques and the diagnostic validity of dental conebeam CT compared with the reference standard CT were assessed by using 3 different scoring systems. Image noise, signal-to-noise ratio, and contrast-to-noise ratio were calculated for both techniques. The absorbed radiation dose to the lenses and thyroid and parotid glands was measured by using a phantom and dosimeter chips. The effective radiation dose for CT was calculated.RESULTS:All dental conebeam CT scans were judged of diagnostic quality. Compared with CT, the conebeam CT image noise was 37.3% higher (P < .001) and the SNR of the bone was 75% lower (P < .001). The effective dose of our conebeam CT protocol was 23 μSv. Compared with CT, the absorbed radiation dose to the lenses and parotid and thyroid glands with conebeam CT was 4%, 7.8%, and 7.3% of the dose delivered to the same organs by conventional CT (P < .001).CONCLUSIONS:Dental conebeam CT is a valid imaging procedure for the evaluation of patients with inflammatory sinonasal disorders.

CT is the criterion standard imaging technique for the evaluation of adult patients with suspected sinonasal inflammatory disease.¹ The use of CT has increased dramatically, and it is estimated that approximately 4 million CT scans of the sinuses are currently obtained each year in the United States.²CT involves considerable ionizing radiation. It accounts for 10% of radiology procedures but represents approximately two-thirds of the total medical radiation dose,^3,4 and 2% of all cancers in the United States may be attributable to the radiation derived from CT studies.⁵ Patients in whom an inflammatory disorder of the paranasal sinuses is suspected are frequently young,^1,6 and in this population, radiation-induced cancer risk is considerably higher.⁵ Besides carcinogenesis, CT of the paranasal sinuses increases the risk of radiation-induced cataracts because the lens of the eye is a highly radiosensitive organ enclosed in the scanning field.^1,7,8One approach to reduce such adverse effects is to decrease the CT-related radiation dose by adjusting downward the scanner settings that determine it. Prior studies^1,4,6,8–11 have shown that, indeed, reducing the radiation dose by 75% does not significantly impact the diagnosis of sinonasal inflammatory diseases. A different approach would be to replace conventional CT with another technique. Dental conebeam CT is an emerging clinical technique. It uses a cone-shaped x-ray beam and an exceptionally radiosensitive flat panel detector to provide high-resolution images with a low radiation dose.^12,13 At present, the clinical use of this technique is largely centered on the dental region, where it is considered more effective and economical than conventional CT.¹⁴ Conebeam CT systems have limited soft-tissue contrast discrimination,¹³ compared with conventional CT. This limitation represents the main barrier to the extension of conebeam of into diagnostic imaging. In the sinonasal region, this technique may not be appropriate for the evaluation of tumors or complicated sinusitis or critical evaluation of small changes in soft-tissue attenuation. The purpose of our investigation was to assess the diagnostic validity and image quality of dental conebeam CT compared with standard CT in the evaluation of inflammatory disorders of the paranasal sinuses and to investigate the potential radiation-dose savings achieved with this technique.     

Cerebral Aneurysm Pulsation: Do Iterative Reconstruction Methods Improve Measurement Accuracy In Vivo?

BACKGROUND AND PURPOSE:Electrocardiogram-gated 4D-CTA is a promising technique allowing new insight into aneurysm pathophysiology and possibly improving risk prediction of cerebral aneurysms. Due to the extremely small pulsational excursions (<0.1 mm in diameter), exact segmentation of the aneurysms is of critical importance. In vitro examinations have shown improvement of the accuracy of vessel delineation by iterative reconstruction methods. We hypothesized that this improvement shows a measurable effect on aneurysm pulsations in vivo.MATERIALS AND METHODS:Ten patients with cerebral aneurysms underwent 4D-CTA. Images were reconstructed with filtered back-projection and iterative reconstruction. The following parameters were compared between both groups: image noise, absolute aneurysm volumes, pulsatility, and sharpness of aneurysm edges.RESULTS:In iterative reconstruction images, noise was significantly reduced (mean, 9.8 ± 4.0 Hounsfield units versus 8.0 ± 2.5 Hounsfield units; P = .04), but the sharpness of aneurysm edges just missed statistical significance (mean, 3.50 ± 0.49 mm versus 3.42 ± 0.49 mm; P = .06). Absolute volumes (mean, 456.1 ± 775.2 mm³ versus 461.7 ± 789.9 mm³; P = .31) and pulsatility (mean, 1.099 ± 0.088 mm³ versus 1.095 ± 0.082 mm³; P = .62) did not show a significant difference between iterative reconstruction and filtered back-projection images.CONCLUSIONS:CT images reconstructed with iterative reconstruction methods show a tendency toward shorter vessel edges but do not affect absolute aneurysm volumes or pulsatility measurements in vivo.

