Real-time simulation of fluoroscopic images

A method includes registering a first coordinate system of a fluoroscopic imaging system and a second coordinate system of a magnetic position tracking system. A three-dimensional (3D) map of an organ of a patient is computed using the magnetic position tracking system. A field-of-view (FOV) of the fluoroscopic imaging system in the second coordinate system is calculated using the registered first and second coordinate systems. Based on the 3D map and the calculated FOV, a two-dimensional (2D) image that simulates a fluoroscopic image that would be generated by the fluoroscopic imaging system is created, and the 2D image that simulates the fluoroscopic image is displayed.

FIELD OF THE INVENTION

The present invention relates generally to medical imaging, and particularly to methods and systems for real-time simulation of fluoroscopic images during medical procedures.

BACKGROUND OF THE INVENTION

Real-time (RT) imaging, such as fluoroscopic imaging, is often used in minimally-invasive medical procedures, sometimes in conjunction with various three-dimensional (3D) imaging modalities. Several techniques deal with registration of RT images with 3D models and 3D maps of patient organs. For example, U.S. Patent Application Publication 2010/0022874, whose disclosure is incorporated herein by reference, describes an image guided navigation system that comprises a memory, a locator, a processor and a display. The memory stores a plurality of CT images and a software program. The locator is capable of indicating a direction to a surgical area, and the indicated direction of the locator is defined as a first direction. The processor is electrically connected to the memory and the locator. At least one corresponding image corresponding to the first direction is obtained from the plurality of CT images by the processor executing the software program. The at least one corresponding image comprises at least one simulated fluoroscopic image. The display is capable of showing the at least one corresponding image.

U.S. Pat. No. 8,515,527, whose disclosure is incorporated herein by reference, describes a method and an apparatus for registering 3D models of anatomical regions of a heart and a tracking system with projection images of an interventional fluoroscopic system.

U.S. Pat. No. 7,327,872, whose disclosure is incorporated herein by reference, describes a method and a system for registering 3D models with projection images of anatomical regions. A first image acquisition system of a first modality employing a catheter at an anatomical region of a patient is configured to produce a first image of the anatomical region using fluoroscopy, the first image comprising a set of fluoroscopy projection images. A second image acquisition system of a second different modality is configured to generate a 3D model of the anatomical region. An anatomical reference system is common to both the first and second image acquisition systems. A processing circuit is configured to process executable instructions for registering the 3D model with the fluoroscopy image in response to the common reference system and discernible parameters associated with the catheter in both the first and second image acquisition systems.

SUMMARY OF THE INVENTION

An embodiment of the present invention that is described herein provides a method including registering a first coordinate system of a fluoroscopic imaging system and a second coordinate system of a magnetic position tracking system. A three-dimensional (3D) map of an organ of a patient is computed using the magnetic position tracking system. A field-of-view (FOV) of the fluoroscopic imaging system in the second coordinate system is calculated using the registered first and second coordinate systems. Based on the 3D map and the calculated FOV, a two-dimensional (2D) image that simulates a fluoroscopic image that would be generated by the fluoroscopic imaging system is created, and the 2D image that simulates the fluoroscopic image is displayed.

In some embodiments, the method includes creating the 2D image without applying radiation by the fluoroscopic imaging system. In other embodiments, the method includes displaying the 2D image and the 3D map in different display windows. In yet other embodiments, the method includes displaying the 2D image in a sub-window of a display window used for displaying the 3D map.

In an embodiment, the method includes identifying anatomical features of the organ in the 3D map and simulating, based on the calculated FOV, a projection of the anatomical features in the 2D image. In another embodiment, the method includes identifying a medical probe in the 3D map, and displaying the medical probe in the 2D image. In an embodiment, computing the 3D map includes importing into the 3D map one or more objects acquired using an imaging modality other than magnetic position tracking.

There is additionally provided, in accordance with an embodiment of the present invention, a system including a memory and a processor. The memory is configured to store a three-dimensional (3D) map of an organ of a patient, which is produced by a magnetic position tracking system. The processor is configured to register a first coordinate system of a fluoroscopic imaging system and a second coordinate system of the magnetic position tracking system, to compute the 3D map using the magnetic position tracking system, to calculate a field-of-view (FOV) of the fluoroscopic imaging system in the second coordinate system using the registered first and second coordinate systems, to create a two-dimensional (2D) image that simulates a fluoroscopic image that would be generated by the fluoroscopic imaging system based on the 3D map and the calculated FOV, and to display the 2D image that simulates the fluoroscopic image.

