EP4694976A1

EP4694976A1 - Localization of brachytherapy applicators with doppler ultrasound imaging

Info

Publication number: EP4694976A1
Application number: EP24724855.2A
Authority: EP
Inventors: Christopher L. Deufel; Eric E. Brost; Bradley J. STISH; Matthew W. Urban; Christine U. LEE; James F. Greenleaf; Justine M. DUPERE
Original assignee: Mayo Foundation for Medical Education and Research; Mayo Clinic in Florida
Current assignee: Mayo Foundation for Medical Education and Research; Mayo Clinic in Florida
Priority date: 2023-04-14
Filing date: 2024-04-15
Publication date: 2026-02-18
Also published as: WO2024216292A1

Abstract

A brachytherapy applicator template includes a template body having channels formed therein, where each of the channels extends from a front surface of the template body to a rear surface of the template body. A vibrational device mechanically coupled to the template body generates mechanical vibrations in the template body. These vibrations are transferred to brachytherapy applicators arranged within the template. Doppler ultrasound data may be acquired while vibrating the template, and thus the brachytherapy applicators. Locations of the brachytherapy applicators can be determined by processing the Doppler ultrasound data to determine or otherwise identify Doppler ultrasound signatures indicating the locations of the brachytherapy applicators.

Description

LOCALIZATION OF BRACHYTHERAPY APPLICATORS WITH DOPPLER ULTRASOUND IMAGING

BACKGROUND

[0001] High dose-rate (HDR) brachytherapy is a type of cancer treatment that uses high-dose radioactive sources to kill cancer cells. This treatment involves placing small, temporary or permanent radioactive sources, which may be referred to as radioactive seeds, directly into or near the tumor. The radioactive seeds deliver a high dose of radiation to the cancer cells while minimizing exposure to surrounding healthy tissue. Multiple needles (e.g., 10-20) may often be used to deliver the radioactive seeds into the tissue to locally treat the tumor. Needle localization can be facilitated using medical imaging, such as x-ray computed tomography (CT) and/or ultrasound imaging.

SUMMARY OF THE DISCLOSURE

[0002] It is an aspect of the present disclosure to provide a brachytherapy applicator template that includes a template body and a vibrational device mechanically coupled thereto. The template body includes a plurality of channels formed therein, each of the plurality’ of channels extending from a front surface of the template body to a rear surface of the template body. The vibrational device is mechanically coupled to the template body such that when the vibrational device is operated mechanical vibrations are transferred from the vibrational device into the template body.

[0003] ft is another aspect of the present disclosure to provide a method for visualizing brachytherapy applicator positions in a region-of-interest (ROI). The method includes acquiring Doppler ultrasound data from a region-of-interest into which one or more brachytherapy applicators have been positioned, while the plurality of brachytherapy applicators are being simultaneously vibrated by an external vibrational device coupled to a brachytherapy placement template within which the one or more brachytherapy applicators are arranged. The Doppler ultrasound data are processed with a computer system to determine a location of each of the plurality of brachytherapy applicators within the region-of-interest based on Doppler ultrasound signatures generated by vibrations of the one or more brachytherapy applicators interacting with ultrasound incident on the plurality' of brachytherapy applicators. The location of each of the one or more brachytherapy applicators may then be presented to a user via the computer system. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 is an example brachytherapy applicator placement template having an edge-mounted vibrational device coupled thereto.

[0005] FIG. 2 is an example brachytherapy applicator placement template having a face-mounted vibrational device coupled thereto.

[0006] FIG. 3 is an example brachytherapy applicator placement template having a stylet-based vibrational device coupled thereto.

[0007] FIG. 4 is an example brachytherapy applicator placement template composed of a frame and insert.

[0008] FIG. 5 is a flowchart setting forth the steps of an example method for visualizing or otherwise determining the locations of brachytherapy applicators in a region-of-interest by simultaneously vibrating the applicators via a vibrating placement template and acquiring Doppler ultrasound data in response thereto.

[0009] FIGS. 6A-6D illustrate an example brachytherapy applicator template and Doppler ultrasound data acquired while vibrating the template, according to some examples described in the present disclosure. FIG. 6D illustrates automated detection of the color VISION signal using thresholding and clustering methods to determine the needle's central shaft.

[0010] FIG. 7 illustrates an analysis of B-mode and color Doppler signals from a single brachytherapy needle being vibrated by a vibrating brachytherapy applicator template.

[0011] FIG. 8 illustrates example Doppler ultrasound data acquired using different gain settings.

[0012] FIG. 9 is a block diagram of an example ultrasound system that can implement the methods described in the present disclosure.

