WO2009019707A1

WO2009019707A1 - Tissue identification method and device

Info

Publication number: WO2009019707A1
Application number: PCT/IL2008/001098
Authority: WO
Inventors: Gad Kenan; Haim Segev; Jacob Reshef
Original assignee: Impediguide Ltd.
Priority date: 2007-08-08
Filing date: 2008-08-10
Publication date: 2009-02-12
Also published as: EP2194895A1

Abstract

A medical device is presented for use in affecting tissue in a subject's body. The device comprised a needle unit (108) and a tissue affecting system. The needle unit comprises a needle (109) having a lumen and configured for penetrating body tissue, and a medical tool configured for passing by its forward portion through said lumen of the needle. The tissue affecting system comprises a probing portion integral with the needle unit and a control utility for operating the probing portion. The tissue affecting system is adapted for carrying out at least one of tissue identification and stimulation.

Description

TISSUE IDENTIFICATION METHOD AND DEVICE

FIELD OF THE INVENTION

The present invention is generally in the field of medical devices, and relates to a tissue identification method and device, particularly useful for the navigation of a probe or medical tool within a body cavity.

BACKGROUND OF THE INVENTION

It is generally necessary to properly guide a medical tool (such as catheter or needle) to a region of interest in a subject for diagnosis and/or treatment purposes. It is also often required to monitor/track the medical tool position to ensure that it remains at the desired location.

Catheters of the type which are insertable into a vessel of a subject for carrying electrical signals to and from the subject are used in various applications. For example, cardiac catheters are inserted within a blood vessel into a subject's heart to detect cardiac electrical signals, to apply electrical stimulation for diagnostic testing and to apply treatment signals, such as tissue ablation signals which are used to eliminate the source of an arrhythmia. US patent No. 6,190,370 discloses a technique for determining proper placement of epidural catheter. Other applications for ablation catheters include the treatment of tumors, such as breast or liver tumors, and the identification of tumor biopsy sampling sites. Using a multi-sensor probe including a tissue penetrating needle is disclosed for example in US 2003/045798. GENERAL DESCRIPTION

It is beneficial to medical practitioners to have a reliably reproducible monitoring system having feedback notification that indicates to an operator when each tissue layer is penetrated and when a body cavity is penetrated by an insertion end of a needle or probe. Further, it is beneficial to have a method for monitoring the stages of penetration of an insertion end of a needle or probe through each one of a plurality of outer layers covering a body cavity of a subject. This is associated with the following.

When a medication delivery device is used, it may be very difficult for the user of the device to determine the exact position of the tip of the injection needle in the body - i.e. whether the injection needle by accident has entered a vein or entered muscular tissue.

For certain applications (e.g. epidural procedures) catheter and needle positioning and re-positioning has conventionally been achieved with the use of fluoroscopic techniques. However, since fluoroscopy typically provides only two-dimensional information, its accuracy in catheter positioning is limited. Furthermore, due to the potential risks associated with exposure to electromagnetic radiation, it is advantageous to limit the use of fluoroscopy.

Insertion techniques for injections of medications typically include insertion of needle and/or a cannula/catheter through the skin and into blood vessels or other body cavities for injection of fluids. Such insertion techniques require the practitioner to be able to judge by the feel of the insertion of the needle as to whether the needle end finds the target vein, layer of tissue, or body cavity. For example, during investigations of the abdominal cavity, a practitioner must determine the progress of insertion of the penetrating needle end through the tissue layers of the umbilical region of the abdominal cavity.

The techniques utilized by practitioners include detection of sound as the needle end penetrates, and/or the utilization of touch and feel of the physical resistance, or lack of resistance, against the needle end during penetration. Furthermore, anesthesiologists and pain management specialists routinely deliver drugs into the epidural space. Such epidural medications are administered to provide analgesia during labor and during surgical procedures, as well as for post-operative pain relief. Epidural analgesia is also used for non- surgical pain relief, while epidural steroid injections are employed to treat back pain that is refractory to oral medications.

