Japanese Journal of Radiological Technology
Online ISSN : 1881-4883
Print ISSN : 0369-4305
ISSN-L : 0369-4305
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Volume 64, Issue 8
Displaying 1-15 of 15 articles from this issue
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Opening Article
Oliginal
  • Necessity of Delivering the Calibration Coefficient of a Dosimeter for Low Energy X-rays Used in Mammography X-ray Units
    Chihiro Matsuo, Masayuki Tachibana, Tsutomu Akasaka
    2008 Volume 64 Issue 8 Pages 915-921
    Published: August 20, 2008
    Released on J-STAGE: September 05, 2008
    DOIhttps://doi.org/10.6009/jjrt.64.915
    JOURNAL FREE ACCESS
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    The calibration coefficient currently supplied by the National Institute of Advanced Industrial Science and Technology (AIST) is measured with an X-ray unit equipped with a W target/Al filter. We compared the calibration coefficient, which is measured with the X-ray unit equipped with a W target/Al filter and the X-ray unit for mammography. For the calibration coefficient, which is measured at the calibration fields of the X-ray units for mammography, the difference in the calibration coefficient measured with the X-ray unit equipped with a W target/Al filter that assumed a difference in the quality index-value of less than 1.5% was 24.2% at the maximum. In addition, many differences of more than unsureness 5% of the calibration coefficient were accepted. Thus, the correct dosimetry is not being performed for mammography. To improve the precision of dosimetry for mammography, at least, it is desirable to employ the calibration coefficient using the Mo target supplied by AIST. Furthermore, the indication of quality of radiation should be made severe, too. To perform equal dosimetry with a diagnosis domain, it is necessary to supply the calibration coefficient of the other target/filters.
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  • Trial Manufacture of a Plunger Shield for a Disposable Plastic Syringe
    Shigeki Murakami, Takashi Emoto, Hiroshige Mori, Katsuhisa Fujita, Nao ...
    2008 Volume 64 Issue 8 Pages 922-929
    Published: August 20, 2008
    Released on J-STAGE: September 05, 2008
    DOIhttps://doi.org/10.6009/jjrt.64.922
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    A syringe-type radiopharmaceutical being supplied by a manufacturer has a syringe shield and a plunger shield, whereas an in-hospital labeling radiopharmaceutical is administered by a disposable plastic syringe without the plunger shield. In cooperation with Nihon Medi-Physics Co. Ltd., we have produced a new experimental plunger shield for the disposable plastic syringe. In order to evaluate this shielding effect, we compared the leaked radiation doses of our plunger shield with those of the syringe-type radiopharmaceutical (Medi shield type). Our plunger shield has a lead plate of 21 mm in diameter and 3 mm thick. This shield is equipped with the plunger-end of a disposal plastic syringe. We sealed 99mTc solution into a plastic syringe (Terumo Co.) of 5 ml with our plunger shield and Medi shield type of 2 ml. We measured leaked radiation doses around syringes using fluorescent glass dosimeters (Dose Ace). The number of measure points was 18. The measured doses were converted to 70 μm dose equivalent at 740 MBq of radioactivity. The results of our plunger shield and the Medi shield type were as follows: 4–13 μSv/h and 3–14 μSv/h at shielding areas, 3–545 μSv/h and 6–97 μSv/h at non-shielding areas, 42–116 μSv/h and 88–165 μSv/h in the vicinity of the syringe shield, and 1071 μSv/h and 1243 μSv/h at the front of the needle. For dose rates of shielding areas around the syringe, the shielding effects were approximately the same as those of the Medi shield type. In conclusion, our plunger shield may be useful for reducing finger exposure during the injection of an in-hospital labeled radiopharmaceutical.
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  • Signal-to-noise Ratio Measurement in Parallel MRI with Subtraction Mapping and Consecutive Methods
    Hiroshi Imai, Tosiaki Miyati, Akio Ogura, Tsukasa Doi, Toshio Tsuchiha ...
    2008 Volume 64 Issue 8 Pages 930-936
    Published: August 20, 2008
    Released on J-STAGE: September 05, 2008
    DOIhttps://doi.org/10.6009/jjrt.64.930
    JOURNAL FREE ACCESS
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    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/√2 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.
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  • Preliminary Survey for Communicating Risk in Medical Exposure–Perception of Risk among Nurses Working in Radiology–
    Reiko Kanda, Satsuki Tsuji, Yoshiyuki Shirakawa, Hidenori Yonehara
    2008 Volume 64 Issue 8 Pages 937-947
    Published: August 20, 2008
    Released on J-STAGE: September 05, 2008
    DOIhttps://doi.org/10.6009/jjrt.64.937
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    A questionnaire survey was conducted on radiation risk and medical exposure, particularly in applications involving children. The survey was targeted at nurses (170 females) engaged in important roles in communicating risk regarding medical exposure. The questionnaire survey yielded the following findings. 1) A significant number of respondents associated the word “radiation” with “cancer treatment,” “exposure,” and “X-ray pictures.” Perceptions about “food exposure” differed between respondents with children and those without. 2) Among the potential health problems posed by radiation, “effects on children,” “cancer and leukemia,” and “genetic effects” were perceived as the most worrisome. Significant differences in perception were noted regarding infertility between respondents with children and those without. 3) Concerning the effects of medical exposure on fetuses/children, only 10 percent of all respondents replied that they were not anxious about negative effects in either case. Among the respondents who felt uneasy about these aspects, most tended to assess exposed parts, doses, damage potentially suffered, timing of occurrence, and uncertainty, based on their professional experience and knowledge, to rationally distinguish acceptable risks from unacceptable ones and to limit concern to the unacceptable aspects.
