[Clinical Validation of Chest X-ray Educational Content for Radiography Students Using Gaze Information].

PURPOSE: Radiography training for students in colleges of radiology should be based on real clinical situations. The purpose of this study was to verify the clinical validity of our originally developed scenarios for chest X-ray training and the instructional contents using gaze information of experienced radiology technologists (RTs). METHODS: We divided 8 RTs with different experiences into an evaluator group (3 RTs) and a subject group (5 RTs). The evaluator group created a validation model consisting of 31 items, a chest X-ray scenario, instructional contents, and gaze attention objects during the scenario. The subject group simulated chest X-ray wearing an eye tracker. The evaluator group evaluated fit rates of the validation model to subjects' procedures based on gaze information to verify the clinical validity of the validation model. RESULTS: The subject group procedures did not deviate from the scenario. We obtained a fit rate of 91.6±6.70%. CONCLUSION: Our validation model showed more than 90% fitting with the chest X-ray techniques of five RTs with different backgrounds. This result suggested that the scenario and instructional contents in this study had clinical validity.

Utilization of upper and lower limits of exposure index in clinical digital radiography.

In many digital X-ray imaging systems, although air kerma on a surface of each detector is used, a standardized dose index called an exposure index (EI) has been proposed by the IEC, which is expected to be utilized for dose management. In clinical practices, EI is effectively utilized using a deviation index (DI), which is a deviation between a target EI (EIT) set for each imaging region and an EIT of the acquired image. However, an important issue in clinical uses of EI is a suppression of excessive doses. It is difficult to achieve a reliable reduction in exposure doses by indicating DI. In this study, physical image characteristics of detectors, visual detectability by charts, and observer experiments using a chest phantom were examined to determine upper (DImax) and lower (DImin) limits of the EIT and DI to achieve a reliable dose reduction in chest examinations. As the result, the tolerance ranges indicated by DImax and DImin, which were set based on the results of physical and visual evaluations, proved to be almost consistent with the distribution of EI values in 735 clinical images taken with a photo-timer control in real clinical practices.

[Genesis of Computed Radiography System: What is Born Between Imagination and Creativity].

In 1982, the Osaka General Medical Center made a modernization plan and started construction of a new hospital. The new radiology department was studied from the layout of the rooms to the newly introduced equipment and data storage system. Just around that time (1983), Fuji Computed Radiography (FCR) was developed.Using this FCR, we took on the challenge of the world's first full digitalization of a general radiography system.At that time, we took the following policies to improve the system.(1) To digitize all general radiography.(2) To review the radiography process, improve the equipment, and build a system to link the equipment together.(3) Change the selection of radiography equipment to one that is compatible with the digital system (small focus: magnified radiography).(4) Convert all ideas, including image processing, to digital systems.These attempts were successful and became the basis for the current field of general radiography.

Comparative evaluation of image quality among different detector configurations using area detector computed tomography.

The 320-detector row computed tomography (CT) system, i.e., the area detector CT (ADCT), can perform helical scanning with detector configurations of 4-, 16-, 32-, 64-, 80-, 100-, and 160-detector rows for routine CT examinations. This phantom study aimed to compare the quality of images obtained using helical scan mode with different detector configurations. The image quality was measured using modulation transfer function (MTF) and noise power spectrum (NPS). The system performance function (SP), based on the pre-whitening theorem, was calculated as MTF2/NPS, and compared between configurations. Five detector configurations, i.e., 0.5 × 16 mm (16 row), 0.5 × 64 mm (64 row), 0.5 × 80 mm (80 row), 0.5 × 100 mm (100 row), and 0.5 × 160 mm (160 row), were compared using a constant volume CT dose index (CTDIvol) of 25 mGy, simulating the scan of an adult abdomen, and with a constant effective mAs value. The MTF was measured using the wire method, and the NPS was measured from images of a 20-cm diameter phantom with uniform content. The SP of 80-row configuration was the best, for the constant CTDIvol, followed by the 64-, 160-, 16-, and 100-row configurations. The decrease in the rate of the 100- and 160-row configurations from the 80-row configuration was approximately 30%. For the constant effective mAs, the SPs of the 100-row and 160-row configurations were significantly lower, compared with the other three detector configurations. The 80- and 64-row configurations were adequate in cases that required dose efficiency rather than scan speed.

