Japanese Journal of Radiological Technology
Online ISSN : 1881-4883
Print ISSN : 0369-4305
ISSN-L : 0369-4305
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Volume 69, Issue 5
Displaying 1-15 of 15 articles from this issue
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Opening Article
Originals
  • Evaluation of Absorbed Dose from Kilovoltage Cone-beam Computed Tomography by Radiotherapy Planning System: Influence on the Radiation Therapy for Prostate Cancer
    Tetsuro Kawamura, Naoki Murakami, Yoshiaki Okamura, Hideki Nishimura, ...
    2013 Volume 69 Issue 5 Pages 491-499
    Published: May 20, 2013
    Released on J-STAGE: May 24, 2013
    DOIhttps://doi.org/10.6009/jjrt.2013_JSRT_69.5.491
    JOURNAL FREE ACCESS
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    Image-guided radiation therapy (IGRT) is increasingly being used in modern radiation therapy, and it is now possible to verify a patient’s position using kilo-voltage cone-beam computed tomography (kV-CBCT). However, if kV-CBCT is used frequently, the dose absorbed by the body cannot be disregarded. A number of studies have been made on the absorbed dose of kV-CBCT, in which absorbed dose measurements were made using a computed tomography dose index (CTDI) or a thermoluminescent dosimeter (TLD). Other methods include comparison of the absorbed dose between a kV-CBCT and other modalities. These techniques are now in common use. However, dose distribution within the patient varies with the patient’s size, posture and the part of the body to which radiation therapy is applied. The chief purpose of this study was to evaluate the dose distribution of kV-CBCT by employing a radiotherapy planning system (RTPS); a secondary aim was to examine the influence of a dose of kV-CBCT radiation when used to treat prostate cancer. The beam data of an on-board imager (OBI) was registered in the RTPS, after which modeling was performed. The radiation dosimetry was arranged by the dosimeter in an elliptical phantom. Rotational radiation treatment was used to obtain the dose distribution of the kV-CBCT within the patient, and the patient dose was evaluated based on the simulation of the dose distribution. In radiation therapy for prostate cancer, if kV-CBCT was applied daily, the dose increment within the planning target volume (PTV) and the organ in question was about 1 Gy.
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  • Fabrication of a Visualization Equipment for Scattered X-rays in the Diagnosis Domain and Proposal of a Practical Training
    Mina Kishida, Hiroaki Hayashi, Tomomi Kuboyabu, Kazuki Takegami, Tadas ...
    2013 Volume 69 Issue 5 Pages 500-507
    Published: May 20, 2013
    Released on J-STAGE: May 24, 2013
    DOIhttps://doi.org/10.6009/jjrt.2013_JSRT_69.5.500
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    We have built equipment that can visualize the angle distributions of scattered X-rays. The main body of the equipment is made of a lead-shielded box 340 mm long, 300 mm wide and 270 mm high. The collimated X-rays are introduced into the equipment from the front face, then scattered by the sample located in the center of the equipment. The X-rays scattering toward the upper side are detected by the phosphor plate. To verify the usability of the equipment, an experiment using diagnostic X-rays was carried out. X-rays with a tube voltage of 100 kV were narrowed down to 6 mmφ and a 2 mm-thick acrylic sample was irradiated. The experimental conditions with a tube current-time product of 300 mAs to 1500 mAs proved appropriate for obtaining suitable images on a 10 inch×12 inch phosphor plate. The obtained images were analyzed using ImageJ. The experimental values were in good agreement with the theoretical distribution calculated by Klein and Nishina. Because the distribution of the scattered X-rays can be visualized in relatively simple experiments using the developed equipment, it is hoped that it will be of use for the practical training of beginners.
