Clinical significance of CT density-based, non-uniform photon attenuation correction of deep-inspiratory breath-hold perfusion SPECT

Abstract

The effect of computed tomography (CT) density-based, non-uniform photon attenuation correction (AC) on lung perfusion distribution and the clinical significance were evaluated. 40 patients with pulmonary emphysema, 32 with pulmonary thromboembolism, 25 with lung cancer and 8 normal controls underwent deep-inspiratory breath-hold (DIBrH) Tc-99m-MAA perfusion SPECT, using a dual-head SPECT system and a respiratory tracking device. Scatter-corrected DIBrH SPECT was automatically co-registered with DIBrH CT. AC of DIBrH SPECT was performed using an attenuation coefficient map of a variable-effective linear coefficient calculated from CT pixel density of the co-registered DIBrH CT. The effect of AC on pulmonary perfusion was evaluated by comparison with uncorrected SPECT. After AC, lung perfusion in normal lungs was increased predominantly at deep lungs near the mediastinum and vertebrae and at the upper-middle lungs, with systematic increases of radioactivity (145 ± 28%) and significant enhancement of physiological gravitational ventral-dorsal gradient (P < 0.01). Throughout the lung diseases, AC significantly enhanced perfusion defect clarity and heterogeneity (P < 0.001), without noticeable artifacts. The correlation between perfusion heterogeneity and the lung diffusing capacity for carbon monoxide was significantly improved in patients with emphysema (P < 0.005). CT density-based, non-uniform AC of DIBrH perfusion SPECT provides better assessment of physiologic or impaired perfusion distributions in normal and lung diseases.