CN111643100B - Phase contrast imaging system information characterization method and system - Google Patents
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Abstract
The invention discloses a phase contrast imaging information characterization method, which comprises the following steps: acquiring original data of phase contrast imaging; extracting phase contrast information and dark field information according to the original data; and the extracted phase contrast information and dark field information are processed by the following formula: and H is the mixed field contrast of the phase contrast information and the dark field information, P 'is the phase shift of adjusting the corresponding data of the phase contrast information to be within [ -pi, pi ], and D' is the image contrast reduction ratio after the exponential operation is carried out on the corresponding data of the dark field information. By processing the extracted phase contrast information and dark field information, the original phase contrast information and dark field information can be represented in a mixed field image, and compared with the original phase contrast image and dark field image, the mixed field image has clear image representation and more definite physical meaning compared with a common image fusion method.
Description
Technical Field
The invention relates to the field of radiation imaging, in particular to a phase contrast imaging information characterization method and system.
Background
The phase contrast imaging technology mainly adopts X-rays to irradiate an object to be measured, can realize local structure resolution on a micron or even submicron level, and is a good supplement to the traditional X-ray attenuation imaging technology. The technology can simultaneously represent three kinds of contrast information of absorption, phase contrast and dark field, and is suitable for low-atomic number and low-density substances, in particular to biological soft tissue structures including mammary glands. At present, the X-ray phase contrast imaging technology mainly represents three kinds of contrast information, including absorption information, phase contrast information and dark field information. The three kinds of contrast information can respectively represent attenuation, phase offset and small-angle scattering of X-rays in an object, and the representation quantities all have relatively clear physical meanings at present, such as attenuation corresponding to a linear attenuation coefficient of the object, phase offset corresponding to a real part of a complex refractive index of the object, and small-angle scattering corresponding to a generalized scattering parameter of the object.
In practical applications (e.g. medical imaging applications), it would be of great practical value for a user (e.g. a radiologist) viewing an image to be able to present all of the most relevant information as compactly as possible. For X-ray phase contrast imaging, it is therefore an important direction of research to select a suitable characteristic quantity to integrate the three contrast information mentioned above as much as possible, especially to integrate the phase contrast information and dark field information that are characteristic of phase contrast imaging. In the prior art and research, the traditional technical means is that three kinds of information of absorption, phase contrast and dark field are fed back to a user in two ways, the first is that the three kinds of information are provided to the user through three different absorption images, phase contrast images and dark field images, which are relatively accurate, but the user needs to check the three images at the same time, which is very inconvenient; the second is to obtain three different images in the first way, and to obtain one image after two images are subjected to image processing operation, three kinds of information can be simultaneously reflected to a user, namely, image fusion through post-processing of several kinds of represented contrast information images is performed.
In order to solve the problems, the invention provides a phase contrast imaging information representation method and a phase contrast imaging information representation system, which can directly represent the original phase contrast information and dark field information in one image and have clear physical definition.
Disclosure of Invention
Technical problem to be solved
In order to enable a user to use the same image to simultaneously check two kinds of information of a phase contrast and a dark field and simultaneously ensure that the image information is clear and accurate, the invention provides a phase contrast imaging information representation method and system and a readable storage medium, which specifically comprise the following steps:
(II) technical scheme
One aspect of the present invention provides a method for characterizing phase contrast imaging information, the method comprising: acquiring original data of phase contrast imaging; extracting phase contrast information and dark field information according to the original data; characterizing the extracted phase contrast information and dark field information by the following formulas:
H＝D′·sin(P′)
wherein, H is the mixed field contrast of the phase contrast information and the dark field information, P 'is the phase shift of adjusting the corresponding data of the phase contrast information to [ -pi, pi ], D' is the image contrast reduction ratio after the exponential operation is carried out on the corresponding data of the dark field information.
Optionally, the extraction of the phase contrast information and the dark field information according to the raw data is implemented by including an FCA algorithm, an SAXS algorithm, or an ASAXS algorithm.
Optionally, after extracting the phase contrast information and the dark field information according to the raw data, the method further includes: carrying out normalization operation on corresponding data of the phase contrast information to obtain a phase deviation P' adjusted to be in [ -pi, pi ]; the image contrast reduction ratio D' obtained by performing an exponential operation on the corresponding data of the dark field information.
