Patent Publication Number: US-2022225951-A1

Title: Seeing through mucus in an ent procedure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 16/841,745, filed on Apr. 7, 2020, which is a divisional of U.S. patent application Ser. No. 15/407,060, filed on Jan. 16, 2017, now U.S. Pat. No. 10,631,798, priority of which is hereby claimed. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to medical imaging, and particularly to imaging using X-rays. 
     BACKGROUND 
     In medical computerized tomography (CT), a large number of X-ray images are taken from different angles of a part of the body of a patient. Using the mathematical procedure of tomographic reconstruction, the X-ray images are processed and combined to yield cross-sectional images of the part of the body, providing a non-invasive three-dimensional (3D) image of the internal structure of the imaged part. 
     U.S. Pat. No. 7,630,529, which is incorporated herein by reference, describes a system for performing a virtual colonoscopy that is stated to include a system for generating digital images, a storage device for storing the digital images, a digital bowel subtraction processor coupled to receive images of a colon from the storage device and for removing the contents of the colon from the image and an automated polyp detection processor coupled to receive images of a colon from the storage device and for detecting polyps in the colon image. 
     U.S. Patent application 2014/0330115, which is incorporated herein by reference, describes a method for displaying a paranasal sinus region of a patient that is executed at least in part on a computer. The method is stated to include acquiring volume image data of the paranasal sinus region of the patient, identifying one or more airways within the paranasal sinus region from the volume image data, displaying the at least one or more airways, and highlighting one or more portions of the displayed airways that are constricted below a predetermined value. 
     U.S. Patent application 2013/0004044, which is incorporated herein by reference, describes a voxel-based technique that is provided for performing quantitative imaging and analysis of tissue image data. Serial image data is collected for tissue of interest at different states of the issue. The collected image data may be deformably registered, after which the registered image data is analyzed on a voxel-by-voxel basis, thereby retaining spatial information for the analysis. Various thresholds are applied to the registered tissue data to identify a tissue condition or state, such as classifying chronic obstructive pulmonary disease by disease phenotype in lung tissue, for example. 
     U.S. Patent application 2008/0008367, which is incorporated herein by reference, describes how an image of an anatomical structure can be analyzed to determine an enclosing three-dimensional boundary when the anatomical structure is filled with two substances, such as air and a fluid. Various techniques can be used to determine the enclosing boundary including: analyzing the virtual structure to segment the structure into air and fluid pockets, determining if there are multiple fluid pockets whose surface touches a single air-fluid boundary, determining a separate threshold for respective fluid pockets, resegmenting the virtual anatomical structure using the separate threshold for different fluid pockets, forming a hierarchical pocket tree which represents the relationship between the fluid and air pockets, pruning the pocket tree based on various criteria which corresponds to deleting those pruned portions from the virtual anatomical structure, and resegmenting the remaining virtual anatomical structure using one or more of fuzzy connectedness, two-dimensional gap filling, and level set segmentation. 
     Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that, to the extent that any terms are defined in these incorporated documents in a manner that conflicts with definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide an improved method for local radiographic imaging within body cavities. 
     There is therefore provided, in accordance with an embodiment of the present invention, a method for radiographic imaging of a body cavity, including imaging the body cavity using computerized tomography (CT) to form a CT image, registering a tracking system with the CT image, inserting into the body cavity a guidewire, including a position sensor, operating in the tracking system, attached to a distal end of the guidewire, in response to signals from the position sensor acquired by the tracking system, displaying a position of the distal end of the guidewire on the CT image. The method further includes assigning voxels within a predefined imaging volume relative to the distal end and having a radiodensity less than a predetermined threshold to have a uniform radiodensity of a predefined default value, incorporating the voxels with the assigned predefined default value into the CT image so as to form an updated CT image, and displaying the updated CT image. 
     In another embodiment the method includes a predefined imaging volume which includes a conical volume having an apex offset from the distal end by a predefined vector. 
