3D GRE Research Articles

Hepatic Iron Quantification Using a Free-Breathing 3D Radial Gradient Echo Technique and Validation With a 2D Biopsy-Calibrated R2* Relaxometry Method.

Hepatic iron content (HIC) is an important parameter for the management of iron overload. Non-invasive HIC assessment is often performed using biopsy-calibrated two-dimensional breath-hold Cartesian gradient echo (2D BH GRE) R2* -MRI. However, breath-holding is not possible in most pediatric patients or those with respiratory problems, and three-dimensional free-breathing radial GRE (3D FB rGRE) has emerged as a viable alternative. To evaluate the performance of a 3D FB rGRE and validate its R2* and fat fraction (FF) quantification with 3D breath-hold Cartesian GRE (3D BH cGRE) and biopsy-calibrated 2D BH GRE across a wide range of HICs. Retrospective. Twenty-nine patients with hepatic iron overload (22 females, median age: 15 [5-25] years). Three-dimensional radial and 2D and 3D Cartesian multi-echo GRE at 1.5 T. R2* and FF maps were computed for 3D GREs using a multi-spectral fat model and 2D GRE R2* maps were calculated using a mono-exponential model. Mean R2* and FF values were calculated via whole-liver contouring and T2* -thresholding by three operators. Inter- and intra-observer reproducibility was assessed using Bland-Altman and intraclass correlation coefficient (ICC). Linear regression and Bland-Altman analysis were performed to compare R2* and FF values among the three acquisitions. One-way repeated-measures ANOVA and Wilcoxon signed-rank tests, respectively, were used to test for significant differences between R2* and FF values obtained with different acquisitions. Statistical significance was assumed at P < 0.05. The mean biases and ICC for inter- and intra-observer reproducibility were close to 0% and >0.99, respectively for both R2* and FF. The 3D FB rGRE R2* and FF values were not significantly different (P > 0.44) and highly correlated (R2 ≥ 0.98) with breath-hold Cartesian GREs, with mean biases ≤ ±2.5% and slopes 0.90-1.12. In non-breath-holding patients, Cartesian GREs showed motion artifacts, whereas 3D FB rGRE exhibited only minimal streaking artifacts. Free-breathing 3D radial GRE is a viable alternative in non-breath-hold patients for accurate HIC estimation. 3 TECHNICAL EFFICACY: Stage 2.

Rapid simultaneous acquisition of macromolecular tissue volume, susceptibility, and relaxometry maps.

A major obstacle to the clinical implementation of quantitative MR is the lengthy acquisition time required to derive multi-contrast parametric maps. We sought to reduce the acquisition time for QSM and macromolecular tissue volume by acquiring both contrasts simultaneously by leveraging their redundancies. The joint virtual coil concept with GRAPPA (JVC-GRAPPA) was applied to reduce acquisition time further. Three adult volunteers were imaged on a 3 Tesla scanner using a multi-echo 3D GRE sequence acquired at 3 head orientations. Macromolecular tissue volume, QSM, , T1 , and proton density maps were reconstructed. The same sequence (GRAPPA R = 4) was performed in subject 1 with a single head orientation for comparison. Fully sampled data was acquired in subject 2, from which retrospective undersampling was performed (R = 6 GRAPPA and R = 9 JVC-GRAPPA). Prospective undersampling was performed in subject 3 (R = 6 GRAPPA and R = 9 JVC-GRAPPA) using gradient blips to shift k-space sampling in later echoes. Subject 1's multi-orientation and single-orientation macromolecular tissue volume maps were not significantly different based on RMSE. For subject 2, the retrospectively undersampled JVC-GRAPPA and GRAPPA generated similar results as fully sampled data. This approach was validated with the prospectively undersampled images in subject 3. Using QSM, , and macromolecular tissue volume, the contributions of myelin and iron content to susceptibility were estimated. We have developed a novel strategy to simultaneously acquire data for the reconstruction of 5 intrinsically coregistered 1-mm isotropic resolution multi-parametric maps, with a scan time of 6 min using JVC-GRAPPA.

Gadoteridol-enhanced MRI of the breast: can contrast agent injection rate impact background parenchymal enhancement?

