Breathing phase-based Transformation of a static Computed Tomography

Abstract

A medical data processing method of determining a transformation for determining a breathing state-dependent geometry of an anatomical body part of a patient's body, the method comprising: a) acquiring planning image data describing a set of tomographic medical planning images describing each a different part of the anatomical body part in the same respiratory state called reference planning respiratory state, wherein the anatomical body part is subject to respiratory movement and wherein the planning images comprise a planning image called reference planning image describing a part of the anatomical body part which is called reference planning body part; b) acquiring breathing image data describing a set of tomographic medical breathing images of the anatomical body part, wherein the breathing images comprise a reference breathing image describing the reference planning body part in a respiratory state called reference breathing respiratory state, which is different from the reference planning respiratory state, and a target breathing image describing at least another part of the anatomical body part, wherein the other part of the anatomical body part is called target body part, in a respiratory state called target respiratory state which is different from the reference planning respiratory state; c) determining, based on the planning image data and the breathing image data, reference transformation data describing a transformation, called reference transformation, between the geometry of the reference planning body part in the reference planning respiratory state and the geometry of the reference planning body part in the reference breathing respiratory state; d) acquiring scaling factor data describing a scaling factor which describes a relationship between the geometry of the reference planning body part in the reference breathing respiratory state and the geometry of the target body part in the target respiratory state; e) determining, based on the reference transformation and the scaling factor data, derived transformation data describing a transformation called derived transformation between the geometry of the target body part in the reference planning respiratory state, and the geometry of the target body part in the reference breathing respiratory state.

Claims

1.-15. (canceled)

16. A radiotherapy system or radiosurgery system, comprising: a treatment beam source; at least one or more processors; the at least one or more processors in communication with at least one memory having instructions which, when executed by the at least one or more processors, cause the processors to determine a transformation for determining a breathing state-dependent geometry of an anatomical body part of a patient's body, the instructions causing the at least one or more processors to: acquire, at the at least one or more processors, planning image data describing a set of tomographic medical planning images each describing a different part of the anatomical body part in the same respiratory state called reference planning respiratory state, wherein the anatomical body part is subject to respiratory movement and wherein the planning images comprise a planning image called reference planning image describing a part of the anatomical body part which is called reference planning body part; acquire, at the at least one or more processors, breathing image data describing a set of tomographic medical breathing images of the anatomical body part, wherein the breathing images comprise a reference breathing image describing the reference planning body part in a respiratory state called reference breathing respiratory state, which is different from the reference planning respiratory state, and a target breathing image describing at least another part of the anatomical body part, wherein the other part of the anatomical body part is called target body part, in a respiratory state called target respiratory state which is different from the reference planning respiratory state; determine, by the at least one or more processors and based on the planning image data and the breathing image data, reference transformation data describing a transformation, called reference transformation, between the geometry of the reference planning body part in the reference planning respiratory state and the geometry of the reference planning body part in the reference breathing respiratory state; acquire, at the at least one or more processors, scaling factor data describing a scaling factor which describes a relationship between the geometry of the reference planning body part in the reference breathing respiratory state and the geometry of the target body part in the target respiratory state; determine, by the at least one or more processors and based on the reference transformation and the scaling factor data, derived transformation data describing a transformation called derived transformation between the geometry of the target body part in the reference planning respiratory state, and the geometry of the target body part in the reference breathing respiratory state wherein the at least one or more processors are operatively connected to the treatment beam source to control the treatment beam source to emit a treatment beam based on the derived transformation data.

