Akira Yamamoto

Osaka City University, Ōsaka, Ōsaka, Japan

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Publications (79)175.65 Total impact

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    ABSTRACT: The aim of this study is to investigate the relationship between abnormal retropharyngeal lymph nodes (RPLNs) and sinonasal malignancies among adults.
    Neuroradiology 09/2014; · 2.70 Impact Factor
  • International Congress of Radiology ICR2014, Dubai, UAE; 09/2014
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    ABSTRACT: Objective: We qualitatively evaluated the differences among susceptibility-weighted (SWI), magnitude (MAG), and high pass filtered phase (PHA) images in depicting inter-lobar differences in the appearance of the signal of the corticomedullary junction (CMJ). We conducted quantitative evaluation to validate the qualitative results. Materials and Methods: We obtained SWI images from 25 preoperative brain tumor patients (12 men, 13 women, aged 19 to 82 years, mean, 52 years). Two trained neuro-radiologists evaluated MAG, PHA, and SWI images. Qualitative evaluation of the CMJ signal and quantitative calculation of the relative signal ratio (RSR) percentages between the CMJ and deep white matter (WM) were conducted at 3 different slice levels of the brain independently for 4 different lobes (frontal, parietal, temporal, and occipital) and com-pared among MAG, PHA, and SWI. The extent of the area of the CMJ signal was graded on a 4-point scale (Grade 3, >75%; Grade 2, 50 to 75%; Grade 1, 25 to 50%; Grade 0, <25%). Data were statistically analyzed using a nonparametric Friedman test. Results: The Kappa coefficients between the qualitative and quantitative grades were 0.002 for MAG, 0.0047 for PHA, and 0.050 for SWI. Qualitatively, on the PHA images and SWI, grades of the occipital lobes were significantly higher than those of the other lobes (P < 0.005). Quantitatively, PHA images showed statistically significant interlobar differences in RSR percentage values of the CMJ (P = 0.025). Conclusion: Qualitatively, the appearance of the CMJ differed significantly among the different lobes of the brain on SWI and underlying PHA images but not on MAG images. Quantitatively, only PHA images showed significant interlobar differences in the RSR. PHA images are most sensitive to the CMJ signal contrast due to local paramagnetic iron content.
    Magnetic Resonance in Medical Sciences 08/2014; · 0.75 Impact Factor
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    ABSTRACT: To evaluate the validity of 3D dynamic pituitary MR imaging with controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA), with special emphasis on demarcation of pituitary posterior lobe and stalk.
    European journal of radiology. 07/2014;
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    ABSTRACT: To optimize visualization of lenticulostriate artery (LSA) by time-of-flight (TOF) magnetic resonance angiography (MRA) with slice-selective off-resonance sinc (SORS) saturation transfer contrast pulses and to compare capability of optimal TOF-MRA and flow-sensitive black-blood (FSBB) MRA to visualize the LSA at 3T. This study was approved by the local ethics committee, and written informed consent was obtained from all the subjects. TOF-MRA was optimized in 20 subjects by comparing SORS pulses of different flip angles: 0, 400°, and 750°. Numbers of LSAs were counted. The optimal TOF-MRA was compared to FSBB-MRA in 21 subjects. Images were evaluated by the numbers and length of visualized LSAs. LSAs were significantly more visualized in TOF-MRA with SORS pulses of 400° than others (P < .003). When the optimal TOF-MRA was compared to FSBB-MRA, the visualization of LSA using FSBB (mean branch numbers 11.1, 95% confidence interval (CI) 10.0-12.1; mean total length 236 mm, 95% CI 210-263 mm) was significantly better than using TOF (4.7, 95% CI 4.1-5.3; 78 mm, 95% CI 67-89 mm) for both numbers and length of the LSA (P < .0001). LSA visualization was best with 400° SORS pulses for TOF-MRA but FSBB-MRA was better than TOF-MRA, which indicates its clinical potential to investigate the LSA on a 3T magnetic resonance imaging.
