CN101422352B - Interactive coronary artery virtual angioscope implementation method - Google Patents

Abstract

The invention relates to a realization method for an interactive coronary artery virtual angioscope, which pertains to the technical field of medical imaging and aims at solving the visible problem of making a diagnosis and giving treatment of coronary artery. The technical proposal is that the realization method obtains the three-dimensional model of blood vessels by means of combining three-dimensional geometrical feature information of lumen by a nearly orthorhombic X-ray visualization picture of coronary artery with the data of the section of lumen by lumen endobronchial ultrasonography, then adopts virtual reality modeling language to interactively describe the model of blood vessels and realizes the visualization of coronary artery in the endoscope roaming mode. The realization method realizes interactive visit and display of the three-dimensional model of blood vessels and provides an ideal platform for the research on the development of coronary atherosclerosis pathological changes, the visible diagnosis and treatment of coronary heart diseases, the involvement in the evaluation of curative effect, and the like, and the training of medical personnel.

Description

A kind of implementation method of interactive coronary artery virtual angioscope

Technical field

The present invention relates to a kind of implementation method of the interactive coronary artery virtual angioscope that merges based on many formation methods, belong to the medical imaging technology field.

Background technology

Virtual endoscopic techniques (Virtual Endoscope, VE) be to utilize medical image as initial data, technology such as comprehensive utilization Digital Image Processing, computer graphics, visualization in scientific computing, virtual reality, reconstruction of three-dimensional images forms the virtual human body tissue; Then viewpoint is inserted in the organ cavity that reconstructs, simulated the tract endoscopy realistically by navigation or roaming technology and pseudo-color technology.

The at present clinical coronary artery interventional imaging means that generally adopt are X ray coronarography (CAG, Coronary ArteryAngiography) and intravascular ultrasound (IVUS, Intravascular Ultrasound), the two carries out simultaneously, and angiography and intravascular ultrasound show the configuration of catheterbased US probe in intraluminal position and corresponding blood vessel wall respectively synchronously.CAG and IVUS have the projected outline of advantage and not enough complementary characteristics: CAG reflection lumen of vessels after by the contrast agent filling, diseases such as energy diagnosing ischemia heart disease and malformation of coronary artery, and significant, but can not provide the structural information and the lesion degree of blood vessel wall to thrombolytic in the coronary artery, the treatment of PTCA intervene operations such as (percutaneous transluminal coronary angioplasties); IVUS can clear demonstration blood vessel transverse section, carries out histological classification according to the speckle acoustic features, finds the vascular lesion that CAG can not show, observes the fuzzy pathological changes of crotch or blood vessel overlapping etc.But owing to adopt the high frequency ultrasound probe, influenced investigation depth, can only measure, can not enter serious narrow tube chamber, and can't determine the axial location and the direction in space in cross section a certain section lesion vessels.

Get involved the imaging detection in addition and also comprise the coronary artery mirror, it is an a kind of small endoscopic imaging technology of utilizing optical fiber technology.But this technology is not accepted extensively clinically, and reason comprises: the morphologic data of luminal surface can only be provided, can not observe the pathological changes DEEP STRUCTURE in the tube wall, can not carry out the quantitative analysis of stenosis and blood flow; The pathological changes that can not be used for pathological changes and anterior descending branch and the Zhi Jinduan that circles round at video picture aorta-coronary ostium place; The blood flow that enters from side opening can make the visual field fuzzy; Conduit lacks navigability, has limited the video picture scope; Need temporary transient plug flow in the checking process, can cause the generation of myocardial ischemia etc.

At present, Non-Invasive cardiovascular image check mainly comprises CTA (CT Angiography) and MRCA (Magnetic ResonanceCoronary Angiography).But the main limitation of heart CT examination is to be easy to generate pseudomorphism, influences picture quality.For MRCA, because arteria coronaria blood vessel itself is thin, distortion and structure are complicated, and has the influence of heartbeat and breathing, signals such as fatty tissue and cardiac muscular tissue can influence the result of its video picture around the arteria coronaria.Though there are not lonizing radiation in the MR checking process simultaneously, comparatively safe, the influence of noise is arranged, the safety of some metal implants (as artificial metal lobe, cardiac pacemaker etc.) also receives publicity.In a word, because deficiency and technical limitation that image-forming principle caused, feasible CTA up to the present and MRCA generally only can be used as a kind of system of selection to heart overall merit, or as the examination measure of coronary heart disease conduit contrast examination, reduce the unnecessary wound inspection, and, can not replace the image check method of intervention property on to the clinical diagnosis and treatment of coronary heart disease fully to the non-invasive follow-up investigation of operation on heart or interventional therapy effect.

In sum, the main image method that the CAG of intervention property and IVUS remain clinical diagnosis and treatment coronary heart disease, and also the two has advantage and not enough complementary characteristics.At present also do not have a kind of interactive coronary artery virtual angioscope system, can realize that the coronary artery of scope roam mode is visual based on CAG and IVUS image co-registration.

Summary of the invention

The objective of the invention is to overcome the deficiencies in the prior art, a kind of implementation method that can realize the visual interactive coronary artery virtual angioscope of coronary artery of scope roam mode is provided.

