Search PubMed⌕ Search

Biomedical subjects

Seiji Ogawa

Publications and source records attributed to Seiji Ogawa.

7 recordsLinked to original sources
PubMed2006

EPI image reconstruction with correction of distortion and signal losses.

PURPOSE: To derive and implement a method for correcting geometric distortions and recovering magnetic resonance imaging (MRI) signal losses caused by susceptibility-induced magnetic field gradients (SFGs) in regions with large static field inhomogeneities in echo-planar imaging (EPI). MATERIALS AND METHODS: Factors to account for field inhomogeneities and SFGs were added in a traditional EPI equation that was a simple Fourier transform (FT) for expressing the actual k-space data of an EPI scan. The inverse calculation of this "distorted EPI" equation was used as a kernel to correct geometric distortions and reductions in intensity during reconstruction. A step-by-step EPI reconstruction method was developed to prevent complicated phase unwrapping problems. Some EPI images of phantom and human brains were reconstructed from standard EPI k-spaces. RESULTS: All images were reconstructed using the proposed multistep method. Geometric distortions were corrected and SFG-induced MRI signal losses were recovered. CONCLUSION: Results suggest that applying our method for reconstructing EPI images to reduce distortions and MRI signal losses is feasible.

Algorithms↗
PubMed2005

Increases in oxygen consumption without cerebral blood volume change during visual stimulation under hypotension condition.

The magnitude of the blood oxygenation level-dependent (BOLD) signal depends on cerebral blood flow (CBF), cerebral blood volume (CBV) and cerebral metabolic rate of oxygen (CMRO2). Thus, it is difficult to separate CMRO2 changes from CBF and CBV changes. To detect the BOLD signal changes induced only by CMRO2 responses without significant evoked CBF and CBV changes, BOLD and CBV functional magnetic resonance imaging (fMRI) responses to visual stimulation were measured under normal and hypotension conditions in isoflurane-anesthetized cats at 4.7 T. When the mean arterial blood pressure (MABP) decreased from 89+/-10 to 50+/-1 mm Hg (mean+/-standard deviation, n=5) by infusion of vasodilator sodium nitroprusside, baseline CBV in the visual cortex increased by 28.4%+/-8.3%. The neural activity-evoked CBV increase in the visual cortex was 10.8%+/-3.9% at normal MABP, but was negligible at hypotension. Positive BOLD changes of +1.8%+/-0.5% (gradient echo time=25 ms) at normal MABP condition became prolonged negative changes of -1.2%+/-0.3% at hypotension. The negative BOLD response at hypotension starts approximately 1 sec earlier than positive BOLD response, but similar to CBV change at normal MABP condition. Our finding shows that the negative BOLD signals in an absence of CBV changes are indicative of an increase in CMRO2. The vasodilator-induced hypotension model simplifies the physiological source of the BOLD fMRI signals, providing an insight into spatial and temporal CMRO2 changes.

Animals↗
PubMed2004

A dynamic system model-based technique for functional MRI data analysis.

Signals in functional magnetic resonance imaging (fMRI) are influenced by physiological fluctuations in addition to local brain activity. We have proposed a dynamic system model-based technique for separation of signal changes related to brain activation inputs from those related to physiological fluctuations. We applied this technique to a visual fMRI experiment to determine the validity and feasibility of this technique for fMRI data analyses. Gradient-echo echo planar images were obtained from 12 healthy volunteers with a Siemens ALLEGRA operating at 3 T, with a repetition time of 500 ms, echo time of 20 ms, field of view of 200-210 mm, matrix size of 64 x 64, and slice thickness of 5 mm. Twelve runs with two stimulation periods of varied duration (2-8 s) with 8-Hz flickering illumination were obtained for each subject. Local signal changes were modeled by an autoregressive model with two exogenous inputs, a visual stimulation input and a global reference signal. Local signal changes were appropriately predicted not only for stimulation periods but also resting periods. A significant linear relationship was found between model static gain based on the dynamic system modeling and beta coefficient based on a general linear model (GLM) analysis for active voxels in the primary visual cortex (analysis of covariance [ANCOVA], P < 0.001; estimated parameter, 0.967; 95% confidence interval, 0.734-1.201). This dynamic system model-based technique is sufficiently accurate and feasible for use in extracting signal changes related to brain activation inputs from measured signals with physiological fluctuations.

Adult↗
PubMed2004

The neutralization of pseudorabies virus by anti-alpha-galactocyl natural antibody in normal serum.

Pseudorabies virus (PrV), a member of herpesviridae alphaherpes subfamily, can infect human cells in vitro. However, the transmission to Old World primates including humans is strongly restricted. In this study, we report the neutralizing activity of normal human serum against PrV grown in CPK cells derived from pig. PrV grown in all Old World primates-derived cells, which was tested in this study, were not neutralized by normal human serum. The virion of PrV grown in CPK cells harbored Galalpha1-3Galbeta1-4GlcNAc-R (alpha-gal epitope) on its surface, while PrV grown in Vero cells did not. Depletion of antibodies reacting to surface antigens of CPK cells negated the neutralization activity of human serum. Blockade of anti-alpha-gal antibodies by adding soluble Galalpha1-3Gal to normal human serum also prevent the inactivation of PrV grown in CPK cells. Although normal swine serum did not neutralize PrV grown in CPK cells, swine serum supplemented with exogenous anti-alpha-gal antibodies did. These results indicate that anti-alpha-gal antibodies in normal human serum contribute to the neutralization of PrV. Anti-alpha-gal antibodies in normal human serum may prevent transmission of PrV into humans.

Animals↗
PubMed2003

Enantioselective synthesis of 15-epi-haterumalide NA methyl ester and revised structure of haterumalide NA.

[structure: see text] The enantioselective synthesis of the enantiomer of the haterumalide NA methyl ester, a cytotoxic macrolide from an Okinawan sponge, was achieved from the threitol derivative in 26 steps. The key steps are the stereoselective construction of a chloroolefin unit and the intramolecular Reformatsky-type reaction. This synthesis revised the absolute stereochemistry of haterumalide NA.

Journal Article↗
PubMed2002

Insights into new techniques for high resolution functional MRI.

Non-invasive functional magnetic resonance imaging (fMRI) has opened a unique window into human and animal brain function, with a spatial resolution of a few millimeters and a temporal resolution of a few seconds. To further improve the current technical limitations of fMRI, various post-processing and data acquisition schemes were developed. Improved fMRI methods include variations of a conventional fMRI technique, mapping a single physiological parameter such as cerebral blood flow or cerebral blood volume, and direct mapping of neural activity. Advances in fMRI techniques allow scientists to map submillimeter columnar and laminar functional structures and to detect tens of millisecond neural activity in certain specific tasks.

Animals↗