Estimation of regional pulmonary perfusion parameters from microfocal angiograms

An important application of functional imaging is the estimation of regional blood flow and volume using residue detection of vascular indicators. An indicator-dilution model applicable to tissue regions distal from the inlet site was developed. Theoretical methods for determining regional blood flow, volume and mean transit time parameters from time-absorbance curves arise from this model. The robustness of the parameter estimation methods was evaluated using a computer-simulated vessel network model. Flow through arterioles, networks of capillaries and venules was simulated. Parameter identification and practical implementation issues were addressed. The shape of the inlet concentration curve and moderate amounts of random noise did not effect the ability of the method to recover accurate parameter estimates. The parameter estimates degraded in the presence of significant dispersion of the measured inlet concentration curve as it traveled through arteries upstream from the microvascular region. The methods were applied to image data obtained using microfocal x-ray angiography to study the pulmonary microcirculation. Time-absorbance curves were acquired from a small feeding artery, the surrounding microvasculature and a draining vein of an isolated dog lung as contrast material passed through the field-of-view. Changes in regional microvascular volume were determined from these curves. Keywords: functional imaging; angiography; regional flow; regional vascular volume; mean transit time; residue detection; microcirculation; pulmonary circulation; indicator-dilution.