. Author manuscript; available in PMC: 2012 Apr 17.

Published in final edited form as: Nat Rev Cardiol. 2010 Oct 26;7(12):686–698. doi: 10.1038/nrcardio.2010.161

Table 1. Modalities for assessment of vascular reserve.

Method	Measured variable	Advantages	Limitations
Transcranial Doppler utrasonography	Ultrasound frequency shift reflecting flow velocity in large arteries	Temporal resolution (beat-to-beat ∼1s) Independent of body position	Insonation window, angle, and signal quality Constant artery diameter assumption
Three-dimensional continuous arterial spin labeling MRI	Arterial H⁺ spin tagging to measure blood flow	Spatial resolution Noninvasive measurements of regional perfusion	Standard template Signal averaging (∼30s per whole brain) T1 time prolongation by hematocrit Magnetic resonance field inhomogeneities
Blood-oxygen-level-dependent MRI	T2*-weighted imaging to detect differences in oxygenated and deoxygenated hemoglobin	Coupling between regional neuronal activity and blood flow, with a basis on changes of blood oxygenation	Indirect measure of blood flow and activity Signal averaging (∼5s) Standard template Magnetic resonance field inhomogeneities
Single photon emission computed tomography	Technetium-99	Spatial resolution	Signal averaging (∼30s per projection, typically 64 projections) Invasive