CN103767733B - The method of estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging - Google Patents
The method of estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging Download PDFInfo
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- CN103767733B CN103767733B CN201410020359.5A CN201410020359A CN103767733B CN 103767733 B CN103767733 B CN 103767733B CN 201410020359 A CN201410020359 A CN 201410020359A CN 103767733 B CN103767733 B CN 103767733B
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Abstract
The invention discloses the method for estimation of RF volume data in a kind of freedom-arm, three-D ultrasonic elastograph imaging, the method is collecting on the basis compressing forward and backward RF frame sequence, before building compression according to the position of scanning area, compress latter two RF data solid, each RF signal sampling point of RF frame sequence before traversal compression, this point to be mapped to before compression in Volume through coordinate transform, amplitude interpolation is carried out to the voxel of close position; Then amplitude information is utilized, the frequency of binding signal and propagation distance, estimate each RF signal in Volume, to each RF signal through low-pass filtering treatment, finally obtain compressing front RF volume data, take the RF frame sequence after same operation traversal compression, calculate the RF volume data after compression.The present invention estimates the method for RF volume data from RF frame sequence, and the RF volume data obtained can directly simply for calculating three dimensional elasticity image, and the method is applicable to the freedom-arm, three-D ultrasonic elastograph imaging in Various Complex scanning situation.
Description
Technical field
The present invention relates to computer-aided medical science technical field of imaging, particularly the method for estimation of ultrasonic radio frequency (RF) signal volume data in a kind of freedom-arm, three-D ultrasonic elastograph imaging.
Background technology
Medical ultrasound diagnosis is the important component part of modern medicine image, in the pathological diagnosis of many tissues (such as heart, liver, breast, superficial tissue etc.) of the person, have very large reference value.The quality of human body soft tissue changes usually and its pathological process close relation, and when organizing generation pathological changes, obvious change can occur the features such as the hard soft degree of tissue or elasticity size.
The elastic information of biological tissue has important reference value for the diagnostic procedure of disease.But, the attributes such as the density of the just tissue that the traditional medicine image mode comprising x-ray imaging, ultra sonic imaging (US), nuclear magnetic resonance (MRI), computed tomography (CT) etc. obtains and thickness, all directly can not provide the information of the basic mechanical attribute of this tissue of elasticity.Clinically; pathological changes (such as cancer) be organized in pathological changes early stage time the attribute such as density and thickness with organize normally very close; so adopt above imaging pattern to be all difficult to early stage pathological changes be detected; and Ultrasonic Elasticity Imaging (Elastography) fast-developing in recent years; carry out imaging by obtaining related organization's elastic information; early lesion can be detected in time; compensate for the deficiency of traditional medicine image mode, there is important clinical value and wide application prospect.
Its ultimate principle of ultrasonic elastograph imaging is to a certain tissue applying inside (comprising self) or outside, dynamic or static state/quasi-static excitation; Under the physical condition such as Elasticity, biomechanics, organize generation one response, such as displacement, strain and the distribution of speed; Utilize Digital Signal Processing and Digital image technology, estimate the parameters such as the displacement of organization internal, strain, thus the difference of indirectly or direct mechanical attributes such as its elastic modelling quantity of reflection.
Two-dimensional ultrasonic image can react the situation in current organization cross section well, but the ultrasonic examination of 2D also has some shortcomings part, 2D ultrasonic examination depends on the Heuristics of diagnosis person to control the movement of ultrasonic probe, the image obtained also only can react the information of current cross-section, and the 3D shape of examine site tissue (the solid geometry shape of such as focus) can only depend on the imagination of diagnosis person and can not show intuitively; 2D ultrasonic examination is difficult to the particular location navigated to by the plane of delineation in organ, is also difficult to the image obtaining organ particular cross section; In 2D ultra sonic imaging, computed range and volume depend on the formula of human organ approximate geometry, also depend on the visual angle of 2D image.From the angle quantized and the angle facilitating follow-up study, 2D is ultrasonic is a kind of very poor imaging pattern, and 3D imaging pattern has three-dimensional display directly perceived, is convenient to measure, can obtain and organize the advantages such as arbitrary section attribute information, can be good at the restriction overcoming 2D imaging pattern.
