METHODS, SYSTEMS, AND COMPUTER READABLE MEDIA FOR IMAGE GUIDED ABLATION
The subject matter described herein includes methods, systems, and computer readable media for image guided ablation. One system for image guided ablation includes an ultrasound transducer for producing a real-time ultrasound image of a target volume and of surrounding tissue. The system further includes an ablation probe for ablating the target volume. The system further includes a display for displaying an image to guide positioning of the ablation probe during ablation of the target volume. The system further includes at least one tracker for tracking position and orientation of the ablation probe during the ablation of the target volume. The system further includes a rendering and display module for receiving a pre-ablation image of the target volume and for displaying a combined image on the display, where the combined image includes a motion tracked, rendered image of the ablation probe and an equally motion tracked real-time ultrasound image registered with the pre-ablation image.
This application is a continuation of U.S. patent application Ser. No. 12/842,261, filed Jul. 23, 2010, which is a continuation of PCT International Patent Application No. PCT/US2009/032028, filed Jan.26, 2009, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/023,268, filed Jan. 24, 2008; the disclosures of each which are incorporated herein by reference in their entireties.
GOVERNMENT INTERESTThis presently disclosed subject matter was made with U.S. Government support under Grant No. 1-R01-CA101186-01A2 awarded by the National Institutes of Health. Thus, the U.S. Government has certain rights in the presently disclosed subject matter.
TECHNICAL FIELDThe subject matter described herein relates to image guided medical treatment systems. More particularly, the subject matter described herein relates to methods, systems, and computer readable media for image guided ablation.
BACKGROUNDAblation, such as radio frequency ablation (RFA), microwave ablation, and cryo-ablation, is a first-line treatment for non-resectable hepatic and other types of tumors. RFA is a minimally invasive intervention (MII) uses high-frequency electrical current, introduced—under 2D ultrasound guidance—via a percutaneous needle-like probe, to heat the targeted tissues to physiologically destructive levels. RFA probes are characterized by manufacturer-specified ablation zones that are typically spheres or ellipsoids. The interventional radiologist who performs the procedure must place the probe such that the entire tumor as well as a safety boundary of several millimeters thickness are contained within the predicted ablation area. Frequent tumor recurrence on the periphery of the original tumor [1] indicates that probe placement accuracy may be a major cause for the low 5-year survival rates of hepatic carcinoma patients.
It is believed that physicians will more accurately target RFA to hepatic and other tumors using a contextually correct 3D visualization system than with standard 2D ultrasound alone. If proven beneficial, 3D guidance could decrease the high post-RFA tumor recurrence rate [3]. Prior experience in developing and evaluating a guidance system for breast biopsy [5] yield results that support this hypothesis.
Accordingly, there exists a long-felt need for methods, systems, and computer readable media for image guided ablation.
SUMMARYThe subject matter described herein includes methods, systems, and computer readable media for image guided ablation. One system for image guided ablation includes an ultrasound transducer for producing a real-time ultrasound image of a target volume to be ablated and surrounding tissue. The system further includes an ablation probe for ablating the target volume. The system further includes a display for displaying an image to guide position of the ablation probe during ablation of the target volume. The system further includes at least one tracker for tracking position of the ablation probe during the ablation of the target volume. The system further includes a rendering and display module for receiving a pre-ablation image of the target volume and for displaying a combined image on the display, where the combined image includes a motion tracked, rendered image of the ablation probe and the real-time ultrasound image registered with the pre-ablation image of the target volume.
The subject matter described herein for image guided ablation may be implemented using a computer readable medium comprising computer executable instructions that are executed by a computer processor. Exemplary computer readable media suitable for implementing the subject matter described herein includes disk memory devices, programmable logic devices, and application specific integrated circuits. In one implementation, the computer readable medium may include a memory accessible by a processor. The memory may include instructions executable by the processor for implementing any of the methods described herein for image guided ablation. In addition, a computer readable medium that implements the subject matter described herein may be distributed across multiple physical devices and/or computing platforms.