The existing techniques for identifying the epidural space involve the introduction of a large bore needle through the intervertebral space. The operator palpates the intervertebral space and then very slowly advances the needle. There is usually an increase in resistance as the needle passes through the interspinous ligament and then the ligamentum flavum alerting the operator to advance the needle very slowly. Once the needle tip has passed the ligamentous resistance, the epidural space is identified by the sudden loss of resistance to the injection of air or saline. If the needle is advanced too far, the dura mater is punctured, the subarachnoid space is entered and cerebrospinal fluid flows through the needle ("wet tap"). This occurrence might be problematic since cerebrospinal fluid (CSF) leak through the hole made by the large bore needle can result in severe headache. In the majority of cases, the procedure is performed using the loss of resistance technique which is essentially a blind insertion where the operator does not know exactly where the tip of the needle lies. The loss of resistance method of epidural catheter insertion however is performed blindly with only tactile feedback as a guide. This procedure is associated with several problems: there may be an inability to reach and/or identify the epidural space; an inability to thread the catheter into the epidural space; an unintentional entry into or puncture of a blood vessel; or an inadvertent puncture of the dura rriater. Some subjects may require multiple attempts, often at multiple intervertebral interspaces, to find the epidural space. These problems can result in failure to deliver medications to the intended location, intravascular injection of local anesthetics or CSF leaks and headaches. Bio-impedance is a non-destructive technique which makes use of low level electrical signals such as those which are already present in bio-materials. Accurate measurement of the impedance of bio-materials over a broad frequency range yields valuable information about the electrical properties of the material. Analysis of these measurements can provide valuable diagnostic information which may be used, for example, for checking organ integrity during transplants or for tumor investigations.

Research studies are frequently performed directly on live subjects (in vivo testing), for example the study of skin impedance to determine tissue healing rates or to examine the effects of creams and lotions. Bio-impedance techniques are also used in dental research, for the detection of decayed or cracked enamel, for assessing the extent of ischemia in organ transplants; Impedance techniques are also used to monitor the extent of tissue damage, organ integrity and the possibility of successfully reviving the organ. The impedance of skin, subcutaneous, muscle, fat, blood, etc. is different, therefore detecting the impedance difference between body compartments enables to identify the navigation of a needle/probe within a body cavity. The navigation of a probe refers to a real time localization of a probe in space and time. The impedance measurement may be performed between at least a pair of electrodes, one for applying an electrical signal (current/voltage) to the tissue to be identified and the other for measuring the electrical signal (voltage/current) from the tissue. The recording electrode may be the exposed electrically conductive tip of a needle, while the needle shaft is electrically isolated. Knowing the applied current/voltage and the measured voltage/current, the impedance is calculated, resulting in two components: Ohmic (Ro) and capacitive (Xc).

According to the technique of the present invention, bio-impedance measurements are carried out while "sweeping" a frequency of the applied electrical signal. During these measurements, the probe (electrodes arrangement carried by needle and/or catheter) may be static or may propagate through the body. The so obtained bio-impedance components (resistance, capacitance, and preferably also phase) are frequency-dependent thus characterizing the tissue or tissue(s) interacting with the probe. Real-time analysis of the measured parameters enables guidance/navigation of an invasive device (e.g. needle/catheter).

In some embodiments, the present invention enables the identification of the epidural space, and/or the subarachnoid space.

A medical device of the present invention may be used for phlebotomy generating a signal (e.g. audio-visual) upon entering a blood vessel. Consecutive impedance measurements may be continuously compared to a database including a model characterizing the tissue structure. Based on the differences in capacitance and/or resistance, and/or preferably also phase between the different body compartments, a blood vessel is detected, generating a signal indicative thereof. The device of the present invention may also be used for intravenous monitoring by getting a continuous signal (e.g. flashing light) while the needle is in the blood vessel, and alarming when the needle is out of the blood vessel.

The device of the present invention may measure the actual impedance (the resistive and capacitive and the phase components) at different frequencies along a needle track. The impedance values may be digitized and stored for analysis. To detect a blood vessel, the different tissue transitions (subcutaneous-muscle, or muscle-vein etc.) and inters human variability are taken into account.

In some embodiments, the present invention enables the prediction of upcoming low/high impedance zone.

Additionally or alternatively to bio-impedance measurements, the device of the present invention maybe configured for carrying out electrical stimulation of a tissue portion in the body. Generally speaking the invention provides a device for affecting a tissue with at least one electrical signal aimed at inducing electrical response for bio-impedance measurements and tissue identification and/or for electrical stimulation of the tissue.

Thus, according to one aspect of the invention, there is provided a medical device comprising: (a) a needle unit comprising a needle having a lumen and configured for penetrating body tissue, and a medical tool configured for passing by its forward portion through said lumen of the needle; and (b) a tissue affecting system comprising a probing portion integral with said needle unit and a control utility for operating said probing portion.

The tissue affecting system is adapted for identifying the tissue and/or affecting one or more of the tissue conditions. Preferably, the tissue affecting system is -configured as an electrical system adapted for carrying out bio- impedance measurements and/or electrical stimulation.

