Minimizing the radiation dose of CT attenuation correction while improving image quality: The case for innovation.

Mok et al in, ‘‘Interpolated Average CT for Cardiac PET/CT Attenuation Correction, present a novel technique for reducing the radiation dose for patients undergoing cardiac PET/CT’’. According to the authors, this technique differs from many in the past by achieving a remarkable 81% reduction in the CT radiation dose when compared to helical CT, while reducing breathing artifacts in the attenuation corrected PET images. Of course, the diagnostic usefulness of the CT images is reduced and the authors’ technique as presented required additional acquisition steps and equipment. This work should be commended for recognizing image quality and reducing radiation dose should not be considered at odds with one another. Reducing radiation dose in diagnostic exams has become a priority for national and international bodies. According to the National Council on Radiation Protection and Measurements, since 1980, there has been a sixfold increase in the total radiation dose patients receive from medical imaging. In 2014, the American Heart Association not only accepted the crucial role cardiac imaging has in patient management, but also recognized we must do more to reduce patient’s dose to ionizing radiation. Internationally, there are over 30 million nuclear medicine procedures performed annually. This is a good thing, representing the increased availability of advanced diagnostic services for the world’s population. The International Atomic Energy Agency stated its hope that utilization will increase, ‘‘... As the benefits for patients are enormous, far exceeding the risks’’. One clear opportunity to improve the diagnostic power of myocardial perfusion imaging is through the implementation of routine attenuation correction. Use of attenuation correction of is becoming more commonplace for in nuclear medicine and myocardial perfusion imaging. In 2007, there were 200 SPECT/CT scanners installed in the United States and 600 SPECT/CT systems worldwide. By comparison, in 2010 there were over 5,000 PET/CT systems worldwide, though only a small fraction of those systems are used for myocardial perfusion imaging. In addition, virtually all dedicated PET and SPECT systems either have line source attenuation correction installed or can be upgraded to allow for attenuation correction. Attenuation correction has been demonstrated to improve image quality and accuracy of myocardial perfusion image interpretation. Specifically, SPECT attenuation correction has been demonstrated to reduce image artifacts, improve specificity, and improve diagnostic certainty. In cardiac PET, attenuation correction is so important that current guidelines require attenuation correction be applied in all cases. This is all good news for the patient; however, attenuation correction often comes at a cost: increased radiation dose. With hybrid imaging systems capable of diagnostic computed tomography, it then has to be asked, how much radiation dose is needed or justified to acquire a high-quality attenuation map for attenuation correction? When should we consider using dual-modality patient assessments and are there more efficient and safer ways of acquiring this information?