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WO2012011014A1 - 3d flow visualization - Google Patents

3d flow visualization Download PDF

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Publication number
WO2012011014A1
WO2012011014A1 PCT/IB2011/053070 IB2011053070W WO2012011014A1 WO 2012011014 A1 WO2012011014 A1 WO 2012011014A1 IB 2011053070 W IB2011053070 W IB 2011053070W WO 2012011014 A1 WO2012011014 A1 WO 2012011014A1
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WO
WIPO (PCT)
Prior art keywords
flow
contrast
vessel
sets
computer program
Prior art date
Application number
PCT/IB2011/053070
Other languages
French (fr)
Inventor
Odile Bonnefous
Sherif Makram-Ebeid
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2012011014A1 publication Critical patent/WO2012011014A1/en

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    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00Image analysis
    • G06T7/20Analysis of motion
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T11/002D [Two Dimensional] image generation
    • G06T11/003Reconstruction from projections, e.g. tomography
    • G06T11/008Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00Indexing scheme for image analysis or image enhancement
    • G06T2207/30Subject of image; Context of image processing
    • G06T2207/30004Biomedical image processing
    • G06T2207/30101Blood vessel; Artery; Vein; Vascular
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00Indexing scheme for image analysis or image enhancement
    • G06T2207/30Subject of image; Context of image processing
    • G06T2207/30004Biomedical image processing
    • G06T2207/30101Blood vessel; Artery; Vein; Vascular
    • G06T2207/30104Vascular flow; Blood flow; Perfusion

Definitions

  • the invention relates to 3D rotational angiography. Particularly, the invention relates to a method and system for visualization of a flow of a fluid in a vessel. Furthermore, the invention relates to a computer program for automatically performing the method.
  • contrast agent injection With contrast agent injection, X-ray produces 2D dynamic sequences of flowing contrast agent within vessels. These images allow the detection and the localization of vessel structures during intervention, useful for a stent placement for instance in coronary or brain aneurysms. On the other hand, 3D rotational angiographic images can be produced to get 3D anatomy of vessels.
  • US 2010/0053209 Al describes a system which creates a visually coated 3D image that depicts 3D vascular function information including transit time of blood flow through the anatomy.
  • the system combines 3D medical image data with vessel blood flow information.
  • the system uses at least one repository for storing 3D image data representing a 3D imaging volume including vessels, in the presence of a contrast agent and 2D image data representing a 2D X-ray image through the imaging volume in the presence of a contrast agent.
  • An image data processor uses the 3D image data and the 2D image data in deriving blood flow related information for the vessels.
  • a display processor provides data representing a composite single displayed image including a vessel structure provided by the 3D image data and the derived blood flow related information.
  • the invention proposes to use only one 3D acquisition to produce 3D anatomy and 3D flow sequences.
  • 3D anatomy and pulsatile time variing flow information are produced with the unique 3D acquisition.
  • the 3D flow information obtained overcome limitations linked to 2D contrast flow sequence acquisitions.
  • Another essential advantage of this invention is that the flow information is directly extracted from patient specific imaging data. In particular, it does not rely on flow simulation as it is offered with computer flow dynamic packages.
  • only one 3D acquisition of an object of interest may be performed, a 3D image of the object is reconstructed on the basis of the received data, and a vessel structure in which a fluid is flowing is identified.
  • the acquired data consist in a set of projected views acquired through the rotation of the X-Ray source, detector assembly, around the object of interest.
  • anatomical representation of the vascular stucture is first computed. Taking advantage of the modulation of the contrast produced by the pulsatility of the arterial flow at the injection point, the data are processed in order to identify and extract the temporal modulation of the contrast agent.
  • the contrast variations due to geometrical perspective variations are seperated from temporal contrast modulation variations prior the 3D contrast sequence reconstruction step.
  • the total contrast variations are reconstructed in function of time everywhere in the volume, and show the propagation of the modulation wihtin the arterial imaged volume. Furthermore, such reconstruction may be wisualized. Also, the flow of the fluid within the vessel may be computed and based on the achieved results, and a flow representation (e.g. the blood velocity), usually together with the vessel structure is visualized.