The alleged problem of the present invention realizes with following technical proposals:

A kind of implementation method of interactive coronary artery virtual angioscope, it is to merge mutually with the tube chamber cross-sectional data that is obtained by intravascular ultrasound by the tube chamber three-dimensional geometry shape information that will be obtained by the X ray coronarogram picture of nearly orthogonal, obtain the threedimensional model of blood vessel, use Virtual Reality Modeling Language (VRML) alternatively to describe vascular pattern then, the coronary artery of realizing the scope roam mode is visual, and concrete steps are as follows:

A, gather the intravascular ultrasound IVUS and the X ray coronarography CAG image of vessel segment simultaneously:

Mechanical type ultrasound catheter probe is placed the far-end of vessel segment, remove in the process of guide wire at the uniform velocity equidistant time, utilize the intravascular ultrasound imaging instrument to gather equidistant IVUS image sequence in the mode of electrocardio ECG gate, promptly with the R ripple of electrocardiosignal as triggering, only identical cardiac phase place images acquired in each cardiac cycle can solve the motion artifacts problem in the coronary artery IVUS image sequence.Simultaneously, utilize C type arm single face X ray angiography machine to return the CAG image that the starting point of removing the path is taken two width of cloth near normal angles of record same cardiac state at conduit;

The threedimensional model that B, the IVUS that utilizes collection and CAG image are set up blood vessel;

C, utilization Virtual Reality Modeling Language are realized coronary artery revascularization result's scope roam mode visual.

The concrete steps of threedimensional model that the implementation method of above-mentioned interactive coronary artery virtual angioscope, the IVUS of described utilization collection and CAG image are set up blood vessel are as follows:

A, according to the CAG image of two near normal angles, three-dimensional reconstruction goes out returning of ultrasound catheter and removes the path;

B, three-dimensional reconstruction goes out vessel lumen from the CAG image:

With the 3D rodding that reconstructs footpath two CAG imaging plane back projections to the left and right, obtain corresponding 2D path, for each point on the 2D path, by on direction perpendicular to the path, seek two maximum of shade of gray, obtain the vessel lumen left and right edges, the cross section at the hypothesis tube chamber is under the prerequisite of ellipse then, finish the three-dimensional reconstruction of whole vessel lumen, this result is used for the follow-up direction in space of determining each frame ultrasonoscopy;

The extraction of c, ivus image sequence medium vessels wall profile:

In first two field picture, manually select the several characteristic point on the inside and outside film profile of blood vessel wall, put formed polygon as initial position to connect these, obtain the profile of the inside and outside film of blood vessel wall by the snake distortion, the speckle that is partitioned into blood vessel wall and may exists, for subsequent frame, then, finish cutting apart to continuous multiple frames IVUS image with the extraction result of former frame initial position as snake;

D, determine the axial location of each frame ivus image:

According to the acquisition order and the spacing of IVUS image, the 3D conduit that the edge reconstructs returns removes the path with each frame IVUS image sequence arrangement, determines the axial location of each two field picture;

E, determine the dimensional orientation of each frame ivus image:

On the 3D conduit path after the reconstruction, set up the local coordinate system of each frame ultrasonoscopy, i.e. Frenet-Serret frame, three secondary method vector b of the tangent vector t of the coordinate axes unit of being respectively, the master of unit method vector n and unit, the position of conduit is positioned at the center of IVUS image;

Each frame ultrasonoscopy is rotated to its correct direction to determine the dimensional orientation of ivus image around conduit:

The centrifugal vector of representing the deviation of gravity center catheter position of blood vessel wall profile with ρ, the elliptic contour of the vessel lumen that goes out from the CAG image reconstruction is projected on the corresponding ultrasonoscopy, represent that with μ vessel lumen elliptic contour centrage departs from the centrifugal vector of catheter position, ε is the mould of vectorial ρ, θ is the angle of ρ and μ, determine the dimensional orientation of ultrasonic image sequence with the statistics optimization method, purpose is to make the θ minimum:

Set the moving window of a fixed width w, carry out statistical analysis in this window, there is n in the ultrasonic image sequence for the N frame is formed _wThe individual moving window of=N-(w-1), at each the window's position m place, accumulative total eccentric distance ∑ ε _m, the eccentric angle meansigma methods of weighting θ _mAnd the weighted standard deviation σ (θ of eccentric angle _m) can calculate by following formula respectively:

$\mathrm{\Σ}{\mathrm{\ϵ}}_m=\underset{i=m}{\overset{m+(w-1)}{\mathrm{\Σ}}}{\mathrm{\ϵ}}_i,{\stackrel{\‾}{\mathrm{\θ}}}_m=\frac{1}{\mathrm{\Σ}{\mathrm{\ϵ}}_m}\underset{i=m}{\overset{m+(w-1)}{\mathrm{\Σ}}}{\mathrm{\ϵ}}_i{\mathrm{\θ}}_i,\mathrm{\σ}{\left({\mathrm{\θ}}_m\right)}^2=\frac{1}{\mathrm{\Σ}{\mathrm{\ϵ}}_m}\underset{i=m}{\overset{m+(w-1)}{\mathrm{\Σ}}}{\mathrm{\ϵ}}_i{({\mathrm{\θ}}_i-{\stackrel{\‾}{\mathrm{\θ}}}_m)}^2$

Utilize these numerical value, in each the window's position place, computed reliability weight factor: r _m=∑ ε _m/ σ (ε _m), give bigger weight factor in the bigger position of eccentric distance, limit σ (θ simultaneously _m) bigger position, calculate one by following formula and proofread and correct eccentric angle θ _Corr:

${\stackrel{\‾}{\mathrm{\θ}}}_{\mathrm{corr}}=\frac{1}{\mathrm{\Σr}}\underset{m=0}{\overset{n_w-1}{\mathrm{\Σ}}}{r}_m{\stackrel{\‾}{\mathrm{\θ}}}_m,\mathrm{\Σr}=\underset{k=0}{\overset{n_w-1}{\mathrm{\Σ}}}{r}_k$

And apply it in all images of sequence, thereby obtain the dimensional orientation of each two field picture;

The drafting of vessel lumen surfaces externally and internally is finished in f, utilization based on the surface extraction method of nurbs surface match.