Another aspect of the present invention provides a phase contrast imaging information characterization system, which applies the above method, and includes: the optical imaging device is used for acquiring original data of phase contrast imaging; the information extraction device is used for extracting the phase contrast information and the dark field information according to the original data obtained by the optical imaging device; information representation means for passing through a formula based on the phase contrast information and the dark field information extracted by the information extraction means:
H＝D′·sin(P′)
and performing characterization, wherein H is the mixed field contrast of the phase contrast information and the dark field information, P 'is the phase shift of adjusting the corresponding data of the phase contrast information into [ -pi, pi ], and D' is the image contrast reduction ratio after performing exponential operation on the corresponding data of the dark field information.
Optionally, the optical imaging device is an analytical imaging device, an edge illumination imaging device, a spot imaging device or a grating imaging device.
Optionally, the grating imaging device is of the Talbot-Lau type, of the geometric projection type or of the bi-phase grating type.
Optionally, the position to be measured for irradiation of the grating imaging device is located between the light source and the first grating or between the first grating and the second grating.
Optionally, the light source of the optical imaging device is a conventional X-ray light source, a microfocus X-ray light source or a synchrotron radiation X-ray light source, and the detector of the optical imaging device is an energy integration type detector or a photon counting type detector.
Another aspect of the invention provides a phase contrast imaging information characterization system, the system comprising: a processor; a memory having stored thereon a computer program operable on a processor, wherein the computer program, when executed by the processor, implements the method described above.
Another aspect of the present invention provides a computer-readable storage medium having a data processing program stored thereon, the data processing program, when executed by a processor, implements the above-mentioned method.
(III) advantageous effects
According to the phase contrast imaging information representation method and system provided by the invention, the extracted phase contrast information and dark field information are processed, so that the original phase contrast information and dark field information can be represented in a mixed field image, and compared with the original phase contrast image and dark field image, the mixed field image has clear image representation and has more definite physical meaning compared with a common image fusion method.
Drawings
FIG. 1 is a flow chart of a phase contrast imaging information characterization method according to an embodiment of the present invention;
FIG. 2 is an imaging contrast diagram of three kinds of information of absorption, phase contrast and dark field correspondingly extracted by respectively adopting three algorithms of FCA, SAXS and ASAXS in the embodiment of the present invention;
fig. 3 is an imaging contrast diagram of dark field information extracted by the FCA and SAXS algorithms respectively and mixed characterization of the ASAXS algorithm in the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.
In order to enable a user to use the same image to simultaneously check two kinds of information of a phase contrast and a dark field and simultaneously ensure that the image information is clear and accurate, the invention provides a phase contrast imaging information representation method and system and a readable storage medium, which specifically comprise the following steps:
one aspect of the present invention provides a method for characterizing phase contrast imaging information, as shown in fig. 1, which is a schematic flow chart of a method for characterizing phase contrast imaging information in an embodiment of the present invention, the method includes:
s110, acquiring original data of phase contrast imaging;
s120, extracting phase contrast information and dark field information according to the original data;
s130, representing the extracted phase contrast information and dark field information through the following formulas:
H＝D′·sin(P′)
wherein, H is the mixed field contrast of the phase contrast information and the dark field information, P 'is the phase shift of adjusting the corresponding data of the phase contrast information to [ -pi, pi ], D' is the image contrast reduction ratio after the exponential operation is carried out on the corresponding data of the dark field information.
Specifically, in the embodiment of the present invention, an X-ray phase-contrast grating imaging device is adopted as the phase-contrast imaging system, and the X-ray phase-contrast grating imaging device includes an X-ray light source, a source grating, a phase grating, an analyzer grating source grating and a detector, specifically, a phase grating spacing of 1020mm, a source grating-analyzer grating spacing of 1280mm, source grating, phase grating and analyzer grating periods of 16.8 μm, 4.2 μm and 2.4 μm, respectively, X-ray tube parameters of 35kVp and 35mA, detector pixels of 74.8 μm × 74.8 μm, and a phase stepping number of 8 are adopted.
