¹²³I-Meta-Iodobenzylguanidine Imaging

Abstract

Abstract123 I-meta-iodobenzylguanidine (MIBG) is a potent prognostic marker of chronic heart failure (CHF). However, inter-institutional variations due to methodological variations required minimization before 123 I-MIBG findings could be universally applied to the diagnosis, treatment and prognosis of CHF. Therefore, protocols including data acquisition, setting regions of interest for calculating heart-to-mediastinum ratios (HMR) and crosscalibration of HMR among institutions required standardization. A cross-calibration phantom was introduced to overcome institutional differences, and a large amount of experimental data were collected, which enabled multicenter comparisons and the creation of large-scale prognostic databases. Thereafter, cardiac mortality risk models to estimate short-and long-term (two and five years, respectively) mortality were created based on a standardized 123 I-MIBG HMR. The ability of these models to accurately determine prognosis is currently Kenichi Nakajima Department of Nuclear Medicine, Kanazawa University Hospital, 13-1 Takara-machi, Kanazawa, Japan 920-8641 E-mail: nakajima@med.kanazawa-u.ac.jp ME general-purpose (MEGP) collimators, but low-energy high-resolution (LEHR), low-energy general-purpose (LEGP), and low-medium-energy (LME) collimators are also popular in Japan. Single-photon emission computed tomography (SPECT) imaging also allows 360º or 180º rotation and it can score defects similar to perfusion defects (7,8). The Japanese Society Nuclear Medicine working group created normal early / late, 180º / 360º and gender-specific databases (9) that work with any software and are applicable to clinical and research purposes. Administration of 123 I-MIBG and data acquisition Heart-to-mediastinum ratio: ROI setting and stabilityThe most popular index of cardiac MIBG uptake is early and late HMR. Although the HMR is a simple average count ratio between the heart and mediastinum, the location, size and (10) and the semiautomatic smartMIBG software used in Japan (5). This software needs only to point towards the center of the heart, and then a circular ROI on the heart and a rectangular ROI on the upper mediastinum are automatically determined. The mediastinal ROI was set at 10% of the body width and 30% of the height from the center of the heart to the upper border of the mediastinum. The optimal mediastinal region was automatically searched vertically to determine the minimal count on the mediastinum. The HMR remains relatively stable for three or four hours, when late images can be acquired (11,12). A washout rate (WR) can also be calculated using the formula:WR (%) = (early heart count-late heart count) / early heart count×100.The mediastinal count in this formula is usually subtracted from the heart count as the background, and a 123 I (half-life, 13 h) decay is corrected using a decay factor at three to four hours after the initial image acquisition (correction factor of ×1.17and ×1.24, respectively). Although ROI settings are generally considered reproducible (13), the sem...