MRI of retinal and choroidal blood flow with laminar resolution

• Published in: NMR in biomedicine Vol. 24; no. 2; pp. 216 - 223
• Main Authors: Muir, Eric R., Duong, Timothy Q.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.02.2011
• Subjects: Anesthesia; Anesthetics; Animals; arterial spin labeling (ASL); Blood vessels; Choroid - blood supply; Differentiation; Female; high-resolution MRI; Isoflurane; Ketamine; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Male; Mice; Mice, Inbred C57BL; N.M.R; ophthalmology; perfusion; Photoreceptors; Regional Blood Flow - physiology; Retina; Retina - physiology; retinal diseases; xylazine
• ISSN: 0952-3480; 1099-1492; 1099-1492
• DOI: 10.1002/nbm.1576

The retina is nourished by two distinct circulations: the retinal vessels within the inner retina and the choroidal vessels behind the neural retina. The outer nuclear layer and the inner and outer segments of the photoreceptors in between are avascular. The aim of this study was to determine whether arterial spin labeling MRI could provide sufficient resolution to differentiate between quantitative retinal blood flow (rBF) and choroidal blood flow (chBF), and whether this technique is sufficiently sensitive to detect vascular‐specific blood flow (BF) changes modulated by anesthetics. Arterial spin labeling MRI was performed at 42 × 42 × 400 µm3 in the mouse retina at 7 T, and was used to investigate the effects of isoflurane and ketamine/xylazine anesthesia on rBF and chBF. MRI yielded unambiguous differentiation of rBF, chBF and the avascular layer in between. Under isoflurane, chBF was 7.7 ± 2.1 mL/g/min and rBF was 1.3 ± 0.44 mL/g/min (mean ± SD, n = 7, p < 0.01). Under ketamine/xylazine anesthesia in the same animals, chBF was 4.3 ± 1.9 mL/g/min and rBF was 0.88 ± 0.22 mL/g/min (p < 0.01). Under ketamine/xylazine anesthesia, rBF was lower by 29% (P < 0.01) and chBF by 42% (P < 0.01) relative to isoflurane. This study demonstrates, for the first time, the quantitative imaging of rBF and chBF in vivo, providing a new method to study basal values and alterations of rBF and chBF. Copyright © 2010 John Wiley & Sons, Ltd. This study demonstrates that arterial spin labeling (ASL) MRI at 42×42×400µm3 at 7 T provides sufficient resolution to differentiate quantitative retinal blood flow (rBF) and choroidal blood flow (chBF), and the avascular layer in between, in mouse retina (which is approximately 270µm thick including the choroid). ASL MRI also detected vascular‐specific blood flow (BF) changes modulated by two anesthetics (isoflurane and ketamine/xylazine). Under isoflurane, chBF was 7.7±2.1mL/g/min and rBF was 1.3±0.44mL/g/min (mean±SD, n=7, p<0.01). Under ketamine/xylazine in the same animals, chBF was 4.3±1.9mL/g/min and rBF was 0.88±0.22mL/g/min (p<0.01).