Method and system for determining a measurement start time

Abstract

Method for determining a measurement start time (ts) for an imaging measurement using a medical imaging system (1) as a function of a time course of concentration values ​​(KD1, ..., KD21) of a contrast agent (CM) in a monitoring area (UB) of an examination object (P) with the following steps: - Recording the concentration values ​​(KD1, ..., KD21) of a current concentration of the contrast agent (CM) in the monitoring area (UB) at various successive recording times (t1, ..., t9), - Determining a current examination-specific enhancement model curve (CM) of a contrast agent enhancement and depletion based on a time course of the concentration values ​​(KD1, ..., KD21) and based on a population-averaged enhancement model curve and / or population-averaged contrast agent impulse response function, - Determination of the measurement start time (ts) based on the examination-specific enhancement model curve (CM).

Description

[0001] The present invention relates to a method for determining a measurement start time for an imaging measurement using a medical imaging system as a function of the temporal profile of concentration values ​​of a contrast agent in a monitored area of ​​an object under investigation. It further relates to a method for controlling a medical imaging system, as well as a control device and a medical imaging system for implementing the methods according to the invention.

[0002] Contrast agents improve the visualization of structures and functions of a living subject or body in imaging procedures such as X-ray diagnostics (e.g., computed tomography), magnetic resonance imaging (MRI), and sonography (ultrasound). For the visualization of blood vessels in the body (angiography), contrast agents are often used in X-ray diagnostics that absorb X-rays more strongly than normal soft tissue. When an iodine-containing solution is used as a contrast agent, the blood vessels into which the solution enters attenuate the X-rays more than the surrounding tissue, thus increasing the image contrast of the blood vessels. An increased concentration of the contrast agent therefore directly and linearly corresponds to an increase in the attenuation value measured in an X-ray-based measurement. In this respect, the terms "concentration value" and "attenuation value" can be used interchangeably.The term "X-ray attenuation value" can also be used synonymously when referring to measurements using X-rays.

[0003] Before contrast-enhanced imaging, such as a computed tomography (CT) scan, can be performed, the contrast agent must be present in a sufficient concentration within a target area or tissue of the body at the time of the CT scan. The target area is, for example, an organ (heart, lungs, kidneys, etc.) from which image data are to be generated for a specific diagnostic purpose.

[0004] A common method for determining the course of contrast agent concentration (hereinafter also referred to as "contrast agent profile"), i.e., the accumulation of contrast agent (CM) and its depletion after maximum accumulation (hereinafter also referred to as the "peak concentration phase" (CP)), is based on... Fig. 1 explained. Fig. Figure 1 shows a diagram with three horizontally and parallel time axes (I, II, III). A lower time axis (III) displays a topogram (TP), a pre-monitoring scan (PM), a bolus monitoring scan (BTS), and a main measurement (HS) of a test subject (P). The topogram (TP) is used to determine the location of a target area (ZB) and a monitoring area (UB) within the test subject (P). The bolus monitoring scan (BTS) is performed in the monitoring area (UB), and the target area (ZB) is subsequently scanned in the main measurement (HS). The pre-monitoring scan (PM) serves to define a region in the body, usually the aorta, within the monitoring area (UB) before the contrast agent is injected. The bolus monitoring scan is then evaluated in this region, and if necessary, the native attenuation value of the blood is determined.A highly simplified representation (as a simple triangular function) of the contrast agent concentration C(t) in the specimen P is shown on a middle time axis (II). A contrast agent administration function IF(t) is shown on an upper time axis (I), extending over a contrast agent administration period IZ. The three time axes (I, II, III) are temporally correlated. In this procedure, the "bolus monitoring scan" (BTS) is performed before the start of the actual main scan (HS) of the target area (ZB). The bolus monitoring scan (BTS) records contrast agent concentration values ​​KD1, KD2, ..., KD9 (given in Hounsfield units, HU) at specific acquisition times t1, t2, ..., t9 at equal time intervals, e.g., every second. The data is captured in a monitoring area of ​​the body that is close to the target area to be measured in the main scan HS.If, for example, image data of a heart is to be generated in the main scan (HS), the bolus monitoring scan (BTS) can be performed in a layer of the ascending aorta.

[0005] Immediately after or with a specific monitoring time delay (DT) following the administration of the contrast agent at a contrast agent administration start time (SC), the bolus monitoring scan (BTS) is initiated. A contrast agent administration period (IP), i.e., a period during which a volume of contrast agent is introduced into the body at a specific injection rate, can last longer than a bolus monitoring scan period (BTS). As soon as an exceedance of a predefined concentration threshold (CS) of the contrast agent in the monitored area is detected at a time point t1, t2, ..., t9 (here: t7), e.g., 150 HU, the main scan (HS) of the target area (ZB) is typically initiated after a predefined scan time delay (SZ, "scan delay"), e.g., 3 seconds after reaching the concentration threshold (CS) (a so-called "post-trigger delay").

[0006] This method offers a high probability that the contrast agent will have reached a minimum enrichment of the HU value specified in the concentration threshold KS (in this case 150 HU) in the target area when the main scan HS is performed.

[0007] However, this method has several disadvantages: The predefined concentration threshold is usually set based solely on experience or average values. Therefore, it is unclear for an individual patient at which stage of the contrast agent concentration curve, according to this predefined post-trigger delay or scan time offset, the main scan will be performed. The contrast agent concentration curve is strongly dependent on the individual patient's physiology. It can thus happen that the scan time offset was not optimally chosen in advance, resulting in a main scan being performed when the contrast agent enhancement in the target area has either not yet reached its peak or a maximum contrast agent concentration has already been exceeded. In both cases, the contrast agent is then used inefficiently: it would have a higher contrast agent concentration, i.e.,Better image data quality could have been achieved, or the same enrichment could have been achieved using a smaller volume of contrast agent.

[0008] Since the contrast agent concentration profile depends on a complex interaction of many parameters (including injection parameters, scan parameters, and patient-specific parameters) and can therefore vary considerably, an optimal scan time offset is difficult to determine in advance. Therefore, a largely standardized scan time offset is usually chosen, which may take into account the current contrast agent administration period or the duration of the main scan. However, this conventional method cannot reliably predict whether a main scan occurred at a peak in contrast agent enhancement or during a concentration peak phase.

[0009] Based on the problem presented here, the invention aims to improve the use of contrast agents in contrast-enhanced imaging measurements.

[0010] This problem is solved by a method according to claim 1, a method according to claim 12, a control device according to claim 13 and a medical imaging system according to claim 14.

[0011] The method according to the invention relates to determining a measurement start time for an imaging measurement using a medical imaging system as a function of a temporal profile of concentration values ​​of a contrast agent in a monitoring area of ​​an object under investigation, comprising the following steps: – Recording the concentration values ​​of the contrast agent in the monitored area at various successive recording times, – Determination of a current study-specific enrichment model curve based on a time course of the concentration values, – Determination of the measurement start time based on the study-specific enrichment model curve.

[0012] The term "imaging measurement" refers to a primary or main measurement of a target area of ​​the object under investigation, performed with a specific diagnostic interest. "Acquisition of concentration values" within the monitored area is understood as a pre-scan or pre-measurement of the object under investigation. Since concentration values ​​or data of the contrast agent are measured at various successive acquisition times—preferably within a consistently identical monitored area—e.g., once per second, a main measurement is preceded by at least one pre-measurement, i.e., for example, five pre-measurements.

[0013] The "monitoring area" can differ from the imaging target area acquired during the main measurement. For example, image data can be generated of a patient's heart (as the target area) during the main measurement. To determine the measurement start time for the main measurement, concentration values ​​of the contrast agent introduced into the patient can be measured beforehand in the ascending aorta (as the monitoring area). Alternatively, the monitoring area can be identical to or a part of the target area of ​​the main measurement. The acquisition of concentration values ​​(preliminary measurement) and the imaging measurement (main measurement) can be performed using any medical imaging system, preferably a computed tomography (CT) system, magnetic resonance imaging (MRI) system, and / or ultrasound system.

