Diffusion-weighted Imaging Of Liver Research Articles

Multiple b value diffusion-weighted MRI of liver: A novel respiratory frequency-modulated continuous-wave radar-trigger technique and comparison with free-breathing technique.

The aim of this study was to evaluate a novel respiratory frequency-modulated continuous-wave radar-trigger (FT) technique for multiple -b-value diffusion-weighted imaging (DWI) of liver and compare it with conventional free breathing (FB) DWI technique. 39 patients with focal liver lesions underwent both frequency-modulated continuous-wave radar-trigger (FT) and conventional free-breathing (FB) multi-b-value diffusion-weighted imaging (DWI,b=0,50,400,800s/mm2). Two abdominal radiologists independently assessed the quality of liver DWI images obtained using both techniques, measured and compared liver signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) at different b-values, as well as apparent diffusion coefficient (ADC) values calculated from all b-values. In terms of image quality, the FT technique is superior to the conventional FB technique, with overall image quality scores (Reader 1, 3.56±0.50 and Reader 2, 3.59±0.55)vs (Reader 1, 2.90±0.75 and Reader 2, 2.97±0.71), respectively. The liver SNR (at b-values of 50,400,and 800 s/mm2) obtained by FT was (138.5±43.48, 96.67±31.95, 71.54±22.03), respectively, which was significantly higher than that obtained by conventional FB (110.90±39.28, 80.86±29.13, 60.43±18.61, P<0.05). The lesion CNR with FT was significantly higher than that with conventional FB (258.99±151.38 vs 174.60±99.90; 164.56±87.25 vs 111.12±42.43; 118.83±68.76 vs 76.01±35.48, P<0.001). There was no significant difference in ADC values of liver and lesions between the two techniques: ADCliver-L and ADCliver-R: (FT 1479.3±270.0 vs FB 1529.3±275.5 and FT 1219.6±127.4 vs FB 1248.7±168.2, P>0.05); ADC lesion:FT(969.0±261.3) vs FB (1017.5±240.4, P>0.05). For multi-b-value liver diffusion-weighted imaging, FT technique has higher image quality and better lesion visibility than conventional FB technique and there is no significant difference in ADC values of liver and lesions between the two techniques.

Optimization of motion-corrected liver diffusion-weighted imaging at 3 Tesla (3T): incorporating complex averaging and reparametrized sinc fatsat pulse with optimized water excitation pulse.

In liver diffusion-weighted imaging (DWI), single-shot echo-planar imaging (SS-EPI) sequences are susceptible to motion artifacts, resulting in image blurring and decreased lesion detection rates. This study aimed to develop and optimize a motion-corrected (MOCO) technique for liver DWI at 3 Tesla (3T). The technique incorporates motion correction, complex averaging, and a combination of a reparametrized sinc fatsat pulse with an optimized water excitation pulse. This prospective cross-sectional study performed at Fujian Medical University Union Hospital included 42 healthy volunteers who underwent four SS-EPI DWI sequences on a 3T magnetic resonance imaging (MRI) system between January 2023 and March 2023. The sequences included a navigator-triggered (NT) MOCO-DWI, two free-breathing (FB) MOCO-DWI, and an FB conventional DWI (FB cDWI) sequence. Motion correction and complex averaging were performed for both MOCO-DWI sequences, and fat suppression was achieved using either a sinc fatsat pulse with optimized water excitation or a conventional spectral attenuated inversion recovery (SPAIR) pulse. Liver signal-to-noise ratio (SNR) was measured at b=1,000 s/mm2. Qualitative parameters were independently evaluated by three radiologists using 5-point Likert scales. Quantitative parameters were assessed using the Kolmogorov-Smirnov test, and variance homogeneity was assessed using Levene's test. Regarding the qualitative analysis, the Friedman test was used to compare subjective scores among the four techniques. The SNRs of the liver were significantly higher with FB MOCO-DWI compared to the other EPI DWI sequences at b=1,000 s/mm2 (P<0.05). In the superior-inferior direction, the SNRs of the inferior level of the liver were higher than those of the superior level in NT MOCO-DWI. The qualitative results showed significantly higher ratings for NT MOCO-DWI and FB MOCO-DWI compared to the other EPI DWI sequences at b=1,000 s/mm2 (P<0.05). Regarding the apparent diffusion coefficient (ADC) quantification, the ADC values of the left lobe were higher than those of the right lobe in all four techniques. The proposed EPI DWI technique, incorporating motion correction, complex averaging, and a modified fat suppression scheme using spectral fat saturation and binomial water excitation, was found to be clinically feasible for liver MRI. The FB MOCO-DWI sequence, with its superior SNR and excellent image quality, is recommended for liver DW imaging at 3T in clinical routine.

