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Effects of Cr addition (0, 3, and 6 wt%) on Charpy impact properties of Fe-C-Mn-Cr-based steels were studied by conducting dynamic compression tests at room and cryogenic temperatures. At room temperature, deformation mechanisms of Charpy impacted specimens were observed as twinning induced plasticity (TWIP) without any transformation induced plasticity (TRIP) in all the steels. At cryogenic temperature, many twins were populated in the Cr-added steels, but, interestingly, fine e-martensite was found in the 0Cr steel, satisfying the Shoji-Nishiyama (S N) orientation relationship, { 111 }γ//{ 0002 }e and 101 >γ// 11 2 ¯ 0 >e. Even though the cryogenic-temperature staking fault energies (SFEs) of the three steel were situated in the TWIP regime, the martensitic transformation was induced by Mn- and Cr-segregated bands. In the 0Cr steel, SFEs of low-(Mn,Cr) bands lay between the TWIP and TRIP regimes which were sensitively affected by a small change of SFE. The dynamic compressive test results well showed the relation between segregation bands and the SFEs. Effects of Cr were known as not only increasing the SFE but also promoting the carbide precipitation. In order to identify the possibility of carbide formation, a precipitation kinetics simulation was conducted, and the predicted fractions of precipitated M23C6 were negligible, 0.4–1.1 × 10−5, even at the low cooling rate of 10 °C/s.

Manufacturing temperatures of severely cold-drawn hyper-eutectoid steel wires are sufficiently high to influence the mobility of dislocations and alloy elements, thereby affecting the materials’ mechanical properties. Herein, we describe the evolution of microstructure and tensile strength of the as-drawn 3.45 GPa steel wire during post-deformation annealing for 30 min at 150−450 °C. Annealing at 150 °C raised the strength to 3.77 GPa by age-hardening through activation of dislocations pinning by carbon, while further temperature rising up to 450 °C caused a severe loss of strength. It was proved that annealing at 300 and 450 °C destabilizes the lamellar microstructure, promoting the formation of carbon-deficient (Fe,Mn,Cr)3C-type cementite particles with preferentially rounded and partially faceted hetero-interfaces. Annealing at 450 °C yielded the accumulation of Mn and Cr at the ferrite/particle interfaces, and their concentrations at the interfaces were dependent on the interface structure; i.e., lower concentrations at rounded interfaces (formed through capillarity–driven coarsening of the spheroidized cementite), and higher concentrations at faceted interfaces (that are initially existing in the as-drawn state). Our proof-of-principle observations, supported by thermodynamic calculations and kinetic assessments, provide a pathway for understanding the changes in microstructural and tensile properties during manufacturing of the hyper-eutectoid steel wires.

Yttrium-90 is a useful therapeutic radioisotope for tumor treatment because of its high-energy-emitting beta rays. However, it has been difficult to select appropriate collimators and main energy windows for Y-90 Bremsstrahlung imaging using gamma cameras because of the broad energy spectra of Y-90. We used a Monte Carlo simulation to investigate the effects of collimator selection and energy windows on Y-90 Bremsstrahlung imaging. We considered both MELP and HE collimators. Various phantoms were employed in the simulation to determine the main energy window using primary-to-scatter ratios (PSRs). Imaging performance was evaluated using spatial resolution indices, imaging counts, scatter fractions, and contrast-to-noise ratios. Collimator choice slightly affected energy spectrum shapes and improved PSRs. The HE collimator performed better than the MELP collimator on all imaging performance indices (except for imaging count). We observed minor differences in SR and SF values for the HE collimator among the five simulated energy windows. The combination of an HE collimator and improved-PSR energy window produced the best CNR value. In conclusion, appropriate collimator selection is an important component of Bremsstrahlung Y-90 photon imaging and main energy window determination. We found HE collimators to be more appropriate for improving the imaging performance of Bremsstrahlung Y-90 photons. Keywords: Yttrium-90, Bremsstrahlung imaging, Collimator, Energy window, Gamma camera

