Magnetic resonance imaging of the knee at 3 and 7 Tesla: a comparison using dedicated multi-channel coils and optimised 2D and 3D protocols

Objectives

To show the feasibility and possible superiority of two 7 Tesla knee protocols (“7?T high resolution” and “7?T quick”) using a new 28-channel knee coil compared to an optimised 3?T knee protocol using an 8-channel knee coil.

Methods

The study was approved by the ethics committee. Both 3?T and 7?T MRI of the knee were performed in 10 healthy volunteers (29.6?±?7.9?years), with two 2D sequences (PD-TSE and T1-SE) and three isotropic 3D sequences (TRUFI, FLASH and PD-TSE SPACE). Quantitative contrast-to-noise ratio (CNR) and qualitative evaluations were performed by different readers, and intra- and inter-rater agreement was assessed.

Results

The signal-to-noise ratio (SNR) as well as the CNR values for cartilage–bone, cartilage–fluid, cartilage–menisci and menisci–fluid were, in most cases, higher at 7?T compared to 3?T, and the 7?T quick measurement was slightly superior compared to the 7?T high-resolution measurement. The results of the subjective qualitative analysis were higher for the 7?T measurements compared to the 3?T measurements. Inter- and intra-observer reliability was high (0.884–0.999).

Conclusions

Through higher field strength and an optimal coil, resolution at 7?T can be increased and acquisition time can be reduced, with superior quantitative and comparable qualitative results compared to 3?T.

Key Points

? 7-Tesla MRI using a dedicated 28-channel knee coil provides high quality. ? Isotropic 3D-MR sequences benefit more from ultra-high-field than basic 2D sequences. ? At 7 T high resolution and short MR acquisition are possible. ? Dedicated coils ensure the clinical applicability of musculoskeletal MRI at ultra-high-field.     

Quantitative assessment of right ventricular function and pulmonary regurgitation in surgically repaired tetralogy of Fallot using 256-slice CT: comparison with 3-Tesla MRI

Objectives

To compare 256-slice cardiac computed tomography (CCT) with cardiac magnetic resonance (CMR) imaging to assess right ventricular (RV) function and pulmonary regurgitant fraction (PRF) in patients with repaired tetralogy of Fallot (TOF).

Methods

Thirty-three consecutive patients with repaired TOF underwent retrospective ECG-gated CCT and 3-Tesla CMR. RV and left ventricular (LV) end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV) and ejection fraction (EF) were measured using CCT and CMR. PRF-CCT (%) was defined as (RVSV???LVSV)/RVSV. PRF-CMR (%) was measured by the phase-contrast method. Repeated measurements were performed to determine intra- and interobserver variability.

Results

CCT measurements, including PRF, correlated highly with the CMR reference (r?=?0.71–0.96). CCT overestimated RVEDV (mean difference, 17.1?±?2.9 ml), RVESV (12.9?±?2.1 ml) and RVSV (4.2?±?2.0 ml), and underestimated RVEF (?2.6?±?1.0 %) and PRF (?9.1?±?2.0 %) compared with CMR. The limits of agreement between CCT and CMR were in a good range for all measurements. The variability in CCT measurements was lower than those in CMR. The estimated effective radiation dose was 7.6?±?2.6 mSv.

Conclusions

256-slice CCT can assess RV function and PRF with relatively low dose radiation exposure in patients with repaired TOF, but overestimates RV volume and underestimates PRF.

Key points

? 256-slice CT assessment of RV function is highly reproducible in repaired TOF. ? Pulmonary regurgitation can be evaluated by biventricular systolic volume difference. ? CT overestimates RV volume and underestimates pulmonary regurgitation, compared with MRI.     

Salvage assessment with cardiac MRI following acute myocardial infarction underestimates potential for recovery of systolic strain

Objectives

Our aim was to evaluate the relationship between the degree of salvage following acute ST elevation myocardial infarction (STEMI) and subsequent reversible contractile dysfunction using cardiac magnetic resonance (CMR) imaging.

Methods

Thirty-four patients underwent CMR examination 1–7 days after primary percutaneous coronary intervention (PPCI) for acute STEMI with follow-up at 1 year. The ischaemic area-at-risk (AAR) was assessed with T2-weighted imaging and myocardial necrosis with late gadolinium enhancement. Myocardial strain was quantified with complementary spatial modulation of magnetisation (CSPAMM) tagging.

