PHANTOM CALIBRATION BODY AND METHOD FOR DETERMINING AT LEAST ONE QUANTITATIVE DIFFUSION PARAMETER EXTRACTED FOR CHARACTERIZATION OF A TISSUE IN MAGNETIC RESONANCE IMAGING

Abstract

A phantom calibration body (110) for a method for determining at least one quantitative diffusion parameter extracted for characterization of a tissue being suspicious to a tumorous modification in magnetic resonance imaging is disclosed, wherein the phantom calibration body (110) is designed for being characterized during characterization of the tissue by the magnetic resonance imaging. Herein, the phantom calibration body (110) comprises a first compartment (112) having a first cross-section, the first compartment (112) being filled with a first solution comprising a calibration substance having a first concentration; and a second compartment (114) having a second cross-section, the second cross-section having at least two different partitions with differing diameters, wherein the second compartment (114) is filled with a second solution comprising the calibration substance having a second concentration, the second concentration differing from the first concentration. The present invention allows determining absolute quantitative parameters in an individualized fashion for each individual tissue independent from various times of recording, applied software algorithms for post-processing of the raw MRI data, MR devices, or MR vendors. The present invention, thus, allows using the absolute quantitative data extracted from the phantom calibration body (110) measured with every tissue for comparability of quantitative data, being a prerequisite for introducing quantitative diffusion weighted imaging (DWI) into clinical routine.

Claims

1. A phantom calibration body for a method for determining at least one quantitative diffusion parameter extracted for characterization of a tissue being suspicious to a tumorous modification in magnetic resonance imaging, wherein the phantom calibration body is designed for being characterized during characterization of the tissue by the magnetic resonance imaging, the phantom calibration body comprising a first compartment having a first cross-section, the first compartment being filled with a first solution comprising a calibration substance having a first concentration; and a second compartment having a second cross-section, the second cross-section having at least two different partitions with differing diameters, wherein the second compartment is filled with a second solution comprising the calibration substance having a second concentration, the second concentration differing from the first concentration.

2. The phantom calibration body of claim 1, wherein the second cross-section of the second compartment exhibits a pair of opposing sides having a non-parallel arrangement, the pair of the opposing sides being inclined by an angle of 5 to 45 with respect to each other.

3. The phantom calibration body of claim 1, wherein the first compartment comprises a first receptacle, wherein the second compartment comprises a second receptacle, wherein the first receptacle and the second receptacle are comprised by a container.

4. The phantom calibration body of claim 3, wherein the first receptacle is the container and wherein the second receptacle is comprised by the first compartment.

5. The phantom calibration body of claim 1, further comprising at least one first opening designed for filling the first solution into the first compartment and at least one second opening being different from the first opening, wherein the second opening is designed for filling the second solution into the second compartment.

6. The phantom calibration body of claim 1, wherein the calibration substance comprises a substance is selected from at least one of polyvinylpyrrolidone, a polyvinyl alcohol, a polyacrylamide, a polyacrylate, a polyethylene glycol, a polysaccharide, cellulose, a derivative thereof, or a copolymer thereof.

7. The phantom calibration body of claim 6, wherein the first concentration and the second concentration are selected from a concentration of 0.01% (w/w) to 100% (w/w).

8. The phantom calibration body of claim 7, wherein the second concentration differs from the first concentration by at least 0.1% (w/w).

9. The phantom calibration body of claim 1, wherein the first concentration and the second concentration are selected from two individual concentrations which are adapted for mimicking two different types of the tissue.

10. The phantom calibration body of claim 1, wherein the first solution and the second solution have a single K-value.

11. The phantom calibration body of claim 1, further comprising a thermometer unit designed for determining a temperature, the thermometer unit being attached to the phantom calibration body or comprised by the phantom calibration body.