Clinical feasibility of deep learning reconstruction in liver diffusion-weighted imaging: Improvement of image quality and impact on apparent diffusion coefficient value

PurposeDiffusion-weighted imaging (DWI) of the liver suffers from low resolution, noise, and artifacts. This study aimed to investigate the effect of deep learning reconstruction (DLR) on image quality and apparent diffusion coefficient (ADC) quantification of liver DWI at 3 Tesla. MethodIn this prospective study, images of the liver obtained at DWI with b-values of 0 (DWI0), 50 (DWI50) and 800 s/mm2 (DWI800) from consecutive patients with liver lesions from February 2022 to February 2023 were reconstructed with and without DLR (non-DLR). Image quality was assessed qualitatively using Likert scoring system and quantitatively using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and liver/parenchyma boundary sharpness from region-of-interest (ROI) analysis. ADC value of lesion were measured. Phantom experiment was also performed to investigate the factors that determine the effect of DLR on ADC value. Qualitative score, SNR, CNR, boundary sharpness, and apparent diffusion coefficients (ADCs) for DWI were compared using paired t-test and Wilcoxon signed rank test. P < 0.05 was considered statistically significant. ResultsA total of 85 patients with 170 lesions were included. DLR group showed a higher qualitative score than the non-DLR group. for example, with DWI800 the score was 4.77 ± 0.52 versus 4.30 ± 0.63 (P < 0.001). DLR group also showed higher SNRs, CNRs and boundary sharpness than the non-DLR group. DLR reduced the ADC of malignant tumors (1.105[0.904, 1.340] versus 1.114[0.904, 1.320]) (P < 0.001), but there was no significant difference in the diagnostic value of malignancy for DLR and non-DLR groups (P = 57.3). The phantom study confirmed a reduction of ADC in images with low resolution, and a stronger reduction of ADC in heterogeneous structures than in homogeneous ones (P < 0.001). ConclusionsDLR improved image quality of liver DWI. DLR reduced the ADC value of lesions, but did not affect the diagnostic performance of ADC in distinguishing malignant tumors on a 3.0-T MRI system.

Impact of velocity- and acceleration-compensated encodings on signal dropout and black-blood state in diffusion-weighted magnetic resonance liver imaging at clinical TEs.

The study aims to develop easy-to-implement concomitant field-compensated gradient waveforms with varying velocity-weighting (M1) and acceleration-weighting (M2) levels and to evaluate their efficacy in correcting signal dropouts and preserving the black-blood state in liver diffusion-weighted imaging. Additionally, we seek to determine an optimal degree of compensation that minimizes signal dropouts while maintaining blood signal suppression. Numerically optimized gradient waveforms were adapted using a novel method that allows for the simultaneous tuning of M1- and M2-weighting by changing only one timing variable. Seven healthy volunteers underwent diffusion-weighted magnetic resonance imaging (DWI) with five diffusion encoding schemes (monopolar, velocity-compensated (M1 = 0), acceleration-compensated (M1 = M2 = 0), 84%-M1-M2-compensated, 67%-M1-M2-compensated) at b-values of 50 and 800 s/mm2 at a constant echo time of 70 ms. Signal dropout correction and apparent diffusion coefficients (ADCs) were quantified using regions of interest in the left and right liver lobe. The blood appearance was evaluated using two five-point Likert scales. Signal dropout was more pronounced in the left lobe (19%-42% less signal than in the right lobe with monopolar scheme) and best corrected by acceleration-compensation (8%-10% less signal than in the right lobe). The black-blood state was best with monopolar encodings and decreased significantly (p < 0.001) with velocity- and/or acceleration-compensation. The partially M1-M2-compensated encoding schemes could restore the black-blood state again. Strongest ADC bias occurred for monopolar encodings (difference between left/right lobe of 0.41 μm2/ms for monopolar vs. < 0.12 μm2/ms for the other encodings). All of the diffusion encodings used in this study demonstrated suitability for routine DWI application. The results indicate that a perfect value for the level of M1-M2-compensation does not exist. However, among the examined encodings, the 84%-M1-M2-compensated encodings provided a suitable tradeoff.

