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Purpose: Cerenkov-light imaging is a new molecular imaging technology that detects visible photons from high-speed electrons using a high sensitivity optical camera. However, the merit of Cerenkov-light imaging remains unclear. If a PET/Cerenkov-light hybrid imaging system were developed, the merit of Cerenkov-light imaging would be clarified by directly comparing these two imaging modalities. Methods: The authors developed and tested a PET/Cerenkov-light hybrid imaging system that consists of a dual-head PET system, a reflection mirror located above the subject, and a high sensitivity charge coupled device (CCD) camera. The authors installed these systems inside a black box for imaging the Cerenkov-light. The dual-head PET system employed a 1.2 × 1.2 × 10 mm³ GSO arranged in a 33 × 33 matrix that was optically coupled to a position sensitive photomultiplier tube to form a GSO block detector. The authors arranged two GSO block detectors 10 cm apart and positioned the subject between them. The Cerenkov-light above the subject is reflected by the mirror and changes its direction to the side of the PET system and is imaged by the high sensitivity CCD camera Results: The dual-head PET system had a spatial resolution of ~1.2 mm FWHM and sensitivity of ~0.31% at the center of the FOV. The Cerenkov-light imaging system's spatial resolution was ~275µm for a 22Na point source. Using the combined PET/Cerenkov-light hybrid imaging system, the authors successfully obtained fused images from simultaneously acquired images. The image distributions are sometimes different due to the light transmission and absorption in the body of the subject in the Cerenkov-light images. In simultaneous imaging of rat, the authors found that 18F-FDG accumulation was observed mainly in the Harderian gland on the PET image, while the distribution of Cerenkov-light was observed in the eyes. Conclusions: The authors conclude that their developed PET/Cerenkov-light hybrid imaging system is useful to evaluate the merits and the limitations of Cerenkov-light imaging in molecular imaging research. [ABSTRACT FROM AUTHOR]

Since a high resolution PET system is needed for small animal imaging, especially for mouse studies, we developed a new small animal PET system that decreased the size of the scintillators to less than 1 mm. Our developed PET system used 0.5 × 0.7 × 5 mm3 LYSO pixels arranged in an 11 × 13 matrix to form a block with a 0.1 mm BaSO4 reflector between the pixels. Two LYSO blocks were optically coupled to two optical fiber based angled image guides. These LYSO blocks and image guides were coupled to a Si-PM array (Hamamatsu MPPC S11064–050P) to form a block detector. Eight block detectors (16 LYSO blocks) were arranged in a 34 mm inner diameter ring to form a small animal PET system. The block detector showed good separation for the 22 × 13 LYSO pixels in the two-dimensional position histogram. The energy resolution was 20% full-with at half-maximum (FWHM) for 511 keV gamma photons. The transaxial resolution reconstructed by filtered backprojection was 0.71 to 0.75 mm FWHM and the axial resolution was 0.70 mm. The point source sensitivity was 0.24% at the central axial field-of-view. High resolution mouse images were obtained using our PET system. The developed ultrahigh resolution PET system showed attractive images for small animal studies and has a potential to provide new findings in molecular imaging researches. [ABSTRACT FROM AUTHOR]

The silicon photomultiplier (Si-PM) is a promising photo-detector for PET for use in magnetic resonance imaging (MRI) systems because it has high gain and is insensitive to static magnetic fields. Recently we developed a Si- PM-based depth-of-interaction PET system for small animals and performed simultaneous measurements by combining the Si-PM-based PET and the 0.15 T permanent MRI to test the interferences between the Si-PM-based PET and an MRI. When the Si-PM was inside the MRI and installed around the radio frequency (RF) coil of the MRI, significant noise from the RF sequence of the MRI was observed in the analog signals of the PET detectors. However, we did not observe any artifacts in the PET images; fluctuation increased in the count rate of the Si-PM-based PET system. On the MRI side, there was significant degradation of the signal-to-noise ratio (S/N) in the MRI images compared with those without PET. By applying noise reduction procedures, the degradation of the S/N was reduced. With this condition, simultaneous measurements of a rat brain using a Si-PM-based PET and an MRI were made with some degradation in the MRI images. We conclude that simultaneous measurements are possible using Si-PM-based PET and MRI. [ABSTRACT FROM AUTHOR]

Carbon kinetics into the fruit is an agricultural issue on the growth and development of the sink organs to be harvested. Particularly, photoassimilate translocation and distribution are important topics for understanding the mechanism. In the present work, carbon-11 (^11\ C) labeled photoassimilate translocation into fruits of tomato has been imaged using carbon-11-labeled carbon dioxide and the positron emission tomography (PET). Dynamice PET data of gradual increasing of ^11\ C activity and its distribution is acquired quantitatively in intact plant body. This indicates that the 3-D photoassimilate translocation into the fruits is imaged successfully and carbon kinetics is analyzable to understand the plant physiology and nutrition. [ABSTRACT FROM AUTHOR]

