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Abstract
Cerebral blood arrival and tissue transit times are sensitive measures of the efficiency
of tissue perfusion and can provide clinically meaningful information on collateral
blood flow status. We exploit the arterial blood oxygen level dependent (BOLD) signal
contrast established by precisely decreasing, and then increasing, arterial hemoglobin
saturation using respiratory re-oxygenation challenges to quantify arterial blood
arrival times throughout the brain. We term this approach the Step Hemoglobin re-Oxygenation
Contrast Stimulus (SHOCS). Carpet plot analysis yielded measures of signal onset (blood
arrival), global transit time (gTT) and calculations of relative total blood volume.
Onset times averaged across 12 healthy subjects were 1.1 ± 0.4 and 1.9 ± 0.6 for cortical
gray and deep white matter, respectively. The average whole brain gTT was 4.5 ± 0.9 s.
The SHOCS response was 1.7 fold higher in grey versus white matter; in line with known
differences in tissue-specific blood volume fraction. SHOCS was also applied in a
patient with unilateral carotid artery occlusion revealing ipsilateral prolonged signal
onset with normal perfusion in the unaffected hemisphere. We anticipate that SHOCS
will further inform on the extent of collateral blood flow in patients with upstream
steno-occlusive vascular disease, including those already known to manifest reductions
in vasodilatory reserve capacity or vascular steal.