DE102018212001B4 - Medical X-ray machine and energy calibration procedure - Google Patents

Abstract

Medical X-ray device (1) having a first X-ray source (2) and a first counting X-ray detector (4), wherebyia. the first X-ray source (2) emits a beam (7) with X-ray photons (8), b. the first counting X-ray detector (4) has a detection surface (11), an angle (14) between the surface normal (13) of the detection surface (11) and a central ray (12) of the beam (7) being adjustable such that the central ray ( 12) of the bundle of rays (7) in a calibration operation does not run in a normal area to the detection area (11), c. a calibration target (6) can be positioned in such a way that calibration photons (9) are triggered in the calibration target (6) by means of the X-ray photons (8) and the calibration photons (9) are incident on at least a portion (15) of the detection surface (11), and the Partial area (15) of the detection surface (11) is essentially shielded from X-ray photons (8) and d. In an imaging mode, the first counting X-ray detector (4) is assigned to a second X-ray source (3) and a second X-ray detector (5) is assigned to the first X-ray source (2).

Description

The invention relates to a medical x-ray device having a first counting x-ray detector, a method for energy calibration of the first counting x-ray detector and a calibration target for this.

In X-ray imaging, for example in radiography, computed tomography or angiography, counting direct-converting X-ray detectors or integrating (in-) direct-converting X-ray detectors can be used. In the development of X-ray detectors for radiation-based, especially X-ray-based imaging such as computed tomography (CT), angiography, radiography or mammography, direct-converting detector materials or converter materials open up new clinical areas of application compared to scintillator materials, for example CsI, Se or GOS. They offer the possibility of counting X-ray quanta or X-ray photons individually and measuring them energetically.

The X-ray radiation or the photons can be converted into electrical impulses in direct-converting X-ray detectors using a suitable converter material. For example, CdTe, CdZnTe (CZT), CdZnTeSe, CdTeSe, CdMnTe, InP, TlBr2, HgI2, GaAs or others can be used as converter material. The electrical impulses are evaluated by evaluation electronics, for example an integrated circuit (Application Specific Integrated Circuit, ASIC). In counting X-ray detectors, incident X-rays are measured by counting the electrical impulses that are triggered by the absorption of X-ray photons in the converter material. The level of the electrical pulse, especially after a preamplifier and a shaper, is usually proportional to the energy of the absorbed X-ray photon. In this way, spectral information can be extracted by comparing the height of the electrical pulse with an energy threshold value. By comparison with several reference signals or the underlying energy threshold values, the impinging photons in the corresponding energy range above an energy threshold are counted in each individual detector element of the X-ray detector.

These reference signals or these energy threshold values are usually set globally during the method for energy calibration by specifying a single digital value (DAC value) per energy threshold for the entire x-ray detector. Each detector element can have a plurality of individually adjustable energy thresholds, each with an energy threshold value. The energy threshold values can be set at least partially the same or at least partially different for all detector elements, in particular after an energy calibration. In the detector element, the digital value is converted into the reference voltage using a digital-to-analog converter. The reference voltage is transferred to a comparator unit, which actually compares the measurement signal with an energy threshold value. Due to manufacturing-related variations in the converter material and the detector elements, the global DAC value can correspond to different photon energies in each individual detector element during the energy calibration process. In order to enable spatially resolved spectral imaging, these variations should be measured and, in particular, the deviations of the individual energy threshold values from the set, global energy threshold value should be determined and corrected in accordance with an energy threshold. The X-ray detector can thus be energy-calibrated, the aim being that all detector elements have essentially the same energy threshold (s) in terms of photon energy and can have different energy threshold values or reference voltages per energy threshold.

Spectrally resolving or directly converting X-ray detectors provide insight into a previously unused area of X-ray information. In order to obtain the spectroscopic information spatially resolved, this information must be evaluated in each pixel.

The response of an ideal energy-resolving or counting X-ray detector without taking charge-sharing effects into account to a series of incident monoenergetic X-ray or calibration photons with constant energy depending on the set energy threshold is essentially step-shaped, with an increasing set energy threshold no more photons from a certain energy threshold are counted. The detector response is essentially the same for all detector elements or pixels and is achieved with the same energy threshold value or DAC value of the energy threshold. In a real X-ray detector, the individual detector elements can have an offset between the set DAC value and the resulting energy threshold value. The differences between the detector elements can be measured and compensated for by means of an energy calibration. The energy calibration can at least in part also be referred to as “trimming”.

If one considers a periodic chain or sequence of signal pulses with an essentially fixed height, one expects a step-shaped detector response for each detector element. As long as that If the set DAC value corresponds to an energy threshold above the pulse height, the pulses are not recorded. If the DAC value corresponds to an energy threshold that is less than or equal to the pulse height, the detector element will essentially count all pulses that arrive during the given recording time. In a real X-ray detector, this ideal case cannot generally be achieved for a number of reasons. Reasons may be differences between the detector elements in signal generation in the converter material (e.g. CdTe), differences in the electrical field on the converter material, in the preamplifier of the respective detector elements, in the shaper of the respective detector elements and in the resulting reference voltage for a given DAC value of the respective detector elements . In order to be able to set the same energy reference or the same energy threshold value in all pixels, it is usually necessary to measure these deviations and take them into account; this is referred to as energy calibration.

