BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for localization and identification of a structure in a projection image with a system having a known system geometry.

Wrong site surgery is a surprisingly common error in medical practice with major ramification to the patient and healthcare system. It not only results in failure to deliver proper therapy to the patient, but it also has profound medical, legal and social implications. In spinal surgery, for example, the potential for wrong-site surgery (viz., “wrong level” surgery, referring to the level of vertebral body) is significant due to the difficulty of localizing the target vertebrae based solely on visual impression, palpation and fluoroscopic imaging. Vertebrae in the mid-thoracic region can be particularly challenging to localize, since they have fairly similar visual and radiographic appearance and are at a distance from unambiguous anatomical landmarks. A common method to accurately localize a given vertebral level is to “count” vertebrae under fluoroscopy, typically beginning at the sacrum and then “counting” under fluoroscopic visualization up to the targeted vertebral level. Such a method involves an undesirable amount of time and ionizing radiation. Even with fluoroscopic counting, surgery delivered to the wrong level is a fairly frequent occurrence. According to a questionnaire study of 3,505 surgeons, carrying out 1,300,000 procedures, 418 (0.032% or 1 in 3,110) wrong-level spine surgeries were performed [see Mody M G, Nourbakhsh A, Stahl D L, Gibbs M, Alfawareh M, Garges K J., “The prevalence of wrong level surgery among spine surgeons,” Spine (Phila Pa. 1976) January 15 33(2), 194-198 (2008)]. Such errors are presumably attributable to foregoing a careful level finding method (e.g., due to time or dose constraints) and/or human errors in counting or otherwise interpreting the fluoroscopic (radiographic) image information (e.g., due to the radiographic similarity between adjacent vertebrae). Several studies [see Perisinakis K, Theocharopoulos N, Damilakis J, Katonis P, Papadokostakis G, Hadjipavlou A, et al., “Estimation of patient dose and associated radiogenic risks from fluoroscopically guided pedicle screw insertion,” Spine (Phila Pa. 1976) July 15 29(14), 1555-1560 (2004), and Mariscalco M W, Yamashita T, Steinmetz M P, Krishnaney A A, Lieberman I H, Mroz T E., “Radiation exposure to the surgeon during open lumbar microdiscectomy and minimally invasive microdiscectomy: a prospective, controlled trial,” Spine (Phila Pa. 1976) February 1 36(3), 255-260 (2011)] also revealed that the radiation exposure to the surgeon during level localization in spine surgery is a notable issue. Singh et. al. [see Singh H, Meyer S A, Hecht A C, Jenkins A L, 3rd., “Novel fluoroscopic technique for localization at cervicothoracic levels,” J. Spinal. Disord. Tech. December 22(8), 615-618 (2009)] proposed to take fluoroscopic images from an oblique direction to facilitate level localization in cervicothoracic spine surgery. The technique helped identifying bony lamina in the image by avoiding interference from chest and shoulders, which can then be used to count spinal levels. Such techniques rely heavily on the surgeon's ability to identify the target level.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method for localization and identification of structures in projection images of a body, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type, which significantly decreases the number of wrong-level surgeries and which is independent of the surgeon's ability to localize and/or identify a target level in the body.

With the foregoing and other objects in view there is provided, in accordance with the invention, a method for localization and identification of a structure in a projection image with a system having a known system geometry. The method comprises:a) acquiring a preoperative computer-tomography (CT) image of a structure;b) preprocessing the CT-image to a volume image;c) acquiring an intraoperative two dimensional (2D) X-ray image;d) preprocessing the 2D X-ray image to a fix image;e) estimating an approximate pose of the structure;f) calculating a digitally reconstructed radiograph (DRR) using:the volume image,the estimated pose andthe system geometry; andg) calculating a correlation between the generated DRR and the fix image, with a correlation value representing matching between the generated DRR and the fix image.

In order to provide a specific illustration of the proposed method, reference is made to the case where the structure to be localized is a vertebra. The structure has been defined (i.e., “segmented” preoperatively in CT, which is referred to as “planning data”), and the 2D images in which the structure (planning data) is to be localized are intraoperative fluoroscopy images obtained on a C-arm. However, the method is fairly general beyond this specific application: the structure could be one or more of any 3D structure(s) of interest, e.g., tumors, anatomical landmarks, vessels, nerves, etc., the structure(s) could be defined in any 3D or 4D image obtained either preoperatively or intraoperatively, and the 2D image in which to localize the structure could be any form of projection image, e.g., fluoroscopy, radiography, or a “projection” MR image. The purpose of the method is to automatically localize (i.e., identify the location of) the structure(s) defined in the 3D image directly within the intraoperative 2D image.

For the specific case of spine surgery and localization of vertebrae (“level finding”), the invention provides information on the target vertebrae location in the intraoperative x-ray image that is acquired with a mobile C-arm. The inventors' initial studies use an intensity-based 3D/2D registration between 3D preoperative CT and 2D intraoperative fluoroscopy, although many variations in the registration technique can be envisioned. By registering the 3D image (in which the structure has been defined preoperatively) to the 2D image, the location of the 3D structure within the 2D image can be automatically computed and displayed to the surgeon.

The invention provides, as an alternative to the state of the art, a method for automatic localization of predefined 3D structures (e.g., vertebrae) in 2D fluoroscopic/radiographic images using 3D-2D registration. 3D/2D registration between preoperative CT and X-ray projections has been explored extensively [see Markelj P, Tomaževič D, Likar B, Pernuš F., “A review of 3D/2D registration methods for image-guided interventions,” Med. Image Anal. In Press, Corrected Proof], e.g., in radiation therapy, with the goal of registering between the patient and the treatment plan. An intensity-based method is one of the prospective approaches to improve the accuracy of 3D/2D registration by using all image information as opposed to a feature-based method. Two commercial radiotherapy systems, CyberKnife® Robotic Radiosurgery System (Accuray Incorporated, Sunnyvale, Calif.) [see Fu D, Kuduvalli G., “A fast, accurate, and automatic 2D-3D image registration for image-guided cranial radiosurgery,” Med. Phys. May 35(5), 2180-2194 (2008)] and Novalis® (BrainLAB AG, Feldkirchen, Germany) [see Agazaryan N, Tenn S E, Desalles A A, Selch M T., “Image-guided radiosurgery for spinal tumors: methods, accuracy and patient intrafraction motion,” Phys. Med. Biol. March 21 53(6), 1715-1727 (2008)], employ intensity-based 3D/2D registration for purposes and methods quite distinct from those proposed herein. Those algorithms are provided for a dedicated linear accelerator which has precise motorized-controlled rotation and thus, multiple accurately calibrated images are available. On the contrary, fixed and mobile C-arms, which are increasingly common to surgery and interventional radiology, can be difficult to use for providing precise intrinsic and extrinsic calibration due to the nature of mechanical instability.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in a method for localization and identification of structures in projection images, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