Electrocardiogram-gated 4D-CT angiography has been used to analyze the pulsation of cerebral aneurysms.^1–7 Insight into aneurysm pathophysiology and improvement of risk prediction of incidental cerebral aneurysms can be expected. The technique is limited by the small pulsational excursions of cerebral aneurysms. If one considers a volume change of 5% within the cardiac cycle, the change in diameter of a spherical aneurysm of 5 mm diameter is on the order of 0.1 mm,^1,2 which is below the resolution of CTA. Exact segmentation of the aneurysm is, therefore, critical and of the utmost importance for the correct analysis of pulsations.In vitro experiments with vascular models have shown that vessel delineation depends on various factors, including intraluminal contrast attenuation, vascular wall thickness, postprocessing, and reconstruction methods.⁸ Iterative reconstruction (IR) algorithms have gained importance in clinical routine CT because the radiation dose can be reduced significantly while image quality is maintained compared with filtered back-projection (FBP) reconstruction. At a constant radiation dose, IR reduces image blur, enhances edges, and increases image resolution.^8–10 Depiction of vessels in the posterior fossa and the spinal canal^11,12 is improved in vivo. Moreover, in vitro studies reveal improvement of the accuracy of quantitative measurement of vessel diameters.⁸These findings and its overall characteristics make IR an interesting tool for improving the accuracy of pulsation measurements of cerebral aneurysms. To our knowledge, the influence of IR on vessel-volume measurement, especially in 4D-CTA, has not been examined in vivo. We hypothesized that IR methods have a measureable effect on the accuracy of quantification of cerebral aneurysm pulsation in vivo.     

Photon-Counting CT of the Brain: In Vivo Human Results and Image-Quality Assessment

BACKGROUND AND PURPOSE:Photon-counting detectors offer the potential for improved image quality for brain CT but have not yet been evaluated in vivo. The purpose of this study was to compare photon-counting detector CT with conventional energy-integrating detector CT for human brains.MATERIALS AND METHODS:Radiation dose–matched energy-integrating detector and photon-counting detector head CT scans were acquired with standardized protocols (tube voltage/current, 120 kV(peak)/370 mAs) in both an anthropomorphic head phantom and 21 human asymptomatic volunteers (mean age, 58.9 ± 8.5 years). Photon-counting detector thresholds were 22 and 52 keV (low-energy bin, 22–52 keV; high-energy bin, 52–120 keV). Image noise, gray matter, and white matter signal-to-noise ratios and GM–WM contrast and contrast-to-noise ratios were measured. Image quality was scored by 2 neuroradiologists blinded to the CT detector type. Reproducibility was assessed with the intraclass correlation coefficient. Energy-integrating detector and photon-counting detector CT images were compared using a paired t test and the Wilcoxon signed rank test.RESULTS:Photon-counting detector CT images received higher reader scores for GM–WM differentiation with lower image noise (all P < .001). Intrareader and interreader reproducibility was excellent (intraclass correlation coefficient, ≥0.86 and 0.79, respectively). Quantitative analysis showed 12.8%–20.6% less image noise for photon-counting detector CT. The SNR of photon-counting detector CT was 19.0%–20.0% higher than of energy-integrating detector CT for GM and WM. The contrast-to-noise ratio of photon-counting detector CT was 15.7% higher for GM–WM contrast and 33.3% higher for GM–WM contrast-to-noise ratio.CONCLUSIONS:Photon-counting detector brain CT scans demonstrated greater gray–white matter contrast compared with conventional CT. This was due to both higher soft-tissue contrast and lower image noise for photon-counting CT.

