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Simultaneous imaging of the SPECT tracer 131I and PET tracer 18F is important in the diagnosis of high- and low-grade thyroid cancers because high-grade thyroid cancers have high 18F-FDG and low 131I uptake, while low-grade thyroid cancers have high 131I and low 18F-FDG uptake. In this study, Na131I and 18F-FDG were simultaneously imaged using the Compton-PET system, in vivo. The angular resolution and sensitivity of the Compton camera with 356 keV gamma ray measured using a 133Ba point source were 12.3° and 2 × 10−5, respectively. The spatial resolution and sensitivity of PET were measured with a 22Na point source. The transaxial and axial spatial resolutions of the PET at the center of the FOV were 1.15 mm and 2.04 mm, respectively. Its sensitivity was 1.2 × 10−4. In-vivo images of the 18F and 131I isotopes were simultaneously acquired from mice. These showed that 18F-FDG was active in the heart, brown fat, and brain, while Na131I was active in the thyroid, stomach, and bladder. Artifacts were found in the Compton camera images when the activity of 131I was much lower than that of 18F. This study demonstrates the potential of simultaneous clinical imaging of 18F and 131I. [ABSTRACT FROM AUTHOR]

We developed a multichannel high time resolution data acquisition (DAQ) system for time-over-threshold (TOT) application specific integrated circuit (ASIC). The developed field-programmable gate array-based DAQ is composed of 144 channels per board with an Ethernet readout to measure energy and timing information simultaneously. The measured time precision of the developed DAQ board was reduced to 62.5 ps. The proposed DAQ with TOT-ASIC can potentially be used for several radiation detection applications, such as positron emission tomography (PET) and Compton imaging. The DAQ board is applied to PET and named PET readout board with a high-speed network (PETNET). In the first version developed, the PETNET had a time precision of 1 ns by implementing a double data rate method. This demonstrates that this method is useful for capturing electron–positron pairs of 22Na using two PETNETs. We obtained 2-D cross-sectional images placing two 8 × 8 detectors facing each other. In the second version developed, the PETNET had a time precision of 125 or 62.5 ps by implementing a delay-line method. Cable length measurements proved that PETNET has a position resolution of 4.5 cm at the speed of light. To synchronize the time of data on several PETNETs, a time-of-flight method was adopted, and all the data were compared with each other with accurate time precision. [ABSTRACT FROM AUTHOR]

Application of Compton cameras to nuclear medicine or small animal imaging is a challenging subject. A major issue is insufficient spatial resolutions of the existing Compton camera systems. We developed an imaging system consisting of two Si/CdTe Compton cameras, which allows us to investigate $\gamma $ – $\gamma $ coincidence imaging for a variety of radioisotopes, including 111In, which emits double photons of 171 and 245 keV per decay and has been used for a long time in nuclear medicine and many commercialized radiotracers. We demonstrated with it a drastic reduction of a tail of the point spread function, compared with that of the traditional method, and obtained a spatial resolution of 4.5 mm full-width at half-maximum (FWHM) at 41.35 mm. [ABSTRACT FROM AUTHOR]

Ce-doped scintillators are capable of shortening the time constant as the luminescence is caused by 5d → 4f transition of Ce3+. A scintillator with a short-time constant is suitable for time-of-flight (TOF)-positron emission tomography (PET). In this article, we conducted an evaluation of the energy resolution and coincidence resolving time (CRT) of Liquinert-processed cerium (III) bromide (CeBr3), which possesses a short-time constant and has a high light yield, using multipixel photon counter (MPPC) as a photon detector. The results indicate that an energy resolution of 5.02% (full width at half maximum (FWHM)) can be obtained from a 5-mm × 5-mm × 5-mm-CeBr3 cube coupled with a 6.0-mm × 6.0-mm-pitch MPPC. Furthermore, a CRT of 97.0 ps (FWHM) was achieved using a 3-mm × 3-mm × 1-mm-CeBr3 array coupled with a 3.0-mm × 3.0-mm-pitch through-silicon-via MPPC array, which has been proven effective for TOF-PET and Compton imaging. Moreover, a CRT of 198.7 ps (FWHM) was obtained using a current comparing type time-over-threshold circuit as a front-end readout application. We also determined that the energy resolution is independent of the shaping time but depends on the temperature. In addition, the CRT was found to be dependent on the frequency bandwidth of the signal measuring instrument. [ABSTRACT FROM AUTHOR]

