Patent Description:
For some advanced medical treatments, it might be relevant to use microrobots inserted in a target body part of a patient in order, for example, to deliver a very precise amount of drug to a very precise point. For safety purposes, this microrobot should be as autonomous as possible and most preferably controlled from outside the patient's body in a contactless manner. This micro-device thus needs a wireless localization system comprising an internal referential, in order to be tracked and precisely located while moving inside the target body part. This system should also be able, in order to enable a surgeon to be in full control of the situation, to offer a precise 3D visualization of the localization of said micro-robot inside the target body part.

There is a need for improving the tracking system and especially the localization for this kind of microrobots in correspondence to the anatomy of the target body part. The position of the microrobot with respect to anatomic features, such as functional areas, vessels or nerve, is of primary importance since it will define the path and target point of the robot, inside the target body part. A 3D imaging modality is thus necessary to envision these features and permit path planning. Moreover, the imaging modality and the microrobot positioning has to be perfectly co-registered with a precision better than <NUM>. It is thus important for the imaging system and the positioning system to be performed in the same internal referential, ideally through the same technique.

Additionally, regarding the specific case of the brain, even if the brain is encapsulated by the skull, it can move, distort, expand or dilate. The micro-robot itself might modify the surrounding anatomy while it moves through tissue. Tissue physiology such as blood flow might be impacted by the micro-robot and its action. Consequently, it would be ideal to provide a frequent refreshment of the images, along with the position of the microrobot, in order to have an up-to-date spatial information of the microrobot localized in the referential space. A commonly known wireless communication path between two elements is ultrasound communication. Such technique could be used for positioning the robot. A commonly known way to obtain reliable 3D body imagery is also ultrasound imaging. Both approaches could therefore be performed in alternance with a similar or identical apparatus.

There are several implementations for 3D ultrasound imaging, Brightness-mode, elastography or Doppler. One of the possibilities for highly precise imaging of the vascular network is ultrasound localization microscopy (ULM). The core idea of the ULM is generally known to be a very highly precise ultrasound imagery method based on the introduction of sparse punctual sources in the medium being imaged, to highlight specific parts. These sources are usually air microbubbles, more precisely millions of microbubbles, also called contrast agents. In order to obtain an ULM image of a target body structure like, for example, the brain vascular system, microbubbles are injected in the patient. Many 3D transcranial images are acquired. Microbubbles are localized and within a few minutes, a 3D ULM image is obtained. Thanks to these microbubbles, the vascular system is resolved under the diffraction barrier (the precision reaching a λ/<NUM> precision). A super-resolved image is thus constructed by localizing each bubble center separately and accumulating their positions to recover the vessel's network, several times smaller than the wavelength. The use of microbubbles (with a diameter ranging from <NUM> to <NUM>), thanks to their high deformation, allows the imaging system to outperform accuracy limitations due to the classical wave diffraction theory which is around half of the wavelength and to bypass the usual compromise to be found between wave penetration (favorized in the low wave frequency range) and image resolution (favorized in the high wave frequency range). This enables to visualize details which remain invisible on images built by conventional echography, Doppler echography in particular. In particular regarding brain vascularization, this technology enables the creation of highly precise images enabling a precise 3D mapping of a patient's brain vascular system.

Approaches proposed in ULM can also be implemented for improving the positioning of the microrobot with ultrasound. Localization of microbubbles in ULM is not limited in resolution by the wavelength, but rather by the signal-to-noise ratio (SNR) linked to the detection of the microbubbles. A similar idea can be implemented for the localization of the robot, which could yield very high SNR and, hence, allow very precise localization. This precision could be well below <NUM> micrometers for frequencies that are capable of penetrating the skull (<<NUM>).

<CIT> relates to a system and a method for real-time localization of a millimetric or submillimetric object in a viscoelastic medium, and employs ultrasound signals.

The present invention aims at solving the visualization and tracking precision issue in co-registering the ultrasound signals used either to acquire a 3D image of the target body part or to track the micro-device.

The invention is defined in claim <NUM>, with further aspects in the dependent claims.

This disclosure thus relates to a micro-device tracking and visualization system configured to monitor a target body part of a patient and localizing a micro-device inside said target body part, the tracking system comprising:.

