Method for optimizing the predetermination of the time profile of a contrast agent concentration in diagnostic imaging using a magnetic resonance system

Abstract

A method of predetermining the time profile of a contrast agent concentration at a vessel position is provided in the context of contrast agent-enhanced MRI of a region of interest only during the initial flooding-in phase of the contrast agent into the vessel situated in the region of interest. The method includes establishing a broadening of a contrast agent bolus profile according to the equation W=W2W1 wherein W1 is a first width of the contrast agent bolus profile at a first vessel position and W2 is a second width of a contrast agent concentration profile at a second vessel position within the region of interest. The broadening is established by determining at least one flow parameter which is dependent on at least one blood flow property of the patient at a third vessel position thereof and which correlates with the broadening of the contrast agent profile.

Claims

1. A method of predetermining a time profile of contrast agent concentration at a position in a blood vessel of a patient in the context of contrast agent-enhanced magnetic resonance (MR) imaging of a region of interest only during an initial flooding-in phase of the contrast agent into the blood vessel situated in the region of interest, the method comprising: establishing an expected broadening of a contrast agent bolus profile B(t) according to the equation W=W2W1 wherein W1 is a first width of the contrast agent bolus profile B(t) at a predetermined first vessel position of the patient and W2 is a second width of a contrast agent concentration profile K(t) at a predetermined second vessel position situated in the region of interest of the patient; such that the expected broadening is established by determining at least one flow parameter which is dependent on at least one blood flow property of the patient at a third vessel position thereof and which correlates with the expected broadening of the contrast agent bolus profile B(t).

2. The method according to claim 1 wherein at least one of the region of interest and the predetermined second vessel position therein is situated downstream of a cardiopulmonary passage of the patient in relation to flow of blood therein.

3. The method according to claim 2 wherein at least one of the region of interest and the predetermined second vessel position therein is situated in a peripheral region of the patient, in particular in a limb thereof.

4. The method according to claim 1 wherein the expected broadening (W=W2W1) is stored in an electronic memory for further use by a computer.

5. The method according to claim 1 wherein the at least one blood flow property is established without the presence of contrast agent by way of a phase contrast magnetic resonance measurement.

6. The method according to claim 1 wherein at least one of a bolus transfer time and a bolus arrival time is additionally determined between the predetermined first vessel position and the predetermined second vessel position.

7. The method according to claim 6 wherein the contrast agent concentration profile (K(t)) at the predetermined second vessel position is determined from the expected broadening (W=W2W1) and the at least one of the bolus transfer time and the bolus arrival time.

8. A method of predetermining a time profile of contrast agent concentration at a position in a blood vessel in a region of interest of a patient (P) in connection with a contrast agent-enhanced magnetic resonance (MR) imaging procedure to be performed on the patient, the method comprising: establishing a correlation between a broadening (W=W2W1) of at least one contrast agent bolus profile (B(t)) having a first width (W1) at a first vessel position (P1) in relation to a contrast agent concentration profile (K(t)) having a second width (W2) at a second vessel position (P2), the correlation being established using a flow parameter (P.sub.G) dependent upon at least a blood flow property (f.sub.B) of the patient (P) at a third vessel position (P3) thereof and taking into account at least one patient parameter (P.sub.P) of an examined patient collective; determining from the patient (P) at least one flow parameter (P.sub.pa) currently representative thereof; selecting a desired contrast agent concentration profile (K(t)) to be achieved at the second vessel position (P2) and, using the correlation, determining a necessary contrast agent bolus profile (B(t)) required therefor, taking into account at least one patient parameter (P.sub.P) of the patient (P); and enabling the necessary contrast agent bolus profile (B(t)) to be one of selectable from or transmittable to an injection device for use in a contrast agent-enhanced MR examination.

9. The method according to claim 8 wherein the blood flow property (f.sub.B) of the patient at the third vessel position (P3) is determined via a phase contrast magnetic resonance examination.

10. The method according to claim 9 wherein the phase contrast magnetic resonance examination for determining the blood flow property (f.sub.B) is performed without the contrast agent being present in a blood circulation of the patient (P).

11. The method according to claim 8, wherein the at least one patient parameter (P.sub.P): is at least one of: sex, weight, height, age, heart rate, body mass index, type of stature, and distance between the vessel positions.

