WO2012025854A1

WO2012025854A1 - Real-time catheter visualization with ultrasound through magnetically induced vibration

Info

Publication number: WO2012025854A1
Application number: PCT/IB2011/053630
Authority: WO
Inventors: Sheng-Wen Huang; Ramon Quido Erkamp; Emil George Radulescu; William Tao Shi
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-08-23
Filing date: 2011-08-17
Publication date: 2012-03-01

Abstract

A system, device and method for locating a medical instrument during a procedure includes an imaging device (102) configured to image a region of interest. A medical instrument (114) has a magnetic portion (124). A signal generator (116) is configured to be coupled to the imaging device and generate an encoded magnetic fluctuation pattern having a temporal relationship with scanning by the imaging device to cause oscillation of a magnetic field in the region of interest. The magnetic fluctuation pattern causes the magnetic portion to correspondingly vibrate to identify the magnetic portion in an image of the region of interest.

Description

REAL-TIME CATHETER VISUALIZATION WITH ULTRASOUND THROUGH

MAGNETICALLY INDUCED VIBRATION

This disclosure relates to medical component tracking, and more particularly a system, device and method for catheter tracking using magnetic fields.

Visualization of catheter tips is essential in many surgical procedures, e.g., in cardiac interventional procedures. Accurate catheter visualization using ultrasound is challenging because, in general, catheters are characterized by uncontrollable angle dependent specular reflection.

Cardiac interventional procedures involve cardiac catheterization, insertion of a catheter into the heart, and visualization of the catheter and its tip. Currently, fluoroscopy (i.e., X-ray imaging) is the standard imaging modality for catheter visualization and guidance. Fluoroscopy's shortcomings include cost, ionizing radiation exposure, limited two- dimensional (2D) projection imaging, lack of soft tissue visualization, transience of contrast enhancement, nephrotoxicity of the X-ray contrast material, etc.

Both magnetic resonance imaging (MRI) and ultrasound can be used as an alternative for catheter tracking. Compared to MRI, live ultrasound imaging for real-time catheter visualization is more desirable because of its low cost and real-time tissue

visualization. However, in B-mode ultrasound images, it is often difficult to separate the tip of a catheter consistently from the background tissue. Even with specular reflection, echo intensity based imaging modalities may not be sufficient for catheter tip identification because there are strong reflections from certain tissues or tissue interfaces. Suboptimal catheter visibility in, e.g., transthoracic echocardiography (TTE) and transesophageal

echocardiography (TEE), limits the potential of live 3D TTE/TEE for cardiac intervention guidance, despite the widespread acceptance of TTE/TEE for diagnostic imaging.

Electromagnetic (EM) tracking sensors mounted on catheters to assist in locating the catheters would be expensive and lack accuracy (e.g., only accurate to within a few millimeters in EM distorted environments). In addition, when EM tracking is used in conjunction with ultrasound, dedicated registration is required.

In accordance with the present principles, a system, device and method for locating a medical instrument during a procedure include an imaging device configured to image a region of interest. A medical instrument has a magnetic portion. A signal generator is configured to be coupled to the imaging device and generate an encoded magnetic fluctuation pattern having a temporal relationship with scanning by the imaging device to cause oscillation of a magnetic field in the region of interest. The magnetic fluctuation pattern causes the magnetic portion to correspondingly vibrate to identify the magnetic portion in an image of the region of interest.

A medical instrument includes a device body and a magnetic portion mounted on the device body. The magnetic portion is configured to be responsive to a fluctuating magnetic field such that the magnetic field causes the magnetic portion to vibrate in accordance with a single-tone or coded signal having a temporal relationship with an imaging scanner to improve visibility of the magnetic portion in images taken during a medical procedure.

A method for locating a medical instrument during a procedure includes generating a single-tone or coded oscillation signal having a temporal relationship with an imaging device; fluctuating a magnetic field in a vicinity of a region of interest in accordance with the oscillation signal; inducing vibrations in a magnetic portion of a medical instrument in accordance with the magnetic field; and displaying the magnetic portion in the region of interest such that the vibrations increase contrast in an image of the region of interest.

These and other objects, features and advantages of the present disclosure will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.

