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Biomedical subjects

I Kanno

Publications and source records attributed to I Kanno.

At least 127 records · Page 7Linked to original sources
PubMed1988

Linearization correction of 99mTc-labeled hexamethyl-propylene amine oxime (HM-PAO) image in terms of regional CBF distribution: comparison to C15O2 inhalation steady-state method measured by positron emission tomography.

The radioisotope distribution following intravenous injection of 99mTc-labeled hexamethylpropyleneamine oxime (HM-PAO) in the brain was measured by single photon emission computed tomography (SPECT) and corrected for the nonlinearity caused by differences in net extraction. The "linearization" correction was based on a three compartment model, and it required a region of reference to normalize the SPECT image in terms of regional cerebral blood flow distribution. Two different regions of reference, the cerebellum and the whole brain, were tested. The uncorrected and corrected HM-PAO images were compared with cerebral blood flow (CBF) image measured by the C15O2 inhalation steady state method and positron emission tomography (PET). The relationship between uncorrected HM-PAO and PET-CBF showed a correlation coefficient of 0.85 but tended to saturate at high CBF values, whereas it was improved to 0.93 after the "linearization" correction. The whole-brain normalization worked just as well as normalization using the cerebellum. This study constitutes a validation of the "linearization" correction and it suggests that after linearization the HM-PAO image may be scaled to absolute CBF by employing a global hemispheric CBF value as measured by the nontomographic 133Xe clearance method.

Adult↗
PubMed1988

Oxygen extraction fraction at maximally vasodilated tissue in the ischemic brain estimated from the regional CO2 responsiveness measured by positron emission tomography.

The oxygen extraction fraction (OEF) at maximally vasodilated tissue in patients with chronic cerebrovascular disease was evaluated using positron emission tomography. The vascular responsiveness to changes in PaCO2 was measured by the H2(15)O autoradiographic method. It was correlated with the resting-state OEF, as estimated using the 15O steady-state method. The subjects comprised 15 patients with unilateral or bilateral occlusion and stenosis of the internal carotid artery or middle cerebral artery or moyamoya disease. In hypercapnia, the scattergram between the OEF and the vascular/responsiveness to changes in PaCO2 revealed a significant negative correlation in 11 of 19 studies on these patients, and the OEF at the zero cross point of the regression line with a vascular responsiveness of 0 was 0.53 +/- 0.08 (n = 11). This OEF in the resting state corresponds to exhaustion of the capacity for vasodilation. The vasodilatory capacity is discussed in relation to the lower limit of autoregulation.

Adolescent↗
PubMed1988

Evaluation of regional differences of tracer appearance time in cerebral tissues using [15O] water and dynamic positron emission tomography.

The tracer appearance time relative to the radial artery-sampling site has been evaluated in six brain locations in five human subjects using dynamic positron emission tomography (PET) following the bolus injection of H2(15)O. There was a maximum difference of +/- 2 s from the average in each location. To globally adjust the timing difference between the measured arterial curve and the PET scan, a correction method was developed based on a nonlinear least-squares fitting procedure. This new technique determined the global time delay with an accuracy of +/- 0.5 s. On the other hand, the linear backward extrapolation method resulted in a systematic error of 4 s.

Brain↗
PubMed1988

Measurement of absolute myocardial blood flow with H215O and dynamic positron-emission tomography. Strategy for quantification in relation to the partial-volume effect.

An in vivo technique was developed for measuring the absolute myocardial blood flow with H215O and dynamic positron-emission tomography. This technique was based on a new model involving the concept of the tissue fraction, which was defined as the fraction of the tissue mass in the volume of the region of interest. The myocardium was imaged dynamically by positron-emission tomography, starting at the time of intravenous bolus injection of H215O. The arterial input function was measured continuously with a beta-ray detector. A separate image after C15O inhalation was also obtained for correction of the H215O radioactivity in the blood. The absolute myocardial blood flow and the tissue fraction were calculated for 15 subjects with a kinetic technique under region-of-interest analysis. These results seem consistent with their coronary angiographic findings. The mean value of the measured absolute myocardial blood flows in normal subjects was 0.95 +/- 0.09 ml/min/g. This technique detected a diffuse decrease of myocardial blood flow in patients with triple-vessel disease.

