Biomedical subjects

Seiichi Yamamoto

Publications and source records attributed to Seiichi Yamamoto.

10 recordsLinked to original sources

PubMed2006

Use of a compact pixellated gamma camera for small animal pinhole SPECT imaging.

OBJECTIVES: Pinhole SPECT which permits in vivo high resolution 3D imaging of physiological functions in small animals facilitates objective assessment of pharmaceutical development and regenerative therapy in pre-clinical trials. For handiness and mobility, the miniature size of the SPECT system is useful. We developed a small animal SPECT system based on a compact high-resolution gamma camera fitted to a pinhole collimator and an object-rotating unit. This study was aimed at evaluating the basic performance of the detection system and the feasibility of small animal SPECT imaging. METHODS: The gamma camera consists of a 22 x 22 pixellated scintillator array of 1.8 mm x 1.8 mm x 5 mm NaI(Tl crystals with 0.2-mm gap between the crystals coupled to a 2" flat panel position-sensitive photomultiplier tube (Hamamatsu H8500) with 64 channels. The active imaging region of the camera was 43.8 mm x 43.8 mm. Data acquisition is controlled by a personal computer (Microsoft Windows) through the camera controller. Projection data over 360 degrees for SPECT images are obtained by synchronizing with the rotating unit. The knife-edge pinhole collimators made of tungsten are attached on the camera and have 0.5-mm and 1.0-mm apertures. The basic performance of the detection system was evaluated with 99mTc and 201Tl solutions. Energy resolution, system spatial resolution and linearity of count rate were measured. Rat myocardial perfusion SPECT scans were sequentially performed following intravenous injection of 201TlCl. Projection data were reconstructed using a previously validated pinhole 3D-OSEM method. RESULTS: The energy resolution at 140 keV was 14.8% using a point source. The system spatial resolutions were 2.8-mm FWHM and 2.5-mm FWHM for 99mTc and 201Tl line sources, respectively, at 30-mm source distance (magnification factor of 1.3) using a 1.0-mm pinhole. The linearity between the activity and count rate was good up to 10 kcps. In a rat study, the left ventricular walls were clearly visible in all scans. CONCLUSIONS: We developed a compact SPECT system using compact gamma camera for small animals and evaluated basic physical performances. The present system may be of use for quantitation of biological functions such as myocardial blood flow in small animals.

Animals↗

PubMed2006

Performance characteristics of a new 3-dimensional continuous-emission and spiral-transmission high-sensitivity and high-resolution PET camera evaluated with the NEMA NU 2-2001 standard.

UNLABELLED: The SET-3000 G/X (clinical tomograph with high resolution and a large axial field of view) is a 3-dimensional (3D) (only) dedicated PET camera with germanium oxyorthosilicate (GSO) and bismuth germanate (BGO) scintillators. The main characteristic of the SET-3000 G/X PET scanner is 3D continuous-emission and spiral-transmission (CEST) scanning, yielding a reduction in whole-body scan time. We evaluated the physical performance of the SET-3000 G/X PET scanner with the National Electrical Manufacturers Association (NEMA) NU 2-2001 standard. METHODS: A GSO 3D emission scanner is combined with a BGO transmission scanner separated axially by a lead shield. In the GSO scanner, small and thick scintillators (2.45 x 5.1 x 30 mm(3)) are arranged in small blocks (23.1 x 52 mm) to achieve high resolution and a high counting rate. The detector ring has a large solid angle with a diameter of 664 mm and an axial coverage of 260 mm (50 rings). The transmission scanner consists of BGO block detectors with a diameter of 798 mm and an axial width of 23.1 mm and is equipped with a rotating (137)Cs point source of 740 MBq and a tungsten collimator. The low- and high-energy thresholds are set to 400 and 700 keV, respectively, in the emission system. The coincidence time window is set to 6 ns. In CEST acquisition, the patient couch moves continuously through the emission and transmission scanners in a 1-way motion. Emission coincidence data are acquired in the histogram mode with on-the-fly Fourier rebinning, and transmission single data are acquired with emission contamination correction. RESULTS: With the NEMA NU 2-2001 standard, the main performance results were as follows: the average (radial and tangential) transverse and axial spatial resolutions (full width at half maximum) at 1 cm and at 10 cm off axis were 3.49 and 5.04 mm and 4.48 and 5.40 mm, respectively; the average sensitivity for the 2 radial positions (0 and 10 cm) was 20.71 cps/kBq; the scatter fraction was 50%; the peak noise equivalent count rate was 62.3 kcps at 9.8 kBq/mL; and the peak random rate was 542.1 kcps at 37.6 kBq/mL. CONCLUSION: The new integrated SET-3000 G/X PET scanner has good overall performance, including high resolution and sensitivity, and has the potential of reducing whole-body acquisition time to less than 10 min while improving small-lesion detectability with a low radiation dose.

Equipment Design↗

PubMed2005

An intra-operative positron probe with background rejection capability for FDG-guided surgery.

