Feature Tracking Using Ultrasound

Abstract

Various implementations of the invention provide techniques and supporting systems that facilitate real-time or near-real-time ultrasound tracking for the purpose of calculating changes in anatomical features during a medical procedure. More specifically, anatomical features within a patient undergoing a medical procedure are tracked by obtaining temporally-distinct three dimensional ultrasound images that include the feature of interest and obtaining a targeted subset of ultrasound images focused on the feature. Based on the targeted subset of ultrasound images, a displacement of the feature is determined and image parameters used to obtain the targeted subset of ultrasound images are adjusted based on the displacement. This results in a time-based sequence of three dimensional images and targeted ultrasound images of the feature that identify changes in the position, size, location, and/or shape of the feature.

1 . A computer-implemented method for tracking an anatomical feature of interest within a patient undergoing a medical procedure, the method comprising:
 obtaining from a memory device a three dimensional image of a region of interest wherein the region of interest includes the feature of interest at a first periodicity;   determining a location of the feature of interest in the region of interest; and   by a processor, iteratively obtaining temporally-displaced targeted subsets of ultrasound images at a periodicity greater than the first periodicity focused on the determined location, each subset being compared with the three dimensional image and determining, based on each comparison, a displacement of the feature.   
     
     
         2 . The method of  claim 1  further comprising determining if the displacement exceeds a displacement threshold and if so, obtaining an updated three dimensional image of the region of interest sooner than would be obtained according to the first periodicity. 
     
     
         3 . The method of  claim 1  wherein the displacement threshold comprises an upper limit of spatial displacement of the feature of interest. 
     
     
         4 . The method of  claim 1  further comprising determining if the displacement exceeds a safety threshold and if so, halting the medical procedure to allow for one or more adjustments to the patient's orientation with respect to a treatment device. 
     
     
         5 . The method of  claim 1  further comprising adjusting one or more image parameters used in obtaining the targeted subset of ultrasound images based on the displacement. 
     
     
         6 . The method of  claim 1  further comprising continuously adjusting one or more treatment apparatus in response to the displacement without interrupting the medical procedure. 
     
     
         7 . The method of  claim 6  wherein the treatment apparatus comprises one or more of a treatment couch and a multi-leaf collimator. 
     
     
         8 . The method of  claim 1  wherein the targeted subset comprises a series of two dimensional image slices of the feature. 
     
     
         9 . The method of  claim 1  wherein the targeted subset comprises two or more tracking planes. 
     
     
         10 . The method of  claim 9  wherein one or more of the tracking planes comprise reconstructed planes. 
     
     
         11 . The method of  claim 1  wherein the targeted subset further comprises three dimensional ultrasound datasets related to a limited region of interest. 
     
     
         12 . The method of  claim 11  wherein the limited reduced region of interest is based at least in part on an adjusted sector size. 
     
     
         13 . The method of  claim 11  wherein the limited reduced region of interest is based at least in part on an adjusted image depth. 
     
     
         14 . The method of  claim 11  wherein the limited reduced region of interest is based at least in part on an adjusted ultrasound sector angle. 
     
     
         15 . The method of  claim 1  wherein the targeted subset further comprises three dimensional ultrasound datasets having a reduced resolution. 
     
     
         16 . The method of  claim 1  wherein the three dimensional ultrasound images are obtained using a motorized probe. 
     
     
         17 . The method of  claim 1  wherein the three dimensional ultrasound images are obtained using a biplanar probe. 
     
     
         18 . The method of  claim 1  wherein the three dimensional ultrasound images are obtained using a matrix probe. 
     
     
         19 . The method of  claim 1  wherein the three dimensional ultrasound images are obtained using a three dimensional ultrasound probe placed external to the patient. 
     
     
         20 . The method of  claim 1  wherein the three dimensional ultrasound images are obtained using a three dimensional ultrasound probe placed internal to the patient. 
     
     
         21 . The method of  claim 1  wherein the medical procedure comprises external beam radiotherapy. 
     
     
         22 . The method of  claim 1  wherein the medical procedure comprises obtaining one or more planning images for radiotherapy. 
     
     
         23 . The method of  claim 1  wherein the feature comprises an organ. 
     
     
         24 . The method of  claim 1  further comprising segmenting a subset of the targeted images. 
     
     
         25 . The method of  claim 1  wherein the comparison comprises comparing grey-scale values of a subset of the targeted images. 
     
     
         26 . The method of  claim 1  wherein the targeted subset of ultrasound images are obtained using an ultrasound probe having trackable markers affixed thereto. 
     
     
         27 . The method of  claim 26  wherein the trackable markers are tracked over time using a tracking system. 
     
     
         28 . The method of  claim 26  wherein the trackable markers are calibrated to pixels within the targeted subset of ultrasound images. 
     
     
         29 . The method of  claim 1  wherein the feature comprises a prostate gland and the targeted subset of ultrasound images are obtained transperineally. 
     
     
         30 . A system for tracking an anatomical feature of interest within a patient undergoing a medical procedure, the system comprising:
 a processor configured to: (i) locate the feature of interest within a series of three dimensional images of a region of interest obtained at a first periodicity wherein the region of interest includes the feature of interest, (ii) iteratively comparing temporally displaced targeted subsets of ultrasound images obtained at a periodicity greater than the first periodicity with the three dimensional image, and (iii) determining, based on each comparison, a displacement of the feature of interest; and   a register for receiving and storing the three dimensional image and the temporally displaced targeted subsets of ultrasound images.   
     
     
         31 . The system of  claim 30  wherein the processor is further configured to determine if the displacement exceeds a displacement threshold and if so, provide instructions to obtain an updated three dimensional image of the region of interest sooner than would be obtained based on the first periodicity. 
     
     
         32 . The system of  claim 31  wherein the displacement threshold comprises an upper limit of spatial displacement of the feature of interest. 
     
     
         33 . The system of  claim 30  wherein the processor is further configured to determine if the displacement exceeds a safety threshold and if so, provide instructions to halt the medical procedure to allow for one or more adjustments to the patient's orientation with respect to a treatment device prior to reinstating the procedure. 
     
     
         34 . The system of  claim 30  further comprising an ultrasound probe for providing the images. 
     
     
         35 . The system of  claim 31  wherein the ultrasound probe comprises a two dimensional ultrasound probe and a housing into which the ultrasound probe is rotatably mounted, thereby providing at least one degree of freedom of movement of the probe within the housing. 
     
     
         36 . The system of  claim 35  further comprising a motor for causing the probe to oscillate within the housing according to the at least one degree of freedom. 
     
     
         37 . The system of  claim 31  wherein the ultrasound probe further comprises trackable markers affixed thereto. 
     
     
         38 . The system of  claim 31  further comprising a controller for providing the adjusted imaging parameters to the ultrasound probe. 
     
     
         39 . The system of  claim 30  further comprising a display for displaying the images.