Purpose
Mean transit time (MTT) is defined as the volume/flow ratio of a capillary bed and reflects tissue perfusion delay. Using high speed fluorescein angiography (FA), image registration algorithm and deconvolution method, MTT of retina was automatically calculated and analyzed with other perfusion factors.
Methods
A camera type FA capable of recording an image of 1920 square pixels at 20 frames per second was constructed. Sodium fluorescein (4.0 mL of a 10%) was injected into the antecubital vein to all 6 normal subjects. Automatic image registration was performed to correct saccadic eye movements with the nonlinear diffusion feature extraction (KAZE) method. After selection of the specific major arteries and veins, MTT was calculated by deconvolution method using time series of the fluorescein intensity of each vessel. The relationship between arteriovenous passage time (AVP), arteriovenous transit time (AVT), peak arterial time (PA), peak venous time (PV) and MTT was investigated using correlation analysis.
Results
The mean age of subjects was 35.2 ± 6.1 years and 24 major arteries and veins were selected. The mean MTT was 1.970 ± 0.898 s. The mean AVP, AVT, PA, and PV were 1.450 ± 0.454, 11.227 ± 1.339, 5.400 ± 1.113, and 7.280 ± 1.368 s. MTT showed a strong correlation with AVP (r = 0.736, p = 0.006), PA (r = 0.637, p = 0.026), and PV (r = 0.769, p = 0.003), but no significant correlation with AVT. AVT was only correlated with PV (r = 0.666, p = 0.018).
Conclusions
In normal subjects, MTT of retina correlated with retinal arterial, venous, and tissue transit times. MTT seems to reflect the perfusion status of all vascular components compared with AVT. A comparative study of patients expected to delay retinal MTT need to be conducted to investigate the clinical significance of MTT.