DETAILED DESCRIPTION

[0013] Described here are systems and methods for improving brachytherapy applicator (e.g., brachy therapy needle, afterloader catheter) visualization and localization with ultrasound imaging. A vibrational device (e.g., a mechanical actuator) is coupled to a brachytherapy template (e.g., a needle template, an afterloader template). By operating the vibrational device, the template is made to vibrate and the mechanical vibrations are transferred from the template to any needles (or catheters) arranged within the channels of the template. In this way. multiple needles (or catheters) can be made to vibrate simultaneously by using a single vibrational device to transmit mechanical vibrations to the brachytherapy needles (or catheters) via vibrating the brachytherapy template. Advantageously, coupling the vibrational device to the brachytherapy template allows for a hands-free operation. As another advantage, coupling the vibrational device to multiple needles at once allows for using a single vibrational device for multiple needles, rather than a different vibrational device for each brachytherapy needle. As more needles are positioned in the tissue, previously placed needles may shift their positions slightly. It is another advantage of the present disclosure that by coupling the vibrational device to multiple needles all of the needles can be simultaneously vibrated after placement to facilitate confirmation that each needle is accurately placed, or to aid in digital reconstruction.

[0014] In some other examples, a vibrational device may be coupled to the proximal (i.e., exposed) end of a brachytherapy needle, or a vibrational device may be coupled to the proximal ends of multiple brachytherapy needles. Additionally or alternatively, a vibrational device may be coupled to the exposed end portion of one or more catheters used with an afterloader. In these instances, mechanical vibrations are transmitted from the vibrational device through the length of each brachytherapy needle (or afterloader catheter), causing it to vibrate.

[0015] The brachytherapy needle(s) and/or afterloader catheter(s) are positioned within a region-of-interest in a patient, such as a region of tissue that is to receive brachytherapy treatment. The vibrational device is then operated to vibrate the brachytherapy needle(s) and/or afterloader catheter(s), either directly or via vibrating the brachytherapy template within which the brachytherapy needle(s) and/or afterloader catheter(s) are arranged. When the brachytherapy needle(s) and/or afterloader catheter(s) are vibrating, ultrasound data may be acquired from the region-of-interest in a patient. As an example, the ultrasound data may be Doppler ultrasound data (e.g., color Doppler ultrasound data, power Doppler ultrasound data, other mathematical analogs of, or signals derived from, color Doppler and/or power Doppler). [0016] A shimmering, or temporally and spatially vary ing, Doppler signal is produced when ultrasound waves reflect off the vibrating surfaces of the brachytherapy needle(s) and/or afterloader catheter(s). The vibrating needle or catheter appears as variegated color pixels that can be overlaid on corresponding grayscale B-mode images in real-time. Accordingly, the systems and methods described in the present disclosure may be referred to as implementing a color VISION (Vibrationally Induced Shimmering for Identifying an Object’s Nature) technique that generates a high contrast color Doppler (“CD”) signal when used with HDR brachytherapy needles and/or afterloader catheters. Additionally or alternatively, power Doppler (“PD’ j signals may also be acquired. The disclosed systems and methods have the potential to improve applicator conspicuity and facilitate automated applicator digitization. [0017] Referring to FIG. 1, an example brachytherapy needle template 10 is shown. The template 10 includes a body 12 that may be composed of metal, plastic, or another suitable material. In some examples, the body 12 may be composed of a single piece. In other examples, the body 12 may be composed of more than one piece, such as an insert and frame (e.g., as shown in FIG. 4). The body 12 may be designed such that the vibrational strength coupled to brachytherapy applicators (e.g., needles or afterloader catheters) is spatially variant. That is, the body 12 may be designed such that some portions of the body 12 transmit stronger mechanical vibrations from the body 12 to the brachytherapy applicators than other portions of the body 12.

[0018] The body 12 of the template 10 includes a plurality' of needle channels 14 formed therein. The needle channels 14 may generally include plurality of holes extending from a front face 16 of the body 12 to a rear face 18 of the body 12. The needle channels 14 may be arranged in an array, variably, or in some other arbitrary pattern. For example, the needle channels 14 may be arranged in a regularly spaced array (e.g., a grid), and thus may be arranged in vertical columns and horizontal rows of needle channels 14. In some alternative constructions, the template 10 body 12 may be configured for use with an afterloader. In these instances, the needle channels 14 may be sized to receive afterloader catheters.

[0019] As described above, in some examples the body 12 of the template 10 may be composed of multiple components that allow for providing spatially variant mechanical vibrations to the brachytherapy applicators. In some instances, these components may be separate or separable components. As one example, individual collets that surround each needle channel 14 may provide for independent control of the mechanical vibrations transferred to each needle.