This disclosure will present in detail the following description of preferred embodiments with reference to the following figures wherein:

FIG. 1 is a block/flow diagram showing a system for locating a medical device in accordance with one illustrative embodiment;

FIG. 2 is diagram showing an illustrative catheter in accordance with one exemplary embodiment;

FIG. 3 is a block/flow diagram showing a system/method for decoding of signals in accordance with one illustrative embodiment; and FIG. 4 is a block/flow diagram showing a system for locating a

medical device in accordance with another illustrative embodiment.

In accordance with the present principles, a system, device and method provide visualization of a catheter tip. In one embodiment, a catheter is modified by attaching one or more miniature permanent magnets onto and around its tip. The size of the magnets used may be, e.g., on the order of 1 mm in diameter. Alternatively, magnetized materials may be employed as the catheter tip and integrated therein or mounted thereon. During use of the system, a coded oscillating magnetic field of low power is induced using an electromagnet in a region of interest in a patient's body to move the tip of the catheter in a coded pattern. The coded vibration of the catheter tip and its surrounding blood/tissue is then detected by a specialized decoding method residing in a conventional ultrasound or other imaging platform. The system is low in cost and can visualize catheters in real time with high accuracy.

Real-time catheter visualization based only on ultrasound imaging in accordance with the present principles is attractive because of its low cost and auto- registration. While catheters are characterized by uncontrollable angle-dependent specular reflection in ultrasound images, the present embodiments provide an accurate position for the catheter during ultrasonic imaging. In B-mode (echo intensity based) ultrasound images, the present embodiments permit separation of the tip of a catheter from the background tissue (especially in the presence of certain strongly reflective tissues). Suboptimal catheter visibility, e.g., in transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE), is no longer limited, and the potential of live 3D TTE/TEE for cardiac intervention guidance is realized in accordance with the present principles.

It should be understood that the present invention will be described in terms of catheters; however, the teachings of the present invention are much broader and are applicable to any components that can be mounted on, positioned in or otherwise placed in a body during a medical procedure. Such devices may include endoscopes or other devices. It should also be understood that the illustrative example, which employs ultrasound imaging, may also include fluoroscopy or other imaging schemes. It should be further understood that the present invention will be described in terms of medical instruments; however, the teachings of the present invention are much broader and are applicable to any instruments employed in tracking or analyzing complex biological or mechanical systems. In particular, the present principles are applicable to internal tracking procedures of biological systems, procedures in all areas of the body such as the lungs, gastro -intestinal tract, excretory organs, blood vessels, etc.

The functions of the various elements shown in the FIGS, can be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions can be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which can be shared. Moreover, explicit use of the term "processor" or "controller" should not be construed to refer exclusively to hardware capable of executing software, and can implicitly include, without limitation, digital signal processor ("DSP") hardware, read-only memory ("ROM") for storing software, random access memory ("RAM"), non-volatile storage, etc.

Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Thus, for example, it will be appreciated by those skilled in the art that the block diagrams presented herein represent conceptual views of illustrative system components and/or circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams and the like represent various processes which may be substantially represented in computer readable storage media and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

Furthermore, embodiments of the present invention can take the form of a computer program product accessible from a computer-usable or computer-readable storage medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable storage medium can be any apparatus that may include, store,

communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk.

Current examples of optical disks include compact disk - read only memory (CD-ROM), compact disk - read/write (CD-R/W) and DVD.

Referring now to the drawings in which like numerals represent the same or similar elements and initially to FIG. 1, an illustrative system 100 is depicted for determining a catheter position in real-time during a procedure. In the embodiment depicted, system 100 includes an ultrasound work station or scanner 102. The work station 102 includes a computer processor 104, a display 105, a user interface 106 (e.g., mouse, keyboard, etc.), an ultrasonic probe 108 and memory 110 for storing data and software. The software may include a decoding module 112 configured to decode vibration patterns of both the magnetic portion itself and the tissue surrounding the magnetic portion of the catheter 114 during a procedure.

A signal generator 116 may be coupled to workstation 102. Signal generator 116 may also be integrated into workstation 102. Signal generator 116 may be configured to generate an encoded magnetic fluctuation pattern including, e.g., single-tone or coded patterns, having a temporal relationship with the imaging device to cause an oscillation of a magnetic field in a region of interest. Signal generator 116 may provide different modes of operation, e.g., a single-tone magnetic excitation asynchronized with the imaging system; a single-tone magnetic excitation synchronized with the imaging system, a coded magnetic excitation asynchronized with the imaging system, a coded magnetic excitation synchronized with the imaging system, etc.