    Academic radiology 06/2014; 21(6):812-6. · 2.09 Impact Factor
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    ABSTRACT: To investigate the diffusion tensor imaging parameters of the optic radiation and surrounding structures using the high-resolution readout-segmented diffusion tensor imaging method. Coronal readout-segmented diffusion tensor images were acquired in 15 healthy volunteers. On three slices of each image, eigenvalue 1, fractional anisotropy, radial diffusivity, apparent diffusion coefficient, and signal intensity on T2-weighted images were measured in the lateral inferior longitudinal fasciculus, external and internal layers of the optic radiation, and the tapetum within regions of interest delineated by two independent observers. Profile curve analysis of regions of interest across the optic radiation and surrounding structures was performed for a representative typical case. Significant differences in fractional anisotropy, radial diffusivity and apparent diffusion coefficient were observed between external and internal layers of the optic radiation, while there was no significant difference in eigenvalue 1. In fractional anisotropy maps, two low signal bands were observed between the inferior longitudinal fasciculus, the optic radiation and the tapetum. Profile curve analysis showed a minimum on the fractional anisotropy and eigenvalue 1 images and a maximum in the radial diffusivity image. Readout-segmented diffusion tensor imaging revealed significant differences in the diffusion tensor imaging parameters between internal and external layers of the optic radiation.
    Anatomia Clinica 04/2014; · 0.93 Impact Factor
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    ABSTRACT: To examine differences in neointimal hyperplasia (NIH) after placing a self-expanding (SE) stent across size-discrepant vessels. The subjects were 6 beagles, and the target vessels were the abdominal aorta and the external iliac artery (EIA). A nitinol SE stent was placed which was normal-sized in the aorta and oversized in the EIA. Angiography and intravascular ultrasound (IVUS) were performed immediately and after 1 and 3 months; histopathologic examinations were then performed. Furthermore, the chronic outward force (COF) on the same type of stent was investigated in vitro. On IVUS, thickened intima was seen on the EIA at 1 month (5.1 ± 4.2 mm(2)) and at 3 months (7.8 ± 2.5 mm(2)). For the aorta, thickening of the intima was negligible at any time. Histopathologically, the percentage of the vessel obliterated by NIH was significantly greater on the iliac side than on the aortic side (33.2 ± 10.4 vs. 13.4 ± 4.4 %). The COF exerted when stent diameter reached that of the EIA and the aorta was 0.73 and 0.17 N/mm(2), respectively. When a non-tapered stent is placed in vessels with a large discrepancy in diameter, attention must be paid to increased NIH in the oversized side.
    Japanese journal of radiology 04/2014; · 0.73 Impact Factor
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    ABSTRACT: Quantitative values of CT attenuation, apparent diffusion coefficient (ADC), and standardized uptake value (SUV) were investigated for differentiation between pineal parenchymal tumors (PPTs) and germinomas. Differences in age, sex, and calcification pattern were also evaluated. Twenty-three patients with PPTs and germinomas in 20 years were retrospectively enrolled under the approval of the institutional review board. CT attenuation, ADC, and SUV (20, 13, and 10 patients, respectively) were statistically compared between the two tumors. Differences in sex and patterns of calcification ("exploded" or "engulfed") were also examined. Mean patient ages were compared among three groups of pineoblastoma, pineal parenchymal tumor of intermediate differentiation, (PPTID) and pineocytoma and germinoma. None of the quantitative values of CT attenuation, ADC, and SUV showed significant differences between PPTs and germinomas (p > .05). However, there was a significant difference in age (p < .05) among the three groups of pineoblastoma (mean age ± standard deviation 7.0 ± 8.7 years), PPTID, and pineocytoma (53.7 ± 11.4 years) and germinoma (19.1 ± 8.1 years). Sex also showed significant differences between PPTs and germinomas (p = .039). Exploded pattern of calcification was found in 9 of 11 PPT patients and engulfed pattern in 7 of 9 patients with germinomas. No reverse pattern was observed, and the patterns of calcification were considered highly specific of tumor types. None of the quantitative imaging values could differentiate PPTs from germinomas. Age, sex, and calcification patterns were confirmed useful in differentiating these tumors to some degree.
