Active rise and fall time compensation algorithm
11792907 · 2023-10-17
Assignee
Inventors
Cpc classification
International classification
Abstract
A method for compensating the settings of a pulsed X-ray system. The method selects current, voltage, and intended pulse width settings for the X-ray pulses. The method then compensates the selected pulse width setting for the set voltage and tube current, in accordance with at least one stored normalized value at a predetermined temperature, taking into account the environmental temperature of the electric circuitry of an X-ray tank of the X-ray system. The at least one normalized value is obtained in a calibration step based on the actual pulse width and the difference thereof with the intended pulse width at a predetermined temperature, taking into account the internal temperature of the X-ray tank.
Claims
1. A method of calibrating an X-ray system, the method comprising: applying settings for a selected current, a selected voltage, and an intended pulse width to an X-ray source of the X-ray system to generate an actual voltage signal and a current signal for the X-ray source to produce at least one X-ray pulse, the produced at least one X-ray pulse having an actual pulse width; measuring the actual voltage signal applied to the X-ray source; determining the actual pulse width based on the measured actual voltage signal; obtaining a difference between the actual pulse width and the intended pulse width; obtaining a normalized value from the difference at a predefined temperature, taking into account the internal temperature of an X-ray tank comprising the X-ray source, the internal temperature being an environmental temperature for electronic circuitry of the X-ray tank; and storing the normalized value as a function of the settings for the selected current and the selected voltage.
2. The method of claim 1, further comprising: measuring the internal temperature of the X-ray tank before obtaining the normalized value from the difference.
3. The method of claim 1, further comprising: obtaining a rise and fall time deviation of the at least one X-ray pulse from the difference between the actual pulse width and the intended pulse width, wherein obtaining normalized values from the difference at the predefined temperature further comprises: obtaining normalized values of the rise and fall time deviation at the predefined temperature by using a predetermined relationship between capacitance variation of the X-ray tank and the internal temperature of the X-ray tank.
4. The method of claim 1, wherein storing the normalized values comprises: storing the normalized values of the rise and fall time deviation as a function of the selected current and the selected voltage.
5. The method of claim 1, further comprising: repeating the method for at least one different selected setting of at least one of a current and a voltage to store a further normalized value from the difference between the actual pulse width and the intended pulse width as a function of the at least one different selected setting of the at least one of the current and the voltage.
6. The method of claim 5, further comprising: calculating, by interpolation, at least one normalized value from at least one of the current and the voltage between a selected setting of at least one of the current and the voltage and a different selected setting of at least one of the current and the voltage.
7. A non-transitory computer-readable storage medium having stored a computer program comprising instructions which, when executed by a processor, cause the processor to: apply settings for a selected current, a selected voltage, and an intended pulse width to an X-ray source of an X-ray system to generate an actual voltage signal and a current signal for the X-ray source to produce at least one X-ray pulse, the produced at least one X-ray pulse having an actual pulse width; measure the actual voltage signal applied to the X-ray source; determine the actual pulse width based on the measured actual voltage signal; obtain a difference between the actual pulse width and the intended pulse width; obtain a normalized value from the difference at a predefined temperature, taking into account an internal temperature of an X-ray tank comprising the X-ray source, the internal temperature being an environmental temperature for electronic circuitry of the X-ray tank; and store the normalized value as a function of the settings for the selected current and the selected voltage.
8. The non-transitory computer-readable storage medium of claim 7, wherein the instructions, when executed by the processor, further cause the processor to: measure the internal temperature of the X-ray tank before obtaining the normalized value from the difference.
9. The non-transitory computer-readable storage medium of claim 7, wherein the instructions, when executed by the processor, further cause the processor to: obtain a rise and fall time deviation of the at least one X-ray pulse from the difference between the actual pulse width and the intended pulse width; and obtain normalized values of the rise and fall time deviation at the predefined temperature by using a predetermined relationship between capacitance variation of the X-ray tank and the internal temperature of the X-ray tank.
10. The non-transitory computer-readable storage medium of claim 9, wherein the instructions, when executed by the processor, further cause the processor to: store the normalized values of the rise and fall time deviation as a function of the selected current and the selected voltage.