  • a flow representation e.g. the blood velocity
  • this method may be performed on a system for visualizing a flow of a fluid in a vessel, which comprises
  • the system further comprises an X-ray source and an X-ray detector, both movable around an object of interest, for generating data of a 3D acquisition.
  • a corresponding computer program is preferably loaded into a work memory of the processing unit.
  • the processing unit is thus equipped to carry out the method of the invention.
  • the invention relates to a computer-readable medium such as a CD-ROM at which the computer program may be stored.
  • the computer program may also be presented over a network like the Worldwide Web and can be downloaded into the work memory of the processing unit from such a network.
  • the data of one 3D acquisition may be stored for example at a database and may be received from that database, or may be acquired immediately from an X- ray detector being part of a C-arm or an X-ray gantry.
  • the system according to the invention may further comprise an input device giving a user the possibility to, for example, choose a view or a direction from which a reprojection should be reconstructed.
  • the processing unit may be realized by only one processor performing all the steps of the invention, or by a group or plurality of processors, for example a system processor for processing the image data, a separate processor specialized on a simulation or representation of a flow of fluid, and a further processor for controlling a monitor for visualizing the result.
  • Fig. 1 is a flow-chart of steps of the method in accordance with the invention.
  • Fig. 2 shows an exemplary visualization of aspects of the method.
  • Fig. 3 shows further aspects of the method.
  • Fig. 4 shows a schematic illustration of an user interface.
  • Fig. 5 is a schematic illustration of a system according to the invention.
  • Fig. 6 shows a comparison of simulated and reconstructed contrast curves.
  • Fig. 7 shows transversal slices and projections of a volume of a 3D sequence.
  • Fig. 1 illustrates the principles of the steps performed in accordance with preferred embodiments of the invention. It will be understood that the steps described are major steps, wherein these major steps might be differentiated or divided into several sub-steps. Furthermore, there might be also sub-steps between these major steps.
  • step SI data of one 3D acquisition especially a 3D RA acquisition (3D rotational angiography acquisition) is generated.
  • These generated data may for example be stored in a memory, and will be transmitted to a processing unit later.
  • step S2 the data of the one 3D acquisition is received by the processing unit.
  • the processing unit As it is possible to receive these data from the above-mentioned memory, it is also possible to immediately receive the data from an X-ray detector.
  • Collection of projection images may be acquired with a rotational system providing a set of projection images each of them being characterized by a projection direction.
  • step S3 a 3D volume is reconstructed using the projection images acquired with the rotational system.
  • Each image is a projection of the injected volume characterized by the angle defining the projection direction.
  • static 3D data are reconstructed.
  • the resulting reconstruction represents the mean 3D object during the rotational sequence.
  • step S4 vessel structures are segmented, for instance, using adapted local thresholding techniques.
  • a 3D mask may be produced on the basis of the segmented vessel structure. By means of this, overlapping parts may be masked before a re-projection, allowing better contrast flow imaging.
  • step S6 a temporal filtering is performed. Due to flow pulsatility, contrast agent mixing varies during injection. When blood flow is fast (systolic flow), more blood is flowing and contrast agent density is low. When flow is slow (diastolic flow), less blood is flowing and contrast density is high. This produces a time modulation of contrast characterized by the cardiac frequency, which propagates within the arterial tree with the natural blood flow.
  • step S7 a view or viewing direction may be chosen.
  • step S8 a flow sequence may be reprojected for this chosen view. It is noted, that also views are possible, which are not accessible with conventional 2D projection acquisitions.
  • step S9 a flow of a fluid is computed in 3D.
  • the cardiac frequency f is used to seperate this cardiac frequency modulation during reconstruction.
  • the successive projection images /( ⁇ (t)) defined by their projection angles ( (t) at time t are multiplied with complex exponential e ⁇ j2 fct .
  • the 3D reconstruction operation R is performed on the 2 components (real and imaginary) of the product set /( ⁇ (t)) * e ⁇ J2 fJ .
  • V(t) M * Re al( 7( ⁇ ( ) * ⁇ ;2 ⁇ / ⁇ ) * e %ft ) ,
  • step S 10 a representation of the flow in 3D is produced, for example streamlines and velocity fields.
  • step SI 1 the flow representation, i.e. the contrast modulation and flow pattern are visualized together with the vessel structure.
