News Column

Patent Application Titled "Calibration for 3d Reconstruction of Medical Images from a Sequence of 2d Images" Published Online

August 21, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors Li, Xin (Grass Valley, CA); Narayanan, Ramkrishnan (US), filed on January 29, 2013, was made available online on August 7, 2014.

No assignee for this patent application has been made.

Reporters obtained the following quote from the background information supplied by the inventors: "Medical imaging instruments are often utilized by doctors and other medical professionals to conduct non-invasive examinations. That is, medical imaging instruments, including X-ray, magnetic resonance (MR), computed tomography (CT), ultrasound, and various combinations of these instruments/techniques are utilized to provide images of internal patient structure for diagnostic purposes as well as for interventional procedures. Such medical imaging instruments allow examination of internal tissue that is not readily examined during normal visual or tactile examination. Applications include imaging in the areas of mammography, urology and brachytherapy.

"Medical imaging devices typically allow for generating 3-D images of internal structures of interest. Such 3-D imaging may improve the accuracy and/or reliability of medical diagnosis. For instance, a medical imaging device may be utilized to generate a 3-D model or map of a patient's prostate such that one or more biopsies may be taken from a desired location of the prostate. For purposes of prostrate imaging, image acquisition and guidance may be provided by a transrectal ultrasound-imaging device (TRUS). In such an application, the ultrasound-imaging device may be inserted into the rectum of a patient to generate an image. Such images may be utilized to take one or more biopsies from a prostate location of interest and/or implant therapy seeds at one or more desired locations in a brachytherapy procedure.

"In order to generate 3-D images, many medical imaging devices obtain a plurality of images (e.g., two dimensional images) and combine these images together to form a 3-D image. Traditionally, medical practitioners have manipulated a medical imaging instrument by hand for medical image acquisition and/or treatment. However, in instances where it is desirable to obtain multiple 2-D images for 3-D image generation, manual manipulation of the device may result in the type of unconstrained movement between images that makes registration difficult or impossible. That is, unconstrained (e.g., random) movement of a medical imaging device between the acquisition of individual images makes it more difficult to properly align (e.g., spatially register) the different images for purposes of generating an accurate 3-D image. Accordingly, a number of holding and manipulating/positioning assemblies have been proposed wherein a holder interfaces with an imaging device such as an ultrasound probe. Such a holder is then interconnected to one or more mechanical armatures and/or actuators such that the probe may be controllably positioned, advanced and/or rotated. In such systems, the position of the probe is known and movement of the probe (e.g., rotational, linear, etc.) is typically limited to a single degree of freedom. In this regard, the offset (e.g., angular or linear) between images is known. Accordingly, registration of such images is simplified."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "Provided herein are systems and methods (i.e., utilities) that are directed to correcting misalignments or offsets between a series or sequence of medical images. Once the offsets or misalignments between the series of medical images is corrected, the series of medical images may be reconstructed into a three dimensional image. In this regard, the correction of the offsets between the images registers these images into a common frame of reference such that they may be reconstructed into a three dimensional image. Accordingly, in order to correct the offsets, it is necessary to determine the transformation between the images. In this regard, the inventors have recognized that one source of offsets between a series of medical images obtained where an imaging device (e.g., ultrasound probe) is supported by a positioning mechanism or device, is the misalignment between the imaging axis or other reference point of the imaging device and the axis of movement of the positioning device. For instance, in the case of an ultrasound imaging device (e.g., two dimensional ultrasound device) an image plane of the ultrasound device may be misaligned with the movement axis of the positioning device. The determination of this offset between these axes allows for calculating a transformation that allows for placing each of the series images into a common frame of reference.