Normal background parenchymal enhancement (BPE) is a dynamic parameter affected by multiple factors. To determine whether contrast agent injection rate affects the degree of BPE in women undergoing breast magnetic resonance imaging (MRI). A total of 85 patients included in our prospective study randomly received 0.1 mmol/kg gadoteridol at a rate of 3 mL/s (group A; n = 46) or 2 mL/s (group B; n = 39). Breast MRI was performed at 3T using a standard protocol including postcontrast axial 3D GRE T1-weighted sequences. Two expert breast radiologists, blinded to clinical and radiological information, independently quantified BPE on early postcontrast subtracted images, assigning a score of 1-4. Mean comparison and regression analysis were performed to assess the influence of injection rate on BPE. Groups were homogeneous in terms of age and final BI-RADS score. The mean BPE score was significantly lower among patients in group A (mean of two readers: 1.36 vs. 1.90; P < 0.01) with 70%-72% of patients assigned a BPE score of 1, compared with 36%-38% of patients in group B. Lower BPE scores were noted with the higher flow rate in subgroup analyses of both pre- and postmenopausal women, although the effect was more evident in premenopausal women. Regression analysis confirmed that the likelihood of a BPE 1 score was significantly increased with a higher flow rate (P < 0.01). The inter-reader agreement was excellent (0.83). A higher contrast agent injection flow rate (3 mL/s) during breast MRI significantly reduces the degree of BPE, potentially allowing improved diagnostic accuracy by reducing false-positive and false-negative findings.

Automation of Quantifying Axonal Loss in Patients with Peripheral Neuropathies through Deep Learning Derived Muscle Fat Fraction.

Axonal loss denervates muscle, leading to an increase of fat accumulation in the muscle. Therefore, fat fraction (FF) in whole limb muscle using MRI has emerged as a monitoring biomarker for axonal loss in patients with peripheral neuropathies. In this study, we are testing whether deep learning-based model can automate quantification of the FF in individual muscles. While individual muscle is smaller with irregular shape, manually segmented muscle MRI images have been accumulated in this lab; and make the deep learning feasible. To automate segmentation on muscle MRI images through deep learning for quantifying individual muscle FF in patients with peripheral neuropathies. Retrospective. 24 patients and 19 healthy controls. 3T; Interleaved 3D GRE. A 3D U-Net model was implemented in segmenting muscle MRI images. This was enabled by leveraging a large set of manually segmented muscle MRI images. B1+ and B1- maps were used to correct image inhomogeneity. Accuracy of the automation was evaluated using Pixel Accuracy (PA), Dice Coefficient (DC) in binary masks; and Bland-Altman and Pearson correlation by comparing FF values between manual and automated methods. PA and DC were reported with their median value and standard deviation. Two methods were compared using the ± 95% confidence intervals (CI) of Bland-Altman analysis and the Pearson's coefficient (r2 ). DC values were from 0.83 ± 0.17 to 0.98 ± 0.02 in thigh and from 0.63 ± 0.18 to 0.96 ± 0.02 in calf muscles. For FF values, the overall ± 95% CI and r2 were [0.49, -0.56] and 0.989 in thigh and [0.84, -0.71] and 0.971 in the calf. Automated results well agreed with the manual results in quantifying FF for individual muscles. This method mitigates the formidable time consumption and intense labor in manual segmentations; and enables the use of individual muscle FF as outcome measures in upcoming longitudinal studies. 3 TECHNICAL EFFICACY STAGE: 1.

Longitudinal Assessment of Patients With Cystic Fibrosis Lung Disease With Multivolume Noncontrast MRI and Spirometry.

MRI has been suggested as a radiation-free imaging modality to investigate early structural alterations and regional functional impairment in cystic fibrosis (CF) lung disease. To compare functional and morphological MRI changes over the course of the disease to changes in spirometry. Longitudinal retrospective study. Twenty patients with CF lung disease (at baseline, age = 16.5 (13.3-20.6) years, forced expiratory volume in 1 second (as % of predicted [%pred]) FEV1 = 71 (59-87) %pred, forced expiratory flow at 25-75% of forced vital capacity FEF25-75 = 39 (25-63) %pred. 1.5T / T2 -weighted HASTE; T2 -weighted TSE-PROPELLER; T2 -weighted bSSFP; T1 -weighted 3D GRE. Nonenhanced chest MRI and spirometry were retrospectively collected over a 3-year period from the initial recruitment visit. Images acquired at end-inspiration and end-expiration were registered by software using the optical flow method to measure expiratory-inspiratory differences in MR signal-intensity (Δ1 H-MRI). Measures of CF functional impairment were defined from Δ1 H-MRI: Δ1 H-MRI median, Δ1 H-MRI quartile coefficient of variation (QCV), and percent low-signal-variation volume (LVV). MR images were also evaluated by three readers using a CF-specific scoring system. Spearman correlation analysis, Spearman rank correlation analysis, linear mixed-effect model analysis, intraclass correlation coefficient. Functional imaging parameters and total morphological score correlated with all spirometric measures, as did subscores of bronchial wall thickening/bronchiectasis, mucus plugging, and consolidation. Overall, the percent change of Δ1H-MRI median correlated with the percent change of FEV1 (ΔFEV1 , r = 0.41, P < 0.01) and the percent change of FEF25-75 (ΔFEF25-75%, r = 0.38, P < 0.01). The percent change of LVV correlated with ΔFEV1 (r = -0.47, P < 0.001) and ΔFEF25-75 (r = -0.50, P < 0.001). These preliminary results suggest that nonenhanced multivolume MRI may provide a feasible tool to regionally map early pulmonary alterations for longitudinal evaluation of CF lung disease, without exposing the patients to ionizing radiation. 3T TECHNICAL EFFICACY STAGE: 5.