12. A computer-implemented method for determining at least one quantitative diffusion parameter extracted for characterization of a tissue being suspicious to a tumorous modification in magnetic resonance imaging, wherein the method comprises the steps of: a) placing a phantom calibration body of claim 1 in a vicinity of the tissue; b) receiving raw magnetic resonance imaging (MRI) data being recorded by applying at least one diffusion weighted imaging (DWI) sequence concurrently to the tissue and to the phantom calibration body; c) extracting at least one quantitative diffusion parameter of the tissue from the raw MRI data, wherein the corresponding quantitative diffusion parameter of the phantom calibration body is considered.

13. The method of claim 12, wherein the quantitative diffusion parameter of each the tissue and the of the phantom calibration body is extracted from the raw MRI data by using at least one quantification scheme, the quantification scheme being selected from diffusional kurtosis imaging (DKI), apparent diffusion coefficient (ADC), intravoxel incoherent motions (IVIM), or fractional order calculus (FROC).

14. The method of claim 12, wherein a minimum lesion size capable of differentiating between two types of the tissue is obtained by determining the corresponding quantitative diffusion parameter for at least two different partitions of the second compartment of the phantom calibration body.

15. A computer program product comprising executable instructions for performing any step of a method of claim 12.

16. The phantom calibration body of claim 2, wherein the second cross-section of the second compartment exhibits a pair of opposing sides having a non-parallel arrangement, the pair of the opposing sides being inclined by an angle of 15 to 30 with respect to each other.

17. The phantom calibration body of claim 7, wherein the second concentration differs from the first concentration by at least 1% (w/w).

18. The phantom calibration body of claim 7, wherein the first concentration is selected of 5% to 60%.

19. The phantom calibration body of claim 7, wherein the second concentration is selected of 20% to 75%.

20. The method of claim 12, wherein the phantom calibration body is placed such that a single image of the tissue under examination and of the phantom calibration body is obtained.

Description

SHORT DESCRIPTION OF THE FIGURES

[0060] Further optional details and features of the present invention may be derived from the subsequent description of preferred embodiments, preferably in combination with the dependent claims. Therein, the respective features may be realized in an isolated way or in arbitrary combinations. The invention is not restricted to the preferred embodiments. Identical reference numbers in the figures refer to identical elements or to elements having identical or similar functions or to elements corresponding to each other with regard to their functionality. Herein

[0061] FIGS. 1A to 1F illustrate various views from different perspectives of a particularly preferred embodiment of a phantom calibration body according to the present invention; and

[0062] FIG. 2 schematically illustrates a computer-implemented method according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0063] FIGS. 1A to 1F illustrate various views from different perspectives of a particularly preferred embodiment of a phantom calibration body 110 according to the present invention which is specifically adapted for being used in a computer-implemented method for determining at least one quantitative diffusion parameter extracted for characterization of a tissue being suspicious to a tumorous modification in magnetic resonance imaging (MRI), preferably as illustrated in FIG. 2. The phantom calibration body 110 and the corresponding method may, specifically, be used in the field of oncologic imaging, wherein, however, other applications are feasible.

[0064] The phantom calibration body 110 as shown in any one of FIGS. 1A to 1F comprises two individual compartments 112, 114, i.e. a first compartment 112 and a second compartment 114, wherein each of the compartments 112, 114 represent an individual partition of the calibration body 110 which is separated from the other compartment 112, 114. As a result of this particular arrangement, an unintentional exchange of liquids, in particular of the solutions as described above and/or below in more detail, from the first compartment 112 to the second compartment 114 or vice-versa is excluded.

[0065] As schematically depicted in FIGS. 1A and 1C to 1F, the first compartment 112 of this exemplary embodiment of the phantom calibration body 110 is implemented as a first receptacle 116 having a form of a container 118 comprising a first volume which is generated by five sides of the container 118 which can, as shown in FIGS. 1D to 1F, additionally be closed by a separate lid 120 which constitutes here a sixth side of the container 118.

[0066] In contrast hereto, the second compartment 114 of this exemplary embodiment of the phantom calibration body 110 is implemented as a second receptacle 122 comprising a second volume which is generated by five sides of the second receptacle 122 as schematically depicted in FIGS. 1A to 1F. Further, the form of the second compartment 114 is selected in a manner that the second compartment 114 is adapted to be introduced into the container 118 which, thus, comprises both the first compartment 112 and the second compartment 114.

