SYSTEMS AND METHODOLOGIES FOR PROTON COMPUTED TOMOGRAPHY

• US 20110220794A1
• Filed: 02/11/2011
• Published: 09/15/2011
• Est. Priority Date: 02/12/2010
• Status: Active Grant

• Current Assignee: LOMA Linda University Medical Center (Mission Healthcare Services LLC), University of Haifa
• Original Assignee: University of Haifa
• Inventors: Censor, Yair, Penfold, Scott N., Schulte, Reinhard W.
• Granted Patent: US 9,207,193 B2
• Time in Patent Office: Days
• US Class Current: 250/307
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4241 using energy resolving detectors, e.g. photon counting
• CPC Class Codes: A61B 6/4258 for detecting non x-ray radiation, e.g. gamma radiation A61B6/037 takes precedence
• CPC Class Codes: A61B 6/4266 characterised by using a plurality of detector units A61B6/4014 takes precedence
• CPC Class Codes: A61B 6/5205 involving processing of raw data to produce diagnostic data
• CPC Class Codes: A61B 6/583 using calibration phantoms
• CPC Class Codes: A61N 2005/1087 Ions; Protons
• CPC Class Codes: A61N 5/10 X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy A61N5/01 takes precedence
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]
• CPC Class Codes: G01T 1/17 Circuit arrangements not adapted to a particular type of detector pulse-selection circuits H03K, G01R
• CPC Class Codes: G01T 1/2985 In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis); using external radiation sources A61B6/02
• CPC Class Codes: G06T 11/006 Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• CPC Class Codes: G16B 40/00 ICT specially adapted for biostatistics; ICT specially adapted for bioinformatics-related machine learning or data mining, e.g. knowledge discovery or pattern finding
• CPC Class Codes: G16B 5/00 ICT specially adapted for modelling or simulations in systems biology, e.g. gene-regulatory networks, protein interaction networks or metabolic networks

Abstract

Disclosed are systems, devices and methodologies relating to proton computed tomography. In some implementations, detection of protons can yield track information before and after an object for each proton so as to allow determination of a likely path of each proton within the object. Further, measurement of energy loss experienced by each proton allows determination that a given likely path results in a given energy loss. A collection of such data allows characterization of the object. In the context of energy loss, such a characterization can include an image map of relative stopping power of the object. Various reconstruction methodologies for obtaining such an image, including but not limited to superiorization of a merit function such as total variation, are disclosed. In some implementations, various forms of total variation superiorization methodology can yield excellent results while being computationally efficient and with reduced computing time. In some implementations, such a methodology can result in high quality proton CT images using relatively low dose of protons.

Claims

1. A method for performing computed tomography, the method comprising:

obtaining measured data for a plurality of protons that pass through an object, the measured data including information about first and second tracks for each of the protons, the first and second tracks corresponding to the proton'"'"'s trajectories before and after its passage through the object, respectively, the measured data further including information about an interaction quantity of each proton resulting from its passage through the object;

for each proton, estimating a path taken by the proton within the object based at least in part on the first and second tracks;

arranging the interaction quantities and the estimated paths of the protons such that the passages of the protons through the object is represented as or representable as a system of equations Ax=b where x is a distribution of a parameter associated with the object, b represents the interaction quantities of the protons resulting from interactions along their respective paths in the object, and A is an operator that operates on x to yield b, the operator A having information about the estimated paths of the protons in the object, the system of equations configured so as to have a plurality of solutions;

estimating an initial solution for the system of equations;

seeking one or more feasible solutions among the plurality of solutions, each feasible solution obtained by perturbing an existing solution and having a superior characteristic for a quantity associated with a reconstruction of the object parameter distribution than another solution obtained without the perturbation of the existing solution; and

calculating the object parameter distribution based on a selected one of the one or more feasible solutions.

2. The method of claim 1, wherein the interaction quantity of the proton comprises an energy loss of the proton resulting from its passage through the object.

3. The method of claim 1, wherein b represents integrated values of the interaction quantity along the estimated paths of the protons.

4. The method of claim 1, wherein the system of equations Ax=b comprises a system of linear equations.

5. The method of claim 4, wherein the operator A comprises a matrix.

6. The method of claim 1, wherein the selected feasible solution comprises a feasible solution that is not an optimal solution among the plurality of solutions.

7. The method of claim 1, wherein the calculating of the object parameter distribution comprises calculating a 3D object parameter distribution.

8. The method of claim 1, further comprising forming an array of tomographic images of the object based on the calculated object parameter distribution.

9. The method of claim 1, wherein the object parameter distribution comprises a distribution of an electron density-based quantity.

10. The method of claim 9, wherein the electron density-based quantity comprises relative proton stopping power with respect to a substantially uniform material.

11. The method of claim 10, wherein the substantially uniform material comprises water.

12. The method of claim 9, wherein the reconstructed object parameter distribution comprises a 3-dimensional distribution of the electron density-based quantity.

13. The method of claim 1, wherein the estimating of the path comprises estimating a most likely path of the proton.

14. The method of claim 1, wherein the quantity associated with the reconstruction of the object parameter distribution comprises a total variation of the reconstructed object parameter distribution.

15. The method of claim 14, wherein the superior characteristic of the total variation comprises a lower value of the total variation.

16. The method of claim 15, wherein the total variation of the reconstructed object parameter distribution comprises a quantity of a function

17. The method of claim 15, wherein the total variation associated with the solution is superior to that associated with other feasible solutions.

18. The method of claim 1, wherein the estimating of the initial solution comprises calculating a filtered backprojection reconstruction solution.

