7 T Musculoskeletal MRI: Fundamentals and Clinical Implementation.

ABSTRACT: This review summarizes the current state-of-the-art of musculoskeletal 7 T magnetic resonance imaging (MRI), the associated technological challenges, and gives an overview of current and future clinical applications of 1 H-based 7 T MRI. The higher signal-to-noise ratio at 7 T is predominantly used for increased spatial resolution and thus the visualization of anatomical details or subtle lesions rather than to accelerate the sequences. For musculoskeletal MRI, turbo spin echo pulse sequences are particularly useful, but with altered relaxation times, B1 inhomogeneity, and increased artifacts at 7 T; specific absorption rate limitation issues quickly arise for turbo spin echo pulse sequences. The development of dedicated pulse sequence techniques in the last 2 decades and the increasing availability of specialized coils now facilitate several clinical musculoskeletal applications. 7 T MRI is performed in vivo in a wide range of applications for the knee joint and other anatomical areas, such as ultra-high-resolution nerve imaging or bone trabecular microarchitecture imaging. So far, however, it has not been shown systematically whether the higher field strength compared with the established 3 T MRI systems translates into clinical advantages, such as an early-stage identification of tissue damage allowing for preventive therapy or an influence on treatment decisions and patient outcome. At the moment, results tend to suggest that 7 T MRI will be reserved for answering specific, targeted musculoskeletal questions rather than for a broad application, as is the case for 3 T MRI. Future data regarding the implementation of clinical use cases are expected to clarify if 7 T musculoskeletal MRI applications with higher diagnostic accuracy result in patient benefits compared with MRI at lower field strengths.

Prediction of extranodal extension in oropharyngeal cancer patients and carcinoma of unknown primary: value of metabolic tumor imaging with hybrid PET compared with MRI and CT.

OBJECTIVES: The aim of this study was to investigate the value of metabolic tumor imaging using hybrid PET for the preoperative detection of extranodal extension (ENE) in lymph node metastases of oropharyngeal squamous cell carcinoma (OPSCC). METHODS: We performed a retrospective analysis of a consecutive cohort of patients with OPSCC treated with primary surgery with or without adjuvant (chemo-) radiotherapy at the Kantonsspital Sankt-Gallen and the University Hospital Zurich, Switzerland, from 2010 until 2019. Hybrid PET was compared to conventional cross-sectional imaging with MRI and CT. Histopathological presence of ENE of neck dissection specimen served as gold standard. RESULTS: A total number of 234 patients were included in the study, 95 (40.6%) of which had pathological ENE (pENE). CT has a good specificity with 93.7%; meanwhile, MRI was the most sensitive diagnostic method (72.0%). The nodal metabolic tumor parameters (SUVmax, TLG, MTV) were significantly higher in patients with positive ENE (p < 0.001 for all three parameters) than in patients with negative ENE (p < 0.001, for all three parameters). CONCLUSIONS: CT achieved the best specificity, while MRI had the best sensitivity to detect ENE. Nodal metabolic tumor parameters differed significantly between ENE-positive/negative and p16-positive/negative patients. Hence, quantitative data obtained by metabolic imaging might predict presence of ENE and, therefore, could be helpful in customizing therapy management.

Lesion follows function: video-oculography compared with MRI to diagnose internuclear ophthalmoplegia in patients with multiple sclerosis.

BACKGROUND: Video-oculography (VOG) is used to quantify functional deficits in internuclear ophthalmoplegia (INO), whereas MRI can detect the corresponding structural lesions in the medial longitudinal fasciculus (MLF). This study investigates the diagnostic agreement of MRI compared to VOG measurements. METHODS: We prospectively compared structural MRI findings and functional VOG measures of 63 MS patients to assess their diagnostic agreement for INO. RESULTS: MRI detected 12 true-positive and 92 true-negative MLF lesions for INO compared to VOG (12 true-positive and 38 true-negative patients) but identified one-third of the MLF lesions on the wrong side. MRI ratings were specific (92.0%) to detect MLF lesions but not sensitive (46.2%) for diagnosing INO (86.4% and 63.2% by patient). Accordingly, MRI has a high positive likelihood ratio of 5.77 but a modest negative likelihood ratio of 0.59 for the probability of INO (4.63 and 0.43) with an accuracy of 82.5% (79.4%). CONCLUSION: MRI assessments are highly specific but not sensitive for detecting INO compared to VOG. While MRI identifies MLF lesions in INO, VOG quantifies the deficit. As a simple, quick, and non-invasive test for diagnosing and tracking functional INO deficits, it will hopefully find its place in the diagnostic and therapeutic pathways of MS.