DETAILED DESCRIPTION OF EMBODIMENTS

Overview

Minimally-invasive medical procedures often use imaging capabilities, such as magnetic position tracking maps. For example, Biosense-Webster, Inc. (Diamond Bar, Calif.) provides the CARTO™ system, used for visualizing a catheter in a patient heart using magnetic-field position tracking. In some cases, there is a need for a real-time (RT) fluoroscopic image of the same location, in parallel to the magnetic position tracking map. Fluoroscopic imaging, however, exposes the patient and staff to potentially-hazardous doses of X-ray radiation. In practice, the Field-Of-View (FOV) of the fluoroscopic system is often narrow, and a considerable portion of X-ray radiation is applied when attempting to position the fluoroscopic system to image the desired location in a patient's body.

Embodiments of the present invention that are described herein provide improved methods and systems for jointly operating a fluoroscopic system and a magnetic position tracking system. In some embodiments, a processor of the magnetic position tracking system registers the coordinate systems of the fluoroscopic system and the magnetic position tracking system, and calculates the FOV of the fluoroscopic system in the coordinate system of the magnetic position tracking system. Using this information, the processor creates a two-dimensional (2D) image that simulates a fluoroscopic image that would be generated if the fluoroscopic imaging system were to be activated at this point.

The 2D image is based on the computed 3D map of the magnetic position tracking system, and does not originate from the fluoroscopic imaging system at all. In the context of the present patent application and in the claims, the term “3D map” refers to a 3D model that is obtained using the magnetic position tracking system as well as possibly imported segmented objects from additional imaging modalities such as Computerized Tomography (CT), Magnetic Resonance Imaging (MRI) or any other suitable imaging techniques. Such a model may comprise various objects, such as contours and anatomical features of the imaged organ, medical probes or instruments in or around the organ, and/or any other suitable object. Any such object of the 3D model may be used for producing the 2D image and/or may appear in the 2D image.

Even though the 2D image is not produced by the fluoroscopic imaging system, the 2D image is visually similar to a fluoroscopic image, and encompasses the same FOV that would have been viewed by the fluoroscopic imaging system if it were active. As a result, the physician can be provided with a real-time display that appears like fluoroscopic imaging but does not involve irradiating the patient.

The disclosed technique may assist the physician to position the fluoroscopic system FOV in the target position, without exposing the patient and medical staff to X-ray radiation, and to accurately position the fluoroscopic system FOV on target with high speed and accuracy. The fluoroscopic system is typically activated only after its FOV is positioned correctly.

System Description

FIG. 1is a schematic pictorial illustration of a fluoroscopic imaging system22and a magnetic position tracking system20during a minimally invasive cardiac procedure, in accordance with an embodiment of the present invention. Fluoroscopic imaging system22is connected to magnetic position tracking system20via an interface56. System20comprises a console26, and a catheter24, which has a distal end34as shown in an insert32ofFIG. 1.

A cardiologist42(or any other user) navigates catheter24in a patient's heart28, until distal end34reaches the desired location in this organ, and then cardiologist42performs a medical procedure using distal end34. In other embodiments, the disclosed techniques can be used with procedures that are performed in any other organ, and instead of cardiologist42, any suitable user (such as a pertinent physician, or an authorized technician) can operate the system.

This method of position tracking is implemented, for example, in the CARTO™ system, produced by Biosense Webster Inc. (Diamond Bar, Calif.) and is described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Pat. No. Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are all incorporated herein by reference.

Console26comprises a processor58, a driver circuit60, and interface56to system22, input devices46, and a display40. Driver circuit60drives magnetic field generators36, which are placed at known positions below a patient's30torso. In case a fluoroscopic image is needed, cardiologist42uses input devices46and a suitable Graphical User Interface (GUI) on display40to request a fluoroscopic image in patient's heart28.

