Hepatic arterial spin labelling MRI: an initial evaluation in mice.

R Ramasawmy,M F Lythgoe,R B Pedley,J A Wells,A E Campbell‐Washburn,S P Johnson,S Walker‐Samuel

doi:10.1002/nbm.3251

Abstract

The development of strategies to combat hepatic disease and augment tissue regeneration has created a need for methods to assess regional liver function. Liver perfusion imaging has the potential to fulfil this need, across a range of hepatic diseases, alongside the assessment of therapeutic response. In this study, the feasibility of hepatic arterial spin labelling (HASL) was assessed for the first time in mice at 9.4 T, its variability and repeatability were evaluated, and it was applied to a model of colorectal liver metastasis. Data were acquired using flow-sensitive alternating inversion recovery-arterial spin labelling (FAIR-ASL) with a Look–Locker readout, and analysed using retrospective respiratory gating and a T1-based quantification. This study shows that preclinical HASL is feasible and exhibits good repeatability and reproducibility. Mean estimated liver perfusion was 2.2 ± 0.8 mL/g/min (mean ± standard error, n = 10), which agrees well with previous measurements using invasive approaches. Estimates of the variation gave a within-session coefficient of variation (CVWS) of 7%, a between-session coefficient of variation (CVBS) of 9% and a between-animal coefficient of variation (CVA) of 15%. The within-session Bland–Altman repeatability coefficient (RCWS) was 18% and the between-session repeatability coefficient (RCBS) was 29%. Finally, the HASL method was applied to a mouse model of liver metastasis, in which significantly lower mean perfusion (1.1 ± 0.5 mL/g/min, n = 6) was measured within the tumours, as seen by fluorescence histology. These data indicate that precise and accurate liver perfusion estimates can be achieved using ASL techniques, and provide a platform for future studies investigating hepatic perfusion in mouse models of disease. Copyright © 2014 John Wiley & Sons, Ltd.

Highlights

The application of arterial spin labelling (ASL) to the liver has not been undertaken extensively, possibly because of the liver’s complex blood supply and respiratory-induced artefacts, and has been restricted to a limited number of clinical investigations [1,2]
Fast spin echo images with the perfusion map overlaid on the liver parenchyma, such as those shown in Figure 3D, revealed that high, nonphysiological perfusion values are present within the major vasculature, as the perfusion model is not valid in these regions
Mean liver perfusion, estimated using Equation [1] in all datasets acquired in this study, was 2.2 ± 0.3 mL/g/min

Summary

Introduction

The application of arterial spin labelling (ASL) to the liver has not been undertaken extensively, possibly because of the liver’s complex blood supply and respiratory-induced artefacts, and has been restricted to a limited number of clinical investigations [1,2] Alternative approaches, such as contrast-enhanced computed tomography, Doppler ultrasound and radioactive microspheres [3], have used perfusion to predict the onset of hepatocyte dysfunction [4], monitor tumour therapy [5] and inform on post-transplant success [6]. The vasculature of the liver is unique, in that the portal vein delivers approximately 75% of the blood [10], whilst the remaining 25% is drawn from the hepatic artery This dual supply means that the quantification of liver blood flow can be challenging, and requires careful consideration of acquisition and modelling methods. Pedley UCL Cancer Institute, Paul O’Gorman Building, London, UK

Methods

Results

Conclusion