[0014] The term "temporal profile of concentration values" implies that the measured concentration values ​​of a contrast agent can change over time, i.e., increase and / or decrease. A profile of concentration values, represented, for example, by measurements of contrast agent fractions in a tissue, acquired at fixed or variable time intervals, can be displayed as a curve. A measurement start time for the imaging measurement can be determined based on the temporal profile of the concentration values ​​by setting it to a specific point on the profile according to predefined criteria.For example, a phase of contrast agent accumulation in the monitored area and / or a phase of depletion can be taken into account by starting a main measurement with a specific time delay before a maximum of contrast agent accumulation, ensuring that the maximum is reached during the main measurement. Determining the start time can also include the start time of contrast agent administration.

[0015] The term "study-specific enhancement model curve" refers to a calculated model curve of contrast agent enhancement and depletion that is specifically "adapted" to the currently measured concentration values. "Adapted" in this sense also includes, as will be explained later, the selection of a suitable enhancement model curve from a collection of previously calculated (candidate) enhancement model curves. This means that the enhancement model curve has a curve segment that closely matches the currently measured concentration values ​​and thus reflects a past, actual course of the contrast agent concentration. It also has another curve segment that describes a projected future development of the contrast agent concentration, calculated based on specific criteria.The entire enrichment model curve, but especially this second curve segment, thus forms a model-like prediction of the concentration profile of the contrast agent in the object under investigation.

[0016] The measurement start time can also depend on the planned duration of a main measurement. This duration can be determined, for example, by the thickness of the cross-sectional image to be generated, or, in the case of a CT scanner, by the ratio of table feed to beam collimation. It is particularly preferred that the measurement start time is chosen such that approximately half of the planned scan duration is before the peak value and half is after the peak value of the contrast agent profile.

[0017] Since the method according to the invention determines a current enhancement model curve, which on the one hand provides a complete model function for the further contrast agent profile and on the other hand is specifically determined for the respective examination based on, for example, only a number of initial concentration values ​​from a relatively short time period after the start of contrast agent administration, i.e., in the first part of the rising phase of the contrast agent profile, a particularly precise determination of the measurement start time of the imaging measurement or the main measurement is possible without the need to measure further concentration values ​​over a longer time period (e.g., until or shortly before reaching the maximum or even beyond the maximum of the contrast agent profile). The main measurement can thus be carried out within a period that guarantees optimal utilization of the volume of contrast agent used.This means that, compared to conventional methods, the amount of contrast agent can potentially be reduced.

[0018] The invention also relates to a method for controlling a medical imaging system to generate image data of an examination object, comprising the following steps: – Determination of a measurement start time for an imaging measurement depending on a temporal course of concentration values ​​of a contrast agent in a monitoring area of ​​the object under investigation according to the procedure described above, – Performing an imaging measurement of a target area of ​​the object under investigation using the determined measurement start time.

[0019] As mentioned, the target area of ​​the object under investigation is an area from which image data is to be generated by means of a functional measurement, e.g., a human organ. The measurement start time can be used for further processing in any way, e.g., incorporating a planned scan duration of the main measurement, a time offset, or other correction factors. Preferably, the medical imaging system is also controlled in such a way that the data acquisition for the imaging measurement or main measurement begins directly at the measurement start time.

[0020] Preferably, the process step of determining a measurement start time is terminated when a defined reliability threshold for predicting a future contrast agent concentration is reached and / or a maximum delay value is reached. This delay value may be necessary for technical reasons, such as to initiate a measurement process and prevent the maximum contrast agent concentration from being exceeded unused. For example, the maximum delay value could represent a time buffer required to switch a computed tomography system from a pre-measurement mode for recording concentration values ​​to a main measurement mode for acquiring image data of the patient, including, for example, the time required to move a patient table.

[0021] Furthermore, the invention relates to a control device for a medical imaging system with an interface for recording or outputting a contrast agent administration start time and a start time determination unit. This start time determination unit comprises – an input interface for recording concentration values ​​of a contrast agent in a monitored area of ​​an object under investigation at various successive recording times, – an enrichment model curve determination unit for determining a current study-specific enrichment model curve based on a time course of the concentration values, – a model curve analysis unit for determining the measurement start time based on the investigation-specific enrichment model curve.

[0022] Preferably, the control device according to the invention also includes a measuring control unit electronically coupled to the start time determination unit for carrying out an imaging measurement of a target area of ​​the object under investigation using the determined start time.

[0023] Furthermore, the invention relates to a medical imaging system for generating image data of a target area inside an object under investigation, comprising a control device as described above.

[0024] A large proportion of the components of the control unit of the medical imaging system according to the invention, in particular the start-time determination unit, the enhancement model curve determination unit, and the model curve analysis unit, can also be designed as software modules. Extensive software implementation of the method according to the invention has the advantage that existing medical imaging systems can be easily retrofitted by a software update to operate according to the invention. In this respect, the problem is also solved by a computer program product that can be directly loaded into the memory of a programmable control unit of a medical imaging system, with program code means to execute all steps of the method according to the invention when the program is run on the control unit.

[0025] Further, particularly advantageous embodiments and developments of the invention result from the dependent claims and from the following description, wherein the independent claims of one claim category may also be further developed analogously to the dependent claims of another claim category and features of different embodiments may also be combined to form further embodiments.

[0026] Preferably, the examination-specific enhancement model curve is determined based on a population-averaged enhancement model curve and / or a population-averaged contrast agent impulse response function. A "population-averaged enhancement model curve" or a "population-averaged contrast agent impulse response function" is understood to be a model curve that represents the mean of a plurality of empirically recorded, i.e., actually measured, time courses of a contrast agent concentration or contrast agent impulse response function. These courses were recorded from a plurality of patients and stored, for example, in a database. With a sufficiently large underlying patient group, the population-averaged enhancement model curve or...Contrast agent impulse response functions possess high statistical significance regarding the average course of contrast agent concentration in a person. The population-averaged enhancement model curve, or contrast agent impulse response function, can be individualized and further processed into an examination-specific enhancement model curve by applying a correction factor. This factor can be based, for example, on examination-specific data of the examination or measurement to be performed, and possibly even on patient-specific data of the current patient / subject on whom the imaging measurement will later be performed. Using this method, an examination-specific enhancement model curve can be generated that predicts the actual course of contrast agent enhancement or decay in a subject with a considerable degree of probability. For example,First, a population-averaged enhancement model curve is determined based on the population-averaged contrast agent impulse response function, and then, based on this, the examination-specific enhancement model curve is determined. Alternatively, as will be explained in more detail later, an examination-specific enhancement model curve is determined directly based on a population-averaged contrast agent impulse response function.

[0027] According to a preferred embodiment, injection protocol data are recorded, and the examination-specific enhancement model curve is determined based on this data. The injection protocol data describe the specific conditions of the administration or delivery of contrast medium into the examination object or into the patient's body. This includes information about the start time, duration, and end time of contrast medium administration, as well as the delivery rate. In particular, it is possible to determine an examination-specific enhancement model curve using a combination of a population-averaged contrast medium impulse response function and the injection protocol data.

[0028] Thus, assuming that a human patient is a linear, time-invariant system, an enhancement model curve C(t), which includes the injection protocol data, can be described as a convolution of a contrast agent delivery function IF(t) with a contrast agent impulse response function AIR(t): C(t) = IF(t) ⊗ AIR(t) (1) where the contrast agent delivery function IF(t) represents the injection protocol data. If a patient-specific or examination-specific contrast agent impulse response function AIR(t) were known, an examination-specific enhancement model curve could be calculated directly. Otherwise, as in a preferred method according to the invention, a population-averaged contrast agent impulse response function AIR can be used. POP-AVG (t) can be used.