  • Figures 2 and 3 show an exemplary visualization of the method according to preferred embodiments of the invention.
  • data are used acquired with a rotation system such as the ones used for 3DRA imaging or CT procedures.
  • a rotation system such as the ones used for 3DRA imaging or CT procedures.
  • temporal 3D sequences of flowing contrast within the vessel tree is reconstructed, at each position.
  • An important technical issue, as also stated above, is the separation of the effect of rotation on the projections from the time modulation of the contrast product.
  • ART Algebraic Reconstruction Technique is a well-known iterative algorithm for the reconstruction of a two-dimensional image from a series of one-dimensional angular projections (a sinogram) typically used in Computed Tomography scanning).
  • the time variations are generally ignored, except when structure displacements are involved, like in cardiac 3D reconstruction. In that case, specific 3D records, synchronized on cardiac frequency are used, giving access to 3D geometry.
  • the reconstructed contrast value is not accurately defined. According to the invention, a different problem is in focus. Objects are considered well localized in space. The contrast variations through a pulsatile periodic modulation due to the pulsatile flow are considered, which is a very strong condition.
  • Figure 2 illustrates the possible separation of projection acquisition variations and contrast modulation in a plane perpendicular to the rotation axis.
  • 2D objects of the cut plane are considered projected on ID projection lines, as shown at I(t) in figure 2.
  • the projection operation is then simply performed using a Radon transformation.
  • the projected object consists of two rectangles characterized by the same dimensions, one being pusatile (upper left corner in I(t)), the other one being static (lower right corner in I(t)).
  • the Radon transform is presented beside on the right side, and mimicking the acquisition system action, displays the two objects differently, the pulsatile one inducing a modulation visible in the projected rays.
  • the next step of the process deals with the 2D sequence reconstruction. It is illustrated on figure 3.
  • the projected pulsatile component is demodulated with the complex exponential defined by the pulsation frequency. It is well known that this operation produces an oscillatory component at the double frequency, and a static component. As described previously, the oscillatory component will be cancelled out by the reconstruction. But the constant one will produce a reconstructed object, containing the phase distribution of the contrast modulation.
  • the reconstruction step associated to the complex product operates as temporal Fourier transform.
  • the temporal 2D sequence is now easy to be fully generated by adding the static component already computed to the remodulated reconstructed component.
  • Fig. 4 shows an exemplary user interface providing for an interaction of a user with the system.
  • a user interface provides for the possibility, to choose a kind of a flow representation as well as a special view and mask on a basis of a 3D reconstruction of the object of interest.
  • the user interface 100 includes an icon for segmentation 110. Further the user interface shows on the left side rotation 120, projection 130 and 2D optical flow 140. On the right side, the user interface 100 shows flow representations like 3D optical flow 150, 3D flow vectors 160, 3D streamlines 170, planar flow cuts 180 as well as flow curves 190.
  • Fig. 5 shows an exemplary embodiment of a system according to the invention. Substantially, necessary for performing the steps according to the invention, a processing unit 100 together with a monitor 400 is part of the system.
  • the exemplary imaging device 200 includes an X-ray source 240, and an X-ray detector 260, wherein these two devices are mounted on a C-arm 220. It will be understood that the system in accordance with the invention may also comprise a non-invasive imaging modality like a computer tomography device, a magnetic resonance device, or an ultrasound device as imaging device instead of or additional to the shown C-arm based X-ray device.
  • a non-invasive imaging modality like a computer tomography device, a magnetic resonance device, or an ultrasound device as imaging device instead of or additional to the shown C-arm based X-ray device.
  • system in Fig. 5 includes an input device 300, by means of which for example a manual selection of the point of view or the flow representation may be performed. Also shown is a connection (as dotted line) to a database 600, located for example in a network.
  • a region of interest 500 for example a heart of a patient may be located.
  • a test object is considered made of one tube inserted in another one. Contrast flows are different in the two tubes. The flows circulate in opposite directions, and the velocity profiles are of different nature too: the velocity profile inside the internal tube is parabolic, while the velocity profile inside the external one is flat. Flow orientation is parallel to the rotational axis. Three harmonic components of the pseudo cardiac frequency are used in the definition of flow patterns. Relations and transport equations are used to mimic the progression of contrast within the tubes in the 3D volume (as described above). This simulation allowed generating the set of 360 2D projections describing the full rotation.
