A strategy to optimize the signal-to-noise ratio in one-coil arterial spin tagging perfusion imaging

Abstract

The signal‐to‐noise ratio of the perfusion image (SNRperfu) in a spin‐tagging experiment is shown to depend on both the degree of spin labeling (α) and the signal‐to‐noise ratio of the proton density images (SNRimage) used to calculate the perfusion image. When a single radiofrequency (RF) coil is used for both spin tagging and magnetic resonance (MR) imaging, magnetization transfer (MT) effects decrease SNRimage, and therefore SNRperfu, by an amount that depends on the strength B1 and offset Δω (determined by the gradient strength Gl applied during spin tagging) of the labeling RF pulse. It is shown that by optimizing B1 and Gl, it is possible to reduce MT effects and thus increase SNRimage, while leaving α unchanged. As a result, SNRperfu will be improved. An equation for calculating perfusion under general conditions of such reduced MT effects is derived and shown to give perfusion rates that are independent of the strength and offset of the labeling RF irradiation. Magn Reson Med 41:563–568, 1999. © 1999 Wiley‐Liss, Inc.

Evolution of Magnetic Resonance Imaging Changes Associated with Cerebral Hypoxia-Ischemia and a Relatively Selective White Matter Injury in Neonatal Rats

“…T 1 maps were calculated within a single posterior coronal slice from a series of eight inversion-recovery T 1 -weighted Snapshot-FLASH images acquired in 5 min (TR ϭ 3.55 ms, TE ϭ 2.1 ms, increasing time of inversion delays of 234, 503, 831, 1233, 1751, 2480, 3728, 9226 ms). Perfusion imaging was performed in the same slice using an arterial spin labeling technique (14) (TR/TE ϭ 3.55/2.1 ms, flip angle ϭ 12 degrees, average of 32) with an adiabatic inversion pulse in a 1.5-G/cm field gradient followed by a TurboFLASH imaging sequence requiring the acquisition of a set of four images (two control and two inversion labeled) in 8 min. CBF (in mL/g/s) was calculated as CBF ϭ (1/T 1 ϩ ␦)(Mbcon Ϫ Mbinv)/2␣Mbcon, using , the blood-brain barrier partition coefficient, as 0.9, ␦ as 0.039 s…”

Intracranial Biomechanics of Acute Experimental Hydrocephalus in Live Rats

“…Details of the arterial spin-labeling method have been published previously. 22 Following a 400-ms posttagging delay, an adiabatic spin-labeling sequence with a 36-echo HASTE readout (repetition time 3.0 seconds, effective TE 12.5 ms, acceleration factor 1.7778) was used. Slice thickness was 2 mm, field of view was 4.0 cm · 4.0 cm, and matrix size was 128 · 72, resulting in an in-plane resolution of 313 · 555 mm.…”

Cerebral blood flow response to a hypoxic-ischemic insult differs in neonatal and juvenile rats

“…Perfusion imaging was performed using a quadrature volume coil to image both the head and neck as required to measure blood flow in a single coronal brain slice at approximately − 0.3 mm from bregma using an arterial spin-labeling technique [18] (Repetition Time (TR)/Echo Time (TE)=3.55/2.1ms, flip angle=12 • , average of 32). Proton shimming was initially performed to optimize field homogeneity within the slice.…”

“…Control images were obtained with the same radiofrequency excitation applied symmetrically opposite to the labeling plane. Two or four sets of proton density images with inversion labeling or controls were acquired and subtracted to eliminate magnetization transfer effects using the equation below [18]. The rate of CBF (ml/g/s) was calculated as…”