Patient and Occupational Radiation Exposure from SPECT Transmission Imaging

Abstract

Objective: SPECT attenuation correction by transmission imaging has attracted interest as a method to reduce tissue attenuation artifacts in myocardial perfusion imaging. A technique has been developed to perform Simultaneous Transmission Emission Protocol (STEP)™ imaging using a line-source of radioactivity positioned at the focal line of a fan-beam collimator. The line-source yields a transmission scan of the patient’s chest to measure individual points of body attenuation which provides an attenuation correction technique for radionuclide imaging. This investigation measured the increase in patient and occupational radiation dose due to the transmission source.

Methods: Using a 19.4-mCi ^99mTc transmission source and thermoluminescent detector (TLD) crystals at various locations on a phantom, we measured radiation dose to a simulated patient and to the technologist.

Results: For a 2-hr exposure period, the maximum dose equivalent was 20 mrem which occurred at the lateral aspects (both left and right) of the chest. The regions of the anterior and posterior mid-chest, thyroid and umbilicus, each measured 10 mrem. The gonads and symphysis pubis doses were less than 3 mrem. All occupational locations measured less than 3 mrem for the 2-hr exposure period.

Conclusion: The maximum radiation surface dose equivalent received by the patient, in a normal 30-min scanning period, would be no greater than 5 mrem. The occupational dose equivalent for the same period is less than 1 mrem from the transmission source. The addition of a transmission source of approximately 20 mCi does not appreciably increase either the patient or technologist radiation dose.