  • the reconstruction operation is implemented. At the end of the processing channel, a 3D sequence of the contrast within the two tubes is received.
  • reconstruction sequence allows to measure contrast temporal variations everywhere within the object.
  • FIG. 6 shows such contrast curves synthesized and measured after reconstruction in the two tubes.
  • the left diagram compares simulated and reconstructed curves at the center of the internal tube.
  • the right diagram presents same results extracted from the external tube. A very good fit between these curves can be seen.
  • the 3D shapes of the two tubes are known and can be used to extract particular temporal 3D objects from the volume. From the 3D reconstructed sequence, projection sequences of the tube set, and projection sequences of each tube segmented out from the full 3D sequence are produced. The direct projection of the two inverted flows does not allow to interpret the 2D sequence. When each tube is projected independently, a clear indication of the flow direction is received, and the contrast progression may be apprehended.
  • Figure 7 presents one image of these projected sequences.
  • image (A) three slices of the tubes, distributed along the axes are shown.
  • B the full projection is presented, showing unclear contrast pattern.
  • the projection on the internal tube (C) depicts the parabolic shape of the velocity profile while the last projection (D), involving only the external tube exhibits a flat profile.
  • the computer program may be stored/distributed on a suitable medium such as an optical storage medium or a solid-state medium supplied together with or as a part of another hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope

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Abstract

In accordance with the invention only one 3D acquisition of an object of interest is performed, a 3D image of the object is reconstructed on the basis of the received data, and a vessel structure in which a fluid is flowing is identified. Furthermore, the flow of the fluid within the vessel is computed and based on the achieved results, a flow representation, usually together with the vessel structure is visualized.

Description

3D FLOW VISUALIZATION
FIELD OF THE INVENTION
The invention relates to 3D rotational angiography. Particularly, the invention relates to a method and system for visualization of a flow of a fluid in a vessel. Furthermore, the invention relates to a computer program for automatically performing the method.
BACKGROUND OF THE INVENTION
With contrast agent injection, X-ray produces 2D dynamic sequences of flowing contrast agent within vessels. These images allow the detection and the localization of vessel structures during intervention, useful for a stent placement for instance in coronary or brain aneurysms. On the other hand, 3D rotational angiographic images can be produced to get 3D anatomy of vessels.
US 2010/0053209 Al describes a system which creates a visually coated 3D image that depicts 3D vascular function information including transit time of blood flow through the anatomy. The system combines 3D medical image data with vessel blood flow information. The system uses at least one repository for storing 3D image data representing a 3D imaging volume including vessels, in the presence of a contrast agent and 2D image data representing a 2D X-ray image through the imaging volume in the presence of a contrast agent. An image data processor uses the 3D image data and the 2D image data in deriving blood flow related information for the vessels. A display processor provides data representing a composite single displayed image including a vessel structure provided by the 3D image data and the derived blood flow related information.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method and system by means of which a radiation dose for a patient is reduced. It may be seen as a further object of the invention to provide a method and system by means of which more information may be gathered from a reduced number of X-ray images. This is achieved by the subject-matter of each of the independent claims. Further embodiments are described in respective dependent claims.
In general, the invention proposes to use only one 3D acquisition to produce 3D anatomy and 3D flow sequences. 3D anatomy and pulsatile time variing flow information are produced with the unique 3D acquisition. The 3D flow information obtained overcome limitations linked to 2D contrast flow sequence acquisitions.
Another essential advantage of this invention is that the flow information is directly extracted from patient specific imaging data. In particular, it does not rely on flow simulation as it is offered with computer flow dynamic packages.
With the reconstruction scheme according to the invention a temporal 3D sequence of flowing contrast agent within the vessel tree at each position is reconstructed. An important technical issue resolved here is to separate the effect of rotation on the projections from the time modulation of the flowing contrast product.
