Single-shot Spin-echo Echo-planar Imaging Research Articles

Characterizing brain mechanics through 7 tesla magnetic resonance elastography

Magnetic resonance elastography (MRE) is a non-invasive method for determining the mechanical response of tissues using applied harmonic deformation and motion-sensitive MRI. MRE studies of the human brain are typically performed at conventional field strengths, with a few attempts at the ultra-high field strength, 7T, reporting increased spatial resolution with partial brain coverage. Achieving high-resolution human brain scans using 7T MRE presents unique challenges of decreased octahedral shear strain-based signal-to-noise ratio (OSS-SNR) and lower shear wave motion sensitivity. In this study, we establish high resolution MRE at 7T with a custom 2D multi-slice single-shot spin-echo echo-planar imaging sequence, using the Gadgetron advanced image reconstruction framework, applying Marchenko-Pastur Principal component analysis denoising, and using nonlinear viscoelastic inversion. These techniques allowed us to calculate the viscoelastic properties of the whole human brain at 1.1 mm isotropic imaging resolution with high OSS-SNR and repeatability. Using phantom models and 7T MRE data of eighteen healthy volunteers, we demonstrate the robustness and accuracy of our method at high-resolution while quantifying the feasible tradeoff between resolution, OSS-SNR, and scan time. Using these post-processing techniques, we significantly increased OSS-SNR at 1.1 mm resolution with whole-brain coverage by approximately 4-fold and generated elastograms with high anatomical detail. Performing high-resolution MRE at 7T on the human brain can provide information on different substructures within brain tissue based on their mechanical properties, which can then be used to diagnose pathologies (e.g. Alzheimer's disease), indicate disease progression, or better investigate neurodegeneration effects or other relevant brain disorders,in vivo.

Effects of oral contrast agent on the viscoelastic properties of the terminal ileum investigated using magnetic resonance elastography.

While standard clinical magnetic resonance (MR) enterography can detect inflammatory bowel disease, it is of limited value in deciding between medical versus surgical treatment. Alternatively, intestinal MR elastography has the potential to contribute additional information to therapeutic decision-making; however, the influence of bowel distension by oral contrast agent on viscoelastic tissue properties remains elusive. Therefore, we aimed to investigate the influence of oral contrast agent-induced bowel distension on the viscoelastic properties of the terminal ileum in healthy volunteers. In this prospective pilot study, 20 healthy volunteers (33.2±8.2 years; 10 men, 10 women) underwent multifrequency MR elastography using a single-shot spin-echo echo planar imaging sequence at 1.5 Tesla and drive frequencies of 40, 50, 60 and 70 Hz. Maps of shear wave speed (c in ms-1) and loss angle (φ in rad), representing stiffness and viscous properties, respectively, were generated using tomoelastography data processing. The volunteers were scanned before and after ingestion of 1,000 mL of 2% mannitol solution as oral contrast agent. There was no significant difference in terminal ileum biomechanical properties before vs. after ingestion of an oral contrast agent (mean c: 1.47±0.24 vs. 1.40±0.25 ms-1 with P=0.37; mean φ: 0.70±0.12 rad vs. 0.68±0.12 rad with P=0.61). Moreover, there was no statistically significant correlation between MR elastography parameters before and after the ingestion of oral contrast (c: r=0.22, P=0.36; φ: r=0.24, P=0.30). The results of this study suggest that bowel distension for intestinal MR elastography has no systematic effect on the biomechanical tissue properties of the terminal ileum determined by MR elastography. Therefore, future study protocols appear feasible with or without oral contrast agents.

Correlation Analysis of Apparent Diffusion Coefficient Histogram Parameters and Clinicopathologic Features for Prognosis Prediction in Uveal Melanoma.

To investigate the correlation between apparent diffusion coefficient (ADC) histograms and high-risk clinicopathologic features related to uveal melanoma (UM) prognosis. This retrospective study included 53 patients with UM who underwent diffusion-weighted imaging (DWI) between August 2015 and March 2024. Axial DWI was performed with a single-shot spin-echo echo-planar imaging sequence. ADC histogram parameters of ADCmean, ADC50%, interquartile range (IQR), skewness, kurtosis, and entropy were obtained from DWI. The relationships between histogram parameters and high-risk clinicopathological characteristics including tumor size, preoperative retinal detachment, histological subtypes, Ki-67 index, and chromosome status, were analyzed by Spearman correlation analysis, Mann-Whitney U test, or Kruskal-Wallis test. A total of 53 patients (mean ± SD age, 55 ± 15 years; 22 men) were evaluated. The largest basal diameter (LBD) was correlated with kurtosis (r = 0.311, P = 0.024). Tumor prominence (TP) was correlated with entropy (r = 0.581, P < 0.001) and kurtosis (r = 0.273, P = 0.048). Additionally, significant correlations were identified between the Ki-67 index and ADCmean (r = -0.444, P = 0.005), ADC50% (r = -0.487, P = 0.002), and skewness (r = 0.394, P = 0.014). Finally, entropy was correlated with monosomy 3 (r = 0.541, P = 0.017). The ADC histograms provided valuable insights into high-risk clinicopathologic features of UM and hold promise in the early prediction of UM prognosis.

