Diffusion-weighted MRI for quantification of liver fibrosis: preliminary experience

State-of-the-art imaging of liver fibrosis and cirrhosis: A comprehensive review of current applications and future perspectives

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MR elastography (MRE) appears to be the most reliable method for grading liver fibrosis.

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CT fibrosis score correlates with the stage of fibrosis.

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Caudate-to-right-lobe ratio and diameters of the liver veins contribute to the CT fibrosis score.

Objective

The purpose of this article is to provide a comprehensive overview of imaging findings in patients with hepatic fibrosis and cirrhosis; and to describe which radiological/clinical modality is best for staging hepatic fibrosis.

Conclusion

MR elastography (MRE) appears to be the most reliable method for grading liver fibrosis, although the CT fibrosis score derived from the combination of caudate-to-right-lobe ratio and the diameters of the liver veins significantly correlates with the stage of fibrosis.

Intravoxel Incoherent Motion Diffusion Weighted MR Imaging at 3.0 T: Assessment of Steatohepatitis and Fibrosis Compared with Liver Biopsy in Type 2 Diabetic Patients

Objective

To evaluate the capability of intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) to assess steatohepatitis and fibrosis determined by histopathology in type 2 diabetic patients.

Methods

Fifty-nine type 2 diabetic patients (49 women, 10 men; mean age, 54 ± 9 years) were submitted to liver biopsy for the evaluation of non-alcoholic fatty liver disease (NAFLD) and underwent DWI on a 3.0T MR system using 10 b values. Institutional approval and patient consent were obtained. Pure molecular-based (D), perfusion-related (D*), and vascular fraction (f) were calculated using a double exponential model and least squares curve fitting. D, D*, and f were compared between patients with and without steatohepatitis and between patients with and without fibrosis. The variables were compared by using the Ranksum test and Student t-test.

Results

Steatohepatitis was observed in 22 patients and fibrosis in 16 patients. A lower D median (0.70 s/mm² vs. 0.83 s/mm², p<0.05) and a lower D* median (34.39 s/mm² vs. 45.23 s/mm², p<0.05) were observed among those with steatohepatitis. A lower D median (0.70 s/mm² vs. 0.82 s/mm², p<0.05) and a lower D* median (35.01 s/mm² vs. 44.76 s/mm², p=0.05) were also observed among those with fibrosis.

Conclusion

IVIM-DWI has the potential to aid in the characterization of steatohepatitis and fibrosis.

Role of diffusion-weighted imaging, apparent diffusion coefficient and correlation with hepatobiliary phase findings in the differentiation of hepatocellular carcinoma from dysplastic nodules in cirrhotic liver

OBJECTIVES

To investigate the utility of diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC) and the correlation with hepatobiliary phase (delayed phase imaging, DPI) findings in the differentiation of cirrhotic hepatocellular nodules.

METHODS

Forty-three patients with 53 pathology-proven nodules (29 hepatocellular carcinomas (HCCs), 13 high-grade (HGDNs) and 11 low-grade dysplastic nodules (LGDNs); mean size 2.17 cm, range 1-4 cm), who underwent liver MRI with DWI and DPI sequences, were retrospectively reviewed. Lesions were classified as hypointense, isointense, or hyperintense relative to the adjacent liver parenchyma. ADC of each nodule, of the surrounding parenchyma, and lesion-to-liver ratio were calculated.

RESULTS

Hyperintensity versus iso/hypointensity on DWI, hypointensity versus iso/hyperintensity on DPI, and the mean lesion-to-liver ratio showed a statistically significant difference both between HCCs versus DNs and between "HCCs + HGDNs" versus LGDNs (p < 0.05); sensitivity, specificity, and accuracy for the diagnosis of "HCCs + HGDNs" were 96.8 %, 100 %, 97.4 % respectively when combining hyperintensity on DWI and hypointensity on DPI, and 90.9 %, 81.0 %, 83.6 % respectively when lesion-to-liver ratio was <0.95.

CONCLUSIONS

Hyperintensity on DWI, especially in association with hypointensity on DPI, and low lesion-to-liver ratios should raise the suspicion of HCC, or at least of HGDN, thus helping the characterization of atypically enhancing lesions.

KEY POINTS

• Usefulness of DWI and ADC is shown in differential diagnosis of cirrhotic nodules. • Correlation of DWI with DPI improves differential diagnosis of cirrhotic nodules. • Characterization of atypically enhancing lesions becomes more confident.

Diffusion-weighted MRI for the assessment of liver fibrosis: principles and applications

The importance of an early identification of hepatic fibrosis has been emphasized, in order to start therapy and obtain fibrosis regression. Biopsy is the gold-standard method for the assessment of liver fibrosis in chronic liver diseases, but it is limited by complications, interobserver variability, and sampling errors. Several noninvasive methods have been recently introduced into clinical routine, in order to detect liver fibrosis early. One of the most diffuse approaches is represented by diffusion-weighted liver MRI. In this review, the main technical principles are briefly reported in order to explain the rationale for clinical applications. In addition, roles of apparent diffusion coefficient, intravoxel incoherent motion, and relative apparent diffusion coefficient are also reported, showing their advantages and limits.

Breast ultrasound elastography and magnetic resonance imaging of fibrotic changes of breast disease: correlations between elastography findings and pathologic and short Tau inversion recovery imaging results, including the enhancement ratio and apparent diffusion coefficient

PURPOSE

Ultrasound (US) elastography provides information regarding tissue hardness and is expected to become a novel diagnostic tool for breast disease. In contrast, magnetic resonance (MR) images reflect the tissue characteristics. Fibrosis of the stroma of breast diseases may affect their hardness. We investigated the correlation among elasticity score (ES) and signal intensity of short Tau inversion recovery MR images, enhancement ratio, apparent diffusion coefficient (ADC), and the fibrosis in the breast lesions.

MATERIALS AND METHODS

We reviewed the findings of US elastography and MR imaging from 41 consecutive patients with breast lesions (25 invasive ductal carcinoma, 3 fibroadenoma, 1 phyllodes tumor, 2 ductal hyperplasia, 2 primary malignant lymphoma, 3 mastopathy, 1 metastasis, 1 tubular adenoma, 1 ductal carcinoma in situ, 1 diabetic mastopathy, and 1 intraductal papilloma). In each patient, elastography images were classified based on Tsukuba ES. We calculated the ratio of signal intensity of the lesion to the muscle on short Tau inversion recovery images (L/M ratio), enhancement ratio of early to precontrast and early to delayed images, and ADC for each lesion. The ES and MR findings were correlated with the degree of fibrosis (based on Masson trichrome stain).

RESULTS

The ES significantly correlated with the L/M ratio (P = 0.0306) and the ADC (P = 0.0256). The stromal fibrosis also correlated with ES (P = 0.0023), the L/M ratio (P = 0.0344), and enhancement ratio of the early-to-delayed images (P = 0.049).

CONCLUSIONS

The ES and L/M ratio are correlated significantly with each other, and they are correlated with the fibrosis. These results suggest that they will provide the information on the fibrosis and may help the diagnosis of breast lesions.

