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Background: Diffusion weighted imaging (DWI) with optimized motion-compensated gradient waveforms reduces signal dropouts in the liver and pancreas caused by cardiovascular-associated motion, however its precision is unknown. We hypothesized that DWI with motion-compensated DW gradient waveforms would improve apparent diffusion coefficient (ADC)-repeatability and inter-reader reproducibility compared to conventional DWI in these organs., Methods: In this IRB-approved, prospective, single center study, subjects recruited between October 2019 and March 2020 were scanned twice on a 3 T scanner, with repositioning between test and retest. Each scan included two respiratory-triggered DWI series with comparable acquisition time: 1) conventional (monopolar) 2) motion- compensated diffusion gradients. Three readers measured ADC values. One-way ANOVA, Bland-Altman analysis were used for statistical analysis., Results: Eight healthy participants (4 male/4 female), with a mean age of 29 ± 4 years, underwent the liver and pancreas MRI protocol. Four patients with liver metastases (2 male/2 female) with a mean age of 58 ± 5 years underwent the liver MRI protocol. In healthy participants, motion-compensated DWI outperformed conventional DWI with mean repeatability coefficient of 0.14 × 10 -3 (CI:0.12-0.17) vs. 0.31 × 10 -3 (CI:0.27-0.37) mm 2 /s for liver, and 0.11 × 10 -3 (CI:0.08-0.15) vs. 0.34 × 10 -3 (CI:0.27-0.49) mm 2 /s for pancreas; and with mean reproducibility coefficient of 0.20 × 10 -3 (CI:0.18-0.23) vs. 0.51 × 10 -3 (CI:0.46-0.58) mm 2 /s for liver, and 0.16 × 10 -3 (CI:0.13-0.20) vs. 0.42 × 10 -3 (CI:0.34-0.52) mm 2 /s for pancreas. In patients, improved repeatability was observed for motion-compensated DWI in comparison to conventional with repeatability coefficient of 0.51 × 10 - 3  mm 2 /s (CI:0.35-0.89) vs. 0.70 × 10 -3  mm 2 /s (CI:0.49-1.20)., Conclusion: Motion-compensated DWI enhances the precision of ADC measurements in the liver and pancreas compared to conventional DWI., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Purpose: To evaluate feasibility and reproducibility of liver diffusion-weighted (DW) MRI using cardiac-motion-robust, blood-suppressed, reduced-distortion techniques., Methods: DW-MRI data were acquired at 3T in an anatomically accurate liver phantom including controlled pulsatile motion, in eight healthy volunteers and four patients with known or suspected liver metastases. Standard monopolar and motion-robust (M1-nulled, and M1-optimized) DW gradient waveforms were each acquired with single-shot echo-planar imaging (ssEPI) and multishot EPI (msEPI). In the motion phantom, apparent diffusion coefficient (ADC) was measured in the motion-affected volume. In healthy volunteers, ADC was measured in the left and right liver lobes separately to evaluate ADC reproducibility between the two lobes. Image distortions were quantified using the normalized cross-correlation coefficient, with an undistorted T2-weighted reference., Results: In the motion phantom, ADC mean and SD in motion-affected volumes substantially increased with increasing motion for monopolar waveforms. ADC remained stable in the presence of increasing motion when using motion-robust waveforms. M1-optimized waveforms suppressed slow flow signal present with M1-nulled waveforms. In healthy volunteers, monopolar waveforms generated significantly different ADC measurements between left and right liver lobes ( p = 0 . 0078 $$ p=0.0078 $$ , reproducibility coefficients (RPC) =  470 × 1 0 - 6 $$ 470\times 1{0}^{-6} $$ mm 2 $$ {}^2 $$ /s for monopolar-msEPI), while M1-optimized waveforms showed more reproducible ADC values ( p = 0 . 29 $$ p=0.29 $$ , RPC = 220 × 1 0 - 6 $$ \mathrm{RPC}=220\times 1{0}^{-6} $$ mm 2 $$ {}^2 $$ /s for M1-optimized-msEPI). In phantom and healthy volunteer studies, motion-robust acquisitions with msEPI showed significantly reduced image distortion ( p < 0 . 