Signal generator 116, which may also include an amplifier, preferably outputs an encoded signal. The encoded signal may rely on an input from the computer processor 104 or the decoding module 112 of the workstation. Alternately, the encoded signal generator 116 may be hardwired or programmed to provide a particular signal pattern. The signal pattern creates a magnetic pulse or alters a magnetic field around the catheter 114. In one

embodiment, the coil 118 is pulsed, and the response of the catheter 114 is measured or viewed on display 105. In another embodiment, the signal pattern may be output to the catheter 114, which may include an electromagnet to generate vibrations.

The magnetic fluctuations may be generated by a coil 118. In this case, the coil 118 or other electromagnetic element alters the generated magnetic field in or around an area of interest to cause a response in a magnetic portion of the catheter 114. The signal to the generator 116 is synchronized or asynchronized with the ultrasound system workstation 102. The decoding module 112 interprets the position of the magnetic portion of the catheter and generates an image which is output to the display 105 along with the ultrasonic image. In this way, the ultrasonic images accurately reflect a position of the catheter 114 in real-time.

In one embodiment, the coil 118 may be embedded on or in a gurney 123 or other patient support platform (e.g., bed). In other embodiments, the coil or coils 118 may be moveable to optimize vibration of the magnetic portion of the catheter 114.

System 100 achieves real-time catheter visualization using ultrasound by tracking vibration of catheter tips and their surrounding tissues induced magnetically. The catheter 114 includes one or multiple miniature permanent magnets 124 on or around its tip 130 (or magnetized material may be used). An electromagnet or coil 118 generates a magnetic field to vibrate the catheter 114 in a coded pattern and in synchrony with an ultrasound scanner 102. A software module (decode module) 112 on the ultrasound scanner 102 is configured to decode the vibration pattern and then locate the catheter 114 using RF data captured by the scanner 102.

The size of the permanent magnets 124 may be on the order of 1 mm in diameter, making the modification fully feasible for interventional procedures. Other sized magnets may be employed. The electromagnet 118 may be integrated into a procedure bed, yielding normal handling of an ultrasound transducer 108 and the catheter 114. The decoding method of module 112 is implementable on the ultrasound imaging system 102. All of the features provided lead to a low-cost system that can visualize catheters with high accuracy in real-time.

For a catheter to be sensitive to a magnetic field, one or more miniature permanent magnets 124 are attached onto and around the tip 130 of the catheter 114. The size of these permanent magnets 124 can be about 1 mm or even less so that only a slight modification of the catheter may be needed. In this case, strong but inexpensive neodymium magnets may be used to provide enough vibration. Other materials may also be employed.

The electromagnet or coil 118 is used to generate a magnetic field that vibrates the catheter. The electromagnet or coil 118 receives a signal from the signal generator 116. The electromagnet 118 outputs a coded oscillating magnetic field to move the tip 130 of the catheter 114 in a controlled pattern. The signal generator 116 is triggered to drive the coil 118 using the ultrasound scanner 102 or is synchronized with the ultrasound scanner 102 so that the induced catheter motion is in full synchrony with image acquisition.

In this way, the induced motion of the catheter 114 can be adjusted to be optimized and of known temporal duration. For example, if the magnetic field is applied around the end of diastole, effects of physiological motion on the catheter can be minimized and therefore be separated more easily from effects of the magnetic field. In addition, to achieve maximum contrast between the coded motion and other motions, the driving signal to the coil 118 may be adjusted and optimized. The coil 118 is preferably placed in close proximity to a region of interest, e.g., the heart or the body. The coil 118 can be embedded into a procedure bed 123 to avoid any undesired operational inconvenience caused by the presence of the coil 118.

In addition, placing the coil 118 in the bed 123 preferably permits a conventional X-ray being taken for conventional catheter localization. Because of the strong permanent magnet(s) 124 on the catheter tip 130 and the short distance between the permanent magnet(s) and the coil 118, the electromagnet 118 does not need to be large or high-powered to induce enough vibration. In addition, considering that the heart beats at ~1 Hz, the operating frequencies of the electromagnet 118 do not need to go beyond 100 Hz. Therefore, the electromagnet 118 can be built with low cost. The coded vibration of the catheter 114 and its tip 130 are detected in real time by a specialized decoding module 112 residing in the ultrasound scanner 102.

