Standardization of 123I- meta-iodobenzylguanidine myocardial sympathetic activity imaging: phantom calibration and clinical applications

Abstract

Purpose: Myocardial sympathetic imaging with ¹²³I-meta-iodobenzylguanidine (¹²³I-mIBG) has gained clinical momentum. Although the need for standardization of ¹²³I-mIBG myocardial uptake has been recognized, the availability of practical clinical standardization approaches is limited. The need for standardization includes the heart-to-mediastinum ratio (HMR) and washout rate with planar imaging, and myocardial defect scoring with single-photon emission computed tomography (SPECT).

Methods: The planar HMR shows considerable variation due to differences in collimator design. These camera-collimator differences can be overcome by cross-calibration phantom experiments. The principles of these cross-calibration phantom experiments are summarized in this article. ¹²³I-mIBG SPECT databases were compiled by Japanese Society of Nuclear Medicine working group. Literature was searched based on the words "¹²³I-mIBG quantification method", "standardization", "heart-to-mediastinum ratio", and its application to "risk model".

Results: Calibration phantom experiments have been successfully performed in Japan and Europe. The benefit of these cross-calibration phantom experiments is that variation in the HMR between institutions is minimized including low-energy, low-medium-energy and medium-energy collimators. The use of myocardial ¹²³I-mIBG SPECT can be standardized using ¹²³I-mIBG normal databases as a basis for quantitative evaluation. This standardization method can be applied in cardiac event prediction models.

Conclusion: Standardization of myocardial ¹²³I-mIBG outcome parameters may facilitate a universal implementation of myocardial ¹²³I-mIBG scintigraphy.

Keywords: Calibration phantom; Collimator; Conversion coefficient; Heart-to-mediastinum ratio; Quantification.

Fig. 1

Cross-calibration phantom with a scout anterior view (a) and transverse X-ray CT cross section (b) illustrating the structure of the phantom and the different simulated organs

Fig. 2

Anterior and posterior phantom images obtained with medium-energy low-penetration (MELP) and low-energy high-resolution (LEHR) collimators. Difference in background count due to septal penetration and scatter can be clearly seen

Fig. 3

Conversion coefficients obtained in Japanese and European centers [16, 27]

Fig. 4

Normal polar plots of the late phase (3–4 h) SPECT ¹²³I-mIBG images based on the normal ¹²³I-mIBG databases from the Japanese Society of Nuclear Medicine working group [25, 28]

Fig. 5

Relationship between heart-to-mediastinum ratio (HMR) and conversion coefficient (CC) using the HMR threshold of 1.6. For example, HMR = 1.6 with a LEHR collimator (CC = 0.55) can be interpreted as 1.9 with the LME collimator (CC = 0.83). Low-energy general-purpose (LEGP) + all-purpose (AP) groups show variable results between Japan (J) and Europe (E). See also average CC in Fig. 3

Fig. 6

Application of the heart-to-mediastinum ratio (HMR) in a risk model. A sample plot of 5-year cardiac mortality risk is shown in a 54-year-old man with chronic heart failure, which is expressed as a function of HMR. This calculation is based on conditions of NYHA class III, left ventricular ejection fraction of 20%, and HMR of 1.4, and estimated mortality is 56%/5 years (purple dot) [45, 46]