Deep Learning-Accelerated Liver Diffusion-Weighted Imaging: Intraindividual Comparison and Additional Phantom Study of Free-Breathing and Respiratory-Triggering Acquisitions.

Deep learning-reconstructed diffusion-weighted imaging (DL-DWI) is an emerging promising time-efficient method for liver evaluation, but analyses regarding different motion compensation strategies are lacking. This study evaluated the qualitative and quantitative features, sensitivity for focal lesion detection, and scan time of free-breathing (FB) DL-DWI and respiratory-triggered (RT) DL-DWI compared with RT conventional DWI (C-DWI) in the liver and a phantom. Eighty-six patients indicated for liver MRI underwent RT C-DWI, FB DL-DWI, and RT DL-DWI with matching imaging parameters other than the parallel imaging factor and number of averages. Two abdominal radiologists independently assessed qualitative features (structural sharpness, image noise, artifacts, and overall image quality) using a 5-point scale. The signal-to-noise ratio (SNR) along with the apparent diffusion coefficient (ADC) value and its standard deviation (SD) were measured in the liver parenchyma and a dedicated diffusion phantom. For focal lesions, per-lesion sensitivity, conspicuity score, SNR, and ADC value were evaluated. Wilcoxon signed rank test and repeated-measures analysis of variance with post hoc test revealed the difference in DWI sequences. Compared with RT C-DWI, the scan times for FB DL-DWI and RT DL-DWI were reduced by 61.5% and 23.9%, respectively, with statistically significant differences between all 3 pairs (all P's < 0.001). Respiratory-triggered DL-DWI showed a significantly sharper liver margin, less image noise, and more minor cardiac motion artifact compared with RT C-DWI (all P's < 0.001), whereas FB DL-DWI showed more blurred liver margins and poorer intrahepatic vessels demarcation than RT C-DWI. Both FB- and RT DL-DWI showed significantly higher SNRs than RT C-DWI in all liver segments (all P's < 0.001). There was no significant difference in overall ADC values across DWI sequences in the patient or phantom, with the highest value recorded in the left liver dome by RT C-DWI. The overall SD was significantly lower with FB DL-DWI and RT DL-DWI than RT C-DWI (all P's ≤ 0.003). Respiratory-triggered DL-DWI showed a similar per-lesion sensitivity (0.96; 95% confidence interval, 0.90-0.99) and conspicuity score to those of RT C-DWI and significantly higher SNR and contrast-to-noise ratio values (P ≤ 0.006). The per-lesion sensitivity of FB DL-DWI (0.91; 95% confidence interval, 0.85-0.95) was significantly lower than that of RT C-DWI (P = 0.001), with a significantly lower conspicuity score. Compared with RT C-DWI, RT DL-DWI demonstrated superior SNR, comparable sensitivity for focal hepatic lesions, and reduced acquisition time, making it a suitable alternative to RT C-DWI. Despite FB DL-DWI's weakness in motion-related challenges, further refinement could potentiate FB DL-DWI in the context of abbreviated screening protocols, where time efficiency is a high priority.

Effect of an Ultrahigh b Value of 3000 s/mm2 and the Minimal Echo-time on Image Quality and the T2 Shine-through Effect in Diffusion-weighted Imaging of the Liver at 3T: Phantom and Clinical Pilot Studies.

