Perfusion imaging

Abstract

Measurement of tissue perfusion is important for the functional assessment of organs in vivo. Here we report the use of 1H NMR imaging to generate perfusion maps in the rat brain at 4.7 T. Blood water flowing to the brain is saturated in the neck region with a slice-selective saturation imaging sequence, creating an endogenous tracer in the form of proximally saturated spins. Because proton T1 times are relatively long, particularly at high field strengths, saturated spins exchange with bulk water in the brain and a steady state is created where the regional concentration of saturated spins is determined by the regional blood flow and regional T1. Distal saturation applied equidistantly outside the brain serves as a control for effects of the saturation pulses. Average cerebral blood flow in normocapnic rat brain under halothane anesthesia was determined to be 105 +/- 16 cc.100 g-1.min-1 (mean +/- SEM, n = 3), in good agreement with values reported in the literature, and was sensitive to increases in arterial pCO2. This technique allows regional perfusion maps to be measured noninvasively, with the resolution of 1H MRI, and should be readily applicable to human studies.

Quantifying CBF with arterial spin labeling

“…With ASL the agent also is labeled water, and the relaxation of the magnetization plays the role of radioactive decay of the 15 O. Much of the original mathematical modeling of ASL experiments was taken directly from earlier models developed for PET studies (2,5), in particular the single-compartment PET model for the kinetics of the tracer. However, there is a key difference between the PET and ASL experiments that makes the single-compartment model inappropriate for ASL: the time scale for a PET study is on the order of 1 minute, while the time scale for an ASL experiment is on the order of 1 second, which is too short for the assumption of a well-mixed compartment.…”

Correlation between arterial blood volume obtained by arterial spin labelling and cerebral blood volume in intracranial tumours

“…As an alternative to DSC-MRI, with regard to cerebral blood flow (CBF) quantification, arterial spin labelling (ASL) techniques have shown considerable potential [10][11][12][13]. ASL does not require injection of contrast agent and is thus completely non-invasive.…”

Measurement of cerebral perfusion territories using arterial spin labelling

“…The first perfusion imaging studies were performed using a single RF coil to perform both the ASL as well as to excite the imaging volume of interest in the brain (36,37). When a single labeling/imaging RF coil is used, the off-resonance RF pulse required for ASL saturates macromolecules in the brain, resulting in a large spatially dependent decrease of the signal intensity due to magnetization transfer (MT) effects (38).…”