Ex vivo MR microscopy of a human brain with multiple sclerosis: Visualizing individual cells in tissue using intrinsic iron

PurposeTo perform magnetic resonance microscopy (MRM) on human cortex and a cortical lesion as well as the adjacent normal appearing white matter. To shed light on the origins of MRI contrast by comparison with histochemical and immunostaining. Methods3D MRM at a nominal isotropic resolution of 15 and 18 µm was performed on 2 blocks of tissue from the brain of a 77-year-old man who had MS for 47 years. One block contained normal appearing cortical gray matter (CN block) and adjacent normal appearing white matter (NAWM), and the other also included a cortical lesion (CL block). Postmortem ex-vivo MRI was performed at 11.7T using a custom solenoid coil and T2*-weighted 3D GRE sequence. Histochemical and immunostaining were done after paraffin embedding for iron, myelin, oligodendrocytes, neurons, blood vessels, macrophages and microglia, and astrocytes. ResultsMRM could identify individual iron-laden oligodendrocytes with high sensitivity (70% decrease in signal compared to surrounding) in CN and CL blocks, as well as some iron-laden activated macrophages and microglia. Iron-deficient oligodendrocytes seemed to cause relative increase in MRI signal within the cortical lesion. High concentration of myelin in the white matter was primarily responsible for its hypointense appearance relative to the cortex, however, signal variations within NAWM could be attributed to changes in density of iron-laden oligodendrocytes. ConclusionChanges in iron accumulation within cells gave rise to imaging contrast seen between cortical lesions and normal cortex, as well as the patchy signal in NAWM. Densely packed myelin and collagen deposition also contributed to MRM signal changes. Even though we studied only one block each from normal appearing and cortical lesions, such studies can help better understand the origins of histopathological and microstructural correlates of MRI signal changes in multiple sclerosis and contextualize the interpretation of lower-resolution in vivo MRI scans.

Diagnostic value of MRI-derived liver surface nodularity score for the non-invasive quantification of hepatic fibrosis in non-alcoholic fatty liver disease.

To assess the accuracy of MRI-derived liver surface nodularity (LSN) score for staging of hepatic fibrosis in patients with non-alcoholic fatty liver disease (NAFLD). Forty-seven patients with clinicopathological diagnosis of NAFLD who underwent 1.5-T liver MRI within 12months of liver biopsy were included. Axial non-contrast T1-weighted 3D GRE was used for image analysis. LSN of the left lobe was measured using a custom semiautomated software. Histopathologic analysis (F0-F4) served as the reference standard for staging of fibrosis. Mann-Whitney test and Spearman's correlation coefficient were used to compare LSN scores between different stages of fibrosis and to assess the correlation. Diagnostic performance of LSN score for detection of significant (F2-F4) and advanced (F3-F4) fibrosis was assessed by receiver operating characteristics (ROC) curve. p value of less than 0.05 was considered statistically significant different. Twenty-one subjects had advanced fibrosis. The LSN scores among different stages of fibrosis were significantly different (p < 0.001). The correlation between LSN score and stage of fibrosis was also strong (ρ = 0.71; p < 0.001). The areas under ROC curves for detection of significant and advanced fibrosis were 0.80 (95% CI 0.66-0.95) and 0.86 (95% CI 0.75-0.97), using a threshold of 2.23 and 2.44, respectively. This method showed 81% sensitivity and 88% specificity for detection of advanced fibrosis. MR-based LSN score is a promising non-invasive objective tool for detection of advanced fibrosis in patients with NAFLD. • Liver surface nodularity (LSN) score is a fast retrospective method for precise quantification of nodularity of liver surface. • MR-based LSN score is a promising non-invasive objective tool to accurately detect different stages of fibrosis in patients with non-alcoholic fatty liver disease (NAFLD).

Free-breathing fat and R2 * quantification in the liver using a stack-of-stars multi-echo acquisition with respiratory-resolved model-based reconstruction.

