Scatter Correction with Combined Single-Scatter Simulation and Monte Carlo Simulation Scaling Improved the Visual Artifacts and Quantification in 3-Dimensional Brain PET/CT Imaging with 15O-Gas Inhalation.

In 3-dimensional PET/CT imaging of the brain with 15O-gas inhalation, high radioactivity in the face mask creates cold artifacts and affects the quantitative accuracy when scatter is corrected by conventional methods (e.g., single-scatter simulation [SSS] with tail-fitting scaling [TFS-SSS]). Here we examined the validity of a newly developed scatter-correction method that combines SSS with a scaling factor calculated by Monte Carlo simulation (MCS-SSS). Methods: We performed phantom experiments and patient studies. In the phantom experiments, a plastic bottle simulating a face mask was attached to a cylindric phantom simulating the brain. The cylindric phantom was filled with 18F-FDG solution (3.8-7.0 kBq/mL). The bottle was filled with nonradioactive air or various levels of 18F-FDG (0-170 kBq/mL). Images were corrected either by TFS-SSS or MCS-SSS using the CT data of the bottle filled with nonradioactive air. We compared the image activity concentration in the cylindric phantom with the true activity concentration. We also performed 15O-gas brain PET based on the steady-state method on patients with cerebrovascular disease to obtain quantitative images of cerebral blood flow and oxygen metabolism. Results: In the phantom experiments, a cold artifact was observed immediately next to the bottle on TFS-SSS images, where the image activity concentrations in the cylindric phantom were underestimated by 18%, 36%, and 70% at the bottle radioactivity levels of 2.4, 5.1, and 9.7 kBq/mL, respectively. At higher bottle radioactivity, the image activity concentrations in the cylindric phantom were greater than 98% underestimated. For the MCS-SSS, in contrast, the error was within 5% at each bottle radioactivity level, although the image generated slight high-activity artifacts around the bottle when the bottle contained significantly high radioactivity. In the patient imaging with 15O2 and C15O2 inhalation, cold artifacts were observed on TFS-SSS images, whereas no artifacts were observed on any of the MCS-SSS images. Conclusion: MCS-SSS accurately corrected the scatters in 15O-gas brain PET when the 3-dimensional acquisition mode was used, preventing the generation of cold artifacts, which were observed immediately next to a face mask on TFS-SSS images. The MCS-SSS method will contribute to accurate quantitative assessments.

Comprehensive assessment of impaired peripheral and coronary artery endothelial functions in smokers using brachial artery ultrasound and oxygen-15-labeled water PET.

BACKGROUND: Comprehensive evaluation of endothelium-dependent and endothelium-independent vascular functions in peripheral arteries and coronary arteries in smokers has never been performed previously. Through the use of brachial artery ultrasound and oxygen-15-labeled water positron emission tomography (PET), we sought to investigate peripheral and coronary vascular dysfunctions in smokers. METHODS AND RESULTS: Eight smokers and 10 healthy individuals underwent brachial artery ultrasound at rest, during reactive hyperemia [250mmHg cuff occlusion (flow-mediated dilatation (FMD)], and following sublingual nitroglycerin (NTG) administration. Myocardial blood flow (MBF) was assessed through O-15-labeled water PET at rest, during adenosine triphosphate (ATP) administration, and during a cold pressor test (CPT). Through ultrasound, smokers were shown to have significantly reduced %FMD compared to controls (6.62±2.28% vs. 11.29±2.75%, p=0.0014). As assessed by O-15-labeled water PET, smokers were shown to have a significantly lower CPT response than were controls (21.1±9.5% vs. 50.9±16.9%, p=0.0004). There was no relationship between %FMD and CPT response (r=0.40, p=0.097). Endothelium-independent vascular dilatation was similar for both groups in terms of coronary flow reserve with PET (p=0.19). Smokers tended to have lower %NTG in the brachial artery (p=0.055). CONCLUSIONS: Smokers exhibited impaired coronary endothelial function as well as peripheral brachial artery endothelial function. In addition, there was no correlation between PET and ultrasound measurements, possibly implying that while smokers may have systemic vascular endothelial dysfunction, the characteristics of that dysfunction may be different in peripheral arteries and coronary arteries.

Regional partition coefficient of water in patients with cerebrovascular disease and its effect on rCBF assessment.

OBJECTIVE: Cerebral blood flow (CBF) estimation with C15O2 PET usually assumes a single tissue compartment model and a fixed brain-blood partition coefficient of water. However, the partition coefficient may change in pathological conditions. The purpose of this study was to investigate the changes in the partition coefficient of water in pathological regions and its effect on regional CBF assessment. METHODS: The study protocol included 22 patients with occlusive cerebrovascular disease to compare the partition coefficients among three regions (infarction area, noninfarct hypoperfusion area, and contralateral area) in the pathological brain (analysis A), and to compare the CBF estimated by using a fixed partition coefficient and CBF estimated using floating partition coefficients (analysis B). RESULTS: The partition coefficient in the infarction area (0.55±0.07 ml/g) was lower than that in the contralateral normal cortex (0.68±0.05 ml/g), whereas noninfarct hypoperfusion area did not show a significant change (0.67±0.06 ml/g). As a result, the use of a fixed partition coefficient of normal volunteers (0.70 ml/g) resulted in an underestimation in regional CBF by 12% in infarction area (P<0.05), whereas the estimation errors were smaller and induced no significant difference in the noninfarct hypoperfusion area or in contralateral areas. CONCLUSION: The partition coefficient is stable except for the infarction area, and CBF estimation using a fixed partition coefficient of normal volunteers provides clinically appreciable information in patients with cerebrovascular disease.