[0029] In a further preferred embodiment, the study-specific enhancement model curve is selected from a plurality of candidate enhancement model curves based on the time course of the concentration values. The candidate enhancement model curves can be calculated prior to the selection step, e.g., using the current injection protocol data and the population-averaged contrast agent impulse response function. They represent possible contrast agent concentration profiles for a number, and preferably for a plurality, of virtual candidates (or virtual patients). The candidate enhancement model curves can thus virtually mimic physiological differences that may characterize different candidates.Preferably, the candidate enhancement model curves take into account a broad, and particularly preferably almost the entire, spectrum of human physiologies that can lead to varying rates and / or degrees of contrast agent accumulation or reduction in the body.

[0030] Their calculation can be based on criteria such as age, height and weight.

[0031] The selection of candidate enhancement model curves for determining the study-specific enhancement model curve can be achieved, for example, by "fitting" them to concentration values ​​recorded prior to the selection point using known methods. With each subsequent recording of contrast agent concentration values, the probability increases that a candidate enhancement model curve selected as the study-specific enhancement model curve will correspond to a future actual contrast agent profile.

[0032] This method offers the advantage that candidate enhancement model curves can be calculated and stored before an examination, and even before a patient receives contrast medium. Based on current concentration values, the recorded concentrations are simply compared with corresponding points on the candidate enhancement model curves, and the most suitable curve is selected. Compared to the alternative of calculating a completely new, examination-specific enhancement model curve in real time during a bolus monitoring scan or after each new acquisition of concentration values, this approach saves considerable computing power.

[0033] Preferably, the candidate enhancement model curves are parameterized by different widths. In a candidate enhancement model curve that is a function of the contrast agent intensity values ​​over time, the width of the curve can illustrate the pumping capacity of the heart (also called "cardiac output") of the patient being examined and, consequently, how quickly an introduced contrast agent spreads throughout the patient's body. The greater the width of the candidate enhancement model curve, the lower the cardiac output of the patient being measured can be. A peak contrast agent concentration in the target area of ​​the body is therefore reached later than in a patient with a comparatively high cardiac output. The depletion of the contrast agent in the target area can also occur more slowly, as the heart distributes the contrast agent more slowly throughout the body.The different widths of the individual candidate enrichment model curves thus represent a spectrum of possible patients and summarize a multitude of physiological characteristics and, where applicable, defects of the patients.

[0034] Alternatively or additionally, the candidate enrichment model curves are preferably parameterized by at least one correction factor. The correction factor can be any factor that can be integrated into an equation for calculating the candidate enrichment model curves. This allows, for example, the processing of previously available or acquired data, enabling a more individualized construction of the candidate enrichment model curves or, ultimately, the study-specific enrichment model curve. One or more correction factors can be derived, for example, from parameters that indicate how a patient currently being examined differs from a virtual "population-averaged patient," such as in terms of sex, weight, or physical performance.

[0035] Preferably, the correction factor of the candidate enrichment model curves is chosen such that candidate enrichment model curves with different widths exhibit an essentially identical integral value. An identical integral value, or an equally large area under the curve, when comparing several candidate enrichment model curves represents the assumption that a virtual body of a "population-averaged patient," just like a body of an individual patient, constitutes a closed system.

[0036] Based on this premise, the correction factor causes a reciprocal change in the amplitude of a candidate enrichment model curve when its width is changed. For example, increasing the width of the curve by a factor of b results in nand thus, over a longer period, such a correction factor is applied that the height of the curve, and therefore the contrast agent intensity value, becomes lower. The candidate enhancement model curves C Kn (t) can be calculated by including such a correction factor (1 / b) n ) e.g., formed as follows: C Kn (t) = IF(t) ⊗ (1 / b n )·a AVG ·AIR(t0 + b n ·t) (2) a AVG Here, is a population-averaged scaling factor that scales the amplitude of the function, and t0 is a parameter that allows the curve to be shifted in time. n is simply an index for the nth candidate enrichment model curve.

[0037] According to a further preferred embodiment, another correction factor is based on the current iodine concentration of the contrast agent and / or the current tube voltage of a computed tomography system used for the current measurement of the subject. Both the iodine concentration of a contrast agent and the tube voltage used to direct X-rays into the subject during a measurement with a radiography system significantly influence the attenuation values ​​of the X-rays in tissue of the subject that is impregnated with contrast agent. They thus affect the measurement of a contrast agent intensity value. Including one or both of these values ​​in a calculation of the candidate enhancement model curves or the examination-specific enhancement model curve therefore leads to a more precise approximation of the model curve to the actual course of a contrast agent concentration..

[0038] Preferably, in addition to the current iodine concentration of the contrast agent and / or the current tube voltage of a radiograph system used, patient-specific iodine concentration and / or tube voltage values ​​are also included in the calculation of the candidate enhancement model curves or the examination-specific enhancement model curve. Similarly, patient-specific enhancement curve values ​​are also included, on the basis of which a population-averaged enhancement curve was calculated. For example, an iodine concentration value co used in determining the population-averaged contrast agent impulse response function can be used. AVG in relation to a current iodine concentration value used in the upcoming examination U be set and / or an iodine vector fKV used in determining the population-averaged contrast agent impulse response function AVGin relation to a current fKV used in the upcoming study U An iodine vector must be set. The so-called "iodine vector" is a tube voltage-dependent constant that indicates which tube voltage of the X-ray source results in which attenuation values ​​at a given iodine concentration. For example, it can be approximately 40 at 80 kV and approximately 25 at 120 kV. The values ​​are preferably determined for the specific system used.

[0039] The candidate enrichment model curves C Kn (t) can be further developed in equation (2) by including the described correction factors (co U / co AVG ; fKV U / fKV AVG ) e.g., formed as follows: C Kn (t) = IF(t) ⊗ (1 / b n )·a POP-AVG ·AIR(t0 + b n ·t)·co U / co AVG ·fKV U / fKV AVG (3)

[0040] Alternatively, instead of using the correction factors b and 1 / b in equations (2) or (3), experimentally determined data could also be used for correction.

[0041] Furthermore, the method according to the invention can preferably be further developed such that the investigation-specific enrichment model curve is determined by fitting the population-averaged enrichment model curve and / or by fitting candidate enrichment model curves to the temporal profile of the concentration values. The adjustments of the curves to the concentration values ​​recorded at specific time points can be carried out in any way, e.g., by scaling, shifting, etc.

[0042] The selection of one or more study-specific enrichment model curves from the candidate enrichment model curves by comparison with the concentration values ​​recorded at specific times or by fitting them to these can be done, for example, using any known fitting procedures that operate with different optimization algorithms.

[0043] According to a preferred embodiment, the fitting of the population-averaged enrichment model curve and / or the fitting of candidate enrichment model curves to the temporal evolution of the concentration values ​​includes at least one of the following mathematical operations: – relative shift of the population-averaged enhancement model curve and / or the candidate enhancement model curves to the concentration values ​​with respect to a reference concentration value (i.e. a shift in height, i.e. in the direction of the contrast agent intensity scale) and / or – relative shift of the population-averaged enrichment model curve and / or the candidate enrichment model curves to the concentration values ​​with respect to a reference time point (i.e. a shift in the direction of time).

[0044] The first mathematical operation is based on the fact that even without the presence of a contrast agent in a patient's blood, the native X-ray attenuation values ​​of the blood can vary. This means that the measured values ​​can fluctuate and oscillate irregularly around a mean value, the X-ray attenuation value of native patient blood (i.e., a virtual zero line). The mean value can be determined, for example, by dividing the sum of the measured values ​​of the patient's blood (before contrast agent administration) by the number of measurements. In this context, the virtual mean value is referred to as the reference concentration value (or, more specifically, a concentration of 0).Preferably, the reference concentration value is set to zero by shifting the curve, so that only a significant increase in concentration values, resulting from the successive enrichment of the blood with contrast medium, exceeds the newly defined zero line. The population-averaged enrichment model curve and / or the candidate enrichment model curves are thus shifted upwards along the contrast medium intensity value axis, in the case of radiological imaging, for example, to a level of an X-ray attenuation value (HU value) that corresponds to the X-ray attenuation value of native patient blood.

