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Purpose: Information about developed positron emission tomography (PET) tracers and obtained clinical PET images is publicly available in a database. However, findings regarding the kinetic parameters of PET tracers are yet to be summarized. Therefore, in this study, we created an open-access database of central nervous system (CNS) kinetic parameters in the healthy human brain for existing PET tracers (DOCK–PET). Methods: Our database includes information on the kinetic parameters and compounds of existing CNS–PET tracers. The kinetic parameter dataset comprises the analysis methods, VT, BPND, K parameters, relevant literature, and study details. The list of PET tracers and kinetic parameter information was compiled through keyword-based searches of PubMed and the Molecular Imaging and Contrast Agent Database (MICAD). The kinetic parameters obtained, including VT, BPND, and K parameters, were reorganized based on the defined brain anatomical regions. All data were rigorously double-checked before being summarized in Microsoft Excel and JavaScript Object Notation (JSON) formats. Results: Of the 247 PET tracers identified through searches using the PubMed and MICAD websites, the kinetic parameters of 120 PET tracers were available. Among the 120 PET tracers, compound structures with chemical and physical properties were obtained from the PubChem website or the ChemDraw software. Furthermore, the affinity information of the 104 PET tracers was gathered from PubChem or extensive literature surveys of the 120 PET tracers. Conclusions: We developed a comprehensive open-access database, DOCK–PET, that includes both kinetic parameters of healthy humans and compound information for existing CNS–PET tracers. [ABSTRACT FROM AUTHOR]

This work reports on the differential and various angle integrated cross sections for the scattering of electrons and positrons by silicon atoms. Moreover, the Sherman function S (θ) and two other spin asymmetry parameters U (θ) and T (θ) have been calculated. Critical minima in the elastic differential cross sections and maximum spin polarization points were identified for this element. Dirac partial wave method with a complex optical model potential is used to carry out these investigations. Transport characteristics of electrons in silicon vapors and mixtures of inert gases (helium, argon) with silicon vapor were calculated using the Monte Carlo method. For electric field strengths ranging from 1 to 100 Td, drift velocity, average electron energy, diffusion and mobility coefficients, and electron energy distribution function are studied. We have shown that impurities of silicon vapor significantly affect electron transport in noble gases. [ABSTRACT FROM AUTHOR]

The present work introduced a framework to investigate the effectiveness of proton boron fusion therapy (PBFT) at the cellular level. The framework consisted of a cell array generator program coupled with PHITS Monte Carlo package with a dedicated terminal-based code editor that was developed in this work. The framework enabled users to model large cell arrays with normal, all boron, and random boron filled cytoplasm, to investigate the underlying mechanism of PBFT. It was found that alpha particles and neutrons could be produced in absence of boron mainly because of nuclear reaction induced by proton interaction with 16O, 12C and 14N nuclei. The effectiveness of PBFT is highly dependent on the incident proton energy, source size, cell array size, buffer medium thickness layer, concentration and distribution of boron in the cell array. To quantitatively assess the effectiveness of PBFT, of the total energy deposition by alpha particle for different cases were determined. The number of alpha particle hits in cell cytoplasm and nucleus for normal and 100 ppm boron were determined. The obtained results and the developed tools would be useful for future development of PBFT to objectively determine the effectiveness of this treatment modality. [ABSTRACT FROM AUTHOR]

Objective: Transarterial Radioembolization (TARE) with 90Y-loaded glass microspheres is a locoregional treatment option for Hepatocellular Carcinoma (HCC). Post-treatment 90Y bremsstrahlung imaging using Single-Photon Emission Tomography (SPECT) is currently a gold-standard imaging modality for quantifying the delivered dose. However, the nature of bremsstrahlung photons causes difficulty for dose estimation using SPECT imaging. This work aimed to investigate the possibility of using glass microspheres loaded with 90Y and Nanoparticles (NPs) to improve the quantification of delivered doses.Methods: The Monte Carlo codes were used to simulate the post-TARE 90Y planar imaging. Planar images from bremsstrahlung photons and characteristic X-rays are acquired when 0, 1.2 mol/L, 2.4 mol/L, and 4.8 mol/L of Gold (Au), Hafnium (Hf), and Gadolinium (Gd) NPs are incorporated into the glass microspheres. We evaluated the quality of acquired images by calculating sensitivity and Signal-to-Background Ratio (SBR). Therapeutic effects of NPs were evaluated by calculation of Dose Enhancement Ratio (DER) in tumoral and non-tumoral liver tissues.Results: The in silico results showed that the sensitivity values of bremsstrahlung and characteristic X-ray planar images increased significantly as the NPs concentration increased in the glass microspheres. The SBR values decreased as the NPs concentration increased for the bremsstrahlung planar images. In contrast, the SBR values increased for the characteristic X-ray planar images when Hf and Gd were incorporated into the glass microspheres. The DER values decreased in the tumoral and non-tumoral liver tissues as the NPs concentration increased. The maximum dose reduction was observed at the NPs concentration of 4.8 mol/L (≈ 7%).Conclusions: The incorporation of Au, Hf, and Gd NPs into the glass microspheres improved the quality and quantity of post-TARE planar images. Also, treatment efficiency was decreased significantly at NPs concentration > 4.8 mol/L. [ABSTRACT FROM AUTHOR]

Artificial intelligence (AI) has been applied to various medical imaging tasks, such as computer-aided diagnosis. Specifically, deep learning techniques such as convolutional neural network (CNN) and generative adversarial network (GAN) have been extensively used for medical image generation. Image generation with deep learning has been investigated in studies using positron emission tomography (PET). This article reviews studies that applied deep learning techniques for image generation on PET. We categorized the studies for PET image generation with deep learning into three themes as follows: (1) recovering full PET data from noisy data by denoising with deep learning, (2) PET image reconstruction and attenuation correction with deep learning and (3) PET image translation and synthesis with deep learning. We introduce recent studies based on these three categories. Finally, we mention the limitations of applying deep learning techniques to PET image generation and future prospects for PET image generation. [ABSTRACT FROM AUTHOR]

Not only visual interpretation for lesion detection, staging, and characterization, but also quantitative treatment response assessment are key roles for 18F-FDG PET in oncology. In multicenter oncology PET studies, image quality standardization and SUV harmonization are essential to obtain reliable study outcomes. Standards for image quality and SUV harmonization range should be regularly updated according to progress in scanner performance. Accordingly, the first aim of this study was to propose new image quality reference levels to ensure small lesion detectability. The second aim was to propose a new SUV harmonization range and an image noise criterion to minimize the inter-scanner and intra-scanner SUV variabilities. We collected a total of 37 patterns of images from 23 recent PET/CT scanner models using the NEMA NU2 image quality phantom. PET images with various acquisition durations of 30–300 s and 1800 s were analyzed visually and quantitatively to derive visual detectability scores of the 10-mm-diameter hot sphere, noise-equivalent count (NECphantom), 10-mm sphere contrast (QH,10 mm), background variability (N10 mm), contrast-to-noise ratio (QH,10 mm/N10 mm), image noise level (CVBG), and SUVmax and SUVpeak for hot spheres (10–37 mm diameters). We calculated a reference level for each image quality metric, so that the 10-mm sphere can be visually detected. The SUV harmonization range and the image noise criterion were proposed with consideration of overshoot due to point-spread function (PSF) reconstruction. We proposed image quality reference levels as follows: QH,10 mm/N10 mm ≥ 2.5 and CVBG ≤ 14.1%. The 10th–90th percentiles in the SUV distributions were defined as the new SUV harmonization range. CVBG ≤ 10% was proposed as the image noise criterion, because the intra-scanner SUV variability significantly depended on CVBG. We proposed new image quality reference levels to ensure small lesion detectability. A new SUV harmonization range (in which PSF reconstruction is applicable) and the image noise criterion were also proposed for minimizing the SUV variabilities. Our proposed new standards will facilitate image quality standardization and SUV harmonization of multicenter oncology PET studies. The reliability of multicenter oncology PET studies will be improved by satisfying the new standards. [ABSTRACT FROM AUTHOR]

