Computed radiography in musculoskeletal imaging

In conclusion, CR offers many advantages in comparison with conventional radiography. Musculoskeletal radiology particularly benefits from the wide dynamic range and image-processing capabilities of CR. Most studies have not shown a statistically significant difference in observer performance (diagnostic accuracy) of CR in comparison with conventional radiography in musculoskeletal applications. In addition, dose reduction in the range of 25% to 50% is possible with many musculoskeletal images. However, disadvantages are also apparent and include reduced spatial resolution, increased noise, and change in image size and format. Overall, the advantages of CR and digital technology outweigh its limitations and for these reasons continue to promote the conversion from conventional radiography.     

Storage phosphor digital mammography

Digital mammography using storage phosphor CR is still in the investigational stage. It is the only digital mammography system that has been tested in preliminary clinical trials with promising early results. Further clinical studies are needed to assess the impact of the limited spatial resolution of storage phosphor technology on its application as a digital screening mammography system. Further studies also are needed to determine the optimum image processing parameters needed in digital mammography.     

N-butyl cyanoacrylate embolization as the primary treatment of acute hemodynamically unstable lower gastrointestinal hemorrhage

Purpose

To evaluate N-butyl cyanoacrylate (NBCA) embolization as the primary treatment for patients with severe and acute hemodynamically unstable lower gastrointestinal bleeding.

Materials and Methods

Twenty-seven patients with acute, unstable hemodynamics caused by lower gastrointestinal bleeding underwent therapeutic NBCA microcatheter embolization over a period of 27 months. The inclusion criteria were hematochezia or melena and hypotension refractory to conservative treatment and requiring blood transfusion. Bleeding was localized to the rectum, colon, or small intestine in all nine such cases. Fifteen patients had severe underlying comorbidities, including sepsis, respiratory failure, malignancy, or renal failure.

Results

The procedure was technically successful in all patients. Twenty-six patients were treated solely with NBCA, and one required microcoil embolization. Embolization was performed at the level of the arteria recta or as close as possible to the point of bleeding. Immediate hemostasis occurred in all cases. Four patients experienced repeat hemorrhage, one of whom died. The other three were treated successfully with repeat NBCA embolization. None of the surviving patients had evidence of bowel ischemia. In addition, none of the patients with severe underlying disease died during the follow-up period (range, 3 mo to 2 y).

Conclusions

The present findings suggest that NBCA embolization may be a safe alternative treatment for the management of lower gastrointestinal bleeding. Further studies are warranted to confirm the findings.     

Application of sonoelastography: comparison of performance between mass and non-mass lesion

Objectives

The purpose of this study was to determine the performance of the conventional ultrasonography (US) and sonoelastography (SE) in three conditions of all lesions, confined to mass, and confined to non-mass lesion and to compare the performance of each modality between mass and non-mass lesion.

Materials and methods

A total 364 patients with 375 lesions were evaluated with US and subsequently SE before performing US-guided biopsy. Two radiologists retrospectively analyzed conventional US and elasticity images by consensus. The US findings were classified as mass or non-mass lesion. With final pathology as reference, in each case of all lesions, masses, and non-mass lesions, areas under the ROC curves (Az) were calculated and compared for the two techniques. The comparison of Az values between the curves for US and SE, and between the curves for mass and non-mass lesion was performed.

Results

Among 375 lesions, 104 (28%) lesions were malignant and 271 (72%) lesions were benign. 36 (9.6%) of 375 lesions were classified as non-mass lesion at US.There were statistically significant difference of performance between US and SE in cases of all lesion (p = 0.003) and mass (p = 0.023). However, there was no statistically significant difference of performance in case of non-mass lesion (p = 0.5). Comparisons of the Az values of US and SE between mass and non-mass lesions were not statistically significant (p = 0.745, p = 0.415, respectively).

Conclusion

There was no statistically significant difference of performance of US and SE between mass and non-mass lesion.     

Development of hepatic pseudotumors for image-guided interventional and surgical research in a large animal model

Purpose

Real-time image guidance and navigation have become increasingly important in an era of minimally invasive interventional and surgical procedures in the liver. To develop, test, and implement tools for real-time image guidance, the authors sought to create an in vivo tumor mimic with realistic imaging and treatment capabilities.

Materials and Methods

Hepatic pseudotumors were created by injecting 1–2 mL of alginate (a hydrocolloid) directly into the liver parenchyma in eight live pigs and two dog cadavers. Tumors were imaged by B-mode ultrasound (US), US elasticity imaging, multi–detector row computed tomography (CT), CT fluoroscopy, and magnetic resonance (MR) imaging to assess imaging capabilities. Procedures performed with the alginate pseudotumors included radiofrequency (RF) ablation and robotic needle guidance.