In accordance with embodiments only one 3D acquisition of an object of interest may be performed, a 3D image of the object is reconstructed on the basis of the received data, and a vessel structure in which a fluid is flowing is identified. The acquired data consist in a set of projected views acquired through the rotation of the X-Ray source, detector assembly, around the object of interest. With this input data, anatomical representation of the vascular stucture is first computed. Taking advantage of the modulation of the contrast produced by the pulsatility of the arterial flow at the injection point, the data are processed in order to identify and extract the temporal modulation of the contrast agent. To enable computation of the fluid flow, the contrast variations due to geometrical perspective variations are seperated from temporal contrast modulation variations prior the 3D contrast sequence reconstruction step. The total contrast variations are reconstructed in function of time everywhere in the volume, and show the propagation of the modulation wihtin the arterial imaged volume. Furthermore, such reconstruction may be wisualized. Also, the flow of the fluid within the vessel may be computed and based on the achieved results, and a flow representation (e.g. the blood velocity), usually together with the vessel structure is visualized.
According to a further embodiment of the invention, this method may be performed on a system for visualizing a flow of a fluid in a vessel, which comprises
substantially a processing unit and a monitor.
According to another embodiment of the invention, the system further comprises an X-ray source and an X-ray detector, both movable around an object of interest, for generating data of a 3D acquisition.
A corresponding computer program is preferably loaded into a work memory of the processing unit. The processing unit is thus equipped to carry out the method of the invention. Further, the invention relates to a computer-readable medium such as a CD-ROM at which the computer program may be stored. However, the computer program may also be presented over a network like the Worldwide Web and can be downloaded into the work memory of the processing unit from such a network.
It is noted, that the data of one 3D acquisition may be stored for example at a database and may be received from that database, or may be acquired immediately from an X- ray detector being part of a C-arm or an X-ray gantry.
The system according to the invention may further comprise an input device giving a user the possibility to, for example, choose a view or a direction from which a reprojection should be reconstructed.
It is noted, that the processing unit may be realized by only one processor performing all the steps of the invention, or by a group or plurality of processors, for example a system processor for processing the image data, a separate processor specialized on a simulation or representation of a flow of fluid, and a further processor for controlling a monitor for visualizing the result.
It has to be noted that embodiments of the invention are described with reference to different subject-matters. In particular, some embodiments are described with reference to method type claims (including computer program) whereas other embodiments are described with reference to apparatus type claims (system). However, a person skilled in the art will gather from the above and the following description that unless other notified in addition to any combination of features belonging to one type of subject-matter also any combination between features relating to different subject-matters is considered to be disclosed with this application.
The aspects defined above and further aspects, features and advantages of the present invention can also be derived from the examples of the embodiments to be described hereinafter and are explained with reference to examples of embodiments also shown in the figures, but to which the invention is not limited.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow-chart of steps of the method in accordance with the invention.
Fig. 2 shows an exemplary visualization of aspects of the method. Fig. 3 shows further aspects of the method.
Fig. 4 shows a schematic illustration of an user interface. Fig. 5 is a schematic illustration of a system according to the invention.
Fig. 6 shows a comparison of simulated and reconstructed contrast curves. Fig. 7 shows transversal slices and projections of a volume of a 3D sequence.
DETAILED DESCRIPTION OF EMBODIMENTS
The flow-chart in Fig. 1 illustrates the principles of the steps performed in accordance with preferred embodiments of the invention. It will be understood that the steps described are major steps, wherein these major steps might be differentiated or divided into several sub-steps. Furthermore, there might be also sub-steps between these major steps.
Therefore, a sub-step is only mentioned if this step may be important for the understanding of the principles of the method according to the invention.
In step SI data of one 3D acquisition, especially a 3D RA acquisition (3D rotational angiography acquisition) is generated. These generated data may for example be stored in a memory, and will be transmitted to a processing unit later.
In step S2, the data of the one 3D acquisition is received by the processing unit. As it is possible to receive these data from the above-mentioned memory, it is also possible to immediately receive the data from an X-ray detector.
Collection of projection images may be acquired with a rotational system providing a set of projection images each of them being characterized by a projection direction.
In step S3, a 3D volume is reconstructed using the projection images acquired with the rotational system. Each image is a projection of the injected volume characterized by the angle defining the projection direction. With known reconstruction techniques, static 3D data are reconstructed. The resulting reconstruction represents the mean 3D object during the rotational sequence.
