Attenuation correction is a mechanism that removes soft tissue artifacts from SPECT images. Attenuation artifacts vary among patients, but the most common corrections are to artifacts associated with breast attenuation in women and diaphragmatic attenuation in men.

Ultimately, the goal is to reduce the impact of attenuation in order to provide images that are more uniform and allow for higher reading confidence.

During SPECT Myocardial Perfusion Imaging, radiation is absorbed by the heart and therefore, the heart becomes the source of gamma rays detected by the camera. The detectors read the rays to produce an image. The size of the patient and the amount of tissue between the heart and the detector lead to attenuation artifacts that adversely affect the image of the heart. The attenuation correction process uses a second form of imaging to develop a density map of each individual patient and corrects the SPECT image accordingly.

Attenuation correction methodologies

There are several methodologies of attenuation correction associated with Myocardial Perfusion Imaging. The primary methods include Gadolinium line source, SPECT/CT, and fluorescence X-ray. Fluorescence X-ray offers attenuation correction with much less radiation exposure to patients compared to SPECT/CT, and a higher quality density map than line source.

By utilizing fluorescence, Digirad’s X-ACT camera can perform attenuation correction with a radiation dose of less than five microsieverts. The X-ACT does not require any shielding, the replacement of any line sources, or any room modifications required for SPECT/CT imaging.

With increased sensitivity in the public and medical community concerning radiation, the fluorescence method contributes to the continued effort of keeping each patient’s lifetime radiation burden at its lowest possible level.