Results

Twenty-four hepatic pseudotumors were created, ranging in size from 10 mm to 28 mm at an average depth of 6 mm. Average time of preparation and insertion was 3 minutes. All tumors were palpable under the surface of the liver and were easily visible on B-mode US, US elasticity imaging, CT, and MR imaging. Tumors were successfully “treated” with RF ablation, and gross examination of the liver showed good encompassment of the tumor by the zone of thermal coagulation. In addition, the pseudotumors allowed for easy introduction of various types of needles, including RF ablation probes and experimental steerable needles.

Conclusions

Alginate pseudotumors can easily be imaged and allow for different procedures to be performed. This model can be used for various research purposes.     

ROC methods for evaluation of fMRI techniques

Receiver operating characteristic (ROC) methods provide a standardized and statistically meaningful means for comparing signal-detection accuracy. A brief overview of ROC methods is presented. Example applications include a comparison of four different postprocessing algorithms operating on simulated fMRI time-course data sets and on human null data sets to which a simulated fMR response had been added. ROC methods also were used to reanalyze one data set from a previously published work. Additional ROC methods that also may be useful for fMRI comparisons are described.     

Sclerotherapy of abdominal lymphatic malformations with doxycycline

Purpose

To assess the safety and efficacy of percutaneous image-guided sclerotherapy with doxycycline as primary treatment of intraabdominal lymphatic malformations (LMs).

Materials and Methods

Retrospective review was performed of all cases of abdominal, mesenteric, or retroperitoneal LMs referred to a single center that were subsequently treated with image-guided percutaneous sclerotherapy.

Results

Ten patients were included, of whom six were male. The mean age was 13 years (range, 2–28 y). Preprocedural cross-sectional imaging demonstrated a macrocystic malformation in nine patients and a mixed macrocystic/microcystic malformation in one. The malformation was accessed under sonographic guidance, followed by injection of opacified sclerosant agent under fluoroscopic guidance. A drainage catheter was placed in eight cases, in which sclerotherapy was repeated through the catheter for another 1 day (n = 2) or 2 days (n = 6). Doxycycline was reconstituted at 10 mg/mL, with a mean per-session dose of 608 mg (range, 80–1,000 mg) and a mean total dose of 1,230 mg (range, 80–3,000 mg). Peritoneal spill was identified in one case, but the patient remained asymptomatic. No other complications were encountered. Follow-up imaging was available in eight patients: complete resolution was seen in seven, with partial resolution in one. There was no recurrence of clinical symptoms in the follow-up period.

Conclusions

Initial results indicate that percutaneous image-guided sclerotherapy of macrocystic intraabdominal LMs with doxycycline is a safe and effective procedure.     

Hepatocellular Carcinoma: Prediction of Blood Supply from an Intercostal Artery with Multidetector Row Computed Tomography

Purpose

To evaluate the ability of multidetector row computed tomography (CT) to detect blood supply from the intercostal artery in patients with hepatocellular carcinoma (HCC).

Materials and Methods

Between January 2003 and December 2007, angiography of the intercostal artery was performed in 93 patients (76 men and 17 women, mean age 58 years) with HCC who had also undergone multidetector row CT. CT scans and digital subtraction angiograms of these patients were retrospectively reviewed by two investigators in consensus to evaluate tumor feeding vessels. Multiple logistic regression analysis was used to identify factors that predict the presence of an HCC blood supply from an intercostal artery.

Results

Tumor staining fed by an intercostal artery was noted in 65 patients (70%; 112 tumor feeding vessels) by intercostal angiography. Readers interpreted that tumor feeding vessels were evident by CT in 35 (54%) of these 65 patients with tumor staining supplied by an intercostal artery by angiography. Multiple logistic regression analysis showed that a visible tumor feeding vessel by CT (P = .003) and hepatic artery attenuation by angiography (P = .014) were significantly related to the presence of a blood supply from an intercostal artery.

Conclusions

Visualization of a tumor feeding vessel from the intercostal artery by multidetector row CT is an important sign of parasitic supply to an HCC.     

CT fluoroscopy-guided placement of inferior vena cava filters: feasibility study in pigs

Purpose

To evaluate the feasibility of computed tomography (CT)–guided placement of inferior vena cava (IVC) filters in a swine model.

Materials and Methods

Five domestic pigs (60–70 kg) underwent transfemoral and transjugular IVC filter placement under real-time CT fluoroscopic guidance. Filter position was confirmed by contrast-enhanced CT and digital subtraction angiography. Filter tilt, distance to target position, and fluoroscopy time were analyzed.

Results

A total of 10 filters were successfully implanted (five via transfemoral approach, five via transjugular approach) without complications. The mean distance to the target position was 0.3 cm ± 0.2. Mean filter tilt was 3.2° ± 2.3 (range, 0°–7°), without differences between deployment techniques (P = .8486). Average fluoroscopy time was 25.9 s ± 6.9 per procedure.

Conclusions

CT fluoroscopy–guided placement of IVC filters is safely feasible. Use of this technique may avoid the need to move critically ill patients.     