11. The non-transitory computer-readable storage medium of claim 7, wherein the instructions, when executed by the processor, further cause the processor to: for at least one different selected setting of at least one of a current and a voltage, obtain and store a further normalized value from the difference between the actual pulse width and the intended pulse width as a function of the at least one different selected setting of the at least one of the current and the voltage.
12. The non-transitory computer-readable storage medium of claim 11, wherein the instructions, when executed by the processor, further cause the processor to: calculate, by interpolation, at least one normalized value from at least one of the current and the voltage between a selected setting of at least one of the current and the voltage and a different selected setting of at least one of the current and the voltage.
13. An X-ray system comprising: an X-ray tank including an X-ray source; and a controller comprising circuitry configured to: apply settings for a selected current, a selected voltage, and an intended pulse width to the X-ray source to generate an actual voltage signal and a current signal for the X-ray source to produce at least one X-ray pulse, the produced at least one X-ray pulse having an actual pulse width; measure the actual voltage signal applied to the X-ray source; determine the actual pulse width based on the measured actual voltage signal; obtain a difference between the actual pulse width and the intended pulse width; obtain a normalized value from the difference at a predefined temperature, taking into account an internal temperature of an X-ray tank comprising the X-ray source, the internal temperature being an environmental temperature for electronic circuitry of the X-ray tank; and store the normalized value as a function of the settings for the selected current and the selected voltage.
14. The X-ray system of claim 13, further comprising: a temperature sensor configured to sense the internal temperature of the X-ray tank.
15. The X-ray system of claim 13, further comprising a data storage configured to store the normalized value, wherein the circuitry of the controller is further configured to receive the stored normalized value from the data storage.
16. The X-ray system of claim 13, wherein the circuitry of the controller is further configured to: measure the internal temperature of the X-ray tank before obtaining the normalized value from the difference.
17. The X-ray system of claim 13, wherein the circuitry of the controller is further configured to: obtain a rise and fall time deviation of the at least one X-ray pulse from the difference between the actual pulse width and the intended pulse width; and obtain normalized values of the rise and fall time deviation at the predefined temperature by using a predetermined relationship between capacitance variation of the X-ray tank and the internal temperature of the X-ray tank.
18. The X-ray system of claim 17, wherein the circuitry of the controller is further configured to: store the normalized values of the rise and fall time deviation as a function of the selected current and the selected voltage.
19. The X-ray system of claim 13, wherein the circuitry of the controller is further configured to: for at least one different selected setting of at least one of a current and a voltage, obtain and store a further normalized value from the difference between the actual pulse width and the intended pulse width as a function of the at least one different selected setting of the at least one of the current and the voltage.
20. The X-ray system of claim 19, wherein the circuitry of the controller is further configured to: calculate, by interpolation, at least one normalized value from at least one of the current and the voltage between a selected setting of at least one of the current and the voltage and a different selected setting of at least one of the current and the voltage.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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(7) The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.
(8) Any reference signs in the claims shall not be construed as limiting the scope.
(9) In the different drawings, the same reference signs refer to the same or analogous elements.
DETAILED DESCRIPTION OF THE EMBODIMENTS
(10) The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
(11) Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
(12) Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
(13) It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. The term “comprising” therefore covers the situation where only the stated features are present and the situation where these features and one or more other features are present. Thus, the scope of the expression “a device comprising means A and B” should not be interpreted as being limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
(14) Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
(15) Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
(16) Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
(17) In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
(18) X-ray systems, including systems for medical applications, usually include an X-ray generator and an X-ray tank, which include an X-rays source. X-ray sources, also known in the technical field as X-ray tubes, usually produce X-ray photons of high energy, generated by the interaction of an electron beam from a cathode with a target anode.
(19) The electron beam is usually provided by applying a voltage between cathode and anode. In pulsed mode, the voltage is applied as pulses, where a predetermined voltage is applied intermittently. Specifically, a constant voltage is applied for an interval of time for the duration of the pulse, and between the pulses, the voltage is not high enough to produce X-ray emission; ideally no voltage (or zero voltage) is applied. The specific pulse parameters, with a desired or intended pulse width, is chosen in accordance with application requisites, for example the type of procedure, the zone to be irradiated, patient body mass, etc.