To evaluate tumor blood flow using 15O-water positron emission tomography (PET) in patients with non-small cell lung cancer (NSCLC) before and after chemotherapy with bevacizumab, and to investigate the effects of bevacizumab on tumor blood flow changes and progression-free survival (PFS). Twelve patients with NSCLC were enrolled. Six patients underwent chemotherapy with bevacizumab and the other six without bevacizumab. 15O-water dynamic PET scans were performed within 1 week before the start of chemotherapy and within 1 week after the first day of chemotherapy. Tumor blood flow was analyzed quantitatively using a single one-tissue compartment model with the correction of pulmonary circulation blood volume and arterial blood volume via an image-derived input function. In the bevacizumab group, mean tumor blood flow was statistically significantly reduced post-chemotherapy (pre-chemotherapy 0.27 ± 0.14 mL/cm3/min, post-chemotherapy 0.18 ± 0.12 mL/cm3/min). In the no bevacizumab group, there was no significant difference between mean tumor perfusion pre-chemotherapy (0.42 ± 0.42 mL/cm3/min) and post-chemotherapy (0.40 ± 0.27 mL/cm3/min). In the bevacizumab group, there was a positive correlation between the blood flow ratio (tumor blood flow post-chemotherapy/tumor blood flow pre-chemotherapy) and PFS (correlation coefficient 0.94). Mean tumor blood flow decreases after bevacizumab administration and was positively correlated with longer PFS. [ABSTRACT FROM AUTHOR]

The D-shuttle dosimeter technique is a convenient approach for estimating the radiation dosimetry in a positron emission tomography (PET) study that employs multiple D-shuttle dosimeters attached to the body surface of a patient. To bring this technique into clinical usage, it is very important to evaluate its performance by investigating the bias associated with D-shuttle dosimeter positioning and by comparing the estimates with those of the whole-body dynamic PET imaging technique. The torso cavity and six spheres of the NEMA body phantom were filled with 18F-FDG solution, and then, the phantom was imaged for 1 h. We assumed the mislocated positioning of the D-shuttle dosimeters by shifting them in the z-direction (upper) in a range of 1–5 cm from the original positions. The cumulative radioactivities, absorbed doses, and effective dose were estimated using accurate and mislocated positions of the D-shuttle dosimeters. For comparison, the cumulative radioactivities were also estimated from the PET images, and then, the absorbed doses and effective dose were computed. The maximum bias of the average estimated cumulated radioactivities and the effective doses was − 15.0% and − 19.7% for the 1 cm shifted positions, respectively. The ratios of absorbed doses obtained from D-shuttle and PET measurement against the actual values were between 0.9 and 1.3, and 0.7 and 1.0, respectively. The bias associated with the D-shuttle dosimeter positions was significant and probably consistent, and both dosimetric techniques exhibited good performance in this phantom study. [ABSTRACT FROM AUTHOR]

Purposes: Subject's motion during brain PET scan degrades spatial resolution and quantification of PET images. To suppress these effects, rigid-body motion correction systems have been installed in commercial PET scanners. In this study, we systematically compare the accuracy of motion correction among 3 commercial PET scanners using a reproducible experimental acquisition protocol.Methods: A cylindrical phantom with two 22Na point sources was placed on a customized base to enable two types of motion, 5° yaw and 15° pitch rotations. Repetitive PET scans (5 min × 5 times) were performed at rest and under 2 motion conditions using 3 clinical PET scanners: the Eminence STARGATE G/L PET/CT (STARGATE) (Shimadzu Corp.), the SET-3000 B/X PET (SET-3000) (Shimadzu Corp.), and the Biograph mMR PET/MR (mMR) (Siemens Healthcare) systems. For STARGATE and SET-3000, the Polaris Vicra (Northern Digital Inc.) optical tracking system was used for frame-by-frame motion correction. For Biograph mMR, sequential MR images were simultaneously acquired with PET and used for LOR-based motion correction. All PET images were reconstructed by FBP algorithm with 1 × 1 mm pixel size. To evaluate the accuracy of motion correction, FWHMs and spherical ROI values were analyzed.Results: The percent differences (%diff) in averaged FWHMs of point sources at 4 cm off-center between motion-corrected and static images were 0.77 ± 0.16 (STARGATE), 2.4 ± 0.34 (SET-3000), and 11 ± 1.0% (mMR) for a 5° yaw and 2.3 ± 0.37 (STARGATE) and 1.1 ± 0.60 (SET-3000) for a 15° pitch respectively. The averaged %diff between ROI values of motion-corrected images and static images were less than 2.0% for all conditions.Conclusions: In this study, we proposed a reproducible experimental framework to allow the systematic validation and comparison of multiple motion tracking and correction methodologies among different PET/CT and PET/MR commercial systems. Our proposed validation platform may be useful for future studies evaluating state-of-the-art motion correction strategies in clinical PET imaging. [ABSTRACT FROM AUTHOR]

With the increasing incidence of dementia worldwide, the frequent use of amyloid and tau positron emission tomography imaging requires low-dose protocols for the differential diagnoses of various neurodegenerative diseases and the monitoring of disease progression. In this study, we investigated the feasibility to reduce the PET dose without a significant loss of quantitative accuracy in 3D dynamic row action maximum likelihood algorithm-reconstructed PET images using [11C]PIB and [18F]THK5351. Eighteen cognitively normal young controls, cognitively normal elderly controls, and patients with probable Alzheimer’s disease (n = 6 each), were included. Reduced doses were simulated by randomly sampling half and quarter of the full counts in list mode data for one independent realization at each simulated dose. Bias was evaluated between the reduced dose from the full dose of standardized uptake value ratio (SUVR), distribution volume ratio (DVR) from reference Logan, and non-displaceable binding potential (BPND) from simplified reference tissue model (SRTM). DVR yielded the least bias at low dose compared to SUVR and BPND, and thus, is highly recommended. The dose of [18F]THK5351 and [11C]PIB can be reduced to a quarter of the full dose using DVR for evaluation, whereas the dose can only be reduced to half and a quarter of the full dose for [18F]THK5351 and [11C]PIB using SUVR. BPND showed inconsistent trend and large bias at low dose. The feasibility of dose reduction was dependent on the selected parameters of interest, reconstruction algorithms, reference regions, and to a lesser degree by motion effects. [ABSTRACT FROM AUTHOR]

Attenuation correction (AC) is required for accurate quantitative evaluation of small animal PET data. Our objective was to compare three AC methods in the small animal Clairvivo-PET scanner. The three AC methods involve applying attenuation coefficient maps generated by simulating a cylindrical map (SAC), segmenting the emission data (ESAC), and segmenting the transmission data (TSAC), imaged using a Cs single-photon source. Investigation was carried out using a 65 mm uniform cylinder and an NEMA NU4 2008 mouse phantom, filled with water or tungsten liquid, to mimic bone. Evaluation was carried out using the difference of the segmented map volume from the known cylindrical phantom volume, the recovery of the radioactivity concentration, and the line profiles. The optimal transmission scan time for achieving accurate AC using TSAC was determined using 5, 10, 15, 20, and 25 min transmission scan time. The effects of scatter correction and reconstruction algorithms on ESAC were investigated. SAC showed the best performance but was unable to correct for different tissues and the scanner bed, and faced difficulty with correct positioning of the attenuation coefficient map. ESAC was affected by scatter correction and reconstruction algorithm, and may result in poor boundary delineation, and hence was unreliable. TSAC showed reasonable performance but required further optimization of the default segmentation setting. A minimum transmission scan time of 20 min is recommended for Clairvivo-PET using Cs source to ensure that sufficient transmission counts are obtained to generate accurate attenuation coefficient map. [ABSTRACT FROM AUTHOR]