"According to a first aspect, the utility is provided where at least first and second images are obtained from an ultrasound imaging device while the ultrasound imaging device is supported by a positioning device. More specifically, the first and second images are obtained while the positioning device supports the ultrasound imaging device in first and second positions. The positioning device is operative to support the ultrasound imaging device in the first and second positions while limiting movement of the ultrasound imaging device to a single axis. Such a single axis may be a linear axis of movement or a rotational axis of movement. The first and second images are analyzed, automatically or manually, to identify and align a common object therein. In this regard, a first distance between the object and a known reference point (e.g., imaging axis) is identified in the first image. The second image is likewise analyzed to identify a second distance between the common object and the reference point. The distances between the common object in the first and second images and the known reference point are utilized to calculate a transformation that aligns the common object from both images. This transformation defines a calibration of offsets between the reference point of the ultrasound images and the axis of movement of the positioning mechanism.

"Once the transformation is calculated for the images, such a transformation may be utilized with subsequently acquired images in order to place those images in a common frame of reference. That is, after calculating a transformation, the utility may allow for acquiring a sequence of additional two dimensional images of an anatomical object using the ultrasound device as supported by the positioning mechanism. Again these two dimensional images may be acquired at multiple different positions about the axis of movement of the positioning device. Once transformed utilizing the calculated transformation, these images are registered to a common frame of reference and may be reconstructed to generate a 3D image of the anatomical object.

"In one arrangement, the acquisition of the images is obtained through the acquisition of first and second images (e.g., image pairs) where these images are obtained about a rotational axis. In this arrangement, the first and second images of each pair of images are acquired at 180 degrees apart. In this regard, each of these pairs of images, images the same anatomical structure. That is, the images are mirror images. Accordingly, a common object in each of these images should be a common distance away from, for example, an imaging axis of the imaging device. Further, it will be appreciated that multiple pairs of 180 degree spaced images may be utilized to calculate a more robust transformation.

"In a further arrangement, during the subsequent stacking of the images that are corrected utilizing the calculated transformation, each image may be registered to an adjacent image in order to account for movement of the anatomical object within each image.

"In a further arrangement, the images may be preprocessed to remove speckle and/or shadow to improve registration between images.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 shows a cross-sectional view of a trans-rectal ultrasound imaging system as applied to perform prostate imaging.

"FIG. 2 illustrates use of a positioning/tracking device to position an ultrasound imaging device to perform prostate imaging.

"FIG. 3A illustrates two-dimensional images generated by the TRUS of FIG. 1.

"FIG. 3B illustrates a 3-D volume image generated from the two dimensional images of FIG. 3A.

"FIG. 4 illustrates an exemplary ultrasound probe.

"FIG. 5A illustrates in-plane translation offset

"FIG. 5B shows a typical ultrasound imaging plane acquired by an end-fired transducer probe.

"FIG. 5C shows a cross-sectional view (as seen from behind an end-fired probe) of in-plane translation offset.

"FIGS. 5D-5F illustrate out-of-plane offset.

"FIG. 6 illustrates the imaging plane with in-plane rotation and translation offset.

"FIG. 7 illustrates the ROI within the image for 3D reconstruction.

"FIG. 8 illustrates the correction for lateral shift.

"FIG. 9 illustrates the correction for combined in-plane and lateral shift.

"FIG. 10 illustrates the different coordinate systems used in a 3-D imaging system.

"FIG. 11 illustrates the different coordinate systems with misalignment transformation.

"FIG. 12 illustrates an overall process for generation of the misalignment transformation

"FIG. 13 illustrates the fan shape vertex detection for TRUS image.

"FIG. 14 illustrates the shadow removal result on TRUS image.

"FIG. 15 compares the information theoretic feature map to gradient map of TRUS image.

"FIG. 16 illustrates image registration based reconstruction correction method."

For more information, see this patent application: Li, Xin; Narayanan, Ramkrishnan. Calibration for 3d Reconstruction of Medical Images from a Sequence of 2d Images. Filed January 29, 2013 and posted August 7, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1767&p=36&f=G&l=50&d=PG01&S1=20140731.PD.&OS=PD/20140731&RS=PD/20140731

Keywords for this news article include: Patents.

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