     In yet another embodiment the method includes a predefined imaging volume which includes a sphere having a center offset from the distal end by a predefined vector. 
     In some embodiments the method includes a predetermined threshold having the radiodensity of mucus or the radiodensity of a selected body tissue. 
     In an embodiment the method includes a predefined default value having the radiodensity of air. 
     In a further embodiment the method includes radiographic imaging of a the body cavity including a nasal sinus. 
     There is also provided, in accordance with an embodiment of the present invention, an apparatus for radiographic imaging of a body cavity, including a guidewire inserted in the body cavity, the guidewire including a position sensor, operating in a tracking system, at its distal end, and a display screen. The apparatus further includes a processor coupled to the position sensor and to the display screen, configured to store and display a CT image of the body cavity, to register the tracking system with the CT image, to track a position of the distal end, to display on the display screen the tracked position of the distal end superimposed on the CT image, to assign voxels within a predefined imaging volume relative to the distal end and having a radiodensity less than a predetermined threshold to have a uniform radiodensity of a predefined default value, to incorporate the voxels with the assigned predefined default value into the CT image so as to form an updated CT image, and to display the updated CT image on the display screen. 
     In another embodiment the predefined imaging volume includes a conical volume having an apex offset from the distal end by a predefined vector. Alternatively, the predefined imaging volume includes a sphere having a center offset from the distal end by a predefined vector. 
     In yet another embodiment the predetermined threshold includes a radiodensity of mucus. Alternatively, the predetermined threshold includes a radiodensity of a selected bodily tissue. 
     In an embodiment the predefined default value includes radiodensity of air. 
     In a further embodiment the body cavity includes a nasal sinus. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a medical procedure, according to an embodiment of the present invention; 
         FIG. 2  shows a frontal section of a CT image of the head of a patient, according to an embodiment of the present invention; 
         FIG. 3  is a flowchart of steps that are implemented during the medical procedure, as relating to imaging, according to an embodiment of the present invention; 
         FIG. 4  shows a definition of a conical imaging volume anchored to distal end of the guidewire, according to an embodiment of the present invention; 
         FIG. 5  shows an enlarged area of a CT image after re-assignment of voxels within a conical imaging volume, and displaying the image with re-assigned voxels, according to an embodiment of the present invention; 
         FIG. 6  shows a spatially offset conical imaging volume, according to an embodiment of the present invention; 
         FIG. 7  shows a definition of a spherical imaging volume, according to an embodiment of the present invention; and 
         FIG. 8  shows a spatially offset spherical imaging volume, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Radiographic imaging of body cavities is commonly performed using computerized tomography (CT). The quality of the obtained radiographic image is often reduced due to the presence of substances other than air in the cavity, and an example of such a situation is CT imaging of the nasal sinuses, when a nasal sinus is filled with mucus instead of air. Although in the following the effect of mucus on the imaging of nasal sinuses is described as an example, it will be appreciated that the embodiments of the present invention comprise CT imaging of other body cavities with substances other than air therein. 
     Embodiments of the present invention that are described herein solve this problem by generating an image of a cavity as if only air fills the cavity. 
     In an embodiment of the present invention, a patient is scanned, in advance of a medical procedure, in a CT imaging device, generating a CT image comprising a body cavity of the patient. In a subsequent medical procedure, a guidewire with a position sensor at its distal end is inserted into the patient&#39;s body cavity, the position sensor enabling tracking of the position of the distal end. Using known registration procedures, a tracking system wherein the position sensor operates has been registered in advance with the CT image. The registration enables the tracked position of the distal end to be displayed on the CT image of the patient&#39;s body cavity. 
     The radiodensities of the voxels in a predefined imaging volume, relative to the distal end of the guidewire, are compared to a predetermined radiodensity threshold. Voxels in the predefined imaging volume having a radiodensity that is less than a predetermined threshold, are assigned a predefined default value. The voxels having the radiodensity that has been assigned with the predefined default value are incorporated into the CT image to form an updated CT image, and this updated CT image is displayed. 
