Kohei Hanaoka

Quantitative Evaluation of Cerebral Blood Flow and Oxygen Metabolism in Normal Anesthetized Rats: 15O-Labeled Gas Inhalation PET with MRI Fusion

PET with 15O gas has been used for the quantitative measurement of cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), oxygen extraction fraction (OEF), and cerebral blood volume (CBV) in humans. However, several technical difficulties limit its use in experiments on small animals. Herein, we describe the application of the 15O gas steady-state inhalation method for normal anesthetized rats. Methods: Eight normal male Sprague–Dawley rats (mean body weight ± SD, 268 ± 14 g) under anesthesia were investigated by 15O-labeled gas PET. After tracheotomy, an airway tube was placed in the trachea, and the animals were connected to a ventilator (tidal volume, 3 cm3; frequency, 60/min). The CBF and OEF were measured according to the original steady-state inhalation technique under artificial ventilation with 15O-CO2 and 15O-O2 gases delivered through the radioactive gas stabilizer. CBV was measured by 15O-CO gas inhalation and corrected for the intravascular hemoglobin-bound 15O-O2. Arterial blood sampling was performed during each study to measure the radioactivity of the whole blood and plasma. MR image was performed with the same acrylic animal holder immediately after the PET. Regions of interest were placed on the whole brain of the PET images with reference to the semiautomatically coregistered PET/MR fused images. Results: The data acquisition time for the whole PET experiment in each rat was 73.3 ± 5.8 (range, 68–85) min. In both the 15O-CO2 and the 15O-O2 studies, the radioactivity count of the brain reached a steady state by approximately 10 min after the start of continuous inhalation of the gas. The quantitative PET data of the whole brain were as follows: CBF, 32.3 ± 4.5 mL/100 mL/min; CMRO2, 3.23 ± 0.42 mL/100 mL/min; OEF, 64.6% ± 9.1%; and CBV, 5.05 ± 0.45 mL/100 mL. Conclusion: Although further technical improvements may be needed, this study demonstrated the feasibility of quantitative PET measurement of CBF, OEF, and CMRO2 using the original steady-state inhalation method of 15O-CO2 and 15O-O2 gases and measurement of CBV using the 15O-CO gas inhalation method in the brain of normal anesthetized rats.

Impact of CT attenuation correction by SPECT/CT in brain perfusion images

PurposeThe aim of this study was to elucidate the regional differences between brain perfusion single photon emission computed tomography (SPECT) images reconstructed with a uniform attenuation correction using Chang’s method (AC-Chang) and a non-uniform attenuation correction with CT using SPECT/CT (AC-CT).MethodsSPECT images of a phantom with and without head holder were obtained, and reconstructed images of AC-Chang and AC-CT were compared. Twenty-eight consecutive patients with brain disease examined by SPECT/CT brain perfusion imaging were selected, and images were reconstructed with AC-Chang and AC-CT. The AC-Chang and AC-CT reconstructed images were then compared by voxel-based analysis using three-dimensional stereotactic surface projections.ResultsCounts in the frontal area of the AC-Chang phantom image with head holder were higher than those in the posterior area. Counts in the frontal area of the AC-Chang clinical images were significantly higher than those in the AC-CT images, while the counts in the margin of the frontal lobe and posterior margin of the parietal, occipital cortices and cerebellum of the AC-Chang images were significantly lower. Relative frontal perfusion was 5.0% higher and relative cerebellar perfusion was 4.6% lower in the AC-Chang images relative to the AC-CT images, on average.ConclusionWe demonstrated the frontal dominant hyper-perfusion and parieto-occipital and cerebellar hypo-perfusion in brain SPECT images reconstructed with AC-Chang compared to those reconstructed with AC-CT. We suggest that to obtain an accurate attenuation-corrected brain perfusion SPECT image, attenuation correction by Chang’s method is inadequate.