Results

Ischaemic segments with poor (<25 %) or intermediate (26–50 %) salvage index were associated with worse Eulerian circumferential (Ecc) strain immediately post-PPCI (?9.1 %?±?0.6, P?=?0.033 and ?11.8 %?±?1.3, P?=?0.003, respectively) than those with a high (51–100 %) salvage index (?14.4 %?±?1.3). Mean strain in ischaemic myocardium improved between baseline and follow-up (?10.1 %?±?0.5 vs. ?16.2 %?±?0.5 %, P?<?0.0001). Segments with poor salvage also showed an improvement in strain by 1 year (?9.1 %?±?0.6 vs. ?15.3 %?±?0.6, P?=?0.033) although they remained the most functionally impaired.

Conclusions

Partial recovery of peak systolic strain following PPCI is observed even when apparent salvage is less than 25 %. Late gadolinium enhancement (LGE) may not equate to irreversibly injured myocardium and salvage assessment performed within the first week of revascularisation may underestimate the potential for functional recovery.

Key Points

? MRI can measure how much myocardium is damaged after a heart attack. ? Heart muscle that appears initially non-viable may sometimes partially recover. ? Enhancement around the edges of infarcts may resolve over time. ? Evaluating new cardio-protective treatments with MRI requires appreciation of its limitations.     

Reduction of metallic coil artefacts in computed tomography body imaging: effects of a new single-energy metal artefact reduction algorithm

Objectives

We evaluated the effect of a single-energy metal artefact reduction (SEMAR) algorithm for metallic coil artefact reduction in body imaging.

Methods

Computed tomography angiography (CTA) was performed in 30 patients with metallic coils (10 men, 20 women; mean age, 67.9?±?11 years). Non-SEMAR images were reconstructed with iterative reconstruction alone, and SEMAR images were reconstructed with the iterative reconstruction plus SEMAR algorithms. We compared image noise around metallic coils and the maximum diameters of artefacts from coils between the non-SEMAR and SEMAR images. Two radiologists visually evaluated the metallic coil artefacts utilizing a four-point scale: 1 = extensive; 2 = strong; 3 = mild; 4 = minimal artefacts.

Results

The image noise and maximum diameters of the artefacts of the SEMAR images were significantly lower than those of the non-SEMAR images (65.1?±?33.0 HU vs. 29.7?±?10.3 HU; 163.9?±?54.8 mm vs. 10.3?±?19.0 mm, respectively; P?<?0.001). Better visual scores were obtained with the SEMAR technique (3.4?±?0.6 vs. 1.0?±?0.0, P?<?0.001).

Conclusions

The SEMAR algorithm significantly reduced artefacts caused by metallic coils compared with the non-SEMAR algorithm. This technique can potentially increase CT performance for the evaluation of post-coil embolization complications.

Key Points

? The new algorithm involves a raw data- and image-based reconstruction technique. ? The new algorithm mitigates artefacts from metallic coils on body CT images. ? The new algorithm significantly reduced artefacts caused by metallic coils. ? The metal artefact reduction algorithm improves CT image quality after coil embolization.

     

Cardiovascular magnetic resonance imaging assessment of diastolic dysfunction in a population without heart disease: a gender-based study

Objectives

Asymptomatic left ventricular (LV) diastolic dysfunction is increasingly recognised as an important diagnosis. Our goal was to study the prevalence and gender differences in subclinical LV diastolic dysfunction, using cardiovascular magnetic resonance imaging (CMR) at 3 T.

Methods

We prospectively studied 48 volunteers (19 male and 29 female, mean age 49?±?7 years) with no evidence of cardiovascular disease. We used CMR to measure left atrium (LA) and LV volumes, LV peak filling rate and transmitral flow.

Results

The overall prevalence of LV diastolic dysfunction in our cohort varied between 20 % (based on evaluation of LV filing profiles) and 24 % (based on the evaluation of the transmitral flow). The prevalence of diastolic dysfunction was higher in men than in women, independently of the criteria used (P between 0.004 and 0.022). Indexed LV end-diastolic volume, indexed LV stroke volume, indexed LV mass, indexed LA minimum volume and indexed LA maximum volume were significantly greater in men than in women (P?<?0.05). All the subjects had LV ejection fractions within the normal range.

Conclusions

It is clinically feasible to study diastolic flow and LV filling with CMR. CMR detected diastolic dysfunction in asymptomatic men and women.

Key Points

? CMR imaging offers new possibilities in assessing left ventricular diastolic function. ? The prevalence of diastolic dysfunction is higher in men than in women. ? The prevalence of some diastolic dysfunction in a normal population is 24 %.     

Evaluation of 100 brain examinations using a 3 Tesla MR-compatible incubator—safety, handling, and image quality

Introduction

Several studies have revealed the importance of brain imaging in term and preterm infants. The aim of this retrospective study was to review safety, handling, and image quality of MR brain imaging using a new 3 Tesla MR-compatible incubator.