Referring to FIG. 2 with continued reference to FIG. 1, an end portion of a catheter 114 includes the tip 130. Rather than relying exclusively on (echo intensity based) B- mode images, visualization of the catheter tip 130 may employ ultrasonic motion tracking. Single tone or coded vibration is induced by the generator 116 on a catheter tip 130 by applying an encoded magnetic force to miniature permanent magnets 124 attached onto and around the tip 130. The vibration of the catheter tip 130 is decoded using decoding software of decoding module 112 on the ultrasound imaging system 102 that can reject motion related to any background physiological motion. In this way, catheter tips 130 can be distinguished from background tissue, and real-time catheter visualization is achieved based solely on ultrasound imaging.

The miniature magnets 124 may be mounted on the catheter tip 130 or, alternatively magnetization can be achieved by embedding fine magnetic particles within the catheter tip material or within a body 125 of the catheter at a different location or locations. Other methods for providing magnets to the catheter may include electromagnets or other schemes.

The magnets 124 may include magnet disks attached around the tip of a catheter. In one embodiment, a 1/16 inch (diameter) by 1/32 inch (thickness) neodymium magnet may be employed. Other sizes and configurations are also contemplated.

In one embodiment, to concentrate the coded motion to the vicinity of the catheter tip 130, instead of mounting permanent magnets 124 directly onto the catheter 114, an elastic material 122 may be inserted between the magnets 124 and the catheter 114. This can reduce the mechanic load of the vibration force, leading to stronger vibration of the magnet 124 while weakening vibration of other parts.

When Doppler-based methods are used to detect tip vibration, only motion along the axial direction can be detected. More than one coil may be employed to vibrate the magnet 124 with high efficiency along the imaging beam direction. To avoid orthogonality between the magnetic field direction and the orientation of permanent magnet 124, multiple permanent magnets 124 can be attached to the catheter 114 with different orientations. This assures that at least one of these magnets 124 will tend to vibrate responsively to the external magnetic field.

Referring to FIG. 3, an illustrative decoding mechanism 200 is illustratively depicted. An ultrasonic scanner 102 collects RF data 202 for generating an image. The scanner 102 performs motion tracking in block 204 on the RF data 202 to get displacement or velocity maps 206 at different temporal instants. Both Doppler-based and speckle-tracking- based techniques may be employed. In block 208, extracting coded motion and rejecting motion caused by background physiological motion from the displacement or velocity maps using slow-time demodulation/filtering techniques is performed. Since the electromagnet operates under the trigger of the ultrasound scanner 102, the scanner 102 knows what the slow-time displacement or velocity profile induced by the magnetic field looks like. Matched filters or other demodulation techniques can be applied to enhance the contrast between the coded motion resulting from a coding signal 209 and other motions. In the case of single vibration frequencies, narrowband slow-time filters can be used. The output of this step is a decoded motion map 210. In block 212, the catheter tip 130 is located using segmentation or other image processing techniques. An output image 214 is displayed.

The feasibility of real-time catheter visualization was demonstrated in accordance with the present principles based on ultrasonically tracking vibration of catheter tips induced magnetically. A segment of wire was used to mimic a catheter, and a 1/16 inch (diameter) x 1/32 inch (thickness) neodymium magnet was attached to its tip. A 60 Hz transformer drove a specially built coil to form an electromagnet. The wire was cast into a tissue-mimicking phantom made of water, 2% agar, and 1.5% graphite. The coil was placed under the phantom, and a linear array probe was connected to a scanner used to image the phantom. Vibration of the tip of the catheter-mimicking wire in the presence of magnetic force was successfully caught in power Doppler mode. No Doppler signal was detected when the electromagnet was off. Although more robust than visualization of a catheter based on B-mode images, visualization of a catheter based on ultrasonic motion tracking still relies on echoes from the region around the catheter tip that shifts in response to the magnetic field. Since angle-dependent specular reflection strongly affects the appearance of a catheter and the permanent magnet on the catheter in ultrasound images, the catheter tip may not be visible and detectable directly. However, the coded vibration of the tip causes correspondingly coded motion of the surrounding blood or tissue, which can then be detected (with the designed vibration codes) using the present principles to help locate the catheter tip. In addition, a layer of ultrasound scattering material can be coated onto the permanent magnets or around the catheter tip to make them visible in ultrasound images. Although ultrasound signals from this layer might not be well distinguished from the background, this layer can be distinguished using motion tracking.