Overall noise characteristics of reduced images on liquid crystal display and advantages of independent subpixel driving technology.

PURPOSE: During soft-copy diagnoses, medical images with a large number of matrices often need to display reduced images on liquid crystal displays (LCDs) because of the spatial resolution limitation of LCDs. A new technology, known as independent subpixel driving (ISD), was recently applied to clinical uses aiming to improve the spatial resolution. The authors' study demonstrates the overall noise characteristics of images displayed on a LCD at various display magnifications, with and without ISD application. METHODS: Measurements of the overall noise power spectra (NPS) of x-ray images displayed on LCD were performed at varying display magnifications, with and without ISD. The NPS of displayed images in several display situations were also simulated based on hypothetical noise factors. RESULTS: The measured and simulated NPS showed that noise characteristics worsened when the display magnification was reduced, due to aliasing errors. The overall noise characteristics were attributed to luminance-value fluctuation converted from pixel values, image-interpolation effects, inherent noise, and blurring of the LCD. ISD improved the noise characteristics because it suppressed noise increments by aliasing errors. CONCLUSIONS: ISD affected the noise-characteristic advantages of reduced images displayed on LCDs, particularly at low frequencies.

[Investigation of practical method for quality assurance and control of medical displays].

Quality assurance (QA) guidelines for medical display systems in Japan, JESRA X-0093, were published in August 2005 and have been used in many medical fields to maintain image quality on medical displays. This report offers detailed explanations of terms and testing methodologies in the guidelines, taking into account users with little knowledge of display technology. The management grade classifications, luminance meters, test patterns, and evaluation methods for executing the QA are supplementally described based on the technical background of related things. In addition, the validity of the evaluation methods and judgment criteria for uniformity and contrast response tests were examined in some experiments. The experimental results of the contrast response indicated that some cases presented inadequate display contrast even if the contrast responses were set within ± 15% of the standard acceptable range for grade 1. The luminance responses of displays used in two computed tomography systems (CTs) and one magnetic resonance imaging system (MRI) were also measured, and the results indicated that their responses with conventional gamma responses were problematic for comparing images with those of medical displays.

Application of pixel truncation to reduce intensity artifacts in myocardial SPECT imaging with Tc-99m tetrofosmin.

BACKGROUND: Technetium 99m-labeled radiopharmaceuticals accumulate in the liver and gallbladder, where they generate intensity artifacts that can result in misdiagnosis of myocardial single photon emission computed tomography (SPECT) images. This study identifies and eliminates factors affecting the magnitude and appearance of intensity artifacts in a gallbladder-heart phantom. METHODS AND RESULTS: The myocardium and background compartments of a phantom were filled with Tc-99m at concentrations of 320 and 26.1 kBq/mL, respectively. A disposable plastic syringe containing 5 mL of Tc-99m as a model of the gallbladder was fixed in a position lateral to the heart phantom. Artifact intensity was determined on SPECT images over a specific activity range in the syringe (28.6, 6.6, and 0.2 MBq/mL). Among 72 projection images, those with maximal heart counts in the region of interest were selected. Counts above and below 110% of the maximal heart count in all projection images were excluded and reconstructed, respectively. At 28.6 and 6.6 MBq/mL, excessive artifacts generated cold pixels immediately around the source, whereas lower activity (0.2 MBq/mL) caused the artifacts to disappear. Truncating the counts in the gallbladder caused the intensity artifacts at specific activities of 28.6 and 6.6 MBq/mL to disappear. CONCLUSIONS: The magnitude and appearance of intensity artifacts depend on contrast between extracardiac activities in the same slices of the heart in myocardial SPECT images with Tc-99m tetrofosmin, and pixel truncation can eliminate them.