Keiji Shimizu

A high resolution animal PET scanner using compact PS-PMT detectors

A new high resolution PET scanner dedicated to animal studies has been designed, built and tested. The system utilizes 240 block detectors, each of which consists of a new compact position-sensitive photomultiplier tube (PS-PMT) and an 8/spl times/4 BGO array. A total number of 7,680 crystals (480 per ring) are positioned to form a 508 mm diameter of 16 detector rings with 7.2 mm pitch and 114 mm axial field of view (FOV). The system is designed to perform activation studies using a monkey in a sitting position. The data can be acquired in either 2D or 3D mode, where the slice collimators are retracted in 3D mode. The transaxial resolution is 2.6 mm FWHM at the center of the FOV, and the average axial resolution on the axis of the ring is 3.3 mm FWHM in the direct slice and 3.2 mm FWHM in the cross slice. The scatter fraction, sensitivity and count rate performance were evaluated for a 10 cm diameter cylindrical phantom. The total system sensitivity is 2.3 kcps/kBq/ml in 2D mode and 22.8 kcps/kBq/ml in 3D mode. The noise equivalent count rate with 3D mode is equivalent to that with 2D mode at five times higher radioactivity level. The applicable imaging capabilities of the scanner was demonstrated by animal studies with a monkey.

Near-infrared time-resolved spectroscopy system for tissue oxygenation monitor

We have developed a three-wavelength (759,797, and 833 nm) time-resolved spectroscopy (TRS) system as a tissue oxygenation monitor employing a time-correlated single photon counting method. This system achieved a high data acquisition rate and system miniaturization maintaining a high sensitivity and time resolution. Our system succeeded in accurately measuring concentrations of oxy-(HbO2) and deoxyhemoglobin (Hb) by means of TRS data observation through studies using a phantom model and living tissue.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High resolution block detectors for PET

New high-resolution blocks detectors in which BGO scintillators are coupled to a position-sensitive photomultiplier tube (PMT), were developed for positron emission tomography (PET) applications. The block detectors, which use two different BGO scintillator structures, were constructed and evaluated: one is a 1.7-mm-wide BGO array which provides a coincidence detector resolution of less than 2 mm FWHM (full width at half maximum) and the other is a BGO block having comb-shaped slits in it, which has a potential capability of improving the resolution uniformity of a PET system because of its ability to detect the depth-of-interaction of gamma -rays in the scintillator. The application of these detectors to a PET system for animal studies is discussed. >

Development of 3-D detector system for positron CT

A detector composed of a bundle of BGO (bismuth germanate) pillars and position-sensitive photomultiplier tubes is proposed. This detector has the ability to provide 3-D position information on gamma -ray absorption in the scintillator. It is expected that the use of this detector for positron-emission tomography (PET) will result in high spatial resolution and sensitivity. In particular, uniform and high spatial resolution over the entire field of view can be obtained because of the detectors ability to detect the depth of interaction of the gamma -rays in the scintillator. The fundamental characteristics were investigated by both experiment and simulation, and the results are discussed. >

Development of a high resolution PET

A high-resolution positron emission tomograph (PET) for brain studies has been developed. It consists of five detector rings (240 BGOs/ring). New multisegment photomultiplier tubes (PMTs) were adopted for the system with 5-mm-wide BGOs. The system is designed to examine a patient sitting or lying down on a chair/bed couch. The functions of PMT auto gain control and real-time image display are implemented in the system. The physical performance of the system was evaluated: the spatial resolution is 3.5 mm in the transaxial plane and 5.7 mm in the axial direction, and the total system sensitivity is 109 kcps/ mu Ci/ml for a uniform phantom 20 cm in diameter with a pulse height threshold of 350 keV. >

A new high resolution PET scanner dedicated to brain research

A high-resolution positron emission tomography (PET) scanner dedicated to brain studies has been developed and its physical performance was evaluated. The block detector consists of a new compact position-sensitive photomultiplier tube (PS-PMT, Hamamatsu R7600-C12) and an 8/spl times/4 bismuth germanate (BGO) array. The size of each crystal is 2.8 mm/spl times/6.55 mm/spl times/30 mm. The system has a total of 11 520 crystals arranged in 24 detector rings 508 mm in diameter (480 per ring). The field of view (FOV) is 330 mm in diameter/spl times/163 mm, which is sufficient to measure the entire human brain. The diameter of the scanners opening is equal to the transaxial FOV (330 mm). The system can be operated in three-dimensional (3-D) data acquisition mode, when the slice septa are retracted. The mechanical motions of the gantry and bed are specially designed to measure the patient in various postures; lying, sitting, and even standing postures. The spatial resolution of 2.9 mm in both the transaxial and axial directions is obtained at the center of the FOV. The total system sensitivity is 6.4 kc/s/kBq/ml in two-dimensional (2-D) mode, with a 20-cm-diameter cylindrical phantom. The imaging capabilities of the scanner were studied with the Hoffman brain phantom and with a normal volunteer.

Whole-body distribution and radiation dosimetry of [11C]telmisartan as a biomarker for hepatic organic anion transporting polypeptide (OATP) 1B3.