From the pamphlet US 8 585 286 B2 a method is known in which an association between the output signal of the detector pixel and a spectral property is included. The method further comprises determining an energy of a photon detected by the detector pixel based on the output signal of the detector pixel and the assignment.

From the pamphlet DE 10 2012 204 350 A1 a method for energy calibration of quantum-counting X-ray detectors in an X-ray system with at least two X-ray systems that can be rotated about a rotation center is known. In the method, a target for generating X-ray fluorescence radiation is positioned between the first X-ray source and the first X-ray detector and irradiated with X-ray radiation from the first X-ray source so that the X-ray radiation from the first X-ray source generates X-ray fluorescence radiation which strikes the second X-ray detector from the target. The energy calibration of the second X-ray detector is then carried out using the X-ray fluorescence radiation from the target. In the same way, the energy calibration of the first X-ray detector can take place with the aid of the X-rays from the second X-ray source. With the proposed method, the X-ray detectors of a dual-source CT X-ray system can be calibrated with little effort under system-related conditions.

• - ein Detektor eingesetzt wird, bei dem den einstellbaren Schwellenwerten der Komparatoren Energieschwellen zugeordnet sind,
• - mit dem Detektor bei unterschiedlichen spektralen Zusammensetzungen der Strahlung jeweils Leermessungen mit unterschiedlich eingestellten Schwellenwerten der Komparatoren durchgeführt werden, und
• - für jeden Kanal, dessen Komparator auf die gleiche Energieschwelle eingestellt werden soll, aus den Leermessungen ein angepasster Schwellenwert für diese Energieschwelle ermittelt wird, wobei jeweils erste Leermessungen bei den unterschiedlichen spektralen Zusammensetzungen der Strahlung durchgeführt werden, bei denen die Schwellenwerte der Komparatoren auf einen der Energieschwelle zugeordneten Wert eingestellt sind, und wobei aus den ersten Leermessungen jeweils die normierten Zählraten berechnet werden und anschließend weitere Leermessungen in gleicher Weise durchgeführt werden, bei denen die Schwellenwerte der Komparatoren variiert werden, bis für jeden der betrachteten Kanäle ein Maß für eine Variation einer normierten Zählrate des Kanals über die unterschiedlichen spektralen Zusammensetzungen der Strahlung verringert oder minimiert ist.

From the pamphlet DE 10 2011 080 656 B4 a method for homogenizing threshold values of a multi-channel quantum-counting radiation detector is known which has at least one comparator with an adjustable threshold value for each channel, in which

• - a detector is used in which the adjustable threshold values of the comparators are assigned energy thresholds,
• - empty measurements are carried out with differently set threshold values of the comparators with the detector at different spectral compositions of the radiation, and
• - For each channel whose comparator is to be set to the same energy threshold, an adapted threshold value for this energy threshold is determined from the empty measurements, with first empty measurements being carried out for the different spectral compositions of the radiation in which the threshold values of the comparators are set to one of the The value assigned to the energy threshold are set, and the normalized counting rates are calculated from the first empty measurements and then further empty measurements are carried out in the same way, in which the threshold values of the comparators are varied until a measure for a variation of a normalized one for each of the channels under consideration Counting rate of the channel is reduced or minimized over the different spectral compositions of the radiation.

From the pamphlet DE 10 2012 204 360 A1 a method for energy calibration of a multichannel quantum-counting X-ray detector which is located opposite an X-ray source in a computer tomograph or C-arm device is known. For energy calibration, at least one target for generating X-ray fluorescence radiation is used, which is or is arranged on one side of the X-ray detector outside the beam path on which the X-ray detector is irradiated with X-rays from the X-ray source in imaging mode. An X-ray beam emanating from the X-ray source is collimated via a beam diaphragm in such a way that the X-ray radiation hits the target and not the detector elements of the X-ray detector and stimulates the target to emit X-ray fluorescence radiation in the direction of the X-ray detector. The energy calibration of the X-ray detector then takes place with the incident X-ray fluorescence radiation.

From the document US 2009/0 180 595 A1 an X-ray imaging system comprising a joint that enables the rotation of a rotatable arm of an X-ray device without being restricted by cabling is known. An x-ray imaging system that can be used in medical interventions includes a rotatable arm. A rotatable arm includes an X-ray Emission device located on one end of the rotatable arm and an x-ray detector device located on the opposite end of the rotatable arm. The detector device detects the x-ray radiation emitted by the emitting device that has passed through a patient. A base unit supports the rotatable arm and includes a hinge that allows the rotatable arm to rotate around a patient on a support surface without being restricted by wiring.

From the pamphlet GB 2,535,566 A an X-ray device consisting of an X-ray source and an X-ray detector is known. Between the source and the detector there is an element that disrupts the properties of X-ray photons. Examples of this are translucent, rotating or movable lamellae, multi-absorption plates with areas of different thicknesses, corrugated memory metal or piezoelectric control of the collimator shape.

