Exploration on the reconstruction of lung image and the estimation of lung tissue volume by single photon emission computed tomography (SPECT)

We studied the use of single photon emission computed tomography (SPECT) for evaluating lung image and measuring lung tissue volume, in a lung phantom and healthy volunteers. Three conditions of image processing were tested using the phantom, and found out a backprojection method with using a Shepp-Logan filter and a pre-reconstruction smoothing of 3 x 3 pixels to be suited. A lung tissue volume was estimated from the summation of voxels in the region where the SPECT value was greater than an arbitrary threshold level. We changed phantom lung density from 0.34 g/cm³ to 0.58 g/cm³, but there was no significant effect in the estimated volume by the density change. Changes in the lung SPECT images and lung tissue volumes in healthy subjects were studied, after changing the lung volume by applying either continuous negative body-surface pressure (CNP) to the thorax or positive end-expiratory pressure (PEEP). Difference of the lung expansion in the two methods was visualized by the SPECT images. The lung tissue volumes obtained by SPECT were correlated with the functional residual capacity by Helium dilution method (r = 0.91, p < 0.001). We concluded that lung SPECT could be used clinically to display the distribution of a tracer radio-isotope in the lungs and also used to estimate the lung tissue volume.