The implementation method of above-mentioned interactive coronary artery virtual angioscope, the visual concrete steps of described utilization Virtual Reality Modeling Language realization coronary artery revascularization result's scope roam mode are as follows:

1. roam the calculating in path:

Return the three-dimensional reconstruction result of removing the path according to ultrasound catheter, with coordinate P along the i frame IVUS image acquisition point of conduit _iBe current view point position, P _I+1Be next viewpoint position, with the direction vector of the negative semiaxis of z axle $-\stackrel{\→}{z}e=\left[\begin{array}{ccc}0& 0& -1\end{array}\right]$ Be the initial viewpoint direction, then in VRML, the position vector of current view point is ${\stackrel{\→}{p}}_i=\left[\begin{array}{ccc}{x}_i& y_i& z_i\end{array}\right],$ Rotating shaft for the current view point direction is ${\stackrel{\→}{d}}_i={\stackrel{\→}{p}}_{i+1}-{\stackrel{\→}{p}}_i=\left[\begin{array}{ccc}{d}_{\mathrm{xi}}& d_{\mathrm{yi}}& d_{\mathrm{zi}}\end{array}\right]$ Unit vector $-{\stackrel{\→}{z}}_i={\stackrel{\→}{d}}_i/\left|\right|{\stackrel{\→}{d}}_i\left|\right|,$ Rotating shaft is ${\stackrel{\→}{r}}_i=\frac{-{\stackrel{\→}{z}}_e\×-{\stackrel{\→}{z}}_i}{\left|\right|-{\stackrel{\→}{z}}_e\×-{\stackrel{\→}{z}}_i\left|\right|},$ The anglec of rotation is

2. the IVUS pixel data is inserted in the virtual scene, and adopts translucent display mode to show;

3. develop interactively user graphical interface.

The implementation method of above-mentioned interactive coronary artery virtual angioscope, described ultrasound catheter returns the three-dimensional rebuilding method of removing the path: at first set up the perspective projection imaging model of CAG system two near normal angles, again according to the distance and the angle parameter of synchronous recording in angiographic procedure, obtain the geometric transformation of imaging system, adopt three-dimensional snake modelling technique then, snake directly is out of shape in the space, finishes conduit and returns the three-dimensional reconstruction of removing the path;

The implementation method of above-mentioned interactive coronary artery virtual angioscope, the span of angle is 60 ° to 120 ° between two acquisition angles of described coronarogram picture, and only returns the starting point of removing the path at ultrasound catheter and take a pair of contrastographic picture.

The blood vessel space geometry information that the present invention will be obtained by the single face contrastographic picture of two nearly orthogonal angles combines with the tube chamber cross section information that is obtained by ivus image, make full use of the complementarity of two kinds of imaging means, finished the accurate three-dimensional reconstruction of blood vessel, and the utilization Virtual Reality Modeling Language realizes that the coronary artery of scope roam mode is visual.The present invention has realized the interactive visit of three-dimensional vascular pattern and demonstration, for the visual diagnosis and treatment of the development of coronary atherosclerosis pathological changes, coronary heart disease, to the research of interventional therapy effect assessment etc., and medical worker's training provides an ideal platform.

Description of drawings

The invention will be further described below in conjunction with accompanying drawing.

Fig. 1 is the flow chart according to the three-dimensional reconstruction blood vessel of the inventive method;

Fig. 2 is according to CAG of the inventive method and IVUS image acquisition sketch map;

Fig. 3 is according to the radiography system of the inventive method imaging sketch map two angles;

Fig. 4 is the definite sketch map according to each frame ultrasonoscopy relative bearing of the inventive method;

Fig. 5 is according to ultrasonoscopy eccentric distance of the inventive method and eccentric angle sketch map;

Fig. 6 is the definite sketch map according to the roaming viewpoint position of the inventive method;

Fig. 7 is the definite sketch map according to the roaming viewpoint direction of the inventive method.

Each symbol is among the figure: Image A, Image B, imaging plane; s ₁, s ₂, the position of x-ray source focus in twice angiographic procedure; s ₁x ₁y ₁z ₁, with s ₁Space coordinates for initial point; s ₂x ₂y ₂z ₂, with s ₂Space coordinates for initial point; U ₁V ₁O ₁, the rectangular coordinate system on the imaging plane A; U ₂V ₂O ₂, the rectangular coordinate system on the imaging plane B; D ₁, s ₁Vertical dimension to imaging plane A; D ₂, s ₂Vertical dimension to imaging plane B; Point on P, the space blood vessel; p ₁, the projection of P point on imaging plane A; p ₂, the projection of P point on imaging plane B; u ₁, p ₁At coordinate system U ₁V ₁O ₁Interior abscissa; v ₁, p ₁At coordinate system U ₁V ₁O ₁Interior vertical coordinate; u ₂, p ₂At coordinate system U ₂V ₂O ₂Interior abscissa; v ₂, p ₂At coordinate system U ₂V ₂O ₂Interior vertical coordinate; The spatial parameter curve in c (s), expression 3D conduit path; The position of conduit in C, the ultrasonoscopy, it also is the center of ultrasonoscopy; O _C, the oval cross section profile center (promptly in the hypothesis vessel cross-sections when being ellipse, pairing blood vessel center line position in the three-dimensional reconstruction based on CAG); O _I, the tube chamber cross section profile that from ultrasonoscopy, extracts center of gravity; ρ, ρ=O _I-C is the centrifugal vector of the deviation of gravity center conduit of ultrasound contour; μ, μ=O _C-C is the centrifugal vector that vessel centerline departs from conduit; The angle of θ, ρ and μ; P _i, P _I+1, viewpoint; Position vector;

Rotating shaft; φ _i, the anglec of rotation;

The direction vector of the negative semiaxis of z axle;

Viewpoint direction to be asked;

The unit vector of y axle also is the direction of giving tacit consent among the VRML that makes progress; ε _i, The anglec of rotation in the x-y plane.

