Technical Advances in Body ASL
Charlotte Buchanan1

1School of Physics and Astronomy, Sir Peter Mansfield Imaging Centre, Nottingham, United Kingdom


There have been a number of recent advances in body ASL. ASL has been applied in the heart, liver, kidney and placenta with studies using ASL in diseases such as diabetes, compensated liver cirrhosis and chronic kidney disease. There are however a number of considerations that are required for use of ASL in the body including which labelling and readout schemes to use and how to deal with respiratory and cardiac motion. Efforts are now needed to harmonise techniques and assess variation in sensitivity, specificity and reproducibility in order to make ASL a clinically useable tool for body applications.


Physicists, radiologists, imaging scientists and MR technologists.


To describe the use of Arterial Spin Labelling (ASL) in the body, highlighting the recent technical advances and describing the associated challenges.


Arterial spin labelling (ASL) is an MRI technique that provides a non-contrast enhanced method to assess tissue perfusion using the intrinsic signal from water in the body. ASL is now becoming a well-established technique in the brain, however applications of ASL in the body are currently limited. To date, in the body ASL has been applied in the heart (1, 2), liver (3), kidney (4, 5), pancreas (6) and placenta (7).

Given the importance of tissue hypoxia and ischaemia to many disease processes, measurement of tissue perfusion using a non-invasive, repeatable method is of clinical relevance. Current techniques to assess perfusion include the use of gadolinium based contrast agents, which are contraindicated in kidney disease due to the risk of nephrogenic systemic fibrosis, and limited for dynamic studies. The development of non-invasive ASL to study abdominal organs is thus important.


There are a number of considerations when applying ASL in the body. First, is the choice of how to label the magnetisation of the inflowing blood, with an option of either pulsed ASL (PASL) or pseudo continuous ASL (pCASL) each having associated pros and cons. There is also the question of which image readout scheme to use (8), with the choice dictating the achievable spatial resolution and number of slices acquired. Finally, there is the decision of how to deal with respiratory motion, with the added complication of cardiac motion for cardiac ASL.

The intrinsically low SNR of ASL leads to large number of signal averages and so a number of repeats required, and motion between these must be minimised. There are many techniques to overcome respiratory motion which include respiratory triggering, breath-holding or use of a navigator echo. Alternatively, motion correction and data sorting techniques can be applied in post-processing to eliminate any motion artefacts. To eliminate cardiac motion, cardiac triggering can be applied using a vectorcardiogram (VCG) or peripheral pulse unit (PPU). Background suppression methods can also be applied to supress any static tissue (9), although this can also decrease the measured perfusion signal.

There have been a number studies that use ASL in clinical studies of kidney and liver disease. Some of these studies combine assessment of organ perfusion with other measures such as T1 relaxation time mapping, diffusion measures and T2* mapping to assess multiparametric changes in disease. Studies have shown a decrease in renal perfusion with diseases such as Acute Kidney Injury (10), diabetes (11) and Chronic Kidney Disease (12). In liver disease, a decrease in liver perfusion as measured with ASL has been demonstrated in patients with compensated cirrhosis (13). There has also been studies looking at the application of ASL of the placenta, including a recent study that applied ASL in the placenta in pregnancies complicated by fetal heart disease (14). Recent work has also looked at cardiac ASL, with applications in dialysis patients (15).

Studies have also applied ASL at 7T to study kidney perfusion (16). 7T provides the advantage of increased SNR and a longer blood and tissue T1, this leads to a reduction in acquisition time as less ASL pairs are required to be averaged, which could minimise motion related artefacts. However, there are significant additional challenges associated with ASL at 7T. The increase of magnetic field strength increases the susceptibility induced inhomogeneity of the B0 field leading to image distortion and signal loss. In addition, the local power deposition, as measured by the specific absorption rate (SAR), is increased at higher field strength.

One major challenge in making body ASL a clinically useable tool is the current lack of large studies to validate or compare the variants in terms of sensitivity, specificity, reproducibility and change with disease. Although MRI vendors are now providing ASL sequences for use in the brain, sequences available for body ASL are limited.


There have been a number of recent advances in body ASL, with studies using ASL in clinical applications. However, to make ASL a clinically useable tool for body applications there now needs to be efforts to harmonise techniques and assess variation in sensitivity, specificity and reproducibility.


No acknowledgement found.


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Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)