(20) The intended pulse may be an ideal pulsed wave, e.g. a square wave, where the voltage reaches the predetermined value instantly and drops also instantly. However, in real conditions, a perfect pulse wave is not obtained by simply applying the suitable settings on an X-ray system or X-ray generator thereof. The voltage actually applied to the source takes a time to reach its intended value and to reach the lowest value after the pulse is turned off. As a result, an effective or actual pulse width may be smaller than the intended pulse width.
(21)
(22) The middle graph 20 shows the change of the actual voltage (kVact) through the source or tube with time, which generates the charge beam (typically electron beam) for generating the photons forming the X-ray pulse. The actual voltage kVact includes rise and fall edges 21, 22. These edges occur due to circuit electronics, parasitic capacitance and resistance and the like, mainly from the circuitry which powers the source. While the voltage is increasing or decreasing, not all the emitted photons can be considered effective. The actual parameters, notably the width, of the generated X-ray have to be calculated taking these edges into account. Per definition, an X-ray is considered as effective X-ray when the voltage is equal or larger than a predetermined percentage of the set voltage. In other words, the effective width of the actual pulse (or actual pulse width, for short) is measured from the moment the voltage rises over a predetermined threshold (usually 75% of the peak value) until the moment the voltage drops under the same threshold.
(23) The actual, effective, X-ray pulse Xact is shown in bottom graph 30 of
(24) Moreover, the inaccuracy increases when using very short pulse widths, e.g. of the order of milliseconds, because in this situation the relative influence of fixed amount of rising and falling time is largest compared to the actual X-ray pulse at the intended settings. For very low voltage (kV) and current (mA) conditions, the inaccuracies increase. It is believed that this is due to the fact that the speed of the high voltage power supply and its circuitry is reduced. In particular, it is due to the discharge exponential curve of the capacitance. At a higher voltage the initial part of the discharging phase of the capacitor is faster than at a lower voltage. For example, from 100% to 75% at 100 kV is 100 kV to 75 kV, whereas for 40 kV it goes from 40 kV to 30 kV, hence the speed of discharge is different.
(25) Further, it has been observed that temperature fluctuations of the X-ray tank cause an increase of inaccuracy. Without wishing to be bound by theory, this increase is believed to be caused by a change in impedance (e.g. capacitance) parameters, due to change of temperature, of the circuitry which provides pulsed voltage and current to the source, usually present in the tank.
(26) The present invention provides a predictive model which allows compensation of the rise and fall time, even for very short pulses, low voltages and currents, and in some embodiments for different temperatures. In particular, the present invention allows correcting the settings of the X-ray generator for the pulse width, as function of the voltage and current, before the X-ray pulse is even generated, taking into account the temperature of the electronic circuitry, e.g. for variations of temperature. In some embodiments, the predictive model is able to predict the behavior of rise and fall times obtained from variation of the electric characteristics of the circuitry in the X-ray generator with the temperature.
(27) In a first aspect, the present invention provides a method of generating or providing X-ray pulses with a pre-calibrated X-ray system.
(28) The normalized value is the value of a deviation between the intended pulse width for a specific tube current and voltage (kV) setting and the effective or actual pulse width, at a predetermined temperature or reference temperature. In the context of the present application, these deviation values are referred to as “normalized” with respect to a predetermined temperature or reference temperature. In determining the normalized values, the temperature may be controlled or it may be measured.
(29) By applying a compensation to an actual pulse width in accordance with the normalized values, the expected variation, or correction factor, of electric characteristics with temperature may be taken into account. The electric characteristics may include impedance, e.g. capacitance, of circuitry, which have an expected or known variation dependent on temperature. During calibration, the normalized values may be calculated from the measurement of the difference of actual and intended pulse width and then stored. Alternatively or in addition, normalized values may be interpolated from previously stored normalized values, for example when for a certain combination of tube current and voltage no matching stored normalized value is available.
(30) A process flow for generating X-rays with an X-ray system, including the service procedure, is shown in
(31) The method comprises accessing 102 at least a stored value related to the pulse width, normalized to a predetermined temperature (the stored value being referred to as “normalized value”, for short).
