Patent Description:
Tracking using ultrasound imaging beams exclusively may not be optimal. For example, ultrasound scanning frequencies for ultrasound imaging may be on an edge of the bandwidth of the ultrasound sensor on the interventional medical device. Also, the tracking region using ultrasound imaging beams exclusively is limited to the imaging field of view. Additional concerns include that all beamforming parameters used for ultrasound imaging beams (e.g., beam positions, repetitions, and waveform characteristics) must be provided, e.g., for use in the tracking.

A method for tracking an interventional medical device in a patient is defined in claim <NUM>.

A system for tracking an interventional medical device in a patient is defined in claim <NUM>.

The example embodiments are best understood from the following detailed descriptions of representative embodiments presented below when considered in conjunction with the accompanying figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements.

In the following detailed description, for purposes of explanation and not limitation, representative embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. Descriptions of known systems, devices, materials, methods of operation and methods of manufacture may be omitted to avoid obscuring the description of the representative embodiments. Nonetheless, systems, devices, materials and methods that are within the purview of one of ordinary skill in the art are within the scope of the present teachings and may be used in accordance with the representative embodiments. It is to be understood that the terminology used herein is for purposes of describing embodiments only, and is not intended to be limiting. The defined terms are in addition to the technical and scientific meanings of the defined terms as commonly understood and accepted in the technical field of the present teachings.

It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements or components, these elements or components should not be limited by these terms. These terms are only used to distinguish one element or component from another element or component. Thus, a first element or component discussed below could be termed a second element or component without departing from the teachings of the inventive concept.

The terminology used herein is for purposes of describing embodiments only, and is not intended to be limiting. As used in the specification and appended claims, the singular forms of terms 'a', 'an' and 'the' are intended to include both singular and plural forms, unless the context clearly dictates otherwise. Additionally, the terms "comprise", and/or "comprising," and/or similar terms when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, elements, components, and/or groups thereof. As used herein, the term "and/or" includes all combinations of one or more of the associated listed items.

Unless otherwise noted, when an element or component is said to be "connected to", "coupled to", or "adjacent to" another element or component, it will be understood that the element or component can be directly connected or coupled to the other element or component, or intervening elements or components may be present. That is, these and similar terms encompass cases where one or more intermediate elements or components may be employed to connect two elements or components. However, when an element or component is said to be "directly connected" to another element or component, this encompasses only cases where the two elements or components are connected to each other without any intermediate or intervening elements or components.

As described herein, time-interleaved imaging frames and tracking frames (or imaging beams and tracking beams) can be tailored each to its specific purpose: imaging or tracking. The tracking beams may have characteristics (e.g., shape, position, waveforms) to optimize the tracking beams for tracking.

<FIG> illustrates an ultrasound system for interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. In <FIG>, an ultrasound system <NUM> includes a central station <NUM> with a processor <NUM> and memory <NUM>, a touch panel <NUM>, a monitor <NUM>, an imaging probe <NUM> connected to the central station <NUM> by wire <NUM>, and an interventional medical device <NUM> connected to the central station by wire <NUM>. A sensor <NUM> is on the interventional medical device <NUM>.

By way of explanation, an interventional medical device <NUM> is placed internally into a patient during a medical procedure. Locations of the interventional medical device <NUM> can be tracked using the sensor <NUM>. For example, the sensor <NUM> may receive and use tracking beams to help determine a location of the sensor <NUM>, in addition to the recent conventional ability to use ultrasound imaging beams to help determine the location of the sensor <NUM>. The sensor <NUM> may be used passively or actively to respond to the received ultrasound tracking beams. As described herein, interleaving imaging and tracking sequences is used to selectively, typically, or always provide different imaging and tracking beams in an interleaved sequence. However, as also noted herein, the tracking can be performed using either or both of the imaging beams and tracking beams.

In <FIG>, wire <NUM> and wire <NUM> are used to connect the interventional medical device <NUM> and imaging probe <NUM> to the central station <NUM>. For the imaging probe <NUM>, a wire <NUM> may not present much of a concern, though the wire <NUM> may still be a distraction. For the interventional medical device <NUM>, a wire <NUM> may be used to send back, for example, images when the interventional medical device <NUM> is used to capture images. However, a wire <NUM> may be of more concern in that the interventional medical device <NUM> is at least partly inserted in the patient. Accordingly, replacing the wire <NUM> and the wire <NUM> with wireless connections will provide some benefit.

<FIG> illustrates another ultrasound system for interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. In <FIG>, the wire <NUM> is replaced with wireless data connection <NUM>, and the wire <NUM> is replaced with wireless data connection <NUM>. Otherwise, the ultrasound system <NUM> in <FIG> includes the same central station <NUM> as in <FIG>, i.e., with the processor <NUM> and memory <NUM>, touch panel <NUM>, monitor <NUM>, imaging probe <NUM>, interventional medical device <NUM>, and sensor <NUM>.

