ABSTRACT
SPECT-CT integrates CT with SPECT, and can use 18F-fluorodeoxyglucose(FDG) for coincidence imaging. Its imaging can simultaneously indicate the function metabolism information from SPECT and the diagnostic information about anatomy from CT. And the target to no-target(T/NT) ratio can be calculated by using relative semi-quantitative analysis after once imaging. So SPECT-CT is one of the important imaging methods of tumor diagnosis and treatment. However, there is no accepted standard about cut-off level of T/NT ratio in the diagnosis for tumor, also about the selection location of region of interest (ROI) when you calculated the T/NT ratio. If T/NT ratio≥ 2.5 was referred as threshold in the diagnose of malignant tumor, there may be some false positive and false negative. This paper reviews the methods of the selection location of ROI for T/NT ratio in coincidence-CT imaging, and its influence factors, and its value of the diagnosis for benign malignancy, as well as its application progress in tumor diagnosis and treatment. It proves that the increased value by CT to the pure SPECT imaging is that it can more accurately detect lesions anatomically. By the way, it provide more accurate positioning information for the rang of ROI. Thereby, it provide more useful imaging information for clinical biopsy, surgery or the rang of radiotherapy target area.