Methods

Between 02/2011 and 05/2012 100 brain MRIs (84 infants, mean gestational age 32.2?±?4.7 weeks, mean postmenstrual age at imaging 40.6?±?3.4 weeks) were performed using a 3 Tesla MR-compatible incubator with dedicated, compatible head coil. Seventeen examinations (13 infants, mean gestational age 35.1?±?5.4 weeks, mean postmenstrual age at imaging 47.8?±?7.4 weeks) with a standard head coil served as a control. Image analysis was performed by a neuroradiologist and a pediatric radiologist in consensus.

Results

All but two patients with known apnea were transferred to the MR unit and scanned without problems. Handling was easier and faster with the incubator; relevant motion artifacts (5.9 vs. 10.8 %) and the need for repetitive sedation (43.0 vs. 86.7 %) were reduced. Considering only images not impaired by motion artifacts, image quality (4.8?±?0.4 vs. 4.3?±?0.8, p?=?0.047) and spatial resolution (4.7?±?0.4 vs. 4.2?±?0.6, p?=?0.011) of T2-weighted images were scored significantly higher in patients imaged with the incubator. SNR increased significantly (171.6?±?54.5 vs. 80.5?±?19.8, p?<?0.001) with the use of the incubator.

Conclusion

Infants can benefit from the use of a 3 Tesla MR-compatible incubator because of its safety, easier, and faster handling (compared to standard imaging) and possibility to obtain high-quality MR images even in unstable patients.     

Cardiac magnetic resonance: is phonocardiogram gating reliable in velocity-encoded phase contrast imaging?

Objectives

To assess the diagnostic accuracy of phonocardiogram (PCG) gated velocity-encoded phase contrast magnetic resonance imaging (MRI).

Methods

Flow quantification above the aortic valve was performed in 68 patients by acquiring a retrospectively PCG- and a retrospectively ECG-gated velocity-encoded GE-sequence at 1.5?T. Peak velocity (PV), average velocity (AV), forward volume (FV), reverse volume (RV), net forward volume (NFV), as well as the regurgitant fraction (RF) were assessed for both datasets, as well as for the PCG-gated datasets after compensation for the PCG trigger delay.

Results

PCG-gated image acquisition was feasible in 64 patients, ECG-gated in all patients. PCG-gated flow quantification overestimated PV (Δ 3.8?±?14.1?cm/s; P?=?0.037) and underestimated FV (Δ -4.9?±?15.7?ml; P?=?0.015) and NFV (Δ -4.5?±?16.5?ml; P?=?0.033) compared with ECG-gated imaging. After compensation for the PCG trigger delay, differences were only observed for PV (Δ 3.8?±?14.1?cm/s; P?=?0.037). Wide limits of agreement between PCG- and ECG-gated flow quantification were observed for all variables (PV: -23.9 to 31.4?cm/s; AV: -4.5 to 3.9?cm/s; FV: -35.6 to 25.9?ml; RV: -8.0 to 7.2?ml; NFV: -36.8 to 27.8?ml; RF: -10.4 to 10.2?%).

Conclusions

The present study demonstrates that PCG gating in its current form is not reliable enough for flow quantification based on velocity-encoded phase contrast gradient echo (GE) sequences.

Key Points

? Phonocardiogram gating is an alternative to ECG-gating in cardiac MRI. ? Phonocardiogram gating shows only limited reliability for velocity-encoded cardiac MRI. ? Further refinements of the post-processing algorithm are necessary.     

Electro-mechanical characteristics of myocardial infarction border zones and ventricular arrhythmic risk: novel insights from grid-tagged cardiac magnetic resonance imaging

Objective

To investigate whether grid-tag myocardial strain evaluation can characterise ‘border-zone’ peri-infarct region and identify patients at risk of ventricular arrhythmia as the peri-infarct myocardial zone may represent an important contributor to ventricular arrhythmia following ST-segment elevation myocardial infarction (STEMI).

Methods

Forty-five patients with STEMI underwent cardiac magnetic resonance (CMR) imaging on days 3 and 90 following primary percutaneous coronary intervention (PCI). Circumferential peak circumferential systolic strain (CS) and strain rate (CSR) were calculated from grid-tagged images. Myocardial segments were classified into ‘infarct’, ‘border-zone’, ‘adjacent’ and ‘remote’ regions by late-gadolinium enhancement distribution. The relationship between CS and CSR and these distinct myocardial regions was assessed. Ambulatory Holter monitoring was performed 14?days post myocardial infarction (MI) to estimate ventricular arrhythmia risk via evaluation of heart-rate variability (HRV).

Results

We analysed 1,222 myocardial segments. Remote and adjacent regions had near-normal parameters of CS and CSR. Border-zone regions had intermediate CS (-9.0?±?4.6 vs -5.9?±?7.4, P?P?P?=?0.03).