    Neuroradiology 02/2014; · 2.70 Impact Factor
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    ABSTRACT: Background:Congenital porto-systemic shunt (CPSS) has the potential to cause hepatic encephalopathy thus needs long-term follow-up, but an effective follow-up method has not been established. We aimed to evaluate the importance of per-rectal portal scintigraphy (PRPS) for long-term follow-up of CPSS.Methods:We retrospectively examined shunt-severity time course in patients (median 9.6y, 5.2-16.6) with intrahepatic (n=3) or extrahepatic (n=3) CPSS by using blood tests, ultrasonography or computed tomography (CT), and PRPS. Per-rectal portal shunt index (SI, cut-off 10%) was calculated by PRPS.Results:PRPS demonstrated the initial SI reduced in all intrahepatic cases from 39.7±9.8% (mean±SD) to 14.6±4.7% and also reduced in all extrahepatic cases from 46.2±10.9% to 27.5±12.6% during follow-up period. However, ultrasonography and CT disclosed the different shunt diameter time course between intrahepatic and extrahepatic CPSS. Initial shunt diameter (5.8±3.5mm) reduced to 2.0±0.3mm in intrahepatic cases, but the initial diameter (6.3±0.7mm) increased to 10.6±1.0mm in extrahepatic cases. All patients had elevated serum total bile acid or ammonia levels at initial screening, but these blood parameters were insufficient to assess shunt severity because the values fluctuate.Conclusions:PRPS can track changes in the shunt-severity of CPSS and is more reliable than ultrasonography and CT in patients with extrahepatic CPSS.Pediatric Research (2014); doi:10.1038/pr.2014.11.
    Pediatric Research 01/2014; · 2.67 Impact Factor
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    ABSTRACT: Central neurocytoma was initially believed to be benign tumor type, although atypical cases with more aggressive behavior have been reported. Preoperative estimation for proliferating activity of central neurocytoma is one of the most important considerations for determining tumor management. To investigate predictive values of image characteristics and quantitative measurements of minimum apparent diffusion coefficient (ADCmin) and maximum standardized uptake value (SUVmax) for proliferative activity of central neurocytoma measured by MIB-1 labeling index (LI). Twelve cases of central neurocytoma including one recurrence from January 2001 to December 2011 were included. Preoperative scans were conducted in 11, nine, and five patients for computed tomography (CT), diffusion-weighted imaging (DWI), and fluorine-18-fluorodeoxyglucose positron emission tomography (FDG-PET), respectively, and ADCmin and SUVmax of the tumors were measured. Image characteristics were investigated using CT, T2-weighted (T2W) imaging and contrast-enhanced T1-weighted (T1W) imaging, and their differences were examined using the Fisher's exact test between cases with MIB-1 LI below and above 2%, which is recognized as typical and atypical central neurocytoma, respectively. Correlational analysis was conducted for ADCmin and SUVmax with MIB-1 LI. A P value <0.05 was considered significant. Morphological appearances had large variety, and there was no significant correlation with MIB-1 LI except a tendency that strong enhancement was observed in central neurocytomas with higher MIB-1 LI (P = 0.061). High linearity with MIB-1 LI was observed in ADCmin and SUVmax (r = -0.91 and 0.74, respectively), but only ADCmin was statistically significant (P = 0.0006). Central neurocytoma had a wide variety of image appearance, and assessment of proliferative potential was considered difficult only by morphological aspects. ADCmin was recognized as a potential marker for differentiation of atypical central neurocytomas from the typical ones.