Fluorodeoxyglucose uptake in the bone marrow after granulocyte colony-stimulating factor administration in patients with non-Hodgkinʼs lymphoma

PurposeTo clarify the change in the fluorodeoxyglucose (FDG) uptake by the bone marrow over time after administration of granulocyte colony-stimulating factor (G-CSF), we evaluated the correlation between the interval from the last day of administration of G-CSF to positron emission tomography/computed tomography (PET/CT) study and spinal bone marrow accumulation in patients with non-Hodgkins lymphoma. MethodsA total of 127 patients with confirmed non-Hodgkins lymphoma who underwent FDG PET within 60 days from the last administration of G-CSF were retrospectively reviewed. Thirty age-matched and sex-matched healthy controls were also included to evaluate physiological FDG uptake. PET/CT examinations were retrospectively reviewed, and maximum standardized uptake value (SUVmax) was measured by placing volumetric regions of interest over each thoracic and lumbar vertebra on PET images referring to CT images. Bone marrow SUV was defined as the mean SUVmax of the vertebra. The correlation between the interval after G-CSF and the bone marrow SUV was plotted and analyzed with polynomial approximation. ResultsIn controls, physiological bone marrow SUV of the spine was determined. In patients with lymphoma, bone marrow SUV decreased over time and reached a plateau at about 14 days after G-CSF administration, and this was higher by 5% than the plateau at 10 days. SUV declined to the ‘physiological range’, that is, mean+1 standard deviation of patients, at about 7 days. ConclusionFor a PET/CT study, an interval of 10 days after G-CSF administration is recommended to minimize the influence of G-CSF on the bone marrow when evaluating treatment response in patients with non-Hodgkins lymphoma.

Decreased brain FDG uptake in patients with extensive non-Hodgkin’s lymphoma lesions

ObjectiveFaint brain [18F]fluoro-2-deoxyglucose (FDG) uptake has sporadically been reported in patients with FDG-avid large or diffusely extended tumors. The purpose of this study was to investigate whether there is a correlation between massive tumor uptake and decreased brain uptake on FDG positron emission tomography/computed tomography (PET/CT).MethodsSixty-five patients with histologically confirmed non-Hodgkin’s lymphoma who underwent FDG-PET/CT were enrolled. Thirty control subjects were also included to evaluate normal brain FDG uptake. PET/CT examinations were retrospectively reviewed. The volumetric regions of interest were placed over lesions by referring to CT and PET/CT fusion images to measure mean standardized uptake value (SUVavg). The products of SUVavg and tumor volume were calculated as total glycolytic volume (TGV). The maximum SUV (SUVmax) and SUVavg were measured in the cerebrum and cerebellum. The values of TGV and brain FDG uptake were plotted and analyzed with a linear regression method.ResultsIn the lymphoma patients, there were statistically significant negative correlations between TGV and brain SUVs.ConclusionDemonstrating a significant negative correlation between TGV and brain uptake validated the phenomenon of decreased brain FDG uptake. Diversion of FDG from the brain to the lymphoma tissue may occur during the FDG accumulation process. Recognition of this phenomenon prevents unnecessary further neurological examinations in such cases.

A novel radiation protection device based on tungsten functional paper for application in interventional radiology

&NA; Tungsten functional paper (TFP), which contains 80% tungsten by weight, has radiation‐shielding properties. We investigated the use of TFP for the protection of operators during interventional or therapeutic angiography. The air kerma rate of scattered radiation from a simulated patient was measured, with and without TFP, using a water‐equivalent phantom and fixed C‐arm fluoroscopy. Measurements were taken at the level of the operators eye, chest, waist, and knee, with a variable number of TFP sheets used for shielding. A Monte Carlo simulation was also utilized to analyze the dose rate delivered with and without the TFP shielding. In cine mode, when the number of TFP sheets was varied through 1, 2, 3, 5, and 10, the respective reduction in the air kerma rate relative to no TFP shielding was as follows: at eye level, 24.9%, 29.9%, 41.6%, 50.4%, and 56.2%; at chest level, 25.3%, 33.1%, 34.9%, 46.1%, and 44.3%; at waist level, 45.1%, 57.0%, 64.4%, 70.7%, and 75.2%; and at knee level, 2.1%, 2.2%, 2.1%, 2.1%, and 2.1%. In fluoroscopy mode, the respective reduction in the air kerma rate relative to no TFP shielding was as follows: at eye level, 24.8%, 30.3%, 34.8%, 51.1%, and 58.5%; at chest level, 25.8%, 33.4%, 35.5%, 45.2%, and 44.4%; at waist level, 44.6%, 56.8%, 64.7%, 71.7%, and 77.2%; and at knee level, 2.2%, 0.0%, 2.2%, 2.8%, and 2.5%. The TFP paper exhibited good radiation‐shielding properties against the scattered radiation encountered in clinical settings, and was shown to have potential application in decreasing the radiation exposure to the operator during interventional radiology.

