Examination of Tissue Perfusion by Arterial Spin Labeling (ASL)

Abstract

Arterial spin labeling (ASL) is a non-invasive magnetic resonance technique for tissue perfusion quantification working without contrast media application. The method uses magnetically labeled blood protons as intrinsic tracer. Perfusion-weighted images are obtained by the signal difference between an image with proximal labeling of the arterial water protons and a control image. Initially designed for cerebral perfusion measurement, the ASL technique is increasingly being used for the evaluation of extracranial organs which might be attributed to the improvements in scanner, coil and sequence technology but also to the elaboration of postprocessing tools. In this review, the basic principles of ASL are explained. Technical difficulties in ASL sequence design are discussed. To illustrate the potential role of ASL in clinical research and diagnostics, comparison of ASL with other methods currently applied for perfusion assessment is performed. Finally, a variety of clinical applications of ASL is presented with respect to the current literature.

Inhibition of Pediatric Glioblastoma Tumor Growth by the Anti-Cancer Agent OKN-007 in Orthotopic Mouse Xenografts

“…Perfusion is defined as the amount of blood delivered to capillary beds in a given tissue per unit time. Delivery of blood to a capillary bed is a critical indicator of tissue viability and function, and the analysis of perfusion [ 83 ], which has markedly contributed to the understanding of physiological and pathological processes in the human body [ 84 ]. Furthermore, the ASL technique has been useful for monitoring the effects of agents designed to modulate tumor blood flow and oxygenation (e.g., carbogen gas) [ 85 ], and for evaluating and guiding the use of anti-angiogenic agents [ 42 ].…”

Striate Artery Infarct After Bilateral Carotid Artery Ligation (BCAL) in a Dog: A Multimodal MRI Study

“…In this case, cerebral perfusion was measured using ASL. This technique uses the protons of the blood as endogenous tracers by applying radiofrequency pulses at the level of the carotid arteries ( 23 – 25 ). In humans delayed arrival of the arterial blood to the brain and reduced CBF has been detected with carotid artery stenosis using ASL with multiple post-labeling delays ( 26 ).…”

Pseudocontinuous Arterial Spin Labeling: Clinical Applications and Usefulness in Head and Neck Entities

“…CASL is the first ASL method documented for perfusion quantification, which requires one single long labeling time, typically 1–3 s, using constant RF energy [ 38 ]. The signal in the image slice is recorded after the end of the labeling pulse [ 41 ]. Perfusion quantification can be falsified by magnetization transfer (MT) effects that occur due to a longer labeling pulse duration, although CASL was initially considered to be easy to implement and provide high signal gain [ 41 , 42 ].…”

“…The signal in the image slice is recorded after the end of the labeling pulse [ 41 ]. Perfusion quantification can be falsified by magnetization transfer (MT) effects that occur due to a longer labeling pulse duration, although CASL was initially considered to be easy to implement and provide high signal gain [ 41 , 42 ]. Additionally, the continuous high-frequency pulse can transfer marked radiofrequency power to a patient exceeding the safety level of the specific absorption rate at higher field strengths [ 43 ].…”

“…PASL was proposed in 1994 [ 44 , 45 ] and employs a single short pulse with a total duration of 10–20 ms to invert a thick slab of arterial water spins, with 10–20 cm thickness [ 38 ]. The signal is recorded in the imaging slice after a defined time, which is termed the inversion time [ 41 ] or the labeling duration. There are much smaller MT effects and a lower specific absorption rate in PASL than in CASL [ 45 ].…”