Patent Description:
The article "<NPL>, demonstrates that A-mode ultrasound allows a 3D surface profile of the os occipitale to be created which can be registered on preoperative patient CT data; the transducer is mechanically positioned with sub-millimeter accuracy on the patients occiput; from the sound echos a 3D surface is generated and registered to the preoperative CT images with the iterative closest point (ICP) algorithm.

Further embodiments of the invention are defined in the dependent claims.

The present application is related to method and apparatus for performing a facial registration. In particular, the present application is directed to a method and apparatus for performing a facial registration for an ear/nose/throat (ENT) procedure, such as a nasal dilation.

In general, a person typically has eight or so sinus openings, (e.g., the frontal, anterior ethmoidal, maxillary, and middle ethmoidal, for each side), although the number of openings varies from person to person. Each of those sinus openings include areas that are very small in diameter. Accordingly, when an opening becomes clogged for one reason or another, no drainage may occur from within the sinuses. In this case, problems can occur. For example, an accumulation of mucus can cause various health issues such as infections.

In order to treat these problems, a medical procedure such as sinus dilation may be used. Sinus dilation is a technique for increasing the size of the sinus passageway to provide a more unrestricted flow of fluids to alleviate sinus congestion. Sinus dilation is performed by using a tool that is inserted into the sinus cavity that includes a balloon which can be inflated. The balloon is inserted into the middle of the small sinus opening and dilated. This dilation applies pressure on the sinus opening to widen it (e.g., by reshaping the tissue structure of the sinus cavity). The opening remains at this increased size once the balloon is taken out, thus providing a larger passageway for fluid flow.

To perform the nasal dilation procedure, or any ENT procedure that is similar, it is important that the physician performing the procedure knows the location of the tool within the nasal cavity with a great degree of accuracy. The physician views an image of the patient's nasal cavities on a display screen and navigates within the patient's actual cavities by manipulating the tool, while looking at an image of the location of the tool on the screen. Any inaccuracies regarding the location of the tool within a patient's nasal cavity may cause the physician to damage the nasal cavity and/or to perform the procedure in the wrong place within the cavity. Therefore, it is very important that the location of the tool on the screen coincides accurately to where the actual tool is within the actual nasal cavity of the patient.

In order to ensure that the physician knows, with accuracy, the location within the nasal cavity where he or she is performing the procedure, a registration procedure is performed. The registration procedure allows the physician to view the image that is on the display screen and register locations on a patient's face in that image. Although a system, apparatus and method are described in more detail below for performing a registration, briefly the image that is displayed is from a computerized tomography (CT) scan that is taken of the patient's head area prior to the ENT procedure. The registration is then performed by an operator, (e.g., physician or other technician), using a registration probe that is placed on various locations of a patient's face. Furthermore, the patient's head is situated in a magnetic field. The registration probe's location is registered on the CT scan that is displayed.

Conventional registration techniques include the operator touching the registration probe to different areas on the patient's face. However, because the tissue is soft on the facial areas, the contact of the registration probe deflects that tissue and potentially causes an inaccuracy in registering that location. Additionally, soft human tissue has a tendency to swell and reduce, (potentially up to <NUM>%), based upon the amount of moisture in it, the humidity, or the like. Therefore, even if the registration probe is placed in substantially the same location on the patient's face as is registered in the CT scan, that facial location may not be in the same spot with respect to the nasal cavities as it was when the CT scan was taken due to swelling or reduction of the soft tissue areas.

Accordingly, described herein is a method, apparatus and system for performing a facial registration. The facial registration is performed on rigid tissue, (such as bone), that does not deflect and is not subject to absorbing moisture in the same way softer tissue is prone to do. The apparatus includes the use of a forward looking ultrasound device in concert with a magnetic registration device in a registration probe.

<FIG> is a diagram of an example system <NUM> for performing a facial registration. The system includes a registration probe <NUM>, a magnetic field emitter <NUM>, a hub <NUM>, a workstation <NUM>, a display <NUM>, and a magnetic driver <NUM>. The registration probe <NUM> and the magnetic field emitter <NUM> may also be connected to the hub <NUM> via the magnetic driver <NUM>, which is connected to the workstation <NUM>, and receives the signals from both the registration probe <NUM> and the magnetic emitter <NUM> to transfer to the workstation <NUM>. However, the registration probe <NUM> and the magnetic driver <NUM> may be in direct communication with the workstation <NUM>, exclusive of a signal traversing through the hub <NUM>.