Quantitative 23 Na-MRI of the intervertebral disk at 3 T.

Monitoring the tissue sodium content (TSC) in the intervertebral disk geometry noninvasively by MRI is a sensitive measure to estimate changes in the proteoglycan content of the intervertebral disk, which is a biomarker of degenerative disk disease (DDD) and of lumbar back pain (LBP). However, application of quantitative sodium concentration measurements in 23 Na-MRI is highly challenging due to the lower in vivo concentrations and smaller gyromagnetic ratio, ultimately yielding much smaller signal relative to 1 H-MRI. Moreover, imaging the intervertebral disk geometry imposes higher demands, mainly because the necessary RF volume coils produce highly inhomogeneous transmit field patterns. For an accurate absolute quantification of TSC in the intervertebral disks, the B1 field variations have to be mitigated. In this study, we report for the first time quantitative sodium concentration in the intervertebral disks at clinical field strengths (3 T) by deploying 23 Na-MRI in healthy human subjects. The sodium B1 maps were calculated by using the double-angle method and a double-tuned (1 H/23 Na) transceive chest coil, and the individual effects of the variation in the B1 field patterns in tissue sodium quantification were calculated. Phantom measurements were conducted to evaluate the quality of the Na-weighted images and B1 mapping. Depending on the disk position, the sodium concentration was calculated as 161.6 mmol/L-347 mmol/L, and the mean sodium concentration of the intervertebral disks varies between 254.6 ± 54 mmol/L and 290.1 ± 39 mmol/L. A smoothing effect of the B1 correction on the sodium concentration maps was observed, such that the standard deviation of the mean sodium concentration was significantly reduced with B1 mitigation. The results of this work provide an improved integration of quantitative 23 Na-MRI into clinical studies in intervertebral disks such as degenerative disk disease and establish alternative scoring schemes to existing morphological scoring such as the Pfirrmann score.

SUVmax for predicting regional control in oropharyngeal cancer.

PURPOSE: To investigate the predictive value of pretherapeutic metabolic tumor imaging using 18-fluorodeoxyglucose positron emission tomography (FDG-PET) for regional response in oropharyngeal cancer patients undergoing primary (chemo)radiation. METHODS: Retrospective analysis of oropharyngeal cancer patients treated with primary (chemo)radiation at the University Hospital Zurich from 2010 to 2019 with available FDG-PET. The SUVmax of the largest lymph node metastases was recorded. Regional response was assessed using posttherapeutic FDG-PET at 12 weeks and regional recurrence-free survival. RESULTS: 95 patients with a mean age of 68.5 years (SD 10.3) were included. The median pretherapeutic nodal SUVmax was 8.3 (interquartile range 4.4-13.3). A pretherapeutic nodal SUVmax above 6 significantly predicted poorer regional recurrence-free survival (log-rank test, P = 0.009) in univariate analysis. However, in multivariate analysis SUVmax above 6 was not significant in predicting regional recurrence-free survival (Cox regression P = 0.189). Clinical N category showed a trend in which a more severe stage had a poorer regional survival (Cox regression P = 0.073). CONCLUSION: The SUVmax of the largest lymph node metastasis seems to play a role in predicting regional response in oropharyngeal cancer patients, after stratifying for N category. More research is needed to investigate whether highly metabolically active disease is less likely to respond to chemoradiation.

MRI of the Elbow: How to Do It.

