Tsukasa Doi

Osaka University, Suika, Ōsaka, Japan

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Publications (11)0 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To improve magnetic resonance (MR) safety, we surveyed the accidents caused by large ferromagnetic materials brought into MR systems accidentally. We sent a questionnaire to 700 Japanese medical institutions and received 405 valid responses (58%). A total of 97 accidents in 77 institutions were observed and we analyzed them regarding incidental rate, the detail situation and environmental factors. The mean accident rate of each institute was 0.7/100,000 examinations, which was widely distributed (0-25.6/100,000) depending on the institute. In this survey, relatively small institutes with less than 500 beds tend to have these accidents more frequently (p<0.01). The institutes in which daily MR examination counts are more than 10 patients have fewer accidents than those with less than 10 daily examinations. The institutes with 6-10 MR examinations daily have significantly more accidents than that with more than 10 daily MR examinations (p<0.01). The main mental factors of the accidents were considered to be "prejudice" and "carelessness" but some advocate "ignorance." Though we could not find significant reduction in the institutes that have lectures and training for MR safety, we should continue lectures and training for MR safety to reduce accidents due to "ignorance."
    Nippon Hoshasen Gijutsu Gakkai zasshi 01/2013; 69(1):99-108.
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    ABSTRACT: Using a questionnaire, we surveyed 2,500 facilities in Japan to clarify medical accidents concerning the magnetic resonance device and its environment. Data derived from 1,319 valid responses (52.8%), allowed us to analyze the situation of (or the reason for) the occurrence of the accidents and their environmental factors. Five hundred and nine facilities (39% of all facilities) had the experience of magnetically induced displacement of the large ferromagnetic material. Intravenous (I.V.) drip stands were involved the largest number of them: 31% (228 cases). Oxygen bottles had the second largest number of incidents: 20%. There were also many incidents involving various materials brought in by non-medical staff (e.g. stepladder for construction). About 20% of the accidents occurred outside of working hours. Patients in 12% of the facilities (154 facilities) experienced burns. In 39 of the cases, burns were received to the inside of the thighs. In 38 of the cases, patients received burns from an electrical cable touching the skin. There were also frequent incidents of burning regarding the boa. We received reports of burns and pain from the halo vest even though it's required to be worn for MR safety. Regarding incidents of contraindications, 280 patients with pacemakers were brought into the magnetic resonance (MR) inspection room. Twelve percent of the facilities experienced natural quench. Lack of training for the staff who introduce and operate high magnetic field devices are considered involving frequently occurring accidents of attractions and burns at hospitals with over 500 beds caused by carrying in materials.
    Nippon Hoshasen Gijutsu Gakkai zasshi 01/2011; 67(8):895-904.
  • Nippon Hoshasen Gijutsu Gakkai zasshi 01/2011; 67(9):1217-36.
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    ABSTRACT: Diffusion weighted imaging (DWI) is now widely used in magnetic resonance (MR) imaging of the head and body. Moreover, the Apparent diffusion coefficient (ADC) value is often used for the differential diagnosis of the tumor. However, the effect of the surroundings on the ADC value has not been reported. In this study, we used the phantom completely sealed up to measure the change in the ADC value depending on the surroundings material. The results showed that the ADC value decreased according to the density of superparamagnetic iron oxide (SPIO) in the surroundings. Clinically, hemorrhage or iron deposit around the tumor may affect the ADC value of the tumor and result in under-estimation.
    Nippon Hoshasen Gijutsu Gakkai zasshi 10/2010; 66(10):1267-74.
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    ABSTRACT: The apparent diffusion coefficient (ADC) values are calculated by using signal intensity in diffusion-weighted images (DWIs) with two or more different b-value. Therefore, the signal to noise ratio (SNR) of DWI with higher b-value may have a big influence on the measured ADC value. We examined the influence of the imaging parameters on the calculated ADC values. The SNR of DWI increased by using a larger voxel size, by means of a decreased number of matrix, an increased slice thickness, and an increased field of view (FOV). However, when the number of excitations was increased to improve the SNR of DWI, the signal intensity of background noise was observed to be slightly increased. It was suggested that the consistency of measured ADC was not preserved when the signal of the DWIs with higher b-value dropped close to the noise level.
    Nippon Hoshasen Gijutsu Gakkai zasshi 09/2010; 66(9):1178-85.
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    ABSTRACT: The definitional equation of the distortion of echo planar imaging(EPI)was examined. We compared measured values with calculated values by using the definitional equation of the chemical shift of the EPI method that first composed the diffusion-weighted image, and examined the possibility of applying it to the distortion. The results showed that the chemical shift with the definitional equation and the measurement corresponded, and the correlation between the chemical shift and the distortion was acquired. Next, the distortion of each images that composed DWI with the increase and the sign acceptable method difference of b value. The difference in the distortion between each image has increased with the increase in b value. It was assumed that the influence of the eddy currents was due to the high motion probing gradient.
    Nippon Hoshasen Gijutsu Gakkai zasshi 11/2009; 65(11):1494-501.
