Biomedical subjects

Hiroki Yamada

Publications and source records attributed to Hiroki Yamada.

23 records · Page 2Linked to original sources

PubMed2002

Functional brain imaging using fMRI and optical topography in infancy.

We performed functional magnetic resonance imaging and optical topography over the visual cortex of subjects during sedation with pentobarbital, and 8-Hz flickering light was intermittently projected onto their eyelids. Two age groups were analyzed: infants <60 days old and those >60 days old (corrected for gestational age at birth). The stimulus-related signal change was positive in the lateral geniculate nucleus regardless of the infant's age, but it reversed in the primary visual cortex from positive in the infants less than 60 days old to negative in the infants more than 60 days old (Experiment 1). We also investigated spontaneous changes in the cerebral oxygenation state of neonates and infants aged 1 month during quiet sleeping by using a form of multi-channel near-infrared spectroscopy: non-invasive optical topography. Spatially synchronized oscillations of changes in the concentration of oxy-hemoglobin (oxy-Hb) and deoxy-Hb were observed throughout the occipital cortex in neonates but not in the infants aged 1 month. Time series analysis based on the theory of non-linear oscillations showed that the mean periods of the oscillation for each infant ranged from 11 to 18s. The phase lag of oxy-Hb relative to deoxy-Hb was stable at about 3 pi/4 in neonates but in the infant aged 1 month, time lag was unstable. These findings may be due to rapid synaptogenesis in early life.

Journal Article↗

PubMed2002

Measurement of the vascularity and vascular leakage of gliomas by double-echo dynamic magnetic resonance imaging: a preliminary study.

RATIONALE AND OBJECTIVE: To evaluate the vascularity and vascular leakage of well-enhanced gliomas by double-echo dynamic magnetic resonance (MR) imaging. MATERIALS AND METHODS: Eight patients with glioblastoma multiforme (GBM) and two patients with juvenile pilocytic astrocytoma (JPA) were studied. Double-echo dynamic MR imaging was utilized to separate the T2* shortening effect and the T1 shortening effect. The former was represented by the vascularity index, and the latter was represented by the leakage index. These indexes were compared with histopathologic data. RESULTS: The mean vascularity index of the GBM was higher than that of the JPA (mean +/- SD, 3.48 +/- 1.57 [GBM] versus 0.51 +/- 0.29 [JPA]), and the mean leakage index of the JPA was higher than that of the GBM (1.35 +/- 0.87 [JPA] versus 0.27 +/- 0.15 [GBM]). Abundant vascularity was noted in the tight interstitial space in the pathologic specimen of GBM. Conversely, sparse vasculature was observed in the wide interstitial space in the pathologic specimen of JPA. CONCLUSION: This method may enable better characterization of grade in well-enhanced glioma by providing the information on the vascularity and leakage indexes.

Adult↗

PubMed2002

[Fatal septic shock caused by transrectal needle biopsy of the prostate; a case report].

A 46-year-old man refer to us because of hemospermia. The prostatic gland was normal in size and consistency at rectal examination. Serum prostate specific antigen was 7.04 ng/ml. Magnetic resonance imaging showed an area of low signal intensity on T2-weighted images in the left peripheral gland, possibly indicative of carcinoma. Transrectal prostate biopsy was performed after intravenous administration of piperacillin. He developed chills and fever (39 degrees C) the next morning following biopsy. He was taken unconscious into the hospital where a diagnosis of septic shock caused by Escherichia coli was made. Five days later, he died. His general condition deteriorated notwithstanding intensive treatment. Postmortem blood cultures were positive for a piperacillin resistant Escherichia coli. Histological examination of the biopsies showed a benign prostatic hyperplasia. Autopsy showed diffuse tissue damage in the heart, lung, liver and kidneys. The prostate had numerous microabscesses. Currently, transrectal prostate biopsy is considered a generally reliable procedure to detect adenocarcinoma of the prostate. Our case seems to the sixth case report of fatal complications.

Bacteremia↗

PubMedDate not supplied

Susceptibility-induced changes in signal intensity from spin-echo versus gradient-echo sequences.

This manuscript describes a study of the evaluation of T2 and T2* changes in a hypervascular tumor model (hemodialyzer phantom) under conditions simulating dynamic perfusion study. The measured 1/T2* was strongly dependent on the compartmentalization of contrast material within the model, whereas the observed 1/T2 was not. Gradient-echo magnetic resonance (MR) imaging may be more suitable than a spin-echo MR imaging for the evaluation of tumor vascularity.

Contrast Media↗

PubMedDate not supplied

Age-dependent change in metabolic response to photic stimulation of the primary visual cortex in infants: functional magnetic resonance imaging study.

The blood oxygen level-dependent (BOLD) response to photic stimulation in the primary visual cortex (V1) reverses from positive to negative around 8 weeks of age. This phenomenon may be caused by increased oxygen consumption during stimulation as the result of a rapid increase of synaptic density at this age. To test this hypothesis, we applied existing mathematic models of BOLD signals to the experimental data from infants. When the stimulus-related increments of cerebral blood flow and cerebral blood volume were fixed at 60% and 20%, respectively, the mean estimated increment of the cerebral metabolic rate of oxygen of the V1 in the elder infant group (57.1% +/- 8.8%) was twice as large as that in the younger infant group (32.2% +/- 4.7%), which corresponds to the reported difference in synaptic density. The present data confirmed that a change in oxygen consumption could explain a transition from a positive to a negative BOLD response.

Age Factors↗