The utility of nuclear medicine depends primarily on non-sealed status of radioisotopes (RIs) because radiopharmaceuticals distribute according to the specific physiological processes after injection. Whereas, the problem due to the use of non-sealed status of RI is that the use of non-sealed RI is limited in RI management areas in hospitals, which can prevent some patients from undergoing nuclear medicine examination. We first described the usefulness and problems in epileptic focus diagnosis as a representative issue. In diagnosing epileptic focus, ¹⁸F-FDG PET is now widely used by depicting hypometabolic area including epileptic focus and related area, therefore, in some patients, the direct method to visualize the epileptic focus is needed. The only way to visualize epileptic focus is to inject a radiopharmaceutical that reflects cerebral blood flow at the same time as the epileptic seizure. However, the injection must be performed in the management area, not in the epilepsy unit, which put the patients at risk, therefore patients who can receive this examination is limited. Second, we presented a proposed method to measure the radioactivity of LNs during surgery, outside the management area. The device has a pair of detectors formed the head of the forceps. We hope this method may expand the utility of nuclear medicine.

  We are developing new SPECT systems for small animals using state-of-the-art sensor technology from astrophysics. The Cadmium Telluride Double-sided Strip Detector (CdTe-DSD) can achieve better energy resolution than existing detectors and thus is expected to be applied to medical imaging. Here, we present imaging results obtained by prototype imagers.

  Medical imaging using X-rays and gamma rays plays an essential role in cancer diagnosis and therapy. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) have been widely used for cancer diagnosis because of their high sensitivity and non-invasive nature. In addition to the diagnostic imaging, there has been a growing demand for a visualization of therapeutic drugs. While the labeling of drug carriers with imaging tracers has been proposed, our study mainly focuses on the direct imaging of drugs without labeling. We have performed in-vivo imaging of alpha-ray emitting radiopharmaceutical using X-rays and gamma rays emitted simultaneously. Moreover, we proposed “activation imaging,” which can even visualize drugs used in a chemical treatment. This method activates the non-radioactive drugs with neutrons and makes them radioactive, which enables the visualization using X-rays and gamma rays emitted from the activated drugs. Imaging of a various medicines requires the visualization of wide-band X-rays and gamma rays, which are sometimes unsuitable energy range for SPECT or PET. Therefore, we visualized the drugs with hybrid Compton camera, which can visualize X-rays and gamma rays ranging from a few tens of keV to more than 1 MeV.

  In this review paper, the future nuclear medicine based on multi-photon time space correlation is discussed. The coincidence detection of multiple gamma-rays provides high signal to background ratio and spatial resolution in the reconstructed image. Moreover, the precise measurement of time-space correlation provides higher order information, such as chemical state or pH in addition to the conventional accumulation information. The principle of double photon emission coincidence imaging (DPECI) and its application to quantum sensing will be introduced here. The multi-channel readout electronics and system are mandatory to realize the modern radiation measurement. Time-over-threshold (ToT) based multi-channel electronics and its application are reviewed in the last part.