Hemodynamic parameter estimation from ocular fluorescein angiograms.

BACKGROUND

A method is proposed for parameterizing choroidal blood flow from fluorescein angiograms.

METHODS

After digitizing and aligning the angiographic sequence, the intensity build-up curves of fluorescence are analysed per pixel (approx. 10 microns in fundo). Two models are compared. A one-compartment model predicts an exponential build-up curve, from which the following parameters are estimated: maximum fluorescence, dye appearance time and local perfusion rate (reciprocal of the time constant of the exponential). To account for the contribution of the systemic circulation to the shape of the build-up curve, a two-compartment model is used which predicts a bi-exponential curve.

RESULTS

Introduction of the second (systemic) compartment resulted in a significant improvement of fit in 37 of 48 patients studied. The rate constants of the systemic compartment found were mainly in the range of 0.30-1.00 s-1.

CONCLUSION

For the individual patient, the local perfusion rates may vary strongly, with lower perfusion rates possibly being of prognostic value for ocular diseases such as glaucoma or diabetic retinopathy.