Enhancing fluid signal in driven-equilibrium short-TI inversion-recovery imaging with short TR times: A feasibility study.

PURPOSE: Fluid-sensitive turbo spin echo (TSE) MRI with short-TI inversion-recovery preparation for fat suppression (STIR) plays a critical role in the diagnostics of the musculoskeletal system (e.g., close to metal implants). Potential advantages of 3D acquisitions, however, are difficult to exploit due to long acquisition times. Shortening the TR incurs a signal loss, and a driven-equilibrium (DE) extension reduces fluid signal even further. METHODS: The phase of the flip-back pulse was changed by 180° relative to the conventional implementation (i.e., 90° along the positive x-axis (90°x) instead of -90°x). After signal modeling and numerical simulations, the modification was implemented in STIR-TSE sequences and tested on a clinical 3T system. Imaging was performed in the lumbar spine, and long-TR images without DE were acquired as reference. CSF SNR and fluid-muscle contrast were measured and compared between the sequences. Imaging was repeated in a metal implant phantom. RESULTS: A shortening of TR by 43%-57% reduced the CSF SNR by 39%-59%. A conventional DE module further reduced SNR to 26%-40%, whereas the modified DE recovered SNR to 59%-108% compared with the long-TR acquisitions. Fluid-tissue contrast was increased by about 340% with the modified DE module compared with the conventional extension. Similar results were obtained in implant measurements. CONCLUSIONS: The proposed DE element for TSE-STIR sequences has the potential to accelerate the acquisition of fluid-sensitive images. DE-STIR may work most efficiently for 3D acquisitions, in which no temporo-spatial interleaving of inversion and imaging pulses is possible.

Stimulated echo acquisition mode (STEAM) diffusion tensor imaging with different diffusion encoding times in the supraspinatus muscle: Test-retest reliability and comparison to spin echo diffusion tensor imaging.

Diffusion tensor imaging (DTI) provides insight into the skeletal muscle microstructure and can be acquired using a stimulated echo acquisition mode (STEAM)-based approach to quantify time-dependent tissue diffusion. This study examined diffusion metrics and signal-to-noise ratio (SNR) in the supraspinatus muscle obtained with a STEAM-DTI sequence with different diffusion encoding times (Δ) and compared them to measures from a spin echo (SE) sequence. Ten healthy subjects (mean age 31.5 ± 4.7 years; five females) underwent 3-Tesla STEAM and SE-DTI of the shoulder in three sessions. STEAM was acquired with Δ of 100/200/400/600 ms. The diffusion encoding time in SE scans was 19 ms (b = 500 s/mm2). Region of interest-based measurement of fractional anisotropy (FA), mean diffusivity (MD), and SNR was performed. Intraclass correlation coefficients (ICCs) were computed to assess test-retest reliability. ANOVA with post-hoc pairwise tests was used to compare measures between different Δ of STEAM as well as STEAM and SE, respectively. FA was significantly higher (FASTEAM: 0.38-0.46 vs. FASE: 0.26) and MD significantly lower (MDSTEAM: 1.20-1.33 vs. MDSE: 1.62 × 10-3 mm2/s) in STEAM compared to SE (p < 0.001, respectively). SNR was significantly higher for SE (72.3 ± 8.7) than for STEAM (p < 0.001). ICCs were excellent for FA in STEAM (≥0.911) and SE (0.960). For MD, ICCs were good for STEAM100ms-600ms (≥0.759) and SE (0.752). STEAM and SE exhibited excellent reliability for FA and good reliability for MD in the supraspinatus muscle. SNR was significantly higher in SE compared to STEAM.

Photon-Counting Detector CT Versus Energy-Integrating Detector CT of the Lumbar Spine: Comparison of Radiation Dose and Image Quality.