(32) The normalized values had been obtained during calibration with selected settings of voltage, current and pulse width, and it is linked to the values of those settings of voltage and current. The normalized value can be obtained during a previous calibration procedure done by the manufacturer, for example as part of the manufacture of the system, or by a service engineer, or by the end user once the system is provided to the user. The obtained normalized values are stored in the data storage 207 as a reference, for accessing during the method of generating X-rays. The calibration is explained with more detail with reference to embodiments of the second aspect of the present invention.
(33) The normalized value or values to correct the pulse width can be obtained for one or more current and/or voltage settings. When the current and voltage settings chosen for generating X-rays coincide with the settings of current and voltage at which one normalized value has been stored in the data storage 207, that normalized value is chosen.
(34) In some embodiments, when the current and voltage settings chosen for generating X-rays do not coincide with any of the values of current and voltage settings stored in the data storage, the normalized value is interpolated 106. Thus, the normalized value for the chosen settings is calculated by interpolating the normalized values for the closest higher setting and the closest lower setting. For example, a chosen voltage and current setting may not correspond to any value used for obtaining a normalized value. In this case, two normalized values are chosen, namely the values corresponding to the voltage settings between which the chosen voltage setting falls, and the closest current setting. The normalized value for the chosen current and voltage setting is calculated by interpolating the two chosen normalized values of the voltage setting. An analogous procedure would apply if it would be necessary interpolation of normalized values based on the closest higher and lower current settings, or a combination of both voltage and current setting. In some embodiments, a voltage/current curve is selected, and the interpolated values are calculated on the basis of selected voltage (the current being dependent thereof).
(35) In some embodiments, linear interpolation can be used. However, other types of interpolation can be used in embodiments of the present invention, e.g. in case of using several voltage settings for a specific voltage/current curve. It is noted that, if interpolation is performed during application of the X-rays, a small amount of normalization values need to be stored, thus reducing the size of the data storage 207. However, interpolation can be also performed during calibration, thus reducing runtime calculations at the expense of larger size of data storage 207.
(36) The at least one normalized value can be used to correct or compensate 103 the width of the pulse (e.g. of the CRTL-X pulse), before the pulse is provided to the X-ray source. Thus, during application, the X-ray settings (e.g. the pulse width) can be updated before the voltage pulse is provided using the stored normalized value for the predetermined temperature, by applying 104 the compensated setting (e.g. the pulse width correction at that temperature for the selected voltage and current setting in order to actually achieve the expected pulse width) to the source. The update can be done with a programmed control unit 208, for example internal to the X-ray generator, or external. The unit 208 may include the data storage 207; however, the update can be done also with an algorithm including instructions to control and adapt the parameters, for example in the X-ray generator including the data storage 207.
(37) To properly account for the influence of the temperature on the electronic characteristics of the tank, particularly on the electric characteristics of the high voltage capacitor and/or of the smoothing capacitor, the following information can be used: the expected variation of one or more electric characteristics of the circuitry in the tank with the temperature, and the temperature of the electronic circuitry.
(38) This temperature can be controlled by a heating and/or cooling sub-system 210 (shown in
(39) Alternatively or additionally, the temperature of the electric circuitry can be measured 105. For example, a temperature sensor 209 (shown in
(40) In the embodiments where the temperature is measured, the expected variation of the electric characteristics (taking into account capacitors of the power supply, cabling, etc.) and the temperature is known, so a correction factor of electric characteristics (e.g. impedance, capacitance) can be used to take into account the rise and fall times, caused by the circuitry, taking into account that the circuitry behaves differently when temperature changes.
(41) It should be underlined that the relationship between the electric characteristics and temperature can be used for normalization during calibration, as it will be seen in the second aspect, and also during application with temperature measurement, for effectively converting the pulse width correction from normalized to actual temperature.
(42)
(43) Finally, the compensated settings can be applied 104 to the source, thereby obtaining an X-ray pulse (e.g. a train of X-ray pulsed, thus providing pulsed X-ray generation) with a corrected pulse width which corresponds more closely to the intended width than the effective pulse width that would be obtained if the settings would be simply used. For example, the corrected pulse width may match the intended width.