After the X-ray Phase contrast imaging system acquires the raw data, it is necessary to extract Absorption (Absorption) information, Phase-contrast (Phase-contrast) information, and Dark-field (Dark-field) information from the raw data by an information extraction algorithm, which are respectively denoted by A, P, D below. The present invention is described in detail with the characterization of the phase contrast information and the dark field information as examples. The phase contrast information can be understood as X-ray phase shift caused by refraction of X-rays through an object after the object is irradiated by the X-rays; dark field information can be understood as the change in contrast of an X-ray image due to scattering of X-rays through an object after the object has been irradiated with the X-rays. The invention defines a brand-new X-ray phase contrast imaging physical characterization quantity H for characterizing dark field information and phase contrast information in the same mixed field, and the mixed field information can be displayed to a user in a single image form. Wherein, the physical characterization quantity of the X-ray phase contrast imaging, namely the contrast H of a 'mixed field' (Hybrid-field), satisfies the following formula (1):
H＝D′·sin(P′)
wherein, H is the mixed field contrast of the phase contrast information and the dark field information, P 'is the phase shift of adjusting the corresponding data of the phase contrast information to [ -pi, pi ], D' is the image contrast reduction ratio after the exponential operation is carried out on the corresponding data of the dark field information.
Optionally, the extraction of the phase contrast information and the dark field information according to the raw data is implemented by including an FCA algorithm, an SAXS algorithm, or an ASAXS algorithm.
Specifically, in the embodiment of the present invention, in the X-ray phase-contrast imaging system based on the grating, the phase-contrast information and the dark-field information are extracted according to the original data, at least three extraction algorithms, namely, fca (fourier Component analysis) algorithm, SAXS (Small Angle X-ray Scattering) algorithm, and ASAXS algorithm, exist in the present invention, and the phase-contrast information and the dark-field information corresponding to the original data can be obtained through all the three extraction algorithms, and the three extraction algorithms are respectively described in detail below:
in the FCA algorithm, both a background displacement curve f (Φ) and an object displacement curve s (Φ) acquired by a grating-based X-ray phase contrast imaging system are assumed to be cosine models, i.e., formula (2) and formula (3):
wherein,
and
respectively taking the zero-order and first-order Fourier component amplitudes of the background displacement curve and the object displacement curve,
the first order Fourier components argument of both.
The FCA algorithm can calculate the parameters of a background displacement curve f (phi) and an object displacement curve s (phi) through fast Fourier transform, and further obtain extracted absorption information AFCAPhase contrast information PFCAAnd dark field information DFCASpecifically, it can be expressed in the following forms, i.e., formulas (4), (5), and (6):
wherein A, P, D represents absorption information, phase contrast information, dark field information, p2The period of the last grating close to the detector in the grating phase contrast imaging is shown, and d is the distance between the last two gratings.
The phase difference for the two displacement curves is,
the contrast of the object displacement curve and the background displacement curve are respectively.
Therefore, it can be seen that the FCA algorithm is based on the cosine model assumption, three kinds of information can be extracted through fast fourier transform, which is convenient and efficient, but the inherent Phase-wrapping problem (Phase-wrapping) exists, which may have a large influence on image quality in practical application, and is likely to cause poor image quality.
In the SAXS algorithm, a grating-based X-ray phase contrast imaging system is based on a background displacement curve and an object displacement curve acquired by the grating-based X-ray phase contrast imaging system. The basic assumption is that the object displacement curve s (φ) can be expressed as the convolution of the background displacement curve f (φ) and the small-angle scattering distribution g (φ), and the expression is as follows, namely, formula (7):
based on the formula (7), deconvolution is performed on the background displacement curve f (phi) and the object displacement curve s (phi) of each acquired detector pixel by a Lucy-Richardson iteration method to obtain a small-angle scattering distribution, and a kth iteration calculation formula in a deconvolution process is a formula (8):
wherein,
representing mirror symmetry of f about the origin, g is usually chosen0S as an initial value. Three kinds of contrast information of absorption (A), phase contrast (P) and dark field (D) extracted by the traditional FCA method can be expressed as zero order moment M of small-angle scattering distribution0(g) First moment M1(g) And second moment M2(g) I.e., formulae (9), (10), and (11):
A→M0(g)＝∫g(φ)dφ
P→M1(g)＝∫φg(φ)dφ/M0(g)
D→M2(g)＝∫(φ-M1(g))2g(φ)dφ/M0(g))
therefore, it can be seen that the SAXS algorithm is based on the convolution assumption, the small-angle scattering distribution is obtained by a deconvolution method, and then three kinds of information can be obtained by calculating the multi-order moments of the small-angle scattering distribution, so that the problem of phase wrapping of the FCA is avoided.