For radio-guided surgery on tumors using F-18-FDG, detection of annihilation gamma photons emanating from other parts of the body produces background radiation counts and limits its use in clinical situations. To overcome this limitation, we have developed an intra-operative positron probe with background-rejection capability. The positron probe uses a phoswich detector composed of a plastic scintillator and a bismuth germinate (BGO). A positron from a positron emitter such as F-18 is detected by the plastic scintillator and emits annihilation photons. The BGO detects one of the annihilation photons while a photo-multiplier tube (PMT) detects scintillation photons from both scintillators. The decay time differences of these two scintillators are used to distinguish whether the event is a true event where a positron and a following annihilation photon are detected simultaneously, or a background event. In this configuration, only positrons can be selectively detected, even in an environment of high background gamma photon flux. Spatial resolution was 11-mm full width at half maximum (FWHM) 5 mm from the detector surface. Measured sensitivity for the F-18 point source was 2.6 cps/kBq 5 mm from the detector surface. The background count rate was less than 0.5 cps for a 20-cm diameter cylindrical phantom containing 37 MBq of F-18 solution measured on the phantom surface, while the positron count rate was almost linear over a range of approximately 6 kcps. These results indicate that our developed intra-operative positron probe is valuable for radio-guided surgery on tumors using F-18-FDG in a high flux of background annihilation gamma photons.

Background Radiation↗

PubMed2005

Investigation of single, random, and true counts from natural radioactivity in LSO-based clinical PET.

OBJECTIVE: Lutetium oxyorthosilicate (LSO) contains natural radioactivity that emits beta particles and three gamma photons simultaneously. These beta particles and gamma photons increase the single and random rates in a positron emission tomography (PET) system while a beta particle and gamma photon produced in the same decay of Lu-176 and detected by another detector can be beta-gamma coincidence true events. The purpose of this work is to measure the single, random, and true count rates due to the natural radioactivity in LSO and determine the optimum lower energy threshold level for an energy window in an LSO-based clinical PET. METHODS: First, we measured the energy spectra of these beta particles and gamma photons in LSO using a single crystal to obtain the basic data. Then, we measured single, random, and true count rates of an LSO-based clinical PET from the natural radioactivity as a function of the lower energy threshold. RESULTS: In the PET, single and random count rates due to the natural background activity were gradually decreased as the lower energy threshold level increased. The true count rates due to the beta-gamma coincidence were more than 10 kcps below a lower energy threshold of 250 keV. However, these true count rates due to the natural radioactivity in LSO can be decreased to less than 1 kcps at a lower energy threshold level set at more than 350 keV. CONCLUSION: With these considerations, in an LSO-based clinical PET, a lower energy threshold level set at above 350 keV is recommended.

Artifacts↗

PubMed2004

Development of an MR-compatible gamma probe for combined MR/RI guided surgery.

We have developed and tested an MR-compatible gamma probe to simultaneously obtain anatomical information and functional information during surgery. The probe consists of a probe head, an optical fibre bundle and a photo-multiplier tube (PMT). The NaI(T1) scintillator contained in the probe head is connected to a 7 m optical fibre bundle that transfers the scintillation photons produced in the NaI(T1) to an area of low magnetic field or out of the MR-scanner's magnetic shielded room. Although the light loss due to the optical fibre bundle was more than 90%, the photo-peak of the gamma for Co-57 (122 keV) could be observed. The point spread function was 4.5 mm full width at half maximum (FWHM) at 5 mm from the collimator surface for 122 keV gamma photons. Furthermore, there was no sensitivity change outside the MR-scanner, inside the MR-scanner without scanning and inside the MR-scanner with scanning. The probe produced a small artefact on the phantom image of the MR-scanner due to the susceptibility difference of the alloy used for the collimator and the shield. However, the artefact was only limited to area surrounding the probe. These results indicate that the developed MR-compatible gamma probe will make it possible to realize the combined MR/RI guided surgery that provides surgeons with anatomical and RI distribution information simultaneously.

Equipment Design↗

PubMed2004

Optimum threshold setting for a positron-sensitive probe with background rejection capability.

In a positron-sensitive probe composed of a plastic scintillator and a bismuth germanate (BGO), scattered annihilation photons in the plastic scintillator become background counts. Although these scattered annihilation photons can be rejected by higher threshold level settings for the scintillation pulse of the plastic scintillator and for that of the BGO, the system sensitivity is reduced. We have theoretically and experimentally optimized the threshold levels for both the plastic scintillator and the BGO. After calculating the energy loss in the plastic scintillator and the BGO for the scattered annihilation photons, we measured the background counts of a positron-sensitive probe by changing these threshold levels. Results revealed that one optimum threshold setting of the positron-sensitive probe was 0.3 of the peak level of the pulse for the plastic scintillator and 0.7 of that for the BGO. With these threshold levels, the background counts could be decreased to less than 0.2% of the true positron counts.