PurposeTo develop a free‐breathing hepatic fat and R2∗ quantification method by extending a previously described stack‐of‐stars model‐based fat‐water separation technique with additional modeling of the transverse relaxation rate R2∗.MethodsThe proposed technique combines motion‐robust radial sampling using a stack‐of‐stars bipolar multi‐echo 3D GRE acquisition with iterative model‐based fat‐water separation. Parallel‐Imaging and Compressed‐Sensing principles are incorporated through modeling of the coil‐sensitivity profiles and enforcement of total‐variation (TV) sparsity on estimated water, fat, and R2∗ parameter maps. Water and fat signals are used to estimate the confounder‐corrected proton‐density fat fraction (PDFF). Two strategies for handling respiratory motion are described: motion‐averaged and motion‐resolved reconstruction. Both techniques were evaluated in patients (n = 14) undergoing a hepatobiliary research protocol at 3T. PDFF and R2∗ parameter maps were compared to a breath‐holding Cartesian reference approach.ResultsLinear regression analyses demonstrated strong (r > 0.96) and significant (P ≪ .01) correlations between radial and Cartesian PDFF measurements for both the motion‐averaged reconstruction (slope: 0.90; intercept: 0.07%) and the motion‐resolved reconstruction (slope: 0.90; intercept: 0.11%). The motion‐averaged technique overestimated hepatic R2∗ values (slope: 0.35; intercept: 30.2 1/s) compared to the Cartesian reference. However, performing a respiratory‐resolved reconstruction led to better R2∗ value consistency (slope: 0.77; intercept: 7.5 1/s).ConclusionsThe proposed techniques are promising alternatives to conventional Cartesian imaging for fat and R2∗ quantification in patients with limited breath‐holding capabilities. For accurate R2∗ estimation, respiratory‐resolved reconstruction should be used.

Early diagnosis of degenerative changes in the articular/fibrocartilaginous disc of the temporomandibular joint in patients with temporomandibular disorders using delayed gadolinium-enhanced MRI at 3 Tesla – preliminary results

BackgroundDelayed gadolinium enhanced MRI of cartilage (dGEMRIC) is a quantitative method for assessment of glycosaminoglycan content in connective tissues. We hypothesize that the early diagnosis of degenerative changes in the temporomandibular joint could be diagnosed using dGEMRIC technique. PurposeTo test the compositional MRI technique, dGEMRIC, at 3 Tesla to diagnosis early the degenerative changes in the fibrocartilaginous disc of the temporomandibular joint (TMJ) in patients with temporomandibular disorders (TMD) and to compare the dGEMRIC index of patients to the healthy volunteers. MethodsSix volunteers (two men, four women; 20.8÷28.1 years) and eleven patients (22 TMJs, seven women, four men; 24÷54 years) were recruited for this prospective trial. Only patients with no morphological abnormality on MRI and without disc dislocations were included. Volunteers were used as a control group. The PD-weighted FSE sequence and the 3D GRE (DESS) sequence protocols were performed for morphological assessment. The Inversion recovery (IR) sequence was performed for T1 relaxation time measurements and intra-venous (IV) contrast agent administration was used according to the dGEMRIC protocol. T1 maps were calculated offline and ROIs were drawn on TMJ discs by a specialist trained in TMD disorders. Statistical evaluation was performed by ANOVA and correlations were calculated. ResultsThe difference between the dGEMRIC values in the TMJ articular discs of the patients and the volunteers was statistically significant (P = .019). After contrast agent administration the T1 values dropped in both groups. In patient group was the T1 drop stronger (−54% from initial pre-contrast value), while in control group was the T1 drop less pronounced (−46% from initial pre-contrast value). ConclusionsdGEMRIC seems to be a useful, compositional, quantitative method, suitable also for small joints, such as the articular disc of the TMJ. The results of the dGEMRIC index in the articular disc of the TMJ imply a lower GAG content in patients with TMJ disorders.

MRI visibility of gold fiducial markers for image-guided radiotherapy of rectal cancer

Background and purposeA GTV boost is suggested to result in higher complete response rates in rectal cancer patients, which is attractive for organ preservation. Fiducials may offer GTV position verification on (CB)CT, if the fiducial-GTV spatial relationship can be accurately defined on MRI. The study aim was to evaluate the MRI visibility of fiducials inserted in the rectum. Materials and methodsWe tested four fiducial types (two Visicoil types, Cook and Gold Anchor), inserted in five patients each. Four observers identified fiducial locations on two MRI exams per patient in two scenarios: without (scenario A) and with (scenario B) (CB)CT available. A fiducial was defined to be consistently identified if 3 out of 4 observers labeled that fiducial at the same position on MRI. Fiducial visibility was scored on an axial and sagittal T2-TSE sequence and a T1 3D GRE sequence. ResultsFiducial identification was poor in scenario A for all fiducial types. The Visicoil 0.75 and Gold Anchor were the most consistently identified fiducials in scenario B with 7 out of 9 and 8 out of 11 consistently identified fiducials in the first MRI exam and 2 out of 7 and 5 out of 10 in the second MRI exam, respectively. The consistently identified Visicoil 0.75 and Gold Anchor fiducials were best visible on the T1 3D GRE sequence. ConclusionThe Visicoil 0.75 and Gold Anchor fiducials were the most visible fiducials on MRI as they were most consistently identified. The use of a registered (CB)CT and a T1 3D GRE MRI sequence is recommended.

Reproducible automated breast density measure with no ionizing radiation using fat-water decomposition MRI.