[0045] The second operation can be performed in addition to or as an alternative to the first. The population-averaged enhancement model curve and / or the candidate enhancement model curves can preferably be synchronized with each other in a prior step by shifting them along the time axis so that they all pass through a recent measurement point of the contrast agent concentration. This measurement point is referred to here as the reference time point.

[0046] After synchronization, the population-averaged enrichment model curve and / or each of the candidate enrichment model curves can be shifted along the time axis to determine a model curve that best fits the recorded concentration values.

[0047] Preferably, the adjustment is performed using only the described simple shift in the time direction and / or a shift in height, i.e., in the direction of the contrast agent intensity scale. Such a simple shift significantly reduces the computational effort required for the adjustment. It has also been found that further adjustment is unnecessary, particularly in a method where a suitable study-specific enhancement model curve can be selected from a sufficiently large number of (population-averaged and width-varying) candidate enhancement model curves.

[0048] In particular, the selection of one or more study-specific enrichment model curves from the candidate enrichment model curves can be achieved by comparing them with the concentration values ​​recorded at specific time points or by fitting the study-specific enrichment model curves to the concentration values ​​using any known fit quality assessment method. These include, for example, the method of least squares, the mean squared error method, the sum of squared errors, or the sum of absolute errors. Model curves with a particularly low residual can then be used as study-specific enrichment model curves.

[0049] On the one hand, it is possible to analyze all pre-calculated candidate enrichment model curves for each new measurement point and only select a specific, study-related enrichment model curve in the final step. On the other hand, it is also possible, as the measurement and analysis processes progress, to restrict the analysis to those enrichment model curves that, according to a predefined criterion, best match the current trend in concentration values. Reducing the number of analysis steps saves computing power.

[0050] Furthermore, in a further development of the invention, population-averaged enhancement model curves and / or contrast agent impulse response functions can be used that are specific to gender, weight, size, defect, and / or age. The defect-specific population-averaged contrast agent impulse response function or enhancement model curve can represent characteristics of one or more different diseases and can be further differentiated. A separate population-averaged contrast agent impulse response function and / or enhancement model curve can be generated for each of the aforementioned physiological groups. The candidate enhancement model curves can thus be calculated based on group-specific contrast agent impulse response functions.If a majority of the described group-specific, population-averaged contrast agent impulse response functions or enhancement model curves are available, it is possible to make a preselection from these population-averaged contrast agent impulse response functions or enhancement model curves based on a patient's findings prior to a main measurement.

[0051] The invention is explained in more detail below with reference to the accompanying figures and exemplary embodiments. The same components are designated with identical reference numerals in the various figures. They show:

[0052] Fig. 1. A flowchart of a state-of-the-art contrast-enhanced scan,

[0053] Fig. 2 a schematic representation of an imaging system with an embodiment of a device according to the invention for carrying out the method according to the invention,

[0054] Fig. 3 a flowchart of a contrast-enhanced scan according to the inventive method,

[0055] Fig. 4 a diagram with several candidate enrichment model curves with different width values,

[0056] Fig. 5 a diagram as in Fig. 4, which presents further candidate enrichment model curves,

[0057] Fig. 6 a diagram with a function of an optimal scan time offset over a width of a contrast agent profile function,

[0058] Fig. 7 a diagram as in Fig. 4, which presents concentration values ​​from the bolus monitoring scan as well as a study-specific enrichment model curve determined for this purpose,

[0059] Fig. 8 a diagram as in Fig. 4, which shows a zero-line correction of recorded concentration values,

[0060] Fig. 9 a diagram as in Fig. 4, which represents a synchronization of several candidate enrichment model curves to a concentration value,

[0061] Fig. 10 a diagram like in Fig. Figure 4, which shows a shift of a candidate enrichment model curve along the time axis,

[0062] Fig. 11 a diagram showing a number of contrast agent concentration maxima plotted against the number of concentration value measurements,

[0063] Fig. 12 a diagram as in Fig. 4, which for comparison shows concentration values ​​of the bolus monitoring scan as well as a study-specific enrichment model curve determined for this purpose and actual measured concentration data of the main scan.

[0064] In the following exemplary embodiments, it is assumed that the imaging system is a computed tomography system (CT system), which can be used, for example, for CT angiography. However, it is expressly pointed out that the invention is not limited to application with computed tomography systems, but can also be used with other medical imaging systems, such as magnetic resonance imaging systems, ultrasound systems, or other types of computed tomography systems.

[0065] The Fig. 1 was already described in the introduction.

[0066] Fig. Figure 2 shows an exemplary embodiment of a CT system. 1 with a device according to the invention 25 to determine a measurement start time. The CT system 1 This features a central control and processing unit 10 and a scanner unit 2on.

[0067] The scanner unit 2 includes a patient table 3 and a gantry enclosure 4 , in which a raw data acquisition facility 5 with a rotatable X-ray source mounted on a gantry 6 as well as a rotatable detector arrangement mounted opposite on the gantry 7 to establish an investigation area 8 appropriate. On the patient's table 3 An object of investigation P, here a test subject or patient P, is positioned and can be moved along a system axis (or rotation axis) z into the examination area. 8 be driven in.

[0068] It is also explicitly pointed out that the item in Fig. 1 shown computed tomography system 1This is only one embodiment and the invention can of course also be used in systems in which the gantry moves along the patient P or test subject P and the patient is on the patient table 3 is located in a fixed position.

[0069] Other types of detectors can also be used, for example detectors extending along the entire circumference that do not move along with the object, but in which only the X-ray radiation source is located. 6 rotates. Furthermore, variants with multiple X-ray sources or other setups are possible.

[0070] In the illustrated embodiment, the patient P or test subject is a human being. However, the procedure can also be used on animals; therefore, the term test subject P or patient P should be interpreted broadly.

[0071] The subject P or patient P can be given an injection needle 40A contrast agent is administered, whereby the flow rate of the contrast agent is controlled by a contrast agent delivery unit as a function of time according to a precisely defined input function, which is specified, for example, in an injection protocol. 18 can be controlled.

[0072] The gantry is controlled 4 with their components via the central control and processing unit 10 , which has a processor 20 and multiple interfaces 11 , 12 , 13 , 14 , 15 , 16 as well as a storage 17 features. Instead of a single processor. 20 Of course, multiple cooperating processors can also be used.

[0073] Via a first output / input interface 11 is a terminal 19 for operating the computed tomography system 1connected. Another input / output interface. 12 It serves to connect to a network, for example a RIS network (Radiological Information System) and / or a PACS network (Picture Archiving and Communication System). Image data and / or raw data can be transmitted via this network to mass storage devices, output units, reporting stations, workstations, or similar equipment.

[0074] Via a control interface 13 Signals can be sent to the gantry via a control line. 4 and the X-ray source 6 The data is transmitted in order to control them appropriately. For the sake of simplicity, the gantry is used for all control tasks. 4 only schematically a common control interface 13 shown.

[0075] To generate the respective recordings in the desired way, the processor contains 20also a control unit 21 , which is implemented in the form of software. This control unit 21 takes over the control of the scanner. 2 for a specific measurement, for example from the memory 17 Specific scan protocols SP. Typically, a control and processing unit is included. 10 for a computed tomography system in a memory 17 a variety of such scan protocols SP for various examination situations, with an operator via the terminal 19 The user can select a suitable scan protocol (SP) and modify it if necessary. After the measurement starts, the entire CT system then operates. 1 according to control parameters in the selected scan protocol SP. Via the terminal 19 However, the operator can control the entire CT system at any time. 1 control and direct.