Angina Pectoris↗
PubMed1988

Delayed radiation necrosis of brain evaluated positron emission tomography.

In four patients highly suspected of having delayed radiation necrosis of the brain, regional cerebral blood flow and metabolism were studied by using positron emission tomography (PET) with the 15O-labelled gases, 18F-fluorodeoxyglucose (18FDG). All four patients showed marked decreases in glucose and oxygen consumption in the lesion with that suspected pathology in comparison with those in normal brain parenchyma. Two of them were histologically proved to have radiation injuries (one was radiation necrosis and another was early delayed reactions). But one patient was histologically proved to have a recurrent tumor. Although metabolic study with PET using 18FDG is generally an excellent procedure for differentiation between radiation injuries and recurrent brain tumor, these results imply that in some cases the differential diagnosis is difficult even with 18FDG. The present study demonstrated considerably more pronounced reduction in the metabolism than the decrease of the blood flow in the lesion with radiation necrosis. This result would indicate that the primary effect causing the radiation necrosis is a direct effect of irradiation on neural tissue rather than the capillary damage.

Adult↗
PubMed1987

A system for cerebral blood flow measurement using an H215O autoradiographic method and positron emission tomography.

A system for CBF measurement using an H215O autoradiographic method and positron emission tomography (PET) has been designed and installed as a clinical tool. Following an intravenous injection of H215O, a radioactivity accumulation in the brain tissue for 60 s and a continuous record of radioactivity in arterial blood were measured by a high counting speed PET device and a beta-ray detector, respectively, and CBF was calculated by a table-lookup procedure. First, this method was compared with the C15O2 inhalation steady-state method on 17 cerebrovascular disease patients and four normal subjects. The two values for CBF agreed with each other when H215O autoradiographic method was applied by correction for the dispersion in the measured arterial radioactivity-time curve. However, without the correction, the CBF by the H215O autoradiographic method revealed substantial overestimation by 30.6 +/- 17.5%. A reduced gray/white ratio of CBF was also observed in the H215O autoradiographic method. Second, simulation was performed in order to determine optimal accumulation time by PET scan; the result was that errors due to dispersion and time mismatch became critical as the accumulation time was shortened to less than 60 s.

Autoradiography↗
PubMed1987

[Cerebral blood flow measurement using H2(15)O intravenous injection and positron emission tomography: description of implementation and applications to cerebrovascular reactivity measurement].

The method for cerebral blood flow (CBF) measurement using an H215O intravenous injection and positron emission tomography (PET) was implemented, examined and applied to measure cerebrovascular reactivity to PaCO2(VRCO2) and to MABP (VRBP) in normal brain and in ischemic brain. Immediately after bolus intravenous injection of 30-40 mCi H2(15)O, a time-activity curve of H2(15)O concentration in the arterial blood and in the brain were measured for 60 sec by a beta detector and a PET, respectively. The PET was HEADTOME III and measured five planes. CBF was determined by the table-look up method based on the autoradiographic principle. Six volunteers were studied to examine region of VRCO2, and a moyamoya patient and a stroke patient with a bilateral-intracarotid circulation defect were studied to examine VRCO2 and VRBP in ischemic brain. The studies were carried out so as to be followed two or three H2(15)O CBF measurements with changing PaCO2 or MABP after control study at rest condition. In addition, prior to the H2(15)O study O15 gas steady state study was performed on all subjects. Validity of the method examined by simulation studies showed 3% error per 1 sec time shift of the artery curve for 60 sec PET scan duration and the error was rapidly increased to the shorter scan duration. Inhomogeneity of a brain tissue gave mild under-estimation by 5% for 60 sec PET scan duration. VRCO2 in normal brain was revealed to be almost uniform except that the infratentorium area showed a slight higher VRCO2 than the supratentorium area. The ischemic brain showed a negative correlation between VRCO2 and oxygen extraction fraction (OEF), and a positive correlation between VRBP and OEF.

Autoradiography↗
PubMed1987

[Oxygen extraction fraction and cerebrovascular reactivity to PaCO2 changes in ischemic brain measured by positron emission tomography].

