Dedicated phantom tools using traceable 68Ge/68Ga point-like sources for dedicated-breast PET and positron emission mammography scanners.

Since the early 2000s, many types of positron emission tomography (PET) scanners dedicated to breast imaging for the diagnosis of breast cancer have been introduced. However, conventional performance evaluation methods developed for whole-body PET scanners cannot be used for such devices. In this study, we developed phantom tools for evaluating the quantitative accuracy of positron emission mammography (PEM) and dedicated-breast PET (dbPET) scanners using novel traceable point-like 68Ge/68 Ga sources. The PEM phantom consisted of an acrylic cube (100 × 100 × 40 mm) and three point-like sources. The dbPET phantom comprised an acrylic cylinder (ø100 × 100 mm) and five point-like sources. These phantoms were used for evaluating the fundamental responses of clinical PEM and dbPET scanners to point-like inputs in a medium. The results showed that reasonable recovery values were obtained based on region-of-interest analyses of the reconstructed images. The developed phantoms using traceable 68Ge/68 Ga point-like sources were useful for evaluating the physical characteristics of PEM and dbPET scanners. Thus, they offer a practical, reliable, and universal measurement scheme for evaluating various types of PET scanners using common sets of sealed sources.

New standards for phantom image quality and SUV harmonization range for multicenter oncology PET studies.

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.

Clinical practice guidelines for high-resolution breast PET, 2019 edition.

Breast positron emission tomography (PET) has had insurance coverage when performed with conventional whole-body PET in Japan since 2013. Together with whole-body PET, accurate examination of breast cancer and diagnosis of metastatic disease are possible, and are expected to contribute significantly to its treatment planning. To facilitate a safer, smoother, and more appropriate examination, the Japanese Society of Nuclear Medicine published the first edition of practice guidelines for high-resolution breast PET in 2013. Subsequently, new types of breast PET have been developed and their clinical usefulness clarified. Therefore, the guidelines for breast PET were revised in 2019. This article updates readers as to what is new in the second edition. This edition supports two different types of breast PET depending on the placement of the detector: the opposite-type (positron emission mammography; PEM) and the ring-shaped type (dedicated breast PET; dbPET), providing an overview of these scanners and appropriate imaging methods, their clinical applications, and future prospects. The name "dedicated breast PET" from the first edition is widely used to refer to ring-shaped type breast PET. In this edition, "breast PET" has been defined as a term that refers to both opposite- and ring-shaped devices. Up-to-date breast PET practice guidelines would help provide useful information for evidence-based breast imaging.

Pre-discard estimation of radioactivated materials in positron emission tomography cyclotron systems and concrete walls of a cyclotron vault.

PURPOSE: The concrete vault, cyclotron body, and peripheral equipment in a cyclotron room become radioactivated by neutrons generated by operating an unshielded cyclotron. Radionuclides and the amounts of radioactivated materials must be identified before discarding a cyclotron system. The present study aimed to reduce the amounts of concrete from cyclotron vaults, as well as cyclotron components and peripheral equipment, that will be disposed of as radioactivated waste by clarifying the nature and quantity of radioactivated materials remaining in facilities after cyclotron operations have ceased. METHODS: Cylindrical concrete cores were bored into all four walls, ceiling, and floor of a room where a Cypris 370 cyclotron had been operated for 22.8 yr and then cooled for 40 months. The accelerated particles comprised protons and deuterons with constant energy of 18 and 10 MeV, respectively. The types and amounts of radionuclides in these cores, in 38 components of the cyclotron including the yoke, and in 13 pieces of equipment in the room, were determined by γ-ray spectrometry. Concentrations of radioactivity were also calculated using an updated version of Particle and Heavy Ion Transport System and DCHAIN-SP. Amounts of materials with both measured and calculated total radioactivity concentration (ΣD) of <0.1 Bq/g were identified as being nonradioactivated. RESULTS: The major radionuclides in the concrete were 60 Co and 152 Eu. The radioactivated concrete was distributed to a depth of <38 cm. Most cyclotron components and equipment were radioactivated by neutrons. The major radionuclides in cyclotron components and equipment were 54 Mn, 60 Co, and 65 Zn. A 33% volume of the yoke was regarded as nonradioactivated. CONCLUSIONS: The estimated amount of radioactivated waste in the concrete was about 70,000 kg (12.5% of the total concrete). Most components of the cyclotron except for the 33% volume of the yoke (20% of the cyclotron body), as well as most peripheral equipment in the room, were radioactivated. Part-by-part assessments of radioactive materials using measurements and calculations could distinguish nonradioactive from radioactive materials before they are discarded.