In internal 131I therapy for thyroid cancer, a decision to continue treatment is made by comparing 131I scintigraphy and [18F]FDG-PET. However, with current SPECT and PET systems, simultaneous imaging of diagnostic PET nuclides and therapeutic 131I nuclides has not been achieved so far. Therefore, we demonstrated that the recently developed Compton PET hybrid camera with Ce:Gd3(Al,Ga)5O12 (GAGG)- Silicon Photomultiplier(SiPM) scintillation detectors can be used to simultaneously image 131I Compton image and 18F PET image. • The Compton PET hybrid camera is useful for theranostics imaging. • The Compton PET hybrid camera enables simultaneous imaging of 131I and 18F. • Simultaneous imaging is not affected by patient condition or misalignment. • The Compton PET hybrid camera is available for imaging mixture of 131I and 18F. [ABSTRACT FROM AUTHOR]

Compton imaging is a powerful imaging method used to acquire the distribution of gamma-ray emitting radioactive sources. It can be used for various applications, including homeland security and medical imaging. Similar to other modalities of radiation imaging, scattering is a source of noise in the reconstructed image. The correction of the scatter effect is important for more quantitatively accurate imaging. In this study, a single scattering correction was conducted by setting arbitrary scattering points on the attenuating material. A Monte Carlo simulation was conducted to observe the effect of scattering on reconstructed images, and an experiment was conducted to validate the proposed method using Geant4. The results showed that the method effectively removed the noise on the reconstructed image while not impairing the image quality. [ABSTRACT FROM AUTHOR]

Compton imaging is a promising gamma-ray imaging method based on the Compton scattering kinematics due to high Compton scattering probability for sub-MeV to MeV gamma-rays. A conventional Compton camera has a disadvantage of low signal-to-background ratio (SBR), which is caused by drawing of multiple Compton cones. A method to solve this fundamental problem is the double-photon emission computed tomography (DPECT), which uses the coincidence detection for cascade gamma-rays and significantly increases the SBR using intersections of two Compton cones. In this study, we demonstrated the DPECT method by using 134Cs radio isotope, which is one of important radioisotopes for the imaging of fuel debris, with two Ce:Gd 3 (Al,Ga) 5 O 12 (GAGG) scintillator Compton cameras. [ABSTRACT FROM AUTHOR]

Positron emission tomography (PET) is considered an important and powerful tool for molecular imaging and medical diagnosis with its high sensitivity. Further, single-photon emission CT (SPECT) is another important imaging modality providing different types of information in medical diagnosis. On the other hand, Compton imaging is a promising technique for future molecular imaging with multi-nuclides based on Compton scattering kinetics. In this regard, previously, we have developed gadolinium aluminum gallium garnet (GAGG)-scintillation-based PET systems and GAGG-scintillation-based Compton imaging systems for environmental applications. Here, we propose and develop a novel PET–Compton hybrid simultaneous imager based on a two-layer structure using thin scatterers and thick absorbers for multi-nuclide imaging, for e.g., simultaneous imaging of PET and SPECT tracers such as 18F-FDG and 111In, respectively. For achieving good spatial resolution of the Compton imager, the energy resolution of the utilized scintillators forms one of the most important characteristics. In this regard, GAGG is a promising scintillator because of its high light yield of over 50 000 photon/MeV and excellent energy resolution of 4% with no background radiation and moderate decay time. In this study, we present the development of a simultaneous PET–Compton detector that consists of an 8 × 8 multi-pixel photon counter/SiPM (MPPC) array individually coupled with a 2.5 × 2. 5 × 9-mm 3 Ce:Gd 3 Ga 2.7 Al 2.3 O 12 scintillators (absorbers) for proof of concept of simultaneous PET and SPECT imaging. The pixel size of the MPPC is 3 mm × 3 mm, and it is operated at 55 V at room temperature. The signals from the MPPC scintillators are individually amplified and converted with a dynamic time over threshold (dTOT) circuit to record the energy and timing information. In image reconstruction, the data acquired with the use of the developed modules are classified into events of either Compton imaging or PET imaging by coincidence detection between scatterer and absorber or between absorber and absorber, respectively. The coincidence events between absorber and absorber are regarded as PET annihilation-gamma events and those between scatterer and absorber are used as Compton imaging events. In our experiment, images of 111In and 18F-FDG, which are used as multi-nuclide tracers, are acquired simultaneously using the developed detector for Compton imaging and PET imaging. We believe that our approach is a significant step forward for medical imaging and related fields. [ABSTRACT FROM AUTHOR]