The device may comprise a housing. The needle unit may be removably mountable to the housing. The housing may be configured as a hand held housing. Moreover, the housing may be configured as an independent unit connectable to a control unit, or as a stand-alone device.

In some embodiments, the needle unit has a connection port linked to the lumen of the needle and serving for inserting the forward portion of the medical tool thereinto. The probing portion of the tissue characterization system may be at least partially incorporated in the needle unit or in the medical tool. The probing portion may comprise at least one element in the forward portion of the medical tool and at least one element in the needle. Alternatively or additionally, the probing portion may be incorporated in the medical tool. In some embodiments, the medical tool comprises a catheter or a stylet.

The electrical system is configured and operable for bio-impedance measurement and/or electrical stimulation. The medical tool may comprise a catheter having at least one pair of electrodes (e.g. bio-impedance electrodes' arrangement) embedded within the catheter walls. The electrodes may extend along the catheter. The needle may be configured and operable to record a bio- impedance signal.

In some embodiments, the control utility of the electrical system is configured and operable as a tissue characterization/identification system. The system operates to localize a distal end of the needle unit positioned within a body portion of a subject and/or to identify a tissue type interacting with the distal end of the needle unit within a body portion of a subject and/or to localize transition between different tissues interacting with a distal end of the needle unit while propagating through the body portion of a subject. In some embodiments, the stylet is configured as an electrode or carries an electrode which is an element of the probing portion of the electrical system (i.e. tissue characterizing and/or stimulating system).

There is also provided a system for controlling local anesthesia. The system comprises (a) a needle unit comprising a needle having a lumen and configured for penetrating body tissue, and a catheter configured for passing by its forward portion through the lumen of the needle; and (b) a tissue characterization system comprising a probing portion integral with the needle unit and a control utility for operating the probing portion.

In another aspect of the present invention, there is provided a blood vessel catheterization system. The system comprises (a) a needle unit comprising: a needle having a lumen and configured for penetrating the blood vessel, and a catheter configured for passing by its forward portion through the lumen of the needle; and (b) a tissue characterization system comprising a probing portion integral with the needle unit and a control utility for operating the probing portion and generating a signal indicative of the penetration of the needle into the blood vessel.

In yet another aspect of the present invention, there is provided a needle unit having: a body; a needle with a lumen projecting from the body; a connection port for introducing a forward portion of a medical tool and allowing its passage through the lumen; an electrical coupler for coupling the needle or an electrode embedded in or carried by the needle to an electrical system.

Preferably, the needle unit comprises a control mechanism for controlling a length of the forward portion of the medical tool interacting with the body. The control mechanism may comprise a window made in said body to enable visual observation of the medical tool displacement with respect to the body. Preferably, the window and/or the medical tool viewed through the window has a scale.

In a further aspect of the present invention, there is provided a method for monitoring the position of a needle within the body. The method comprises performing continuous impedance measurements at different operating frequencies to obtain an impedance profile; and analyzing impedance profile variations between different frequencies to characterize the tissue and thereby determine position. The method may comprise propagating the needle within a body portion and concurrently determining an impedance profile. A change in the impedance profile while propagating the needle through a body portion is indicative of passage between one tissue to another. The method may comprise identifying the epidural space and/or detecting a blood vessel. In some embodiments, the method comprises predicting upcoming of a certain impedance zone.

BRIEF DESCRIPTION OF THE FIGURES

In order to understand the invention and to see how it may be implemented in practice, preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawing, in which

Fig. 1 schematically illustrates an example of the medical device of the present invention configured and operable for tissue identification; Fig. 2 schematically illustrates an example of a needle unit suitable for use in the device of Fig. 1, and configured and operable to connect a needle and a catheter and enable operational coupling between them;

Fig. 3 schematically illustrates electrical connection of the needle unit of Fig. 2 to a housing of the device;

Figs. 4A-4E schematically illustrate examples - of different configurations of the probing portion of a tissue characterization system used in the device of the present invention;

Fig. 5 schematically illustrates another example of the device of the present invention configured and operable for affecting a tissue within a body;

Fig. 6 schematically illustrates an enlarged view of an electrical contact unit of the device of Fig. 5;

Figs. 7A-7B schematically illustrate two examples of the configuration and operation of the device of the present invention; Fig. 7C schematically illustrates the device of the present invention configured as a hand held unit;

Figs. 8 to 12 graphically illustrate the principles of a method of the present invention for guiding/navigating and/or monitoring the position of a medical tool within a body: Fig. 8 shows three graphs representing measured tissue impedance as a function of frequency, for three different tissues respectively;