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    ABSTRACT: When measuring the signal-to-noise ratio (SNR) of an image the used parallel magnetic resonance imaging, it was confirmed that there was a problem in the application of past SNR measurement. With the method of measuring the noise from the background signal, SNR with parallel imaging was higher than that without parallel imaging. In the subtraction method (NEMA standard), which sets a wide region of interest, the white noise was not evaluated correctly although SNR was close to the theoretical value. We proposed two techniques because SNR in parallel imaging was not uniform according to inhomogeneity of the coil sensitivity distribution and geometry factor. Using the first method (subtraction mapping), two images were scanned with identical parameters. The SNR in each pixel divided the running mean (7 by 7 pixels in neighborhood) by standard deviation/radical2 in the same region of interest. Using the second (consecutive) method, more than fifty consecutive scans of the uniform phantom were obtained with identical scan parameters. Then the SNR was calculated from the ratio of mean signal intensity to the standard deviation in each pixel on a series of images. Moreover, geometry factors were calculated from SNRs with and without parallel imaging. The SNR and geometry factor using parallel imaging in the subtraction mapping method agreed with those of the consecutive method. Both methods make it possible to obtain a more detailed determination of SNR in parallel imaging and to calculate the geometry factor.
    Nippon Hoshasen Gijutsu Gakkai zasshi 09/2008; 64(8):930-6.
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    ABSTRACT: Parallel magnetic resonance imaging (MRI) with arrays of receiver coils such as those of sensitivity encoding (SENSE) are being widely used. However, conventional methods of image signal-to-noise ratio (SNR) determination cannot be used for parallel MRI, and a novel method has been reported in JSRT. However, this method of SNR determination is for phantom images not for clinical images. Therefore, we researched accurate measurement of the image noise of parallel MRI reconstruction including the unfolding process and uniformity filters. The possibility of a subtraction method using clinical images and the accuracy of standard deviation (SD) of clinical images for optimum ROI were studied because it was not possible to use the air-signal method. The results indicated that the position of the ROI was selected for uniformity of signal intensity area and that the size of the ROI was about 50 pixels. However, under these conditions, the noise value of SNR was higher than that using the phantom-subtraction method. In addition, the tissue-subtraction method was useful when the two scanning images were in agreement.
    Nippon Hoshasen Gijutsu Gakkai zasshi 10/2007; 63(9):1099-104.
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    ABSTRACT: We devised two kinds of new methods for accurate measurement of the image signal-to-noise ratio (SNR) in parallel magnetic resonance imaging (MRI) because image noise of the parallel MRI was not spatially constant. Using the first (Consecutive) method, more than fifty consecutive scans of the uniform phantom were obtained with identical scan parameters. Then the SNRs in each pixel were calculated from the ratio of mean signal intensity to the standard deviation of the time domain on a pixel-by-pixel. With the second (Remove) method, the phantom was removed after the first scan, and the second scan was done with identical parameters and the RF coil loading device. The SNRs in each pixel were then obtained from the ratio of the signal intensity of the first scan to the second scan (w/o phantom) image which was multiplied by the square root of 2/pi and filtered by the running mean (7 by 7 pixels). Moreover, actual geometry factors were calculated from image SNRs of parallel and no parallel MRI. The image SNR and actual geometry factor of parallel MRI with the Consecutive method agreed with that of the Remove method. The SNRs of the no parallel MRI with the above two methods conformed with that of the conventional SNR method (NEMA standard). Both new methods make it possible to obtain a more detailed determination of SNR in parallel MRI, and to calculate the actual geometry factor.
    Proc SPIE 03/2006;
  • Nippon Hoshasen Gijutsu Gakkai zasshi 02/2006; 62(1):145-8.
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    ABSTRACT: PURPOSE/AIM purpose of Aim of the exhibit 1. To review precision of the apparent diffusion coefficient (ADC) value in magnetic resonance imaging. 2. To identify whether the same ADC value can be obtained in certain scanning parameter ranges for different system units and different field strengths. 3. To develop a method for obtaining highly precise ADC values. CONTENT ORGANIZATION 1. A phantom study of different scanning parameters (e.g., TR, TE, b-value, FOV, slice thickness) considering different field strengths and system units of different vendors. 2. Study of the human brain using different scanning parameters for different field strengths and system units of different vendors. 3. Comparison of the coefficient of variation in ADCs under various scanning conditions. SUMMARY The major teaching points of this exhibit are: The ADC values are affected by a low signal-to-noise ratio in the diffusion weighted images. In addition, the averaging time was not effective in improving the precision of the ADC values. Therefore, for obtaining high precision ADC value, FOV and slice thickness must be increased instead of increasing the averaging time. The certain ranges included TR > 2000ms, shortest TE, same b-values, and sufficient SNR.
    Radiological Society of North America 2013 Scientific Assembly and Annual Meeting;

Publication Stats

12 Citations


  • 2011
    • Osaka University
      Suika, Ōsaka, Japan
  • 2007
    • Kyoto City Hospital
      Kioto, Kyōto, Japan
  • 2006
    • Kanazawa University
      • Graduate School of Medical Sciences
      Kanazawa, Ishikawa, Japan