Shoichi Suzuki

Effective radiation doses of CT examinations in Japan: a nationwide questionnaire-based study

OBJECTIVE The aims of this study were to estimate the effective radiation doses from CT examinations of both adults and children in Japan and to study the impact of various scan parameters on the effective doses. METHODS A questionnaire, which contained detailed questions on the CT scan parameters employed, was distributed to 3000 facilities throughout Japan. For each scanner protocol, the effective doses for head (non-helical and helical), chest and upper abdomen acquisitions were estimated using ImPACT CT Patient Dosimetry Calculator software v. 1.0.4 (St Georges Hospital, London, UK). RESULTS The mean effective doses for chest and abdominal examinations using 80-110 kV were significantly lower than those using 120 kV. However, there was no statistically significant difference in the mean effective doses for head scans between facilities employing 80-110 kV and 120 kV. In chest and abdominal examinations, the mean effective doses using CT scanners from Western manufacturers [Siemens (Forchheim, Germany), Philips (Eindhoven, Netherlands) and GE Medical Systems (Milwaukee, WI)] were significantly lower than those of examinations using Japanese scanners [Hitachi (Kashiwa, Japan) and Toshiba (Otawara, Tochigi, Japan)], except for in paediatric chest examinations. CONCLUSION The mean effective doses for adult head, chest and abdominal CT examinations were 2.9, 7.7 and 10.0 mSv, respectively, whereas the corresponding mean effective doses for paediatric examinations were 2.6, 7.1 and 7.7 mSv, respectively. ADVANCES IN KNOWLEDGE Facilities using CT scanners by Western manufacturers commonly adopt low-tube-voltage techniques, and low-tube-voltage CT may be useful for reducing the radiation doses to the patients, particularly for the body region.

Effect of tube current modulation for dose estimation using a simulation tool on body CT examination

The purpose of this study was to evaluate the effect of tube current modulation for dose estimation of a body computed tomography (CT) examination using a simulation tool. The authors also compared longitudinal variations in tube current values between iterative reconstruction (IR) and filtered back-projection (FBP) reconstruction algorithms. One hundred patients underwent body CT examinations. The tube current values around 10 organ regions were recorded longitudinally from tube current information. The organ and effective doses were simulated by average tube current values and longitudinal modulated tube current values. The organ doses for the bladder and breast estimated by longitudinal modulated tube current values were 20 % higher and 25 % lower than those estimated using the average tube current values, respectively. The differences in effective doses were small (mean, 0.7 mSv). The longitudinal variations in tube current values were almost the same for the IR and FBP algorithms.

Evaluation of geometric efficiency and radiation exposure in z-axis for volume scan

The International Electrotechnical Commission (IEC) recommended that a display be provided on the operating console of medical computed tomography (CT) scanners when the geometric efficiency (GE) in the z-axis is 70% or less. Taking into account the increase in the number of detector rows and the changes in the scanning method, the present study was conducted to review the GE and to evaluate the exposure dose in the z-axis direction. The GE for a single-rotation scan was calculated in accordance with IEC-606024 Ed. 2. The findings of the present study suggest that 320-row area detector computed tomography volume scan (single axial scan with no table movement in which it just happened to use a very large beam width) extends 18.8 mm beyond the nominal beam collimation, even when the GE is >70%. However, compared with the helical scan, which is the present mainstream of CT examinations, the dose beyond the scan length is narrower in volume scan for a limited scan length of 160 mm or less.

Dose evaluation for foetal computed tomography with a 320-row unit in wide-volume mode and an 80-row unit in helical scanning mode: a phantom study

The purpose of this study was to evaluate the maternal and foetal effective doses during foetal computed tomography (CT) and to compare the radiation dose, dose profile and image noise on 80-row CT in helical scanning mode and 320-row CT in wide-volume scanning mode. The radiation doses were measured using thermoluminescent dosemeters implanted at various organ sites of an anthropomorphic pregnant phantom. The foetal doses in the 320-row multi-detector CT (MDCT) and 80-row MDCT units were higher than the volume CT dose index (CTDIvol). The dose profile in the 320-row MDCT overlapped in two places but showed no overlap in the 80-row MDCT. There were no significant differences in image noise between the two scanning modes. The foetal dose evaluation by CTDIvol may underestimate the foetal radiation risk. When using the wide-volume mode, operators must take into account the number of scans and overlap between volumetric sections.

