Quantitative analysis of regional lung ventilation and perfusion PET with (68)Ga-labelled tracers

The aims of this study were to determine the quantitative parameters of ventilation (V) and perfusion (Q) PET scans assessing V/Q quotients in patients with various lung pathologies, as well as the influence of patient position on regional perfusion patterns.

Fifty-three patients (24 male and 29 female) underwent lung scintigraphy with (68)Ga-labelled radiopharmaceuticals. (68)Ga Galligas and B20 microspheres used for V and Q imaging were produced in-house. Images were acquired under a standard setup with two emission scans of the whole lung in the supine (S) position (acquisition time 3 min/bed position) on a PET/CT scanner combined with low-dose computed tomography (CT) for attenuation correction. In 27 patients the Q scan was repeated in the prone (P) position. Parametric images were calculated (V/Q, P/S when applicable) for each patient. Patients were grouped according to diagnostic findings, and V/Q ratio distributions were further analysed. Gradients of the regional blood flow in both the supine and prone position were calculated.

The results from visual interpretation could be confirmed with parametric images. Voxel-wise V/Q analysis revealed significant differences in descriptive parameters such as median, mean and SD between normal patients and patients with acute and previous pulmonary embolism. Skewness and kurtosis were not significantly different. The effect of gravitation could be demonstrated by significant position-dependent changes of the gradients in the ventral-dorsal and apical-basal directions.

PET/CT using (68)Ga-labelled tracers allows the application of quantitative procedures to improve functional pulmonary imaging in clinical diagnosis and research.