(44) Additionally, the fall time can be updated by measuring the temperature runtime and updating the normalized values, which may vary after long periods of time due to deterioration of the X-ray source and/or the X-ray tank. This reduces the need of recalibration and the need of a service engineer. The method would be analogous to the one described, without the introduction of the defined voltage and current settings.
(45) In a second aspect, the present invention provides a method of calibration based on a predictive model, for compensation of the rise and fall time of the pulse rise and fall edges 21, 22 (shown in
(46)
(47) The settings are applied 502 to the source 203, which is activated and at least a pulse is provided. Subsequently, the actual voltage signal applied to the X-ray source is measured 503. The measurement can be done with a sub-system for measuring voltage, e.g. an electronic circuit in the control unit 208, or e.g. in the X-ray generator 202, etc.
(48) Based on this measurement, the actual pulse width is determined 504. The actual pulse width can be determined 504 as the time interval between the moment at which the actual voltage signal surpasses a predetermined threshold and the moment at which the actual voltage signal drops under that predetermined threshold.
(49) In other words, the effective width of the actual X-ray pulse (“actual pulse width”) can be determined 504 taking into account the rise time T.sub.RISE and fall time T.sub.FALL of the voltage signal, thus the time interval between the moment at which the voltage surpasses a predetermined threshold (by convention, 75% of the voltage fixed in the settings) and the moment at which the voltage drops under that predetermined threshold.
(50) The difference between intended pulse width (T.sub.IW) and actual pulse width (T.sub.effPW) is then obtained 505.
(51) Further, the temperature of the circuitry is accounted 506 for. This may be done by obtaining the temperature of the circuitry which may comprise setting the temperature to a predetermined value before applying 502 the settings to the source, or it may comprise measuring the temperature of the circuitry while applying 502 the settings to the source and generating the pulses.
(52) Setting the temperature may comprise heating or cooling the temperature of the circuits, using heaters or coolers, for example of the fluid surrounding the electronics, e.g. the oil in the tank, as explainer earlier. Measuring the temperature may comprise, also explained earlier, measuring the environmental temperature of the electronics, e.g. of the converter, e.g. of the HV and smoothing capacitor or capacitors, for example by sensing the temperature of the fluid of the tank, for example with a temperature sensor 209 including a sensing probe.
(53) Then, the difference between the actual and intended width can be normalized 507 to a predetermined temperature, for example the temperature of the circuitry set by the user, or a temperature typically found in transformers, for example room temperature, e.g. between 20° C. and 40° C., for example 25° C.
(54) Not only the rise and fall times can be compensated, but also the influence of changes of electric characteristics with temperature in the rise and fall edges. In particular, the rise and fall times depend on electric characteristics (such as impedance, e.g. the capacity) of the specific circuitry of the X-ray tank, including transformers, capacitors, cabling, which in turn depend on the temperature. Hence, the variation of the electric characteristics such as impedance can be obtained 508 by measurements, or from specification of the fabricant of the circuitry, as explained earlier. The normalized value can be then obtained 509 from the measurement of the actual pulse width and of the intended pulse width, measured for predetermined settings of current and voltage, taking into account the temperature of the X-ray tank and the previously obtained 508 variation of the electric characteristics.
(55) For example, the variation of the capacitance of the HV and smoothing capacitors with temperature can be obtained 508 or known, as shown in
(56) The obtained normalized value is stored 510, for example in a data storage 207, together with the current and voltage setting at which that normalized value was obtained.
(57) The cycle can be repeated for several settings. In general, the current setting and the voltage setting can be chosen differently, for example for different settings (high and low current, for instance).
(58) For example, normalized values can be provided for few voltage settings, linked to predetermined values of current settings, and the same cycle can be repeated for the same few voltage settings, linked to predetermined but different current settings. This means that calibration can be provided for only few voltage and current settings, so values of voltage or current settings not chosen for calibration do not have a normalized value assigned to them.
(59) In some embodiments of the present invention, those normalized values corresponding to values of voltage or current settings not chosen for calibration can still be interpolated 511 from the normalized values of chosen settings, in analogous way as in the interpolation performed with reference to embodiments of the first aspect, for example interpolating the normalized values from values obtained with values of the voltage which are higher, respective lower, than the non-chosen setting, but closest thereto. When this interpolation is performed during calibration, a larger data storage 207 is needed, but processing time is saved during utilization of the X-ray system.
