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Shinji Naganawa

Publications and source records attributed to Shinji Naganawa.

At least 37 records · Page 2Linked to original sources
PubMed2004

Whole-brain vascular reactivity measured by fMRI using hyperventilation and breath-holding tasks: efficacy of 3D prospective acquisition correction (3D-PACE) for head motion.

Functional MR imaging (fMRI) study using hyperventilation and breath-holding task has been reported to be one of the non-invasive methods to examine whole-brain vascular reactivity. The purpose of this study was to evaluate the efficacy of a method for 3D prospective detection and correction of head motion (3D-PACE) in a study of whole-brain vascular reactivity using hyperventilation and breath-holding tasks. Eight healthy volunteers were scanned using an fMRI protocol of hyperventilation and breath-holding task blocks at 3 T in separate runs with and without 3D-PACE. In two subjects, two more runs with and without 3D-PACE were repeated. The mean total number of activated voxels +/- standard deviation was 26,405.3+/-1,822.2 in the run with 3D-PACE and 17,329.9+/-2,766.3 in the run without 3D-PACE ( P<0.05), although there is some intersubject variation regarding the effect of 3D-PACE. In the two subjects whose performed two more runs, the number of activated voxels were smaller in the run without 3D-PACE than even in the run with 3D-PACE performed later. We conclude that 3D-PACE is beneficial for fMRI studies of whole-brain vascular reactivity induced by hyperventilation and breath-holding.

Adult↗
PubMed2004

Enlarged endolymphatic duct and sac syndrome: relationship between MR findings and genotype of mutation in Pendred syndrome gene.

Pendred syndrome (PDS) is characterized by profound deafness in childhood, positive perchlorate challenge, and goiter. PDS is often associated with enlarged endolymphatic duct and sac (EEDS), and recently, PDS gene mutations have been reported even in those patients with EEDS without classic Pendred syndrome. In a previous report, the number of mutant alleles was correlated with the degree of subclinical thyroid abnormality, but not with hearing loss, in patients with missense mutation H723R. It also has been reported that the hearing loss in EEDS was not correlated with the EEDS volume, cochlear modiolar area, or signal intensity of the endolymphatic sac. We evaluated the correlations between the number of mutant alleles and these parameters in patients with EEDS to investigate the mechanisms underlying this condition. The study group was comprised of 16 Japanese patients with EEDS diagnosed by MR imaging. The H723R mutation was homozygous in six patients and heterozygous in six patients, with no mutation found in four patients. The modiolar area, EEDS volume, and signal intensity ratio (sac signal/cerebrospinal fluid signal) were not significantly correlated with the number of mutant alleles. PDS gene mutations may not be the only cause of EEDS, and the mechanisms underlying EEDS remain unclear.

Adolescent↗
PubMed2004

High-speed imaging at 3 Tesla: a technical and clinical review with an emphasis on whole-brain 3D imaging.

Improvements to the inherently high specific-absorption rate (SAR) of high-speed imaging at 3T are necessary in order to render this method clinically feasible. Various efforts have been undertaken to improve the associated hardware and software. In this review, we focus on whole-brain isotropic 3D imaging with a turbo spin-echo sequence with variable flip-angle echo trains (3D-TSE-VFL) and present its technical and clinical features. This sequence can be used to acquire images of various contrasts including T2-weighted, fat-suppressed T2-weighted, fluid-attenuated inversion recovery (FLAIR), fat-suppressed FLAIR, and STIR (short tau inversion recovery). Various aspects of 3D-TSE-VFL are discussed, including CSF (cerebrospinal fluid) and metal artifacts, STIR contrast, small-part visualization other than brain, and the possibility of serial subtraction. Some images from clinical cases are presented.

Adult↗
PubMed2003

Optimization of diffusion-tensor MR imaging data acquisition parameters for brain fiber tracking using parallel imaging at 3 T.

