[Study on the effect of setting the region of interest for exposure index computing].

Exposure index (EI) is expected as important standard for the optimization of image quality and exposed dose in digital radiography. It is set a region of interest (ROI) in a radiograph, to obtain a histogram of pixel values within an ROI, it is computed as EI of the image representative value of the histogram. In this study, we examined the effects of setting the ROI for EI computing. We set five different ROIs in chest or cervical spine frontal radiograph, and compared the computed EI in each ROIs. From the result, in some cases, we found that EI varied greatly as those compared to the case of ROI set in full image. We should consider about setting the ROI for EI computing when we use EI as standard for optimization of image quality and exposed dose in digital radiography.

Optimization of dual-energy subtraction chest radiography by use of a direct-conversion flat-panel detector system.

We aimed to optimize the exposure conditions in the acquisition of soft-tissue images using dual-energy subtraction chest radiography with a direct-conversion flat-panel detector system. Two separate chest images were acquired at high- and low-energy exposures with standard or thick chest phantoms. The high-energy exposure was fixed at 120 kVp with the use of an auto-exposure control technique. For the low-energy exposure, the tube voltages and entrance surface doses ranged 40-80 kVp and 20-100 % of the dose required for high-energy exposure, respectively. Further, a repetitive processing algorithm was used for reduction of the image noise generated by the subtraction process. Seven radiology technicians ranked soft-tissue images, and these results were analyzed using the normalized-rank method. Images acquired at 60 kVp were of acceptable quality regardless of the entrance surface dose and phantom size. Using a repetitive processing algorithm, the minimum acceptable doses were reduced from 75 to 40 % for the standard phantom and to 50 % for the thick phantom. We determined that the optimum low-energy exposure was 60 kVp at 50 % of the dose required for the high-energy exposure. This allowed the simultaneous acquisition of standard radiographs and soft-tissue images at 1.5 times the dose required for a standard radiograph, which is significantly lower than the values reported previously.

[Relationship between the effect of medial rotation of the foot axis by ankle dorsiflexion and the ability to visualize the femoral neck axis in the hip joint anterio-posterior radiography: evaluation by magnetic resonance images].

In scanning of the hip joint anterio-posterior radiography, by changing the lower extremities to the extension position and moving the foot axis (base line of the foot) by medial rotation, the angle of anteversion of the femoral neck is corrected. In this study, we assessed the effects on medial rotation of the femoral neck when keeping the planta vertically-positioned by ankle dorsiflexion (intermediate position of the ankle) and making change of the medial rotation angle of the foot axis by scanning the magnetic resonance (MR) images of knee joints and hip joints. The subjects in this study were 12 males (age: 37.9±13.8, weight: 67.3±5.5 kg) and 7 females (age: 27.6±5.1, weight: 50.0±4.5 kg). We measured the medial rotation angles of knee joints and femoral necks on MR images. Also, differences of these angles between males and females were compared. Although the gender differences were not found in medial rotation angle of both joints at all leg positions (P>0.05), the medial rotation angles increased by approximately 1.5 to 2.0 times larger by putting them at the intermediate position, and there were significant differences between the naturally plantar-flexed position and the intermediate position (P<0.05). In conclusion, our results showed that the optimal leg position for correcting the angle of anteversion was 20 degrees medial rotation of the foot axis at the naturally plantar-flexed position, or 10 degrees medial rotation of the foot axis at the intermediate position, regardless of gender.

[Difference in the level of patient treatment safety analysed by the years of experience of the radiological technologists].

According to the report of the reporting project of medical accidents (from July 2010 to March 2011) which was issued by the Ministry of Health, Labour, and Welfare, a lot of incidents involving radiological technologists occurred among young ages or experienced ages; therefore, we focused on this matter. We carried out questionnaires for the radiological technologists at the radiology department of our hospital to see how concerned they are about the patient treatment safety. We examined the causal relationship between years of their experience and their concerns about the patient treatment safety. As a result, we found that their concerns about the patient treatment safety are characteristically different depending on the years of experience. The results showed that the new technologists were on a low level of caring with a similar philosophy to the saying "To err is human". They also lack a positive attitude. Moreover, they stated that the causes of the errors were neither the devices nor the system of the devices. Mid-career technologists stated that the most common cause of errors is the liability of the person concerned. They are concerned that education to improve individual abilities is important. Experienced technologists stated that the cause of the error is excluding the person concerned, but due to the devices, patients, or advanced specialization of the examinations. However, they also had the positive attitude to promote the patient treatment safety.

[Study of appropriate dosing in consideration of image quality and patient dose on the digital radiography].

Recently about 90% of radiographs have been taken by the digital radiographic system in Japan, but the exposure dose of the patients are about ten-times different among the systems. We understood it by a surveytaken in 2007. We studied the visual evaluation with varying exposure doses using the image phantom of the lumber AP, lumber lateral and hip AP. Additionally we measured quantum efficiency (DQE) of the digital systems. We also studied the exposure index (EI) of IEC standard to see whether it is able to be the sensitivity index among the digital systems. DQE in 1.0 cycle/mm of CR, FPD (GOS), FPD (CsI, a-Se) became 0.2-0.25, 0.3, 0.5, respectively. Our results display that the dose reduction is relative to DQE. The visual evaluation results also show that dose reduction is possible among the systems. From these results, we are able to reduce the exposure dose of the patients at the clinical site. We also suggest that we manage the exposure dose using the E.I of the IEC standard.

[Gravity sag view of lateral radiography of the knee].

The gravity sag view(GSV)is a lateral radiograph taken in the same position when the posterior sag sign is observed. The purpose of this study was to standardize the radiography technique for GSV by adjusting lateral rotation. To confirm the benchmark and correction angle(CA)for the GSV position, we assessed three-dimensional(3D)CT of the GSV position of the knee using normal volunteers. The benchmark is established at the 3-point of the leg and adjusting the CA of the knee is established by estimating from Rosenberg technique radiography. This helped not only to correct external rotation in the initial radiography but also to correct rotation for repeat radiography. Our method is quantitative and highly reproducible, and it increases the success rate in adjusting lateral radiography of the knee.

[Usefulness of high energy radiation using copper filter on CR chest radiography]

The bone contrast on chest radiographs obtaind with computed radiography (CR, hereafter) is not decreased enough compaired with that for screen/film combination, even if we use a high tube voltage. This may be because the Exporsure Data Recognizer which can normalize the density and contrast of the chest images is performed. In order to increase the diagnostic accuracy for the lung disease,we propose to use a copper additional filter to decrease the bone contrast. Consequently, in order to have satisfied the bone contrast and the patient expousure dose, additional 0.3 mm copper filter and effective energy was 59.3 keV or more were required of the tube voltage of 140kV. Further, the effective energy of 140 kV tube voltage with a 0.7 mm copper, which is the maximum thickness of the additional filter within 50 m seconds in exporsure time, was 68 keV. Concluding these results, optimum range of additional copper filter is from 0.3 mm to 0.7 mm in chest high voltage radiography using CR. The bone contrast decreases sufficiently, if we use X-rays which have effective energy within this range. Our method is also useful to reduce patient dose.