BACKGROUND. Photon-counting detector (PCD) CT could be useful to help address the typically high radiation doses of conventional energy-integrating detector (EID) CT of the lumbar spine. OBJECTIVE. The purpose of our study was to compare PCD CT and EID CT of the lumbar spine, both performed using tin filtration, in terms of radiation dose and image quality. METHODS. This study included a prospective sample of 39 patients (22 men, 17 women; mean age, 27.2 years) who underwent investigational PCD CT of the lumbar spine as part of a separate study and a retrospective sample of 39 patients (22 men, 17 women; mean age, 34.9 years) who underwent clinically indicated EID CT of the lumbar spine. In both groups, all examinations were performed using unenhanced technique with tin prefiltration between June 2022 and January 2023. Patients were matched between groups using age, sex, and BMI. A custom gaussian curve-fitting algorithm was used to automatically calculate image noise, SNR, and CNR for each examination, on the basis of all voxels within the image set. Three radiologists independently reviewed examinations to perform a subjective visual assessment of visualization of trabecular architecture, cortical bone, neuroforaminal content, paraspinal muscles, and intervertebral disk, as well as overall image quality, using a 4-point Likert scale (1 = poor, 4 = excellent). PCD CT and EID CT examinations were compared. RESULTS. Mean CTDIvol was 4.4 ± 1.0 (SD) mGy for PCD CT versus 11.1 ± 1.9 mGy for EID CT (p < .001). Mean size-specific dose estimate (SSDE) was 6.2 ± 1.0 (SD) mGy for PCD CT versus 14.2 ± 1.8 mGy for EID CT (p < .001). PCD CT and EID CT examinations were not significantly different in terms of image noise or SNR (both p > .05). PCD CT, in comparison with EID CT, showed significantly higher CNR (mean ± SD, 33.6 ± 3.3 vs 29.3 ± 4.1; p < .001). For all three readers, the median score for overall image quality was 4 (range, 3-4) for both PCD CT and EID CT. PCD CT and EID CT examinations showed no significant difference in terms of any qualitative measure for any reader (all p > .05). CONCLUSION. PCD CT, in comparison with EID CT, yielded significantly lower radiation dose with preserved image quality. CLINICAL IMPACT. The findings support expanded use of PCD CT for lumbar spine evaluation.

Photon-Counting Detector CT With Denoising for Imaging of the Osseous Pelvis at Low Radiation Doses: A Phantom Study.

BACKGROUND. Photon-counting detector (PCD) CT may allow lower radiation doses than used for conventional energy-integrating detector (EID) CT, with preserved image quality. OBJECTIVE. The purpose of this study was to compare PCD CT and EID CT, reconstructed with and without a denoising tool, in terms of image quality of the osseous pelvis in a phantom, with attention to low radiation doses. METHODS. A pelvic phantom comprising human bones in acrylic material mimicking soft tissue underwent PCD CT and EID CT at various tube potentials and radiation doses ranging from 0.05 to 5.00 mGy. Additional denoised reconstructions were generated using a commercial tool. Noise was measured in the acrylic material. Two readers performed independent qualitative assessments that entailed determining the denoised EID CT reconstruction with the lowest acceptable dose and then comparing this reference reconstruction with PCD CT reconstructions without and with denoising, using subjective Likert scales. RESULTS. Noise was lower for PCD CT than for EID CT. For instance, at 0.05 mGy and 100 kV with tin filter, noise was 38.4 HU for PCD CT versus 48.8 HU for EID CT. Denoising further reduced noise; for example, for PCD CT at 100 kV with tin filter at 0.25 mGy, noise was 19.9 HU without denoising versus 9.7 HU with denoising. For both readers, lowest acceptable dose for EID CT was 0.10 mGy (total score, 11 of 15 for both readers). Both readers somewhat agreed that PCD CT without denoising at 0.10 mGy (reflecting reference reconstruction dose) was relatively better than the reference reconstruction in terms of osseous structures, artifacts, and image quality. Both readers also somewhat agreed that denoised PCD CT reconstructions at 0.10 mGy and 0.05 mGy (reflecting matched and lower doses, respectively, with respect to reference reconstruction dose) were relatively better than the reference reconstruction for the image quality measures. CONCLUSION. PCD CT showed better-quality images than EID CT when performed at the lowest acceptable radiation dose for EID CT. PCD CT with denoising yielded better-quality images at a dose lower than lowest acceptable dose for EID CT. CLINICAL IMPACT. PCD CT with denoising could facilitate lower radiation doses for pelvic imaging.

Ligaments of the scapho-trapezial-trapezoidal joint: MR anatomy in asymptomatic and symptomatic individuals.