Investigating MRI-Associated Biological Aspects of Racial Disparities in Prostate Cancer for African American and White Men.

Understanding the characteristics of multiparametric MRI (mpMRI) in patients from different racial/ethnic backgrounds is important for reducing the observed gaps in clinical outcomes. To investigate the diagnostic performance of mpMRI and quantitative MRI parameters of prostate cancer (PCa) in African American (AA) and matched White (W) men. Retrospective. One hundred twenty-nine patients (43 AA, 86 W) with histologically proven PCa who underwent mpMRI before radical prostatectomy. 3.0 T, T2-weighted turbo spin echo imaging, a single-shot spin-echo EPI sequence diffusion-weighted imaging, and a gradient echo sequence dynamic contrast-enhanced MRI with an ultrafast 3D spoiled gradient-echo sequence. The diagnostic performance of mpMRI in AA and W men was assessed using detection rates (DRs) and positive predictive values (PPVs) in zones defined by the PI-RADS v2.1 prostate sector map. Quantitative MRI parameters, including Ktrans and ve of clinically significant (cs) PCa (Gleason score ≥ 7) tumors were compared between AA and W sub-cohorts after matching age, prostate-specific antigen (PSA), and prostate volume. Weighted Pearson's chi-square and Mann-Whitney U tests with a statistically significant level of 0.05 were used to examine differences in DR and PPV and to compare parameters between AA and matched W men, respectively. A total number of 264 PCa lesions were identified in the study cohort. The PPVs in the peripheral zone (PZ) and posterior prostate of mpMRI for csPCa lesions were significantly higher in AA men than in matched W men (87.8% vs. 68.1% in PZ, and 89.3% vs. 69.6% in posterior prostate). The Ktrans of index csPCa lesions in AA men was significantly higher than in W men (0.25 ± 0.12 vs. 0.20 ± 0.08 min-1; P < 0.01). This study demonstrated race-related differences in the diagnostic performances and quantitative MRI measures of csPCa that were not reflected in age, PSA, and prostate volume. 3 TECHNICAL EFFICACY: Stage 2.

Three-Dimensional Multifrequency MR Elastography for Microvascular Invasion and Prognosis Assessment in Hepatocellular Carcinoma.

Pretreatment identification of microvascular invasion (MVI) in hepatocellular carcinoma (HCC) is important when selecting treatment strategies. To improve models for predicting MVI and recurrence-free survival (RFS) by developing nomograms containing three-dimensional (3D) MR elastography (MRE). Prospective. 188 patients with HCC, divided into a training cohort (n = 150) and a validation cohort (n = 38). In the training cohort, 106/150 patients completed a 2-year follow-up. 1.5T 3D multifrequency MRE with a single-shot spin-echo echo planar imaging sequence, and 3.0T multiparametric MRI (mp-MRI), consisting of diffusion-weighted echo planar imaging, T2-weighted fast spin echo, in-phase out-of-phase T1-weighted fast spoiled gradient-recalled dual-echo and dynamic contrast-enhanced gradient echo sequences. Multivariable analysis was used to identify the independent predictors for MVI and RFS. Nomograms were constructed for visualization. Models for predicting MVI and RFS were built using mp-MRI parameters and a combination of mp-MRI and 3D MRE predictors. Student's t-test, Mann-Whitney U test, chi-squared or Fisher's exact tests, multivariable analysis, area under the receiver operating characteristic curve (AUC), DeLong test, Kaplan-Meier analysis and log rank tests. P < 0.05 was considered significant. Tumor c and liver c were independent predictors of MVI and RFS, respectively. Adding tumor c significantly improved the diagnostic performance of mp-MRI (AUC increased from 0.70 to 0.87) for MVI detection. Of the 106 patients in the training cohort who completed the 2-year follow up, 34 experienced recurrence. RFS was shorter for patients with MVI-positive histology than MVI-negative histology (27.1 months vs. >40 months). The MVI predicted by the 3D MRE model yielded similar results (26.9 months vs. >40 months). The MVI and RFS nomograms of the histologic-MVI and model-predicted MVI-positive showed good predictive performance. Biomechanical properties of 3D MRE were biomarkers for MVI and RFS. MVI and RFS nomograms were established. 2 TECHNICAL EFFICACY: Stage 2.

Understanding Spatial Correlation Between Multiparametric MRI Performance and Prostate Cancer.