12. The method according to claim 8 wherein the blood flow property (f.sub.B) is at least one of: (a) maximum, minimum or mean blood flow velocity (v.sub.G) at at least one predetermined position in a cross section of the blood vessel at the vessel position; (b) maximum, minimum or mean blood flow velocity (v.sub.G) at at least one predetermined position in a cross section of the blood vessel at the vessel position at a given heart or pulse phase; (c) maximum, minimum or mean blood flow velocity (v.sub.G) at at least one predetermined position in a cross section of the blood vessel at the vessel position at a given heart or pulse phase over a predetermined measurement time period; (d) maximum, minimum or mean blood flow volume at at least one predetermined position in a cross section of the blood vessel at the vessel position; (e) maximum, minimum or mean blood flow volume at at least one predetermined position in a cross section of the blood vessel at the vessel position at a given heart or pulse phase; (f) maximum, minimum or mean blood flow volume at at least one predetermined position in a cross section of the blood vessel at the vessel position at a given heart or pulse phase over a predetermined measurement time period; (g) a geometric property of a velocity profile over a cross section of the blood vessel at the vessel position; and (h) net forward volume over a predetermined period of time or per heartbeat.

13. The method according to claim 8 wherein the blood flow property (f.sub.B) itself is used as the flow parameter (P.sub.G).

14. The method according to claim 8 wherein an absolute or percentage difference between the blood flow property (f.sub.B) at the third vessel position (P3) in relation to the blood flow property (f.sub.B) of a same type at a fourth vessel position (P4) is used as the flow parameter (P.sub.G).

15. The method according to claim 8 wherein the first vessel position (P1) satisfies at least one of the following locations or conditions: (a) the first vessel position (P1) lies in a venous vessel; (b) the first vessel position (P1) lies in an arm vein; (c) the first vessel position (P1) lies on the back of the hand; (d) the first vessel position (P1) lies at a central venous catheter; (e) the first vessel position (P1) lies between the back of the hand and the V. axillaris; (f) the first vessel position (P1) lies between a foot and the V. saphena magna; and (g) the first vessel position (P1) lies in a central venous vessel.

16. The method according to claim 8 wherein the second vessel position (P2) satisfies at least one of the following locations or conditions: (a) the second vessel position (P2) lies in an arterial vessel; (b) the second vessel position (P2) lies in a leg artery; (c) the second vessel position (P2) lies downstream of the third vessel position (P3); (d) the second vessel position (P2) lies downstream of the bifurcation of the aorta; (e) the second vessel position (P2) lies in a peripheral artery in a knee region; (f) the second vessel position (P2) lies in an arm region; and (g) the second vessel position (P2) lies in a neck region.

17. The method according to claim 8 wherein the third vessel position (P3) satisfies at least one of the following locations or conditions: (a) the third vessel position (P3) is the second vessel position (P2); (b) the third vessel position (P3) lies in the Aorta thorakalis; (c) the third vessel position (P3) lies in the Aorta abdominalis; (d) the third vessel position (P3) lies between the Aorta thorakalis and the second vessel position (P2); (e) the third vessel position (P3) lies upstream of the bifurcation of the aorta; and (f) the third vessel position (P3) lies between the bifurcation and second vessel position (P2).

18. The method according to claim 14 wherein the fourth vessel position (P4) satisfies at least one of the following locations or conditions: (a) the fourth vessel position (P4) lies upstream of the third vessel position (P3); (b) the fourth vessel position (P4) lies downstream between the third vessel position (P3) and the second vessel position (P2); and (c) the fourth vessel position (P4) lies downstream of the second vessel position (P2).

19. The method according to claim 8 wherein a width of the contrast agent bolus profile (B(t)) lies in the range of 3 to 15 seconds preferably but not outside of the range of 1 to 20 seconds.

20. The method according to claim 8 wherein the correlation between the broadening (W=W2W1) and the flow parameter (P.sub.G) is gathered from a stored lookup table.

21. The method according to claim 20 wherein the stored lookup table is predetermined from reference measurements and the at least one patient parameter (P.sub.P) is at least one of: sex, weight, height, age, heart rate, body mass index, type of stature, and distance between the vessel positions.

