Methods for detecting damage to silicone implants and computed tomography equipment

Abstract

Method for detecting damage to silicone implants in an object area of ​​a human body using a computed tomography device (10) comprising the following steps: a) Taking at least two computed tomography images of the object area at different X-ray spectra or different individual energies of the X-ray radiation, b) Reconstruction of at least two computed tomography scans into 3D datasets containing X-ray attenuation values ​​or equivalent material densities in the sense of a base material decomposition of voxels of the object area, c) Determination of a data point (18) in a diagram for each voxel of interest, wherein the X-ray attenuation values ​​for different X-ray energies are plotted against each other, d) Comparison of the data point (18) or any other value determined from the X-ray attenuation values ​​for each voxel of interest with known data points or values ​​of body tissue (15, 16) and of silicone (17), and e) Issuance of a notification or warning when the data point (18) or other value deviates from the known data points or values ​​for body tissue (15, 16) by at least one predetermined first threshold and simultaneously approaches the known data point or value for silicone (17) by less than one second threshold.

Description

[0001] The invention relates to a method for detecting damage to silicone implants in a human body using a computed tomography device according to claim 1 and a computed tomography device according to claim 8.

[0002] The document DE 10 2006 009 222 A 1 is known as the state of the art.

[0003] The detection of damage to silicone implants permanently inserted into the human body is of current interest. If such a silicone implant is damaged, silicone can leak out and enter the surrounding tissue. To prevent potential health problems caused by the silicone, leaking implants must be removed as quickly as possible. One problem is that such damage to a silicone implant must first be detected.

[0004] Several methods are known for detecting damage to silicone implants, such as magnetic resonance imaging (MRI), ultrasound, or computed tomography (CT). MRI is a suitable detection method, but it cannot be used for every patient and is also very complex. Furthermore, the patient's positioning must be changed compared to a subsequent surgical procedure, complicating surgical planning. Ultrasound measurements generally do not allow for a 3D representation of the area, meaning the back of the implant is not visible. A single CT scan often yields unreliable results. Because silicone implants have a density close to that of soft tissue (the implants should not be perceived as foreign bodies), the CT value of the silicone used is close to that of soft tissue and relatively nonspecific.Extensive damage to the implant shell with significant leakage of silicone material is generally visible; minor damage and cracks with small amounts of silicone leaking from the implant are not easily detectable.

[0005] The object of the present invention is to provide a method that enables the detection of silicone in the human body, even in small quantities. Furthermore, the object of the invention is to provide an X-ray device suitable for carrying out the method.

[0006] The problem is solved according to the invention by a method for detecting damage to silicone implants in a human body using a computed tomography device according to claim 1 and a computed tomography device according to claim 8. Advantageous embodiments of the invention are the subject of the respective dependent claims.

[0007] The inventive method for detecting damage to silicone implants in an object area of ​​a human body using a computed tomography device comprises the following steps: a) Taking at least two computed tomography images of the object area at different X-ray spectra or different individual energies of the X-ray radiation, b) Reconstruction of at least two computed tomography scans into 3D datasets containing X-ray attenuation values ​​or equivalent material densities in the sense of a base material decomposition of voxels of the object area, c) Determination of a data point in a diagram for each voxel of interest, where the X-ray attenuation values ​​for different X-ray energies are plotted against each other, d) Comparison of the data point or any other value determined from the X-ray attenuation values ​​for each voxel of interest with known data points or values ​​of body tissue and silicone, and e) Issuance of a notification or warning when the data point or other value deviates from the known data points or values ​​for body tissue by at least one predetermined first threshold and simultaneously approaches the known data point or value for silicone by less than one second threshold.

[0008] The method according to the invention enables the simple, automatic, and unambiguous detection of even very small amounts of silicone leakage from a silicone implant into the surrounding body tissue for any area of ​​interest, thus revealing even minor damage to the implant. The invention is based on the finding that the X-ray attenuation values ​​of silicone in a single computed tomography scan are very close to those of soft tissue, but a significant difference is discernible when comparing computed tomography scans with different radiation spectra. By automatically comparing the values ​​of the area of ​​interest with known values ​​for body tissue and silicone, damage to the implant can be detected with a high degree of probability. The threshold values ​​can be selected accordingly.The procedure can also facilitate surgical planning for a subsequent surgical procedure to remove the implant or the leaked silicone.

[0009] The indication or warning could, for example, take the form of a visual marker (e.g., colored) of the affected areas on a CT image display, possibly after three-dimensional reformatting of the images. It could also include, for example, a complex display of the affected data points in the diagram, a 3D volume representation of the object area, or a text display.