To assess the effect of an ultrahigh b value of 3000 s/mm2 and the minimal TE of 53 ms on image quality and T2 shine-through effect in liver diffusion-weighted imaging (DWI) using a 3-Tesla MRI scanner with a peak gradient of 100 mT/m. At b values of 1000 and 3000 s/mm2 and at the minimal (44-53 ms) and routine TEs (70 ms), DWI of our original phantom and liver DWI in 10 healthy volunteers and 26 patients with 35 hepatic hemangiomas were acquired with this scanner, and the quantified SNR of the phantom and the hepatic parenchyma in the volunteers and the contrast-to-noise ratio (CNR) of the hepatic hemangiomas were calculated; two independent readers qualitatively graded the overall image quality in the volunteers and determined the presence or absence of the T2 shine-through effect related to the hemangiomas in the patients. We compared the SNR and subjective overall image quality between the minimal and routine TEs and the CNR and incidence of the T2 shine-through effect between b values of 1000 and 3000 s/mm2. Inter-reader agreement was also evaluated. The SNR at both b values was significantly higher, and the subjective overall image quality at a b value of 3000 s/mm2 was significantly better at the minimal TE than at the routine TE (P < 0.05 for all). The CNR at both TEs and the incidence of the T2 shine-through effect at the minimal TE were significantly lower at a b value of 3000 s/mm2 than at a b value of 1000 s/mm2 (P < 0.05 for all). Inter-reader agreement was excellent. Liver DWI at the ultrahigh b value can reduce the T2 shine-through effect with improvement of image quality using the minimal TE.

Modern Possibilities of Liver Diffusion-Weighted Magnetic Resonance Images in the Diagnosis of Alcoholic Liver Disease

Objective: to evaluate the current possibilities of diffusion-weighted imaging (DWI) in liver magnetic resonance imaging (MRI) for the diagnosis of alcoholic liver disease (ALD).Material and methods. The examined patients were at the inpatient and outpatient stages of observation in the gastroenterology department on the basis of the Clinical Hospital No. 1 (Smolensk) and received treatment for diffuse liver diseases of alcoholic etiology. The study included 128 patients: 76 (59%) males and 52 (41%) females, mean age 42.3 ± 4.7 years. Patients were monitored from 2019 to 2022. All of them underwent abdominal organs ultrasound with liver clinical elastography and liver MRI with DWI; in 34 cases liver multi-slice computed tomography was performed.Results. When comparing the results of a qualitative assessment of liver DWI MRI with the CAGE (Cut, Annoyed, Guilty, Eye-opener) test data and the results of patients and relatives survey about the use of alcoholic beverages, a high correlation was established between the diffusion restriction in the liver during MRI and impaired withdrawal regimen (r = 0.901). The diagnostic and prognostic significance of the developed criteria for liver DWI MRI in patients with ALD at admission was assessed: for qualitative assessment AUROC 0.827 (95% CI 0.792–0.873), for quantitative assessment AUROC 0.949 (95% CI 0.912–0.981); in dynamic observation: for qualitative assessment AUROC 0.958 (95% CI 0.925–0.984), for quantitative assessment AUROC 0.947 (95% CI 0.947–0.981).Conclusion. The obtained quantitative indicators of liver DWI MRI make it possible to predict the clinical form of ALD: apparent diffusion coefficient for steatosis is 2.66 ± 0.9 × 10–3 mm2/s, for steatohepatitis – 2.14 ± 0.5 × 10–3 mm2/s, for hepatitis – 1.75 ± 0.6 × 10–3 mm2/s, for cirrhosis – 1.15 ± 0.6 × 10–3 mm2/s (AUROC 0.948; 95% CI 0.922–0.983). Qualitative parameters of liver DWI MRI (there is/is not a diffusion restriction) predict violations of the withdrawal regimen in patients with ALD in all its clinical forms (AUROC 0.931; 95% CI 0.822–0.979).

Alkolün Karaciğer Görünür Difüzyon Katsayısı Değerleri Üzerine Etkileri: Tek Merkez Çalışması

Background and Aims: This study aimed to investigate the relationship between liver apparent diffusion coefficient values and potential early-stage liver injury by comparing apparent diffusion coefficient values obtained by liver diffusion-weighted magnetic resonance imaging between individuals with a history of excessive alcohol consumption and healthy volunteers. Materials and Methods: This study enrolled 35 individuals with a history of excessive alcohol consumption and 32 healthy volunteers. In all cases, blood samples were taken to measure biochemical parameters and complete blood count. Upper abdominal magnetic resonance imaging including liver diffusion-weighted imaging was performed. Results: In total, 19 individuals with a history of excessive alcohol consumption and 20 healthy volunteers were included in the study. The mean apparent diffusion coefficient values obtained by high b value (b 1000) diffusion-weighted imaging in individuals with a history of excessive alcohol consumption were lower than those in healthy volunteers. Although no significant difference was observed between the two groups in terms of biochemical parameters, hepatic apparent diffusion coefficient values in both groups were positively correlated with international normalized ratio values and negatively correlated with gamma-glutamyl transferase and alkaline phosphatase levels (r = 0.002, r = −0.007, r = −0.049, respectively). Conclusion: Diffusion-weighted imaging is a noninvasive imaging technique that can be used for the detection and follow-up of liver fibrosis induced by alcohol consumption.

