Diffusion weighted imaging (DWI) is now widely used in magnetic resonance (MR) imaging of the head and body. Moreover, the Apparent diffusion coefficient (ADC) value is often used for the differential diagnosis of the tumor. However, the effect of the surroundings on the ADC value has not been reported. In this study, we used the phantom completely sealed up to measure the change in the ADC value depending on the surroundings material. The results showed that the ADC value decreased according to the density of superparamagnetic iron oxide (SPIO) in the surroundings. Clinically, hemorrhage or iron deposit around the tumor may affect the ADC value of the tumor and result in under-estimation.
We performed a fundamental study for the measurement of the bone mineral density (BMD) of the calcaneus by using the radiographic contrast (RC). The RC of the bone radiography is proportional to the product of the thickness of the bone Hb, the gradient of the image detector system and the difference of the linear attenuation coefficient between the bone and the soft tissue. Therefore, the radiographic contrast per unit bone thickness (RC/Hb) can be used as a good measure of the BMD. Though the linearity of RC/Hb is maintained for x-rays with the monochromatic energy spectrum, the energy spectrum of the x-rays employed in clinical examinations is continuous. The relationship between RC/Hb value and BMD value was examined by two kinds of added filter (Al with 5 mm and 15 mm thickness) and two kinds of bone phantoms (the phantom with 1 cm and 4 cm thickness, which is made by a bone equivalent material). The experimental results obtained from the 1 cm bone phantom indicated an approximately linear relationship. However, the experimental results obtained from the 4 cm bone phantom indicated a non-linear relationship due to the beam hardening. Therefore, the estimation of the calcaneus BMD value in clinical practice is performed by using the relationship between RC/Hb and BMD values obtained from experimental results for the bone phantom with 4 cm thickness.
We proposed and optimized a simple method of temporal subtraction image between successive bone single photon emission computed tomography (SPECT) images for supporting interpretation of temporal changes, and we evaluated its clinical utility. This method consisted of image registration, count normalization, and image subtraction. For image registration, we used a BEAT-Tl software. For count normalization, a pixel value of the normal accumulation part in a SPECT image was used as a reference region. We evaluated accuracy of image registration and optimized the normalization procedure. The accuracy of image registration ranged within 1 pixel in all directions (x, y, x-axis, and rotation). As the reference region, the second lumbar vertebra showed the best results in terms of the normalization procedure. Our method simply allowed the production of a temporal subtraction image. Because the software used in this method can be used free, this method would be available in every institution.
Automatic contouring system using electrostatic capacitance sensor can sense electrostatic capacitance between a detector and patients’ side space. So the system can be set it at an arbitrary distance. On the other hand, this system is so complicated that it is difficult to forecast the detector motion. We studied the difference of the distance according to the rotation direction and verified the system accuracy. In addition, we studied it again after software updating. We compared the set distance with the distance between phantom and detector surface at the closest point. Next, we scanned the phantom with relative 90 degree detector position in a clockwise direction (CW) and a counterclockwise direction (CCW). We took a video of the detector trajectories and compared them. Finally, we compared the results before and after updating the software. At the set distance of 10 mm, the distance between phantom and detector surface distance was 12.00 mm. And at the set distance of 50 mm, it was 52.00 mm. Thus we confirmed the accuracy and repeatability of this system. For the rotation orbit, the CCW rotation kept the distance near the set distance. But the CW rotation rotated over a bigger distance than the set distance at the center position over the phantom. After software updating, this difference became small. Using this system, the rotation orbits differed by their rotation direction. However, after updating software, results indicated that selecting an adequate set distance for every patient and examination makes the image optimum.
It is well known that Interventional Radiology (IVR) is useful. However, the patient dose in IVR is increasing because of the prolongation of fluoroscopic time and the increase in the number of radiographies in recent years. We studied the adequacy of the additional filter for the decrease of the skin surface dose in patients with hepatocellular carcinoma of transcatheter arterial embolization (TAE). In 20 patients (15 men and 5 women, average age: 66.9 and 72.0 years old) who had undergone TAE, we estimated the skin surface dose from the records of their exposure condition (tube voltage, tube current, time, and field size of image intensifier) and the results of the phantom experiment with 2 kinds of additional filter. The estimated skin surface dose of the patient was 1.75±0.84 with the additional filter of 1.5 mm thickness of aluminum (1.5 mmAl), 1.46±0.67 Gy with 0.03 mm thickness tantalum (0.03 mmTa) and 1.17±0.55 Gy with 0.06 mm thickness of tantalum (0.06 mmTa). Against a skin surface dose of 1.5 mmAl, the dose reduction of 16.7% was shown in 0.03 mmTa and 33.2% in 0.06 mmTa. With a DSA phantom of iodine density 0.5 and 1.0 and 2.0 mgI/ml, DSA images were acquisitioned at tube voltage 70, 80 and 90 kV to compare the detectability of contrast media in 0.06 mmTa with 1.5 mmAl. To evaluate the detectability of contrast media in 0.06 mmTa in 1.5 mmAl, receiver operating characteristic (ROC) analysis was performed with the pixel value of the phantom image. The area under the ROC curve in a 1.5 mmAl filter and the 0.06 mmTa filter provided with each contrast media density and each tube voltage was approximately a constant value. It was suggested that there was no differences in the detectability of contrast media in both additional filters. In conclusion, the skin surface dose of the patient was able to be reduced 33.2% without decreasing contrast media detectability by changing the additional filter from 1.5 mmAl to 0.06 mmTa. It was most suitable in TAE in our hospital to choose 0.06 mmTa as an additional filter.
In this study, the sensitivity in the diagnostic X-ray region of the single crystalline Si photovoltaic solar panel, which is expected to grow further, was measured by using an X-ray tube. The output voltage of the solar panel was clearly proportional to the tube voltage and a good time response in the irradiation time setting of the tube was measured. The factor which converts measured voltage to irradiation dose was extracted experimentally using a correction filter to investigate the ability of the solar panel as a dose monitor. The obtained conversion factors were NS=13±1[μV/μSv/s] for the serial and NP=58±2[μV/μSv/s] for the parallel connected solar panels, both with the Al 1 mm+Cu 0.1 mm correction filter, respectively. Therefore, a good dose dependence of the conversion factor was confirmed by varying the distance between the X-ray tube and the solar panel with that filter. In conclusion, a simple extension of our results pointed out the potential of a new concept of measurements using, for example, the photovoltaic solar panel, the direct dose measurement from X-ray tube and real time estimation of the exposed dose in IVR.