Brain CT remains the first-line technique of choice for the evaluation of traumatic and nontraumatic brain injury and is the most-often-performed CT examination in many emergency departments.^1,2 However, there is limited gray matter–white matter differentiation with brain CT, decreasing the ability to assess the hypoattenuation and loss of GM–WM differentiation seen in early ischemic brain changes.^3,4 In addition, beam-hardening artifacts due to attenuation by the skull of lower energy photons degrade brain CT diagnostic image quality, potentially mimicking intracranial hemorrhage and reducing GM–WM differentiation.⁵The energy spectrum of x-ray tubes for CT is usually characterized by the peak kilovoltage, but the applied x-ray spectrum consists of a wide distribution of lower energy photons. Conventional CT uses energy-integrating detectors (EIDs) to combine the effects of x-ray photon number and photon energy into an intensity value through conversion of x-rays to light photons to electrical pulses. Consequently, with EID CT, low-energy photons (eg, 40–70 keV) have less contribution to the CT intensity value than high-energy photons (eg, 110–140 keV). For brain imaging however, it is these low-energy photons that have better soft-tissue discrimination for identification of gray–white matter contrast.Photon-counting detectors (PCDs) are a new technology for CT imaging that directly converts x-ray photons into electrical pulses. PCDs measure the number of detected x-ray photons (ie, photon count) and their photon energy.^6–11 These characteristics allow equal weighting of low- and high-energy photons and may therefore be useful for improving soft-tissue contrast in the brain.⁸ In addition, the direct conversion and counting of individual photons provide a better estimate of the underlying photon statistics, which, in turn, may improve image quality by reducing image noise.^8,12–14 We hypothesized that the combined effects of better contrast and reduced noise may lead to better overall GM–WM differentiation in brain PCD CT.To date, PCD CT scanning of a cadaver head¹⁵ has suggested the feasibility of PCD for brain CT, but in vivo results have not been previously studied, to our knowledge. Thus, the purpose of the current study was to compare the image quality of PCD with that of conventional EID for human brain CT.     

Diagnostic Yield of Emergency Department Arch-to-Vertex CT Angiography in Patients with Suspected Acute Stroke

BACKGROUND AND PURPOSE:Our aim was to investigate how often relevant diagnostic findings in an arch-to-vertex CTA scan, obtained specifically as part of the acute stroke CT protocol, are located in the head, neck, and upper chest regions.MATERIALS AND METHODS:Radiology reports were reviewed in 302 consecutive patients (170 men, 132 women; median ages, 66 and 73 years, respectively) who underwent emergency department investigation of suspected acute stroke between January and July 2010. Diagnostic CTA findings relevant to patient management were recorded for the head, neck, and chest regions individually. Additionally, the contributions to the total CTA scan effective dose were estimated from each of the 3 anatomic regions by using the ImPACT CT Dose Calculator.RESULTS:Of the 302 patients, 161 (54%) had relevant diagnostic findings in the head; 94 (31%), in the neck; and 4 (1%), in the chest. The estimated contributions to the total CTA scan dose from each body region, head, neck, and upper chest, were 14 ± 2%, 33 ± 5%, and 53 ± 6%, respectively.CONCLUSIONS:Most clinically relevant findings are in the head and neck, supporting inclusion of these regions in arch-to-vertex CTA performed specifically in patients with acute stroke in the emergency department. Further studies are required to investigate extending the scan to the upper chest because only 1% of patients in our study had clinically relevant findings in the mediastinum, yet half the CTA effective dose was due to scanning in this region.

