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Timothy Q. Duong, Yi Zhang, Oscar San Emeterio Nateras, Qi Peng; Quantitative Blood Flow MRI of the Human Retina during Normocarpnia, Hypercapnia and Isometric Exercise. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2884.
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The purpose of the present study was to develop and apply magnetic resonance imaging (MRI) to image quantitative blood flow (BF) during normocapnia, hypercapnia, isometric exercise (handgrip) in the unanesthetized human retina.
MRI was performed on 5 healthy subjects with normal vision on a 3-Tesla MRI scanner with a custom-made high-sensitivity eye coil. A single axial image transecting the optic nerve head at 0.5*0.8*3.0 mm3 was acquired. Serial BF MRI was acquired continuously during 4 minutes (mins) normocapnia (air) followed by 4 mins hypercapnia (5% CO2 in air). Similarly, BF MRI was acquired during 1 min rest and 1 min squeezing of a stress ball, with the rest-exercise cycle repeated 3 times. Physiological parameters were monitored continuously during MRI scanning.
Quantitative BF image showed excellent BF contrast under basal condition, with high BF localized to the posterior retina. The group-averaged BF from a large region of interest at the posterior retina/choroid complex was 93±31mL/100mL/min (mean±SD, N=5). Hypercapnia increased BF by 12±2% relative to air (P<0.01, paired t-test). Isometric exercise increased BF by 44±15%, heart rate by 21±8%, mean arterial pressure by 20±8%, and ocular perfusion pressure by 27±6% (P<0.05 for all), but did not change intraocular pressure, arterial O2 saturation, End-tidal CO2, and respiration rate (P>0.1 for all).
This study demonstrates quantitative BF MRI during normocapnia, hypercapnia and isometric exercise in the human retina. Given that BF is intricately coupled to basal metabolic function under normal physiological conditions and it’s often perturbed in retinal diseased states, BF MRI has the potential to provide clinically relevant, depth-resolved and quantitative information on BF regulation in the normal and diseased retinas. Future studies will need to improve sensitivity and spatiotemporal resolution to detect retinal and choroidal BF and incorporate three-dimensional BF mapping. This approach could open up new avenues for retinal research and complement existing retinal imaging techniques.
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