The purpose of this study was to optimize the parameters of diffusion-tensor magnetic resonance imaging (DT MRI) for brain fiber tracking using a slice thickness of 2 mm, a resolution advantage allowed by the high signal-to-noise ratio at 3 T, combined with an 8-channel phased-array head coil. The b-factor, number of motion probing gradient (MPG) directions, and number of averages were varied, and the results of brain fiber tracking for the pyramidal tract and trigeminal nerve were compared qualitatively and quantitatively. The DT MRI data sufficient for brain fiber tracking in healthy subjects can be obtained in <2 min with a 2-mm slice thickness, 700-s/mm2 b-factor, 6 MPG directions, and no averaging (number of averages=1).

Adult↗
PubMed2003

Flow ghost artifact in slice-encoding direction mimicking vestibular schwannoma in contrast-enhanced 3D spoiled gradient-echo sequence.

The value of MR imaging by post-contrast T1-weighted 3D spoiled gradient-echo (3D SPGR) is well established for the detection of small vestibular schwannomas in the cerebellopontine angle region. We describe a case in which a flow ghost artifact in the slice-encoding direction mimicked a vestibular schwannoma and heavily T2-weighted MR cisternography and multiplanar reconstruction images helped us to reach the correct diagnosis. In addition, we conducted a volunteer study to demonstrate that changing the k-space trajectory can reduce this artifact in post-contrast 3D SPGR images.

Adult↗
PubMed2003

Pre-surgical mapping of primary motor cortex by functional MRI at 3 T: effects of intravenous administration of Gd-DTPA.

The functional magnetic resonance imaging (fMRI) is often performed at the end of a routine MRI examination during which, dependent on the clinical indication, contrast agent has been administered; however, the effects of Gd-DTPA injection on the results of blood oxygenation level dependent (BOLD)-fMRI remain unknown. The present study was conducted to investigate the effects of the intravenous administration of Gd-DTPA on the results of pre-surgical localization of the primary motor cortex by BOLD-fMRI at 3 T. Eight normal subjects were included in this study. After the anatomical scans, pre- and post-contrast fMRI scanning was performed. The number of significantly activated voxels and the mean percentage signal change were compared. The mean number of significantly activated voxels was 115.0+/-27.0 in pre-contrast runs and 90.8+/-27.1 in post-contrast runs (mean value of all 8 volunteers+/-standard deviation; p<0.05). The mean mean percentage signal change was 4.07+/-0.39 in pre-contrast runs and 3.86+/-1.91 in post-contrast runs ( p=0.16). Pre-surgical localization of the motor area by BOLD-fMRI should be performed before the administration of Gd contrast material.

Adult↗
PubMed2003

High-resolution T1-weighted 3D real IR imaging of the temporal bone using triple-dose contrast material.

The small structures in the temporal bone are surrounded by bone and air. The objectives of this study were (a) to compare contrast-enhanced T1-weighted images acquired by fast spin-echo-based three-dimensional real inversion recovery (3D rIR) against those acquired by gradient echo-based 3D SPGR in the visualization of the enhancement of small structures in the temporal bone, and (b) to determine whether either 3D rIR or 3D SPGR is useful for visualizing enhancement of the cochlear lymph fluid. Seven healthy men (age range 27-46 years) volunteered to participate in this study. All MR imaging was performed using a dedicated bilateral quadrature surface phased-array coil for temporal bone imaging at 1.5 T (Visart EX, Toshiba, Tokyo, Japan). The 3D rIR images (TR/TE/TI: 1800 ms/10 ms/500 ms) and flow-compensated 3D SPGR images (TR/TE/FA: 23 ms/10 ms/25 degrees) were obtained with a reconstructed voxel size of 0.6 x 0.7 x 0.8 mm3. Images were acquired before and 1, 90, 180, and 270 min after the administration of triple-dose Gd-DTPA-BMA (0.3 mmol/kg). In post-contrast MR images, the degree of enhancement of the cochlear aqueduct, endolymphatic sac, subarcuate artery, geniculate ganglion of the facial nerve, and cochlear lymph fluid space was assessed by two radiologists. The degree of enhancement was scored as follows: 0 (no enhancement); 1 (slight enhancement); 2 (intermediate between 1 and 3); and 3 (enhancement similar to that of vessels). Enhancement scores for the endolymphatic sac, subarcuate artery, and geniculate ganglion were higher in 3D rIR than in 3D SPGR. Washout of enhancement in the endolymphatic sac appeared to be delayed compared with that in the subarcuate artery, suggesting that the enhancement in the endolymphatic sac may have been due in part to non-vascular tissue enhancement. Enhancement of the cochlear lymph space was not observed in any of the subjects in 3D rIR and 3D SPGR. The 3D rIR sequence may be more sensitive than the 3D SPGR sequence in visualizing the enhancement of small structures in the temporal bone; however, enhancement of the cochlear fluid space could not be visualized even with 3D rIR, triple-dose contrast, and dedicated coils at 1.5 T.