Used symbol: t, unit tangent vector in the literary composition; N, the master of unit method vector; B, the secondary method vector of unit; The mould of ε, vectorial ρ; W, moving window width; θ _mThe eccentric angle meansigma methods of weighting; σ (θ _m), the weighted standard deviation of eccentric angle; r _m, the reliability weight factor; θ _Corr, proofread and correct eccentric angle.

The specific embodiment

Describe step of the present invention in detail below in conjunction with accompanying drawing:

(1) image acquisition:

Collecting device comprises C type arm single face X ray angiography machine and intravascular ultrasound imaging instrument.

Referring to Fig. 2, IVUS and CAG imaging are carried out simultaneously.Conventional brachial artery puncture through right femoral artery or upper arm, the row selectivity pulse prefixing contrast.Under the guidance of radioscopy image, insert high frequency ultrasound probe conduit, to the blood vessel far-end.Ultrasonic probe is connected the pseudo-movie queen of removal with ultrasonic imaging device, at the uniform velocity equidistantly returns through motor control and remove conduit.When doing 360 ° of rotations with 1800 rev/mins, the probe conduit obtains the real-time blood vessel tangent plane picture of 30 frame/seconds continuously.Adopt clinical commonly used, allow patient return the method for holding the breath in the process of removing at conduit, reduce respirometric influence.Adopt the mode of ECG gate to gather ultrasonoscopy, thereby reduce the influence of heart movement.

Only return the starting point of removing the path, adopt the mode of ECG gate, take the contrastographic picture of a pair of near normal angle at corresponding cardiac phase place at conduit.Because adopt mechanical type ultrasound catheter probe, ultrasonic transducer is positioned at a flexible axle center head end, the axle center is at epitheca pipe internal rotation, and the sheath pipe is fixed, therefore can guarantee back to remove the stable of path.Record radiography angle and x-ray source focus are to the distance of receiving screen in the imaging process.

(2) extraction and the three-dimensional reconstruction at conduit path and tube chamber edge in the contrastographic picture:

The present invention at first sets up the perspective projection imaging model (accompanying drawing 3) of CAG system two near normal angles.Afterwards, according to the distance and the angle parameter of synchronous recording in angiographic procedure, obtain the geometric transformation of imaging system.Utilize three-dimensional snake modelling technique then, finish the three-dimensional reconstruction in conduit path.

The snake model claims movable contour model (active contour model) again, be a kind of distorted pattern technology (the Kass M that proposed in 1987 by Kass etc., Witkin A, Terzopoulos T.Snakes:active contour models.International Journal of Computer Vision, 1987,1 (4): 321-331), application is very extensive in image processing field in recent years, finishes image segmentation, coupling and motion tracking.

The specific implementation method is: the initial position of snake adopts manually gets an acquisition, promptly in a projection of conduit, manually choose some sampled points (generally choosing back starting point, terminal point and 3～4 intermediate points of removing the path gets final product), obtain these corresponding point in another projection according to outer utmost point constraint then.Obtain their three-dimensional coordinate respectively by these several groups of corresponding point, connect these 3D points with straightway, the gained broken line is as the initial position of 3D snake.

The energy function of snake model is:

$E={\∫}_0^1[E_{\mathrm{int}}\left(c\left(s\right)\right)+E_{\mathrm{ext}}\left(c\left(s\right)\right)]\mathrm{ds}---\left(1\right)$

C (s)=(x (s), y (s), z (s)) wherein, s ∈ [0,1] are the B-spline Curve of expression conduit.Internal energy E in the formula (1) _IntExpression formula be:

E _int(c(s))＝(α|c′(s)| ²+β|c＂(s)| ²)/2 (2)

Wherein c ' (s) and c " (s) be respectively single order and the second dervative of c (s).Internal energy guarantees the continuous and smooth of curve.

External energy function E _ExtBe to guarantee snake astringent external force, comprise two parts, correspond respectively to left and right sides projection, guarantee that the projection of three-dimensional curve on two angle imaging planes is positioned at corresponding conduit projection place just:

$E_{\mathrm{ext}}=\mathrm{\&gamma;}(I_L({\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2008100800020E00032.png"\; state="\{\{state\}\}">u</figure-callout>}}_1,v_1)+I_R({\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="H2008100800020E00031.png"\; state="\{\{state\}\}">u</figure-callout>}}_2,v_2))+\mathrm{\&lambda;}(|\&dtri;I_L({\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2008100800020E00032.png"\; state="\{\{state\}\}">u</figure-callout>}}_1,v_1)|+|\&dtri;I_R({\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="H2008100800020E00031.png"\; state="\{\{state\}\}">u</figure-callout>}}_2,v_2)|)$ (3)

$=\mathrm{\&gamma;}(I_L\left(F_L\left(c\right)\right)+I_R\left(F_R\left(c\right)\right))+\mathrm{\&lambda;}(|\&dtri;I_L\left(F_L\left(c\right)\right)|+|\&dtri;I_R\left(F_R\left(c\right)\right)|)$

I wherein _L(u ₁, v ₁) and

IL (u ₁, v ₁) be respectively the gray scale and the shade of gray value of left subpoint; I _R(u ₂, v ₂) and

I _R(u ₂, v ₂) be respectively the gray scale and the shade of gray of right subpoint.Because in the contrastographic picture, the gray value of blood vessel is littler than background, thus weight coefficient γ get on the occasion of.According to the geometrical relationship and the outer polar curve restriction relation of perspective projection imaging, can derive u ₁, v ₁, u ₂And v ₂All be spatial point three-dimensional coordinate c=(x ₁, y ₁, z ₁) function:

[u ₁v ₁] ^T＝F _L(c)，[u ₂v ₂] ^T＝F _R(c) (4)

Afterwards, minimize by the energy function that makes formula (1), the three-dimensional axis of conduit has just been determined in the final position of snake curve.This method has been avoided having improved reconstruction precision and arithmetic speed based on the pointwise coupling between two angles of outer utmost point constraint.

