Contrast ultrasound imaging of the ocular circulation
Purpose. Many ocular structures may be visualized using ultrasound. We speculated that, with use of an ultrasound contrast agent, it would be possible to obtain images of ocular blood vessels not usually visible because of their size or location. Also, we evaluated the feasibility of measuring retinal perfusion using this methodology. Methods. Adult dogs (20-25 kg) were anesthetized using halothane and oxygen, and mechanically ventilated to maintain normoxia and normocarbia. A 7.5 mHz ultrasound transducer was held in place on the cornea. An intravenous (iv) catheter was placed in the inferior vena cava, and a pigtail catheter was advanced from a femoral artery into the left ventricle of the heart. 2-D and color doppler ultrasound images were recorded to videotape using an HP Sonos 2500 ultrasound machine. An ultrasound contrast agent (FS069, Molecular Biosystems, Inc) was injected either iv or into a left ventricular catheter. Time-intensity curves were analyzed off-line using gamma-variate analysis. Results. After iv injection of FS069 in doses as small as 0.1 ml, doppler images of posterior ciliary arteries were significantly enhanced. IV injections of as much as 10 ml produced minimal contrast enhancement in the retina/choroid. With left ventricular injection of 2-3 ml, gray-scale enhancement of 2-D images was clearly evident in the retina/choroid, an effect that was present for 1-2 minutes. Increases in ultrasound power significantly decreased retina/choroid image enhancement after FS069. Conclusions. The study demonstrated the feasibility of contrast ultrasound measurement of retinal perfusion, using intra-arterial injection of contrast agent. IV injection of remarkably small doses may permit visualization of ocular blood vessels not routinely imaged. These benefits of contrast ultrasound may be useful in the evaluation of patients with vascular disorders of the retina or optic nerve.
Roth, S; Block, R; Park, SS; Fernandez, A; Lupu, VD; Aronson, S; Feinstein, SB
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