[0020] In use, the channels 14 receive a brachytherapy needle 40 and guide or otherwise direct the brachytherapy needle 40 towards the tissue of interest (e.g.. by guiding the needle 40 from the front face 16 of the body towards the rear face 18 of the body 12 along a trajectory defined by the respective needle channel 14). In some alternative constructions, the template 10 body 12 may be configured for use with an afterloader. In these instances, the needle channels 14 may receive catheters from the afterloader in lieu of brachytherapy needles. [0021] A vibrational device 30 is coupled to the body 12 of the template 10 to provide vibrational motion to the brachytherapy needle(s) 40 arranged within the needle channels 14 of the template 10. For example, the mechanical vibrations are transmitted from the vibrational device 30 into the body 12 where they propagate into and along the length of the brachytherapy needle(s) 40. As illustrated in FIG. 1, the vibrational device 30 is coupled to an edge 20, or periphery of the template 10 body 12. The vibrational device 30 may be coupled to the edge 20 of the body 12 using any suitable mechanical coupling, including adhesives, fasteners (e.g., screws), an interference fit, a snap fit, an interlocking fit, and the like. As illustrated in FIG. 2, in other examples the vibration device 30 may be coupled to a face of the template 10 body 12, such as the front face 16 of the body 12 (as illustrated in FIG. 4), or the rear face 18 of the body 12. In some other examples, the vibrational device 30 may be integrated within the body 12 of the template 10. The vibrational device 30 may include a mechanical actuator, a shaker, an audio amplifier, an electromagnetic actuator, or other suitable device that can be controlled to generate mechanical vibrations. As one example, the vibrational device 30 may include an eccentric rotating mass motor. The vibrational device 30 is operable over a range of different frequencies, such that different vibrational frequencies can be selected for use by the vibrational device 30.

[0022] As shown in FIG. 3, in some examples the vibrational device 30 may be a sty let that can be vibrated. In these instances, the vibrational device 30 may include a stylet body 32 and an elongate tip 34 extending from the stylet body 32. The elongate tip 34 may be sized to be received by one of the needle channels 14 in the template 10 body 12 or alternatively to be received by the inner lumen of a brachytherapy needle 40 arranged within one of the needle channels 14. In use, the elongate tip 34 is arranged within one of the needle channels 14 or inner lumens of a brachytherapy needle 40. A vibrator 36 (e.g., a shaker, a mechanical actuator) coupled to or housed within the st let body 32 is made to vibrate and the mechanical vibrations are transferred to the elongate tip 34 into the template 10 body 12 (or brachytherapy needle 40 into which the elongate tip 34 has been inserted) and into other brachytherapy needle(s) 40. The vibrations from the stylet actuator can thus produce signals in nearby brachytherapy needles 40 from the transfer of the vibrations via the template 10 body 12 and/or tissue medium. The strength of the stylet signal can be adjusted based on the fit of the stylet inside of the brachytherapy needle 40, the pressure applied to the brachytherapy needle wall through angulation, and/or by varying the stylet insertion depth. [0023] In some examples, such as those shown in FIGS. 1 and 2, the template 10 body 12 may be constructed as a single piece. The body 12 may be composed of a plastic or other polymer, such as polyphenylsulfone (PPSU). As shown in FIG. 4, in some examples, the template 10 body 12 may be composed of a frame 22 and an insert 24. The insert 24 may be received by the frame 22, such as by sliding the insert 24 into slots formed along the inner edges of the frame 22. As a non-limiting example, the frame 22 may be composed of a plastic or other polymer (e.g., PPSU) and the insert 24 may be composed of a metal, such as titanium. Advantageously, the frame and insert design allows for the insert 24 to be removed and sterilized after use.

[0024] The template 10 body 12 may include markings to indicate the rows and columns of needle channels 14. In the example illustrated in FIG. 4, the markings include letters to denote different vertical columns of needle channels 14 and numbers to denote different horizontal rows of needle channels 14. The markings may be, for example, laser etched or engraved in the template 10 body 12 or frame 22.

[0025] As will be described in more detail, in operation the vibrational device 30 vibrates the template 10 body 12. The mechanical vibrations are transferred from the body 12 to the brachytherapy needle(s) 40 arranged within the needle channel(s) 14 of the template 10. By vibrating the brachytherapy needle(s) 40 in this way, the needle(s) 40 can be visualized by acquiring ultrasound data from a region-of-interest into which the needle(s) 40 have been introduced, such as a treatment region in a patient. As an example, the ultrasound data may be Doppler ultrasound data, in which the vibrating needle(s) 40 present with a unique Doppler signature that can be used to localize or otherwise visualize the placement of the needle(s) 40 in the region-of-interest.

[0026] The vibrational device 30 may be controlled by a controller of the ultrasound system. For instance, the controller of the ultrasound system may set or otherwise vibration stimulus settings for driving the vibrational device 30. The controller of the ultrasound system may also process those settings to send control signals to the vibrational device 30, which cause the vibrational device 30 to vibrate and generate mechanical vibrations according to the vibration stimulus settings. Additionally or alternatively, an external device (e.g., a separate computer system or controller) can be used to control the operation of the vibrational device 30. The external device may communicate with the vibrational device 30 via a wired or wireless connection. [0027] Additionally or alternatively, the vibrational device 30 may be a device that is implanted in the subject and driven to generate mechanical vibrations in the tissue that are transferred to the brachytherapy needle(s) 40 when they are arranged within the tissue of the subject. In this way, the brachytherapy needle(s) 40 can be vibrated indirectly rather than by vibrating the applicator template 10 or the needles 40 themselves. In some instances, one or more additional markers may be implanted in the subject and used to provide synergistic vibrational detection of the brachytherapy needle(s) 40. For instance, coated marker can be implanted within the subject, where the coated markers are coated in a material that generates a twinkling artifact signature in response to ultrasound waves incident on the coated marker.

