Hidetoshi Yatake

Reducing Non-uniformity Error of Radiochromic Film in the Diagnostic Range by Ultraviolet Exposure: Preliminary Study

Thickness irregularity of active layer is made to express density irregularity. True data by the X-rays are extracted by exposing Ultraviolet (UV) rays that prohibited exposure are exposed for radiochromic film (RF). When UV is exposed, the density irregularity is corrected. In addition, RF is initialized, thereby improving of data acquisition.

Improved detection of gastric cancer during screening by additional radiographs as judged necessary by the radiographer

PurposeThe aim of this study was to determine whether additional radiographs, as judged necessary by the radiographer, improves cancer detection during gastric cancer screening.Materials and methodsWe analyzed 144 gastric cancer cases among 137 744 individuals who underwent X-ray screening for gastric cancer. Radiographs were obtained by 17 radiographers at a screening center in Japan from April 2004 to March 2008. Additional radiographs were taken based on the radiographer’s judgment in cases of suspected cancer. During double-blind reinterpretation of the cancer case radiographs by two radiologists, we determined the number of cancer cases that were detected by standard radiographs alone. We next determined the number of cancer cases detected using both standard radiographs and additional radiographs.ResultsCompared to the number of cancer cases detected with standard radiographs alone (120 cases detected, 24 cases undetected), the number of cancer cases detected with both standard and additional radiographs (137 cases detected, 7 cases undetected) significantly increased (17 cases; P < 0.001, McNemar test).ConclusionWe found that taking additional radiographs, when judged necessary by the radiographer during radiographic gastric cancer screening, improves cancer detection.

Film-reading ability of radiographers in detecting gastric cancer during screening using X-ray examination

PurposeThe aim of this study was to evaluate the film-reading ability of radiographers in detecting gastric cancer during screening X-ray examinations.Materials and methodsA test set of 100 patients (50 negative and 50 positive; mean age 62 years, range 33–78 years) given a stomach X-ray examination were selected from those who underwent gastric cancer screening in Osaka, Japan, between 2000 and 2003. Eleven radiographers and four radiologists scored the test set on a five-point scale. A receiver operating characteristic (ROC) analysis was performed, and the area under the ROC curve (AUC) was defined as a measure of film-reading ability to detect cancer.ResultsNo significant difference (two-tailed P = 0.962, Welch’s t-test) was observed between averaged AUC values from radiographers (0.76, range 0.85–0.62) and radiologists (0.75, range 0.86–0.62).ConclusionFilm-reading ability of radiographers in detecting gastric cancer during screening X-ray examinations was not significantly different from that of radiologists. Our results suggest that radiographers can assist radiologists to detect gastric cancer during screening.

Measurement of half-value layer for QA and QC: Simple method using radiochromic film density

Although it is considered that the half-value layer (HVL) of diagnostic X-rays is important for quality assurance (QA) and quality control (QC), the HVL is not constantly monitored because ionization-chamber dosimetry is time-consuming and complicated. To verify the applicability of GAFCHROMIC XR type R (GAF-R) film for HVL measurement instead of monitoring the ionization-chamber, a single-strip method for measuring the HVL has been evaluated.

Exposure Dose Reduction of Lead Acrylic Filter for Gastric Cancer Mass Screening

It is important to reduce x-ray exposure in subjects who undergo mass screening for gastric cancer. We constructed three types of lead acrylic filters and evaluated their ability to reduce exposure. X-ray tube load increase, dose area reduction, density of gastric phantom images and lead acrylic filter shadows were evaluated. Three different thicknesses of lead acrylic filters were examined, one was a regular thickness, another was half the thickness, and the other was twofold the thickness. Objectivization, reduction rate of exposure, x-ray tube load increase, and the density of each gastric phantom image was taken with or without the three types of lead acrylic filters. The filter shadow in the image of the gastric phantoms using the three types of lead acrylic filters were evaluated with 4 levels. Dose area reductions using the three types of filters were 6.03%, 10.92%, and 13.64%, for the half thickness, regular thickness, and twofold thickness, respectively (p 0.05). There was no significant difference between the density of gastric phantom images with or without the filters (p>0.05). The lead acrylic filter shadows were significantly difference among the three types filters (p<0.05). We conclude that the use of lead acrylic filters is effective for the reduction of exposure in screening for gastric cancer. A lead acrylic filter of twofold thickness is most effective for the reduction of exposure.