22. The method according to claim 8 wherein the correlation between the broadening (W=W2W1) and the flow parameter (P.sub.G) is calculated by a function (f(P.sub.G, P.sub.P)) predetermined from reference measurements.

23. The method according to claim 22 wherein the at least one patient parameter (p.sub.p) within the function (f(P.sub.G, P.sub.P)) is at least one of: sex, weight, height, age, heart rate, body mass index, type of stature, and distance between the vessel positions.

24. A magnetic resonance system comprising a contrast agent injector controlled by a computer, the computer being equipped with a memory for storing a program therein, the program comprising a method of predetermining a time profile of contrast agent concentration at a position in a blood vessel of a patient in the context of contrast agent-enhanced magnetic resonance imaging of a region of interest only during an initial flooding-in phase of the contrast agent into the blood vessel situated in the region of interest, the method, when executed by the computer, performing the following: establishing an expected broadening of a contrast agent bolus profile B(t) according to the equation W=W2W1 wherein W1 is a first width of the contrast agent bolus profile B(t) at a predetermined first vessel position of the patient and W2 is a second width of a contrast agent concentration profile K(t) at a predetermined second vessel position situated in the region of interest of the patient; such that the expected broadening is established by determining at least one flow parameter which is dependent on at least one blood flow property of the patient at a third vessel position thereof and which correlates with the expected broadening of the contrast agent bolus profile B(t).

Description

DETAILED DESCRIPTION OF THE DRAWINGS

(1) Subsequently, the invention is described in more detail on the basis of the figures, wherein only features required for the understanding of the invention are depicted. In detail:

(2) FIG. 1 shows an illustration of an MRI system according to the invention;

(3) FIG. 2 shows an illustration of the circulation of a patient;

(4) FIG. 3 shows an illustration of the change in the width of a contrast agent bolus profile at a first vessel position in relation to the width of the contrast agent concentration profile at a second vessel position;

(5) FIG. 4 shows an illustration of the measured signal strengths in a contrast agent-enhanced MR examination at the Vena cava and Aorta descendens (AD) vessel positions in the case of a laboratory animal (E639, miniature pig) in the case of a flow of 33 ml/s at the AD; and

(6) FIG. 5 shows an illustration of the measured signal strengths in a contrast agent-enhanced MR examination at the Vena cava and Aorta descendens (AD) vessel positions in the case of a laboratory animal (E639, miniature pig) in the case of a flow of 23 ml/s at the AD.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 schematically depicts a magnetic resonance imaging system (MRI system) 1. In this MRI system 1, magnetic coils 2 for generating a strong main magnetic field are situated in a housing 6. As a result of the magnetic field, the hydrogen nuclei in the body of the patient 7, in accordance with the spin thereof, are aligned parallel or antiparallel to the magnetic field lines. By exciting the atomic nuclei with an alternating electromagnetic field at the resonance frequency, the atomic nuclei resonate. After switching off the excitation frequency, the atomic nuclei return to their unexcited state and emit energy in the form of electromagnetic radiation energy, which is measured with the aid of reception coils 3, which are arranged, where possible, in the vicinity of the ROI to be observed on the patient 7. Additional magnetic fields with defined field gradients are generated by additional magnet coils 4, as a result of which the signals emitted by the nuclei contain spatial information, by means of which the position of the emitted signal is definable. The control and computer unit 8 controls this system 1, evaluates the measurement signals and, in the memory thereof, has programs 9 which, in addition to control and image calculation, also carry out the method according to the invention.

(8) For an improved depiction of blood vessels, it is sometimes necessary to briefly enrich the blood circulation of the patient with contrast agent, for the purposes of which use is usually made of a contrast agent injector 5 which, under electronic controleither by the computer unit 8 or by a different, separate computer unitgenerates the volume flow of a contrast agent to be applied for the measurement.

(9) With the aid of such an MRI system, it is possible, even when using a plurality of reception antennas, to obtain blood flow information, such as, e.g., flow velocities, velocity profiles or volume flows, without the application of a contrast agent. In this respect, reference is made, merely by way of example, to U.S. Patent Application Publication 2014/0285194A1 and German Patent Application Publication DE 102013204994 A1 corresponding thereto.