In <FIG>, the ultrasound system <NUM> may be an arrangement with an interventional medical device <NUM> with the sensor <NUM> on board. The interventional medical device <NUM> may be, e.g., a needle with the sensor <NUM> at its tip. The sensor <NUM> may be configured to listen to and analyze data from tracking beams coming from the imaging probe <NUM>. The "sending" of the tracking beams from the imaging probe <NUM>, and the "listening" to the tracking beams by the sensor <NUM>, are synchronized.

In <FIG>, the imaging probe <NUM> may send an interleaved pulse sequence of imaging beams and tracking beams. The pulse sequence may include both imaging beams and tracking beams. Mechanisms for interleaving are described herein below.

An explanation of the relationship between the central station <NUM>, imaging probe <NUM> and the sensor <NUM> follows. In this regard, central station <NUM> in <FIG> may include a beamformer (not shown) that is synchronized by a clock (not shown) to send properly delayed signals in a transmit mode to elements of an imaging array in the imaging probe <NUM>. In a receive mode, the beamformer may properly delay and sum signals from the individual elements of the imaging array in the imaging probe <NUM>. The interleaving described herein is performed using the imaging probe <NUM>, and may be in accordance with beamforming performed by the beamformer of the central station <NUM>.

In an alternative exemplary one-way relationship, the imaging probe <NUM> may emit tracking beams that impinge on the sensor <NUM> (i.e., when the sensor <NUM> is in the field of view of the tracking beams). The sensor <NUM> may receive and convert the energy of the tracking beams into signals so that the sensor <NUM>, or even the interventional medical device <NUM>, can determine the position of the sensor <NUM> relative to the imaging array of the imaging probe <NUM>. The relative position of the sensor <NUM> can be computed geometrically based on the received tracking beams received by the sensor <NUM>.

The central station <NUM> may be considered a control unit that controls the imaging probe <NUM>. As described in <FIG>, the central station <NUM> includes a processor <NUM> connected to a memory <NUM>. The central station <NUM> may also include a clock (not shown) which provides clock signals to synchronize the imaging probe <NUM> with the sensor <NUM>.

The imaging probe <NUM> is adapted to scan a region of interest that includes the interventional medical device <NUM> and the sensor <NUM>. Of course, as is known for ultrasound imaging probes, the imaging probe <NUM> uses ultrasound imaging beams to provide images on a frame-by-frame basis. The imaging probe <NUM> can also use separate tracking beams to obtain the location of the sensor <NUM>.

As noted, in the one-way relationship, the sensor <NUM> may be adapted to convert tracking beams provided by the imaging probe <NUM> into electrical signals, and to provide either the raw data from the sensor <NUM>, or partially or completely processed data (e.g., calculated sensor location) from the sensor <NUM> to the central station <NUM>, either directly or indirectly (e.g., via a transmitter or repeater located in a proximal end of the interventional medical device <NUM>). These data, depending on their degree of processing, are either used by the central station <NUM> to determine the location of the sensor <NUM> and the location of the distal end of the interventional medical device <NUM> to which the sensor <NUM> is attached, or to provide the central station <NUM> with the location of the sensor <NUM> and the location of the distal end of the interventional medical device <NUM> to which the sensor <NUM> is attached.

As described herein, the position of the sensor <NUM> is determined by or provided to the central station <NUM>. The position of the sensor <NUM> can be used by the processor <NUM> to overlay the position of the sensor <NUM> onto an image frame for display on the monitor <NUM>, and thus the distal end of the interventional medical device <NUM> relative to the image frame. In another representative embodiment, instructions stored in memory <NUM> are executed by the processor <NUM> to determine a position of the sensor <NUM> relative to an image frame, and to overlay the position of the sensor <NUM>, and thus the distal end of the interventional medical device <NUM> relative to the image frame.

Broadly, in operation, the processor <NUM> initiates a scan by the imaging probe <NUM>. The scan can include interleaved imaging beams and tracking beams across a region of interest. The imaging beams are used to form an image of a frame; and the tracking beams are used to determine the location of the sensor <NUM>. As can be appreciated, the image from imaging beams is formed from a two-way transmission sequence, with images of the region of interest being formed by the transmission and reflection of sub-beams. By contrast, in the one-way relationship, the tracking beams are incident on the sensor <NUM>, which converts the tracking beams into electrical signals (i.e., rather than or in addition to reflecting the tracking beams). In the two-way relationship, the tracking beams are reflected by the sensor <NUM>, so that the imaging probe <NUM> determines the location of the sensor <NUM> using the reflected tracking beams.