17. A computer-implemented method of determining a transformation for determining a breathing state-dependent geometry of an anatomical body part of a patient's body, the method comprising executing, by at least one processor of at least one computer, steps of: acquiring, at the at least one processor, planning image data describing a set of tomographic medical planning images describing each a different part of the anatomical body part in the same respiratory state called reference planning respiratory state (y), wherein the anatomical body part is subject to respiratory movement and wherein the planning images comprise a planning image called reference planning image describing a part of the anatomical body part which is called reference planning body part; acquiring, at the least one processor, breathing image data describing a set of tomographic medical breathing images of the anatomical body part, wherein the breathing images comprise a reference breathing image describing the reference planning body part in a respiratory state called reference breathing respiratory state, which is different from the reference planning respiratory state, and a target breathing image describing at least another part of the anatomical body part, wherein the other part of the anatomical body part is called target body part, in a respiratory state called target respiratory state which is different from the reference planning respiratory state; determining, by the at least one processor and based on the planning image data and the breathing image data, reference transformation data describing a transformation, called reference transformation, between the geometry of the reference planning body part in the reference planning respiratory state and the geometry of the reference planning body part in the reference breathing respiratory state; acquiring, at the least one processor, scaling factor data describing a scaling factor which describes a relationship between the geometry of the reference planning body part in the reference breathing respiratory state and the geometry of the target body part in the target respiratory state; determining, by the at least one processor and based on the reference transformation and the scaling factor data, derived transformation data describing a transformation called derived transformation between the geometry of the target body part in the reference planning respiratory state, and the geometry of the target body part in the reference breathing respiratory state.

18. The method according to claim 17, wherein the anatomical body part comprises at least one of at least part of the lung or at least part of the diaphragm.

19. The method according to claim 17, wherein the breathing image data comprises a comparative breathing image describing a further part of the anatomical body part in the reference breathing respiratory state, which further part is called comparative breathing body part and is different from the reference body part and the target body part, wherein acquiring the scaling factor data comprises: acquiring, at the at least one processor, image spacing data describing the spatial relationship, for example the distance, between the positions at which the reference breathing image, the target breathing image and the comparative breathing image were generated; and determining, by at least one processor, the scaling factor data based on the image spacing data and the reference breathing image data.

20. The method according to claim 19, wherein the spatial relationship is defined as the ratio r of the distance between the positions at which the reference breathing image and the target breathing image were generated, and the distance between the positions at which the reference breathing image and the comparative breathing image were generated.

21. The method according to claim 20, wherein a target factor is determined, by a processor, by multiplying by the geometry of the reference planning body part in the reference breathing respiratory state and adding thereto the product of r and the geometry of the comparative breathing body part in the reference breathing respiratory state.

22. The method according to claim 17, wherein the target factor is determined, by the at least one processor, based on a function describing the expected geometries of different parts of the anatomical body part as a function of the position of the breathing image showing a part of the anatomical body part in the set of breathing images under the assumption that that part of the anatomical body part is in the reference planning respiratory state.

23. The method according to claim 21, wherein the scaling factor is determined, by the at least one processor, by dividing the target factor by the geometry of the target body part in the target respiratory state.

24. The method according to claim 20, comprising: acquiring, at the at least one processor, imaging movement data describing the movement of a medical imaging apparatus relative to the anatomical body parts while it is being used for generating the breathing medical images; acquiring, at the at least one processor, respiratory cycle data describing the time period required by the patient for a respiratory cycle; determining, by the at least one processor, the comparative breathing image from the breathing images based on the imaging movement data and the respiratory cycle data.

25. The method according to claim 23, comprising: acquiring, at the at least one processor, the comparative breathing image from the breathing images based on the imaging movement data and a consistency optimization that uses metrics derived from the reconstructed datasets.

26. The method according to claim 17, wherein the scaling factor is predetermined by analysis of a plurality of tomographic image sets taken for a plurality of patients during respiratory movement.

27. The method according to claim 17, wherein the derived transformation is determined, by the at least one processor, by multiplying the reference transformation by the scaling factor (sf).

28. The method according to claim 17, wherein the breathing image data was generated over the whole length of a breathing cycle of the patient and wherein the method is executed repeatedly until a breathing image has been used as a reference breathing image for each of the respiratory states described by the breathing image data.

29. The method according to claim 17, wherein the position of the reference body part in the target respiratory state is determined, by the at least one processor, by subjecting the reference planning image to the derived transformation.

