Comparison of attenuation correction by variation of tube current-time of CT in myocardial perfusion SPECT : a phantom study

Abstract

Attenuation correction is the method to improve error of myocardial perfusion scintigraphy interpretation and is increasing used nowadays. The methods had demonstrated improved diagnostic accuracy and quality of myocardial perfusion SPECT images. Recently SPECT-CT hybrid instrument which obtain statistically rich of x-ray transmission scan in a very short time solve many of the issues associated with radioisotope-based attenuation correction methods and afford better anatomic localization of abnormal radiopharmaceutical accumulations. This research objective is to study the effect of attenuation correction by varying the x-ray tube current-time, in myocardial perfusion phantom. The SPECT/CT system used in this study is manufactured by Siemens Medical Solutions, Symbia T6 Model, Germany. The system integrates the SPECT detectors, with a 6 multi-slice CT scan. Anthropomorphic phantom (Model ECT/TOR/P, Data Spectrum Corporation) used in this study includes liver, lung, heart and spine inserts. Lung inserts filled with Styrofoam beads and water to simulate lung tissue density. Cardiac insert (Model ECT/CAR/I, Data Spectrums Corporation) simulates normal and abnormal uptake in myocardium. First we studied the effect of 5 different tube current-time of CT scan i.e. 34, 43-48, 100, 150 and 200, on the uniformity of attenuation corrected myocardial perfusion phantom images. Then effects of 3 different tube current-time i.e. 34, 43-48 and 200 on image contrast were selected with varying defect size, location and activity concentration. The results show that the uniformity of the images acquired by mAs 43-48, 100, 150 and 200 do not significantly differ but significantly better than those acquired by mAs 34. The image contrast studies show that the activity concentration of 25% and 75% results in significant difference of the contrast of the image. But the difference of defect size between 1 x 1.5 and 1 x 2 cm[superscript 2] has no significant effect on image contrast. And also there is no significant difference of percent contrast of lesion using different tube current-time on the same defect size and activity concentration matter what location of the defect is. In conclusion, low tube-current time results in low uniformity of the attenuation corrected image. However, the value of mAs 43-48 gives comparable image quality as the high tube-current time of 200 and is the preferable choice because of the lower radiation dose to patient.