[0076] Via a raw data acquisition interface 14are transmitted via a data line from the detector arrangement 7 At specific, for example selected, times, raw data (RD), that is, projection measurement data, is acquired. The measured raw data (RD) is then sent to an image reconstruction unit. 22 The data is transmitted, and the system creates image data sets from it, writing them, for example, to DICOM files or other image files, which are then available for various further functions. These functions include, for example, storage in internal memory. 17 or an external storage device via the network NW, a display on the terminal screen 19 , but also automatic evaluation, for example segmentation and / or determination of contrast agent enhancement values ​​in a previously defined body region of interest. This region can, for example, be determined by a display on the terminal. 19It may have been manually defined by an operator using a graphical user interface. However, automatic selection of the body region is also possible. As explained further later (see Fig. 3) The region or target area ZB of patient P can be acquired in a main measurement HS. A preliminary measurement to prepare for the main measurement HS, e.g., to monitor the contrast agent enhancement profile, can be performed in a monitoring area UB of patient P, which – as shown here – can be very close to the target area ZB. If, for example, image data BD of the heart of patient P is to be acquired as the target area ZB in the main measurement HS, the preliminary measurement can be performed on the ascending aorta as monitoring area UB.

[0077] Via another control interface 15 can be used to control the gantry 4 , the X-ray source 6and the detector arrangement 7 the table extension of the patient table 3 The system can be controlled, for example, to acquire raw data RD from the desired area of ​​the object under investigation P using a sequential or helical (spiral) process, depending on the control protocol, and to reconstruct the image data BD from this. Both individual layers and volume data can be acquired.

[0078] Via another output / input interface 16 Is it possible to use the control and processing unit? 10 the external contrast agent delivery unit 18 synchronized with the other units of the CT system 1 to be controlled. For this purpose, the control and processing unit can be used. 10 a start signal SS to the contrast agent delivery unit 18 be transmitted. Via this interface 16For example, information on the injection protocol (such as the contrast agent concentration, flow rate, volume, etc.) can also be obtained from the control and processing unit. 10 to the external contrast agent delivery unit 18 or vice versa. Alternatively, the contrast agent delivery unit can be used. 18 also part of the control and processing unit 10 be.

[0079] In the illustrated embodiment, the processor 20 the control and processing unit 10 a measurement start time determination unit 25 This is implemented for the automatic determination of a measurement start time for a main measurement of the object under investigation P. It has an input interface. 26 for the acquisition of image data BD and, if applicable, concentration values ​​KD, which are optionally provided by the image reconstruction unit. 22The measurement start time determination unit can be determined from the image data. 25 It also features an input interface. 27 to take over a number of population-averaged enhancement model curves and / or contrast agent impulse response functions, which are stored, for example, in memory 17 They may be stored there. She also receives the aforementioned information about the injection protocol.

[0080] Furthermore, the measurement start time determination unit includes 25 a candidate curve calculation unit 28 to generate a number of candidate enhancement model curves based on a population-averaged contrast agent impulse response function, a fitting unit 29 to adapt the candidate enrichment model curves to the study-specific concentration values, an enrichment model curve determination unit 30to determine a current study-specific enrichment model curve based on the fitting, and a model curve analysis unit 24 to determine the measurement start time t s based on the study-specific enrichment model curve. The measurement start time determination unit. 25 is via an output interface 37 with the control unit 21 connected, to which the measurement start time t s is transmitted and then the scanner 2 appropriately controls the system.

[0081] The exact functionality of the measurement start time determination unit 25 will be explained later using the Fig. 4 to Fig. 12 explained in more detail.

[0082] The image reconstruction unit 22 , the measurement start time determination unit 25 as well as the model curve analysis unit 24 are here in the form of software on the processor20 realized. In principle, however, all these units can also be implemented, at least partially, as hardware components.

[0083] It is clear that a CT system used for the invention 1 Furthermore, it may also have a large number of other common components, which, however, are omitted for the sake of simplicity. Fig. 2 are not shown further and do not need to be explained further, as they are known to the expert.

[0084] Fig. 3 corresponds in its structure to the Fig. 1, with the difference that a fourth time axis (IV) represents a calculation period in which, within the framework of a model curve determination process, MKE is determined based on the previously measured concentration values ​​KD1, KD2, ..., KD5, ..., KD8, one or more investigation-specific enrichment model curves C Mto be determined, in a temporal relationship with a contrast agent delivery function IF(t), a contrast agent profile function C(t), a bolus monitoring scan BTS and a main measurement HS.

[0085] As in Fig. 1. Immediately after or with a specific monitoring time delay (UZ) following the administration of the contrast agent (KM) at a contrast agent administration start time (SK), a bolus monitoring scan (BTS) is initiated. At acquisition time points t1, t2, t3, ..., t8, concentration values ​​KD1, KD2, KD3, ..., KD8 (whose numbering corresponds to the number of the respective acquisition time points) of the contrast agent (KM) are measured in the monitoring area (UB) of the body (P). A concentration value KD5 that is the first to significantly exceed previously acquired blood values ​​KD1, ..., KD4 triggers a calculation process that computes an initial current contrast agent profile function C(t). This calculation replaces the main scan (HS) of the target area (ZB) according to a previously defined scan time delay (SZ), as is part of the described conventional procedure.

[0086] The calculation process operates with population-averaged enhancement model curves (based on a population-averaged contrast agent impulse response function AIR). AVG), which describes contrast enhancement as the mean value for a population. The population can be defined as the entire population or as a population specific to sex, weight, height, defect, and / or age. This means that for a patient P, a mean value is calculated for a specific group of patients, where the group preferably shares as many similar physiological characteristics as possible with patient P with respect to at least one parameter. For example, the group includes people of the same sex, similar weight, similar height, or similar age. The measured values ​​underlying the population-averaged enhancement model curve can be stored, for example, in a database (DB).In a candidate curve calculation process KB, a number of candidate enhancement model curves C are calculated using the population-averaged contrast agent impulse response function and a tube voltage constant fkV (derived from the tube voltage of the CT scanner used in determining the population-averaged measurement data) and corresponding injection protocol data ID (e.g., with information on the total amount of contrast agent used, an injection rate, and the iodine content of the contrast agent). K1 , C K2 , ..., C K7 (see also Fig. 4) calculated, representing possible scenarios of a time course of contrast agent concentration. These curves C K1 , C K2 , ..., C K7After their calculation, they can also be stored in the database DB. The selection of a population-averaged contrast agent impulse response function and the calculation of candidate enhancement model curves C K1 , C K2 , ..., C K7 Contrast agent administration can be performed even before the start time of the contrast agent administration.

[0087] An algorithm that uses injection protocol data ID, i.e., at least a contrast agent administration period IZ, a contrast agent injection rate KMR, and its current iodine concentration co u , as well as a currently used tube voltage fkV U It takes into account and calculates which of the candidate enrichment model curves C K1 , C K2 , ..., C K7 a real contrast agent enhancement curve, which here is only described by the first significant concentration value KD5 recorded at time t5.

[0088] The calculation process is repeated iteratively for each subsequent concentration value KD6, KD7, KD8 of the contrast agent KM. After each subsequent acquisition time point t6, t7, t8 corresponding to the concentration values ​​KD6, KD7, KD8, a study-specific enhancement model curve C is generated. M , which are from the group of candidate enrichment model curves C K1 , C K2 , ..., C Kn is calculated with greater reliability of an actual contrast agent enhancement curve. In the present embodiment, the acquisition of concentration values ​​and the subsequent calculation are terminated at the latest after the eighth concentration value KD8 has been acquired, as a point in time has been reached that is necessary as a buffer for controlling or setting up the scanner for a main scan HS. This termination of the bolus monitoring scan BTS is caused by the event at the end of the model curve determination process MKE between axes IV and III in Fig. 3 upward-pointing arrows symbolize this. Based on the last calculated contrast agent profile function C(t), which is then used as the examination-specific enhancement model curve C M is used (see Fig. 7), a measurement start time t is now determined. s The HS is calculated at the start of the main scan. The measurement start time t s It takes into account a previously determined duration of the main scan HS and is, for example, positioned so that the main scan HS takes place in a concentration peak phase KG, which extends from a calculated peak KP of the contrast agent concentration in the target area ZB in equal parts into the time before the peak KP and after the peak KP.