Digital mammography: observer performance study of the effects of pixel size on the characterization of malignant and benign microcalcifications

RATIONALE AND OBJECTIVES: The authors performed this study to evaluate the effects of pixel size on the characterization of mammographic microcalcifications by radiologists. MATERIALS AND METHODS: Two-view mammograms of 112 microcalcification clusters were digitized with a laser scanner at a pixel size of 35 microm. Images with pixel sizes of 70, 105, and 140 microm were derived from the 35-microm-pixel size images by averaging neighboring pixels. The malignancy or benignity of the microcalcifications had been determined with findings at biopsy or 2-year follow-up. Region-of-interest images containing the microcalcifications were printed with a laser imager. Seven radiologists participated in a receiver operating characteristic (ROC) study to estimate the likelihood of malignancy. The classification accuracy was quantified with the area under the ROC curve (Az). The statistical significance of the differences in the Az values for different pixel sizes was estimated with the Dorfman-Berbaum-Metz method and the Student paired t test. The variance components were analyzed with a bootstrap method. RESULTS: The higher-resolution images did not result in better classification; the average Az with a pixel size of 35 microm was lower than that with pixel sizes of 70 and 105 microm. The differences in Az between different pixel sizes did not achieve statistical significance. CONCLUSION: Pixel sizes in the range studied do not have a strong effect on radiologists' accuracy in the characterization of microcalcifications. The low specificity of the image features of microcalcifications and the large interobserver and intraobserver variabilities may have prevented small advantages in image resolution from being observed.     

ROC Analysis of Detection of Metastatic Pulmonary Nodules on Digital Chest Radiographs with Temporal Subtraction

RATIONALE AND OBJECTIVES: The authors' purpose was to evaluate the effect of temporal subtraction on digital chest radiographs in the detection of metastatic pulmonary nodules. MATERIALS AND METHODS: The study included 21 cases with metastatic pulmonary nodule and 21 cases without metastatic nodule. Eleven radiologists, including eight residents and three certified radiologists, provided their confidence levels for the presence or absence of pulmonary nodules without and with temporal subtraction. Their performances without and with temporal subtraction were evaluated by means of receiver operating characteristic analysis with both independent and sequential tests. RESULTS: For the independent test, the radiologists' Az (area under the receiver operating characteristic curve) values were 0.871 without and 0.954 with temporal subtraction, compared with 0.882 and 0.955, respectively, for the sequential test. Diagnosis accuracy was significantly improved with the use of temporal subtraction. There was no significant difference in Az values between the independent and sequential tests. CONCLUSION: Temporal subtraction is useful in the detection of metastatic pulmonary nodules, and this technique augments the value of digital chest radiography.     

Continuous versus categorical data for ROC analysis: some quantitative considerations

RATIONALE AND OBJECTIVES: Several authors have encouraged the use of a quasi-continuous rating scale for data collection in receiver operating characteristic (ROC) curve analysis of diagnostic modalities, rather than rating scales based on five to seven ordinal categories or levels of suspicion. Although many investigators have gone over to this method, a discussion of the issues continues. The present work provides a quantitative analysis from the viewpoint of measurement science. MATERIALS AND METHODS: A simple model of the effect of data discretization or quantization on the measurement of the variance of noisy data was developed. Then Monte Carlo simulations of multiple-reader, multiple-case ROC experiments were performed and analyzed in terms of components-of-variance models to investigate the effect of data quantization in that more complex setting. RESULTS: For single-reader studies, discretization into five categories can reduce the precision of ROC measurements by a large amount. The effect may be attenuated in multireader studies. CONCLUSION: More precise measurements of diagnostic detection performance and thus more efficient use of resources are served by good measurement methods. These are promoted by the use of a quasi-continuous rating scale in ROC studies.     

Validation of the summary ROC for diagnostic test meta-analysis: a Monte Carlo simulation

RATIONALE AND OBJECTIVES: The author performed this study to test a technique for validating the logit regression method for summary receiver operating characteristic (ROC) meta-analysis, perform initial validation studies, and identify areas for further investigation. MATERIALS AND METHODS: Monte Carlo simulation was performed by using a custom macro program for a personal computer spreadsheet. The program creates simulated data sets based on user-specified parameters, performs a meta-analysis on the data sets, and logs the results so the accuracy and variability of the method can be measured. The program can also be used to measure the effects of changes in study design and meta-analysis parameters. RESULTS: For the base case of a small meta-analysis (10 studies) of small trials (mean, 50 patients), the meta-analysis results closely matched the input sensitivity and specificity when they were less than 80%. Systematic errors, if any, were small. At sensitivities and specificities greater than 80%, the true sensitivity or specificity was underestimated by up to 2% in the meta-analysis. Confidence intervals calculated with the summary ROC curve were reasonably conservative, although they too fell below the true results when sensitivity or specificity was greater than 80%. The underestimation was eliminated when the simulation was repeated for a much larger trial (mean, 1,000 cases per study)--even with a sensitivity and specificity of 98%. CONCLUSION: The Littenberg-Moses method for summary ROC meta-analysis is effective for obtaining an accurate summary estimate of diagnostic test performance, although the continuity correction introduces a small downward bias in the meta-analysis of small trials.