PURPOSE: To evaluate the MRI anatomy of the scapho-trapezial-trapezoidal (STT) ligament complex in asymptomatic and symptomatic individuals. MATERIAL AND METHODS: In this retrospective study, STT ligament complex of 42 (male 69%, median age 37.5 years) asymptomatic (n = 25) and symptomatic (n = 17) (defined as pain described over the STT joint) individuals was examined using a high-resolution 3D proton density-weighted isovoxel sequence (MR arthrogram) with multiplanar reconstructions. Two musculoskeletal radiologists independently assessed visibility, signal intensity (SI), morphology, and thickness of the radiopalmar scapho-trapezial ligament (rpSTL), palmar scapho-capitate capsular ligament (pSCL), palmar STT capsule (pSTTC), and dorsal STT capsule (dSTTC). RESULTS: Interreader agreement ranged from fair to good and intraclass correlations were good. The rpSTL was almost always visible (85.7%/80.1%; reader 1/reader 2). The pSCL and dSTTC were visible in all cases. The pSTTC was visible in only 52.4%/42.9%. Mean thickness of the rpSTL, pSCL, pSTTC, and dSTTC was 1.4 ± 0.5 mm/1.3 ± 0.5 mm, 2.8 ± 0.7 mm/2.7 ± 0.6 mm, 0.5 ± 0.5 mm/0.4 ± 0.4 mm, and 0.5 ± 0.3 mm/0.3 ± 0.3 mm. Both readers rated SI of the rpSTL significantly more often as increased in the symptomatic group (increased SI in asymptomatic group: 20%/15%; symptomatic group: 56%/50%) (p-values < 0.005). For all other ligaments, no significant difference was observed for SI between symptomatic and asymptomatic group (p-values ranging between 0.188 and 0.890). For all other ligaments, no significant differences were observed regarding ligament visibility, morphology, and thickness (p-values ranging between 0.274 and 1.000). CONCLUSION: The anatomy of the STT ligament complex can consistently be visualized on high-resolution 3D MRI. Increased signal intensity of rpSTL is significantly more frequent in patients with radial-sided wrist pain.

High-resolution in vivo MR imaging of intraspinal cervical nerve rootlets at 3 and 7 Tesla.

OBJECTIVES: No routine imaging technology allows reliable visualization of nerve rootlets inside the spinal canal with positive contrast. The stronger MR signal at 7 T, with optimized protocols, may offer a solution. The purpose was to evaluate the potential of 3D Dual-Echo Steady-State (DESS) MR imaging of the cervical spine at 3 and 7 T in assessing the micro-anatomy of the nerve rootlets. MATERIALS/METHODS: This prospective study was approved by the local ethics committee. Twenty-one patients, clinically referred to cervical-spine MRI, underwent additional MR exams at 3 T and 7 T, each of which consisted of a single 3D-DESS series with equal acquisition times. Artifacts, visualization quality, and number of identified rootlets (C2 to C8) were rated by two musculoskeletal radiologists. Results were compared by Wilcoxon tests. Interobserver reliability was assessed using weighted κ statistics and intraclass correlation coefficient (ICC). RESULTS: Intraspinal rootlets could successfully be visualized at both field strengths. Rating differences for artifacts and quality of rootlet depiction were not significant for the two field strengths. The mean number of identified rootlets was larger for 7-T than for 3-T MR for every assessed nerve; however, this difference was not statistically significant using the Bonferroni correction (p values ranging from 0.002 to 0.53). Interobserver agreement was substantial to almost perfect (weighted κ values of 0.69 and 0.82). The ICC for the number of identified rootlets was 0.80. CONCLUSION: Non-invasive 3D-DESS MR-imaging at 3 and 7 T has the potential to provide precise assessments of the micro-anatomy of intraspinal cervical nerve roots. KEY POINTS: • Cervical rootlets can be successfully visualized with positive contrast using 3D-DESS MR-imaging. • 3D-DESS MR-imaging at 3 and 7 T provides precise assessments of the micro-anatomy of cervical nerves. • The mean number of identified cervical rootlets using 3D-DESS was larger for 7 T than for 3 T MR; however, this difference was not statistically significant.

Ultra-high resolution 3D MRI for chondrocalcinosis detection in the knee-a prospective diagnostic accuracy study comparing 7-tesla and 3-tesla MRI with CT.

OBJECTIVES: To test the diagnostic accuracy of a 3D dual-echo steady-state (DESS) sequence at 7-T MRI regarding the detection of chondral calcific deposits of the knee in comparison to 3-T MRI, using CT as cross-sectional imaging reference standard. METHODS: CT and 7-T MRI (DESS) of knee joints in 42 patients with radiographically known chondrocalcinosis (13 of 42 bilateral) were prospectively acquired for all included patients (n = 55 knee joints). Additionally, 3-T MRI (DESS) was performed for 20 of these 55 knee joints. Two fellowship-trained musculoskeletal radiologists scored eight cartilage regions of each knee joint separately regarding presence of cartilage calcification, diagnostic confidence level, and sharpness of calcific deposits. In an explorative subanalysis, micro-CT of the menisci was evaluated after knee arthroplasty in one patient. Diagnostic performance metrics and nonparametric tests were used to compare between modalities. p values < 0.05 were considered to represent statistical significance. RESULTS: Sensitivity for chondrocalcinosis detection was significantly higher for 7-T MRI (100%) compared to 3-T MRI (reader 1: 95.9%, p = 0.03; reader 2: 93.2%, p = 0.002). The diagnostic confidence was significantly higher for both readers at 7 T compared to both 3-T MRI (p < 0.001) and to CT (p = 0.03). The delineation of chondral calcifications was significantly sharper for 7-T compared to both 3-T MRI and CT (p < 0.001, both readers). Micro-CT in one patient suggested that 7-T MRI may potentially outperform standard CT in diagnosing chondral calcifications. CONCLUSION: 3D-DESS imaging at 7-T MRI offers a significantly higher sensitivity in detection of chondral calcific deposits compared to 3-T MRI. KEY POINTS: • 3D dual-echo steady-state (DESS) MRI at 7 T has a higher sensitivity in detection of chondral calcific deposits compared to 3-T MRI (p ≤ 0.03). • 3D DESS MRI at 7 T yields no false-negative cases regarding presence of chondral calcific deposits. • 3D DESS MRI at 7 T offers better delineation and higher diagnostic confidence in detection of chondral calcific deposits compared to 3-T MRI (p < 0.001).