Regional Differences in Amyloid Deposition between 11C-Pib PET PositivePatients with and without Elevated Striatal Amyloid Uptake

Purpose: In subjects showing an increased level of 11C-Pittsburgh compound B (PiB) in positron emission tomography (PET) imaging of the brain, two groups can be distinguished: those with and without elevated PiB uptake in the striatum. We examined regional PiB uptake differences between these groups, and additionally compared them with PiB-negative subjects. Methods: This study included 141 subjects complaining of cognitive impairment. Their clinical diagnoses were Alzheimer’s disease (AD), mild cognitive impairment, dementia with Lewy bodies, frontotemporal lobar degeneration, or subjective cognitive impairment. PiB and 18F-fluorodeoxy-D-glucose (FDG) PET were performed in all subjects. PiB PET images were visually classified into three groups: 1) PiB-positive with uptake in any region of the cortex accompanied by striatal PiB uptake (STRPOS), 2) PiB-positive with cortical uptake but without striatal PiB uptake (STRNEG), and 3) both cortex and striatum PiB-negative (PiBNEG). Standardised uptake value ratios (SUVR) and regional differences in PiB uptake were evaluated using voxelbased analysis of PiB and FDG uptake images. Results: Eighty subjects were visually rated as PiB-positive: 11 had no increased PiB uptake in the striatal area, while 69 showed an elevated striatal PiB level. Sixty-one subjects were PiB-negative. Mean cortical SUVR was 1.46 ± 0.23 for STRNEG, 2.00 ± 0.44 for STRPOS and 0.99 ± 0.19 for PiBNEG. Apart from the striatum, PiB accumulation in the medial orbitofrontal cortex of STRPOS subjects was higher than in STRNEG subjects. No significant differences in regional FDG distribution were observed. Conclusion: PiB-positive cases with high striatal PiB uptake have an increased mean cortical SUVR in comparison to PiB-positive subjects without striatal uptake. This difference is most distinctive in the orbitofrontal cortex. We conclude that a high amyloid load in the striatum is linked to amyloid deposition occurring mostly in the frontal region, and may occur later in the course of AD progression.

Resistance and Heterogeneity of Intratumoral Antibody Distribution

Even though ibritumomab tiuxetan provides clinical benefit to follicular lymphoma patients, resistance to ibritumomab tiuxetan develops. Follicular lymphoma shows a remarkable diversity in phenotypic, genetic, and microenvironment intratumoral heterogeneities.

MEASUREMENT OF ABSORPTION DOSE OUTSIDE IRRADIATION FIELD IN IMRT

The absorption dose outside the irradiation field for prostate intensity-modulated radiation therapy was measured and evaluated by comparison with calculated values of radiation treatment planning system (TPS). The values of TPS calculated were using Varian CLINAC21EX/Eclipse and TomoTherapy Planning System for constant irradiation time. The absorption dose was measured by placing a glass-element dosemeter in a human-bone enclosure phantom with a planning target volume inside the irradiation field. The organs at risk were the rectum, spinal cord, thyroid, eyeball and the left lung. The calculated values of TPS, Varian CLINAC21EX/Eclipse and TomoTherapy Planning System were calculated, up to 17 and 55 cm from the isocenter, respectively. The absorbed dose outside the irradiation field diverged with increased distance from the isocenter (Varian/Eclipse: p = 0.03, TomoTherapy Planning System: p = 0.25). The calculated values for the absorbed dose outside the irradiation field were underestimated.