Faculty Profiles - NAGANAWA, Shinji

Papers - NAGANAWA, Shinji

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

Naganawa S, Koshikawa T, Fukatsu H, Ishigaki T, Aoki I

Eur Radiol Vol. 14 ( 3 ) page： 496-499 2004

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1007/s00330-003-2113-3

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

Naganawa S, Nihashi T, Fukatsu H, Ishigaki T, Aoki I

Eur Radiol Vol. 14 ( 1 ) page： 112-114 2004

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1007/s00330-003-2147-6

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

Naganawa S, Koshikawa T, Kawai H, Fukatsu H, Ishigaki T, Maruyama K, Takizawa O

Eur Radiol Vol. 14 ( 2 ) page： 234-238 2004

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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).

DOI： 10.1007/s00330-003-2163-6

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

Naganawa S, Koshikawa T, Fukatsu H, Ishigaki T, Sato E, Sugiura M, Yoshino T, Nakashima T

Magn Reson Imaging Vol. 22 ( 1 ) page： 25-30 2004

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1016/j.mri.2003.07.002

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

Naganawa S, Koshikawa T, Fukatsu H, Ishigaki T, Maruyama K, Takizawa O

Eur Radiol Vol. 14 ( 8 ) page： 1484-1488 2004

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1007/s00330-004-2342-0

Comparison of flow artifacts between 2D-FLAIR and 3D-FLAIR sequences at 3 T. Reviewed

Naganawa S, Koshikawa T, Nakamura T, Kawai H, Fukatsu H, Ishigaki T, Komada T, Maruyama K, Takizawa O

Eur Radiol Vol. 14 ( 10 ) page： 1901-1908 2004

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

It has been reported that 3D-FLAIR can reduce the flow artifact resulting from cerebrospinal fluid (CSF) at 1.5 T compared to 2D-FLAIR. Flow-related artifacts tend to be worse at 3 T than at 1.5 T. The purpose of this study was to compare the CSF flow artifacts of 2D-FLAIR and 3D-FLAIR sequences at 3 T in eight healthy volunteers. The grade of CSF-related artifacts were scored through observing the perimedullary cistern, cerebellopontine angle cisterns, fourth ventricule, prepontine cistern, suprasellar cistern, ambient cisterns, sylvian fissures, third ventricle and lateral ventricles. Grading was performed on either axial or sagittal images. The CSF in-flow artifact scores were significantly higher on axial 2D-FLAIR than on axial 3D-FLAIR MPR images in all areas except the bilateral sylvian fissures, and higher on sagittal 2D-FLAIR than on sagittal 3D-FLAIR MPR images in perimedullary, bilateral CP angle and suprasellar cisterns. The CSF-related flow artifacts were significantly reduced by 3D-FLAIR, while structures in the cistern were depicted more clearly, even at 3 T. Further study is necessary to compare the clinical efficacy between 2D-FLAIR and 3D-FLAIR in depicting subtle abnormalities.

DOI： 10.1007/s00330-004-2372-7

MRIの最新トッピックス　3T MRIの臨床

長縄慎二

映像情報メディカル Vol. 36 page： 1056-1060 2004

頭頚部画像診断に必要不可欠な臨床画像解剖（１）側頭骨　（内耳、内耳道）

長縄慎二

画像診断 Vol. 24 ( 11 ) page： 2-4 2004

Magnetic resonance imaging of endolymphatic sac in acute low-tone sensorineural hearing loss without vertigo. Reviewed

Sugiura M, Naganawa S, Nakashima T, Misawa H, Nakamura T

ORL J Otorhinolaryngol Relat Spec Vol. 65 ( 5 ) page： 254-260 2003

Language：English Publishing type：Research paper (scientific journal)

The etiology of acute low-tone sensorineural hearing loss (ALHL) may be associated with deteriorated function of the endolymphatic sac. Using magnetic resonance (MR) imaging on a 1.5-tesla MR system, we evaluated the frequency of visualization and contrast enhancement of the endolymphatic sac in 25 patients (9 men and 16 women; age range 11-64 years) with ALHL and 21 control subjects. The present study demonstrated that the frequency of visualization and enhancement of the endolymphatic sac in patients with ALHL was not significantly higher than in control subjects.