According to the geometric transformation of imaging system,, obtain corresponding 2D path with the 3D rodding that reconstructs footpath two CAG imaging plane back projections to the left and right.For each point on the 2D path, by on direction, seek two maximum of shade of gray perpendicular to the path, finish extraction to the vessel lumen left and right edges.Afterwards, be under the prerequisite of ellipse at the cross section of supposing tube chamber, finish the three-dimensional reconstruction of whole tube chamber, this result is that the direction in space of follow-up definite each frame ultrasonoscopy is used.

(3) extraction of ivus image sequence medium vessels wall profile:

The present invention adopts in conjunction with the snake model of dynamic programming and finishes extraction to adventitia profile in the IVUS image sequence medium vessels wall.The operator only needs the several characteristic point on the manual select target profile in first frame, connects these and puts the initial position of formed polygon as snake.For subsequent frame, with the extraction result of former frame initial position, finish the cutting apart of continuous multiple frames IVUS image as next frame snake, can save computation time greatly.

(4) fusion of IVUS and CAG data:

Here mainly need solve two problems: 3D axial location and the dimensional orientation of determining each IVUS frame.

(4.1) determining of the three-dimensional axial location of ultrasonoscopy:

In gathering the process of ultrasonoscopy, the mode that adopts motor to drive at the uniform velocity equidistantly pulls straight conduit from far-end to near-end.The speed of conduit is pulled out in adjusting, can regulate the tangent plane spacing as required.Adopt the CAG image reconstruction to go out after the axis of conduit, according to axially each frame IVUS image sequence being arranged, can determine the axial location of each two field picture according to known tangent plane spacing.

(4.2) each frame ultrasonoscopy dimensional orientation determines

The present invention utilizes a kind of non-iterative statistics optimization method to calculate the dimensional orientation of each frame ultrasonoscopy.At first on the 3D conduit path after the reconstruction, set up the local coordinate system of each frame ultrasonoscopy, it is the Frenet-Serret frame, three secondary method vector b (accompanying drawing 4) of the tangent vector t of the coordinate axes unit of being respectively, the master of unit method vector n and unit, zero is the position of conduit in the IVUS image.Behind the three-dimensional reconstruction of finishing the conduit path, can obtain its 3D curvilinear equation c (s), according to differential geometric knowledge, t, n and b can be calculated as follows according to curvilinear equation:

$\left\{\begin{array}{c}t=\frac{c\&prime;\left(s_0\right)}{|c\&prime;\left(s_0\right)|}\\ b=\frac{c\&prime;\left(s_0\right)\&times;c\&prime;\&prime;\left(s_0\right)}{|c\&prime;\left(s_0\right)\&times;c\&prime;\&prime;\left(s_0\right)|}\\ n=\frac{{\left|c\left(s_0\right)\right|}^{2}c\&prime;\&prime;\left(s_0\right)-c\&prime;\left(s_0\right)(c\&prime;\&prime;\left(s_0\right)\&CenterDot;c\&prime;\left(s_0\right))}{|{\left|c\left(s_0\right)\right|}^{2}c\&prime;\&prime;\left(s_0\right)-c\&prime;\left(s_0\right)(c\&prime;\&prime;\left(s_0\right)\&CenterDot;c\&prime;\left(s_0\right))|}\end{array}\right.---\left(5\right)$

Wherein " * " represents the multiplication cross of vector; The dot product of " " expression vector; C ' (s) and c " (s) be respectively single order and the second dervative of c (s).

The position of conduit is positioned at the center of IVUS image, and the center of gravity of the objective contour that is partitioned into does not generally overlap with catheter position, and as shown in Figure 5, wherein the C point is represented conduit, O _CBe the center of elliptic contour (promptly when the hypothesis vessel cross-sections is ellipse, pairing blood vessel center line position in the three-dimensional reconstruction based on CAG), 0 ₁Center of gravity for the vascular cross-section profile that from ultrasonoscopy, extracts.Adopt centrifugal vectorial ρ to represent the degree of the deviation of gravity center catheter position of profile: ρ=O _I-C.

Because vessel centerline and conduit path do not overlap, the elliptic contour orientation that reconstructs at the ultrasonoscopy profile at blood vessel same position place with based on contrastographic picture is inconsistent, and elliptic contour is projected on the corresponding ultrasonoscopy.The same centrifugal vectorial μ of elliptic contour that adopts represents that vessel centerline departs from the degree of catheter position: μ=O _C-C.