As noted above, data used to determine location of the sensor <NUM> may comprise raw data, partially processed data, or fully processed data, depending on where location is to be determined. Depending on the degree of processing, these data can be provided to the processor <NUM> for executing instructions stored in the memory <NUM> (i.e., of the central station <NUM>) to determine the position of the sensor <NUM> in the coordinate system of ultrasound images from the beamformer. Alternatively, these data may include the determined position of the sensor <NUM> in the coordinate system which is used by the processor <NUM> when executing instructions stored in the memory <NUM> to overlay the position of the sensor <NUM> on the ultrasound image in the monitor <NUM>. To this end, the beamformer of the central station <NUM> may process the beamformed signal for display as an image of a frame. The output from the beamformer can be provided to the processor <NUM>. The data from the sensor <NUM> may be raw data, in which case the processor <NUM> executes instructions in the memory <NUM> to determine the position of the sensor <NUM> in the coordinate system of the image; or the data from the sensor <NUM> may be processed by the interventional medical device <NUM> to determine the location of the sensor <NUM> in the coordinate system of the image. Either way, the processor <NUM> is configured to overlay the position of the sensor <NUM> on the image on the monitor <NUM>. For example, a composite image may include the image of the frame (e.g., the last frame) based on imaging beams, and the superposed position of the sensor <NUM> in that frame providing real-time feedback to a clinician of the position of the sensor <NUM> and the distal end of the interventional medical device <NUM> relative to the region of interest. As can be appreciated, the superposing of the position of the sensor <NUM> may be repeated for each frame to enable complete real-time in-situ superposition of the position of the sensor <NUM> relative to the composite image of the frame.

<FIG> is an illustrative embodiment of a general computer system, on which a method of interleaved imaging and tracking sequences for ultrasound-based instrument tracking can be implemented. The computer system <NUM> can include a set of instructions that can be executed to cause the computer system <NUM> to perform any one or more of the methods or computer based functions disclosed herein. The computer system <NUM> may operate as a standalone device or may be connected, for example, using a network <NUM>, to other computer systems or peripheral devices. Any or all of the elements and characteristics of the computer system <NUM> in <FIG> may be representative of elements and characteristics of the central station <NUM>, the imaging probe <NUM>, or even the sensor <NUM> in <FIG>.

In a networked deployment, the computer system <NUM> may operate in the capacity of a client in a server-client user network environment. The computer system <NUM> can also be fully or partially implemented as or incorporated into various devices, such as a control station, imaging probe, image beam receiver, tracking beam receiver, stationary computer, a mobile computer, a personal computer (PC), or any other machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. The computer system <NUM> can be incorporated as or in a device that in turn is in an integrated system that includes additional devices. In an embodiment, the computer system <NUM> can be implemented using electronic devices that provide video or data communication. Further, while the computer system <NUM> is illustrated, the term "system" shall also be taken to include any collection of systems or sub-systems that individually or jointly execute a set, or multiple sets, of instructions to perform one or more computer functions.

As illustrated in <FIG>, the computer system <NUM> includes a processor <NUM>. A processor <NUM> for a computer system <NUM> is tangible and non-transitory. As used herein, the term "non-transitory" is to be interpreted not as an eternal characteristic of a state, but as a characteristic of a state that will last for a period. The term "non-transitory" specifically disavows fleeting characteristics such as characteristics of a carrier wave or signal or other forms that exist only transitorily in any place at any time. Any processor described herein is an article of manufacture and/or a machine component. A processor for a computer system <NUM> is configured to execute software instructions to perform functions as described in the various embodiments herein. A processor for a computer system <NUM> may be a general-purpose processor or may be part of an application specific integrated circuit (ASIC). A processor for a computer system <NUM> may also be a microprocessor, a microcomputer, a processor chip, a controller, a microcontroller, a digital signal processor (DSP), a state machine, or a programmable logic device. A processor for a computer system <NUM> may also be a logical circuit, including a programmable gate array (PGA) such as a field programmable gate array (FPGA), or another type of circuit that includes discrete gate and/or transistor logic. A processor for a computer system <NUM> may be a central processing unit (CPU), a graphics processing unit (GPU), or both. Additionally, any processor described herein may include multiple processors, parallel processors, or both. Multiple processors may be included in, or coupled to, a single device or multiple devices.

Moreover, the computer system <NUM> includes a main memory <NUM> and a static memory <NUM> that can communicate with each other via a bus <NUM>. Memories described herein are tangible storage mediums that can store data and executable instructions, and are non-transitory during the time instructions are stored therein. As used herein, the term "non-transitory" is to be interpreted not as an eternal characteristic of a state, but as a characteristic of a state that will last for a period. The term "non-transitory" specifically disavows fleeting characteristics such as characteristics of a carrier wave or signal or other forms that exist only transitorily in any place at any time. A memory described herein is an article of manufacture and/or machine component. Memories described herein are computer-readable mediums from which data and executable instructions can be read by a computer. Memories as described herein may be random access memory (RAM), read only memory (ROM), flash memory, electrically programmable read only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, a hard disk, a removable disk, tape, compact disk read only memory (CD-ROM), digital versatile disk (DVD), floppy disk, blu-ray disk, or any other form of storage medium known in the art. Memories may be volatile or non-volatile, secure and/or encrypted, unsecure and/or unencrypted.