001 $$ p<0.001 $$ ) compared to ssEPI. Patient scans showed reduction of wormhole artifacts when combining M1-optimized waveforms with msEPI., Conclusion: Synergistic effects of combined M1-optimized diffusion waveforms and msEPI acquisitions enable reproducible liver DWI with motion robustness, blood signal suppression, and reduced distortion., (© 2022 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose: The purpose of this work was to obtain precise tri-exponential intravoxel incoherent motion (IVIM) quantification in the liver using 2D (b-value and first-order motion moment [M 1 ]) IVIM-DWI acquisitions and region of interest (ROI)-based fitting techniques., Methods: Diffusion MRI of the liver was performed in 10 healthy volunteers using three IVIM-DWI acquisitions: conventional monopolar, optimized monopolar, and optimized 2D (b-M 1 ). For each acquisition, bi-exponential and tri-exponential full, segmented, and over-segmented ROI-based fitting and a newly proposed blood velocity SDdistribution (BVD) fitting technique were performed to obtain IVIM estimates in the right and left liver lobes. Fitting quality was evaluated using corrected Akaike information criterion. Precision metrics (test-retest repeatability, inter-reader reproducibility, and inter-lobar agreement) were evaluated using Bland-Altman analysis, repeatability/reproducibility coefficients (RPCs), and paired sample t-tests. Precision was compared across acquisitions and fitting methods., Results: High repeatability and reproducibility was observed in the estimations of the diffusion coefficient (D tri  = [1.03 ± 0.11] × 10 -3  mm 2 /s; RPCs ≤ 1.34 × 10 -4  mm 2 /s), perfusion fractions (F 1  = 3.19 ± 1.89% and F 2  = 16.4 ± 2.07%; RPCs ≤ 2.51%), and blood velocity SDs (V b,1  = 1.44 ± 0.14 mm/s and V b,2  = 3.62 ± 0.13 mm/s; RPCs ≤ 0.41 mm/s) in the right liver lobe using the 2D (b-M 1 ) acquisition in conjunction with BVD fitting. Using these methods, significantly larger (p < 0.01) estimates of D tri and F 1 were observed in the left lobe in comparison to the right lobe, while estimates of V b,1 and V b,2 demonstrated high interlobar agreement (RPCs ≤ 0.45 mm/s)., Conclusions: The 2D (b-M 1 ) IVIM-DWI data acquisition in conjunction with BVD fitting enables highly precise tri-exponential IVIM quantification in the right liver lobe., (© 2022 International Society for Magnetic Resonance in Medicine.)

Objectives: To prospectively compare image quality and apparent diffusion coefficient (ADC) quantification for reduced field-of-view (rFOV)- and multi-shot echo-planar imaging (msEPI)-based diffusion weighted imaging (DWI), using single-shot echo-planar-imaging (ssEPI) DWI as the reference., Methods: Under IRB approval and after informed consent, msEPI, rFOV, and ssEPI DWI acquisitions were prospectively added to clinical prostate MRI exams at 3.0 T. Image distortion was quantitatively evaluated by root-mean-squared displacement (d r.m.s. ). Histogram-based quantitative ADC parameters were compared in a sub-set of patients for proven sites of prostate cancer and matched non-cancerous prostate. Three radiologists also independently evaluated the DWI sequences for subjective image quality and distortion/artifact on a 5-point Likert scale., Results: Twenty-five patients were included (15 with proven sites of cancer). Average d r.m.s. demonstrated a small but statistically significant reduction in distortion for both rFOV and msEPI relative to ssEPI. Quantitative ADC parameters for prostate tumors demonstrated no significant difference across the 3 DWI acquisitions and each acquisition demonstrated a statistically significant decrease in mean ADC for tumor compared to normal prostate. Qualitative reader assessment demonstrated favorable image quality for rFOV and msEPI, more notable for msEPI., Conclusions: rFOV and msEPI DWI techniques achieved reduction in image distortion, improvement in image quality, and maintained reproducible ADC quantification compared to the standard ssEPI., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Purpose: To design a b value and first-order motion moment (M 1 ) optimized data acquisition for repeatable intravoxel incoherent motion (IVIM) quantification in the liver., Methods: Cramer-Rao lower bound optimization was performed to determine optimal monopolar and optimal 2D samplings of the b-M 1 space based on noise performance. Monte Carlo simulations were used to evaluate the bias and variability in estimates obtained using the proposed optimal samplings and conventional monopolar sampling. Diffusion MRI of the liver was performed in 10 volunteers using 3 IVIM acquisitions: conventional monopolar, optimized monopolar, and b-M 1 -optimized gradient waveforms (designed based on the optimal 2D sampling). IVIM parameter maps of diffusion coefficient, perfusion fraction, and blood velocity SD were obtained using nonlinear least squares