From the pamphlet EP 2 596 751 A2 an imaging system is known which comprises a radiation source which emits a first radiation and which traverses an examination region. The imaging system further comprises a detector arrangement which detects the first radiation and generates a signal indicative of the same. The imaging system further includes a detector calibration device having a radiation block that prevents the first radiation from illuminating the detector array and at least one target that receives the first radiation and generates a second radiation having a known spectral characteristic and illuminating the detector array.

The invention is based on the problem that the known methods, in particular from the field of computer tomography, cannot be transferred to systems that differ therefrom.

It is the object of the invention to specify a medical x-ray device, a method for energy calibration and a calibration target which enable energy calibration of the medical device in a clinical setting.

The object is achieved according to the invention by a medical X-ray device according to claim 1, a method for energy calibration according to claim 12 and a calibration target according to claims 13 and 14.

The invention relates to a medical x-ray device having a first x-ray source and a first counting x-ray detector. The first X-ray source sends out a bundle of rays with X-ray photons. The first counting X-ray detector has a detection surface. An angle between the surface normal of the detection surface and a central ray of the bundle of rays can be set in such a way that the central ray of the bundle of rays does not run surface-normal to the detection surface in a calibration mode. A calibration target can be positioned in such a way that calibration photons are triggered in the calibration target by means of the X-ray photons and the calibration photons are incident on at least a partial area of the detection surface, and the partial area of the detection surface is essentially shielded from X-ray photons. The essentially, in particular complete, shielding of the partial area from X-ray photons can mean that essentially only calibration photons are incident on the partial area. Essentially no X-ray photons are incident on the partial area.

The first counting X-ray detector has a detection surface. The detection surface is (X-ray) radiation sensitive. In the imaging mode, the detection surface generally faces the first or second X-ray source, so that X-ray photons can strike the detection surface. The detection surface faces the calibration target in calibration mode so that calibration photons can strike the detection surface. The detection area comprises at least one detector element. As a rule, the detection area comprises a plurality of detector elements in a matrix-like arrangement. The detector elements can also be referred to as pixels or subpixels, with several subpixels being able to form a (macro) pixel. Each detector element can be designed for energy-resolving or counting measurement.

An angle between the surface normal of the detection surface and the central ray of the beam or the first X-ray source can be set. In particular, an angle other than 0 or 180 degrees can be set. The central beam of the beam can thus run in a calibration mode that is not surface-normal to the detection surface. The surface normal of the detection surface can in particular have an intersection with a surface of the calibration target at which the calibration photons are triggered. The calibration photons can thus advantageously impinge on the detection area or a partial area of the detection area, while the X-ray photons can be simplified and essentially completely shielded at least from the partial area of the detection area.

The calibration photons can also be referred to as fluorescence photons. In a preferred embodiment, the angle of incidence of the X-ray photons essentially corresponds to the angle of emergence of the calibration photons, which fall into the partial area of the detection area. The surface normal of the first X-ray detector can strike the calibration target in particular at the angle of reflection. In a further preferred embodiment, the angle of reflection can run almost parallel to the surface normal of the calibration target, the deviation from the surface normal being less than 10 degrees and preferably less than 5 degrees. Increased shielding of the partial area from X-ray photons can advantageously be achieved in each case. An improved signal yield of the calibration photons at the first x-ray detector can advantageously be achieved.

The imaging mode is an operating state that is different from the calibration mode. In the imaging mode, there is usually an examination subject between the X-ray detector and the X-ray source, so that an image of the examination subject is generated by means of the X-ray radiation. A recording of medical image data of an examination subject is available in the imaging mode. In the calibration mode, no object to be examined, in particular in the form of a patient, is arranged between the X-ray detector and the X-ray source.

For energy calibration and in calibration mode, a calibration target with a (fluorescent) material with known fluorescent properties, for example iodine, tin, molybdenum or tungsten, is arranged in the medical device instead of the object to be examined. The first x-ray source is moved to the first x-ray detector by an angle that is, in particular, freely optimized in order to ensure the most efficient possible energy calibration. For example, in an optimized case, the angle of incidence of the x-ray photons on the calibration target can correspond to the angle of reflection of the calibration photons. Those photons triggered by means of fluorescence can be referred to as calibration photons which essentially take the direct path from the calibration target to the first x-ray detector and in particular strike the first x-ray detector essentially perpendicularly. The first X-ray detector of the medical device can directly measure the fluorescence radiation or the calibration photons of the calibration target, which is generated by irradiating the X-rays from the system's own first X-ray source. The angle is advantageously not fixed, but can be optimized for the medical device.

The beam emitted by the first X-ray source is preferably faded in such that only the calibration target is illuminated and the first X-ray detector is not illuminated. The calibration target is placed in such a way that the calibration photons preferably illuminate the essentially entire detection area of the first X-ray detector.

Due to the radiation characteristics of the calibration target, however, there may be areas outside the sub-area that are not adequately illuminated with calibration photons and thus cannot be calibrated. In preferred embodiments, the first X-ray source can be moved independently of the first X-ray detector, so that the method according to the invention can be carried out at different angular positions and thus a complete energy calibration of the first X-ray detector can be achieved.