[0028] As a non-limiting example, the vibrational device 30 may be a vibratable marker that is implanted in the subject and driven to generate vibrations that interact with and cause mechanical vibrations within the brachytherapy needle(s) 40. In this way, vibrational energy can be transferred from the vibratable marker to the brachytherapy needle(s) 40, similar to transferring vibrational energy from the applicator template 10 to the brachytherapy needle(s) 40. The vibratable marker can include an actuator housed with a housing. Electronics for powering and controlling the actuator can also be housed within the housing. In some embodiments, the vibrations used to drive the vibratable marker may be matched with a resonant frequency of the vibratable marker to provide a synergy between the vibratable marker and the driver (e.g., the actuator).

[0029] The vibratable marker can be driven based on instructions received by the control electronics of the vibratable marker from an external controller, which may be a controller of the ultrasound system or a separate, external device (e.g., a mobile phone, a tablet computer, a computer system). The instructions can be sent to the vibratable marker from the controller using a wireless communication device that communicates over a network. The network may be a long-range wireless network such as the Internet, a local area network (LAN), a wide area network (WAN), or a combination thereof. In other embodiments, the network may be a short-range wireless communication network. In some embodiments, the network may include both wired and wireless devices and connections.

[0030] In some embodiments, the wireless communication device is a Bluetooth® controller. The Bluetooth® controller communicates with the vibratable marker employing the Bluetooth® protocol. In such embodiments, therefore, the vibratable marker and controller are within a communication range (i.e., in proximity) of each other while they exchange data. In other embodiments, the wireless communication device communicates using other protocols (e.g., Wi-Fi® wireless protocol. Zigbee® wireless protocol, cellular protocols, a proprietary protocol, etc.) over a different type of wireless network. For example, the wireless communication device may be configured to communicate via Wi-Fi® through a wide area network such as the Internet or a local area network, or to communicate through a piconet (e.g., using infrared or NFC communications).

[0031] Referring now to FIG. 5. a flowchart is illustrated, setting forth the steps of an example method for localizing or otherwise visualizing the positions of brachytherapy applicators (e.g., brachytherapy needles, afterloader catheters) positioned within a region-of- interest in a patient.

[0032] The method includes acquiring ultrasound data with an ultrasound system, as indicated at step 502. The ultrasound data are acquired from a region-of-interest in a patient, such as a tissue region to be treated using brachytherapy. Accordingly, the region-of-interest contains a plurality of brachytherapy applicators for delivering brachytherapy seeds to the tissue region either permanently (e.g., by implanting the brachytherapy seeds via brachytherapy needle) or temporarily (e.g., by moving the brachytherapy seeds into and out of the tissue region using afterloader catheters). In general, the ultrasound data include Doppler ultrasound data. Additionally or alternatively, the ultrasound data may include B-mode ultrasound data. In some instances, the ultrasound data may include both B-mode and Doppler ultrasound data. Doppler ultrasound data may include color Doppler ultrasound data, power Doppler ultrasound data, or other analogs or derivatives of color and/or power Doppler ultrasound data.

[0033] The ultrasound data may be acquired using a single detector (e g., a single ultrasound system, a single ultrasound transducer, a single aperture of an ultrasound transducer), or the ultrasound data may be acquired using multiple detectors (e.g., more than one ultrasound system, more than one ultrasound transducers, more than one apertures of a single ultrasound transducer). As a non-limiting example, the ultrasound data may be acquired using multiple transducers or transducer elements that are arranged at different spatial positions or locations around the subject.

[0034] In addition to acquiring ultrasound data, other medical imaging data acquired from the subject may also be accessed by the ultrasound system or a computer system in communication with the ultrasound system. These additional medical imaging data may include images of the subject acquiring using x-ray imaging, computed tomography (CT), magnetic resonance imaging (MRI), or the like. As will be described below in more detail, the locations of the brachytherapy applicators can be registered with these medical images, or with the original ultrasound images, to help visualization of the brachytherapy applicators relative to the subject’s anatomy.