fitting. Noise performance (SDs), stability (outlier percentage), and test-retest or scan-rescan repeatability (intraclass correlation coefficients) were evaluated and compared across acquisitions., Results: Cramer-Rao lower bound and Monte Carlo simulations demonstrated improved noise performance of the optimal 2D sampling in comparison to monopolar samplings. Evaluating the designed b-M 1 -optimized waveforms in healthy volunteers, significant decreases (p < 0.05) in the SDs and outlier percentages were observed for measurements of diffusion coefficient, perfusion fraction, and blood velocity SD in comparison to measurements obtained using monopolar samplings. Good-to-excellent repeatability (intraclass correlation coefficients ≥ 0.77) was observed for all 3 parameters in both the right and left liver lobes using the b-M 1 -optimized waveforms., Conclusions: 2D b-M 1 -optimized data acquisition enables repeatable IVIM quantification with improved noise performance. 2D acquisitions may advance the establishment of IVIM quantitative biomarkers for liver diseases., (© 2022 International Society for Magnetic Resonance in Medicine.)

Diffusion MRI has enormous potential and utility in the evaluation of various abdominal and pelvic disease processes including cancer and noncancer imaging of the liver, prostate, and other organs. Quantitative diffusion MRI is based on acquisitions with multiple diffusion encodings followed by quantitative mapping of diffusion parameters that are sensitive to tissue microstructure. Compared to qualitative diffusion-weighted MRI, quantitative diffusion MRI can improve standardization of tissue characterization as needed for disease detection, staging, and treatment monitoring. However, similar to many other quantitative MRI methods, diffusion MRI faces multiple challenges including acquisition artifacts, signal modeling limitations, and biological variability. In abdominal and pelvic diffusion MRI, technical acquisition challenges include physiologic motion (respiratory, peristaltic, and pulsatile), image distortions, and low signal-to-noise ratio. If unaddressed, these challenges lead to poor technical performance (bias and precision) and clinical outcomes of quantitative diffusion MRI. Emerging and novel technical developments seek to address these challenges and may enable reliable quantitative diffusion MRI of the abdomen and pelvis. Through systematic validation in phantoms, volunteers, and patients, including multicenter studies to assess reproducibility, these emerging techniques may finally demonstrate the potential of quantitative diffusion MRI for abdominal and pelvic imaging applications., (© 2021 American Association of Physicists in Medicine.)

Purpose: To assess the effects of cardiovascular-induced motion on conventional DWI of the pancreas and to evaluate motion-robust DWI methods in a motion phantom and healthy volunteers., Methods: 3T DWI was acquired using standard monopolar and motion-compensated gradient waveforms, including in an anatomically accurate pancreas phantom with controllable compressive motion and healthy volunteers (n = 8, 10). In volunteers, highly controlled single-slice DWI using breath-holding and cardiac gating and whole-pancreas respiratory-triggered DWI were acquired. For each acquisition, the ADC variability across volunteers, as well as ADC differences across parts of the pancreas were evaluated., Results: In motion phantom scans, conventional DWI led to biased ADC, whereas motion-compensated waveforms produced consistent ADC. In the breath-held, cardiac-triggered study, conventional DWI led to heterogeneous DW signals and highly variable ADC across the pancreas, whereas motion-compensated DWI avoided these artifacts. In the respiratory-triggered study, conventional DWI produced heterogeneous ADC across the pancreas (head: 1756 ± 173 × 10 -6 mm 2 /s; body: 1530 ± 338 × 10 -6 mm 2 /s; tail: 1388 ± 267 × 10 -6 mm 2 /s), with ADCs in the head significantly higher than in the tail (P < .05). Motion-compensated ADC had lower variability across volunteers (head: 1277 ± 102 × 10 -6 mm 2 /s; body: 1204 ± 169 × 10 -6 mm 2 /s; tail: 1235 ± 178 × 10 -6 mm 2 /s), with no significant difference (P ≥ .19) across the pancreas., Conclusion: Cardiovascular motion introduces artifacts and ADC bias in pancreas DWI, which are addressed by motion-robust DWI., (© 2021 International Society for Magnetic Resonance in Medicine.)

