Kenyu Yamamoto

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.

Sonographic analysis of hyoid bone movement during swallowing

Purpose: Videofluoroscopy is generally considered a “gold standard” technique; however t technique exposes subjects to radiation. Ultrasonography is applied widely in clinical practice because of low cost, safety of the technique, and absence of radiation exposure. The aim of this study was to evaluate hyoid bone movement trajectories during swallowing in healthy subjects using ultrasonography.Subject and Methods: Data were obtained from 15 healthy volunteers (mean age: 34.9± 9.3).The subjects were divided into 3 groups: 5 subjects in their 20s, 5 subjects in their 30s and 5 subjects in their 40s. The subjects were examined while sitting in an upright position, with the back against a wall to control movement. The transducer was placed in a longitudinal scan above the larynx. The hyoid bone was identified on the scan as a high echoic area with posterior acoustic shadow. Then, the subjects swallowed 5 mL of mineral water, with a measurement frequency of 5 times. The digital-ultrasonographic recordings were viewed at 30 frames/s for 3 seconds. Results: The movement was divided into 4 phases: A, slowly ascending phase; B, rapidly ascending phase; C, temporary pause phase (position of maximum rise); D, rapid and slow descending shifts toward the resting position phase. We easily visualized the hyoid bone trajectory using ultrasonography. In all cases, ultrasonographic analysis of the hyoid bone was confirmed to have a similar trajectory as determined with videofluoroscopy. Ultrasonography can accurately determine swallowing duration and trajectory of hyoid bone movement. There was a significant difference in swallowing duration between the 20s groups and 30s groups and between the 20s groups and 40s groups (P < 0.05). However, the difference between the 30s group and 40s group was not significant (P=0.87).Conclusion: The results show that the dynamic phase image of the hyoid bone movement can be revealed by ultrasonographic visualization.

Exposure Dose in Gastric Cancer Mass Screening using High Concentration Barium Sulfate — Comparison with Moderate Concentration Barium Sulfate —

The efficacy of high-concentration barium sulfate has been reported from several perspectives, but not in terms of radiation exposure. This study compared the exposure doses used with high-concentration and moderate-concentration barium sulfate. The exposure dose was evaluated with an experimental method, using a gastric phantom, and with a clinical examination. In the former, the exposure dose and X-ray tube load were measured on the phantom applied with both concentrations barium sulfate. In the latter, the fluoroscopic exposure dose, the radiographic exposure dose, and their sum, the total exposure dose, were investigated in 150 subjects (112 males, 38 females) treated with both concentration barium sulfate. The results of the experimental evaluations indicated that the exposure dose and X-ray tube load were greater with high-concentration barium sulfate than with moderate-concentration barium sulfate (P < 0.05). The results of the clinical evaluations indicated that the fluoroscopic exposure dose was greater with moderate-concentration barium sulfate than with high-concentration barium sulfate (P < 0.05), but the radiographic exposure dose was quite the reverse, so the total exposure dose was the same with both concentrations barium sulfate. We conclude that high-concentration barium sulfate does not increase the radiation exposure in mass screening for gastric cancer.

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.

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.

UV Intensity of Pre-irradiation in Gafchromic XR-RV3 and XR-SP2

UV-A irradiation of Gafchromic XR-RV3 and XR-SP2 are considered to be a substitute for X-ray irradiation in the double irradiation of Gafchromic XR-RV3 and XR-SP2. It makes it possible to compensate for heterogeneity errors in the active layers of Gafchromic XR-RV3 and XR-SP2. UV-A with a wavelength of 395-nm was irradiated to Gafchromic XR-RV3 and XR-SP2, and irradiation time and color density change were investigated. At first, Gafchromic XR-RV3 and XR-SP2 were pre-irradiated for 2 and 4 hours, respectively, by UV-A with a wavelength of 365-nm, with UV-A fluorescent lamp as the radiation source, located at a distance of 72 cm. Secondly, a UV-A light emitting diode (LED) capable of generating 395-nm UV-A was used. The irradiation times of UV-A for Gafchromic XR-RV3 and XR-SP2 were from 5 to 120 minutes and from 30 to 300 minutes at a distance of 5.0 cm, respectively. From these results, appropriate irradiation time was considered. A 0.5 inchs diameter region of interest was set for each irradiation area, and a histogram of pixel values was obtained. The selected condition was two items “There is not 0 in a mode”, “A 1/10 level intersects both sleeves of graph”.