Conclusion

Grid-tagged CMR-derived myocardial strain accurately characterises the mechanical characteristics of ‘border-zone’ peri-infarct region. Presence of ‘border-zone’ peri-infarct region correlated with a surrogate marker of heightened arrhythmia risk following STEMI.

Key Points

? Grid-tagged cardiac magnetic resonance (CMR) offers new insights into myocardial mechanical function. ? Grid-tagged CMR identified different characteristics in ‘border-zone’ and ‘adjacent’ peri-infarct myocardial regions. ? Reduced very-low-frequency (VLF) power is associated with arrhythmic and mortality risk. ? The presence of ‘border-zone’ peri-infarct region correlated with reduced VLF power.     

Cardiac MRI: evaluation of phonocardiogram-gated cine imaging for the assessment of global und regional left ventricular function in clinical routine

Objectives

To validate a phonocardiogram (PCG)-gated cine imaging approach for the assessment of left ventricular (LV) function.

Methods

In this prospective study, cine MR imaging of the LV was performed twice in 79 patients by using retrospectively PCG- and retrospectively ECG-gated cine SSFP sequences at 1.5?T. End-diastolic volumes (EDV), end-systolic volumes (ESV), stroke volumes (SV), ejection fraction (EF), muscle mass (MM), as well as regional wall motion were assessed. Subgroup analyses were performed for patients with valvular defects and for patients with dysrhythmia.

Results

PCG-gated imaging was feasible in 75 (95%) patients, ECG-gating in all patients. Excellent correlations were observed for all volumetric parameters (r?>?0.98 for all variables analysed). No significant differences were observed for EDV (?0.24?±?3.14?mL, P?=?0.5133), ESV (?0.04?±?2.36?mL, P?=?0.8951), SV (?0.20?±?3.41?mL, P?=?0.6083), EF (?0.16?±?1.98%, P?=?0.4910), or MM (0.31?±?4.2?g, P?=?0.7067) for the entire study cohort, nor for either of the subgroups. PCG- and ECG-gated cine imaging revealed similar results for regional wall motion analyses (115 vs. 119 segments with wall motion abnormalities, P?=?0.3652).

Conclusion

The present study demonstrates that PCG-gated cine imaging enables accurate assessment of global and regional LV function in the vast majority of patients in clinical routine.

Key Points

• Phonocardiogram-gating is an alternative to electrocardiographic-gating in cardiac MR.
• Phonocardiogram-gated imaging allows reliable assessment of global and regional left-ventricular function.
• Phonocardiogram-gating is feasible in patients with valvular lesions or cardiac dysrhythmia.
• Because phonocardiogram-gating is insensitive to magneto-hydrodynamic effects, it is suitable for ultra-high field.

     

Imaging characterization of benign and malignant pheochromocytoma or paraganglioma: comparison between MIBG uptake and MR signal intensity ratio

Objective

We compared metaiodobenzylguanidine (MIBG) uptake and magnetic resonance (MR) signal intensity ratio in differentiating benign and malignant disease in patients with pheochromocytoma or paraganglioma.

Methods

Eighteen patients (9 men, mean age 37?±?8?years) with pheochromocytoma or paraganglioma underwent MR imaging and iodine-131 MIBG scintigraphy. MR signal intensity ratio was measured on T1 and T2-weighted images using region of interest analysis and intensity ratio of MIBG uptake was calculated for each tumor lesion on 48?h images.

Results

A total of 28 tumor lesions was analyzed of which 12 were benign and 16 malignant. MIBG uptake intensity ratio was significantly higher in malignant lesions compared to benign (5.2?±?2.4 and 2.9?±?1.4, respectively, p?<?0.01). On the contrary, no significant difference in tumor size and MR signal intensity ratio between malignant and benign tumor lesions was observed.

Conclusions

In patients with pheochromocytoma or paraganglioma, iodine-131 MIBG uptake is able to differentiate between benign and malignant disease, while MR imaging is not useful for this purpose. The higher MIBG uptake observed in malignant lesions could reflect major tumor storage of catecholamines compared to benign lesions.     

Dixon-based MRI for assessment of muscle-fat content in phantoms,healthy volunteers and patients with achillodynia: comparison to visual assessment of calf muscle quality

Objectives

To quantify the muscle fat-content (MFC) in phantoms, volunteers and patients with achillodynia using two-point Dixon-based magnetic resonance imaging (2pt-MRI_DIXON) in comparison to MR spectroscopy (MRS) and visual assessment of MFC.

