Thermoacoustic imaging with quantitative extraction of absorption map

• US 9,271,654 B2
• Filed: 06/29/2009
• Issued: 03/01/2016
• Est. Priority Date: 06/29/2009
• Status: Active Grant

• Current Assignee: Helmholtz Zentrum München Deutsches Forschungszentrum für. Gesundheit und Umwelt (GmbH)
• Original Assignee: Helmholtz Zentrum München Deutsches Forschungszentrum für. Gesundheit und Umwelt (GmbH)
• Inventors: Razansky, Daniel, Ntziachristos, Vasilis, Rosenthal, Amir
• Primary Examiner(s): Fernandez, Katherine
• Assistant Examiner(s): KELLOGG, MICHAEL S
• Application Number:
  US13/381,207
• Publication Number:
  US 20120123256A1
• Time in Patent Office: 2,437 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/0093 Detecting, measuring or recording by applying one single type of energy and measuring its conversion into another type of energy
• CPC Class Codes: A61B 5/0095 by applying light and detecting acoustic waves, i.e. photoacoustic measurements
• CPC Class Codes: G01N 21/17 Systems in which incident light is modified in accordance with the properties of the material investigated where the material investigated is optically excited causing a change in wavelength of the incident light G01N21/63
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids

Abstract

A method of thermoacoustic imaging of an object includes providing thermoacoustic signals representing a mechanical wave response to a delivery of electromagnetic energy into the imaged object, reconstructing an energy deposition image representing a local energy absorption within the object based on the thermoacoustic signals, and decomposing the energy deposition image into a quantitative absorption image representing a distribution of a local absorption coefficient in the object and at least one further image component.

Claims

1. A method of thermoacoustic imaging of an object, the method comprising:

pre-calculating, with a processor, a forward model matrix M that represents a relation between (i) absorption of electromagnetic energy within the object and (ii) pressure signals generated in response to said absorption of electromagnetic energy within the object, the forward model matrix M satisfying a forward model matrix equation expressed as p=Mh, wherein h is a vector having a plurality of elements h_i that correspond to respective amounts h(x_i) of electromagnetic energy absorbed at respective grid coordinates x_i within the object and p is a vector having a plurality of elements p_j corresponding to respective pressures p(x_j, t_j) at respective coordinates x_j at respective times t_j;

irradiating, with an electromagnetic enemy source, the object with a quantity of electromagnetic energy;

detecting, with at least one acoustic detection element, pressure signals generated in response to said absorption of the quantity of electromagnetic energy within the object;

generating a data vector that contains the detected pressure signals;

reconstructing an energy deposition image of the object by inverting the forward model matrix equation p=Mh to recover the vector h by either of;

calculating, with said processor, a pseudo-inverse of the forward model matrix M and multiplying the pseudo-inverse of the forward model matrix M with the data vector;

or

using the data vector as the vector p in the forward model matrix equation p=Mh and performing, with said processor, a least square error minimization of the forward model matrix equation p=Mh; and

outputting via an interface of said processor the energy deposition image to a control device that is configured to perform further data handling of the energy deposition image, said further data handling comprising displaying the energy deposition image.

2. The imaging method according to claim 1, wherein the forward model matrix M is adjusted in dependency on at least one of:

an acoustic heterogeneity of the object, a geometric profile of illumination of the imaged object by light pulses, or a frequency response of the detector device via which said detecting pressure signals is accomplished.

3. The imaging method according to claim 1, wherein the forward model matrix M has elements corresponding to values that are calculated by solving an integral expressed as

4. The imaging method according to claim 3, wherein solving the integral proceeds over a surface that is inconsistent with the grid coordinates x_i such that certain coordinates x′

are spaced apart from the grid coordinates x_i.

5. The imaging method according to claim 3, wherein the grid coordinates x_i are predetermined, and wherein calculation of the function ƒ

(x_n, . . . , x_m) is independent of the detected pressure signals contained in the data vector.

6. The imaging method according to claim 5, wherein said pre-calculating the forward model matrix M takes place before said irradiating the object with the quantity of electromagnetic energy.

7. The imaging method according to claim 3, wherein ƒ

_i(x_n, . . . , x_m, x′

) are differentiable or piecewise differentiable interpolation functions.