As shown, the computer system <NUM> may further include a video display unit <NUM>, such as a liquid crystal display (LCD), an organic light emitting diode (OLED), a flat panel display, a solid-state display, or a cathode ray tube (CRT). Additionally, the computer system <NUM> may include an input device <NUM>, such as a keyboard/virtual keyboard or touch-sensitive input screen or speech input with speech recognition, and a cursor control device <NUM>, such as a mouse or touch-sensitive input screen or pad. The computer system <NUM> can also include a disk drive unit <NUM>, a signal generation device <NUM>, such as a speaker or remote control, and a network interface device <NUM>.

In an embodiment, as depicted in <FIG>, the disk drive unit <NUM> may include a computer-readable medium <NUM> in which one or more sets of instructions <NUM>, e.g. software, can be embedded. Sets of instructions <NUM> can be read from the computer-readable medium <NUM>. Further, the instructions <NUM>, when executed by a processor, can be used to perform one or more of the methods and processes as described herein. In an embodiment, the instructions <NUM> may reside completely, or at least partially, within the main memory <NUM>, the static memory <NUM>, and/or within the processor <NUM> during execution by the computer system <NUM>.

In an alternative embodiment, dedicated hardware implementations, such as application-specific integrated circuits (ASICs), programmable logic arrays and other hardware components, can be constructed to implement one or more of the methods described herein. One or more embodiments described herein may implement functions using two or more specific interconnected hardware modules or devices with related control and data signals that can be communicated between and through the modules. Accordingly, the present disclosure encompasses software, firmware, and hardware implementations. Nothing in the present application should be interpreted as being implemented or implementable solely with software and not hardware such as a tangible non-transitory processor and/or memory.

In accordance with various embodiments of the present disclosure, the methods described herein may be implemented using a hardware computer system that executes software programs. Virtual computer system processing can be constructed to implement one or more of the methods or functionality as described herein, and a processor described herein may be used to support a virtual processing environment.

The present disclosure contemplates a computer-readable medium <NUM> that includes instructions <NUM> or receives and executes instructions <NUM> responsive to a propagated signal; so that a device connected to a network <NUM> can communicate video or data over the network <NUM>. Further, the instructions <NUM> may be transmitted or received over the network <NUM> via the network interface device <NUM>.

<FIG> illustrates a process for interleaved imaging and tracking sequences for ultrasound-based instrument tracking, that may be used in a representative embodiment. In <FIG>, the process starts at S222 by setting a pulse sequence. The pulse sequence is for interleaving imaging beams and tracking beams. At S222, the pulse sequence is set based on specified types of the interventional medical device <NUM>, the sensor <NUM>, and/or the imaging probe <NUM>. Accordingly, pulse sequences to use may vary by different types of the interventional medical device <NUM>, the sensor <NUM>, and/or the imaging probe <NUM>, and at S222 the pulse sequence can be set by, for example, inputting or detecting which types are being used.

At S224, a waveform of the tracking beams is matched based on a bandwidth characteristic of the sensor <NUM>. That is, different types of sensor <NUM> will have different bandwidth characteristics, and a waveform of the tracking beams can be matched based on the bandwidth characteristic.

At S226, transmission of the interleaved pulse sequence and receipt of the tracking beams by the sensor <NUM> is synchronized in advance. That is, the expected timing patterns are established in advance, since the receipt of the tracking beams is the intended purpose of the interleaving by the ultrasound system <NUM>. Accordingly, a transmit/receive/transmit/receive timing sequence for transmitting the interleaved pulse sequence and receiving the tracking beams by the sensor <NUM> is established in advance.

At S228, the pulse sequence is interleaved with the imaging beams and the tracking beams. Several examples of specific interleaving patterns will be described herein with respect to <FIG>.

At S230, the interleaved pulse sequence is transmitted. From <FIG>, the imaging probe <NUM> emits the interleaved pulse sequence, and the interventional medical device <NUM> and the sensor <NUM> receive the interleaved pulse sequence. The imaging beams of the interleaved pulse sequence will result in imaging results being detected by the imaging probe <NUM>. Indeed, the synchronization at S226 is in anticipation of the tracking beams being received by the sensor <NUM>, whereas the reflected imaging beams are alternately received by the imaging probe <NUM>.

At S234, a response to the tracking beams is received. The tracking beams are different than the imaging beams in most circumstances described herein, such as when the tracking beams have waveforms matched based on bandwidth characteristics of the sensor <NUM>. As noted throughout this disclosure, the tracking beams result in tracking location of the sensor <NUM> and the interventional medical device <NUM> in the patient.

