Comparison of BOLD and ASL

Biomedical Imaging Technology Center

BOLD, ASL & CBV [Home] [Archive] [BOLD, ASL and CBV]

Abbreviations

BOLD = Blood Oxygenation Level Dependent
ASL = Arterial Spin Labeling
(r)CBF = (regional) Cerebral Blood Flow
(r)CBV = (regional) Cerebral Blood Volume
(r)MTT = (regional) Mean Transmit Time
SPECT = Single Photon Emission Computed Tomography
PET = Positron Emission Tomography
BBB = Brain Blood Barrier

Definitions

rCBV(μL/g) = [Volume of blood in a voxel(μL)]/[Mass of the voxel(g)]

rCBV(%) = 100 • [Volume of blood in a voxel(μL)]/[Volume of the voxel(μL)]

rCBV(%) = 0.104 rCBV(μL/g)

rCBF(μLg^-1second^-1) =[Net blood flow through the voxel(μLsecond^-1)]/[Mass of the voxel(g)]

rMTT = rCBV / rCBF

Comparison between imaging characteristics of fMRI using BOLD and ASL perfusion contracts

ref: J.A. Detre, J. Wang / Clinical Neurophysiology 113 (2002) 621-634, Table 1

	BOLD	ASL perfusion
Signal mechanism	Blood flow, blood volume, oxygenation consumption	Blood flow
Contrast parameter	T2^*	T1
Spatial specificity	Venules and draining veins	Capillaries, arterioles
Typical signal change	0.5-5%	<1%
Imaging methods	Gradient-echo Offset spin-echo	Gradient-echo Spin-echo
Optimal task frequency (block design)	0.01-0.06 Hz	<0.01 Hz
Sample rate (TR)	1-3 s per image	3-8 s per perfusion image
Relative contrast-to-noise ratio	>2 with high task frequency <0.5 with low task frequency	1
Intersubject variability	High	Low
Image coverage	Whole brain	Part or most of brain cortex
Major artifacts	Susceptibility; motion; baseline drift	Vascular artifact

Typical CBV and CBF Values, Obtained Using Non-NMR Methods

ref: Barbier et al. / JMRI 13 (2001) 496-520, Table 1

Tissue	CBV	Method	Reference	CBF	Method	Reference
Human brain	48.4 μL g^-1	SPECT	Sakai et al., JCBFM 5 (1985) 207-213	9.66 μL g^-1 s^-1	PET	Martin et al., JCBFM 11 (1991) 684-689
Baboon	31 μL g^-1	PET	Archer et al., Anesthesiology 72 (1990) 1031-1037	7.33 μL g^-1 s^-1	PET	Archer et al., Anesthesiology 72 (1990) 1031-1037
Rat brain, cortical parietal surface	34 μL g^-1	Optical technique: bolus tracking	Shockley et al., Brain Res. 454 (1988) 170-178	24 μL g^-1 s^-1	Optical technique: bolus tracking	Shockley et al., Brain Res. 454 (1988) 170-178
Rat, whole brain	26.7 μL g^-1	Autoradiography	Todd et al., JCBFM 13 (1993) 328-336	16.8 μL g^-1 s^-1	Autoradiography	Todd et al., JCBFM 13 (1993) 328-336