The features of the present invention lead to a cost-effective solution to visualize catheters and other devices such as endoscopes, needles, etc. and guide

interventional procedures in real-time with high accuracy using medical ultrasound scanners such as the ultrasound imaging systems iE33™ and iU22™ manufactured by Philips^®

Healthcare (Andover, MS).

Referring to FIG. 4, a method for locating a medical instrument during a procedure is illustratively presented. In block 302, an encoded oscillation signal is generated. This preferably includes a temporal relationship between the oscillation signal and an imaging device to enhance the display of the medical instrument in block 304. The temporal relationship may include a synchronous or asynchronous relationship. The encoded signal may include a single tone or a coded oscillation. In block 306, a magnetic field is fluctuated in a vicinity of a region of interest in accordance with the oscillation signal. This may include energizing an electromagnet in block 308. In block 310, vibrations are induced in a magnetic portion of a medical instrument in accordance with the magnetic field. This may include vibrating magnetic material on a catheter in block 312. In block 314, the magnetic portion is displayed in the region of interest such that the vibrations increase contrast in an image of the region of interest. In block 316, image data is decoded in accordance with the encoded oscillation signal. A decoded motion map of the vibrating magnetic portion may be segmented in block 318.

In interpreting the appended claims, it should be understood that: a) the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim;

b) the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements;

c) any reference signs in the claims do not limit their scope;

d) several "means" may be represented by the same item or hardware or software implemented structure or function; and

e) no specific sequence of acts is intended to be required unless specifically indicated.

Having described preferred embodiments for systems, devices and methods for real-time catheter visualization with ultrasound through magnetically induced vibration (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the disclosure disclosed which are within the scope of the embodiments disclosed herein as outlined by the appended claims. Having thus described the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.

Claims

CLAIMS:

1. A system for locating a medical instrument during a procedure, comprising: an imaging device (102) configured to image a region of interest; a medical instrument (114) having a magnetic portion (124); and a signal generator (116) configured to be coupled to the imaging device and generate an encoded magnetic fluctuation pattern having a temporal relationship with scanning by the imaging device to cause oscillation of a magnetic field in the region of interest, the magnetic fluctuation pattern causing the magnetic portion to correspondingly vibrate to identify the magnetic portion in an image of the region of interest.

2. The system as recited in claim 1, wherein the imaging device (102) includes an ultrasound scanner and the temporal relationship includes one of a synchronized or an asynchronized relationship with the scanning.

3. The system as recited in claim 1, wherein the medical instrument (114) includes a catheter and the magnetic portion includes a permanent magnet (124).

4. The system as recited in claim 3, wherein the permanent magnet (124) is mounted on a tip of the catheter.

5. The system as recited in claim 3, wherein the permanent magnet (124) is mounted on an elastic base in contact with the tip of the catheter.

6. The system as recited in claim 1, wherein the medical instrument (114) includes a catheter and the magnetic portion includes magnetic material integrally formed with the catheter.

7. The system as recited in claim 1, wherein the magnetic fluctuation pattern is caused by an electromagnet energized by the signal generator in one of a coded pattern and a single tone.

8. The system as recited in claim 7, wherein the electromagnet includes a coil (118) embedded in a patient supporting platform (123).

9. A medical instrument, comprising:

a device body (125); and

a magnetic portion (124) mounted on the device body, the magnetic portion being configured to be responsive to a fluctuating magnetic field such that the magnetic field causes the magnetic portion to vibrate in accordance with a single-tone or coded signal having a temporal relationship with an imaging scanner to improve visibility of the magnetic portion in images taken during a medical procedure.

10. The medical instrument as recited in claim 9, wherein the medical instrument includes a catheter (114) and the magnetic portion includes a permanent magnet (124).

11. The medical instrument as recited in claim 10, wherein the permanent magnet (124) is mounted on a tip of the catheter.

12. The medical instrument as recited in claim 11, wherein the permanent magnet (124) is mounted on an elastic base (122) in contact with the tip of the catheter.

13. The medical instrument as recited in claim 10, wherein the permanent magnet includes a neodymium magnet.

14. The medical instrument as recited in claim 9, wherein the medical instrument includes a catheter and the magnetic portion includes magnetic material integrally formed with the catheter.

15. The medical instrument as recited in claim 9, wherein the magnetic portion includes a plurality of magnets (124), each magnet including a different orientation to enhance a vibrational response.