Adult↗
PubMed2003

Pseudostenosis of the internal carotid artery in 3D time-of-flight MR angiography: effects of a magnetization transfer contrast pulse and metallic material.

Pseudostenosis or pseudoocclusion of the internal carotid artery in 3D time-of-flight MR angiography has been reported to be caused by susceptibility artifacts due to the presence of a metallic foreign body in the subject's neck. We experimentally demonstrate that the use of a non-slice-selective magnetization transfer contrast (MTC) pulse increases the degree of pseudostenosis, whereas slice-selective MTC does not. Selective MR angiography demonstrating this phenomenon was also performed. We then report a case that exhibited this phenomenon. We conclude that the magnetic field inhomogeneity induced by metallic material causes the non-slice-selective MTC pulse to act as a local presaturation pulse. Selective MR angiography using this phenomenon can be applied on varieties of MR scanners from different vendors.

Adult↗
PubMed2003

Disorders of cochlear blood flow.

The cochlea is principally supplied from the inner ear artery (labyrinthine artery), which is usually a branch of the anterior inferior cerebellar artery. Cochlear blood flow is a function of cochlear perfusion pressure, which is calculated as the difference between mean arterial blood pressure and inner ear fluid pressure. Many otologic disorders such as noise-induced hearing loss, endolymphatic hydrops and presbycusis are suspected of being related to alterations in cochlear blood flow. However, the human cochlea is not easily accessible for investigation because this delicate sensory organ is hidden deep in the temporal bone. In patients with sensorineural hearing loss, magnetic resonance imaging, laser-Doppler flowmetry and ultrasonography have been used to investigate the status of cochlear blood flow. There have been many reports of hearing loss that were considered to be caused by blood flow disturbance in the cochlea. However, direct evidence of blood flow disturbance in the cochlea is still lacking in most of the cases.

Animals↗
PubMed2003

Imaging of a congenital perilymphatic fistula.

A 7-year-old boy with a history of purulent meningitis and watery rhinorrhea was studied using computed tomography (CT) and magnetic resonance imaging (MRI). He had a common cavity in the left inner ear. With high-resolution heavily T2-weighted MRI, leakage of the inner ear fluid into the middle ear at the oval window area through a congenital perilymphatic fistula could be visualized. Surgery to close the fistula showed a perforation in the stapes footplate.

Child↗
PubMed2003

Determination of cerebrovascular reactivity by means of FMRI signal changes in cerebral microangiopathy: a correlation with morphological abnormalities.

BACKGROUND AND PURPOSE: A reduced cerebrovascular reactivity (CR) is a risk factor of cerebrovascular disease. In this study, we implemented a protocol to assess CR by means of functional MRI (fMRI) using hyperventilation. SUBJECTS AND METHODS: In 5 patients with cerebral microangiopathy (CM/lacunar infarction and white matter degeneration), 6 healthy elderly subjects (age-matched control), and 6 young healthy subjects, the CR in response to hyperventilation was evaluated by fMRI using gradient echo-planar Imaging. The percentage signal change normalized by end-tidal CO(2) value was measured in various brain regions. RESULTS: All subjects performed hyperventilation well without adverse reaction and significant gross motion. Patients with CM showed significant qualitative and quantitative differences (p < 0.05) as compared to controls. The volume of gray matter showing significant CR was significantly reduced in patients: by 40% in comparison to the age-matched elderly control group and by 60% when compared with the young controls. The CR impairment was most pronounced in the frontal cortices with a drastically reduced magnitude of the magnetic resonance (MR) signal change in the patients (-0.62 +/- 0.2% in patients versus -2.0 +/- 0.36% in age-matched controls, p < 0.0001). A strong relation was evident between the fMRI-based CR reduction in patients with CM and the individual severity of structural MR abnormalities (p = 0.002). CONCLUSION: This study demonstrates that fMRI-based signal changes in response to hyperventilation reliably reflect cerebral vasoreactivity. The protocol is feasible in healthy young and elderly controls and patients with CM. Quantitative and qualitative assessment of the signal decrease in the T(2)-weighted MR sequence and coregistration with individual anatomical data allow the generation of an individual cerebral vasoreactivity map. Future research will address the effect of CR reduction on neuropsychological parameters in patients with CM.