Fig. 9 illustrates an electric current as a function of the depth within a body including different tissue layers, for measured (Al) and modeled (A2) data; Fig. 10 illustrates the transition between different tissue layers having different impedance characteristics, illustrated by a change in the impedance measurement as a function of depth within a body; Fig. 11 illustrates the resistance (in kilo-Ohm) as a function of the frequency (in kHz) of different tissues along the path of a needle measured by the device of the present invention; and

Fig. 12 illustrates the capacity (in pico-Farad) as a function of the frequency (in kHz) of different tissues along the path of a needle as measured by the device of the present invention;

Fig. 13A exemplifies a configuration of the probing portion of the tissue characterization system;

Figs. 13B-13C illustrate resistance (in Ohm) and capacity (in pico- Farad) measurements as a function of time (in second) for different frequencies along the path of an epidural needle, as measured by the probe of Fig. 13 A;

Figs. 14A to 14C illustrate three more examples of a configuration of the probing portion of the tissue characterization system;

Figs. 14D-14E illustrate resistance (in Ohm) and capacity (in pico- Farad) measurements as a function of the time (in second) for different frequencies along the path of an epidural needle, as measured by the probe configuration of Fig. 14A; and

Figs. 15A-15B illustrate the experimental data for the ratio between the impedance in the epidural space and average measurement in the preceding tissue layers, as a function of the frequency (in kHz), measured using the method of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference is made to Fig. 1, representing an example of a medical device 100 of the present invention for use in affecting a tissue by electrical signal(s). The device may be configured and operable for tissue identification/characterization, suitable for guiding/monitoring the position of a medical tool (e.g. a needle tip) within a body. The device 100 comprises a housing 102, which in the present example is configured as a hand held unit, a needle unit 108, and an electrical system (not shown here) which in the present example is configured and operable as a tissue characterization system. The electrical system comprises a probing portion integral with the needle unit 108 and a control utility for operating the probing portion (providing a probing energy).

In the present example, the housing 102 has an elongated shape defining front and back ends 104 and 106. Needle unit 108 is fitted at the front end 104. Needle unit 108 comprises a needle 109 for penetrating the body tissue. The device 100 is configured for carrying a catheter (not shown) for delivery of medication; a lumen of the needle 109 serves for accommodating a forward (distal) portion of the catheter.

It should be noted that the control utility incorporated in the device 100 may also be configured for at least partially carrying out the measured signal analysis, and/or may be connectable (via wires or wireless signal transmission) to an external control unit (not shown). Preferably, considering the use of handheld configuration of the device 100, it is configured as an autonomous measurement/monitoring device. The control utility may comprise a display 110. The anatomy of the targeted tissue may be displayed on the display 110, and the needle tip may be tracked in real-time.

In the present example, the probing portion is configured and operable as a bio-impedance measurement unit. The control utility operates the probing portion to carry out bio-impedance measurements; bio-impedance measured data is indicative of a tissue type with which the probe interacts while inside the body, for example indicative of a plurality of different tissues along the path of the probe and the transitions between the tissues. This can be achieved by providing, in real-time, the resistance and the capacitance of the tissue and of the transitions between the tissues, as a function of the frequency and depth with the tissue structure. The real-time analysis of the measured parameters enables guidance/navigation of a medical tool (e.g. needle/catheter). - The device of the present invention may be used for local and/or regional anesthesia. The needle is inserted through the body tissue towards a region to be anesthetized. A small voltage or current is injected to the body tissue via the probing portion integral with the needle unit; and the probing portion measures the current/voltage from the body tissue. The control utility may calculate the impedance of the tissue at different frequencies and analyze data indicative thereof to identify the body tissue interacting with the probing portion, when the probing portion is static with respect to the tissue or while the probing portion propagates through the tissue along a certain needle track. Such monitoring/measurement procedure can be performed in real-time on each tissue and each tissue transition during the needle propagation through the body portion until identifying the proper location of the needle for achieving a desired effect (e.g. treatment, drug delivery, or localization of peripheral nerves, or in the specific but not limiting example - anesthesia or analgesia) of the region of interest. The so-obtained measured data actually presents bio- impedance profiles (data indicative of the bio-impedance as a function of coordinate in the body) for different operational frequencies. This data can be continuously compared with a theoretical model indicative of a determined impedance profile based on impedance characteristic of the tissue structure calculated for a predetermined needle track. When the tissue characterization system identifies the target tissue or cavity (region of interest), the catheter delivers the anesthetic or analgesics medication, which is injected through the needle, without need to move out the needle. The catheter typically remains in its operative position; when a further delivery of anesthesia is required, the assembly (tissue characterization system) is actuated for monitoring the type of the tissue interacting with the catheter tip.