At S250, images of the patient are displayed based on the imaging results, and location of the sensor <NUM> is displayed based on the response to the tracking beams. Accordingly, the location of the sensor <NUM> may be displayed as, for example, a bright spot on an ultrasound image to show approximately or exactly where the sensor <NUM> is relative to the patient.

<FIG> illustrates a process for interleaved imaging and tracking sequences for ultrasound-based instrument tracking according to aspects of the invention. In <FIG>, imaging beams are initially transmitted without interleaving or tracking beams at S310. In <FIG>, the tracking using tracking beams is only selectively used as explained herein.

At S312, a check is made whether a signal-to-noise ratio in the imaging beams received by the sensor <NUM> is below a predetermined threshold. If the signal-to-noise ratio is above the threshold (S312 = No), the process continues in a loop without using the tracking beams or interleaving. In other words, an ultrasound can be used in a conventional manner unless and until a signal-to-noise ratio in the imaging beams received by the sensor <NUM> is below a predetermined threshold, and the imaging beams are then used for tracking purposes in a one-way configuration. Tracking beams are enabled when, for example, the signal-to-noise ratio reflects that the interventional medical device <NUM> and sensor <NUM> may not be where they are supposed to as shown by an unexpectedly low signal-to-noise ratio from the imaging beams received by the sensor <NUM>. Signal-to-noise levels in imaging results based on the echo received by the imaging probe <NUM> may also or alternatively be used to determine when to selectively begin using tracking beams.

At S326, transmission of the interleaved pulse sequence is synchronized with receipt of the tracking beams by the sensor <NUM>, and at S328 the imaging beams and tracking beams are interleaved in the pulse sequence. At S330 the interleaved pulse sequence is transmitted, and at S332, the imaging results are received from the imaging beams, and at S334 the response to the tracking beams is received. At S350, images of the patient and location of the sensor <NUM> are displayed based on the imaging results and the response to the tracking beams. In other words, the process from S326 to S350 is the same as the process from S226 to S250. However, at S350, the process reverts to transmitting imaging beams without interleaving or tracking beams at S310, to see if the signal-to-noise ratio has improved such that location of the sensor <NUM> can be reliably established using imaging beams only as in the prior art, for the time being. If the signal-to-noise ratio in the imaging beams received at sensor <NUM> (and, optionally, pulse-echo signal-to-noise ratio from the imaging beams) is again below the threshold at S312, the process will resume using the interleaving and the tracking beams.

<FIG> illustrates another process for interleaved imaging and tracking sequences for ultrasound-based instrument tracking, that may be used in a representative embodiment. In <FIG>, the process begins at S430 by transmitting an interleaved pulse sequence. At S434, the response to tracking beams is received, and at S435 the process measures the depth of the sensor <NUM> based on the response to the tracking beams. In other words, the depth of the sensor <NUM> is measured based on the location of the sensor <NUM> derived from the response to the tracking beams.

At S436, a focal point of the tracking beams is adjusted to the depth of the sensor <NUM> measured at S435. At S450, images of the patient and the location of the sensor <NUM> are displayed based on the imaging results and the response to the tracking beams. At S452, a check is made whether the pulse sequence has ended, and if so (S452 = Yes) the process ends at S490. If the pulse sequence has not ended (S452 = No), a count of the sequence is incremented at S454, and the process returns to transmitting the interleaved pulse sequence at S430.

The process of <FIG> shows two aspects to be noted. The first is that a focus point of the tracking beams may be matched to the depth of the sensor <NUM>. The second is that the sequence may be tracked by counting, e.g., imaging frames, tracking frames, imaging/tracking super-frames, and other characteristics of the pulse sequence. The count at S454 can be used to track an end to the pulse sequence when sub-processes such as adjusting focal points are performed.

<FIG> illustrates relative fields of view from an imaging probe in an embodiment of interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. In <FIG>, the imaging probe <NUM> emits imaging beams in an imaging field of view <NUM>, and tracking beams in a tracking field of view <NUM>. As can be seen, the tracking field of view <NUM> extends beyond the imaging field of view <NUM>. The tracking field of view <NUM> shows that tracking beams can be directed in directions to which the imaging beams are not directed, which means that the sensor <NUM> can be located even when the interventional medical device is not in the imaging field of view <NUM> and will not appear in the images. <FIG> is applicable to a two-dimensional (2D) probe, for example. When tracking is performed exclusively using imaging beams, tracking of the sensor <NUM> is limited to the imaging field of view. However, as shown in <FIG> it will be possible to track outside of the imaging field of view using separate tracking beams.

For example, tracking outside of the imaging field of view may be useful for guiding needles with two-dimensional (2D) curvilinear or linear probes, wherein using only imaging beams the guiding needle is not visible until a few centimeters into tissue. In another example, tracking a needle out of a plane may be useful even when only a plane is being imaged using a 2D array. For the needle guidance example, the tracking beams can be extended to cover a larger field of view by steering. For out of plane tracking, a tracking volume can be used even when only a plane is being imaged using the 2D array.