(60) However, interpolation can be done during calibration and also, if required, during runtime, if the chosen settings are not between the ones used to obtain the normalized values or the normalized values interpolated during calibration.
(61) In the following, exemplary procedural steps for calibration and for subsequent application flow are provided:
(62) Exemplary Steps for Calibration:
(63) Obtaining voltage, current and intended pulse width settings
(64) Emitting the pulse
(65) Measuring the actual (effective) width of the pulse
(66) Measuring the environmental temperature of the internal electrical circuitry of the tank
(67) Comparing deviation between effective and intended pulse width by: Calculating expected variation of capacitance of capacitor in high voltage converter from the measured temperature, and obtaining the rise time and fall time deviation values of the pulse for a defined temperature using the actual capacitance (normalization)
(68) Storing the rise time and fall time deviation values and the temperature in a LUT for the selected voltage and current settings.
(69) Exemplary Steps for Application Flow:
(70) Introducing voltage and current settings and the width for an intended pulse width, taking into account the normalized compensation
(71) Measuring Temperature
(72) From the temperature, obtaining the expected variation of capacitance compared to the capacitance at the predetermined temperature
(73) From the voltage and current settings and said expected variation of capacitance, obtaining the required compensation for the rise and fall times that can be expected
(74) Applying the voltage and current settings and width (including de-normalized compensation) for emitting the corrected pulse
(75) The following Table I show exemplary values of the settings and obtained normalized values for several calibration settings, in a particular calibration method where the temperature of the tank is measured. The voltage, current and intended pulse width, as well as the predetermined temperature Tp are values set by the user, while the effective pulse width and temperature are measured, then the difference between the pulse widths (Delta) and normalized values NV are calculated.
(76) TABLE-US-00001 TABLE I Calibration file. Nor- Cur- Pred malized Voltage rent T.sub.IW T.sub.EFFPW Delta Temp. value Curve kV mA (ms) (ms) D T Tp NV A 40 1 10 15 −5 40 25 −5.4 A 80 5 10 12 −2 40 25 −2.2 A 120 10 10 8 2 40 25 2.2 B 40 2 10 11 −1 25 25 −1.0 B 80 10 10 10 0 20 25 0.0 B 120 20 10 8 2 25 25 2.0
(77) For the Table I, two curves (A and B) with different current settings are used. For each, the intended pulse width is 10 ms, but the effective width of the actual pulse (obtained from the measured actual voltage) is different for each setting. The difference (Delta) is obtained from the difference between the intended pulse width and the effective pulse width:
Delta D=T.sub.IW−T.sub.EFFPW
(78) The temperature is measured for each setting, and the normalized value of the Delta is obtained from the delta by normalizing to Tp=25° C., using the relationship of
Normalized value NV=D(1+(0.005(T−Tp))
(79) In this case, the relationship is linear, but in other cases different factors for calculating NV can be used, depending on the circuitry components.
(80) The following Table II shows an exemplary correction of the pulse width, shown in the column “CTRL-X programmed APW”, using the normalized values of Table I, for each of the curves A and B. It is noted that each voltage setting is linked to a value of current setting in curve A and a different value of current setting in curve B. In case of Table II, the number of voltage settings chosen is larger than the voltage settings used for calibration, so interpolation is used to obtain the intermediate values (interpolated NV).
(81) In this case, linear interpolation is used. The temperature is also measured (Tm), the predetermined temperature Tp of the normalized values being the same as in the calibration. The linear interpolation is done on the basis of the values of the voltage settings, but a different linear interpolation is done for each current setting (each curve A, B). The difference in linear interpolation between the curves is dependent on the difference in current (or curve shape). The measured temperature Tm results in a percentage variation. The intended pulse width has been chosen as different for each setting of the curve A and each setting of the curve B.
