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Hiroshi Watabe

Publications and source records attributed to Hiroshi Watabe.

28 records · Page 2Linked to original sources
PubMed2004

(18)F-FDG accumulation in atherosclerotic plaques: immunohistochemical and PET imaging study.

UNLABELLED: The rupture of atherosclerotic plaques and the subsequent formation of thrombi are the main factors responsible for myocardial and cerebral infarctions. Thus, the detection of vulnerable plaques in atherosclerotic lesions is a desirable goal, and attempts to image these plaques with (18)F-FDG have been made. In the present study, the relationship between the accumulation of (18)F-FDG and the biologic characteristics of atherosclerotic lesions was investigated. Furthermore, PET imaging of vulnerable plaques was performed with an animal model of atherosclerosis, Watanabe heritable hyperlipidemic (WHHL) rabbits. METHODS: WHHL (n = 11) and control (n = 3) rabbits were injected intravenously with (18)F-FDG, and the thoracic and abdominal aortas were removed 4 h after injection. The accumulated radioactivity was measured, and the number of macrophages and the intimal area were investigated by examination of stained sections. PET and CT images were also acquired at 210 min after injection of the radiotracer. RESULTS: (18)F-FDG accumulated to a significantly higher level in the aortas of the WHHL rabbits (mean +/- SD differential uptake ratio [DUR], 1.47 +/- 0.90) than in those of the control rabbits (DUR, 0.44 +/- 0.15); DUR was calculated as (tissue activity/tissue weight)/(injected radiotracer activity/animal body weight), with activities given in becquerels and weights given in kilograms. (18)F-FDG uptake and the number of macrophages were strongly correlated in the atherosclerotic lesions of the WHHL rabbits (R = 0.81). In the PET analysis, intense (18)F-FDG radioactivity was detected in the aortas of the WHHL rabbits, whereas little radioactivity was seen in the control rabbits. CONCLUSION: The results suggest that macrophages are responsible for the accumulation of (18)F-FDG in atherosclerotic lesions. Because vulnerable plaques are rich in macrophages, (18)F-FDG imaging should be useful for the selective detection of such plaques.

Animals↗
PubMed2003

Accelerated median root prior reconstruction for pinhole single-photon emission tomography (SPET).

Pinhole collimation can be used to improve spatial resolution in SPET. However, the resolution improvement is achieved at the cost of reduced sensitivity, which leads to projection images with poor statistics. Images reconstructed from these projections using the maximum likelihood expectation maximization (ML-EM) algorithms, which have been used to reduce the artefacts generated by the filtered backprojection (FBP) based reconstruction, suffer from noise/bias trade-off: noise contaminates the images at high iteration numbers, whereas early abortion of the algorithm produces images that are excessively smooth and biased towards the initial estimate of the algorithm. To limit the noise accumulation we propose the use of the pinhole median root prior (PH-MRP) reconstruction algorithm. MRP is a Bayesian reconstruction method that has already been used in PET imaging and shown to possess good noise reduction and edge preservation properties. In this study the PH-MRP algorithm was accelerated with the ordered subsets (OS) procedure and compared to the FBP, OS-EM and conventional Bayesian reconstruction methods in terms of noise reduction, quantitative accuracy, edge preservation and visual quality. The results showed that the accelerated PH-MRP algorithm was very robust. It provided visually pleasing images with lower noise level than the FBP or OS-EM and with smaller bias and sharper edges than the conventional Bayesian methods.

Algorithms↗
PubMed2003

Evaluation of penetration and scattering components in conventional pinhole SPECT: phantom studies using Monte Carlo simulation.