In the evaluation of patients presenting to the emergency department within 4.5 hours of the onset of acute stroke or strokelike symptoms, emphasis is placed on the immediate identification of inclusion and exclusion criteria for the administration of intravenous thrombolytic therapy.^1–6 Subsequent investigation of risk factors for stroke is an elective process and typically does not begin until after the acute event has passed.^7–9With improvement in CT technology, the limitations on scan coverage of neurovascular CTA have relaxed, and single-pass imaging from the aortic arch to the skull vertex has become commonplace.^10–15 Nevertheless, we have found no studies that evaluated benefit to the patient from this practice. Furthermore, current guidelines for the emergency management of patients with acute stroke remain focused on noncontrast head CT and CTA evaluation only of the intracranial circulation.^1,16–17Our primary purpose was to investigate the incidence of diagnostically relevant findings reported in the head, neck, and chest components of an arch-to-vertex CTA performed in the emergency department as part of the immediate evaluation and triage of acute stroke. A secondary aim was to estimate the individual contributions to the total effective dose in these regions.     

Dual-Energy CT in Enhancing Subdural Effusions that Masquerade as Subdural Hematomas: Diagnosis with Virtual High-Monochromatic (190-keV) Images

BACKGROUND AND PURPOSE:Extravasation of iodinated contrast into subdural space following contrast-enhanced radiographic studies results in hyperdense subdural effusions, which can be mistaken as acute subdural hematomas on follow-up noncontrast head CTs. Our aim was to identify the factors associated with contrast-enhancing subdural effusion, characterize diffusion and washout kinetics of iodine in enhancing subdural effusion, and assess the utility of dual-energy CT in differentiating enhancing subdural effusion from subdural hematoma.MATERIALS AND METHODS:We retrospectively analyzed follow-up head dual-energy CT studies in 423 patients with polytrauma who had undergone contrast-enhanced whole-body CT. Twenty-four patients with enhancing subdural effusion composed the study group, and 24 randomly selected patients with subdural hematoma were enrolled in the comparison group. Postprocessing with syngo.via was performed to determine the diffusion and washout kinetics of iodine. The sensitivity and specificity of dual-energy CT for the diagnosis of enhancing subdural effusion were determined with 120-kV, virtual monochromatic energy (190-keV) and virtual noncontrast images.RESULTS:Patients with enhancing subdural effusion were significantly older (mean, 69 years; 95% CI, 60–78 years; P < .001) and had a higher incidence of intracranial hemorrhage (P = .001). Peak iodine concentration in enhancing subdural effusions was reached within the first 8 hours of contrast administration with a mean of 0.98 mg/mL (95% CI, 0.81–1.13 mg/mL), and complete washout was achieved at 38 hours. For the presence of a hyperdense subdural collection on 120-kV images with a loss of hyperattenuation on 190-keV and virtual noncontrast images, when considered as a true-positive for enhancing subdural effusion, the sensitivity was 100% (95% CI, 85.75%–100%) and the specificity was 91.67% (95% CI, 73%–99%).CONCLUSIONS:Dual-energy CT has a high sensitivity and specificity in differentiating enhancing subdural effusion from subdural hematoma. Hence, dual-energy CT has a potential to obviate follow-up studies.