The subject matter described herein will now be explained with reference to the accompanying drawings of which:
The subject matter described herein includes methods, systems, and computer readable media for image guided ablation. The following paragraphs describe how an exemplary implementation of the present subject matter was designed, comparing the two designs introduced in
Our research team has developed 3D guidance for Mils since the mid-1990s; all our systems were based on see-through head-mounted displays (ST-HMDs) [6]. We demonstrated superior targeting accuracy in breast lesions when comparing ST-HMD guidance with the standard 2D method [5]. In addition to stereoscopy and head-motion parallax, the system based on motion-tracked ST-HMDs provided a view of the patient that included a synthetic opening into the patient, showing live echography data and 3D tool guidance graphics in registration with the “real world,” and therefore also with the patient (
Stereoscopic visualization with head-motion parallax can also be implemented with fixed displays, i.e. without mounting the display on the user's head. Such “fish tank” displays may use CRT monitors and frame-sequential shutter glasses [2], or (at a larger scale) projection displays and passive polarized glasses, for example. Recently, devices based on LCD panels and a semi-transparent mirror have become available from Planar Systems, Inc. [4]; these use passive linearly polarized glasses.
While we obtained encouraging results in the past with ST-HMD systems, we are disappointed with the bulky and uncomfortable, low-resolution devices resulting from today's state of the art in HMDs. Moreover, since there are no satisfactory video see-through devices on the market, we always constructed our own, with rather modest resources [6]. For these reasons, when designing the RFA 3D guidance system, we considered both an ST-HMD approach and a commercial fish tank system (
The above considerations led us to favor a fish tank type display even though it does not offer registration between virtual display and internal patient anatomy. Since our display metaphor proposes life-size representations of the ultrasound image and of the ablation probe, projection displays are unsuitable; and CRT-based stereo has disadvantages such as the requirement for active stereo glasses, which can exhibit flicker. The Planar SD1710 display [4] was almost ideally suited: its small 17-inch 1280×1024 display can fully contain our 3D display elements at life size. Furthermore, it does not exhibit flicker and has manageable bulk.
In
The system illustrated in
The subject described herein is not limited to using a fish tank VR display. As stated above, a virtual see through head mounted display may be used without departing from the scope of the subject matter described herein. In an embodiment that uses a virtual see through head mounted display, tracker 408 can track both the display and the user's head using headband 406, since the display is worn on the user's head.
A rendering and display module 412 receives the real-time ultrasound image, pre-ablation image data, tracking data from tracker 408, produces combined, stereoscopic, head tracked imagery and displays the imagery on display 410. The combined imagery may include a motion tracked, rendered image of the RFA probe, the real-time ultrasound image registered with the pre-ablation image of the target volume, shown from a viewpoint of the user. Exemplary images that may be computed and displayed by rendering and display module 412 will be illustrated and described in detail below.
2. Display System Implementation DetailsIn one exemplary implementation of the present subject matter, a motion tracker is mounted on the display as in handheld augmented reality applications. Thus, both the tracker base and the stereoscopic display can be moved relative to each other at any time without recalibration to adjust for space and/or line-of-sight constraints within the operating environment; this aims to improve visibility of the tracked system components by the tracker and thereby tracking accuracy and/or reliability. The control software, i.e., rendering and display module 412, ensures that the 3D display preserves orientation; e.g., the virtual representations of tracked devices such as the RFA probe in the display are always shown geometrically parallel to the actual devices, in this case the handheld ablation probe 402. The same applies to the ultrasound transducer 400. In other words, as opposed to the registration in both position and orientation provided by the ST-HMD, this technique maintains only orientation alignment; it introduces a translational offset between the location of the instruments in the real world on the one hand, and their virtual counterparts in the 3D display on the other hand. The interface implemented by rendering and display module 412 has three presentation modes that differ in how these user-induced translational movements of the instruments are echoed in the 3D display (orientation changes are always fully shown, as mentioned):
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- A. Centered mode: The ultrasound image is always shown in the center of the 3D display. It is not possible to move the ultrasound transducer such that it leaves the display area.
- B. Free mode: The user can interactively define the position offset between an area within the patient and the 3D space seen inside the display. Translational motion of the instruments is shown fully within the display, and it is possible to move the ultrasound transducer such that it leaves the display area.
- C. Delayed mode: This is a combination of the above two modes. The ultrasound image is initially centered as in (A), but the user may move the ultrasound transducer, even outside the display. However after a short lag, the system “catches up” and re-centers the ultrasound image. This allows the user to perceive high-speed translational motion of the ultrasound transducer and image; at low speeds or statically, this is equivalent to (A), at high speeds, to (B).