[0089] In this procedure, taking into account all relevant scan parameters, injection parameters (ID), and patient characteristics, an optimal time window for performing the patient's main scan (HS) is determined in real time based on the concentration values ​​(KD) of the bolus monitoring scan (BTS) in the form of the peak concentration phase (KG) of the examination-specific enrichment model curve. Prior definition of a concentration threshold (KS) and a scan time offset (SZ) is no longer mandatory.

[0090] Fig. Figure 4 shows seven candidate enrichment model curves C K1 , ..., C K7 , which were calculated and stored based on a population-averaged contrast agent impulse response function prior to a main measurement HS and represent possible profiles of contrast agent concentration KM in a patient P's body. Each of these candidate enhancement model curves C K1 , ..., CK7 is a function of the contrast agent intensity IK (in Hounsfield units HU) over time t (in s). The calculation is performed for each of the functions C. ki (t) (with i = 1 to 7) using the above-mentioned equation (3).

[0091] Various width values ​​are used in this process. n (with n = 1 to 7) substituted into equation (3), which here lie between 1.0 and 4.0 in steps of 0.5, resulting in the following candidate enrichment model curve C K1 , ..., C K7 arise: C K1 for b1 = 1.0 C K2 for b2 = 1.5 C K3 for b3 = 2.0 C K4 for b4 = 2.5 C K5 for b5 = 3.0 C K6 for b6 = 3.5 C K7 for b7 = 4.0

[0092] The different width values ​​b1, ..., b7 represent or imitate, in a model, physiological differences of individual patients P, whose bodies exhibit a different rate of accumulation / depletion of contrast agent KM.

[0093] The correction factor (1 / b n ) in equation (3) takes into account, as already mentioned above, that a human being forms a closed system and therefore, when the width of the contrast agent impulse response function AIR changes, AVG (t) changes the amplitude reciprocally. As a result, as in Fig. 4 can be seen to be an integral value of the candidate enrichment model curves C K1 , ..., C K7 or the areas under the candidate enrichment model curves C K1 , ..., C K7 Each one is identical.

[0094] It can be experimentally demonstrated that if the assumption of reciprocity is not fulfilled in a measurement of an individual patient P, the discrepancy between the inventive model calculation and the actual properties of an individual patient P has an effect on a measurement start time t. s The main measurement HS is very low. With a study-specific enrichment model curve C M In this case, the amplitude or absolute contrast agent intensity values ​​(IK) change. However, due to a very similar temporal course, the contrast agent concentration maximum (IP), which determines the peak phase (KG), lies at a similar location. Therefore, the above assumption of reciprocity applies generally.

[0095] Alternatively, instead of using the correction factor b and its reciprocal value, 1 / b, in equations (2) or (3), experimental data could be used which describe the relationship between the width and amplitude of the contrast agent impulse response function via a look-up table (LUT).

[0096] The calculated or “simulated” candidate enrichment model curves C K1 , ..., C K7 Ideally, they should have a high temporal resolution, e.g. between 0.01s and 0.001s, compared to the temporal resolution of the bolus monitoring scan BTS (which is usually around 1 to 2s in CT measurements).

[0097] The equation (3) mentioned at the beginning also takes into account the iodine concentration co U of the contrast agent used in the current measurement in relation to the iodine concentration co AVG, which formed the basis for the measurements from which a population-averaged contrast agent impulse response function AIR was derived AVG (t) was calculated.

[0098] The one in Fig. The values ​​shown in 4 are still based on injection protocol data ID or on a contrast agent delivery function IF(t), where, for example, a contrast agent volume of 70 ml is introduced into body P at an injection rate of 5 ml / s, and the contrast agent KM has a concentration of 300 mg iodine / ml. Equation (3) also takes into account the iodine vector fKV. U , which, as explained above, depends on the tube voltage with which a radiological imaging system is operated in the current measurement (more precisely, the bolus monitoring scan BTS of the current measurement). This iodine vector fKV U forms a quotient with the iodine vector fKV AVG, which in turn depends on the tube voltage on which the measurements were based, from which the population-averaged contrast agent impulse response function AIR was derived. AVG (t) was formed.

[0099] Other parameters that can determine how far an individual patient P differs from the population-averaged values ​​used, such as heart rate, cardiac output or weight, could in principle be additionally taken into account in equation (3) by means of their own correction factors.

[0100] The candidate enrichment model curves C K1 , ..., C K7This shows that a comparatively high width value b is reflected in a broader contrast agent impulse response function AIR(t), and that a contrast agent concentration maximum IP is only reached after a comparatively longer time. From the curve's shape, it can be concluded that such a patient has a low cardiac output. Thus, in this method, a patient's physiological characteristics are determined from an ultimately selected, examination-specific enhancement model curve C. M , without having been enriched with patient-specific parameters from the outset.

[0101] Fig. Figure 5 shows three candidate enrichment model curves C K10 , C K11 , C K12 , where latitude values ​​b 10 , b 11 , b 12 (see here) Fig. 6) their respective underlying contrast agent impulse response functions AIR(t) with 1.0 (C K10 ), 2.0 (C K11) and 3.0 (C K12 ) are specified. The injection protocol data ID for calculating these curves shows, as an example, a total amount of contrast agent KM of 90 ml, which is introduced into the patient's body P at an injection rate of 5 ml per second. An iodine concentration co U The iodine concentration of the contrast agent used is 300 mg / ml. The tube voltage of an X-ray tube used during the main measurement (HS) is used to calculate the tube voltage constant (fkV). U The voltage used is 100kV.

[0102] Taking into account the planned duration of the main scan HS (the duration results, for example, from the scan length and the "pitch", i.e., the ratio of table feed to beam collimation of a CT scanner), an enrichment model curve C can be determined for each candidate. K10 , ..., C K12 a concentration peak phase KG 10 , ..., KG 12This is determined as a period with the duration of the main scan, which includes, for example, a maximum contrast agent enhancement IP. The peak concentration phase KG is defined here as a period of highest contrast agent enhancement. However, it can also be defined as the period before a maximum contrast agent enhancement is reached. The second option offers greater certainty that a measurement start time t determined in this way is accurate. s a main measurement HS is closer to the time as determined according to the conventional method starting from a concentration threshold KS (see Fig. 1) However, it is also less efficient, as maximum contrast agent enhancement is not fully utilized. In the example described here, the peak concentration phase (KG) lasts [duration not specified]. 10 , ..., KG 12 Each scan time is predefined as 4 seconds, but it can also be defined as shorter or longer, depending on the scan duration of the main scan (HS).

[0103] After the in Fig. In accordance with the state-of-the-art procedure described in section 1, the bolus monitoring scans (BTS) would be terminated at a concentration threshold (KS) of 150 HU. After a scan time delay (SZ) of a fixed value, e.g., 3 seconds, a main measurement (HS) would automatically start. Fig. However, Figure 5 shows that for each of the three candidate enrichment model curves C K10 , ..., C K12 a different scan time offset SZ 10 , SZ 11 , SZ 12 would be optimal. For the candidate enrichment model curve C K10 It would be approximately 11s for the candidate enrichment model curve C. K11 approximately 9s and for the candidate enrichment model curve C K12 only about 7 seconds. This shows that with a scan time offset SZ of, for example, 3 seconds (as in Fig. 1) a main measurement HS would be performed significantly before a contrast agent concentration maximum IP, and would therefore result in suboptimal contrast agent enrichment in the image data BD.