A drop impact on high-curvature structures at high temperatures is observable in various engineering platforms and understanding its dynamics about the heat transfer mechanism will significantly advance existing thermal applications. However, most studies on the drop impact on complex structures have focused solely on the dynamics of the fluidic motion at ambient temperatures. Herein, we report experimental and theoretical analyses of the drop impact on heated metal wires within a wide temperature range and demonstrate the transition modes depending on the contact surface temperatures as functions of the physicochemical properties (ethanol, water, and acetone), the impact velocity, and the dimensions of the liquid drops. According to an increase in the wire temperature from ambient temperature to beyond the Leidenfrost point, the impacting drops revealed three distinct impact regimes, which can be classified as tail, splash, and jumping modes. The onset of splash mode, in which tiny mono-dispersed drops are circularly sprayed, is observed at a higher temperature than the nucleate boiling temperatures of all liquids used, whereas the drops in tail mode show a wrapping of the nichrome wire and a consecutive free-fall. At over the Leidenfrost temperature, a jumping mode indicating the presence of bouncing daughter drops appears around the wire in a half-ring shape owing to the instant formation of the vapor cushion between the wire and droplets. Theoretical analyses were conducted to develop a general model reflecting the underlying physics of the transition between the three distinct modes. The diameter and the impact velocity of the drops are crucial for determining the threshold temperature of the jumping mode, whereas liquid properties such as the nucleate boiling temperature and We numbers of the drops are more decisive factors for the initiation of splash mode. The outcomes of this work will contribute toward advancing the fundamental understanding and application using the drop impacts on high-curvature structures at high temperatures.

Aims CREB (cAMP response element-binding protein)-regulated transcription coactivator (CRTC2) has been reported to act as a coactivator of CREB during gluconeogenesis. The role of CRTC2 in osteoblastic differentiation has not yet been elucidated. The aim of this study is to identify the mechanism of CRTC2 in osteoblast differentiation. Main methods The mRNA expression was determined by RT-PCR and qPCR. Protein levels were measured using Western blot assay. Alkaline phosphatase (ALP) staining was performed to evaluate ALP activity. Alizarin red S (ARS) staining was performed to measure extracellular mineralization. Transcriptional activity was detected using a luciferase assay. Key findings In the present study, TNF-α was found to stimulate CRTC2 expression. However, TNF-α did not increase the gene expression of osteoblast differentiation markers and inhibited BMP2-induced osteoblastic differentiation. Overexpression of CRTC2 decreased the expression of osteogenic genes, ALP activity and extracellular matrix mineralization. Knockdown of CRTC2 restored BMP2-induced osteogenic gene expression and ALP activity. CRTC2 increased Smurf1 mRNA expression, Smurf 1 promoter activity, and protein level. Furthermore, Smurf 1 decreased Smad 1/5/9 protein levels. These results suggest that CRTC2 decreased BMP2-induced osteoblastic differentiation via Smurf 1 expression. Significance Our results indicate that CRTC2 regulates the expression of Smurf1 in osteoblast differentiation.

Interatomic potentials for pure Zn and Mg–Zn binary system have been developed on the basis of the second nearest-neighbor modified embedded-atom method formalism. The potentials describe fundamental material properties of pure Zn (bulk, defect, and thermal properties) reasonably and reproduce the alloy behavior (thermodynamic, structural, and elastic properties of compounds and solution phases) of Mg-Zn alloys well in good agreement with experiments, first-principles and CALPHAD. The applicability of the developed potentials to atom-scale investigations on the slip behavior of Mg-Zn alloys is also demonstrated by showing that the calculated effects of Zn on the general stacking fault energy on the basal, prismatic and pyramidal planes are consistent with first-principles calculations.

