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Biomedical subjects

Harushi Mori

Publications and source records attributed to Harushi Mori.

At least 19 recordsLinked to original sources
PubMed2006

Flexible ex vivo phantoms for validation of diffusion tensor tractography on a clinical scanner.

PURPOSE: The aim of this study was to develop ex vivo diffusion tensor (DT) flexible phantoms. MATERIALS AND METHODS: Materials were bundles of textile threads of cotton, monofilament nylon, rayon, and polyester bunched with spiral wrapping bands and immersed in water. DT images were acquired on a 1.5-Tesla clinical magnetic resonance scanner using echo planar imaging sequences with 15 motion probing gradient directions. DT tractography with seeding and a line-tracking method was carried out by software originally developed on a PC-based workstation. RESULTS: We observed relatively high fractional anisotropy on the polyester phantom and were able to reconstruct tractography. Straight tracts along the bundle were displayed when it was arranged linearly. It was easy to bend arcuately or bifurcate at one end; and tracts followed the course of the bundle, whether it was curved or branched and had good agreement with direct visual observation. Tractography with the other fibers was unsuccessful. CONCLUSION: The polyester phantom revealed a diffusion anisotropic structure according to its shape and would be utilizable repeatedly under the same conditions, differently from living central neuronal system. It would be useful to validate DT sequences and to optimize an algorithm or parameters of DT tractography software. Additionally, the flexibility of the phantom would enable us to model human axonal projections.

Anisotropy↗
PubMed2006

Brachial plexus injury: clinical manifestations, conventional imaging findings, and the latest imaging techniques.

Brachial plexus injury (BPI) is a severe neurologic injury that causes functional impairment of the affected upper limb. Imaging studies play an essential role in differentiating between preganglionic and postganglionic injuries, a distinction that is crucial for optimal treatment planning. Findings at standard myelography, computed tomographic (CT) myelography, and conventional magnetic resonance (MR) imaging help determine the location and severity of injuries. MR imaging sometimes demonstrates signal intensity changes in the spinal cord, and enhancement of nerve roots and paraspinal muscles at MR imaging indicates the presence of root avulsion injuries. New techniques including MR myelography, diffusion-weighted neurography, and Bezier surface reformation can also be useful in the evaluation and management of BPI. MR myelography with state-of-the-art technology yields remarkably high-quality images, although it cannot replace CT myelography entirely. Diffusion-weighted neurography is a cutting-edge technique for visualizing postganglionic nerve roots. Bezier surface reformation allows the depiction of entire intradural nerve roots on a single image. CT myelography appears to be the preferred initial imaging modality, with standard myelography and contrast material-enhanced MR imaging being recommended as additional studies. Work-up will vary depending on the equipment used, the management policy of peripheral nerve surgeons, and, most important, the individual patient.

Brachial Plexus↗
PubMed2005

Quantitative evaluation of the pyramidal tract segmented by diffusion tensor tractography: feasibility study in patients with amyotrophic lateral sclerosis.

PURPOSE: Diffusion tensor imaging can evaluate the cerebral white matter quantitatively using fractional anisotropy (FA) and also can extract a certain tract by tractography, but these two have been used separately and not combined. The purpose of this study was to assess the clinical feasibility of ROI analysis using diffusion tensor tractography (DTT) in patients with amyotrophic lateral sclerosis (ALS). MATERIALS AND METHODS: Sixteen patients with ALS (9 limb-onset type, 7 bulbar-onset type) and nine age-matched volunteers were studied. DTT of the corticobulbar tract (DTT-CBT) and corticospinal tract (DTT-CST) were visualized by free software (dTV/VOLUME-ONE). Regions-of-interest (ROIs) were semi-automatically placed on the tracts defined by DTT methods, and FA values within the ROIs were measured. RESULTS: Mean FA values of ALS patients in the ROIs along the DTT-CST (bulbar-onset: 0.574, limb-onset: 0.594) were significantly lower than those of controls (DTT-CST: 0.629) (p<0.05). The mean FA of DTT-CBT of the bulbar-onset type (0.509) was significantly lower than that of the limb-onset type (0.558) and that of volunteers (0.561). CONCLUSION: DTT could segmentate certain white matter tracts and evaluate them quantitatively. It could depict the subtle changes between subtypes of ALS as well as the changes between the patients and volunteers.

