The radiation exposure to the patient caused by the transmission measurement for myocardial perfusion SPECT

Aim: The aim was the determination of the radiation exposure to the patient caused by the transmission measurement for myocardial perfusion SPECT. Met hod and material: Beside the emission measurement (Tc-99m-MIBI, A = 500 MBq ) the myocardial perfusion SPECT simultaneously includes a transmission mea surement using a Am-241-line source (A = 5550 MBq). During a simulation of the myocardial perfusion SPECT (without Tc-99m-MIBI) dose measurements with thermoluminescent dosimeters were carried out using a thorax phantom. Resu lts: For an acquisition time of 20 min the absorbed doses amounted to: surf ace (xyphoid) 30 mu Gy, heart 25 mu Gy, lung 14 mu Gy, second thoracic vert ebra 16 mu Gy, upper anterior mediastinum 16 mu Gy, liver 0 mu Gy. An estim ation of the ratio of the effective doses caused by the transmission and th e emission measurement of 3.6 x 10(-3) and 4.1 mSv, respectively, resulted in a value of 9 x 10(-4). Conclusion: The radiation exposure of the patient caused by the transmission measurement can be neglected, and is therefore not a limiting factor regarding the general application of transmission mea surement for clinical myocardial perfusion SPECT.