Basic research on countermeasures against barium sulfate aggregation using a gastric phantom

The principal aim of this study was to conduct basic experiments to examine countermeasures against barium sulfate aggregation caused by denture adhesive in gastric cancer screening test. Experiment 1; barium sulfate aggregation was reconstructed in petri dishes and the degree of reducing aggregation by seven types of commercial drink and tap water was assessed visually. The most effective one was tap water. Experiment 2; two types of aggregation (severe and mild aggregation) were reconstructed using gastric phantom BMU-1, tap water of 30-150ml was added and the degree of reducing aggregation was assessed with the images. In the case of severe aggregation, the most effective quantity of tap water was 120 ml and the next was 150 ml with the following of 90, 60 and 30 ml (P < 0.05). In the case of mild aggregation, the order of effective quantity was 90, 60, 120, 30 and 150 ml (P < 0.05). The results of this study suggested that tap water drinking of the subject was effective for the reduction of barium sulfate aggregation in gastric cancer screening and the most effective quantity of tap water was 120 ml in the case of severe aggregation and 90 ml in the case of mild aggregation.

Influence of scattered radiation on Gafchromic EBT3

Gafchromic EBT3 (EBT3) is used as a radiochromic film in half-value layer (HVL) measurement methods, which are used to calculate the effective energy for QA and QC. HVL measurements using EBT3 display a precision of less than 5 % compared with the results of standard method with an ionization chamber (IC) dosimeter, and offer a simple procedure for determining the HVL consistently and quickly without the need for an IC. However, it is difficult to apply this technique because of the scattered radiation caused by the geometric layout of the X-ray computed tomography (CT) apparatus. In this study, the effect of scattered radiation on EBT3 is investigated. It was found that the EBT3 is not affected by scattered radiation at positions beyond 50 mm from the scattering substance. Therefore, the results suggest that EBT3 is suitable for use in X-ray CT HVL measurements. On the other hand, when the distance from the scattering substance was 10 mm or less, EBT3 showed very high absorption compared to a semiconductor detector. Therefore, EBT3 is more sensitive than the semiconductor detector at a close range and can be used to measure scattered radiation when the distance from the scattering substance is 10 mm or less.

Effects of Bolus Volume on Geniohyoid Muscle Movement during Swallowing: Ultrasonographic M-Mode Study in Healthy Adults

Purpose: Videofluoroscopy is generally considered a “gold standard” technique for diagnosing dysphagia; however this technique exposes subjects to radiation. Ultrasonography is applied widely in clinical practice because of low cost, safety of the technique, and absence of radiation exposure. The purpose of this study was to investigate the application of B+M-mode ultrasound imaging as a new approach to quantify activity patterns of the geniohyoid muscles during swallowing and to assess the effect of bolus volume in healthy subjects.

Half-Value Layer Measurement for Effective Energy, Using Radiochromic Film and Step-Shaped Aluminum Filter

The effective energy of diagnostic X-rays is important for quality assurance and quality control purposes. However, the half-value layer (HVL), which is necessary to evaluate the effective energy, has not been ascertained because of the high cost of the ionization chamber (IC) required and because the measurements are time-consuming and complicated. To solve these problems, a method using radiochromic film (RCF) and step-shaped aluminum (SSAl) filters has been developed. Gafchromic EBT (GAF-EBT), which has a weak energy dependence, was used as the RCF. The X-ray tube voltage for HVL was measured as 120 kV. The SSAl filter area, the full exposure area, and the non-exposure area were set on the GAF-EBT so as to obtain correct data. The density ratio of the SSAl filter area was calculated using the densities of the full exposure area and the non-exposure area. The GAF-EBT was scanned using a flat-bed scanner before and after exposure. To remove the image acquisition error of the flat-bed scanner, the scanning image of the GAF-EBT before exposure was subtracted from it after exposure. The HVL was evaluated using the density attenuation ratio of the GAF-EBT. Then, the effective energies obtained using the GAF-EBT and the IC were compared. The HVL and the effective energy with X-ray tube voltage of 120 kV using the GAF-EBT were 4.56 mm and 41.0 keV, respectively. The difference ratio of the effective energy between the GAF-EBT and IC methods was 5.9%. The effective energy can be measured using GAF-EBT easily and with high precision. The measurement time using GAF-EBT is extremely short compared with the IC method. Moreover, the effective energy can be measured inexpensively using the GAFEBT.