US-20260124016-A1 - METHOD FOR REGISTERING A 3D MEDICAL IMAGE WITH A REGISTRATION PHANTOM

US20260124016A1US 20260124016 A1US20260124016 A1US 20260124016A1US-20260124016-A1

Abstract

The invention relates to a method for registering a 3D medical image obtained by an X-ray imaging system with a registration phantom ( 1 ), wherein the registration phantom ( 1 ) is positioned onto the patient and comprises a set of radiopaque fiducials ( 10 ) having a known position in a coordinate system of said registration phantom ( 1 ), said set of radiopaque fiducials not being detectable in the 3D image, the method comprising the steps of:—obtaining at least two 2D X-ray images acquired by the X-ray imaging system wherein at least one radiopaque fiducial ( 10 ) of the registration phantom ( 1 ) is detectable in each 2D image;—for each of said at least two 2D images, registering the 2 D X-ray image with the registration phantom ( 1 ) by detecting and determining the position of the at least one radiopaque fiducial ( 10 ) in the respective 2D image;-registering each of said at least two 2D X-ray images with the 3D image using an image-to-image registration technique;—registering the registration phantom ( 1 ) with the 3D medical image using said at least two 2D X-ray images.

Inventors

Stéphane LaVallee
Clément Vidal
Arnaud PIERRE

Assignees

ECENTIAL ROBOTICS

Dates

Publication Date: 20260507
Application Date: 20221025
Priority Date: 20211026

Claims (10)

1 . A method for registering a 3D medical image obtained by an X-ray imaging system with a registration phantom, wherein the registration phantom is positioned onto the patient and comprises a set of radiopaque fiducials having a known position in a coordinate system of said registration phantom, said set of radiopaque fiducials not being detectable in the 3D image, the method comprising: obtaining at least two 2D X-ray images acquired by the X-ray imaging system wherein at least one radiopaque fiducial of the registration phantom is detectable in each 2D image; for each of said at least two 2D images, registering the 2D X-ray image with the registration phantom by detecting and determining the position of the at least one radiopaque fiducial in the respective 2D image; registering each of said at least two 2D X-ray images with the 3D image using an image-to-image registration technique; and registering the registration phantom with the 3D medical image using said at least two 2D X-ray images.
2 . The method of claim 1 , wherein an anatomical region of interest of the patient is detectable in each of the at least two 2D images and in the 3D image, and the image-to-image registration technique computes an optimization between a projection of said region of interest in the 3D image onto an image detector of the X-ray imaging system and said region of interest in each of the 2D X-ray images.
3 . The method of claim 1 , wherein the 3D medical image is reconstructed from a set of 2D images acquired by the X-ray imaging system and the at least two 2D images are selected from said set of 2D images.
4 . The method of claim 1 , wherein the 3D medical image is reconstructed from a set of 2D images acquired by the X-ray imaging system and the 2D images are acquired with the X-ray imaging system after reconstructing the 3D medical image.
5 . The method of claim 1 , wherein the 3D medical image is reconstructed from a set of 2D images acquired by the X-ray imaging system and the 2D images are acquired with the X-ray imaging system before reconstructing the 3D medical image.
6 . The method of claim 1 , wherein the image-to-image registration technique comprises at least one of the following techniques: cross-correlation techniques, mutual information techniques, gradient correlation techniques.
7 . An intraoperative surgical system comprising: a registration phantom comprising a set of radiopaque fiducials having a known position in a coordinate system of said registration phantom, said registration phantom being adapted to be positioned onto a patient, an X-ray imaging system configured to acquire a set of 2D X-ray images and to reconstruct a 3D medical image from said set of 2D X-ray images, and a computer system configured to: (i) obtain at least two 2D X-ray images acquired by the X-ray imaging system wherein at least one radiopaque fiducial of the registration phantom is detectable in each 2D image; (ii) for each of said at least two 2D images, register the 2D X-ray image with the registration phantom by detecting and determining the position of the at least one radiopaque fiducial in the respective 2D image; (iii) register each of said at least two 2D X-ray images with the 3D image using an image-to-image registration technique; and (iv) register the registration phantom with the 3D medical image using said at least two 2D X-ray images.
8 . The intraoperative surgical system of claim 7 , wherein the X-ray imaging system is a motorized C-arm.
9 . The intraoperative surgical system of claim 7 , further comprising a radiotransparent base configured to be attached to the patient's anatomy, said base comprising a fixation system for removably attaching the registration phantom to the base.
10 . The intraoperative surgical system of claim 7 , further comprising a localization system and at least one tracker adapted to be tracked by the localization system, the base comprising a fixation system for removably attaching the tracker to the base.

