Optimizing pseudo-spiral sampling for abdominal DCE MRI using a digital anthropomorphic phantom

Purpose: For reliable DCE MRI parameter estimation, k-space undersampling is essential to meet resolution, coverage, and signal-to-noise requirements. Pseudo-spiral (PS) sampling achieves this by sampling k-space on a Cartesian grid following a spiral trajectory. The goal was to optimize PS k-space sampling patterns for abdomin al DCE MRI. Methods: The optimal PS k-space sampling pattern was determined using an anthropomorphic digital phantom. Contrast agent inflow was simulated in the liver, spleen, pancreas, and pancreatic ductal adenocarcinoma (PDAC). A total of 704 variable sampling and reconstruction approaches were created using three algorithms using different parametrizations to control sampling density, halfscan and compressed sensing regularization. The sampling patterns were evaluated based on image quality scores and the accuracy and precision of the DCE pharmacokinetic parameters. The best and worst strategies were assessed in vivo in five healthy volunteers without contrast agent administration. The best strategy was tested in a DCE scan of a PDAC patient. Results: The best PS reconstruction was found to be PS-diffuse based, with quadratic distribution of readouts on a spiral, without random shuffling, halfscan factor of 0.8, and total variation regularization of 0.05 in the spatial and temporal domains. The best scoring strategy showed sharper images with less prominent artifacts in healthy volunteers compared to the worst strategy. Our suggested DCE sampling strategy also showed high quality DCE images in the PDAC patient. Conclusion: Using an anthropomorphic digital phantom, we identified an optimal PS sampling strategy for abdominal DCE MRI, and demonstrated feasibility in a PDAC patient

Single Breath‐Hold MR Elastography for Fast Biomechanical Probing of Pancreatic Stiffness

International audienceBackground Pancreatic ductal adenocarcinoma (PDAC) stromal disposition is thought to influence chemotherapy efficacy and increase tissue stiffness, which could be quantified noninvasively via MR elastography (MRE). Current methods cause position‐based errors in pancreas location over time, hampering accuracy. It would be beneficial to have a single breath‐hold acquisition. Purpose To develop and test a single breath‐hold three‐dimensional MRE technique utilizing prospective undersampling and a compressed sensing reconstruction (CS‐MRE). Study Type Prospective. Population A total of 30 healthy volunteers (HV) (31 ± 9 years; 33% male) and five patients with PDAC (69 ± 5 years; 80% male). Field Strength/Sequence 3‐T, GRE Ristretto MRE. Assessment First, optimization of multi breath‐hold MRE was done in 10 HV using four combinations of vibration frequency, number of measured wave‐phase offsets, and TE and looking at MRE quality measures in the pancreas head. Second, viscoelastic parameters delineated in the pancreas head or tumor of CS‐MRE were compared against (I) 2D and (II) 3D four breath‐hold acquisitions in HV (N = 20) and PDAC patients. Intrasession repeatability was assessed for CS‐MRE in a subgroup of healthy volunteers (N = 15). Statistical Tests Tests include repeated measures analysis of variance (ANOVA), Bland–Altman analysis, and coefficients of variation (CoVs). A P ‐value <.05 was considered statistically significant. Results Optimization of the four breath‐hold acquisitions resulted in 40 Hz vibration frequency, five wave‐phases, and echo time (TE) = 6.9 msec as the preferred method (4BH‐MRE). CS‐MRE quantitative results did not differ from 4BH‐MRE. Shear wave speed (SWS) and phase angle differed significantly between HV and PDAC patients using 4BH‐MRE or CS‐MRE. The limits of agreement for SWS were [−0.09, 0.10] m/second and the within‐subject CoV was 4.8% for CS‐MRE. Data Conclusion CS‐MRE might allow a single breath‐hold MRE acquisition with comparable SWS and phase angle as 4BH‐MRE, and it may still enable to differentiate between HV and PDAC. Level of Evidence: 2 Technical Efficacy Stage:

Viscoelastic properties of small bowel mesentery at MR elastography in Crohn’s disease: a prospective cross-sectional exploratory study

Abstract Background Creeping fat is a pathological feature of small bowel Crohn’s disease (CD), with literature suggesting that bowel resection with extended mesenteric resection is related to less postoperative recurrences. Conventional imaging is unable to accurately quantify the disease involvement (i.e., fibrosis) of creeping fat. Quantification of disease involvement could be useful in decision-making for additional extended mesenteric resection. We investigated the feasibility of magnetic resonance elastography (MRE) of the mesentery and if MRE is capable to detect fibrotic disease involvement of mesentery in active CD. Methods Multifrequency MRE yielded spatial stiffness (shear wave speed, SWS, |G*|) and fluidity maps (φ). Viscoelastic properties of seven CD patients’ mesentery were compared to age- and sex-matched healthy volunteers (HV) (Mann–Whitney U-test). Within CD patients, the affected and “presumably” unaffected mesentery were compared (Wilcoxon-signed rank test). Repeatability was tested in 15 HVs (Bland–Altman analysis, coefficient of variation [CoV]). Spearman rank correlations were used to investigate the relation between microscopically scored amount of mesenteric fibrosis and viscoelastic parameters. Results SWS, |G*|, and φ of affected mesentery in CD were higher compared to HV (p = 0.017, p = 0.001, p = 0.017). Strong correlations were found between percentage of area of mesenteric fibrosis and SWS and |G*| (p < 0.010). No differences were found within CD between affected and presumably unaffected mesentery. Repeatability of SWS showed 95% limits of agreement of (-0.09, 0.13 m/s) and within-subject CoV of 5.3%. Conclusion MRE may have the potential to measure fibrotic disease involvement of the mesentery in CD, possibly guiding clinical decision-making with respect to extended mesenteric resection. Trial registration Dutch trial register, NL9105 , registered 7 December 2020. Relevance statement MRE may have the potential to measure the amount of mesenteric fibrosis of the affected mesenteric fat in active Crohn’s disease, giving more insight into disease progression and could potentially play a role in clinical decision-making for extended mesenteric resection. Key points • MRE of the mesentery in patients with active CD is feasible. • Fluidity and stiffness of the mesentery increase in active CD, while stiffness correlates with the histopathological amount of mesenteric fibrosis. • MRE provides biomarkers to quantify mesenteric disease activity in active CD. Graphical Abstrac