Automated registration of frontal and lateral radionuclide lung scans withdigital chest radiographs

Rationale and Objectives. The purpose of this study was to develop and eval uate a fully automated method that spatially registers anterior, posterior, and lateral ventilation/perfusion (V/Q) images with posteroanterior and la teral digital chest radiographs to retrospectively combine the physiologic information contained in the V/Q scans with the anatomic detail in the ches t radiographs. Materials and Methods. Gray-level thresholding techniques were used to segm ent the aerated lung regions in the radiographic images. A variable-thresho lding technique combined with an analysis of image noise was used to segmen t the adequately perfused or ventilated lung regions in the scintigraphic i mages. The physical dimensions of the segmented lung regions in images from both modalities were used to properly scale the radiographic images relati ve to the radionuclide images. Computer-determined locations of anatomic la ndmarks were then used to rotate and translate the images to achieve regist ration. Pairs of corresponding radionuclide and radiographic images were en hanced with color and then merged to create superimposed images. Results. Five observers used a five-point rating scale to subjectively eval uate four image combinations for each of 50 cases. Of these ratings, 95.5% reflected very good, good, or fair registration. Conclusion. The automated method for the registration of radionuclide lung scans with digital chest radiographs to produce images that combine functio nal and structural information should benefit nuclear medicine physicians a nd radiologists, who must visually correlate images that differ greatly in physical size, resolution properties, and information content.