Diffusion of contrast material into the subdural space following intravascular contrast administration can result in hyperdense enhancing subdural effusions (ESDEs) on follow-up noncontrast head CTs.^1,2 These effusions can be mistaken for subdural hematomas (SDHs).^1,2 Three case reports have previously described ESDEs, all following intra-arterial contrast administration during conventional angiography with resolution documented on short-term follow-up CT examinations.^1,2We have frequently observed ESDEs in our busy level 1 trauma center, where patients usually undergo admission contrast-enhanced whole-body CT followed by serial noncontrast head CTs for documented or suspected traumatic brain injury. Because ESDEs can be mistaken for SDHs, lack of awareness of this entity can potentially result in needless delays in instituting thromboprophylaxis and trigger unnecessary follow-up CT studies. Patients with polytrauma usually require thromboprophylaxis to prevent deep vein thrombosis. A number of authors have posited a mandatory 24- to 72-hour period of documented stability of intracranial bleeds before beginning thromboprophylaxis.^3–6 Hence, early discrimination of SDHs from ESDEs has important clinical implications.On single-energy CT (SECT), the hyperattenuation caused by hemorrhage and contrast medium is difficult to distinguish due to overlapping Hounsfield units (HU).^1,2,7,8 Present recommendations for differentiating SDH from ESDE involve serial follow-up imaging.^1,2 ESDEs shows rapid washout of contrast, hence decreasing hyperattenuation, while SDH retains hyperattenuation from blood for 2–3 weeks.^1,2,9 Dual-energy CT (DECT) can potentially obviate follow-up scans by differentiating iodine from hemorrhage.^7,10,11 Iodine overlay maps and virtual noncontrast (VNC) images can discriminate contrast and hemorrhage with a high degree of accuracy.¹¹ If VNC images can be used to reliably identify hematoma, even in the presence of iodine, differentiation between ESDEs and SDHs can be a simple and straightforward task. The utility of DECT in diagnosing ESDE was recently demonstrated in a case in which a subdural hyperdense collection that developed after endovascular treatment of an intracranial aneurysm was hyperdense on iodine-overlay images and hypodense on VNC images.¹² This evidence suggests that DECT may play a vital role in providing an early definitive diagnosis without the need for follow-up CT studies to document resolution of ESDEs.The purpose of this study was to identify the factors associated with ESDE, characterize the diffusion and washout kinetics of iodine in ESDE, and assess the utility of DECT in differentiating ESDE from SDH.     

Diagnostic Performance of Ultrafast Brain MRI for Evaluation of Abusive Head Trauma

BACKGROUND AND PURPOSE:MR imaging with sedation is commonly used to detect intracranial traumatic pathology in the pediatric population. Our purpose was to compare nonsedated ultrafast MR imaging, noncontrast head CT, and standard MR imaging for the detection of intracranial trauma in patients with potential abusive head trauma.MATERIALS AND METHODS:A prospective study was performed in 24 pediatric patients who were evaluated for potential abusive head trauma. All patients received noncontrast head CT, ultrafast brain MR imaging without sedation, and standard MR imaging with general anesthesia or an immobilizer, sequentially. Two pediatric neuroradiologists independently reviewed each technique blinded to other modalities for intracranial trauma. We performed interreader agreement and consensus interpretation for standard MR imaging as the criterion standard. Diagnostic accuracy was calculated for ultrafast MR imaging, noncontrast head CT, and combined ultrafast MR imaging and noncontrast head CT.RESULTS:Interreader agreement was moderate for ultrafast MR imaging (κ = 0.42), substantial for noncontrast head CT (κ = 0.63), and nearly perfect for standard MR imaging (κ = 0.86). Forty-two percent of patients had discrepancies between ultrafast MR imaging and standard MR imaging, which included detection of subarachnoid hemorrhage and subdural hemorrhage. Sensitivity, specificity, and positive and negative predictive values were obtained for any traumatic pathology for each examination: ultrafast MR imaging (50%, 100%, 100%, 31%), noncontrast head CT (25%, 100%, 100%, 21%), and a combination of ultrafast MR imaging and noncontrast head CT (60%, 100%, 100%, 33%). Ultrafast MR imaging was more sensitive than noncontrast head CT for the detection of intraparenchymal hemorrhage (P = .03), and the combination of ultrafast MR imaging and noncontrast head CT was more sensitive than noncontrast head CT alone for intracranial trauma (P = .02).CONCLUSIONS:In abusive head trauma, ultrafast MR imaging, even combined with noncontrast head CT, demonstrated low sensitivity compared with standard MR imaging for intracranial traumatic pathology, which may limit its utility in this patient population.