In a preferred embodiment, the calibration target can be exchanged, the fluorescent material of the first calibration target differing from the fluorescent material of the second calibration target. In particular, several fluorescent materials can be used for energy calibration. The accuracy of the energy calibration can be increased with the number of fluorescent materials used.

The proposed medical X-ray device and the method for it enable the generation and detection of characteristic fluorescence radiation or calibration photons, which can be used for energy calibration. The proposed arrangements of the first x-ray source in connection with the first x-ray detector allow the angle to be set and advantageously also take into account the peculiarities of dual plane systems with two x-ray source-x-ray detector pairs that can be flexibly arranged with respect to one another. The invention advantageously allows the angle between the first X-ray source, calibration target and first X-ray detector to be freely selected. In contrast to the known methods, the energy calibration can also be carried out at several different angles and thus the entire first X-ray detector or its detector elements of the entire detection surface can be calibrated step by step.

According to one aspect of the invention, the first counting X-ray detector is mounted rotatably about an axis perpendicular to the central beam. By suspending the first X-ray detector in a rotatable manner, for example on a C-arm of an angiography or radiography system, an angle can also be set between the first X-ray source and the first X-ray detector without relative changes in position. For angles of rotation of θ> 90 °, an additional shielding of the X-ray radiation from the first X-ray detector can be dispensed with, since the rear side of the first X-ray detector fulfills this task by means of an, in particular additional, shielding configuration, for example in Can take the form of a shielding element. The shielding configuration of the rear side of the first X-ray detector can in particular be configured in such a way that the X-ray photons are essentially completely shielded and thus the first X-ray detector is protected or shielded from the incidence of X-ray photons, for example in an evaluation unit or the converter material. An angle of rotation of θ> 90 ° can in particular mean that, due to the arrangement of the detection surface opposite the central beam or the first X-ray source, fewer or essentially no X-ray photons can incident on the detection surface. The detection surface can face away from the first X-ray source. The angle of rotation can correspond to the angle. The angle of rotation can also be used to optimize the signal strength of the calibration photons or the optimal angle.

If the first X-ray detector is tilted or rotated by θ n / 2, an additional absorber may be required to shield the direct radiation. With an angle of rotation of θ> n / 2, the first X-ray detector can advantageously be calibrated without additional shielding.

According to one aspect of the invention, the first X-ray source is adjustable, in particular rotatable or movable, relative to the first counting X-ray detector. The first X-ray source can be designed to be rotatable about the focus or on the suspension of the first X-ray source.

In a preferred embodiment, the medical x-ray device is designed in such a way that the first x-ray source can be moved around an object to be examined or the angle can be adjusted essentially independently of the first x-ray detector. Such a medical X-ray device can be designed as a mammography system which offers a tomosynthesis or an option for a biopsy.

The angle can be achieved by adjusting the relative position of the first x-ray source to the first x-ray detector. In a preferred embodiment, the medical x-ray device can be a system with a robotic emitter holder. The angle can advantageously be adjusted flexibly.

In an embodiment not according to the invention, the first counting X-ray detector is assigned to the first X-ray source in an imaging operation. The medical x-ray device can be a mammography system or a C-arm system, for example with a tiltable first x-ray detector. An energy calibration of the first x-ray detector can advantageously be carried out in a medical x-ray device with only one x-ray source / x-ray detector pair.

According to the invention, in an imaging mode, the first counting X-ray detector is assigned to a second X-ray source and a second X-ray detector is assigned to the first X-ray source.

In a preferred embodiment, the medical x-ray device can be a dual-plane C-arm system which has two x-ray source / x-ray detector pairs. The first x-ray source / x-ray detector pair comprises the second x-ray source and the first counting x-ray detector. The second x-ray source / x-ray detector pair comprises the first x-ray source and the second counting x-ray detector. The first x-ray source / x-ray detector pair defines a first imaging plane (plane). The second pair of x-ray source and x-ray detectors defines a second imaging plane (plane). The two x-ray source / x-ray detector pairs can be positioned essentially independently of one another. The second x-ray detector can be a counting or integrating x-ray detector. Due to the greater freedom in positioning the second imaging plane compared to, for example, a dual source computed tomography system, the angle between the first X-ray detector and the first X-ray source can be optimized so that an optimal or maximum signal of the calibration photons is achieved on the first X-ray detector. An improved Signal yield of the calibration photons can be achieved at the first X-ray detector. The energy calibration can advantageously be carried out more quickly and / or more precisely.

According to one aspect of the invention, the calibration target is arranged at the point of intersection of the central ray and the surface normal. For example, the center point or a suitable point on the surface of the calibration target or the center of gravity of the calibration target can be arranged at the point of intersection. The calibration target can in particular be arranged in such a way that the angle of incidence of the x-ray photons, in particular in relation to the central beam, essentially corresponds to the angle of reflection of the calibration photons. The calibration target can alternatively be arranged such that the angle of reflection run almost parallel to the surface normal of the calibration target, the deviation from the surface normal being less than 10 degrees and preferably less than 5 degrees. The surface normal of the detection surface and a surface normal of the calibration target can in particular be arranged at half the angle to one another. The central beam and the surface normal of the calibration target can in particular be arranged at half the angle to one another. An improved signal yield of the calibration photons at the first x-ray detector can advantageously be achieved.

