Comparison of Retinal and Cerebral Blood Flow Between Continuous Arterial Spin Labeling MRI and Fluorescent Microsphere Techniques

Purpose: To compare basal retinal and cerebral blood flow (BF) values using continuous arterial spin labeling (CASL) MRI and fluorescent microspheres. Materials and Methods: A total of 41 animals were used. BF was measured using an established microsphere technique (a mixture of 2.5 million 8 mm green and 0.5 million 10 mm blue fluorescent microspheres) and CASL MRI blood flow measurement in the rat retina and brain at 7 Tesla (T) and 11.7T, respectively. Results: Retinal BF by MRI was 1.18 +/- 0.57 mL/g/min and choroidal BF was 8.14 +/- 1.8 mL/g/min (n = 6). Microsphere retinal BF was 9.12 +/- 2.8 mu L/min per tissue and choroidal BF was 73.38 +/- 44 mL/min per tissue (n = 18), corresponding to a retinal BF value of 1.22 +/- 0.36 mL/g/min by means of a wet weight conversion. The wet-weight of the choroid could not be determined. To corroborate our findings, cerebral BF (CBF) by MRI was also analyzed. In the cerebral cortices, CBF was 0.91 +/- 0.29 mL/g/min (n = 14) by CASL MRI and 1.09 +/- 0.37 mL/g/min (n = 6) by microspheres. There were no significant differences found between MRI and microsphere blood flow in the retina and brain. Conclusion: BF values in the rat retina and cerebral cortex by MRI are in agreement with those obtained by the microsphere technique.