[0104] Fig. Figure 6 illustrates the one in the Fig. 5. Established relationship between the width of the contrast agent impulse response function AIR(t) and an optimal scan time offset SZ o , which represents a period between the end of a bolus monitoring scan (BTS) and a measurement start time t s indicates. The larger a width value (b = 0.5 to 3.0) of a candidate enrichment model curve C K or a study-specific enrichment model curve C M The lower the value of an optimal scan time offset (SZ), the better. 10 , SZ 11 , SZ 12 (These three values ​​shown here specifically correspond to the width values ​​b) 10 = 1, b 11 = 2, b 12= 3), which here lies between 7s and 13s.

[0105] In the Fig. 7 are those within the framework of the bolus monitoring scan BTS in measurement intervals, such as 1s each, at measurement times t1, t2, ..., t 21 recorded concentration values ​​KD1, KD2, ..., KD 21 The bolus monitoring scan (BTS) is started with a monitoring time delay (UZ), here for example of approximately 8 seconds, after the contrast agent administration start time (SK). The concentration value (KD) is then recorded. 13 is a previously defined threshold value, here e.g. of 30 HU, above a baseline level in the form of the previously recorded concentration values ​​KD1, KD2, ..., KD 12 The initial level of the concentration values ​​KD1, KD2, ..., KD has been reached. 12This represents a native X-ray attenuation or HU value of the patient's blood (which is approximately 50 HU in this case). Exceeding this threshold triggers a calculation. The algorithm used (see Fig. 4) Determined in real-time after each measurement KD 13 , ..., KD 21 A current, study-specific enrichment model curve. After a final recording of concentration values ​​KD. 21 The resulting enrichment model curve C is the study-specific curve. M (see also Fig. 4) based on the recorded concentration values ​​KD1, ..., KD 21 This determination of the study-specific enrichment model curve C M This is done according to the preferred variant of the procedure by selecting a candidate enrichment model curve C. K (see below), which are particularly well suited to the course of the data up to a current recording time (here t 21The recorded concentration values ​​KD are adjusted. The exact procedure for selecting the most suitable candidate enrichment model curve C K The following will be based on the Fig. 8 to Fig. 11 explained in more detail.

[0106] First, the concentration values ​​KD or candidate enrichment model curves C must be determined. K so that the native X-ray attenuation value or HU value of patient blood is adjusted in the calculation of an examination-specific enrichment model curve C M (implicitly) taken into account. For this purpose, a "zero line" or a reference concentration value C0, which is defined by an X-ray attenuation value for pure water at 0 HU, is shifted to an X-ray attenuation value of a blood volume of the patient being measured P, which must always be determined individually ("baseline offset", i.e., zero-line shift). This is in Fig. Figure 8 illustrates this. For example, if a patient's blood volume P has a native value of 50 HU without contrast agent administration, and a contrast agent concentration value KD of 80 HU is detected in the blood image data BD after contrast agent administration, the difference results in a contrast agent increase of 30 HU. First, a baseline or zero line with the mean value MW is determined for a period without contrast agent administration during a pre-monitoring phase (e.g., at approximately 50 HU). Subsequently, all concentration values ​​KD recorded during this phase are corrected downwards to the corrected mean value MW. k (with 0 HU). Also all concentration values ​​KD1 to KD 21 , which are recorded during a bolus monitoring scan (BTS) or monitoring scans of an examination subject P with the influence of the contrast agent KM, are subsequently virtually corrected downwards by 50 HU to concentration values ​​KD. 1’ up to KD21‘ This is achieved by shifting the zero line on one axis of the contrast agent intensity values ​​(IC) upwards by the same amount, so that the patient's blood is set to 0 HU. This shift can be determined during the pre-monitoring phase and / or from a number of concentration measurements within the monitoring range (UB), e.g., an average of the first four measurements for which it can be assumed with absolute certainty that the contrast agent (CM) has not yet reached the monitoring range (UB).

[0107] Alternatively, the simulated candidate enrichment model curves C KThe value is increased by the currently determined HU value of the patient's blood. This method ultimately leads to the same result. All subsequent mathematical operations refer to the increase in contrast agent concentration or to the concentration values ​​KD' corrected with respect to the zero-line offset, and not to the absolute X-ray attenuation or HU values.

[0108] Fig. Figure 9 therefore shows C as part of a fitting of candidate enrichment model curves. K The candidate enrichment model curves C represent a visual representation of a synchronization procedure based on the temporal progression of recorded concentration values ​​KD. K1 , ..., C K7 , which differ from each other by the width values ​​b1, ..., b7, are each shifted along the time axis t such that they all pass through a measurement point of the contrast agent concentration KD. 18’ proceeding, which at a measurement time t 18was recorded. For each candidate enrichment model curve C K1 , ..., C K7 The time at which they reach the concentration value KD is determined separately. 18‘ This step results in reference times t0 that differ in time or are shifted relative to each other, at which the candidate enrichment model curves C K1 , ..., C K7 rise from a virtual zero line. Specifically, these are t 0,1 (for C K1 ), t 0,2 (for C K2 ), t 0,3 (for C K3 ), ..., t 0,7 (for C K7 ).

[0109] Fig. Figure 10 illustrates the necessary step for determining the most suitable curves, which follows the synchronization procedure according to Fig. 9 is completed. The candidate enrichment model curve C K5 as an example for each of the in Fig. 9 candidate enrichment model curves shown C K1 , ..., CK7 The concentration value KD is adjusted by a specific time range along the time axis, e.g. 3s, in steps of e.g. 0.1s from the last recorded (and corrected with respect to the zero-line offset) concentration value KD. 18‘ The candidate enrichment model curve C is then calculated using the "least squares method". K5 (b5 = 3.0) a best possible match and therefore an optimal time shift t v wanted.

[0110] After analyzing the entire time range, the candidate enrichment model curve C is obtained. K5o The curve with the best fit was determined using a time shift value t. v The result is the curve with the smallest possible residual in terms of agreement with the recorded concentration values ​​KD. Subsequently, the specific parameters of this best-fitting candidate enrichment curve C are determined. K5oStored: the aforementioned residual ("goodness of fit"), a latitude value b, the reference time t0 and a time shift value t v This adjustment step is performed for each of the candidate enrichment model curves C. K1 , ..., C K7 KD was repeated after measuring each new concentration value.

[0111] After analyzing all previously calculated candidate enrichment model curves C K1 , ..., C K7 A candidate enrichment model curve C will be used. K determined with the lowest residual. The corresponding study-specific enrichment model curve C M (t + t0 + t v ) is used to predict contrast agent enhancement after recording the last concentration value KD.

[0112] As mentioned, the mean squared error method can be used as a fit-quality determination procedure to achieve an optimal fit of a study-specific enrichment model curve C. M to determine the temporal progression of the concentration values ​​KD. Alternatively, other similarity methods can be used, such as the sum of squared errors or the sum of absolute errors.

[0113] Alternatively to an analysis of all pre-calculated candidate enrichment model curves C K After each new acquisition of concentration values ​​KD, with an increasing number of acquisitions, each subsequent iteration can be restricted to those candidate enrichment model curves C. K, which, in a previous adjustment after a certain threshold, best matched the previously recorded concentration values ​​KD. This offers the advantage of a gradual reduction in the required computing resources.

[0114] This procedure is repeated as long as the bolus monitoring scan (BTS) continues. After each subsequent acquisition of concentration values ​​(KD) within the BTS, the reliability of the prediction increases because the current study-specific accumulation model curve (C) is more accurate. M The concentration value KD will always contain one more value than the previously performed calculation.