To get highly efficient quasi-solid-state dye-sensitized solar cells (QSS-DSSCs) with long-term stability using polymer gel electrolytes (PGEs), well-defined ABA triblock copolymers ([Poly(methyl methacrylate)]2-block-poly(ethylene glycol)) with different end functionality and components of I-/I3- liquid electrolytes (LEs) are studied and optimized for the fabrication of PGE-based QSS-DSSCs. Triblock copolymers are synthesized in a one-step reaction using bifunctional PEG-macro chain transfer agent (MCTA) by reversible addition-fragmentation chain transfer (RAFT) polymerization. Due to the high reactivity and toxicity of sulfur-containing trithiocarbonate end groups, ABA triblock copolymers prepared from RAFT polymerization are further modified to sulfur-free 2-methylpropionitrile and 4-cyanopentanoic acid end functional triblock copolymers by radical-induced exchange reactions. Dodecyl trithiocarbonate end functional PEG-MCTA and triblock copolymers absorb UV-light in the region of 260–380 nm, whereas sulfur-free carboxylic acid and 2-methylpropionitrile end functional polymers do not absorb in that UV-light region. Among three different end functional polymers, the carboxylic acid end functional triblock copolymer has the highest thermal stability. Based on electrochemical parameters, photovoltaic performance, and long-term stability, 1,2-dimethyl-3-propylimidazolium iodide (DMPII) ionic liquid and 4-tert-butylpyridine (TBP) additive containing acetonitrile-based I-/I3- LEs are effective for PGEs. The highest power conversion efficiency (PCE) for QSS-DSSCs achieved under simulated 1-sun illumination is up to 10.34%, which is comparable with the highest PCE of 10.39% for LE-DSSCs. Considering the high reactivity, thermal stability, UV-absorption, and the toxicity of the trithiocarbonate end group, the SGT-643-C triblock copolymer with carboxylic acid end group can be a promising candidate as a sulfur-free polymeric matrix for gel electrolytes of QSS-DSSCs.

Aims Mammalian circadian rhythms regulate many metabolic processes. Recent studies suggest that brain and muscle Arnt-like 1 (BMAL1), an important component of mammalian circadian rhythm, is associated with insulin signaling. Several studies have shown that insulin is associated with bone metabolism; however, the relationship between BMAL1 and osteoblasts remains unclear. Main methods Expression of osteogenic markers and Bmal1 in MC3T3-E1 cells was measured by RT-PCR and Western blotting. Alizarin red S staining was performed to assess matrix mineralization in MC3T3-E1 cells. Key findings mRNA levels of osteogenic genes and Bmal1 were up-regulated in MC3T3-E1 cells upon insulin treatment. In addition, Bmal1 overexpression increased the expression of osteogenic genes including inhibitor of DNA binding (Id1), Runt-related transcription factor 2 (Runx2), and osteocalcin (OC). Interestingly, expression of Bone morphogenetic protein-2 (BMP2), an important upstream factor of Id1, Runx2, and OC, was markedly increased by Bmal1. Finally, we confirmed that insulin-induced BMP2 expression was attenuated in Bmal1 knockout (KO) cells. PCR analysis and alizarin red S staining showed that insulin-mediated increases gene expression and calcium deposition were reduced in Bmal1 KO cells compared to wild-type cells. Significance Taken together, these results demonstrate that Bmal1 promotes osteoblast differentiation by regulating BMP2 expression in MC3T3-E1 cells.

