[Investigation of the columnar carbon-scatterer length for X-ray spectral measurement on 320-slice computed tomography].

A short length scatterer is adopted to measure the X-ray spectrum of computed tomography (CT) equipment with a wide irradiation field in the body axis direction. The purpose of this study is to compare X-ray spectra measured using different length scatterers and determine the most appropriate length for the scatterer. 320-slice CT equipment (Aquilion ONE) was used in this study. Circular carbonrods (3 cm diameter) with five different lengths (1-16 cm) were used as scatterers. The effect of the beam hardening phenomenon from different length carbon rods was evaluated according to the effective energy. The measurement accuracy for photon information was also evaluated based on the photon count corresponding to the characteristic X-ray. As a result, the beam hardening effect was scarcely observed when the 1 cm long scatterer was used, and the number of the photons measured for the characteristic X-ray was the most. Therefore, it was concluded that the 1 cm long circular carbon rod scatterer was the most suitable.

[Production of a leaf electroscope having separators and proposal of an experiment using the diagnostic X-ray equipment].

In order to use the practical training for beginners by means of a diagnostic X-ray, a leaf electroscope (which has a function to explain the ionization) was newly produced. The X-ray was introduced to the air in the electroscope having the electric charged leaf (the leaf was open at this time). The air irradiated by the X-ray was ionized, and then the produced ions or electrons were combined with charges on the leaf. As a result, the leaf was closed. In this way, experimenters can know the production and/or movement of charges by observing the conditions of the leaf. For the developed leaf electroscope, we added separators to divide the inner space into two regions; one is the irradiation area and the other is the space including the leaf. The separators have through-holes and/or a metallic mesh in order to create various conditions. In this paper, we described that different experimental results based on uses of the different separators were reflected in the ionization of the irradiated air and in the interaction of the charged particles. We summarized that the practical training by means of the developed leaf electroscope was valuable to educate beginners.

[Proposal of a cloud chamber experiment using diagnostic X-ray apparatus and an analysis assisted by a simulation code].

A cloud chamber is a radiation detector that can visualize the tracks of charged particles. In this study, we developed a middle-type cloud chamber for use in practical training using a diagnostic X-ray apparatus. Because our cloud chamber has a heater to vaporize ethanol and features antifogging glass, it is possible to observe the vapor trails for a long time without the need for fine adjustments. X-rays with a tube voltage of 40 kV or of 120 kV (with a 21-mm aluminum filter) were irradiated at the chamber and the various phenomena were observed. We explain these phenomena in terms of the range of electrons and/or interactions between X-rays and matter and conclude that our analysis is consistent with analysis using the Monte Carlo simulation code EGS5.

[Fabrication of a visualization equipment for scattered X-rays in the diagnosis domain and proposal of a practical training].

We have built equipment that can visualize the angle distributions of scattered X-rays. The main body of the equipment is made of a lead-shielded box 340 mm long, 300 mm wide and 270 mm high. The collimated X-rays are introduced into the equipment from the front face, then scattered by the sample located in the center of the equipment. The X-rays scattering toward the upper side are detected by the phosphor plate. To verify the usability of the equipment, an experiment using diagnostic X-rays was carried out. X-rays with a tube voltage of 100 kV were narrowed down to 6 mm(phi) and a 2 mm-thick acrylic sample was irradiated. The experimental conditions with a tube current-time product of 300 mAs to 1500 mAs proved appropriate for obtaining suitable images on a 10 inch x 12 inch phosphor plate. The obtained images were analyzed using ImageJ. The experimental values were in good agreement with the theoretical distribution calculated by Klein and Nishina. Because the distribution of the scattered X-rays can be visualized in relatively simple experiments using the developed equipment, it is hoped that it will be of use for the practical training of beginners.

[An experiment to estimate locations of radioisotopes producing black spots on medical images].

Caused by the accident of nuclear power plants in the Fukushima at 2011, many radioisotopes (RI) were diffused to the environment. As a result, X-ray detectors were stained with RIs and black spots appeared on the medical images. Using the RI of (134)Cs and (137)Cs, black spots which appeared on the photostimulable phosphor plate (X-ray detector) were reproduced experimentally. The aim of this study is the following two points; firstly, to clarify the relationship between long-time irradiations of RI and fading effect, and secondly, to clarify the positional relationship between the RI sources and the X-ray detector based on irradiation times of RI. For the latter experiment, the samples were made by spraying water (containing the RI) in order to reproduce small point sources. Then, the sources were placed on the photostimulable phosphor plate or on the cassette, and corresponding images with different irradiation times were taken. The black spots could be reproduced with the condition, in which sources were directly adhered to the photostimulable phosphor plate. We observed the black spots when sources were placed on the cassette for one week. Based on the result, we summarized that the RI which are directly adhered on the photostimulable phosphor plate may produce the black spots.

