News Column

Patent Issued for Method for Characterizing a Blood Vessel

September 11, 2014



By a News Reporter-Staff News Editor at Computer Weekly News -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventor Ohlson, Fredrik (Torslanda, SE), filed on September 10, 2010, was published online on August 26, 2014.

The assignee for this patent, patent number 8818061, is Orzone AB (Goteborg, SE).

Reporters obtained the following quote from the background information supplied by the inventors: "Angiography is a medical imaging technique to image blood vessels and blood vessel systems, and can be used for example to enable diagnostics, surgical planning, and simulation.

"Angiographic image data can be generated by injecting a contrast agent intravenously to a patient and scanning the patient using e.g. Computed Tomography (CT) or Magnetic Resonance Imaging (MRI). The resulting angiographic image data is typically a set of DICOM-images forming a voxel volume with discrete image intensities. The voxel volume can be processed to segment organs, blood vessels, skeleton etc. In particular, the segmentation and further characterization can provide a segmented surface that delimits the blood vessel or vessel system from other tissues.

"An example of such a characterization method for characterizing a vascular system in a three-dimensional angiographic image comprised of voxels is disclosed in U.S. Pat. No. 6,842,638. Here a two-dimensional slice formed of pixels is extracted from the angiographic image. Imaged vascular structures in the slice are located and flood-filled. The edges of the filled regions are iteratively eroded to identify vessel centres. The extracting, locating, flood-filling, and eroding is repeated for a plurality of slices to generate a plurality of vessel centres that are representative of the vascular system. A vessel centre is selected, and a corresponding vessel direction and orthogonal plane are found. The vessel boundaries in the orthogonal plane are identified by iteratively propagating a closed geometric contour arranged about the vessel centre. The selecting, finding, and estimating are repeated for the plurality of vessel centres, and the estimated vessel boundaries are then interpolated to form a vascular tree.

"However, sometimes a portion of the boundary of a blood vessel may be 'missing', or not discernable, such that the boundary does not continuously enclose the blood vessel in the dimensional slice. If so, the flood-filling procedure will fail as it expands outside the blood vessel. This makes the method suggested in U.S. Pat. No. 6,842,638 sensitive to imperfections in the DICOM-image. Thus, there is a need for a more robust method to characterize a blood vessel."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "In view of the above, an object of the invention is to at least alleviate the problem discussed above. According to an aspect of the invention, there is provided a method for characterizing a blood vessel represented by vascular image data from a DICOM-image, wherein the vascular image data comprises a plurality of voxels each having an image intensity. The method comprises the steps of identifying a set of voxels representing at least a portion of a boundary of the blood vessel, determining a gradient vector of the image intensity for each voxel in the set of voxels representing the boundary of the blood vessel, selecting, from the set of voxels representing the boundary of the blood vessel, a subset of voxels such that all voxels in the subset of voxels have a common intersection point for their respective gradient vector extensions, and determining a vector product based on the gradient vectors for the subset of voxels, wherein the common intersection point indicates a centre of the blood vessel and the vector product indicates a direction in which the blood vessel extends.

"The present invention is based on the understanding that since a blood vessel typically has a tubular shape, the gradient vectors of the image intensities at the boundary of the blood vessel will be directed radially outwards and thus the point where extensions of these gradient vectors meet may serve as an indication of the centre of the blood vessel. Furthermore, the vector product between two gradient vectors located at the boundary can be used to indicate the direction in which the blood vessel extends. The inventive method is advantageous in that even though a portion of the boundary is missing, or not discernable, the centre of the blood vessel may still be found from the available portion of the boundary.

"A boundary is here intended to indicate a segment of the blood vessel that delimits the blood vessel from other tissue. It shall be noted that the boundary may be continuous or discontinuous (i.e. a portion of the boundary may be missing). The common intersection point may typically be a small discrete volume. For example, the subset may include all voxels having gradient vector extensions that pass through a common voxel. Further, each gradient vector extension starts from the voxel in which the gradient vector is calculated.

"A set of voxels representing a boundary of the blood vessel can be found by computing a gradient vector of the image intensity for each of the plurality of voxels, and selecting a set of voxels having a gradient vector norm that exceeds a predetermined threshold value. Note that, in this case, the gradient vectors for the voxels are determined before the set of voxels representing the boundary of the blood vessel is identified, instead of after.

"According to an embodiment, any voxel that has an adjacent voxel, in a direction of the gradient vector, with a larger gradient vector norm may be excluded from the set of voxels representing the boundary of a blood vessel. An advantage is that this may result in a thinner, more well-defined boundary region. This can also be achieved by only including voxels where a second derivative of the image intensity is essentially zero.