Longitudinal effects of aging on 18F-FDG distribution in cognitively normal elderly individuals.

Previous studies of aging effects on fluorine-18-labeled fluorodeoxyglucose (18F-FDG) distribution have employed cross-sectional designs. We examined aging effects on 18F-FDG distribution using both cross-sectional and longitudinal assessments. We obtained two 18F-FDG positron emission tomography scans at two different time points from 107 cognitively normal elderly participants. The participants' mean ages at baseline and second scans were 67.9 and 75.7, respectively. The follow-up period ranged from 4 to 11 years with a mean of 7.8 years. The voxel-wise analysis revealed significant clusters in which 18F-FDG uptake was decreased between baseline and second scans (p < 0.05, family-wise error corrected) in the anterior cingulate cortex (ACC), posterior cingulate cortex/precuneus (PCC/PC), and lateral parietal cortex (LPC). The cross-sectional analysis of 18F-FDG uptake and age showed significant correlations in the ACC (p = 0.016) but not the PCC/PC (p = 0.240) at baseline, and in the ACC (p = 0.004) and PCC/PC (p = 0.002) at the second scan. The results of longitudinal assessments suggested that 18F-FDG uptake in the ACC, PCC/PC, and LPC decreased with advancing age in cognitively normal elderly individuals, and those of the cross-sectional assessments suggested that the trajectories of age-associated 18F-FDG decreases differed between the ACC and PCC/PC.

Validation of scatter limitation correction to eliminate scatter correction error in oxygen-15 gas-inhalation positron emission tomography images.

OBJECTIVE: High levels of radioactivity inside a facemask cause scatter correction (SC) errors that appear as photopenic artifacts on quantitative oxygen-15 (O) gas-inhalation positron emission tomography (PET) images. The present study aimed to validate the ability of scatter limitation correction (SLC) to eliminate SC errors in O gas-inhalation PET images acquired from patients and a phantom. MATERIALS AND METHODS: We analyzed the SC errors in phantom images and calculated parametric images of the cerebral blood flow (CBF), cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO2). Phantoms comprised a cylinder and paper with radioactivity to simulate a facemask during (O)O2 gas inhalation. Parametric images were calculated from O gas-inhalation PET images of ten participants. All PET data were reconstructed using conventional SC as model-based SC and SLC. Images acquired from the phantoms and parametric images were assessed visually and quantitatively in the presence and absence of SC error. RESULTS: SC error was evident in images derived from the paper phantom and at the slice level of the cerebellum in CBF, OEF, and CMRO2 images. The radioactivity concentration in the cylindrical phantom with the paper phantom significantly improved with SLC. The SLC also increased the quantitative indices of CBF, OEF, and CMRO2 by 23.8, 42.2, and 44.4%, respectively. CONCLUSION: SLC visually eliminated the SC error and increased the quantitative parameters on O gas-inhalation images derived from a phantom and from patients.

Increased Binding Potential of Brain Adenosine A1 Receptor in Chronic Stages of Patients with Diffuse Axonal Injury Measured with [1-methyl-11C] 8-dicyclopropylmethyl-1-methyl-3-propylxanthine Positron Emission Tomography Imaging.