Methods

Two-point Dixon-based MRI was used to measure the MFC of 15 phantoms containing 0-100 % fat-content and calf muscles in 30 patients (13 women; 57?±?15 years) with achillodynia and in 20 volunteers (10 women; 30?±?14 years) at 1.5 T. The accuracy of 2pt-MRI_DIXON in quantification of MFC was assessed in vitro using phantoms and in vivo using MRS as the standard of reference. Fat-fractions derived from 2pt-MRI_DIXON (FF_DIXON) and MRS (FF_MRS) were related to visual assessment of MFC (Goutallier grades 0–4) and Achilles-tendon quality (grade 0-4).

Results

Excellent linear correlation was demonstrated for FF_DIXON with phantoms and with FF_MRS in patients (p _c?=?0.997/0.995; p?<?0.001). FF_DIXON of the gastrocnemius muscle was significantly higher (p?=?0.002) in patients (7.0 %?±?4.7 %) compared with volunteers (3.6 %?±?0.7 %), whereas visual-grading showed no difference between both groups (p?>?0.05). FF_MRS and FF_DIXON were significantly higher in subjects with (>grade 1) structural damage of the Achilles-tendon (p?=?0.01).

Conclusions

Two-point Dixon-based MRI allows for accurate quantification of MFC, outperforming visual assessment of calf muscle fat. Structural damage of the Achilles tendon is associated with a significantly higher MFC.

Key points

? Two-point Dixon-based MRI allows accurate quantification of muscular fat content (MFC). ? Quantitative analysis outperforms visual analysis in the detection of elevated MFC. ? Achillodynia results in an increased MFC of the gastrocnemius muscles. ? Structural damage of the Achilles tendon further increases the MFC.     

Accuracy of dual-energy computed tomography for the measurement of iodine concentration using cardiac CT protocols: validation in a phantom model

Purpose

To assess the accuracy of dual-energy CT (DECT) for the quantification of iodine concentrations in a thoracic phantom across various cardiac DECT protocols and simulated patient sizes.

Materials and methods

Experiments were performed on first- and second-generation dual-source CT (DSCT) systems in DECT mode using various cardiac DECT protocols. An anthropomorphic thoracic phantom was equipped with tubular inserts containing known iodine concentrations (0–20 mg/mL) in the cardiac chamber and up to two fat-equivalent rings to simulate different patient sizes. DECT-derived iodine concentrations were measured using dedicated software and compared to true concentrations. General linear regression models were used to identify predictors of measurement accuracy

Results

Correlation between measured and true iodine concentrations (n?=?72) across CT systems and protocols was excellent (R?=?0.994–0.997, P?<?0.0001). Mean measurement errors were 3.0?±?7.0 % and ?2.9?±?3.8 % for first- and second-generation DSCT, respectively. This error increased with simulated patient size. The second-generation DSCT showed the most stable measurements across a wide range of iodine concentrations and simulated patient sizes.

Conclusion

Overall, DECT provides accurate measurements of iodine concentrations across cardiac CT protocols, strengthening the case for DECT-derived blood volume estimates as a surrogate of myocardial blood supply.

Key Points

? Dual-energy CT provides new opportunities for quantitative assessment in cardiac imaging. ? DECT can quantify myocardial iodine as a surrogate for myocardial perfusion. ? DECT measurements of iodine concentrations are overall very accurate. ? The accuracy of such measurements decreases as patient size increases.     

Follow-up of coiled intracranial aneurysms: comparison of 3D time-of-flight and contrast-enhanced magnetic resonance angiography at 3T in a large, prospective series

Objectives

To compare 3D-TOF magnetic resonance angiography (MRA) and contrast-enhanced MRA (CE-MRA) sequences at 3T in the follow-up of coiled aneurysms with digital subtracted angiography (DSA) as the gold standard.

Methods

DSA, 3D-TOF and CE-MRA were performed in a prospective series of 126 aneurysms in 96 patients (57 female, 39 male; age: 25–75 years, mean: 51.3?±?11.3 years). The quality of aneurysm occlusion was assessed independently and anonymously by a core laboratory.

Results

Using DSA (gold standard technique), total occlusion was depicted in 57 aneurysms (45.2%), neck remnant in 34 aneurysms (27.0%) and aneurysm remnant in 35 aneurysms (27.8%). Sensitivity, specificity, positive predictive value and negative predictive value were very similar with 3D-TOF and CE-MRA. Visibility of coils was much better with 3D-TOF (95.2%) than with CE-MRA (23.0%) (P?P?=?0.012).

Conclusions

In this large prospective series of patients with coiled aneurysms, at 3T 3D-TOF MRA was equivalent to CE-MRA for the evaluation of aneurysm occlusion, but coil visibility was superior at 3D-TOF. Thus the use of 3D-TOF at 3T is recommended for the follow-up of coiled intracranial aneurysms.