3D MRI: Technical Considerations and Practical Integration.

One of the main advantages of three-dimensional (3D) magnetic resonance imaging (MRI) is the possibility of isotropic voxels and reconstructed planar cuts through the volumetric data set in any orientation with multiplanar reformation software through real-time evaluation. For example, reformats by the radiologist during reporting allows exploitation of the full potential of isotropic 3D volumetric acquisition or through standardized retrospective reformats of thicker predefined slices of an isotropic volumetric data set by technologists. The main challenges for integrating 3D fast spin echo (FSE) and turbo spin-echo (TSE) MRI in clinical practice are a long acquisition time and some artifacts, whereas for integrating 3D gradient-recalled echo protocols, the main challenges are lower signal-to-noise ratios (SNRs) and the inability to produce intermediate, and T2-weighted contrast. The implementation of bidirectional parallel imaging acquisition and random undersampling acceleration strategies of 3D TSE pulse sequences substantially shortens the examination time with only minor SNR reductions. This article provides an overview of general technical considerations of 3D FSE and TSE sequences in musculoskeletal MRI. It also describes how these sequences achieve efficient data acquisition and reviews the main advantages and challenges for their introduction to clinical practice.

Novel observations of Pacinian corpuscle distribution in the hands and feet based on high-resolution 7-T MRI in healthy volunteers.

Pacinian corpuscles represent special nerve endings that serve as mechanoreceptors sensitive to vibration and pressure and are crucial for proprioception. This work demonstrates that the complex network of Pacinian corpuscles in hands and feet can be examined with three-dimensional Dual Echo Steady State (DESS) MR imaging at 7 T, while previous dedicated MRI reports were either limited to two-dimensional images or focused on the hands. The high-resolution MR images show the detailed architecture of the complex receptor network and reveal a "chain-like" arrangement of Pacinian corpuscles, a predilection for clustering around metacarpophalangeal/metatarsophalangeal joints, proximal phalanges and fingertips, and specific sensor locations both in the superficial subcutaneous tissue and adjacent to deep soft tissue structures such as tendons and joint capsules.

Dependency of the blood oxygen level dependent-response to hyperoxic challenges on the order of gas administration in intracranial malignancies.

PURPOSE: Literature reports contradicting results on the response of brain tumors to vascular stimuli measured in T2*-weighted MRI. Here, we analyzed the potential dependency of the MRI-response to (hypercapnic) hyperoxia on the order of the gas administration. METHODS: T2* values were quantified at 3 Tesla in eight consenting patients at rest and during inhalation of hyperoxic/hypercapnic gas mixtures. Patients were randomly divided into two groups undergoing different gas administration protocols (group A: medical air-pure oxygen-carbogen; group B: medical air-carbogen-pure oxygen). Mann-Whitney U test and Wilcoxon signed rank test have been used to proof differences in T2* regarding respiratory challenge or different groups, respectively. RESULTS: T2* values at rest for gray and white matter were 50.3 ± 2.6 ms and 46.1 ± 2.0 ms, respectively, and slightly increased during challenge. In tumor areas, T2* at rest were: necrosis = 74.1 ± 10.1 ms; edema = 60.3 ± 17.6 ms; contrast-enhancing lesions = 48.6 ± 20.7 ms; and solid T2-hyperintense lesions = 45.0 ± 3.0 ms. Contrast-enhancing lesions strongly responded to oxygen (+ 20.7%) regardless on the gas protocol (p = 0.482). However, the response to carbogen significantly depended on the order of gas administration (group A, + 18.6%; group B, - 6.4%, p = 0.042). In edemas, a different trend between group was found when breathing oxygen (group A, - 9.9%; group B, + 19.5%, p = 0.057). CONCLUSION: Preliminary results show a dependency of the T2* response of contrast-enhancing brain tumor lesions on the order of the gas administration. The gas administration protocol is an important factor in the interpretation of the T2*-response in areas of abnormal vascular growth.