The workstation <NUM> includes, for example, a processor <NUM>, a memory <NUM>, an input/output (I/O) driver <NUM>, and storage <NUM>, which allow the workstation <NUM> to receive input data and output data via the I/O driver <NUM>, and store data in the storage <NUM> and/or memory <NUM> as needed for processing. The workstation <NUM> is also connected to the display <NUM>. The driver <NUM> is connected to the magnetic emitter <NUM> to emit one or more magnetic fields and frequencies around a patient's head H. As can be seen on the display <NUM>, an image S is displayed that has a target T on it. The target T indicates a current location of the registration probe <NUM> in space with respect to head H. An operator can then see the target on the image S and register areas of the patient's face on the image S for later use in an ENT procedure. It should be noted that the location of the magnetic field emitter <NUM> is shown for example purposes and the emitter <NUM> could be located in additional areas to provide a magnetic image. For example, a portion of the emitter <NUM> could be located beneath the patient's head H, and may include a plurality of magnetic field generators to increase the accuracy of the location. In the case where a plurality of field generators are utilized, the registration probe would be configured to register the plurality of magnetic fields.

To perform a registration, the registration probe <NUM> includes components to allow it to be accurately located with respect to the head H, and more particularly to the patient's face.

<FIG> is a flow diagram of an example conventional method <NUM> for performing a facial registration. In step <NUM>, a CT scan is loaded and displayed. For example, referring back to <FIG>, a CT scan file that has been captured previously and loaded onto a memory device or electronically sent is loaded into the workstation <NUM> and displayed on the display <NUM> as image S.

Once the image is displayed, an operator touches the registration probe to a reference point on the patient's face to register that target location on the image (step <NUM>). For example, the operator touches registration probe <NUM> to an area of the patient's face depicted in the display <NUM> of <FIG>.

A target location between the magnetic modality is displayed on the CT scan (step <NUM>). That is, the location that the coils <NUM> determine the registration probe <NUM> exists in three-dimensional space based on the magnetic field or fields received from the magnetic emitter <NUM> are displayed as a target location on the CT scan. This target location is then registered (step <NUM>). This may be accomplished by the registration probe <NUM> transmitting its location information to the workstation <NUM> based on the detected magnetic fields by the coils <NUM>, where the workstation <NUM> processes the location and determines where to overlay the location on the displayed image.

If enough facial locations have been registered for a complete registration (step <NUM>), then the patient's facial structure is completely registered for the conventional procedure (step <NUM>). If there are not enough locations registered in step <NUM>, then the method returns to step <NUM>, where the operator continues to touch other areas of the patient's face in order to cover a significant enough portion of the patient's face, (e.g., two-thirds), to completely register the patient's face for the ENT procedure.

<FIG> is an example facial image for use during the facial registration method of <FIG>. For purposes of example, the facial image in <FIG> may be image S from <FIG>. As can be seen in <FIG>, targets T (designated T<NUM>, T<NUM>, and T<NUM> are shown as solid crosshairs. Referring back to step <NUM> of method <NUM>, Target T<NUM> corresponds to a first point on the patient's face touched by the operator, target T<NUM> corresponds to a second point on the patient's face touched by the operator, and target T<NUM> corresponds to a third point on the patient's face touched by the operator. A number of nasal cavities <NUM> can also be seen in the image S as depicted in <FIG>. Also shown in <FIG> are targets T<NUM>, T<NUM>, and T<NUM> (shown as dashed crosshairs). These targets represent the actual location of the probe <NUM> in three-dimensional space. As described previously, due to the error induced by utilizing a conventional registration method such as method <NUM> above, it can be seen that the registered targets T<NUM>, T<NUM>, and T<NUM> do not completely coincide with the actual target locations T<NUM>, T<NUM>, and T<NUM>.

<FIG> is a diagram of an example registration probe <NUM> for use in the system <NUM> of <FIG>. The registration probe <NUM> includes electronics <NUM> that operate the probe <NUM> and receive inputs from other components. The electronics <NUM> are connected to the hub <NUM> for eventual transmission to the workstation <NUM>. The registration probe includes an ultrasonic emitter/receiver <NUM>, which is a forward looking ultrasonic emitter/receiver, and coil <NUM>. That is, the ultrasonic emitter/receiver <NUM> emits and receives an ultrasonic wave in an axial direction of the registration probe <NUM> toward the patient. The example registration probe <NUM> shown in <FIG> may be formed of a transparent material (such as plastic), making visible the internal components. However, the probe can be formed of other non-transparent materials as well.