This approach guarantees a perfect alignment between the localization of the micro-device and the ultrasound image. It thus enables a precise visualization of the micro-device inside the body target part and allows a precise and appropriate control and path planning of said micro-device.

The tracking system may comprises one or several of the following features, taken separately from each other or combined with each other:.

The disclosure also relates to a micro-device tracking and localization method implemented by means of the tracking system according to any one of the preceding features, wherein the method may enable, at the same time:.

the method further enables, at the same time:.

The method may include following steps taken separately from each other or combined with each other:.

the at least one probe may be switched from the acquisition mode to the tracking mode at least one time,.

As can be seen on <FIG>, a typical target body part <NUM> like a brain vascular system <NUM> counts an amazingly high number of blood vessels <NUM>. In order to treat some health issues, like for example tumours, some treatments might imply a micro-device <NUM>, for example a micro-robot, to specifically target a precise point in said target body part <NUM> to deliver, on this point, a given amount of drug. Such a micro-device <NUM> usually measures between <NUM> and <NUM> in diameter and up to <NUM> in length.

In order to be able to work at the micro-device <NUM> scale, and obtain a precise enough visualization of the micro-device <NUM> while it is moving inside the target body part <NUM>, it is essential to rely on a very precise remote tracking system, like the tracking system <NUM> according to the present invention. This remote paradigm imposes high constraints on the volume and energy used by the embedded tracker. In this perspective, a tracking system must answer several strong requirements: sub-millimetric position accuracy, depth from <NUM> and more, real time update (from <NUM>), non-invasiveness, minimal and at best micro size, at best energetically passive and not harming human body.

In order to achieve this visualization, the tracking system <NUM> comprises:.

In the embodiment illustrated on <FIG>, the system <NUM> includes two probes <NUM>, each secured to a temple of the patient. The securing body part <NUM> in this embodiment is thus the forehead, and more precisely, the skull, of the patient.

The at least one probe <NUM> is brought into contact with the securing body part <NUM>. In some embodiments (not represented), the probe <NUM> is manually handled around the securing body part <NUM>. It is commonly known that, for technical reasons, some gel is spread on the body part <NUM> and the at least one probe <NUM>. It is nevertheless considered that the at least one probe <NUM> is brought into contact with the securing body part <NUM>. In some alternative embodiments, the probes <NUM> are secured to the body part <NUM> for example by means of a helmet or an elastic holder, as can be seen on <FIG>. The probes <NUM> might also directly be secured to the securing body part <NUM> by means, for example, of a screwing system. In this case, the probes <NUM> should be secured surgically to the securing body part <NUM> of the patient.

Each probe <NUM> is in constant communication with the control unit <NUM> on one hand and with the at least one tracker <NUM> fixed to the micro-device <NUM> on the other hand. Each probe <NUM> comprises at least one ultrasound transducer, for example a piezo-electric transducer.

In the current application, the term "transducer" is used synonymously as "emitter" and the term "sensor" is used synonymously as "receptor".

This transducer sends ultrasounds to the tracker <NUM> on the micro-device <NUM> inside the target body part <NUM> (as can be seen on <FIG>). In some embodiments, the tracker <NUM> is a passive tracker and comprises, for example, an encapsulated gas pocket <NUM> like illustrated on <FIG>. In this passive paradigm, the probes <NUM>, (external transducers in the embodiment illustrated on <FIG>), secured on the patient's securing body part <NUM> (in this case, the skull), send ultrasounds inside the target body part <NUM> (in this case, the human brain). The passive tracker <NUM> receives the incident waves and scatters them. The waves travel until the securing body part <NUM> (in this case, the skull) back towards the probe <NUM>. The time of flight between the initial sending and the reception is used to obtain the distance travelled by the waves. Using several probes <NUM> allows to obtain the 3D position of the tracker <NUM> relatively to the probes <NUM>.

In some alternative embodiment, the tracker <NUM> can be an active tracker, actively emitting signals to the probes <NUM>. In those cases, each probe <NUM> comprises at least one ultrasound sensor and the tracker <NUM> comprises at least one ultrasound transducer, for example a piezo-electric transducer. The global functioning of the system remains the same, with the ultrasound waves being emitted by the tracker <NUM> and travelling up to the securing part <NUM>, towards the probes <NUM>.