The diagnostic cascade for elbow complaints starts with the physical examination and radiographs that already can clarify or rule out many causes. Depending on the suspected pathology, additional imaging is necessary. Magnetic resonance imaging (MRI) has the advantage of accurately demonstrating a broad spectrum of diseases. The main indication for noncontrast MRI of the elbow is chronic epicondylitis. For magnetic resonance (MR) arthrography, it is suspected chondral and osteochondral abnormalities. Indirect MR arthrography is an option when direct arthrography is not practicable. MR arthrography of the elbow with traction is feasible, with promising results for the assessment of the radiocapitellar cartilage.

Measurement variations of MRI and CT in the assessment of tumor depth of invasion in oral cancer: A retrospective study.

PURPOSE: In oral squamous cell carcinoma (OSCC), depth of invasion (DOI) is an important predictive, prognostic, and staging parameter. While it is known that DOI can be estimated from preoperative imaging, an analysis of measurements variations according to imaging modality and to depth of tumor itself is lacking. The aim of the study was to assess the accuracy of imaging-based estimation of DOI in relation with the tumor histological DOI. METHODS: We retrospectively reviewed 121 patients with OSCC treated at University Hospital Zurich. The radiologic DOI of CT, T1-weighted, and T2-weighted MRI were compared with histological DOI. Frequency of relevant imaging artifacts was assessed as well. RESULTS: A total of 110 CT (90.9 %) and 90 MRI (74 %) were analyzed. Both modalities were available for 79 patients (65.3 %). The median histological depth of invasion was 9 mm (IQR 4.5-14). The median depth of invasion was 14 mm (IQR 10-20) on CT, 13 mm (IQR 8.25-18) on T1-weighted MRI, and 13 mm (IQR 9-18.75) on T2-weighted MRI. All diagnostic modalities tended towards an overestimation of the histopathologic DOI from about 5-15 %. This trend was most pronounced for thin tumors, for which both CT and MRI lead to upstaging in over 50 % of the cases. For 25 (22.7 %) patients, dental scattering on CT rendered DOI not estimable. For MRI, 18 patients (20 %) had artifacts (blooming, motion artifacts) rendering DOI not estimable. CONCLUSION: CT and MRI measurements of DOI in OSCC lead to an overestimation of histological DOI, especially in tumors with DOI<5 mm, with upstaging by imaging in over 50 % of the cases. Artifacts were present in more than 20 % of performed images.

Abnormal Connectivity and Brain Structure in Patients With Visual Snow.

OBJECTIVE: Visual snow (VS) is a distressing, life-impacting condition with persistent visual phenomena. VS patients show cerebral hypermetabolism within the visual cortex, resulting in altered neuronal excitability. We hypothesized to see disease-dependent alterations in functional connectivity and gray matter volume (GMV) in regions associated with visual perception. METHODS: Nineteen patients with VS and 16 sex- and age-matched controls were recruited. Functional magnetic resonance imaging (fMRI) was applied to examine resting-state functional connectivity (rsFC). Volume changes were assessed by means of voxel-based morphometry (VBM). Finally, we assessed associations between MRI indices and clinical parameters. RESULTS: Patients with VS showed hyperconnectivity between extrastriate visual and inferior temporal brain regions and also between prefrontal and parietal (angular cortex) brain regions (p < 0.05, corrected for age and migraine occurrence). In addition, patients showed increased GMV in the right lingual gyrus (p < 0.05 corrected). Symptom duration positively correlated with GMV in both lingual gyri (p < 0.01 corrected). CONCLUSION: This study found VS to be associated with both functional and structural changes in the early and higher visual cortex, as well as the temporal cortex. These brain regions are involved in visual processing, memory, spatial attention, and cognitive control. We conclude that VS is not just confined to the visual system and that both functional and structural changes arise in VS patients, be it as an epiphenomenon or a direct contributor to the pathomechanism of VS. These in vivo neuroimaging biomarkers may hold potential as objective outcome measures of this so far purely subjective condition.

Immunocytokines are a promising immunotherapeutic approach against glioblastoma.