"Preferably, the gradient vector extension may be adapted to extend in a direction opposite to the direction of the gradient vector. Furthermore, a length of the gradient vector extension may be determined by a predetermined end condition. An example of an end condition would be that the gradient vector extension only extends until the opposite boundary of the blood vessel is reached, or that the gradient vector extension extends a predetermined length. The predetermined length may preferably be set sufficiently low to prevent that the gradient vector extension intersects gradient vector extensions associated with other blood vessels. An advantage with putting restrictions on the length of the gradient vector extension is that the risk of unintentionally including gradient vector extensions from adjacent blood vessels in the subset of voxels having a common intersection point for their respective gradient vector extensions is reduced.

"The method may further comprise the step of iteratively selecting an additional subset of voxels from the set of voxels representing the boundary of the blood vessel, wherein all voxels in the additional subset of voxels have a common intersection point for their respective gradient vector extensions and the common intersection point indicates a possible centre point of the blood vessel.

"Furthermore, the method according to the present invention may advantageously be included in a method for determining a blood vessel path by: finding a plurality of possible centre points of the blood vessel, selecting a voxel that corresponds to one of the centre points as a starting point for the blood vessel, tracing the blood vessel path by iteratively: identifying a possible centre point that is located in a plane that is orthogonal to the direction of the blood vessel, wherein the plane extends through a voxel that is located within a predetermined range from (e.g. next to) the current centre point in a direction of the blood vessel, including the identified possible centre point in the blood vessel path. The predetermined range may preferably be one voxel thereby making full use of the resolution in the DICOM-image.

"Additionally, when there is more than one possible centre point located in the plane, the centre point to be included in the vessel path may be selected by iteratively comparing the gradient vector norm of the current voxel with the gradient vector norm of all neighbouring voxels located in the plane and changing to the neighbouring voxel located in the plane that has the largest gradient vector norm until a voxel is found having a gradient vector norm larger than all neighbouring voxels in the plane.

"Tracing of the blood vessel path may preferably stop when an end condition is fulfilled. The end condition may, for example, be at least one of that the boundary of the voxel volume is reached, that a blood vessel path that has already been traced is reached, that the intensity of the centre point is below a predetermined threshold value and that the vector product associated with the centre point is a zero vector. The method may also comprise the step of removing vessel paths that are not attached to the rest of the vessel structure. This removes objects that are not blood vessels.

"Also, the method according to the present invention may advantageously be included in a method for creating a blood vessel system by: determining a plurality of blood vessel paths as described above, removing blood vessel paths that are not attached to the rest of the blood vessel system. Additionally, after a blood vessel path has been determined, a blood vessel surface may be created by sampling in a plane normal to a direction of the path.

"According to another aspect of the present invention there is provided a device for characterizing a blood vessel represented by vascular image data from a DICOM-image, wherein said vascular image data comprises a plurality of voxels each having an image intensity, said device comprising means for identifying a set of voxels representing at least a portion of a boundary of the blood vessel, determining a gradient vector of the image intensity for each voxel in said set of voxels representing the boundary of the blood vessel, selecting, from said set of voxels representing the boundary of the blood vessel, a subset of voxels such that all voxels in said subset of voxels have a common intersection point for their respective gradient vector extensions, and determining a vector product based on said gradient vectors for said subset of voxels, wherein the common intersection point indicates a centre of said blood vessel and said vector product indicates a direction in which said blood vessel extends. This aspect of the invention provides similar advantages as discussed above in relation to the previous aspect of the invention. Additionally, the inventive device may be comprised in a blood vessel characterizing system, further comprising means for acquiring a DICOM-image.

"According to a still further aspect of the present invention there is provided a computer program product comprising a computer readable medium having stored thereon computer program means for causing a computer to provide a method for characterizing a blood vessel represented by vascular image data from a DICOM-image, wherein said vascular image data comprises a plurality of voxels each having an image intensity, visual categorization method, wherein the computer program product comprises code for identifying a set of voxels representing at least a portion of a boundary of the blood vessel, code for determining a gradient vector of the image intensity for each voxel in said set of voxels representing the boundary of the blood vessel, code for selecting, from said set of voxels representing the boundary of the blood vessel, a subset of voxels such that all voxels in said subset of voxels have a common intersection point for their respective gradient vector extensions, and code for determining a vector product based on said gradient vectors for said subset of voxels, wherein the common intersection point indicates a centre of said blood vessel and said vector product indicates a direction in which said blood vessel extends. This aspect of the invention provides similar advantages as discussed above in relation to the previous aspects of the invention. Also, the computer readable medium may be one of a removable nonvolatile random access memory, a hard disk drive, a floppy disk, a CD-ROM, a DVD-ROM, a USB memory, an SD memory card, or a similar computer readable medium known in the art.

"Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled addressee realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention."

For more information, see this patent: Ohlson, Fredrik. Method for Characterizing a Blood Vessel. U.S. Patent Number 8818061, filed September 10, 2010, and published online on August 26, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8818061.PN.&OS=PN/8818061RS=PN/8818061

Keywords for this news article include: Orzone AB.

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Source: Computer Weekly News


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