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Background15O-oxygen inhalation PET is unique in its ability to provide fundamental information regarding cerebral hemodynamics and energy metabolism in man. However, the use of 15O-oxygen has been limited in a clinical environment largely attributed to logistical complexity, in relation to a long study period, and the need to produce and inhale three sets of radiopharmaceuticals. Despite the recent works that enabled shortening of the PET examination period, radiopharmaceutical production has still been a limiting factor. This study was aimed to evaluate a recently developed radiosynthesis/inhalation system that automatically supplies a series of 15O-labeled gaseous radiopharmaceuticals of C15O, 15O2, and C15O2 at short intervals.MethodsThe system consists of a radiosynthesizer which produces C15O, 15O2, and C15O2; an inhalation controller; and an inhalation/scavenging unit. All three parts are controlled by a common sequencer, enabling automated production and inhalation at intervals less than 4.5 min. The gas inhalation/scavenging unit controls to sequentially supply of qualified radiopharmaceuticals at given radioactivity for given periods at given intervals. The unit also scavenges effectively the non-inhaled radioactive gases. Performance and reproducibility are evaluated.ResultsUsing an 15O-dedicated cyclotron with deuteron of 3.5 MeV at 40 μA, C15O, 15O2, and C15O2 were sequentially produced at a constant rate of 1400, 2400, and 2000 MBq/min, respectively. Each of radiopharmaceuticals were stably inhaled at < 4.5 min intervals with negligible contamination from the previous supply. The two-hole two-layered face mask with scavenging device minimized the gaseous radioactivity surrounding subject’s face, while maintaining the normocapnia during examination periods. Quantitative assessment of net administration doses could be assessed using a pair of radio-detectors at inlet and scavenging tubes, as 541 ± 149, 320 ± 103, 523 ± 137 MBq corresponding to 2-min supply of 2574 ± 255 MBq for C15O, and 1-min supply of 2220 ± 766 and 1763 ± 174 for 15O2 and C15O2, respectively.ConclusionsThe present system allowed for automated production and inhalation of series of 15O-labeled radiopharmaceuticals as required in the rapid 15O-Oxygen PET protocol. The production and inhalation were reproducible and improved logistical complexity, and thus the use of 15O-oxygen might have become practically applicable in clinical environments.

Assessment of physiological ischemia is recently essential for the indication of coronary revascularization; such as percutaneous coronary intervention (PCI) and coronary artery bypass graft (CABG) in patients with coronary artery disease. Moreover, quantitative assessment of myocardial flow reserve (MFR) is also getting important role for the evaluation of prognosis of heart diseases including non-ischemic cardiomyopathy. In the field of nuclear cardiology, positron emission tomography (PET) has been the only modality for the quantitative assessment of myocardial blood flow (MBF) and MFR. However, since availability of PET is much less than that of single photon emission computed tomography (SPECT) imaging, quantitative MBF/MFR assessment has been limited. Recently, high sensitivity gamma camera which equipped semiconductor detectors has been developed. It is reported that its image quality and spatial resolution are much superior to conventional Anger-type gamma camera. Moreover, since high sensitivity gamma camera consists of plural detectors, it can evaluate whole heart perfusion simultaneously. These advances make quantitative MBF/MFR analysis feasible like PET imaging. Although quantitative assessment with high sensitivity gamma camera is getting useful in clinical practice, several points; such as acquisition protocol and analysis methods, are immature compared to PET. Therefore, we have to investigate the solutions for these issues in near future for diagnostic certainty.

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Heart transplantation(HTx)in Japan started in 1992 after putting the Organ Transplant Law into force. Even after the amendment of this law in 2010, numbers of HTx performed in Japan has been much less than other countries, however, the outcome of HTx in Japan is much superior to that of international registry. For the management after HTx, surveillance of acute cellular rejection, cardiac allograft vasculopathy(CAV) , infections, renal dysfunction, malignancies is essential.Nuclear medicine, such as myocardial perfusion imaging, 67 Ga scintigraphy, 18 F-FDG PET, etc., has been utilized for detection of these rejections and complications, adding to other modalities.Moreover, re-innervation from denervated heart is unique phenomenon which is observed in HTx recipients. For the evaluation of re-innervation in transplanted heart, 123 I-metaiodobenzylguanidine (MIBG) , which is the analogue of norepinephrine, has been utilized. Then, several reports described that the degree of re-innervation was related to sympathetic functional recovery, such as responses of the heart rate and contractile function to exercise.As described above, nuclear medicine has contributed to recipient s care and management after HTx.However, invasive techniques, such as endomyocardial biopsy, coronary angiography, etc., have played a major role in management of recipients, because of high reliability for detection of rejections and complications, compared with other non-invasive modalities. So, we professional of imaging diagnosis have to keep on challenging to offer securer and easier care to HTx recipients.