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  • Examination of Axial Zygomatic Arch Radiographs Using the Bisector Method
    Nobuhiro Yada, Koji Uchida, Akiko Nagami, Kanae Itakura, Akihiko Matsu ...
    2008 Volume 64 Issue 8 Pages 948-954
    Published: August 20, 2008
    Released on J-STAGE: September 05, 2008
    DOIhttps://doi.org/10.6009/jjrt.64.948
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    An axial radiograph of the zygomatic arch is taken in cases of patients with facial traumatic injury. Maintaining the patient’s head in the retroflex position to take such axial radiographs is sometimes difficult because of medical conditions. In addition, since different positioning techniques for retroflexion are used by radiological technologists, the visibility of the zygomatic arch was poorly in reproduced. We contrived a novel technique for use in taking a zygomatic arch radiograph. We call it the “bisector method,” and it does not require the retroflex position. We can take a zygomatic arch radiograph equal in quality to conventional axial radiographs (retroflex position) by exposing X-rays perpendicularly to the bisector of the angle between the casette and the zygomatic arch. This bisector method is relatively easy in that it does not require either the retroflex position or the expertise of a radiological technologist.
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  • Optimized Control of X-ray Exposure and Image Noise Using a Particular Multislice CT Scanner
    Shuji Yamamoto, Yoshihiro Koyama, Masahiro Suzuki, Hirofumi Nagasawa, ...
    2008 Volume 64 Issue 8 Pages 955-959
    Published: August 20, 2008
    Released on J-STAGE: September 05, 2008
    DOIhttps://doi.org/10.6009/jjrt.64.955
    JOURNAL FREE ACCESS
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    Patient dose reduction in computed tomography (CT) always results in a trade off between radiation exposure and image quality. There are few reports that estimate the relationship between image quality and X-ray exposure in CT examinations as one optimal index. The purpose of this study was to determine the optimal parameter settings enabling a low radiation exposure without compromising image quality using a particular 4-row multislice CT (MSCT) scanner (Aquilion VZ 4-slice CT scanner, Toshiba Medical Systems Corporation, Otawara, Tochigi, Japan). Normalized dose divided by image noise for helical pitches (nDNR: normalized dose to noise ratio) were calculated in consideration of beam collimation and tube current-time product. Optimal tube current-time product was calculated using the nDNR for the helical pitches based on user-defined standards of quality of the CT image. As a result, the nDNR proved to be well-supported to decrease the patient exposure in various exposure conditions of MSCT scans; however, the dose and image noise did not show a linear relation to the helical pitch. In conclusion, nDNR can be applied to patient dose reduction while keeping an acceptable image quality using a particular 4-row MSCT scanner.
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Note
  • Compensation for Influence on Image Deterioration Occurring Because of Gantry Inclination—Compensation of image quality obtained by a newly devised phantom—
    Ken Furuya, Kouji Nakamura, Makiko Onizuka, Rie Watanabe, Yuusuke Hase ...
    2008 Volume 64 Issue 8 Pages 960-970
    Published: August 20, 2008
    Released on J-STAGE: September 05, 2008
    DOIhttps://doi.org/10.6009/jjrt.64.960
    JOURNAL FREE ACCESS
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    The influence of gantry inclination on image quality was examined in the Y and Z directions and an increase in the volume of a scan part. FWHM (full width at half maximum) in the Y direction decreased at the rate of 2.53%, which was caused by leaving the center of the gantry, and spatial resolution was improved. FWHM (y) in the Z direction increased at a rate of y=2.4× (1/cosθ)+0.91 which was caused by an increase in the gantry angle of inclination, and spatial resolution was declined. The relation between FWHM (y) and pitch (x) was y=0.19x+3.12. The increase in FWHM caused by the increase in the gantry angle of inclination was revised with pitch from two formulae, and it became constant. Noise was corrected in the same way, and it became constant. The increase in the noise that occurs due to the increase in the volume of the body caused by the gantry tilt angle was corrected with the tube current, and applied to AEC (automatic exposure control). The influence of gantry inclination on image quality was adjusted, and image quality was improved.
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The 34th Autumn Scientific Congress
Educational Lecture—Interpreting Medical Images for Radiological Technologists
Basic Lectures—The Image Processing Technology that You Should Learn on Examination
Clinical Technology Cource
Scientific Committee Report
JIRA Topics
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