Myocardial oxidative metabolism is increased due to haemodynamic overload in patients with aortic valve stenosis: assessment using 11C-acetate positron emission tomography.

PURPOSE: The relationship between myocardial oxidative metabolism and pressure overload in aortic valve stenosis (AS) is not fully elucidated. We identified the determinants of myocardial oxidative metabolism by measuring its changes after aortic valve replacement (AVR) in patients with AS. METHODS: Myocardial 11C-acetate clearance rate constant (Kmono), an index of oxidative metabolism, was measured non-invasively by using positron emission tomography in 16 patients with moderate to severe AS and 7 healthy controls. The severity of AS was assessed by echocardiography. Of 16 patients, 5 were reexamined at 1 month after AVR. RESULTS: Kmono was significantly higher in patients with AS than healthy controls by 42% (0.068±0.014 vs 0.048±0.007/min, p<0.01). Kmono was significantly correlated with age (r=0.58, p<0.01), left ventricular (LV) mass index (r=0.61, p<0.01) and estimated systolic LV pressure (r=0.81, p<0.001) measured by echocardiography. By multivariate analysis, estimated LV systolic pressure was an independent predictor of Kmono (ß=0.93, p<0.01). After AVR, Kmono (from 0.075±0.012 to 0.061±0.014/min, p=0.043) and LV mass index (from 183±49 to 124±41 g/ml2, p=0.043) were significantly decreased despite no significant changes in rate-pressure product. CONCLUSION: Myocardial oxygen metabolism was increased in patients with AS, which was decreased after AVR. The increased myocardial oxidative metabolism in AS was largely attributable to the pressure overload of the LV.

Quantitative assessment of regional myocardial flow reserve using tc-99m-sestamibi imaging.

BACKGROUND: The aims of this study were to develop a method for quantitative estimation of the myocardial blood flow index (MBFI) and myocardial flow reserve (MFR) of the whole left ventricle using (99m)technetium (Tc-99m)-sestamibi imaging. METHODS AND RESULTS: Twenty-two patients with suspected coronary artery disease and 7 controls underwent both Tc-99m-sestamibi imaging and O-15 water positron emission tomography (PET). The global MBFI was calculated on the basis of the microsphere model from the ratio of the myocardial count to the area under the time - activity curve on the aortic arch. The regional MBFI was calculated from the relative distributions of Tc-99m-sestamibi uptake values. The regional MBFI and MFR (Tc-MFR) obtained using single-photon emission computed tomography were compared with the myocardial blood flow (MBF) and MFR (PET-MFR) obtained using PET as the gold standard. Regional MBFI significantly correlated with the MBF obtained using PET. Regional Tc-MFR also correlated with the regional PET-MFR, with some underestimation. CONCLUSION: These results indicate that regional MBF and MFR may be estimated by dynamic Tc-99m-sestamibi imaging and can be used for the early detection and estimation of the functional severity of coronary lesions without the need for a PET camera.

Assessment of coronary function in children with a history of Kawasaki disease using (15)O-water positron emission tomography.

BACKGROUND: Coronary abnormalities after Kawasaki disease (KD) may be associated with endothelial dysfunction due to intimal hypertrophy. The purpose of this study was to evaluate myocardial flow reserve (MFR) and endothelial function in regressed aneurysmal regions after KD. Methods and Results- Subjects were 12 patients aged 16.0+/-2.6 years who suffered from KD at 1.7+/-1.5 years and 12 normal subjects aged 26.5+/-3.4 years. MFR and endothelial function were estimated, respectively, by changes in myocardial blood flow (MBF) during ATP infusion and by that during cold pressor test using (15)O-water positron emission tomography. Data from 24 regressed aneurysmal regions were compared with those from the corresponding regions (n=36) in the control group. Although the MBF at rest in the regressed aneurysmal regions was similar to that in controls, the MBF at a hyperemic state induced by ATP infusion in the regressed aneurysmal regions was significantly lower than that in the control regions. Therefore, the MFR in regressed aneurysmal regions was significantly lower than that in controls (3.53+/-0.95 versus 4.60+/-1.14; P<0.05). MBF at rest and during the cold pressor test did not change in the control regions, but it was significantly reduced in regressed aneurysmal regions. The ratio of MBF during the cold pressor test to MBF at rest was significantly lower in regressed aneurysmal regions than in control regions (0.67+/-0.15 versus 1.00+/-0.15; P<0.05). CONCLUSIONS: MFR and endothelial function are often impaired in regressed aneurysmal regions after KD, and tomography enables the noninvasive evaluation of coronary function.