Quantitative evaluation of the administrated dose affecting image quality in myocardial perfusion SPECT

BACKGROUND: Myocardial perfusion imaging (MPI) can provide the valuable cardiac functions. Image quality in nuclear medicine tomography is critically dependent on the activity administered into patients. OBJECTIVE: This study was designed to evaluate the optimum injected dose of 99mTc-MIBI for quantitative assessment of image quality as compared with standard injected dose used for that purpose. METHODS: The image quality parameters (Contrast, relative noise and contrast to noise ratio) were determined in 32 patients (21 male, 11 female, age 45-60 y) with weight 60 +/- 15 kg. Patients were classified into four groups; each one consisted of 8 patients. The first group received 370 MBq, the second one received 555 MBq, the third group received 740 MBq and the last group received 925 MBq. RESULTS: Qualitative assessments of the images revealed equivalent scintigraphic patterns in all patients. There was a significant difference in the image contrast. The image contrast in the 370 MBq group was greater than other groups. The image noise between the four groups was significantly different. It increased with injected dose reduction. Contrast to noise ratio (CNR) was significantly different between 370 MBq and other groups. CONCLUSION: It is concluded that results from the first group which received 370 MBq are sufficiently similar to those of the fourth group (standard group) which received 925 MBq. Consequently, accurate estimations of differential cardiac functions are possible with the 370 MBq dose.