Liver magnetic resonance diffusion weighted imaging: 2011 update

Standard-b-Value Versus Low-b-Value Diffusion-Weighted Imaging in Hepatic Lesion Discrimination: A Meta-analysis

OBJECTIVE

We sought to determine the comparative diagnostic performance of standard-b-value (500-1000s/mm) versus low-b-value (≤500 s/mm) diffusion-weighted imaging (DWI) in the discrimination of hepatic lesions.

METHODS

A total of 1775 hepatic malignant lesions and 1120 benign hepatic lesions from 21 studies were included.

RESULTS

(1) The global sensitivity was 0.86 (95% confidence interval [CI], 0.847-0.879), the specificity was 0.82 (95% CI, 0.797-0.842), the positive likelihood ratio (PLR) was 6.234 (95% CI, 4.260-9.123), the negative likelihood ratio (NLR) was 0.175 (95% CI, 0.135-0.227), and diagnostic odds ratio (DOR) was 42.836 (95% CI, 24.134-76.031). The area under the curve (AUC) and Q* index were 0.93 and 0.87. Publication bias was not present (P > 0.05). (2)The sensitivity of a subgroup meta-analysis of standard-b-value DWI was 0.858 (95% CI, 0.835-0.880), the specificity was 0.836 (95% CI, 0.807-0.863), the PLR was 6.527 (95% CI, 3.857-11.046), the NLR was 0.168 (95% CI, 0.123-0.239), and the DOR was 49.716 (95% CI, 22.897-107.98). The AUC and Q* index were 0.941 and 0.88. (3)The sensitivity of a subgroup meta-analysis of low-b-value DWI was 0.87 (95% CI, 0.84-0.89), the specificity was 0.80 (95% CI, 0.76-0.83), the PLR was 6.22 (95% CI, 3.29-11.76), the NLR was 0.19 (95% CI, 0.12-0.29), and the DOR was 37.14 (95% CI, 14.80-93.18). The AUC and Q* index were 0.922 and 0.86.

CONCLUSIONS

Hepatic DWI is useful in differentiating between malignant and benign hepatic lesions. Standard-b-value DWI displayed an overall superior diagnostic accuracy over low-b-value DWI. Further trials needed to determine whether increasing b values beyond 1000 s/mm affects the diagnostic accuracy of hepatic lesion discrimination.

Utility of Diffusion-Weighted MRI to Detect Changes in Liver Diffusion in Benign and Malignant Distal Bile Duct Obstruction: The Influence of Choice of b-Values

PURPOSE

The study sought to evaluate the potential of diffusion-weighted magnetic resonance imaging to detect changes in liver diffusion in benign and malignant distal bile duct obstruction and to investigate the effect of the choice of b-values on apparent diffusion coefficient (ADC).

METHODS

Diffusion-weighted imaging was acquired with b-values of 200, 600, 800, and 1000 s/mm². ADC values were obtained in 4 segments of the liver. The mean ADC values of 16 patients with malignant distal bile duct obstruction, 14 patients with benign distal bile duct obstruction, and a control group of 16 healthy patients were compared.

RESULTS

Mean ADC values for 4 liver segments were lower in the malignant obstruction group than in the benign obstruction and control groups using b = 200 s/mm² (P < .05). Mean ADC values of the left lobe medial and lateral segments were lower in the malignant obstruction group than in the benign obstructive and control groups using b = 600 s/mm² (P < .05). Mean ADC values of the right lobe posterior segment were lower in the malignant and benign obstruction groups than in the control group using b = 1000 s/mm² (P < .05). Using b = 800 s/mm², ADC values of all 4 liver segments in each group were not significantly different (P > .05). There were no correlations between the ADC values of liver segments and liver function tests.

CONCLUSION

Measurement of ADC shows good potential for detecting changes in liver diffusion in patients with distal bile duct obstruction. Calculated ADC values were affected by the choice of b-values.

Comparison of magnetic resonance elastography and diffusion-weighted imaging for staging hepatic fibrosis

Background:

To compare the diagnostic values of magnetic resonance elastography (MRE) and diffusion-weighted imaging (DWI) in staging hepatic fibrosis (HF) in an animal model.