What three-D ultrasonic elastogram obtained is the three-dimensional elastic modulus information of tissue.Three-D ultrasonic elastogram process mainly comprises the acquisition of RF volume data, the calculating of tissue strain, the several step of display of 3D image reconstruction and 3-D view.Wherein, it is a vital step that RF volume data obtains, and before and after compression, the matching of RF volume data will directly decide the correctness of strain calculation result.The data capture method of 3-D supersonic imaging can be divided into two kinds: 1, adopt one dimensional linear array probe to obtain 2D sequence image, 2D image sequence is reconstructed 3-D view volume data; 2, two-dimensional array probe is adopted directly to obtain 3-D view volume data.2D sequence image has free arm (free-hand) scanning usually, Mechanical Driven scans two kinds of scan modes wherein to adopt one dimensional linear array probe to obtain; When adopting free arm scanning, need a kind of positioner (acoustics is located, optical alignment or electromagnetic locator etc.) to be fixed on ultrasonic probe, the spatial positional information of record image when gathering each two field picture.
For the three-D ultrasonic elastogram of free arm scanning, when image data, operator needs to hold probe and is adjacent to artificial skin surface and moves the RF sequence of data frames before a segment distance collect and process with certain speed, and then to apply the tissue at same position with popping one's head in and to keep certain pressure again to move the RF sequence of data frames after a segment distance collect and process with same speed.When calculating elastic image, find compression RF frame that is front and coupling after compressing according to the data of twice collection and calculate elastic image, several elastic images are carried out three-dimensional reconstruction and shows.The thought of said method two-dimension elastic figure computational methods is expanded simply a dimension to three-dimensional, its prerequisite be compression before and after gather RF sequence of data frames time need ensure probe vertical in tissue surface pop one's head in simultaneously rate travel and direction identical, but the method has significant limitation in practical operation, this is because:
1, popping one's head in moving process may run-off the straight or deflection;
2, during compress tissue scanning, be difficult to ensure that probe applied pressure is even, the direction of exerting pressure vertically;
3, pop one's head in and to be difficult to ensure that rate travel is identical in front and back are moved for twice, moving direction is identical.
In free arm scanning, above-mentioned three kinds of situations belong to FAQs, if operator does not have good experience, the RF frame sequence compressing forward and backward collection will be difficult to coupling, and then cause follow-up organizing in time shift estimation and strain calculation to occur larger error, finally obtain three dimensional elasticity result and actually to differ greatly.Therefore, for the common operator not having too much experience, how to utilize the RF frame sequence that free arm scan method collects in the ordinary course of things, calculating correct tissue three-dimensional elastic image is a urgent problem.
Summary of the invention
The object of the invention is to overcome the shortcoming of prior art and deficiency, the method for estimation of RF volume data in a kind of freedom-arm, three-D ultrasonic elastograph imaging is provided.
Object of the present invention is achieved through the following technical solutions:
In freedom-arm, three-D ultrasonic elastograph imaging, the method for estimation of RF volume data, comprises the steps:
(1) build former and later two RF volume datas of compression, determine position and the size of two RF volume datas;
(2) each sampled point of each the RF signal before traversal compression in RF frame sequence, to be mapped to before compression in RF volume data by this point through Coordinate Conversion, to carry out amplitude interpolation to its neighboring voxel; For compression after RF frame sequence, adopt use the same method to compression after RF volume data carry out interpolation;
(3) interpolation complete after, for each " RF signal " in RF volume data, utilize the amplitude of each point on this " RF signal " and frequency, the propagation distance of signal, estimate an approximate real RF signal;
(4) low-pass filtering treatment is carried out to the RF signal that in RF volume data, each estimates, finally obtain RF volume data.