[Experimental study of detectability of simulated lung nodule on computed radiography system using various X-ray beam qualities].

The purpose of this study was to discuss the optimal X-ray beam quality for detection of simulated lung nodule on a computed radiography system. We set up four types of X-ray beam quality (90 kV, 120 kV, 150 kV, and 120 kV + gadolinium filter), and kept the incident dose on the patient at 0.3 mGy. A receiver operating characteristic (ROC) analysis and a granularity measurement were used to evaluate the relationship between the detection of a low-contrast object and X-ray beam quality. As a result, the areas under the ROC curve (AUC) of 90 kV and 120 kV + gadolinium filter were significantly superior to those of 120 kV and 150 kV (p<0.05). However, a significant difference was not observed between 90 kV and 120 kV + gadolinium filter, 120 kV and 150 kV. The order of the granularity values gave good agreement with the results of visual evaluation. In conclusion, we considered that the optimal X-ray beam quality was 90 kV or 120 kV + gadolinium filter.

Proposal of a new method to prove that unnecessary information is not drawn on the image using statistical analysis.

The purpose of this study is to propose a new method of image evaluation using statistical analysis. We used the Sign test and the Wilcoxon test to analyze the statistical significance of image differences. Using this method, we evaluated whether the small electrode of the DAP meter appears in the X-ray image. Two observed values, which were obtained by averaging all values under all exposure conditions, were compared. All the observation tests showed the same sign. Thus, the results proved that the small electrode of the DAP meter is not present on the image. Using this method, it became possible to prove that the electrode was not depicted, which was impossible to determine using conventional methods. The method combining both the Sign test and the Wilcoxon test can be useful in image evaluation.

Postprocessing technique with MDCT data improves the accuracy of the detection of lung nodules.

PURPOSE: The aim of this study was to determine whether postprocessing techniques could improve the accuracy of detecting lung nodules. MATERIALS AND METHODS: A total of 154 segmented lung volumes of multidetector-row computed tomography (MDCT) data were the subject of the study. Lung nodules were present in 88 volumes and absent in 66 volumes. We prepared four groups: (1) 7- or 10-mm thick-section axial images; (2) 1-mm thin-section axial images; (3) sliding slab maximum intensity projection (MIP) images with a slab thickness of 15 mm; and (4) sliding slab volume rendering (VR) images with a slab thickness of 15 mm. Sixteen physicians reviewed each group in interactive cine mode. The observers' performance in the detection of lung nodule was evaluated by receiver operating characteristic (ROC) analysis. RESULTS: The observers' performance of the MIP and VR groups was significantly better than in other two groups. There was no significant difference statistically between the thin and thick groups. CONCLUSION: The detectability of lung nodules is improved with the use of sliding slab MIP and VR using thin-section image data. Thin-section volume data are essential for improving diagnostic accuracy, but observation of thin-section images without utilization of image-processing techniques dose not improve diagnostic accuracy.

Evaluation of osteoporosis in X-ray CT examination: a preliminary study for an automatic recognition algorithm for the central part of a vertebral body using abdominal X-ray CT images.

We have developed an algorithm that can distinguish the central part of the vertebral body from abdominal X-ray CT images to determine whether it is possible to aid a diagnosis of osteoporosis. We classified three measures for the principal component analysis and linear discriminant function. When we judged whether patients had osteoporosis or not, the ratio usable for diagnosing osteoporosis (sensitivity) was 1.00 (15/15), and for diagnosing as normal (specificity) was 0.64 (7/11). We believe that this algorithm can be used to aid in diagnosing osteoporosis, utilizing the measures obtained from the CT images.

[Significance of the visual evaluation method using the two-visit method (two-sample preference test suggested by Ferris)].

To increase the accuracy of the visual evaluation method, we studied the significance of the two-sample preference test using the two-visit method, as proposed by Ferris. Advantages of this method include not only its ability to estimate whether the image quality of the sample is statistically the same but also its ability to distinguish the difference between samples more clearly than when using the conventional two-sample preference test or paired-comparison method. However, a disadvantage is that this method involves two observations of the same sample. When using chest images, even if a difference between the samples is not recognizable by the conventional method, a significant difference can be elicited with this method. The data obtained by this method can be evaluated with the paired-comparison method, so some samples may be ranked as well. Therefore, we verified that the two-sample preference test, which Ferris formulated, is useful in visual evaluations.