On the dependence of the cardiac motion artifact on the breathing cycle in liver diffusion-weighted imaging.

PurposeThe purpose of this study was to investigate whether the cardiac motion artifact that regularly appears in diffusion-weighted imaging of the left liver lobe might be reduced by acquiring images in inspiration, when the coupling between heart and liver might be minimal.Materials and methods43 patients with known or suspected focal liver lesions were examined at 1.5 T with breath hold acquisition, once in inspiration and once in expiration. Data were acquired with a diffusion-weighted echo planar imaging sequence and two b-values (b50 = 50 s/mm² and b800 = 800 s/mm²). The severity of the cardiac motion artifact in the left liver lobe was rated by two experienced radiologists for both b-values with a 5 point Likert scale. Additionally, the normalized signal S(b800)/S(b50) in the left liver lobe was computed. The Wilcoxon signed-rank test was used comparing the scores of the two readers obtained in inspiration and expiration, and to compare the normalized signal in inspiration and expiration.ResultsThe normalized signal in inspiration was slightly higher than in expiration (0.349±0.077 vs 0.336±0.058), which would indicate a slight reduction of the cardiac motion artifact, but this difference was not significant (p = 0.24). In the qualitative evaluation, the readers did not observe a significant difference for b50 (reader 1: p = 0.61; reader 2: p = 0.18). For b800, reader 1 observed a significant difference of small effect size favouring expiration (p = 0.03 with a difference of mean Likert scores of 0.27), while reader 2 observed no significant difference (p = 0.62).ConclusionAcquiring the data in inspiration does not lead to a markedly reduced cardiac motion artifact in diffusion-weighted imaging of the left liver lobe and is in this regard not to be preferred over acquiring the data in expiration.

Association between liver diffusion-weighted imaging apparent diffusion coefficient values and other measures of liver disease in pediatric autoimmune liver disease patients

Multiple quantitative magnetic resonance imaging (MRI) methods have been described to noninvasively detect and characterize liver fibrosis, including diffusion-weighted imaging (DWI). To evaluate associations between liver MRI DWI apparent diffusion coefficient (ADC) values and clinical factors and other quantitative liver MRI metrics in pediatric patients with autoimmune liver disease (AILD). Fifty-seven research liver MRI examinations performed from January 2017 to August 2018 for pediatric AILD registry participants were evaluated. Liver DWI ADC values, liver and spleen stiffness (kPa), and iron-corrected T1 (cT1; Perspectum Diagnostics) were measured at four anatomic levels. Participant age, sex, and laboratory data (alanine aminotransferase [ALT], total bilirubin, alkaline phosphatase, gamma-glutamyl transferase [GGT]) were recorded. Spearman's rank-order correlation (rho) and multiple linear regression were used to evaluate the associations between liver ADC values and predictor variables. Mean (SD) participant age was 14.8 (4.0) years, 45.6% (26/57) were girls. Mean liver DWI ADC value was 1.34 (0.14 × 10-3) mm2/s. Liver ADC values showed weak to moderate correlations with liver stiffness (r = - 0.42, p = 0.001), spleen stiffness (r = - 0.34; p = 0.015), whole-liver mean cT1 (r = - 0.39; p = 0.007), ALT (r = - 0.50; p = 0.0001), and GGT (r = - 0.48; p = 0.0004). Multiple linear regression showed liver stiffness (p = 0.0009) and sex (p = 0.023) to be independent predictors of liver ADC values. Liver DWI ADC values are significantly associated with liver and spleen stiffnesses, liver cT1, ALT, GGT, and participant sex, with liver stiffness and sex remaining significant at multivariable regression. Liver ADC ultimately may play a role in multi-parametric prediction of chronic liver disease/fibrosis severity.