Multiparametric MRI (mpMRI) has shown a substantial impact on prostate cancer (PCa) diagnosis. However, the understanding of the spatial correlation between mpMRI performance and PCa location is still limited. To investigate the association between mpMRI performance and tumor spatial location within the prostate using a prostate sector map, described by Prostate Imaging Reporting and Data System (PI-RADS) v2.1. Retrospective. One thousand one hundred forty-three men who underwent mpMRI before radical prostatectomy between 2010 and 2022. 3.0 T. T2-weighted turbo spin-echo, a single-shot spin-echo EPI sequence for diffusion-weighted imaging, and a gradient echo sequence for dynamic contrast-enhanced MRI sequences. Integrated relative cancer prevalence (rCP), detection rate (DR), and positive predictive value (PPV) maps corresponding to the prostate sector map for PCa lesions were created. The relationship between tumor location and its detection/missing by radiologists on mpMRI compared to WMHP as a reference standard was investigated. A weighted chi-square test was performed to examine the statistical differences for rCP, DR, and PPV of the aggregated sectors within the zone, anterior/posterior, left/right prostate, and different levels of the prostate with a statistically significant level of 0.05. A total of 1665 PCa lesions were identified in 1143 patients, and from those 1060 lesions were clinically significant (cs)PCa tumors (any Gleason score [GS] ≥7). Our sector-based analysis utilizing weighted chi-square tests suggested that the left posterior part of PZ had a high likelihood of missing csPCa lesions at a DR of 67.0%. Aggregated sector analysis indicated that the anterior or apex locations in PZ had the significantly lowest csPCa detection at 67.3% and 71.5%, respectively. Spatial characteristics of the per-lesion-based mpMRI performance for diagnosis of PCa were studied. Our results demonstrated that there is a spatial correlation between mpMRI performance and locations of PCa on the prostate. 4 TECHNICAL EFFICACY: Stage 2.

Exploring Radial Asymmetry in MR Diffusion Tensor Imaging and Its Impact on the Interpretation of Glymphatic Mechanisms.

Diffusion imaging holds great potential for the non-invasive assessment of the glymphatic system in humans. One technique, diffusion tensor imaging along the perivascular space (DTI-ALPS), has introduced the ALPS-index, a novel metric for evaluating diffusivity within the perivascular space. However, it still needs to be established whether the observed reduction in the ALPS-index reflects axonal changes, a common occurrence in neurodegenerative diseases. To determine whether axonal alterations can influence change in the ALPS-index. Retrospective. 100 participants (78 cognitively normal and 22 with mild cognitive impairments) aged 50-90 years old. 3T; diffusion-weighted single-shot spin-echo echo-planar imaging sequence, T1-weighted images (MP-RAGE). The ratio of two radial diffusivities of the diffusion tensor (i.e., λ2/λ3) across major white matter tracts with distinct venous/perivenous anatomy that fulfill (ALPS-tracts) and do not fulfill (control tracts) ALPS-index anatomical assumptions were analyzed. To investigate the correlation between λ2/λ3 and age/cognitive function (RAVLT) while accounting for the effect of age, linear regression was implemented to remove the age effect from each variable. Pearson correlation analysis was conducted on the residuals obtained from the linear regression. Statistical significance was set at p < 0.05. λ2 was ~50% higher than λ3 and demonstrated a consistent pattern across both ALPS and control tracts. Additionally, in both ALPS and control tracts a reduction in the λ2/λ3 ratio was observed with advancing age (r = -0.39, r = -0.29, association and forceps tract, respectively) and decreased memory function (r = 0.24, r = 0.27, association and forceps tract, respectively). The results unveil a widespread radial asymmetry of white matter tracts that changes with aging and neurodegeration. These findings highlight that the ALPS-index may not solely reflect changes in the diffusivity of the perivascular space but may also incorporate axonal contributions. 3 TECHNICAL EFFICACY: Stage 2.

Breast DWI Analyzed Before and After Gadolinium Contrast Administration-An Intrapatient Analysis on 1.5 T and 3.0 T.

Diffusion-weighted magnetic resonance imaging (MRI) is gaining popularity as an addition to standard dynamic contrast-enhanced breast MRI. Although adding diffusion-weighted imaging (DWI) to the standard protocol design would require increased scanning-time, implementation during the contrast-enhanced phase could offer a multiparametric MRI protocol without any additional scanning time. However, gadolinium within a region of interest (ROI) might affect assessments of DWI. This study aims to determine if acquiring DWI postcontrast, incorporated in an abbreviated MRI protocol, would statistically significantly affect lesion classification. In addition, the effect of postcontrast DWI on breast parenchyma was studied. Screening or preoperative MRIs (1.5 T/3 T) were included for this study. Diffusion-weighted imaging was acquired with single-shot spin echo-echo planar imaging before and at approximately 2 minutes after gadoterate meglumine injection. Apparent diffusion coefficients (ADCs) based on 2-dimensional ROIs of fibroglandular tissue, as well as benign and malignant lesions at 1.5 T/3.0 T, were compared with a Wilcoxon signed rank test. Diffusivity levels were compared between precontrast and postcontrast DWI with weighted κ. An overall P ≤ 0.05 was considered statistically significant. No significant changes were observed in ADC mean after contrast administration in 21 patients with 37 ROI of healthy fibroglandular tissue and in the 93 patients with 93 (malignant and benign) lesions. This effect remained after stratification on B 0 . In 18% of all lesions, a diffusion level shift was observed, with an overall weighted κ of 0.75. This study supports incorporating DWI at 2 minutes postcontrast when ADC is calculated based on b150-b800 with 15 mL 0.5 M gadoterate meglumine in an abbreviated multiparametric MRI protocol without requiring extra scan time.