Glioblastoma is a poorly immunogenic cancer, and the successes with recent immunotherapies in extracranial malignancies have, so far, not been translated to this devastating disease. Therefore, there is an urgent need for new strategies to convert the immunologically cold glioma microenvironment into a hot one to enable effective antitumor immunity. Using the L19 antibody, which is specific to a tumor-associated epitope of extracellular fibronectin, we developed antibody-cytokine fusions-immunocytokines-with interleukin-2 (IL2), IL12, or tumor necrosis factor (TNF). We showed that L19 accumulated in the tumor microenvironment of two orthotopic immunocompetent mouse glioma models. Furthermore, intravenous administration of L19-mIL12 or L19-mTNF cured a proportion of tumor-bearing mice, whereas L19-IL2 did not. This therapeutic activity was abolished in RAG-/- mice or upon depletion of CD4 or CD8 T cells, suggesting adaptive immunity. Mechanistically, both immunocytokines promoted tumor-infiltrating lymphocytes and increased the amounts of proinflammatory cytokines within the tumor microenvironment. In addition, L19-mTNF induced tumor necrosis. Systemic administration of the fully human L19-TNF fusion protein to patients with glioblastoma (NCT03779230) was safe, decreased regional blood perfusion within the tumor, and was associated with increasing tumor necrosis and an increase in tumor-infiltrating CD4 and CD8 T cells. The extensive preclinical characterization and subsequent clinical translation provide a robust basis for future studies with immunocytokines to treat malignant brain tumors.

Diagnostic accuracy of computed tomography and magnetic resonance imaging compared to surgical exploration for anterior skull base and medial orbital wall infiltration in advanced sinonasal tumors.

BACKGROUND: Knowledge of medial orbital wall (MOW) and anterior skull base (ASB) infiltration is of uttermost importance for staging and therapy planning of advanced sinonasal tumors. METHODS: We assessed the diagnostic performance of preoperative computed tomography (CT) and magnetic resonance imaging (MRI) for MOW and ASB infiltration compared to intraoperative exploration. RESULTS: Both CT and MRI yielded higher diagnostic accuracy for MOW infiltration (Reader 1: 83.6% CT; 89.0% MRI, Reader 2: 91.8% CT, 93.2% MRI) than for ASB infiltration (Reader 1: 82.2% CT, 82.2% MRI, Reader 2: 67.7% CT, 67.7% MRI). Both modalities were equal to the gold standard, except for ASB assessment by Reader 2 with MRI. A postoperative change of T classification is common (Reader 1: 28.8%, Reader 2: 31.5%). CONCLUSIONS: CT and MRI are accurate methods for the assessment of MOW infiltration. ASB assessment is challenging and false-positive and false-negative findings are common with both methods, emphasizing the need for intraoperative exploration.

Quantitative blood oxygenation level-dependent (BOLD) response of the left ventricular myocardium to hyperoxic respiratory challenge at 1.5 and 3.0 T.

The aim of this study was to quantify the response of the myocardial transverse relaxation times (ΔT2*) to hyperoxic respiratory challenge (HRC) at different field strengths in an intra-individual comparison of healthy volunteers and in a patient with coronary artery disease. Blood oxygenation level-dependent (BOLD) cardiovascular MR (CMR) data were acquired in 10 healthy volunteers (five women, five men; mean age, 29 ± 3 years; range, 22-35 years) at 1.5 and 3.0 T. Medical air (21% O2 ), pure oxygen and carbogen (95% O2 , 5% CO2 ) were administered in a block-design temporal pattern to induce normoxia, hyperoxia and hyperoxic hypercapnia, respectively. Average T2* times were derived from measurements by two independent and blind readers in 16 standard myocardial segments on three short-axis slices per patient. Inter- and intra-reader correlations of T2* measurements were good [intra-class correlation coefficient (ICC) = 0.75 and ICC = 0.79, both p < 0.001]. During normoxia, the mean T2* times were 29.9 ± 6.1 ms at 1.5 T and 27.1 ± 6.6 ms at 3.0 T. Both hyperoxic gases induced significant (all p < 0.01) T2* increases (∆T2* hyperoxia: 1.5 T, 12.7%; 3.0 T, 11.2%; hyperoxic hypercapnia: 1.5 T, 13.1%; 3.0 T, 17.7%). Analysis of variance (ANOVA) results indicated a significant (both p < 0.001) effect of the inhaled gases on the T2* times at both 1.5 T (F = 17.74) and 3.0 T (F = 39.99). With regard to the patient imaged at 1.5 T, HRC induced significant T2* increases during hyperoxia and hyperoxic hypercapnia in normal myocardial segments, whereas the T2* response was not significant in ischemic segments (p > 0.23). The myocardial ∆T2* response to HRC can reliably be imaged and quantified with BOLD CMR at both 1.5 and 3.0 T. During HRC, hyperoxia and hyperoxic hypercapnia induce a significant increase in T2*, with ∆T2* being largest at 3.0 T and during hyperoxic hypercapnia in normal myocardial segments.