     System Description 
       FIG. 1  is a schematic illustration of a medical procedure using apparatus  10 , according to an embodiment of the present invention. The procedure is performed by a surgeon  12 , and, by way of example, the procedure in the description hereinbelow is assumed to comprise inserting a guidewire into the nasal sinus of a patient  14  for a medical procedure within the nasal sinus. However, it will be understood that embodiments of the present invention are not just applicable to this specific procedure, and may include substantially any procedure on biological tissue. 
     Surgeon  12  inserts a guidewire  16  into a nostril  18  of patient  14 , so that a distal end  20  of the guidewire enters a nasal sinus cavity  21  of the patient. Distal end  20  comprises position sensor  22 . A proximal end  24  of guidewire  16  is coupled to a console  26  of apparatus  10 . 
     Apparatus  10  is controlled by a processor  28 , which is located in console  26 . Console  26  comprises controls  30 , which are used by surgeon  12  to communicate with the processor. During the procedure, processor  28  tracks a location and an orientation of distal end  20  of the catheter, using any method known in the art. For example, processor  28  may use a magnetic tracking method, wherein magnetic transmitters  31 , external to patient  14 , generate signals in coils located in position sensor  22 . The signals from the sensor coils are connected to console  26  and further to magnetic tracking module  23  and are analyzed by the magnetic tracking module communicating with processor  28 . The Carto® system produced by Biosense Webster, of Diamond Bar, CA, uses such a tracking method. 
     The software for processor  28  may be downloaded to the processor in electronic form, over a network, for example. Alternatively or additionally, the software may be provided on non-transitory tangible media, such as optical, magnetic, or electronic storage media. Processor  28  is coupled to a display screen  32 . 
     In order to operate apparatus  10 , processor  28  communicates with electronics  34 , which incorporates a magnetic tracking module  23  and other modules used by the processor to operate the apparatus. For simplicity, such other modules, which may comprise hardware as well as software elements, are not illustrated in  FIG. 1 . Proximal end  24  of guidewire  16 , coupled to console  26 , is further coupled to magnetic tracking module  23  so that the module is able to use the signals generated by sensor  22  for position tracking. 
     Processor  28  further communicates with a memory  36 , which stores data required for operating apparatus  10 . The data comprises CT images of a head  38  of patient  14 . 
       FIG. 2  shows a frontal section of a CT image  40  of head  38  of patient  14 , according to an embodiment of the present invention. Using known registration procedures, the magnetic tracking system is registered with the CT imaging system. Utilizing the registration together with the detected position of distal end  20 , the position is superimposed as a fiducial mark  42  on CT image  40 . In CT image  40 , surgeon  12  is assumed to have inserted distal end  20  of guidewire  16  into a right maxillary sinus  44  of patient  14 , as shown by the position of fiducial mark  42  within CT image  40 . A CT image  46 , which is an enlarged part of CT image  40 , is shown to the right of CT image  40 . 
     A comparison of the image of right maxillary sinus  44  with the image of a left maxillary sinus  48  in CT image  40  shows that the image of right maxillary sinus  44  is lighter than the image of left maxillary sinus  48 . This difference indicates a different radiographic density of the two maxillary sinuses  44  and  48 , respectively. The different radiographic density, in turn, is due to the fact that right maxillary sinus  44  is filled with mucus. 
     The radiodensity is conventionally expressed in Hounsfield units (HU), and the radiodensity of mucus is typically between −100 HU and +100 HU. Left maxillary sinus  48  is filled with air, with a radiographic density of −1000 HU. As is described with reference to the flowchart of  FIG. 3 , in an embodiment of the present invention, in further processing of CT image  46  in  FIG. 2 , the upper radiodensity of mucus, +100 HU, is selected as a radiodensity threshold for the re-assignment of voxel radiodensities, and the radiodensity of air, −1000 HU, is selected as the default radiodensity for the assigned value. 