Purpose: To suppress partial volume effect (PVE) in brain PET, there have been many algorithms proposed. However, each methodology has different property due to its assumption and algorithms. Our aim of this study was to investigate the difference among partial volume correction (PVC) method for tau and amyloid PET study.Methods: We investigated two of the most commonly used PVC methods, Müller-Gärtner (MG) and geometric transfer matrix (GTM) and also other three methods for clinical tau and amyloid PET imaging. One healthy control (HC) and one Alzheimer's disease (AD) PET studies of both [18F]THK5351 and [11C]PIB were performed using a Eminence STARGATE scanner (Shimadzu Inc., Kyoto, Japan). All PET images were corrected for PVE by MG, GTM, Labbé (LABBE), Regional voxel-based (RBV), and Iterative Yang (IY) methods, with segmented or parcellated anatomical information processed by FreeSurfer, derived from individual MR images. PVC results of 5 algorithms were compared with the uncorrected data.Results: In regions of high uptake of [18F]THK5351 and [11C]PIB, different PVCs demonstrated different SUVRs. The degree of difference between PVE uncorrected and corrected depends on not only PVC algorithm but also type of tracer and subject condition.Conclusion: Presented PVC methods are straight-forward to implement but the corrected images require careful interpretation as different methods result in different levels of recovery. [ABSTRACT FROM AUTHOR]

Objective: Cerenkov-light imaging provides inherently high resolution because the light is emitted near the positron radionuclide. However, the magnitude for the high spatial resolution of Cerenkov-light imaging is unclear. Its potential molecular imaging applications also remain unclear. We developed an ultrahigh-resolution Cerenkov-light imaging system, measured its spatial resolution, and explored its applications to molecular imaging research. Methods: Our Cerenkov-light imaging system consists of a high-sensitivity charged-coupled device camera (Hamamatsu Photonics ORCA2-ER) and a bright lens (Xenon 0.95/25). An extension ring was inserted between them to magnify the subject. A ~100-μm-diameter Na point source was made and imaged by the system. For applications of Cerenkov-light imaging, we conducted F-FDG administered in vivo, ex vivo whole brain, and sliced brain imaging of rats. Results: We obtained spatial resolution of ~220 μm for a Na point source with our developed imaging system. The F-FDG rat head images showed high light intensity in the eyes for the Cerenkov-light images, although there was no accumulation in these parts in the PET images. The sliced rat brain showed much higher spatial resolution for the Cerenkov-light images compared with CdWO scintillator-based autoradiography, although some contrast decrease was observed for them. Conclusion: Even though the Cerenkov-light images showed ultrahigh resolution of ~220 μm, their distribution and contrast were sometimes different from the actual positron accumulation in the subjects. Care must be taken when evaluating positron distribution from Cerenkov-light images. However, the ultrahigh resolution of Cerenkov-light imaging will be useful for transparent subjects including phantom studies. [ABSTRACT FROM AUTHOR]

Objective: YSO (Ce-doped YSiO) is a promising scintillator for a single-photon imaging system since it has relatively high light output and does not contain any natural radioactivity. Since YSO is not hygroscopic, it may be possible to fabricate a block with small pixels for a high-resolution system. For this purpose, we developed a high-resolution gamma camera system that employs smaller than 1-mm YSO pixels. Methods: The gamma camera's detector used 0.8 × 0.8 × 7-mm YSO pixels. All the surfaces of these YSO pixels were mechanically polished, combined with a 0.1-mm-thick BaSO reflector to form a 48 × 48 matrix, and optically coupled to a high quantum efficiency, 2-inch square position sensitive photomultiplier tube (Hamamatsu Photonics H10966 A-100). The YSO block was 43.2 × 43.2 mm. The YSO gamma camera was encased in a 5-mm-thick tungsten container, and a parallel collimator was mounted on its front. The parallel hole collimator was made of a 3-layer (each layer was 5-mm thick) tungsten plate, and each plate had 48 × 48, 0.6-mm holes that were positioned by one-to-one coupling with the YSO pixels. Results: Even with the 0.8-mm YSO pixels, we clearly resolved most of the pixels in a 2-dimensional histogram with a peak-to-valley ratio of 2.9 for the 122-keV gamma photons. The energy resolution was 20.4 % FWHM. The spatial resolutions with a parallel hole collimator 2 mm from the collimator surface were 0.7- and 1.3-mm FWHM for the 122- and ~35-keV gamma photons, respectively. We successfully obtained phantoms and small animal images with our YSO gamma camera system. Conclusion: Our high-resolution system has a potential to be useful for molecular imaging research. [ABSTRACT FROM AUTHOR]

Background: Patient movement has been considered an important source of errors in cardiac PET. This study was aimed at evaluating the effects of such movement on myocardial blood flow (MBF) and perfusable tissue fraction (PTF) measurements in intravenous ¹⁵O-water PET.Methods: Nineteen ¹⁵O-water scans were performed on ten healthy volunteers and three patients with severe cardiac dysfunction under resting conditions. Motions of subjects during scans were estimated by monitoring locations of markers on their chests using an optical motion-tracking device. Each sinogram of the dynamic emission frames was corrected for subject motion. Variation of regional MBF and PTF with and without the motion corrections was evaluated.Results: In nine scans, motions during ¹⁵O-water scan (inter-frame (IF) motion) and misalignments relative to the transmission scan (inter-scan (IS) motion) larger than the spatial resolution of the PET scanner (4.0 mm) were both detected by the optical motion-tracking device. After correction for IF motions, MBF values changed from 0.845 ± 0.366 to 0.780 ± 0.360 mL/minute/g (P < .05). In four scans with only IS motion detected, PTF values changed significantly from 0.465 ± 0.118 to 0.504 ± 0.087 g/mL (P< .05), but no significant change was found in MBF values.Conclusions: This study demonstrates that IF motion during ¹⁵O-water scan at rest can be source of error in MBF measurement. Furthermore, estimated MBF is less sensitive than PTF values to misalignment between transmission and ¹⁵O-water emission scans. [ABSTRACT FROM AUTHOR]

Background: Patient movement has been considered an important source of errors in cardiac PET. This study was aimed at evaluating the effects of such movement on myocardial blood flow (MBF) and perfusable tissue fraction (PTF) measurements in intravenous O-water PET. Methods: Nineteen O-water scans were performed on ten healthy volunteers and three patients with severe cardiac dysfunction under resting conditions. Motions of subjects during scans were estimated by monitoring locations of markers on their chests using an optical motion-tracking device. Each sinogram of the dynamic emission frames was corrected for subject motion. Variation of regional MBF and PTF with and without the motion corrections was evaluated. Results: In nine scans, motions during O-water scan (inter-frame (IF) motion) and misalignments relative to the transmission scan (inter-scan (IS) motion) larger than the spatial resolution of the PET scanner (4.0 mm) were both detected by the optical motion-tracking device. After correction for IF motions, MBF values changed from 0.845 ± 0.366 to 0.780 ± 0.360 mL/minute/g ( P < .05). In four scans with only IS motion detected, PTF values changed significantly from 0.465 ± 0.118 to 0.504 ± 0.087 g/mL ( P< .05), but no significant change was found in MBF values. Conclusions: This study demonstrates that IF motion during O-water scan at rest can be source of error in MBF measurement. Furthermore, estimated MBF is less sensitive than PTF values to misalignment between transmission and O-water emission scans. [ABSTRACT FROM AUTHOR]