Diffusion-weighted imaging in pediatric body MR imaging: principles, technique, and emerging applications

Diffusion-weighted (DW) imaging is an emerging technique in body imaging that provides indirect information about the microenvironment of tissues and lesions and helps detect, characterize, and follow up abnormalities. Two main challenges in the application of DW imaging to body imaging are the decreased signal-to-noise ratio of body tissues compared with neuronal tissues due to their shorter T2 relaxation time, and image degradation related to physiologic motion (eg, respiratory motion). Use of smaller b values and newer motion compensation techniques allow the evaluation of anatomic structures with DW imaging. DW imaging can be performed as a breath-hold sequence or a free-breathing sequence with or without respiratory triggering. Depending on the mobility of water molecules in their microenvironment, different normal tissues have different signals at DW imaging. Some normal tissues (eg, lymph nodes, spleen, ovarian and testicular parenchyma) are diffusion restricted, whereas others (eg, gallbladder, corpora cavernosa, endometrium, cartilage) show T2 shine-through. Epiphyses that contain fatty marrow and bone cortex appear dark on both DW images and apparent diffusion coefficient maps. Current and emerging applications of DW imaging in pediatric body imaging include tumor detection and characterization, assessment of therapy response and monitoring of tumors, noninvasive detection and grading of liver fibrosis and cirrhosis, detection of abscesses, and evaluation of inflammatory bowel disease.

Diffusion-weighted magnetic resonance imaging indicates the severity of acute pancreatitis

PURPOSE

To test the use of diffusion-weighted magnetic resonance imaging (DW-MRI) to differentiate between different degrees of severity of acute pancreatitis (AP).

METHOD

Thirty-six patients who underwent DW-MRI and magnetic resonance cholangiopancreatography were divided into patients with mild AP (mAP, n = 15), patients with necrotizing AP (nAP, n = 8), and patients with a normal pancreas (nP, n = 15; controls). The pancreas was divided into head, body, and tail, and each segment was classified according to image features: pattern 1, normal; pattern 2, mild inflammation; and pattern 3, necrosis. Apparent diffusion coefficients (ADCs) were measured in each segment and correlated with clinical diagnoses.

RESULTS

A total of 108 segments was assessed (three segments per patient). Segments classified as pattern 1 in the nP and mAP groups showed similar ADC values (P = 0.29). ADC values calculated for the pancreatic segments grouped according to the different image patterns (1-3) were significantly different (P < 0.001). Comparisons revealed significant differences in signal intensity between all three patterns (P < 0.05).

CONCLUSIONS

DW-MRI was a compatible and safe image option to differentiate tissue image patterns in patients with mAP, nAP, and nP, mainly in those with contraindications to contrast-enhanced MRI (which is classically required for determining the presence of necrosis) or computed tomography. ADC measures allowed precise differentiation between patterns 1, 2, and 3.

Assessment of Liver Fibrosis with Diffusion-Weighted Magnetic Resonance Imaging Using Different b-values in Chronic Viral Hepatitis

OBJECTIVE

To examine the effectiveness of apparent diffusion coefficient (ADC) values and to compare the reliability of different b-values in detecting and identifying significant liver fibrosis.

SUBJECTS AND METHODS

There were 44 patients with chronic viral hepatitis (CVH) in the study group and 30 healthy participants in the control group. Diffusion-weighted magnetic resonance imaging (DWI) was performed before the liver biopsy in patients with CVH. The values of ADC were measured with 3 different b-values (100, 600, 1,000 s/mm2). In addition, liver fibrosis was classified using the modified Ishak scoring system. Liver fibrosis stages and ADC values were compared using areas under the receiver-operating characteristic (ROC) curve.

RESULTS

The study group's mean ADC value was not statistically significantly different from the control group's mean ADC value at b = 100 s/mm2 (3.69 ± 0.5 × 10-3 vs. 3.7 ± 0.3 × 10-3 mm2/s) and b = 600 s/mm2 (2.40 ± 0.3 × 10-3 vs. 2.5 ± 0.5 × 10-3 mm2/s). However, the study group's mean ADC value (0.99 ± 0.3 × 10-3 mm2/s) was significantly lower than that of the control group (1.2 ± 0.1 × 10-3 mm2/s) at b = 1,000 s/mm2. With b = 1,000 s/mm2 and the cutoff ADC value of 0.0011 mm2/s for the diagnosis of liver fibrosis, the mean area under the ROC curve was 0.702 ± 0.07 (p = 0.0015). For b = 1,000 s/mm2 and the cutoff ADC value of 0.0011 mm2/s to diagnose significant liver fibrosis (Ishak score = 3), the mean area under the ROC curve was 0.759 ± 0.07 (p = 0.0001).

CONCLUSION

Measurement of ADC values by DWI was effective in detecting liver fibrosis and accurately identifying significant liver fibrosis when a b-value of 1,000 s/mm2 was used.

IVIM Diffusion-weighted Imaging of the Liver at 3.0T: Comparison with 1.5T

Purpose

To compare intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) of the liver between 1.5 T and 3.0 T in terms of parameter quantification and inter-platform reproducibility.

Materials and methods

In this IRB approved prospective study, 19 subjects (17 patients with chronic liver disease and 2 healthy volunteers) underwent two repeat scans at 1.5 T and 3.0 T. Each scan included IVIM DWI using 16 b values from 0 to 800 s/mm². A single observer measured IVIM parameters for each platform and estimated signal to noise ratio (eSNR) at b0, 200, 400 and 800 s/mm². Wilcoxon paired tests were used to compare liver eSNR and IVIM parameters. Inter-platform reproducibility was assessed by calculating within-subject coefficient of variation (CV) and Bland–Altman limits of agreement. An ice water phantom was used to test ADC variability between the two MRI systems.

Results

The mean invitro difference in ADC between the two platforms was 6.8%. eSNR was significantly higher at 3.0T for all selected b values (p = 0.006–0.020), except for b0 (p = 0.239). Liver IVIM parameters were significantly different between 1.5 T and 3.0 T (p = 0.005–0.044), except for ADC (p = 0.748). The inter-platform reproducibility of true diffusion coefficient (D) and ADC were good, with mean CV of 10.9% and 11.1%, respectively. Perfusion fraction (PF) and pseudodiffusion coefficient (D*) showed more limited inter-platform reproducibility (mean CV of 22.6% for PF and 46.9% for D*).

Conclusion

Liver D and ADC values showed good reproducibility between 1.5 T and 3.0 T platforms; while there was more variability in PF, and large variability in D* parameters between the two platforms. These findings may have implications for drug trials assessing the role of IVIM DWI in tumor response and liver fibrosis.

Three-Tesla magnetic resonance elastography for hepatic fibrosis: Comparison with diffusion-weighted imaging and gadoxetic acid-enhanced magnetic resonance imaging

AIM: To evaluate the feasibility of 3-Tesla magnetic resonance elastography (MRE) for hepatic fibrosis and to compare that with diffusion-weighted imaging (DWI) and gadoxetic acid-enhanced magnetic resonance (MR) imaging.

METHODS: Forty-two patients were included in the study. On MRE, mean stiffness values were measured on the elastograms in kilopascals. The apparent diffusion coefficient (ADC) of the liver was measured using DWI. On gadoxetic acid enhanced MR, the contrast enhancement index (CEI) was calculated as signal intensity (SI)_post/SI_pre, where SI_post is liver-to-muscle SI ratio on hepatobiliary phase images and SI_pre is that on nonenhanced images. Correlation between aspartate aminotransferase to the platelet ratio index (APRI) and three MR parameters was assessed. Each MR parameter was compared between a hepatic fibrosis (HF) group and non-hepatic fibrosis (nHF) group.

RESULTS: Liver stiffness showed strong positive correlation with APRI [Spearman correlation coeffiecient (r) = 0.773, P < 0.0001], while ADC and CEI showed weak or prominent negative correlation (r = -0.28 and -0.321, respectively). In the HF group, only liver stiffness showed strong correlation with APRI (r = 0.731, P < 0.0001). Liver stiffness, ADC, and APRI were significantly different between the HF group and nHF group.

CONCLUSION: MRE at 3-Tesla could be a feasible method for the assessment of hepatic fibrosis.

Prediction of pancreatic anastomotic failure after pancreatic head resection using preoperative diffusion-weighted MR imaging

PURPOSE

To determine whether the preoperative pancreatic apparent diffusion coefficient (ADC) can be used to predict the development of postoperative pancreatic anastomotic failure (PAF).

