Validity of the mediastinum as a reference region to evaluate cardiac accumulation of iodine-123 metaiodobenzylguanidine
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TECHNICAL NOTE
Validity of the mediastinum as a reference region to evaluate cardiac accumulation of iodine-123 metaiodobenzylguanidine Yusuke Inoue1 • Yutaka Abe2 • Yuji Asano1 • Kei Kikuchi2
Received: 8 April 2015 / Accepted: 18 May 2015 / Published online: 30 May 2015 Ó The Japanese Society of Nuclear Medicine 2015
Abstract Objective The heart-to-mediastinum (H/M) ratio, the heart count normalized for the mediastinum count, is commonly used in cardiac 123I-metaiodobenzylguanidine (MIBG) imaging. However, there are reports describing age-dependent increases in the mediastinum count with or without correction for the injected dose (ID) and a poor correlation between the H/M ratio and heart count normalized for ID. We evaluated the validity of the mediastinum count as a reference in comparison with the ID. Methods Results of cardiac 123I-MIBG imaging in 200 patients were analyzed. The mean counts for the heart and mediastinum were estimated to calculate the H/M ratio. Additionally, the heart and mediastinum counts were normalized for ID measured with a dose calibrator. ID was corrected for body size represented by body weight, body surface area, or lean body mass. Results The coefficient of variance of the ID-normalized mediastinum count was reduced by correcting ID for body size. The indicators of body size showed significant negative correlations with age. Although a positive correlation was found between age and the ID-normalized mediastinum counts, the age-dependence was reduced by body size correction. There was a close correlation between the H/M ratio and ID-normalized heart counts, and body size correction improved the correlation.
& Yusuke Inoue [email protected] 1
Department of Diagnostic Radiology, Kitasato University School of Medicine, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0374, Japan
2
Department of Radiology, Kitasato University Hospital, Sagamihara, Japan
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Conclusion The results of this study indicate the validity of the mediastinum as a reference region and support the use of the H/M ratio as an index of cardiac accumulation of 123 I-MIBG. Keywords 123I-metaiodobenzylguanidine (MIBG) Heart-to-mediastinum (H/M) ratio Quantitative evaluation Injected dose
Introduction Accumulation of 123I-metaiodobenzylguanidine (MIBG) in the left ventricular wall decreases in patients with impaired cardiac sympathetic nerve function. The heart-to-mediastinum (H/M) ratio is commonly used as an index of cardiac accumulation of 123I-MIBG [1], and a low H/M ratio indicates a poor prognosis in heart failure [2–4]. Impaired cardiac sympathetic function also occurs in neurodegenerative disorders, and a low H/M ratio is accepted as a finding indicative of Parkinson’s disease [5] and dementia with Lewy bodies [6]. To calculate the H/M ratio, regions of interest (ROIs) are placed for the heart and mediastinum on planar anterior chest images to determine the mean count for each region. The H/M ratio represents the heart count normalized for the mediastinum count. Despite the extensive clinical
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