[0067] However, the phantom calibration body 110 may also be implemented in a different fashion, specifically by providing the first compartment 112 and the second compartment 114 in manner that both compartments 112, 114 are introduced into a separate container (not depicted here) which may be adapted for receiving both the first compartment 112 and the second compartment 114. In addition, further kinds of embodiments (not depicted here) of the phantom calibration body 110 may also be feasible.

[0068] According to the present invention, the first compartment 112 has a first cross-section, wherein the first cross-section of the first compartment 112 exhibits a slight variation of a diameter 124 along a lateral extension or length 126 of the first compartment 112. In contrast hereto, the second compartment 114 has a second cross-section wherein the second cross-section of the second compartment 114 in this exemplary embodiment is generated by a pair of opposing sides 128, 130, which exhibit a non-parallel arrangement a lateral extension or length 132 of the second compartment 114. As schematically depicted in FIGS. 1A to 1F, the pair of the opposing sides 128, 130 is inclined with respect to each other by an angle of 5 to 45, specifically of 15 to 30, as depicted here. As a result, the second compartment 114 in this exemplary embodiment comprises a triangularly varying cross-section, resulting in a linearly increasing or decreasing diameter 134 along the length 132 of the second compartment 114. The particular advantages of this exemplary embodiment of the second compartment 114 are described above and/or below in more detail.

[0069] Further according to the present invention, the first compartment 112 of the phantom calibration body 110 is filled with a first solution which comprises a calibration substance having a first concentration. For a purpose of filling the first solution into the first compartment 112, the first compartment 112 can in the exemplary embodiment of FIGS. 1A and 1C to 1F be opened by removing the lid 120. In contrast hereto, the second compartment 114 is filled with a second solution comprising the same calibration substance as filled in the first compartment 112 but having a second concentration, wherein the second concentration differs from the first concentration. For a purpose of filling the second solution into the second compartment 114, the second compartment 114 in the exemplary embodiment of FIGS. 1A to 1F comprises a second opening 136. However, other opportunities for filling the first solution into the first compartment 112 may exist, such as first openings 138 introduced into the lid 120 and specifically adapted for this purpose. However, further opportunities may also exist here.

[0070] In the exemplary embodiment as illustrated herein, the calibration substance is polyvinylpyrrolidone (PVP), wherein a different calibration substance as described elsewhere herein may equally be selected. Without restricting the scope of the present invention, the first concentration may, preferably, be selected to provide an ADC of 1.42 m.sup.2/ms at room temperature (21 C.) for the first compartment 112 while the second concentration may, preferably, be selected to provide an ADC of 0.87 m.sup.2/ms for the second compartment 114 in the exemplary embodiment as illustrated herein. As a result, the first concentration used for the first solution comprised by the first compartment 112 has, exemplarily, been selected as 15% (w/w) PVP (K30) while the second concentration as used for the second solution comprised by the second compartment 114 has, exemplarily, been selected as 30% (w/w) PVP (K30), such that, in this particular example, both concentrations differ with respect to each other by a concentration of 15% (w/w). However, other concentrations may also be feasible.

[0071] In particular contrast to US 2017/0242090 A1, the first solution and the second solution have a single K-value, such K15, K30 or K90 in the case of PVP, wherein the K-value here refers to a molecular weight of PVP. As a result, the calibration substance does not comprise a dedicated mixture of polymers having a high molecular weight as denoted by a first K-value and a low molecular weight as denoted by a second K-value which considerably differs from the first K-value but only a regular solution having have the selected single K-value. By way of example, an aqueous solution of PVP may be generated by using PVP powder, preferably, as described in DE 737 663 A.