Magnetic resonance imaging of the liver: apparent diffusion coefficients from multiexponential analysis of b values greater than 50 s/mm2 do not respond to caloric intake despite increased portal-venous blood flow.

PURPOSE: The purpose of this study was to measure potential changes of the apparent diffusion coefficient (ADC) in diffusion-weighted imaging of the liver before and after caloric challenge in correlation to the induced changes in portal vein flow. MATERIALS AND METHODS: The study was approved by the local ethics committee. Each of 10 healthy volunteers underwent 4 measurements in a 1.5-T whole-body magnetic resonance scanner on 2 different days: a first scan after fasting for at least 8 hours and a second scan 30 minutes after intake of a standardized caloric either a protein- or carbohydrate-rich meal. Diffusion-weighted spin-echo echo-planar magnetic resonance images were acquired at b values of 0, 50, 150, 250, 500, 750, and 1000 s/mm. In addition, portal vein flow was quantified with 2-dimensional phase-contrast imaging (velocity encoding parallel to flow direction, 60 cm/s). Mean ADC values for regions of interest in 3 different slices were measured from b50 to b250 and from b500 to b1000 images. RESULTS: Carbohydrate- and protein-rich food intake both resulted in a substantial increase in the portal vein flow (fasting state, 638.6 ± 202.3 mL/min; after protein intake, 1322 ± 266.8; after carbohydrate intake, 1767 ± 421.6). The signal decay with increasingly strong diffusion weighting (b values from 0 to 1000 s/mm2) exhibited a triexponential characteristic, implying fast, intermediate, and slow-moving water-molecule proton-spin ensembles in the liver parenchyma. Mean ADC for high b values (b500-b1000) after fasting was 0.93 ± 0.09 × 10 mm/s; that after protein intake, 0.93 ± 0.11 × 10; and that after carbohydrate intake, 0.93 ± 0.08 × 10. For intermediate b values (b50-b250), the signal-decay constants were 1.27 ± 0.14 × 10 mm/s, 1.28 ± 0.15 × 10, and 1.31 ± 0.09 × 10, respectively. There was no statistically significant difference between fasting and caloric challenge. CONCLUSIONS: The postprandial increase in portal vein flow is not accompanied by a change of liver parenchymal ADC values. In clinical diffusion imaging, patients may be scanned without prescan food-intake preparations. To minimize interference of perfusion effects, liver-tissue molecular water diffusion should be quantified using high b values (≥500 s/mm) only.

Quantitative breast MRI: 2D histogram analysis of diffusion tensor parameters in normal tissue.

OBJECT: Diffusion tensor imaging (DTI) of the breast may provide a powerful new approach for the detection of intraductal processes. The aim of this investigation was to characterize the relation between diffusion tensor parameters [fractional anisotropy (FA), mean diffusivity (MD)] in normal breast tissue to obtain information on the microenvironment of the diffusing water molecules and to provide a systematic approach for DTI analysis. MATERIALS AND METHODS: Seven female, healthy volunteers underwent prospective double-spin-echo prepared echo-planar diffusion-weighted sequence (TR/TE 8,250 ms/74 ms, b values 0 and 500 s/mm (2), six encoding directions, 12 averages, 35 slices) in 4 consecutive weeks (3.0 T). Quantitative maps of diffusion tensor parameters were computed offline with custom routines. The interdependence of MD and FA in different voxels was analysed by linear and exponential regression. RESULTS: All MD and FA maps were of excellent quality. A consistent pattern was observed in that lower fractional anisotropy values were more likely associated with higher mean diffusivity values. The dependence exhibited an exponential behavior with a correlation coefficient R = 0.60 (R linear = 0.57). CONCLUSION: The likelihood with which FA and MD values are observed in a voxel within normal breast tissue is characterized by a specific pattern, which can be described by an exponential model. Moreover, we could show that the proposed technique does not depend on the menstrual cycle.