Determination of optimized set of b-values for Apparent Diffusion Coefficient mapping in liver Diffusion-Weighted MRI.

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 (S0 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.

Diagnostic performance of quantitative magnetic resonance imaging biomarkers for predicting portal hypertension in children and young adults with autoimmune liver disease.

Primary sclerosing cholangitis, autoimmune hepatitis and autoimmune sclerosing cholangitis are forms of chronic, progressive autoimmune liver disease (AILD) that can affect the pediatric population. To determine whether quantitative MRI- and laboratory-based biomarkers are associated with conventional imaging findings of portal hypertension (radiologic portal hypertension) in children and young adults with AILD. Forty-four patients with AILD enrolled in an institutional registry underwent a research abdominal MRI examination at 1.5 tesla(T). Five quantitative MRI techniques were performed: liver MR elastography, spleen MR elastography, liver iron-corrected T1 mapping, liver T2 mapping, and liver diffusion-weighted imaging (DWI, quantified as apparent diffusion coefficients). Two anatomical sequences were used to document splenomegaly, varices and ascites. We calculated aspartate aminotransferase (AST)-to-platelet ratio index (APRI) and fibrosis-4 (FIB-4) scores - laboratory-based biomarkers of liver fibrosis. We used receiver operating characteristic (ROC) curve analyses to establish the diagnostic performance of quantitative MRI and laboratory biomarkers for indicating the presence of radiologic portal hypertension. Twenty-three (52%) patients were male; mean age was 15.2±4.0years. Thirteen (30%) patients had radiologic portal hypertension. Liver and spleen stiffness demonstrated the greatest diagnostic performance for indicating the presence of portal hypertension (area-under-the-ROC-curve [AUROC]=0.98 and 0.96, respectively). The APRI and FIB-4 scores also demonstrated good diagnostic performance (AUROC=0.87 and 0.88, respectively). MRI-derived measures of liver and spleen stiffness as well as laboratory-based APRI and FIB-4 scores are highly associated with imaging findings of portal hypertension in children and young adults with AILD and thus might be useful for predicting portal hypertension impending onset and directing personalized patient management.

Intravoxel incoherent motion diffusion-weighted MR imaging of the liver using respiratory-cardiac double triggering

To investigate the influence of respiratory-cardiac double triggering (RCT) on intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) for the liver, twelve healthy volunteers underwent liver DWI twice respectively with respiratory triggering (RT) and RCT schemes. Signal-to-noise ratios (SNRs) of the images, values, repeatability (evaluating with within-subject coefficient of variation), and variability of quantitative parameters, including apparent diffusion coefficient (ADC), pure diffusion coefficient (D), perfusion fraction (f), and perfusion-related diffusion coefficient (D*), were evaluated for each DWI sequence. Results showed that the use of RCT scheme significantly enhanced SNRs (P < 0.001), improved the measurement precision (P ≤ 0.023) and repeatability (P ≤ 0.009) of ADC, D, and f values, decreased the variability of ADC and D values (P ≤ 0.015). Furthermore, this improvement was not completely confined to the left liver lobe, but also observed for the right liver lobe. Moreover, the precision of D* values in the right lobe (P < 0.001) and its repeatability in the left lobe (P = 0.002) were also significantly improved. Thus, our findings suggest that RCT is a more effective physiological scheme for improving SNRs, the precision, repeatability, and variability of quantitative parameters than RT for IVIM-DWI in the liver.

Diffusion-weighted imaging of the liver at 3 T using section-selection gradient reversal: emphasis on chemical shift artefacts and lesion conspicuity

To assess the value of section-selection gradient reversal (SSGR) in liver diffusion-weighted imaging (DWI) by comparing it to conventional DWI with an emphasis on chemical shift artefacts and lesion conspicuity. Forty-eight patients (29 men and 19 women; age range 33-80 years) with 48 liver lesions underwent two DWI examinations using spectral presaturation with inversion recovery fat suppression with and without SSGR at 3 T. Two reviewers evaluated each DWI (b = 100 and b = 800 image) with respect to chemical shift artefacts and liver lesion conspicuity using five-point scales and performed pairwise comparisons between the two DWIs. The signal-to-noise ratio (SNR) of the liver and the lesion and the lesion-liver contrast-to-noise ratio (CNR) were also calculated. SSGR-DWI was significantly better than conventional DWI with respect to chemical shift artefacts and lesion conspicuity in both separate reviews and pairwise comparisons (p < 0.05). There were significant differences in the SNR of the liver (b = 100 and b = 800 images) and lesion (b = 800) between SSGR-DWI and conventional DWI (p < 0.05). Applying the SSGR method to DWI using SPIR fat suppression at 3 T could significantly reduce chemical shift artefacts without incurring additional acquisition time or SNR penalties, which leads to increased conspicuity of focal liver lesions.