[0010] If necessary, noise reduction and / or artifact correction can be performed at any time to eliminate measurement errors from the data points in the diagram. According to one embodiment of the invention, the attenuation coefficients µ or the CT values ​​for each voxel of interest are plotted in a diagram or table as X-ray attenuation values, and the data points are compared with known values. The linear attenuation coefficient or absorption coefficient µ generally describes the attenuation of the intensity of electromagnetic radiation as it passes through a material. The CT value, which is measured in Hounsfield units (HU), is by definition derived from the attenuation coefficient of the material in question and that of water. [CT value]:=μ−μwaterμwater⋅1000HU

[0011] To reduce deviations in the measured CT value through so-called beam hardening, a known correction method (raw data-based dual energy CT method, specifically for calculating monoenergetic images; iterative method with forward projection of segmented image areas) can be used.

[0012] According to a further embodiment of the invention, at least one effective atomic number or equivalent material density is determined from the X-ray attenuation values ​​in the sense of a base material decomposition and compared for each voxel of interest with the known effective atomic numbers or equivalent material densities of body tissue and silicone. The effective atomic number and equivalent material density can be unambiguously calculated from the at least two computed tomography scans. In particular, no similarity between body tissue and silicone is discernible at these values, so that the detection of silicone can be achieved even more effectively.

[0013] Furthermore, raw data-based methods also make it possible to perform a base material decomposition without first calculating attenuation values. In this case, these material densities are plotted on the diagram. Based on this, all other mentioned values ​​can be determined from the equivalent material densities of the two base materials.

[0014] In a further embodiment of the invention, any combination of soft tissue and fat is used as a reference value for body tissue. These two tissue types generally describe the properties of body tissue very well, particularly in the breast area, which represents the main application area for silicone implants. As an advantageous embodiment where body tissue is considered to be any combination of soft tissue and fat, a perpendicular distance of the data point from a line connecting the known values ​​of soft tissue and fat is determined for comparison and compared with the first threshold value. If the first threshold value is exceeded and the known data point for silicone is approached by less than a second threshold value, a notification or warning is then issued.

[0015] According to a further embodiment of the invention, three or more computed tomography images of the object area are acquired at different radiation spectra or different individual energies of the X-rays. This allows for a more complex determination of X-ray attenuation values ​​or data points and corresponding comparisons, resulting in even more definitive detection of silicone.

[0016] Regardless of which of the aforementioned parameters is used to detect the presence of silicone, the data point can also be mapped to a measured value using a predefined table. The table contains the measured values ​​for a fixed number of attenuation levels at low and high tube voltages. The measured value is then obtained by appropriate interpolation of the adjacent table values.

[0017] To carry out the procedure, a computed tomography device can be used which has a dual-energy imaging unit for acquiring at least two computed tomography images of the object area at different radiation spectra or different individual energies of the X-ray radiation, as well as a system control with a computing unit for reconstructing the computed tomography images and for carrying out steps c and d, and an output unit for carrying out step e of the procedure.

[0018] The invention and further advantageous embodiments according to features of the dependent claims are explained in more detail below with reference to schematically illustrated exemplary embodiments in the drawing, without thereby limiting the invention to these exemplary embodiments. The drawing shows: Fig. 1 a sequence of a method according to the invention, Fig. 2 a view of a device for carrying out the procedure, Fig. 3 a diagram with example values ​​plotted against each other to illustrate the method according to the invention and Fig. 4 a sequence of an alternative method according to the invention.

[0019] In the Fig. Figure 1 shows an exemplary sequence of a method according to the invention.

[0020] In a first step, a) at least two computed tomography (CT) scans of the object area are acquired with different spectral distributions of the X-rays. A multi-energy CT scanner, such as a dual-energy CT scanner, is used for acquiring these scans. This scanner allows for the simultaneous or nearly simultaneous acquisition of at least two CT scans with different spectral distributions of the X-rays or different X-ray energies. Different spectral distributions or different X-ray energies can be achieved, for example, by using different tube voltages in the X-ray tube.

[0021] In a second step (b), at least two 3D datasets are reconstructed from the raw data of the two computed tomography scans. These datasets contain X-ray attenuation values ​​of voxels within the object region for the respective spectral distribution of the X-ray radiation. X-ray attenuation values ​​can be understood here as linear attenuation coefficients µ, as well as, for example, the derived CT value or equivalent material densities in the sense of a base material decomposition. Additionally, smoothing filters or correction algorithms can be applied before or after the reconstruction to compensate for noise, measurement errors, or blurring.

