Arterial Transit Time‐Based Multidelay Combination Strategy Improves Arterial Spin Labeling Cerebral Blood Flow Measurement Accuracy in Severe Steno‐Occlusive Diseases

Abstract

Background Although perfusion imaging plays a key role in the management of steno‐occlusive diseases, the clinical usefulness of arterial spin labeling (ASL) is limited by technical issues. Purpose To examine the effect of arterial transit time (ATT) prolongation on cerebral blood flow (CBF) measurement accuracy and identify the best CBF measurement protocol for steno‐occlusive diseases. Study Type Prospective. Population Moyamoya (n = 10) and atherosclerotic diseases (n = 8). Field Strength/Sequence A 3.0T/3DT1‐weighted and ASL. Assessment Hadamard‐encoded multidelay ASL scans with/without vessel suppression (VS) and single‐delay ASL scans with long‐label duration (LD) and long postlabeling delay (PLD), referred to as long‐label long‐delay (LLLD), were acquired. CBF measurement accuracy and its ATT dependency, measured as the correlation between the relative CBF measurement difference (ASL—single‐photon emission computed tomography [SPECT]) and ATT, were compared among 1) Combo (incorporating multidelay and LLLD data based on ATT), 2) standard (LD/PLD = 1333/2333 msec), and 3) LLLD (LD/PLD = 4000/4000 msec) protocols, using whole‐brain voxel‐wise correlation with reference standard SPECT CBF. The effect of VS on CBF measurement accuracy was also assessed. Statistical Tests Pearson's correlation coefficient, repeated‐measures analysis of variance, t‐test. P< 0.05 was considered significant. Results Pearson's correlation coefficients between ASL and SPECT CBF measurements were as follows: Combo = 0.55 ± 0.09; standard = 0.52 ± 0.12; LLLD = 0.41 ± 0.10. CBF measurement was least accurate in LLLD and most accurate in Combo. VS significantly improved overall CBF measurement accuracy in the standard protocol and in moyamoya patients for the Combo. ATT dependency analysis revealed that, compared with Combo, the standard and LLLD protocols showed significantly lower and negative and significantly higher and positive correlations, respectively (standard = −0.12 ± 0.04, Combo = −0.04 ± 0.03, LLLD = 0.17 ± 0.03). Data Conclusion By using ATT‐corrected CBF derived from LD/PLD = 1333/2333 msec as a base and by compensating underestimation in delayed regions using multidelay scans, the ATT‐based Combo strategy improves CBF measurement accuracy compared with single‐delay protocols in severe steno‐occlusive diseases. Evidence Level 1 Technical Efficacy Stage 2

Reliability and Sensitivity to Longitudinal CBF Changes in Steno‐Occlusive Diseases: ASL Versus 123I‐IMP‐SPECT

“…The ATT‐corrected PLD = 2333 msec (tcCBF2) data were used to represent the ASL CBF in the main analysis. This is because it is closest to the PLD in the adult patient protocol (2000 msec) recommended in the consensus statement from the International Society for Magnetic Resonance in Medicine perfusion study group 29 and because it gave a higher correlation with the SPECT CBF measurement compared with those acquired with a PLD of 1000 and 3666 msec or LD/PLD of 4000/1000 and 4000/4000 msec in our previous study 6 …”

“…This is because it is closest to the PLD in the adult patient protocol (2000 msec) recommended in the consensus statement from the International Society for Magnetic Resonance in Medicine perfusion study group 29 and because it gave a higher correlation with the SPECT CBF measurement compared with those acquired with a PLD of 1000 and 3666 msec or LD/PLD of 4000/1000 and 4000/4000 msec in our previous study. 6 Data Processing Raw perfusion-weighted images from ASL scans, realigned to the saturation recovery reference M0 images, and SPECT images were normalized to the Montreal Neurological Institute (MNI) template by SPM12 (https://www.fil.ion.ucl.ac. uk/spm/software/spm12/).…”

“…ASL CBF images were smoothed using an 8-mm full-width at half-maximum Gaussian filter to obtain a smoothing radius comparable to that of the SPECT CBF. 6 All ASL and SPECT data were resampled to 2-mm isotropic-voxels.…”

“…ASL uses magnetically labeled arterial blood water as an endogenous tracer. 4,5 Several studies comparing ASL and positron emission tomography (PET) or single-photon emission computed tomography (SPECT) have reported the potential of ASL for delineating hypoperfused tissue [6][7][8][9] or detecting postoperative hyperperfusion syndrome 10 in the brain, similar to reference standard SPECT or PET. However, considering technical advances in ASL-such as the pseudo-continuous ASL technique for improved labeling efficiency, 11 background suppression, 12 and segmented three-dimensional (3D) readout module 13 for improved signal-to-noise ratio (SNR)state-of-the-art ASL might even be more sensitive to subtle CBF changes than conventional nuclear medicine examinations.…”

Enhanced Arterial Spin Labeling Magnetic Resonance Imaging of Cerebral Blood Flow of the Anterior and Posterior Circulations in Patients With Intracranial Atherosclerotic Stenosis

“…The disadvantages of eASL lie in the longer scanning time and low signal-to-noise ratio due to the short label durations ( Haller et al, 2016 ). Optimization of the number of post-label delay acquisitions and excitations to reduce the acquisition time with a sparse model-based image reconstruction ( Tsujikawa et al, 2016 ), and/or use of more complex but efficient Hadamard time-encoding strategies ( Amemiya et al, 2021 ), will be needed to establish guidelines for routine use in future clinical applications.…”