<FIG> illustrates relative fields of view from an imaging probe in another embodiment of interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. In <FIG>, multiple tracking fields of view <NUM> are shown for a single imaging field of view <NUM>. <FIG> is applicable to a three-dimensional (3D) probe, for example.

A frame rate of imaging beams is reduced when imaging beams and tracking beams are interleaved. Accordingly, the frame rates of each of the imaging beams and tracking beams can be optimized. The optimization of tracking beam characteristics may allow for interleaving a single tracking sequence with multiple or all so-called imaging tissue-specific presets (TSPs) which are preset imaging settings specific to particular tissues. This, in turn, eliminates any requirement to transmit many beam parameters from a scanning module to a tracking module.

As a general matter, resolution for tracking beams does not have to be as high as for imaging beams, as only a spatial peak is sought in the received signals of the tracking beams. The tracking performance is better characterized in terms of accuracy than resolution, and resolution only secondarily affects accuracy. In other words, performance of the existing use exclusively of imaging beams is dependent on the shape and density of transmit imaging beams, but the dependency is not straightforward and is affected by the processing algorithms to obtain position from signals of the tracking beam. Therefore, in general, lower-resolution transmit beams (i.e., broad beams) can be used to maintain frame rate.

Additionally, transmit beam reconstruction can be performed on received signals to improve resolution. Ultrafast tracking sequences with plane waves or diverging beams can therefore be used to improve tracking frame rate. Conversely, if sensitivity of tracking is to be optimized, an oversampled transmit beam sequence may be used to enhance a signal-to-noise ratio.

To maximize tracking sensitivity, a waveform of the tracking beams can be matched to a bandwidth characteristic of the sensor <NUM> aboard the interventional medical device <NUM>. For instance, if an interventional medical device <NUM> is a needle, and a sensor <NUM> has a <NUM> characteristic, the tracking signal-to-noise ratio will vary widely between preset settings for different tissues, where imaging frequencies can range from <NUM> to <NUM>. In addition, tracking beams suited for "penetration" may use a larger number of cycles, lower frequency, and coded excitation. Such tracking beams can be repeated or strongly overlapped to maximize signal-to-noise ratio. Empirical observations reveal that these waveform changes typically benefit tracking more in sensitivity improvements than in degradation of accuracy. Since the tracking may be limited to searching for a spatial peak in received data, accuracy may be sacrificed as a secondary concern compared to imaging resolution.

As noted with respect to <FIG>, tracking beams can also be focused at the depth of the sensor <NUM> by, e.g., measuring the sensor depth by tracking the sensor location with ultrasound imaging beams and feeding this information back to the transmit beamformer. By focusing tracking beams at the depth of the sensor <NUM>, signal-to-noise ratio and accuracy can be maximized for tracking. Moreover, the focal depth for tracking frames can be maintained independent of a transmit focal depth for the imaging frames, so that it may be preferable to independently set focus depth for each of imaging and for tracking.

In an embodiment, frame interleave can be used, wherein one or more imaging frames are interleaved with one or more tracking frames. However, frame interleave may introduce lag between imaging frames and tracking frames, which may be detectable at very low imaging / tracking rates (<<NUM>). When beam interleave is alternatively used, imaging beams are interleaved with tracking beams within a frame. Frame interleave versus beam interleave are illustrated and explained more below in <FIG>. Using either frame interleave or beam interleave, a ratio of imaging frames to tracking frames or imaging beams to tracking beams can be adapted.

<FIG> illustrates a timing diagram for an embodiment of interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. <FIG> shows an example of frame interleave. In <FIG>, an imaging frame <NUM> and a tracking frame <NUM> are alternatively and sequentially emitted in a pulse sequence. The imaging beams in the imaging frame <NUM> are shown thinner than the tracking beams in the tracking frame <NUM>. As shown, the horizontal axis is in the time dimension, so the sequential emission of imaging frame <NUM>, tracking frame <NUM>, imaging frame <NUM>, tracking frame <NUM>, is sequential in the time dimension.

<FIG> illustrates a timing diagram for another embodiment of interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. <FIG> shows an example of beam interleave. In <FIG>, an imaging/tracking superframe <NUM> is followed by another imaging/tracking superframe <NUM>. Again, the horizontal axis is in the time dimension, so the sequential emission of imaging/tracking superframe <NUM>, imaging/tracking superframe <NUM> is sequential in the time dimension. Each of the imaging/tracking superframes <NUM>, <NUM> includes alternating sequences of two imaging beams, one tracking beam, two imaging beams, one tracking beam.

To lessen the impact from tracking beams on frame rate, tracking beams might only be transmitted in a sub-region of an imaging volume surrounding an expected location of sensor <NUM>. An expected location of sensor <NUM> can be based on historical positions of the sensor <NUM>, or by processing sensor data from the imaging beams. Data from the imaging frame can be used to provide a coarse position estimate that is refined using tracking beams.