Interrelations between oxygen extraction (OEF) and cerebrovascular reactivity to PaCO2 change (VRCO2) in ischemic brain were measured by the 15O gases steady state method and the H215O autoradiographic method using a positron emission tomography. OEF at rest and VRCO2 for hypercapnia and hypocapnia were assessed successively in five cross sections of 10 mm image resolution. With each study correlation coefficients between OEF and VRCO2 were calculated using 30 to 40 regions of interest. In hypercapnic measurements those which had a larger ischemic region resulted in a higher incident of a negative correlation. Fifteen of 19 studies (79%) showed the negative correlation. From the regression lines which showed significant correlation a mean OEF at VRCO2 =0 was 0.54 +/- 0.09, which might indicate the point at the maximal dilatation of the resistance vessels. On the other hand, in hypocapnic studies only five of 18 (28%) showed apositive correlation, and the other measurements showed diffusely negative VRCO2 over the whole regions in the brain.

Autoradiography↗
PubMed1987

[Assessment of myocardial circulation and metabolism using positron CT].

Positron CT measurement can provide valuable information of myocardial circulation and metabolism. Our institute has participated in the development and use of this measurement since April 1983. At present, we can assess the circulation and metabolism of myocardium using a position CT device (HEADTOME-III) and some radiopharmaceuticals labeled with positron emitters. In this paper, we introduced our method about its measuring device, radiopharmaceuticals and theoretical model, and also indicated the clinical usefulness of the measurement.

Carbon Monoxide↗
PubMed1986

Tomographic mapping of kinetic rate constants in the fluorodeoxyglucose model using dynamic positron emission tomography.

A quick computing algorithm to calculate the rate constants (k*1, k*2, k*3) in the [18F]2-fluoro-2-deoxy-D-glucose (FDG) model was developed. The algorithm solved for the rate constants pixel by pixel using a conventional least-squares method and two tables consisting of a set of various rate constants, to shorten the computing time. Five planes of rate constant images were obtained. A combined study using the dynamic FDG method and the 15O-labeled gas continuous inhalation method was performed on seven healthy male volunteers aged 26-35 years. Results indicated an apparent discrepancy between CMRglu and CMRO2 in the cerebellum, where the low glucose utilization was correlated with a low FDG phosphorylation rate (k*3) despite a sufficient FDG transportation rate (k*1) from plasma to tissue.

Autoradiography↗
PubMed1986

Error analysis of a quantitative cerebral blood flow measurement using H2(15)O autoradiography and positron emission tomography, with respect to the dispersion of the input function.

The effect of the inaccuracy of the input function on CBF measured by the H2(15)O autoradiographic method was investigated. In H2(15)O autoradiography the measured input function usually includes a larger dispersion than the true input function, as well as the absolute time axis having been already lost. The time constant of the external dispersion that occurred in our continuous sampling system was evaluated as 10-12 s when the dispersion function was approximated by a monoexponential function. The internal dispersion occurring in arterial lines in a human body was evaluated as 4-6 s. Such dispersion, indispensable in a patient study, was found to produce large errors in calculating CBF, e.g., 5(10) s of the dispersion caused +15(33) and +10(20)% systematic overestimations for the 40- and 60-s accumulation time respectively. An analytical correction employing an inverse Laplace transform was applied to clinical CBF studies, and the results were compared with those from the C15O2 steady-state inhalation method. Correction by 10 s in time constant, corresponding to the external dispersion, reduced the overestimation significantly from 70-100% to approximately 20%. Further correction by 5 s, corresponding to the internal dispersion, resulted in a negligible difference (less than a few percent) from the steady-state method.

Autoradiography↗
PubMed1986

[A simulation study to evaluate the statistical noise and spatial resolution in image reconstruction of emission computed tomography--with respect to the optimization of the filter function in the convolution integral].

Filtered backprojection method has been commonly used to reconstruct images in the field of the computed tomography (CT). However, in the emission CT such as positron and single photon CT, poor counting static which are caused by limited dosage to patients, limited counting rate capacity and limited efficiency of the imaging device, produce a statistical noise in the reconstructed image. The magnitude of the statistical noise and the spatial resolution were evaluated for various shapes of the filter used in the convolution integrals of the filtered back-projection procedure. The statistical noise was proportional to the inverse of the root of the total number of counts for any filters. The high-frequency-cut characteristic of the filter reduced the statistical noise, but increased the spatial resolution in the images. It was possible to optimize the shape of the filter for given total number of counts and required statistical noise and spatial resolution.

Humans↗