The assembly of the present invention may also be used to monitor the stages of the penetration of the needle within a body cavity for, for example, intravenous (IV) monitoring or detection of a blood vessel. The needle is inserted through the body tissue (e.g. patient's hand) towards a blood vessel. A small voltage or current is injected to the body tissue via a probing portion integral with the needle unit. The probing portion measures the current/voltage from the body tissue. The control utility calculates the impedance of the tissue" at different frequencies or along a predetermined needle track and analyses the data indicative thereof to identify the body tissue. The first measurement is then performed on the skin followed by the fat/subcutaneous layer, muscle, etc. and concluding with a blood vessel. The measured impedance is continuously compared with an impedance data, and upon detecting a blood vessel, a signal indicative of vessel penetration is outputted, for example via a speaker and/or a light unit. For IV monitoring, the control utility may be configured and operable to generate a signal indicative of the exit of the needle/catheter from a vein during perfusion, or indicative of the catheter being clogged or a blood vessel clogging at the catheter tip region thus impeding the drug delivery through the catheter to the blood vessel.

It should be understood that the electrical system, incorporated within a needle unit, according to the invention may alternatively or additionally to the bio- impedance measurements, carry out electrical stimulation of tissue(s). For example, the needle unit penetrates through the body portion and upon arriving to a targeted location, is operated to apply electrical stimulation. The identification of the needle unit (its distal end) arrival to the targeted location can be carried by the same electrical system (probing portion and control utility) carried by the needle unit, by applying bio-impedance measurements, or may be carried by another system and/or using any other type of known suitable monitoring (e.g. imaging technique).

In the example of Fig. 1, needle unit 108 is a separate unit removably mountable onto the front end of hand held housing 102. Reference is made to Figs. 2 and 3 schematically illustrating such needle unit 108.

The needle unit 108 comprises a body or housing 108A comprising a first connection port 108B for mounting needle 109 and a second connection port 108C for installing a catheter 112. In this configuration, where the probing portion is adapted for electrical measurements, the needle unit 108 comprises an electrical system (e.g. tissue characterization and/or stimulation system) formed by an arrangement of electrodes (generally at least one pair of electrodes) and electrical contacts properly mounted on the housing 108A. The arrangement of electrodes may be associated with the needle and/or catheter, as will be described further below. In the present example, needle 109 carriers at least one electrode (for example presents a recording electrode). As shown in Fig. 2, an electrical connector 114 is provided for connecting the needle 109 to an electrical contact (not shown here) in the needle unit 108. As shown in Fig. 3, the electrical circuit of the needle unit is electrically coupled, by a connector arrangement 116, to a corresponding electrical circuit at the control utility incorporated in the hand-held housing 102. As seen in the figures, when the needle 109 is mounted in its associated port 108B, the needle-electrode is connected to the electrical circuit via connector 114, and a forward portion of catheter 112 can be connected, via its associated port 108C so as to pass through the needle lumen. The needle unit 108 may comprise a mechanism adapted to controllably thread the catheter 112 within the needle and to push the catheter through the body cavity.

As indicated above, in some embodiments, the electrical system is configured and operable as a tissue characterization system carrying out bio- impedance measurement and/or as an electrical stimulation system. The electrode arrangement may comprises a pair of electrodes, one electrode for providing a probing energy (e.g. applying a potential/current) to a target tissue to be identified, and the other electrode for recording current/voltage from the target tissue. Different tissues have highly different resistance ranges, for example, the impedance characteristic values for a certain frequency range are in the range of about 1.5-3 kilo-ohm for the interspinal space (skin, subcutaneous tissue, interspinous ligaments, ligamentum flavum) and of about 9-15 kilo-ohm for the epidural space. Knowing the applied potential/current for a given frequency range, and the measured current/voltage, the impedance _B1can be calculated, resulting in two components: Ohmic (Ro) and capacitive (Xc), characterizing the tissue. With these two known and measured parameters, the impedance can be calculated continuously and analyzed, by the control utility (e.g. digital signal processor (DSP)). In one configuration of the electrodes arrangement, the first electrode

(e.g. recording electrode) may be carried by the needle, which is partially insulated and has an exposed electrically conductive tip (e.g. operable to record impedance measurements). The second electrode (e.g. reference electrode) may be an external electrode (conducting strip, defibrillator electrode, conductive belt, electrode embedded in a clip) in contact with the skin of a subject in the vicinity (e.g. 5-10 cm) of the region of interest. The tissue impedance can be measured between the exposed tip of the needle and the reference electrode.

