A simple method of reducing radiation exposure from myocardial perfusion imaging (MPI) exams. Voiding!

Objectives Patients and medical professionals are scrutinizing the need for diagnostic testing and how radiation exposure can be reduced. Technetium-99m tetrofosmin is one of the most common used tracers for perfusion in MPI studies. Published data states that 40% of tetrofosmin is excreted in the urine. Exposure time to the radiotracer is associated to the effects of radiation so by clearing the tracer from the body one may reduce these unwanted effects. The objective of this study was to evaluate the degree of techetium-99m (tetrofosmin) eliminated from the bladder in the first hours after injection as a simple method to reduce radiation exposure after an MPI study.

Methods In the current workflow in a nuclear cardiology laboratory for the purposes of improving image quality, patients are sent to eat and drink after the stress test prior to imaging. For this study, hydration was encouraged so patients would be able to void when they returned for their stress image acquisition. Radiation was measured at one meter from the patient with an ion chamber prior to their stress images with a full bladder and again after emptying their bladder. Patients who could not void were excluded.

Results Consecutive patients (n=98) measured an average of 10.6 mR/hr at one meter prior to voiding and 8.9 mR/hr a few minutes after voiding. This is a reduction of 16% in patients receiving an average of 41.6 mCi of Tc99m tetrofosmin (rest and stress) for their exam.

Conclusions Reduced radiation exposure to patients and the general public is an ongoing concern. Encouraging patient hydration and voiding will effectively reduce the dose from an MPI study both to the patient and the community. This method is simple and applicable to all laboratories that perform MPIs around the world. Small and technical changes like the one proposed in this study may add up considerably and result in a substantial reduction in unnecessary radiation exposure.