Increased breast density is a significant independent risk factor for breast cancer, and recent studies show that this risk is modifiable. Hence, breast density measures sensitive to small changes are desired. Utilizing fat-water decomposition MRI, we propose an automated, reproducible breast density measurement, which is nonionizing and directly comparable to mammographic density (MD). Retrospective study. The study included two sample sets of breast cancer patients enrolled in a clinical trial, for concordance analysis with MD (40 patients) and reproducibility analysis (10 patients). The majority of MRI scans (59 scans) were performed with a 1.5T GE Signa scanner using radial IDEAL-GRASE sequence, while the remaining (seven scans) were performed with a 3T Siemens Skyra using 3D Cartesian 6-echo GRE sequence with a similar fat-water separation technique. After automated breast segmentation, breast density was calculated using FraGW, a new measure developed to reliably reflect the amount of fibroglandular tissue and total water content in the entire breast. Based on its concordance with MD, FraGW was calibrated to MR-based breast density (MRD) to be comparable to MD. A previous breast density measurement, Fra80-the ratio of breast voxels with <80% fat fraction-was also calculated for comparison with FraGW. Pearson correlation was performed between MD (reference standard) and FraGW (and Fra80). Test-retest reproducibility of MRD was evaluated using the difference between test-retest measures (Δ1-2 ) and intraclass correlation coefficient (ICC). Both FraGW and Fra80 were strongly correlated with MD (Pearson ρ: 0.96 vs. 0.90, both P < 0.0001). MRD converted from FraGW showed higher test-retest reproducibility (Δ1-2 variation: 1.1% ± 1.2%; ICC: 0.99) compared to MD itself (literature intrareader ICC ≤0.96) and Fra80. The proposed MRD is directly comparable with MD and highly reproducible, which enables the early detection of small breast density changes and treatment response. 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:971-981.

Investigating the accuracy of FatNav-derived estimates of temporal B0 changes and their application to retrospective correction of high-resolution 3D GRE of the human brain at 7T.

To investigate the precision of estimates of temporal variations of magnetic field achievable by double-echo fat image navigators (FatNavs), and their potential application to retrospective correction of 3-dimensional gradient echo-based sequences. Both head motion and temporal changes of B0 were tracked using double-echo highly accelerated 3-dimensional FatNavs as navigators, allowing estimation of the temporal changes in low spatial-order field coefficients. The accuracy of the method was determined by direct comparison to controlled offsets in the linear imaging gradients. Double-echo FatNavs were also incorporated into a high-resolution, 3-dimensional gradient echo-based sequence to retrospectively correct for both motion and temporal changes in B0 during natural and deep breathing. The additional scan time was 5 min (a 40% increase). Correction was also investigated using only the first echo of the FatNav to explore the trade-off in accuracy versus scan time. Excellent accuracy (0.27 Hz, 1.57-2.75 Hz/m) was achieved for tracking field changes, and no significant bias could be observed. Artifacts in the 3-dimensional gradient echo-based images induced by temporal field changes, if present, were effectively reduced using either the field estimates from the double echo or the first echo only from the FatNavs. The FatNavs were shown to be an excellent candidate for accurate, fast, and precise estimation of global field variations for the tested patterns of respiration. Future work will investigate ways to increase the temporal sampling to increase robustness to variations in breathing patterns. Magn Reson Med 80:585-597, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Pulmonary nodule detection in oncological patients – Value of respiratory-triggered, periodically rotated overlapping parallel T2-weighted imaging evaluated with PET/CT-MR

PurposeTo prospectively evaluate the detection and conspicuity of pulmonary nodules in an oncological population, using a tri-modality PET/CT-MR protocol including a respiration-gated T2-PROPELLER sequence for possible integration into a simultaneous PET/MR protocol. Methods149 patients referred for staging of malignancy were prospectively enrolled in this single-center study. Imaging was performed on a tri-modality PET/CT-MR setup and was comprised of PET/CT and 3T-MR imaging with 3D dual-echo GRE pulse sequence (Dixon) and an axial respiration-gated T2-weighted PROPELLER (T2-P) sequence. Images were assessed for presence, conspicuity, size and interpretation of the pulmonary parenchymal nodules. McNemar’s test was used to evaluate paired differences in nodule detection rates between MR and CT from PET/CT. The correlation of pulmonary nodule size in CT and MR imaging was assessed using Pearson correlation coefficient. Results299 pulmonary nodules were detected on PET/CT. The detectability was significantly higher on T2-P (60%, p<0.01) compared to T1-weighted Dixon-type sequences (16.1-37.8%). T2-P had a significantly higher detection rate among FDG-positive (92.4%) and among confirmed malignant nodules (75.9%) compared to T1-Dixon. Nodules <10mm were detected less often by MR sequences than by CT (p < 0.01). However, nodules >10mm were detected equally well with T2-P (92.2%) and CT (p >0.05). In a per-patient analysis, there was no significant change in the clinical interpretation of the nodules detected with T2-P and CT. ConclusionDespite the overall lower detection rate compared with CT, the free-breathing respiratory gating T2-w sequence showed higher detectability in all evaluated categories compared to breath-hold T1–weighted MR sequences. Specifically, the T2-P was found to be not statistically different from CT in FDG-positive nodules, in detection of nodules >10mm and concerning conspicuity of pulmonary nodules. Overall, the additional time investment into T2-P seems to be justified since clinical relevant assessment of pulmonary lung nodules can mostly be done by T2-P in a whole body PET/MR staging of oncologic patients.