In quantitative pinhole SPECT, photon penetration through the collimator edges (penetration), and photon scattering by the object (object scatter) and collimator (collimator scatter) have not been investigated rigorously. Monte Carlo simulation was used to evaluate these three physical processes for different tungsten knife-edge pinhole collimators using uniform, hotspot and donut phantoms filled with 201Tl, 99mTc, 123I and 131I solutions. For the hotspot phantom, the penetration levels with respect to total counts for a 1 mm pinhole aperture were 78%, 28% and 23% for 131I, 123I and 99mTc, respectively. For a 2 mm aperture, these values were 65% for 131I, 16% for 123I and 12% for 99mTc. For all pinholes, 201Tl penetration was less than 4%. The evaluated scatter (from object and collimator) with a hotspot phantom for the 1 mm pinhole was 24%, 16%, 18% and 13% for 201Tl, 99mTc, 123I and 131I, respectively. Summation of the object and collimator scatter for the uniform phantom was approximately 20% higher than that for the hotspot phantom. Significant counts due to penetration and object and collimator scatter in the reconstructed image were observed inside the core of the donut phantom. The collimator scatter can be neglected for all isotopes used in this study except for 131I. Object scatter correction for all radionuclides used in this study is necessary and correction for the penetration contribution is necessary for all radionuclides but 201Tl.

Absorption↗
PubMed2003

Dependency of energy and spatial distributions of photons on edge of object in brain SPECT.

OBJECTIVES: Accurate mu maps are important for quantitative image reconstruction in SPECT. The Compton scatter energy window (CSW) technique has been proposed to define the outline of objects. In this technique, a lower energy window image is acquired in addition to the main photo-peak energy window. The image of the lower energy window is used to estimate the edge of the scanned object to produce a constant attenuation map. The aim of this study was to investigate the dependency of CSW on the spatial and energy distribution of radioisotope to predict the edges of objects. METHODS: Two particular cases of brain study were considered, namely uniform distribution and non-uniform distribution using Monte Carlo simulation and experiments with uniform cylindrical phantom and hotspot phantom. The phantoms were filled with water and a radioactive solution of 99mTc. For each phantom, 20%, 30%, 40% and 50% thresholds of the mean profile were applied to estimate Ewt, the energy window for minimum difference between the estimated and true edge of objects. RESULTS: The Ewt's were 100-120 keV with a 40% threshold and 92-114 keV with a 30% threshold for uniform and hotspot phantoms, respectively. CONCLUSIONS: Edge of the objects with CSW technique varies with energy window and thresholds. Careful setting of the energy window is required to use the CSW technique.

Algorithms↗
PubMed2003

Activation of the anterior cingulate gyrus by 'Green Odor': a positron emission tomography study in the monkey.

The equivalent mixture of cis-3-hexenol and trans-2-hexenal (hexenol/hexenal), 'green odor', is known to have a healing effect on the psychological damage caused by stress. Behavioral studies in humans and monkeys have revealed that hexenol/hexenal prevents the prolongation of reaction time caused by fatigue. In the present study, we investigated which brain regions are activated by the odor of hexenol/hexenal using positron emission tomography with alert monkeys. Regional cerebral blood flow (rCBF) in the prepyriform area (the primary olfactory cortex) was commonly increased by the passive application of odor: acetic acid, isoamylacetate or hexenol/hexenal. We observed rCBF increases in the orbitofrontal cortex (the secondary olfactory cortex) by these olfactory stimuli in two of three monkeys, and found no predominance of laterality of the activated hemisphere. Furthermore, rCBF increase in the cerebellum was observed in two of three monkeys, and the odor of acetic acid increased rCBF in the substantia innominata in all monkeys. In addition to these olfactory related regions, the anterior cingulate gyrus was activated by the odor of hexenol/hexenal. These findings suggest that the increase of rCBF in the anterior cingulate gyrus by the odor of hexenol/hexenal may contribute the healing effects of this mixture observed in the monkey.

Aldehydes↗
PubMed2003

A theoretical model of oxygen delivery and metabolism for physiologic interpretation of quantitative cerebral blood flow and metabolic rate of oxygen.

