Asako Yamamoto

Teikyo University, Edo, Tokyo, Japan

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Publications (9)13.28 Total impact

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    [Show abstract] [Hide abstract] ABSTRACT: IntroductionPatients with disorders such as acetabular dysplasia or femoroacetabular impingement are at risk of developing hip osteoarthritis. Assessment of the cartilage and labrum in the hip joint based on magnetic resonance imaging (MRI) has been challenging because of the low signal-to-noise ratio (SNR) due to its deep location, ball and socket structure, and small volume of those structures compared with the whole joint size. To achieve better imaging assessment, direct MR arthrography (d-MRA) [1] and other techniques such as T2* mapping [2], T2 mapping [3], T1rho [4], and delayed gadolinium-enhanced MRI (dGEMRIC) [5] have been developed along with the increasing use of high-field MRI. In patients with no apparent osteoarthritic changes such as joint space narrowing or osteophyte and subchondral cyst formation on radiographs, these techniques can detect early cartilage or labral damage [6].A recently developed semiquantitative MRI-based scoring system for hip osteoarthritis [7] in ...
    Preview · Article · Jan 2015 · Skeletal Radiology
  • Asako Yamamoto · Hiroshi Oba · Shigeru Furui
    [Show abstract] [Hide abstract] ABSTRACT: Purpose: To elucidate the influence of age and sex on the signal intensity (SI) of the posterior lobe of the pituitary gland (PPG) on T1-weighted images (T1WI) from 3 T MRI. Materials and methods: Sagittal T1WI acquired from three-dimensional fast spoiled gradient recalled acquisition in the steady state in 1,634 subjects without conditions affecting antidiuretic hormone were evaluated retrospectively. The presence or absence of a bright signal in the PPG was assessed qualitatively. The SI ratio of the PPG to the pons (SIR) was obtained from quantitative measurements. We statistically analyzed these data, creating 14 subject groups categorized according to age and sex, and applied a Poisson generalized linear model to the SIR data. Results: The characteristic bright signal was absent in 47 subjects (2.8 %), with no significant difference in incidence among the groups. The SIR was inversely related to age in both males (r > 0.7) and females (r > 0.9), and was significantly higher in females in the third to the eighth decades (p < 0.05). Analysis of the whole SIR dataset using a generalized linear model showed that the estimated SIR decreased by 1.7 % per decade and is higher in females. Conclusion: Age and sex influence the SI of the PPG on T1WI. These findings may aid the recognition of PPG signal abnormalities on T1WI.
    No preview · Article · Dec 2012 · Japanese journal of radiology
  • [Show abstract] [Hide abstract] ABSTRACT: Collagenous fibroma, also known as desmoplastic fibroblastoma, is a benign fibrous soft tissue tumor showing gradual growth, commonly without aggressive local infiltration. Today, preoperative radiological diagnosis is important to avoid over-treatment and unnecessary extensive procedures, but is difficult because diagnostic imaging findings for collagenous fibroma have not been established. We report MR imaging findings of three collagenous fibromas in correlation with their histopathology. The characteristic rim enhancement on post-contrast T1-weighted images with fat suppression was present in all three cases, and we consider this to represent the difference in vascularity between the outer capsule-like fibrous tissue and the inside of the tumor.
    No preview · Article · Jul 2012 · Skeletal Radiology
  • [Show abstract] [Hide abstract] ABSTRACT: Proteus syndrome is a rare, sporadic, hamartomatous disorder manifesting with multifocal overgrowth of tissue. The features seem to develop most often during childhood. Vertebral overgrowth with severe spinal canal stenosis is unusual, although scoliosis with abnormal vertebral bodies is one of the typical features of Proteus syndrome. We report a case of Proteus syndrome with severe spinal canal stenosis, scoliosis, cervical kyphosis, and thoracic deformity with airway obstruction because of asymmetrical overgrowth of vertebrae and ribs associated with a tethered cord, lipomas, strawberry hemangioma, flat nasal bridge, and bilateral hypoplasty of the first metatarsal bones with hyperplasty of soft tissue.
    No preview · Article · Jan 2012 · Japanese journal of radiology
  • [Show abstract] [Hide abstract] ABSTRACT: Chondromyxoid fibroma (CMF) of the rib is exceedingly unusual and few detailed image findings have been reported. Plain radiograph, computed tomography (CT), and magnetic resonance (MR) imaging findings and pathological aspects of a case of CMF of the right 2nd rib in a 15-year-old woman are reported, which was difficult to diagnose preoperatively. Though it is challenging to diagnose CMF preoperatively, it is important to be aware that CMF can exhibit atypical prominent exophytic features in unexpected locations such as the ribs.