In another configuration, the needle is configured and operable as a guard-ring holding, namely comprises an insulated tube embedded within the electrically conductive needle, which is grounded. Here, at least a portion of the tube may be exposed to interaction with tissue and be operable to apply/record electrical signal. For example, the tissue impedance can be measured between the exposed tip of the tube and a reference electrode in contact with the skin of the subject. Another example for electrodes arrangement carried by such a guard- ring holding needle is the use of at least two electrodes carried by the tube in a spaced-apart and electrically isolated from each other relationship. The tissue impedance can be measured between the two electrodes of the tube.

Yet another suitable example for electrodes' arrangement for tissue characterization and/or stimulation procedure consists of incorporating electrodes in a catheter installed within the needle. The tissue impedance can for example be measured between the catheter and a reference electrode in contact with the skin of the subject. In yet another configuration, the needle unit carries at least two electrodes electrically isolated from each other. The tissue impedance can be measured between these two electrodes.

The electrodes (at least one pair) may be carried by the needle or by the 5 catheter. In this connection, reference is made to Fig. 4A illustrating a needle 109 carrying two electrodes El and E2 isolated from each other. The electrodes extend along the needle in a spaced-apart parallel relationship inside the needle's lumen. As exemplified in the figure, a forward portion of catheter 112 is linked to (pass through) the lumen of the needle. As also shown in the figure,

10 alternatively to placing the electrodes in the needle, or additionally thereto, one or more electrodes - two such electrodes E'l and E'2 in the present example - are located in the catheter 112 wall. In this case, the catheter may for example be patterned along its wall to define electrically conductive regions (e.g. conductive polymer, conductive fluid, etc.) serving as the electrodes spaced by

15 electrically insulating material of the catheter.

In yet further suitable configuration, the probing portion (e.g. one pair of electrodes) is incorporated in a catheter (e.g. within the wall of the catheter). In this connection, reference is made to Fig. 4B illustrating a needle 109 accommodating a catheter 112 having two electrodes El and E2 within the

20 wall of the catheter. The catheter is isolated from the needle. As indicated above, embedding electrodes in the catheter wall can be implemented by patterning the catheter material with regions of conductive polymer. With this configuration, where the catheter carries at least a part of the probing portion, the catheter is inserted within the needle unit prior to the

25 measurement/monitoring procedure.

As exemplified in Fig. 4C, the electrodes denoted as El, E2 and E3

(those inside the needle and/or catheter) extend along the needle/catheter axis in a spaced-apart relationship and have different lengths. This arrangement is similar to a phase-array of sensors, and allows for collecting spatial data (e.g.

-i-30 3D localization of the needle unit, direction of movement, speed of movement) by a phase difference in the measured signals, and by difference in the resistance and capacitance measurement.

In yet another configuration, the electrodes' arrangement comprises the exposed electrically conductive tip of an electrically insulated needle and an electrode embedded within the catheter. This is illustrated in Fig. 4D: a needle 109 has an exposed electrically conductive tip 402 (presenting electrode El) and an electrode E2 (e.g. stainless steel/silver) is embedded within a catheter 112.

Fig. 4E exemplifies yet another option for the needle unit configuration, where needle 109 has an electrode El formed by an electrically conductive tip

402 of the needle. An insulated tube 404 is embedded within the needle 109 and carries an electrode E2. The latter may be constituted by a stylet made of an electrically conductive material. Electrodes El and E2 present first and second measurement points in the impedance measurements and/or first and second stimulation points. The tissue impedance can thus be measured between the electrode of the needle (El) and the electrode of the tube (E2). As shown in the figure, needle 109 has an exposed tip 402 and an electrode E2 is embedded in an insulated tube 404 such as a stylet.

The electrodes' arrangement may comprise three electrodes, two of them measuring the impedance in the tissue internally (exposed tip of the needle, exposed tip of an insulated tube embedded within the needle, two electrodes located on the insulated tube, catheter embedded within the needle and having at least one electrode), and the third one being used as a reference electrode located in contact with the skin of a subject. This configuration may provide a compensation of local and/or distant measurement errors.