[0072] As a result, form, size, and respective arrangement of the two individual compartments 112, 114 within the phantom calibration body 110 are provided in a manner that the two individual compartments 112, 114 of the phantom calibration body 110 are adapted in order to be capable of mimicking two types of the tissues, specifically, the benign tissue and the malignant tissue, of an examined body region, such as a mammal liver. However, further body regions may also be selected.

[0073] In a further exemplary embodiment (not depicted here), the phantom calibration body 110 may, additionally, comprise a thermometer unit which may be designed for determining a temperature. Herein, the thermometer unit may be attached to the phantom calibration body 110 or comprised by the phantom calibration body 110, such as within the container 118. However, further arrangements of the thermometer unit may also be feasible.

[0074] As further illustrated in FIG. 1F, the lid 120 may be used not only to cover to first compartment 112 but also the container 118, such as in order to provide an additional protection for keeping both the first solution and the second solution within the phantom calibration body 110 over a long time, thus, avoiding, a spilling of the first solution and/or the second solution or a partition thereof from the phantom calibration body 110. For this purpose, the lid 120 may, as depicted in FIG. 1F, be attached to the container 118 by using screws. However, other kinds of closing one or both of the two individual compartments 112, 114 may be feasible. By way of example, the two individual compartments 112, 114 may, after being filled with the calibration substance, be closed without being able to be reopened without a danger of destroying the respective compartment, such as by applying an adhesive or a welding procedure.

[0075] FIG. 2 schematically illustrates a computer-implemented method 140 for determining at least one quantitative diffusion parameter extracted for characterization of a tissue being suspicious to a tumorous modification in magnetic resonance imaging (MRI) according to the present invention.

[0076] Herein, the method 140 comprises a first step a) of placing 142 a phantom calibration body, in particular the phantom calibration body 110 of FIG. 1, in a vicinity of the tissue. As already indicated above, step a) comprises the placing 142 of the phantom calibration body 110 in a manner that a single image of the tissue under examination and of the phantom calibration body can be obtained. Herein, the phantom calibration body 110 can, in particular, have a design which may allow placing the phantom calibration body 110 within one of the MR coils of the MRI device. For example, the phantom may be placed in an reception of the body matrix coil. Thus, the phantom may, in general, be placed in each MR vendor machine independent of the actual coil design.

[0077] Further, the method 140 comprises a further step b) of receiving 144 raw magnetic resonance imaging (MRI) data being recorded by applying at least one diffusion weighted imaging (DWI) sequence concurrently to the tissue and to the phantom calibration body 110. Herein, an apparent diffusion coefficient (ADC) of the tissue may be extracted from the raw MRI data. Alternatively, a diffusional kurtosis coefficient (DKC), Intravoxel incoherent motions' (IVIM), or fractional order calculus (FROC) may also be applied. Further, the exemplary method 140 as depicted here may, additionally, comprise an optional further step of post-processing 146 the raw MRI data as received in step b).

[0078] In an exemplary embodiment, a tissue undergoes a magnetic resonance (MR) examination, wherein a first MR device denoted by MR1 may be employed. Using the first MR device MR1, the ADC of the tissue of a liver lesion may provide an ADC value of 1.9 m.sup.2/ms, thus, indicating a benign tissue. Consequently, in the first solution in the phantom calibration body 110 which is subject of being measured concurrently with the tissue an ADC value of 1.9 m.sup.2/ms may, preferably, be adjusted. Later, a further examination may be performed with a second MR device denoted by MR2 originating from a different vendor. Using the second MR device MR2, the ADC value obtained for a liver lesion may be 1.2 m.sup.2/ms, which would, accordingly to the state of the art procedures, indicate a malignant liver. However, the first solution as used in the phantom calibration body 110 which is measured concurrently with the tissue, provides as well an ADC value of 1.2 m.sup.2/ms, thus, clarifying that no change of the ADC value of the lesion but only a change of the parameters due to different setting of the second MR device MR2 has been occurred.