MATERIALS AND METHODS

We retrospectively examined the cases of 79 patients who underwent pancreatic head resection between January 2010 and October 2013. The patients underwent 1.5-T MR imaging including diffusion-weighted imaging before surgery. The main pancreatic duct diameter (MPD), the pancreatic parenchymal thickness (PT), and the ADC of the pancreatic remnant parenchyma were measured. Two radiologists blinded to the patients' outcomes performed the measurements. The imaging parameters were compared between the patients who developed PAF and those who did not. The cut-off ADC for the development of PAF was calculated with a receiver operating characteristic analysis.

RESULTS

The imaging parameters were highly correlated between the two observers. The MPD and PT did not differ significantly among the patients. The mean pancreatic ADCs were significantly higher in the patients with PAF than in those without PAF. An ADC higher than 1.50 × 10(-3) mm(2)/s (Az = 0.719, observer-1) or 1.35 × 10(-3) mm(2)/s (Az = 0.752, observer-2) was optimal for predicting the development of postoperative PAF.

CONCLUSION

Measuring the preoperative non-tumorous pancreatic ADC may be useful for the prediction of a postoperative PAF.

Non-invasive diagnosis of advanced fibrosis and cirrhosis

Liver cirrhosis is a common and growing public health problem globally. The diagnosis of cirrhosis portends an increased risk of morbidity and mortality. Liver biopsy is considered the gold standard for diagnosis of cirrhosis and staging of fibrosis. However, despite its universal use, liver biopsy is an invasive and inaccurate gold standard with numerous drawbacks. In order to overcome the limitations of liver biopsy, a number of non-invasive techniques have been investigated for the assessment of cirrhosis. This review will focus on currently available non-invasive markers of cirrhosis. The evidence behind the use of these markers will be highlighted, along with an assessment of diagnostic accuracy and performance characteristics of each test. Non-invasive markers of cirrhosis can be radiologic or serum-based. Radiologic techniques based on ultrasound, magnetic resonance imaging and elastography have been used to assess liver fibrosis. Serum-based biomarkers of cirrhosis have also been developed. These are broadly classified into indirect and direct markers. Indirect biomarkers reflect liver function, which may decline with the onset of cirrhosis. Direct biomarkers, reflect extracellular matrix turnover, and include molecules involved in hepatic fibrogenesis. On the whole, radiologic and serum markers of fibrosis correlate well with biopsy scores, especially when excluding cirrhosis or excluding fibrosis. This feature is certainly clinically useful, and avoids liver biopsy in many cases.

The value of liver and spleen ADC measurements in the diagnosis and follow up of hepatic fibrosis in chronic liver disease

AIMS

To evaluate the value of spleen and liver apparent diffusion coefficients (ADC) in chronic liver disease patients, with and without hepatocellular carcinoma (HCC), and to investigate the use of diffusion-weighted imaging (DWI) in the diagnosis and follow-up of hepatic fibrosis.

MATERIALS AND METHODS

This study population comprised 68 chronic liver disease patients (Group 1) and 70 healthy volunteers as controls (Group 2). In Group 1, 40 patients had chronic hepatitis-B, 20 had chronic hepatitis-C, 5 had non-alcoholic steatohepatitis and 3 had alcoholic steatohepatitis. Diagnosis of chronic liver disease was made by percutaneous liver biopsy and the degree of fibrosis (stage) was determined using the METAVIR scoring system. HCC diagnosis was made with a lesion biopsy. The patient group was subdivided based on the degree of fibrosis (F1, F2, F3 and F4) and presence of HCC. After patient and control groups underwent b-value 600 s/mm(2) DWI examination, liver and spleen ADC values were mapped and measured. The ADC values of the patient groups (F1, F2, F3, F4; with HCC, without HCC) were compared with each other and with the control group.

RESULTS

Liver ADC values were lower in Group 1 compared to Group 2 (P<0·001). There was a statistically significant difference between the patient and control groups liver right lobe, left lobe and caudate lobe ADC values (P<0·001). Comparing the F1, F2, F3 and F4 groups, there was no statistically significant difference found in terms of ADC values (P>0·05). However, as degree of fibrosis increased there was a reduction in ADC values, though not statistically significant. Comparing the groups with HCC and without HCC, there was no statistically significant difference in ADC values (P>0·05). There was no statistical difference in average spleen ADC values between patient and control groups (P>0·05).

CONCLUSIONS

In chronic liver disease, ADC values were lower. As the degree of liver fibrosis increased, ADC levels decreased, though the relationship between ADC values and fibrosis degree was not statistically significant. Quantitative DWI may help in the diagnosis of fibrosis in chronic liver disease patients, however as it does not show the degree of fibrosis, its use in treatment planning and follow-up is controversial. Spleen DWI measurement is not a sufficient method to diagnose and determine the degree of fibrosis in chronic liver disease patients.

Pretransplant diagnosis of hepatocellular carcinoma by gadoxetic acid-enhanced and diffusion-weighted magnetic resonance imaging

We sought to evaluate the diagnostic performance of gadoxetic acid-enhanced magnetic resonance imaging (MRI) with and without additional diffusion-weighted imaging (DWI) in the detection of hepatocellular carcinoma (HCC) in pretransplant patients. We included 63 liver transplant patients (54 men and 9 women; mean age = 52 years) who had undergone gadoxetic acid-enhanced MRI with DWI at 3.0 T within 90 days before transplantation. Two image sets were reviewed for HCC in 2 separate sessions by 2 independent observers: the gadoxetic acid set and the combined set (gadoxetic acid plus DWI). The sensitivity, specificity, positive predictive value, and negative predictive value were calculated for each image set. In all, 113 HCCs (size range = 0.5-7.8 cm, mean = 2.0 ± 1.3 cm) were identified in the 52 liver explants. The per-lesion sensitivity of the combined set (78.8% for both observers) was higher than the sensitivity of the gadoxetic acid set [71.7% (P = 0.02) and 72.6% (P = 0.03) for the 2 observers], with the highest trend for Child-Pugh class A (94.4% and 97.2% for gadoxetic acid and 97.2% for combined), which was followed by class B (73.2% for gadoxetic acid and 82.9% for combined) and then class C (47.2% for gadoxetic acid and 55.6% for combined, P = 0.01). The per-patient negative predictive value of the combined set was higher than that of the gadoxetic acid set for both observers (P = 0.046). There was no difference in specificity between the 2 image sets (P > 0.05). The addition of DWI to gadoxetic acid-enhanced MRI resulted in significantly higher sensitivity to detect HCC. However, the sensitivity decreased with increasing cirrhosis severity for both imaging types.

Intravoxel incoherent motion MRI evaluation for the staging of liver fibrosis in a rat model

PURPOSE

To explore the characteristics of intravoxel incoherent motion (IVIM) in various stages of liver fibrosis, and their relationships with fibrotic stages in rats.

MATERIALS AND METHODS

Fifty rats were given various doses of carbon tetrachloride (CCl4 ) to induce various fibrotic stages in rats; 15 untreated rats served as controls. Diffusion-weighted magnetic resonance imaging (MRI) was performed and eight b-values (0-800 s/mm(2) ) were applied to obtain IVIM parameters (D, pure molecular diffusion; f, perfusion fraction; D*, pseudodiffusion). The stages of liver fibrosis (stages F0-F4) were evaluated histologically using METAVIR scores. Fifty-seven rats (15 controls and 42 with fibrosis) were analyzed by nonparametric methods and receiver operating characteristic curves to determine diagnostic accuracy.