In some embodiments, display40comprises two windows, as shown in an insert37ofFIG. 1. A 3D CARTO map38window displays a 3D magnetic position tracking map of an organ at the position of distal end34. A simulated 2D fluoroscopic image39window displays a simulated 2D fluoroscopic image at the position of system22.

In an embodiment, the simulated 2D fluoroscopic image is created based on the 3D magnetic position tracking map and not based on parameters of system22, as described herein below in details.

In the example ofFIG. 1catheter24is present. However, once systems20and22are registered, the presence of the catheter is not mandatory. Registration may be performed, for example, using a special registration jig and can be done before or after the catheter is inserted into the patient. In an embodiment, if the catheter is positioned within the covered frame area, then it appears in map38and in image39.

In another embodiment, cardiologist42may decide to exclude catheter24or any other object from image39as it is a simulated image. Such decisions may also be taken automatically by the system. In other words, processor58may filter the objects that are displayed in the simulated 2D image. Objects that can be shown or hidden may comprise, for example, tags, maps, catheters and/or imported segmented images, among others.

The configuration of system20shown inFIG. 1is an example configuration, which is chosen purely for the sake of conceptual clarity. In alternative embodiments, any other suitable configuration can be used for implementing the system. Certain elements of system20can be implemented using hardware, such as using one or more Application-Specific Integrated Circuits (ASICs) or Field-Programmable Gate Arrays (FPGAs) or other device types. Additionally or alternatively, certain elements of system20can be implemented using software, or using a combination of hardware and software elements.

Creation of a Simulated 2D Fluoroscopic Image

In the example presented inFIG. 1, processor58of system20displays on display40a 3D map of patient's heart28comprising distal end34, so cardiologist42knows the exact location of distal end34with respect to the pertinent area in heart28. During a minimally-invasive medical procedure, cardiologist42may need fluoroscopic images in the vicinity of distal end34. The embodiments described herein fulfill the need for minimizing X-ray irradiation while acquiring a 3D fluoroscopic image.

Conventionally, in case a fluoroscopic image is needed, cardiologist42defines the desired area by positioning system22to point the desired location and then activating system22to irradiate X-rays in order to position the fluoroscopic system to image the desired area of heart28. Typically, the Field-Of-View (FOV) of system22is often narrow and may not actually cover the desired area of heart28. In such cases, cardiologist42has to reposition system22and re-irradiate X-rays to reach the desired location. This process exposes the patient and medical staff to excess X-ray radiation.

In some embodiments, the presented technique shows on display40two images (typically but not necessarily in two windows): 3D CARTO map38, showing a 3D position tracking map of distal end34within heart28, and image39at the position of system22.

In a typical flow, processor58of system20calculates a FOV that would be irradiated by fluoroscopic imaging system22in the coordinate system of magnetic position tracking system20, based on a registration of the coordinate systems of system22and system20. Subsequently, processor58uses the calculated FOV of system22in the coordinate system of magnetic position tracking system20, and 3D map38, to create a simulated 2D image (shown as image39inFIG. 1) without irradiating X-rays by system22.

As demonstrated inFIG. 1, fluoroscopic imaging system22is positioned at some arbitrary angle relative to the coordinate system of magnetic position tracking system20. Nevertheless, simulated 2D image39is displayed as if taken from the position of fluoroscopic imaging system22or from any other selected angle regardless the current position of system22, even though it is calculated from the 3D map of position tracking system20.

In an embodiment cardiologist42may move system22relative to patient30in the same way that it is performed during a conventional procedure, but without irradiating patient30. As system22moves, processor58continuously displays simulated 2D images that reflect the changing FOV of system22in real time.

In some embodiments the processor is using anatomical features of the heart, which appear as elements in the 3D map of the magnetic position tracking system, to create the simulated 2D fluoroscopic image. For example, a 3D map of an interface between an atrium and a ventricle can be used to create image39.

Note that image39is created without using radiation from system22, and it is based on map38. Accordingly, in case the FOV of system22falls outside 3D map38of system20, image39would not show a simulated image of its current position since it does not have the attributes provided by map38to create the required simulated image.