<FIG> is an expanded schematic diagram <NUM> of the electronics <NUM> of the registration probe <NUM> in operation with a target T on the patient's head H and the workstation <NUM>. As shown in <FIG>, the electronics <NUM> includes a microcontroller <NUM>, function generator <NUM>, switch <NUM>, gain amplifiers <NUM>, a voltage limiter <NUM>, a transmitter <NUM> and a receiver <NUM>. The microcontroller <NUM> is in communication with the workstation <NUM> and controls the transmitter <NUM> via the switch <NUM> to transmit ultrasonic waves. The microcontroller <NUM> receives the returned ultrasonic waves from the target T via the receiver <NUM> for transmission to the workstation <NUM>. The function generator <NUM> generates an impulse for which a received echo is amplified by gain amplifiers <NUM>. The voltage limiter <NUM> limits the voltage produced by the amplifier to avoid the sampling system becoming saturated.

The ultrasonic emitter/receiver <NUM> of the registration probe <NUM> emits ultrasonic waves which are reflected back, (e.g., from the bone surface of the patient's skull), and read to determine a location of the registration probe <NUM> with respect to the CT scan image S. The coil <NUM> receives the magnetic waves emitted by the magnetic emitter <NUM> to also locate the registration probe <NUM> in space with respect to the face of the head H. The coil <NUM> may be a series of windings (e.g., copper), that are arranged to receive the magnetic field emitted by the magnetic emitter in such a way to locate within the field where the registration probe <NUM> is.

As mentioned above, the accuracy of the registration is important because the ENT procedure performed will rely on an accurate registration to aid the physician performing the procedure in knowing where he or she is within the nasal cavity. The ultrasonic wave emitted and received by the ultrasonic emitter/receiver <NUM> of the registration probe <NUM> is correlated (described in more detail below) with the magnetic receiver, (i.e., the coil <NUM>), in order to accurately locate the registration probe <NUM>. This correlation then allows the physician performing the procedure to be able to locate the tool used for the procedure in the nasal cavity of the patient on the image S.

<FIG> is a flow diagram of an example method <NUM> for performing a facial registration. In step <NUM>, a CT scan is loaded and displayed. For example, referring back to <FIG>, a CT scan file that has been captured previously and loaded onto a memory device or electronically sent is loaded into the workstation <NUM> and displayed on the display <NUM> as image S.

Once the image is displayed, an operator hovers or touches the registration probe over a reference point on the patient's face to register that target location on the image (step <NUM>). For example, the operator hovers registration probe <NUM> over an area of the patient's face depicted in <FIG>. The registration probe emits an ultrasonic wave which is echoed off of a rigid structure, such as a facial bone, and read by the registration probe (step <NUM>). For example, the ultrasonic emitter/receiver <NUM> of the registration probe <NUM> emits the ultrasonic wave into the patient's face, which is then echoed off of a bone, or bony structure. The registration probe <NUM> then reads the echo/return of the wave via the ultrasonic emitter/receiver <NUM> to determine the location of the target T in the image S.

Once the ultrasonic wave is received, a target location between the magnetic modality and the ultrasonic modality is correlated on the CT scan (step <NUM>). That is, the ultrasonic wave received by ultrasonic emitter/receiver <NUM> of the registration probe <NUM> is correlated to the location that the coils <NUM> determine the registration probe <NUM> exists in three-dimensional space based on the magnetic field received from the magnetic emitter <NUM>. This correlation allows an accurate target location T to be determined and registered (step <NUM>). This may be accomplished by the registration probe <NUM> transmitting its location information to the workstation <NUM>, where the workstation <NUM> processes the location and determines where to overlay the location on the displayed image.

If enough facial locations have been registered for a complete registration (step <NUM>), then the patient's facial structure is completely registered for the procedure (step <NUM>). If there are not enough locations registered in step <NUM>, then the method returns to step <NUM>, where the operator continues to hover over other areas of the patient's face in order to cover a significant enough portion of the patient's face, (e.g., two-thirds), to completely register the patient's face for the ENT procedure. That is, for example, the operator may hover the registration probe over an area such as two-thirds of the patient's face. A physician monitoring the convergence of the probe <NUM> in real time on the image, (e.g., CT scan), may determine that a sufficient amount of the patient's face has been registered Alternatively, a mathematical algorithm, such as a minimum mean square error (MMSE) algorithm may be utilized to determine when enough of a patient's face has been registered.