Algorithms↗

PubMed2004

[Toxicological analyses over the past five years at a single institution].

We investigated 352 patients with acute poisoning, 145 males and 207 females, who were sent to the Department of Emergency and Critical Care Center between June 1999 and March 2004. The insurance application rate averaged 72.5%. The causative agents included 98 prescribed drugs, 23 pesticides and herbicides, cyanide, arsenic and boric acid. Hypnotic and psychotropic drugs accounted for 192 cases (47.5%); antipyretics and analgesics, 93 (23.0%); pesticides and herbicides, 65 (16.1%); amphetamine-like drugs, 6 (1.5%); boric acid, 4 (1.0%); cyanide, 3 (0.7%); arsenic, 1 (0.2%); and other agents, 40 (9.9%). In young people, the most prevalent cause of poisoning was hypnotic,or psychotropic drugs prescribed in psychiatry clinics. In people older than 30, poisoning due to pesticides and herbicides was increased, reaching a peak among those in their 40s. Of 23 patients who died, 20 took Paraquat and Diquat, 2 took organophosphates and 1 took an overdose of antidepressants. The other 329 were transferred to different medical departments or were discharged from our hospital after recovery.

Acute Disease↗

PubMed2003

[Development of GC/MS library for analyzing pesticides and drugs].

To analyze the root components of compounds causing drug addiction, we have developed our own GC/MS libraries(PESTICID.LIB consisting of 20 pesticides and Herbicides, and DRUG.LIB with 57 drugs). We have usually utilized standardized agents, but gastric contents, gastric specimens, serum and urine samples from patients were also used for the analyses. We were able to add libraries of various difficult to purchase psychotropic drugs and legally restricted agents by extracting them from the patient samples. Comments about the retention time, the base peak of the mass spectrum and 5 typical ion chromatograms in the libraries have been useful for laboratory analysis, and consequently have improved the accuracy of detection and identification. They were also found to be a useful guideline for discrimination of the unchanged materials and the metabolites. We are attempting to improve the accuracy of the library to avoid the effects of GC column conditions such as the column size, column temperature and different inserts by using a retention time index.

Gas Chromatography-Mass Spectrometry↗

PubMed2002

[A patient with advanced gastric cancer in the gastric tube whose QOL was improved by TS-1].

We present the case of a 72-year-old man with gastric tube cancer accompanied by multiple liver metastases, after esophagectomy for esophageal cancer, whose quality of life (QOL) was improved with a small dosage of TS-1. The patient's high serum AFP level suggested alpha-fetoprotein-producing gastric cancer. He was treated with half the standard dose of TS-1, because the patient's poor general condition necessitated chemotherapy with low toxicity and high efficacy. The daily dose was 40 mg for the first three courses and 50 mg for the last two. Each treatment course consisted of a four-week administration followed by two drug-free weeks. The patient received five courses of chemotherapy at our outpatient clinic before his death from re-progression of liver metastasis. No serious side effect except temporary stomatitis was observed. A decrease in tumor markers, alpha-fetoprotein and carcinoembryonic antigen, was obtained after 4 weeks. After 2 cycles, computed tomography and endoscopy examinations showed regression of the primary tumor and liver metastases, and tumor markers were decreased remarkably. The patient's QOL improved gradually after the treatment. His performance status before the chemotherapy was 3, and improved to 1 after two cycles. The small dosage of TS-1 was effective without any adverse effects, and improved the patient's QOL, for 6 months.

Adenocarcinoma↗

PubMed2002

[Performance evaluation of continuous blood sampling system for PET study: comparison of three detector-systems].

OBJECTIVES: To measure cerebral blood flow with 15O'PET, it is necessary to measure the time course of arterial blood radioactivity. We examined the performance of three different types of continuous blood sampling system. METHODS: Three kinds of continuous blood sampling system were used: a plastic scintillator-based beta detector (conventional beta detector (BETA)), a bismuth germanate (BGO)-based coincidence gamma detector (Pico-count flow-through detector (COINC)) and a Phoswich detector (PD) composed by a combination of plastic scintillator and BGO scintillator. Performance of these systems was evaluated for absolute sensitivity, count rate characteristic, sensitivity to background gamma photons, and reproducibility for nylon tube geometry. RESULTS: The absolute sensitivity of the PD was 0.21 cps/Bq for 68Ga positrons at the center of the detector. This was approximately three times higher than BETA, two times higher than COINC. The value measured with BETA was stable, even when background radioactivity was increased. The count rate characteristic of the PD and COINC was linear up to 8 kcps. The reproducibility of sensitivity for nylon tube geometry of COINC was the smallest (C.V. = 1.00%) among the three. PD was the weights the least (3.5 kg) among the three, which is convenient for clinical use. CONCLUSIONS: Each detector has unique characteristics derived from its own structure. Although the performance of all three detectors meets clinical requirement, PD had the highest physical performance.

Cerebrovascular Circulation↗