Quantitative analysis of nonuniform distributions in lung perfusion scintigraphy

Nonuniform distributions of lung perfusion scintiscans obtained by SPECT were quantified to supplement qualitative lung scintiscans. A total of 126 lung perfusion scintigraphy examinations were performed between February and December 1996 on a subject population of 102 patients, including 8 control subjects. All of the subjects were broadly classified according to whether they had pulmonary disease or nonpulmonary disease. The latter group was subdivided into a group with cardiac disease and other diseases. The grade of breathlessness was classified according to whether oxygen inhalation was required, the clinical severity of the breathlessness and patient's performance status. Blood gas analysis was performed in 21 cases, and pulmonary function testing was performed in 26 cases.

With the subjects resting in the supine position, 185 MBq 99mTc-macroaggregate albumin was infused. From reconstructed SPECT images, the volume of lung as a whole calculated at 10% of threshold was assumed to be the functional lung volume, and the functional volume rates were calculated in 10% threshold widths from 10% to 100% of thresholds. Assuming the total absolute difference in functional volume rate between each subject and the control to be the distribution index of the lung as a whole (D index), we quantified the degree of nonuniform distribution in each subject.

The D index of all subjects ranged from 2.7 to 72.2. The mean D index in pulmonary disease was significantly higher than in nonpulmonary disease (p < 0.0005) and cardiac disease (p < 0.005). It was significantly positively correlated with the grade of breathlessness, significantly negatively correlated with the oxygenation index and significantly positively correlated with measured vital capacity and forced expiratory volume in 1 sec as percentages of their predicted values.

The D index is a useful indicator for quantifying nonuniform distributions on lung scintiscans. If it is used as a supplement to qualitative interpretation of scintiscans, pulmonary perfusion scintigraphy will become a more useful technique for clinical evaluation of treatment and assessment of breathlessness and respiratory failure than the usual one.