Biomedical subjects

Naoto Hayashi

Publications and source records attributed to Naoto Hayashi.

10 recordsLinked to original sources

PubMed2003

MR diffusion tensor imaging: recent advance and new techniques for diffusion tensor visualization.

Recently, diffusion tensor imaging is attracting the biomedical researchers for its application in depiction of fiber tracts based on diffusion anisotropy. In this paper, we briefly describe the basic theory of diffusion tensor MR imaging, the determination process of diffusion tensor, and the basic concepts of diffusion tensor visualization techniques. Several results of clinical application in our institute are also introduced. Finally, the limitations, advantages and disadvantages of the techniques are discussed for further application of diffusion tensor visualization.

Anisotropy↗

PubMed2003

MR imaging of ischemic penumbra.

Cerebral ischemic stroke is one of the most fatal diseases despite current advances in medical science. Recent demonstration of efficacy using intravenous and intra-arterial thrombolysis demands therapeutic intervention tailored to the physiologic state of the individual tissue and stratification of patients according to the potential risks for therapies. In such an era, the role of the neuroimaging becomes increasingly important to evaluate the extent and location of tissues at risk of infarction (ischemic penumbra), to distinguish it from unsalvageable infarcted tissues or doomed hemorrhagic parenchyma. In this review, we present briefly the current role and limitation of computed tomography and conventional magnetic resonance imaging (MRI). We also present the possible applications of advanced MR techniques, such as diffusion and perfusion imaging, concentrating on the delineation or detection of ischemic penumbra.

Brain Ischemia↗

PubMed2003

Hemangiomas in the face and extremities: MR-guided sclerotherapy--optimization with monitoring of signal intensity changes in vivo.

The feasibility of a method of magnetic resonance (MR)-guided sclerotherapy for hemangioma was evaluated. The distribution of a test injection and a contiguous sclerosant injection was monitored clearly with MR fluoroscopy. Postsclerotherapy T2-weighted MR images depicted areas with and those without effective sclerosant concentration, which enabled performance of selective supplemental sclerotherapy. This method of MR-guided sclerotherapy seems feasible for clinical application.

Adolescent↗

PubMed2003

[Simple visualization of the corticospinal pathway using tractography: one-ROI and two-ROI methods].

Diffusion tensor imaging (DTI), a magnetic resonance (MR) technique to analyze diffusion anisotropy of the brain, is able to demonstrate subtle white matter anatomy. Tractography is expected to be a unique, non-invasive tool to provide more pertinent insights into brain structure and orientation not accessible by conventional MRI. In this report, preliminary experiences of visualization of the corticospinal tract using tractography are described. DTI of the brain was performed in 5 normal volunteers using single-shot echo-planar imaging, then tractography was generated by our original software. We determined that the two-region-of-interest (ROI) method is superior to the one-ROI method.

Adult↗

PubMed2002

Accuracy of abnormal paraspinal muscle findings on contrast-enhanced MR images as indirect signs of unilateral cervical root-avulsion injury.

PURPOSE: To evaluate the accuracy of abnormal magnetic resonance (MR) findings in the paraspinal muscles as indirect signs of nerve-root avulsion injury. MATERIALS AND METHODS: Forty-three consecutive patients suspected of having unilateral root-avulsion injury underwent MR imaging and were evaluated. Paraspinal muscles were evaluated for abnormal signal intensity on T1- and T2-weighted images, abnormal enhancement on images obtained after contrast material enhancement, and muscle volume loss. MR images were interpreted independently by two observers for interobserver variability. MR findings were compared with findings of root continuity, determined with a combination of surgery and clinical evaluation. Sensitivities, specificities, and kappa values of the findings were calculated. RESULTS: Sensitivities of MR findings in the paraspinal muscles indicating root-avulsion injury were 88% (36 of 41 patients) for abnormal enhancement, 83% (34 of 41 patients) for high signal intensity on T2-weighted images, 37% (15 of 41 patients) for high signal intensity on T1-weighted images, and 71% (29 of 41 patients) for muscle volume loss. Specificities for all findings were 100% (two of two patients). Of the paraspinal muscles, findings in the multifidus muscle were the most accurate and provided the highest interobserver agreement (kappa = 0.81). CONCLUSION: Contrast material-enhanced abnormal MR findings in the paraspinal muscles are accurate in indicating root-avulsion injuries, and abnormal enhancement in the multifidus muscle is the most accurate among paraspinal muscle findings.

