Takuya Hayashi

Use of a clinical MRI scanner for preclinical research on rats

This study evaluated the feasibility of imaging rat brains using a human whole-body 3-T magnetic resonance imaging (MRI) scanner with specially developed transmit-and-receive radiofrequency coils. The T1- and T2-weighted images obtained showed reasonable contrast. Acquired contrast-free time-of-flight magnetic resonance angiography images clearly showed the cortical middle cerebral artery (MCA) branches, and interhemispheric differences could be observed. Dynamic susceptibility contrast MRI at 1.17xa0mm3 voxel resolution, performed three times following administration of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA, 0.1xa0mmol/kg), demonstrated that the arterial input function (AIF) can be obtained from the MCA region, yielding cerebral blood flow (CBF), cerebral blood volume, and mean transit time (MTT) maps. The hypothalamus (HT) to parietal cortex (Pt) CBF ratio was 45.11xa0±xa02.85%, and the MTT was 1.29xa0±xa00.40xa0s in the Pt region and 2.32xa0±xa00.17xa0s in the HT region. A single dose of Gd-DTPA enabled the assessment of AIF within MCA territory and of quantitative CBF in rats.

Estimation of input function for rapid dual table ARG method

Measurements of the oxygen consumption in brain have been studied by PET. Autoradiographic method(ARG) was suggested (Mintum et al.) to yield CMRO2. This method required separately obtained information about CBF, CBV, thus time of 30-60 min. is required for three separate scans. We developed a rapid dual table method, in which water and oxygen are continuously administrated with the 90-180 sec of water and 180 sec of oxygen scan. In order to derive the quantitative CMRO2 in PET scan, it is necessary to obtain the arterial blood time activity curve. In this study, a method to estimate the input functions corresponds to [/sup 15/O] water injection and [/sup 15/O] oxygen inhalation, in a continuously administration study, was developed. A method developed was model-based, employing a fitting method. In order to estimate the reliability of developed method, input functions of [/sup 15/O] water injection and [/sup 15/O]oxygen inhalation obtained separately in a clinical study was combined with time lag of 90 seconds and 180 seconds. The reproducibility was examined by comparing the blood input functions obtained from present method and from original input functions obtained in clinical study. After fitting the combined input function with model function, each input function of [/sup 15/O] water injection and [/sup 15/O] oxygen inhalation was derived. The whole shapes were in agreement with each other. This method could be used for estimation of each input function in continuously water and oxygen administrated study.

Development of fully automatic technique to parametric images of myocardial blood flow with /sup 15/O-water and positron emission tomography using basis function method

Regional myocardial blood flow (MBF) can be measured with I5O-water and PET using the one-tissue compartment model (IT model) with perfusable tissue fraction (PTF), which provides MBF value that is free from the partial volume effect (PVE). Study with I5O-water has several advantages such as the ability of repeated scan. However, the image quality of 15O-water is limited, which impedes the computation of MBF and PTF values at the voxel level. We implemented the basis function method (BFM) for generating parametric images of MBF, PTF and arterial blood volume (Va) with 15O-water and PET. The BFM is to linearize the solution of IT model, which results in a computationally much faster method than the conventional non-linear least squares fitting method (NLM) in estimating the parameters. In order to fully automate the process of the BFM, PET images were realigned to a reference image using Affine transformation. Arterial input function with PVE correction was derived from the realigned PET images using templates of regions of left ventricle and myocardium. In order to validate the BFM, series of PET studies were performed on infarction model pigs (n=4). PET scans with 15O-water were performed with varying doses of adenosine (5-7 scans for each pig). The results by the BFM were well correlated to ones by the NLM. The method automatically generated functional maps computationally fast enough for clinical application.

Statistical error analysis based on non-parametric bootstrap method of quantitative MBF measurement with H/sub 2//sup 15/O/spl I.bar/PET

Knowledge of the precision in the physiological parameters estimated by positron emission tomography (PET) is helpful for optimizing PET study and accurate diagnosis. Nonparametric bootstrap method proposed by Buvat is resampling techniques that can be used to accurately estimate the statistical properties of PET images in one scan and determine statistics of pixel values. The standard deviation (SD) of time activity curves (TAC) generated by region of interests (ROI) also are estimated by using the bootstrap method and the SD would propagate to estimated parameters such as blood flow. In order to evaluate the present method, a PET study for myocardial blood flow (MBF) measurement with H/sub 2//sup 15/O/spl I.bar/PET was performed. The statistical properties of MBF were estimated and the effects of scan-duration time and ROI size on the SD of MBF were developed.

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.

Model-based noninvasive estimation of arterial input function from dynamic H/sub 2//sup 15/O PET images

For the application of a kinetic model to PET data, it is necessary to obtain the arterial input function. Since arterial blood sampling is invasive and labor intensive, a method to evaluate the input function without arterial blood sampling is important. In case of the [/sup 15/O] water injection study, because of the noise in the time activity curve obtained from the PET reconstructed image round the carotid artery region, a model based evaluation method might be promised. In this study, a model function is composed or combination of blood time activity curve function and tissue time activity curve function which is generated from blood activity curve function. The present method was applied to 15 of dynamic PET scans or /sup 15/O water (10 normal subjects, 10 : Rest, and 5 : Diamox) for normal volunteers. The time activity curve obtained was fitted with the above model function. The shapes or input function obtained was in agreement with that by arterial blood sampling. The accuracy of height of the peak was 14 % and the accuracy of area under the curve was 10 %. This study supposed that present method could be used for direct extraction of the carotid artery input function from the dynamic PET image, and could be used in a quantitative CBF study using /sup 15/O water PET.

Performance test and application of GSO detector assembly for a continuous blood sampling system

A new input function monitoring system has been developed using a GSO detector for both PET and SPECT quantitative studies. The paired assembly of crystals provided an absolute sensitivity of approximately 7% for PET tracers and 70% for /sup 99m/Tc and /sup 201/Tl (SPECT tracers). This system was applied to clinical use and animal study such as monkey and rat. This study demonstrates that the present system can he of use in both clinical and small animal studies using SPECT and PET tracers.