Biomedical subjects

Yasuhiro Wada

Publications and source records attributed to Yasuhiro Wada.

12 recordsLinked to original sources

PubMed2006

Usefulness of FDG-microPET for early evaluation of therapeutic effects on VX2 rabbit carcinoma.

PURPOSE: The aim of this study was to determine the potential use of high-resolution FDG-microPET for predicting the primary effects of radiotherapy and/or hyperthermia on tumor-bearing rabbits. METHODS: Twenty-eight VX2 xenografts in the thighs of rabbits were divided into the following 5 treatment groups: radiotherapy at a single dose of 10, 20 or 30 Gy, hyperthermia (43 degrees Celsius, 1 hour), and the combination of radiotherapy and hyperthermia (10 Gy + 43 degrees Celsius, 1 hour). FDG-microPET images were obtained by using a microPET P4 system at pretreatment and at 24 hours and 7 days after treatment. For the evaluation by FDG-microPET, tumor/muscle (T/M) ratios, retention index [RI = (T/M ratio at 120 min - T/M ratio at 60 min) / T/M ratio at 60 min], and time activity curve (TAC) were acquired. RESULTS: We divided the xenografts into a responder group (partial response + stable disease, n=14) and a non-responder group (progressive disease, n = 14). The T/M ratio at 24 hours after the treatment in the responder group was decreased remarkably with that at pre-treatment (p < 0.05), while in the non-responder group it showed no significant change between the time points. The RI and TAC patterns were comparable to T/M ratios in each treatment group. T/M ratios, RI, and TAC indicated marked changes at the time point of 24 hours in the responder group, although the tumors did not show any significant hange in volume at that time. Photomicrographs of sections showed that the number of viable tumor cells in the responder group decreased at 24 hours after treatment and that inflammatory cell infiltration was marked and almost all viable tumor cells had disappeared by day 7 after treatment. CONCLUSION: These results suggest that early evaluation by FDG-microPET, especially 24 hours after treatment, is useful to predict the primary effects of the treatment. Histological analysis showed that inflammatory cell infiltration at 7 days after treatment was considered to be a cause of accumulation of FDG in the tumors that showed a significant decrease in tumor cell number. This false-positive should be noted when predicting tumor response by FDG accumulation.

Animals↗

PubMed2005

[2D imaging simulations of a small animal PET scanner with DOI measurement: jPET-RD.].

We present a preliminary study on the design of a high sensitivity small animal DOI-PET scanner: jPET-RD (for Rodents with DOI detectors), which will contribute to molecular imaging. The 4-layer DOI block detector for the jPET-RD that consists of scintillation crystals (1.4 mm x 1.4 mm x 4.5 mm) and a flat panel position-sensitive photomultiplier tube (52 mm x 52 mm) was previously proposed. In this paper, we investigate imaging performance of the jPET-RD through numerical simulations. The scanner has a hexagonal geometry with a small diameter and a large axial aperture. Therefore DOI information is expected to improve resolution uniformity in the whole field of view (FOV). We simulate the scanner for various parameters of the number of DOI channels and the crystal length. Simulated data are reconstructed using the maximum likelihood expectation maximization with accurate system modeling. The trade-off results between background noise and spatial resolution show that only shortening the length of crystal does not improve the trade-off at all, and that 4-layer DOI information improves uniformity of spatial resolution in the whole FOV. Excellent performance of the jPET-RD can be expected based on the numerical simulation results.

Animals↗

PubMed2004

Optimal impedance control for task achievement in the presence of signal-dependent noise.

There is an infinity of impedance parameter values, and thus different co-contraction levels, that can produce similar movement kinematics from which the CNS must select one. Although signal-dependent noise (SDN) predicts larger motor-command variability during higher co-contraction, the relationship between impedance and task performance is not theoretically obvious and thus was examined here. Subjects made goal-directed, single-joint elbow movements to either move naturally to different target sizes or voluntarily co-contract at different levels. Stiffness was estimated as the weighted summation of rectified EMG signals through the index of muscle co-contraction around the joint (IMCJ) proposed previously. When subjects made movements to targets of different sizes, IMCJ increased with the accuracy requirements, leading to reduced endpoint deviations. Therefore without the need for great accuracy, subjects accepted worse performance with lower co-contraction. When subjects were asked to increase co-contraction, the variability of EMG and torque both increased, suggesting that noise in the neuromotor command increased with muscle activation. In contrast, the final positional error was smallest for the highest IMCJ level. Although co-contraction increases the motor-command noise, the effect of this noise on the task performance is reduced. Subjects were able to regulate their impedance and control endpoint variance as the task requirements changed, and they did not voluntarily select the high impedance that generated the minimum endpoint error. These data contradict predictions of the SDN-based theory, which postulates minimization of only endpoint variance and thus require its revision.