Whole-body adipose tissue and lean muscle volumes and their distribution across gender and age: MR-derived normative values in a normal-weight Swiss population.

PURPOSE: To determine age- and gender-dependent whole-body adipose tissue and muscle volumes in healthy Swiss volunteers in Dixon MRI in comparison with anthropometric and bioelectrical impedance (BIA) measurements. METHODS: Fat-water-separated whole-body 3 Tesla MRI of 80 healthy volunteers (ages 20 to 62 years) with a body mass index (BMI) of 17.5 to 26.2 kg/m2 (10 men, 10 women per decade). Age and gender-dependent volumes of total adipose tissue (TAT), visceral adipose tissue (VAT), total abdominal subcutaneous adipose tissue (ASAT) and total abdominal adipose tissue (TAAT), and the total lean muscle tissue (TLMT) normalized for body height were determined by semi-automatic segmentation, and correlated with anthropometric and BIA measurements as well as lifestyle parameters. RESULTS: The TAT, ASAT, VAT, and TLMT indexes (TATi, ASATi, VATi, and TLMTi, respectively) (L/m2 ± standard deviation) for women/men were 6.4 ± 1.8/5.3 ± 1.7, 1.6 ± 0.7/1.2 ± 0.5, 0.4 ± 0.2/0.8 ± 0.5, and 5.6 ± 0.6/7.1 ± 0.7, respectively. The TATi correlated strongly with ASATi (r > 0.93), VATi, BMI and BIA (r > 0.70), and TAATi (r > 0.96), and weak with TLMTi for both genders (r > -0.34). The VAT was the only parameter showing an age dependency (r > 0.32). The BMI and BIA showed strong correlation with all MR-derived adipose tissue volumes. The TAT mass was estimated significantly lower from BIA than from MRI (both genders P < .001; mean bias -5 kg). CONCLUSIONS: The reported gender-specific MRI-based adipose tissue and muscle volumes might serve as normative values. The estimation of adipose tissue volumes was significantly lower from anthropometric and BIA measurements than from MRI. Magn Reson Med 79:449-458, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Enhanced quantitative susceptibility mapping (QSM) using real-time field control.

PURPOSE: To assess the potential of a real-time field-control (FC) system for mitigating effects of spatiotemporal field fluctuations in quantitative susceptibility mapping (QSM) at 7 T. METHODS: Magnitude, phase, and QSM images of phantoms and healthy volunteers were acquired under standard conditions and under induced field perturbation (FP) (phantoms: periodic water-bottle displacement; volunteers: deep breathing and forearm movement) with and without FC, which continuously detects and minimizes magnetic-field variations. RESULTS: Field control successfully eliminated FP-induced impairment of phantom image quality and deviations from a linear susceptibility increase for increasing gadolinium concentration in a Gd dilution series (y = 320x - 0.60, R2 = 0.93 for the scan with FP and FC versus y = 259x - 0.54, R2 = 0.78 for the scan with FP and no FC (slope literature value: 326 ppm L/mol)). Similarly, in volunteers, FC allowed a recovery of a FP-induced loss of identifiable brain structures and reduced the relative change of mean susceptibilities and standard deviations (93 ± 53% to 34 ± 46%) in all regions of interests with respect to the reference scan. CONCLUSIONS: Real-time FC improved the delineation of brain structures and the match of susceptibility values with reference values obtained without FP. Magn Reson Med 79:770-778, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

A comprehensive numerical analysis of background phase correction with V-SHARP.

Sophisticated harmonic artifact reduction for phase data (SHARP) is a method to remove background field contributions in MRI phase images, which is an essential processing step for quantitative susceptibility mapping (QSM). To perform SHARP, a spherical kernel radius and a regularization parameter need to be defined. In this study, we carried out an extensive analysis of the effect of these two parameters on the corrected phase images and on the reconstructed susceptibility maps. As a result of the dependence of the parameters on acquisition and processing characteristics, we propose a new SHARP scheme with generalized parameters. The new SHARP scheme uses a high-pass filtering approach to define the regularization parameter. We employed the variable-kernel SHARP (V-SHARP) approach, using different maximum radii (Rm ) between 1 and 15 mm and varying regularization parameters (f) in a numerical brain model. The local root-mean-square error (RMSE) between the ground-truth, background-corrected field map and the results from SHARP decreased towards the center of the brain. RMSE of susceptibility maps calculated with a spatial domain algorithm was smallest for Rm between 6 and 10 mm and f between 0 and 0.01 mm-1 , and for maps calculated with a Fourier domain algorithm for Rm between 10 and 15 mm and f between 0 and 0.0091 mm-1 . We demonstrated and confirmed the new parameter scheme in vivo. The novel regularization scheme allows the use of the same regularization parameter irrespective of other imaging parameters, such as image resolution. Copyright © 2016 John Wiley & Sons, Ltd.

