Temporal and Spatial Variances in Arterial Spin-Labeling Are Inversely Related to Large-Artery Blood Velocity

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Fig 1.
Vascular characteristics of the bilateral (left and right) internal carotid (LICA and RICA) and vertebral arteries (LVA and RVA) for each group. Panel 3 shows the relative contribution to total CBF by each vessel.
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Fig 2.
The association of mean blood velocity with GM-CBF (panel 1), ASL-to-PC ratio for whole-brain CBF (panel 2), ASL temporal SNR (panel 3), and CBF spatial CoV (panel 4). Velocity is shown as a weighted mean of all 4 extracranial vessels relative to their contribution to total CBF. GM-CBF is uncorrected for labeling efficiency. Age, sex, and group-adjusted linear models are reported in Table 3.
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Fig 3.
GM-CBF between groups calculated with 2 labeling efficiency estimates. White bars incorporate a constant labeling efficiency (ie, 0.85), and gray bars incorporate individual labeling efficiency based on the ASL-to-PC ratio for whole-brain CBF. Post hoc group comparisons are indicated at P_Bonferroni < .05 for differences from the young group (asterisk) and differences from old group (dagger) within the same calibration technique.

Table 1:

Participant characteristics^{^a}

	Young	Old	WMH	Stroke	P Value
No.	15	22	15	30
Age (range) (yr)	25.7 ± 4.6 (20–36)	69.1 ± 7.0^{^b} (55–81)	72.0 ± 8.2^{^b} (51–83)	67.9 ± 10.4^{^b} (51–88)	<.001
Sex, female (%)	7 (47)	17 (77)	8 (53)	9 (30)	.009
Hemodynamics
ICA mean velocity (cm/s)	18.2 ± 4.5	11.9 ± 2.9^{^b}	10.3 ± 3.3^{^b}	9.7 ± 3.1^{^b}	<.001
ICA area (cm²)	0.21 ± 0.04	0.24 ± 0.06	0.26 ± 0.06	026 ± 0.09	.102
VA mean velocity (cm/s)	10.0 ± 2.5	6.7 ± 1.6^{^b}	6.5 ± 1.7^{^b}	5.6 ± 2.1^{^b}	<.001
VA area (cm²)	0.13 ± 0.03	0.13 ± 0.03	0.14 ± 0.04	0.12 ± 0.03	.190
PC-CBF (mL/100 g/min)	49.0 ± 8.5	41.4 ± 8.1	40.6 ± 12.9	33.8 ± 6.3^{^b,^c}	<.001
ASL-CBF (mL/100 g/min)	44.1 ± 10.2	40.8 ± 8.8	31.4 ± 9.6^{^b,^c}	34.3 ± 10.5^{^b}	<.001

Note:—VA indicates vertebral artery.
↵a Data are mean ± SD or count (proportion). Area and velocity are reported as the mean of bilateral vessels. ASL-CBF is uncorrected for labeling efficiency.
↵b Group differences compared with the young group at P_Bonferroni < .05.
↵c Group differences compared with the old group at P_Bonferroni < .05.

Table 2:

Comparison of MRI methods for whole-brain CBF estimation^{^a}

Table 3:

Linear regression parameters for the association of extracranial mean blood velocity and cross-sectional area with ASL characteristics^{^a}

Model	Independent Variables	β	95% CI	T-Statistic	P Value
GM-CBF	Area (cm²)	46.5	(8.2–84.7)	2.03	.046
Adjusted R² = 0.43	Velocity (cm/s)	1.5	(0.8–2.3)	3.42	.001
ASL-CBF:PC-CBF	Area (cm²)	−0.79	(−1.58–0.01)	−1.65	.103
Adjusted R² = 0.21	Velocity (cm/s)	−0.02	(−0.04–0.01)	−2.78	.007
GM-temporal SNR	Area (cm²)	1.78	(0.24–3.32)	1.93	.058
Adjusted R² = 0.47	Velocity (cm/s)	0.07	(0.04–0.10)	3.99	<.001
GM-spatial CoV	Area (cm²)	−0.11	(−0.61–0.39)	−0.36	.720
Adjusted R² = 0.31	Velocity (cm/s)	−0.01	(−0.02–0.00)	−2.01	.048