Single-photon emission computed tomography (SPECT) is a nuclear medical imaging method enabling the user to view functional images of patients. The collimator, which is an essential component of the SPECT, limits the direction of the incident gamma rays, such that the distribution of the gamma photons from the body can be observed. Collimators are composed of shielding materials with high atomic number and density, thus it is difficult to fabricate them in complex shapes. Among the existing collimators, the pinhole collimator consists of a small aperture perforated in a shielding material, and the modification of the pinhole parameters, such as the hole diameter and acceptance angle, during the scan is also challenging. A variable pinhole (VP) collimator comprises several thin tungsten layers with various hole sizes. Thus, the pinhole parameters can be varied for the region of interest (ROI) by forming the desired pinhole shape using a combination of holes. In this study, we implemented the concept of a VP collimator and applied it in a SPECT system to enhance its performance. The collimator was composed of five layers of with a diameter of 170 mm and thickness of 1 mm and with six holes of different sizes in each layer. Two point sources (Co-57, 122 keV) were used for the performance analysis by changing the system parameters. The spatial resolution and sensitivity of the SPECT system were affected by the variation of the pinhole diameters, with the peak-to-valley ratio increasing by up to 3.3 times with the increase in the magnification of the SPECT system. Two line source phantoms (Tc-99m, 140 keV) with an internal diameter of 1 mm were used for the performance evaluation of the system. The phantoms were positioned 20 mm apart inside the ROI with a diameter of 50 mm at a position of 29 mm from the object center. By applying the VP collimator, the resolution and the sensitivity performance were improved, achieving a full width at half maximum value of 2.7 times and counts of 2.8 times those of the conventional SPECT system. In future research, we aim to improve the system efficiency by conducting simultaneous experimental driving test of the dual-head VP collimator SPECT system.

Positron emission tomography (PET) can be utilized in particle beam therapy to verify the dose distribution of the target volume as well as the accuracy of the treatment. We present an in-beam PET scanner that can be integrated into a particle beam therapy system. The proposed PET scanner consisted of 14 detector modules arranged in a C-shape to avoid blockage of the particle beam line by the detector modules. Each detector module was composed of a 9×9 array of 4.0 mm×4.0 mm×20.0 mm LYSO crystals optically coupled to four 29-mm-diameter PMTs using the photomultiplier-quadrant-sharing (PQS) technique. In this study, a Geant4 Application for Tomographic Emission (GATE) simulation study was conducted to design a C-shaped PET scanner and then experimental evaluation of the proposed design was performed. The spatial resolution and sensitivity were measured according to NEMA NU2-2007 standards and were 6.1 mm and 5.61 cps/kBq, respectively, which is in good agreement with our simulation, with an error rate of 12.0%. Taken together, our results demonstrate the feasibility of the proposed C-shaped in-beam PET system, which we expect will be useful for measuring dose distribution in particle therapy.

A computational and experimental study has been carried out to produce highly value-added {100} textured steel sheets. This study is based on an idea that an anisotropic surface segregation tendency of impurity atoms would cause an inversion of relative surface energy between {110} and {100} surfaces in bcc Fe and may induce the formation of {100} texture in steel sheets during grain coarsening. A phase field model that can consider surface segregation of impurity atoms (and resultant decrease of surface energy) and grain growth simultaneously is newly developed. The phase field model and surface property data obtained from an atomistic approach are used to simulate grain coarsening behavior of phosphorus-containing iron and to find an optimum process condition that can induce the {100} texture in steel sheets. The phase field simulation indicates that the surface segregation and resultant change in the relative difference in surface energy should be accomplished before the start of grain coarsening for an effective formation of the {100} texture. A strong {100} texture is indeed generated experimentally in phosphorus-containing bcc Fe-3.5wt% Si steel sheets through a two-step annealing process, one at a relatively low temperature where only surface segregation can occur but not the grain coarsening and the other at a relatively high temperature where the grain coarsening can also occur.

For NiMn2O4 systems, the mixed valence of manganese on B-sites arises from the displacement of bivalent cations, such as Ni2+, from A-sites to B-sites which results in a corresponding proportion of Mn3+ cations on B-sites disproportionate to Mn2+ and Mn4+, and the Mn2+ cations move to the A-sites to compensate Ni2+ vacancies. With the assistance of random crystal field fluctuations and the mixed valence of manganese eventually leads to the formation of localized small polarons which accomplish a thermally activated hopping conduction between Mn3+ and Mn4+ cations on octahedral sites. In this study, we have investigated the structural and electrical properties of NixMn3-xO4 system. And, we have comprehensively measured the electrical transport mechanism, the temperature coefficient of resistance and infrared detection performance for the application of infrared radiation detectors.