For all three modes above, rendering and display module 412 continually calculates the appropriate transformations for the RFA probe, in order to always show the correct pose relationship between it and the ultrasound image.
Given the small size of the display, it is important for the system to accurately track the user's eyes, in order to minimize geometric distortions. A fast and accurate method to calibrate the user's eyes to the head tracker is referenced in the context of which is set forth below [7].
Table 1 summarizes the principal characteristics of the two display techniques we have considered using for the RFA guidance system (ST-HMD and fish tank VR system).
At present there is no controlled study comparing the performance of the head-tracked fish tank display to an ST-HMD device. An interventional radiologist (Charles Burke, MD, UNC Radiology) who has used the head-tracked fish tank display extensively, reports that depth perception is good and that the display correctly portrays three-dimensional relationships during RFA probe targeting. A depth perception study conducted with this display revealed that most subjects (a randomly selected group of 23) were able to determine which of two objects located only a few millimeters apart in depth was closer, based solely on stereoscopic and motion parallax cues provided by the fish tank display.
The present 3D RF ablation guidance system has been tested on specially constructed liver phantoms; the completed system is currently used in a controlled animal study to ablate liver carcinomas in woodchucks (FIG. 5, left). The study randomizes each woodchuck to either the ultrasound-only conventional guidance method or to the present ultrasound-with-3D-guidance technique.
According to one aspect of the subject matter described herein, rendering and display module 412 may display the target volume, such as the tumor, with successively smaller size as ablated regions are eliminated from display with each ablation pass. Such an image is useful for multiple pass techniques that are aim to treat a large tumor with multiple overlapping ablations. In one embodiment, an initial target volume to be ablated may be shown as a three dimensional structure on a display screen. The initial target volume may be rendered from the pre-ablation image data, such as MRI or CT image data.
After a first ablation pass, the volume affected by the first ablation pass may be subtracted from the displayed representation of the initial target volume. The volume affected by the first ablation pass may be determined mathematically based on the position of the ablation probe at the time of the first ablation pass, the geometry of the ablation probe, and the tine deployment and power settings of the ablation probe during the first ablation pass. For example, if the probe is the above-referenced LeVeen needle electrode probe, the affected volume for an ablation pass may be determined based on manufacturers specifications. In one current implementation, a constant ellipsoid based on what the probe data sheet indicates is used as the affected ablation volume may be subtracted from the image of the target volume. In alternate implementations, pre-calibrated volumes (shapes measured in a test ablated human-organ-like phantom) or varying the shape based on time deployment can be used to determine the affected sub volume. However, the probes are usually specified to be used with fully deployed times, and manufacturers do not give partial deployment information. Additional bio-chemo-thermo-geometric calibration and simulation work, possibly taking into account fluid flow through blood vessels, may be utilized to increase the accuracy of the affected ablation volume estimates.
Region 504 illustrated in
As stated above, rendering and display module 412 may both calculate and display in real-time the amount of tumor and background tissue that would be ablated for the momentary location of the ablation probe, in order to illustrate on the display the impact of probe position. The calculation and display of the amount of tumor and background tissue that would be affected by an ablation can be performed in real-time or may use a lookup table based on the geometry and location of the probe. As stated above, the affected volume can be determined using the data from the probe manufacturer or using experimental data. The volume that would be affected by the ablation can be super imposed about the ablation probe position and displayed to the user.
According to another aspect of the subject matter described herein, the guidance system will benefit from accurate registration of the user's eyes for precise head tracked stereoscopic visualization. An exemplary method for accurate registration of the user's eyes for precise head tracked stereoscopic visualization will now be described.
The high accuracy is achieved in the same calibrated, stereoscopic head-tracked viewing environment used by the guidance system. While the current implementation requires a head-mounted tracker, future embodiments may use un-encumbering tracking, such as vision-based head pose recovery. It is important to note that the technique described here does not require pupil tracking; it uses only head pose, which can generally be obtained less intrusively, with higher reliability, and from a greater distance away than camera-based pupil tracking. An additional pupil tracker is not required unless the system must know the user's gaze direction, for example in order to record user behavior in training-related applications [14].
