We have investigated the role assignment and radiation exposure of medical workers (including receptionists) in PET (positron emission tomography) facilities in Japan using a questionnaire. The survey period was from October 1st to November 15th 2006. The response rate for the questionnaire was 60.0% (72/120 facilities). Nurses were engaged in the intravenous administration of radioactive FDG in 66.9% of PET facilities. In 89.5% of PET facilities, radiological technologists mainly performed the PET examination. The average radiation exposure to medical workers was 0.13 mSv/month (n: 709, S.D.: 0.16) as the effective dose. It was shown that radiation exposure was significantly different depending on the occupation and content of work (p<0.01). The radiation exposure of cyclotron operators and radiological technologists was higher than that of the other occupations (p<0.01). The highest radiation dose to one worker per a PET facility was 0.60 [mSv month−1], which was 4.6 times higher than the average dose of 0.13 [mSv month−1]. We have clarified the actual conditions of radiation protection in PET facilities in Japan for the first time.
Purpose: To investigate the effect of maximum tube current threshold for dose modulation at MDCT on the reduction rate of radiation dose and variability of image noise. Materials and Methods: A chest CT phantom was scanned with a 64-detector row CT scanner using an automatic exposure control (AEC) technique. The technique consisted of X-Y-Z modulation and Z modulation. We set the desired image noise at 10 HU. Maximum tube current threshold was set at 200 and 300 mA and minimum tube current threshold was fixed at 10 mA. For comparison, we also performed scanning with a fixed tube current at 300 mA. Parameters for helical scanning were: tube voltage, 120 kV; rotation time, 0.5 sec/rot; collimation, 64×0.5 mm; beam pitch, 0.825; reconstructed section thickness, 5.0 mm. After scanning, we recorded the actual mA value of each image. Image noise was also measured with and without the dose modulation technique. Results: Using X-Y-Z modulation, when maximum tube current threshold was 300 and 200 mA, the reduction rates of radiation dose with the dose modulation technique were 29.9% and 45.0%, respectively, compared with the fixed tube current technique. Actual mean image noise was 9.6 and 11.4 HU corresponding to 300 and 200 mA. The standard deviation of image noise at 200 mA (2.47 HU) was larger than that at 300 mA (1.96 HU). Conclusion: A lower maximum tube current setting (200 mA) could achieve larger dose reduction. However, it induced larger variability of the level of image noise in the AEC technique at MDCT.
From the difference of a clinical dose and the molarity of hepatic specificity contrast agent Gadoxetate Sodium (Gd-EOB-DTPA) and Meglumine Gadopentetate (Gd-DTPA), we make one’s own phantom this time, we performed a study of the base about contrast-to-noise ratio (CNR) of the three dimensional-fast spoiled gradient echo (3D-FSPGR) technique and an optimum flip angle (FA) and the bandwidth (BW) for Gd-DTPA dilution 0.3 mmol/l which assumed T1 value of the liver parenchyma of Gd-DTPA dilution 6.0 mmol/l and Gd-EOB-DTPA dilution 1.5 mmol/l which assumed large arterial blood maximum density of first pass in Dynamic study. We assume CNR of FA10˚ in each BW criteria, CNR of Gd-DTPA dilution 6.0 mmol/l becomes the 3.63–4.38 double at the maximum in FA30˚ with each BW; CNR of Gd-EOB-DTPA dilution 1.5mmol/l is with 1.95–2.36 double at the maximum in FA 20–25˚ with each BW. When CNR compares it with a value of FA becoming biggest, with each BW, as for Gd-EOB-DTPA dilution 1.5 mmol/l, about around 40% CNR lowered for Gd-DTPA dilution 6.0 mmol/l. In Dynamic study in Gd-EOB-DTPA, we did not use an imaging condition totally same as Gd-DTPA and understood that we required the setting of the imaging condition that considered the influence of the T1 relaxation time by the difference of a clinic dose and the molarity in first pass.
We performed an estimation of longitudinal (T1) and transverse relaxation (T2) time using the general-purpose spreadsheet software Microsoft Excel. The Excel tool “solver” is useful for the simultaneous estimation of both T1 and steady-state magnetization from the non-linear least square method. The estimation time is quick enough for the purpose. T1 and T2 estimated from handwritten semi-log plots were compared with the results from spreadsheet software from the viewpoint of accuracy using the phantom data. Although the data from handwritten plots include an estimation error of several percent among the subjects, the mean values are almost the same as compared with the data from spreadsheet software.
The advantage of the higher signal-to-noise ratio (SNR) of 3-Tesla magnetic resonance imaging (3-Tesla) has the possibility of contributing to the improvement of high spatial resolution without causing image deterioration. In this study, we compared SNR and the apparent diffusion coefficient (ADC) value with 3-Tesla as the condition in the diffusion-weighted image (DWI) parameter of the 1.5-Tesla magnetic resonance imaging (1.5-Tesla) and we examined the high spatial resolution images in the imaging method [respiratory-triggering (RT) method and breath free (BF) method] and artifact (motion and zebra) in the upper abdominal region of DWI at 3-Tesla. We have optimized scan parameters based on phantom and in vivo study. As a result, 3-Tesla was able to obtain about 1.5 times SNR in comparison with the 1.5-Tesla, ADC value had few differences. Moreover, the RT method was effective in correcting the influence of respiratory movement in comparison with the BF method, and image improvement by the effective acquisition of SNR and reduction of the artifact were provided. Thus, DWI of upper abdominal region was a useful sequence for the high spatial resolution in 3-Tesla.
In accordance with a questionnaire survey of diagnostic X-ray equipment enforced in 2005, this report was focused mainly on a photography device. The paper questionnaire was mailed to 667 institutions, and the collection rate was 20.4%. Introductions of digital photographic devices are progressing and flat panel detectors (FPD) are spreading in addition to computed radiography (CR). Examination revealed that the spread rate of FPD was 14.4%. The inverter-type device occupied 73.4% in group of high-voltage-generation devices. We reason that the spread rate indicates changeover to an inverter-type device. Changes in photography equipment and photography devices will bring change in photographic technology. Such investigation will be necessary in the future.
In this report, we summarize the survey of diagnostic X-ray equipment conducted in 2005, focusing on exposure conditions. What we would like to point out in this report is how prevalent digital image receptor systems have become, including flat panel detectors (FPD), which did not exist in our last survey five years ago. FPD have become popular very quickly among the digital receptor systems used in general radiography. Twenty-three percent of all chest standing-position X-ray equipment now have FPD. Since FPD has become prevalent, exposure conditions are becoming somewhat different from screen/film systems (s/f) and computed radiography (CR). While the image receptor system is expected to shift to FPD, we would like to continue our survey to determine what exposure conditions will be like in the near future.