The coupling of cerebral blood flow (CBF) and metabolic rate of oxygen (CMRO2) during physiologic and pathophysiologic conditions remains the subject of debate. In the present study, we have developed a theoretical model for oxygen delivery and metabolism, which describes the diffusion of oxygen at the capillary-tissue interface and the nonlinear nature of hemoglobin (Hb) affinity to oxygen, allowing a variation in simple-capillary oxygen diffusibility, termed "effective oxygen diffusibility (EOD)." The model was used to simulate the relationship between CBF and CMRO2, as well as oxygen extraction fraction (OEF), when various pathophysiologic conditions were assumed involving functional activation, ischemia, hypoxia, anemia, or hypo- and hyper-capnic CBF variations. The simulations revealed that, to maintain CMRO2 constant, a variation in CBF and Hb required active change in EOD. In contrast, unless the EOD change took place, the brain allowed small but significant nonlinear change in CMRO2 directly dependent upon oxygen delivery. Application of the present model to quantitative neuroimaging of CBF and CMRO2 enables us to evaluate the biologic response at capillary level other than Hb- and flow-dependent properties of oxygen transport and may give us another insight regarding the physiologic control of oxygen delivery in the human brain.

Biological Transport↗
PubMed2003

Contribution of scatter and attenuation compensation to SPECT images of nonuniformly distributed brain activities.

UNLABELLED: Correction of scatter and attenuation is essential for quantitative SPECT. In this work, we evaluated the accuracy gained from a method of transmission-dependent convolution subtraction (TDCS) in the quantitation of activity that is highly concentrated in the striatum (STR). METHODS: SPECT data were acquired from an (123)I-containing phantom with a constant activity in the STR but differing background (BKG) activities, so as to simulate various STR/BKG ratios (19.7:1, 9.7:1, 4.8:1, 1.9:1, and 1:1). In a study of healthy humans (n = 6), a transmission scan followed by an emission scan was performed 24 h after injection of (123)I-2beta-carbomethoxy-3beta-(4-iodophenyl)-tropane ((123)I-beta-CIT). All SPECT data was reconstructed with ordered-subset expectation maximization. TDCS was applied for scatter correction. Values of activity in the STR and occipital lobe (for BKG) were used to calculate binding potential V(3)" (= [STR - BKG]/BKG). The effect of SPECT collimator dependency on scatter correction was also evaluated for 6 collimators from 3 different SPECT cameras in the phantom experiment. RESULTS: Scatter correction in the phantom experiment increased the measured values of STR activity (36.2%), resulting in a substantial increase in V(3)" (66.1%). Scatter and attenuation corrections with recovery correction showed an overall bias of -7.3% for the STR, -4.0% for BKG activity, and -7.8% for V(3)". TDCS corrections of phantom activities were relatively uniform for the 6 different collimators, with variabilities of <5.5% for the STR and <3.0% for BKG activities. TDCS correction of human (123)I-beta-CIT images was of a similar, although slightly larger, magnitude than for the phantom data, with increased V(3)" values of 9.4 +/- 2.3 and 4.9 +/- 0.6, with and without scatter correction, respectively. CONCLUSION: The TDSC method significantly improved the accuracy of SPECT images with a nonuniform distribution of activity highly concentrated in central regions. The value of V(3)" was significantly increased in phantom and human data, with most of the improvement derived from an increase in STR activity. This scatter correction method was approximately equally useful with data from the 6 different collimators and is recommended for more accurate quantitation of nonuniformly distributed brain activities.

Adult↗
PubMed2002

Evaluation of a commercial PET tomograph-based system for the quantitative assessment of rCBF, rOEF and rCMRO2 by using sequential administration of 15O-labeled compounds.

The purpose of this study was to develop a reliable and practical strategy that generates quantitative CBF and OEF maps accurately from PET data sets obtained with 15O-tracers. Sequential sinogram data sets were acquired after the administration of 15O-tracers, and combined single-frame images were obtained. The delay time between sampled input function and the brain was estimated from the H2(15)O study with the whole brain and the arterial time-activity curves (TACs). The whole-brain TACs were obtained from the reconstructed images (image-base method) and the sinogram data (sinogram-base method). Six methods were also evaluated for the dead-time and decay correction procedures in the process of generating a single-frame image from the dynamic sinogram. The estimated delay values were similar with both the sinogram-based and image-based methods. A lumped correction factor to a previously added single-frame sinogram caused an underestimation of CBF, OEF and CMRO2 by 16% at maximum, as compared with the correction procedure for a short sinogram. This suggested the need for a dynamic acquisition of a sinogram with a short interval. The proposed strategy provided an accurate quantification of CBF and OEF by PET with 15O-tracers.

Adult↗