The mould ε of the matching error availability vector ρ of ultrasonoscopy and the angle theta of ρ and μ are represented.The present invention utilizes the statistics optimization method to determine that the absolute orientation of ultrasonic image sequence, purpose are the angle theta minimums that makes between the centrifugal vector of elliptic contour and ultrasound contour.Set the moving window of a fixed width w, in this window, carry out statistical analysis.There is n in ultrasonic image sequence for the N frame is formed _wThe individual moving window of=N-(w-1).At each the window's position m place, accumulative total eccentric distance ∑ ε _m, the eccentric angle meansigma methods of weighting θ _mAnd the weighted standard deviation σ (θ of eccentric angle _m) can calculate by following formula respectively:

$\mathrm{\&Sigma;}{\mathrm{\&epsiv;}}_m=\underset{i=m}{\overset{m+(w-1)}{\mathrm{\&Sigma;}}}{\mathrm{\&epsiv;}}_i,{\stackrel{\&OverBar;}{\mathrm{\&theta;}}}_m=\frac{1}{\mathrm{\&Sigma;}{\mathrm{\&epsiv;}}_m}\underset{i=m}{\overset{m+(w-1)}{\mathrm{\&Sigma;}}}{\mathrm{\&epsiv;}}_i{\mathrm{\&theta;}}_i,\mathrm{\&sigma;}{\left({\mathrm{\&theta;}}_m\right)}^2=\frac{1}{\mathrm{\&Sigma;}{\mathrm{\&epsiv;}}_m}\underset{i=m}{\overset{m+(w-1)}{\mathrm{\&Sigma;}}}{\mathrm{\&epsiv;}}_i{({\mathrm{\&theta;}}_i-{\stackrel{\&OverBar;}{\mathrm{\&theta;}}}_m)}^2$

Utilize these numerical value, in each the window's position place, computed reliability weight factor: r _m=∑ ε _m/ σ (ε _m).Give bigger weight factor in the bigger position of eccentric distance, limit σ (θ simultaneously _m) bigger position.Calculate one by following formula and proofread and correct eccentric angle θ _Corr:

${\stackrel{\&OverBar;}{\mathrm{\&theta;}}}_{\mathrm{corr}}=\frac{1}{\mathrm{\&Sigma;r}}\underset{m=0}{\overset{n_w-1}{\mathrm{\&Sigma;}}}{r}_m{\stackrel{\&OverBar;}{\mathrm{\&theta;}}}_m,\mathrm{\&Sigma;r}=\underset{k=0}{\overset{n_w-1}{\mathrm{\&Sigma;}}}{r}_k$

And apply it in all images of sequence, thereby obtain the dimensional orientation of each two field picture.

(5) match of lumen of vessels surfaces externally and internally

After the IVUS image sequence being finished edge extracting and being determined the locus of each frame, the present invention adopts NURBS (non-uniform rational B-spline) surface fitting to return the sampled point of removing on correct each cross section arranged in path along three-dimensional, obtains the continuous three-dimensional blood vessel surface.

(6) interactive coronary artery virtual endoscopic system

Utilize virtual reality modeling language to show the reconstructed results of scope roam mode, not only can show the overall appearance of rebuilding the back vessel segment, and can show major axis profilograph picture.

The demonstration of IVUS view data and the exploitation of interactively user graphical interface in the drafting of the tube chamber surfaces externally and internally that comprise the calculating of roaming the path, reconstructs, the virtual scene.

(6.1) calculating in roaming path

The roaming path is the sequence of forming in a series of viewpoints of target blood intracavity.For each viewpoint, all need to determine its position and direction, wherein direction adopts observer place local coordinate system to represent around the rotation of arbitrary axis.

Determining of viewpoint position: in VRML, 1 P on the roaming path _iThe position of (being viewpoint) and direction ternary number

Represent, wherein

Be position vector,

Be rotating shaft, φ _iIt is the anglec of rotation (as shown in Figure 6).

The roaming of virtual observer in target blood both can be removed the path along returning of IVUS conduit and carried out, and also can carry out along the tube chamber centrage.So ${\stackrel{\&RightArrow;}{p}}_i=\left[\begin{array}{ccc}{x}_i& y_i& z_i\end{array}\right]$ Can directly obtain according to both three-dimensional reconstruction result: for the former,

Be exactly coordinate along the i frame IVUS image acquisition point of conduit, the also i.e. centre coordinate of this two field picture; For the latter, The barycentric coodinates of the tube chamber profile that from i frame IVUS image, is partitioned into exactly.Because the rigidity and the seriality of conduit are all good than the tube chamber centrage that calculates, so the present invention adopts first method to determine

Thereby obtain more continuous slick animation effect.

Determining of viewpoint direction: the initial value of viewpoint direction is set at the negative semiaxis along the z axle, as shown in Figure 6, and wherein $-\stackrel{\&RightArrow;}{z}e=\left[\begin{array}{ccc}0& 0& -1\end{array}\right]$ The direction vector of the negative semiaxis of expression z axle also is the initial viewpoint direction.The path carries out because roaming is to remove along returning of conduit, therefore according to definite method of above-mentioned viewpoint position, by current view point P _iNext as can be known viewpoint P _I+1Position vector ${\stackrel{\&RightArrow;}{p}}_{i+1}=\left[\begin{array}{ccc}{x}_{i+1}& y_{i+1}& z_{i+1}\end{array}\right],$ Thereby obtain vector ${\stackrel{\&RightArrow;}{d}}_i={\stackrel{\&RightArrow;}{p}}_{i+1}-{\stackrel{\&RightArrow;}{p}}_i=\left[\begin{array}{ccc}{d}_{\mathrm{xi}}& d_{\mathrm{yi}}& d_{\mathrm{zi}}\end{array}\right],$ Its unit vector is viewpoint direction to be asked $-{\stackrel{\&RightArrow;}{z}}_i={\stackrel{\&RightArrow;}{d}}_i/\left|\right|{\stackrel{\&RightArrow;}{d}}_i\left|\right|.$

With

Cross product be rotating shaft:

${\stackrel{\&RightArrow;}{r}}_i=\frac{-{\stackrel{\&RightArrow;}{z}}_e\&times;-{\stackrel{\&RightArrow;}{z}}_i}{\left|\right|-{\stackrel{\&RightArrow;}{z}}_e\&times;-{\stackrel{\&RightArrow;}{z}}_i\left|\right|}---\left(6\right)$

