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Noninvasive quantification of myocardial blood flow with PET is a vital tool for detecting and monitoring of coronary artery disease. However, current standard cylindrical PET scanners are not optimized for cardiac imaging because they are designed mainly for whole-body imaging. In this study, we proposed two compact geometries, the elliptical geometry and the D-shape geometry, for cardiac-dedicated PET systems. We then evaluated their performance compared with a whole-body-size cylindrical geometry by using the Geant4 Monte Carlo simulation toolkit. In the simulation, an elliptical water phantom was scanned for 10-sec, and we calculated the sensitivity and the noise-equivalent count rate (NECR). Subsequently, a digital chest phantom was scanned for 30-sec and the coincidence data were reconstructed by in-house image reconstruction software. We evaluated the image noise in the liver region and the contrast recoveries in the heart region. Even with the limited number of detectors, the proposed compact geometries showed higher sensitivity than the whole-body geometry. The D-shape geometry achieved 47% higher NECR and 44% lower image noise compared with the whole-body cylindrical geometry. However, the contrast in the hot area obtained by the proposed compact geometries were not as good as that obtained by the whole-body cylindrical geometry. There was no considerable difference in image quality between the elliptical geometry and the D-shape geometry. In conclusion, the compact geometries we have proposed are promising designs for a high-sensitivity and low-cost cardiac-dedicated PET system. A further study using a defect phantom model is required to evaluate the contrast of cold areas.

核医学診断法は「縦割り」状態にある．原理の違いからPETとSPECTに分かれているが，我々は，これが核医学の潜在能力を生かせていない一因であると考えた．そこで，「計測可能な放射線の全てを画像化に生かす」という新しいコンセプトを掲げ，WGIと名付けた．具体的には，他分野で発展してきたコンプトンカメラの方法をPETに組み合わせた．複数の検査が同時にできるだけでなく，これまでは敬遠されてきた高エネルギーガンマ線を出す陽電子放出核種にスポットライトを当て，新しいイメージング法が可能になると期待される．本稿では，WGI装置試作による原理実証について紹介する．

核医学診断法は、画像化原理の違いからPET とSPECT に分かれている。我々は、もしこの垣根をなくすことができれば、核医学診断法はもっと分子イメージング研究に貢献できるのではないかと考えた。 そこで、「計測可能な放射線のすべてを画像化に活かす」という新しいコンセプトを掲げ、whole gamma imaging（WGI）と名付けた。具体的には、宇宙物理分野で発展してきたコンプトンカメラの方法をPETに組み合わせた。WGI により、複数の検査が同時にできるだけでなく、これまでは敬遠されてきた高エネルギガンマ線を出す陽電子放出核種にスポットライトをあてた、新しいイメージング法が可能になると期待される。本稿では、WGI の原理実証実験の結果を紹介し、WGI が持つ可能性について述べる。

Michel M. Ter-Pogossian (Fig. 1) was a great pioneer in the field of nuclear medicine. His achievements include the development and medical use of the cyclotron, realization of a positron emission tomography (PET) scanner, time-of-flight (TOF) implementation in PET, and clinical use of Oxygen-15 (15O) tracers. He was born on April 21, 1925. He received his undergraduate and graduate degrees from the Paris University, France, and received his master’s and doctoral degrees from the Washington University, St. Louis. He joined the faculty of the Washington University School of Medicine in 1950 as an instructor, and from 1961, he held a professorship in Radiation Physics and Physiology. He was also director of Mallinckrodt Institute’s Division of Radiation Sciences from 1963 to 1991. He was the first editor of the IEEE Transactions on Medical Imaging. Unfortunately, on June 19, 1996, he suddenly died in Paris due to a heart attack; he was 71 years old. We believe that, if Ter-Pogossian had lived another 10 years, he would have won the Nobel Prize for his contributions to innovation in PET. He received many awards for his pioneering work related to the medical use of the cyclotron, 15O tracer study, its kinetic analysis, and PET system development. These many honors were an expression of his ability to collaborate with many other experts from different disciplines, both as a leader and as a team player. His scientific accomplishments were based on his endless motivation for understanding biology and medicine. He published a textbook on diagnostic radiology as a summary of his early carrier in 1967, which has been recognized as the first textbook in the field of diagnostic radiology physics [1]. From him, we can learn that achievements in nuclear medicine require inputs of many specialists, such as physicians, physicists, engineers, physiologists, chemists, computer scientists, and other philosophies of nature.