RESULTS

Significant differences (P < 0.001) were found between stages (stages F0-F4) by D, f, D*, and apparent diffusion coefficient (ADC). There were inverse correlations between fibrosis stages and D, f, D*, ADC (r = -0.657, r = -0.631, r = -0.711 r = -0.719, respectively). Multivariate analysis showed that the combination models (D, f, D*) were better than the individual parameter (ADC) for the evaluation fibrosis stages (area under the curve [AUC]: 0.821-1.000 vs. AUC: 0.753-0.918) CONCLUSION: IVIM-derived parameters showed significant correlations with stages of liver fibrosis in a rat model.

Magnetic resonance imaging of the liver: apparent diffusion coefficients from multiexponential analysis of b values greater than 50 s/mm2 do not respond to caloric intake despite increased portal-venous blood flow

PURPOSE

The purpose of this study was to measure potential changes of the apparent diffusion coefficient (ADC) in diffusion-weighted imaging of the liver before and after caloric challenge in correlation to the induced changes in portal vein flow.

MATERIALS AND METHODS

The study was approved by the local ethics committee. Each of 10 healthy volunteers underwent 4 measurements in a 1.5-T whole-body magnetic resonance scanner on 2 different days: a first scan after fasting for at least 8 hours and a second scan 30 minutes after intake of a standardized caloric either a protein- or carbohydrate-rich meal. Diffusion-weighted spin-echo echo-planar magnetic resonance images were acquired at b values of 0, 50, 150, 250, 500, 750, and 1000 s/mm. In addition, portal vein flow was quantified with 2-dimensional phase-contrast imaging (velocity encoding parallel to flow direction, 60 cm/s). Mean ADC values for regions of interest in 3 different slices were measured from b50 to b250 and from b500 to b1000 images.

RESULTS

Carbohydrate- and protein-rich food intake both resulted in a substantial increase in the portal vein flow (fasting state, 638.6 ± 202.3 mL/min; after protein intake, 1322 ± 266.8; after carbohydrate intake, 1767 ± 421.6). The signal decay with increasingly strong diffusion weighting (b values from 0 to 1000 s/mm2) exhibited a triexponential characteristic, implying fast, intermediate, and slow-moving water-molecule proton-spin ensembles in the liver parenchyma. Mean ADC for high b values (b500-b1000) after fasting was 0.93 ± 0.09 × 10 mm/s; that after protein intake, 0.93 ± 0.11 × 10; and that after carbohydrate intake, 0.93 ± 0.08 × 10. For intermediate b values (b50-b250), the signal-decay constants were 1.27 ± 0.14 × 10 mm/s, 1.28 ± 0.15 × 10, and 1.31 ± 0.09 × 10, respectively. There was no statistically significant difference between fasting and caloric challenge.

CONCLUSIONS

The postprandial increase in portal vein flow is not accompanied by a change of liver parenchymal ADC values. In clinical diffusion imaging, patients may be scanned without prescan food-intake preparations. To minimize interference of perfusion effects, liver-tissue molecular water diffusion should be quantified using high b values (≥500 s/mm) only.

Diagnostic value of magnetic resonance elastography for detecting and staging of hepatic fibrosis: a meta-analysis

AIM

A meta-analysis was performed to evaluate the diagnostic value of magnetic resonance elastography (MRE) in detecting and staging hepatic fibrosis.

MATERIALS AND METHODS

A systematic search of PubMed, EMBASE, Web of Science, and Cochrane Library Database up to October 2013 was undertaken to find studies on the evaluation of MRE in patients suspected of hepatic fibrosis. Data from the articles were analysed using Meta-disc 1.4 and Stata 12.0 software. The sensitivity, specificity, and area under the summary receiver operating characteristic (ROC) curve (AUROC) were pooled for all stages of hepatic fibrosis (F ≥ 1, F ≥ 2, F ≥ 3, and F = 4). Publication bias was assessed through the Deeks' funnel plot asymmetry tests.

RESULTS

Thirteen studies comprising 989 patients met the inclusion criteria. The pooled sensitivity and specificity for F ≥ 1, F ≥ 2, F ≥ 3, and F = 4 were 0.87 (95% CI = 0.84-0.89) and 0.92 (95% CI = 0.87-0.96), 0.87 (95% CI = 0.84-0.90) and 0.92 (95% CI = 0.89-0.95), 0.88 (95% CI = 0.85-0.91) and 0.91 (95% CI = 0.88-0.93), 0.91 (95% CI = 0.87-0.94) and 0.92 (95% CI = 0.89-0.94), respectively. The pooled AUROC for F ≥ 1, F ≥ 2, F ≥ 3, and F = 4 were 0.9502, 0.9663, 0.9644, and 0.9768, respectively. The non-significant slope of Deeks' funnel plot asymmetry tests indicated that no significant bias was found.

CONCLUSIONS

MRE has a high diagnostic accuracy for the quantitative detection and staging of hepatic fibrosis.

Optimal b value of diffusion-weighted imaging on a 3.0T magnetic resonance scanner in Crohn’s disease

AIM: To determine the optimal b value of diffusion-weighted imaging for detecting active inflammation in Crohn’s disease.

METHODS: Thirty-one patients clinically diagnosed with active Crohn’s disease were referred for magnetic resonance examination. All patients were scanned on a 3.0T magnetic resonance scanner using the same protocol involving four different b values (800, 1500, 2000 and 2500 s/mm²). The diagnostic effect of diffusion-weighted imaging was evaluated and compared with endoscopic findings. The diffusion-weighted image quality of four b value groups was evaluated and apparent diffusion coefficient was measured for both normal and inflammatory intestinal segments.

RESULTS: The contrast-to-noise ratio and signal-to-noise ratio were not satisfied when b value 2000 or 2500 s/mm² was adopted (36.52 ± 14.95 vs 34.78 ± 24.83, P > 0.05; 53.58 ± 23.45 vs 47.58 ± 29.67, P > 0.05). The qualitative image quality was not enough to meet diagnostic requirement. No matter which b value was chosen, the apparent diffusion coefficient of inflammatory intestinal segments was significantly lower than that of normal intestinal segments (1.38 ± 0.28 vs 2.00 ± 0.38, P < 0.01; 1.09 ± 0.20 vs 1.50 ± 0.28, P < 0.01; 0.95 ± 0.19 vs 1.34 ± 0.28, P < 0.01; 0.88 ± 0.14 vs 1.20 ± 0.21, P < 0.01). The lesion detection rate (90.32%), diagnostic sensitivity (81.18%) and specificity (95.10%) would be appropriate when b value 1500 s/mm² was adopted.

CONCLUSION: High b value is suitable for intestinal DW examination on a high field MR scanner.

Diffusion-weighted magnetic resonance for assessing ileal Crohn's disease activity

BACKGROUND

Endoscopy and imaging objectively assess Crohn's disease (CD) activity. Magnetic resonance enterography (MRE) uses no ionizing radiation, carries no significant morbidity, and is highly sensitive in revealing soft tissues inflammation. Diffusion-weighted imaging can distinguish intestinal inflammation from a lower diffusion of water molecules giving rise to a reduced apparent diffusion coefficient. The magnetic resonance index of activity score and, more recently, the Clermont score were recently developed for staging CD activity. The aim of this study was to compare the MRE scores and the Simple Endoscopic Score for CD in identifying ileal CD activity.

METHODS

Fifty-five patients with ileal and ileocolonic CD were consecutively enrolled between June 2012 and June 2013. All patients underwent clinical examination, biochemical tests, MRE, and colonoscopy to assess disease activity.

RESULTS

MRE assessed active ileal disease in 31 patients (56.3%). The Clermont score significantly correlated with the magnetic resonance index of activity score (r = 0.91; P < 0.0001) and the Simple Endoscopic Score for CD (r = 0.76; P < 0.0001). The apparent diffusion coefficient correlated with the Simple Endoscopic Score for CD (r = -0.63; P < 0.0001) especially in unoperated patients.