Feedback field control improves the precision of T2 * quantification at 7 T.

T2 * mapping offers access to a number of important structural and physiological tissue parameters. It is robust against RF field variations and overall signal scaling. However, T2 * measurement is highly sensitive to magnetic field errors, including perturbations caused by breathing motion at high baseline field. The goal of this work is to assess this issue in T2 * mapping of the brain and to study the benefit of field stabilization by feedback field control. T2 * quantification in the brain was investigated by phantom and in vivo measurements at 7 T. Repeated measurements were made with and without feedback field control using NMR field sensing and dynamic third-order shim actuation. The precision and reliability of T2 * quantification was assessed by studying variation across repeated measurements as well as fitting errors. Breathing effects were found to introduce significant error in T2 * mapping results. Field control mitigates this problem substantially. In a phantom it virtually eliminates the effects of emulated breathing fluctuations in the head. In vivo it enhances the structural fidelity of T2 * maps and reduces fitting residuals along with standard deviation. In conclusion, feedback field control improves the fidelity of T2 * mapping in the presence of field perturbations. It is an effective means of countering bulk susceptibility effects of breathing and hence holds particular promise for efforts to leverage high field for T2 * studies in vivo.

Simultaneous multislice readout-segmented echo planar imaging for accelerated diffusion tensor imaging of the mandibular nerve: A feasibility study.

PURPOSE: To assess the feasibility of diffusion tensor imaging (DTI) using simultaneous multislice (SMS) acquisition with blipped controlled aliasing in parallel imaging (CAIPI) for accelerated readout-segmented echo planar imaging (rs-EPI) of the mandibular nerves. DTI of the mandibular nerves using EPI is challenging due to susceptibility artifacts. Rs-EPI is less prone to artifacts but associated with longer scan durations. MATERIALS AND METHODS: Eight asymptomatic volunteers were imaged at 3T using a 64-channel head/neck coil. Conventional, 2-fold (2xSMS) and 3-fold (3xSMS) slice-accelerated rs-EPI sequences were acquired. Tractography of the mandibular nerves was performed. Signal-to-noise ratio (SNR), fractional anisotropy (FA), mean diffusivity (MD), and number of tracts were calculated. Artifacts were evaluated qualitatively on Likert scales. Parameters were compared statistically. Clinical feasibility of 2xSMS rs-EPI was tested in four patients. RESULTS: SNR was similar for conventional (mean ± SD; 8.55 ± 3.90) and 2xSMS rs-EPI (7.83 ± 3.15) but lower for 3xSMS rs-EPI (5.42 ± 2.93; analysis of variance, P = 0.004). FA was similar for all sequences (rs-EPI, 0.42 ± 0.08; 2xSMS rs-EPI, 0.43 ± 0.08; 3xSMS rs-EPI, 0.44 ± 0.06), while 3xSMS rs-EPI showed lower MD (rs-EPI, 0.0015 ± 0.0003; 2xSMS rs-EPI, 0.0014 ± 0.0001; 3xSMS rs-EPI, 0.0013 ± 0.0003) and lower number of tracts (rs-EPI, 66.56 ± 51.31; 2xSMS rs-EPI, 65.75 ± 55.40; 3xSMS rs-EPI, 37.93 ± 52.42) compared to rs-EPI and 2xSMS rs-EPI. Additionally, 2xSMS rs-EPI was feasible in four clinical patients and provided robust imaging results. CONCLUSION: 2xSMS rs-EPI yielded similar SNR, FA, and MD values compared to conventional rs-EPI at reduced scan time and is feasible in clinical patients. These findings suggest the potential clinical applicability of rs-EPI for DTI of the mandibular nerve. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:663-677.

Probing neuronal activation by functional quantitative susceptibility mapping under a visual paradigm: A group level comparison with BOLD fMRI and PET.