(10) For an improved understanding of the invention, FIG. 2 shows a schematic depiction of the blood circulation of a patient. This closed circulation is divided into a venous circulation (dashed lines) and an arterial circulation (full lines) and is substantially operated by the pumping action of the heart. In the pulmonary circulationin contrast to the remaining circulationthe arterial blood has a low oxygen content and the venous blood has a high oxygen content. In accordance with such a natural profile and the relatively easily producible and usable accesses in the venous zone, for example at an arm or hand vein, contrast agents are usually applied through such accesses, usually with the aid of automatically controlled contrast agent injectors. Accordingly, a bolus placed there initially passes the right cardiac chambers (not depicted in any more detail), is guided by the pulmonary passage to the left chambers of the heart (likewise not depicted here) and from there it reaches the regions of the body which are intended to be depicted with an MR image and which are of interest in relation to the invention; in particular, it also reaches the peripheral vessel regions.

(11) In the schematic illustration of FIG. 2, the essential vessel positions P1 to P4 and the region of interest ROI to be imaged are marked at exemplary and typical positions. As mentioned previously, the application usually occurs in the zone of the venous circulation, corresponding to the plotted vessel position P1 at a peripheral vessel, e.g. of an arm or hand vein. The region of interest ROI, which is to be examined by imaging, canas plotted herefor example lie in the region of a leg artery, in which the vessel position P2 is then also situated. The further measurement positions, at which blood flow properties are then determined, then generally lie in the arterial vessel system between the left atrium of the heart and the ROI. However, reference is made to the fact that positioning of the measurement points at vessel positions which, as seen in the flow direction, are arranged downstream of the ROI or P2 is also possible.

(12) A contrast agent bolus, which is applied at a first vessel position P1, usually has a bolus profile B(t) as plotted in the upper part of FIG. 3. There, the volume flow of a bolus B is plotted over time t. Such a bolus profile canas depicted hereassume a rectangular profile but it can also reproduce any function B(t) by means of appropriate setting on a contrast agent injector. Such a volume flow B is selected dependent upon the employed contrast agent (e.g. Gadovist or Magnevist) and specific patient properties in order to achieve a desired contrast agent concentration at the location of examination in the vessel to be depicted. As shown in FIG. 2, after application in the venous vessel zone, such a bolus passes at least the heart twice and the lung with significant branching of the vessels in between. Particularly as a result thereof, but also due to additional turbulences, non-laminar flows and velocity differences across the vessel cross section, as well as thinning effects in the venous system, this creates a stronger or weaker dispersion of the applied contrast agent bolus, leading to a broadened contrast agent concentration profile K(t). At the bottom of FIG. 3, such a contrast agent concentration profile K(t) at a vessel position P2 is shown in an exemplary manner. It is easy to identify that the width of the applied bolus W1 has substantially broadened over the travelled vessel path between positions P1 and P2 such that now, taking into account a full width at half maximum, a width W2 is present. The broadening W is then calculated as W=W2W1.

(13) According to the invention, the assumption is made that the size of such broadening directly has a unique correlation with blood flow properties, measurable without a contrast agent, on the transport path of the contrast agent, or with flow parameters derivable therefrom, such that the flow-dependent broadening of an applied bolus can be determined and therefore predicted by establishing this flow parameter, in particular by using contrast agent-free measurements of blood flow properties. Then, when simultaneously establishing the bolus transfer time BTT and/or bolus arrival time BAT, it is possible to determine the time profile of the contrast agent concentration at a vessel, in particular a peripherally situated vessel, and hence predict this due to knowledge of the applied bolus. Accordingly, this naturally also allows retrospective determination of the required profile of a bolus application which leads then to a desired contrast agent concentration profile being obtained and therefore also leads to a desired signal profile in the case of an MR measurement at an ROI.

(14) As emerges from FIGS. 4 and 5, such a correlation can be verified between a simple flow parameterin the form of a volume flow measured without contrast agentand the generated broadening, even in animal testingin this case using a miniature pig.

(15) FIG. 4 showscorresponding to a bolus application width of W1=1 sa measured signal profile of an MR measurement, measured directly after the application site (auricular vein) using diamond-shaped measurement points and a signal profile of an MR measurement at the Aorta descendens (AD). The mean volume flow v(AD) in the Aorta descendens, which was 33 ml/s in the shown example, was determined as the blood flow property, which is directly also used as the flow parameter. The measured width in relation to the full width at half maximum of the signal profile is 4.5 seconds. Accordingly, the broadening in relation to the bolus width W1 of 1 second was W=W2W1=4.5 s1.0 s=3.5 s.