Evaluation of two radiochromic films for HVL measurement

Although the half-value layer (HVL) is one of the important parameters for quality assurance (QA) and quality control (QC), constant monitoring has not been performed because measurements using an ionization chamber (IC) are time-consuming. To solve these problems, a method using radiochromic film and step-shaped aluminum (Al) filters has been developed. In this study, GAFCHROMIC EBT2 dosimetry film (GAF-EBT2) and GAFCHROMIC XR TYPE-R dosimetry film (GAF-R) has been used. The measurement X-ray tube voltage was 120 kV. Two radiochromic films were scanned using a flat-bed scanner. To remove the nonuniformity error of scanned images, image J version 1.40g image analysis software has been used. HVL was evaluated using the density attenuation ratio. The HVLs and second HVLs of GAF-EBT2, GAF-R, and an IC dosimeter were compared. The HVLs (second HVLs) at 120 kV using GAF-EBT2, GAF-R, and an IC dosimeter were 4.47 mm (10.97 mm), 4.17 mm (8.61 mm), and 4.03 mm (10.35 mm) respectively, and the effective energies were 40.6 keV, 39.3 keV, and 38.7 keV, respectively. The difference ratios of the second HVLs using GAF-EBT2 (GAF-R) and an IC dosimeter were 6.0% (– 16.8%), –10.6% (–11.6%), and 5.1% (–0.2%), respectively. In addition, the difference ratio of the second HVLs at 120 kV using GAF-EBT2 and GAF-R was 27.4%. GAF-EBT2 and GAF-R proved to be capable of measuring effective energy within an error range of less than 5%. However, in HVL measurements of devices operating in the high-energy range (X-ray CT, radiotherapy machines, and so on), GAF-EBT2 was found to offer higher measurement precision than GAF-R, because it shows only a slight energy dependency.

Dose Distribution in Pediatric CT Abdominal Examination: Phantom Study

To keep radiation doses during computed tomography (CT) examinations as low as reasonably achievable, performing a detailed dose measurement is important. A flexible acrylic sheet roll CT dosimetry phantom (SRCT-P) with radiochromic film (RF) was developed to estimate in detail the dose distribution during pediatric CT examination. The SRCT-Ps were elliptically-shaped by rolling up flexible acrylic sheets (1.1 g/cm3). The dose distributions in the SRCT-P (body thickness and width: 6-8 cm [neonates], 10-12 cm [infants], and 14-16 cm [three-year-old children]) were evaluated. RFs were positioned from the center to the surface along the long- and short-axis directions in each SRCT-P. The scanning parameters of the single detector CT were 120 kV, 250 mA, 1.0 sec/rot, a slice thickness of 5 mm, and a 1.0 beam pitch. When the mean center dose at 10-12 cm on the SRCT-P was taken as 100%, the mean center doses at 6-8..or 14-16 cm were 145..or 43%, respectively, and the mean surface doses for 0, 90, and 180 degrees at 6-8, 10-12, and 14-16 cm of the SRCT-P were as follows: 158%, 159%, and 140%; 132%, 125%, and 116%; and 164%, 128%, and 131%, respectively. The center dose was increased with a decrease in the phantom size. The surface doses were decreased with decreasing phantom sizes of 14-16 to 10-12 cm; however, surface doses were increased with decreasing phantom sizes of 10-12 to 6-8 cm. The detail dose distribution of a CT examination can be measured separately by using a SRCT-P with a RF.

