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Biomedical subjects

Hiroshi Toyama

Publications and source records attributed to Hiroshi Toyama.

8 recordsLinked to original sources
PubMed2003

Anticipatory activation of postural muscles associated with bilateral arm flexion in subjects with different quiet standing positions.

We investigated changes in activation timing and magnitude of the postural muscles according to initial standing positions. The subjects were divided into three groups depending on the position of the center of foot pressure (CFP) during quiet standing, namely backward, middle, and forward. Subjects maintained standing postures at various CFP positions in the anteroposterior direction, and then started bilateral arm movement at their own pace. The activation magnitude of the biceps femoris (BF) and erector spinae (ES) did not differ among any of the initial CFP positions. In only the BF, the preceding action to the anterior deltoid (AD) was clearly observed at more forward CFP positions in the order of the forward, middle and backward groups. Between initial CFP positions adjacent to quiet standing posture, the smallest change was observed in the preceding activation time of the BF. Significant correlation was observed between the background activity and activation time in both the BF and ES.

Adult↗
PubMed2003

Linearized reference tissue parametric imaging methods: application to [11C]DASB positron emission tomography studies of the serotonin transporter in human brain.

SUMMARY: The authors developed and applied two new linearized reference tissue models for parametric images of binding potential (BP) and relative delivery (R1) for [11C]DASB positron emission tomography imaging of serotonin transporters in human brain. The original multilinear reference tissue model (MRTM(O)) was modified (MRTM) and used to estimate a clearance rate (k'2) from the cerebellum (reference). Then, the number of parameters was reduced from three (MRTM) to two (MRTM2) by fixing k'2. The resulting BP and R1 estimates were compared with the corresponding nonlinear reference tissue models, SRTM and SRTM2, and one-tissue kinetic analysis (1TKA), for simulated and actual [11C]DASB data. MRTM gave k'2 estimates with little bias (<1%) and small variability (<6%). MRTM2 was effectively identical to SRTM2 and 1TKA, reducing BP bias markedly over MRTM(O) from 12-70% to 1-4% at the expense of somewhat increased variability. MRTM2 substantially reduced BP variability by a factor of two or three over MRTM or SRTM. MRTM2, SRTM2, and 1TKA had R1 bias <0.3% and variability at least a factor of two lower than MRTM or SRTM. MRTM2 allowed rapid generation of parametric images with the noise reductions consistent with the simulations. Rapid parametric imaging by MRTM2 should be a useful method for human [11C]DASB positron emission tomography studies.

Aniline Compounds↗
PubMed2003

Latency of saccadic eye movement during contraction of bilateral and unilateral shoulder girdle elevators.

We compared the timed latencies of saccadic eye movement during isometric contraction of the bilateral and unilateral shoulder girdle elevators in a sitting posture. Muscle contraction force was increased in 10% increments from 0% to 60% of the maximal voluntary contraction (MVC) of each side. Saccadic latency was measured as the latency to the beginning of eye movement toward the lateral target that was moved at random intervals in 20 degree amplitude jumps. Eye movement was measured using the electro-oculogram technique. During bilateral contraction, saccadic latency decreased until 30% MVC and then began to increase at 40% MVC. During unilateral contraction, saccadic latency decreased until 30% MVC in a similar pattern as in bilateral condition, was constant from 30% MVC to 50% MVC, followed by a slight increase at 60% MVC. The saccadic latencies at 10% and 40-60% MVC were significantly shorter during unilateral contraction than bilateral contraction. Thus, the relative force for producing a marked shortening of saccadic latency is observed within a wider range during unilateral contraction than bilateral contraction.

Adolescent↗
PubMed2003

Perceived standing position after reduction of foot-pressure sensation by cooling the sole.

