PubMed Health⌕ Search

Biomedical subjects

M Imazawa

Publications and source records attributed to M Imazawa.

At least 19 recordsLinked to original sources
PubMed2001

Characteristics of acoustic noise in echo-planar imaging.

Characteristics of the acoustic noise generated by magnetic resonance imagers of different systems and performance levels were studied when operating in echo-planar imaging (EPI) sequence. Continuous equivalent A-weighted sound pressure levels (Leq) and peak impulse sound pressure levels (Lpeak) during EPI were measured in 12 clinical super-conducting MRI systems (0.5-1.5 T). Sound pressure levels and frequency spectra of EPI were compared with those of nine different pulse sequences. EPI sound pressure levels differed among institutions (Leq = 94.2 +/- 2.7 dBA. Lpeak = 109.1 +/- 3.5 dB), but these were within permissible noise exposure levels. Sound pressure levels during EPI were not significantly different from those during other pulse sequences. However, compared to other pulse sequences. EPI had a significantly greater proportion of acoustic noise in the high octave-frequency band. Single-shot EPI had relatively higher frequency noise and greater Leq than multishot EPI, but the difference in Leq decreased when the number of slices in multishot EPI was increased.

Echo-Planar Imaging↗
PubMed1999

Acoustic noise analysis in echo planar imaging: multicenter trial and comparison with other pulse sequences.

The purpose of this study was to evaluate acoustic noise in echo planar imaging (EPI) at various magnetic resonance imaging (MRI) centers and to compare EPI acoustic noise with that in other fast pulse sequences. We measured A-weighted root-mean-square sound pressure levels and peak impulse sound pressure levels for EPI, under the same conditions, in eleven clinical super-conducting MRI systems. We also compared sound pressure levels for the EPI and six different pulse sequences and analyzed the acoustic noise spectra. Sound pressure levels during the use of the EPI differed greatly among institutions. Moreover, sound pressure levels of the EPI were not significantly different from those of other fast pulse sequences and were within permissible noise exposure levels. In comparison to other fast sequences, the EPI had significantly greater acoustic noise in the high-octave band frequency.

Acoustics↗
PubMed1997

Micellar electrokinetic capillary chromatography of benzodiazepine antiepileptics and their desmethyl metabolites in blood.

A fast and reliable method for the MEKC separation and determination of benzodiazepine antipileptics and their active metabolites in serum has been developed, using a separation buffer composed of borate (pH 9.5), SDS (18 mM), and acetonitrile (14%) as an organic modifier. The method is sensitive enough to be used clinically with a precision of less than 3% for the analysis of nitrazepam, clonazepam, clobazam, diazepam and their desmethyl metabolites in serum.

Anticonvulsants↗
PubMed1996

Fast RARE MR imaging with variable flip angle excitation.

A method was developed for performing T1-weighted magnetic resonance imaging with the rapid acquisition with relaxation enhancement (RARE) sequence by altering the excitation flip angle. This method was called variable flip angle turbo spin-echo (VF-TSE) imaging. When the effective echo time corresponds to the first echo, the resolution worsens as the echo train length becomes longer. For this reason, the echo train length was set at three, the repetition time (TR) was shortened (100- 200 msec) to decrease imaging time, and the initial flip angle was adjusted (120 degrees-140 degrees) to improve image quality. Another advantage of this method is that the initial flip angle can be reduced to below 90 degrees when a longer TR is needed. Measured signal intensities for VF-TSE imaging matched theoretic predictions. VF-TSE imaging yielded high contrast-to-noise and signal-to-noise ratios without sacrificing resolution. The VF-TSE technique was useful for breath-hold, three-dimensional, and cardiac synchronization imaging.

Humans↗
PubMed1989

Inositol trisphosphate (IP3) receptors and epileptic seizure.

The effects of anticonvulsants and Ca2+ channel antagonists on the inositol trisphosphate (IP3) binding and IP3-induced Ca2+ release were examined in brain membrane fractions. Anticonvulsant (PHT and valproate) and Ca2+ channel antagonists (verapamil, diltiazem, flunarizine, nicardipine and cinnarizine), examined did not significantly inhibit the IP3-receptor binding. The Kd and Bmax values of the IP3 binding did not change significantly in the various brain regions of the amygdala-kindled rats, killed 10 days after the last seizure, compared to those of controls. On the other hand, PHT, PB and carbamazepine inhibited the Ca2+ releasing activity of IP3 in the cerebellar membrane fractions by approximately 20% at therapeutic concentrations.

Amygdala↗
PubMed1987

Mechanism of arachidonic acid liberation during ischemia in gerbil cerebral cortex.