Promptly Perpendicular to

With The plane that is determined, as shown in Figure 7, the inceptive direction of viewpoint

Around rotating shaft

Rotation φ _iThe angle promptly obtains the current viewpoint direction

Promptly by current view point P _iPoint to next viewpoint P _I+1Direction, the anglec of rotation is:

By the computing formula of vector cross product as can be known,

The z component be 0, the expression In the x-y plane, so

Also can be by the unit vector of y axle

At x-y plane internal rotation ε _iObtain:

${\stackrel{\&RightArrow;}{r}}_i={\stackrel{\&RightArrow;}{y}}_e{R}_z\left({\mathrm{\&epsiv;}}_i\right)---\left(8\right)$

R wherein _z(ε _i) expression is around the spin matrix of z axle,

It is the direction of giving tacit consent among the VRML that makes progress.

Terminal point in the roaming path is promptly for viewpoint set { P ₀, P ₁..., P _N-1In 1 P _i, when i=n-1, owing to there is not P _I+1So unavailable preceding method calculates the rotating shaft and the anglec of rotation, at this moment: ${\stackrel{\&RightArrow;}{r}}_{n-1}={\stackrel{\&RightArrow;}{r}}_{n-2},$

(6.2) demonstration of IVUS pixel data among the VRML

The present invention adopts translucent display mode to the IVUS pixel data that inserts in the virtual scene, and promptly the transparence value of each pixel is not same constant in the frame IVUS image, but depends on the position of pixel in image and its gray value.In the ultrasonoscopy except blood vessel wall and speckle, other structure all should be sightless in virtual scope scene, utilize the two-dimentional segmentation result of front this moment to ultrasonoscopy, to be set to full impregnated bright for the pixel of echo signal beyond expression tube chamber and the adventitia, allows the roaming path to pass through these zones unobstructedly.And for tube wall and these area-of-interests of speckle, its transparence value depends on the gray value of pixel, for example, and the speckle that bright echo signal expresses possibility and exists, so its opacity value should be set to higher numerical value; The tube chamber of other blood vessel may be represented or not have echogenic other structure that its opacity value should be made as lower numerical value in dark space in the image.

(6.3) interactively user graphical interface

The present invention designs and develops out simple and clear clear, convenient, flexible user's control panel in the VRML environment, make it can finish following function: 1. user's opening and closing control panel at any time, and when opening, with as far as possible not the shelter target scene be principle.2. when advancing, at certain viewpoint place, can switch between different display modes by the user along the roaming path for virtual observer, for example: the IVUS image that obtains at this point according to correct direction and position display; The luminal surface (can open or close translucent IVUS frame simultaneously) that perhaps only shows this some place; Perhaps show the luminal surface of having finished coloud coding, wherein coloud coding is represented measures of quantization result etc.Simultaneously, the user can enter or withdraw from the observing pattern of virtual scope at any time, shows the overall appearance of rebuilding the back vessel segment, perhaps major axis longitudinal section image.3. can adjust the speed and the direction of roaming, virtual observer can stop in intraluminal optional position.

Claims (3)

1. the implementation method of an interactive coronary artery virtual angioscope, it is characterized in that, it merges with the tube chamber cross-sectional data that is obtained by intravascular ultrasound mutually by the tube chamber three-dimensional geometry shape information that will be obtained by the X ray coronarography CAG image of nearly orthogonal, obtain the threedimensional model of blood vessel, use Virtual Reality Modeling Language VRML alternatively to describe vascular pattern then, the coronary artery of realizing the scope roam mode is visual, and concrete steps are as follows:

The threedimensional model that A, the intravascular ultrasound IVUS image that utilizes collection simultaneously and X ray coronarography CAG image are set up blood vessel;

Described intravascular ultrasound IVUS image is at the far-end that mechanical type ultrasound catheter probe is placed vessel segment, at the uniform velocity equidistant returning removed in the process of guide wire, the equidistant intravascular ultrasound IVUS image sequence that utilizes the intravascular ultrasound imaging instrument to collect at identical cardiac phase place in the mode of ECG gate, described X ray coronarography CAG image are to utilize C type arm single face X ray angiography machine to return the X ray coronarography CAG image that the starting point of removing the path is taken two width of cloth near normal angles of record same cardiac state at conduit;

The described concrete steps of setting up blood vessel three-dimensional model are as follows:

A, according to two X ray coronarography CAG images that become the near normal angles, reconstruct the three-D ultrasonic conduit and return and remove the path;

B, from X ray coronarography CAG image, reconstruct three-dimensional vessel lumen:

The three-D ultrasonic conduit that reconstructs returned remove the path imaging plane back projection of two X ray coronarography CAG images to the left and right, the bidimensional ultrasound catheter that obtains correspondence returns removes the path, return each point of removing on the path for the bidimensional ultrasound catheter, by returning perpendicular to the bidimensional ultrasound catheter on the direction of removing the path, seek two maximum of shade of gray, obtain the vessel lumen left and right edges, cross section at the hypothesis tube chamber is under the prerequisite of ellipse then, finish the reconstruction of whole three-dimensional vessel lumen, described three-dimensional vessel lumen is used for the follow-up direction in space of determining each frame intravascular ultrasound IVUS image;

The extraction of c, intravascular ultrasound IVUS image sequence medium vessels wall profile:

In first frame intravascular ultrasound IVUS image, manually select the several characteristic point on the inside and outside film profile of blood vessel wall, to connect the formed polygon of these characteristic points as initial position, obtain the profile of the inside and outside film of blood vessel wall by the snake distortion, the speckle that is partitioned into blood vessel wall and may exists, for subsequent frame, then, finish cutting apart to continuous multiple frames intravascular ultrasound IVUS image with the extraction result of former frame initial position as snake;