Evaluation of apparent diffusion coefficient of two-dimensional BLADE turbo gradient- and spin-echo diffusion-weighted imaging with a breast phantom.

This study aimed to evaluate the reliability of apparent diffusion coefficient (ADC) values generated with two-dimensional turbo gradient- and spin-echo with BLADE trajectory diffusion-weighted imaging (TGSE-BLADE-DWI) sequence using a breast diffusion phantom. TGSE-BLADE-DWI and single-shot spin-echo echo-planar imaging (SS-EPI-DWI) were performed using a 3.0T magnetic resonance imaging scanner. Concordance rates of ADC values and the signal-to-noise ratio (SNR) were compared between TGSE-BLADE-DWI and SS-EPI-DWI. TGSE-BLADE-DWI provided a higher concordance rate for ADC values than SS-EPI-DWI when b-values > 2000s/mm2 and a slice thickness of 1mm were used. TGSE-BLADE-DWI showed less image distortion than SS-EPI-DWI. The SNR of TGSE-BLADE-DWI was higher than that of SS-EPI-DWI, except at a number of excitations of 7 and a slice thickness of 1mm. In conclusion, TGSE-BLADE-DWI can offer a better SNR, less distortion, and more reliable ADC measurements than SS-EPI-DWI in a breast phantom.

An Unsupervised Deep Learning Approach for Dynamic-Exponential Intravoxel Incoherent Motion MRI Modeling and Parameter Estimation in the Liver.

Dynamic-exponential intravoxel incoherent motion (IVIM) imaging is a potential technique for prediction, monitoring, and differential diagnosis of hepatic diseases, especially liver tumors. However, the use of such technique at voxel level is still limited. To develop an unsupervised deep learning approach for voxel-wise dynamic-exponential IVIM modeling and parameter estimation in the liver. Prospective. Ten healthy subjects (4 males; age 28 ± 6 years). Single-shot spin-echo echo planar imaging (SE-EPI) sequence with monopolar diffusion-encoding gradients (12 b-values, 0-800 seconds/mm2 ) at 3.0 T. The proposed deep neural network (DNN) was separately trained on simulated and in vivo hepatic IVIM datasets. The trained networks were compared to the approach combining least squares with Akaike information criterion (LSQ-AIC) in terms of dynamic-exponential modeling accuracy, inter-subject coefficients of variation (CVs), and fitting residuals on the simulated subsets and regions of interest (ROIs) in the left and right liver lobes. The ROIs were delineated by a radiologist (H.-X.Z.) with 7 years of experience in MRI reading. Comparisons between approaches were performed with a paired t-test (normality) or a Wilcoxon rank-sum test (nonnormality). P < 0.05 was considered statistically significant. In simulations, DNN gave significantly higher accuracy (91.6%-95.5%) for identification of bi-exponential decays with respect to LSQ-AIC (79.7%-86.8%). For tri-exponential identification, DNN was also superior to LSQ-AIC despite not reaching a significant level (P=0.08). Additionally, DNN always yielded comparatively low root-mean-square error for estimated parameters. For the in vivo IVIM measurements, inter-subject CVs (0.011-0.150) of DNN were significantly smaller than those (0.049-0.573) of LSQ-AIC. Concerning fitting residuals, there was no significant difference between the two approaches (P=0.56 and 0.76) in both the simulated and in vivo studies. The proposed DNN is recommended for accurate and robust dynamic-exponential modeling and parameter estimation in hepatic IVIM imaging. 2 TECHNICAL EFFICACY: Stage 1.

The Conversion of MRI Data With Multiple b-Values into Signature-Like Pictures to Predict Treatment Response for Rectal Cancer.

Diffusion weighted imaging (DWI) at multiple b-values has been used to predict the pathological complete response (pCR) to neoadjuvant chemoradiotherapy for locally advanced rectal cancer. Non-Gaussian models fit the signal decay of diffusion by several physical values from different approaches of approximation. To develop a deep learning method to analyze DWI data scanned at multiple b-values independent on Gaussian or non-Gaussian models and to apply to a rectal cancer neoadjuvant chemoradiotherapy model. Retrospective. A total of 472 participants (age: 56.6 ± 10.5 years; 298 males and 174 females) with locally advanced adenocarcinoma were enrolled and chronologically divided into a training group (n=200; 42 pCR/158 non-pCR), a validation group (n= 72; 11 pCR/61 non-pCR) and a test group (n=200; 44 pCR/156 non-pCR). A 3.0 T MRI scanner. DWI with a single-shot spin echo-planar imaging pulse sequence at 12 b-values (0, 20, 50, 100, 200, 400, 600, 800, 1000, 1200, 1400, and 1600 sec/mm2 ). DWI signals from manually delineated tumor region were converted into a signature-like picture by concatenating all histograms from different b-values. Pathological results (pCR/non-pCR) were used as the ground truth for deep learning. Gaussian and non-Gaussian methods were used for comparison. Analysis of variance for age; Chi-square for gender and pCR/non-pCR; area under the receiver operating characteristic (ROC) curve (AUC); DeLong test for AUC. P < 0.05 for significant difference. The AUC in the test group is 0.924 (95% CI: 0.866-0.983) for the signature-like pictures converted from 35 bins, and it is 0.931 (95% CI: 0.884-0.979) for the signature-like pictures converted from 70 bins, which is significantly (Z=3.258, P < 0.05) larger than Dapp , the best predictor in non-Gaussian methods with AUC=0.773 (95% CI: 0.682-0.865). The proposed signature-like pictures provide more accurate pretreatment prediction of the response to neoadjuvant chemoradiotherapy than the fitted methods for locally advanced rectal cancer. 3 TECHNICAL EFFICACY: Stage 2.