Additionally, to lessen the impact from tracking beams on frame rate, the tracking beams can be restricted to directions where imaging beams are not already being sent. For example, in the extended field of views in <FIG>, additional beams could be restricted beyond a normal to the surface where the imaging field of view does not overlap the tracking field of view.

Generally, tracking frames and interleaving may be used. However, according to the invention, the use of tracking beams and interleaving is selectively activated as back-up while imaging beams are used for tracking as a default. Examples of this are described below, and the embodiment of <FIG> describes such selective use of tracking beams.

Alternatively and not according to the claimed inventions, the interleaved imaging beams and tracking beams can each, separately, be used to track the sensor <NUM> aboard the interventional medical device <NUM>. Using both the interleaved imaging beams and tracking beams separately has the advantage that tracking frame rate is not lost whereas additional measurements that may either be in an expanded field of view or with more sensitivity are affirmatively gained. High-confidence measurements of tracking beams and lower confidence measurements of imaging beams can be used in several ways. For instance, a low-pass or Kalman filter can be used across beams or frames as a filter. The Kalman filter can weight the measurements of tracking beams more than the measurements of imaging beams. Similarly, a tool trajectory can be modeled, and the model can be constrained with the measurements of tracking beams and estimates of the error of the model on all measurements. Different modalities can be used to remove artefacts from the measurements of the imaging beams. For instance, if the positions computed for the imaging and tracking measurements differ too much, the maximum peak in the imaging results can be used in a region seeded by the measurements of the tracking beams.

When the field of view is expanded, some instances of the measurements based on tracking beams may result in a confident estimate when the measurements based on imaging beams are just noisy. In these cases, measurements from the imaging beams are discarded. The discarding may be based on a threshold of signal-to-noise ratio. For example, a high signal-to-noise ratio in the measurements of tracking beams and a lower signal-to-noise ratio in the measurements of imaging beams likely reflects that the sensor <NUM> is in the tracking field of view but outside the imaging field of view.

<FIG> illustrates another process for interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. In the embodiment of <FIG>, an expanded field of view using high sensitivity tracking beams or frames may be activated only when the measurements based on imaging results reflect a low signal-to-noise ratio suggesting that the signals of the imaging beams have been effectively lost. The low signal-to-noise ratio results in a signal being sent to the system for tracking the interventional medical device to start searching for the sensor <NUM>, i.e., to activate the tracking beams/frames. This results in a trade-off in that the imaging frame rate is temporarily lowered, but this will last only until the sensor <NUM> is found again and returned into the field of view for the imaging beams. When the sensor <NUM> is found again and returned into the field of view for the imaging beams, special tracking frames are turned off and tracking returns to the default of using only the imaging beams. When the imaging signal-to-noise drops again, the use of tracking beams or frames is selectively restarted.

In <FIG>, the process starts at S701. At S702, a pulse sequence with tracking beams and imaging beams is used. At S704, a check is made whether the signal-to-noise ratio in the imaging results (i.e., from the imaging beams) is above a threshold. If the signal-to-noise ratio is above the threshold (S704) = Yes), only the imaging sequence is emitted, along with a display marker at S706. The imaging sequence and display marker are repeatedly emitted until the signal-to-noise ratio falls back below the threshold in a check at S708, at which time the tracking beams and imaging beams are used.

At S704, if the signal-to-noise ratio is not above the threshold when using the tracking beams and imaging beams (S704 = No), a check is made for the signal-to-noise ratio in the tracking sequence at S710. If the signal-to-noise in the tracking sequence is above a threshold (S710 = Yes), a marker is displayed at S712 and the process returns to S702. If the signal-to-noise in the tracking sequence is not above the threshold at S710 (S710 = No), no marker is displayed at S714, and the process returns to using tracking beams and imaging beams at S702.

According to the embodiment of <FIG>, tracking and imaging are used until the signal-to-noise in the imaging sequence falls below a threshold at S704 or S708. Additionally, the process checks if signal-to-noise in the tracking sequence is below a threshold if the signal-to-noise ratio is below the threshold at S704, so not even a marker for the sensor <NUM> is displayed if the signal-to-noise in both the imaging sequence (S704 = No) and the tracking sequence (S710 = No) are both too low.

The embodiment of <FIG> represents an efficient use of tracking beams in an interleaved pulse sequence. The selective use of tracking beams is activated only when the imaging sequence is not able to detect the sensor <NUM>. The embodiment of <FIG> therefore helps put an interventional medical device <NUM> and sensor <NUM> back into the field of view.