According to one aspect of the invention, an anti-scatter element is arranged on the first X-ray detector, which element has a selectable direction, so that essentially only calibration photons are incident on the partial area of the detection surface. The anti-scatter element can have a lamellar or lattice-shaped structure, the passage openings being arranged between the lamellas or the lattice walls. The lamellas or lattice walls can be arranged in parallel or aligned at a common point. The lamellas or lattice walls can in particular have a fixed association with one another, which can in particular be mechanically fixed. Alternatively, the lamellas or lattice walls can have an adjustable association with one another. The direction of the anti-scatter element can be selected by changing the position of the anti-scatter element with grid walls or lamellas that are permanently assigned to one another, or the adjustable assignment. The direction can in particular denote the transmission direction of the anti-scatter grid. The grid walls or lamellae have an X-ray absorbing material, for example tungsten. Advantageously, essentially only calibration photons can be incident on the partial area through the passage openings and the X-ray photons can essentially be shielded from the partial area.

According to one aspect of the invention, a shielding element is arranged in such a way that the partial area of the detection surface is essentially shielded from x-ray photons. The shielding element can in particular shield over the entire surface, i.e. the shielding element preferably has no passage openings. The shielding element can in particular shield a part of the beam of rays from the first X-ray source from the sub-area of the detection surface, with another part of the beam in particular incident on the calibration target. The shielding element can in particular be arranged between the first X-ray source and the first X-ray detector. The shielding element can be arranged, for example, on the X-ray detector or in the vicinity of the X-ray detector. A particularly effective shielding of the partial area can advantageously be achieved through the selection of suitable absorption properties, such as, for example, material which is highly absorbent for X-rays and a corresponding thickness of the material. According to one aspect of the invention, a collimator is arranged on the first X-ray source in such a way that the partial area of the detection surface is essentially shielded from X-ray photons. A collimator can be arranged after the exit window of the X-ray source. The collimator can in particular have at least two diaphragms; in a special embodiment, the collimator can be a multi-leaf collimator. The collimator causes the beam to be faded in or collimated. The collimator can be set in such a way that the partial area of the detection surface is at least partially shielded by the collimator and the calibration target is illuminated. Shielding on the X-ray source side can thus advantageously be achieved. A proportion of scattered radiation can advantageously be reduced. A particularly effective shielding of the partial area can advantageously be achieved through the selection of suitable absorption properties, such as, for example, material which is highly absorbent for X-rays and a corresponding thickness of the material. The collimator can preferably comprise tungsten as material.

According to one aspect of the invention, the calibration target comprises a shielding element or a collimator, so that essentially only calibration photons are incident on the partial area of the detection surface and the partial area of the detection surface is essentially shielded from x-ray photons. In a further embodiment, the shielding element or the collimator can be encompassed by the calibration target or connected to it. An alignment of the calibration target and the shielding element or the collimator can advantageously be established; in particular, the alignment can be optimized to an optimal, set angle.

According to one aspect of the invention, the calibration target has a material that can be excited to fluoresce by means of X-ray photons. The material can be an element, for example Cu, Sn, Ag, Pb, W, I. The fluorescence energy can be in the range between 5 and 85 keV, in particular between 20 and 85 keV. The energy calibration can advantageously be used in particular for applications in medical X-ray imaging.

According to one aspect of the invention, the calibration target has several materials that can be excited to give different fluorescences. The calibration target can preferably have the multiple materials in different, separate areas. The different, separate areas can be designed, for example, as quadrants or segments of a circle, so that it is possible to switch from one area to the next by means of a rotating mechanism. The calibration target can have the multiple materials mixed in a common area. The calibration photons of the different fluorescence can be detected, for example, in a so-called threshold scan. In the threshold scan, at least one measured value is recorded for a large number of threshold values. The Energy calibration can be performed essentially without changing the angle.

According to one aspect of the invention, the calibration target can be arranged or positioned or fastened on a patient bed, on a C-arm or on an accessory. The calibration target can be arranged in the medical device, for example, by being clamped to the medical device or essentially free positioning on a patient bed. The calibration target can be arranged or fastened, for example, to an uroscope, a compression unit or to a movable axis, for example comprising the first X-ray source. Alternatively, instead of a known accessory, for example an uroscope or compression unit, the calibration target can be arranged or fastened by means of the existing locking devices. The calibration target can be integrated in an accessory and, for example, additionally have a shielding element which shields the calibration target in the imaging mode so that the imaging mode is undisturbed and the calibration target can be used for the energy calibration in the calibration mode. The arrangement of the calibration target within the medical X-ray device can advantageously be determined in an essentially reproducible manner by the type and location of the attachment.