High Concentration Barium Sulfate Used in Gastric Cancer Screening ¿ Viscosity Change Dependent on the Volume of Artificial Gastric Juice-

High concentration barium sulfate has been de- veloped and used in mass screening for gastric cancer. Howev- er, high concentration barium sulfate flows out from the sto- mach faster than moderate concentration one, which often interferes with diagnosis. The speed of flow is seemed to de- pend on the viscosity of barium sulfate. Previously, the authors reported viscosity changes of high concentration barium sul- fate with pH and temperature changes. In this study, it is ex- amined that the viscosity of barium sulfate also changes with artificial gastric juice volume. The results indicate that the viscosity of high concentration barium sulfate is more stable than that of moderate concentration one and the image of gastric phantom with high concentration barium sulfate is evaluated to be better than that with moderate concentration one. The study on characteristics of barium sulfate may im- prove radiography technology in mass screening for gastric cancer.

The usefulness of film reading to detect cancer by untrained radiographer in X-ray examination of the stomach

Until now, the evaluations of the film reading performance of radiographers have been studied to assist diagnosis and to alleviate the shortage of radiologists. However, little has been reported on evaluating the film reading by radiographers in X-ray examination of the stomach. To investigate whether present radiographer can assist diagnosis in X-ray examination of the stomach or not, the film reading performance of untrained radiographer to detect cancer was evaluated. The institutional review board approved this retrospective study and informed consent was not required. A test set films of 100 cases (50 negative and 50 positive; mean age, 55 years; range, 33–78) in X-ray examination of the stomach were selected from 192,404 people in gastric cancer screening that was performed in Osaka, Japan between 2000 and 2002. The positive cases were defined as cancer cases, which were selected by 10 on the grade of five scales for difficulty. The negative cases were selected at random from without cancers that were confirmed by screening result at least two years later. Eleven radiographers and one radiologist scored the test set on a 5-point scale. A receiver operating characteristic (ROC) analysis was performed and area under the ROC curve (AUC) was defined as the film reading performance of radiographer or radiologist to detect cancer. The ROC analysis was performed according to the method of DeLong et al. A p value of less than 0.05 was required for significance. As a result, 5 of the 11 radiographers’ AUC (0.85–0.79) were slightly lower than the radiologist’s AUC (0.86) (p> 0.05). However, the other 6 radiographers’ AUC (0.74–0.62) were lower than the radiologist’s AUC (0.86) (p < 0.05). The highest AUC of radiographer (AUC, 0.85; sensitivity, 78%; specificity, 84%) and the AUC of radiologist (AUC, 0.86; sensitivity, 86%; specificity, 76%) were almost equal (p = 0.673). These results show a possibility that untrained radiographers with higher film reading performance to detect cancer can assist diagnosis in X-ray examination of the stomach, because some higher film reading performance of several untrained radiographers was comparable to that of a radiologist.

Size and Shape of Spherical Objects on Full-Field Digital Mammography and Digital Breast Tomosynthesis Images

This study assessed the accuracy of shape and size representation of spherical objects on full-field digital mammography (FFDM) and digital breast tomosynthesis (DBT) images. Six 5-mm-thick polymethylmethacrylate slabs were positioned on the breast support table with 9 aluminum spherical objects of 30 (± 0.1) mm diameters between the first and second slabs. X-ray imaging was performed using FFDM and DBT (angular range 15°–40°, with correction of magnification), and repeated with the objects placed between the third and fourth slabs, and subsequently between the fifth and sixth slabs. The aspect ratio of the spherical objects and longer diameter were measured to evaluate the shape and size, respectively. A Steel-Dwass test was performed for comparative analysis. A P value <0.05 was considered significant. No significant differences in the aspect ratio of the spherical objects imaged using FFDM, DBT15°, or DBT40° images were observed (overall median: 1.02, overall range: 1.00–1.06). The longer diameter on the FFDM was increasingly magnified (median, range) with increasing distances of 20 mm (32.5, 31.8–33.5 mm) and 40 mm (33.6, 32.9–34.7 mm) between the breast support table and object center. However, in the case of DBT, the longer diameter was approximately the same as that of the actual object (overall, 30.4, 30.0–31.7 mm). At each height, the longer diameter was significantly different between the FFDM and DBT15° images and between the FFDM and DBT40° images (all P = 0.001), with no significant difference in that between the DBT15° and DBT40° images. The size on the FFDM images was magnified as compared to the size of the actual objects, and that on the DBT images was approximately the same as that of the actual objects. Thus, preoperative tumor size determination using FFDM images should be avoided.