Adult↗
PubMed2002

Regional ADC values of the normal brain: differences due to age, gender, and laterality.

The purpose of this study was to evaluate the stability of measurement for apparent diffusion coefficient (ADC) values in normal brain, to clarify the effect of aging on ADC values, to compare ADC values between men and women, and to compare ADC values between right and left sides of the brain. To evaluate the stability of measurements, five normal volunteers (four men and one woman) were examined five times on different days. Then, 294 subjects with normal MR imaging (147 men and 147 women; age range 20-89 years) were measured. The ADC measurement in normal volunteers was stable. The ADC values stayed within the 5% deviation of average values in all volunteers (mean+/-standard deviation 2.3+/-1.2%). The ADC values gradually increased by aging in all regions. In thalamus, no significant difference was seen between right and left in the subjects under 60 years; however, right side showed higher values in the subjects over 60 years (p<0.01). In the subjects under 60 years, women showed higher values in right frontal, bilateral thalamus, and temporal (p<0.01); however, in the subjects over 60 years, no region showed difference between men and women. The knowledge obtained in this study may be helpful to understand the developmental and aging mechanisms of normal brain and may be useful for the future quantitative study as a reference.

Adult↗
PubMed2002

Serial MR imaging studies in enlarged endolymphatic duct and sac syndrome.

Large vestibular aqueduct syndrome (LVAS) is a congenital disorder characterized by progressive or fluctuating sensorineural hearing loss of unknown etiology. Serial MR examinations were performed before and after the development of hearing loss in two patients with LVAS. The signal and volume of the enlarged endolymphatic sac (EES) vary even in ears with stable hearing. In ears with fluctuating hearing, changes in EES signals were observed in only one of two patients. The finding that the EES volume and signal intensity vary dynamically independently of hearing is important for future research into the pathophysiology of hearing loss in this syndrome.

Adult↗
PubMed2002

Regional differences of fMR signal changes induced by hyperventilation: comparison between SE-EPI and GE-EPI at 3-T.

PURPOSE: To evaluate whether reproducible signal change of brain tissues by hyperventilation (HV) can be seen on spin-echo (SE)-echo planar imaging (EPI) at 3-T and to examine the sensitivity of SE-EPI for measuring vascular reactivity in regions of the brain, such as the hippocampal formation, that are difficult to visualize with gradient-echo (GE)-EPI due to susceptibility artifacts. MATERIALS AND METHODS: Six healthy human subjects performed a voluntary HV task. The task design was as follows: two minutes normal breathing (rest) followed by two minutes HV, giving a basic four-minute block that was repeated three times for a total scan time of 12 minutes for one run. Each subject performed the run both for SE-EPI and GE-EPI. Statistical analysis was performed to detect the area with significant cerebrovascular reactivity. The percentage signal change was also obtained for each cerebral region. RESULTS: Both GE-EPI and SE-EPI showed globally significant signal decreases in the cerebral cortex. In GE-EPI, the frontal cortex showed a larger signal decrease than the other gray matter tissues (P < 0.05). In SE-EPI, the differences among gray matter tissues except for the hippocampal formation were not significant. The hippocampal formation showed the largest signal change (P < 0.05) in SE-EPI, but no significant signal change was observed in GE-EPI due to the presence of susceptibility artifacts. CONCLUSION: HV using SE-EPI at 3-T provides robust and reproducible signal decreases and may make the evaluation of the vascular reactivity in hippocampal formation feasible.