• - Positionieren einer ersten Röntgenquelle und eines ersten zählenden Röntgendetektors, wobei ein Winkel zwischen der Flächennormale der Detektionsfläche und einem Zentralstrahl des Strahlenbündels derart eingestellt ist, dass der Zentralstrahl des Strahlenbündels nicht-flächennormal zur Detektionsfläche verläuft,
• - Auslösen von ersten Kalibrationsphotonen aufweisend eine erste Energie und zweiten Kalibrationsphotonen aufweisend eine von der ersten Energie verschiedene zweite Energie in mindestens einem Kalibrationstarget durch einfallende Röntgenphotonen der ersten Röntgenquelle,
• - Detektieren der ersten Kalibrationsphotonen als ersten Messwert und der zweiten Kalibrationsphotonen als zweiten Messwert in einem Detektorelement des ersten zählenden Röntgendetektors,
• - Bestimmen eines Ergebnisschwellwertes indikativ für eine Photonenenergie für das Detektorelement basierend auf dem ersten Messwert und dem zweiten Messwert, und
• - Einstellen des Ergebnisschwellwertes am ersten zählenden Röntgendetektor.

The invention also relates to a method for energy calibration of a first counting X-ray detector in a medical X-ray device, comprising the steps:

• - Positioning a first X-ray source and a first counting X-ray detector, an angle between the surface normal of the detection surface and a central ray of the beam being set in such a way that the central beam of the beam is not surface-normal to the detection surface,
• - Triggering of first calibration photons having a first energy and second calibration photons having a second energy different from the first energy in at least one calibration target by incident X-ray photons from the first X-ray source,
• - Detecting the first calibration photons as the first measured value and the second calibration photons as the second measured value in a detector element of the first counting X-ray detector,
• Determining a result threshold value indicative of a photon energy for the detector element based on the first measured value and the second measured value, and
• - Setting the result threshold value on the first counting X-ray detector.

The triggering step and the detecting step can form a unit in such a way that initially the triggered first calibration photons are detected at a large number of set energy threshold values or reference voltages and then the triggered second calibration photons are detected at the large number of set energy threshold values or reference voltages. The first or second measured value can be determined based on the number of detected first or second calibration photons as a function of the energy threshold value, in particular for essentially each detector element individually. For example, the measured value can designate the energy threshold value or the reference voltage, which can be assigned to the energy of the calibration photons.

The step of determining the result threshold value is based on the first measured value and the second measured value; more than two measured values are preferably used. For example, a, in particular linear, dependency of the measured values on the respective energy of the calibration photons can be used as the basis for determining the result threshold value. The result threshold value denotes the energy threshold value or the reference voltage at which the energy threshold of the detector element corresponds to the desired photon energy. The result threshold is in particular a DAC value. The energy threshold can in particular be given in keV. The individual result threshold value of a detector element as a DAC value corresponds in particular to a photon energy in keV, with essentially X-ray photons being able to be detected, for example in imaging mode, with a greater photon energy above this energy threshold. The energy threshold can in particular lie between the first and the second photon energy. The result threshold value can be determined or estimated by extrapolation for photon energies above or below both photon energies.

In the setting step, the result threshold value is set in the detector element. The method is preferably carried out for all detector elements, it being possible for the individual steps to be carried out in parallel in the individual detector elements. After all detector elements have been set, all detector elements can advantageously have essentially the same energy threshold.

The method can advantageously include more than two energies of calibration photons and correspondingly more than two measured values, so that the accuracy of the energy calibration can advantageously be increased. Detecting the The first and second calibration photons can each comprise a first or second measured value above a threshold value. In particular, the first or second measured values can be determined for a large number of threshold values, for example by means of a so-called threshold scan. The measurement value can be a count of calibration photons above the threshold value. The measured value can also indicate a measure for an energy, for example time-over-threshold. Different calibration targets can be used to absorb the first and second energy. A calibration target with several materials that can be excited to form different fluorescences can be used to record the first and second energy, in which case a threshold scan is advantageously included in the detection step. A reliable and stable energy calibration of the individual detector elements can advantageously be achieved. The method can further comprise a step of repeating in order to calibrate the entire detection area, a further partial area being illuminated by the calibration photons. The principles of known methods can be used advantageously in particular in the step of determining the result threshold value.

In an alternative embodiment, the first X-ray source and the first X-ray detector can be aligned with one another in such a way that the central ray of the beam runs surface-normal to the detection surface. At least the partial area of the detection surface can be shielded from x-ray photons, for example by means of a collimator and / or a shielding element and / or an anti-scatter element. The calibration target can be arranged in such a way that the calibration photons impinge on the partial area and can be detected there.

The invention also relates to a calibration target for use in a method according to the invention. The calibration target is designed in such a way that calibration photons can be triggered by means of the X-ray radiation from the first X-ray source and can be detected in a partial area of the first X-ray detector.

The invention also relates to a calibration target for use in a medical X-ray device according to the invention. The calibration target can, in particular, be able to be arranged in a reproducible manner in the medical X-ray device.

The medical device can furthermore comprise a computing unit having means for performing a method according to the invention, which has a determination unit for determining the result threshold value and a memory unit for storing the result threshold value. A computer program with program code can be provided in order to carry out the method according to the invention when the computer program is executed on a computer or the computing unit. Furthermore, a computer-readable data carrier with the program code of a computer program can be provided in order to carry out the method according to the invention when the computer program is executed on a computer or the processing unit.