The incidence of abusive head trauma (AHT) in the United States from 2000 to 2009 was 39.8 per 100,000 children younger than 1 year of age and 6.8 per 100,000 children 1 year of age.¹ The outcomes of patients with AHT are worse than those of children with accidental traumatic brain injury, including higher rates of mortality and permanent disability from neurologic impairment.^2–5 The diagnosis of AHT is frequently not recognized when affected patients initially present to a physician, and up to 28% of children with a missed AHT diagnosis may be re-injured, leading to permanent neurologic damage or even death.⁶ Because neuroimaging plays a central role in AHT, continued improvement in neuroimaging is necessary.Common neuroimaging findings of AHT include intracranial hemorrhage, ischemia, axonal injury, and skull fracture, with advantages and disadvantages for both CT and MR imaging for the detection of AHT.⁷ A noncontrast head CT (nHCT) is usually the initial imaging study in suspected AHT due to its high sensitivity for the detection of acute hemorrhage and fracture and the high level of accessibility from the emergency department, and it can be performed quickly and safely without the need for special monitoring equipment.^8,9 The disadvantages of CT include ionizing radiation, particularly in children, and the reduced sensitivity in detecting microhemorrhages, axonal injury, and acute ischemia compared with MR imaging.¹⁰MR imaging is frequently performed in AHT and adds additional information in 25% of all children with abnormal findings on the initial CT scan.¹¹ Brain MR imaging can also be useful for identifying bridging vein thrombosis, differentiating subdural fluid collections from enlarged subarachnoid spaces, characterizing the signal of subdural blood, and demonstrating membrane formation within subdural collections.^12–16 Brain MR imaging findings have correlated with poor outcomes associated with findings on diffusion-weighted imaging and susceptibility-weighted imaging in AHT; however, disadvantages of MR imaging continue to include the need for sedation in children and compatible monitoring equipment.^17–22 Although there is greater accessibility of CT compared with MR imaging, the availability of MR imaging is relatively high and imaging techniques that allow neuroimaging in patients with potential AHT without sedation would be valuable, particularly given the potential adverse effects of sedation on the developing brain.^23,24A potential solution for diagnostic-quality brain MR imaging without sedation in AHT is the use of ultrafast MR imaging (ufMRI) sequences, also termed “fast MR imaging,” “quick MR imaging,” or “rapid MR imaging.” Ultrafast MR imaging uses pulse sequences that rapidly acquire images, potentially reducing motion artifacts and the need for sedation. ufMRI has been most commonly used in pediatric neuroradiology for the evaluation of intracranial shunts in children with hydrocephalus, and most of the reported ufMRI brain protocols include only multiplanar T2-weighted HASTE sequences.^25–34 Consequently, previously reported limitations of ufMRI in detecting intracranial hemorrhage is primarily due to the lack of blood sensitive sequences.³⁵Recently, an ufMRI protocol incorporating sequences in addition to T2 sequences has been reported in pediatric patients with trauma.³⁶ This study did not compare findings with those of a standard MR imaging (stMRI) and included a wider age range of pediatric patients, so the value of ufMRI in pediatric abusive head trauma remains uncertain.³⁶ Therefore, the purpose of our study was to evaluate an ufMRI brain protocol performed without sedation for feasibility in terms of scanning time and diagnostic value as well as diagnostic accuracy compared with nHCT and stMRI of the brain for the detection of intracranial traumatic pathology in patients with suspected AHT.     

Minimizing Radiation Exposure in Evaluation of Pediatric Head Trauma: Use of Rapid MR Imaging