Objective: Gastrointestinal stromal tumors (GISTs) and malignant lymphomas (MLs) in the abdomen are often observed as tumors of unknown origin on F-18 FDG PET/CT. The purpose of this study was to evaluate the intratumoral metabolic heterogeneity of F-18 FDG uptake on PET to determine if it might be helpful to discriminate between these tumors. Methods: The F-18 FDG PET/CT findings of 21 large abdominal tumors were retrospectively evaluated (9 GISTs and 12 MLs). Intratumoral heterogeneity was evaluated by visual scoring (visual score: 0, homogeneous; 1, slightly heterogeneous; 2, moderately heterogeneous; 3, highly heterogeneous) and by the cumulative standardized uptake value (SUV) histograms on transaxial PET images at the maximal cross-sectional tumor diameter. Percent tumor areas above a threshold from 0 to 100% of the maximum SUV were plotted and the area under curve of the cumulative SUV histograms (AUC-CSH) was used as a heterogeneity index, where lower values corresponded with increased heterogeneity. Correlation between the visual score and the AUC-CSH was investigated by the Spearman's rank test. Results: GISTs exhibited heterogeneous uptake of F-18 FDG, whereas MLs showed rather homogeneous uptake on visual analysis (visual score: 2.67 ± 0.50 and 0.58 ± 0.79, respectively; p < 0.001). The AUC-CSH was significantly lower for the GISTs than for the MLs (0.41 ± 0.14 and 0.64 ± 0.08, respectively; p < 0.001). Significant correlations were observed between the visual score and the AUC-CSH ( ρ = −0.866, p < 0.001). Conclusion: GISTs exhibited significantly heterogeneous intratumoral tracer uptake as compared with the MLs. Evaluation of the intratumoral heterogeneity of F-18 FDG uptake may help in the discrimination between these tumors. [ABSTRACT FROM AUTHOR]

In quantitative measurements of small animal PET studies, blood sampling is limited due to the small amounts of blood such animals can provide. In addition, injection doses are quite limited. In this situation, a high-sensitivity well counter would be useful for reducing the amount of the blood sample needed from small animals. Bismuth germinate (BGO) has a high stopping power for high-energy gamma rays compared to NaI(Tl), which is commonly used for conventional well counters. We have developed a BGO well counter and have tested it for blood-sampling measurements in small animals. The BGO well counter uses a square BGO block (59 × 59 × 50 mm) with a square open space (27 × 27 × 34 mm) in the center of the block. The BGO block was optically coupled to a 59-mm square-shaped photomultiplier tube (PMT). Signals from the PMT were digitally processed for the integration and energy window setting. The results showed that the energy spectrum of the BGO well counter measured with a Na-22 point source provided counts that were about 6 times higher for a 1022-keV (511 keV × 2) gamma peak than the spectrum of a 2-in. NaI(Tl) well counter. The relative sensitivity of the developed BGO well counter was 3.4 times higher than that of a NaI(Tl) well counter. The time activity curve of arterial blood was obtained successfully with the BGO well counter for a F-18-FDG study on rat. The BGO well counter will contribute to reducing the amount of sampled blood and to improving the throughput of quantitative measurements in small animal PET studies. [ABSTRACT FROM AUTHOR]

Purpose: In normotensive eyes, reduced ocular blood flow can lead to glaucoma pathogenesis. Drugs that reduce intraocular pressure (IOP) often cause vasodilation of the ciliary arteries and improve blood flow to the eye. A novel class of drugs called Rho-associated coiled coil-forming protein kinase (ROCK) inhibitors can lower IOP. Therefore, we tested the ability of two ROCK inhibitors, Y-27632 and Y39983, to relax rabbit ciliary arteries. Methods: We measured in vitro ciliary artery smooth muscle contractions by isometric tension recordings and changes of intracellular free calcium concentration ([Ca]) by fluorescence photometry. Results: Both Y-27632 and Y-39983 induced a concentration-dependent relaxation in rabbit ciliary arteries precontracted with a high-potassium (high-K) solution. The amplitude of relaxation induced by Y-27632 and Y-39983 was not affected by either 100 μM N-nitro- l-arginine methyl ester ( l-NAME) or 10 μM indomethacin. In Ca-free solution, Y-27632 and Y-39983 significantly inhibited the transient contraction of ciliary arteries induced by 10 μM histamine. However, neither Y-27632 nor Y-39983 affected the elevation of [Ca] induced by high-K solution and histamine. Conclusions: We concluded that Y-27632 and Y-39983 relaxed isolated rabbit ciliary artery segments in vitro. The mechanism of relaxation was not dependent on endothelial-derived factors such as nitric oxide (NO) or prostacyclin, nor was it dependent on changes in intracellular Ca concentration. [ABSTRACT FROM AUTHOR]

Purpose: Cerebral blood flow (CBF), oxygen extraction fraction (OEF) and cerebral metabolic rate of O(2) (CMRO(2)) can be quantified by PET with the administration of H (2) (15) O and (15)O(2). Recently, a shortening in the duration of these measurements was achieved by the sequential administration of dual tracers of (15)O(2) and H (2) (15) O with PET acquisition and integration method (DARG method). A transmission scan is generally required for correcting photon attenuation in advance of PET scan. Although the DARG method can shorten the total study duration to around 30 min, the transmission scan duration has not been optimized and has possibility to shorten its duration. Our aim of this study was to determine the optimal duration for the transmission scan. We introduced 'N-index', which estimates the noise level on an image obtained by subtracting two statistically independent and physiologically equivalent images. The relationship between noise on functional images and duration of the transmission scan was investigated by N-index. Methods: We performed phantom studies to test whether the N-index reflects the pixel noise in a PET image. We also estimated the noise level by the N-index on CBF, OEF and CMRO(2) images from DARG method in clinical patients, and investigated an optimal true count of the transmission scan. Results: We found tight correlation between pixel noise and N-index in the phantom study. By investigating relationship between the transmission scan duration and N-index value for the functional images by DARG method, we revealed that the transmission data with true counts of more than 40 Mcounts results in CBF, OEF, and CMRO(2) images of reasonable quantitative accuracy and quality. Conclusion: The present study suggests that further shortening of DARG measurement is possible by abridging the transmission scan. The N-index could be used to determine the optimal measurement condition when examining the quality of image. [ABSTRACT FROM AUTHOR]

Cerebral blood flow (CBF), oxygen extraction fraction (OEF) and cerebral metabolic rate of O2 (CMRO2) can be quantified by PET with the administration of HO and 15O2. Recently, a shortening in the duration of these measurements was achieved by the sequential administration of dual tracers of 15O2 and HO with PET acquisition and integration method (DARG method). A transmission scan is generally required for correcting photon attenuation in advance of PET scan. Although the DARG method can shorten the total study duration to around 30 min, the transmission scan duration has not been optimized and has possibility to shorten its duration. Our aim of this study was to determine the optimal duration for the transmission scan. We introduced ‘ N-index’, which estimates the noise level on an image obtained by subtracting two statistically independent and physiologically equivalent images. The relationship between noise on functional images and duration of the transmission scan was investigated by N-index. We performed phantom studies to test whether the N-index reflects the pixel noise in a PET image. We also estimated the noise level by the N-index on CBF, OEF and CMRO2 images from DARG method in clinical patients, and investigated an optimal true count of the transmission scan. We found tight correlation between pixel noise and N-index in the phantom study. By investigating relationship between the transmission scan duration and N-index value for the functional images by DARG method, we revealed that the transmission data with true counts of more than 40 Mcounts results in CBF, OEF, and CMRO2 images of reasonable quantitative accuracy and quality. The present study suggests that further shortening of DARG measurement is possible by abridging the transmission scan. The N-index could be used to determine the optimal measurement condition when examining the quality of image. [ABSTRACT FROM AUTHOR]