No damage of joint cartilage of the lower limbs in an ultra-endurance athlete--an MRI-study.

BACKGROUND: Osteoarthritis is an increasing burden in an ageing population. Sports, especially when leading to an overstress of joints, is under suspicion to provoke or at least accelerate the genesis of osteoarthritis. We present the radiologic findings of a 49-years old ultra-endurance athlete with 35 years of training and competing, whose joints of the lower limbs were examined using three different types of magnetic resonance imaging, including a microscopic magnetic resonance imaging coil. To date no case report exists where an ultra-endurance athlete was examined such detailed regarding overuse-injuries of his joints. CASE PRESENTATION: A 49 years old, white, male ultra-endurance athlete reporting no pain during training and racing and with no significant injuries of the lower limbs in his medical history was investigated regarding signs of chronic damage or overuse injuries of the joints of his lower limbs. CONCLUSION: Despite the age of nearly 50 years and a training history of over 35 years, the athlete showed no signs of chronic damage or overuse injuries in the joints of his lower limbs. This leads to the conclusion that extensive sports and training does not compulsory lead to damages of the musculoskeletal system. This is a very important finding for all endurance-athletes as well as for their physicians.

Blood oxygen level-dependent magnetic resonance imaging of the kidneys: influence of spatial resolution on the apparent R2* transverse relaxation rate of renal tissue.

OBJECTIVES: The aim of this study was to quantify the influence of image resolution on the apparent transverse relaxivity (R2*) of the magnetic resonance (MR) signal in human renal tissue in vivo and in phantom measurements. MATERIALS AND METHODS: This prospective study included 17 healthy volunteers (age, 32 ± 8 years, 6 women). Parametrical R2* maps were computed via monoexponential fitting of multiecho 2-dimensional fast-field echo data measured at 1.5 T (repetition time [TR], 150 milliseconds; flip angle [FA], 40°; minimum echo time [TE], 4.6 milliseconds; ΔTE, 5 milliseconds; 16 echoes) and at 3 T (TR, 140 milliseconds; FA, 70°; minimum TE, 2 milliseconds; ΔTE, 5 milliseconds; 16 echoes) with varying nominal volumes of the encoded voxels (from 5.76 to 36.0 mm). For each voxel size, mean R2* values were computed in regions of interest drawn in the left and right renal parenchyma. For data acquired using minimum voxel size, the mean R2* values were computed over the cortex and medulla separately. The squared 2-norm of the residuals was computed to evaluate the goodness of the pixel-wise exponential fits. Six multiecho MR images of a water phantom were acquired using a 2-dimensional fast-field echo sequence (FA, 50°; TR, 108 milliseconds; TE, 4 milliseconds; ΔTE, 20 milliseconds) at 3 T after shim adjustment and in the presence of a uniform background gradient of 40 µT/m. The nominal voxel size was varied in a range between 2 and 12.5 mm. RESULTS: Mean R2* values of 13.04 ± 0.71 s (right renal cortex) and 16.47 ± 1.92 s (right renal medulla) were computed at 1.5 T. At 3 T, the R2* of the right medulla was 28.27 ± 1.52 s and the cortical R2* was 19.22 ± 2.32 s. Comparable relaxivity values were found over the left kidney at both field strengths. Increasing R2* values were observed for increasing voxel volume in both the water phantom and renal tissue data. At a constant slice thickness of 4 mm, the decrease in the in-plane resolution from 1.2 × 1.2 mm to 3.0 × 3.0 mm led to a maximum increase of the renal R2* of 15% at 1.5 T and of 12% at 3 T. Increasing the slice thickness from 3 to 8 mm at a constant in-plane resolution of 1.5 × 1.5 mm resulted in a maximum increase of the renal R2* of 30% at 1.5 T and of 26% at 3 T. On the other hand, increasing the voxel size improved the goodness of the fit implied by the smaller residuals. CONCLUSIONS: The phantom experiments and in vivo acquisitions of healthy renal tissue documented a significant dependence of the apparent R2* relaxation rate on the spatial resolution of the MR imaging data. In clinical practice, the voxel volume for the quantification of renal R2* should be optimized in a compromise between minimizing the effects of macroscopic field inhomogeneity and maintaining a sufficiently high signal-to-noise ratio and goodness of fit. When comparing quantitative R2* among different publications, the influence of the spatial resolution should be taken into account.