The positron emission tomography (PET) radioligand for adenosine A1 receptor (A1R) [1-methyl-11C] 8-dicyclopropylmethyl-1-methyl-3-propylxanthine (MPDX) has recently been developed for human brain imaging. In the present study, we evaluated the alteration of the A1R in patients with diffuse axonal injury (DAI) in chronic stage in vivo. Ten patients with DAI (7 men and 3 women) were included in this study. Three PET examinations were sequentially performed to measure A1R binding with 11C-MPDX, glucose metabolism with 18F-fluorodeoxyglucose (FDG), and central benzodiazepine receptor binding with 11C-flumazenil (FMZ), and decreases of 11C-FMZ uptake indicate neuronal loss. 11C- MPDX did not depict any lesion with significantly decreased nondisplaceable binding potential (BPND) in comparison to healthy controls (14 men) in region of interest (ROI) analysis. Instead, it showed a significant increase of BPND in the lower frontal and posterior cingulate cortexes and rolandic area (p < 0.05) in ROI analysis. In 18F-FDG PET, the standardized uptake values (SUVs) ratio to the whole brain were decreased in anterior and posterior cingulate gyrus compared to controls (14 men and 9 women; p < 0.01). In 11C-FMZ PET, the SUV ratio to the cerebellum was decreased in anterior cingulate gyrus in ROI analysis (controls, 9 men and 6 women; p < 0.01). The area with significantly increased 11C-MPDX binding, lower frontal cortex, rolandic area, and posterior cingulate gyrus, did not overlap with the areas of neuronal loss detected by decreased 11C-FMZ binding and did not completely overlap with area of reduced18F-FDG uptake. We obtained the first 11C-MPDX PET images reflecting the A1R BPND in human DAI brain in vivo. 11C-MPDX depicted increased A1R BPND in the areas surrounding the injured brain, whereas 18F-FDG demonstrated reduction throughout the brain. The results suggested that A1R might continuously confer neuroprotective or neuromodulatory effects in DAI even in the chronic stage.

Comparison between new-generation SiPM-based and conventional PMT-based TOF-PET/CT.

PURPOSE: This study aimed to determine whether the SiPM-PET/CT, Discovery MI (DMI) performs better than the PMT-PET/CT system, Discovery 710 (D710). METHODS: The physical performance of both systems was evaluated using NEMA NU 2 standards. Contrast (%), uniformity and image noise (%) are criteria proposed by the Japanese Society of Nuclear Medicine (JSNM) for phantom tests and were determined in images acquired from Hoffman and uniform phantoms using the DMI and D710. Brain and whole-body [18F]FDG images were also acquired from a healthy male using the DMI and D710. RESULTS: The spatial resolution at 1.0cm off-center in the DMI and D710 was 3.91 and 4.52mm, respectively. The sensitivity of the DMI and D710 was 12.62 and 7.50cps/kBq, respectively. The observed peak noise-equivalent count rates were 185.6kcps at 22.5kBq/mL and 137.0kcps at 29.0kBq/mL, and the scatter fractions were 42.1% and 37.9% in the DMI and D710, respectively. The D710 had better contrast recovery and lower background variability. Contrast, uniformity and image noise in the DMI were 61.0%, 0.0225, and 7.85%, respectively. These outcomes were better than those derived from the D710 and satisfied the JSNM criteria. Brain images acquired by the DMI had better grey-to-white matter contrast and lower image noise at the edge of axial field of view. CONCLUSIONS: The DMI offers better sensitivity, performance under conditions of high count rates and image quality than the conventional PMT-PET/CT system, D710.

Effects of a novel tungsten-impregnated rubber neck shield on the quality of cerebral images acquired using 15O-labeled gas.

The present study aimed to validate the effects of a novel tungsten-impregnated rubber neck shield on the quality of phantom and clinical 15O-labeled gas positron emission tomography (PET) images. Images were acquired in the presence or absence of a neck shield from a cylindrical phantom containing [15O]H2O (phantom study) and from three individuals using [15O]CO2, [15O]O2 and [15O]CO gas (clinical study). Data were acquired in three-dimensional (3D) mode using a Discovery PET/CT 710. Values for cerebral blood flow, cerebral blood volume, oxygen extraction fraction, and cerebral metabolic rate of oxygen with and without the neck shield were calculated from 15O-labeled gas images. Arterial radioactivity and count characteristics were evaluated in the phantom and clinical studies. The coefficient of variance (CV) for the phantom study and the standard deviation (SD) for functional images were also analyzed. The neck shield decreased the random count rates by 25-59% in the phantom and clinical studies. The noise equivalent count rate (NECR) increased by 44-66% in the phantom and clinical studies. Random count rates and NECR in [15O]CO2 images significantly differed with and without the neck shield. The improvement in visual and physical image quality with the neck shield was not observed in the phantom and clinical studies. The novel neck shield reduced random count rate and improved NECR in a 3D PET study using 15O-labeled gas. The image quality with the neck shield was similar to that without the neck shield.

Effects of exercise on brain activity during walking in older adults: a randomized controlled trial.