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Notes
  • Evaluation of the Individual Tube Current Setting in Electrocardiogram-gated Cardiac Computed Tomography Estimated from Plain Chest Computed Tomography Using Computed Tomography Automatic Exposure Control
    Junichi Kishimoto, Toshio Sakou, Yasutoshi Ohta
    2013 Volume 69 Issue 5 Pages 508-513
    Published: May 20, 2013
    Released on J-STAGE: May 24, 2013
    DOIhttps://doi.org/10.6009/jjrt.2013_JSRT_69.5.508
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    The aim of this study was to estimate the tube current on a cardiac computed tomography (CT) from a plain chest CT using CT-automatic exposure control (CT-AEC), to obtain consistent image noise, and to optimize the scan tube current by individualizing the tube current. Sixty-five patients (Group A) underwent cardiac CT at fixed tube current. The mAs value for plain chest CT using CT-AEC (AEC value) and cardiac CT image noise were measured. The tube current needed to obtain the intended level of image noise in the cardiac CT was determined from their correlation. Another 65 patients (Group B) underwent cardiac CT with tube currents individually determined from the AEC value. Image noise was compared among Group A and B. Image noise of cardiac CT in Group B was 24.4±3.1 HU and was more uniform than in Group A (21.2±6.1 HU). The error with the desired image noise of 25 HU was lower in Group B (2.4%) than in Group A (15.2%). Individualized tube current selection based on AEC value thus provided consistent image noise and a scan tube current optimized for cardiac CT.
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  • Trial for Power Spectrum Analysis in Various Injection Timing for Contrast Medium
    Yasuo Takatsu, Yasuyoshi Inoue, Tosiaki Miyati, Takayuki Nakatsuka
    2013 Volume 69 Issue 5 Pages 514-520
    Published: May 20, 2013
    Released on J-STAGE: May 24, 2013
    DOIhttps://doi.org/10.6009/jjrt.2013_JSRT_69.5.514
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    Frequency analysis is a method of measuring the spatial frequency component in images. We attempted to analyze and assess frequency analyses of images of various contrast medium injection timings using a normalized integral power spectrum. In magnetic resonance imaging, the k-space order was linear and sequential. During the twenty-second scanning time, we injected contrast medium at 3 ml/s and varied the duration of the injection from zero to four seconds, four to eight seconds, eight to twelve seconds, twelve to sixteen seconds, and sixteen to twenty seconds. We then analyzed the images. The rates of change and area values were calculated, and a dendrogram of area value by cluster analysis was made. The element of high frequency area’s power values rose when the contrast medium was in the high-frequency area, and the element of low frequency area’s power values rose when the contrast medium was in the low-frequency area. These data lines crossed at 0.092–0.115 cycles/mm. Five time durations were identified: these were a function of rate of change and area value. Frequency analysis of injection timing for contrast medium using the normalized integral power spectrum can thus be applied; this method can thus be employed as a method of examining injection timing for contrast medium and choosing a k-space order of optimization.
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  • Investigation of Radio Frequency Heating of Dental Implants Made of Titanium in 1.5 Tesla and 3.0 Tesla Magnetic Resonance Procedure: Measurement of the Temperature by Using Tissue-equivalent Phantom
    Takahiro Ideta, Masaru Yamazaki, Sadahiro Kudou, Mitsuji Higashida, Sh ...
    2013 Volume 69 Issue 5 Pages 521-528
    Published: May 20, 2013
    Released on J-STAGE: May 24, 2013
    DOIhttps://doi.org/10.6009/jjrt.2013_JSRT_69.5.521
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    Titanium (Ti) implants are increasingly being used for dental parts. There is no problem with the attraction of a static magnetic field for Ti in magnetic resonance imaging (MRI), since Ti is paramagnetic. However, there is a risk of radio frequency (RF) heat generation within Ti. 3.0 T-MRI scanners are becoming increasingly common. The specific absorption rate (SAR) of 3.0 T-MRI is quadruple that of SAR compared with 1.5 T-MRI due to its being proportional to the square of the strength of a static magnetic field. The effect of heat generation in 3.0 T-MRI can thus be greater than in 1.5 T-MRI. So, using 1.5 T and 3.0 T-MRI scanners, we measured the temperature of several Ti implants using the same scanning parameters during MRI scanning. Our measurements showed the rise in temperature of the Ti implants to be a maximum of 0.4°C. In this study, however, Ti in a human mouth was not directly measured, so we need to attempt to perform MRI carefully on patients with Ti implants.