8. An imaging device for thermoacoustic imaging of an object, the device comprising:

an electromagnetic energy source configured to irradiate the object with a quantity of electromagnetic energy;

at least one acoustic detection element configured to detect pressure signals representing a mechanical wave response to the irradiation of the object with the quantity of electromagnetic energy; and

an image processor configured to reconstruct an energy deposition image representing a local energy deposition within the object based on the detected pressure signals by;

pre-calculating a forward model matrix M that represents a relation between (i) absorption of electromagnetic energy within the object and (ii) pressure signals generated in response to said absorption of electromagnetic energy in the object, the forward model matrix M satisfying a forward model matrix equation expressed as p=Mh, wherein h is a vector having a plurality of elements h_i that correspond to respective amounts h(x_i) of electromagnetic energy absorbed at respective grid coordinates x_i within the object and p is a vector having a plurality of elements p_j corresponding to respective pressures p(x_j, t_j) at respective coordinates x_j at respective times t_j; and

inverting the forward model matrix equation p=Mh to recover the vector h using the detected pressure signals by either;

calculating a pseudo-inverse of the forward model matrix M and multiplying the pseudo-inverse of the forward model matrix M with a data vector that contains the detected pressure signals;

or

using the data vector that contains the detected pressure signals as the vector p in the forward model matrix equation p=Mh and performing a least square error minimization of the forward model matrix equation p=Mh,

wherein the image processor comprises an interface via which the image processor is configured to output the energy deposition image to a control device that is configured to perform further data handling of the energy deposition image, said further data handling comprising displaying the energy deposition image.

9. The imaging device according to claim 8, wherein the mage processor comprises a digital storage medium configured to store the forward model matrix M.

10. The imaging device according to claim 8, wherein the electromagnetic energy source comprises an illumination device that illuminates the object by electromagnetic pulses.

11. The imaging device according to claim 8, wherein the at least one acoustic detection element corn rises at least one of a detector array and a single detector.

12. The imaging device according to claim 8, wherein the at least one acoustic detection element and the object are movable relative to each other.

13. The imaging device according to claim 8, wherein the image processor is configured to adjust the forward model matrix in dependency on at least one of:

an acoustic heterogeneity of the object, a geometric profile of an illumination of the object via light pulses, or a frequency response of the at least one acoustic detection element.

14. The imaging device according to claim 8, wherein the forward model matrix M includes elements corresponding to values that are calculated by solving an integral expressed as

15. The imaging device according to claim 14, wherein ƒ

_i(x_n, . . . , x_m, x′

) are differentiable or piecewise differentiable functions.

16. A method of thermoacoustic imaging of an object to be imaged, the method comprising:

pre-calculating, with a processor, a forward model matrix M that represents a relation between (i) absorption of electromagnetic energy within the object and (ii) pressure signals generated in response to said absorption of electromagnetic energy in the object, the forward model matrix M satisfying a forward model matrix equation expressed as p=Mh, wherein h is a vector having a plurality of elements each corresponding to an amount of electromagnetic energy absorbed at a discrete spatial grid coordinate and p is a vector having a plurality of elements each corresponding to a pressure value at both a spatial coordinate of a detector device and a temporal coordinate, wherein said pre-calculating the forward model matrix M does not depend on the object;

irradiating, with an electromagnetic energy source, the object with a quantity of electromagnetic energy;

detecting, with at least one acoustic detection element, pressure signals generated in response to an absorption of the quantity of electromagnetic energy in the object;

generating a data vector that contains the detected pressure signals;

reconstructing an energy deposition image by inverting the forward model matrix equation p=Mh to recover the vector h by calculating, with the processor, a pseudo-inverse of the forward model matrix M and multiplying the pseudo-inverse of the forward model matrix M with the data vector; and

outputting via an interface of said processor the energy deposition image to a control device that is configured to perform further data handling of the energy deposition image, said further data handling comprising displaying the energy deposition image.

17. The method according to claim 16, wherein each discrete spatial grid coordinate is at a position within the object at which an amount of electromagnetic energy is absorbed when said irradiating the object with the quantity of electromagnetic energy takes place.

18. The method according to claim 16, wherein:

the vector h has elements h_i corresponding to an amount h(x_i) of electromagnetic energy absorbed at a grid coordinate x_i in the object;

the vector p has elements p_j corresponding to a pressure p(x_j, t_j) at a coordinate x_j at a time t_j; and

pre-calculating the forward model matrix M comprises solving an integral expressed as

19. The method according to claim 16, wherein the relation between said absorption of electromagnetic energy within the object and said pressure signals generated in response to said absorption of electromagnetic energy in the object is expressed as

20. The method of claim 19, wherein the values of g_i(x, t, x_k, . . . , x_l) are calculated by solving an integral expressed as

21. The method of claim 20, wherein ƒ

_i(x_n, . . . , x_m, x′

) are differentiable or piecewise differentiable interpolation functions.

22. The method according to claim 16, wherein the forward model matrix M is calculated before the object is irradiated with the quantity of electromagnetic energy.