Amyotrophic Lateral Sclerosis↗
PubMed2005

[In-vitro phantoms for estimating diffusion tensor tractography].

No literature has reported on in-vitro diffusion tensor tractography, although it is a useful method to visualize neuronal fiber projections in the living human brain. We applied this technique to phantoms of asparagus stems and bundled polyester yarn, and obtained tractography with high-quality images. On the asparagus stem phantom, straight tracts along the axis were displayed. On the polyester phantom, these tracts followed the course of the bundle whether it was straight or curved. These phantoms are useful for in-vitro evaluation of diffusion tensor tractography.

Algorithms↗
PubMed2004

Papillary neuroepithelial tumor of the pineal region. A case report.

We present here an unusual case of papillary neuroepithelial tumor of the pineal region. The patient was a 29-year-old female who presented with headaches. A computed tomography scan revealed a tumorous lesion at the pineal region and hydrocephalus. The resected tumor was composed of columnar and cuboidal cells showing characteristics of papillary growth. The tumor cells exhibited diffuse and intense immunoreactivity to cytokeratins and neural cell adhesion molecule. The tumor expressed abundant levels of transthyretin (prealbumin) and appeared ependymal in nature, with numerous microlumens delineated by punctate and ring-like patterns in epithelial membrane antigen staining. Reactivity to synaptophysin and glial fibrillary acidic protein was observed only in the infiltrated non-neoplastic pineal parenchyma. These histological characteristics matched the description of the recently reported papillary tumor of the pineal region thought to originate from the specialized ependyma of the subcommissural organ (SCO). Transthyretin expression of the present case further supports the likelihood of SCO origin, as transthyretin is one of the proteins presumed to be secreted by human SCO.

Adult↗
PubMed2004

The optimal trackability threshold of fractional anisotropy for diffusion tensor tractography of the corticospinal tract.

PURPOSE: In order to ensure that three-dimensional diffusion tensor tractography (3D-DTT) of the corticospinal tract (CST), is performed accurately and efficiently, we set out to find the optimal lower threshold of fractional anisotropy (FA) below which tract elongation is terminated (trackability threshold). METHODS: Thirteen patients with acute or early subacute ischemic stroke causing motor deficits were enrolled in this study. We performed 3D-DTT of the CST with diffusion tensor MR (magnetic resonance) imaging. We segmented the CST and established a cross-section of the CST in a transaxial plane as a region of interest. Thus, we selectively measured the FA values of the right and left corticospinal tracts at the level of the cerebral peduncle, the posterior limb of the internal capsule, and the centrum semiovale. The FA values of the CST were also measured on the affected side at the level where the clinically relevant infarction was present in isotropic diffusion-weighted imaging. RESULTS: 3D-DTT allowed us to selectively measure the FA values of the CST. Among the 267 regions of interest we measured, the minimum FA value was 0.22. The FA values of the CST were smaller and more variable in the centrum semiovale than in the other regions. The mean minus twice the standard deviation of the FA values of the CST in the centrum semiovale was calculated at 0.22 on the normal unaffected side and 0.16 on the affected side. CONCLUSION: An FA value of about 0.20 was found to be the optimal trackability threshold.

Aged↗
PubMed2004

Utilization of low-field MR scanners.

