Altered Blood Flow in the Ophthalmic and Internal Carotid Arteries in Patients with Age-Related Macular Degeneration Measured Using Noncontrast MR Angiography at 7T

Abstract

Background and purpose: Age-related macular degeneration is associated with reduced perfusion of the eye; however, the role of altered blood flow in the upstream ophthalmic or internal carotid arteries is unclear. We used ultra-high-field MR imaging to investigate whether the diameter of and blood flow in the ophthalmic artery and/or the ICA are altered in age-related macular degeneration and whether any blood flow changes are associated with disease progression.

Materials and methods: Twenty-four patients with age-related macular degeneration and 13 similarly-aged healthy controls participated. TOF and high-resolution dynamic 2D phase-contrast MRA (0.26 × 0.26 × 2mm³, 100-ms effective sampling rate) was acquired at 7T. Vessel diameters were calculated from cross-sectional areas in phase-contrast acquisitions. Blood flow time-series were measured across the cardiac cycle.

Results: The ophthalmic artery vessel diameter was found to be significantly smaller in patients with age-related macular degeneration than in controls. Volumetric flow through the ophthalmic artery was significantly lower in patients with late age-related macular degeneration, with a significant trend of decreasing volumetric ophthalmic artery flow rates with increasing disease severity. The resistance index was significantly greater in patients with age-related macular degeneration than in controls in the ophthalmic artery. Flow velocity through the ophthalmic artery and ICA was significantly higher in patients with age-related macular degeneration. Ophthalmic artery blood flow as a percentage of ipsilateral ICA blood flow was nearly double in controls than in patients with age-related macular degeneration.

Conclusions: These findings support the hypothesis that vascular changes upstream to the eye are associated with the severity of age-related macular degeneration. Additional investigation into the potential causality of this relationship and whether treatments that improve ocular circulation slow disease progression is warranted.

FIG 1.

Positioning of PC-MRA slices using the 3D-TOF-MRA data as an anatomic guide. A, Red lines depict cross-sections of the triple-oblique positioning and location of PC-MRA slices centered on and perpendicular to each OA (green arrows), identified from the reference 3D-TOF image. The OA cross-section can be visualized in the center of the magnitude (B and C) and phase (D and E) images from a PC-MRA scan (yellow box represents an enlarged region from B and D in C and E, respectively).

FIG 2.

Analysis procedure for correcting EC bias and defining the vessel ROI. A, A PC-MRA magnitude image is used to place a 12-mm-diameter ROI for EC correction in vessel-free tissue adjacent to the vessel ROI (blue). The red line in the inset TOF image indicates the PC-MRA slice position. The vessel ROI (yellow) is shown within the yellow box, which depicts the region enlarged in B and C. Enlarged PC-MRA magnitude images show the vessel cross-section alone (B) and with the vessel ROI superimposed (C). D, Time-series of EC-corrected flow data in units of centimeters/second from 1 example PC-MRA acquisition with a single VENC value in 1 subject.

FIG 3.

Boxplots of unnormalized flow velocities (A and B) and volumetric flow rates (C and D) in the OAs (A and C) and ICAs (B and D). Vessels were divided into 4 groups: healthy controls, early AMD, intermediate AMD, and late AMD. The asterisk signifies P < .05 compared with controls.

FIG 4.

Linear trend test plot, which demonstrates that the rate of decline in OA volumetric flow with disease progression is statistically significant.

FIG 5.

Boxplots of flow velocity (A) and volumetric flow (B) in the OA normalized to upstream ICA flow rates. Normalized flow values represent the OA flow as a ratio of ICA flow. Vessels are divided into 4 groups: healthy controls, early AMD, intermediate AMD, and late AMD. The asterisk signifies P < .05 compared with controls.

FIG 6.

Resistance indices for the OA (A) and ICA (B). Vessels are divided into 4 groups: healthy controls, early AMD, intermediate AMD, and late AMD. The asterisk signifies P < .05 compared with controls.