BACKGROUND AND PURPOSE:With >473,000 annual emergency department visits for children with traumatic brain injuries in the United States, the risk of ionizing radiation exposure during CT examinations is a real concern. The purpose of this study was to assess the validity of rapid MR imaging to replace CT in the follow-up imaging of patients with head trauma.MATERIALS AND METHODS:A retrospective review of 103 pediatric patients who underwent initial head CT and subsequent follow-up rapid MR imaging between January 2010 and July 2013 was performed. Patients had minor head injuries (Glasgow Coma Scale, >13) that required imaging. Initial head CT was performed, with follow-up rapid MR imaging completed within 48 hours. A board-certified neuroradiologist, blinded to patient information and scan parameters, then independently interpreted the randomized cases.RESULTS:There was almost perfect agreement in the ability to detect extra-axial hemorrhage on rapid MR imaging and CT (κ = 0.84, P < .001). Evaluation of hemorrhagic contusion/intraparenchymal hemorrhage demonstrated a moderate level of agreement between MR imaging and CT (κ = 0.61, P < .001). The ability of MR imaging to detect a skull fracture also showed a substantial level of agreement with CT (κ = 0.71, P < .001). Detection of diffuse axonal injury demonstrated a slight level of agreement between MR imaging and CT (κ = 0.154, P = .04). However, the overall predictive agreement for the detection of an axonal injury was 91%.CONCLUSIONS:Rapid MR imaging is a valid technique for detecting traumatic cranial injuries and an adequate examination for follow-up imaging in lieu of repeat CT.

Head trauma continues to be a leading cause of death and disability in children in the United States.¹ Every year, >473,000 visits to the emergency department are related to brain injury,² most resulting from minor injuries or falls. Although most head injuries are classified as mild, approximately 10%–15% of children sustain a severe one. The incidence of intracranial injury following minor head trauma is unknown; however, with increasing public awareness of traumatic brain injury and concussion, there has been a rise in research of minor head injuries. Methods of diagnosis,^3,4 hospital admission criteria,^5,6 and return-to-play criteria^7,8 are a few of the active areas of research.Children with head trauma, at risk for intracranial injury, should be initially imaged with CT⁹ because it remains the criterion standard technique for the evaluation of head trauma.¹⁰ Although the incidence of injuries requiring neurosurgical intervention in children with minor head injuries is low, the use of CT for evaluation has been increasing. The use of CT increased from 13% to 22% from 1995 to 2003, with a peak of 29% in 2000.¹¹ The decision to obtain neuroimaging for children with minor head trauma must balance the importance of identifying head injuries with the risks of CT. There is growing awareness in the medical community and public of increased cancer risk caused by ionizing radiation.¹² Brenner et al¹³ estimated that 170 additional fatal cancers will develop due to head CT examinations performed in children younger than 15 years of age in the United States in a single year. In addition, some children may require sedation to obtain an adequate CT examination, which can be associated with as high as a 20.1% chance of an adverse event.¹⁴MR imaging is an alternative technique that avoids ionizing radiation exposure altogether and produces high-quality images. A study with conventional sequences requires long acquisition times and is susceptible to motion artifacts. The need for sedation increases the risk to the patient, lengthens the time needed to acquire patient images, and further increases the cost of standard MR imaging.^14,15Modified MR imaging protocols with reduced acquisition times have been used successfully in non-neurosurgical patients,^16,17 and rapid MR imaging (rMRI) or “quick-brain” MR imaging protocols have become an accepted technique to evaluate and follow patients with hydrocephalus.^18–20 Missios et al²¹ investigated the use of rMRI in patients without hydrocephalus and concluded that it was an adequate neuroimaging tool for evaluation and follow-up. The use of rMRI protocols in evaluating pediatric patients with minor head injuries remains to be validated.As far as we are aware, a systematic search of current literature did not yield a previous study examining the validity of rMRI in the imaging of pediatric patients with head trauma. The purpose of our study was to demonstrate the efficacy of replacing ionizing CT imaging with nonionizing rMRI for follow-up of patients with minor head trauma.     