The ASAXS information extraction algorithm does not depend on the assumption of a cosine model as the SAXS method, and can be directly based on an original data background displacement curve f (phi) and an object displacement curve s (phi) acquired by an X-ray phase contrast imaging system of a grating and absorption (M)0) Phase contrast (M)1) And dark field (M)2) Three kinds of information are extracted, and can be specifically expressed as three kinds of multi-order moments, namely, formulas (12), (13) and (14):
wherein, SinM1(. o.) and CosM1(. cndot.) is defined as follows, i.e., equations (15) and (16):
SinM1(y)＝∫sin(φ)y(φ)dφ，
CosM1(y)＝∫cos(φ)y(φ)dφ.
therefore, the ASAXS algorithm avoids the phase wrapping problem of the FCA algorithm and the deconvolution iteration problem of the SAX algorithm, and the operation efficiency is higher.
It should be noted that, the above three information extraction algorithms may all adopt the form of formula (1), and by processing the phase contrast information and the dark field information, corresponding P 'and D' are obtained, and then mixed field information H of the phase contrast information and the dark field information, that is, the mixed field contrast of the phase contrast information and the dark field information is obtained, and further the dark field information and the phase contrast information may be represented in the same mixed field, and the mixed field information may be presented to a user in the form of a single image.
Optionally, extracting the phase contrast information and the dark field information according to the raw data includes: acquiring absorption information according to the original data; phase contrast information and dark field information are extracted from the raw data and/or the absorption information. In the embodiment of the present invention, as shown in formulas (12), (13), and (14), the absorption information M is obtained from the original data0Phase contrast information M1Based on the original data and the absorption information M0Obtaining, while dark field information M2Based on the original data and the absorption information M0Phase contrast information M1And (6) obtaining.
Optionally, after extracting the phase contrast information and the dark field information according to the raw data, the method further includes: carrying out normalization operation on corresponding data of the phase contrast information to obtain a phase deviation P' adjusted to be in [ -pi, pi ]; the image contrast reduction ratio D' obtained by performing an exponential operation on the corresponding data of the dark field information.
In the embodiment of the present invention, taking the ASAXS algorithm as an example, the cosine model in formulas (2) and (3) is substituted into formulas (12), (13) and (14), and a connection between the FCA algorithm and the ASAXS algorithm is established, that is, the absorption (M) extracted by the ASAXS algorithm can be extracted0) Phase contrast (M)1) And dark field (M)2) The three kinds of information are re-expressed as absorption information (A)ASAXS) Phase contrast information (P)ASAXS) And dark field information (D)ASAXS) I.e., formulae (17), (18), and (19):
one obtained by equation (18)The order moment information is essentially a mixed form of phase contrast information and dark field information extracted by the original FCA algorithm, and the mixed field information clearly fuses the phase contrast information and the dark field information physically and can highlight one of the phase contrast information and the dark field information through simple processing in some cases. For example, in imaging a light material uniform object, the phase shift φcOften close to 0, so at this time the logarithm can be taken to equation (18), and dark field information similar to that in equation (6), i.e. dark field information D', i.e. equation (20), can be obtained:
wherein the first item is the dark field information in (6), the second item is a small quantity, and the third item is a constant quantity.
In addition, when an object with less scattering is imaged, if the degree of contrast reduction is not significant, the phase contrast information in the formula (5) can be approximated to the formula (18), and accordingly, the phase contrast information P' can be obtained. Therefore, the mixed field contrast H in equation (1) can be defined information accordingly. Based on the above expression, whether the original data is directly extracted according to, for example, the ASAXS algorithm or indirectly extracted according to, for example, the FCA algorithm, the phase contrast information and the dark field information can be expressed by the mixed field contrast H provided by the present invention, and therefore, the mixed field contrast H provided by the present invention has a certain universality.