Methods:

This study consisted of 44 rabbits served as HF group and 9 normal rabbits. HF group was divided into two subgroups: Group A (n = 32) and Group B (n = 12). Rabbits in Group B were served as a complementary group when rabbits in Group A suddenly died during the study. Rabbits from control and Group A underwent abdominal MR imaging (MRI), MRE, and DWI. In Group A, random eight rabbits underwent MRI examinations at 4, 5, 6, 10 weeks after carbon tetrachloride oil subcutaneous injection. Liver stiffness (LS) and apparent diffusion coefficient (ADC) values of liver parenchyma were measured. The diagnostic performance of MRE and DWI for staging HF was compared using the receiver operating characteristic curve analysis on the basis of the histopathological analysis of HF.

Results:

Significant differences of LS and DWI values were present among HF stages (P < 0.005). The LS values measured on MRE (r = 0.838, P < 0.001) were more strongly correlated with the HF stages than with ADC values (r = −0.527, P < 0.001). The area under the receiver operating characteristic curve values of LS were significantly larger than those of DWI were for discriminating two stages of HF (0.979 vs. 0.712 for ≥ S1, 0.922 vs. 0.699 for ≥ S2). MRE showed higher specificity for predicting all stages of HF compared to DWI.

Conclusions:

MRE more strongly correlated with the HF stages than DWI and is more specific in predicting all HF stages.

Recent advances in molecular magnetic resonance imaging of liver fibrosis

Liver fibrosis is a life-threatening disease with high morbidity and mortality owing to its diverse causes. Liver biopsy, as the current gold standard for diagnosing and staging liver fibrosis, has a number of limitations, including sample variability, relatively high cost, an invasive nature, and the potential of complications. Most importantly, in clinical practice, patients often reject additional liver biopsies after initiating treatment despite their being necessary for long-term follow-up. To resolve these problems, a number of different noninvasive imaging-based methods have been developed for accurate diagnosis of liver fibrosis. However, these techniques only reflect morphological or perfusion-related alterations in the liver, and thus they are generally only useful for the diagnosis of late-stage liver fibrosis (liver cirrhosis), which is already characterized by "irreversible" anatomic and hemodynamic changes. Thus, it is essential that new approaches are developed for accurately diagnosing early-stage liver fibrosis as at this stage the disease may be "reversed" by active treatment. The development of molecular MR imaging technology has potential in this regard, as it facilitates noninvasive, target-specific imaging of liver fibrosis. We provide an overview of recent advances in molecular MR imaging for the diagnosis and staging of liver fibrosis and we compare novel technologies with conventional MR imaging techniques.

Test-retest reliability of diffusion tensor imaging of the liver at 3.0 T

PURPOSE

This study was done to evaluate test-retest reliability of liver diffusion tensor imaging (LDTI).

MATERIALS AND METHODS

Ten healthy volunteers (median age 23 years) underwent two LDTI scans on a 3.0 T magnet during two imaging sessions separated by 2 weeks (session-1/-2, respectively). Fifteen gradient directions and b values of 0-1,000 s/mm(2) were used. Two radiologists in consensus assessed liver apparent diffusion coefficient (ADC) and fraction of anisotropy (FA) values on ADC and FA maps at four reference levels, namely: right upper level (RUL), right lower level (RLL), left upper level (LUL) and left lower level (LLL). We then assessed (a) whether ADC and FA values overlapped when measured on different levels within the same imaging session or between different imaging sessions; (b) the degree of variability on an intra-session and inter-session basis, respectively, using the coefficient of variation (CV).

RESULTS

In sessions 1 and 2, the ADC/FA values were significantly larger in the left liver lobe (LUL/LLL) compared to right liver lobe (RUL/RLL) (p < 0.05/6). Intra-session CVs were 9.51 % (session 1) and 9.73 % (session 2) for ADC, and 12.93 % (session 1) and 11.82 % (session 2) for FA, respectively. When comparing RUL, RLL, LUL and LLL on an inter-session basis, CVs were 6.52, 8.20, 6.52 and 11.06 % for ADC, and 15.42, 15.80, 15.42 and 6.80 % for FA, respectively.

CONCLUSION

LDTI provides consistent and repeatable measurements. However, since larger left lobe ADC/FA values can be attributed to artefacts, right lobe values should be considered the most reliable measurements of water diffusivity within the liver.

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.

Colorectal liver metastases: state of the art imaging

Colorectal cancer is a leading cause of death with mortality determined predominately by metastatic involvement of the liver. Treatment of liver metastases continues to evolve and imaging plays an essential role in initial staging, preoperative planning, and treatment monitoring. This review article discusses the current role of imaging in the management of patients with colorectal liver metastases. Particular challenges such as hepatic steatosis, disappearing metastases, and following treated lesions are addressed.