The evident advantage of high-field MR (magnetic resonance) scanners is their higher signal-to-noise ratio, which results in improved imaging. While no reliable efficacy studies exist that compare the diagnostic capabilities of low- versus high-field scanners, the adoption and acceptance of low-field MRI (magnetic resonance imaging) is subject to biases. On the other hand, the cost savings associated with low-field MRI hardware are obvious. The running costs of a non-superconductive low-field scanner show even greater differences in favor of low-field scanners. Patient anxiety and safety issues also reflect the advantages of low-field scanners. Recent technological developments in the realm of low-field MR scanners will lead to higher image quality, shorter scan times, and refined imaging protocols. Interventional and intraoperative use also supports the installation of low-field MR scanners. Utilization of low-field systems has the potential to enhance overall cost reductions with little or no loss of diagnostic performance.

Cost-Benefit Analysis↗
PubMed2004

Amyotrophic lateral sclerosis: diffusion tensor tractography and voxel-based analysis.

The purpose of this study is to investigate whether the diffusional anisotropy of water molecules is disrupted in the pyramidal and extra-pyramidal regions in patients with amyotrophic lateral sclerosis (ALS). We studied seven patients with probable ALS (four women, mean age +/- SD, 57.3 +/- 6.2 years old) according to the criteria of the World Federation of Neurology. A control group consisted of 11 age- and sex-matched volunteers (six women, 57.1 +/- 4.5) without disorders affecting the central nervous system. Voxel-based diffusion tensor analysis was made with statistical parametric mapping (SPM99). We also created the normalized corticospinal tractography from the diffusion tensor data. The significant fractional anisotropy (FA) decrease in the ALS group was found in the right frontal subgyral white matter and left frontal precentral white matter. These clusters with significant FA decrease corresponded well to the average group map of the corticospinal tract in a standard reference frame. These results suggested that the combination of voxel-based diffusion tensor analysis and diffusion tensor tractography might help determine the location of the affected neuronal tissues among ALS patients in a non-invasive manner.

Algorithms↗
PubMed2004

[Distinguishing between occluded and low-flow vessels with PROPELLER DWI sequence: a phantom study].

PURPOSE: To evaluate the ability of periodically rotated overlapping parallel lines with enhanced reconstruction diffusion-weighted imaging (PROPELLER DWI) to distinguish between vessel occlusion and slow flow. MATERIALS AND METHODS: Using a flow phantom with various velocities (1.37 to 11.1 cm/s), the signal-intensity ratios of the phantom, with the intensity of no flow as baseline, were measured using the following imaging sequences: PROPELLER DWI, spin-echo T1-weighted imaging (SE T1WI), fast-spin-echo T2-weighted imaging (FSE T2WI), two-dimensional phase-contrast imaging (2D PC), and two-dimensional time-of-flight imaging (2D TOF). The b-factor of PROPELLER DWI was varied from 0 to 1000 s/mm(2). The velocity encoding of 2D PC was varied from 2 to 30 cm/s. RESULTS: At the lowest flow velocity (1.37 cm/s) , the signal-intensity ratio was 0.0075 for PROPELLER DWI (b-factor=1000 s/mm(2)), 1.8 for SE T1WI, 0.67 for FSE T2WI, 11 for 2D PC (velocity encoding=2 cm/s), and 1.4 for 2D TOF. The signal-intensity ratio was smallest for PROPELLER DWI, even when the reciprocals of the signal-intensity ratio of 2D PC or 2D TOF were considered. CONCLUSION: The results indicate that PROPELLER DWI provides the best signal intensity-ratio between vessel occlusion and slow flow. Although DWI with single-shot echo-planar imaging (EPI) or multi-shot EPI may have similarly high sensitivity for slow flow, these sequences do not have high spatial resolution or robustness to susceptibility artifacts. PROPELLER DWI would be a better choice for distinguishing between occluded and low-velocity arteries in the skull base or parasellar regions.

Blood Flow Velocity↗
PubMed2004

[Imaging characteristics of PROPELLER T2-weighted imaging].