In step S4, vessel structures are segmented, for instance, using adapted local thresholding techniques.
In step S5, a 3D mask may be produced on the basis of the segmented vessel structure. By means of this, overlapping parts may be masked before a re-projection, allowing better contrast flow imaging.
In step S6, a temporal filtering is performed. Due to flow pulsatility, contrast agent mixing varies during injection. When blood flow is fast (systolic flow), more blood is flowing and contrast agent density is low. When flow is slow (diastolic flow), less blood is flowing and contrast density is high. This produces a time modulation of contrast characterized by the cardiac frequency, which propagates within the arterial tree with the natural blood flow.
In step S7, a view or viewing direction may be chosen.
In step S8, a flow sequence may be reprojected for this chosen view. It is noted, that also views are possible, which are not accessible with conventional 2D projection acquisitions.
In step S9, a flow of a fluid is computed in 3D.
The cardiac frequency f is used to seperate this cardiac frequency modulation during reconstruction. The successive projection images /(Θ (t)) defined by their projection angles ( (t) at time t are multiplied with complex exponential e~j2 fct . The 3D reconstruction process performs the time integration and produce a 3D time Fourier component of the 3D flow sequence V(f) = R(I(Q (t)) * e~j2nft ) . The 3D reconstruction operation R is performed on the 2 components (real and imaginary) of the product set /(Θ (t)) * e~J2 fJ . The correspondent time 3D sequence is generated using the product V(t) = V(f) * ej2%fJ .
A full frequency spectrum, describing more in detail the flow modulation may be used for this reconstruction. The 3D reconstructed Flow sequence is expressed as flows:
V(t) = M * Re al( 7(θ ( ) * έ ;2π/ί ) * e %ft ) ,
/
where the mask M is used to extract the Vessel object.
In step S 10, a representation of the flow in 3D is produced, for example streamlines and velocity fields.
Finally in step SI 1 , the flow representation, i.e. the contrast modulation and flow pattern are visualized together with the vessel structure.
Figures 2 and 3 show an exemplary visualization of the method according to preferred embodiments of the invention. In this example, data are used acquired with a rotation system such as the ones used for 3DRA imaging or CT procedures. With the adequate reconstruction scheme, described in the following, temporal 3D sequences of flowing contrast within the vessel tree is reconstructed, at each position. An important technical issue, as also stated above, is the separation of the effect of rotation on the projections from the time modulation of the contrast product.
When acquiring rotational angiographic sequences, the variations observed from one image to the following one is mainly due to the change of the perspective angle. This assumption is the basis of all the 3D reconstruction techniques like FDK (Feldkamp reconstruction algorithm as known notably from "Practical cone-beam algorithm", L. A.
Feldkamp, L. C. Davis, and J. W. Kress, JOSA A, Vol. 1, Issue 6, pp. 612-619 (1984)), ART (Algebraic Reconstruction Technique is a well-known iterative algorithm for the reconstruction of a two-dimensional image from a series of one-dimensional angular projections (a sinogram) typically used in Computed Tomography scanning). The time variations are generally ignored, except when structure displacements are involved, like in cardiac 3D reconstruction. In that case, specific 3D records, synchronized on cardiac frequency are used, giving access to 3D geometry. However, it is known that the reconstructed contrast value is not accurately defined. According to the invention, a different problem is in focus. Objects are considered well localized in space. The contrast variations through a pulsatile periodic modulation due to the pulsatile flow are considered, which is a very strong condition.
It is easier to analyze this problem using a 2D example: Figure 2 illustrates the possible separation of projection acquisition variations and contrast modulation in a plane perpendicular to the rotation axis. In this case 2D objects of the cut plane are considered projected on ID projection lines, as shown at I(t) in figure 2. The projection operation is then simply performed using a Radon transformation. The projected object consists of two rectangles characterized by the same dimensions, one being pusatile (upper left corner in I(t)), the other one being static (lower right corner in I(t)).The Radon transform is presented beside on the right side, and mimicking the acquisition system action, displays the two objects differently, the pulsatile one inducing a modulation visible in the projected rays. Applying the inverse radon transform, a static object is reconstructed showing two identical static rectangles correctly positioned in the reconstruction plane. This reconstructed object is reprojected using the Radon transform again, and of course, no more contrast modulation is observed on the projection trace of the initial pulsatile rectangle. When operating the subtraction of this 'static' reprojected data to the original one, the projection of the modulated part of the contrast is received. The separation of the two time variation effects is accomplished.