• 1 eine schematische Darstellung eines zur Erfindung alternativen medizinischen Röntgengeräts in einer ersten Ausführungsform;
• 2 eine schematische Darstellung eines zur Erfindung alternativen medizinischen Röntgengeräts in einer zweiten Ausführungsform;
• 3 eine schematische Darstellung eines zur Erfindung alternativen medizinischen Röntgengeräts in einer dritten Ausführungsform;
• 4 eine schematische Darstellung eines zur Erfindung alternativen medizinischen Röntgengeräts in einer vierten Ausführungsform;
• 5 eine schematische Darstellung eines zur Erfindung alternativen medizinischen Röntgengeräts in einer fünften Ausführungsform;
• 6 eine schematische Darstellung des erfindungsgemäßen medizinischen Röntgengeräts in einer sechsten Ausführungsform;
• 7 eine schematische Darstellung eines zur Erfindung alternativen medizinischen Röntgengeräts in einer siebten Ausführungsform; und
• 8 eine schematische Darstellung des erfindungsgemäßen Verfahrens.

Exemplary embodiments of the invention are explained in more detail below with reference to drawings. Here shows:

• 1 a schematic representation of a medical X-ray device alternative to the invention in a first embodiment;
• 2 a schematic representation of a medical X-ray device alternative to the invention in a second embodiment;
• 3 a schematic representation of a medical X-ray device alternative to the invention in a third embodiment;
• 4th a schematic representation of a medical X-ray device alternative to the invention in a fourth embodiment;
• 5 a schematic representation of a medical X-ray device alternative to the invention in a fifth embodiment;
• 6th a schematic representation of the medical X-ray device according to the invention in a sixth embodiment;
• 7th a schematic representation of a medical X-ray device alternative to the invention in a seventh embodiment; and
• 8th a schematic representation of the method according to the invention.

the 1 shows an exemplary embodiment of a medical x-ray device 1 in a first embodiment in an alternative to the invention. The medical x-ray machine 1 has a first x-ray source 2 and a first counting x-ray detector 4th on, being the first x-ray source 2 a bundle of rays 7th with x-ray photons 8th sends out. The first counting X-ray detector 4th has a detection area 11 on, taking an angle 14th between the surface normal 13th the detection area 11 and a central ray 12th of the beam 7th is adjustable in such a way that the central beam 12th of the beam 7th in a calibration operation not surface normal to the detection surface 11 runs. A calibration target 6th can be positioned in such a way that in the calibration target 6th by means of the X-ray photons 8th Calibration photons 9 are triggered and the calibration photons 9 on at least a partial area 15th the detection area 11 fall, and where the sub-area 15th the detection area 11 of x-ray photons 8th is essentially shielded. In an imaging operation, the first counting x-ray detector is 4th the first X-ray source 2 assigned. A shielding element 10 is arranged such that the sub-area 15th the detection area 11 of x-ray photons 8th is essentially shielded. The calibration target 6th exhibits one by means of the X-ray photons 8th to fluorescence excitable material. The calibration target 6th can have several materials that can be excited to give different fluorescences.

the 2 shows an exemplary embodiment of a medical x-ray device 1 in a second embodiment in an alternative to the invention. An anti-scatter element 18th is on the first X-ray detector 4th arranged, which has a selectable direction, so that essentially only calibration photons 9 on the sub-area 15th the detection area 11 get an idea. The X-ray photons 8th' are from the anti-scatter element 18th essentially completely absorbed.

the 3 shows an exemplary embodiment of a medical x-ray device 1 in a third embodiment in an alternative to the invention. The first X-ray source 2 is relative to the first counting X-ray detector 4th adjustable, in particular rotatable or movable, for example along the path 17th , is. A collimator 16 is at the first X-ray source 2 arranged such that the sub-area 15th the detection area 11 of x-ray photons 8th is essentially shielded and the calibration target 6th with the X-ray photons 8th is illuminated so that calibration photons 9 to be triggered.

the 4th shows an exemplary embodiment of a medical x-ray device 1 in a fourth embodiment in an alternative to the invention. The first counting X-ray detector 4th can be rotated around an axis perpendicular to the central beam 12th stored. The shielding element 10 is arranged such that essentially no x-ray photons 8th on the first X-ray detector 4th get an idea.

the 5 shows an exemplary embodiment of a medical x-ray device 1 in a fifth embodiment in an alternative to the invention. The first X-ray detector 4th is so far at the angle 14th opposite the central ray 12th rotated that no x-ray photons 8th directly on the detection surface 11 get an idea. The back of the first X-ray detector 4th can be used as a shielding element 10 works.

the 6th shows an exemplary embodiment of a medical x-ray device according to the invention 1 in a sixth embodiment. In an imaging operation, the first counting x-ray detector is 4th a second X-ray source 3 and a second X-ray detector 5 the first X-ray source 2 assigned. The calibration target 6th is at the intersection of the central ray 12th and surface normals 13th arranged. The medical x-ray device is in particular a dual-plane C-arm system.

the 7th shows an exemplary embodiment of a medical x-ray device 1 in a seventh embodiment in an alternative to the invention. The calibration target 6 ' is on a patient couch 19th arranged. The calibration target is an alternative 6th , 6 ' Can be arranged on a C-arm or on an accessory. The calibration target 6 ' includes the calibration target 6th per se as well as a shielding element or a collimator, so that essentially only calibration photons 9 on the sub-area 15th the detection area 11 come up and the sub-area 15th the detection area 11 of x-ray photons 8th is essentially shielded.

