JPS6253770B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a test chart used for evaluating the image quality of radiographs of diagnostic areas.

In X-ray diagnosis, evaluating the image quality of X-ray photographs is an important task in order to make a proper diagnosis. By the way, the following three items can be cited as important factors when evaluating the image quality of an X-ray photograph.

(1) Resolution of the photographic image (resolving power), (2) Degree of shading of the photographic image (contrast), (3) Condition of surface density of the photographic image (graininess), and by comprehensively evaluating these, Appropriate image quality evaluation can be performed.

However, in the past, these were measured and evaluated individually. That is, for example, regarding resolving power, a resolving power chart is taken on an X-ray photograph, and based on that, the limiting resolving power and MTF (Modulation
Transfer Function) was measured, and photographic contrast was determined by taking an X-ray photograph of an aluminum staircase and determining the photographic contrast from the difference in photographic density of each step. Furthermore, regarding graininess, the roughness and density of the surface has been observed using a measuring instrument such as a microphotometer. In this way, each factor that determines image quality has been measured individually and without taking into account their mutual relationships, so it is important to evaluate the quality of X-ray images, which is determined by integrating these factors, especially in a quantitative manner. was becoming difficult.

The present invention has been made based on the above circumstances, and it is an object of the present invention to provide a test chart for evaluating X-ray photographs that can perform accurate evaluation, especially quantitative evaluation, of X-ray image quality. It is something.

The present invention will be specifically explained below using Examples.

1 and 2 are plan views showing an example of a test piece used in the test chart of the present invention. These test pieces 1 are made by processing metal foils (for example, foils of aluminum, copper, phosphor bronze, etc.) using foil processing technology (for example, etching process), and the test pieces 1 shown in FIG. Test piece 1 whose planar shape is C-shaped is shown in FIG.
is processed to have an O-shape. Here, the dimensions of each part are, for example, if the distance of the C-shaped notch is A, the inner diameter of the disc part is B, and the outer diameter is C, the ratio of these is A:B:C=1:3:5 It is formed so that

3 and 4 show a case where a plurality of the test pieces 1 are arranged on a rectangular or disc-shaped substrate 2 to form a test chart. In either case, the substrate 2 is made of a material with low X-ray absorption rate, such as a synthetic resin plate. In addition, each test piece 1 is arranged on a rectangular board 2 as shown in Figure 3, so that the external dimensions change in the vertical direction from large to small, and the external dimensions are the same in the horizontal direction. Arrange things so that they are lined up. Further, for a disk-shaped substrate as shown in FIG. 4, the outer diameters are arranged radially from the center toward the outside, from the smallest to the largest. The thickness of each test piece 1 is also selectively formed to have various thicknesses as appropriate. For example, for test pieces arranged on a rectangular substrate, the thickness may be gradually reduced in the horizontal direction, and for test pieces arranged on a disk-shaped substrate, the thickness may be gradually reduced within the same circumference. Form. Here, substrate 2
The test piece 1 is fixed to the test piece 1 using an appropriate adhesive or the like. Incidentally, the shape of the test piece 1 is not limited to the case where only one type of C-shape or O-shape is disposed on one substrate, but a suitable combination of both may be disposed. Especially for C-shaped test pieces, the direction of the notch is
For example, the substrate 2 may be arranged facing upward, facing left, or facing downward, and the shape of the substrate 2 may be square.

Such a test chart is used by being placed in an X-ray apparatus as shown in FIG. In the figure, 3 is an X-ray tube device, 4 is a water phantom having almost the same X-ray transmittance as the human body, 5 is the aforementioned test chart, 6 is a top plate, and 7 is an X-ray film and an intensifying screen. This is the cassette that was housed.

First, an X-ray control device (not shown) is operated to drive the X-ray tube device 3 to emit X-rays. The emitted X-rays pass through the water phantom 4 and the test chart 5 and reach the film in the cassette 7. The film on which the X-ray transmission image was taken in this way is developed and
Obtain line pictures. The following evaluations are performed using this X-ray photograph.

