Hisashi Oka

Fatty acid myocardial imaging using 123I-β-methyl-iodophenyl pentadecanoic acid (BMIPP): comparison of myocardial perfusion and fatty acid utilization in canine myocardial infarction (Occlusion and reperfusion model)

To evaluate the relationship between myocardial perfusion and fatty acid metabolism in canine myocardial infarction, 16 dogs were studied using thallium and 123I-β-methyl-iodophenyl pentadecanoic acid (BMIPP). Eight dogs (group A) had left anterior coronary arterial occlusion (6 h ligation), 6 dogs (group B) had reperfusion (3 h ligation and 1 h reperfusion) and 2 dogs served as the normal control. Myocardial imaging with BMIPP was excellent, owing to its higher uptake and longer retention in myocardium and rapid blood disappearance in addition to diminished liver and lung uptake. The mean half time value which was generated from the BMIPP myocardial washout curve, was significantly larger in the reperfused myocardium. The gamma camera imaging showed uncoupling of BMIPP and thallium (BMIPP uptake greater than thallium uptake) in five dogs in group B. On the other hand, all dogs in group A had a persistent defect in BMIPP and thallium uptake. Our findings indicate that the combination of BMIPP and thallium for myocardial imaging supply different information about the zone of infarction and ischemia, which may be useful for the assessment of myocardial viability.

Evaluation of a commercial PET tomograph-based system for the quantitative assessment of rCBF, rOEF and rCMRO2 by using sequential administration of 15O-labeled compounds.

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 H215O 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.

Serial assessment of denervated but viable myocardium following acute myocardial infarction in dogs using iodine-123 metaiodobenzylguanidine and thallium-201 chloride myocardial single photon emission tomography

Iodine-123 metaiodobenzylguanidine (mIBG) is taken up by sympathetic nerve endings, allowing scintigraphic imaging of myocardial sympathetic innervation. We investigated the denervated but viable canine myocardium after acute myocardial infarction by serial mIBG and thallium-201 chloride (201TIC1) single photon emission tomography (SPET). In 12 dogs, acute myocardial infarction was produced by ligation of the left circumflex coronary artery. Images of mIBG and thallium SPET were obtained 6 h, 1, 4 and 6 weeks later. The defect size was calculated in percentage points from short axial views, and the 123I-mIBG/201TlCl ratio was determined. The uptake ratio was high at 1 week but gradually decreased. Three dogs were killed at each time point, and tissue samples were obtained from infarcted (both 201TICl and 123I-mIBG defects), peri-infarcted (123I-mIBG defect and 201TICl normal) and normal myocardium (both mIBG and 201TIC1 normal). The changes in tissue content of noradrenaline in these lesions were measured. Noradrenaline tissue content gradually recovered in the peri-infarcted area. However, no recovery was noted in the infarcted area at 6 weeks. We conclude that sympathetic denervation and re-innervation occur following acute myocardial infarction, and the denervated but viable myocardium could be detected non-invasively by combined mIBG and thallium SPET.

Myocardial glucose metabolism in patients with hypertrophic cardiomyopathy: Assessment by F-18-FDG PET study

In an investigation of myocardial metabolic abnormalities in hypertrophic myocardium, the myocardial glucose metabolism was evaluated with F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) in 32 patients with hypertrophie cardiomyopathy, and the results were compared with those in 9 patients with hypertensive heart disease. F-18-FDG PET study was performed in the fasting and glucose-loading states. The myocardial regional %dose uptake was calculated quantitatively. The average regional %dose uptake in the fasting state in the patients with asymmetric septal hypertrophy and dilated-phase hypertrophie cardiomyopathy was significantly higher than that in the patients with hypertensive heart disease (0.75 ± 0.34%, 0.65 ± 0.25%, and 0.43 ± 0.22%/100 g myocardium, respectively). In contrast, the average %dose uptake in the glucose-loading state in the patients with asymmetric septal hypertrophy and dilated-phase hypertrophie cardiomyopathy was not significantly different from that in patients with hypertensive heart disease (1.17 + 0.49%, 0.80 ± 0.44% and 0.99 ± 0.45%, respectively). The patients with apical hypertrophy had also low %dose uptake in the fasting state (0.38 ± 0.21%) as in the hypertensive heart disease patients, so that the characteristics of asymmetric septal hypertrophy and dilatedphase hypertrophic cardiomyopathy are considered to be high FDG uptake throughout the myocardium in the fasting state. Patients with apical hypertrophy are considered to belong to other disease categories metabolically. F-18-FDG PET study is useful in the evaluation of the pathophysiologic diagnosis of patients with hypertrophie cardiomyopathy.

Acquisition of attenuation map for brain PET study using optical tracking system

Attenuation correction (AC) is essential in order to get quantitative data with positron emission tomography (PET). AC is normally carried out using transmission scan, which is obtained by scanning a subject with external radiation source before the administration of radiopharmaceuticals. The transmission scan makes longer time of PET study and additional radiation exposure to the subject. To avoid these inconveniences, we have aimed to develop a technique to generate attenuation map without the transmission scan for brain PET study. In the procedure, a special cap was designed to put on the head of the subject to be scanned for brain PET study. The surface of the cap has 22 points of markers. An optical tracking system was utilized to determine positions of these 22 markers. In order to obtain the reference attenuation map and positions of 22 markers, the cap was put on the head of a reference subject and the transmission scan was performed. In order to generate a subjects attenuation map, the subject put on the cap and the positions of 22 markers were determined by the optical tracking system. The thin plate spline (TPS) technique was employed to transform from the reference attenuation map to a target subjects attenuation map using 22 markers as control points. Preliminary experiment showed good agreement between the attenuation map computed by the present method and the actual attenuation map by the transmission scan. The present method has potential to shorten brain PET study and reduce the exposure of radiation to the subject. The method might provide an accurate attenuation map for single-photon emission computed tomography (SPECT) study.

Simulation study of noise property of CMRO/sub 2/ quantitation methods with inhalation of /sup 15/O/sub 2/

Measurements of the oxygen consumption in brain have been studied by PET. Autoradiographic method(ARG) was suggested (Mintum et al.) to yield CMRO/sub 2/. This method required separately obtained information about CBF, CBV, thus time of 30-60 min. is required for three separate scans. To decrease the scan time, a new protocol was suggested as a rapid dual table method(ARG-D), in which [/sup 15/O]water injection scan and [/sup 15/O]O/sub 2/ inhalation scan are continuously carried out. Another method of weighted integration(WI) method with single 3 min. /sup 15/O/sub 2/ inhalation scan was suggested (Ohta et W.). We modified this method by taking into account the water re-circulation(WI-WR). In this study, the statistical noise properties and effects of error propagated from dispersion, delay and volume of distribution on CMRO/sub 2/ image, derived by these methods were evaluated. Tissue time activity curves was generated from typical blood time activity curves. A 80% of noise at a peak in [/sup 15/O]water tissue time activity curve was added to study the noise propagation and accuracy in CMRO/sub 2/ image. Also dispersion, delay, and volume of distribution was varied and evaluated the error propagation. Methods of ARG, WI-WR and ARG-D, reproduce the given CMRO/sub 2/ within 2% accuracy, while method WI gives CMRO/sub 2/ 5-15 The effect of noise in unit of %SD was 12 % for ARG, 25 % for WI and WI-WR, and 17 % for ARG-D method. On the basis of simulation study suggests that the ARG-D method developed could be used to estimate the CMRO/sub 2/ values in clinic.