CONCLUSIONS

The Clermont score and the apparent diffusion coefficient value can stage ileal CD, avoiding the need to use contrast agents.

Diffusion-weighted imaging of the liver: techniques and applications

Diffusion-weighted imaging (DWI) is a technique that assesses the cellularity, tortuosity of the extracellular/extravascular space, and cell membrane density based on differences in water proton mobility in tissues. The strength of the diffusion weighting is reflected by the b value. DWI using several b values enables the quantification of the apparent diffusion coefficient. DWI is increasingly used in liver imaging for multiple reasons: it can add useful qualitative and quantitative information to conventional imaging sequences; it is acquired relatively quickly; it is easily incorporated into existing clinical protocols; and it is a noncontrast technique.

Detection of small (≤2 cm) HCC in cirrhotic patients: added value of diffusion MR-imaging

OBJECTIVES

To evaluate the usefulness of the diffusion-weighted sequence in the detection of small (≤2 cm) hepatocellular carcinoma (HCC) in patients with cirrhosis.

METHODS

Seventy cirrhotic patients with 93 HCCs underwent MR-Imaging at 1.5 T. MR acquisitions comprised unenhanced T1- and T2-weighted images and post-contrast Gd-BOPTA-enhanced T1W GRE-3D images acquired after approximately 25, 60, 180 s (dynamic phases) and 90 min (hepatobiliary phase). DWI was performed by a SSEPI sequence (b values 0, 50, 400, 800 s/mm(2)). Quantitative analysis was performed to establish significant difference of ADC values of benign lesions compared with that of HCC. Sensitivity, specificity, positive and negative predictive values and diagnostic accuracy of two different protocols with and without diffusion MRI sequence were also calculated and compared each other.

RESULTS

A good inverse correlation was found between reference standard and ADC values (ρ = -0.688). The mean ADC value of HCC was significantly lower than the mean value of benign focal liver lesions (p < 0.0001). No significant difference was reported in term of sensitivity, specificity, PPV, NPV and diagnostic accuracy between the two datasets. A trend to a better sensitivity was found when DWI images were considered.

CONCLUSIONS

The adjunction of DWI does not significantly improve the diagnostic accuracy in the detection of small HCC.

Optimization of intra-voxel incoherent motion imaging at 3.0 Tesla for fast liver examination

BACKGROUND

Optimization of multi b-values MR protocol for fast intra-voxel incoherent motion imaging of the liver at 3.0 Tesla.

METHODS

A comparison of four different acquisition protocols were carried out based on estimated IVIM (DSlow , DFast , and f) and ADC-parameters in 25 healthy volunteers. The effects of respiratory gating compared with free breathing acquisition then diffusion gradient scheme (simultaneous or sequential) and finally use of weighted averaging for different b-values were assessed. An optimization study based on Cramer-Rao lower bound theory was then performed to minimize the number of b-values required for a suitable quantification. The duration-optimized protocol was evaluated on 12 patients with chronic liver diseases

RESULTS

No significant differences of IVIM parameters were observed between the assessed protocols. Only four b-values (0, 12, 82, and 1310 s.mm(-2) ) were found mandatory to perform a suitable quantification of IVIM parameters. DSlow and DFast significantly decreased between nonadvanced and advanced fibrosis (P < 0.05 and P < 0.01) whereas perfusion fraction and ADC variations were not found to be significant.

CONCLUSION

Results showed that IVIM could be performed in free breathing, with a weighted-averaging procedure, a simultaneous diffusion gradient scheme and only four optimized b-values (0, 10, 80, and 800) reducing scan duration by a factor of nine compared with a nonoptimized protocol. Preliminary results have shown that parameters such as DSlow and DFast based on optimized IVIM protocol can be relevant biomarkers to distinguish between nonadvanced and advanced fibrosis.

Value of hepatic diffusion-weighted magnetic resonance imaging in evaluating liver fibrosis following transarterial chemoembolization with low doses of chemotherapy

The aim of the present study was to investigate the value of apparent diffusion coefficients (ADCs) measured with magnetic resonance (MR) diffusion-weighted imaging (DWI) in evaluating liver fibrosis and curative effects on hepatocellular carcinoma (HCC) following transcatheter arterial chemoembolization (TACE) with low doses of chemotherapy. In total, 84 patients with HCC not recommended for surgical resection underwent TACE. The patients were divided into small dose (n=46) and conventional dose (n=38) chemotherapy groups, and underwent MR-DWI prior to and following TACE. Examination of the four liver fibrosis indexes, hyaluronate, laminin, human procollagen type-III and collagen type-IV, as well as ADC values (b=600 sec/mm²), was conducted in the two groups. With small dose chemotherapy, the ADC values were not significantly different preoperatively and postoperatively (P>0.05). By contrast, with a conventional dose, statistically significant differences were observed between the preoperative and postoperative ADC values (P<0.01). ADC values in the small and conventional dose chemotherapy groups prior to the first cycle of TACE were 1.613±0.133×10⁻³ and 1.488±0.248×10⁻³ mm²/sec, respectively, while following four cycles of TACE, the ADC values were 1.598±0.147×10⁻³ and 1.206±0.222×10⁻³ mm²/sec, respectively. With regard to chemotherapy, the ADC values before and after TACE were significantly different (P<0.05). A significant negative correlation was observed between the ADC values and the fibrosis stage (P<0.05). Therefore, hepatic MR-DWI plays a key role in evaluating liver fibrosis following TACE with low doses of chemotherapy, resulting in improved curative effects of TACE.

Apparent diffusion coefficient value of hepatic fibrosis and inflammation in children with chronic hepatitis

PURPOSE

This study was done to prospectively evaluate the usefulness of apparent diffusion coefficient (ADC) in the diagnosis and grading of hepatic fibrosis and inflammation in children with chronic hepatitis.

MATERIALS AND METHODS

Institutional Review Board approval was obtained. This prospective study was carried out on 50 children with chronic hepatitis (mean age 8.3 ± 3.2 years; 33 boys and 17 girls) and 20 age- and sex-matched healthy control children. The children underwent diffusion-weighted magnetic resonance imaging of the liver. The ADC value of the liver was calculated. The hepatic fibrosis stages (F1-F6) and necroinflammatory activity grades (A1-A4) were calculated. The ADC values of different stages of hepatic fibrosis and grades of necroinflammatory activity were calculated.

RESULTS

The mean ADC value of the liver parenchyma was 1.53 ± 0.17 × 10(-3) mm(2)/s in children with chronic hepatitis and 1.74 ± 0.16 × 10(-3) mm(2)/s in controls. The ADC value was significantly lower in children with hepatic fibrosis compared to controls (p = 0.001). There was a significant difference (p = 0.001) in ADC between mild (F1-F3) and advanced (F4-F6) stages of fibrosis. There was a significant difference (p = 0.004) in ADC between mild (A1-A2) and advanced (A3-A4) grades of necroinflammation. The cut-off ADC values used to differentiate mild from advanced fibrosis and necroinflammation were 1.62 and 1.64 mm(2)/s with an area under the curve of 0.898 and 0.807, respectively. The ADC value negatively correlated with stages of hepatic fibrosis (r = -0.799, p = 0.001) and necroinflammatory activity grade (r = -0.468, p = 0.001).

CONCLUSIONS

We conclude that ADC value is an effective noninvasive parameter for the diagnosis and grading of hepatic fibrosis and inflammation in children with chronic hepatitis.