BACKGROUND: Physical activity may preserve neuronal plasticity, increase synapse formation, and cause the release of hormonal factors that promote neurogenesis and neuronal function. Previous studies have reported enhanced neurocognitive function following exercise training. However, the specific cortical regions activated during exercise training remain largely undefined. In this study, we quantitatively and objectively evaluated the effects of exercise on brain activity during walking in healthy older adults. METHODS: A total of 24 elderly women (75-83 years old) were randomly allocated to either an intervention group or a control group. Those in the intervention group attended 3 months of biweekly 90-min sessions focused on aerobic exercise, strength training, and physical therapy. We monitored changes in regional cerebral glucose metabolism during walking in both groups using positron emission tomography (PET) and [18F]fluorodeoxyglucose (FDG). RESULTS: All subjects completed the 3-month experiment and the adherence to the exercise program was 100%. Compared with the control group, the intervention group showed a significantly greater step length in the right foot after 3 months of physical activity. The FDG-PET assessment revealed a significant post-intervention increase in regional glucose metabolism in the left posterior entorhinal cortex, left superior temporal gyrus, and right superior temporopolar area in the intervention group. Interestingly, the control group showed a relative increase in regional glucose metabolism in the left premotor and supplemental motor areas, left and right somatosensory association cortex, and right primary visual cortex after the 3-month period. We found no significant differences in FDG uptake between the intervention and control groups before vs. after the intervention. CONCLUSION: Exercise training increased activity in specific brain regions, such as the precuneus and entorhinal cortices, which play an important role in episodic and spatial memory. Further investigation is required to confirm whether alterations in glucose metabolism within these regions during walking directly promote physical and cognitive performance. TRIAL REGISTRATION: UMIN-CTR ( UMIN000021829 ). Retrospectively registered 10 April 2016.

Adenosine A1 receptors measured with 11 C-MPDX PET in early Parkinson's disease.

Adenosine A1 receptors (A1 Rs) interact negatively with dopamine D1 receptors (D1 Rs) in neurons of the basal ganglia's direct pathway, while adenosine A2A receptors (A2A Rs) negatively interact with dopamine D2 receptors (D2 Rs) in indirect-pathway neurons. The aim of this study was to investigate the cerebral density of A1 Rs in Parkinson's disease (PD) in its early stages, using PET scans with the radioligand 8-dicyclopropylmethyl-1-11 C-methyl-3-propylxanthine (11 C-MPDX). We studied 10 drug-naïve patients with early PD. Each patient was also examined for dopamine transporters (DATs) and D2 Rs by PET using 11 C-2-ß-carbomethoxy-3-ß-(4-fluorophenyl)-tropane (11 C-CFT) and 11 C-raclopride (11 C-RAC), respectively. Ten elderly, healthy volunteers were recruited as controls for 11 C-MPDX PET scanning and eight elderly volunteers were recruited as controls for 11 C-CFT and 11 C-RAC PET scanning. The PET scans revealed a decrease in the uptake ratio index (URI) of 11 C-CFT and an increase in the URI of 11 C-RAC in patients. In the temporal lobe, the binding potential for 11 C-MPDX was higher in the patient group than in healthy subjects, but not in the other regions examined, including the striatum. In patients, we observed motor-symptom asymmetry and a relationship between parkinsonism and the striatal density of DATs, but not A1 R density. In the putamen of early PD, asymmetrical down-regulation of A2A Rs is likely a compensatory mechanism in response to a decrease in dopamine. However, our study suggests that A1 Rs are unaltered in the putamen of early PD.

The neural substrate of gait and executive function relationship in elderly women: A PET study.

AIM: Understanding the relationship between age-related gait impairment, such as slow gait, and executive functioning in seniors may help identify individuals at higher risk of mobility decline, falls, and progression to dementia at earlier stages. We aim to identify brain regions concomitantly associated with poor gait and executive functioning in a cohort of well-functioning elderly women. METHODS: In total, 149 well-functioning women aged 70.1 ± 6.2 years underwent FDG-PET to evaluate regional cerebral metabolic rates of glucose normalized in reference to cerebellar glucose metabolic value (normalized-rCMRglc) in 16 brain areas. We assessed gait speed, step length and cadence under usual and fast conditions. Executive function was assessed using Trail-Making-Tests (TMT) A and B. RESULTS: Adjusted multiple regression analyses for potential covariates showed that TMT-B and ΔTMT (TMT B-A) were associated with gait speed and cadence at fast condition. Lower normalized-rCMRglc in the posterior cingulate and primary sensorimotor cortices were associated with longer TMT-B and ΔTMT times (i.e., lower executive function) as well as with slower gait speed and lower cadence at fast condition. Slower gait speed and lower cadence at fast condition were also associated with lower normalized-rCMRglc in the occipital and parietal cortices. There were no other significant associations. CONCLUSIONS: In healthy elderly women without impending disability or cognitive impairment, reduced glucose metabolism in the posterior cingulate and primary sensorimotor cortices were associated with both lower gait performance and executive functioning. Our results suggest that gait control and executive functions might share the same neural substrate. Geriatr Gerontol Int 2017; 17: 1873-1880.