[0035] While the ultrasound data are acquired, vibrations are applied to the brachytherapy applicators, as indicated at step 504. In particular, the brachytherapy applicators are arranged within a brachytherapy placement template. A vibrational device coupled to the template is operated to generate mechanical vibrations in the template. These vibrations are then transferred from the template to the brachytherapy applicators, causing the applicators to be vibrated. As one example, the vibrational device may be operated to generate mechanical vibrations at a frequency in the range of 40-5000 Hz, in the range of 200-450 Hz or other such subranges within 40-5000 Hz. The device may also blend more than one frequency for optimal vibration. The frequency choices may be optimized for needle vibration, such as to account for variable vibrational strength as a function of needle position within the template, to minimize the vibration of patient tissue, and so on.

[0036] The mechanical vibrations applied to the template may be modulated to improve the visualization of the brachytherapy applicators in the ultrasound data. For example, the vibration stimulus used to drive the vibrational device may be optimized to highlight the interface between the brachytherapy applicators and surrounding tissues. As an example, the vibration stimulus can be optimized by using an accelerometer to study the frequency and amplitude output of the vibrational device in tissue across a broad range of frequencies.

[0037] Ultrasound data can be acquired and the vibration frequency/ amplitude combination that best highlights interface between brachytherapy applicators and tissue can be selected and stored by the computer system as optimized vibration stimulus settings. Additionally or alternatively, Doppler scanning parameters (e.g., frequency, gain, pulse repetition frequency (“PRF”), and so on) used by the ultrasound system when acquiring the ultrasound data can be optimized to improve visualization of the brachytherapy applicators. For instance, experimental data can be collected to assess optimal settings for the vibration stimulus (e.g., vibration frequency, vibration amplitude) used to drive the vibrational device and the Doppler scanning parameters may be selected for the optimized vibration stimulus parameters. The optimized Doppler scanning parameters may be stored by the computer system and/or the ultrasound system.

[0038] The gain (e.g., the color gain) of the ultrasound system can be adjusted to optimize visualization of the brachytherapy applicators. A higher gain can increase the signal within the brachytherapy applicator, but may also amplify artifacts or noise within the tissue. It has been observed that when two brachytherapy needles are far apart (e.g., > 3 cm apart) it can be difficult to select a single gain setting that provides for a well-constrained color Doppler signal in all brachytherapy applicators. For example, a larger gain emphasizing anterior needles might result in excessive signal noise in the posterior region of the tissue. Conversely, if the gain settings were optimized for posterior needles, the shimmering signal might be faint for anterior needles. These signal differences can be managed with one or more mitigation strategies.

[0039] As one example, a user-definable ROI for the color Doppler signal can be set, whereby the color Doppler signal is restricted to within the defined ROI. The adjustable ROI could be used to manage differences between the signal strength closer and further from the probe. For example, the user could select an upper ROI for anterior needles and adjust the gain to optimize needle shimmering, and then select a lower ROI and readjust the gain for the posterior needles. As another example, a higher actuator frequency can be used to help decrease coupling of vibrations into the tissue, which can reduce the signal noise in surrounding tissue. As yet another example, the color Doppler signal coming directly from the ultrasound system can be isolated and a non-linear color Doppler gain can be applied to the signal as a function of distance from the probe to optimize the signal in all needles.

[0040] The ultrasound data may then be processed with a computer system to determine a location of each of the brachytherapy applicators within the region-of-interest based on Doppler ultrasound signatures generated by vibrating the plurality of brachytherapy applicators, as indicated at step 506. Additionally or alternatively, the ultrasound data may be used without further analysis to localize or otherwise visualize the locations of brachytherapy applicators within the region-of-interest.

[0041] As one non-limiting example, the interaction of ultrasound incident on the brachytherapy applicators and the vibrating surfaces of those applicators causes a Doppler ultrasound signature that can be detected, measured, or otherwise analyzed to determine the locations of the brachytherapy applicators. In some examples, processing the ultrasound data may include overlaying Doppler ultrasound data on B-mode images also acquired from the region-of-interest with the ultrasound system. In some other examples, processing the ultrasound data may include isolating Doppler ultrasound signatures of the vibrating brachytherapy applicators. These isolated Doppler ultrasound signals may then be overlaid on B-mode images also acquired from the region-of-interest using the ultrasound system. Alternatively, the isolated Doppler ultrasound signals can be processed to compute, or otherwise determine, centroids (e.g., inner lumen) for each brachytherapy applicator. These centroids can be stored as positional data for the brachytherapy applicators, and may also be overlaid on B-mode images acquired from the region-of-interest using the ultrasound system. The digitized display of the brachytherapy applicator may include additional features such as needle tip, inner lumen, needle width, radiation dwell locations, and so on.

