Focusing on delayed clearance for identifying small-sized metastatic lung tumors using synchrotron radiation angiography with a highly sensitive receiver

Objectives To detect metastatic lung tumors of less than 1 mm in size by focusing on the clearance of contrast material using synchrotron radiation (SR) angiography characterized by high spatial resolution and high-sensitivity receiver. Methods C6 cells, derived from rat glioma cells, were injected to the rat tail vein. Two weeks after injection, the rats underwent SR angiography using a high-gain avalanche rushing amorphous photoconductor (HARP) receiver of extra-high sensitivity with high contrast resolution. The 256-grayscale value was employed in the analysis of images. Results 19 nodules were identified in images. The tumors were confirmed histopathologically. The average tumor size was 621 ± 193 µm. The clearance curve of the densities was expressed as a logarithm function. Tumors showed delayed clearance of contrast material, taking up to 28 s, compared with arteries, which cleared rapidly at 8 s. In 256 grayscale, the distance was 50. This gap in density clearance made it possible to identify tumors. Conclusions SR angiography with a HARP receiver provides high sensitivity and spatial resolution and makes it possible to diagnose metastatic lung tumors of less than 1 mm in size by focusing on differences in the clearance times of contrast material.