The next step of the process deals with the 2D sequence reconstruction. It is illustrated on figure 3. The projected pulsatile component is demodulated with the complex exponential defined by the pulsation frequency. It is well known that this operation produces an oscillatory component at the double frequency, and a static component. As described previously, the oscillatory component will be cancelled out by the reconstruction. But the constant one will produce a reconstructed object, containing the phase distribution of the contrast modulation. The reconstruction step associated to the complex product operates as temporal Fourier transform. The temporal 2D sequence is now easy to be fully generated by adding the static component already computed to the remodulated reconstructed component.
Fig. 4 shows an exemplary user interface providing for an interaction of a user with the system. Such a user interface provides for the possibility, to choose a kind of a flow representation as well as a special view and mask on a basis of a 3D reconstruction of the object of interest.
In Fig. 4, the user interface 100 includes an icon for segmentation 110. Further the user interface shows on the left side rotation 120, projection 130 and 2D optical flow 140. On the right side, the user interface 100 shows flow representations like 3D optical flow 150, 3D flow vectors 160, 3D streamlines 170, planar flow cuts 180 as well as flow curves 190.
Fig. 5 shows an exemplary embodiment of a system according to the invention. Substantially, necessary for performing the steps according to the invention, a processing unit 100 together with a monitor 400 is part of the system.
The exemplary imaging device 200 includes an X-ray source 240, and an X-ray detector 260, wherein these two devices are mounted on a C-arm 220. It will be understood that the system in accordance with the invention may also comprise a non-invasive imaging modality like a computer tomography device, a magnetic resonance device, or an ultrasound device as imaging device instead of or additional to the shown C-arm based X-ray device.
Furthermore, the system in Fig. 5 includes an input device 300, by means of which for example a manual selection of the point of view or the flow representation may be performed. Also shown is a connection (as dotted line) to a database 600, located for example in a network.
Finally, there is shown a region of interest 500. Within said region, for example a heart of a patient may be located.
To prove the validity of the principle detailed above, a 3D sequence simulation has been performed. This allows understanding the mechanisms involved in these processes. With simulation, it is possible to compare input data to reconstructed one with objective measures.
For the sake of demonstrative results, a test object is considered made of one tube inserted in another one. Contrast flows are different in the two tubes. The flows circulate in opposite directions, and the velocity profiles are of different nature too: the velocity profile inside the internal tube is parabolic, while the velocity profile inside the external one is flat. Flow orientation is parallel to the rotational axis. Three harmonic components of the pseudo cardiac frequency are used in the definition of flow patterns. Relations and transport equations are used to mimic the progression of contrast within the tubes in the 3D volume (as described above). This simulation allowed generating the set of 360 2D projections describing the full rotation.
The reconstruction operation is implemented. At the end of the processing channel, a 3D sequence of the contrast within the two tubes is received.
This combination of tubes, one inside the other ones, gives a clear demonstration of the validity of the main idea. Indeed, with 2D projections only, there is absolutely no way to get a clear image of what is happening within each tube. 3D
reconstruction sequence allows to measure contrast temporal variations everywhere within the object.
In order to judge of the consistency of the results, contrast curves describing original contrast variations are compared to the reconstructed ones. Figure 6 shows such contrast curves synthesized and measured after reconstruction in the two tubes. The left diagram compares simulated and reconstructed curves at the center of the internal tube. The right diagram presents same results extracted from the external tube. A very good fit between these curves can be seen.
The 3D shapes of the two tubes are known and can be used to extract particular temporal 3D objects from the volume. From the 3D reconstructed sequence, projection sequences of the tube set, and projection sequences of each tube segmented out from the full 3D sequence are produced. The direct projection of the two inverted flows does not allow to interpret the 2D sequence. When each tube is projected independently, a clear indication of the flow direction is received, and the contrast progression may be apprehended.
