Tow different experiments were conducted on shielding against neutron leakage from the maze of a medical linear accelerator room. One experiment was performed by placing neutron shielding materials made from boron carbide (B_4C) and polyethylene (manufactured by Tore Co., Ltd.) inside the entrance door, and the other by placing Lucite boards at the mouth of the maze. From the first experiment, the following facts were obtained. 1. The materials were mainly effective for thermal neutron shielding and the experimental values for thermal neutrons agreed well with the calculated results which considered only thermal neutron absorption in ^<10>B. 2. Tenth-value thickness of the materials was about 0.8kg/m^2 in B_4C thickness for thermal neutrons. 3. When materials were placed inside the entrance door to the maze, the dose equivalent for the capture gamma-rays in vicinity of the door decreased very effectively. Form the second experiment, the following became clear. 1. Tenth-value thickness of Lucite for a neutron dose equivalent depended on the position of the neutron source (Linac head) in the treatment room. The value was 7.5 cm nearest the source position and 5.5 cm farthest from the source position. 2. Dose equivalent transmission curve through a Lucite slab shield was nearly exponential within the limits of this experiment. A plan for leakage neutron shielding was made on the basis of above experimental results.
In the previous paper, we confirmed the clinical usefulness of hepatic clearance (hepatic blood flow), which is the hepatic uptake and blood disappearance rate coefficients. These were obtained by the initial slope index of each minute during a period of five frames of a hepatogram by injecting ^<99m>Tc-Sn-colloid 37 MBq. To analyze the information simply, rapidly and accurately, we developed a automatic quantitative analysis for liver functions. Information was obtained every quarter minute during a period of 60 frames of the sequential image. The sequential counts were measured for the heart, whole liver, both left lobe and right lobes using a computer connected to a scintillation camera. We measured the effective hepatic blood flow, from the disappearance rate multiplied by the percentage of hepatic uptake as follows, [numerical formula] Our method of analysis automatically recorded the reappearance graph of the disappearance curve and uptake curve on the basis of the heart and the whole liver, respectively ; and computed using BASIC language. This method makes it possible to obtain the image of the initial uptake of ^<99m>Tc-Sn-colloid into the liver by a small dose of it.
In this paper, an estimation was made of the image quality of the radiographic imaging system, the joint between probability matrix and frequency analysis theory was made clear with mediating the idea of the whitening noise filter. The detectivity d' of the ideal detector is defined as, [numerical formula] Where S_1 denotes the signal matrix, Φ^<-1>_<mn> the variance and co-variance inverse matrix, S (u), the signal spectrum and W(u), the Wiener spectrum of noise. The next fomula used was, Φ^<-1>_<mn>=G^TG Where G is the triangular matrix of the whitening noise filter. G corresponds to √<W (u)^<-1>> and GS_1 to the convolution between the whitening noise filter function on the spatial area and the signal distribution. Thus, Φ_<nn> can be represented by a non singular and symmetric matrix whose normal diagonal elements are all same, and G can be represented by a triangular matrix whose normal diagonal elements are all same. This proved that the noise process of the radiographic imaging system is a necessary ergodic.
We applied the digital angiography of the whole body on eleven occasions using the FCR system and large format cassette changer (Angiorapid 2). The results clearly discribed the image of the vascular system of the whole body using one injection of contrast medum, a valuable diagnosis was obtained which we consider useful for whole body digital subtraction angiography in widespread vascular and kidny disease. This paper presents the results of our investigation.
For protection against radiation leakage of neutrons, which is derived from a linear accelerator, polyethylene pannel of 20 mm thickness containing 10% B_2O_3 was placed inside the door of a radiotherapy room. This made it possible to diminish the leakage of neutrons by about 70%. Using various protective materials, containing boron and polyethylene mixed in different ratios, the effect of leakage raduction was studied. But in all cases, the results were essentially the same.
The motivation for development of digital radiography (DR) systems are related to cost reduction in diagnostic examinations, improvement in diagnostic accuracy and utility, reduction in patient exposure, flexibility of image display and processing, efficient image data storage and retrieval, and overall convenience. Major components of DR systems include x-ray detection, digitization, image processing and image display. Prototype units currently available are AS&E Medical Miro-Dose X-ray System, Picker Digital Chest System, various DSA units using image intensifier-TV system, ADAC Projection Digital X-ray System, Fuji Computed Radiography, and film-based DR system. Important physical properties of DR systems are sensitivity (or relative patient exposure), resolution, noise, system response (or dynamic range), scatter rejection and contrast sensitivity. Factors affecting resolution properties of DR systems involve X-ray beam characteristics, detector response, sampling aperture (or pixel size), sampling rate, display aperture and image processing. Factors affecting their noise are quatum noise, sampling aperture, sampling rate, quantization level, image processing and inherent system noise. Image processing techniques employed include windowing, zooming, filtering (smoothing, highpass filtering, unsharp masking, etc.), averaging, temporal subtraction, recursive filtering, matched filtering, energy subtraction, and hybrid subtraction. Effects of these image processing techniques are to eliminate structured noise, to increase dynamic range and/or to improve detection and visibility of radiologic objects. Digital radiography is a promising new approach for x-ray imaging system in diagnostic radiology. However, DR is, in many respects, much more complicated than conventional analog approach. Prior to the replacement of conventional techniques, it will be necessary to fully understand the impact of this new approach to all phases of diagnostic radiology.