Staging liver fibrosis on multiparametric MRI in a rabbit model with elastography, susceptibility-weighted imaging and T1ρ imaging: a preliminary study

On the relationship between metabolic capacities and in vivo viscoelastic properties of the liver

The liver is the central metabolic organ. It constantly adapts its metabolic capacity to current physiological requirements. However, the relationship between tissue structure and hepatic function is incompletely understood; this results in a lack of diagnostic markers in medical imaging that can provide information about the liver's metabolic capacity. Therefore, using normal rabbit livers, we combined magnetic resonance elastography (MRE) with proteomics-based kinetic modeling of central liver metabolism to investigate the potential role of MRE for predicting the liver's metabolic function in vivo. Nineteen New Zealand white rabbits were investigated by multifrequency MRE and positron emission tomography (PET). This yielded maps of shear wave speed (SWS), penetration rate (PR) and standardized uptake value (SUV). Proteomic analysis was performed after the scans. Hepatic metabolic functions were assessed on the basis of the HEPATOKIN1 model in combination with a model of hepatic lipid-droplet metabolism using liquid chromatography-mass spectrometry. Our results showed marked differences between individual livers in both metabolic functions and stiffness properties, though not in SUV. When livers were divided into 'stiff' and 'soft' subgroups (cutoff SWS = 1.6 m/s), stiff livers showed a lower capacity for triacylglycerol storage, while at the same time showing an increased capacity for gluconeogenesis and cholesterol synthesis. Furthermore, SWS was correlated with gluconeogenesis and PR with urea production and glutamine exchange. In conclusion, our study indicates a close relationship between the viscoelastic properties of the liver and metabolic function. This could be used in future studies to predict non-invasively the functional reserve capacity of the liver in patients.

Detection of tumour boundary in metastatic liver disease with 2D multibreath-hold susceptibility-weighted imaging

PURPOSE

To investigate the feasibility of susceptibility weighted imaging (SWI) in detecting tumour boundaries in metastatic liver disease (MLD) without contrast agent, and whether SWI can provide pathophysiologic information for preoperative evaluation.

METHODS

Thirty patients with MLD underwent tumour resection. All patients underwent conventional MRI (T1-weighted and T2-weighted imaging), contrast-enhanced (CE) MRI and multibreath-hold 2D SWI. The conspicuity of the tumour boundary was assessed using a 4-grade scale. The detection rate of tumour boundaries and areas were reviewed and measured. The longest dimension was used to estimate the tumour size from the MR image. The conspicuity of the tumour boundary and area were compared using a nonparametric multi-group comparison (Friedman M). The McNemar test was applied to examine differences in the detection rate of tumour boundaries.

RESULTS

Among four different MRI sequences, SWI exhibited increased conspicuity of the tumour boundary than the conventional MRI (P < 0.001). SWI (91.8%) and CE-MRI (64.4%) exhibited higher detection rates of the tumour boundary than T1WI and T2WI (6.8% and 12.3% respectively). Longer tumour maximum diameters were measured with SWI (29.1 ± 17.2 mm) and CE-MRI (28.2 ± 16.8) compared to conventional MRI (P < 0.05).

CONCLUSION

2D multibreath-hold SWI enables enhanced noninvasive detection of tumour boundaries in patients with MLD compared with conventional MRI and CE-MRI without using an exogenous contrast agent. SWI has the potential to become a preoperative assessment standard that complements conventional MRI.

Comparing and combining MRE, T1ρ, SWI, IVIM, and DCE-MRI for the staging of liver fibrosis in rabbits: Assessment of a predictive model based on multiparametric MRI

PURPOSE

To establish and validate an optimal predictive model based on multiparametric MRI for staging liver fibrosis (LF) in rabbits with magnetic resonance elastography (MRE), spin-lattice relaxation time in the rotating frame (T1ρ imaging), SWI, intravoxel incoherent motion (IVIM), and DCE-MRI.

METHODS

The LF group included 120 rabbits induced by subcutaneous injections of carbon tetrachloride (CCl₄ ); 30 normal rabbits served as the control group. Multiparametric MRI was performed, including MRE, T1ρ, SWI, IVIM, and DCE-MRI. The quantitative parameters were analyzed in two groups, with histopathological results serving as the reference standard. The diagnostic performance of multiparametric MRI and the predictive model established by multivariable logistic regression analysis were evaluated by receiver operating characteristic (ROC) curve analysis.

RESULTS

In total, 32, 67, and 51 rabbits were histologically diagnosed as no fibrosis (stage F0), early-stage LF (F1-F2), and advanced-stage LF (F3-F4), respectively. The LF stages presented a strong correlation with liver stiffness (LS) on MRE (r = 0.90), signal-intensity ratio (SIR) on SWI (r = -0.84), and K^trans on DCE-MRI (r = 0.71; p < 0.05 for all). The LS and SIR parameters had higher AUC values for distinguishing early-stage LF from both no fibrosis (0.94 and 0.93, respectively) and advanced-stage LF (0.95 and 0.87, respectively). The predictive model showed a slightly higher AUC value of 0.97 (0.90-0.99) than LS and SIR in distinguishing early-stage LF from no fibrosis (p > 0.05), a significantly higher AUC value of 0.98 (0.93-0.99) than the SIR in distinguishing early-stage from advanced-stage LF (p < 0.05).

CONCLUSION

SWI, DCE-MRI, and MRE in particular showed improved performance for LF diagnosis and stage. The predictive model based on multiparametric MRI was found to further enhance diagnostic accuracy and could serve as an excellent imaging tool for staging LF.