Once brain ischemia was induced in the gerbil cerebral fronto-parietal cortex, serial changes occurred in energy metabolites and various lipids. The amounts of inositol-containing phospholipids began to decrease immediately after energy failure, followed by an increase in the amount of 1,2-diacylglycerol with a subsequent liberation of arachidonic acid and other free fatty acids. The fatty acid compositions of inositol-containing phospholipids, of 1,2-diacylglycerols produced by ischemia, and of free fatty acids liberated during ischemia were quite similar. The amount of stearic acid liberated was much larger than that of arachidonic acid between 30 s and 1 min of ischemia. On the other hand, there was no significant decrease in the amount of the other phospholipids except for phosphatidic acid. Furthermore, there was also no change in the fatty acid composition of phosphatidylcholine or phosphatidylethanolamine throughout 15 min of ischemia. The amount of cytidine-monophosphate reached a peak (36.7 nmol/g wet wt) at 2 min of ischemia. These results indicated that arachidonic acid was predominantly liberated from inositol-containing phospholipids by phospholipase C, and by the diglyceride lipase and monoglyceride lipase system rather than from phosphatidylcholine or phosphatidylethanolamine by phospholipase A2 or plasmalogenase or choline phosphotransferase during the early period of ischemia.

Animals↗
PubMed1986

Unusual morphological changes in cultured oligodendrocytes induced by cytochalasin B.

When cultured chick oligodendrocytes were treated with more than 1 microM of cytochalasin B (CB), an unusual effect, namely the extension of curly processes, was observed in a dose-dependent manner within 2 h after CB was added, that is, the processes with long, thin and curled shapes developed. The effect was found to be reversible and to be inhibited by colchicine. It was demonstrated by immunofluorescence that CB induced the depolymerization of actin filaments and the enhanced assembly of microtubules in cellular processes.

Actins↗
PubMed1983

Computer-assisted conformation radiotherapy system. An application of CT.

A newly developed computer-assisted conformation radiotherapy system is presented and its accuracy discussed in an experimental investigation and a clinical study. The system consists of a CT scanner, radiotherapy treatment planning system and linear accelerator. These systems are smoothly interconnected. Planning of multi-split conformation radiotherapy can be performed accurately and rapidly. Opening of the multi-split collimators was accurately controlled by computer on the basis of the treatment planning data. Dosage distributions in the irradiated body reconstructed using transit x-rays are also presented. As a simple back-projection method was used for calculation, the reconstructed dosage distribution resembling that of beam-focus radiography. Further investigation is required to complete this technique and to use it for the verification of radiotherapy treatment planning.

Computers↗
PubMed1982

Enzyme immunoassay of the myelin basic protein.

An enzyme immunoassay using a double-antibody solid-phase technique for myelin basic protein (MBP) has been developed. Antisera were prepared by immunizing rabbits with the purified MBP from chick brain. The conjugation of MBP with horseradish peroxidase was performed by the periodate oxidation method in triethanolamine-acetate buffer (pH 8.5). The sample, antiserum, and conjugate were incubated at 4 degrees C for 16 h, after which the insoluble second antibody was added and the reaction mixture was incubated at 4 degrees C for 3 h. The peroxidase activity of the insoluble conjugate was assayed fluorometrically with hydrogen peroxide and 3-(p-hydroxyphenyl)propionic acid as substrates. The method had an analytical range from 50 pg to 1 ng (from 2.3 x 10(-15) to 4.5 x 10(-14) mol). The within-assay coefficient of variation (CV) was between 4 and 11% and the between-assay CV for 200 and 400 pg of MBP was 5.5 and 7.1%, respectively. A weak cross-reactivity was observed between chick MBP and bovine MBP, while no reactivity was shown with calf thymus histone. The MBP content of the brain during development increased markedly from the 3rd embryonic week to the 3rd post-hatch week (from 0.01 to 2.4 mg/g of fresh tissue), and the adult level was 3.2 mg/g of fresh tissue.

Animals↗
PubMed1979

Synthesis of sugar-modified nucleoside 5'-triphosphates with partially purified nucleotide kinases from calf thymus.

The partial purification of some nucleoside monophosphate kinases (ATP:nucleosidemonophosphate phosphotransferases, EC 2.7.4.4) from calf thymus by chromatography on Blue Sepharose to remove interfering phosphatase activity is described. Their specificities towards nucleoside monophosphates modified in the sugar are investigated. Pyrimidine nucleoside monophosphate kinase is not very much affected by such modifications, whereas GMP kinase does not tolerate such alteration. The effect on AMP kinase is intermediate.

Animals↗