Description

TECHNICAL FIELD The present disclosure relates to a method for registering a 3D medical image with a registration phantom, and an intraoperative surgical system configured to implement such a method. TECHNICAL BACKGROUND X-Ray imaging systems are frequently used during medical surgical procedures to provide physicians with image-based information about the anatomical situation and/or the position and orientation of surgical instruments. Such X-ray imaging systems typically provide two-dimensional (2D) projection images with different structures superimposed along the path of the X-rays. A typical example of an X-ray imaging system for use in an intra-operative setting is the so-called C-arm used in a mobile or stationary manner and essentially consisting of a base frame on which a C-shaped arm is attached with several intermediate joints allowing moving the C-shaped arm in space along several degrees of freedom. One end of the C-shaped arm carries an X-ray source and the other end an image detector. Due to the limited information provided by these 2D images, three-dimensional (3D) imaging techniques have become indispensable over the past decades. While computer tomography (CT) systems are a well-established class of stationary X-ray imaging systems used for reconstruction of a 3D image in a radiology department, these systems are in general not usable inside the operating room. Recent years have seen an increasing interest in tomographic reconstruction techniques, also known as cone-beam reconstruction techniques (CBCT), using two-dimensional image detectors. Special efforts have been made to enable the aforementioned C-arms to provide three-dimensional information by automatically acquiring a set of 2D images of a region of interest and subsequently reconstructing a 3D image based on said cone-beam reconstruction techniques. Surgical navigation is the application of real-time navigation on intraoperatively acquired fluoroscopic images to achieve the above-mentioned goals. In view of carrying out said navigation, the tools used during the surgical intervention are equipped with a tracker, e.g. an optical, electromagnetic, ultrasonic, or inertial tracker which is tracked in real time by at least one localization system. Another tracker is mounted onto the patient and is also tracked in real time by the localization system. In this way, the position and orientation of the tools relative to the patient is known in real time. In view of navigating surgical tools with respect to images acquired by the X-ray imaging device, it is necessary to know the position of said images (or the position the X-ray image detector during acquisition of said images) with respect to the tracker fixed on the patient. To that end, an instrument may be used such as described in [1]. As shown in FIG. 1A, the instrument comprises a registration phantom 1 comprising a plurality of radiopaque fiducials 10 arranged according a known geometry, such that the position of each radiopaque fiducial is known in a coordinate system of the registration phantom. The instrument also comprises a base 2 supporting the registration phantom 1. Preferably, the registration phantom 1 can be removed from the base 2, and a tracker (not shown) can instead be fixed to the base 2 to allow tracking the patient during surgery. The base 2 is rigidly fixed to a patient's bone by at least one percutaneous pin 3, the base 2 and the registration phantom 1 being located outside the patient's body, above the patient's skin S. The dotted line schematically represents the volume V that is reconstructed from 2D X-ray images of the patient. Since said volume V includes not only the region of interest, which is a part of the bone, but also the registration phantom 1, the radiopaque fiducials 10 that are visible in the 3D image allow determining the position of the volume V in the coordinate system of the registration phantom and thus register the 3D image with the registration phantom. Since the tracker is fixed to the same base as the registration phantom, it is thus possible to navigate a surgical instrument within the 3D image. But sometimes, especially if the patient is obese, the distance between the registration phantom and the region of interest to image is such that said phantom lies outside the reconstructed volume. In that case, traditional methods prove ineffective to register the imaging space with the navigation space. This situation is illustrated in FIG. 1B. Due to the larger thickness of tissues between the bone B and the skin S, the base 2 and registration phantom 1 are located farther from the bone B. Thus, for a same volume V reconstructed from the 2D X-ray images, the registration phantom 1 is located outside the volume V. Since the radiopaque fiducials 10 are not inside the volume V, it is not possible to determine the position of the volume V in the coordinate system of the registration phantom and thus register the 3D image with the registration pha