MRI of blood flow of the human retina

Abstract

This study reports a high-resolution MRI approach to image basal blood flow and hypercapnia-induced blood-flow changes in the unanesthetized human retina on a 3-Tesla MRI scanner. Pseudo-continuous arterial-spin-labeling technique with static-tissue suppression was implemented to minimize movement artifacts and improve blood-flow sensitivity. Turbo spin-echo acquisition was used to achieve high spatial resolution free of susceptibility artifacts. The size, shape and position of a custom-made receive radiofrequency coil were optimized for sensitivity in the posterior retina. Synchronized eye blink and respiration to the end of each data readout minimized eye movement and physiological fluctuation. Robust high-contrast blood-flow MRI of the unanesthetized human retina was obtained at 500×800μm2 in-plane resolution. Blood flow in the posterior retina was 93±31mL/100mL/min (mean±SD, N=5). Hypercapnic inhalation (5% CO2) increased blood flow by 12±2% relative to air (P<0.01, N=5). This study demonstrates the feasibility of blood-flow MRI of the retina of unanesthetized human. Because blood flow is tightly coupled to metabolic function under normal conditions and it is often perturbed in diseases, this approach could provide unique insights into retinal physiology and serve as an objective imaging biomarker for disease staging and testing of novel therapeutic strategies. This approach could open up new avenue of retinal research.

Blood Flow MRI of the Human Retina/Choroid during Rest and Isometric Exercise

“…11,13 Briefly, pCASL used maximum labeling gradient ¼ 6 mT/m, labeling duration ¼ 2000 ms, and postlabeling delay ¼ 1500 ms with balanced gradient scheme. The control images were acquired with a 1808 phase shift to the labeling radiofrequency (RF) pulse.…”

“…The feasibility of MRI to image quantitative retina/choroid BF in the human retina was recently demonstrated under basal 10,11 and gaschallenge conditions. 11 The goal of the present study was to explore a novel application of BF MRI to investigate BF changes in the retina/ choroid complex associated with isometric exercise in the unanesthetized human retina. A custom-made receive-only eye coil was used to improve SNR on a 3-Tesla clinical MRI scanner.…”

Evaluating anesthetic protocols for functional blood flow imaging in the rat eye

“…This interest is attributable to the importance of ocular blood flow as a parameter in studies of ocular pathophysiology and its potential to serve as an early marker of a variety of ocular diseases, including age-related macular degeneration, diabetic retinopathy, and glaucoma. The importance of ocular blood flow has driven the development of multiple measurement technologies including retinal/dynamic vessel analysis, 1 microsphere methods, [2][3][4] laser Doppler-based velocimetry [5][6][7][8] and flowmetry, [9][10][11] laser speckle imaging, [11][12][13] magnetic resonance imaging (MRI), [14][15][16] color Doppler ultrasound imaging, [17][18][19] and optical coherence tomography (OCT). [20][21][22][23][24][25][26][27][28][29][30][31] En face Doppler OCT, the modality used in this study, is a noninvasive, OCT-based technique that measures the Doppler velocities in the en face plane.…”

Layer-Specific Manganese-Enhanced MRI of the Retina in Light and Dark Adaptation

“…These approaches have been applied to study retinal degeneration, 5,12 diabetic retinopathy, 14 and glaucoma 15 in animal models. More recently, feasibility of anatomical, 16 BOLD, 17 and blood-flow 18,19 MRI of the human retina have also been demonstrated.…”