Central µ-Opioidergic System Activation Evoked by Heavy and Severe-Intensity Cycling Exercise in Humans: a Pilot Study Using Positron Emission Tomography with 11C-Carfentanil.

The central opioid receptor system likely contributes to the mechanism underlying the changes in affect elicited by exercise. Our aim was to use positron emission tomography (PET) to test whether exercise intensity influences activation of the µ-opioid receptor system in the brain, and whether changes in opioid receptor activation correlate with exercise-induced changes in affect. 7 healthy young male subjects (23±2 years) performed 20-min constant-load cycling exercises at heavy (ExH) and severe-intensity (ExS), and PET was performed using [11C]carfentanil as a tracer before and after each exercise. Exercise elicited the µ-opioidergic system activation in the large areas of the limbic system, particularly in the insular cortex, and cerebellum. Of note, deactivation of the µ-opioidergic system in the pituitary gland was identified as a specific finding in ExS, which evoked a distinctive sensation of fatigue. Within these brain areas, µ-opioid receptor activation correlated positively with increased positive affect (R2=0.67-0.95) in ExH and negative affect (R2=0.63-0.77) in ExS. These findings suggest that central µ-opioidergic neurotransmission evoked by continuous exercise is discriminated by work intensity. Notably, we also observed a possible contribution of the central µ-opioidergic system to the development of the sensation of fatigue during exhaustive exercise.

Age-Related Decrease in Male Extra-Striatal Adenosine A1 Receptors Measured Using11C-MPDX PET.

Adenosine A1 receptors (A1Rs) are widely distributed throughout the entire human brain, while adenosine A2A receptors (A2ARs) are present in dopamine-rich areas of the brain, such as the basal ganglia. A past study using autoradiography reported a reduced binding ability of A1R in the striatum of old rats. We developed positron emission tomography (PET) ligands for mapping the adenosine receptors and we successfully visualized the A1Rs using 8-dicyclopropylmethyl-1-11C-methyl-3-propylxanthine (11C-MPDX). We previously reported that the density of A1Rs decreased with age in the human striatum, although we could not observe an age-related change in A2ARs. The aim of this study was to investigate the age-related change of the density of A1Rs in the thalamus and cerebral cortices of healthy participants using 11C-MPDX PET. We recruited eight young (22.0 ± 1.7 years) and nine elderly healthy male volunteers (65.7 ± 8.0 years). A dynamic series of decay-corrected PET scans was performed for 60 min starting with the injection of 11C-MPDX. We placed the circular regions of interest of 10 mm in diameter in 11C-MPDX PET images. The values for the binding potential (BPND) of 11C-MPDX in the thalamus, and frontal, temporal, occipital, and parietal cortices were calculated using a graphical analysis, wherein the reference region was the cerebellum. BPND of 11C-MPDX was significantly lower in elderly participants than young participants in the thalamus, and frontal, temporal, occipital, and parietal cortices. In the human brain, we could observe the age-related decrease in the distribution of A1Rs.

Evaluation of a New Motion-correction Algorithm Using On-rigid Registration in Respiratory-gated PET/CT Images of Liver Tumors.

OBJECTIVE: The present study aimed to determine the qualitative and quantitative accuracy of the Q.Freeze algorithm in PET/CT images of liver tumors. METHODS: A body phantom and hot spheres representing liver tumors contained 5.3 and 21.2 kBq/mL of a solution containing 18F radioactivity, respectively. The phantoms were moved in the superior-inferior direction at a motion displacement of 20 mm. Conventional respiratory-gated (RG) and Q.Freeze images were sorted into 6, 10, and 13 phase-groups. The SUVave was calculated from the background of the body phantom, and the SUVmax was determined from the hot spheres of the liver tumors. Three patients with four liver tumors were also clinically assessed by whole-body and RG PET. The RG and Q.Freeze images derived from the clinical study were also sorted into 6, 10 and 13 phase-groups. Liver signal-to-noise ratio (SNR) and SUVmax were determined from the RG and Q.Freeze clinical images. RESULTS: The SUVave of Q.Freeze images was the same as those derived from the body phantom using RG. The liver SNR improved with Q.Freeze, and the SUVsmax was not overestimated when Q.Freeze was applied in both the phantom and clinical studies. Q.Freeze did not degrade the liver SNR and SUVmax even though the phase number was larger. CONCLUSIONS: Q.Freeze delivered qualitative and quantitative motion correction than conventional RG imaging even in 10-phase groups.