Based on the spatial frequency characteristics (spatial resolution) between the X-ray tube device 3 and the top plate 6, different patterns of photographic images are obtained corresponding to each test piece. For example, resolving power can be determined and evaluated by observing how blurred the periphery of a pattern corresponding to a C-shaped or O-shaped test piece is. In particular, since it is difficult to identify patterns corresponding to thin test pieces with small outer diameters, it is possible to accurately evaluate the resolution depending on the degree of difficulty in identifying them. Next, since differences in shading should appear in stages in patterns obtained from test pieces whose thickness gradually becomes thinner, we can determine the contrast by determining this gradation. Evaluation can be carried out. At this time, if only an O-shaped test piece is used, the tester will judge that everything is circular due to psychological influence, and accurate judgment cannot necessarily be made.However, if a C-shaped test piece is used, By arranging the notches in various directions as described above, there is an advantage that resolution and contrast can be accurately evaluated without being psychologically influenced to the extent that the directions of the notches can be recognized. Further, by using a test chart in which O-shaped and C-shaped test pieces are appropriately combined and arranged, measurements can be made without being influenced by the preconceived notions of the measurer, making it possible to perform more objective evaluation. Furthermore, by observing the pattern of a test piece with a particularly small outer diameter, the graininess of the intensifying screen and film housed in the cassette can be evaluated.

By the way, when taking X-ray pictures with various X-ray devices using the same test chart,
Sometimes the measurer memorizes the placement of the test pieces and recognizes patterns that cannot actually be seen during evaluation; in this case, a disk-shaped test chart like the one described above is used. However, if it is rotated appropriately each time it is used, such problems will not occur and objective evaluations can always be made.

FIG. 6 is a characteristic diagram showing the measurement results when using the test chart as described above. Here, we used six types of test pieces (2.5, 4.5, 6, 7.5, and 9 mmφ) with an outer diameter of 50 μm and evaluated them by photographing them together with a 20 cm water phantom. Figure 6 shows three types of X-ray tube voltages (60, 100,
120kV) measurement results are shown. For each outer diameter of the test piece, it is shown that the correct answer rate generally decreases as the tube voltage increases. Furthermore, it can be seen that at each X-ray tube voltage, the correct answer rate and the outer diameter of the test piece are quantified as a constant function.

By using the test chart of the present invention described in detail above, it is possible to comprehensively evaluate resolution, contrast, and graininess at the same time just by observing the obtained X-ray photograph, and therefore to accurately evaluate image quality. be able to. Then, a quantitative evaluation can be performed based on the measurement results. Furthermore, when X-ray photographs of a plurality of X-ray apparatuses are obtained using the same test chart, the X-ray image quality of each X-ray apparatus can be quantitatively evaluated by comparing them with each other.

[Brief explanation of the drawing]

1 and 2 are plan views showing an example of the test piece used in the test chart of the present invention;
4 and 4 are plan views showing an example of a test chart configured by arranging the test piece on a board, and FIG. 5 shows an example of an X-ray device in which the test chart is arranged. Schematic diagram, No. 6
The figure is a characteristic diagram showing the measurement results when using the test chart of the present invention. 1... Test piece, 2... Board, 3... X-ray tube device, 4... Phantom, 5... Test chart, 6... Top plate, 7... Cassette.

Claims (1)

[Claims] 1. A test piece comprising a substrate made of a material with good X-ray transparency and a plurality of test pieces made of metal foil having a C-shape or an O-shape, and having an external dimension of the test piece. Thicknesses are sequentially varied in a stepwise manner in a predetermined direction, and the thicknesses are sequentially varied in a stepwise manner corresponding to each of the different external dimensions. A test chart for evaluating X-ray photographs. 2. For X-ray photograph evaluation according to claim 1, wherein the substrate is disk-shaped, and the test pieces are arranged in stages radially with respect to the center of the disk. test chart.