D, determine the axial location of each frame intravascular ultrasound IVUS image:

According to the acquisition order and the spacing of intravascular ultrasound IVUS image, the three-D ultrasonic conduit that the edge reconstructs returns removes the path with each frame intravascular ultrasound IVUS image sequence arrangement, determines the axial location of each frame intravascular ultrasound IVUS image;

E, determine the dimensional orientation of each frame intravascular ultrasound IVUS image:

Return at the three-D ultrasonic conduit after the reconstruction and to remove the local coordinate system of setting up each frame intravascular ultrasound IVUS image on the path, it is the Frenet-Serret frame, three secondary method vector b of the tangent vector t of the coordinate axes unit of being respectively, the master of unit method vector n and unit, the position of conduit is positioned at the center of intravascular ultrasound IVUS image;

Each frame intravascular ultrasound IVUS image is rotated to its correct direction to determine the dimensional orientation of intravascular ultrasound IVUS image around conduit:

The centrifugal vector of representing the deviation of gravity center catheter position of blood vessel wall profile with ρ, the elliptic contour of the vessel lumen that goes out from X ray coronarography CAG image reconstruction is projected on the corresponding intravascular ultrasound IVUS image, represent that with μ vessel lumen elliptic contour centrage departs from the centrifugal vector of catheter position, ε is the mould of vectorial ρ, θ is the angle of ρ and μ, determine the dimensional orientation of intravascular ultrasound IVUS image sequence with the statistics optimization method, purpose is to make the θ minimum:

Set the moving window of a fixed width w, carry out statistical analysis in this window, there is n in the intravascular ultrasound IVUS image sequence for the N frame is formed _wThe individual moving window of=N-(w-1), at each the window's position m place, accumulative total eccentric distance ∑ ε _m, the eccentric angle meansigma methods of weighting And the weighted standard deviation σ (θ of eccentric angle _m) calculate by following formula respectively:

$\mathrm{\&Sigma;}{\mathrm{\&epsiv;}}_m=\underset{i=m}{\overset{m+(w-1)}{\mathrm{\&Sigma;}}}{\mathrm{\&epsiv;}}_i,$ ${\stackrel{\&OverBar;}{\mathrm{\&theta;}}}_m=\frac{1}{\mathrm{\&Sigma;}{\mathrm{\&epsiv;}}_m}\underset{i=m}{\overset{m+(w-1)}{\mathrm{\&Sigma;}}}{\mathrm{\&epsiv;}}_i{\mathrm{\&theta;}}_i,$ $\mathrm{\&sigma;}{\left({\mathrm{\&theta;}}_m\right)}^2=\frac{1}{\mathrm{\&Sigma;}{\mathrm{\&epsiv;}}_m}\underset{i=m}{\overset{m+(w-1)}{\mathrm{\&Sigma;}}}{\mathrm{\&epsiv;}}_i{({\mathrm{\&theta;}}_i-{\stackrel{\&OverBar;}{\mathrm{\&theta;}}}_m)}^2$

Utilize these numerical value, in each the window's position place, computed reliability weight factor: r _m=∑ ε _m/ σ (ε _m), give bigger weight factor in the bigger position of eccentric distance, limit σ (θ simultaneously _m) bigger position, calculate one by following formula and proofread and correct eccentric angle

${\stackrel{\&OverBar;}{\mathrm{\&theta;}}}_{\mathrm{corr}}=\frac{1}{\mathrm{\&Sigma;r}}\underset{m=0}{\overset{n_w-1}{\mathrm{\&Sigma;}}}{r}_m{\stackrel{\&OverBar;}{\mathrm{\&theta;}}}_m,$ $\mathrm{\&Sigma;r}=\underset{k=0}{\overset{n_w-1}{\mathrm{\&Sigma;}}}{r}_k$

And apply it in all intravascular ultrasound IVUS images of sequence, thereby obtain the dimensional orientation of each frame intravascular ultrasound IVUS image;

The drafting of blood vessel surface is finished in f, utilization based on the surface extraction method of nurbs surface match;

B, utilization Virtual Reality Modeling Language VRML realize coronary artery revascularization result's scope roam mode visual:

Concrete steps are as follows:

1. roam the calculating in path:

Returning the reconstructed results of removing the path according to the three-D ultrasonic conduit, is the current view point position with the coordinate Pi along the i frame intravascular ultrasound IVUS image acquisition point of conduit, P _I+1Be next viewpoint position, with the direction vector of the negative semiaxis of z axle Be the initial viewpoint direction, then in VRML, the position vector of current view point is

Rotating shaft for the current view point direction is

Unit vector Rotating shaft is

The anglec of rotation is

2. intravascular ultrasound IVUS image pixel data is inserted in the virtual scene, and adopts translucent display mode to show;

3. develop interactively user graphical interface.

2. according to the implementation method of the described interactive coronary artery virtual angioscope of claim 1, it is characterized in that, described three-D ultrasonic conduit returns the method for reconstructing of removing the path: at first set up the perspective projection imaging model of X ray coronarography CAG picture system two near normal angles, again according to the distance and the angle parameter of synchronous recording in angiographic procedure, obtain the geometric transformation of imaging system, adopt three-dimensional snake modelling technique then, snake directly is out of shape in the space, finishes the three-D ultrasonic conduit and returns the reconstruction of removing the path.

3. according to the implementation method of the described interactive coronary artery virtual angioscope of claim 2, it is characterized in that, the span of angle is 60 ° to 120 ° between two acquisition angles of described X ray coronarography CAG image, and only returns the starting point of removing the path at the three-D ultrasonic conduit and take a pair of contrastographic picture.

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