Distribution of ventilation-to-perfusion ratios analysed in planar scintigrams of emphysematous patients

Abstract

The aim of the present study was to develop and evaluate a method for semi-quantification of ventilation-to-perfusion ratios in small regions in planar pulmonary scintigrams using 99mTc-Technegas (Tetley Manufacturing Ltd, Sydney, Australia) and 99mTc-macro-aggregated human albumin. Eight emphysematous patients and eight healthy volunteers were investigated in the supine position. Anterio-posterior and posterio-anterior images of ventilation and ventilation-and-perfusion were acquired consecutively. Perfusion images were obtained by subtracting the corrected ventilation images from ventilation-and-perfusion images. Lung regions of interest were divided into 2.03 x 2.03 cm regions. The ratio of normalized counts of ventilation-to-perfusion (V/Q) was calculated in each square region. The log (V/Q)s of healthy volunteers were distributed symmetrically and similarly around 0, whereas the corresponding ratios in patients distributed unevenly. The standard deviations of log (V/Q)s were significantly higher in patients than in healthy volunteers. Parametric images of V/Q distribution were constructed to visualize the magnitude and location of 'waste ventilation' and 'shunt' effects. In conclusion, the present semi-quantitative method is validated by confirming the expected dispersed V/Q distribution in emphysematous patients compared to healthy volunteers.