Objectives: Conventional spin-echo (SE) DWI leads to a fundamental trade-off depending on the b value: high b value provides better lesion contrast-to-noise ratio (CNR) by sacrificing signal-to-noise ratio (SNR), image quality, and quantitative reliability. A stimulated-echo (STE) DWI acquisition is evaluated for high-CNR imaging of prostate cancer while maintaining SNR and reliable apparent diffusion coefficient (ADC) mapping., Methods: In this prospective, IRB-approved study, 27 patients with suspected prostate cancer (PCa) were scanned with three DWI sequences (SE b = 800 s/mm 2 , SE b = 1500 s/mm 2 , and STE b = 800 s/mm 2 ) after informed consent was obtained. ROIs were drawn on biopsy-confirmed cancer and non-cancerous tissue to perform quantitative SNR, CNR, and ADC measurements. Qualitative metrics (SNR, CNR, and overall image quality) were evaluated by three experienced radiologists. Metrics were compared pairwise between the three acquisitions using a t test (quantitative metrics) and Wilcoxon rank test (qualitative metrics)., Results: Quantitative measurements showed that STE DWI at b = 800 s/mm 2 has significantly better SNR compared to SE DWI at b = 1500 s/mm 2 (p < 0.0001) and comparable CNR to high-b value SE DWI at b = 1500 s/mm 2 (p < 0.05) in the peripheral zone. Qualitative assessment showed preference to STE b = 800 s/mm 2 in SNR and SE b = 1500 s/mm 2 in CNR. The overall image quality and lesion detectability among most readers showed no significant preference between STE b = 800 s/mm 2 and SE b = 1500 s/mm 2 . Further, STE DWI had similar ADC contrast between lesion and normal tissue as SE DWI at b = 800 s/mm 2 (p = 0.90)., Conclusion: STE DWI has the potential to provide high-SNR, high-CNR imaging of prostate cancer while also enabling reliable ADC mapping., Key Points: • Quantitative analysis showed that STE DWI at b = 800 s/mm 2 is able to achieve simultaneously high CNR, high SNR, and reliable ADC mapping, compared to SE b = 800 s/mm 2 and SE b = 1500 s/mm 2 . • Qualitative assessment by three readers showed that STE DWI at b = 800 s/mm 2 has significantly higher SNR than SE b = 1500 s/mm 2 . No preference between SE b = 1500 s/mm 2 and STE b = 800 s/mm 2 was determined in terms of CNR with no missed lesions were found in both acquisitions. • A single STE DWI acquisition at moderate b value (800-1000 s/mm 2 ) may provide sufficient image quality and quantitative reliability for prostate cancer imaging within a shorter scan time, in place of two DWI acquisitions (one with moderate b value and one with high b value).

In this manuscript we derive the Cramér-Rao Lower Bound (CRLB) of the monoexponential diffusion-weighted signal model under a realistic noise assumption, and propose a formulation to obtain optimized sets of b-values that maximize the noise performance of the Apparent Diffusion Coefficient (ADC) maps given a target ADC and a signal-to-noise ratio. Therefore, for various sets of parameters (S 0 and ADC), signal-to-noise ratios (SNR) and noise distribution, we computed optimized sets of b-values using CRLB-based analysis in two different ways: (i) through a greedy algorithm where b-values from a pool of candidates were added iteratively to the set, and (ii) through a two b-value search algorithm were all two b-value combinations of the pool of candidates were tested. Further, optimized sets of b-values were computed from synthetic data, phantoms, and in-vivo liver diffusion-weighted imaging (DWI) experiments to validate the CRLB-based analysis. The optimized sets of b-values obtained through the proposed CRLB-based analysis showed good agreement with the optimized sets obtained experimentally from synthetic, phantoms, and in-vivo liver data. The variance of the ADC maps decreased when employing the optimized set of b-values compared to various sets of b-values proposed in the literature for in-vivo liver DWI, although differences of notable magnitude between noise models and optimization strategies were not found. In addition, the higher b-values decreased