[0042] In some embodiments, the signal -to-noise ratio (SNR) for the vibrational signals versus background signals can be enhanced by processing the ultrasound data prior to localizing the brachytherapy applicator(s). As one example, the vibrational signals may be isolated from the background signals to improve the SNR of the vibrational signals. For instance, a lock-in amplifier, or the like, can be used to isolate the vibrational signals based on the frequencies of the vibrations. As an example, a lock-in amplifier may be used to demodulate the vibrational signals from the ultrasound data based on a reference frequency matched to the vibrational frequencies. Additionally or alternatively, the vibrational signals can be isolated based on pulsing the vibrations in a pattern or other manner such that the pulsed vibrations can be isolated from the ultrasound data. The SNR of the vibrational signals can additionally or alternatively be improved by filtering the ultrasound data, such as by using low pass filtering, high pass filtering, or combinations of both. In still other examples, the SNR of the vibrational signals can be improved by optimizing the ultrasound system parameters, as described above. For instance, spatially variable signal gain settings can be used (e.g., using a split-gain approach) to improve SNR of the vibrational signals.

[0043] The determined locations of the brachytherapy applicators may then be presented to a user, or stored for later use or processing, by the computer system, as indicated at step 508. For instance, the locations may be displayed to a user as described above (e.g., by one or more different overlays on B-mode images). As another example, the locations of the brachytherapy applicators may be digitized and these digitized positional data may be provided to a radiation treatment planning system to facilitate developing or modifying a radiation treatment plan for the patient.

[0044] As a non-limiting example of automated digitization of one or more brachytherapy applicators, ultrasound data (e.g., static color Doppler ultrasound image acquisitions) can be processed. First, pixels or voxels are identified within the image set that are associated with the brachytherapy applicators. As one example, thresholding methods can be used. As another example, deep learning-based detection methods can be used and may be preferred when the image set contains artifacts or poor contrast. [0045] After the brachytherapy applicators are identified, the identified pixels or voxels are clustered into distinct applicators. As a non-limiting example, a density-based clustering algorithm (e.g., a DBSCAN algorithm) can be used to generate the clusters. The clusters are then processed into arrays of points that denote the inner lumens of the brachytherapy applicators. As an example, in sagittal images the clusters can be fit to a polynomial (e.g., a second-order polynomial) to generate the array of points, and in axial images that centroids for each cluster can be calculated. These arrays of points may be output as the digitized brachytherapy applicators. Additionally or alternatively, the arrays of points can be used to generate a digitized representation of the brachytherapy applicators, such as by generated a three-dimensional model, or the like.

[0046] As described above, in some examples, the determined locations of the brachytherapy applicators and/or the digitized representations of the brachytherapy applicators, can be registered to, and displayed with, one or more medical images of the subject. The medical images can include images acquired using an x-ray imaging system, a CT system, an MRI system, the ultrasound system, or the like. The locations of the brachytherapy applicators and/or the digitized representations of the brachytherapy applicators can be displayed with the medical images by, in some examples, overlaying the locations of the brachytherapy applicators and/or the digitized representations of the brachytherapy applicators over the medical images after coregistration.

[0047] In an example implementation, images were cropped to remove static image tags, including the scale and patient information. Within the cropped images, the color-pixel values were isolated and subsequently clustered into distinct needles using DBSCAN, a density-based clustering algorithm with parameters £ = 2 and minimum points = 5. Each cluster was then processed to create an array of points that denoted the needle's inner lumen. In sagittal images, the clusters were fit to a second-order polynomial. In axial images, the centroids for each cluster were calculated.

[0048] An initial qualitative evaluation was performed followed by a comprehensive quantitative analysis of accuracy along the needle shaft using a needle cadaver implant. For the quantitative study, each needle of the cadaveric implant was imaged on the sagittal plane with an ROI restricted to needle shaft with a 1 cm margin and color Doppler gain ranging from 0- 30% in 5% increments. A single midgland axial image was obtained with a split-gain approach using separate ROIs encompassing the posterior (n=8 needle, gain=0%), middle (n=5 needles, gain=20%), or anterior (n=6 needles. gain=30%) needles. In a split-gain approach, separate color Doppler gain settings can be used for needles. For example, for a 12-needle implant, the upper region of the implant may be imaged at 15% gain, and the lower region of the implant may be imaged at 0% gain. The two images can be merged in postprocessing to illustrate how a region can be visualized using gain settings that are optimized to different regions of the implant. All needles were digitized with the aforementioned approach.

[0049] For sagittal images, the natively registered B-mode and color Doppler images were separated, and points were placed along the needle shaft near the needle tip, 1.5 cm inferior to the tip, and 3 cm inferior to the tip separately for B-mode and color Doppler images. The distance between corresponding points was calculated and binned according to posterior (n=24 points), middle (n=15 points), and anterior (n=18 points) locations.

[0050] For axial images, the locations of the needles in the B-mode images were manually identified, and the locations in the color Doppler images were calculated from the center of mass of the 19 largest clusters produced using DBSCAN. The Euclidean distance between B-mode and color Doppler positions was calculated for each needle.