Adult↗

PubMed2004

Use of FDG-microPET for detection of small nodules in a rabbit model of pulmonary metastatic cancer.

OBJECTIVE: The performance of microPET using 18F-FDG was evaluated in a rabbit model of hematogenous pulmonary metastatic cancer. METHODS: A total of 15 Japanese white rabbits and VX-2 carcinoma were used in this study. In the microPET study, tumor-bearing rabbits were administered intravenously 74 MBq of 18F-FDG, and 30 min later, the emission data were acquired for 60 min. The transmission scans were performed with a 68Ge/68Ga external point source. To augment the anatomical information, we performed multi-detector row computed tomography (MDCT) in the combination with MDCT and microPET on 10 rabbits. The other 5 rabbits were followed once a week for 5 weeks only by microPET. Tumor/muscle (T/M) ratios were used for quantitative evaluation in this study. RESULTS: Multiple pulmonary nodules were detected by MDCT and microPET starting 14 days after the tumor injection. The high-uptake lesions in the lung detected by microPET corresponded well to the tumors detected by MDCT. The smallest nodule detected by microPET was ca. 1.5 mm in diameter. Overall, 87 nodules were detected by MDCT and the ratios of lesions detected by microPET to those by MDCT were 35.3%, 77.5%, and 90% for tumors equal to or smaller than 2 mm, 2-4 mm, and 4-6 mm in diameter, respectively. The respective T/M ratios were 2.41 +/- 0.41, 2.93 +/- 0.55, and 3.34 +/- 0.71. The T/M ratio increased with tumor size, but it was similar in each tumor size category. In the 35-day follow-up protocol, it was possible to follow sequentially the same tumor by the microPET. CONCLUSIONS: By FDG-microPET, it is possible to evaluate tumors larger than 2 mm in diameter and to follow the growth of individual tumors. Our results also suggest that the rabbit model of VX-2 pulmonary metastasis is a stable experimental model for evaluation using FDG. Monitoring of the therapeutic effects of anticancer drugs and radiation therapy could be tried by using this model and microPET.

Animals↗

PubMed2004

A via-point time optimization algorithm for complex sequential trajectory formation.

In our previous research, we proposed a method for the reproduction of complex movement trajectories and robot arm control that could mimic fast, skilled human movements. That method is based on bi-directional theory and uses a representation of a set of via-points as boundary conditions or control variables to perform robot arm trajectory control. The via-points are extracted from human movement data and the resultant via-point representation is able to regenerate handwritten characters, control a Kendama toy, and perform a tennis serve. The via-point information contains both spatial and temporal information, that is, the position on the trajectory and the time of passing through the via-point position, respectively. Trajectory generation is performed using the trajectory formation model based on the optimal criterion, namely, the smoothness criterion, for which the boundary conditions are both the position and the timing of the via-point information. However, generating a smooth trajectory at different movement speeds is quite difficult if the time of passing through the via-point position is unknown or different from the extracted via-point time. In this paper, we therefore propose a new algorithm which can determine temporal via-point information. Our proposed algorithm can generate roughly the same trajectory as the measured human trajectory from only the spatial information of via-point locations. The optimality and the convergence of the new algorithm are investigated theoretically, and the trajectory generated by the algorithm is shown in numerical experiments. It is shown that starting from arbitrary temporal information the proposed algorithm can produce an appropriate trajectory.

Algorithms↗

PubMed2004

Congenital hepatic arteriovenous fistula with intrahepatic portosystemic shunt and aortic stenosis in a dog.

Examination of a 2-month-old male golden retriever presented to the hospital revealed malnutrition, ascites, cardiac murmur and hyperammonemia. Identification of subaortic stenosis and hepatic arteriovenous fistula was made through ultrasonography and angiocardiography. In addition, intrasurgical mesenteric portography showed an intrahepatic portosystemic shunt. The dog did not show portal hypertension and secondary multiple extrahepatic portosystemic shunts. Surgical correction was attempted after medical treatment. The hepatic artery branch which was connected to the hepatic arteriovenous fistula was separated, and completely ligated using silk ligature. However, the separation of the intrahepatic shunt blood vessel was unsuccessful and the dog died 15 hr postoperatively.

