Continuous Arterial Spin Labeling (CASL) in clinical practice at 3.0 T – Results on Reliability and Quantification

Purpose: Continuous Arterial spin labeling (CASL) is a know alternative to DSC, where the T1 relaxation of magnetized “labeled“ protons are used as a freely diffusible intrinsic contrast medium. The positive aspect of this method is that the absolute cerebral blood flow is to be quantified

Due to its dependence on the T1 relaxation time of the blood and the SNR, the acquisition was highly time consuming und the brain coverage limited to a few slices at field strengths up to 1.5 Tesla. These boundaries restricted the common use of CASL in clinical diagnostics and should be improved by using clinical high field MRI scanners for CASL.

In order to explore the new opportunities at high field, especially at a clinical whole body 3 Tesla systems it seamed necessary to evaluate the “Single Coil CASL“ technique in a clinical setting concerning reliability and quantification of this technique.

Methods: Prospective continuous arterial spin labeling (CASL) perfusion study in routine clinical examinations in patients and volunteers at 3 Tesla MRI. The datasets were analyzed regarding the image quality, motion artifacts and quantitative values in normal white and gray matter and pathologies. 154 Patients and Volunteers (Mean age 35±17) were examined at an Intera 3.0T MR System (Philips Medical Systems, Best, The Netherlands) using a standard Transmit/Receive Head Coil for single coil CASL. We used a SSH – SE EPI Sequence (TR/TE 4000–4500/37–39 ms, 11–17 slices, thickness 5–8mm, matrix 64×64, labeling delay“ 700–1200 ms, 20–50 dyn. scans, max. scan time 6min). All CASL datasets were analyzed for motion using the a Pride/IDL CASL-Tool (PMS, Best, NL/Idl. Inc., USA). Prior to calculation of CBF maps (LCQP-CASLTools, Radiology University of Bonn, Germany – based on Detre et al.), all acquired datasets were realigned using the SPM2 package (Wellcome Department of Imaging Neuroscience, GB). A visual grading of the CBF Maps was performed using a 3-point Scale (not diagnostic, adequate, good) and the datasets were analyzed regarding motion artefacts.

An automated ROI analysis was performed on spatially normalized CASL CBF maps in Cortex and White Matter, the unit of cerebral perfusion is ml/min/100g.

Results: The visual grading showed that 115/154 (74%) datasets were of good diagnostic quality. 21/154 (14%) datasets were of adequate diagnostic quality, whereas 18/154 (12%) datasets were not of diagnostic quality. Decreased diagnostic quality as in the majority of cases (32/154) due to motion, and only in 3 cases due to technical problems during acquisition.

A mean CBF in the withe matter of 14ml/min/100g (SD±2.6) and a mean CBF of 36ml/min/100g (SD±4.3) was calculated, resulting in a Grey/White Matter ratio of approx. 2.5.

Conclusion: Single Coil CASL can be used reliable in clinical routine at 3.0 Tesla. Image quality of the CASL-Perfusion maps was of diagnostic value in the majority (88%) of the examinations.