Preferably, in step (1), the position of the forward and backward RF volume data of compression built and size are determined according to the position range scanning the RF frame obtained, the upper surface of RF volume data will be positioned at the top of the locus of all RF frames collected, before RF volume data region will comprise compression RF frame sequence place area of space with compress after the region of occuring simultaneously mutually; Determine the voxel number of RF volume data on length direction according to the number of unit length pixel in RF frame, namely determine the size of RF volume data.
Preferably, the position of the compression of structure forward and backward RF volume data is all identical with size.
Preferably, in step (2), first amplitude interpolation is carried out to whole RF volume data; Whenever traversing the starting point of a certain bar RF signal of a certain frame in RF frame sequence, calculate the analytic signal of this RF signal, remember that this RF signal is rf=FS
i,j, FS
i,jrepresent the jth bar RF signal of the i-th frame in frame sequence frame sequences, its analytic signal is a (t)=s (t) e
j φ (t), amplitude is s (t), and phase place is φ (t).
Preferably, during the amplitude of carrying out interpolation, i-th of RF signal sampled point is mapped to a bit in RF volume data, with this point for the centre of sphere, R is radius, value is assigned to each tissue points in spheroid, when a tissue points is asked the average of summation during repeatedly assignment, when a tissue points be not once all assigned out-of-date, by the average of the range value of its adjacent voxels to its assignment.
Preferably, with to centre of sphere inverse distance for weight is weighted assignment to contiguous voxel.
Preferably, in step (3), the estimation of RF signal, according to the amplitude of each " RF signal " and the frequency of signal of the RF volume data RF volume data obtained after interpolation, propagation distance, recalculates actual RF signal with RF signal approximation formula; The initial phase Φ compressing the RF signal of forward and backward RF volume data correspondence position is identical.
Preferably, in step (3), the estimation of RF signal, phase estimation is not carried out to each sampled point on RF signal, but estimate in units of a sinusoidal cycles or half sinusoidal cycles according to RF signal frequency and sample rate, the starting point phase place of each cycle or half period only need be calculated when carrying out phase estimation.
Preferably, in step (4), build a FIR low pass filter, low-pass filtering treatment is carried out, the high-frequency information that filtering is artificially introduced to each the RF signal estimated, thus obtains final RF volume data.
The present invention has following advantage and effect relative to prior art:
(1) in freedom-arm, three-D ultrasonic elastograph imaging, the present invention is equivalent to provide a kind of general interface scanning between the RF frame sequence that obtains and calculating elastic image, this interface can the nonstandard data acquisition modes of masking operation person, and the RF frame sequence obtained by acquisition mode lack of standardization can well be calculated for follow-up elastic image.
(2) novelty of the present invention propose a kind of RF signal estimation method, by carrying out amplitude interpolation to each sampled point on a RF signal, utilize amplitude, frequency, velocity of wave, the information such as propagation distance estimate the waveform of RF signal, then pass through the high fdrequency component of low pass filter filtered signal, thus estimate approximate real RF signal.
Accompanying drawing explanation
Fig. 1 is flow chart of the present invention;
Fig. 2 is the main use scenes schematic diagram of the present invention;
Fig. 3 (a) is position and the size of determining to compress front RF volume data according to RF frame sequence;
Fig. 3 (b) is position and the size of determining to compress rear RF volume data according to RF frame sequence;
Fig. 4 is a sampled point of certain RF signal before traversal to compression in RF frame sequence in a certain frame;
Fig. 5 carries out amplitude interpolation and phase estimation to the voxel in RF volume data;
Fig. 6 is three RF signals of adjacent position;
Fig. 7 estimates the 2nd bars according to the 1st, 3 bars in Fig. 6, and upper part is actual signal, lower part
For the signal estimated.
Detailed description of the invention
Below in conjunction with embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention are not limited thereto.
