Supine acceptance of a conventional imaging position may make you less prone to success

Cardiac SPECT imaging, like most medical imaging employing planar and tomographic data acquisition techniques, has traditionally been performed with the patient in the supine position, i.e. lying face up on the imaging bed. It is easy to understand that this position, while convenient from a procedural standpoint, may not be the most comfortable for all patients. Several studies suggest that the side-lying position is by far the most common adult sleep position. The prolonged imaging times in the supine position, with arms held awkwardly over the head, frequently results in significant patient motion, reported between 26% and 32% of the time. Moreover, supine SPECT imaging is often associated with attenuation artifacts, commonly affecting the anterior myocardial wall in females and the inferior wall in males. Prone SPECT imaging was proposed by Esquerré et al as a means to reduce inferior wall attenuation in 201-Tl studies, and was later found by Kiat et al to improve the overall specificity for the detection of coronary artery disease in a male population. In both of those studies, dedicated imaging tables with cutouts were used to reduce the effect of table attenuation, though nowadays that is no longer considered necessary due to the use of new table materials. Of course, it is well understood that imaging a patient in the prone position only changes the relative position of the heart and the attenuating structures that surround it (breasts, diaphragm, etc.), and therefore prone imaging does not solve the problem of attenuation; rather, it changes the manner in which it affects the final images. In addition to changing the attenuation patterns in the anterior and inferior walls, a major appeal of the prone imaging approach is its demonstrated ability to substantially reduce the incidence of patient motion, thanks to the anterior chest wall (with the heart immediately beneath) being in direct contact with the table and to the more comfortable arm position, usually maintained by folding the arms under the patient’s head. Shin et al have recently suggested that the diagnostic performance of a prone-only SPECT imaging approach is quite comparable to standard supine SPECT imaging, with sensitivities of 88% and 92% for detecting coronary artery stenoses C50% and C70%, respectively, and a normalcy rate of 95% obtained by visual expert analysis. Our group has demonstrated that prone images are associated with different normal count distributions compared to supine images, similar to the differences between attenuation-corrected and non-corrected studies; therefore, interpreting physicians must be aware of these differences and learn how to read prone SPECT images. Computer quantification of myocardial perfusion prone images can be helpful in this regard and can be automatically accomplished through the use of pronespecific normal limits. Of note, it is important to realize that prone imaging is only a subsample of ‘‘non-supine’’ SPECT imaging, which has increased significantly with the advent of newer, small footprint cameras in which the patient is either sitting or reclining as if in a dentist chair. Efforts are ongoing to ascertain the relative performance of supine and non-supine SPECT in terms of quantitative results and diagnostic/prognostic assessment, and it is likely that some intrinsic differences will be found and will be difficult to eliminate. Our professional societies’ approach to prone imaging has been one of caution—as Shin et al point out, ‘‘recent MPS guidelines recommend prone imaging only in combination with supine imaging, and caution against performing prone imaging alone.’’ Of course, combining supine and prone imaging increases the duration of the overall study, a matter of some concern at a time of declining reimbursement. At Cedars-Sinai, prone SPECT is routinely performed immediately after supine SPECT, but for a shorter time compared to the supine study (15 seconds/stop vs 25 seconds/stop). While we tried to perform prone imaging alone as a protocol for a year in the past, we found that there was still uncertainty regarding soft tissue attenuation and From the Department of Medicine, and Department of Imaging, UCLA School of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA. Reprint requests: Guido Germano, PhD, Department of Medicine, UCLA School of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA; [email protected]. J Nucl Cardiol 2010;17:16–8. 1071-3581/$34.00 Copyright 2009 by the The Author(s). This article is published with open access at Springerlink.com doi:10.1007/s12350-009-9187-5