In the embodiment of the invention, in the grating phase-contrast imaging system, an experimental sample is a living mouse, the distance between a source grating and a phase grating is 1020mm, the distance between the source grating and an analysis grating is 1280mm, the periods of the source grating, the phase grating and the analysis grating are respectively 16.8 μm, 4.2 μm and 2.4 μm, the parameters of an X-ray bulb tube are 35kVp and 35mA, the pixel of a detector is 74.8 μm multiplied by 74.8 μm, and the phase stepping number is 8. As shown in fig. 2, which is an imaging contrast diagram of three kinds of information of absorption, phase contrast, and dark field correspondingly extracted by using three algorithms of FCA, SAXS, and ASAXS in the embodiment of the present invention, and as shown in fig. 3, which is an imaging contrast diagram of dark field information respectively extracted by performing mixed characterization on the ASAXS algorithm and the FCA and SAXS algorithms in the embodiment of the present invention, it can be seen from fig. 2 that most areas of a mixed field image (i.e., a phase contrast image of ASAXS) proposed by the present invention are very consistent with an original phase contrast image, and it can be seen from fig. 3 that after a simple operation of taking an absolute value logarithm of formula (15), the mixed field image proposed by the present invention is very similar to the dark field information in fig. 1, and the above results indicate that the proposed physical characterization quantity of the mixed field can better reflect the characteristics of two kinds of information of phase contrast and dark field.
For other embodiments of X-ray phase contrast imaging, the physical characteristic quantity of the mixed field provided by the present invention can be calculated according to formula (1), that is, the phase contrast information and the dark field information can be calculated by a conventional method, and then the mixed field information can be obtained by calculation according to formula (1).
Another aspect of the present invention provides a phase contrast imaging information characterization system, which applies the above method, and includes: the optical imaging device is used for acquiring original data of phase contrast imaging; the information extraction device is used for extracting the phase contrast information and the dark field information according to the original data obtained by the optical imaging device; information representation means for passing through a formula based on the phase contrast information and the dark field information extracted by the information extraction means:
H＝D′·sin(P′)
and performing characterization, wherein H is the mixed field contrast of the phase contrast information and the dark field information, P 'is the phase shift of adjusting the corresponding data of the phase contrast information into [ -pi, pi ], and D' is the image contrast reduction ratio after performing exponential operation on the corresponding data of the dark field information.
Optionally, the optical imaging device is an analytical imaging device, an edge illumination imaging device, a spot imaging device or a grating imaging device. The optical Imaging device is not limited to various types of phase-contrast Imaging systems such as analytical-crystal-based Imaging devices (ABI), Edge-Illumination-based Imaging devices (EI), Speckle-based Imaging devices (Speckle-based Imaging), and Grating-based Imaging devices (GI) as a device for acquiring raw data, so that raw data of three kinds of information, i.e., absorption information, phase-contrast information, and dark-field information can be acquired.
Optionally, the grating imaging device is of the Talbot-Lau type, of the geometric projection type or of the bi-phase grating type. The type of the grating imaging device is not limited, and various types of systems such as a Talbot-Lau type, a geometric projection type, and a bi-phase grating type may be included. So as to obtain the original data of three information of absorption information, phase contrast information and dark field information.
Optionally, the position to be measured for irradiation of the grating imaging device is located between the light source and the first grating or between the first grating and the second grating. In addition, the object position can be placed between the light source and the first grating or between the two gratings. The grating imaging device is generally a light source, a first grating and a detector, or a light source, a first grating, a second grating and a detector, so that the irradiation position of the object to be measured can be located between the light source and the first grating, or between the first grating and the second grating. The variation of the illumination measured position is relevant to the acquisition of the imaging information and the accuracy of the imaging information.
Optionally, the light source of the optical imaging device is a conventional X-ray light source, a microfocus X-ray light source or a synchrotron radiation X-ray light source, and the detector of the optical imaging device is an energy integration type detector or a photon counting type detector. In addition, the X-ray source can be a conventional X-ray source, a microfocus X-ray source or a synchrotron X-ray source. Furthermore, the detector may be either an energy integrating type detector or a photon counting type detector.
According to the phase contrast imaging information representation method and system provided by the invention, the extracted phase contrast information and dark field information are processed, so that the original phase contrast information and dark field information can be represented in a mixed field image, and compared with the original phase contrast image and dark field image, the mixed field image has clear image representation and has more definite physical meaning compared with a common image fusion method.