As the PROPELLER sequence is a combination of the radial scan and fast-spin-echo (FSE) sequence, it can be considered an FSE sequence with a motion correlation. However, there are some differences between PROPELLER and FSE owing to differences in k-space trajectory. We clarified the imaging characteristics of PROPELLER T2-weighted imaging (T2WI) for different parameters in comparison with usual FSE T2WI. When the same parameters were used, PROPELLER T2WI showed a higher signal-to-noise ratio (SNR) and lower spatial resolution than usual FSE. Effective echo time (TE) changed with different echo train lengths (ETL) or different bandwidths on PROPELLER, and imaging contrast changed accordingly to be more effective.

Artifacts↗
PubMed2003

Development of intraarterial contrast-enhanced 2D MRDSA with a 0.3 tesla open MRI system.

PURPOSE: The purpose of this study was to develop a new technique for a high temporal resolution two-dimensional MR digital subtraction angiography (2D MRDSA) sequence under intraarterial injection of contrast material to permit the visualization of vascular anatomy and hemodynamics. METHODS: 2D MRDSA was imaged on a 0.3T open MR scanner with a T(1)-weighted fast gradient echo sequence. The phantom study examined vials containing gadolinium (Gd) solutions ranging in concentration from 0.5 mmol/L to 100 mmol/L. Repetition time and echo time were fixed at minimal values in order to achieve high temporal resolution, and only the flip angle was changed in 10-degree increments between 10 and 90 degrees. The in vivo study examined a brachial artery of a human volunteer. MRDSA images were acquired continuously during intraarterial injections of Gd solutions ranging in concentration from 0.5 mmol/L to 100 mmol/L. The subtracted images were displayed on the monitor in real time at a frame rate of one frame per second and evaluated to determine the optimal concentration of contrast material. RESULTS: In the phantom study, a 10-mmol/L Gd concentration with a flip angle of 50 degrees -90 degrees and a 25-mmol/L Gd concentration with a flip angle of 60 degrees -90 degrees showed high signal-to-noise ratios. In the human brachial artery experiment, the forearm arteries were well visualized when solutions of 5-50 mmol/L Gd concentration were used. The 10- and 25-mmol/L Gd concentrations were considered optimal. The palmar digital arteries were also visualized. Higher Gd concentrations showed a paradoxical signal increase when diluted by blood. CONCLUSION: We successfully developed an intraarterial contrast-enhanced 2D MRDSA sequence. With appropriate settings of imaging parameters and Gd concentrations, we obtained acceptable vessel visualization in the human study. The low Gd concentration for optimal visualization permits repeated intraarterial injections. This technique can be a useful tool for investigating the vascular anatomy and hemodynamics required for MR-guided vascular interventions.

Adult↗
PubMed2003

Feasibility of a curvature-based enhanced display system for detecting cerebral aneurysms in MR angiography.

PURPOSE: To assess the feasibility of a curvature-based enhanced display system for detecting cerebral aneurysms in MR angiography. METHODS: MR angiography studies of 18 patients (eight male and 10 female, average age 65.7, age range 50 to 75 years old) with 23 known aneurysms were evaluated with a curvature-based display system. The two curvature features-the volumetric shape index and curvedness values-were calculated at each voxel. These were displayed independently on a workstation, overlaid on volume-rendered images. Two neuroradiologists evaluated the images for visibility and diagnosis of the cerebral aneurysms. The diagnostic results were compared with the original reports. RESULTS: The calculation time for each curvature index was 30 to 40 s for 120 to 140 slices of original MR angiography data. Shape index images emphasized smooth and round aneurysms more than aneurysms with irregular surfaces. Curvedness images revealed aneurysms well when the aneurysms had diameters that differed from those of the surrounding vessels. The computer-assisted-detection method detected 24 aneurysms, three of which were not pointed out in the initial report. CONCLUSION: Our results show that the curvature-based display system we have developed is feasible and that it may help to detect small aneurysms that are prone to be overlooked in routine readings.

Aged↗
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

[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

[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↗