Test body and method for checking the transmission properties of volume tomographs

Abstract

The invention relates to a test body for checking the transmission properties of volume tomographs, in particular radiological tomographs, which comprises several plates (2) that are connected to form a stack, in which adjacent plates (2) contact each other and said body comprises spheres (4) made of at least one material that is different from the plates (2) and having different diameters, wherein the respective spheres (4) are arranged in and/or between at least some of the plates (2), and wherein on/in the test body, preferably in the stack, at least one rod-shaped hollow profile, in particular at least one pipe having a circular cross section, is arranged. The invention further relates to a method for checking the transmission properties of a tomograph using such a test body (1).

Claims

1. A test body for checking the transmission properties of radiological tomographs, the test body comprising: a plurality of plates connected to form a stack in which adjacent plates contact each other, one of the plates being formed with a plurality of recesses, spheres made of at least one material different from the plates, of at least two different diameters, each in a respective one of the recesses, and each engaging an adjacent one of the plates, the spheres being in or between the one of the plates and the adjacent plate, and a tube is on/in the stack.

2. The test body as claimed in claim 1, wherein the tube passes through the plates forming the stacks and connects the plates forming the stack to one another.

3. The test body as claimed in claim 1, further comprising: a sensor in the tube for measuring a radiation dose that occurs during a test.

4. The test body as claimed in claim 1, wherein the stack forms a passage holding the tube removably.

5. The test body as claimed in claim 4, wherein two of the tubes that are axially aligned and axially spaced are in the passage.

6. The test body as claimed in claim 5, further comprising: a sensor for measuring a radiation dose that occurs during a test in the passage in a space between the two tubes.

7. The test body as claimed in claim 1, wherein the stack has an external shape corresponding at least substantially to a human or animal body part.

8. The test body as claimed in claim 1, wherein the sphere diameter lies between 5 and 10 mm.

9. The test body as claimed in claim 1, wherein the sphere diameter is between 1 and 5 mm.

10. The test body as claimed in claim 1, wherein the adjacent plate is also formed with recesses in which the spheres are also partly received.

11. The test body as claimed in claim 1, wherein the recesses of the one plate are throughgoing cylindrical holes.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Embodiments of the invention are explained in more detail with reference to the following figures:

(2) FIG. 1a is a side view of the test body according to the invention;

(3) FIG. 1b is an axial section through the test body with only the center plate shown;

(4) FIG. 1c is a top view of the test body;

(5) FIG. 1d is a top view showing a possible plate construction according to the invention;

(6) FIG. 2 shows 3D views taken according to the invention by various tomographs;

(7) FIG. 3 is a graph illustrating the MTF with various tomographs;

(8) FIG. 4a is a side view of another test body in accordance with the invention;

(9) FIG. 4b is a section taken along line IVb-IVb of FIG. 4a; and

(10) FIG. 5 is a partly sectional view of the body of FIGS. 4a and 4b.

SPECIFIC DESCRIPTION OF THE INVENTION

(11) In a side view and in plan, FIGS. 1a-1d show a test body 1 according to the invention that is made up of a plurality of plates 2 that are stacked on top of one another and that here are connected by a cylindrically tubular rod 3 that passes through the plates 2 centrally. In this embodiment, the tube 3 is formed from aluminum and has threads at its ends in order to press the plates 2 against one another by nuts on these threaded ends.

(12) As described in the general part, the invention is not restricted to such a design. Also at least one tube that does not perform the function of connecting the plates 2, can provided in or outside the stack.

(13) According to the embodiments discussed above, a plurality of spheres 4 that according to the invention have at least two different diameters can be provided on the faces of the individual plates 2 or between two adjacent plates 2. FIG. 1b shows this while omitting the plates 2. There are therefore at least spheres of a first group with a large diameter and spheres of a second group with a small diameter, the spheres from the group with the larger or largest diameter of all spheres being provided to determine a measure of the MTF, and the spheres with a smaller diameter than the largest diameter being provided to determine the geometric imaging accuracy or the distortion of the tomograph or of the evaluation algorithms that it is using. According to the invention, the MTF can also be determined based on the at least one tube 3, as needed exclusively or in combination with spheres.

(14) Regardless of the shape of a test body 1, a larger number of the smaller spheres are provided for determining the distortion than are provided of the larger/largest spheres.

(15) In the case of a ball-shaped test body, as shown here, at least one of the larger/largest spheres is provided per octant of the spherical test body.

(16) Here, FIG. 1a shows an external view of such a test body 1 that is substantially spherically ball-shaped and therefore represents a head of a human being that, for example, is to be measured with the tomograph in a subsequent examination or treatment.