Angiography, Digital Subtraction↗

PubMed2004

[Reduction of reconstruction time and data volume of sinogram by angular compression for clinical three-dimensional whole body FDG-PET].

In positron emission tomography (PET), the large number of lines of responses in three-dimensional (3D) acquisition mode creates a high volume of sinogram data and increases reconstruction time in iterative reconstruction. We tried to decrease sinogram data volume by reducing the number of views using angular compression and then evaluated the accuracy of this mashed mode. Three methods were compared, conventional mode (CONV), X2 mashed mode (X2: two adjacent projection angles are added together), and X4 mashed mode (X4: four adjacent angles added). A point source of (18)F was used to measure spatial resolution. A hot spot phantom made of 6 hot spheres (10-38 mm in diameter) within water of 20 cm in diameter was scanned to evaluate the recovery coefficient (RC). A lung-heart-liver phantom made of homogeneous radioactive myocardium, a spherical hot mass in the lung (10 mm in diameter), and background activity in the liver was scanned to evaluate the homogeneity of the myocardial wall. The quality of the reconstructed images was evaluated in terms of the normalized mean square error (NMSE), Bull's eye map, profile curve, and peak value of the spherical hot mass. The reconstruction times of X2 and X4 were one-half and one-quarter, respectively, of that of CONV. In terms of spatial resolution, FWHM of CONV, X2, and X4 were, 4.26, 4.33, and 4.48 (mm) at the center, 4.81, 5.68, and 8.73 tangentially, and 8.01, 8.19, and 8.27 radially at R=200 mm, respectively. RC was similar for all methods. The NMSE values of X2 and X4 compared with CONV were 0.0003 and 0.0014, respectively. In the hot mass, these methods showed almost the same profile curves, although the peak value of X4 was only -1.95% less than that of CONV. Although the result of spatial resolution of X4 was slightly degraded, image quality and physical performance were good. Therefore, the X4 mashed mode used with angular compression was considered clinically useful.

Humans↗

PubMed2004

[Evaluation of noise equivalent count per line of response: new parameter for count statistics for PET systems].

OBJECTIVE: The noise equivalent count (NEC) is a useful, widely accepted method of evaluating image quality in positron emission tomography (PET) from the standpoint of effective count statistics. However, NEC cannot be used when different types of PET scanners are compared owing to the differences in slice thickness and field of view. Moreover, NEC should be treated differently depending on whether the 2D or 3D mode is used for a given PET scanner. A new parameter "Specific NEC," which is NEC per line of response (LOR) was devised to compare image quality between different PET scanners and acquisition modes. METHODS: Two PET scanners were employed, the CTI-Siemens ECAT EXACT HR(+) and ECAT EXACT 47. Images of a cylindrical (68)Ge phantom were scanned in 2D and 3D modes using various acquisition times ranging from 15 secx20 frames to 120 secx20 frames in order to examine the effect of count statistics on the quality of image reconstruction. The data were reconstructed using a ramp filter with a cutoff frequency of 0.5 cycles/pixel, corrected for dead time, random, attenuation, and scatter. The quality of the reconstructed images was evaluated with the coefficient of variation (COV; SD/average for the pixels within a 16 cm region of interest). Specific NEC was defined as NEC divided by the number of LOR for the entire scanner at detector level. RESULTS: COV showed a linear relationship with Specific NEC in double logarithmic plot within a given experiment. When the Specific NEC was used, all 2D and 3D mode showed the same relationship. The slight difference between the two scanners was attributed to the difference in slice thickness. CONCLUSION: Image quality was dependent on effective count statistics per number of LOR. Our method was considered effective for evaluating image quality in both 2D and 3D modes.

Artifacts↗

PubMed2003

Assessment of microPET performance in analyzing the rat brain under different types of anesthesia: comparison between quantitative data obtained with microPET and ex vivo autoradiography.