19. The method of claim 1, wherein the seeking of the one or more feasible solutions comprises performing an iteration of:

perturbing a vector representation x^k of the object parameter distribution x so as to yield a perturbed vector y^k;

evaluating the quantity associated with the reconstructed object parameter distribution associated with the perturbed vector y^k; and

if the quantity associated with the perturbed vector y^k is superior to the quantity associated with the unperturbed vector x^k, projecting y^k so as to yield a next vector representation x^k+1.

20. The method of claim 19, wherein the perturbing of the vector x^k comprises calculating y^k such that y^k=x^k+β

_kv^k, where β

_k is representative of a perturbation magnitude and v^k is a perturbation vector.

21. The method of claim 20, wherein the perturbation vector v^k is calculated as a negative of a normalized subgradient of the quantity associated with the reconstructed object parameter distribution at x^k.

22. The method of claim 19, wherein the quantity associated with the perturbed vector y^k is superior with respect to the quantity associated with the unperturbed vector x^k if the quantity evaluated for y^k is less than or equal to the quantity evaluated for x^k.

23. The method of claim 19, wherein the projecting comprises calculating x^k+1 as a mathematically-defined projection of x^k onto some relevant convex set.

24. The method of claim 23, wherein the projecting comprises projecting onto hyperplanes, half-spaces, hyperslabs, or other convex sets using a block-iterative projection algorithm such that the measured data is divided into a plurality of blocks.

25. The method of claim 24, wherein the projecting comprises projecting using a diagonally relaxed orthogonal projection (DROP) based algorithm configured to allow diagonal component-wise relaxation in conjunction with orthogonal projections onto individual hyperplanes of the system.

26. The method of claim 25, wherein the DROP based algorithm includes a diagonally relaxed orthogonal matrix λ

_kU_t(k), where λ

_k is a relaxation parameter for the k-th iteration and U_t(k) is a diagonal matrix with diagonal elements min(1,1/h^t_j)) for the t-th block and h^t_j being a number of proton histories in the t-th block that intersect with a j-th voxel of the vector x^k.

27. The method of claim 24, wherein the projecting is performed cyclically through the blocks until all of the blocks are processed before proceeding to the next iteration.

28. The method of claim 24, wherein iteration is performed for each block so that for a given block being processed, the projecting is performed only for the given block.

29. The method of claim 19, wherein the performing the iteration further comprises calculating a feasibility proximity check to verify that the iteration with respect to an additional task of evaluating the quantity associated with the reconstructed object parameter distribution does not steer the solution away from a desired agreement with the measure data.

30. A method for performing proton computed tomography, the method comprising:

obtaining measured data for a plurality of protons that pass through an object; and

applying a projection based reconstruction algorithm in iterations based on total variation superiorization to the measured data so as to yield a distribution of relative stopping power of the object.

31. The method of claim 30, further comprising forming a visual image of the object based on the relative stopping power distribution.

32. A proton computed tomography system, comprising:

a proton delivery system configured to deliver a plurality of protons having a selected average energy sufficient to pass through an object;

a detector system configured to measure, for each of the protons, trajectories before and after the object and energy after passing through the object;

a data acquisition system configured to read out signals from the detector system so as to yield measured data representative of the trajectories and the energy of each of the protons; and

a processor configured to process the measured data and perform an image reconstruction so as to yield a computed tomography image of the object, the image reconstruction comprising projection based reconstruction algorithm in iterations based on total variation superiorization.

33. A proton therapy system, comprising:

a proton delivery system configured to deliver a beam of protons having a first average energy and a second average energy, the first average energy selected such that a first Bragg peak occurs at a location within a target region inside a portion of a body, the second average energy selected such that the beam of protons passes through the portion of the body;

a first detector system configured to facilitate the delivery of the first-energy beam to the target region;

a second detector system configured to measure, for each of the protons having the second energy and passing through the portion of the body, trajectories before and after the portion of the body and energy after passing through the portion of the body;

a data acquisition system configured to read out signals from at least the second detector system so as to yield measured data representative of the trajectories and the energy of each of the second-energy protons; and

a processor configured to process the measured data and perform an image reconstruction so as to yield a computed tomography image of the portion of the body, the image reconstruction comprising projection based reconstruction algorithm in iterations based on total variation superiorization.

34. A tangible computer readable storage medium having computer-executable instructions stored thereon, the computer-executable instructions readable by a computing system comprising one or more computing devices, wherein the computer-executable instructions are executable on the computing system in order to cause the computing system to perform operations comprising:

obtaining data about a plurality of protons, the data including information about first and second tracks for each of the protons, the data further including information about energy loss of each proton between the first and second tracks;

for each proton, estimating a path between the first and second tracks;

performing a tomography analysis of relative stopping power distribution based on the energy losses and the paths of the protons using projection based reconstruction algorithm in iterations based on total variation superiorization.

35. A particle radiation therapy system, comprising:

a particle radiation delivery system configured to deliver a beam of ions having a first average energy and a second average energy, the first average energy selected such that a first Bragg peak occurs at a location within a target region inside a portion of a body, the second average energy selected such that the beam of ions passes through the portion of the body;

a first detector system configured to facilitate the delivery of the first-energy beam to the target region;

a second detector system configured to measure, for each of the ions having the second energy and passing through the portion of the body, trajectories before and after the portion of the body and energy after passing through the portion of the body;

a data acquisition system configured to read out signals from at least the second detector system so as to yield measured data representative of the trajectories and the energy of each of the second-energy ions; and

a processor configured to process the measured data and perform an image reconstruction so as to yield a computed tomography image of the portion of the body, the image reconstruction comprising projection based reconstruction algorithm in iterations based on total variation superiorization.

36. The system of claim 35, wherein the ions comprise protons.

37. The system of claim 35, wherein the ions comprise carbon ions.