Although 15O-O2 gas inhalation can provide a reliable and accurate myocardial metabolic rate for oxygen by PET, the spillover from gas volume in the lung distorts the images. Recently, we developed an injectable method in which blood takes up 15O-O2 from an artificial lung, and this made it possible to estimate oxygen metabolism without the inhalation protocol. In the present study, we evaluated the effectiveness of the injectable 15O-O2 system in porcine hearts. PET scans were performed after bolus injection and continuous infusion of injectable 15O-O2 via a shunt between the femoral artery and the vein in normal pigs. The injection method was compared to the inhalation method. The oxygen extraction fraction (OEF) in the lateral walls of the heart was calculated by a compartmental model in view of the spillover and partial volume effect. A significant decrease of lung radioactivity in PET images was observed compared to the continuous inhalation of 15O-O2 gas. Furthermore, the injectable 15O-O2 system provides a measurement of OEF in lateral walls of the heart that is similar to the continuous-inhalation method (0.71 ± 0.036 and 0.72 ± 0.020 for the bolus-injection and continuous-infusion methods, respectively). These results indicate that injectable 15O-O2 has the potential to evaluate myocardial oxygen metabolism. [ABSTRACT FROM AUTHOR]

Objective: Cardiac (15)O-water PET studies provide an accurate quantitation of regional myocardial blood flow (rMBF). We developed a motion correction system using an optical motion-tracking device to detect a subject's global movement for cardiac study. Methods: PET studies were carried out on a cardiac phantom and a healthy volunteer at rest. The three-dimensional locations of the markers attached to the subjects during scans were measured using an optical motion-tracking system. In the phantom study, we performed a transmission scan and seven (18)F emission scans of a baseline and with artificial misalignment of shifts and rotations. The correlation coefficients between the baseline and the other images before and after the corrections for the misalignment were calculated. In the human study, we performed a (15)O-water dynamic scan with a transmission and axially 30 mm-shifted transmission scans. Motion of the subject was estimated by the information from the system, and was corrected on each sinogram using attenuation maps realigned to dynamic frames. Reconstructed dynamic images were then realigned to the transmission data. We calculated rMBF values for nine segments and myocardial images from the emission images, which were reconstructed with the first attenuation map (reference) and with the misaligned attenuation map before and after our corrections. Results: In the phantom study, the correlation coefficients were improved from 0.929 +/- 0.022 to 0.987 +/- 0.010 (mean +/- SD) after the corrections. In the human study, the global and cyclic movements were detected. The cyclic movement due to respiration was smoothed by frame-averaging, and reasonable information of the global movement was obtained. The rMBF value (mean +/- SD) was 0.94 +/- 0.12 mL/min/g for the reference. The rMBF values using the misaligned attenuation map changed from 1.03 +/- 0.21 to 0.93 +/- 0.11 mL/min/g after the correction, and spurious defects in myocardial images were also recovered. Conclusions: Our technique provided reasonable information for correcting the global movement of the subject. It was shown that this system was applicable to detect and correct subject movement in cardiac PET studies at rest. [ABSTRACT FROM AUTHOR]

Cardiac 15O-water PET studies provide an accurate quantitation of regional myocardial blood flow (rMBF). We developed a motion correction system using an optical motion-tracking device to detect a subject’s global movement for cardiac study. PET studies were carried out on a cardiac phantom and a healthy volunteer at rest. The three-dimensional locations of the markers attached to the subjects during scans were measured using an optical motion-tracking system. In the phantom study, we performed a transmission scan and seven 18F emission scans of a baseline and with artificial misalignment of shifts and rotations. The correlation coefficients between the baseline and the other images before and after the corrections for the misalignment were calculated. In the human study, we performed a 15O-water dynamic scan with a transmission and axially 30 mm-shifted transmission scans. Motion of the subject was estimated by the information from the system, and was corrected on each sinogram using attenuation maps realigned to dynamic frames. Reconstructed dynamic images were then realigned to the transmission data. We calculated rMBF values for nine segments and myocardial images from the emission images, which were reconstructed with the first attenuation map (reference) and with the misaligned attenuation map before and after our corrections. In the phantom study, the correlation coefficients were improved from 0.929 ± 0.022 to 0.987 ± 0.010 (mean ± SD) after the corrections. In the human study, the global and cyclic movements were detected. The cyclic movement due to respiration was smoothed by frame-averaging, and reasonable information of the global movement was obtained. The rMBF value (mean ± SD) was 0.94 ± 0.12 mL/min/g for the reference. The rMBF values using the misaligned attenuation map changed from 1.03 ± 0.21 to 0.93 ± 0.11 mL/min/g after the correction, and spurious defects in myocardial images were also recovered. Our technique provided reasonable information for correcting the global movement of the subject. It was shown that this system was applicable to detect and correct subject movement in cardiac PET studies at rest. [ABSTRACT FROM AUTHOR]

For diagnosing patients with ischemic cerebrovascular disease, non-invasive count-based method with 15O2 and HO positron-emission tomography (PET) data is widely used to measure asymmetric increases in oxygen extraction fraction (OEF). For shortening study time, we have proposed dual-tracer autoradiographic (DARG) protocol in which 15O2 gas and C15O2 gas are sequentially administrated within short period. In this paper, we evaluated feasibility of the non-invasive count-based method with the DARG protocol. Twenty-three patients [67.8 ± 9.9 (mean ± SD) years] with chronic unilateral brain infarction were examined by the use of measurements of asymmetric OEF elevation. As DARG protocol, 15O2 and C15O2 gases were inhaled with 5-min interval and dynamic PET data were acquired for 8 min. Quantitative OEF (qOEF) image was computed with PET data and arterial input function. Ratio image of 15O2 and C15O2 phases of PET data was computed as count-based OEF (cbOEF) image. The asymmetric indices (AI) of qOEF (qOEF-AI) and cbOEF (cbOEF-AI) were obtained from regions of interest symmetric placed on left and right sides of cerebral hemisphere. To optimize the summation time of PET data for the cbOEF image, qOEF and cbOEF images with various summation times were compared. Image quality of cbOEF image was better than that of qOEF image. The best correlation coefficient of 0.94 was obtained when the cbOEF image was calculated from 0 to 180 s of 15O2 summed image and 340 to 440 s of C15O2 summed image. Using the appropriate summation time, we obtained the cbOEF image with good correlation with qOEF image, which suggests non-invasive cbOEF image can be used for evaluating the degree of misery perfusion in patients with chronic unilateral brain infarction. The count-based method with DARG protocol has a potential to dramatically reduce the examination time of 15O PET study. [ABSTRACT FROM AUTHOR]

Cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), oxygen extraction fraction (OEF), and cerebral blood volume (CBV) are quantitatively measured with PET with 15O gases. Kudomi et al. developed a dual tracer autoradiographic (DARG) protocol that enables the duration of a PET study to be shortened by sequentially administrating 15O2 and C15O2 gases. In this protocol, before the sequential PET scan with 15O2 and C15O2 gases (15O2–C15O2 PET scan), a PET scan with C15O should be preceded to obtain CBV image. C15O has a high affinity for red blood cells and a very slow washout rate, and residual radioactivity from C15O might exist during a 15O2–C15O2 PET scan. As the current DARG method assumes no residual C15O radioactivity before scanning, we performed computer simulations to evaluate the influence of the residual C15O radioactivity on the accuracy of measured CBF and OEF values with DARG method and also proposed a subtraction technique to minimize the error due to the residual C15O radioactivity. In the simulation, normal and ischemic conditions were considered. The 15O2 and C15O2 PET count curves with the residual C15O PET counts were generated by the arterial input function with the residual C15O radioactivity. The amounts of residual C15O radioactivity were varied by changing the interval between the C15O PET scan and 15O2–C15O2 PET scan, and the absolute inhaled radioactivity of the C15O gas. Using the simulated input functions and the PET counts, the CBF and OEF were computed by the DARG method. Furthermore, we evaluated a subtraction method that subtracts the influence of the C15O gas in the input function and PET counts. Our simulations revealed that the CBF and OEF values were underestimated by the residual C15O radioactivity. The magnitude of this underestimation depended on the amount of C15O radioactivity and the physiological conditions. This underestimation was corrected by the subtraction method. This study showed the influence of C15O radioactivity in DARG protocol, and the magnitude of the influence was affected by several factors, such as the radioactivity of C15O, and the physiological condition. [ABSTRACT FROM AUTHOR]

This study evaluated the feasibility of imaging rat brains using a human whole-body 3-T magnetic resonance imaging (MRI) scanner with specially developed transmit-and-receive radiofrequency coils. The T1- and T2-weighted images obtained showed reasonable contrast. Acquired contrast-free time-of-flight magnetic resonance angiography images clearly showed the cortical middle cerebral artery (MCA) branches, and interhemispheric differences could be observed. Dynamic susceptibility contrast MRI at 1.17 mm3 voxel resolution, performed three times following administration of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA, 0.1 mmol/kg), demonstrated that the arterial input function (AIF) can be obtained from the MCA region, yielding cerebral blood flow (CBF), cerebral blood volume, and mean transit time (MTT) maps. The hypothalamus (HT) to parietal cortex (Pt) CBF ratio was 45.11 ± 2.85%, and the MTT was 1.29 ± 0.40 s in the Pt region and 2.32 ± 0.17 s in the HT region. A single dose of Gd-DTPA enabled the assessment of AIF within MCA territory and of quantitative CBF in rats. [ABSTRACT FROM AUTHOR]

Regional cerebral blood flow (CBF), cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO2) can be estimated from C15O, H2 15O, and 15O2 tracers and positron emission tomography (PET) using an autoradiographic (ARG) method. Our objective in this study was to optimize the scan time for 15O2 gas study for accurate estimation of OEF and CMRO2. We evaluated statistical noise in OEF by varying the scan time and error caused by the tissue heterogeneity in estimated OEF and CMRO2 using computer simulations. The characteristics of statistical noise were investigated by signal-to-noise (S/N) ratio from repeated tissue time activity curves with noise, which were generated using measured averaged arterial input function and assuming CBF = 20, 50, and 80 (ml/100 g per minute). Error caused by tissue heterogeneity was also investigated by estimated OEF and CMRO2 from tissue time activity curve with mixture of gray and white matter varying fraction of mixture. In the simulations, three conditions were assumed (i) CBF in gray and white matter (CBFg and CBFw) was 80 and 20, OEF in gray and white matter ( E g and E w) was 0.4 and 0.3, (ii) CBFg and CBFw decreased by 50%, and E g and E w increased by 50% when compared with conditions (i) and (iii). CBFg and CBFw decreased by 80%, and E g and E w increased by 50% when compared with condition (i). The longer scan time produced the better S/N ratio of estimated OEF value from three CBF values (20, 50, and 80). Errors of estimated OEF for three conditions owing to tissue heterogeneity decreased, as scan time took longer. Meanwhile in the case of CMRO2, 3 min of scan time was desirable. The optimal scan time of 15O2 inhalation study with the ARG method was concluded to be 3 min from taking into account for maintaining the S/N ratio and the quantification of accurate OEF and CMRO2. [ABSTRACT FROM AUTHOR]

The quality of single-photon emission computed tomography (SPECT) imaging is hampered by attenuation, collimator blurring, and scatter. Correction for all of these three factors is required for accurate reconstruction, but unfortunately, reconstruction-based compensation often leads to clinically unacceptable long reconstruction times. Especially, efficient scatter correction has proved to be difficult to achieve. The objective of this article was to extend the well-known transmission-dependent convolution subtraction (TDCS) scatter-correction approach into a rapid reconstruction-based scatter-compensation method and to include it into a fast 3D reconstruction algorithm with attenuation and collimator-blurring corrections. Ordered subsets expectation maximization algorithm with attenuation, collimator blurring, and accelerated transmission-dependent scatter compensation were implemented. The new reconstruction method was compared with TDCS-based scatter correction and with one other transmission-dependent scatter-correction method using Monte Carlo simulated projection data of 99mTc-ECD and 123I-FP-CIT brain studies. The new reconstruction-based scatter compensation outperformed the other two scatter-correction methods in terms of quantitative accuracy and contrast measured with normalized mean-squared error, gray-to-white matter and striatum-to-background ratios, and also in visual quality. Highest accuracy was achieved when all the corrections (i.e., attenuation, collimator blurring, and scatter) were applied. The developed 3D reconstruction algorithm with transmission-dependent scatter compensation is a promising alternative to accurate and efficient SPECT reconstruction. [ABSTRACT FROM AUTHOR]

201Tl has been extensively used for myocardial perfusion and viability assessment. Unlike 99mTc-labelled agents, such as 99mTc-sestamibi and 99mTc-tetrofosmine, the regional concentration of 201Tl varies with time. This study is intended to validate a kinetic modelling approach for in vivo quantitative estimation of regional myocardial blood flow (MBF) and volume of distribution of 201Tl using dynamic SPECT. Dynamic SPECT was carried out on 20 normal canines after the intravenous administration of 201Tl using a commercial SPECT system. Seven animals were studied at rest, nine during adenosine infusion, and four after beta-blocker administration. Quantitative images were reconstructed with a previously validated technique, employing OS-EM with attenuation-correction, and transmission-dependent convolution subtraction scatter correction. Measured regional time–activity curves in myocardial segments were fitted to two- and three-compartment models. Regional MBF was defined as the influx rate constant ( K 1) with corrections for the partial volume effect, haematocrit and limited first-pass extraction fraction, and was compared with that determined from radio-labelled microspheres experiments. Regional time–activity curves responded well to pharmacological stress. Quantitative MBF values were higher with adenosine and decreased after beta-blocker compared to a resting condition. MBFs obtained with SPECT (MBFSPECT) correlated well with the MBF values obtained by the radio-labelled microspheres (MBFMS) (MBFSPECT = −0.067 + 1.042 × MBFMS, p < 0.001). The three-compartment model provided better fit than the two-compartment model, but the difference in MBF values between the two methods was small and could be accounted for with a simple linear regression. Absolute quantitation of regional MBF, for a wide physiological flow range, appears to be feasible using 201Tl and dynamic SPECT. [ABSTRACT FROM AUTHOR]

Positron emission tomography dynamic studies have been performed to quantify several biomedical functions. In a quantitative analysis of these studies, kinetic parameters were estimated by mathematical methods, such as a nonlinear least-squares algorithm with compartmental model and graphical analysis. In this estimation, the uncertainty in the estimated kinetic parameters depends on the signal-to-noise ratio and quantitative analysis method. This review describes the reliability of parameter estimates for various analysis methods in reversible and irreversible models. [ABSTRACT FROM AUTHOR]