[0079] Irrespective whether the optional further step of post-processing 146 the raw MRI data has been performed or omitted, a further step c) of extracting 148 at least one quantitative diffusion parameter of the tissue from the raw MRI data is comprised by the method 140, wherein, during the extracting 148, the corresponding quantitative diffusion parameter of the phantom calibration body is taken into account. In particular, by applying Equation (1) above to a volume of interest in the first solution in the phantom calibration body 110, using the known ADC value for the first solution at a given temperature and a the signal S.sub.0 which has been acquired for b=0, actually applied b-values by the MR scanner can be estimated, which may, in general, differ from the b-values as entered by the operator into the MR scanner user interface. As a result, the actually applied b-values may, subsequently, be used to determine the desired two-dimensional (map) or three-dimensional representation of the at least one selected quantitative diffusion parameter of the tissue, specifically the ADC map, in the tissue which has been acquired, concurrently, during the same measurement. In the previous example as provided above, this procedure leads to obtaining the correct value of 1.9 m.sup.2/ms by using the second MR device MR2, too.

[0080] Table 1 provides a comparison of three MR examinations performed in a tissue of a particular tissue pursuant to the method according to the present invention and pursuant to known procedures according to the state of the art.

TABLE-US-00001 TABLE 1 MR Examination of the same tissue Quantitative Quantitative State-of-the-art Result pursuant MR ADC data for ADC data for result to invention device phantom tissue Tissue rating Tissue rating MR1 2.0 m.sup.2/ms 2.0 m.sup.2/ms Baseline Baseline (e.g. benign) (e.g. benign) MR2 1.0 m.sup.2/ms 1.0 m.sup.2/ms Significant No change change to data after correction recorded with using phantom MR1 MR3 2.0 m.sup.2/ms 1.0 m.sup.2/ms No change to Significant previous data change after recorded with correction using MR2 phantom

[0081] As a result, in a first MR examination in a first MR device MR1 the tissue reveals a lesion with an ADC of 2.0 m.sup.2/ms, which is considered as benign in the tissue rating.

[0082] In a second MR examination in a second MR device MR2, the tissue now shows a significant change in the lesion ADC value to 1.0 m.sup.2/ms. This observation could trigger a change in therapy of the corresponding patient without the present invention. However, when applying the method according to the present invention, it becomes apparent that not only the ADC of the lesion but also the ADC of the phantom has changed, thus, the observed change can be attributed to the different MR device rather than to the lesion itself. Using the above-mentioned correction scheme for the b-values, after correction, one would then obtain the correct value 2.0 m.sup.2/ms in MR2, too.

[0083] In a third MR examination in a third MR device MR3, no change seems to be present in the lesion due to an observed ADC value of 1.0 m.sup.2/ms. However, when applying the method according to the present invention, it becomes apparent that the ADC did actually change since the phantom clearly demonstrates that, in comparison to the previous examination using the second MR device MR2, there is occurs a mismatch between ADC in the phantom and the tissue.

[0084] As a result, the method according to the present invention allows determining absolute quantitative parameters in an individualized fashion for each individual origin of the tissue, specifically for each patient, independent from various times of recording, applied software algorithms for post-processing of the raw MRI data, MR devices, MR vendors, etc. In contrast to the current state of the art, the present invention, thus, allows using the absolute quantitative data extracted from the phantom measured with every tissue for comparability of quantitative data, which appears as a prerequisite for introducing quantitative DWI imaging into clinical routine.

LIST OF REFERENCE NUMBERS

[0085] 110 phantom calibration body [0086] 112 first compartment [0087] 114 second compartment [0088] 116 first receptacle [0089] 118 container [0090] 120 lid [0091] 122 second receptacle [0092] 124 diameter [0093] 126 length [0094] 128 opposing side [0095] 130 opposing side [0096] 132 length [0097] 134 diameter [0098] 136 second opening [0099] 138 first opening [0100] 140 method [0101] 142 placing of the phantom calibration body [0102] 144 receiving raw magnetic resonance imaging (MRI) data [0103] 146 post-processing the raw MRI data [0104] 148 extracting quantitative diffusion parameter of the tissue from the raw MRI data.

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