Published online Jun 21, 2020. doi: 10.3748/wjg.v26.i23.3304
Peer-review started: December 30, 2019
First decision: February 18, 2020
Revised: March 26, 2020
Accepted: May 29, 2020
Article in press: May 29, 2020
Published online: June 21, 2020
Liver fibrosis (LF) is a common pathological feature of all chronic liver diseases. Liver biopsy is the current reference standard in detecting and staging LF. However, liver biopsy is invasive, observer dependent, and prone to sampling variability, all of which hampers its widespread use in clinical practice; thus, a noninvasive method to quantify LF is urgently needed. Recently, magnetic resonance imaging techniques have been increasingly applied to LF detection and staging and could possibly be the noninvasive alternative to liver biopsy. With the accumulation of extracellular matrix in the fibrotic liver, the true molecular water diffusion and perfusion-related diffusion would be restricted. Intravoxel incoherent motion (IVIM) could capture the information of tissue diffusivity and microcapillary perfusion separately and reflect the fibrotic severity with diffusion coefficients.
IVIM, a bi-exponential model based on diffusion-weighted imaging, allows for the separate evaluation of true molecular diffusion and perfusion-related diffusion. Although several recent studies focused on the diagnostic performances of IVIM in LF staging, the reported results were discrepant among studies
With more eligible studies and patients included, the purpose of this meta-analysis is to investigate the diagnostic performance of IVIM in different LF stages with histology as reference.
A comprehensive literature search was conducted to identify studies on the diagnostic accuracy of IVIM for assessment of histology proven LF. The stages of LF were classified as F0 (no fibrosis), F1 (portal fibrosis without septa), F2 (periportal fibrosis with few septa), F3 (septal fibrosis) and F4 (cirrhosis), according to histopathological findings. Data were extracted to calculate the pooled sensitivity, specificity, positive and negative likelihood ratios and diagnostic odds ratio, as well as the area under the summary receiver operating characteristic curve (AUC) in each group.
Twelve studies with 923 subjects were included in this meta-analysis with 5 studies (n = 465) for LF ≥ F1, 9 studies (n = 757) for LF ≥ F2, 4 studies (n = 413) for LF ≥ F3 and 6 studies (n = 562) for LF = F4. The pooled sensitivity and specificity were estimated to be 0.78 (95% confidence interval: 0.73-0.82) and 0.81 (0.74-0.86) for LF ≥ F1 detection with IVIM; 0.82 (0.79-0.86) and 0.80 (0.75-0.84) for staging F2 fibrosis; 0.85 (0.79-0.90) and 0.83 (0.77-0.87) for staging F3 fibrosis, and 0.90 (0.84-0.94) and 0.75 (0.70-0.79) for detecting F4 cirrhosis, respectively. The AUCs for LF ≥ F1, F2, F3, F4 detection were 0.862 (0.811-0.914), 0.883 (0.856-0.909), 0.886 (0.865-0.907) and 0.899 (0.866-0.932), respectively. Moderate to substantial heterogeneity was observed with inconsistency index (I2) ranging from 0% to 77.9%. No publication bias was detected.
IVIM is a noninvasive tool with good diagnostic performance in detecting and staging LF. Optimized and standardized IVIM protocols are needed for further improving its diagnostic accuracy in clinical practice.
The results showed that IVIM is a valuable tool in noninvasively detecting and staging LF. However, field strength, the number and distribution of b-values, as well as the triggering methods would affect the diagnostic accuracy. There is still a need to establish an optimized and standardized IVIM protocol for LF diagnosis in clinical practice.