(16) For comparison purposes, FIG. 5 likewise shows, with the same bolus application width of W1=1 s, a measured signal profile of an MR measurement, measured directly after the application site (auricular vein) using diamond-shaped measurement points and a signal profile of an MR measurement at the Aorta descendens (AD). However, the mean volume flow v(AD) in the Aorta descendens was 23 ml/s in this measurement. The measured width in relation to the full width at half maximum of the signal profile is 7.5 seconds. Accordingly, the broadening in relation to the bolus width W1 of 1 second was W=W2W1=7.5 s1.0 s=6.5 s.

(17) Thus, there clearly is a correlated relationship between the measured blood flow volume v(AD) at the Aorta descendens and the magnitude of the broadening W, as was also confirmed by further experimental results.

(18) According to the invention, such a relationship can be provided in the form of a lookup table (LUT), which is stored in a computer memory and which can serve for predetermining the broadening of a bolus.

(19) An example of such a lookup table (LUT) for predetermining the broadening could accordingly look as follows:

(20) TABLE-US-00001 TABLE 1 P.sub.G W1 P.sub.G.sup.2 P.sub.G.sup.1 P.sub.G.sup.avg P.sub.G.sup.+1 P.sub.G.sup.+2 W1.sup.2 W(P.sub.G.sup.2, . . . W(P.sub.G.sup.avg, . . . W(P.sub.G.sup.+2, T1.sup.2) T1.sup.2) T1.sup.+2) W1.sup.1 . . . . . . . . . W1.sup.avg W(P.sub.G.sup.2, . . . W(P.sub.G.sup.avg, . . . W(P.sub.G.sup.+2, T1.sup.avg) T1.sup.avg) T1.sup.avg) W1.sup.+1 . . . . . . . . . W1.sup.+2 W(P.sub.G.sup.2, . . . W(P.sub.G.sup.avg, . . . W(P.sub.G.sup.+2, T1.sup.+2) T1.sup.+2) T1.sup.+2)

(21) The LUT 1 depicted in Table 1 describes the bolus broadening W=W2W1 as a function of the bolus application width W1 and of the flow parameter P.sub.G. Here, using the two input parameters W1 and P.sub.G, as a function of the bolus application width W1 and, in this example, a single measured parameter P.sub.G, the empirically predetermined bolus broadening W correlated therewith is made available. The flow parameter P.sub.G can, e.g., represent the blood volume flow, measured at the vessel position P3=Aorta descendens v(AD). The superscript indices denote the different value ranges of the parameters in the row or column headers. Intermediate values can, where necessary, be obtained by interpolation.

(22) In a complementary or else independent manner, it is also possible in the same way to determine and represent the correlation between flow parameters measured preferably without contrast agent and the BTT or BAT. Accordingly, an appropriate LUT can be designed as follows:

(23) TABLE-US-00002 TABLE 2 BTT from P1 to P2 P.sub.G.sup.2 P.sub.G.sup.1 P.sub.G.sup.avg P.sub.G.sup.+1 P.sub.G.sup.+2 d.sup.2(ROI)/cm BTT(d.sup.2(ROI), P.sub.G.sup.2) . . . BTT(d.sup.2(ROI), P.sub.G.sup.avg) . . . BTT(d.sup.2(ROI), P.sub.G.sup.+2) d.sup.1(ROI)/cm . . . . . . . . . d.sup.avg(ROI)/cm BTT(d.sup.avg(ROI), P.sub.G.sup.2) . . . BTT(d.sup.avg(ROI), P.sub.G.sup.avg) . . . BTT(d.sup.avg(ROI), P.sub.G.sup.+2) d.sup.+1(ROI)/cm . . . . . . . . . d.sup.+2(ROI)/cm BTT(d.sup.+2(ROI), P.sub.G.sup.2) . . . BTT(d.sup.+2(ROI), P.sub.G.sup.avg) . . . BTT(d.sup.+2(ROI), P.sub.G.sup.+2)

(24) Table 2 shows an exemplary LUT 2, in which the values for the bolus travel time

