DIBrH SPECT is acceptable for routine application to improve respiratory motion effects and accuracy of SPECT/CT image fusion. Confirmative perfusion-morphologic correlation with reliable fusion images appears useful for clarifying the cause of perfusion defects and abnormal lung CT attenuation.
We propose a method for correcting the motion of the lungs between different phase images obtained by respiratory-gated single photon emission computed tomography (SPECT). This method is applied to SPECT images that show a preserved activity distribution in the lungs such as 99m-Tc macro aggregated albumin (99m-Tc-MAA) perfusion images and 99m-Tc-Technegas ventilation images. In the proposed method, an objective function, which consists of both the degree of similarity between a reference image and a deformed image, and the smoothness of deformation is defined and optimized using a simulated annealing algorithm. For the degree of similarity term in the objective function, an expansion ratio, defined as the ratio of change in local volume due to deformation, is introduced to preserve the total activity during the motion correction process. This method was applied to data simulated from computer phantoms, data acquired from a physical phantom, and 17 sets of clinical data. In all cases, the motion correction between inspiration and expiration phase images was successfully achieved.
Regional computed tomography attenuation (CTA) alteration at perfusion defects in acute pulmonary thromboembolism (PTE) was comprehensively assessed using deep-inspiratory breath-hold SPECT-CT fusion images. Subjects were 14 acute and 9 chronic PTE patients and 13 control subjects. Regional perfusion, CTA, and intravascular clots were correlated on deep-inspiratory breath-hold SPECT-unenhanced/angiographic CT fusion images. Fusion images visualized hypo-CTA in 57% of the acute PTE patients, which preferentially occurred at extensively and severely decreased perfusion areas caused by central clots. CTA at 35 defects of acute PTE was significantly decreased compared with that of normal lungs (P<0.001), but the degree was less compared with chronic PTE (P<0.0001). Fusion images also revealed variable relationships of clots and regional perfusion/CTA in the distal lungs of each central clot. Fusion images provide important information about the actual effects of intravascular clots on peripheral perfusion/CTA and indicate that lung CTA can be decreased at perfusion defects in acute PTE.
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