Since the registration is bone to bone, (i.e., bone from the ultrasonic registration to bone in the CT scan), it is possible to know the distance from the tip of the registration probe <NUM> to the edge of the bone. Accordingly, the bone in the CT scan can be correlated to the bone detected by the ultrasonic wave. The soft tissue thickness can also be estimated in this manner. For example, if hovering on the bridge of a nose, the soft tissue appears rigid because the distance between the bony structure and facial surface is very small. This additional information can be utilized by a physician to determine whether or not enough of the face has been registered to the CT scan or mathematically by including the location in the MMSE algorithm described above in calculating the error.

<FIG> is an example facial image for use during the facial registration method <NUM> performed in <FIG>. For purposes of example, the facial image in <FIG> may be image S from <FIG>. Additionally, the facial image in <FIG> is substantially similar to that in <FIG>. As can be seen in <FIG>, targets T (designated T<NUM>, T<NUM>, and T<NUM>) are shown as solid crosshairs. Referring back to step <NUM> of method <NUM>, Target T<NUM> corresponds to a first correlated point on the patient's face registered by the operator, target T<NUM> corresponds to a second correlated point on the patient's face registered by the operator, and target T<NUM> corresponds to a third correlated point on the patient's face registered by the operator. As in <FIG>, a number of nasal cavities <NUM> can also be seen in the image S as depicted in <FIG>. Also shown in <FIG> for example purposes are targets T<NUM>, T<NUM>, and T<NUM> (shown as dashed crosshairs). These targets represent the targets that would be registered in a conventional magnetic modality registration method, such as method <NUM> described above. Targets T<NUM>, T<NUM>, and T<NUM> represent the actual location of the probe <NUM> in three-dimensional space. It can therefore be seen then that an ENT procedure performed utilizing the correlated target locations acquired in method <NUM> would be performed in a correct area with relation to the nasal cavities <NUM> as compared to performing the procedure utilizing the target areas acquired in the conventional method <NUM>.

Accordingly, above is described a forward looking ultrasound system near the distal end of a registration probe that generates some impact on human rigid tissue and waits for an echo. By calculating the amount of time that passes the registration system can determine where, (i.e., how deep), the tissue is. Since bony structures reflect virtually all of the ultrasound energy without absorbing any of it, it is easy to identify using ultrasound. By hovering the registration probe and utilizing the ultrasound registration along with the magnetic registration technique, a more accurate registration can be achieved.

It should be noted that the method, apparatus and system described above can include additional modifications. For example, the registration probe, (e.g., registration probe <NUM>), can be a high-frequency probe that hovers on the surface of the skin with a matching impedance such as a gel, and leaves a gel trace. Additionally, components in communication with one another can be in wired or wireless communication. That is, transceivers and antennas may be included in the devices, (e.g., registration probe <NUM> and other components of system <NUM>), that can transmit and receive data wirelessly to one another.

The methods provided can be implemented in a general purpose computer, a processor, or a processor core. Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. Such processors can be manufactured by configuring a manufacturing process using the results of processed hardware description language (HDL) instructions and other intermediary data including netlists (such instructions capable of being stored on a computer readable media). The results of such processing can be maskworks that are then used in a semiconductor manufacturing process to manufacture a processor which implements features of the disclosure.

Claim 1:
A method for performing facial registration on rigid tissue for an ear/nose/throat procedure, comprising:
loading (<NUM>, <NUM>) a reference image (S) into a workstation; wherein a registration probe is in communication with the workstation; and
displaying the reference image on a display in communication with the workstation;
hovering (<NUM>, <NUM>) the registration probe (<NUM>) over a plurality of target locations (T) on a face of a patient;
controlling, using a microcontroller, a transmitter to emit (<NUM>) an ultrasonic wave from the registration probe at each of the target locations;
receiving, via the registration probe, a return of the ultrasonic wave from each of the target locations;
receiving, via the registration probe, a magnetic signal from a magnetic emitter located proximate to the face of the patient to identify a location in space of the registration probe relative to the magnetic emitter; and
correlating (<NUM>) each of the target locations of the received ultrasonic return to a location identified in space relative to the magnetic emitter;
wherein correlating each of the target locations of the received ultrasonic return to a location identified in space relative to the magnetic emitter includes correlating each of the target locations on the reference image displayed; and
wherein the reference image (S) is a computerized tomography, CT, scan of the face of the patient, and wherein the reference image (S) includes an image of nasal cavities (<NUM>) of the patient and bone structure of the patient; and
wherein the ultrasonic return is a wave reflected from a location on the bone structure of the patient and is received to determine a location of the registration probe with respect to the reference image, which location is compared to the location in space of the registration probe (<NUM>) relative to the magnetic emitter to acquire a correlated target location.