Reference is made to Fig. 5 illustrating another example of the medical device 200 of the present invention for electrically affecting tissue(s) in a body, e.g. aimed at controlling the position of a medical tool (e.g. a needle tip, and/or catheter) within a body. The device 200 comprises a housing 210, which in the present example is configured as a hand held unit, and which carriers a needle unit 108 having a needle 109 and a medical tool (catheter) 212. The device 200 also has an inlet port 206 for material injection (e.g. medication). The hand held unit 210 comprises a mechanism 204 adapted to controllably thread the forward portion of the catheter 212 within the needle 208 and to push said forward portion of the catheter through the body cavity (e.g. by rotating). Such controllable threading is implemented by forming the hand held unit 210 with a window 202 enabling visual observation of the catheter movement through the device. The device may be configured for controlling the length of the catheter's portion penetrating in the body. To this end, as shown in the figure, the window 202 and/or the catheter may be formed with an appropriate scale. The hand held unit 210 also comprises an electrical contact unit 213 for operating an electrode arrangement carried by the medical tool (catheter in the present example).

Reference is made to Fig. 6 illustrating a specific but not limiting example of the electrical contact unit 213 for operating an electrode arrangement carried by the medical tool. In the present example a catheter 212 comprises two electrodes El and E2 (e.g. embedded in the catheter walls) with the proximal ends of the electrodes projecting out of the catheter. Electrical contacts 214 are located on a bracket 215, which has spring-legs 216, by which it can be installed into an opening in the body 210, thus being locked therein and closing the electrical circuit (contacting with the' electrodes).

Reference is made to Figs. 7A-7B showing that the hand held unit 200 of the present invention may be configured as a sterile disposed kit in which the catheter is prior inserted within the needle unit. An electric card 220 carrying the control utility of the electrical system (tissue characterization and/or stimulation system) is inserted in the hand held unit and is connectable to the electrode arrangement. The electric card 220 is configured as an autonomous measurement/monitoring device (chip). In Fig.7A, the electrode arrangement is carried by the catheter 212. In Fig.7B, the electrode arrangement is carried by the catheter 212 and t -3h" e needle unit 208. The device 200 may comprise an indication device (e.g. display) indicating the position of the medical tool within the body. For example, the indicator may include an optical unit producing three lights, red (R), yellow (Y) and green (G), wherein one of them (e.g. red light) indicates the penetration into a muscle, the yellow one - the penetration into the flavum and the green light - the penetration into the epidural space. Fig. 7C illustrates a bottom view of the hand held unit 200 comprising a port 222 for the insertion of the electronic card 220.

Turning back to Fig. 5, it should be noted that the device 200 may be configured and operable for using the electrical system for both the tissue identification and stimulation or for tissue stimulation only. In the latter case, if the tissue identification is required, this can be carried out using the principles of the lost of resistance measurements via the port 206.

According to the teachings of the present invention, the impedance measurements are performed at different operating frequencies to obtain an impedance profile, i.e. measured electrical parameter indicative of the impedance as a function of time and/or coordinate (depth). The use of different operating frequencies enables the differentiation between tissues due to different frequency dispersion of each tissue. Each tissue providing a different dispersion pattern can be characterized by its spectral impedance.

Reference is made to Fig. 8 illustrating simulation data for three different tissue impedance profiles as a function of operating frequency, for three different tissues. This is a general representation of the frequency dependence of the impedance measured from different tissues. The complex impedance parts can be measured (capacitance/resistance), adding the phase information.

To characterize all the tissues in the immediate vicinity of the needle

(i.e. a region of interaction between the probing portion and the tissue), a theoretical model is calculated taking into account the general properties of each tissue such as the tissue thickness, geometry, density and the electric constants characteristic of the tissue, and the tissue dielectric properties such as the resistivity and the capacitance of the tissue. The general tissue properties might be found in the literature, while the tissue dielectric properties are measured as a function of an electromagnetic frequency. Data indicative of the expected values measured by the tissue characterization system is therefore calculated. The theoretical model of the tissue structure enables to predict the current behavior on the probing portion.

The measurements are continuously compared to the modeled data to determine the needle position which is represented continuously. In this connection, reference is made to Fig. 9, illustrating the transition between two types of tissue, Layer 1 /Layer 2 and Layer 2/Layer 3, having different impedance characteristics illustrated by a change in the impedance measurement as a function of depth within a body portion. Curve A₁ represents the measured current as a function of .depth through three different layers (different tissue types). Curve A₂ represents the theoretical calculated current as a function of depth through the respectively three different layers. Arrows between the curves show the correspondence between the theoretical and the measured data.

