Comprehensive assessment of lung CT attenuation alteration at perfusion defects of acute pulmonary thromboembolism with breath-hold SPECT-CT fusion images.

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.

Preferential location of acute pulmonary thromboembolism induced consolidative opacities: assessment with respiratory gated perfusion SPECT-CT fusion images.

PURPOSE: Preferential location of acute pulmonary thromboembolism (PTE) induced consolidative opacities (infarction/atelectasis) was determined on respiratory gated perfusion SPECT-CT fusion images. METHOD: Gated end-inspiratory perfusion SPECT images were obtained in 21 patients with acute PTE and 17 patients with inflammatory diseases, using a triple-headed SPECT system and a respiratory tracking device. Anatomical relationships of consolidative opacities and perfusion defects were assessed on gated SPECT-rest inspiratory CT fusion images. The size and radioactivity of perfusion defects with acute PTE consolidative opacities were compared with those of defects without these opacities. The contribution of fusion images for differential diagnosis of acute PTE induced and inflammatory disease induced lesions was evaluated by receiver operating characteristic (ROC) curve analysis. RESULTS: Of the total 56 acute PTE induced consolidative opacities, 42 (75%) were located at the peripheral interface between the severely decreased and adjacent relatively preserved perfusion areas within wedge shaped perfusion defects on fusion images. These defects with consolidative opacities were significantly larger and had taken up less radioactivity compared with those in the 86 defects without these lesions (P<0.0001). In contrast, of the 29 inflammatory disease induced opacities, 14 (48.2%) had the matched defects and 13 (44.8%) were located at the proximal portion of defects. These preferential locations of acute PTE induced and inflammation induced lesions were significantly different (P<0.01). In ROC curves, the combined reading of fusion images showed a significantly higher differential diagnostic accuracy compared with the reading of CT and SPECT images alone (P<0.01). CONCLUSIONS: Acute PTE induced consolidative opacities preferentially occur at the peripheral lung interface between severely decreased and adjacent relatively preserved perfusion areas within relatively large and severely decreased perfusion defects. The fusion images, which provide an accurate assessment of the morphological-perfusion defect relationship could, potentially, provide a differential diagnosis between acute PTE induced and inflammatory disease induced lesions.

Assessment of regional lung functional impairment with co-registered respiratory-gated ventilation/perfusion SPET-CT images: initial experiences.

In this study, respiratory-gated ventilation and perfusion single-photon emission tomography (SPET) were used to define regional functional impairment and to obtain reliable co-registration with computed tomography (CT) images in various lung diseases. Using a triple-headed SPET unit and a physiological synchroniser, gated perfusion SPET was performed in a total of 78 patients with different pulmonary diseases, including metastatic nodules (n = 15); in 34 of these patients, it was performed in combination with gated technetium-99m Technegas SPET. Projection data were acquired using 60 stops over 120 degrees for each detector. Gated end-inspiration and ungated images were reconstructed from 1/8 data centered at peak inspiration for each regular respiratory cycle and full respiratory cycle data, respectively. Gated images were registered with tidal inspiration CT images using automated three-dimensional (3D) registration software. Registration mismatch was assessed by measuring 3D distance of the centroid of the nine selected round perfusion-defective nodules. Gated SPET images were completed within 29 min, and increased the number of visible ventilation and perfusion defects by 9.7% and 17.2%, respectively, as compared with ungated images; furthermore, lesion-to-normal lung contrast was significantly higher on gated SPET images. In the nine round perfusion-defective nodules, gated images yielded a significantly better SPET-CT match compared with ungated images (4.9 +/- 3.1 mm vs 19.0 +/- 9.1 mm, P<0.001). The co-registered SPET-CT images allowed accurate perception of the location and extent of each ventilation/perfusion defect on the underlying CT anatomy, and characterised the pathophysiology of the various diseases. By reducing respiratory motion effects and enhancing perfusion/ventilation defect clarity, gated SPET can provide reliable co-registered images with CT images to accurately characterise regional functional impairment in various lung diseases.