Dynamic changes of brain-tissue magnetic susceptibility provide the basis for functional MR imaging (fMRI) via T2*-weighted signal-intensity modulations. Promising initial work on a detection of neuronal activity via quantitative susceptibility mapping (fQSM) has been published but consistently reported on ill-understood positive and negative activation patterns (Balla et al., 2014; Chen and Calhoun, 2015a). We set out to (i) demonstrate that fQSM can exploit established fMRI data acquisition and processing methods and to (ii) better describe aspects of the apparent activation patterns using fMRI and PET as standards of reference. Under a standardized visual-stimulation paradigm PET and 3-T gradient-echo EPI-based fQSM, fMRI data from 9 healthy volunteers were acquired and analyzed by means of Independent Component Analysis (ICA) at subject level and, for the first time, at group level. Numbers of activated (z-score>2.0) voxels were counted and their mean z-scores calculated in volumes of interest (occipital lobe (Nocc_lobe), segmented occipital gray-matter (NGM_occ_lobe), large veins (Nveins)), and in occipital-lobe voxels commonly activated in fQSM and fMRI component maps. Common but not entirely congruent regions of apparent activation were found in the occipital lobe in z-score maps from all modalities, fQSM, fMRI and PET, with distinct BOLD-negatively correlated regions in fQSM data. At subject-level, Nocc_lobe, NGM_occ_lobe and their mean z-scores were significantly smaller in fQSM than in fMRI, but their ratio, NGM_occ_lobe/Nocc_lobe, was comparable. Nveins did not statistically differ and the ratio Nveins/NGM_occ_lobe as well as the mean z-scores were higher for fQSM than for fMRI. In veins and immediate vicinity, z-score maps derived from both phase and fQSM-data showed positive and negative lobes resembling dipole shapes in simulated field and phase maps with no correlate in fMRI or PET data. Our results show that standard fMRI tools can directly be used for fQSM processing, and suggest that fQSM may have the potential to detect gray-matter activation distant from large veins, to improve detection of veins with stimulus-induced venous oxygen saturation (SvO2) variations, and to better localize areas of activation. However, our results seem to clearly expose issues that phenomenologically resemble an incomplete dipolar inversion and that need to be subject to further investigation.

MR neurographic orthopantomogram: Ultrashort echo-time imaging of mandibular bone and teeth complemented with high-resolution morphological and functional MR neurography.

PURPOSE: Panoramical radiographs or cone-beam computed tomography (CT) are the standard-of-care in dental imaging to assess teeth, mandible, and mandibular canal pathologies, but do not allow assessment of the inferior alveolar nerve itself nor of its branches. We propose a new technique for "MR neurographic orthopantomograms" exploiting ultrashort echo-time (UTE) imaging of bone and teeth complemented with high-resolution morphological and functional MR neurography. MATERIALS AND METHODS: The Institutional Review Board approved the study in 10 healthy volunteers. Imaging of the subjects mandibles at 3.0T (Magnetom Skyra, Siemens-Healthcare) using a 64-channel head coil with isotropic spatial resolution for subsequent multiplanar reformatting, was performed. Bone images were acquired using a 3D PETRA sequence (TE, 0.07 msec). Morphological nerve imaging was performed using a dedicated 3D PSIF and 3D SPACE STIR sequence. Functional MR neurography was accomplished using a new accelerated diffusion-tensor-imaging (DTI) prototype sequence (2D SMS-accelerated RESOLVE). Qualitative and quantitative image analysis was performed and descriptive statistics are provided. RESULTS: Image acquisition and subsequent postprocessing into the MR neurographic orthopantomogram by overlay of morphological and functional images were feasible in all 10 volunteers without artifacts. All mandibular bones and mandibular nerves were assessable and considered normal. Fiber tractography with quantitative evaluation of physiological diffusion properties of mandibular nerves yielded the following mean ± SD values: fractional anisotropy, 0.43 ± 0.07; mean diffusivity (mm(2) /s), 0.0014 ± 0.0002; axial diffusivity, 0.0020 ± 0.0002, and radial diffusivity, 0.0011 ± 0.0001. CONCLUSION: The proposed technique of MR neurographic orthopantomogram exploiting UTE imaging complemented with high-resolution morphological and functional MR neurography was feasible and allowed comprehensive assessment of osseous texture and neural microarchitecture in a single examination. J. Magn. Reson. Imaging 2016;44:393-400.

Normative values for volume and fat content of the hip abductor muscles and their dependence on side, age and gender in a healthy population.