Embodiment
As shown in Figure 1 and Figure 2, in freedom-arm, three-D ultrasonic elastograph imaging, the method for estimation of RF volume data, comprises the steps:
(1) build former and later two RF volume datas of compression, determine position and the size of two RF volume datas;
(2) each sampled point of each the RF signal before traversal compression in RF frame sequence, to be mapped to before compression in RF volume data by this point through Coordinate Conversion, to carry out amplitude interpolation to its neighboring voxel; For compression after RF frame sequence, adopt use the same method to compression after RF volume data carry out interpolation;
(3) interpolation complete after, for each " RF signal " in RF volume data, utilize each amplitude of point on this " RF signal " and the frequency of signal, propagation distance, estimate an approximate real RF signal;
(4) low-pass filtering treatment is carried out to the RF signal that in RF volume data, each estimates, finally obtain RF volume data.
As shown in Fig. 3 (a) He Fig. 3 (b), under normal circumstances, the RF frame sequence that free arm collects can not be the arrangement of parallel rule, but have angle rotation and frame density difference etc. complicated situation, in this case, before compression, RF frame sequence and the rear RF frame sequence of compression are difficult to coupling, therefore can not be directly used in elasticity number and calculate; The present invention can utilize these RF frame sequences, a regular RF volume data (Volume) is gone out by Interpolate estimation, make to compress front RF volume data each RF signal can with compression after RF volume data in each RF signal well mate, thus utilize former and later two RF volume datas of compression directly to carry out calculating elastic image.Because the computational methods compressing rear RF volume data are identical with process with the RF volume data computational methods before compression with process, therefore, only to compress front RF volume data, concrete implementation step is as follows:
(1) position and the size of compressing front RF volume data is determined.As shown in Fig. 3 (a), according to the three-dimensional coordinate (X of each pixel in each frame in RF frame sequence before compression
i, Y
i, Z
i) obtain the scope [X at three coordinate axess of RF frame sequence
min, X
max], [Y
min, Y
max], [Z
min, Z
max]; Same as shown in Fig. 3 (b), ask for the rear scope of RF frame sequence on coordinate axes of compression, get common factor part, obtain the coordinate range [X of common factor part
1 min, X
1 max], [Y
1 min, Y
1 max], [Z
1 min, Z
1 max]; Find minima in the y-axis direction in all RF frames, the upper surface using this minima as RF volume data, object is exactly the top allowing RF volume data completely enough can cover all RF frames.After determining the position of RF volume data, according to x in RF frame, the number of y-axis unit length pixel determines the voxel number of RF volume data on x, y, z direction, namely determines the size of RF volume data.
(2) amplitude interpolation is carried out to the voxel in RF volume data.Each RF signal of each frame before traversal compression in RF frame sequence, obtains analytic signal a (t)=s (t) e of this RF signal
j φ (t)obtain amplitude s (t), then travel through each sampled point of this RF signal, as shown in Figure 4, this sampled point rf (i) is carried out coordinate transform, if the point after conversion is not in RF volume data, abandon it, otherwise, find with this point for the centre of sphere, R=1 is the voxel in the ball of radius, cross the centre of sphere perpendicular to x-axis sectional view as shown in Figure 5; Wherein, A point is the starting sample point of a certain bar RF signal in a certain frame, B point is that traversal is mapped to RF volume data mid point to 1 rf (i) of certain in RF signal after coordinate transform, the range value of current point in RF signal is assigned to all voxels in ball, if voxel is by repeatedly assignment, record the number of times that is assigned and by the value composed add and, average.
(3) RF signal is estimated.After obtaining the range value of every bar " RF signal " in RF volume data, then estimate the phase place of RF signal.As shown in Figure 5, the string discrete point in the y-axis direction of RF volume data is stray RF signal to be estimated; Known sound wave speed c in the tissue, frequency is f
0, propagation distance is x (t), gets initial phase Φ=0, substitutes into rf=s (t) cos (φ+2 π f
0x (t)/c) in just can estimate a RF signal.It should be noted that initial phase Φ can set arbitrarily, but need ensure that the initial phase of the RF signal compressing forward and backward correspondence position (matching) is identical.Fig. 6 is three RF signals of adjacent position, estimates the 2nd bars by the 1st, 3 bars, and as shown in Figure 7, Fig. 7 top is divided into real 2nd article of RF signal to result, and bottom is divided into the 2nd article of RF signal estimated.