2. Calibration System for Exact Eye LocationsThe calibration system uses the following main components (
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- a Planar Systems SD1710 (“Planar”) stereoscopic display with two 17″ LCD monitors and a semi-transparent mirror that reflects the upper monitor's image onto the lower monitor. The user wears linearly polarized glasses that restrict viewing of the lower monitor to the left eye and viewing of the upper monitor's reflection to the right eye. The LCDs' native resolution is 1280×1024.
- a sub-millimeter precision Northern Digital Optotrak Certus optoelectronic tracking system (“Certus”). Both the Planar and the user's head are tracked by the Certus in all six degrees of freedom with clusters of infrared (IR) LEDs (11 on the head, 4 on the Planar). As mentioned, the advantage of tracking the display as in handheld augmented reality applications [15] is that both the display and the tracker can be moved with respect to each other while the system is running, for example, to improve LED visibility. The Certus also provides a calibration stylus for precise measurements (visible in
FIG. 9 ).
The user dons the head tracker and performs a simple, fast eye calibration procedure.
In fish tank VR systems, the calibration between the head tracker and the eyes is usually obtained from measurements such as the user's inter-pupillary distance (IPD, measured with a pupillometer) [8], the location of the tracker on the user's head, as well as from assumptions about the most suitable location of the projection origin inside the eye. Popular choices for the latter include the eye's 1st nodal point [2], the entrance pupil [9], and the center of the eye [10]. Our method uses the eye center [10] because it is easy to calibrate and yields exact synthetic imagery in the center of the field of view regardless of the user's gaze. However, the 1st nodal point and the entrance pupil are better approximations for the actual optics within the eye. Therefore, by rendering stereo images from the eye centers, i.e. from a few mm too far back, and thus with a slightly exaggerated separation, the EEC system deforms the stereoscopic field [11] ever so slightly. For higher accuracy, a pupil tracker could detect the user's gaze directions, and assuming that the user converges onto the virtual object found along those directions, the rendering and display module could move the projection origins forward to the 1st nodal point, or all the way to the pupil. Calibration. The eye calibration technique (
Since the current head band tracker (
As stated above, the user's head or eyes can be tracked during image guided ablation and the combined display shown by the rendering and display module 412 can adjust the combined display of the treatment volume based on the current position of the user's head and/or eyes. For example, in the images illustrated in
Exact eye calibration in an ablation procedure can be used to produce the same 3D effect illustrated in
According to another aspect of the subject matter described herein, rendering and display module 412 may render preoperative data, including an anatomical context for the ablation of the target volume. For example, rendering and display module 412 may render organs or anatomical structures such as bones or blood vessels adjacent to the target volume.
The disclosure of each of the following references is hereby incorporated herein by reference in its entirety.
REFERENCES
- [1] O. Catalano et al. “Multiphase helical CT findings after percutaneous ablation procedures for hepatocellular carcinoma.” Abdom. Imaging, 25(6), 2000, pp. 607-614.
- [2] Michael Deering. “High Resolution Virtual Reality.” Proceedings of SIGGRAPH '92, Computer Graphics, 26(2), 1992, pp. 195-202.
- [3] G. D. Dodd et al. “Minimally invasive treatment of malignant hepatic tumors: at the threshold of a major breakthrough.” Radiographics 20(1), 2000, pp. 9-27.
- [4] http://www.planarcom/products/flatpanel_monitors/stereoscopic/
- [5] Michael Rosenthal, Andrei State, Joohi Lee, Gentaro Hirota, Jeremy Ackerman, Kurtis Keller, Etta D. Pisano, Michael Jiroutek, Keith Muller and Henry Fuchs. “Augmented reality guidance for needle biopsies: An initial randomized, controlled trial in phantoms.” Medical Image Analysis 6(3), September 2002, pp. 313-320.
- [6] Andrei State, Kurtis P. Keller, Henry Fuchs. “Simulation-Based Design and Rapid Prototyping of a Parallax-Free, Orthoscopic Video See-Through Head-Mounted Display.” Proc. International Symposium on Mixed & Augmented Reality 2005 (Vienna, Austria, Oct. 5-8, 2005), pp. 28-31.