Key Points

? Different Magnetic Resonance (MR) imaging techniques are used to evaluate intracranial aneurysms. ? At 3T MR, 3D-TOF and CE-MRA appear equivalent for evaluating coiled aneurysms.. ? Coils are better visualised on 3D-TOF than on CE-MRA. ? Combined analysis of 3D-TOF and CE-MRA does not seem helpful. ? At 3T, 3D-TOF techniques are recommended for monitoring patients with coiled aneurysms.     

Diffusivity of intraorbital lymphoma vs. IgG4-related DISEASE: 3D turbo field echo with diffusion-sensitised driven-equilibrium preparation technique

Objectives

3D turbo field echo with diffusion-sensitised driven-equilibrium preparation (DSDE-TFE) is a novel non-echo planar technique for diffusion-weighted (DW) imaging. The purpose of this study was to differentiate intraorbital lymphoma from immunoglobulin G4-related disease (IgG4-RD) using the apparent diffusion coefficient (ADC) derived from DSDE-TFE.

Methods

Fifteen patients with lymphomas and 8 with IgG4-RDs underwent imaging. ADC and signal intensities compared with normal grey matter on T1-weighted images, fat-suppressed T2-weighted images and fat-suppressed postcontrast T1-weighted images were measured. Statistical analyses were performed using the Mann–Whitney U test and receiver operating characteristic (ROC) analysis.

Results

Intraorbital lesions were clearly visualised on DSDE-TFE without obvious geometrical distortion. The ADC of lymphoma (1.25?±?0.50?×?10^?3 mm²/s; mean ± standard deviation) was significantly lower than that of IgG4-RD (1.67?±?0.84?×?10^?3 mm²/s; P?<?0.05). Conventional sequences could not separate lymphoma from IgG4-RD (0.93?±?0.18 vs. 0.94?±?0.21 on T1-weighted images, 0.92?±?0.17 vs. 0.95?±?0.14 on T2-weighted images and 2.03?±?0.35 vs. 2.30?±?0.58 on postcontrast T1-weighted images, for lymphoma and IgG4-RD, respectively; P?>?0.05). ROC analysis showed the best diagnostic performance with ADC.

Conclusion

The apparent diffusion coefficient derived from diffusion-sensitised driven-equilibrium preparation techniques may help to differentiate lymphoma from immunoglobulin G4-related disease.

Key Points

? Distinguishing between orbital lymphoma and immunoglobulin G4-related disease can be difficult ? Intraorbital lesions were clearly visualised on diffusion-sensitised driven-equilibrium preparation magnetic resonance techniques. ? Variations in field homogeneity do not affect DSDE-TFE techniques all that much. ? ADCs derived from DSDE-TFE may help differentiate lymphoma from IgG4-RD.     

Anatomical and functional volume concordance between FDG PET,and T2 and diffusion-weighted MRI for cervical cancer: a hybrid PET/MR study

Purpose

To evaluate the concordance among ¹⁸F-FDG PET imaging, MR T2-weighted (T2-W) imaging and apparent diffusion coefficient (ADC) maps with diffusion-weighted (DW) imaging in cervical cancer using hybrid whole-body PET/MR.

Methods

This study prospectively included 35 patients with cervical cancer who underwent pretreatment ¹⁸F-FDG PET/MR imaging. ¹⁸F-FDG PET and MR images were fused using standard software. The percent of the maximum standardized uptake values (SUV_max) was used to contour tumours on PET images, and volumes were calculated automatically. Tumour volumes measured on T2-W and DW images were calculated with standard techniques of tumour area multiplied by the slice profile. Parametric statistics were used for data analysis.

Results

FDG PET tumour volumes calculated using SUV_max (14.30?±?4.70) and T2-W imaging volume (33.81?±?27.32 cm³) were similar (P?>?0.05) at 35 % and 40 % of SUV_max (32.91?±?18.90 cm³ and 27.56?±?17.19 cm³ respectively) and significantly correlated (P?<?0.001; r?=?0.735 and 0.766). The mean DW volume was 30.48?±?22.41 cm³. DW volumes were not significantly different from FDG PET volumes at either 35 % SUV_max or 40 % SUV_max or from T2-W imaging volumes (P?>?0.05). PET subvolumes with increasing SUV_max cut-off percentage showed an inverse change in mean ADC values on DW imaging (P?<?0.001, ANOVA).

Conclusion

Hybrid PET/MR showed strong volume concordance between FDG PET, and T2-W and DW imaging in cervical cancer. Cut-off at 35 % or 40 % of SUV_max is recommended for ¹⁸F-FDG PET/MR SUV-based tumour volume estimation. The linear tumour subvolume concordance between FDG PET and DW imaging demonstrates individual regional concordance of metabolic activity and cell density.     

