Original Article
Semi-automated algorithm for calculating heart-to-mediastinum ratio in cardiac Iodine-123 MIBG imaging

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Abstract

Background

We have developed novel software for semi-automatically measuring heart-to-mediastinum (H/M) ratio in cardiac Iodine-123 (123I)-labeled meta-iodobenzylguanidine (MIBG) imaging. Our aim is to improve the reproducibility of the H/M ratio using the semi-automated method as opposed to the manual method.

Methods and Results

The software algorithm automatically determined the mediastinal region of interest (ROI) using information from 123I-MIBG uptake of the heart, lung, liver, and thyroid after a cardiac circular ROI was manually set. A total of 37 patients who underwent both early and delayed 123I-MIBG imaging was retrospectively selected. The heart-to-mediastinum (H/M) ratios were calculated by both semi-automated and manual methods and assessed for the intra- and inter-observer variability. All H/M ratios were classified into three groups: normal, slight abnormality, and severe abnormality. The H/M ratios with the new method were higher than those obtained manually (P<.001). In the test-retest reliability, the intra-class correlation coefficient from the semi-automated method showed excellent reproducibility for early (0.99) and delayed (0.99) imaging. The Bland-Altman plots demonstrated better agreement using the semi-automated method (a range of 95% limits −0.11 to 0.10) than that in the manual method (−0.34 to 0.27). The inter-observer agreement was also good using the semi-automated method (κ = 0.866).

Conclusions

The H/M ratio using the semi-automated method showed high reproducibility in both early and delayed imaging.

Introduction

Iodine-123 (123I)-labeled meta-iodobenzylguanidine (MIBG) is a radiopharmaceutical for cardiac sympathetic nerve imaging which has been used to assess heart failure, dilated cardiomyopathy, and cardiac arrhythmia.1, 2, 3, 4, 5, 6 Recently, 123I-MIBG cardiac scintigraphy has played an important role in evaluation of neurodegenerative disease such as dementia with Lewy bodies.7,8 For quantitative assessment of cardiac 123I-MIBG uptake, planar imaging has been utilized, and its usefulness has been supported by a large amount of evidence.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11

The heart-to-mediastinum (H/M) ratio and washout rate in the planar image have been used for quantifying cardiac 123I-MIBG uptake. These indices, however, are considerably influenced by both the choice of collimator and the location and size of the cardiac and mediastinal regions of interests (ROIs).10,12, 13, 14, 15, 16, 17, 18 The reason for quantitative variation is that 123I-MIBG planar image acquisition and processing have not been standardized.12,15,18 The use of institution-specific criteria for interpreting 123I-MIBG imaging limits the generalizability of published results.

Therefore, the purpose of this study is to develop a semi-automated method for standardizing the size and positioning of the myocardial and mediastinal ROIs. We validated intra- and inter-observer variations of the H/M ratio and assessed reproducibility with a semi-automatic method instead of using the manual method.

Section snippets

Study Population

A total of 37 clinical studies of 18 females and 19 males who underwent early and delayed 123I-MIBG scintigraphy were retrospectively selected between October 2007 and May 2008. The characteristics of the subjects are shown in Table 1. Indications for 123I-MIBG scintigraphy included patients with cardiac disease (n = 13), neurodegenerative and psychiatric diseases (n = 12), and normal volunteers (n = 12). The subjects with disease were selected randomly and the volunteers were selected from the

Cardiac ROI

A preliminary study was performed to evaluate the appropriate cardiac ROI size. When we compared the average counts between the polygonal ROI (average 73 ± 43 count/pixel) and circular ROI with the radii of 20, 30, 40, and 50 mm, the differences of average count between the circular and polygonal ROIs were 1.7 ± 3.1, 1.5 ± 2.0, −1.1 ± 2.3, and −3.8 ± 4.8 counts/pixel, respectively. Since the circular ROIs with 20 and 30 mm radii did not include the hepatic and pulmonary uptakes in all the

Discussion

In this study, we have developed an algorithm for calculating the H/M ratio, which automatically determined the mediastinal ROI by using information of a manually defined circular cardiac ROI. The aim of this study is to assess reproducibility of the H/M ratio using the semi-automated method in intra- and inter-observer studies. According to the results of ICCs, Bland-Altman analyses and κ statistics, the semi-automated method improved reproducibility of calculating the H/M ratio in comparison

Conclusion

We developed software for semi-automatically determining the H/M ratio and assessed its reproducibility. The H/M ratio obtained from the semi-automated method had good intra- and inter-observer reproducibility. The application of the semi-automated method in 123I-MIBG planar image processing yielded a quantitative H/M ratio.

Acknowledgments

We thank Drs Junichi Taki and Kawano Masaya for their scientific advices, and Masato Yamada, RT, Minoru Tobisaka, RT, Shigeto Matsuyama, RT and Hiroto Yoneyama, RT for their technological assistance. We also thank Ryo Maeda, Shunsuke Nagare, Tsuyoshi Kouke and Hiroyuki Yamanishi (FUJIFILM RI Pharma Co., Ltd., Tokyo, Japan) for their research assistance.

References (23)

  • MatsuoS et al.

    Characterization of Japanese standards for myocardial sympathetic and metabolic imaging in comparison with perfusion imaging

    Ann Nucl Med

    (2009)
  • Cited by (0)

    This work was supported in part by Grants-in-Aid for Scientific Research in Japan (No. 22591320, PI: Kenichi Nakajima).

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