Characterizing and eliminating errors in enhancement and subtraction artifacts in dynamic contrast-enhanced breast MRI: Chemical shift artifact of the third kind.

To characterize errors in enhancement in breast dynamic contrast-enhanced (DCE) MRI studies as a function of echo time and determine the source of dark band artifacts in clinical subtraction images. Computer simulations, oil and water substitute (methylene chloride), as well as an American College of Radiology quality control phantom were tested. Routine clinical DCE breast MRI study was bracketed with (accelerated) in-phase DCE acquisitions in five patients. Simulation results demonstrated up to -160% suppression of the expected enhancement caused by differential enhancement of fat and water. Two-dimensional gradient-recalled echo and fat-suppressed 3D GRE phantom imaging confirmed the simulation results and showed that fat suppression does not eliminate the artifact. In vivo in-phase DCE images showed increased enhancement consistent with predictions and also confirmed increased spatial blurring on in-phase 3D gradient-recalled echo images. Combined multi-dimensional partial Fourier and parallel imaging provided a time-equivalent in-phase DCE MRI acquisition. Errors in expected enhancement occur in DCE breast MRI subtraction images because of differential enhancement of fat and water and incomplete fat signal suppression. These errors can lead to artificial suppression of enhancement as well as dark band artifacts on subtraction images. These artifacts can be eliminated with a time-equivalent in-phase fat-suppressed 3D gradient-recalled echo sequence. Understanding chemical shift artifact of the third kind, a unique artifact of artificial enhancement suppression in the presence of intravoxel fat and water signal, will aid DCE breast MRI image interpretation. In-phase acquisitions (combined with simultaneous minimum echo time or opposed-phase echoes) may facilitate qualitative, quantitative and longitudinal analysis of contrast enhancement. Magn Reson Med 79:2277-2289, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Pancreatic fat content by magnetic resonance imaging in subjects with prediabetes, diabetes, and controls from a general population without cardiovascular disease

Background/ObjectiveDespite the relevance of pancreatic fat content in the development of metabolic diseases, its association with impaired glucose metabolism, diabetes, and other adipose tissue compartments remains unclear. Thus, we determined differences in pancreatic fat content by magnetic resonance imaging (MRI) between subjects with prediabetes, diabetes, and normal controls in a cohort from the general population.MethodsSubjects without history of cardiovascular disease with established diabetes or prediabetes as well as normal controls were included and underwent whole-body MRI on a 3T scanner. Pancreatic fat content was quantified by measuring the proton-density fat fraction (PDFFpanc) using a 3D multi-echo GRE sequence (increment: 1.23 ms, 6 echoes) by placing ROIs in the pancreatic head, body, and tail by independent readers. In addition, hepatic fat content as well as abdominal subcutaneous and visceral adipose tissue (SAT and VAT) were measured by multi-echo GRE and 3D 2-point volume-interpolated DIXON MRI, respectively. Univariate and multivariate analyses were employed to determine associations.ResultsA total of 385 subjects were included in the analysis (median age: 57 years, 58.2% males), of them 53 were classified as subjects with diabetes, 95 as prediabetes, and 237 as controls (13.8%, 24.7%, and 61.6%; respectively). The median PDFFpanc was 5.2% [IQR 3.3–9.4], and significantly higher in subjects with prediabetes and diabetes as compared to controls (PDFFpanc: 6.2% [IQR: 3.5–12] vs. 8.6% [IQR: 4.3–17.5] vs. 4.9% [3.1–7.4], p<0.001, respectively). After adjusting for age, gender and BMI the association was attenuated (all p>0.12). While in univariate analysis BMI, PDFFhepatic, SAT and VAT were associated with PDFFpanc (all p<0.05), only VAT predicted PDFFpanc independently (β: 0.02, 95%-confidence interval: 0.01–0.04, p<0.001).ConclusionWhile pancreatic fat content differs significantly between subjects with prediabetes, diabetes and controls, this association may be confounded by age, gender, and the amount of VAT in this cross-sectional study.