Motion of the head during brain positron emission tomography (PET) acquisitions has been identified as a source of artifact in the reconstructed image. A number of techniques have been proposed to correct for this motion artifact, but they are unable to correct for a motion during an acquisition. The aim of this study was to develop a sinogram-based motion correction (SBMC) technique to correct directly the head motion during a PET scan using a motion tracking system and list-mode data acquisition. This method uses a rebinning procedure whereby the lines of response (LOR) are geometrically transformed according to the current values of six-dimensional motion data. A Michelogram was recomposed using the rebinned LOR, and the motion-corrected sinogram was generated. In the motion corrected image, the blurring artifact due to the motion was reduced by the SBMC technique. This technique was applied to actual PET data acquired in the list-mode, and demonstrated the potential for real-time motion correction of head movements during a PET acquisition. [ABSTRACT FROM AUTHOR]

Transmission-dependent convolution subtraction (TDCS) is a promising technique in quantitative SPECT for subtracting the scatter components from emission images. Usually, a 20% photopeak energy window is used in SPECT acquisitions. To date, no investigation has assessed the effects of energy windows in the subtraction of scatter components from emission images with the TDCS technique. To evaluate the energy dependence of the TDCS technique, we analyzed photopeak energy windows of 5%, 10%, 15%, 20%, 25%, 30%, and 35% using 99mTc radionuclide. The scatter fractions for a point source placed in a water phantom were estimated using the triple-energy-window (TEW) technique. These estimates were used to establish the parameters of the TDCS equation as a function of transmission. The estimated parameters were applied to the TDCS technique to subtract the scatter components from data of corresponding energy windows using nonuniform and uniform phantoms. All data were reconstructed with the OSEM algorithm. The energy window dependence of the TDCS technique was verified by comparing the coefficients of variance (COV) of the data from the uniform phantom of each energy window. Ten Poisson deviates were generated from each projection's data from the uniform phantom. The nonuniform phantom results showed that the estimated parameters effectively estimated the scatter component from the projection image for each energy window. The COV for the 5%, 10%, 15%, 20%, 25%, 30%, and 35% windows were 2.10%, 1.76%, 1.44 %, 1.39%, 1.34%, 1.37%, and 1.61%, respectively. In the TDCS technique, any photopeak energy window from 15% to 30% may work almost as well as judged by the COV measured for a uniform phantom in this study. The best window by that measure was the 25% window. [ABSTRACT FROM AUTHOR]

Head movement during positron emission tomography (PET) studies causes loss of image quality and quantity and is problematic for brain PET study. During the PET scan, the head of the subject is often fixed by a head holder. However, the head holder is not perfect and it is sometimes difficult to use the head holder for a less cooperative patient. Moreover, head fixation might generate unwanted signals in neural activation studies. There are several software packages, such as AIR and SPM, offering software tools to correct head motion between two scans. These tools, however, cannot correct head motions during scanning. We developed a system to correct the head motion during PET scanning using list-mode acquisition and an optical tracking system. To compensate for escaped photon from the FOV of the PET scanner, the concept of a “virtual ring” was introduced. The present system has the potential to do real-time motion correction during PET scanning and makes it possible to scan a subject without any head fixation, which provides a new aspect of brain research using PET. [Copyright &y& Elsevier]

Presents a study which developed the profile fitting method to measure the input function from positron emission tomography images of the aorta. Discussions on positron emission tomography; How the diameter of the aorta was determined; Methods used in the study; Discussion on the results of the study.

Repetitive transcranial magnetic stimulation (rTMS) has recently been assessed as a non-invasive treatment modality for neuropsychiatric disorders. However, the mechanisms underlying the therapeutic effects are still not understood. Studies in rodents revealed lasting effects in limbic-related regions, but species difference in brain structures makes it difficult to infer the regional effect in primate brain. To reveal how rTMS affects primate brain function, we performed positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) and 11C-raclopride (RAC) in anaesthetized macaque monkeys. A total of 2000 pulses of 5Hz-rTMS were delivered on the unilateral primary motor cortex using a small coil. Voxel-based analysis revealed statistically robust changes in FDG activity in the motor, cingulate, and orbitofrontal cortices, as well as in binding potential of RAC in the ventral striatum. Interestingly, the change in FDG activity persisted at least 8 days. These results demonstrate that motor cortical rTMS induces dynamic functional changes in motor and limbic associated structures, suggesting its therapeutic effect on dysfunction of motor and motivation system. [Copyright &y& Elsevier]