[0051] An example of Doppler ultrasound data acquired using the systems and methods described in the present disclosure is illustrated in FIG. 6A. In this example, 12 brachytherapy needles were positioned in a region-of-interest. Three different vibrational device configurations were used in the example: a template face-mounted actuator, a template top (i.e., edge)-mounted actuator, and a stylet actuator (e.g.. as illustrated in FIG. 6B). FIG. 6C illustrates the effect that changing the vibrational frequency has on the resultant Doppler ultrasound signatures that indicate the location of the brachytherapy applicators. FIG. 6D shows an example of the automated digitization of brachytherapy applicators using the thresholding and clustering methods described above to determine the central shaft of each brachytherapy applicator.

[0052] As shown, each of the three vibrational device configurations was able to produce high contrast and localized color VISION in implanted brachytherapy needles in both the axial and sagittal planes. The color VISION signal was processed with centroid detection to overlay a needle’s position onto the B-mode image, providing for automated applicator digitization. The face-mounted actuator produced a strong and consistent signal that coupled into all needles, whereas the stylet actuator was beneficial for selective highlighting of a needle of interest in an area of low signal. In areas with low B-mode signal, such as behind bowel gas, the decrease in color VISION signal may be partially mitigated by increasing the vibrational strength or adjusting the color gain on the ultrasound system. [0053] FIG. 7 illustrates an example analysis of the B-mode and color Doppler signals for a single needle implant. The ROI was used to calculate the needle contrast in the B-mode and color Doppler images using the geometric dimensions of the needle. The center of the needle was identified on the B-mode image. The profile (right) shows the mean pixel value in the vertical direction in the B-mode and color Doppler images. It can be observ ed from this profile data that color Doppler signals provide a more accurate localization of the brachytherapy needle than the B-mode image.

[0054] FIG. 8 illustrates Doppler ultrasound data acquired from a 12-needle implant in a phantom. The Doppler ultrasound data show the shimmering signal as a function of increasing color Doppler gain. At 0% gain, the anterior needles do not exhibit shimmering and the shimmering signal is well constrained in the posterior needles. At 15% gain, the anterior needles exhibit a well constrained shimmering signal, yet a large amount of noise is observed around the posterior needles. The right panel shows a merged image taken at 0% gain for the posterior needles and 15% gain for the anterior needles.

[0055] FIG. 9 illustrates an example of an ultrasound system 900 that can implement the methods described in the present disclosure. The ultrasound system 900 includes a transducer array 902 that includes a plurality of separately driven transducer elements 904. The transducer array 902 can include any suitable ultrasound transducer array, including linear arrays, curved arrays, phased arrays, and so on. Similarly, the transducer array 902 can include a ID transducer, a 1.5D transducer, a 1.75D transducer, a 2D transducer, a 3D transducer, and so on.

[0056] When energized by a transmitter 906, a given transducer element 904 produces a burst of ultrasonic energy. The ultrasonic energy reflected back to the transducer array 902 (e.g.. an echo) from the object or subject under study is converted to an electrical signal (e.g., an echo signal) by each transducer element 904 and can be applied separately to a receiver 908 through a set of switches 910. The transmitter 906, receiver 908, and switches 910 are operated under the control of a controller 912, which may include one or more processors. As one example, the controller 912 can include a computer system.

[0057] The transmitter 906 can be programmed to transmit unfocused or focused ultrasound waves. In some configurations, the transmitter 906 can also be programmed to transmit diverged waves, spherical waves, cylindrical waves, plane waves, or combinations thereof. Furthermore, the transmitter 906 can be programmed to transmit spatially or temporally encoded pulses. [0058] The receiver 908 can be programmed to implement a suitable detection sequence for the imaging task at hand. In some embodiments, the detection sequence can include one or more of line-by-line scanning, compounding plane wave imaging, synthetic aperture imaging, and compounding diverging beam imaging. The receiver 908 may also include variable signal gain as a function of spatial position

[0059] In some configurations, the transmitter 906 and the receiver 908 can be programmed to implement a high frame rate. For instance, a frame rate associated with an acquisition pulse repetition frequency (“PRF”) of at least 100 Hz can be implemented. In some configurations, the ultrasound system 900 can sample and store at least one hundred ensembles of echo signals in the temporal direction.

[0060] The controller 912 can be programmed to control transmitter 906 and the receiver 908 according to a selected imaging sequence. In some embodiments, the controller 912 receives user inputs defining various factors used in the imaging sequence.

[0061] A scan can be performed by setting the switches 910 to their transmit position, thereby directing the transmitter 906 to be turned on momentarily to energize transducer elements 904 during a single transmission event according to the imaging sequence. The switches 910 can then be set to their receive position and the subsequent echo signals produced by the transducer elements 904 in response to one or more detected echoes are measured and applied to the receiver 908. The separate echo signals from the transducer elements 904 can be combined in the receiver 908 to produce a single echo signal.