As already mentioned, in some embodiments, the tracker <NUM> when being a passive tracker, can comprise at least one encapsulated gas pocket <NUM> attached to the micro-device <NUM>. This solution is inspired from the principle of ultrasound contrast agents. In this embodiment, each encapsulated gas pocket <NUM> forms as a very ultrasound reflective object. These encapsulated gas pocket <NUM> have a large acoustic impedance compared to tissue. This gives them the ability to scatter efficiently the incident ultrasound waves sent by the probes <NUM> and therefore improve locally the contrast. As object localization precision depends on the signal-to-noise ratio, it allows to track micro-devices <NUM> smaller than the wavelength deeply inside the target brain part <NUM>, especially the brain, in a non-invasively way. Regarding this embodiment, the tracker <NUM> comprises several encapsulated gas pockets <NUM> which are separated by more than half of the detection wavelength are combined to build a full 3D orientation and localization tracker <NUM>. At least two encapsulated gas pocket <NUM> are needed to obtain the orientation of the micro-device <NUM>.

The control unit <NUM> further comprises a memory <NUM> which stores an internal referential R. This internal referential R is defined with reference to the absolute position of each probe <NUM> with regards to the target body part <NUM>.

The memory <NUM> further stores at least one ultrasound image <NUM> of the target body part <NUM>. The ultrasound image <NUM> can be ULM images or B-mode images, or a Doppler images or an elastography image. All those ultrasound images <NUM> can be implemented with the same ultrasound probe. The internal referential R enables the co-registration of the ultrasound tracking of the tracker <NUM> with the ultrasound image <NUM> acquisition. In some embodiments, the memory also stores at least one pre-established image of the securing body part <NUM> on which each probe <NUM> is secured. In those cases, the control unit <NUM> aligns the at least two images within the internal referential R to precisely position the target body part with respect to each probe <NUM>. In any case, the control unit <NUM> is able to precisely locate any point of the target body part <NUM> inside the internal referential R.

The information sensed by each probe <NUM> is then, in real time, sent to the control unit <NUM> and the control unit <NUM> is thus able to localize, in real time, the at least one tracker <NUM> inside the target body part <NUM>, with regards to the internal referential R.

As already mentioned, the memory <NUM> is configured to store at least one ultrasound image <NUM> of the target body structure <NUM>, like for example the image illustrated on <FIG>. This ultrasound image can, for example, be an ULM image. The control unit <NUM> aligns each stored ultrasound image <NUM> with the internal referential R. This aligned ultrasound image <NUM> provides a precise 3D mapping of the target body structure <NUM> of the patient. In case of an ULM image, it provides a very precise 3D mapping of the target body structure <NUM>. This ultrasound image <NUM> is either obtained prior to the monitoring of the target body part <NUM> by the system <NUM>, or during the monitoring of the target body structure <NUM> by the system <NUM>. More particularly, in some embodiments, in order to improve the co-registration, the ultrasound image <NUM> is performed with the same probe <NUM> as the one used for tracking and positioning the tracker <NUM>.

In order to reach the desired co-registration, the at least one probe <NUM> displays two working modes:.

the at least one probe <NUM> is switched from the acquisition mode to the tracking mode at least one time. This enables the system <NUM> to simultaneously track the micro-device <NUM> and acquire ultrasound images <NUM>.

In some embodiments, the memory <NUM> of the control unit <NUM> can store several ultrasound images <NUM> of the target body part <NUM>. The memory <NUM> can thus store a succession of ultrasound image <NUM> of the target body structure <NUM>. In some embodiments, in order to reduce storage energy, each new ultrasound image <NUM> replaces the prior one inside the memory <NUM>. In order to increase the precision and accuracy of the mapping of the target body part <NUM> during its monitoring by the system <NUM>, the ultrasound image acquisition is done in real time. Depending on the ultrasound technique, the ultrasound image <NUM> acquisition can last several minutes. It it nevertheless considered to be real time acquisition. This provides a real time mapping of the target body part <NUM> and enables to take quick structure changes into consideration. This real time mapping occurs in that a new ultrasound image <NUM> acquisition is launched, by the control unit <NUM>, as soon the prior ultrasound image <NUM> acquisition is terminated, each new ultrasound image <NUM> thus replacing the prior one as soon its acquisition is terminated. One example could be that the first ultrasound image <NUM> is an ULM image, further replaced by a Doppler image, which is quicker to acquire.