The Diagnostic Value of CT Myelography,MR Myelography,and Both in Neonatal Brachial Plexus Palsy

BACKGROUND AND PURPOSE:Although most infants with brachial plexus palsy recover function spontaneously, approximately 10–30% benefit from surgical treatment. Pre-operative screening for nerve root avulsions is helpful in planning reconstruction. Our aim was to compare the diagnostic value of CT myelography, MR myelography, and both against a surgical criterion standard for detection of complete nerve root avulsions in birth brachial plexus palsy.MATERIALS AND METHODS:Nineteen patients who underwent a preoperative CT and/or MR myelography and subsequent brachial plexus exploration were included. Imaging studies were analyzed for the presence of abnormalities potentially predictive of nerve root avulsion. Findings of nerve root avulsion on surgical exploration were used as the criterion standard to assess the predictive value of imaging findings.RESULTS:Ninety-five root levels were examined. When the presence of any pseudomeningocele was used as a predictor, the sensitivity was 0.73 for CT and 0.68 for MR imaging and the specificity was 0.96 for CT and 0.97 for MR imaging. When presence of pseudomeningocele with absent rootlets was used as the predictor, the sensitivity was 0.68 for CT and 0.68 for MR imaging and the specificity was 0.96 for CT and 0.97 for MR imaging. The use of both CT and MR imaging did not increase diagnostic accuracy. Rootlet findings in the absence of pseudomeningocele were not helpful in predicting complete nerve root avulsion.CONCLUSIONS:Findings of CT and MR myelography were highly correlated. Given the advantages of MR myelography, it is now the single technique for preoperative evaluation of nerve root avulsion at our institution.

Brachial plexus palsy occurs in approximately 1 in 1000 neonates.^1,2 Downward traction on the shoulder girdle produces stereotyped patterns of plexus injury.³ Nerve lesions occur first at higher levels, with more severe traction resulting in progressive inferior extension.^3,4 More superior nerve injury is typically extraforaminal, at the level of the superior trunks, because a well-developed investing fascia protects the upper nerve roots from proximal traction. In contrast, inferior lesions are more often intraforaminal, manifesting as either partial or complete avulsion of the nerve root.⁴Clinical manifestations and spontaneous recovery depend on the extent, location, and type of nerve lesions. The clinical presentation can generally be grouped into 1 of 4 patterns outlined by Narakas⁵: Type I involves C5 and C6 deficits (Erb-Duchenne type) with loss of shoulder abduction, shoulder external rotation, elbow flexion, and forearm supination. Type II involves C5 to C7/C8 deficits, resulting in a “waiter''s tip” posture from additional loss of wrist extension. Type III involves C5 to C8/T1 deficits, resulting in an arm that is generally paralyzed. Type IV involves C5 to T1 and the sympathetic chain, resulting in a flail arm with Horner syndrome. Upward traction on the brachial plexus can result in isolated lower plexus deficits that manifest as paralysis of the hand only.^6,7 This pattern is known as Klumpke palsy.The decision to proceed with surgical exploration and reconstruction is based on the clinical presentation and progression. While 70%–90% of infants are treated with therapy alone, 10%–30% have indications for surgical treatment.^8–11 Nerve injuries distal to the intervertebral foramen can be reconstructed by using nerve grafts, whereas intraforaminal nerve root avulsions require nerve transfer. While both partial and complete nerve root avulsions are described,^12,13 there is no clear consensus on the surgical approach to partial nerve root avulsions. Preoperative imaging capable of accurately identifying complete nerve root avulsions and distinguishing them from extraforaminal nerve injuries is, therefore, critical for optimal surgical planning.The current standard for preoperative assessment of nerve root avulsions in infants is CT myelography.^12,14–19 A pseudomeningocele is suggestive of nerve root avulsion, and the additional finding of absent rootlets traversing the pseudomeningocele greatly increases the specificity of this finding.¹⁴ CT myelography requires a lumbar puncture for injection of intrathecal contrast, with attendant risks of infection and seizure.^20–22 Recent studies have also raised concern for malignancy with early exposure of children to radiation.^23,24 MR myelography can be performed without injection of contrast and is a promising alternative.^17,25 However, the performance of MR myelography for predicting nerve root avulsion is not yet established²⁶ in neonatal brachial plexus injury, and the diagnostic value of MR myelography has yet to be compared with CT myelography in this setting.The purpose of this study was to determine the predictive value of CT myelography, MR myelography, and both CT and MR myelography for detecting complete nerve root avulsions in neonatal brachial plexus palsy, by using a surgical criterion standard.