       FIG. 3  is a flowchart of steps that are implemented during the medical procedure, as relating to imaging, according to an embodiment of the present invention. In a CT scan step  50 , head  38  of patient  14  is scanned by computerized tomography (CT), herein by way of example assumed to be fluoroscopic CT, and the CT data from the scan is acquired by processor  28  and stored in memory  36 . The CT scan of patient  14  may be performed independently of the implementation of the remaining steps of the flowchart, which correspond to a nasal sinus procedure. Typically, CT scan step  50  may be performed a number of days before the following steps of the procedure. 
     In an initial procedure step  52 , the magnetic tracking system, comprising magnetic transmitters  31 , position sensor  22 , and magnetic tracking module  23 , is registered with the CT imaging system. The registration may be implemented by any method known in the art. In step  52 , surgeon  12  defines a level of the preset radiodensity threshold, and the level is herein, by way of example, assumed to be +100 HU. Also in step  52 , the surgeon defines a level for the default radiodensity, and this level is herein, by way of example, assumed to be that of air, i.e., 1000 HU. 
     In an insertion step  54 , surgeon  12  inserts guidewire  16  into nostril  18  of patient  14 , so that distal end  20  of the guidewire enters nasal sinus cavity  21  of the patient. Utilizing the registration between the magnetic tracking system and the CT imaging system, together with the detected position of distal end  20 , this position is superimposed as fiducial mark  42  on CT image  46 , as is illustrated in  FIG. 2 . 
     In a defining step  56 , surgeon  12  moves distal end  20  into a desired position, utilizing fiducial mark  42  on CT image  46  for guidance. In defining step  56 , surgeon  12  further defines an imaging volume by its shape, size, and anchoring to distal end  20 , as is described in more detail with respect to  FIGS. 4 and 6-8 . 
       FIG. 4  shows, with reference to  FIGS. 1-2 , in CT image  46  a definition of a conical imaging volume  70  anchored to distal end  20  of guidewire  16 , according to an embodiment of the present invention. Surgeon  12  defines the anchoring of conical imaging volume  70  by defining the apex of the conical imaging volume to coincide with fiducial mark  42 . Surgeon  12  further defines an apex angle of conical imaging volume  70 , and a typical angle is 60°, although the surgeon may select any other convenient value for the angle. Typically, processor  28  defines a length of conical imaging volume  70 . 
       FIG. 6  shows a spatially offset conical imaging volume  74 , according to an embodiment of the present invention. Offset conical imaging volume  74  has been defined by surgeon similarly to conical imaging volume  70  with respect to  FIG. 4 , but the surgeon has additionally defined an offset vector  75  separating an apex  76  from fiducial mark  42 . 
       FIG. 7  shows a definition of a spherical imaging volume  80 , according to an embodiment of the present invention. Surgeon  12  has defined a radius of spherical imaging volume  80 , and has also defined the volume center to coincide with fiducial mark  42 . A typical radius for volume  80  is 5 mm, but the surgeon may select any other convenient value for the radius. 
       FIG. 8  shows a spatially offset spherical imaging volume  82 , according to an embodiment of the present invention. Offset spherical imaging volume  82  has been defined by surgeon  12  similarly to spherical imaging volume  80  in  FIG. 7 , but the surgeon has additionally defined an offset vector  83  separating a center  84  of spherical imaging volume  82  from fiducial mark  42 . 
     In the examples described above defining the anchoring of the imaging volume to fiducial mark  42 , surgeon  12  has used finite (non-zero) offset vectors  75 ,  83  in  FIG. 6  and in  FIG. 8 . However, it will be understood that in embodiments of the present invention offset vectors comprise both finite (non-zero) and zero-length vectors. 