We investigated the influence of the reduction of foot-pressure sensation by cooling the sole of the foot, at 1 degree C for 30 or 40 minutes, on the perception of standing position varied in the anteroposterior direction. The subjects were 16 healthy undergraduates. Firstly, for 4 of the subjects, cooling the sole of the foot decreased sensory information from the mechanoreceptors in the sole, by testing for an increase in the threshold for two-point discrepancy discrimination on the sole of the foot and for the disappearance of postural change with vibration to the sole. Next, the perception of standing position was measured by reproduction of a given standing reference position involving forward or backward leaning under both normal and cooled conditions of the feet. Standing position was varied in relation to the location of the center of foot pressure, defined as distance from the heel in percentage of the length of the foot. The reference positions, representing various locations of the center of foot pressure, were set at 10% increments from 20% to 80% of the length of the foot. With eyes closed, the subject first experienced the reference position and then attempted to reproduce it. The mean location of the center of foot pressure in the quiet standing posture was 45.7%. At the 40%, 50%, and 60% reference positions, those closest to quiet standing, absolute errors of reproduction were significantly larger than at other reference positions in both the normal and the cooled conditions. They were significantly larger in the cooled than in the normal condition. The 50% and 60% reference positions were reproduced significantly further forward in the cooled than in the normal condition. These results may be explained as due to an absence of marked changes in sensory information from both muscular activity and foot pressure when moving to reference positions close to the quiet standing posture.

Adult↗
PubMed2003

Evaluation of 2 scatter correction methods using a striatal phantom for quantitative brain SPECT.

OBJECTIVE: Scatter correction is an important factor in quantitative SPECT. In this study, we evaluated 2 methods of scatter correction for brain SPECT. The first is based on thresholding the energy spectrum (ES), and the second is based on a modification of the transmission-dependent convolution subtraction (TDCS) method. METHODS: SPECT imaging of a skull striatal phantom was performed using a triple-head camera with and without scatter correction. The striatal compartments were filled with (123)I, and the brain shell cavity (background) was filled with varying concentrations of (123)I to obtain striatal-to-background ratios of 2, 5, 10, 15, 20, and 25 to 1, respectively, which were considered to be the expected ratios. SPECT-measured ratios of striatal-to-background counts were determined with scatter correction (both ES and TDCS methods) and without scatter correction and were then compared with the expected ratios. RESULTS: Without scatter correction, measured striatal-to-background ratios were underestimated by an average of 41.7%, compared with the expected ratios. The ES method of scatter correction underestimated the striatal-to-background ratios by an average of 27.4%, a significant improvement (P < 0.04) over those without scatter correction. With the TDCS method of scatter correction, the ratios were underestimated by only 3.3% (P < 0.03). TDCS ratios were significantly (P < 0.04) higher than ES ratios and were nearly identical to the expected ratios. CONCLUSION: These results suggest that scatter correction significantly improves the striatal-to-background ratios. The TDCS method appears to correct scatter more effectively than does the ES method for the striatal phantom, thus providing more accurate quantification.

Algorithms↗
PubMed2002

Strategies to improve neuroreceptor parameter estimation by linear regression analysis.

In an attempt to improve neuroreceptor distribution volume (V) estimates, the authors evaluated three alternative linear methods to Logan graphical analysis (GA): GA using total least squares (TLS), and two multilinear analyses, MA1 and MA2, based on mathematical rearrangement of GA equation and two-tissue compartments, respectively, using simulated and actual PET data of two receptor tracers, [(18)F]FCWAY and [(11)C]MDL 100,907. For simulations, all three methods decreased the noise-induced GA bias (up to 30%) at the expense of increased variability. The bias reduction was most pronounced for MA1, moderate to large for MA2, and modest to moderate for TLS. In addition, GA, TLS, and MA1, methods that used only a portion of the data (T > t*, chosen by an automatic process), showed a small underestimation for [(11)C]MDL 100,907 with its slow kinetics, due to selection of t* before the true point of linearity. These noniterative methods are computationally simple, allowing efficient pixelwise parameter estimation. For tracers with kinetics that permit t* to be accurately identified within the study duration, MA1 appears to be the best. For tracers with slow kinetics and low to moderate noise, however, MA2 may provide the lowest bias while maintaining computational ease for pixelwise parameter estimation.

Basal Ganglia↗