Original ArticleVisual patterns of breast attenuation artifacts in women and men with an upright and supine cadmiun-zinc-telluride camera
Introduction
Breast attenuation is a common source of artifacts in single photon emission computerized tomography (SPECT) myocardial perfusion imaging (MPI), particularly in women. Often, breast attenuation artifacts can be differentiated from myocardial scar by the presence of a fixed myocardial defect in the absence of a corresponding regional wall motion abnormality.1 Possible approaches to soft tissue attenuation artifacts include the use of a transmission source to identify and restore counts lost to attenuation. Use of attenuation correction has demonstrated that in some cases shifting breast attenuation artifact, more apparent on stress than rest images, may mimic the presence of ischemia.2 Alternatively, multiple imaging positions may be used to identify shifting defects resulting from overlying soft tissue.3
Introduction of Cadmium-Zinc-Telluride (CZT) imaging systems has provided several advantages over the conventional Anger camera, including improved image acquisition times, lower radiation dose, and higher image resolution.4,5 Most currently used CZT imaging systems do not include transmission scans for attenuation correction and must rely on shifting of artifacts with change in patient imaging position to differentiate impaired myocardial perfusion from soft tissue artifact. One such approach is to image patients in the upright and supine positions. Nakazato and associates demonstrated that the combination of upright and supine imaging on the D-SPECT camera provides higher diagnostic accuracy for detection of coronary artery disease than either upright or supine imaging alone,6 and, therefore, imaging in both positions is advised.3,6 It remains challenging however, to identify breast attenuation artifacts on upright imaging in women, resulting from shifting breast position. In this study, we aimed to identify breast attenuation artifacts in a cohort of patients who underwent CZT MPI, in whom significant coronary artery disease was excluded by coronary angiography. We studied the effects of supine versus upright position, stress versus rest acquisitions, and demographic factors such as gender and body mass index (BMI) on the presence and location of breast attenuation artifacts.
Section snippets
Study Population
The study was approved by the Institutional Review Board of the University of Cincinnati as a retrospective review and was exempt from informed consent.
Between June 20th, 2014 and June 19th, 2015, 1889 patients underwent exercise or regadenoson pharmacologic SPECT MPI in the University of Cincinnati Exercise Laboratory. From this cohort, 216 patients (102 women and 114 men) who completed both upright and supine stress and rest images and underwent coronary angiography within 3 months of the
Statistical Analysis
Quantitative data were expressed with mean values while categorical data were summarized with frequency and proportion. The baseline characteristics of subjects were summarized by gender and obesity status within each gender and compared using either unpaired t test or Fisher’s exact test. The comparisons of visual defects between upright and supine positions or between anterior and inferior walls were evaluated by McNemar’s test separately for rest and stress conditions and separately for each
Results
Two hundred and sixteen patients (114 men and 102 women) were included in the study. Demographic characteristics and representative nuclear variables by gender are shown in Table 1. Women had a higher BMI, higher stress and rest left ventricular ejection fractions, and larger quantitative supine summed stress and summed rest scores compared to men. Obese women were younger than non-obese women (mean age 55.4 vs 61.5 years, p < 0.01) and more often underwent pharmacologic stress (84% vs. 55%, p
Discussion
With cardiac nuclear imaging in the supine position, inferior wall attenuation artifacts related to diaphragm attenuation usually predominate in men, and anterior wall attenuation artifacts related to breast attenuation usually predominate in women.1 Visual defects result when there is a difference in the imaged activity between different left ventricular walls. In the present study, we observed that upright imaging in women on the D-SPECT CZT camera produced visual inferior wall attenuation
Conclusions
With upright CZT myocardial perfusion imaging, women often have visible inferior wall attenuation artifact defects, related to pendant breast tissue. These upright inferior wall attenuation artifacts are common in non-obese women and may also be related to less scatter from sub-diaphragmatic abdominal activity with exercise compared to predominant pharmacologic stress in obese women. The value of acquiring stress images on a CZT camera in both supine and upright positions remains an accepted
New Knowledge Gained
With CZT based myocardial perfusion imaging in the upright position, women often have visible inferior wall defects due to attenuation artifact, likely from pendant breast tissue. In nearly 1/3 of these women the upright defect is more apparent at stress than at rest falsely suggesting the presence of inferior wall ischemia.
Acknowledgement
The authors thank Marge Duke for her invaluable assistance with data management.
Funding
Funded by a grant from the John R. Strauss Fund for Research and Education in Cardiovascular Imaging.
Disclosures
None of the authors have any conflicts of interest. The study is funded by a grant from the John R. Strauss Fund for Research and Education in Cardiovascular Imaging.
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