Evidence of Tri-Exponential Decay for Liver Intravoxel Incoherent Motion MRI: A Review of Published Results and Limitations

Abstract

Diffusion weighted imaging (DWI) and intravoxel incoherent motion (IVIM) have been explored to assess liver tumors and diffused liver diseases. IVIM reflects the microscopic translational motions that occur in voxels in magnetic resonance (MR) DWI. In biologic tissues, molecular diffusion of water and microcirculation of blood in the capillary network can be assessed using IVIM DWI. The most commonly applied model to describe the DWI signal is a bi-exponential model, with a slow compartment of diffusion linked to pure molecular diffusion (represented by the coefficient Dslow), and a fast compartment of diffusion, related to microperfusion (represented by the coefficient Dfast). However, high variance in Dfast estimates has been consistently shown in literature for liver IVIM, restricting its application in clinical practice. This variation could be explained by the presence of another very fast compartment of diffusion in the liver. Therefore, a tri-exponential model would be more suitable to describe the DWI signal. This article reviews the published evidence of the existence of this additional very fast diffusion compartment and discusses the performance and limitations of the tri-exponential model for liver IVIM in current clinical settings.

Self-supervised neural network improves tri-exponential intravoxel incoherent motion model fitting in non-alcoholic fatty liver disease

“…The clinical implications are less clear in our cohort, as both the bi- and tri-exponential models showed comparable correlations with histopathology. However, NAFLD is known to cause vascular changes 26 , thus particularly the evaluation of the additional perfusion parameter f 2 could be of interest, as this signal originates from larger vessels 11 . We (visually) observed a large decrease in f 2 volumes with increasing levels of fibrosis (Figure 4), which could lead to radiological markers for disease severity.…”

“…For healthy volunteers, an overview of average tri-exponential IVIM-values was published in a recent review 11 . Values for ‫ܦ‬ ranged between 0.98-1.35 *10 -3 mm 2 /s which is in line with what we found with the IVIM 3 -NET and higher than our tri-exponential LSQ fit as seen in Table 1.…”

“…Recent literature suggests that the bi-exponential IVIM model may be insufficient for fitting the liver’s complex structure. The marked signal decay in the IVIM signal intensity plots seen at low b-values has given rise to the hypothesis that a tri-exponential model will provide a more accurate representation of the data and improve fit accuracy 11 . Herein, an extra exponent is added to improve this fitting of rapid signal decay at very low b-values: where diffusion ( D ), slow and fast pseudo-diffusion , and slow ( f 1 ) and fast perfusion fraction ( f 2 ) are estimated.…”

More promising results of liver intravoxel incoherent motion imaging analysis for the assessment of nonalcoholic steatohepatitis and fibrosis

“…One recent review suggested MRE had a summary AUC, sensitivity and specificity for diagnosing stage ≥F1 of 0.87, 71%, 85%, respectively (12). It is possible that additional approaches such as a combination all of all diffusion metrics and removal of b-value=0 s/mm 2 data from IVIM modeling can further improve the results of Troelstra et al As starting from b=0 image, the relationship between liver DWI signal and b-value does not follow bi-exponential decay (2,26), in our experience, removal of b-value=0 s/mm 2 data from IVIM modeling greatly improves the diagnostic performance of resulted IVIM parameters (2,9). The fact that slow diffusion measure and fast slow diffusion measures are mutually constrained further increases the necessity of checking all IVIM parameters together (instead of evaluating these parameters individually) (7,27).…”

Editorial for “Using Intravoxel Incoherent Motion and Dynamic Contrast‐Enhanced MR Imaging to Early Detect Tissue Injury and Microcirculation Alteration in Hepatic Injury Induced by Intestinal Ischemia Reperfusion in the Rat Model”

“…Recent advances in MRI technology have made it possible to acquire not only morphological information, but also functional information even in MR equipment of clinical use. In terms of hepatic functional information, diffusion and perfusion parameters such as apparent diffusion coefficient (ADC) measurement, bi‐exponential intravoxel incoherent motion (IVIM), 1 and tri‐exponential IVIM 2 technique are getting used in clinical analyses of liver disease. IVIM is first established by Le Bihan, 1 which is used as a quantitative parameter of diffusion and perfusion of water molecules.…”