Evaluation of spatial dependence of point spread function-based PET reconstruction using a traceable point-like 22Na source.

BACKGROUND: The point spread function (PSF) of positron emission tomography (PET) depends on the position across the field of view (FOV). Reconstruction based on PSF improves spatial resolution and quantitative accuracy. The present study aimed to quantify the effects of PSF correction as a function of the position of a traceable point-like 22Na source over the FOV on two PET scanners with a different detector design. METHODS: We used Discovery 600 and Discovery 710 (GE Healthcare) PET scanners and traceable point-like 22Na sources (<1 MBq) with a spherical absorber design that assures uniform angular distribution of the emitted annihilation photons. The source was moved in three directions at intervals of 1 cm from the center towards the peripheral FOV using a three-dimensional (3D)-positioning robot, and data were acquired over a period of 2 min per point. The PET data were reconstructed by filtered back projection (FBP), the ordered subset expectation maximization (OSEM), OSEM + PSF, and OSEM + PSF + time-of-flight (TOF). Full width at half maximum (FWHM) was determined according to the NEMA method, and total counts in regions of interest (ROI) for each reconstruction were quantified. RESULTS: The radial FWHM of FBP and OSEM increased towards the peripheral FOV, whereas PSF-based reconstruction recovered the FWHM at all points in the FOV of both scanners. The radial FWHM for PSF was 30-50 % lower than that of OSEM at the center of the FOV. The accuracy of PSF correction was independent of detector design. Quantitative values were stable across the FOV in all reconstruction methods. The effect of TOF on spatial resolution and quantitation accuracy was less noticeable. CONCLUSIONS: The traceable 22Na point-like source allowed the evaluation of spatial resolution and quantitative accuracy across the FOV using different reconstruction methods and scanners. PSF-based reconstruction reduces dependence of the spatial resolution on the position. The quantitative accuracy over the entire FOV of the PET system is good, regardless of the reconstruction methods, although it depends slightly on the position.

Cerebral Functional Response during Eyelid Opening/Closing with Bell's Phenomenon and Volitional Vertical Eye Movements in Humans.

Bell's phenomenon is a physiological phenomenon wherein the eye ball involuntarily rolls upward during eyelid closing. Although this phenomenon occurs in healthy individuals, the neural mechanism related to Bell's phenomenon has not yet been identified. We aimed to investigate the brain regions relevant to Bell's phenomenon and volitional eye movement using [15O] H2O and positron emission tomography (PET). We measured regional cerebral blood flow (rCBF) in 8 normal subjects under 3 conditions: at rest with eyes closed, during opening and closing of the eyelids in response to sound stimuli (lid opening/closing), and during vertical movement of the eyes with lids closed in response to sound stimuli (volitional eye movement). The supplementary motor area (SMA) proper, right superior temporal gyrus, right insular cortex and left angular gyrus were activated during lid opening/closing. The right frontal eye field (FEF), pre-SMA, left primary motor area, right angular gyrus, and SMA proper were activated during volitional eye movement. The SMA proper was active during both tasks, while the FEF and pre-SMA were active during volitional eye movement, but not during eyelid opening/closing. A comparison of activation during volitional eye movements and lid opening/closing tasks revealed a relative increase in rCBF in the FEF. There were no areas that are activated in relation to Bell's phenomenon. In conclusion, activation in the FEF mainly occurs during volitional eye movement. Since Bell's phenomenon is a reflexive eye movement, the FEF is scarcely concerned in Bell's phenomenon.

Improvement of Glucose Metabolism in the Visual Cortex Accompanies Visual Field Recovery in a Patient with Hemianopia.