Fat confounds the observed apparent diffusion coefficient in patients with hepatic steatosis

Triglyceride signal contained in peaks near the water peak remains unsuppressed by conventional fat suppression techniques used in diffusion-weighted imaging. In this work, we investigated the dependence of the apparent diffusion coefficient (ADC) on liver fat content and whether it is confounded by fat signal. 43 patients underwent liver diffusion-weighted imaging (b = 0, 500 s/mm(2)) and single-voxel MR-spectroscopy. Proton density fat-fraction (PDFF; range 0.23-34.5%) was measured from MR-spectroscopy. A theoretical model was developed to account for the effects of fat on observed ADC, and used to correct the ADC. Linear correlation analysis was performed to assess the relationship between PDFF and ADC before and after correction. Linear correlation analysis showed an inverse dependence between observed ADC and PDFF before correction (r(2) = 0.132; P = 0.017), and no dependence after correction (r(2) = 0.033; P = 0.24). The observed decrease in ADC in patients with fatty liver is, at least in part, artifactual due to residual fat signal near the water peak.

Liver diffusivity in healthy volunteers and patients with chronic liver disease: Comparison of breathhold and free‐breathing techniques

To compare liver ADC obtained with breathhold and free-breathing diffusion weighted imaging (DWI) in healthy volunteers and patients with liver disease. Twenty-eight subjects, 12 healthy volunteers and 16 patients (9 NAFLD, 7 chronic active HCV), underwent breathhold (BH) and free-breathing (FB) DWI MRI at 1.5 Tesla. Pearson's correlation coefficient was used to determine correlation while paired t-tests assessed differences between BH and FB ADC. Estimated bias was calculated using the Bland-Altman method. Liver ADC (×10(-3) mm(2) /s) was lower on BH for all groups (mean difference 0.36 ± 0.20; P < 0.01). ADC was higher in healthy volunteers (BH 1.80 ± 0.18; FB 2.24 ± 0.20) compared with NAFLD patients (BH 1.43 ± 0.27; FB 1.78 ± 0.28) (P < 0.001) and HCV patients (BH 1.63 ± 0.191; FB 1.88 ± 0.12). Overall correlation between BH and FB ADC was (r = 0.75), greatest in NAFLD (r = 0.90) compared with the correlation in HCV (r = 0.24) and healthy subjects (r = 0.34). Bland-Altman plots did not show agreement in mean absolute difference and estimated bias between subjects. Correlation between BH and FB liver ADC is moderate indicating that BH and FB should not be used interchangeably. Additionally, the lower ADC values in BH versus FB should be accounted for when comparing different liver DWI studies.

Cardiac motion in diffusion‐weighted MRI of the liver: artifact and a method of correction

To characterize cardiac motion artifacts in the liver and assess the use of a postprocessing method to mitigate these artifacts in repeat measurements. Three subjects underwent breathhold diffusion-weighted (DW) scans consisting of 25 repetitions for three b-values (0, 500, 1000 sec/mm(2)). Statistical maps computed from these repetitions were used to assess the distribution and behavior of cardiac motion artifacts in the liver. An objective postprocessing method to reduce the artifacts was compared with radiologist-defined gold standards. Signal dropout is pronounced in areas proximal to the heart, such as the left lobe, but also present in the right lobe and in distal liver segments. The dropout worsens with b-value and leads to overestimation of the diffusivity. By reference to a radiologist-defined gold standard, a postprocessing correction method is shown to reduce cardiac motion artifact. Cardiac motion leads to significant artifacts in liver DW imaging; we propose a postprocessing method that may be used to mitigate the artifact and is advantageous to standard signal averaging in acquisitions with multiple repetitions.