A conventional pinhole single-photon emission computed tomography (SPECT) with a single circular orbit has limitations associated with non-uniform spatial resolution or axial blurring. Recently, we demonstrated that three-dimensional (3D) images with uniform spatial resolution and no blurring can be obtained by complete data acquired using two-circular orbit, combined with the 3D ordered subsets expectation maximization (OSEM) reconstruction method. However, a long computation time is required to obtain the reconstruction image, because of the fact that 3D-OSEM is an iterative method and two-orbit acquisition doubles the size of the projection data. To reduce the long reconstruction time, we parallelized the two-orbit pinhole 3D-OSEM reconstruction process by using a Beowulf personal computer (PC) cluster. The Beowulf PC cluster consists of seven PCs connected to Gbit Ethernet switches. Message passing interface protocol was utilized for parallelizing the reconstruction process. The projection data in a subset are distributed to each PC. The partial image forward- and back-projected in each PC is transferred to all PCs. The current image estimate on each PC is updated after summing the partial images. The performance of parallelization on the PC cluster was evaluated using two independent projection data sets acquired by a pinhole SPECT system with two different circular orbits. Parallelization using the PC cluster improved the reconstruction time with increasing number of PCs. The reconstruction time of 54 min by the single PC was decreased to 10 min when six or seven PCs were used. The speed-up factor was 5.4. The reconstruction image by the PC cluster was virtually identical with that by the single PC. Parallelization of 3D-OSEM reconstruction for pinhole SPECT using the PC cluster can significantly reduce the computation time, whereas its implementation is simple and inexpensive. [ABSTRACT FROM AUTHOR]

Physiological functions (e.g., cerebral blood flow, glucose metabolism, and neuroreceptor binding) can be investigated as parameters estimated by kinetic modeling using dynamic positron emission tomography (PET) images. Imaging of these physiological parameters, called parametric imaging, can locate the regional distribution of functionalities. However, the most serious technical issue affecting parametric imaging is noise in dynamic PET data. This review describes wavelet denoising of dynamic PET images for improving image quality in estimated parametric images. Wavelet denoising provides significantly improved quality directly to dynamic PET images and indirectly to estimated parametric images. The application of wavelet denoising to radio-ligand and kinetic analysis is still in the development stage, but even so, it is thought that wavelet techniques will have a substantial impact on nuclear medicine in the near future. [ABSTRACT FROM AUTHOR]

The Logan plot is a widely used algorithm for the quantitative analysis of neuroreceptors using PET because it is easy to use and simple to implement. The Logan plot is also suitable for receptor imaging because its algorithm is fast. However, use of the Logan plot, and interpretation of the formed receptor images should be regarded with caution, because noise in PET data causes bias in the Logan plot estimates. In this paper, we describe the basic concept of the Logan plot in detail and introduce three algorithms for the Logan plot. By comparing these algorithms, we demonstrate the pitfalls of the Logan plot and discuss the solution. [ABSTRACT FROM AUTHOR]

PET enables not only visualization of the distribution of radiotracer, but also has ability to quantify several biomedical functions. Compartmental model is a basic idea to analyze dynamic PET data. This review describes the principle of the compartmental model and categorizes the techniques and approaches for the compartmental model according to various aspects: model design, experimental design, invasiveness, and mathematical solution. We also discussed advanced applications of the compartmental analysis with PET. [ABSTRACT FROM AUTHOR]

Objective: We compared the diagnostic accuracy achieved by a human observer (nuclear medicine physician) and a channelized Hotelling (CH) observer on the basis of receiver-operating characteristics (ROC) curve for the differential diagnosis of Alzheimer's disease (AD) from SPECT images.Methods: The I-123-IMP brain perfusion SPECT images of 42 subjects (21 AD patients and 21 healthy controls) were used for an interpretation study and those of 10 healthy subjects were for a normal database. SPECT images were processed into four types: original SPECT images, three-dimensional stereotactic surface projection (3DSSP) images derived from them, Z-scores of SPECT images, and Z-scores of 3DSSP images. Five nuclear medicine physicians evaluated the test dataset sequentially as to whether the presented images were those of AD patients, which were rated using five categories of certainty: definitely, possibly, equivocally, possibly not, and definitely not. The test statistics (lambda) of the dataset generated by the CH observer were rated for ROC analysis. The areas under the ROC curves (Az) for the four image types interpreted by the human and CH observers were estimated and compared.Results: Among the four image types, the best performance based on Az obtained by both the CH and human observers was observed for the Z-score of 3DSSP images, and the lowest was for the original SPECT images.Conclusions: The performance of the CH observer was similar to that of the human observers, and both were dependent on the image type. This indicates that the CH observer may predict human performance in discriminating Alzheimer's dementia and can be useful for comparing and optimizing image processing methods of brain perfusion SPECT without human observers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recently, small animal imaging by pinhole SPECT has been widely investigated by several researchers. We developed a pinhole SPECT system specially designed for small animal imaging. The system consists of a rotation unit for a small animal and a SPECT camera attached with a pinhole collimator. In order to acquire complete data of the projections, the system has two orbits with angles of 90 degrees and 45 degrees with respect to the object. In this system, the position of the SPECT camera is kept fixed, and the animal is rotated in order to avoid misalignment of the center of rotation (COR). We implemented a three dimensional OSEM algorithm for the reconstruction of data acquired by the system from both the orbitals. A point source experiment revealed no significant COR misalignment using the proposed system. Experiments with a line phantom clearly indicated that our system succeeded in minimizing the misalignment of the COR. We performed a study with a rat and 99mTc-HMDP, an agent for bone scan, and demonstrated a dramatic improvement in the spatial resolution and uniformity achieved by our system in comparison with the conventional Feldkamp algorithm with one set of orbital data. [ABSTRACT FROM AUTHOR]

Recently, list mode (event-by-event) data acquisition with positron emission tomography (PET) has been widely noticed because list mode acquisition is superior to conventional frame mode data acquisition in terms of (1) higher efficiency of data storage, (2) higher temporal resolution, and (3) higher flexibility of data manipulation. The aim of this study is to investigate the performance of list mode data acquisition with ECAT EXACT HR and HR+ PET scanners (CTI PET Systems) and its feasibility in clinical applications. A cylindrical phantom (16 cm in diameter and length) filled with a ’ ’C solution for the HR and a15O solution for the HR+ was scanned several times by varying the radioactivity concentration with the list mode and frame mode acquisitions. The scans were also carried out with a septa (2D mode) and without a septa (3D mode) in order to evaluate the effect of the interplane septa on the quality of the list mode data. The acquired list mode data were sorted into a sinogram and reconstructed using a filtered back-projection algorithm. The count rate performance of the list mode data was comparable to that of the frame mode data. However, the list mode acquisition could not be performed when the radioactivity concentration in the field-of-view was high (exceeding 24 kBq/m/ for the 3D mode) due to a lack of sufficient transfer speed for sending data from the memory to hard disk. In order to estimate the pixel noise in a reconstructed image, ten replicated data sets were generated from one list mode data. The reconstructed images with the 3D mode had a signal-to-noise ratio that was more than 60% better than that of the image with the 2D mode. The file size of the generated list mode data was also evaluated. In the case of ECAT EXACT HR+ with the 3D list mode, the list mode data with a generated file size of 2.31 Mbytes/s were generated for 37 MBq injections. Our results suggest that careful attention must be paid to the protocol of the list mode data acquisition in order to obtain the highest performance of the PET scanner. [ABSTRACT FROM AUTHOR]

Purpose: An image-based scatter correction (IBSC) method was developed to convert scatter-uncorrected into scatter-corrected SPECT images. The purpose of this study was to validate this method by means of phantom simulations and human studies with 99mTc-labeled tracers, based on comparison with the conventional triple energy window (TEW) method. Methods: The IBSC method corrects scatter on the reconstructed image IACμb with Chang's attenuation correction factor. The scatter component image is estimated by convolving IACμb with a scatter function followed by multiplication with an image-based scatter fraction function. The IBSC method was evaluated with Monte Carlo simulations and 99mTc-ethyl cysteinate dimer SPECT human brain perfusion studies obtained from five volunteers. The image counts and contrast of the scatter-corrected images obtained by the IBSC and TEW methods were compared. Results: Using data obtained from the simulations, the image counts and contrast of the scatter-corrected images obtained by the IBSC and TEW methods were found to be nearly identical for both gray and white matter. In human brain images, no significant differences in image contrast were observed between the IBSC and TEW methods. Conclusion: The IBSC method is a simple scatter correction technique feasible for use in clinical routine. [ABSTRACT FROM AUTHOR]