MicroPET (positron emission tomography) has been implemented for use in experiments with small animals. However, the quantification and optimal conditions for scanning are not established yet. The aim of this study was to compare the results obtained by microPET with those by ex vivo autoradiography of rat brain slices, based on the 2-[18F]fluoro-2-deoxy-D-glucose (FDG) method, and to establish the optimal conditions for scanning. As an example, we examined glucose metabolism in the rat brain under 6 types of anesthesia and in the conscious state. The scanning conditions for the rat brain were (1) use of a 4-mm-thick leaden jacket, (2) an energy window of 350-650 keV, and (3) a coincidence time window of 6 ns. Under these conditions, the quantitative ROI data from microPET showed a good correlation with the corresponding ROI data from FDG autoradiography in the animal study (r2=0.81). With our protocol, when anesthesia was started 40 min after the FDG injection, the glucose metabolism was almost the same as that in the conscious rat brain.

Algorithms↗

PubMed2003

Acquisition and contextual switching of multiple internal models for different viscous force fields.

Humans can learn an enormous number of motor behaviors in different environments. To explain this, the MOSAIC model proposes that multiple internal models are acquired in the brain, which can be switched. However, previous behavioral studies that examined arm-movement adaptations to multiple environments reported a rather limited learning capability. Hitherto, humans have been believed incapable of learning two opposite viscous force fields, which are both dynamic transformations and depend on the same state variable, presented in a random order with only a visual cue. In contrast, this study found that humans are capable of this. Elbow joint movements to specified targets were perturbed by either resistive or assistive viscous force fields generated by a single degree-of-freedom manipulandum. The resistive or assistive viscous force fields were cued by a blue or red color on a CRT screen, respectively. The squared distance between the end point and the target, and the variance of the joint angular velocities were used as kinematic performance indices. These movement errors decreased significantly as a function of the training days. Aftereffects and learning consolidation were demonstrated in the random presentation of the two force fields. Consequently, humans were able to learn the multiple and distinct internal models of the two force fields and appropriately switch them even for a random presentation cued only by color after several days of training. This study suggests that none of the previously proposed conditions for multiple internal model learning are necessary prerequisites, and indicates that the difficulty in learning is determined by the balance between the effectiveness of contextual information and the similarity of force fields.

Adaptation, Psychological↗

PubMed2003

[A multicenter evaluation of seven commercial ML-EM algorithms for SPECT image reconstruction using simulation data].

The maximum likelihood expectation maximization (ML-EM) algorithm has become available as an alternative to filtered back projection in SPECT. The actual physical performance may be different depending on the manufacturer and model, because of differences in computational details. The purpose of this study was to investigate the characteristics of seven different types of ML-EM algorithms using simple simulation data. Seven ML-EM algorithm programs were used: Genie (GE), esoft (Siemens), HARP-III (Hitachi), GMS-5500UI (Toshiba), Pegasys (ADAC), ODYSSEY-FX (Marconi), and Windows-PC (original software). Projection data of a 2-pixel-wide line source in the center of the field of view were simulated without attenuation or scatter. Images were reconstructed with ML-EM by changing the number of iterations from 1 to 45 for each algorithm. Image quality was evaluated after a reconstruction using full width at half maximum (FWHM), full width at tenth maximum (FWTM), and the total counts of the reconstructed images. In the maximum number of iterations, the difference in the FWHM value was up to 1.5 pixels, and that of FWTM, no less than 2.0 pixels. The total counts of the reconstructed images in the initial few iterations were larger or smaller than the converged value depending on the initial values. Our results for the simplest simulation data suggest that each ML-EM algorithm itself provides a simulation image. We should keep in mind which algorithm is being used and its computational details, when physical and clinical usefulness are compared.

Algorithms↗

PubMed1996

A Kendama Learning Robot Based on Bi-directional Theory.

A general theory of movement-pattern perception based on bi-directional theory for sensory-motor integration can be used for motion capture and learning by watching in robotics. We demonstrate our methods using the game of Kendama, executed by the SARCOS Dextrous Slave Arm, which has a very similar kinematic structure to the human arm. Three ingredients have to be integrated for the successful execution of this task. The ingredients are (1) to extract via-points from a human movement trajectory using a forward-inverse relaxation model, (2) to treat via-points as a control variable while reconstructing the desired trajectory from all the via-points, and (3) to modify the via-points for successful execution. In order to test the validity of the via-point representation, we utilized a numerical model of the SARCOS arm, and examined the behavior of the system under several conditions. Copyright 1996 Elsevier Science Ltd.

Journal Article↗