Evaluation of Staff Radiation Exposure during Transthoracic Echocardiography Study Close to Myocardial Perfusion Imaging

Introduction: Trans-thoracic echocardiography (TTE) and myocardial perfusion imaging (MPI) are essential in the workup of patients with chest pain. The degree of ionizing radiation exposure for sonography staff performing TTE on patients who recently underwent cardiac nuclear MPI studies was evaluated, since it has not yet been adequately studied.

Methods: Thirty patients scheduled for a same day Tc-99m sestamibi MPI and TTE and 10 patients in a control group who underwent just TTE were included in the study. Group 1 consisted of 10 TTE studies performed right-handed by an echocardiographer. The remaining studies were performed by a cardiac sonographer. Group 2 (10 patients) underwent right-handed TTE, Group 3 (10 patients) underwent left-handed TTE and Group 4, a control group consisted of right-handed TTE, but no MPI. Both examiners had 7 thermoluminescent dosimeter badges (TLDs) arrayed on the forehead, wrists, anterolateral right and left chest, at the sternal notch, and at the umbilical region. Group clinical characteristics, estimated residual radioactivity at TTE, and TTE duration were compared. Radiation exposures recorded by the TLDs were compared with respect to position, type of examination and examiner. TLD estimates of radiation exposure were deemed positive if above threshold (> 0.1 mSv), indicating if exposure to the examiner was at a level measurable by a common personal monitoring method.

Results: There was no significant difference between the 4 groups in patient weight (respectively: 78.1±16.2, 80.6±14.7, 79.2±20.7, and 85.4±17.6 kg, p= 0.52), and BMI (respectively: 28.8±4.2, 28.5±6.2, 31.2±7.6, and 29.8±5.7 kg/m², p= 0.41). The third group had moderately higher estimated residual radioactivity at the start of the TTE (979±73 MBq) than either of the first 2 groups (906±81 MBq, p=0.04, or 884±73 MBq, p=0.01, respectively), and Group 4 had a moderately longer duration of TTE (51.1±6.4 minutes) compared to Group 2 (39.0±8.2 minutes, p<0.01). Estimates of radiation exposure were positive in the badges positioned in the anterolateral right chest and hand, 0.45 mSv and 1.02 mSv respectively in Group 1, the anterolateral right chest, right wrist and the umbilical region, 0.59 mSv, 1.06 mSv, and 0.15 mSv respectively, in Group 2. In Group 3, positive readings were in the left chest and hand, 0.12 mSv and 0.34 mSv respectively. There was zero reading in the control Group 4.

Conclusions: Same day MPI followed by TTE can expose staff performing TTE to radiation levels sufficient to make personal monitoring advisable. Minimizing such occupational exposure is achievable by altering the sequence of the studies, where TTE is performed first or adopting the left handed approach. If exposures are expected to fall in the range of 1 to 20 mSv/year, echocardiographer and sonographers should be personally monitored according to International Commission of Radiological Protection (ICRP) recommendations.