[0062] The echo signals are communicated to a processing unit 914, which may be implemented by a hardware processor and memoiy, to process echo signals or images generated from echo signals. As an example, the processing unit 914 can process Doppler ultrasound signals to determine the locations of brachytherapy applicators being vibrated by a vibrating brachytherapy placement template using the methods described in the present disclosure. Images produced from the echo signals by the processing unit 914 can be displayed on a display system 916.

[0063] The present disclosure has described one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention.

Claims

1. A brachytherapy applicator template, comprising: a template body having a plurality of channels formed therein, each of the plurality of channels extending from a front surface of the template body to a rear surface of the template body; and a vibrational device mechanically coupled to the template body such that when the vibrational device is operated mechanical vibrations are transferred from the vibrational device into the template body.

2. The brachytherapy applicator template of claim 1, wherein the vibrational device is coupled to one of the front face or the rear face of the template body.

3. The brachytherapy applicator template of claim 1, wherein the vibrational device is coupled to an edge extending betw een the front face and the rear face of the template body.

4. The brachytherapy applicator template of claim 1, wherein the vibrational device is a stylet comprising: a stylet body, an elongate tip extending from the stylet body, and a vibrator coupled to the stylet body.

5. The brachytherapy applicator template of claim 4, wherein the elongate tip is sized to be received by one of the plurality' of channels.

6. The brachytherapy applicator template of claim 4, wherein the vibrator comprises a mechanical actuator.

7. The brachytherapy applicator template of claim 4, wherein the elongate tip is sized to be received by an inner lumen of a brachytherapy applicator arranged in one of the plurality of channels.

8. The brachytherapy applicator template of claim 1, wherein the vibrational device is integrated into the template body.

9. The brachytherapy applicator template of claim 1, comprising a plurality of collets, wherein each of the plurality of collets surrounds one of the plurality of channels.

10. The brachytherapy applicator template of claim 9, wherein the plurality of collets are adjustable to control a mechanical vibration coupling of the plurality of channels.

11. The brachytherapy applicator template of claim 1, wherein the vibrational device comprises a mechanical actuator.

12. The brachytherapy applicator template of claim 1. wherein the vibrational device comprises one of an audio amplifier or an electromagnetic actuator.

13. The brachytherapy applicator template of claim 12, wherein the vibrational device comprises an eccentric rotating mass motor.

14. The brachytherapy applicator template of claim 1, wherein the template body comprises a frame and an insert, wherein the insert is received by the frame and the plurality of channels are formed in the insert.

15. A method for visualizing brachytherapy applicator positions in a region-of- interest, comprising: acquiring Doppler ultrasound data from a region-of-interest into which a plurality of brachytherapy applicators have been positioned while the plurality of brachytherapy applicators are being simultaneously vibrated by an external vibrational device coupled to a brachytherapy placement template within which the plurality of brachytherapy applicators are arranged; processing the Doppler ultrasound data with a computer system to determine a location of each of the plurality of brachytherapy applicators within the region-of- interest based on Doppler ultrasound signatures generated by vibrations of the plurality' of brachytherapy applicators interacting with ultrasound incident on the plurality’ of brachytherapy applicators; and presenting the location of each of the plurality of brachytherapy applicators to a user via the computer system.

16. The method of claim 15, wherein processing the Doppler ultrasound data comprises isolating the Doppler ultrasound signatures from the Doppler ultrasound data.

17. The method of claim 16, wherein processing the Doppler ultrasound data comprises computing a centroid for the Doppler ultrasound signatures, wherein each centroid represents a location within one of the plurality⁷ of brachy therapy applicators.

18. The method of claim 15, wherein presenting the location of each of the plurality of brachytherapy applicators comprises overlaying the processed Doppler ultrasound data with B-mode images acquired from the region-of-interest.

19. The method of claim 15, wherein the vibrational device is operated to generate mechanical vibrations within a frequency range of 40-5000 Hz.

20. The method of claim 15, wherein processing the Doppler ultrasound data comprises generating a digitization of each brachytherapy applicator by: identifying pixels in the Doppler ultrasound data associated with each brachytherapy applicator; clustering the identified pixels using a clustering technique; and storing the clustered pixels as the digitization of each brachytherapy applicator.

21. The method of claim 20, wherein the clustering technique comprises a densitybased clustering technique.

22. The method of claim 20, wherein the pixels are identified by thresholding the Doppler ultrasound data.

23. The method of claim 15, wherein processing the Doppler ultrasound data with the computer system includes processing the Doppler ultrasound data to isolate vibrational signals from background signals, such that the location of each of the plurality of brachytherapy applicators within the region-of-interest is determined based on the isolated vibrational signals.

24. The method of claim 23, wherein the vibrational signals are isolated using a lock-in amplifier.

25. The method of claim 23, wherein the vibrational signals are isolated based on pulsing vibrations generated by the external vibrational device.

26. The method of claim 15, wherein the external vibration device comprises an implantable marker that is vibrated in response to instructions received by the computer system.