(82) TABLE-US-00002 TABLE II Correction based on stored normalized values. Chosen Delta CTRL-X voltage correction T.sub.IW programmed Curve V (kV) mA IntNV Tm Tp Dc (ms) APW A 41 1 −5.3 40 25 −4.9 10 5.1 A 42 1.1 −5.2 40 25 −4.8 11 6.2 A 43 1.2 −5.1 40 25 −4.7 12 7.3 A 44 1.3 −5.1 40 25 −4.7 13 8.3 A 45 1.4 −5.0 40 25 −4.6 14 9.4 A 46 1.5 −4.9 40 25 −4.5 15 10.5 A 47 1.6 −4.8 40 25 −4.4 16 11.6 A 48 1.7 −4.7 40 25 −4.4 17 12.6 A 49 1.8 −4.6 40 25 −4.3 18 13.7 A 50 1.9 −4.6 40 25 −4.2 19 14.8 B 41 2 −1.0 20 25 −1.0 10 9.0 B 42 2.2 −1.0 50 25 −0.8 11 10.2 B 43 2.4 −0.9 40 25 −0.9 12 11.1 B 44 2.6 −0.9 40 25 −0.8 13 12.2 B 45 2.8 −0.9 40 25 −0.8 14 13.2 B 46 3 −0.9 40 25 −0.8 15 14.2 B 47 3.2 −0.8 40 25 −0.8 16 15.2 B 48 3.4 −0.8 40 25 −0.7 17 16.3 B 49 3.6 −0.8 40 25 −0.7 18 17.3 B 50 3.8 −0.8 40 25 −0.7 19 18.3
The chosen voltage V ranges between 41 and 50. Thus, the interpolated normalized values are interpolated from the normalized values obtained for the settings of 40 kV and 80 kV, for each curve (each different mA setting), being −5.4 and −2.2 for the curve A and −1 and 0 for the curve B, respectively (see Table I).
(83) The linear interpolation is in each case:
Interpolated NV IntNV=−5.4+(V−40kV)(−2.2−(−5.4))/(80kV−40kV), for curve A
Interpolated NV IntNV=−1.0+(V−40kV)/(80kV−40kV), for curve B
(84) In case of curve A, the actual temperature of the circuitry (e.g. the tank) is constant, and equal to 40° C. In case of curve B, the measurement of the temperature of the circuitry presents variation. The predetermined temperature Tp for the normalization (25° C., in this case) is used again to obtain the actual Delta correction Dc that should be applied:
Dc=IntNV(1−(0.005(Tm−Tp))
(85) Finally, the delta correction is used to obtain the actual pulse width (APW) that the user needs to program, for an intended pulse width T.sub.IW:
CTRL-X programmed APW=T.sub.IW+Dc
(86) Thus, it is clear that the calibration method of the second aspect can be used to provide the normalized values used in the method of providing X-ray pulses of the first aspect of the present invention.
(87) In a third aspect, the present invention provides a software product, e.g. a computer program product, or a data carrier including such program, such that when linked to an X-ray system, it allows providing X-ray pulses in accordance with the method of the first aspect of the present invention.
(88) The software product may be adapted for receiving a required pulse width setting, further adapted for receiving normalized values obtained by the calibration method of the second aspect of the present invention.
(89) An X-ray system including such software product (e.g. in a control unit 208, or in the X-ray generator 202) can improve the performance of the system, enabling the use of pulses with small width, thus increasing the usable range. The control unit also allows X-ray generation with lower power, which in turn increases the useful life of X-ray sources. Moreover, because the difference between intended pulse and the pulse obtained is reduced, for the same settings of the voltage and current, international regulatory requirements of accuracy can be more easily met. This also helps in increasing the usable range of pulse widths in the lower range, e.g. providing small width (very short pulses) accurately.
(90) In a fourth aspect of the present invention, a software product is provided for calibrating an X-ray system. The software product may be adapted for receiving pulse width measurements, it may optionally be adapted for receiving temperature measurements, and it may include instructions for executing the calibration method of embodiments of the second aspect of the present invention, when implemented in an X-ray system. Such software product can build a prediction model for compensating deviations of the pulse width including the temperature variations of the tank, thus providing a compensated pulse width X-ray system when the software is implemented in an X-ray system.
(91) A software product in accordance with embodiments of the present invention may include the third and fourth aspects of the present invention, thus allowing calibrating an X-ray system and providing pulsed X-rays with corrected pulse widths obtained during calibration.