Breast MRI at 7 Tesla with a bilateral coil and T1-weighted acquisition with robust fat suppression: image evaluation and comparison with 3 Tesla

Objectives

To evaluate the image quality of T1-weighted fat-suppressed breast MRI at 7 T and to compare 7-T and 3-T images.

Methods

Seventeen subjects were imaged using a 7-T bilateral transmit-receive coil and 3D gradient echo sequence with adiabatic inversion-based fat suppression (FS). Images were graded on a five-point scale and quantitatively assessed through signal-to-noise ratio (SNR), fibroglandular/fat contrast and signal uniformity measurements.

Results

Image scores at 7 and 3 T were similar on standard-resolution images (1.1?×?1.1?×?1.1-1.6 mm³), indicating that high-quality breast imaging with clinical parameters can be performed at 7 T. The 7-T SNR advantage was underscored on 0.6-mm isotropic images, where image quality was significantly greater than at 3 T (4.2 versus 3.1, P?≤?0.0001). Fibroglandular/fat contrast was more than two times higher at 7 T than at 3 T, owing to effective adiabatic inversion-based FS and the inherent 7-T signal advantage. Signal uniformity was comparable at 7 and 3 T (P?<?0.05). Similar 7-T image quality was observed in all subjects, indicating robustness against anatomical variation.

Conclusion

The 7-T bilateral transmit-receive coil and adiabatic inversion-based FS technique produce image quality that is as good as or better than at 3 T.

Key Points

? High image quality bilateral breast MRI is achievable with clinical parameters at 7 T. ? 7-T high-resolution imaging improves delineation of subtle soft tissue structures. ? Adiabatic-based fat suppression provides excellent fibroglandular/fat contrast at 7 T. ? 7- and 3-T 3D T1-weighted gradient-echo images have similar signal uniformity. ? The 7-T dual solenoid coil enables bilateral imaging without compromising uniformity.     

Comparison of left ventricular function assessment using phonocardiogram- and electrocardiogram-triggered 2D SSFP CINE MR imaging at 1.5 T and 3.0 T

Objective

As high-field cardiac MRI (CMR) becomes more widespread the propensity of ECG to interference from electromagnetic fields (EMF) and to magneto-hydrodynamic (MHD) effects increases and with it the motivation for a CMR triggering alternative. This study explores the suitability of acoustic cardiac triggering (ACT) for left ventricular (LV) function assessment in healthy subjects (n?=?14).

Methods

Quantitative analysis of 2D CINE steady-state free precession (SSFP) images was conducted to compare ACT’s performance with vector ECG (VCG). Endocardial border sharpness (EBS) was examined paralleled by quantitative LV function assessment.

Results

Unlike VCG, ACT provided signal traces free of interference from EMF or MHD effects. In the case of correct R-wave recognition, VCG-triggered 2D CINE SSFP was immune to cardiac motion effects—even at 3.0 T. However, VCG-triggered 2D SSFP CINE imaging was prone to cardiac motion and EBS degradation if R-wave misregistration occurred. ACT-triggered acquisitions yielded LV parameters (end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF) and left ventricular mass (LVM)) comparable with those derived from VCG-triggered acquisitions (1.5 T: ESV_VCG?=?(56?±?17) ml, EDV_VCG?=?(151?±?32) ml, LVM_VCG?=?(97?±?27) g, SV_VCG?=?(94?±?19) ml, EF_VCG?=?(63?±?5)% cf. ESV_ACT?=?(56?±?18) ml, EDV_ACT?=?(147?±?36) ml, LVM_ACT?=?(102?±?29) g, SV_ACT?=?(91?±?22) ml, EF_ACT?=?(62?±?6)%; 3.0 T: ESV_VCG?=?(55?±?21) ml, EDV_VCG?=?(151?±?32) ml, LVM_VCG?=?(101?±?27) g, SV_VCG?=?(96?±?15) ml, EF_VCG?=?(65?±?7)% cf. ESV_ACT?=?(54?±?20) ml, EDV_ACT?=?(146?±?35) ml, LVM_ACT?=?(101?±?30) g, SV_ACT?=?(92?±?17) ml, EF_ACT?=?(64?±?6)%).

Conclusions

ACT’s intrinsic insensitivity to interference from electromagnetic fields renders it suitable for clinical CMR.     

Combination of chemical suppression techniques for dual suppression of fat and silicone at diffusion-weighted MR imaging in women with breast implants

Objectives

Silicone breast prostheses prove technically challenging when performing diffusion-weighted MR imaging in the breasts. We describe a combined fat and chemical suppression scheme to achieve dual suppression of fat and silicone, thereby improving the quality of diffusion-weighted images in women with breast implants.