OBJECTIVE: To determine normative values for volume and fat content of the gluteus medius (GMed) and minimus (GMin) muscle in healthy volunteers and to evaluate their dependence on age, gender and leg dominance. MATERIALS AND METHODS: The IRB approval was obtained for this study. 80 healthy volunteers (females, 40; males, 40; age range 20-62 years), divided into four age groups, were included. Fat- and water-signal-separated MR images of the pelvis were acquired on a 3.0 T MR with a 3-point mDIXON sequence. Normalized volume and fat-signal fraction (FSF) of the GMed (ViGMed, FSFGMed) and GMin (ViGMin, FSFGMin) muscles were determined. RESULTS: The overall mean volumes (normalized) and FSF ± SD: ViGMed 105.13 ± 16.30 cm(3); ViGMin 30.24 ± 5.15 cm(3); FSFGMed 8.13 ± 1.70 % and FSFGMin 9.89 ± 2.72 %. Comparing different age subgroups within each gender no significant differences were found concerning the volumes and FSFs (except FSFGMin in male subgroup aged 20-29 versus 50-62 years, P = 0.014). Comparing FSFs differences between the two genders, only in 20-29 years subgroup, FSFGMed (P =0.003) and FSFGMin (P =0.002) were greater in female. Volume differences between the two legs were not significant (P > 0.077); FSFGMed and FSFGMin (P =0.005 for both) were significantly lower in the dominant leg in female but not in male group (P = 0.454 for FSFGMed and P = 0.643 for FSFMin). CONCLUSION: No age dependency was evident for volume normative data for GMed and GMin and normative data for FSF values showed no age- or gender dependency.

Effect of respiratory hyperoxic challenge on magnetic susceptibility in human brain assessed by quantitative susceptibility mapping (QSM).

The purpose of this study was to measure the regional change of magnetic susceptibility in human brain upon inhalation of 100% oxygen by MRI quantitative susceptibility mapping (QSM). Fourteen healthy volunteers were scanned in a 3 T MR scanner with a 3D multi-gradient-echo sequence while breathing medical air (normoxia) and pure oxygen (hyperoxia). QSM images and R2* maps were calculated. Mean susceptibility differences versus white matter were measured in regions of interest covering veins, gray matter (GM), and cerebrospinal fluid (CSF) under both conditions. Hyperoxia resulted in a strong susceptibility decrease in large veins (-154.4 ± 65.9 ppb, p < 10(-6)), in a smaller reduction in GM (-1.3 ± 1 ppb, p < 0.001), and in a susceptibility increase in ventricular CSF (3.8 ± 1.8 ppb, p < 10(-5)). The susceptibility decrease in veins implied an increase of venous oxygen saturation (SvO2) by 10.1 ± 4.0%. Compared with QSM, R2* was more seriously affected by long-distance effects not related to local tissue oxygenation and increased in cerebral frontal regions (3 ± 2 s(-1), p < 0.0004) due to paramagnetic molecular oxygen in cavities. The results highlight the potential of QSM to yield region-specific quantitative oxygenation information, and, thus, for applications such as oxygen-therapy monitoring or identification of hypoxic tumor tissue during radiotherapy planning.

Quantitative and qualitative MR-imaging assessment of vastus medialis muscle volume loss in asymptomatic patients after anterior cruciate ligament reconstruction.

BACKGROUND: To quantitatively and qualitatively assess vastus medialis muscle atrophy in asymptomatic patients with anterior cruciate ligament reconstruction, using the nonoperated leg as control. METHODS: Prospective Institutional Review Board approved study with written informed patient consent. Thirty-three asymptomatic patients (men, 21; women,12) with ACL-reconstruction underwent MR imaging of both legs (axial T1-weighted spin-echo and 3D spoiled dual gradient-echo sequences). Muscle volume and average fat-signal fraction (FSF) of the vastus medialis muscles were measured. Additionally, Goutallier classification was used to classify fatty muscle degeneration. Significant side differences were evaluated using the Wilcoxon test and, between volumes and FSF, using student t-tests with P-value < 0.05 and < 0.025, respectively. RESULTS: The muscle volume was significantly smaller in the operated (mean ± SD, 430.6 ± 119.6 cm(3) ; range, 197.3 to 641.7 cm(3) ) than in the nonoperated leg (479.5 ± 124.8 cm(3) ; 261.4 to 658.9 cm(3) ) (P < 0.001). Corresponding FSF was 6.3 ± 1.5% (3.9 to 9.2%) and 5.8 ± 0.9% (4.0 to 7.4%), respectively, with a nonsignificant (P > 0.025) difference. The relative muscle-volume and FSF differences were -10.1 ± 8.6% (7.1 to -30.1%) and 10.9 ± 29.4% (39.7 to 40.1%). The qualitative assessment revealed no significant differences (P > 0.1). CONCLUSION: A significant muscle volume loss of the vastus medialis muscle does exist in asymptomatic patients with ACL-reconstruction, but without fatty degeneration.