[Development of a counting method for black spots caused by radioactive contamination on the imaging plate].

Due to accidents of the nuclear power plants in Fukushima prefecture, a lot of radioisotopes were diffused into the environment. They adhered onto the surface of the X-ray detector (imaging plate; IP) and many black spots were seen on the medical images. The process to count them is important to evaluate the degree of contamination and/or removal. In this study, we aimed to develop a counting method for black spots. Based on the analysis of the medical images having black spots, we summarized that areas affected by the certain black spots were limited to the eight pixels surrounding the most intensive pixel. The newly developed counting method was applied to these nine pixels (3×3 pixels) and selection rules were based on the following two information: 1. differences between the digital value of the most intensive pixel and those of the surrounding eight pixels, and 2. total summation of the digital values in the nine pixels. The estimated image based on our method showed a good concordance with the original image. Therefore, we summarized that our counting method is a powerful tool for estimating numbers of black spots.

[Radioisotope decontamination of X-ray detector (photostimulable phosphor plate)].

We tried to remove contamination of radioisotope (RI) for an X-ray detector (photostimulable phosphor plate; IP) and verified that our procedure suggested by Nishihara et al. was effective for decontamination. The procedure was as follows. First, the IP was kept for approximately twelve hours, and then it was processed [image (A)] as well as a clinical processing mode. Second, using a wet-type chemical wiper, we scavenged the IP to remove the adhered RI on its surface. Then, once again, the IP was kept for approximately fifteen hours and processed [image (B)] in order to check an effect of decontamination. Finally, the two images of (A) and (B) were analyzed using ImageJ, which can be downloaded as a free software, and a percentage of removal was calculated. The procedure was applied to two IPs using the FCR 5501 plus. In the present case, the percentage of removal was approximately 96%. The removed radioisotopes in the chemical wipers were analyzed by Ge detector. Then, (134)Cs and (137)Cs were found with activities of 2.9 4.3 Bq and 3.5 5.2 Bq, respectively. For three months after that, we cannot see black spots on the IPs owing to the contamination of the RI and there are no defects caused by decontamination using a wet-type chemical wiper.

[Development of a pin-hole camera using a phosphor plate, and visualization of the scattered X-ray distribution and optical image].

In order to obtain an image of scattered X-ray in the diagnosis domain, we have newly developed a pin-hole camera. Because of the necessity of the X-ray shielding, the pin-hole part has a depth corresponding to that of the shielded material. As a result, efficiencies of obliquely incident X-rays are reduced. To decrease the descent of the efficiencies, we developed a large camera using a 10 × 12 inch size phosphor plate as an X-ray detector. A phantom was irradiated by X-rays with conditions of 500 mAs and 5000 mAs, and images of scattered X-rays were obtained. The former image showed scattered X-rays from the phantom. The latter image showed those from the air of beam axis as well as from the phantom. Moreover, we made a new proposal to obtain an optical image using the fading effect.

[Estimation of activities caused by black spots in digital radiography systems: analysis of black spots by the low concentrate radioisotopes adhered directly to the surface of the phosphor plate].

Because of an accident of the nuclear power plants in the Fukushima, many radioisotopes (RI) have been diffused to the environment. As a result, black spots were appearing on the medical images which were taken by the phosphor plate. The aim of this study is to evaluate the activity (Bq) of radioactive contaminated IP based on the experiment using RI. The radioactive material ((134)Cs and/or (137)Cs) in the form of liquid was dropped on filter paper (25 mm(2)), and radioactive sources having 40-240 Bq activities were made. These sources were closely attached to the IP with irradiation times of 2-22 h. Then, we obtained the relationship between pixel values and products of activities and irradiation times. Using these relationships, we evaluated the activity in the contaminated IP. The evaluated value of approximately 7 Bq was in good agreement with a value which was inhered in a chemical wiper used for the decontamination of the IP. Based on the results, we summarized that almost all black spots were created by the RI adhered directly to the IP.

[Effective method for decontaminating radioactive X-ray detectors (imaging plates)].