Methods

MR imaging was performed at 3.0 and 1.5?T in women with silicone breast implants using short-tau inversion recovery (STIR) fat-suppressed echo-planar (EPI) diffusion-weighted MR imaging (DWI) on its own and combined with the slice-select gradient-reversal (SSGR) technique. Imaging was performed using dedicated breast imaging coils.

Results

Complete suppression of the fat and silicone signal was possible at 3.0?T using EPI DWI with STIR and SSGR, evaluated with dedicated breast coils. However, a residual silicone signal was still perceptible at 1.5?T using this combined approach. Nevertheless, a further reduction in silicone signal at 1.5?T could be achieved by employing thinner slice partitions and the addition of the chemical-selective fat-suppression (CHESS) technique.

Conclusions

DWI using combined STIR and SSGR chemical suppression techniques is feasible to eliminate or reduce silicone signal from prosthetic breast implants.

Key Points

? Breast magnetic resonance imaging (MRI) is frequently needed following breast implants ? Unsuppressed signal from silicone creates artefacts on diffusion-weighted MR sequences ? Dual fat/chemical suppression can eliminate signal from fat and silicone ? STIR with slice selective gradient reversal can suppress fat and silicone signal     

T2 relaxometry of the infrapatellar fat pad after arthroscopic surgery

Objective

To investigate the T2 relaxation values of the infrapatellar fat pad (IFP) after arthroscopic surgery.

Materials and methods

This study was approved by the institutional review board; all individuals signed informed consent. We performed MRI in 16 knees from 8 subjects. Prior to imaging, each subject had unilateral arthroscopic knee surgery and an asymptomatic non-operated contralateral knee. We used a 10-echo multiple-TE fast-spin echo pulse sequence for creation of T2 relaxation time maps. Two musculoskeletal radiologists independently placed regions of interest in the IFP, suprapatellar subcutaneous and deep intermuscular adipose tissue. Qualitative assessments were performed to assess fibrotic changes affecting patellar retinaculum and IFP. Statistical analyses of T2 values determined differences between groups, correlation with time after surgery, and cut-off values to differentiate groups.

Results

The average time between arthroscopy and imaging was 3.5?±?0.4 years. IFP of knees with prior surgery had significantly shorter mean T2 values (133?±?14 ms) compared with control knees (147?±?8 ms, P?=?0.03). There was no significant difference between operated and control knees regarding T2 values of suprapatellar subcutaneous (P?=?0.3) or deep intermuscular adipose tissue (P?=?0.2). There was no correlation between IFP T2 values and time after surgery (P?>?0.2). IFP T2 values?≤?139 ms had 75 % sensitivity and 88 % specificity in identifying prior arthroscopy.

Conclusion

Shortening of T2 relaxation values is present in IFP chronically after arthroscopic surgery and may be an indicator of adipose tissue fibrosis.     

MRI assessment of experimental gliomas using 17.6 T

Introduction

Using ultra-high-field contrast-enhanced magnetic resonance imaging (MRI), an increase of field strength is associated with a decrease of T ₁ relaxivity. Yet, the impact of this effect on signal characteristics and contrast-enhanced pathology remains unclear. Hence, we evaluated the potential of a 17.6-T MRI to assess contrast-enhancing parts of experimentally induced rat gliomas compared to 3 T.

Methods

A total of eight tumor-bearing rats were used for MRI assessments either at 17.6 T (four rats) or at 3 T (four rats) at 11 days after stereotactic implantation of F98 glioma cells into the right frontal lobe. T ₁-weighted sequences were used to investigate signal-to-noise-ratios, contrast-to-noise-ratios, and relative contrast enhancement up to 16 min after double-dose contrast application. In addition, tumor volumes were calculated and compared to histology.

Results

The 17.6-T-derived contrast-enhancing volumes were 31.5?±?15.4 mm³ at 4 min, 38.8?±?12.7 mm³ at 8 min, 51.1?±?12.6 mm³ at 12 min, and 61.5?±?10.8 mm³ at 16 min after gadobutrol injection. Corresponding histology-derived volumes were clearly higher (138.8?±?8.4 mm³; P?<?0.01). At 3 T, contrast-enhancing volumes were 85.2?±?11.7 mm³ at 4 min, 107.3?±?11.0 mm³ at 8 min, 117.0?±?10.5 mm³ at 12 min, and 129.1?±?10.0 mm³ at 16 min after contrast agent application. Averaged histology-derived volumes (139.1?±?13.4 mm³) in this group were comparable to the 16-min volume (P _{?16 min}?=?0.38). Compared to ultra-high-field MRI, all 3-T-derived volumes were significantly higher (P?<?0.02).

Conclusion

Compared to 3-T-derived images and histology, tumor volumes were underestimated by approximately 50 % at 17.6 T. Hence, contrast-enhanced 17.6-T MRI provided no further benefits in tumor measurement compared to 3 T.