Damage to the visual cortex or the geniculostriatal pathways could cause homonymous visual field (VF) defects at the contralateral side of the lesion. In clinical practice, it is known that the VF defects are gradually recovered over months on the cases. We report a case with recovered homonymous hemianopia following an infarction in the visual cortex by positron emission tomography (PET) with (18)F-fluorodeoxyglucose (FDG) and (11)C-flumazenil (FMZ). A 58-year-old man experienced defect of left VF, and magnetic resonance imaging (MRI) revealed a localized infarction in the right occipital lobe. Goldmann VF perimetry revealed left homonymous hemianopia, but central VF was intact. Three months after the onset of infarction, we measured cerebral glucose metabolism with FDG and FMZ binding using PET. FMZ binding reflects the density of surviving neurons. Moreover, eight months after the onset, FDG-PET scan was performed. Goldmann VF perimetry was also performed at the same times of PET examinations. Decrease of cerebral glucose metabolism in the right anterior striate cortex was observed at three months after onset, while FMZ binding in the same area did not decrease in the patient. At eight months after onset, we observed recovery of VF and improvement of cerebral glucose metabolism in the anterior striate cortex. We presented change of cerebral glucose metabolism using PET accompanying improvement of VF. Evaluation of cerebral glucose metabolism and FMZ binding in the striate cortex is useful for estimating the prognosis of hemianopia caused by organic brain damage.

Comparison of dosimetry between PET/CT and PET alone using (11)C-ITMM.

We used a new tracer, N-[4-[6-(isopropylamino) pyrimidin-4-yl]-1,3-thiazol-2-yl]-4-(11)C-methoxy-N-methylbenzamide ((11)C-ITMM), to compare radiation doses from positron emission tomography (PET)/computed tomography (CT) with previously published doses from PET alone. Twelve healthy volunteers [six males (mean age ± SD, 27.7 ± 6.7 years) and six females (31.8 ± 14.5 years)] in 12 examinations were recruited. Dose estimations from PET/CT were compared with those from PET alone. Regions of interest (ROIs) in PET/CT were delineated on the basis of low-dose CT (LD-CT) images acquired during PET/CT. Internal and external radiation doses were estimated using OLINDA/EXM 1.0 and CT-Expo software. The effective dose (ED) for (11)C-ITMM calculated from PET/CT was estimated to be 4.7 ± 0.5 µSv/MBq for the male subjects and 4.1 ± 0.7 µSv/MBq for the female subjects. The mean ED for (11)C-ITMM calculated from PET alone in a previous report was estimated to be 4.6 ± 0.3 µSv/MBq (males, n = 3). The ED values for (11)C-ITMM calculated from PET/CT in the male subjects were almost identical to those from PET alone. The absorbed doses (ADs) of the gallbladder, stomach, red bone marrow, and spleen calculated from PET/CT were significantly different from those calculated from PET alone. The EDs of (11)C-ITMM calculated from PET/CT were almost identical to those calculated from PET alone. The ADs in several organs calculated from PET/CT differed from those from PET alone. LD-CT images acquired during PET/CT may facilitate organ identification.

Brain histamine H1 receptor occupancy measured by PET after oral administration of levocetirizine, a non-sedating antihistamine.

OBJECTIVE: Histamine H1 receptor (H1R) antagonists often have sedative side effects, which are caused by the blockade of the neural transmission of the histaminergic neurons. We examined the brain H1R occupancy (H1RO) and the subjective sleepiness of levocetirizine, a new second-generation antihistamine, comparing fexofenadine, another non-sedating antihistamine, as a negative active control. METHODS: Eight healthy volunteers underwent positron emission tomography (PET) imaging with [(11)C]doxepin, a PET tracer that specifically binds to H1Rs, after a single oral administration of levocetirizine (5 mg), fexofenadine (60 mg) or placebo in a double-blind crossover study. Binding potential ratios and H1ROs in the cerebral cortices regions were calculated using placebo. Subjective sleepiness was assessed with the Line Analogue Rating Scale and the Stanford Sleepiness Scale. RESULTS: There was no significant difference between the mean brain H1RO after levocetirizine administration (8.1%; 95% CI: -9.8 to 26.0%) and fexofenadine administration (-8.0%; 95% CI: -26.7 to 10.6%). Similarly, subjective sleepiness was not significantly different between the two antihistamines and placebo. Neither subjective sleepiness nor plasma concentrations was significantly correlated with the brain H1RO of the two antihistamines. CONCLUSION: At therapeutic dose, levocetirizine does not bind significantly to the brain H1Rs and does not induce significant sedation.