Free-breathing dynamic liver examination using a radial 3D T1-weighted gradient echo sequence with moderate undersampling for patients with limited breath-holding capacity

PurposeTo compare free-breathing radial VIBE with moderate undersampling (us-radial-VIBE) with a standard breathhold T1-weighted volumetric interpolated sequence (3D GRE VIBE) in patients unable to suspend respiration during dynamic liver examination. Material and methods23 consecutive patients underwent dynamic liver MR examination using the free-breathing us-radial-VIBE sequence as part of their oncologic follow-up. All patients were eligible for the free-breathing protocol due to severe respiratory artifacts at the planning or precontrast sequences. The us-radial-VIBE acquisitions were compared to the patientś last staging liver MRI including a standard breathhold 3D GRE VIBE.For an objective image evaluation, signal intensity (SI), image noise (IN), signal-to-noise ratio (SNR) and contrast-enhancement ratio (CER) were compared. Representative image quality parameters, including typical artifacts were independently, retrospectively and blindly scored by four readers. ResultsUs-radial-VIBE had significant lower SNR (p<0.0001) and higher IN (p<0.0001), whereas SI did not differ (p=0.62). Temporal resolution assessed with CER in the arterial phase showed higher values for us-radial-VIBE (p=0.028). Subjective image quality parameters received generally slightly higher scores for 3D GRE VIBE. In a smaller subgroup comprising patients with severe respiratory artifacts also at reference breathhold 3D GRE VIBE examination, us-radial-VIBE showed significantly higher image quality scores. Furthermore, there were generally more severe respiratory artifacts in 3D GRE VIBE, whereas streaking was characteristic in almost all us-radial-VIBE acquisitions but did not affect diagnostic validity. ConclusionFree-breathing dynamic liver imaging using us-radial-VIBE delivers accurate temporal resolution, low motion artifact susceptibility and good image quality and represents a promising alternative in patients unable to suspend respiration.

USPIO enhanced lymph node MRI using 3D multi-echo GRE in a rabbit model.

Ultrasmallsuperparamagnetic iron oxide (USPIO) has been suggested to be a negative MR contrast agent to detect metastatic lymph nodes. Previously reported studies have evaluated the diagnostic performance of USPIO-enhanced MR lymph node imaging based on signal intensity. In this study, we investigate the specific performance of three different parametric approaches (normalized signal intensity, R2 * and susceptibility) using 3D multi-echo gradient echo to quantify the USPIO particles in lymph nodes. Nine rabbits with VX2 tumor implants were scanned before and after USPIO injection. From 3D multi-echo GRE magnitude and phase data, we generated multi-echo combined T2 *-weighted images, an R2 * map, and a quantitative susceptibility map. Eighteen lymph nodes (nine reactive and nine metastatic) were evaluated and showed remarkable signal drops in the area of USPIO accumulation. On parametric analysis, the R2 * difference before and after USPIO injection was significantly different (p < 0.05) between reactive and metastatic lymph nodes; in contrast, the normalized signal intensity and susceptibility were not significantly different between the nodes. Our study showed the potential utility of USPIO-enhanced MRI using R2* mapping from 3D multi-echo GRE for the detection of lymph node metastasis and parametric analysis of lymph node status in a rabbit model. Copyright © 2016 John Wiley & Sons, Ltd.

TU‐H‐206‐06: B1 Inhomogeneity Correction for Measuring T1 From DCE MRI

Purpose:3D MRI sequences typically used in DCE MRI suffer from B1 inhomogeneities associated with the slab‐selective RF pulse. B1 inhomogeneities affect the calculation of tissue T1 often used to solve the two‐compartment model. Previously, the inhomogeneities were corrected based on Bloch equation simulations of the RF pulse. However, the RF pulse specification may not be readily available or the simulation may not represent the actual scan conditions. The objective of this work was to directly measure B1 inhomogeneities and apply an inhomogeneity correction to minimize quantification errors in T1 fitting.Methods:We used a 3D GRE sequence with varied flip angles (2–30°) to measure T1‐weighted signals in phantoms at 3 T on a Siemens mMR. 2D EPI B1 maps were acquired to measure the B1 inhomogeneity associated with the RF coils. Inversion recovery T1 maps were acquired for ground truth. Two B1 inhomogeneity correction methods were compared: 1) A 3D segmented EPI sequence measured the RF slab selective excitation profile; and 2) The T1's of phantom standards were used to normalize the 3D GRE images.Results:Only the central 1/3 of the 3D GRE slices yielded accurate T1 values without correction. The slice profiles measured with 3D EPI were consistent between measurements made with different flip angles. The two correction approaches resulted in similar T1 values for at least 2/3 of the slices. Approach 2 yielded more slices with values comparable to the ground truth. However, Approach 1 resulted in less error than Approach 2 for the upper 2/3 of the slices.Conclusion:Using a phantom standard with a short T1 allowed us to shorten the acquisition time of the 3D EPI sequence to less than 1 minute or increase spatial resolution. The B1 inhomogeneity correction technique requires further testing in vivo for DCE MRI studies.