Carbohydrate responsive element binding protein (ChREBP) is a major transcription factor of lipogenesis regulated by glucose status in the liver. However, the function of ChREBP in osteogenic differentiation is unclear. The present study examined the role of ChREBP in osteoblast differentiation in MC3T3-E1 preosteoblast cell line. The mRNA expression of ChREBP, protein phosphatase 2A catalytic subunit-α (PP2A Cα) and the osteogenic genes such as, DNA-binding protein inhibitor (Id1), runt-related transcription factor-2 (Runx2), and alkaline phosphatase (ALP) was measured by qPCR and RT-PCR. Runx2, ChREBP, and PP2A Cα, protein levels were evaluated by Western blotting. ALP staining experiment was carried out to evaluate ALP enzyme activity, and a luciferase reporter assay was performed to analyze Runx2 transcriptional activity. Expression of ChREBP and PP2A Cα did not change during bone morphogenetic protein-2 (BMP2)-induced osteoblast differentiation. Overexpression of ChREBP reduced the osteogenic genes (Runx2 and ALP) expression and ALP activity, while knockdown of ChREBP had the opposite effects. Overexpression of PP2A Cα increased ChREBP expression, while inhibition of PP2A Cα using okadaic acid not only inhibited the expression of ChREBP, but also restored the mRNA and protein expression of Runx2 and activity of ALP enzyme. These results demonstrate that ChREBP inhibits BMP2-induced osteoblast differentiation in a PP2A Cα- dependent manner.

In the recent past, gamma-ray imaging detectors have achieved an intrinsic spatial resolution of less than 1 mm within a few centimeters of a useful field of view (UFOV). Unlike to conventional gamma cameras, which are large and heavy, the compact gamma-ray imaging detectors can improve the performances of the gamma cameras used in the various fields. In this study, we developed a sub-miniature gamma camera for a multimodal imaging system. The camera has a gamma-ray detector, miniature electronics modules, and a diverging hole collimator . The detector consisted of the sub-millimeter pixelated Ce:GAGG array and the silicon photomultiplier (SiPM) array module. We organized the miniature electronics modules according to the functions; an MPPC base board, analog signal processing board, integrated power supply board, and compact data acquisition (DAQ) base board. The diverging hole collimator widened an imaging area of the gamma camera from the UFOV of the detector. On the detector side, dimensions of each hole and septa were identical to the pixel and inter-pixel thickness of the reflector of scintillator array. For the intrinsic performance test, we acquired a flood map image of 729 (27 × 27) scintillator pixels, and the energy resolution was 18.9% for an integrated energy histogram of 99m Tc (140 keV). For the extrinsic performance test, we used the 57Co sheet source, and made a 99m Tc line source using a capillary tube. The sources located at 10 cm apart from the collimator surface. The imaging area was three times wider than the UFOV of the detector. The system sensitivity was 19 CPM/ μ Ci and the spatial resolution was 3.5 mm. The usability of the proposed gamma camera will not be confined to existing applications due to its compactness and novelty.

Cadmium zinc telluride (CZT)-based small-animal single-photon emission computed tomography (SPECT) has desirable characteristics such as superior energy resolution, but data acquisition for SPECT imaging has been widely performed with a conventional energy window. The aim of this study was to determine the optimal energy window settings for technetium-99 m ( 99m Tc) and thallium-201 ( 201 Tl), the most commonly used isotopes in SPECT imaging, using CZT-based small-animal SPECT for quantitative accuracy. We experimentally investigated quantitative measurements with respect to primary count rate, contrast-to-noise ratio (CNR), and scatter fraction (SF) within various energy window settings using Triumph X-SPECT. The two ways of energy window settings were considered: an on-peak window and an off-peak window. In the on-peak window setting, energy centers were set on the photopeaks. In the off-peak window setting, the ratios of energy differences between the photopeak from the lower- and higher-threshold varied from 4:6 to 3:7. In addition, the energy-window width for 99m Tc varied from 5% to 20%, and that for 201 Tl varied from 10% to 30%. The results of this study enabled us to determine the optimal energy windows for each isotope in terms of primary count rate, CNR, and SF. We selected the optimal energy window that increases the primary count rate and CNR while decreasing SF. For 99m Tc SPECT imaging, the energy window of 138–145 keV with a 5% width and off-peak ratio of 3:7 was determined to be the optimal energy window. For 201 Tl SPECT imaging, the energy window of 64–85 keV with a 30% width and off-peak ratio of 3:7 was selected as the optimal energy window. Our results demonstrated that the proper energy window should be carefully chosen based on quantitative measurements in order to take advantage of desirable characteristics of CZT-based small-animal SPECT. These results provided valuable reference information for the establishment of new protocol for CZT-based small-animal study, and may offer insights into the potential of multiple-isotope imaging with CZT-based small-animal SPECT.