for lower SNR under the Rician noise distribution. Optimization of the set b-values is critical to maximize the noise performance (i.e., maximize the precision and minimize the variance) of the estimated ADC maps in diffusion-weighted MRI. Hence, the proposed approach may help to optimize and standardize liver diffusion-weighted MRI acquisitions by computing optimized set of b-values for a given set of parameters., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Purpose: To develop motion-robust, blood-suppressed diffusion-weighted imaging (DWI) of the liver with optimized diffusion encoding waveforms and evaluate the accuracy and reproducibility of quantitative apparent diffusion coefficient (ADC) measurements., Methods: A novel approach for the design of diffusion weighting waveforms, termed M1-optimized diffusion imaging (MODI), is proposed. MODI includes an echo time-optimized motion-robust diffusion weighting gradient waveform design, with a small nonzero first-moment motion sensitivity (M1) value to enable blood signal suppression. Experiments were performed in eight healthy volunteers and five patient volunteers. In each case, DW images and ADC maps were compared between acquisitions using standard monopolar waveforms, motion moment-nulled (M1-nulled and M1-M2-nulled) waveforms, and the proposed MODI approach., Results: Healthy volunteer experiments using MODI showed no significant ADC bias in the left lobe relative to the right lobe (p < .05) demonstrating robustness to cardiac motion, and no significant ADC bias with respect to monopolar-based ADC measured in the right lobe (p < .05), demonstrating blood signal suppression. In contrast, monopolar-based ADC showed significant bias in the left lobe relative to the right lobe (p < .01) due to its sensitivity to motion, and both M1-nulled and M1-M2-nulled-based ADC showed significant bias (p < .01) due to the lack of blood suppression. Preliminary patient results also suggest MODI may enable improved visualization and quantitative assessment of lesions throughout the entire liver., Conclusions: This novel method for diffusion gradient waveform design enables DWI of the liver with high robustness to motion and suppression of blood signals, overcoming the limitations of conventional monopolar waveforms and moment-nulled waveforms, respectively., (© 2019 International Society for Magnetic Resonance in Medicine.)

Purpose: To present a novel Optimized Diffusion-weighting Gradient waveform Design (ODGD) method for the design of minimum echo time (TE), bulk motion-compensated, and concomitant gradient (CG)-nulling waveforms for diffusion MRI., Methods: ODGD motion-compensated waveforms were designed for various moment-nullings M n (n = 0, 1, 2), for a range of b-values, and spatial resolutions, both without (ODGD-M n ) and with CG-nulling (ODGD-M n -CG). Phantom and in-vivo (brain and liver) experiments were conducted with various ODGD waveforms to compare motion robustness, signal-to-noise ratio (SNR), and apparent diffusion coefficient (ADC) maps with state-of-the-art waveforms., Results: ODGD-M n and ODGD-M n -CG waveforms reduced the TE of state-of-the-art waveforms. This TE reduction resulted in significantly higher SNR (P < 0.05) in both phantom and in-vivo experiments. ODGD-M 1 improved the SNR of BIPOLAR (42.8 ± 5.3 vs. 32.9 ± 3.3) in the brain, and ODGD-M 2 the SNR of motion-compensated (MOCO) and Convex Optimized Diffusion Encoding-M 2 (CODE-M 2 ) (12.3 ± 3.6 vs. 9.7 ± 2.9 and 10.2 ± 3.4, respectively) in the liver. Further, ODGD-M 2 also showed excellent motion robustness in the liver. ODGD-M n -CG waveforms reduced the CG-related dephasing effects of non CG-nulling waveforms in phantom and in-vivo experiments, resulting in accurate ADC maps., Conclusions: ODGD waveforms enable motion-robust diffusion MRI with reduced TEs, increased SNR, and reduced ADC bias compared to state-of-the-art waveforms in theoretical results, simulations, phantoms and in-vivo experiments., (© 2018 International Society for Magnetic Resonance in Medicine.)