     Returning to the flowchart in a comparison step  57 , processor  28  compares the radiodensity of each voxel within the imaging volume defined in step  56  to the preset radiodensity threshold defined in step  52 , and passes each voxel within the imaging volume on to a decision step  58 . With respect to  FIGS. 4 and 6-8 , the imaging volume whose voxels are processed in comparison step  57  and decision step  58  are conical imaging volume  70  ( FIG. 4 ), offset conical imaging volume  74  ( FIG. 6 ), spherical imaging volume  80  ( FIG. 7 ), and offset spherical imaging volume  82  ( FIG. 8 ). 
     In decision step  58 , the following two alternative decisions are taken: if the radiodensity of the voxel under comparison is less than the predetermined threshold, which surgeon  12  has in step  52  defined as +100 HU, processor  28  directs the handling to a re-assignment step  59 , whereas if the radiodensity of the voxel under comparison is not less than the predetermined threshold of +100 HU, processor  28  directs the handling to a no-change step  60 . 
     In re-assignment step  59 , the voxel that processor  28  has passed to the re-assignment step is re-assigned by the processor a radiodensity value equal to the predefined default radiodensity, which is set in step  52 , and is herein assumed to be that of air, −1000 HU. After the re-assignment, processor  28  passes the re-assigned voxel to a re-assembly step  61 . 
     In no-change step  60 , the voxel that processor  28  has passed to the no-change step is further passed on by the processor to re-assembly step  61 , leaving the radiodensity of the voxel intact. 
     Re-assembly step  61  receives the voxels of the imaging volume from re-assignment step  59  and no-change step  60  with their re-assigned or unchanged values, respectively. In re-assembly step  61  processor  28  re-assembles the portion of CT image  46  within the imaging volume from the received voxels, with the portion of CT image  46  outside the imaging volume remaining intact. 
     In a display step  62 , processor  28  displays CT image  46  with re-assembled voxels on display  32 . 
       FIG. 5  illustrates an example of a CT image  46 ′ with re-assembled voxels, according to an embodiment of the present invention.  FIG. 5  shows the change in the image of  FIG. 4 , after display step  62  has been implemented. The voxels within an area  72  within conical imaging volume  70  have an original radiographic density less than +100 HU, and processor  28  has consequently assigned them the radiographic density of air, −1000 HU, using steps  57 ,  58  and  59 . CT image  46 ′ illustrates the re-assignment of the radiodensity of the voxels in area  72 , making them radiographically transparent and increasing the contrast and clarity of the features within conical imaging volume  70 , as compared to CT image  46  in  FIG. 4 . 
     Similarly to the re-assignment for conical imaging volume  70  and with respect to  FIGS. 6-8 , processor  28  re-assigns the radiodensity of the voxels within offset conical imaging volume  74  ( FIG. 6 ), spherical imaging volume  80  (FIG.  7 ), and offset spherical imaging volume  82  ( FIG. 8 ) in the same fashion as that for conical imaging volume  70  in  FIG. 5 . The images displayed after re-assignment of the voxels (not shown here) show mucus as air, increasing the contrast and clarity of the features within these imaging volumes. 
     Returning to the flowchart, in a decision step  63 , surgeon  12  decides whether he/she wants to move guidewire  16  to a new position within nasal sinus cavity  21 . If he/she desires to move guidewire  16 , he/she may at defining step  56  either re-define the imaging volume, or alternatively leave it as previously defined. The latter alternative corresponds to moving distal end  20  within nasal sinus cavity  21  and imaging in a scanning fashion. Scanning distal end  20  within nasal sinus cavity  21  has the effect of increasing the contrast and clarity of the features within the scanned imaging volume. 
     If surgeon  12  decides not to move guidewire  16  further, the procedure ends. 
     The description above has assumed the predetermined threshold to be that of mucus, but it will be understood that other threshold values may be used. For example, surgeon  12  may choose the radiodensity threshold to be the radiodensity of a selected tissue or bone, which will have the effect of making the tissue or bone radiographically transparent within the imaging volume defined by surgeon  12  in defining step  56 . 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.