    Acta Radiologica 01/2014; · 1.33 Impact Factor
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    ABSTRACT: Balloon-occluded retrograde transvenous obliteration (B-RTO) has shown great potential in controlling acute gastric variceal hemorrhage, although rebleeding related to the procedure may occur in a small percentage of patients. The purpose of this study was to identify risk factors of perioperative rebleeding and prognostic factors of postoperative survival in B-RTO performed for acute episodes of gastric variceal hemorrhage. We retrospectively analyzed 39 consecutive patients who underwent B-RTO for gastric variceal rupture at our hospital between June 2003 and May 2011. Uni- and multi-variate analyses were performed to assess risk factors for perioperative rebleeding and prognostic factors for postoperative survival. Surgical success and complete eradication of varices were achieved in 36 cases (92.3 %) and 35 cases (89.7 %), respectively. Six patients experienced rebleeding either intraoperatively (n = 3) or within 1 h after B-RTO (n = 3). Child-Pugh class C was identified as a risk factor for rebleeding on univariate (P = 0.018) and multivariate analyses (odds ratio, 6.003; P = 0.014). With a median follow-up of 23 months (range 0-106.6 months), overall survival rates at 1, 3, and 5 years were 91.7, 74.7, and 67.2 %, respectively. Multivariate analyses revealed Child-Pugh class C as a prognostic factor for survival (relative risk, 4.014; P = 0.023). Although B-RTO is generally effective in the treatment of acute gastric variceal rupture, patients classified as Child-Pugh class C have a higher risk of perioperative rebleeding and shorter survival.
    CardioVascular and Interventional Radiology 01/2014; · 2.09 Impact Factor
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    ABSTRACT: Oxygen causes an increase in the longitudinal relaxation rate of tissues through its T1-shortening effect owing to its paramagnetic properties. Due to such effects, MRI has been used to study oxygen-related signal intensity changes in various body parts including cerebrospinal fluid (CSF) space. Oxygen enhancement of CSF has been mainly studied using MRI sequences with relatively longer time resolution such as FLAIR, and T1 value calculation. In this study, fifteen healthy volunteers were scanned using fast advanced spin echo MRI sequence with and without inversion recovery pulse in order to dynamically track oxygen enhancement of CSF. We also focused on the differences of oxygen enhancement at sulcal and ventricular CSF. Our results revealed that CSF signal after administration of oxygen shows rapid signal increase in both sulcal CSF and ventricular CSF on both sequences, with statistically significant predominant increase in sulcal CSF compared with ventricular CSF. CSF is traditionally thought to mainly form from the choroid plexus in the ventricles and is absorbed at the arachnoid villi, however, it is also believed that cerebral arterioles contribute to the production and absorption of CSF, and controversy remains in terms of the precise mechanism. Our results demonstrated rapid oxygen enhancement in sulcal CSF, which may suggest inhaled oxygen may diffuse into sulcal CSF space rapidly probably due to the abundance of pial arterioles on the brain sulci.
    PLoS ONE 01/2014; 9(6):e100723. · 3.53 Impact Factor
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    ABSTRACT: To retrospectively evaluate risk factors for aggravation of esophageal varices (EV) within 1 year after balloon-occluded retrograde transvenous obliteration (B-RTO) of gastric varices (GV) and to clarify suitable timing for upper endoscopy to detect EV aggravation after B-RTO. Participants included 67 patients who underwent B-RTO for GV between January 2006 and December 2010. Whether EV aggravation occurred within 1 year was evaluated, and the time interval from B-RTO to aggravation was calculated. Factors potentially associated with EV aggravation were analyzed. B-RTO was successfully performed in all patients. EV aggravation at 1 year after B-RTO was found in 38 patients (56.7 %). Multivariate logistic regression analysis showed that total bilirubin (T-bil) (P = 0.032) and hepatic venous pressure gradient (HVPG) (P = 0.011) were significant independent risk factors for EV aggravation after B-RTO. Cutoff values of T-bil and HVPG yielding maximal combined sensitivity and specificity for EV aggravation were 1.6 mg/dL and 13 mmHg, respectively. The patients with T-bil ≥ 1.6 mg/dL or HVPG ≥ 13 mmHg had a median aggravation time of 5.1 months. All five patients with ruptured EV belonged to this group. In contrast, patients with T-bil < 1.6 mg/dL and HVPG < 13 mmHg had a median aggravation time of 21 months. T-bil and HVPG were significant independent risk factors for EV aggravation after B-RTO. The patients with T-bil ≥ 1.6 mg/dL or HVPG ≥ 13 mmHg require careful follow-up evaluation, including endoscopy.