Adolescent↗

PubMed2002

Radiation-induced arteritis: thickened wall with prominent enhancement on cranial MR images report of five cases and comparison with 18 cases of Moyamoya disease.

PURPOSE: To evaluate magnetic resonance (MR) imaging findings of radiation-induced cranial arteritis regarding arterial wall thickening and degree of enhancement, as well as to compare the findings with those of idiopathic moyamoya disease. MATERIALS AND METHODS: We reviewed cerebral MR images in five patients with radiation-induced large cerebral arteritis. All patients had undergone irradiation 2-25 years prior to this study. Conventional nonenhanced MR, MR angiographic, and contrast material-enhanced MR images were evaluated. Special attention was paid to wall enhancement of the affected arteries (distal internal carotid artery). Wall enhancement was staged in three levels by two neuroradiologists. We also reviewed MR images in 18 patients with primary moyamoya disease for comparison and analyzed them statistically (Fisher exact test). RESULTS: Wall thickening and prominent ring enhancement of the wall of the affected large cerebral arteries were observed in all (five of five) patients with radiation-induced arteritis. In contrast, wall thickening and prominent ring enhancement of the wall of the occluded arteries either were not seen (13 of 18 patients) or were faint (five of 18 patients) in patients with moyamoya disease. Contrast enhancement of the arterial walls in patients with radiation-induced arteritis was significantly more prominent than in patients with moyamoya disease (P =.003). CONCLUSION: MR images of wall thickening and prominent ring enhancement of the wall of affected large cerebral arteries may be a diagnostic clue in differentiating radiation-induced arteritis from moyamoya disease.

Adolescent↗

PubMed2002

[Selective intraarterial infusion chemotherapy using a combined MRI-angiography system for head and neck cancers].

We performed selective intraarterial infusion chemotherapy using a combined MRI-angiography system for head and neck cancers. In three patients, three or five infusions of CDDP (100 mg/body) were administered to the feeding arteries selectively. For the evaluation of drug distribution, MRI during arteriography through the infusion pump was performed before CDDP administration. When a distribution mismatch was found, arterial selection was attempted again under a mechanically unstable C-arm system, and further evaluation under an MR system was carried out. Thus, more ideal treatment could be provided. We consider MRI during arteriography to be useful in assessing for distribution during intraarterial chemotherapy.

Antineoplastic Agents↗

PubMed2002

[Evaluation of PROPELLER MR imaging: preliminary experiences].

Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER) MR imaging (MRI) has a unique ability to correct motion artifacts and is expected to be useful in diffusion-weighted MRI. This article describes preliminary experiences with PROPELLER MRI. PROPELLER uses a radial scan variation of the fast spin-echo sequence and it shows much less spatial deterioration than the echo-planar imaging sequence. To determine the optimal parameters of this technique, we calculated the signal intensities of phantoms and brains in various settings. PROPELLER MR examinations were also performed in 66 patients for clinical use. PROPELLER MRI appears to be a promising and useful technique.

Artifacts↗

PubMed2002

[MR angiography].

Explore the source record for details and available documents.

Angiography, Digital Subtraction↗

PubMedDate not supplied

Normal aging in the central nervous system: quantitative MR diffusion-tensor analysis.

The purpose of this study is to elucidate changes in mean diffusivity (ADC) and fractional anisotropy (FA) using MR diffusion tensor imaging (DTI) in the central nervous system during normal aging. We studied 50 normal volunteers (30 men, 20 women; mean age 44.8 +/- 14.0; age range, 21-69 years) without disorders affecting the central nervous system. The frontal, parietal white matter, lentiform nucleus, posterior limb of internal capsule, thalamus, genu and splenium of the corpus callosum were selected for investigation. There was no significant difference in ADC or FA between male and female or between the right and left hemisphere. A significant ADC increase with advancing age was observed in frontal white matter (P = 0.010) and lentiform nucleus (P = 0.022). A significant FA decline was found only in the genu of the corpus callosum (P < 0.001) with advancing age. Quantitative diffusion tensor analysis correlate with normal aging and may help in assessing normal age-related changes and serve as a standard for comparison with neurodegenerative disorders.

Adult↗