<FIG> illustrate relative directionality for tracking beams and imaging beams for interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. In <FIG>, an imaging probe <NUM> emits a tracking beam in a direction <NUM>° below horizontal clockwise. In <FIG>, the imaging probe <NUM> emits a first imaging beam in a direction of <NUM>° below horizontal clockwise. In <FIG>, the imaging probe <NUM> emits a second imaging beam in a direction of <NUM>°below horizontal clockwise. In other words, <FIG> illustrate that tracking beams and imaging beams may be centered in different directions, even <NUM>°or more apart. The divergence in directions of tracking beams and imaging beams may be for even immediately adjacent/sequential emissions of the tracking beams and imaging beams.

<FIG> illustrate relative regions for imaging and tracking from an imaging probe in an embodiment of interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. In <FIG>, an imaging region is shown to extend entirely below the imaging probe <NUM>, whereas the tracking region is shown to extend within a sub-region of the imaging region. In <FIG> the tracking sub-region is to the left side of the imaging region.

<FIG> illustrates relative regions for imaging and tracking from an imaging probe in another embodiment of interleaved imaging and tracking sequences for ultrasound-based instrument tracking, in accordance with a representative embodiment. In <FIG>, an imaging region is shown to extend again entirely below the imaging probe <NUM>, whereas the tracking region is shown to extend again within a sub-region of the imaging region but to the right side of the imaging region.

<FIG> illustrates a block diagram of an interventional medical device for interleaved imaging and tracking sequences, in accordance with a representative embodiment. In <FIG>, the interventional medical device <NUM> includes an image beam receiver <NUM>, an input/output transceiver <NUM>, a processor <NUM> and a memory <NUM>. In <FIG>, the interventional medical device <NUM> is therefore a logical device. However, in almost all embodiments described herein, an interventional medical device <NUM> does not have to be a logical device, and may instead be a simple needle etc..

<FIG> illustrates a block diagram of a sensor for interleaved imaging and tracking sequences, in accordance with a representative embodiment. In <FIG>, the sensor <NUM> includes a tracking beam receiver <NUM>, an input/output transceiver <NUM>, a processor <NUM>, and a memory <NUM>. In <FIG>, the sensor <NUM> is therefore a logical device. A sensor <NUM> may be either passive or active, in that the sensor <NUM> may passively reflect received tracking beams to respond to the tracking beams, or may actively process received tracking beams and logically generate a response to the received tracking beams. If the sensor <NUM> is a logical device, the processor <NUM> may execute instructions stored in the memory <NUM>, to respond to received tracking beams using the input/output transceiver <NUM>.

Accordingly, interleaved imaging and tracking sequences for ultrasound-based instrument tracking enables optimal tracking of sensor <NUM>. Optimization can be varied for interventional medical devices <NUM> that differ, such as needles, catheters, and guidewires etc. Optimization can also be varied for different types of sensor <NUM>, such as piezoelectric (PZT), polyvinylidene difluoride (pvdf). In an embodiment, multiple tracking beam or frame parameters can be programmed into an ultrasound system, for example as tracking frame parameter set # <NUM>, tracking parameter set # <NUM>. Accordingly, sensor specific presets can be defined for an ultrasound system, analogous to tissue specific presets (TSPs) for tissue imaging. A user can be allowed to choose a desired tracking frame parameter set as a sensor specific preset (SSP) to use for a given combination of imaging probe <NUM>, interventional medical device <NUM>, and sensor <NUM>. For example, if the tracked interventional medical device <NUM> is a guidewire, the sensor <NUM> is PZT and optimized for <NUM>, and the imaging probe <NUM> is a linear probe L12-<NUM>, the tracking parameter set programmed for the highest frequency setting (closest to <NUM>) can be used. The user choice for tracking settings can be provided, for example, via an ultrasound system user interface next to a button for tissue specific presets.

The illustrations are not intended to serve as a complete description of all the elements and features of the disclosure described herein.

One or more embodiments of the disclosure may be referred to herein, individually and/or collectively, by the term "invention" merely for convenience and without intending to voluntarily limit the scope of this application to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description.

Claim 1:
A method for tracking an interventional medical device in a patient, comprising:
transmitting (S310), by an imaging probe (<NUM>) external to the patient, imaging beams from the imaging probe to the interventional medical device (<NUM>) in the patient;
determining (S312), based on a response to the imaging beams received from a sensor (<NUM>) on the interventional medical device (<NUM>), whether a signal-to-noise ratio in the response is equal to or below a predetermined threshold;
performing, if the signal-to-noise ratio in the response is equal to or below the predetermined threshold, the following steps:
interleaving (S328), by the imaging probe, a pulse sequence of imaging beams and tracking beams to obtain an interleaved pulse sequence;
transmitting (S330), from the imaging probe to the interventional medical device in the patient, the interleaved pulse sequence, and
determining, based on a response to the tracking beams received from the sensor on the interventional medical device, a location of the sensor in the patient;
else, if the signal-to-noise ratio in the response is above the predetermined threshold, using the imaging beams for tracking purposes in a one-way configuration.