    CardioVascular and Interventional Radiology 12/2013; · 2.09 Impact Factor
  • Radiological Society of North America 2013, Chicago, USA; 12/2013
  • Radiological Society of North America 2013, Chicago, USA; 12/2013
  • Radiological Society of North America 2013, Chicago, USA; 12/2013
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    ABSTRACT: PURPOSE/AIM To review basic concepts of SWI and discuss the origins of low signal on SWI with emphasis on the importance of the underlying high-pass filtered phase images in differentiating hemorrhage from other causes of low signal. CONTENT ORGANIZATION 1. Basic concepts of SWI T2*WI vs SWI, magnitude and high-pass filtered phase images, minIP SWI images, QSM 2. Clinical image examples of SWI Tumors, Vascular diseases, Degenerative diseases, Inflammatory and infectious diseases 3. Low signal on SWI Diamagnetic vs. paramagnetic causes 4. Methods to differentiate low signal High-pass filtered phase images can differentiate between diamagnetic vs. paramagnetic substances 5. Pitfalls of SWI: Susceptibility artifacts, Orientation within main magnetic field, chemical shift artfiacts SUMMARY The major teaching points of this exhibit are: 1. To offer an easy to understand explanation of SWI basic concepts 2. To shed a spotlight on causes of low signal on SWI other than hemorrhage 3. To offer an easy to use method to differentiate between possible causes of low signal on SWI based on high-pass filtered phase image contrast with no further post processing.
    Radiological Society of North America (RSNA) 2013, Chicago, USA; 12/2013
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    ABSTRACT: Purpose: We investigated the ability to detect the articular disk and joint effusion of the temporomandibular joint (TMJ) of a method of dual echo volumetric isotropic turbo spin echo acquisition (DE-VISTA) additional fusion images (AFI). Methods: DE-VISTA was performed in the 26 TMJ of 13 volunteers and 26 TMJ of 13 patients. Two-dimensional (2D) dual echo turbo spin echo was performed in the 26 TMJ of 13 volunteers. On a workstation, we added proton density-weighted images (PDWI) and T2 weighted images (T2WI) of the DE-VISTA per voxel to reconstruct DE-VISTA-AFI. Two radiologists reviewed these images visually and quantitatively. Results: Visual evaluation of the articular disk was equivalent between DE-VISTA-AFI and 2D-PDWI. The sliding thin-slab multiplanar reformation (MPR) method of DE-VISTA-AFI could detect all articular disks. The ratio of contrast (CR) of adipose tissue by the articular disk to that of the articular disk itself was significantly higher in DE-VISTA-AFI than DE-VISTA-PDWI (P<0.05) in patients and volunteers with closed or open mouth. In volunteers, the CR between adipose tissue and the disk on DE-VISTA-AFI was marginally significant to that on 2D-PDWI at opened mouth (P=0.071) and not significantly different (P=0.18) from that at closed mouth. Joint effusion could be identified in DE-VISTA-AFI in all 8 joints that had joint effusion in DE-VISTA-T2WI but in only 3 of those joints in 2D-T2WI. The CR of joint effusion to adipose tissue on DE-VISTA-AFI did not differ significantly from that on DE-VISTA-PDWI. However, using DE-VISTA-T2WI in addition to DE-VISTA-PDWI, we could visually identify joint effusion on DE-VISTA-AFI that could not be identified on DE-VISTA-PDWI alone. Conclusion: DE-VISTA-AFI can depict the articular disk and a small amount of joint effusion by the required plane of MPR using the sliding thin-slab MPR method.