SU‐E‐I‐49: Influence of the Phantom Length in Computed Tomography Dose Profile Dosimetry

PURPOSE We measured the computed tomography (CT) dose profile with CT dose phantom for several X-ray beam widths on 64-slice, and 320-slice multi detector-row CT (MDCT) using micro ionization chamber, and assessed the association of the CTDI100 value with CT dose phantom length. METHODS The CT dose profile (CTDP) was measured as Dm using radiation monitor (Model 9015, Radcal, Monrovia, CA) with micro ionization chamber (10X5-0.18, Radcal, Monrovia, CA) which have an active length of 19 mm and a 0.18 cm3 active area on 64-slice MDCT (Aquilion CX, Toshiba Medical Systems, Tochigi, Japan), and 320-slice MDCT (Aquilion One, Toshiba Medical Systems, Tochigi, Japan). The MDCT systems were used with a tube voltage of 120 kV, tube current of 100 mA, rotation time of 1 second, and nominal X-ray beam widths of 4, 12, 32, and 160 mm (4*1 mm, 4*3 mm, 64*0.5 mm, and 320*0.5 mm axial slice acquisitions, respectively). A micro ionization chamber was placed in the center of the single CT dose phantom, and we acquired several axial scans as 5 mm increments of phantom length. Then two, and three coupled dose phantom were placed together to simulate a 300-mm-long, and 450-mm-long phantom. We acquired several axial scans in similar method. RESULTS The observed percent increase of the Dm with extended length from 150 mm to 300 mm of the CT dose phantom was 120 % at range from -60 to 60 mm. However, it was greatly increased toward peripheral area of the DP. With extended length from 300 mm to 450 mm of CT dose phantom, the observed percent increase of the Dm was slightly increased. There was no difference in the form of the CTDP between 300-mm-long phantom and 450-mm-long phantom. CONCLUSION In upward of the 300-mm-long CT dose phantom, there is no difference in the form of the CTDP.

Pelvic axis-based gait analysis for ataxic mice

BACKGROUND Although different gait analysis methods such as Walking Track Analysis exist, they cannot be used to demonstrate the physical condition of mice with specific gait disorder characteristic. Therefore, we developed a new method for the gait analysis of such mice to accurately assess hind limb angle based on the pelvic axis. NEW METHOD We established and verified a gait analysis method capable of pelvic axis-based limb angle measurement by video-recording the gait of a control mice group (C57BL/6J(B6)) and three ataxic mice (ataxic B6-wob/t, Parkinsons disease model (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treated (MPTP)), and cerebellum hypoplasia (cytosine-β-d-arabinofuranoside treated)) from the ventral side. RESULTS The assessed hind limb angles of B6-wob/t and MPTP-treated mice were significantly wider than B6 mice (p<0.01). Moreover, we could draw separating lines with slopes of minus one that could separate the data of each group in the scatter plot of the normalized hind limb step width and angle. COMPARISON WITH EXISTING METHODS We found no significance when we applied the already existing nose-tail method for the analysis of the hind limb angles of B6 and B6-wob/t mice. In the nose-tail method, since the whole body axis of the trunk varies while the trunk of the mouse is laterally bent changing the hind limb angle, B6 and B6-wob/t mice could not be differentiated. However, the two mice groups could be differentiated by the pelvic axis-based gait analysis method. CONCLUSION The pelvic axis-based gait analysis method is promising and valid for mice with gait disorder.

USEFULNESS OF SIZE-SPECIFIC DOSE ESTIMATES IN PEDIATRIC COMPUTED TOMOGRAPHY: REVALIDATION OF LARGE-SCALE PEDIATRIC CT DOSE SURVEY DATA IN JAPAN

The objective of this research is to calculate the organ equivalent dose and effective dose from the scanning conditions at 165 centers in Japan using computed tomography (CT) Dose software and compare the results with the CT dose index volume (CTDIvol), dose length product (DLP) and size-specific dose estimates (SSDE) to validate the usefulness of SSDE. The CTDIvol and DLP were significantly lower in infants than in children (p < 0.05). No significant differences were found in the bone marrow equivalent dose and effective dose for the torso between infants and children (p > 0.05), and the bone marrow equivalent dose and effective dose for the head were higher in infants than children (p < 0.05). No significant difference was found in SSDE for the torso between infants and children (p > 0.05). Organ equivalent and effective doses for head CT scans are higher in infants than in children (I/P ratio ≥ 1). The I/P ratios of CTDIvol and DLP for chest and abdominal CT scans are also higher in Japan than in other countries. CTDIvol and DLP are not accurate when used as a dose index, and SSDE was considered suitable for dose assessment of the torso. However, for head CT in infants, a further reduction in radiation exposure is required.