Quantitative liver MRI combining phase contrast imaging, elastography, and DWI: assessment of reproducibility and postprandial effect at 3.0 T

PURPOSE

To quantify short-term reproducibility (in fasting conditions) and postprandial changes after a meal in portal vein (PV) flow parameters measured with phase contrast (PC) imaging, liver diffusion parameters measured with multiple b value diffusion-weighted imaging (DWI) and liver stiffness (LS) measured with MR elastography (MRE) in healthy volunteers and patients with liver disease at 3.0 T.

MATERIALS AND METHODS

In this IRB-approved prospective study, 30 subjects (11 healthy volunteers and 19 liver disease patients; 23 males, 7 females; mean age 46.5 y) were enrolled. Imaging included 2D PC imaging, multiple b value DWI and MRE. Subjects were initially scanned twice in fasting state to assess short-term parameter reproducibility, and then scanned 20 min. after a liquid meal. PV flow/velocity, LS, liver true diffusion coefficient (D), pseudodiffusion coefficient (D*), perfusion fraction (PF) and apparent diffusion coefficient (ADC) were measured in fasting and postprandial conditions. Short-term reproducibility was assessed in fasting conditions by measuring coefficients of variation (CV) and Bland-Altman limits of agreement. Differences in MR metrics before and after caloric intake and between healthy volunteers and liver disease patients were assessed.

RESULTS

PV flow parameters, D, ADC and LS showed good to excellent short-term reproducibility in fasting state (CV <16%), while PF and D* showed acceptable and poor reproducibility (CV = 20.4% and 51.6%, respectively). PV flow parameters and LS were significantly higher (p<0.04) in postprandial state while liver diffusion parameters showed no significant change (p>0.2). LS was significantly higher in liver disease patients compared to healthy volunteers both in fasting and postprandial conditions (p<0.001). Changes in LS were significantly correlated with changes in PV flow (Spearman rho = 0.48, p = 0.013).

CONCLUSIONS

Caloric intake had no/minimal/large impact on diffusion/stiffness/portal vein flow, respectively. PC MRI and MRE but not DWI should be performed in controlled fasting state.

Assessment of diffusion tensor MR imaging (DTI) in liver fibrosis with minimal confounding effect of hepatic steatosis

PURPOSE

Given the potential confounding effect of fat on apparent diffusion coefficient (ADC) in the liver, we have assessed diffusion tensor imaging in liver fibrosis with minimal effect of fat on ADC and fractional anisotropy (FA).

METHODS

Thirty-six mice were used, among which 20 mice were CCl4 treated for fibrosis induction. Diffusion tensor imaging was performed at 9.4T using a spin-echo diffusion tensor imaging sequence with six gradient directions. Hepatic fat fraction obtained by MR spectroscopy was used as hepatic fat content. Fibrosis scores were obtained from histopathology.

RESULTS

The hepatic fat fractions of the two animal groups were below 5.5% and not different (5.3 ± 1.5 vs. 4.6 ± 1.1%; P = 0.115). Fibrosis scores were higher in CCl4 -treated mice (0.0 ± 0.0 vs. 2.1 ± 0.7; P < 0.001). Nonetheless, there was no difference in ADC between the two groups (0.711 ± 0.068 × 10(-3) vs. 0.718 ± 0.095 × 10(-3) mm(2) s(-1) ; P = 0.911). The treated group had a lower FA than control (0.552 ± 0.050 vs. 0.586 ± 0.013; P = 0.023). ADC was not correlated with hepatic fat fraction and fibrosis. FA was correlated with hepatic fat fraction (r = 0.418, P = 0.011) and fibrosis (r = -0.411, P = 0.012).

CONCLUSION

FA may be more sensitive to mild-to-moderate liver fibrosis than ADC. In addition to ADC, FA may also be sensitive to hepatic fat content, and therefore need careful interpretation in liver fibrosis with concomitant fatty liver.

Evaluation of hepatic fibrosis using intravoxel incoherent motion in diffusion-weighted liver MRI

OBJECTIVES

To determine whether intravoxel incoherent motion (IVIM)-diffusion-weighted image (DWI)-derived parameters showed better diagnostic performance than the apparent diffusion coefficient (ADC(total)) for the evaluation of hepatic fibrosis (HF).

METHODS

This retrospective study was approved by institutional review board, and informed consent was waived. Fifty-five patients with chronic liver disease who had undergone IVIM-DWI using 8 b-values at 3 T were included. True diffusion coefficient (Dt), pseudo-diffusion coefficient (Dp), perfusion fraction (f), and ADC(total) were calculated. Receiver operating characteristic analysis was performed for all parameters for the HF staging.

RESULTS

All parameters showed a significant correlation with the HF stages (-0.31 to -0.72, P < 0.05). All parameters were significantly higher in F0 to F1 than in F4 (P < 0.05). The Dp showed better performance than the ADC(total) in differentiating significant HF (≥F2) from F0 to F1.

CONCLUSIONS

The IVIM-derived parameters and ADC(total) showed significant correlation with HF. The D p showed better diagnostic performance for differentiating significant HF than did ADC(total).

Diffusion Weighted MRI for Hepatic Fibrosis: Impact of b-Value

Background

Hepatic fibrosis is a typical complication of chronic liver diseases resulting in cirrhosis that remains a major public health problem worldwide. Liver biopsy is currently the gold standard for diagnosing and staging hepatic fibrosis. Percutaneous liver biopsy; however, is an invasive procedure with risks of complications. Therefore, there is need for alternative non-invasive techniques to assess liver fibrosis and chronic liver diseases. In recent years, MRI techniques, including diffusion weighted imaging (DWI), have been developed for in vivo quantification of liver fibrosis.

Objectives

The purpose of this study is to evaluate the utility of diffusion weighted MRI in the diagnosis and quantification of the degree of hepatic fibrosis and to investigate the influence of b-value.

Patients and Methods

Twenty-four patients (13 males, 11 females), with a mean age of 46 years (36-73 years) diagnosed as chronic hepatitis and histopathologically proven liver fibrosis and 22 other patients (8 males, 14 females) with no clinical or biochemical findings of liver disease, with a mean age of 51.2 years (32-75 years) were included in the study. All patients with chronic hepatitis underwent percutaneous liver biopsy by an experienced hepatologist without sonographic guidance. The Knodell histology activity index (HAI) for grading of necroinflammatory changes and Metavir scoring system for staging of the liver fibrosis were used to record the severity of the disease. All patients were examined with a 1.5 Tesla MRI system and the patients underwent diffusion weighted imaging (DWI) with a routine hepatic MRI protocol. Different b-values including 250, 500, 750, and 1000 sec/mm ² were used to calculate apparent diffusion coefficients.

Results

We detected decreased apparent diffusion coefficient values in patients with hepatic fibrosis compared to patients without chronic hepatitis and there was a trend toward decrease in hepatic apparent diffusion coefficient values with an increasing degree of fibrosis.

Conclusions

Our findings suggest that hepatic apparent diffusion coefficient measurement with a b-value of 750 sec/mm ² or greater is useful in accurate quantification of liver fibrosis and necroinflammation.

Added value of diffusion-weighted MRI for evaluating viable tumor of hepatocellular carcinomas treated with radiotherapy in patients with chronic liver disease

OBJECTIVE

The purpose of this article is to evaluate the added value of diffusion-weighted imaging (DWI) to the diagnostic performance of conventional MRI in diagnosing viable hepatocellular carcinoma (HCC) tumors treated with radiotherapy in patients with chronic liver disease.

MATERIALS AND METHODS

Twenty-nine patients with viable tumor and 35 patients without viable tumor were enrolled. We assessed the signal intensity of viable tumor compared with irradiated liver on MRI and DWI. Signal intensity ratios and apparent diffusion coefficient (ADC) ratios of viable tumor to nonirradiated liver were also assessed on DWI with ADC maps. Two observers reviewed conventional MRI and combined MRI and DWI and rated them using a 5-point scale. Diagnostic performance was evaluated using a receiver operating characteristic (ROC) curve.