Two new MRI contrast agents, Gd-DOTA-c(RGD-ACP-K) (1) and Gd-DOTA-c(RGD-ACH-K) (2), which were designed by incorporating aminocyclopentane (ACP)- or aminocyclohexane (ACH)-carboxylic acid into Gd-DOTA (gadolinium-tetraazacyclo dodecanetetraacetic acid) and cyclic RGDK peptides, were synthesized and evaluated for tumor-targeting ability in vitro and in vivo. Binding affinity studies showed that both 1 and 2 exhibited higher affinity for integrin receptors than cyclic RGDyK peptides, which were used as a reference. These complexes showed high relaxivity and good stability in human serum and have the potential to improve target-specific signal enhancement in vivo MR images.

The goal of this investigation was to evaluate the effects of structural differences between FIAU and FIRU on their ability to serve as a potential tracer for reporter gene imaging. To examine the characteristics of different configurations of FIAU and FIRU, a series of evaluations were done on HSV1-TK gene-expressing cells and on mice with HSV1-TK gene-expressing tumor. The results showed that, as an imaging agent for HSV1-TK-expressing cells, radiolabeled FIAU was more efficient for in vivo imaging than FIRU.

This retrospective study was performed to evaluate a possible association between the presence of epidermal growth factor receptor (EGFR) mutations and the standardized uptake value (SUV) of (18)F-fluoro-2-deoxy-glucose ((18)F-FDG) uptake in patients with non-small cell lung cancer (NSCLC). We included 100 patients who were tested for EGFR mutations by direct sequencing of resected tissues and who underwent preoperative positron emission tomography/computed tomography at the time of diagnosis. The maximum SUV by the primary tumor was chosen for further analysis. EGFR mutations in exons 19 and 21 were detected in 21 NSCLC patients (21%). EGFR mutations were more frequent in never-smokers than ever-smokers (35% versus 11%; P=0.003), in adenocarcinomas than non-adenocarcinomas (34% versus 6%; P=0.001), and in females than males (41% versus 12%; P=0.001). The SUV ranged from 1.3 to 33.0 (median 10.6). Area under receiver operating characteristic curve for SUVs in respect to the presence of EGFR mutations was 0.74 (95% CI: 0.62-0.85). When a cut off value was used, patients with low SUVs were more likely to have EGFR mutations than those with high SUVs (40% versus 11%; P=0.001). On multivariate analysis, a low SUV remained a significant predictors for EGFR mutations (P=0.025). (18)F-FDG uptake was associated with the presence of EGFR mutation. These results extrapolate that (18)F-FDG uptake might be helpful to discriminate patients who harbor EGFR mutations, especially when a genetic test is not feasible.