(4) low-pass filtering treatment is carried out to RF signal.According to frequency and the sample rate of RF signal, design FIR filter, carries out low-pass filtering treatment to each the RF signal estimated in RF volume data, obtains final RF volume data.
Above-described embodiment is the present invention's preferably embodiment; but embodiments of the present invention are not restricted to the described embodiments; change, the modification done under other any does not deviate from spirit of the present invention and principle, substitute, combine, simplify; all should be the substitute mode of equivalence, be included within protection scope of the present invention.
Claims (9)
1. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging, is characterized in that, comprise the steps:
(1) build former and later two RF volume datas of compression, determine position and the size of two RF volume datas;
(2) each sampled point of each the RF signal before traversal compression in RF frame sequence, to be mapped to before compression in RF volume data by this point through Coordinate Conversion, to carry out amplitude interpolation to its neighboring voxel; For compression after RF frame sequence, adopt use the same method to compression after RF volume data carry out interpolation;
(3) interpolation complete after, for each " RF signal " in RF volume data, utilize the amplitude of each point on this " RF signal " and frequency, the propagation distance of signal, estimate an approximate real RF signal;
(4) low-pass filtering treatment is carried out to the RF signal that in RF volume data, each estimates, finally obtain RF volume data.
2. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging according to claim 1, it is characterized in that, in step (1), the position of the forward and backward RF volume data of compression built and size are determined according to the position range scanning the RF frame obtained, the upper surface of RF volume data will be positioned at the top of the locus of all RF frames collected, before RF volume data region will comprise compression RF frame sequence place area of space with compress after the region of occuring simultaneously mutually; Determine the voxel number of RF volume data on length direction according to the number of unit length pixel in RF frame, namely determine the size of RF volume data.
3. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging according to claim 1 and 2, it is characterized in that, the position of the compression forward and backward RF volume data of structure is all identical with size.
4. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging according to claim 1, is characterized in that, in step (2), first carry out amplitude interpolation to whole RF volume data; Whenever traversing the starting point of a certain bar RF signal of a certain frame in RF frame sequence, calculate the analytic signal of this RF signal, remember that this RF signal is rf=FS
i,j, FS
i,jrepresent the jth bar RF signal of the i-th frame in frame sequence frame sequences, its analytic signal is a (t)=s (t) e
j φ (t), amplitude is s (t), and phase place is φ (t).
5. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging according to claim 4, it is characterized in that, during the amplitude of carrying out interpolation, i-th of RF signal sampled point rf (i) is mapped to a bit in RF volume data, with this point for the centre of sphere, R is radius, s (i) value is assigned to each tissue points in spheroid, when a tissue points is asked the average of summation during repeatedly assignment, when a tissue points be not once all assigned out-of-date, by the average of the range value of its adjacent voxels to its assignment.
6. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging according to claim 4, is characterized in that, with to centre of sphere inverse distance for weight is weighted assignment to contiguous voxel.
7. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging according to claim 1, it is characterized in that, in step (3), the estimation of RF signal, according to the amplitude of each " RF signal " and the frequency of signal of the RF volume data RF volume data obtained after interpolation, propagation distance, with RF signal approximation formula rf=s (t) cos (φ+2 π f
0x (t)/c) recalculate actual RF signal; Wherein, s (t) is amplitude, and c is speed, f
0for frequency, x (t) is propagation distance, and the initial phase Φ compressing the RF signal of forward and backward RF volume data correspondence position is identical.
8. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging according to claim 1, it is characterized in that, in step (3), the estimation of RF signal, phase estimation is not carried out to each sampled point on RF signal, but estimate in units of a sinusoidal cycles or half sinusoidal cycles according to RF signal frequency and sample rate, the starting point phase place of each cycle or half period only need be calculated when carrying out phase estimation.
9. the method for estimation of RF volume data in freedom-arm, three-D ultrasonic elastograph imaging according to claim 1, it is characterized in that, in step (4), build a FIR low pass filter, low-pass filtering treatment is carried out to each the RF signal estimated, the high-frequency information that filtering is artificially introduced, thus obtain final RF volume data.
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