Diffusion-weighted MRI of solid pancreatic lesions: Comparison between reduced field-of-view and large field-of-view sequences

PurposeTo compare the image quality, presence of artifacts and apparent diffusion coefficient (ADC) values of reduced field-of-view (rFOV) and large FOV (lFOV) single-shot spin-echo echo-planar diffusion-weighted imaging (DWI) in the evaluation of solid pancreatic lesion. MethodThe 3T MR examinations of 60 patients with solid pancreatic lesions were examined. Two Readers independently performed qualitative analysis and quantitative measurements of the ADC values of the solid pancreatic lesions in both rFOV and lFOV DWI sequence. The qualitative analysis parameters included: 1) Sharpness, 2) Distortion, Ghosting, Motion and Susceptibility artifacts, 3) Lesion Conspicuity and 4) Overall Image Quality. These parameters were evaluated using a 4-point scale. The T-test for paired data was used to compare qualitative scores and the ADC values of the rFOV and lFOV DWI sequences, and to assess inter-reader agreement. ResultsThe qualitative analysis yielded scores for the rFOV DWI sequence, which were better for sharpness, artifacts, and overall image quality as compared to the lFOV DWI sequence according to the only Reader 2 (the most experienced) (p ≤ 0.001). As to lesion conspicuity, no significant difference was found by either Reader (p ≥ 0.245). As to quantitative analysis, both Readers found no significant difference between the two sequences in the ADC values of various solid pancreatic lesions (p ≥ 0.156). ConclusionsThe rFOV DWI sequence of the pancreas provides better anatomic structure visualization, reduced artifacts, and better overall image quality as compared to the lFOV DWI sequence according to the Reader with the more experience in abdominal MRI. The ADC values were not significantly different in the two sequences. The rFOV DWI sequence could be included in the standard MRI protocol for the pancreas.

Short-Term Repeatability of in Vivo Cardiac Intravoxel Incoherent Motion Tensor Imaging in Healthy Human Volunteers.

Intravoxel incoherent motion (IVIM) tensor imaging is a promising technique for diagnosis and monitoring of cardiovascular diseases. Knowledge about measurement repeatability, however, remains limited. To evaluate short-term repeatability of IVIM tensor imaging in normal in vivo human hearts. Prospective. Ten healthy subjects without history of heart diseases. Balanced steady-state free-precession cine sequence and single-shot spin-echo echo planar IVIM tensor imaging sequence (9 b-values, 0-400 seconds/mm2 and six diffusion-encoding directions) at 3.0 T. Subjects were scanned twice with an interval of 15 minutes, leaving the scanner between studies. The signal-to-noise ratio (SNR) was evaluated in anterior, lateral, septal, and inferior segments of the left ventricle wall. Fractional anisotropy (FA), mean diffusivity (MD), mean fraction (MF), and helix angle (HA) in the four segments were independently measured by five radiologists. IVIM tensor indexes were compared between observers using a one-way analysis of variance or between scans using a paired t-test (normal data) or a Wilcoxon rank-sum test (non-normal data). Interobserver agreement and test-retest repeatability were assessed using the intraclass correlation coefficient (ICC), within-subject coefficient of variation (WCV), and Bland-Altman limits of agreements. SNR of inferior segment was significantly lower than the other three segments, and inferior segment was therefore excluded from repeatability analysis. Interobserver repeatability was excellent for all IVIM tensor indexes (ICC: 0.886-0.972; WCV: 0.62%-4.22%). Test-retest repeatability was excellent for MD of the self-diffusion tensor (D) and MF of the perfusion fraction tensor (fp ) (ICC: 0.803-0.888; WCV: 1.42%-9.51%) and moderate for FA and MD of the pseudo-diffusion tensor (D* ) (ICC: 0.487-0.532; WCV: 6.98%-10.89%). FA of D and fp and HA of D presented good test-retest repeatability (ICC: 0.732-0.788; WCV: 3.28%-8.71%). The D and fp indexes exhibited satisfactory repeatability, but further efforts were needed to improve repeatability of D* indexes. 2 TECHNICAL EFFICACY: Stage 1.