Magnetization transfer for the assessment of bowel fibrosis in patients with Crohn's disease: initial experience.

OBJECT: To assess the feasibility of magnetization transfer (MT) imaging of the bowel wall in patients with Crohn's disease (CD), and to evaluate its utility for the detection of intestinal fibrosis. MATERIALS AND METHODS: In this prospective study, 31 patients (age 39.0 ± 13.2 years) with CD were examined in a 1.5T MR scanner. To establish a standard of reference, two independent readers classified the patients in different disease states using standard MR enterography, available clinical data and histological findings. In addition to the standard protocol, a 2D gradient-echo sequence (TR/TE 32 ms/2.17 ms; flip angle 25°) with/without 1,100 Hz off-resonance prepulse was applied. MT ratios (MTR) of the small bowel wall were computed off-line on a pixel-by-pixel basis. RESULTS: The MT sequences acquired images of sufficient quality and spatial resolution for the evaluation of the small bowel wall without detrimental motion artefacts. In normal bowel wall segments, an intermediate MTR of 25.4 ± 3.4 % was measured. The MTR was significantly increased in bowel wall segments with fibrotic scarring (35.3 ± 4.0 %, p < 0.0001). In segments with acute inflammation, the mean MTR was slightly smaller (22.9 ± 2.2 %). CONCLUSION: MT imaging of the small bowel wall is feasible in humans with sufficient image quality and may help with the identification of fibrotic scarring in patients with CD.

Liver: segment-specific analysis of B1 field homogeneity at 3.0-T MR imaging with single-source versus dual-source parallel radiofrequency excitation.

PURPOSE: To measure B1 field distribution in different liver segments with and without dual transmission and to quantify the contrast-to-noise ratio (CNR) between normal liver tissue and segmental venous vessels on standard clinical 3.0-T liver magnetic resonance (MR) images. MATERIALS AND METHODS: This prospective study was approved by the local ethics committee. All subjects gave written informed consent. Six patients with liver lesions and nine healthy volunteers were included. Average hepatic B1 field values in all Couinaud liver segments were assessed by using actual flip-angle imaging (first and second repetition times msec/echo time msec: 72, 192/2.2; transmission angle: 60°) for both single and dual transmission in a 3.0-T MR imaging unit that allowed both transmission modes. Additionally, two-dimensional T1-weighted gradient-echo (repetition time msec/echo time msec, 180/2.3; transmission angle, 55°) and T2-weighted single-shot fast spin-echo images (1501/80) were acquired. Average CNR between liver parenchyma and segmental veins were measured in each segment. Two-sided paired Student t tests were used for statistical evaluation. Two blinded radiologists independently identified lesions in images from acquisitions in both transmission modes. RESULTS: Mean flip angles achieved with conventional single transmission were 44%-53% of the nominal value in segments II-IV and 67% and 63% of the nominal value in segments VI and VII, respectively, and were less than 77% in all segments. Mean actual flip angles measured for dual transmission were between 82% and 100% of the nominal value in all segments. T1-weighted single-transmission images exhibited areas of low B1 field strength with reduced image contrast. T2-weighted single-transmission images displayed significantly reduced signal intensity but nearly unchanged contrast weighting in these areas. On T1-weighted dual-transmission images, the two readers detected 22 and 14 additional lesions that they did not identify on the single-transmission images. On the dual-transmission T2-weighted images, they detected 11 and five additional lesions, respectively. CONCLUSION: Dual transmission can generate a B1 field with significantly improved homogeneity over all liver segments at a field strength of 3.0 T.