INTRODUCTION Telmisartan, a nonpeptide angiotensin II AT1 receptor antagonist used as an antihypertensive drug, is specifically taken up by the liver through the OATP1B3. PET imaging with [(11)C]telmisartan is expected to provide information about the whole body pharmacokinetics of telmisartan as well as its transport property by OATP1B3. The purpose of the study was to determine the biodistribution and radiation dosimetry of [(11)C]telmisartan in humans. METHODS Biodistribution of [(11)C]telmisartan was measured in three rats and six healthy male human volunteers. In the rat study, a dynamic emission scan was performed for 90 min. In the human study, dynamic whole-body PET images were acquired after intravenous injection of [(11)C]telmisartan. ROIs were defined for source organs on the PET images to measure time-course of [(11)C]telmisartan uptake as percentage injected dose and the number of disintegration for each organ. Radiation dosimetry was calculated with OLINDA/EXM. RESULTS In the rat study, most radioactivity was rapidly taken up by the liver and part of it was excreted into the biliary tract and intestine. Extrapolating from the rat data, the effective dose for the adult human being was estimated to be 3.65±0.01 microSv/MBq (n=3). In the human study, most of the tracer was taken up by the liver as well, although not as rapidly as in the rat. The activity in the gall bladder and intestine increased gradually. The effective dose for the adult human being was 4.24±0.09 microSv/MBq (n=6). CONCLUSIONS [(11)C]Telmisartan is a safe PET tracer with a dosimetry profile comparable to other common (11)C PET tracers.

Development of a Brain PET System, PET-Hat: A Wearable PET System for Brain Research

Brain functional studies using PET have advantages over fMRI in some areas such as auditory research in part because PET systems produce no acoustic noise during acquisition. However commercially available PET systems are designed for whole body studies and are not optimized for brain functional studies. We developed a low cost, small, wearable brain PET system named PET-Hat dedicated for brain imaging. It employs double counter-balanced systems for mechanical supports of the detector ring while allowing the subject some freedom of motion. The motion enables subject to be measured in the sitting position and move relatively freely with the PET during acquisition. The detector consists of a Gd2 SiO5 (GSO) block, a tapered light guide and a flat panel photomultiplier tube (FP-PMT). Two types of GSO are used for depth-of-interaction (DOI) separation allowing the use of a small ring diameter without resolution degradation. The tapered light guide allows the use of larger GSO blocks with fewer FP-PMTs. Sixteen detector blocks are arranged in a 280 mm diameter ring. Transaxial and axial field-of-view (FOV) are 20 cm and 4.8 cm, respectively. Energy resolution of the block detectors was ~15% full width at half maximum (FWHM) and timing resolution was ~4.6 ns FWHM. Transaxial resolution and axial resolution at the center of the FOV were ~4.0 mm FWHM and ~3.5 mm FWHM, respectively. Sensitivity was 0.7% at the center of the axial FOV. Scatter fraction was ~0.6. Hoffman brain phantom images were successfully obtained. We conclude that the PET-Hat is a promising, low cost, small, wearable brain PET system for brain functional studies.

Development of an APD-Based PET Module and Preliminary Resolution Performance of an Experimental Prototype Gantry

The development of a high-resolution Positron Emission Tomography (PET) technique with sub-millimeter spatial resolution, which utilizes newly designed reverse-type APD-arrays, is uderway. All the detector blocks are modularized with the overall dimension of each module, including the APD array, LYSO scintillator matrix and Front-End Circuits (FECs), which are only 30 × 30 × 80 mm3. Each APD device also has a monolithic 16 × 16 pixel structure with an active area of 1.0 mm2 per pixel. The FEC includes two identical analog ASICs specifically designed for APDs with a noise characteristic of 560 + 30 e-/pF and a timing resolution of 460 ps (rms), respectively. An energy resolution of 13.7 ± 1.1% (FWHM) with 662 keV gamma-rays was measured using the 16 × 16 arrays. At this stage a pair of module and coincidence circuits has been assembled into an experimental prototype gantry. Spatial resolutions of 0.9, 1.4, and 1.3 mm (FWHM) were obtained from FBP reconstructed images in preliminary experiments with a point source positioned centrally, and 1 and 5 mm off-center, respectively. Comparison with a Monte-Carlo simulation of a fully-designed gantry over a wider range of field-of-view showed good correlation with the experimental data. A simple but conceptual design of a DOI configuration is also proposed as a test example of a future APD-PET scanner.

Development of a Small Animal PET Scanner Using DOI Detectors

A small animal PET scanner using 256-channel PS-PMTs has been designed, constructed, and evaluated. The scanner has twelve detector modules, each of which consists of a double-layer array of LYSO crystals and three PS-PMTs (Hama- matsu R8400-00-M256). In the LYSO crystal block, 32 times 53 crystal elements are optically coupled to 32 times 54 crystal elements with a shift of half the element pitch in the axial direction. The dimension of each crystal element is 1.275 times 2.675 mm2 in cross section and 7 mm in depth. The twelve detector modules are positioned on a 182 mm diameter ring to form 107 detector rings with 1.4 mm pitch. The transaxial FOV is 100 mm in diameter and the axial FOV is 151 mm, which is sufficient to cover the whole body of a mouse. In order to compensate for non-uniform outputs from the multi-anodes of the PS-PMTs, ASICs having 64-channel variable gain amplifiers and summing amplifiers are used in the front-end circuits. The preliminary experimental results are the transaxial resolution of 2.0 mm FWHM in the CFOV, and the axial resolution of 2.8 mm FWHM on the axis of the ring. The absolute coincidence sensitivity is 8.1% for a point source at the CFOV with setting an energy window of 350-750 keV and a timing window of 10 ns. The applicable imaging capability of the scanner was demonstrated by animal studies with a rat.