Several hospitals have been observing black spots in medical images, and the radioisotopes (RIs) that cause the spots needs to be removed from the X-ray receptors. Our purpose is to show a flowchart for finding out under which conditions an imaging plate (IP) and other parts (for example, the cassette) are contaminated by RIs and to propose an effective method to remove them. The procedure follows. (1) Is RI activity low? (2) Are the surfaces of other parts contaminated? (3) Is the surface of the IP contaminated? (4) Are the insides of the other parts contaminated? To remove the adhered RIs, we applied a wipe test method using a wet type of chemical wiper. A certain hospital that observed black spots experimented with this method. As a result, the contaminated condition of the X-ray receptor was identified. In addition, we were able to remove the RIs from the IP. Therefore, our procedure is very effective for decontaminating adhered RIs from receptors.

Using the MDCT thick slab MinIP method for the follow-up of pulmonary emphysema.

PURPOSE: The purpose of this study was to evaluate the usefulness of thick slab minimum intensity projection (MinIP) as a follow-up method in patients with pulmonary emphysema. This method was used to determine the presence or absence of changes over time in the lung field based on multi-detector-row CT (MDCT) data. METHODS: Among patients diagnosed with pulmonary emphysema who underwent 16-MDCT (slice thickness, 1 mm) twice at an interval of 6 months or more, 12 patients without changes in the lung field and 14 with clear changes in the lung field were selected as subjects. An image interpretation experiment was performed by five image interpreters. Pulmonary emphysema was followed up using two types of thick slab MinIP (thick slab MinIP 1 and 2) and multi-planar reformation (MPR), and the results of image interpretation were evaluated by receiver operating characteristic (ROC) analysis. In addition, the time required for image interpretation was compared among the three follow-up methods. RESULTS: The area under the ROC curve (Az) was 0.794 for thick slab MinIP 1, 0.778 for the thick slab MinIP 2, and 0.759 for MPR, showing no significant differences among the three methods. Individual differences in each item were significantly more marked for MPR than for thick slab MinIP. The time required for image interpretation was around 18 seconds for thick slab MinIP 1, 11 seconds for thick slab MinIP 2, and approximately 127 seconds for MPR, showing significant differences among the three methods. CONCLUSION: There were no significant differences in the results of image interpretation regarding the presence or absence of changes in the lung fields between thick slab MinIP and MPR. However, thick slab MinIP showed a shorter image interpretation time and smaller individual differences in the results among image interpreters than MPR, suggesting the usefulness of this method for determining the presence or absence of changes with time in the lung fields of patients with pulmonary emphysema.

Accuracy of computed tomography attenuation measurements for diagnosing anemia.

PURPOSE: The purpose of this study was to determine which computed tomography (CT) attenuation parameter was the most appropriate to predict the presence or severity of anemia. MATERIALS AND METHODS: The subjects of the study wer 500 patients who had undergone a peripheral blood examination within 24 h of an unenhanced CT scan. Regions of interest were placed in the left ventricular (LV) cavity, thoracic and abdominal aortic lumens, inferior vena cava, and interventricular septum. The CT attenuation difference between the LV cavity and interventricular septum was also calculated. The relation between these measurements and the blood hemoglobin level was analyzed. In addition, using several selected parameters, a receiver operating characteristic (ROC) analysis was also performed. RESULTS: The difference in CT attenuation between the LV cavity and interventricular septum revealed the greatest correlation. ROC analyses also revealed the greatest area under the ROC curve in the differences between CT attenuation. CONCLUSION: The best quantitative method for the diagnosis of anemia was the difference in CT attenuation between the left ventricle and interventricular septum.

[Physical imaging properties of a flat panel X-ray detector system].

We report the physical imaging properties of a flat panel detector (FPD) designed for radiographic imaging applications (Revolution XQ/i digital chest imaging system, G.E. Medical Systems). The imaging properties of the detector were evaluated through measurements of the characteristic curve, modulation transfer function (MTF), and Wiener spectrum. The digital characteristic curves of the FPD system were measured for the two tube voltages (80 kV and 120 kV). They showed that the correlation between the pixel values of FPD and the incident exposure to the FPD was a linear correlation. The dynamic range of characteristic curves had a range from about 0.003 to 2 microC/kg at the exposure. The presampling MTFs for different tube voltage were almost the same, when we measured the MTFs at 80 kV and 120 kV. And also, there was no significant difference between the MTFs measured with the slit in the direction parallel to the horizontal direction and with the slit in the perpendicular direction. The relative resolution of the FPD system was a 46% higher than that of ST-V imaging plate of FCR (Fuji Computed Radiography) system at 2 cycles/mm. The digital Wiener spectrum of the FPD system was about 1/10 lower than that of the CR system. Thus the FPD system can provide superior imaging performance due to both high resolution and low noise.