Adult↗
PubMed2002

The role of contrast-enhanced MR mammography for determining candidates for breast conservation surgery.

PURPOSE: The aim of this study was to assess the impact of preoperative magnetic resonance mammography (MRM) on the surgical determination of breast conservation treatment for breast cancer patients. METHODS: From September 1997 to March 2000, 57 consecutive breast conservation treatment candidates were prospectively evaluated with conventional imaging studies (mammography and ultrasonography) and preoperative MRM. RESULTS: In 47 of 54 (87% ) breast cancer patients breast conservation surgery (BCS) was indicated on the basis of mammography (MMG) and ultrasonography (US). However in 40 of the 54 (74% ) patients BCS was indicated on the basis of MRM. Thirty-eight of the 40 patients ultimately underwent BCS and only 1 showed a positive margin. There were 7 patients whose MRM findings suggested that more aggressive treatment than BCS was needed but for whom US/MMG suggested that BCS was appropriate. Five of the 7 patients underwent mastectomy rather than BCS based on the MRM findings, which were justified by post-surgical histological findings. Of the 2 remaining patients who underwent BCS, one had a positive histological margin and one had recurrence, both of which resulted in salvage mastectomy. CONCLUSION: Our study suggests that high resolution preoperative MRM provides more accurate information compared with US and MMG for selecting candidates for BCS. Using MRM as a routine staging tool may reduce unnecessary repeated excisions. A larger study will be required to confirm these findings and to define the patients most likely to benefit from breast MR imaging.

Adult↗
PubMed2002

Tympanometric findings in patients with enlarged vestibular aqueducts.

OBJECTIVES: The purpose of this study was to study systematically some relationships between the resonance frequency of the middle-ear transmission system and the volume of the endolymphatic duct and sac in patients with an enlarged vestibular aqueduct (EVA). STUDY DESIGN: Prospective study. METHODS: Thirteen patients (24 ears) with EVA, 17 subjects (29 ears) with normal hearing, and 17 patients (21 ears) with sensorineural hearing loss without EVA served as experimental subjects. Standard pure-tone audiometry, standard clinical tympanometry (using a 226-Hz probe tone), and multifrequency tympanometry were performed on each ear. Magnetic resonance imaging was used to determine the area of the cochlear modiolus and the volume of the endolymphatic duct and sac. RESULTS: The audiometric configurations for most patients sloped downward from the low to the high frequencies. A significant air-bone gap was computed at each of these test frequencies. Multifrequency tympanometry yielded resonance frequencies for the patients with EVA that was significantly lower than those measured for the control subjects. In general, for patients with EVA, the resonance frequency of the middle ear system decreased as the volume of the endolymphatic duct and sac increased. This inverse relation was significant (correlation coefficient = -0.483, P =.0157). However, there was no correlation between resonance frequency and the degree of cochlea modiolar deficiency. CONCLUSIONS: Clinically, our findings suggest that EVA probably should be included in the differential diagnosis for a patient who presents with a moderate to severe mixed hearing loss, a normal tympanogram at 226 Hz, and a resonance frequency that is abnormally low.

Acoustic Impedance Tests↗
PubMed2002

Fast recovery 3D fast spin-echo MR imaging of the inner ear at 3 T.

High-resolution MR imaging of the inner ear with a heavily T2-weighted 3D fast spin-echo sequence has been performed successfully at 1.5 T. However, at 3 T, the longer T1 time of CSF necessitates a longer TR, resulting in significantly prolonged imaging times. In this study, the fast recovery 3D fast spin-echo sequence, which permits the TR to be reduced while maintaining T2 contrast, was optimized at 3 T for imaging of the inner ear. The optimized sequence parameters are as follows: 1500/294 (TR/TE); echo spacing, 18.1 ms; bandwidth, 38 kHz at 512 readout; and imaging time, 13 minutes.

Ear, Inner↗