[0022] In a third step (c), a data point is determined for each voxel of interest within the object area in a diagram or table, where the X-ray attenuation values ​​for different spectral distributions or X-ray energies are plotted against each other. For example, for a given voxel, the CT value at high X-ray energy is plotted on one axis of the diagram against the CT value at low X-ray energy on the other axis. The corresponding data points are used as the basis for the subsequent evaluation; they can also be displayed on a display unit.

[0023] In a fourth step d), for each voxel of interest, the data point or another value determined from the X-ray attenuation values ​​is compared with known data points or values ​​from body tissue and silicone. This fourth step d) can be divided into two sub-steps. The first sub-step d1) comprises the comparison with known values ​​from body tissue, and the second sub-step d2) the comparison with known values ​​from silicone, not necessarily in this order. Only one of the sub-steps can be performed at a time, as shown in Fig. 1 shown, or alternatively both sub-steps can be carried out as shown in Fig. 4 shown.

[0024] For the first sub-step d1), the data point of the plotted CT values ​​for the voxels of interest is compared with a known data point for soft tissue or fat, or a mixture of both. For this comparison, the distance between the data point of the voxel of interest and the known value is determined and compared with a first, e.g., previously defined, threshold value.

[0025] If, for example, a mixture of soft tissue and fat of an unknown composition is expected, it is advantageous to calculate the perpendicular distance of the data point of the voxel of interest from a connecting line linking the known data points for fat and soft tissue. A data point of body tissue consisting of any mixture of soft tissue and fat (as well as water) will certainly lie on such a connecting line between the pure substances soft tissue and fat. If, on the other hand, the data point is at a distance from the connecting line, then it is highly probable that another material is contained in the body tissue. Such a method for three-material decomposition is known, for example, from DE 10 2006 009 222 A1.

[0026] In the Fig. Three examples are the data point for fat 15 and the data point for soft tissue 16 in a plot of high-energy CT values.high against CT values ​​of low X-ray energy Ct low The diagram shows the line connecting the two points, 19 and 19. The data point of the voxel of interest, 18, has a perpendicular distance 20, as indicated by the dashed line, to the line connecting the two points, 19.

[0027] Alternatively, another value, such as the effective atomic number or the material density, can be determined from the X-ray attenuation values ​​for each voxel of interest and compared with the known effective atomic numbers or material densities of body tissue (here again, for example, fat, soft tissue, or a mixture thereof). The comparison includes, in particular, determining the distance between the values ​​and comparing them with the first threshold value previously defined in this context.

[0028] For the second sub-step d2), the data point of the plotted CT values ​​for the voxels of interest is compared with a known data point for silicone, whereby in particular the distance between the data point of the voxel of interest and the known value is determined and compared with a second, e.g. previously defined, threshold value. This is also described in the Fig. Figure 3 shows the data point of interest, 18, at a distance 21 from a known data point for silicone, 17. The plot can alternatively show other X-ray attenuation values, such as the linear attenuation coefficient m. The effective atomic number or the equivalent material densities can also be compared with the values ​​for silicone. The data point for the corresponding silicone being sought (variations may occur depending on the manufacturer, for example) can also be measured beforehand.

[0029] In the Fig. Figure 4 shows that both sub-steps, the first sub-step d1 and then the second sub-step d2, are performed first. Alternatively, this can also be done in reverse order.

[0030] In a fifth step (e), a notification or warning is issued or displayed if the distance of the data point of the voxel or other value of interest deviates from body tissue (e.g., fat, soft tissue, a mixture of fat and soft tissue in the form of the connecting line) by at least one first threshold value, or from silicone by less than one second threshold value, or alternatively, if both conditions are met. The notification or warning can take many forms. For example, it can be displayed as text or a graphic with the corresponding markers on a display unit (e.g., a monitor). A 3D representation of the object area can also be shown, with the critical voxels highlighted in a signal color or flashing. Color coding (e.g., red / yellow / green) is also possible in conjunction with multiple threshold levels for the first and second thresholds.In particular, the 3D displays can be used for surgical planning if the damaged implant is to be removed after the examination. The visualization of contaminated tissue and lymph nodes is also possible and relevant for this purpose.

[0031] When using three or more computed tomography scans with different spectral distributions or X-ray energies (multi-energy CT), the data point can be plotted in the multidimensional space. Here, too, a comparison with threshold values ​​can be performed. The silicone lies within a clearly defined region of three-dimensional or higher space, making the unambiguous detection of silicone in body tissue possible.