One of the positron emission radionuclides, (64)Cu, has been reported to be a particularly effective radioisotope in PET imaging study. This utility of (64)Cu depends on the chemical stability in water with proper energy and half-life as gamma-emitters. Hence, we tried to develop a simple method for producing this isotope using an old cyclotron model in our site (50MeV, Scantronics co.). In particular, we designed the equipments of enrich (64)Ni plating system and radioactive (64)Cu separation using plastic cartridge column; (64)Ni plating system on gold foil which located in the 13 degrees angle target toward beam irradiation. For the nuclear reaction of (64)Cu, it was applied to (64)Ni(p, n) (64)Cu at low energy under the degrader composed of Al and Ta foils. After beam irradiation, (64)Cu was identified by multichannel analyzer installed for a HPGe detector and its utility was certified by the microPET images of (64)Cu-ATSM (CT-26 tumor bearing mouse as reported previously). The image quality of (64)Cu was also very similar to that of (18)F radioisotope in microPET scanner. In conclusion, a method of (64)Cu production and its application was successfully established in old cyclotron having high energy.

Small animal positron emission tomography (PET) with 18 F-FDG has been increasingly used for tumor imaging in the murine model. The aim of this study was to establish the anesthesia condition for imaging of lung metastasis tumor using small animal 18 F-FDG PET. Methods To determine the impact of anesthesia on 18 F-FDG distribution in normal mice, five groups were studied under the following conditions: no anesthesia, ketamine and xylazine (Ke/Xy), 0.5% isoflurane (Iso 0.5), 1% isoflurane (Iso 1) and 2% isoflurane (Iso 2). The ex vivo counting, standard uptake value (SUV) image and glucose SUV of 18 F-FDG in various tissues were evaluated. The 18 F-FDG images in the lung metastasis tumor model were obtained under no anesthesia, Ke/Xy and Iso 0.5, and registered with CT image to clarify the tumor region. Results Blood glucose concentration and muscle uptake of 18 F-FDG in the Ke/Xy group markedly increased more than in the other groups. The Iso 2 group increased 18 F-FDG uptake in heart compared with the other groups. The Iso 0.5 anesthesized group showed the lowest 18 F-FDG uptake in heart and chest wall. The small size of lung metastasis tumor (2 mm) was clearly visualized by 18 F-FDG image with the Iso 0.5 anesthesia. Conclusion Small animal 18 F-FDG PET imaging with Iso 0.5 anesthesia was appropriate for the detection of lung metastasis tumor. To acquire 18 F-FDG PET images with small animal PET, the type and level of anesthetic should be carefully considered to be suitable for the visualization of target tissue in the experimental model.

A new method has been developed for diffusible tracers, to quantify CBF at rest and after pharmacological stress from a single session of dynamic scans with dual bolus administration of a radiotracer. The calculation process consisted of three steps, including the procedures of incorporating background radioactivity contaminated from the previous scan. Feasibility of this approach was tested on clinical SPECT studies on 16 subjects. Two sequential SPECT scans, 30 min apart, were carried out on each subject, after each of two split-dose administrations of 111 MBq IMP. Of these, 11 subjects received acetazolamide at 10 min before the second IMP injection. Additional PET scans were also carried out on 6 subjects on a separate day, at rest and after acetazolamide administration. The other 5 subjects were scanned only at rest during the whole study period. Quantitative CBF obtained by this method was in a good agreement with those determined with PET (y(ml/100 g/min) = 1.07 × (ml/100 g/min) − 1.14, r = 0.94). Vasareactivity was approximately 40% over the whole cerebral area on healthy controls, which was consistent with a literature value. Reproducibility of CBF determined in the rest–rest study was 1.5 ± 5.7%. Noise enhancement of CBF images, particularly the second CBF, was reduced, providing reasonable image quality. Repeat assessment of quantitative CBF from a single session of scans with split-dose IMP is accurate, and may be applied to clinical research for assessing vascular reactivity in patients with chronic cerebral vascular disease.