Purpose: To present a stimulated-echo based mapping (STEM) approach for simultaneous T 1 , T 2 , and ADC mapping., Methods: Diffusion-weighted stimulated-echo images with various combinations of mixing time (TM), TE, and b-value were acquired to enable simultaneous mapping of T 1 , T 2 , and ADC. The proposed STEM method was performed by densely sampling the TM-TE-b space in a phantom and in brain and prostate of healthy volunteers. T 1 , T 2 , and ADC from STEM were compared to reference mapping methods. Additionally, protocol optimization was performed to enable rapid STEM acquisition within 2 min by sparsely sampling the TM-TE-b space. The T 1 , T 2 , and ADC measurements from rapid acquisitions were compared to the densely sampled STEM for evaluation. Finally, a patient with biopsy-proven high-risk prostate cancer was imaged to demonstrate the ability of STEM to differentiate cancer and healthy tissues., Results: Relative to the reference measurements, densely sampled STEM provided accurate quantitative T 1 , T 2 , and ADC mapping in phantoms (R 2  = 0.999, slope between 0.97-1.03), as well as in brain and prostate. Further, the T 1 , T 2 , and ADC measurements from the optimized rapid STEM acquisitions agreed closely with densely sampled STEM. Finally, STEM showed decreased T 2 and ADC in prostate cancer compared to healthy prostate tissue., Conclusion: STEM provides accurate simultaneous mapping of T 1 , T 2 , and ADC. This method may enable rapid and accurate multi-parametric tissue characterization for clinical and research applications., (© 2018 International Society for Magnetic Resonance in Medicine.)

Purpose: To evaluate the reproducibility of quantitative diffusion measurements obtained with reduced Field of View (rFOV) and Multi-shot EPI (msEPI) acquisitions, using single-shot EPI (ssEPI) as a reference., Methods: Diffusion phantom experiments, and prostate diffusion-weighted imaging in healthy volunteers and patients with known or suspected prostate cancer were performed across the three different sequences. Quantitative diffusion measurements of apparent diffusion coefficient, and diffusion kurtosis parameters (healthy volunteers), were obtained and compared across diffusion sequences (rFOV, msEPI, and ssEPI). Other possible confounding factors like b-value combinations and acquisition parameters were also investigated., Results: Both msEPI and rFOV have shown reproducible quantitative diffusion measurements relative to ssEPI; no significant difference in ADC was observed across pulse sequences in the standard diffusion phantom (p = 0.156), healthy volunteers (p ≥ 0.12) or patients (p ≥ 0.26). The ADC values within the non-cancerous central gland and peripheral zone of patients were 1.29 ± 0.17 × 10 -3  mm 2 /s and 1.74 ± 0.23 × 10 -3  mm 2 /s respectively. However, differences in quantitative diffusion parameters were observed across different number of averages for rFOV, and across b-value groups and diffusion models for all the three sequences., Conclusion: Both rFOV and msEPI have the potential to provide high image quality with reproducible quantitative diffusion measurements in prostate diffusion MRI., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Purpose: To compare the abilities of three intravoxel incoherent motion (IVIM) imaging approximation methods to discriminate the histological grade of hepatocellular carcinomas (HCCs)., Methods: Fifty-eight patients (60 HCCs) underwent IVIM imaging with 11 b-values (0-1000 s/mm 2 ). Slow (D) and fast diffusion coefficients (D * ) and the perfusion fraction (f) were calculated for the HCCs using the mean signal intensities in regions of interest drawn by two radiologists. Three approximation methods were used. First, all three parameters were obtained simultaneously using non-linear fitting (method A). Second, D was obtained using linear fitting (b = 500 and 1000), followed by non-linear fitting for D * and f (method B). Third, D was obtained by linear fitting, f was obtained using the regression line intersection and signals at b = 0, and non-linear fitting was used for D * (method C). A receiver operating characteristic analysis was performed to reveal the abilities of these methods to distinguish poorly-differentiated from well-to-moderately-differentiated HCCs. Inter-reader agreements were assessed using intraclass correlation coefficients (ICCs)., Results: The measurements of D, D * , and f in methods B and C (Az-value, 0.658-0.881) had better discrimination abilities than did those in method A (Az-value, 0.527-0.607). The ICCs of D and f were good to excellent (0.639-0.835) with all methods. The ICCs of D * were moderate with methods B (0.580) and C (0.463) and good with method A (0.705)., Conclusion: The IVIM parameters may vary depending on the fitting methods, and therefore, further technical refinement may be needed.