(25) $\left(\mathrm{BTT}=\frac{d\left(\mathrm{ROI}\right)}{v_G\left(\mathrm{AD}\right)}{r}_{\mathrm{fl}}\right)$
as a function of the distance d(ROI) of a selected typical vessel position from the ROI and an established flow parameter P.sub.G from measured specific blood flow properties v.sub.G(AP) and v.sub.G(AB), with P.sub.G=v.sub.G(AP)/v.sub.G(AB), can be read off, wherein, as a matter of principle, the BTT is derived from the flow velocity v.sub.G(AD) in the Aorta descendens, the travelled distance d(ROI) and a flow parameter-dependent correction factor

(26) $r_{\mathrm{fl}}=\frac{v_G\left(\mathrm{AP}\right)}{v_G\left(\mathrm{AB}\right)}$
and flow velocity comes from the equation

(27) $v_G=\frac{d}{\mathrm{BTT}}.$
The superscript indices in each case denote the different value ranges of the respective parameters in the row or column headers. Intermediate values can, where necessary, be obtained by interpolation.

(28) In this LUT 2, both specific patient parameters and current flow parameters are used as input parameters for determining a bolus travel time (BTT): a patient parameter is specified in the form of a distance d.sup.i(ROI), which here constitutes the difference in cm between a vessel position P3, at which the flow parameter r.sub.fl is measured, and a vessel position P2 in the region of the target region ROI. Moreover, the current blood flow velocity flow parameters v.sub.G(AD), v.sub.G(AB) and v.sub.G(AP) at different vascular positions are represented as input parameters. The blood flow velocities v.sub.G(AP), representing the blood flow velocity in the region of the Aorta poplitealis in an exemplary manner, and the blood flow velocity v.sub.G(AB), representing the blood flow velocity in the region of the bifurcation in an exemplary manner, are in this case included in the LUT as quotient and correction factor and can therefore map patient-specific factors which determine the mean flow velocity and therefore the BTT. The blood flow velocity v.sub.G(AD) once again represents in an exemplary manner the blood flow velocity measured in the region of the Aorta descendens.

(29) Therefore, the timing of a contrast agent bolus application with the contrast agent-free determination of different blood flow and patient parameters can be determined by the interaction of an accordingly adapted LUT 1 and LUT 2.

(30) Although the invention was illustrated and described more closely in detail by the preferred exemplary embodiment, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention. In particular, the invention is not restricted to the combination of features specified here, but it is also possible to form other combinations and partial combinations, which are clearly reproducible by a person skilled in the art, from the disclosed features. Moreover, the invention is not restricted to the claim categories used in the claims but also comprises the disclosed features in combination with all further claim categories.

(31) Thus, overall, the invention proposes a method, in which, for the purposes of optimizing the predetermination of the time profile of a contrast agent concentration at a vessel position in a region of interest (ROI) in the case of a contrast agent-enhanced MR imaging of a patient (P) only during the first flooding-in phase of the contrast agent, the correlation of a broadening and/or a bolus transfer time of a contrast agent bolus between two vessel positions and at least one flow parameterwhich constitutes a function of at least one flow propertyis predetermined in the blood circulation of a patient collective such that subsequently, prior to an MR examination of a patient to be carried out, these flow parameters are determined by a contrast agent-free phase contrast MR examination and, by way of the pre-known correlations in relation to the broadening and/or bolus transfer time, the contrast agent concentration profile to be expected is determined at a vessel position in the examination region.

LIST OF REFERENCE SIGNS

(32) 1 Magnetic resonance imaging system (MRI system) 2 Magnetic coils 3 Reception coil 4 Magnetic coils 5 Contrast agent injector 6 Housing 7 Patient 8 Control and computer unit/computer with memory and display 9 Computer programs AA Aorta ascendens AD Aorta descendens AP Aorta poplitealis B Bolus B(t) Bolus profile over time K Contrast agent concentration K(t) Contrast agent concentration profile over time P1 First vessel position P2 Second vessel position P3 Third vessel position P4 Fourth vessel position ROI Examination region/region of interest SI Signal t Time VC Vena cava v.sub.G(AD) Blood flow velocity in the Aorta descendens W1 Bolus width=bolus duration W2 Width=duration of the contrast agent concentration profile W Broadening