RESULTS

Viable tumors showed hyperintensity on T2-weighted and arterial phase images (16/29 [55.2%]) and hypointensity on portal (22/29 [75.9%]), 3-minute late (19/29 [65.5%]), and hepatobiliary phase (23/29 [79.3%]) images. Twenty-seven (93.1%) viable tumors showed hyperintensity on DWI and hypointensity on ADC maps. Mean signal intensity ratios and ADC ratios of viable tumor on DWI with ADC maps were significantly higher and lower than those of irradiated liver. Diagnostic performance (area under the ROC curve) improved significantly after adding DWI, and interobserver agreement was moderate for conventional MRI (κ = 0.450) and good after adding DWI (κ = 0.748).

CONCLUSION

Adding DWI to conventional MRI can improve the detection of viable HCC tumors treated with radiotherapy compared to conventional MRI alone.

Diagnosis of focal liver lesions with gadoxetic acid-enhanced MRI: is a shortened delay time possible by adding diffusion-weighted imaging?

PURPOSE

To determine whether the diagnostic performance of combined gadoxetic acid-enhanced dynamic phases and diffusion-weighted imaging (DWI) is comparable to the standard protocol with hepatobiliary phase (HBP) and DWI for detection and characterization of focal liver lesions in chronic liver disease.

MATERIALS AND METHODS

A total of 176 patients with 181 HCCs, 15 cholangiocarcinomas, and 32 benign lesions were included. Three combined gadoxetic acid-enhanced and DWI sets (dynamic phases [arterial, portal, and 3-min delay {3-min set} and dynamic phases with 10-min HBP [10-min set] or 20-min HBP [20-min set]) were analyzed by two observers to determine the diagnostic accuracy and sensitivity in detection of malignancy, and ability for lesion characterization.

RESULTS

There was a trend, although not statistically significant, toward highest diagnostic accuracy and sensitivity for detecting malignancies in the 20-min set (mean, 0.945, 96.2), followed by the 10-min set (0.937, 95.9), and the 3-min set (0.923, 94.1) (P > 0.05). For lesion characterization, three image sets were equivalent (P > 0.05).

CONCLUSION

For lesion detection and characterization in chronic liver diseases, 3-min set with DWI showed comparable efficacy to 10-min or 20-min set. However, the best diagnostic performance could be achieved by combination of all image sets.

Efficacy of HGF carried by ultrasound microbubble-cationic nano-liposomes complex for treating hepatic fibrosis in a bile duct ligation rat model, and its relationship with the diffusion-weighted MRI parameters

Hepatic fibrosis is a major consequence of liver aggression. Finding novel ways for counteracting this damaging process, and for evaluating fibrosis with a non-invasive imaging approach, represent important therapeutic and diagnostic challenges. Hepatocyte growth factor (HGF) is an anti-fibrosis cell growth factor that induces apoptosis in activated hepatic stellate cells, reduces excessive collagen deposition, and stimulates hepatocyte regeneration. Thus, using HGF in gene therapy against liver fibrosis is an attractive approach. The aims of the present study were: (i) to explore the efficacy of treating liver fibrosis using HGF expression vector carried by a novel ultrasound microbubble delivery system; (ii) to explore the diagnostic interest of diffusion-weighted MRI (DWI-MRI) in evaluating liver fibrosis. We established a rat model of hepatic fibrosis. The rats were administered HGF linked to novel ultrasound micro-bubbles. Progression of hepatic fibrosis was evaluated by histopathology, hydroxyproline content, and DWI-MRI to determine the apparent diffusion coefficient (ADC). Our targeted gene therapy produced a significant anti-fibrosis effect, as shown by liver histology and significant reduction of hydroxyproline content. Moreover, using DWI-MRI, the b value (diffusion gradient factor) was equal to 300s/mm(2), and the ADC values significantly decreased as the severity of hepatic fibrosis increased. Using this methodology, F0-F2 could be distinguished from F3 and F4 (P<0.01). This is the first in vivo report of using an ultrasound microbubble-cationic nano-liposome complex for gene delivery. The data indicate that, this approach is efficient to counteract the fibrosis process. DWI-MRI appears a promising imaging technique for evaluating liver fibrosis.

Characterizing non-gaussian, high b-value diffusion in liver fibrosis: Stretched exponential and diffusional kurtosis modeling

PURPOSE

To employ the stretched exponential and diffusional kurtosis models to study the non-Gaussian behavior of diffusion-related signal decay of the liver in an animal model of hepatic fibrosis.

MATERIALS AND METHODS

High b-value diffusion imaging data (up to 3500 s/mm(2) ) of ex vivo murine liver specimens was acquired using a 9.4 T MRI scanner. A simple monoexponential model as well as the stretched exponential and diffusional kurtosis models were employed to analyze the diffusion data, the results of which were correlated with liver histopathology.

RESULTS

Strong correlations between histopathological assessments of hepatic fibrosis and parameters derived from the stretched exponential and diffusional kurtosis models were found. Using Akaike's Information Criterion (AIC) analyses, the kurtosis model was found to result in an improved fit of the high b-value diffusion data when compared to both the monoexponential and stretched exponential models.

CONCLUSION

The use of diffusional kurtosis or stretched exponential models, applied to the characterization of the non-Gaussian behavior of the molecular diffusion of liver exhibited over an extended b-factor range, affords the potential for an increased capability of magnetic resonance imaging (MRI) in the characterization of chronic liver disease.

Liver lobe volumes and the ratios of liver lobe volumes to spleen volume on magnetic resonance imaging for staging liver fibrosis in a minipig model

OBJECTIVE

To investigate liver lobe volumes and the ratios of liver lobe volumes to spleen volume measured with magnetic resonance imaging (MRI) for quantitatively monitoring and staging liver fibrosis.

METHODS

Animal study was approved by Institutional Animal Care and Use Committee. Sixteen minipigs were prospectively used to model liver fibrosis, and underwent abdominal gadolinium-enhanced MRI on 0, 5(th), 9(th), 16(th) and 21(st) weekend after modeling this disease staged by biopsy according to METAVIR classification system. On MRI, volume parameters including left lateral liver lobe volume (LLV), left medial liver lobe volume (LMV), right liver lobe volume (RV), caudate lobe volume (CV), and spleen volume (SV) were measured; and LLV/SV, LMV/SV, RV/SV and CV/SV were calculated. Statistical analyses were performed for staging this fibrosis.

RESULTS

LLV and CV increased with increasing stage of fibrosis (r = 0.711, 0.526, respectively; all P < 0.05). RV and LMV increased from stage 0 to 2 and decreased from 2 to 4; and RV/SV decreased from 0 to 1, increased from 1 to 2, and decreased from 3 to 4 (all P > 0.05). LLV/SV, LMV/SV and CV/SV decreased from stage 0 to 4 (r = -0.566, -0.748 and -0.620, respectively; all P < 0.05). LLV, CV, LLV/SV, LMV/SV, RV/SV, and CV/SV could distinguish stage 0-1 from 2-4 and 0-2 from 3-4 (all P < 0.05). Among these parameters, LLV and LMV/SV could best classify stage ≥2 and ≥3, respectively (area under receiver operating characteristic curve = 0.893 and 0.946, respectively).

CONCLUSION

LLV and LMV/SV complement each other in staging liver fibrosis, and both parameters should be used to stage this disease.

Spleen magnetic resonance diffusion-weighted imaging for quantitative staging hepatic fibrosis in miniature pigs: An initial study

AIM

To determine whether spleen diffusion-weighted imaging (DWI) parameters might classify liver fibrosis stage.

