Abstract
PurposeThis study was aimed to experimentally and numerically investigate the feasibility of measuring cerebral white matter perfusion using pseudocontinuous arterial spin labeling (PCASL) 3T magnetic resonance imaging (MRI) at a relatively fine resolution to mitigate partial volume effect from gray matter.Materials and MethodsThe Institutional Research Ethics Committee approved this study. On a clinical 3T MR system, ten healthy volunteers (5 females, 5 males, age = 28±3 years) were scanned after providing written informed consent. PCASL imaging was performed with varied combinations of labeling duration (τ = 1000, 1500, 2000, and 2500 ms) and post-labeling delay (PLD = 1000, 1400, 1800, and 2200 ms), at a spatial resolution (1.56x1.56x5 mm3) finer than commonly used (3.5x3.5 mm2, 5-8 mm in thickness). Computer simulations were performed to calculate the achievable perfusion-weighted signal-to-noise ratio at varied τ, PLD, and transit delay.ResultsBased on experimental and numerical data, the optimal τ and PLD were found to be 2000 ms and 1500-1800 ms, respectively, yielding adequate SNR (~2) to support perfusion measurement in the majority (~60%) of white matter. The measurement variability was about 9% in a one-week interval. The measured white matter perfusion and perfusion ratio of gray matter to white matter were 15.8-27.5 ml/100ml/min and 1.8-4.0, respectively, depending on spatial resolution as well as the amount of deep white matter included.ConclusionPCASL 3T MRI is able to measure perfusion in the majority of cerebral white matter at an adequate signal-to-noise ratio by using appropriate tagging duration and post-labeling delay. Although pixel-wise comparison may not be possible, region-of-interest based flow quantification is feasible.
Highlights
Abundant studies have revealed a close relationship between cerebral perfusion and brain function as well as physiology [1,2]
While the majority of CBF related studies have focused on gray matter, aberrant white matter perfusion has been observed in schizophrenia [7], normal pressure hydrocephalus [8], and multiple sclerosis [9]
Obtained from the sixth slice of the same subject in Figure 1, data in Figure 2 shows that with post-labeling delay (PLD) fixed at 1800 ms, dM increases with τ and reaches a plateau when τ is around 2000 ms, whereas no τ dependence is observed in dM intensity when control/labeling pulses are applied distally
Summary
Abundant studies have revealed a close relationship between cerebral perfusion ( referred to as cerebral blood flow, CBF) and brain function as well as physiology [1,2]. Arterial spin labeling (ASL) magnetic resonance imaging (MRI) is a technique devised to measure perfusion free of administering exogenous contrast medium [10]. With ASL, the protons of arterial blood that feeds the area one wishes to measure perfusion from are magnetically labeled (or tagged) by radiofrequency (RF) pulses through inversion or saturation, and serve as an endogenous tracer. ASL has proven capable of providing reliable flow measurement in gray matter [11,12] whereas its feasibility in white matter is still under debate [13,14]
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