(17) Here, this spherical shape is approximately formed in that, starting from a central plate with circular cross section and the largest diameter, further plates with diameters that become successively smaller in steps are stacked above and below this plate so that the diameter of the test body upward and downward is reduced in steps. This results in an approximately spherical shape with a diameter specified here by way of example of 17 cm.

(18) Of course, any other dimensions are possible here, as well as other designs of the test body in order to simulate other body parts.

(19) FIG. 2 is 3D views that are formed from the individual layer images of an image stack, the position of the individual spheres in the particular representation being represented by their visual reproductions.

(20) Here, FIG. 2 shows the recordings that have been made or calculated with the same test body 1 for different tomographs or manufacturers thereof. Here, the individual spheres or their visual reproduction 4′ in the image stack have been investigated to establish how great the deviation of the visual representation of a sphere 4 is compared with the actual desired position in the test body, where the magnitude of the deviation established is marked in color.

(21) It can be seen here that different tomographs produce different deviations and therefore different imaging errors in the visual reproduction of the test body even though they are measuring the same test body.

(22) Accordingly, with a knowledge of these deviations, it is also possible to match visual reproductions of different tomographs to one another using one and the same test body, for example in order to examine or treat the actual body part in a later application, for example in diagnostic examinations or therapy, using different types of tomographic method.

(23) For example, it is possible to match, i.e. to superimpose, tomographic images of a magnetic resonance tomograph with the X-ray images of a computer tomograph when, namely, on the one hand, such a test body that opens up the possibility of reproducing the spheres in the individual X-ray layer images is used to determine the geometric distortion of the computer tomograph and, on the other, to check an MRT with one test body, plastic spheres or at least non-magnetic/non-magnetizable spheres being used in this test body instead of, for example, metallic spheres. Here, the two different test bodies are formed only from different materials with regard to the plates and spheres, but have the same size and shape, in particular with the same manufacturing tolerances.

(24) Furthermore, FIG. 3 shows that, based on the larger or largest spheres and/or the at least one tube 3, it is possible to check the modulation transmission function by the same test body with different tomographs. Here, the results of FIGS. 2 and 3 can be determined from the same series of measurements.

(25) Here, FIG. 3 represents the modulation transmission function for the different tomographs tested by way of the graph shown that plots the MTF against the radius. Preferably, according to the invention, the MTF is determined as mentioned in the general part of the description described in the introduction, in particular with the over-sampling principle described therein.

(26) Here too, it can be seen that, when using the same test body as shown in FIGS. 1a-1d, this results in different modulation transmission functions of the different tomographs. Accordingly, these different tomographs with the different modulation transmission functions can be compared with one another and therefore chosen specifically for the application.

(27) FIGS. 4a and 4b show a cylindrical test body that is made up of a plurality of axially stacked plates 2. The left-hand sectional view shows, in one plate, the spheres 4 of different diameter therein and also—here centrally—at least one tube 3, for example made of metal such as aluminum or magnesium, in the circular plate 2. The advantage here is that the tube 3 extends through a plurality of plates 2 and thus provides the same circular image in a plurality of layer images, thus enabling the MTF to be tested in this plurality of layer images based on the same criterion in all cases.

(28) FIG. 4b also shows a possible development with a plurality of additional rods 6 that are shown dashed and all converge on the right-hand tube 3. The additional rods are only around the right-hand tube and here preferably only over a part of its length, in particular starting from a cover plate of the stack. FIG. 5 also shows this as a possible dashed development.

(29) FIG. 5 shows an embodiment in which a test body, here by way of example cylindrical, has an internal passage 5 into which two tubes 3a and 3b that are axially aligned but axially spaced are inserted. As a result of the spacing, an inner free passage region 5a is produced between the tubes 3a and 3b that is not surrounded by raw material, in particular therefore not by metal, and into which, for example, a sensor 7, or another device can be inserted in order to record additional measurements of the layer images such as, for example, the radiation dose that was used. FIG. 4b also shows this free passage region 5a.

(30) A significant advantage according to the invention lies in that both the modulation transmission function and also a measure of the geometric distortions can be obtained from the same data record that is produced with one and the same test body during the tomographic recording, where applicable with measurement of a radiation dose or other measured values.

(31) Not shown is the fact that the noise-power spectrum and the signal-noise ratio can also be tested with a test body of the kind according to the invention. Algorithms that are basically known from the prior art can be called upon here, however using the test body according to the invention.

(32) As a general principle, in a development, also a test body of the kind described in the general part or in the execution part is used in a further body, in particular in a test body, likewise of the kind described above, but with an internal free volume. This enables a modular system to be created.