Another aspect of the invention provides a phase contrast imaging information characterization system, the system comprising: a processor; a memory having stored thereon a computer program being executable on a processor, wherein the computer program realizes the method steps of the above embodiments when executed by the processor. The raster imaging system information extraction device in the embodiment of the present invention includes a processor (e.g., a microprocessor (μ P), a Digital Signal Processor (DSP), or the like). The processor may be a single processing unit or a plurality of processing units for performing the different actions of the method flows described in the embodiments of the invention. Further, the apparatus may include at least one computer readable storage medium in the form of non-volatile or volatile memory, as described in more detail below.
Another aspect of the present invention proposes a computer-readable storage medium having stored thereon a data processing program which, when executed by a processor, implements the method of the above embodiment. The information extraction methods of embodiments of the present invention may take the form of a computer program product on a computer-readable storage medium having instructions stored thereon for use by or in connection with an instruction execution system (e.g., one or more processors). In the context of embodiments of the present invention, a computer-readable storage medium may be any medium that can contain, store, communicate, propagate, or transport the instructions. For example, a computer readable storage medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. Specific examples of the computer-readable storage medium include: magnetic storage devices, such as magnetic tape or Hard Disk Drives (HDDs); optical storage devices, such as compact disks (CD-ROMs); a memory, such as a Random Access Memory (RAM) or a flash memory; and/or wired/wireless communication links.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for characterizing phase contrast imaging information, the method comprising:
acquiring original data of phase contrast imaging;
extracting phase contrast information and dark field information according to the original data;
characterizing the extracted phase contrast information and dark field information by the following formulas:
H＝D′·sin(P′)
wherein, H is a mixed field contrast of the phase contrast information and the dark field information, P 'is a phase shift for adjusting the corresponding data of the phase contrast information to [ -pi, pi ], and D' is an image contrast reduction ratio after performing an exponential operation on the corresponding data of the dark field information.
2. The method of claim 1, wherein extracting phase contrast information and dark field information from the raw data is performed by including an FCA algorithm, a SAXS algorithm, or an ASAXS algorithm.
3. The method of claim 1, wherein after extracting the phase contrast information and the dark field information from the raw data, further comprising:
carrying out normalization operation on corresponding data of the phase contrast information to obtain phase deviation P' adjusted to be in [ -pi, pi ];
and the image contrast reduction ratio D' is obtained by performing exponential operation on the corresponding data of the dark field information.
4. A phase contrast imaging information characterization system, applying the method according to any of claims 1-3, characterized in that the system comprises:
the optical imaging device is used for acquiring original data of phase contrast imaging;
the information extraction device is used for extracting phase contrast information and dark field information according to the original data obtained by the optical imaging device;
information characterization means for performing a formula based on the phase contrast information and dark field information extracted by the information extraction means:
H＝D′·sin(P′)
and performing characterization, wherein H is the mixed field contrast of the phase contrast information and the dark field information, P 'is the phase shift of adjusting the corresponding data of the phase contrast information into [ -pi, pi ], and D' is the image contrast reduction ratio after performing exponential operation on the corresponding data of the dark field information.
5. The system of claim 4, wherein the optical imaging device is an analytical imaging device, an edge illumination imaging device, a spot imaging device, or a grating imaging device.
6. The system of claim 5, wherein the grating imaging device is of the Talbot-Lau type, a geometric projection type, or a bi-phase grating type.
7. The system of claim 5, wherein the illumination measurement location of the grating imaging device is located between the light source and the first grating or between the first grating and the second grating.
8. The system of claim 4, wherein the light source of the optical imaging device is a conventional X-ray light source, a microfocus X-ray light source or a synchrotron X-ray light source, and the detector of the optical imaging device is an energy integration type detector or a photon counting type detector.
9. A phase contrast imaging information characterization system, the system comprising:
a processor;
a memory having stored thereon a computer program operable on the processor, wherein the computer program, when executed by the processor, implements the method of any of claims 1-3.
10. A computer-readable storage medium, having stored thereon a data processing program which, when executed by a processor, implements the method of any one of claims 1-3.
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