The control unit <NUM> is also designed to display, on a screen <NUM>, each acquired and/or stored ultrasound image <NUM>. This is illustrated on <FIG>.

By combining the real time ultrasound information obtained from each probe <NUM> regarding the at least one tracker <NUM> and the information of the stored ultrasound image <NUM>, the control unit <NUM> is able to display, in real time, the localization of the at least one tracker <NUM> on said ultrasound image <NUM>. This enables the surgeon to know, precisely, where the micro-device <NUM> is.

The control unit <NUM> further may include a user interface <NUM> enabling, for example, an operator to indicate, to the micro-device <NUM> which precise point to reach inside the target body part <NUM>. This user interface may also allow an operator to direct said micro-device <NUM> in a contactless manner.

The improvement of the micro-device <NUM> visualization by means of an ultrasound super-resolution technique (like for example the ULM technique) enables a surgeon to precisely monitor the micro-device in a far deeper part of any target body part <NUM>, as for example the brain. Using classic ultrasound imagery enables, for a wave frequency of <NUM> to obtain an image resolution of <NUM>,<NUM>. Using super-resolution imaging technology enables, for the same frequency, a resolution of <NUM>, <NUM>. The super-resolution imaging technology further enables the visualization of little veins which are not visualizable on classic ultrasound imagery. This can help a surgeon to remotely navigate the micro-device <NUM> around those veins and thus, avoiding to damage or hurt one of those veins and cause internal bleeding.

The micro-device <NUM> can for example be actuated by either an external engine (for example an external coil, see document <CIT>) or an internal engine. It is therefore able to move inside the human body, in any sort of biological medium. The control could be achieved directly with a joystick or through a more complex controller (like a phantom haptic controller) manipulated by a user. The control could also be achieved automatically by following a pre-set pathway. The control signals could be either sent wirelessly or using wires connected to the microdevice.

Using super-resolution ultrasound technology for the tracking further enables the localization of the micro-device <NUM> to reach a precision better than half the size of the wavelength of the ultrasound used to perform the localization. More particularly, when using ULM technology, one can reach a precision of λ/<NUM> regarding localization and λ/<NUM> regarding visualization.

The ultrasound image <NUM> thus allows the surgeon to visualize the micro-device <NUM> and the precise point to be reached by said micro-device <NUM>. Thus, the surgeon can:.

The tracking system <NUM> according to the invention thus enables to implement a micro-device <NUM> tracking and localization method, wherein the method enables:.

If the same probes <NUM> are used to acquire the ultrasound image <NUM> and to track the tracker <NUM>, the method thus enables the system <NUM> to alternate between:.

without changing the probes <NUM> and with no need to withdraw the micro-device <NUM> from the target body part <NUM> of the patient. This enables an improved real time tracking of the micro-device <NUM> and an improved real time visualization of the target body part <NUM>.

Claim 1:
Micro-device (<NUM>) tracking and visualization system (<NUM>) configured to monitor a target body part (<NUM>) of a patient and localizing a micro-device (<NUM>) inside said target body part (<NUM>), the tracking system (<NUM>) comprising:
- a micro-device (<NUM>) designed to be remotely steered and controlled from outside the target body part (<NUM>),
- a control unit (<NUM>) comprising a memory (<NUM>), the memory being configured to store at least one ultrasound image (<NUM>) of the target body part (<NUM>),
- at least one probe (<NUM>) configured to be brought in contact with a securing body part (<NUM>) of the patient, the securing body part (<NUM>) surrounding at least partially the target body part (<NUM>),
- at least one tracker (<NUM>) configured to be connected to the micro-device (<NUM>),
- at least a screen (<NUM>),
wherein the at least one probe (<NUM>) and the at least one tracker (<NUM>) communicate by means of ultrasound technology, the control unit (<NUM>) being thus able to localize, in real time, the at least one tracker (<NUM>) inside the target body part (<NUM>) within an internal referential (R) defined with regards to the at least one probe (<NUM>),
wherein the control unit (<NUM>) is further designed to display, on the screen (<NUM>), the at least one stored ultrasound image (<NUM>) and to display, in real time, the localization of the micro-device (<NUM>) on said at least one ultrasound image (<NUM>).