Diagnostic reference levels and achievable doses for common computed tomography examinations: Results from the Japanese nationwide dose survey

OBJECTIVE: To propose a new set of Japanese diagnostic reference levels (DRLs) and achievable doses (ADs) for 2017 and to verify the usefulness of Japanese DRLs (DRLs 2015) for CT, by investigating changes in the volume CT dose index (CTDIvol) from 2014 to 2017. METHODS: Detailed information on the CT scan parameters used throughout Japan were obtained by questionnaire survey. The CTDIvol and dose-length product for the 11 commonest adult and 6 commonest paediatric CT examinations were surveyed and compared with 2014 data and DRLs 2015. RESULTS: Evaluations of adult head (helical), and abdomen and pelvis without contrast agent, paediatric chest without contrast agent, and abdomen and pelvis without contrast agent showed a slightly lower mean CTDIvol in 2017 than in 2014 (t-test, p < 0.05). The interquartile range of CTDIvol for all 2017 examinations was lower than in 2014. CONCLUSIONS: This study verified the lower mean, 75th percentile, and interquartile range by investigating changes in the CTDIvol from 2014 to 2017. The DRLs 2015 contributed to CT radiation dose reduction. ADVANCES IN KNOWLEDGE: The widespread implementation of iterative reconstruction algorithms and low-tube voltage in CT scanners is likely to facilitate further reduction in the CT radiation dose used in Japan. Although radiological technologists may require further education on appropriate CTDIvol and DLP usage, the DRLs 2015 greatly contributed to the reduction of the CT radiation dose used in Japan.

Dose reduction technique in diagnostic X-ray computed tomography by use of 6-channel multileaf collimators

Recently, region-setting computed tomography (CT) has been studied as a region of interest imaging method. This technique can strongly reduce the radiation dose by limiting the irradiation field. Although mathematical studies have been performed for reduction of the truncation artifact, no experimental studies have been performed so far. In this study, we developed a three-dimensional region-setting CT system and evaluated its imaging properties. As an experimental system, we developed an X-ray CT system with multileaf collimators. In this system, truncated projection data can be captured by limiting of the radiation field. In addition, a truncated projection data correction was performed. Finally, image reconstruction was performed by use of the Feldkamp–Davis–Kress algorithm. In the experiments, the line profiles and the image quality of the reconstructed images were evaluated. The results suggested that the image quality of the proposed method is comparable to that of the original method. Furthermore, we confirmed that the radiation dose was reduced when this system was used. These results indicate that a 3D region-setting CT system using 6-channel multileaf collimators can reduce the radiation dose without in causing a degradation of image quality.

PATIENT EXPOSURE DURING PLAIN RADIOGRAPHY AND MAMMOGRAPHY IN JAPAN IN 1974–2014

We investigated changes in the entrance skin dose (ESD) and the mean glandular dose (MGD) during plain radiography or mammography in Japan from 1974 to 2014. Surveys regarding the conditions used for plain radiography and mammography were performed throughout Japan in 1974, 1979, 1989, 1993, 1997, 2001, 2003, 2007, 2011 and 2014. The anatomical regions considered were categorised as follows: skull anteroposterior (AP), lumbar AP, lumbar lateral (LAT), pelvis (AP), ankle, chest posteroanterior (PA), Guthmann (lateral pelviography for pregnant women), infant hip joint and mammography. The doses for all anatomical regions decreased from 1974 to 1993. The MGD for mammography remained low from 1993 to 2014, and the ESDs for chest (PA) radiography trended upward. After the 2000s, the use of digital imaging increased in Japan. This is the first long-term study to examine changes in ESDs and MGDs in Japan.