DOI： 10.1159/000075222

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

Naganawa S, Sato K, Katagiri T, Mimura T, Ishigaki T

Eur Radiol Vol. 13 ( 1 ) page： 6-11 2003

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1007/s00330-002-1549-1

Imaging of a congenital perilymphatic fistula. Reviewed

Nakashima T, Sone M, Teranishi MA, Tominaga M, Sugiura M, Naganawa S

Int J Pediatr Otorhinolaryngol Vol. 67 ( 4 ) page： 421-425 2003

Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1016/S0165-5876(02)00397-X

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

Naganawa S, Koshikawa T, Sato K, Katagiri T, Mimura T, Ishigaki T, Aoki I

Eur Radiol Vol. 13 ( 10 ) page： 2298-2303 2003

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1007/s00330-003-1860-5

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

Naganawa S, Koshikawa T, Nakamura T, Fukatsu H, Ishigaki T, Aoki I

Eur Radiol Vol. 13 ( 12 ) page： 2650-2658 2003

Contrast enhancement of the cochlear aqueduct in MR imaging: its frequency and clinical significance. Reviewed

Nakamura T, Naganawa S, Fukatsu H, Sakurai Y, Aoki I, Ninomiya A, Nakashima T, Ishigaki T

Neuroradiology Vol. 45 ( 9 ) page： 626-630 2003

Language：English Publishing type：Research paper (scientific journal)

There have been no previous reports on contrast enhancement of the cochlear aqueduct in magnetic resonance imaging. The purpose of the present study was to evaluate the frequency and significance of this finding. Thirty-one patients (15 men and 16 women; age range 18-81 years) with otologic symptoms (sudden sensorineural hearing loss, vertigo, or tinnitus) were examined using contrast-enhanced imaging on a 1.5-T MR scanner. The normal ear served as the control. Two radiologists evaluated contrast enhancement in the area of the cochlear aqueduct. Forty-eight of 62 ears (77.4%) showed contrast enhancement of the cochlear aqueduct, but no significant differences in the frequency of contrast enhancement were observed between patients with and patients without vertigo, tinnitus, sensorineural hearing loss, cerebellopontine angle tumors, or a high-riding jugular bulb. In addition, no gender- or age-related differences were noted. Contrast enhancement of the cochlear aqueduct was frequently observed, but the frequency of enhancement in symptomatic ears was not significantly higher than in control ears. The results of this study may prove helpful in avoiding unnecessary examinations and potential diagnostic confusion.

DOI： 10.1007/s00234-003-1051-8

Disorders of cochlear blood flow. Reviewed

Nakashima T, Naganawa S, Sone M, Tominaga M, Hayashi H, Yamamoto H, Liu X, Nuttall AL

Brain Res Brain Res Rev Vol. 43 ( 1 ) page： 17-28 2003

Language：English Publishing type：Research paper (scientific journal)

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.

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

Hund-Georgiadis M, Zysset S, Naganawa S, Norris DG, Von Cramon DY.

Cerebrovasc Dis Vol. 16 ( 2 ) page： 158-165 2003

超高磁場磁気共鳴画像診断(MRI)について

長縄慎二

健康文化振興財団紀要 Vol. 38 page： 40-42 2002.4

Authorship：Lead author Language：Japanese

はじめに

　脳ドックや腰椎の椎間板ヘルニア、膝の半月板損傷などで磁気共鳴画像診断(MRI)を受けられた方も多いと思います。MRIは磁石と電波をつかって体の断層像を得る検査です。X線CTと異なり、電離放射線被爆のない安全な検査で、この15年ほどで国内でも急速に普及しました。

　従来までは1.5T(テスラ)という磁石の強さが国内ではもっとも強いものでしたが、この3年ほどで超高磁場とよばれる3Tの製品が実用化されてきました。１Tは１万ガウスで、3Tは３万ガウスという強力な磁石です。今回は、この超高磁場MRIについて、述べてみたいと思います。

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

Naganawa S, Koshikawa T, Fukatsu H, Ishigaki T, Nakashima T

Eur Radiol Vol. 12 ( 3 ) page： 114-117 2002

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1007/s00330-002-1525-9

Tympanometric findings in patients with enlarged vestibular aqueducts. Reviewed

Sato E, Nakashima T, Lilly DJ, Fausti SA, Ueda H, Misawa H, Uchida Y, Furuhashi A, Asahi K, Naganawa S

Laryngoscope Vol. 112 ( 9 ) page： 1642-1646 2002

Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1097/00005537-200209000-00021

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

Naganawa S, Norris DG, Zysset S, Mildner T

J Magn Reson Imaging Vol. 15 ( 1 ) page： 23-30 2002

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1002/jmri.10028

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Papers - NAGANAWA, Shinji