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Clinical Technologies
  • Optimized Magnetic Resonance Sequences and Parameters with Operative Assisted Images for Radical Prostatectomy at 3 Tesla-Magnetic Resonance Image
    Ryuji Shirase, Yuuki Sakurai, Hiroshi Nagahama, Kuniaki Harada, Hiroyu ...
    2013 Volume 69 Issue 5 Pages 529-534
    Published: May 20, 2013
    Released on J-STAGE: May 24, 2013
    DOIhttps://doi.org/10.6009/jjrt.2013_JSRT_69.5.529
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    The objective of our study was to optimize magnetic resonance image (MRI) sequences and parameters using operative assisted images (three-dimensional images) for radical prostatectomy at 3 tesla (T) MRI. Five healthy volunteers underwent MRI on the 3.0 T scanner. Various sequences and parameters [Cube (TE/TR=18, 50, 90 ms/2000 ms), FIESTA (TE/TR/FA=2.4 ms/5 ms/40°, 90°), fSPGR (TE/TR/FA=2.3 ms/11.2 ms/20°), slice thickness=1.2 mm, matrix=192×160] were respectively compared. Several structures of the pelvis (the central zones and transition zones of the prostate, the peripheral zones of the prostate, seminal vesicles, rectum wall, bladder, muscle and fat) were determined. The signal intensities of these structures were measured on reformatted axial images and compared against several structures of the pelvis. Correlation with various sequences and parameters was based on the signal-to-noise ratio (SNR), the contrast ratio (CR) and the presence of artifacts. Student’s t-test was used for statistical analysis. With Cube (TE/TR=50 ms/2000 ms), the average value of visual evaluation with artifacts was high, and SNR and CR were higher than for other sequence and parameters. Optimized MRI sequences and parameters were Cube (TE/TR=50 ms/2000 ms) which provides improved SNR and CR and the presence of artifacts with operative assisted images for radical prostatectomy. These operative assisted images obtained from Cube (TE/TR=50 ms/2000 ms) are likely to be useful for surgery.
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  • Application of N-Isopropyl-p-[123I] Iodoamphetamine Quantification of Regional Cerebral Blood Flow Using Iterative Reconstruction Methods: Selection of the Optimal Reconstruction Method and Optimization of the Cutoff Frequency of the Preprocessing Filter
    Akira Asazu, Masuo Hayashi, Mami Arai, Yoshiaki Kumai, Hiroyuki Akagi, ...
    2013 Volume 69 Issue 5 Pages 535-544
    Published: May 20, 2013
    Released on J-STAGE: May 24, 2013
    DOIhttps://doi.org/10.6009/jjrt.2013_JSRT_69.5.535
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    In cerebral blood flow tests using N-Isopropyl-p-[123I] Iodoamphetamine 123I-IMP, quantitative results of greater accuracy than possible using the autoradiography (ARG) method can be obtained with attenuation and scatter correction and image reconstruction by filtered back projection (FBP). However, the cutoff frequency of the preprocessing Butterworth filter affects the quantitative value; hence, we sought an optimal cutoff frequency, derived from the correlation between the FBP method and Xenon-enhanced computed tomography (XeCT)/cerebral blood flow (CBF). In this study, we reconstructed images using ordered subsets expectation maximization (OSEM), a method of successive approximation which has recently come into wide use, and also three-dimensional (3D)-OSEM, a method by which the resolution can be corrected with the addition of collimator broad correction, to examine the effects on the regional cerebral blood flow (rCBF) quantitative value of changing the cutoff frequency, and to determine whether successive approximation is applicable to cerebral blood flow quantification. Our results showed that quantification of greater accuracy was obtained with reconstruction employing the 3D-OSEM method and using a cutoff frequency set near 0.75–0.85 cycles/cm, which is higher than the frequency used in image reconstruction by the ordinary FBP method.
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The 68th Annual Scientific Congress Symposium
The 68th Annual Scientific Congress Educational Lecture
Educational Lecture–Statistical Methods for Radiologic Research
Basic Lecture–Three-dimensional Computer Graphics
Basic Lecture–Heart Disease: From Diagnosis to Treatment
JIRA Topics
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