Feasibility of Intestinal MR Elastography in Inflammatory Bowel Disease.

While MR enterography allows detection of inflammatory bowel disease (IBD), the findings continue to be of limited use in guiding treatment-medication vs. surgery. To test the feasibility of MR elastography of the gut in healthy volunteers and IBD patients. Prospective pilot. Forty subjects (healthy volunteers: n=20, 37 ± 14 years, 10 women; IBD patients: n=20 (ulcerative colitis n=9, Crohn's disease n=11), 41 ± 15 years, 11 women). Multifrequency MR elastography using a single-shot spin-echo echo planar imaging sequence at 1.5 T with drive frequencies of 40, 50, 60, and 70 Hz. Maps of shear-wave speed (SWS, in m/s) and loss angle (φ, in rad), representing stiffness and solid-fluid behavior, respectively, were generated using tomoelastography data processing. Histopathological analysis of surgical specimens was used as reference standard in patients. Unpaired t-test, one-way analysis of variance followed by Tukey post hoc analysis, Pearson's correlation coefficient and area under the receiver operating characteristic curve (AUC) with 95%-confidence interval (CI). Significance level of 5%. MR elastography was feasible in all 40 subjects (100% technical success rate). SWS and φ were significantly increased in IBD by 21% and 20% (IBD: 1.45 ± 0.14 m/s and 0.78 ± 0.12 rad; healthy volunteers: 1.20 ± 0.14 m/s and 0.65 ± 0.06 rad), whereas no significant differences were found between ulcerative colitis and Crohn's disease (P=0.74 and 0.90, respectively). In a preliminary assessment, a high diagnostic accuracy in detecting IBD was suggested by an AUC of 0.90 (CI: 0.81-0.96) for SWS and 0.84 (CI: 0.71-0.95) for φ. In this pilot study, our results demonstrated the feasibility of MR elastography of the gut and showed an excellent diagnostic performance in predicting IBD. 1 TECHNICAL EFFICACY: Stage 1.

Characteristics of diffusion-weighted and blood oxygen level-dependent magnetic resonance imaging in Tubulointerstitial nephritis: an initial experience

BackgroundDiffusion-weighted (DW) and blood oxygen level-dependent (BOLD) magnetic resonance imaging are classical sequences of functional MR, but the exploration in non-transplanted kidney disease is limited. Objects: To analyze the characteristics of apparent diffusion coefficient (ADC) and R2* value using DW and BOLD imaging in tubulointerstitial nephritis (TIN).MethodsFour acute TIN, thirteen chronic TIN patients, and four controls were enrolled. We used multiple gradient-echo sequences to acquire 12 T2*-weighted images to calculate the R2* map. DW imaging acquired ADC values by combining a single-shot spin-echo echo-planar imaging pulse sequence and the additional motion probing gradient pulses along the x,y, z-axes with two b values:0 and 200, as well as 0 and 800 s/mm2. ATIN patients performed DW and BOLD magnetic resonance at renal biopsy(T0) and the third month(T3). We assessed the pathological changes semiquantitatively, and conducted correlation analyses within functional MR, pathological and clinical indexes.ResultsIn ATIN, ADCs were significantly lower(b was 0,200 s/mm2, 2.86 ± 0.19 vs. 3.39 ± 0.11, b was 0,800 s/mm2, 1.76 ± 0.12 vs. 2.16 ± 0.08, P < 0.05) than controls, showing an obvious remission at T3. Cortical and medullary R2* values (CR2*,MR2*) were decreased, significant difference was only observed in MR2*(T0 24.3 ± 2.1vs.T3 33.1 ± 4.1,P < 0.05). No relationship was found between functional MR and histopathological indexes.MR2* had a close relationship with eGFR (R = 0.682,P = 0.001) and serum creatinine(R = -0.502,P = 0.012). Patients with lower ADC when b was 0,200 s/mm2 showed more increase of ADC(R = -0.956,P = 0.044) and MR2*(R = -0.949,P = 0.05) after therapy. In CTIN group, lowered MR2* and MR2*/CR2* provided evidence of intrarenal ischemia. CTIN with advanced CKD (eGFR< 45) had significantly lower ADCb200 value.ConclusionsWe observed the reduction and remission of ADC and R2* values in ATIN case series. ATIN patients had concurrently decreased ADCb800 and MR2*. The pseudo normalization of CR2* with persistently low MR2* in CTIN suggested intrarenal hypoxia.

Understanding diffusion-weighted MRI analysis: Repeatability and performance of diffusion models in a benign breast lesion cohort.