Pinhole single-photon emission computed tomography (SPECT) with high spatial-resolution is suitable for small-animal imaging, but has limitations associated with spatial-resolution inhomogeneity or axial blurring. We have hypothesized that this blurring is due to incompleteness of projection data acquired by a single circular pinhole orbit. And we have developed a pinhole SPECT system with two circular orbits which satisfy Tuy's condition so as to provide complete data for 3D pinhole SPECT reconstruction within the whole field-of-view (FOV); a dedicated 3D ordered subsets expectation maximization (3D-OSEM) reconstruction method for two-orbit data. This study is aimed at evaluating accuracy and impact of this system. In this system, not the camera but the object rotates and the two orbits are 90° and 45° relative to object's axis. Experiments using a multiple-disk phantom filled with 99m Tc solution and a mouse bone scan using 99m Tc-labeled HMDP agent were carried out. The Feldkamp's filtered back-projection (FBP) method and the 3D-OSEM method were applied to these data sets. The axial blurring was apparent on images reconstructed by FBP for single-orbit data, while the 3D-OSEM using two-orbit data dramatically improved the resolution homogeneity and statistical noise property, and also demonstrated considerably better image quality in the mouse scan.

The coupling of cerebral blood flow (CBF) and metabolic rate of oxygen (CMRO2) during physiological and pathological conditions remains a subject of debate. We have developed a physiological model for oxygen delivery and metabolism, which allows the estimation of net oxygen diffusibility at the capillary level, termed “effective oxygen diffusibility (EOD).” The results of PET in monkeys showed dynamic changes in EOD in response to changes in oxygen delivery and consumption. EOD is defined as capillary volume and permeability product, but its change mainly reflects the pericapillary oxygen gradient as long as capillary architecture is preserved. EOD may have sufficient predictability to represent the tissue oxygen demand and application of the model to PET data. In the future, EOD may give us further insight to understand the physiological regulatory system for oxygen demand in the brain.

Recently, techniques for converting site-specific normal databases to other databases have been required for SPECT image statistical analysis. To implement scatter correction, we developed an image conversion technique named image-based scatter correction (IBSC). Furthermore, we evaluated the applicability of IBSC for SPM analysis. SPECT studies were performed on 28 normal volunteers and 10 patients with Alzheimer's disease (AD) using 123 I-IMP. Two sets of scatter uncorrected images, I AC μ b , and a corrected image by TEW, I TEW , were reconstructed with attenuation correction using Chang's method. Scatter corrected images by IBSC, I IBSC , were generated from I AC μ b . Normal databases of I AC μ b , I TEW and I IBSC were compared by SPM analysis. The Z -score (=(mean−AD)/S.D.) of I TEW was compared with that of I AC μ b . Significant differences ( p I AC μ b and I TEW observed at the global posterior cingulate and precuneus regions almost disappeared when I TEW and I IBSC were compared . The Z -score at the posterior cingulate by I TEW was increased compared with that of I AC μ b . We conclude that for SPM analysis of IMP-SPECT, IBSC can convert a normal database of scatter uncorrected images into corrected images, which is equivalent to correction by a conventional TEW method. Scatter correction may improve the ability to detect AD.

The values of cerebral blood flow (CBF) and vascular volume (V0) can be estimated using H215O dynamic PET and the two-compartment model. In this study, we present a method that can generate parametric images of both CBF and V0, with improvement of image quality, by a single computational procedure. This method is based on the two-compartment model, and employs linear least square algorithm and cluster analysis for parameter estimation and suppressing noise on image data, respectively. The results in computer simulation showed that this method could provide the reduction of error in parameter estimation, as well as noise on parametric images of both CBF and V0, and the smaller effect of changes of CBF and V0 on the estimation of both parameters. In the PET study, this method could provide the images of CBF and V0 with improvement in quality, compared with those without clustering by showing the clear location of arterial vascular components on the V0 image. In the simulation, the error in parameter estimation was sufficiently small for K1, but not for V0. These results reveal that the presented method has the potential to make a contribution to the improved diagnosis of cerebral vascular disease and activation.

This chapter describes a brief overview of present advances and challenges in PET methodology from the engineering side. Topics are as follows: (1) advances in hardware design and sophisticated software development for registering PET and anatomical images, (2) higher spatial resolution approaching sub-millimeters, (3) improved temporal resolution, (4) repeat assessment of physiologic functions, (5) corrections for partial volume effect (PVE), and (6) motion correction capability. These features provide potentials of using PET in new application fields.