the 8th shows an exemplary embodiment of a method according to the invention 100 for energy calibration of a first counting X-ray detector in a medical X-ray device. In the first step of positioning 101 a first X-ray source and a first counting X-ray detector are positioned, an angle between the surface normal of the detection surface and a central ray of the beam being set in such a way that the central beam of the beam is not surface-normal to the detection surface. In the next step of triggering 102 first calibration photons having a first energy and second calibration photons having a second energy different from the first energy in at least one calibration target, for example different calibration targets with different materials for triggering a first or second energy or a calibration target with several materials for triggering the first or second energy second energy, triggered by incident X-ray photons from the first X-ray source. In the next step of detection 103 first calibration photons are detected as the first measured value and second calibration photons as the second measured value in a detector element of the first counting X-ray detector. In the next step of determining 104 a result threshold value indicative of a photon energy for the detector element is determined based on the first measured value and the second measured value. In the next step of setting 105 the result threshold value is set on the first counting X-ray detector.

Although the invention has been illustrated in more detail by the preferred exemplary embodiment, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

Claims (14)

Medical X-ray device (1) having a first X-ray source (2) and a first counting X-ray detector (4), wherein a. the first X-ray source (2) emits a beam (7) with X-ray photons (8), b. the first counting X-ray detector (4) has a detection surface (11), an angle (14) between the surface normal (13) of the detection surface (11) and a central ray (12) of the beam (7) being adjustable such that the central ray ( 12) of the bundle of rays (7) in a calibration operation is not normal to the surface of the detection surface (11), c. a calibration target (6) can be positioned in such a way that calibration photons (9) are triggered in the calibration target (6) by means of the X-ray photons (8) and the calibration photons (9) are incident on at least a portion (15) of the detection surface (11), and the Sub-area (15) of the detection surface (11) is essentially shielded from X-ray photons (8) and d. in an imaging mode, the first counting X-ray detector (4) is assigned to a second X-ray source (3) and a second X-ray detector (5) is assigned to the first X-ray source (2). Medical X-ray device (1) according to Claim 1 , wherein the first counting X-ray detector (4) is mounted rotatably about an axis perpendicular to the central beam (12). Medical X-ray device (1) according to one of the preceding claims, wherein the first X-ray source (2) is adjustable, in particular rotatable or movable, relative to the first counting X-ray detector (4). Medical X-ray device (1) according to one of the preceding claims, wherein the calibration target (6) is arranged at the intersection of the central beam (12) and the surface normal (13). Medical X-ray device (1) according to one of the preceding claims, wherein a scattered radiation element (18) is arranged on the first X-ray detector (4), which has a selectable direction, so that essentially only calibration photons (9) onto the sub-area (15) of the detection surface ( 11) come up with. Medical X-ray device (1) according to one of the preceding claims, wherein a shielding element (10) is arranged in such a way that the partial area (15) of the detection surface (11) is essentially shielded from X-ray photons (8). Medical X-ray device (1) according to one of the preceding claims, wherein a collimator (16) is arranged on the first X-ray source (2) in such a way that the partial area (15) of the detection surface (11) is essentially shielded from X-ray photons (8). Medical X-ray device (1) according to one of the Claims 6 until 7th , wherein the calibration target (6) comprises a shielding element or a collimator, so that essentially only calibration photons (9) are incident on the sub-area (15) of the detection surface (11) and the sub-area (15) of the detection surface (11) of X-ray photons (8 ) is essentially shielded. Medical X-ray device (1) according to one of the preceding claims, wherein the calibration target (6) has a material that can be excited to fluoresce by means of the X-ray photons (8). Medical X-ray device (1) according to Claim 9 , wherein the calibration target (6) has a plurality of materials which can be excited to give different fluorescences. Medical X-ray device (1) according to one of the preceding claims, wherein the calibration target (6, 6 ') can be arranged on a patient bed (19), on a C-arm or on an accessory. Method for energy calibration (100) of a first counting X-ray detector (4) in a medical X-ray device (1) according to one of the Claims 1 until 11 comprising the steps: a. Positioning (101) a first X-ray source (2) and a first counting X-ray detector (4), an angle (14) between the surface normal (13) of the detection surface (11) and a central ray (12) of the beam (7) being set in this way that the central ray (12) of the bundle of rays (7) is not normal to the surface of the detection surface (11), b. Triggering (102) first calibration photons (9) having a first energy and second calibration photons having a second energy different from the first energy in at least one calibration target (6) by incident X-ray photons (8) from the first X-ray source (2), c. Detecting (103) the first calibration photons (9) as the first measured value and the second calibration photons as the second measured value in a detector element of the first counting X-ray detector (4), d. Determining (104) a result threshold indicative of a photon energy for the Detector element based on the first measured value and the second measured value, and e. Setting (105) the result threshold value on the first counting X-ray detector (4). Calibration target (6, 6 ') for use in a method (100) according to Claim 12 . Calibration target (6, 6 ') for use in a medical X-ray device (1) according to one of the Claims 1 until 11 .

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