FIELD OF THE INVENTION

The invention relates to a medical system for use in interventional radiology, allowing determining the position of the tip of a needle which is partially inserted into a patient's body during a navigated surgical intervention.

BACKGROUND OF THE INVENTION

Surgical interventions performed in interventional radiology consist in introducing a surgical instrument, such as a needle or equivalent instruments, in the body of the patient.

The interventional radiologist uses an imaging system, most likely a Computed Tomography Scan (spiral-CT or cone beam-CT (CBCT)) or a Magnetic Resonance Imaging system (MRI), to see the organs of the patient and choose the target for the tip and the trajectory to be followed by the needle to reach this target.

In order to help the interventional radiologist to reach the target, a navigation system is necessary. Such navigation systems use a tracking system based on optical, electromagnetic, radiofrequency, inertial, ultrasound or mechanical technology.

The objective of the tracking system is to give the spatial position and orientation in real time of one or more trackers.

Document WO 2010/086374 describes a method for navigating a surgical instrument such as a needle in a 3D medical image of a patient. To that end, the needle is slidingly arranged in a surgical guide to which a tracker is rigidly attached, and a reference marker is attached to the patient's body and localized by the tracking system. It is possible that said reference marker is rigidly attached to the tracking system. Since the reference marker can be detected in the 3D medical image, it is possible to determine the position and orientation of the surgical guide with respect to the 3D medical image in real-time. The needle being a linear instrument, its axis is supposed to coincide with the axis of the guide. Hence, even if the needle is not itself tracked, the system allows determining the position and orientation of the needle axis in the 3D medical image.

However, the system does not allow determining the position of the tip of the needle. As the needle is sliding into the needle guide, only the position and the orientation of the needle axis in the 3D medical image are known, and not the position of the tip of the needle. Thus, the radiologists cannot estimate how far the needle tip is from the target.

A sensor can be put at the tip of the needle, but such an arrangement requires very tiny sensors which are expensive and sometimes less accurate than normal size sensors.

BRIEF DESCRIPTION OF THE INVENTION

A goal of the invention is to determine the position of the needle tip in the 3D medical image. Instead of placing a sensor at the needle tip, it is proposed in this invention to use the needle guide and the fact that the needle is able to slide into this needle guide to compute the position of the needle tip.

To this end, an object of the invention is a medical system for use in interventional radiology, adapted to be coupled to a navigation system, comprising:a needle to be inserted into a patient's body toward a target, said needle comprising a distal tip and a proximal stop;a needle guide, the needle being able to slide within said guide along a longitudinal axis thereof, said needle guide comprising a tracker for navigating the needle guide with respect to a 3D medical image of a patient;a processor configured to detect a contact between the needle guide and the proximal stop and to determine, from navigation data of the needle guide when said needle guide is in contact with the proximal stop of the needle and from the length of said needle, a position of the distal needle tip with respect to the 3D medical image; anda user interface coupled to said processor and configured to display, on at least one image of the patient, a representation of the needle and a point on said representation of the needle to represent the needle tip in said determined position.

According to an embodiment, the system further comprises an information medium for informing the user that said displayed point is a true representation of the needle tip only when the needle guide is in contact with the needle proximal stop.

According to an embodiment, the user interface is further configured to allow the user to enter the length of the needle.

According to an embodiment, the processor is configured to memorize an orientation and position of the needle when the guide is close to the patient's skin, and the user interface is configured to display, on the image of the patient's body, the point representing the needle tip on a representation of the needle in said memorized orientation and position.

In such case, the time at which the orientation and the position of the needle is memorized can be:

(i) a time given by the user by interacting with the user interface, or

(ii) a time computed by the processor by detecting automatically that the needle guide is sliding along the direction of the needle towards the proximal stop of the needle, or

(iii) a time computed by the processor using a sensor put in the proximal portion of the needle in order to automatically detect a time at which the needle guide is contacting the proximal stop of the needle, and then, to retrieve automatically the time at which the orientation and the position of the needle has to be memorized.

According to an embodiment, the processor is configured to compute a distance from the needle guide position in contact with the proximal stop to the memorized orientation and position of the needle and to compare said distance with a given threshold.

If said distance is greater than said threshold, the processor may be configured to emit a flag, a sound or a message to inform a user that the displayed position of the needle tip is not accurate. Alternatively, the processor may be configured to make the displayed needle tip disappear from the image.

According to an embodiment, the processor is configured to compute a curvilinear distance from the position of the needle guide close to the patient's skin to the position of the needle guide in contact with the needle stop using a circular arc model and to detect at least one inflection point on the curve connecting the skin position and the stop position.

If at least one inflection point is detected, the processor may be configured to emit a flag, a sound or a message to inform a user that the displayed position of the needle tip is not accurate. Alternatively, the processor may be configured to make the displayed needle tip disappear from the image.

According to an embodiment, the processor is configured to compute the total length of the needle with an on-line calibration using one of the following methods:using a ruler;using a pointer to determine the position of the tip and the stop of the needle and to compute the length of the needle; ordetermining the respective virtual positions of the needle guide when a guide tip is at the level of the tip of the needle and when a rear face of the guide is contacting the proximal stop of the needle.

Advantageously, the user interface may be coupled to a database containing length data for a plurality of needles and is configured to allow a user selecting a needle among said plurality of needles.

According to an embodiment, the processor is configured to detect a contact between the needle guide and the proximal stop by recognizing a motion pattern of the needle guide.

According to an embodiment, the system further comprises a sensor coupled to the processor and arranged in a proximal region of the needle for sensing a contact between the needle guide and the proximal stop.

The above-described system allows implementing the following procedure for determining the position of the needle tip in the 3D medical image during insertion of the needle into the patient's body.

A needle comprising a distal tip and a proximal stop is provided, the length of the needle between the distal tip and the proximal stop being known.

A needle guide comprising a tracker allowing navigation of the tracker in the 3D medical image is provided. The needle is able to slide within the needle guide.

Once the needle has been at least partially inserted into the patient's body, a user can determine the position of the distal tip in the following way:determining a direction of insertion of the needle by localizing the needle guide;sliding the needle guide along the needle in the proximal direction until contacting the needle stop;based on the known needle length, determining the position of the distal tip on the direction of insertion,displaying, on at least one image of the patient, a representation of the needle and a point on said representation of the needle to represent the needle tip in said determined position.