    Magnetic Resonance in Medical Sciences 10/2013; · 0.75 Impact Factor
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    ABSTRACT: To quantitatively compare the diagnostic capability of double inversion-recovery (DIR) with F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) for detection of seizure focus laterality in temporal lobe epilepsy (TLE). This study was approved by the institutional review board, and written informed consent was obtained. Fifteen patients with TLE and 38 healthy volunteers were enrolled. All magnetic resonance (MR) images were acquired using a 3T-MRI system. Voxel-based analysis (VBA) was conducted for FDG-PET images and white matter segments of DIR images (DIR-WM) focused on the whole temporal lobe (TL) and the anterior part of the temporal lobe (ATL). Distribution of hypometabolic areas on FDG-PET and increased signal intensity areas on DIR-WM were evaluated, and their laterality was compared with clinically determined seizure focus laterality. Correct diagnostic rates of laterality were evaluated, and agreement between DIR-WM and FDG-PET was assessed using κ statistics. Increased signal intensity areas on DIR-WM were located at the vicinity of the hypometabolic areas on FDG-PET, especially in the ATL. Correct diagnostic rates of seizure focus laterality for DIR-WM (0.80 and 0.67 for the TL and the ATL, respectively) were slightly higher than those for FDG-PET (0.67 and 0.60 for the TL and the ATL, respectively). Agreement of laterality between DIR-WM and FDG-PET was substantial for the TL and almost perfect for the ATL (κ = 0.67 and 0.86, respectively). High agreement in localization between DIR-WM and FDG-PET and nearly equivalent detectability of them show us an additional role of MRI in TLE.
    Epilepsia 10/2013; · 3.96 Impact Factor
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    ABSTRACT: OBJECTIVE. In a clinical setting, lipoma can sometime show low signal intensity on susceptibility-weighted imaging (SWI) mimicking hemorrhage. The purpose of this study was to evaluate the fat-water interface chemical-shift artifacts between SWI and T2*-weighted imaging with a phantom study and evaluate SWI in lipoma cases. MATERIALS AND METHODS. SWI, magnitude, high-pass filtered phase, and T2*-weighted imaging of a lard-water phantom were evaluated in the in-phase, out-of phase, and standard partially out-of-phase TE settings used for clinical 3-T SWI (19.7, 20.9, and 20.0 ms, respectively) to identify the most prominent fat-water interface low signal. SWI of five cases of CNS lipoma were retrospectively evaluated by two neuroradiologists. RESULTS. TE at 19.7 ms (in-phase) showed the minimum fat-water interface low signal in the phase-encoding direction on magnitude, high-pass filtered phase, and SWI. TE at 20.9 ms (out-of-phase) showed the maximum fat-water interface in the phase-encoding direction on magnitude, high-pass filtered phase, and SWI. TE at 20.0 ms (partially out-of-phase) showed more fat-water interface low signal on SWI than on T2*-weighted imaging, especially in the phase-encoding direction. All lipomas in the five patients showed high signal intensity with surrounding peripheral dark rim on SWI. CONCLUSION. Fat-water interface is more prominent on the standard TE setting used for clinical SWI (20.0 ms) than that of T2*-weighted imaging and shows a characteristic surrounding peripheral low-signal-intensity rim in lipoma. Knowing the fat-water appearance on SWI is important to avoid misinterpreting intracranial lipomas as hemorrhages.
    American Journal of Roentgenology 10/2013; 201(4):902-7. · 2.90 Impact Factor

Publication Stats

543 Citations
175.65 Total Impact Points


  • 2005–2014
    • Osaka City University
      • • Department of Radiology
      • • Graduate School of Medicine
      Ōsaka, Ōsaka, Japan
    • Kinki University
      • Department of Radiology
      Ōsaka-shi, Osaka-fu, Japan
  • 2004–2013
    • Kyoto University
      • • Department of Diagnostic Imaging and Nuclear Medicine
      • • Graduate School of Medicine / Faculty of Medicine
      Kyoto, Kyoto-fu, Japan
  • 2009
    • Kyoto City Hospital
      Kioto, Kyōto, Japan