Figure 7 presents one image of these projected sequences. On top of the image (A), three slices of the tubes, distributed along the axes are shown. On B, the full projection is presented, showing unclear contrast pattern. On the contrary, the projection on the internal tube (C) depicts the parabolic shape of the velocity profile while the last projection (D), involving only the external tube exhibits a flat profile. These results are even more impressive when animated sequences are displayed.
While the invention has been illustrated and described in detail in the drawings and aforegoing description, such illustrations and descriptions are to be considered illustrative or exemplary and not restrictive, the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practising the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the wording "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims.
The mere fact that certain measures are recited and mutually different dependent claims does not indicate that a combination of these measures can not be used to advantage. The computer program may be stored/distributed on a suitable medium such as an optical storage medium or a solid-state medium supplied together with or as a part of another hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope
LIST OF REFERENCE SIGNS:
100 Processing unit
120 rotation
130 projection
140 2D optical flow
150 3D optical flow
160 3D flow vectors
170 3D streamlines
180 planar flow cuts
190 flow curves
200 Imaging device
220 C-arm
240 X-ray source
260 X-ray detector
300 Input device
400 Monitor
500 Region of interest
510 Heart
600 Database

Claims

CLAIMS:
1. A computer program for reconstructing a 3D sequence of flow of a fluid within a vessel, the computer program comprising:
sets of instructions for receiving data of one 3D acquisition of an original object, sets of instructions for reconstructing a 3D image of the original object on the basis of the received data,
sets of instructions for segmenting vessel structures in the 3D image,
sets of instructions for separating of contrast variations due to geometrical perspective variations from temporal contrast modulation variations,
sets of instruction for reconstructing 3D sequences of temporal contrast modulations in the vessel structures, based on the temporal contrast modulation variations,
sets of instructions for visualizing at least the vessel structure and the reconstruted 3D sequences of temporal contrast modulation in the vessel structures.
2. The computer program of claim 1, further comprising sets of instructions for computing flow of a fluid in the vessel structures, for generating and visulaizing a
representation of this computed flow.
3. The computer program of claim 1, wherein the separating includes applying an inverse contrast transformation to reconstruct a static object, reprojecting the reconstructed object using the contrast transformation again, and substracting the static object from the original object to achieve a projection of the contrast modulation variations.
4. The computer program of claim 1, further comprising sets of instructions for masking overlapping parts in the 3D image.
5. The computer program of claim 1, further comprising sets of instructions for identifying a view and for generating a reprojection based on the identified view on the 3D image.
6. The computer program of claim 1, further comprising sets of instructions for generating the data of one 3D acquisition.
7. A method for visualizing a flow of a fluid in a vessel, the method comprising the steps of:
performing one 3D acquisition of an object of interest,
reconstructing a 3D image of the object of interest,
identifying a vessel structure in which a fluid is flowing,
separating contrast variations due to geometrical perspective variations from temporal contrast modulation variations,
reconstructing 3D sequences of temporal contrast modulations in the vessel structures, based on the temporal contrast modulation variations;
visualizing at least the vessel structure and the reconstituted 3D sequences of temporal contrast modulation in the vessel structures a flow representation together with the vessel structure.
8. The method of claim 7, further comprising computing flow of a fluid in the vessel structures, generating and visulaizing a representation of this computed flow.
9. The method of claim 7, wherein the separating includes applying an inverse contrast transformation to reconstruct a static object, reprojecting the reconstructed object using the contrast transformation again, and substracting the static object from the original object to achieve a projection of the contrast modulation variations.
10. The method of claim 7, further comprising masking overlapping parts in the 3D image.
11. The method of claim 7, further comprising identifying a view and for generating a reprojection based on the identified view on the 3D image.
12. A system for visualizing a flow of a fluid in a vessel, the system comprising: a processing unit, a monitor coupled with the processing unit, and
a computer program according to claim 1,
wherein the computer program, when executed on the processing unit, causes the processing unit to visualize on the monitor a flow representation of a fluid together with a vessel structure, based on data of one 3D acquisition.
13. The system of claim 12, further comprising an X-ray source and an X-ray detector, both movable around an object of interest, for generating data of one 3D acquisition.
14. The system of claim 12, further comprising an input device for manually identifying a view for a reprojection.
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