TU‐H‐206‐03: Characterizing B1 Inhomogeneities in DCE MRI

Purpose:Dynamic Contrast Enhanced (DCE) MRI is a valuable technique for measuring perfusion and permeability characteristics of tumors. Exogenous contrast concentrations are calculated based on changes in T1 measured using fast 3D gradient echo (FLASH) sequences. However, the slab selective pulses used in 3D MRI may result in B1 inhomogeneities across the volume of interest that can lead to errors in T1 and thus the estimated gadolinium concentration. We compared three FLASH DCE sequences (GRE, TWIST, and VIBE) to determine their signal homogeneity across slices and the accuracy in calculating T1 using acquisitions with variable flip angles.Methods:The sequences were tested at 3 T on a Siemens mMR (VB20P) using a doped water phantom 3.75 g/L NiSO4 ‐ 6H2O + 5 g/L NaCl (T1 = 104 ms) and a 2% agar, 0.67% NaCl phantom (T1= 1.71 s). 2D EPI B1 maps and inversion recovery T1maps were acquired for ground truth. 3D MRI was acquired at different flip angles to generate a T1 map. Regions of interest were drawn to measure signal inside the phantoms as a function of slice position. The T1 for each slice ROI was fit to the FLASH steady‐state model of magnetization.Results:Based on the data, GRE gave the most uniform signal homogeneity and T1 values in the middle slices of the 3D volume. The 3D VIBE sequence had the largest region of signal inhomogeneity compared to the 3D GRE and TWIST sequences. VIBE's B1 inhomogeneity is inconsistent at low flip angles. However, VIBE resulted in more slices with T1 values similar to the ground truth.Conclusion:The central 1/3 of the slices yielded signals that result in T1 fits consistent with the ground truth. However, the remaining slices required some form of B1 inhomogeneity correction for quantitative DCE analysis.The research was supported in part by NIH NCI Grant R01CA159471.

Non-invasive assessments of cartilage macromolecular composition in patients with acute cartilage injury

Purpose: Cartilage degeneration or defective repair after an injury is typically associated with changes in the macromolecular composition of cartilage. The major function of large aggregating glycosaminoglycans (GAGs) is hydration of the cellular matrix, ensuring cartilage resiliency through electrostatic repulsion. A decrease in GAGs is likely to expose cartilage to dehydration, predisposing the joint to further degeneration. In parallel, roughening of the articular surface may also occur as a result of cartilage fibrillation, a process involving loosening of the collagen network, denaturation of the collagen and loss of the collagen fiber organization. Such a complex matrix makes any progression or repair of the defect challenging to monitor. New MRI developments allowing for a combined evaluation of both macromolecules are considered as a non-invasive alternative to cartilage biopsies. Thus, recent reports suggest that GAG chemical exchange saturation transfer (gagCEST) and T2 mapping MRI sequences are well suited for the detection of change in GAGs and collagen content and structure, respectively. However, clinical proof is still required to monitor cartilage degeneration after injury using biochemical MRI methods. Therefore, the purpose of this study is to establish sensitivity and reproducibility of quantitative imaging biomarkers, such as gagCEST asymmetry values and T2 relaxation times values of the superficial and deep layers of cartilage. Combined MRI measurements were performed in patients with an acute cartilage injury likely to worsen during the observational period due to several risk factors. Methods: Imaging sessions were performed on 7 patients with cartilage defect(s) in the knee joint (ICRS grade 1 or 2) as well as high risk factors (concomitant meniscus damage and/or ligament instability) for further progression of defect. Cartilage gagCEST and T2 images (Fig.1) were obtained for all patients at 7T using following MRI sequences and acquisition parameters: a 3D RF-spoiled GRE sequence with a resolution of 0.9x0.9x2.2 mm3 for gagCEST imaging, and a 3D-TESS sequence with a resolution of 0.25x0.25x3 mm3 for T2 mapping. For image analysis, regions-of-interest were defined on 2D-TSE morphological images in the suspicious regions for defective and normal appearing cartilage, and transferred to gagCEST and T2 images for quantitative analysis. All MRI measurements were repeated 8 days later for reproducibility assessment Results: The gagCEST asymmetry values (N=5 , preliminary data) were 28% lower in damaged areas as compared to adjacent healthy regions in cartilage (3.06±2.18% vs 4.27±1.61%, p=0.17). Disruption in the zonal organization of collagen fibrils was also observed in the damaged areas. T2 relaxation values becoming more uniform between the superficial and deep cartilage layers in defect region ([superficial/deep]T2 ratio in the defective region: 0.81±0.22 vs in the healthy region: 0.68±0.10, p=0.08). Both, gagCEST and T2 measurements showed high correlation between baseline and day-8 values (r=0.78 and r=0.86 , both p<0.0005, respectively). Conclusions: Both MRI methods, as applied here in combination to patients with low-grade cartilage injury, appear to be reproducible and might be able to detect differences between a defective and healthy region of cartilage. These preliminary results support the use of a comprehensive MRI approach in observational and therapeutic trials to differentiate early formation of hyaline from fibrotic cartilage without resorting to serial biopsies.