Diffusion-weighted MRI (DWI) is an important tool for oncology research, with great clinical potential for the classification and monitoring of breast lesions. The utility of parameters derived from DWI, however, is influenced by specific analysis choices. The purpose of this study was to critically evaluate repeatability and curve-fitting performance of common DWI signal representations, for a prospective cohort of patients with benign breast lesions. Twenty informed, consented patients with confirmed benign breast lesions underwent repeated DWI (3 T) using: sagittal single-shot spin-echo echo planar imaging, bipolar encoding, TR/TE: 11,600/86 ms, FOV: 180 x 180 mm, matrix: 90 x 90, slices: 60 x 2.5 mm, iPAT: GRAPPA 2, fat suppression, and 13 b-values: 0-700 s/mm2 . A phase-reversed scan (b = 0 s/mm2 ) was acquired for distortion correction. Voxel-wise repeat-measures coefficients of variation (CoVs) were derived for monoexponential (apparent diffusion coefficient [ADC]), biexponential (intravoxel incoherent motion: f, D, D*) and stretched exponential (α, DDC) across the parameter histograms for lesion regions of interest (ROIs). Goodness-of-fit for each representation was assessed by Bayesian information criterion. The volume of interest (VOI) definition was repeatable (CoV 13.9%). Within lesions, and across both visits and the cohort, there was no dominant best-fit model, with all representations giving the best fit for a fraction of the voxels. Diffusivity measures from the signal representations (ADC, D, DDC) all showed good repeatability (CoV < 10%), whereas parameters associated with pseudodiffusion (f, D*) performed poorly (CoV > 50%). The stretching exponent α was repeatable (CoV < 12%). This pattern of repeatability was consistent over the central part of the parameter percentiles. Assumptions often made in diffusion studies about analysis choices will influence the detectability of changes, potentially obscuring useful information. No single signal representation prevails within or across lesions, or across repeated visits; parameter robustness is therefore a critical consideration. Our results suggest that stretched exponential representation is more repeatable than biexponential, with pseudodiffusion parameters unlikely to provide clinically useful biomarkers.

Assessment of Neuroprotective Effects of Low-Intensity Transcranial Ultrasound Stimulation in a Parkinson's Disease Rat Model by Fractional Anisotropy and Relaxation Time T2∗ Value.

Background: Low-intensity transcranial ultrasound (LITUS) may have a therapeutic effect on Parkinson’s disease (PD) patients to some extent. Fractional anisotropy (FA) and relaxation time T2∗ that indicate the integrity of fiber tracts and iron concentrations in brain tissue have been used to evaluate the therapeutic effects of LITUS.Purpose: This study aims to use FA and T2∗ values to evaluate the therapeutic effects of LITUS in a PD rat model.Materials and Methods: Twenty Sprague-Dawley rats were randomly divided into a hemi-PD group (n = 10) and a LITUS group (n = 10). Single-shot spin echo echo-planar imaging and fast low-angle shot T2WI sequences at 3.0 T were used. The FA and T2∗ values on the right side of the substantia nigra (SN) pars compacta were measured to evaluate the therapeutic effect of LITUS in the rats.Results: One week after PD-like signs were induced in the rats, the FA value in the LITUS group was significantly larger compared with the PD group (0.214 ± 0.027 vs. 0.340 ± 0.032, t = 2.864, P = 0.011). At the 5th and 6th weeks, the FA values in the LITUS group were significantly smaller compared with the PD group (5th week: 0.290 ± 0.037 vs. 0.405 ± 0.027, t = 2.385, P = 0.030; 6th week: 0.299 ± 0.021 vs. 0.525 ± 0.028, t = 6.620, P < 0.0001). In the 5th and 6th weeks, the T2∗ values in the injected right SN of the LITUS group were significantly higher compared with the PD group (5th week, 12.169 ± 0.826 in the LITUS group vs. 7.550 ± 0.824 in the PD group; 6th week, 11.749 ± 0.615 in the LITUS group vs. 7.550 ± 0.849 in the PD group).Conclusion: LITUS had neuroprotective effects and can reduce the damage of 6-OHDA-induced neurotoxicity in hemi-PD rats. The combination of FA and T2∗ assessments can potentially serve as a new and effective method to evaluate the therapeutic effects of LITUS.

Whole-Lesion Histogram Analysis of the Apparent Diffusion Coefficient as a Quantitative Imaging Biomarker for Assessing the Level of Tumor-Infiltrating Lymphocytes: Value in Molecular Subtypes of Breast Cancer.

PurposeTo assess whether apparent diffusion coefficient (ADC) metrics can be used to assess tumor-infiltrating lymphocyte (TIL) levels in breast cancer, particularly in the molecular subtypes of breast cancer.MethodsIn total, 114 patients with breast cancer met the inclusion criteria (mean age: 52 years; range: 29–85 years) and underwent multi-parametric breast magnetic resonance imaging (MRI). The patients were imaged by diffusion-weighted (DW)-MRI (1.5 T) using a single-shot spin-echo echo-planar imaging sequence. Two readers independently drew a region of interest (ROI) on the ADC maps of the whole tumor. The mean ADC and histogram parameters (10th, 25th, 50th, 75th, and 90th percentiles of ADC, skewness, entropy, and kurtosis) were used as features to analyze associations with the TIL levels in breast cancer. Additionally, the correlation between the ADC values and Ki-67 expression were analyzed. Continuous variables were compared with Student’s t-test or Mann-Whitney U test if the variables were not normally distributed. Categorical variables were compared using Pearson’s chi-square test or Fisher’s exact test. Associations between TIL levels and imaging features were evaluated by the Mann-Whitney U and Kruskal-Wallis tests.ResultsA statistically significant difference existed in the 10th and 25th percentile ADC values between the low and high TIL groups in breast cancer (P=0.012 and 0.027). For the luminal subtype of breast cancer, the 10th percentile ADC value was significantly lower in the low TIL group (P=0.041); for the non-luminal subtype of breast cancer, the kurtosis was significantly lower in the low TIL group (P=0.023). The Ki-67 index showed statistical significance for evaluating the TIL levels in breast cancer (P=0.007). Additionally, the skewness was significantly higher for samples with high Ki-67 levels in breast cancer (P=0.029).ConclusionsOur findings suggest that whole-lesion ADC histogram parameters can be used as surrogate biomarkers to evaluate TIL levels in molecular subtypes of breast cancer.