- [7] Andrei State. “Exact Eye Contact with Virtual Humans.” Proc. IEEE International Workshop on Human Computer Interaction 2007 (Rio de Janeiro, Brazil, Oct. 20, 2007), pp. 138-145.
[8] Meehan, M., Razzaque, S., Whitton, M., Brooks, F.: Effects of Latency on Presence in Stressful Virtual Environments. Proceedings of IEEE Virtual Reality 2003, IEEE Computer Society, 141-148 (2003).
- [9] Rolland, J. P., Burbeck, C. A., Gibson, W., Ariely, D.: Towards Quantifying Depth and Size Perception in 3D Virtual Environments. Presence: Teleoperators and Virtual Environments 4(1), 24-48 (1995).
- [10] Holloway, R.: Registration Error Analysis for Augmented Reality. Presence: Teleoperators and Virtual Environments 6(4), 413-432 (1997).
- [11] Lipton, L.: Foundations of the Stereoscopic Cinema. Van Nostrand Reinhold (1982).
- [12] Azuma, R., Bishop, G.: Improving Static and Dynamic Registration in an Optical See-Through HMD. Proceedings of SIGGRAPH '94, Computer Graphics, Annual Conference Series, 1994, 197-204 (1994).
- [13] Fuhrmann, A., Splechtna, R., Pikryl, J.: Comprehensive calibration and registration procedures for augmented reality. Proc. Eurographics Workshop on Virtual Environments 2001, 219-228 (2001).
- [14] Raij, A. B., Johnsen, K., Dickerson, R. F., Lok, B. C., Cohen, M. S., Duerson, M., Pauly, R. R., Stevens, A. O., Wagner, P., Lind, D. S.: Comparing Interpersonal Interactions with a Virtual Human to Those with a Real Human. IEEE Transactions on Visualization and Computer Graphics 13(3), 443-457 (2007).
- [15] Billinghurst, M., Henrysson, A.: Research Directions in Handheld AR. Int. J. of Virtual Reality 5(2), 51-58 (2006).
Although the examples described above relate primarily to RFA, the subject matter described herein is not limited to image guided RFA. The image guided techniques and systems described herein can be used with any type of ablation, including microwave ablation and cryo-ablation. In microwave ablation, a needle delivers microwave energy to the target volume. In cryo-ablation, a needle delivers cold fluid to the target volume. The tracking, rendering, and display techniques and systems described above can be used to track, render, and display microwave and cryo-ablation needles in the same manner described above. In addition, the techniques and systems described above for displaying predicted ablation volumes and ablated volumes for successive ablation passes can be applied to microwave and cryo-ablation probes by configuring rendering and display module 412 with manufacturer's specifications for these types of probes.
It will be understood that various details of the subject matter described herein may be changed without departing from the scope of the subject matter described herein. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the subject matter described herein is defined by the claims as set forth hereinafter.
Claims
1. A system for image guided ablation, the system comprising:
- an ultrasound transducer for producing a real-time ultrasound image of surrounding tissue and a target volume and surrounding tissue;
- an ablation probe for ablating the target volume;
- a display for displaying an image to guide positioning of the ablation probe during ablation of the target volume;
- at least one tracker for tracking position of the ablation probe during the ablation of the target volume; and
- a rendering and display module for receiving a pre-ablation-treatment image of the target volume and for displaying a combined image on the display, where the combined image includes a motion tracked, rendered image of the ablation probe and the real-time ultrasound image registered with the pre-ablation image of the target volume, wherein the at least one tracker tracks the positions and orientations of the user's head and of the display, wherein the rendering and display module displays the combined image from the viewpoint of the user based on the tracked positions and orientations of the display and the user's head, wherein the rendering and display module receives eye calibration data indicating positions of the user's left and right eyes with respect to the tracked position and orientation of the user's head, and wherein combined image comprises a stereoscopic image with left and right eye images generated based on the eye calibration data and the tracked position and orientation of the user's head.
Type: Application
Filed: Feb 11, 2016
Publication Date: Sep 22, 2016
Inventors: Henry Fuchs (Chapel Hill, NC), Hua Yang (Chapel Hill, NC), Tabitha Peck (Chapel Hill, NC), Anna Bulysheva (Richmond, VA), Andrei State (Chapel Hill, NC)
Application Number: 15/041,868