[0032] In the Fig.Figure 2 shows a computed tomography (CT) scanner 10 configured for carrying out the method according to the invention. It can be a dual-energy or multi-energy CT scanner. The CT scanner 10 has a rotating gantry 11, which includes an imaging system with at least one line detector and at least one X-ray source. The imaging system is configured to acquire at least two CT images of an object area at different radiation spectra or different individual energies of the X-rays. The configuration of such an imaging system is generally known to those skilled in the art. For example, several X-ray sources at different X-ray voltages (typical values, e.g., 10 ...80 kV and 140 kV), different detectors with different spectral sensitivities, different filters in front of the X-ray sources and / or X-ray detectors, or a combination of the aforementioned techniques may be provided.

[0033] The computed tomography device also includes a control unit 12, which is configured to control the method according to the invention, and a processing unit 13, which performs, for example, the reconstruction, the determination of data points, the calculation of values, and the comparison with predefined threshold values. The processing unit 13 can, for example, be a PC. Furthermore, the computed tomography device includes an output unit, for example, a monitor 14, on which information or warnings are displayed. Alternatively, loudspeakers or other displays may also be provided.

[0034] The invention can be summarized as follows: For the detection of even minute defects in silicone implants, a method for detecting damage to silicone implants in a specific area of ​​the human body using a computed tomography (CT) scanner is provided, comprising the following steps: Acquisition of at least two CT scans of the specific area at different X-ray spectra or different individual energies of the X-ray radiation; reconstruction of the at least two CT scans into 3D datasets containing X-ray attenuation values ​​or equivalent material densities in the sense of a base material decomposition of voxels of the specific area; determination of a data point in a diagram or table for each voxel of interest, wherein the X-ray attenuation values ​​for different X-ray energies are plotted against each other.Comparison of the data point or any other value determined from the X-ray attenuation values ​​for each voxel of interest with known data points or values ​​of body tissue and silicone, and output of a hint or warning if the data point or other value deviates from the known data points or values ​​for body tissue by at least one predetermined first threshold and simultaneously approaches the known data point or value for silicone by less than one second threshold.

Claims

[1] Method for detecting damage to silicone implants in an object area of ​​a human body using a computed tomography device (10) comprising the following steps: a) Taking at least two computed tomography images of the object area at different X-ray spectra or different individual energies of the X-ray radiation, b) Reconstruction of at least two computed tomography scans into 3D datasets containing X-ray attenuation values ​​or equivalent material densities in the sense of a base material decomposition of voxels of the object area, c) Determination of a data point (18) in a diagram for each voxel of interest, wherein the X-ray attenuation values ​​for different X-ray energies are plotted against each other, d) Comparison of the data point (18) or any other value determined from the X-ray attenuation values ​​for each voxel of interest with known data points or values ​​of body tissue (15, 16) and of silicone (17), and e) Issuance of a notification or warning when the data point (18) or other value deviates from the known data points or values ​​for body tissue (15, 16) by at least one predetermined first threshold and simultaneously approaches the known data point or value for silicone (17) by less than one second threshold. [2] Method according to claim 1, wherein the attenuation coefficients µ or the CT values ​​for each voxel of interest are plotted in a diagram as X-ray attenuation values ​​and the data points (18) are compared with known values. [3] Method according to one of the preceding claims, wherein at least one effective atomic number or equivalent material density is determined from the X-ray attenuation values ​​and compared for each voxel of interest with the known effective atomic numbers or equivalent material densities of body tissue and silicone. [4] Method according to claim 1, wherein any combination of soft tissue and fat is used as reference values ​​for the body tissue. [5] Method according to claim 4, wherein a notification or warning is issued when a perpendicular distance (20) of the data point (18) from a connecting line (19) between the known data points of soft tissue (16) and fat (15) exceeds the first threshold and simultaneously falls below a second threshold to the known data point for silicone (17). [6] Method according to one of the preceding claims, wherein three or more computed tomography images of the object area are taken at different radiation spectra or different individual energies of the X-ray radiation. [7] Method according to claim 2, wherein the CT values ​​of the different X-ray energies are mapped to a measured quantity by interpolation of pre-calculated tabulated values. [8] Computed tomography device (10) for carrying out a method according to one of claims 1 to 7, comprising a dual-energy imaging unit for taking at least two computed tomography images of the object area at different radiation spectra or different individual energies of the X-ray radiation, as well as a system control (12) with a computing unit (13) for reconstructing the computed tomography images and for carrying out steps c and d, and an output unit for carrying out step e.

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