Feasibility and Initial Results of Daily Diffusion Weighted Imaging (DWI) Metrics Obtained during Stereotactic Body Radiation Therapy (SBRT) delivered using a 1.5 MR Linac

Changes in DWI metrics, specifically the apparent diffusion coefficient (ADC), of tumors following concurrent chemotherapy and radiation therapy (chemo-RT) were shown to correlate with clinical outcomes. Such changes have been primarily described in patients undergoing conventionally fractionated chemo-RT. DWI changes that occur following treatment with SBRT remain poorly understood. We sought to characterize changes in daily DWI metrics collected during the short course of SBRT, using a 1.5 MR Linac. Patients of various tumor sites undergoing SBRT on a 1.5 MR Linac were included. On each treatment day, patients had a fully quantitative DWI that was acquired during the time for daily treatment adaption. DWI was acquired using a single-shot spin echo EPI sequence (FOV: 380 mm2, matrix: 128x128, TE: 69 ms, TR: 5500 ms, four b-values ranging from 0 to 550 s/mm). Fat suppression, acceleration, and number of averages per b-value were optimized to maximize image quality and minimize geometric distortion. Gross tumor volumes (GTVs) were contoured daily by the attending physician using an image processing software. Distributions of ADC values for voxels contained in the GTV were used to determine imaging features including mean, median, kurtosis, skewness and standard deviation. Student’s t-test was used to compare tumor ADC values. Of 38 patients screened, 27 patients (17 males, 10 females) had daily DWI scans available for analysis. The median age was 68. Patients received total doses ranging from 24Gy to 60Gy and fraction number ranged from 3 to 6. 128 DWI scans were analyzed. Mean tumor ADCs ranged from 0.79 to 2.08, median ADCs ranged from 0.75 to 1.99, kurtosis ranged from -1.11 to 3.61, standard deviations ranged from 0.23 to 0.93 and skewness ranged from -0.86 to 1.36. The comparison of mean tumor ADC values measured on the first day of treatment to those measured on the last day of treatment failed to reveal a statistically significant difference (p = 0.087). 59% of patients had an increase in mean ADC at the time of delivery of the second fraction. That percentage was 63% at the third fraction, 80% at the fourth fraction and 75% at the fifth fraction. We characterized daily DWI metrics for patients undergoing SBRT using a 1.5 MR Linac. We observe measurable changes in certain image features (mean, median, kurtosis, standard deviation and skewness) of tumor ADC maps. Although there was no statistical difference between the mean ADC values measured at the first and last fractions, we noted that an increasing proportion of patients exhibits a favorable rise in mean or median tumor ADC throughout the course of SBRT. The ability to longitudinally track MRI metrics represents a novel potential biomarker of response to SBRT that warrants further investigation and correlation with clinical endpoints.

Role of diffusion-weighted imaging in differentiation between posterior fossa brain tumors

BackgroundDiffusion-weighted imaging (DWI) is an imaging modality using multi-section single-shot spin echo planar imaging (EPI) sequence which is extremely sensitive for detection of water motion within intra, extra, and transcellular regions. This character is important to differentiate between brain tumors either low (benign) or highly (malignant) cellular tumors.ObjectiveTo evaluate the role of DWI and apparent diffusion coefficient (ADC) in evaluation and differentiation between different brain posterior fossa tumors in children and adults.Patients and methodsThe study included 34 patients with different brain posterior fossa tumors for evaluation by conventional MRI (using 1.5 T MRI PHILIPS Achieva 2.1 Best Netherland) and DWI.ResultsOur study showed that mean ADC values were significantly different between the four groups of posterior fossa tumors in children: juvenile pilocytic astrocytoma (JPA), medulloblastoma, ependymoma, and brain stem glioma while mean ADC values were not significantly different between posterior fossa tumors in the adult group. Regions of interest were manually positioned, and all values were automatically calculated and expressed in 10−3 mm2/s.ConclusionDWI is an ideal additional imaging technique, which is a rapid, easy, non-invasive imaging modality, with no contrast injection needed. It has been widely applied in the differentiation between posterior fossa brain tumors and in the diagnosis of various intracranial diseases.