30. A non-transitory computer storage medium storing a program which, when executed by at least one processor of at least one computer, causes the at least one computer to determine a transformation for determining a breathing state-dependent geometry of an anatomical body part of a patient's body, the instructions when executed perform operations comprising: acquiring, at the at least one processor, planning image data describing a set of tomographic medical planning images describing each a different part of the anatomical body part in the same respiratory state called reference planning respiratory state, wherein the anatomical body part is subject to respiratory movement and wherein the planning images comprise a planning image called reference planning image describing a part of the anatomical body part which is called reference planning body part; acquiring, at the at least one processor, breathing image data describing a set of tomographic medical breathing images of the anatomical body part, wherein the breathing images comprise a reference breathing image describing the reference planning body part in a respiratory state called reference breathing respiratory state, which is different from the reference planning respiratory state, and a target breathing image describing at least another part of the anatomical body part, wherein the other part of the anatomical body part is called target body part, in a respiratory state called target respiratory state which is different from the reference planning respiratory state; determining, by the at least one processor and based on the planning image data and the breathing image data, reference transformation data describing a transformation, called reference transformation, between the geometry of the reference planning body part in the reference planning respiratory state and the geometry of the reference planning body part in the reference breathing respiratory state; acquiring, at the at least one processor, scaling factor data describing a scaling factor which describes a relationship between the geometry of the reference planning body part in the reference breathing respiratory state and the geometry of the target body part in the target respiratory state; determining, by the at least one processor and based on the reference transformation and the scaling factor data, derived transformation data describing a transformation called derived transformation between the geometry of the target body part in the reference planning respiratory state, and the geometry of the target body part in the reference breathing respiratory state.

Description

DESCRIPTION OF THE FIGURES

[0060] In the following, the invention is described with reference to the enclosed figure which represent preferred embodiments of the invention. The scope of the invention is not however limited to the specific features disclosed in the figures, wherein

[0061] FIG. 1 illustrates the principles of the disclosed method; and

[0062] FIG. 2 illustrates the sequence of transformations determined by the disclosed method.

[0063] FIG. 1 comprises a diagram showing the respiratory curve of a patient as the breathing level against time and/or position the imaging apparatus during acquisition of the reference CT (comprising the planning images) and the free-breathing CT (comprising the breathing images) and/or the time passed since initiation of the acquisition of the reference CT and the free-breathing CT, respectively. The planning images are included in a reference CT (comprising the planning images) which was taken at reference planning respiratory state y, which in the case shown by the diagram corresponds to a state of full inhalation. The term of breathing level corresponds to the amplitude of a respiratory state. A breathing level x is selected as the amplitude of the reference breathing respiratory state a associated with the reference breathing image A contained in the set 1 of breathing images which are included in the free-breathing CT. The comparative breathing image B is associated with a respiratory state b at breathing level x. For execution of the disclosed method, respiratory state b is equal to respiratory state a. Out of the set 1, two images, namely the reference breathing image A and the comparative breathing image B, are selected as images which are associated with the same respiratory state a. The geometry of the reference planning body part shown in the breathing reference image is denoted as Factor A, the geometry of the comparative breathing body part shown in the comparative breathing image B is denoted as Factor B. The positions along the rightward axis of the diagram at which the reference breathing image A and the comparative breathing image B and the target breathing image C associated with target respiratory state c were taken during acquisition of the free-breathing CT serve as a basis for calculating a relative position r=|C−A|/|B−A|, where A, B, and C denote the positions associated with the acquisition of the reference breathing image A, the comparative breathing image B and the target breathing image C, respectively. The target factor is calculated as tf=Factor A*(1−r)+Factor B*r and serves as a basis for calculating the scaling factor sf as sf=tf/Factor C, where Factor*C denotes the geometry of the target body part shown in the target breathing image C. The derived transformation T between the geometry of the target body part Factor C shown in the target breathing image C and the geometry of the target body part C′ as it is shown in the reference breathing respiratory state a (i.e. in the target planning image) is then calculated as T=R*sf, where R is the reference transformation between the reference planning image (which is associated with the reference planning respiratory state y) and the reference breathing image A.

[0064] As illustrated by FIG. 2, the derived transformation T is a transformation for transforming the geometry of the target body part from the one shown in the target planning image (which is associated with the same reference planning respiratory state y as the reference planning image) into the geometry it would have in an image associated with the same respiratory state as the reference breathing image A (namely in the breathing reference respiratory state a) by application of the scaling factor sf to the reference transformation R, wherein the scaling factor sf defines a spatial relationship between the image features in the reference breathing image A and the image features in the target breathing image C.