METHODS

Sixteen miniature pigs were prospectively used to model liver fibrosis, and underwent spleen DWI by using b = 300, 500 and 800 s/mm(2) on 0, 5th, 9th, 16th and 21st weekend after the beginning of modeling. Signal intensity ratio of spleen to paraspinous muscles (S/M), spleen exponential apparent diffusion coefficient (eADC) and apparent diffusion coefficient (ADC) for each b-value were statistically analyzed.

RESULTS

With increasing stages of fibrosis, S/M for all b-values showed a downward trend; and spleen eADC and ADC for b = 300 s/mm(2) showed downward and upward trends, respectively (all P < 0.05). The area under the receiver-operator curve (AUC) of spleen DWI parameters was 0.777 or more by S/M for classifying each fibrosis stage, and 0.65 or more by eADC and 0.648 or more by ADC for classifying stage ≥3 or cirrhosis. Among the spleen DWI parameters, S/M for b = 300 s/mm(2) was the best parameter in classifying stage 1 or more, 2 or more and 3 or more with AUC of 0.875, 0.851 and 0.843, respectively; and spleen eADC for b = 300 s/mm(2) was best in classifying stage 4 with an AUC of 0.988.

CONCLUSION

Spleen DWI may be used to stage liver fibrosis.

Diffusion analysis with triexponential function in hepatic steatosis

Our purpose was to assess the influence of liver steatosis on diffusion by triexponential analysis. Thirty-three patients underwent diffusion-weighted magnetic resonance imaging with multiple b values for perfusion-related diffusion, fast free diffusion, and slow restricted diffusion coefficients (D p, D f, D s) and fractions (F p, F f, F s). They also underwent dual-echo gradient-echo imaging for measurement of the hepatic fat fraction (HFF). Of these, 13 patients were included in the control group and 20 in the fatty liver group with HFF >5 %. The parameters of the two groups were compared by use of the Mann-Whitney U test. The relationships between diffusion coefficients and HFFs were assessed by use of the Pearson correlation. D p and D f were reduced significantly in the steatotic liver group compared with those in the control group (D p = 27.72 ± 6.61 × 10(-3) vs. 33.33 ± 6.47 × 10(-3) mm(2)/s, P = 0.0072; D f = 1.70 ± 0.53 × 10(-3) vs. 2.06 ± 0.40 × 10(-3) mm(2)/s, P = 0.0224). There were no significant differences in the other parameters between the two groups. Furthermore, D p and D f were correlated with HFF (P < 0.0001, r = -0.64 and P = 0.0008, r = -0.56, respectively). Decreased liver perfusion in steatosis caused the reduction in D p, and extracellular fat accumulation and intracellular fat droplets in steatosis led to the reduction in D f. Thus, the influence of hepatic steatosis should be taken into consideration when triexponential function analysis is used for assessment of diffuse liver disease.

Diffusion-weighted MRI of hepatocellular carcinoma in cirrhosis

The internationally accepted diagnostic criteria for hepatocellular carcinoma (HCC) in cirrhosis are highly accurate for large tumours, but offer relatively low sensitivity for small (<2 cm) tumours. Diffusion-weighted imaging (DWI) is a functional magnetic resonance imaging (MRI) technique that has been studied extensively as an aid to visualize various abdominal malignancies, including HCC in cirrhosis. DWI maps water diffusivity, which in HCC may be restricted as a result of changes ensuing from hepatocarcinogenesis. The present review is based on up-to-date evidence and describes the strengths and weaknesses of DWI, both as a standalone technique and as an adjunct sequence to conventional protocols, in the diagnosis, staging, prognostication, and assessment of treatment response of HCC in cirrhosis.

Focal nodular hyperplasia: characterisation at gadoxetic acid-enhanced MRI and diffusion-weighted MRI

PURPOSE

The aim of this study was to assess the enhancement patterns of hepatic focal nodular hyperplasia (FNH) on gadoxetic acid-enhanced MRI and diffusion-weighted (DW) MRI.

METHODS

This retrospective study had institutional review board approval. Gadoxetic acid-enhanced and DW MR images were evaluated in 23 patients with 30 FNHs (26 histologically proven and 4 radiologically diagnosed). The lesion enhancement patterns of the hepatobiliary phase images were classified as heterogeneous or homogeneous signal intensity (SI), and as dominantly high/iso or low SI compared with those of adjacent liver parenchyma. Heterogeneous (any) SI lesions and homogeneous low SI lesions were categorised into the fibrosis group, whereas homogeneous high/iso SI lesions were categorised into the non-fibrosis group. Additionally, lesion SI on T2 weighted images, DW images and apparent diffusion coefficient (ADC) values were compared between the two groups.

RESULTS

The lesions showed heterogeneous high/iso SI (n=16), heterogeneous low SI (n=5), homogeneous high/iso SI (n=7) or homogeneous low SI (n=2) at the hepatobiliary phase MR images. The fibrosis group lesions were more likely to show high SI on DW images and T2 weighted images compared with those in the non-fibrosis group (p<0.05). ADC values tended to be lower in the fibrosis group than those in the non-fibrosis group without significance.

CONCLUSION

FNH showed variable enhancement patterns on hepatobiliary phase images during gadoxetic acid-enhanced MRI. SI on DW and T2 weighted images differed according to the fibrosis component contained in the lesion.

ADVANCES IN KNOWLEDGE

FNH shows a wide spectrum of imaging findings on gadoxetic acid-enhanced MRI and DW MRI.

Diffusion-weighted imaging (DWI) of the spleen in patients with liver cirrhosis and portal hypertension

OBJECTIVE

The purpose of this study was to assess the influence of liver cirrhosis and portal hypertension on diffusion coefficients of the spleen.

MATERIAL AND METHODS

We retrospectively evaluated 50 patients with liver cirrhosis and 50 patients without any history of liver disease who underwent magnetic resonance imaging of the upper abdomen, including echo planar diffusion-weighted imaging using b values of 50, 300 and 600mm(2)/s. Spleen apparent diffusion coefficient (ADC), liver ADC, muscle ADC and normalized spleen ADC (defined as the ratio of spleen ADC to muscle ADC) were compared between cirrhotic patients and patients in the control group and correlated with Child-Pugh stages. Reproducibility was assessed by measuring interclass correlation coefficient (n=11). Additionally, in eight patients, ADC measurements were performed 1 day before and 3 days after transjugular intrahepatic portosystemic shunt (TIPSS) implantation.

RESULTS

Compared with control subjects, patients with cirrhosis and portal hypertension had significantly higher spleen ADCs (P=.0001). There was a statistically significant correlation between Child-Pugh grade and spleen ADC (Pearson correlation coefficient, observer 1 r=0.6, P=.0001; observer 2 r=0.5, P=.0001). After TIPSS implantation, we observed a reduction in spleen ADC values. Spleen ADC measurements showed a high reproducibility (interclass correlation coefficient 0.75, P=.001).

CONCLUSION

Our data suggest that different stages of liver cirrhosis and portal hypertension correlate with ADC values of the spleen. Furthermore, ADC values of the spleen decrease after TIPSS implantation. Further studies are required to understand the potential clinical values of these observations.

Diffusion-weighted MRI of the abdomen: current value in clinical routine

Magnetic resonance imaging (MRI) provides high tissue contrast without ionizing radiation exposure and unenhanced images are often diagnostic. Therefore, MRI is especially an attractive tool for patients with allergies for gadolinium-based contrast agents or renal failure. Technical advantages have led to the increasing use of diffusion-weighted (DW) MRI in abdominal imaging, which provides qualitative and quantitative information of tissue cellularity and the integrity of cellular membranes. This review article presents the current status of noncontrast MRI with the focus of DW-MRI. Technical background and clinical applications are explained and discussed.