Assessment of liver fibrosis using fast strain‐encoded MRI driven by inherent cardiac motion

Abstract

Purpose An external driver-free MRI method for assessment of liver fibrosis offers a promising non-invasive tool for diagnosis and monitoring of liver disease. Lately, the heart’s intrinsic motion and MR tagging have been utilized for the quantification of liver strain. However, MR tagging requires multiple breath-hold acquisitions and substantial post-processing. This work proposes a fast strain-encoded (FSENC) MRI methodology to measure the peak strain (Sp) in the liver’s left lobe, which is in close proximity and caudal to the heart. Additionally, a new method is introduced to measure heart-induced shear wave velocity (SWV) inside the liver. Methods Phantom and in-vivo experiments (11 healthy subjects, and 11 patients with liver fibrosis) were conducted. Reproducibility experiments were performed in seven healthy subjects. Results Peak liver strain Sp significantly decreased in fibrotic liver compared healthy liver (6.46%±2.27% vs. 12.49%±1.76%, P<0.05). Heart-induced SWV significantly increased in patients compared to healthy subjects (0.15±0.04 m/s vs. 0.63±0.32 m/s, P<0.05). Reproducibility analysis yielded no significant difference in Sp (P=0.47) or SWV (P=0.56). Conclusion Accelerated external driver-free noninvasive assessment of left liver lobe strain and shear wave velocity is feasible using strain-encoded MRI. The two measures significantly separate healthy subjects from patients with fibrotic liver.

Liver fibrosis: Review of current imaging and MRI quantification techniques

“…The final step is to select an ROI for measuring representative strain for each patient . Alternatively, strain‐encoded imaging gives a direct measurement of strain through a similar process that encodes strain into the signal by varying the spatial frequency of artificial tags in the image …”

Assessment of cardiac‐driven liver movements with filtered harmonic phase image representation, optical flow quantification, and motion amplification

“…However, in the right liver lobe, they identified little or no displacement. Harouni et al used fast strain‐encoded imaging at 3T which measures a left liver lobe strain, directly defined as the percentage change in length of the tissue compared with the tissue initial length before deformation. Sprengers et al studied bowel motion patterns in the abdomen by means of a continuous tagging, while Watanabe et al used tagging to evaluate the bending energy in patients with liver fibrosis.…”

“…However, in the right liver lobe, they identified little or no displacement. Harouni et al 19 These tagging methods were, however, not very sensitive to very small displacements, in contrast our approach did not deal with liver elastography and no strain maps were presented, but was able to detect and analyze very small movements in the right liver with motion amplification Interestingly, at a given location in the liver, we applied our method to detect the time interval inside the cardiac cycle for which the displacement is minimum (lowest amplitude, lowest velocity and acceleration). The minimum displacement trigger delay found with this approach matched the delay for which the DWI images were less affected by the cardiac-related signal loss.…”

MRI cine‐tagging of cardiac‐induced motion for noninvasive staging of liver fibrosis

“…This method, initially developed for cardiac imaging, uses a magnetization grid (or "tags") to track the underlying tissue deformation without extra hardware. Recent studies have assessed liver fibrosis using the tagging method with different postprocessing analyses, including bending energy measurement, Gabor filter, harmonic phase (HARP) analysis, and strain‐encoded MRI, the latter method measuring strain without the need for tagged images . Among these, the HARP postprocessing technique has stood out for its fast and automated analysis of tagged images, providing a measure of strain at each point of the liver .…”

“…Among these, the HARP postprocessing technique has stood out for its fast and automated analysis of tagged images, providing a measure of strain at each point of the liver . Most previous studies have compared normal volunteers to cirrhotic patients; therefore, the diagnostic accuracy of liver strain remains to be assessed in a representative patient population with a range of fibrosis stages.…”