    No preview · Article · Dec 2011 · Japanese journal of radiology
  • No preview · Article · Jul 2011 · Journal of Orthopaedic Science
  • [Show abstract] [Hide abstract] ABSTRACT: The purpose of this study was to evaluate the effective dose during abdominal three-dimensional (3D) imaging on phantoms and estimate the dose-area product (DAP) for effective dose conversion factors for three types of angiographic units. Three-dimensional imaging was performed for three sizes (small, medium, large) of human-shaped phantoms using three types of angiographic units (Allura Xper FD20/10, INNOVA 4100, AXIOM Artis dTA). We calculated 25 organ doses and effective doses using Monte Carlo technique for the three phantoms with a program for a personal computer. As benchmark studies to back up the results by Monte Carlo technique, we measured the organ doses directly on the small phantom using radiophotoluminescent glass dosimeters. The DAP value increased as the phantom size increased. The organ doses and the effective doses during the 3D imaging increased as the phantom size increased. The effective doses for the small phantom by Monte Carlo technique were 1.9, 2.2, and 2.1 mSv for the Allura Xper FD20/10, INNOVA 4100, and AXIOM Artis dTA, respectively, while those by direct measurement were 1.6, 2.0, and 2.6 mSv. The effective doses to DAP ratios by Monte Carlo technique were 0.37-0.45, 0.26-0.32, and 0.13-0.15 (mSv Gy⁻¹ cm⁻²) for the Allura Xper FD20/10, INNOVA 4100, and AXIOM Artis dTA, respectively. In conclusion, the effective doses during 3D imaging and the dose-to-DAP ratios differ among angiographic units, and the effective dose can be estimated using a proper conversion factor for each angiographic unit.
    No preview · Article · Apr 2011 · CardioVascular and Interventional Radiology
  • [Show abstract] [Hide abstract] ABSTRACT: To evaluate the precision and accuracy in CT attenuation measurement of vascular wall using region-of-interest (ROI) supported by differentiation curves. We used vascular models (actual attenuation value of the wall: 87HU) with wall thicknesses of 1.5, 1.0, or 0.5mm, filled with contrast material of 250, 348, or 436HU. The nine vascular models were scanned with a 64-detector CT. The wall attenuation values were measured using three sizes (diameter: 0.5, 1.0, and 1.5mm) of ROIs without differentiation curves. Sixteen measurements were repeated for each vascular model by each of two operators. Measurements supported by differentiation curves were also performed. We used analyses of variance with repeated measures for the measured attenuations for each size of the ROI. Without differentiation curves, there were significant differences in the attenuation values of the wall among the three densities of contrast material, and the attenuation values tended to be overestimated more as the contrast material density increased. Operator dependencies were also found in measurements for 0.5- and 1.5-mm thickness models. With differentiation curves, measurements were not possible for 0.5- and 1.0-mm thickness models. Using differentiation curves for 1.5-mm thickness models with a ROI of 1.0- or 1.5-mm diameter, the wall attenuations were not affected by the contrast material densities and were operator independent, measuring between 75 and 103HU. The use of differentiation curves can improve the precision and accuracy in wall attenuation measurement using a ROI technique, while measurements for walls of ≤1.0mm thickness are difficult.
    No preview · Article · Feb 2011 · European journal of radiology
  • [Show abstract] [Hide abstract] ABSTRACT: To evaluate the skin dose during cerebral CT perfusion on a phantom, and estimate the weighted CT dose index (CTDIw) to maximum skin dose conversion factors for four types of CT scanners. We evaluated the relationship between surface dose during cerebral CT perfusion and distance from the scan center in the x-y plane using a 64-multidetector row CT scanner. Skin doses were also assessed with 4 different 64-multidetector CT scanners. The surface doses decreased with the distance from the scan center in the x-y plane. The surface doses at the points 6 cm and 10 cm from the scan center in the x-y plane were different from the dose at the point 8 cm by about 15%. CTDIw and skin doses differed among the CT scanners (CTDIw, 143-590 mGy; averaged temporal skin dose, 126-590 mGy). For all the four types of CT scanner, the doses increased in the following order: occipital point<frontal point<temporal points. The ratios of the maximum skin dose (averaged temporal skin dose) to CTDIw differed among the CT scanners (64-100%). The maximum skin dose during cerebral CT perfusion and the dose to CTDIw ratios differs among CT scanners. The CTDIw is useful for estimation of the maximum skin dose during cerebral CT perfusion using a proper conversion factor specific to each type of CT scanner.
    No preview · Article · Oct 2010 · European journal of radiology