(92) In a fifth aspect, the present invention provides a data storage comprising the normalized values obtained by the method of the second aspect of the present invention. Such data storage may be linked to a control unit, for example one unit including a software product in accordance with embodiments of the third and/or fourth aspect of the present invention. In some embodiments, the data storage is implemented in software. For example, it may be implemented as part of the software product of the third and/or fourth aspect of the present invention.
(93) Such data storage may be reprogrammable, and updated normalized values can be included, for example by interpolation or by the method of calibration in accordance with embodiments of the second aspect of the present invention.
(94) In a sixth aspect, the present invention provides an X-ray system adapted for generating pulses with an effective width, compensated for different values of the voltage or current setting and independent of the temperature, in accordance with embodiments of the first aspect, and/or for performing the calibration described with reference to embodiments of the second aspect. For example, the X-ray system may include a software product or program product in accordance with embodiments of the third and/or fourth aspects of the present invention.
(95) The voltage provided by the X-ray system may range between 35 kV and 150 kV, for example between 40 kV and 120 kV. Traditional X-ray systems have an optimal setting where the settings coincide fairly well with the effective pulse, typically between 70 kV and 80 kV for example. For higher and lower kV settings the deviations between intended and effective pulse width increase. The present invention provides an effective correction of the pulse width for a wider range of voltage and current settings, even for low values of current and/or voltage, which allows optimization of the dosage, reduction of the wasted power. Because the pulse width is more accurate, the average current can be obtained with higher accuracy, in compliance with regulations of current and voltage accuracy, and in turn enabling smaller pulse widths.
(96) Going back to
(97) The X-ray system may be adapted to take into account the temperature of the circuitry, or part thereof, which is used to provide the pulses, e.g. the high voltage converter, and/or the HV and smoothing capacitor. In some embodiments, the temperature can be measured by a temperature sensor 209, which include any sensor that measures a parameter which is a function of temperature. For example, a temperature sensor may include an element that measures changes in the resistance of a conductor due to changes of temperature. In some embodiments of the present invention, the environmental temperature of the circuitry in the tank is measured. For example, the temperature of the HV and smoothing capacitor 205 can be measured. For example, the temperature of the environment surrounding the circuitry of the high voltage converter 204, or both the converter 204 and the smoothing capacitor 205, can be measured, optionally including wiring, etc. In some embodiments, the environment surrounding at least part of the circuitry is fluid 206, for example oil (e.g. transformer oil, usually present for cooling, but the present invention is not limited to cooling functions). The temperature of the fluid is an important indicator for the environmental temperature, especially where this fluid 206 surrounds the HV and smoothing capacitors 205, as these capacitors plays a major role in the shape of the voltage pulse and its edges 21, 22. Thus, in embodiments of the present invention, the fluid temperature is measured, e.g. using one or more NTC thermistors, thermocouples or the like, for example in the immediate surroundings of the smoothing capacitor.
(98) In some embodiments, the fluid can be circulated in order to provide evenly distributed temperature in the tank. For example, an oil pump could be included. Cooling may be implemented e.g. as passive cooling.
(99) In alternative embodiments, in order to take into account the temperature of the circuitry, the system 200 includes a heating and/or a cooling temperature sub-system 210, for example heaters, and/or heat extractors, for setting the temperature of the fluid 206. In this case, the temperature sensor 209 can still be optionally present. The sub-system 210 may be actuated by the X-ray system, e.g. by the control unit 208 thereof, for example during calibration and/or during utilization of the X-ray system.
(100) The X-ray system may include a sub-system 211 for measuring the effective width of the actual pulse provided during calibration. The sub-system 211 may comprise electronic circuitry in the control unit 208, and/or in the X-ray generator, for example. The actual voltage level in the X-ray tank can be measured, and the measurements can be processed (e.g. in a system controller, control unit, etc.) in order to determine signal level.
(101) The X-ray system 200 may be included in a monoblock, integrating at least the tank 201, optionally also the X-ray generator 202 in a single block, which can be part of a CR unit, mammography unit, part of a mobile x-ray equipment, for example for mobile surgery applications, the present invention not being limited to these applications.
(102)