[0115] To determine whether the appropriate curve has been found, it shows Fig. 11 a change in each case after recording the concentration values ​​KD 13 , ..., KD 21 through the algorithm (see Fig. 4) calculated contrast agent concentration maximum IP1, ..., IP9 of the examination-specific enhancement model curve C M According to the first, second, and third calculations (at concentration measurement points MP 13 to 15), the predicted contrast agent concentration maximum IP1, IP2, IP3 occurs approximately 42 seconds after the start of contrast agent administration SK. According to the fourth calculation (at concentration measurement point MP 16), the predicted contrast agent concentration maximum IP4 occurs approximately 43 seconds after the start of contrast agent administration SK. The figure shows that after each further acquisition of concentration values ​​KD 14 , ..., KD 17 After exceeding a predefined threshold, a calculated contrast agent concentration maximum IP2, ..., IP5 is adjusted until the algorithm is used after the 18th measurement (of the concentration value KD). 18At the corresponding 18th concentration value measurement point (MP), the peak concentration value IP6 is calculated at approximately 40 seconds after the start time of contrast agent administration (SK). This value is then used in this example through the following measurements and calculations up to the 21st measurement (of the concentration value KD). 21 ; repeatedly confirmed at the corresponding 21st concentration value measurement point (MP).

[0116] A control device (see Fig. 2) of the CT system used 1 terminates a calculation process performed using the algorithm and the bolus monitoring scan (BTS) if, for example, the study-specific enrichment model curve C calculated on the basis of a last recorded concentration value KD is reached. MThe system is triggered when a previously defined reliability threshold is exceeded, meaning it predicts the future course of an examination-specific enhancement model curve with sufficient probability. This can occur, for example, if two or more successively determined contrast agent concentration maxima (IP) exhibit essentially constant values ​​(i.e., values ​​with a variance of less than 5%), as is the case here with contrast agent concentration maxima IP6 to IP9. If the reliability threshold is not reached, the calculation process and the bolus monitoring scan (BTS) are stopped at a time that guarantees a buffer sufficient to prepare the scan setup before a main measurement (HS) ("maximum scan delay").The time buffer allows, for example, the patient table of the CT system to move into a suitable position for performing the main measurement HS after the bolus monitoring scan (BTS) has been completed.

[0117] Fig. Figure 12 shows, once again to confirm the reliability of the procedure, a study-specific enrichment model curve C. M’ , which differs from the study-specific enrichment model curve C M after Fig. 7 was calculated using other specific values. The predicted curve shape was subsequently determined by recording concentration values ​​KD (marked by asterisks; in contrast to the concentration values ​​KD marked by circles, which were used to calculate the study-specific enrichment model curve C). M’ (served) verified. This proves that a calculation of a concentration peak phase KG based on the algorithm according to the invention (see Fig. 4) also produces realistic results in patients under altered conditions, e.g. a different width value of the contrast agent impulse response function, a different injection protocol and a different kV level.

[0118] Finally, it should be noted once again that the devices described in detail above are merely exemplary embodiments which can be modified in various ways by a person skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Likewise, the term "unit" does not preclude the possibility that it consists of several interacting components, which may also be spatially distributed.

Claims

[1] Method for determining a measurement start time (t s ) for an imaging measurement using a medical imaging system ( 1 ) depending on a time course of concentration values ​​(KD1, ..., KD) 21 ) of a contrast agent (CM) in a monitoring area (MO) of an examination object (P) using the following steps: – Recording of concentration values ​​(KD1, ..., KD) 21 ) of the current concentration of the contrast agent (CM) in the monitoring area (MU) at various successive recording times (t1, ..., t9), – Determination of a current study-specific enrichment model curve (C M ) based on a time course of the concentration values ​​(KD1, ..., KD 21 ), – Determination of the measurement start time (t s ) based on the study-specific enrichment model curve (C M ). [2] Method according to claim 1, wherein the investigation-specific enrichment model curve (C M ) is determined on the basis of a population-averaged enhancement model curve and / or population-averaged contrast agent impulse response function. [3] Method according to claim 1 or 2, wherein injection protocol data (ID) are recorded and the study-specific enrichment model curve (C) is generated. M ) is determined based on the injection protocol data (ID). [4] Method according to any of the preceding claims, wherein the investigation-specific enrichment model curve (C M ) based on the temporal progression of the concentration values ​​(KD1, ..., KD 21 ) from a plurality of candidate enrichment model curves (C K1 , ..., C K12 ) is selected. [5] Method according to claim 4, wherein the candidate enrichment model curves (C K1 , ..., C K12) by different widths (b1, ..., b 12 are parameterized. [6] Method according to claim 4 or 5, wherein the candidate enrichment model curves (C K1 , ..., C K12 ) are parameterized by at least one correction factor. [7] Method according to claims 5 and 6, wherein the correction factor of the candidate enrichment model curves (C K1 , ..., C K12 ) is chosen such that candidate enrichment model curves (C K1 , ..., C K12 ) with different widths (b1, ..., b 12 ) exhibit an essentially identical integral value. [8] Method according to claim 6 or 7, wherein the correction factor is based on a current iodine concentration (co U ) of the contrast agent (CM) and / or a current tube voltage of a computed tomography system used in the current measurement ( 1 ) is based. [9] Method according to any one of claims 2 to 8, wherein the investigation-specific enrichment model curve (C M ) by fitting the population-averaged enrichment model curve and / or by fitting candidate enrichment model curves (C K1 , ..., C K12 ) on the time course of the concentration values ​​(KD1, ..., KD 21 ) is determined. [10] Method according to claim 9, wherein the fitting of the population-averaged enrichment model curve and / or a fitting of candidate enrichment model curves (C M , C K1 , ..., C K12 ) on the time course of the concentration values ​​(KD1, ..., KD 21 ) includes at least one of the following operations: – relative shift of the population-averaged enrichment model curve (C M ) and / or the candidate enrichment model curves (C K1 , ..., C K12 ) to the concentration values ​​(KD1, ..., KD21 ) with respect to a reference concentration value (C0). and / or – relative shift of the population-averaged enrichment model curve (C M ) and / or the candidate enrichment model curves (C K1 , ..., C K12 ) to the concentration values ​​(KD1, ..., KD 21 ) with respect to a reference time (t0). [11] Method according to any one of claims 2 to 10, wherein a sex-specific and / or weight-specific and / or size-specific and / or defect-specific and / or age-specific population-averaged enhancement model curve and / or population-averaged contrast agent impulse response function is used. [12] Method for controlling a medical imaging system ( 1 ) to generate image data (BD) of an object under investigation (P) using the following steps: – Determining a measurement start time (t s) for an imaging measurement as a function of a time course of concentration values ​​(KD1, ..., KD) 21 ) of a contrast agent (CM) in a monitoring area (ME) of the object under investigation (P) according to one of claims 1 to 11, – Performing an imaging measurement of a target area (ZB) of the object under investigation (P) using the determined measurement start time (t) s ). [13] Control unit ( 10 ) for a medical imaging system ( 1 ) with – an interface ( 16 ) for recording or outputting a contrast agent administration start time (SK), – a measurement start time determination unit ( 25 ) with – an input interface ( 16 ) for recording concentration values ​​(KD1, ..., KD 21) of a current concentration of a contrast agent (CM) in a monitoring area (ME) of an object under investigation (P) at various successive recording times (t1, ..., t9), – an enrichment model curve determination unit ( 30 ) to determine a current study-specific enrichment model curve (C M ) based on a time course of the concentration values ​​(KD1, ..., KD 21 ), – a model curve analysis unit ( 24 ) to determine the measurement start time (t s ) based on the study-specific enrichment model curve (C M ). [14] Medical imaging system ( 1 ) for generating image data (BD) of a target area (ZB) inside an object under investigation (P) comprising a control unit ( 10 ) according to claim 13. [15] Computer program product which is directly loaded into the memory of a control device ( 10 ) a medical imaging system ( 1 ) is loadable, with program code means to execute all steps of a method according to any one of claims 1 to 11, when the program product is on the control device ( 10 ) is executed.