In an embodiment, cardiologist42uses the simulated 2D fluoroscopic image and the 3D position tracking map to position system22at the desired location and then, to apply X-ray by system22and acquire a real fluoroscopic image.

Typically, map38comprises anatomical features of the organ in question, and optionally additional elements in the FOV of map38such as catheters. In cardiac imaging, such objects may comprise, for example, cardiac chambers, valves, arteries, and other objects. In some embodiments processor58identifies such anatomical features (e.g., tissue types, anatomical landmarks) in map38and calculates how they would appear in 2D when viewed from the FOV of system22to create image39from map38.

Image39is simulated from map38, however typically it is visually similar to a real fluoroscopic image (e.g., same grey scale, same resolution, same look-and-feel), even though it does not originate from nor based on imaging attributes from system22. In some embodiments, image39may have enhancements over the radiation-based fluoroscopic image, such as higher resolution, display in color, and additional simulated enhancements.

In the example ofFIG. 1, the 3D map and the 2D image are displayed in separate display windows. In an alternative embodiment, the simulated 2D image is displayed as a “picture-in-picture,” i.e., in a sub-window of the window used for displaying the 3D map. In an embodiment, the 2D image is refreshed in response to the physician pressing a pedal or other input device of the magnetic position tracking system. Such a pedal has a similar look-and-feel to the pedal that is commonly used to acquire fluoroscopic images, but in the present example is part of system20, not22.

FIG. 2is a flow chart that schematically illustrates a method for creating a simulated two-dimensional (2D) fluoroscopic image39, in accordance with an embodiment of the present invention. The method begins at a coordinate acquisition step100, in which processor58acquires the coordinate systems of system22and system20. At a coordinate system registration step102, processor58registers the coordinate systems of system22and system20, in order to match positions of a pertinent organ in patient30at both systems.

At a position tracking presentation step104, processor58displays 3D position tracking map38of a given organ of patient30on display40. In an embodiment, the organ is heart28, but may be any pertinent organ of patient30in other embodiments. At a FOV calculation step106, processor58uses a registration of the coordinate systems of system22and system20to calculate the FOV of system22in the coordinate system of magnetic position tracking system20. In some embodiments, the position of system22is measured by position sensors attached to a radiation head of system22. In alternative embodiments, TCP/IP communication with system22can be used to extract geometrical information and detector settings. Such alternative embodiments allows to use the correct magnification (“zoom”), which may not be applicable while using sensors.

At a simulation step108, processor58uses the calculated FOV of fluoroscopic imaging system22in the coordinate system of magnetic position tracking system20, and 3D CARTO map38, to create a simulated 2D fluoroscopic image (image39inFIG. 1) without irradiating X-rays by system22and without using any radiation parameters of system22.

In some embodiments image39is displayed in a window near map38as shown in insert37ofFIG. 1. In other embodiments image39is displayed at the same window of map38, side by side or at any other suitable manner. At a decision step112, cardiologist42examines image39with respect to map38and decides whether system22is positioned at the desired location to acquire a real fluoroscopic image. If cardiologist42decides that system22is positioned at the desired location, he/she uses input devices46and GUI on display40to command system22(via processor58and interface56) to acquire a fluoroscopic image, at an image acquisition step116. In other embodiments the cardiologist may count on the simulated image to avoid radiation, or may use old fluoroscopic images as a reference and use the simulated image for tracking the catheter.

Note that all the method steps prior to step116are typically performed while fluoroscopic system22does not emit X-ray radiation.

If cardiologist42decides that system22is not positioned at the desired location, the cardiologist repositions the fluoroscopic system relative to the patient, at a repositioning step114.

At this point, in various embodiments, the method may loop back to various previous stages of the process. In an embodiment where system22is tracked using TCP/IP communication with system22, the simulated image can be displayed during the motion of the radiation head of system22.

In other embodiments the flow may loop back to position tracking presentation step104or to coordinate acquisition step100, according to the nature of the source of the registration error of system22with respect to patient30and magnetic position tracking system20

Although the embodiments described herein refer mainly to cardiac imaging using fluoroscopy and magnetic position tracking, in alternative embodiments the disclosed techniques may be used with other imaging techniques, such as Magnetic Resonance Imaging (MRI), and applied on other human organs.