The aim of the present study is to evaluate the validity of the simplified reference tissue model (SRTM) and of Logan graphical analysis with reference tissue (LGAR) for quantification of histamine H1 receptors (H1Rs) by using positron emission tomography (PET) with [11C]doxepin. These model-based analytic methods (SRTM and LGAR) are compared to Logan graphical analysis (LGA) and to the one-tissue model (1TM), using complete datasets obtained from 5 healthy volunteers. Since HIR concentration in the cerebellum can be regarded as negligibly small, the cerebellum was selected as the reference tissue in the present study. The comparison of binding potential (BP) values estimated by LGAR and 1TM showed good agreement; on the other hand, SRTM turned out to be unstable concerning parameter estimation in several regions of the brain. By including the results of noise analysis, LGAR became a reliable method for parameter estimation of [11C]doxepin data in the cortical regions. [ABSTRACT FROM AUTHOR]

Pinhole single-photon emission computed tomography (SPECT) is able to provide information on the biodistribution of several radioligands in small laboratory animals, but has limitations associated with non-uniform spatial resolution or axial blurring. We have hypothesised that this blurring is due to incompleteness of the projection data acquired by a single circular pinhole orbit, and have evaluated a new strategy for accurate image reconstruction with better spatial resolution uniformity. A pinhole SPECT system using two circular orbits and a dedicated three-dimensional ordered subsets expectation maximisation (3D-OSEM) reconstruction method were developed. In this system, not the camera but the object rotates, and the two orbits are at 90° and 45° relative to the object’s axis. This system satisfies Tuy’s condition, and is thus able to provide complete data for 3D pinhole SPECT reconstruction within the whole field of view (FOV). To evaluate this system, a series of experiments was carried out using a multiple-disk phantom filled with 99mTc solution. The feasibility of the proposed method for small animal imaging was tested with a mouse bone study using 99mTc-hydroxymethylene diphosphonate. Feldkamp’s filtered back-projection (FBP) method and the 3D-OSEM method were applied to these data sets, and the visual and statistical properties were examined. Axial blurring, which was still visible at the edge of the FOV even after applying the conventional 3D-OSEM instead of FBP for single-orbit data, was not visible after application of 3D-OSEM using two-orbit data. 3D-OSEM using two-orbit data dramatically reduced the resolution non-uniformity and statistical noise, and also demonstrated considerably better image quality in the mouse scan. This system may be of use in quantitative assessment of bio-physiological functions in small animals. [ABSTRACT FROM AUTHOR]

Prior studies with anthropomorphic phantoms and single, static in vivo brain images have demonstrated that scatter correction significantly improves the accuracy of regional quantitation of single-photon emission tomography (SPET) brain images. Since the regional distribution of activity changes following a bolus injection of a typical neuroreceptor ligand, we examined the effect of scatter correction on the compartmental modeling of serial dynamic images of striatal and extrastriatal dopamine D2 receptors using [123I]epidepride. Eight healthy human subjects [age 30±8 (range 22–46) years] participated in a study with a bolus injection of 373±12 (354–389) MBq [123I]epidepride and data acquisition over a period of 14 h. A transmission scan was obtained in each study for attenuation and scatter correction. Distribution volumes were calculated by means of compartmental nonlinear least-squares analysis using metabolite-corrected arterial input function and brain data processed with scatter correction using narrow-beam geometry μ (SC) and without scatter correction using broad-beam μ (NoSC). Effects of SC were markedly different among brain regions. SC increased activities in the putamen and thalamus after 1–1.5 h while it decreased activity during the entire experiment in the temporal cortex and cerebellum. Compared with NoSC, SC significantly increased specific distribution volume in the putamen (58%, P=0.0001) and thalamus (23%, P=0.0297). Compared with NoSC, SC made regional distribution of the specific distribution volume closer to that of [18F]fallypride. It is concluded that SC is required for accurate quantification of distribution volumes of receptor ligands in SPET studies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract. The purpose of this study was to measure the cumulated activity and absorbed dose in organs after intravenous administration of 2-[F-18]fluoro-2-deoxy-Dglucose ([sup 18]F-FDG) using whole-body positron emission tomography (PET) and magnetic resonance imaging (MRI). Whole-body dynamic emission scans for [sup 18]FFDG were performed in six normal volunteers after transmission scans. The total activity of a source organ was obtained from the activity concentration of the organ measured by whole-body PET and the volume of that organ measured by whole-body TI-weighted MRI. The cumulated activity of each source organ was calculated from the time-activity curve. Absorbed doses to the individuals were estimated by the MIRD (medical internal radiation dosimetry) method using S-values adjusted to the individuals. Another calculation of cumulated activities and absorbed doses was performed using the organ volumes from the MIRD phantom and the "Japanese reference man" to investigate the discrepancy of actual individual results against the phantom results. The cumulated activities of 18 source organs were calculated, and absorbed doses of 27 target organs estimated. Among the target organs, bladder wall, brain and kidney received the highest doses for the above three sets of organ volumes. Using measured individual organ volumes, the average absorbed doses for those organs were found to be 3.1x10[sup -1], 3.7x10[sup -2] and 2.8x10[sup -2] mGy/MBq, respectively. The mean effective doses in this study for individuals of... [ABSTRACT FROM AUTHOR]

We have developed a miniature γ-ray endoscopic probe consisting of dual BGO detector probes for tumor detection inside the body cavities. The dual detector system was coupled with random coincidence to decrease the distant background radiation and to improve its spatial resolution for tumor localization. Method: The performance of the probe was investigated with a point source and a water phantom. A solution of positron emitting18F isotope was used as the source. Clinical trials of the probe were done to localize tumors on the skin surface of four subjects carrying tumors close to the body surfaces, into whom67Ga-citrate and18F-FDG radiopharmaceuticals were injected. Results: Measurements indicated that the spatial resolution of the dual detector probes is around 1.5 times better than the single detector probe, and both single and dual detector endoscopic probe systems are capable of localizing a tumor on a large photon background. Conclusion: The endoscopic probe may be easier to insert inside body cavities due to the small crystal size and the flexible light guides. A single detector probe with higher sensitivity may be useful in searching for tumors over a wide intracavity area but a dual detector probe can be used for precise tumor localization. The detector probe may also be suitable for intraoperative observation. [ABSTRACT FROM AUTHOR]

Visualizing the dynamics of cesium (Cs) is desirable to understand the impact of radiocesium when accidentally ingested or inhaled by humans. However, visualization of radiocesium in vivo is currently limited to plants. Herein, we describe a method for the production and purification of 127Cs and its use in visualizing Cs dynamics in a living animal. The positron-emitting nuclide 127Cs was produced using the 127I (α, 4n) 127Cs reaction, which was induced by irradiation of sodium iodide with a 4He2+ beam from a cyclotron. We excluded sodium ions by using a material that specifically adsorbs Cs as a purification column and successfully eluted 127Cs by flowing a solution of ammonium sulfate into the column. We injected the purified 127Cs tracer solution into living rats and the dynamics of Cs were visualized using positron emission tomography; the distributional images showed the same tendency as the results of previous studies using disruptive methods. Thus, this method is useful for the non-invasive investigation of radiocesium in a living animal. [ABSTRACT FROM AUTHOR]