Purpose: To propose and evaluate an acetone-D 2 O phantom that has an extended range of apparent diffusion coefficient (ADC) for quantitative diffusion magnetic resonance imaging (MRI), as well as to compare its properties to previously described water-based phantoms., Materials and Methods: The proposed acetone-D 2 O, and previously described sucrose water solution and polyvinylpyrrolidone (PVP) water solution phantoms, were constructed in a number of concentrations between 0% and 50%. At 1.5T field strength, diffusion-weighted MR spectroscopy (DW-MRS), based on a point-resolved spectroscopy (PRESS) acquisition, nondiffusion-weighted stimulated echo acquisition mode (STEAM)-MRS, and diffusion-weighted echo-planar imaging (DW-EPI) were used to evaluate each phantom. The MR spectra, diffusion-weighted signal decay pattern, tunability of ADC, and ADC range of each phantom were all evaluated., Results: When placed in an ice-water bath, all phantoms provided desirable signal properties, including single-peak signal with Gaussian diffusion and tunable ADC. At 0°C, however, water-based phantoms had ADC limited to less than 1.1·10 -3 mm 2 ·s -1 (0.2-1.1·10 -3 mm 2 ·s -1 ), while the proposed acetone-based phantom had ADC values spanning a wider range (0.6-3.5·10 -3 mm 2 ·s -1 )., Conclusion: The proposed acetone-D 2 O phantom provided desirable signal properties over a wide range of ADCs with temperature controlled using an ice-water bath., Level of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1683-1692., (© 2017 International Society for Magnetic Resonance in Medicine.)

Objectives: To investigate the reliability of diffusion-weighted magnetic resonance imaging (DW-MRI) for staging liver fibrosis in the presence of fat and iron., Methods: Ninety-five patients, including 48 men and 47 women, aged 57.0 ± 14.2 years, underwent liver biopsy. Ninety-six samples were histologically staged for liver fibrosis (0-Ishak score 0; 1-Ishak score 1-4; 2-Ishak score 5-6) and semiquantitatively graded for hepatic iron (0, no; 1, low; 2, moderate; 3, high iron) and for hepatic steatosis. Within 72 h after biopsy, navigator-triggered DW-MRI using b-values of 50/400/800 s/mm(2) was performed in a 1.5-T system, and apparent diffusion coefficients (ADC) were analysed. ADCs were correlated with fibrosis stage, steatosis grade, and iron grade using linear regression., Results: ADC did not correlate with fibrosis stages in either the overall group (n = 96; R (2) = 0.38; P = 0.17) or in the subgroup without liver iron and steatosis (n = 40; R (2) = 0.01; P = 0.75). ADC decreased significantly with steatosis grade in cases without iron and fibrosis (n = 42; R (2) = 0.28; ß = -5.3; P < 0.001). Liver iron was modestly correlated with ADC in patients without fibrosis and steatosis (n = 33; R (2) = 0.29; P = 0.04), whereas high iron concentrations were associated with low ADC values (group 3: β = -489; P = 0.005; reference:group 0) but intermediate levels were not (group 1/group 2: P = 0.93/P = 0.54; reference group: 0)., Conclusions: ADC values are confounded by fat and iron. However, even in patients without fat or iron, DW-MRI does not adequately discriminate the stage of fibrosis., Key Points: • Diffusion-weighted magnetic resonance imaging (DW-MRI) is increasingly used to evaluate liver disease. • DWI using b-values of 50/400/800 s/mm (2) does not adequately quantify fibrosis. • Assessment of the apparent diffusion coefficient (ADC) is confounded by fat and iron. • Fat may influence ADCs by altering water diffusion. • Iron may influence ADCs by signal decay and noise floor effects.

Diffusion-weighted (DW) MRI has emerged as a key tool for assessing the microstructure of tissues in healthy and diseased states. Because of its rapid acquisition speed and insensitivity to motion, single-shot echo-planar imaging is the most common DW imaging technique. However, the presence of fat signal can severely affect DW-echo planar imaging acquisitions because of the chemical shift artifact. Fat suppression is usually achieved through some form of chemical shift-based fat saturation. Such methods effectively suppress the signal originating from aliphatic fat protons, but fail to suppress the signal from olefinic protons. Olefinic fat signal may result in significant distortions in the DW images, which bias the subsequently estimated diffusion parameters. This article introduces a method for removing olefinic fat signal from DW images, based on an echo time-shifted acquisition. The method is developed and analyzed specifically in the context of single-shot DW-echo-planar imaging, where image phase is generally unreliable. The proposed method is tested with phantom and in vivo datasets, and compared with a standard acquisition to demonstrate its performance., (Copyright © 2010 Wiley-Liss, Inc.)