Fig. 10 represents impedance measurements for a muscle-fat bi-layer along a needle track. The muscle-fat transition point is marked as the "zero" point in the graph. The "zero" point is used as a reference when the needle is in the muscle. The needle is inserted to the muscle through the fat while measuring the impedance every 1 mm (Entrance 1). The needle is then retracted while measuring the impedance every 1 mm (Exit 1). The process is repeated twice (Entrance 2, Exit 2). The impedance measurements reveal a significant difference between the muscle and fat impedance. The muscle impedance is in the range of about 70-130 ohm, while the fat impedance is in the range of about 350-430ohm. The transition between the muscle and the fat tissue is noticed over a space of about 2-3mm. This transition point is abrupt and significant. The change is observed after the penetration to the fat tissue in a depth of about lmm. After 2 mm in the fat, the impedance values reach the average value of the fat tissue. It should be noted that the change in the clinical range for epidural space detection is about 3mm, which is the narrowest part of the epidural space (generally in the cervical zone of adults) or the depth of the ES in children).

Reference is made to Fig. 11, showing three-dimensional representation of the resistance (R in KΩ) as a function of the alternating current frequency and time (in KHz and second). This is an ex-vivo experimental data measured by the device of the present invention in a region in the vicinity of the epidural space. The graph shows a sharp increase in the resistance when penetrating into the epidural space (indicated by the circle). Similarly, as illustrated in Fig. 12, when the tip of a needle penetrates through the ligament flavum into the epidural space, a significant decrease in the capacity can be seen.

There are significant changes in the measured bio-impedance (resistance and capacity) along the insertion path of the epidural needle. Therefore, transition between various tissues can be identified based on the measured bio- impedance and the differences in the bio-impedance relative to the surrounding tissue layers. Particularly, the results indicate that transition from the ligament flavum into the epidural space can be identified based on a sharp change in the measured resistance and capacitance. The resistance and capacitance decreases sharply as the frequency of the alternating current increases.

Reference is made to Figs. 13A-13C illustrating experimental data obtained in an animal study representing resistance (Fig. 13B) and capacitance (Fig. 13C) measurements for different frequencies. Fig. 13A shows schematically the probing portion configuration utilized in the device used in these experiments, namely the probing portion that has an insulated epidural needle with electrically conductive exposed tip and an external reference electrode (patch). The resistance (in Ohm) and the capacity (in pico-Farad) were measured as a function of time (in second) along the path of the epidural needle advancing towards the epidural space (the higher point) ^and then withdrawing backwards. Thus, the technique of the invention enables mapping of the path of the needle and correlating between the multi-frequency bioimpedance measurement and the anatomy. Using a database collecting such data from multiple subjects enables the needle/catheter guidance. Reference is made to Figs. 14A-14E showing another experimental data obtained in the animal study. Here, Figs. 14A-14C show three different configurations of the probing portion: Fig. 14A shows a needle or catheter with two spaced-apart electrodes El and E2 extending the needle/catheter lumen; Fig. 14B shows an electrically insulated needle having an electrically conductive exposed region presenting an electrode El and carrying a stylet-like electrode E2 extending along the needle thereinside; Fig. 14C shows an insulating needle with exposed electrically conductive tip El and a stylet-like second electrode E2. Figs. 14D-14E illustrate experimental data similar to those of Figs. 13B-13C but obtained with the probing portion configuration of Fig. 14B.

Reference is made to Figs. 15A-15B illustrating a representing analysis of the data obtained for various depths (corresponding to different tissue layers) divided by the average measurements of the preceding tissues. These graphs indicate that the ratio between the impedance in the epidural space and the average impedance of the preceding tissue layers is significantly higher compared to the ratio calculated for the other layers in the path of the needle. Also, the ratio mentioned above increases with the increase in frequency. Fig. 15A presents the above-mentioned ratio when applying measurement using the needle of the configuration shown in Fig. 13A. Fig. 15B presents the above- mentioned ratio when applying measurement using the needle configuration shown in Fig. 14B.

In some embodiments, the device of the present invention may comprise a trocar needle unit adapted to introduce cannulas and other similar implements into blood vessels or body cavities or as ports in laparoscopic surgery. The trocar needle may comprise an outer cannula and an inner stylet. The stylet typically has a sharp, pointed tip for skin and tissue penetration and the outer cannula defining a channel to provide subsequent access for endoscopic examination, biopsy, or the like. Sometimes the cannula has a sharp distal edge, in which case the stylet may be a blunt obturator and/or inner cannula. The control utility is configured and operable to guide the trocar within a body cavity and to determine its position.

Claims

CLAIMS:

1. A medical device comprising: a needle unit comprising a needle having a lumen and configured for penetrating body tissue, and a medical tool configured for passing by its forward portion through said lumen of the needle; and a tissue affecting system comprising a probing portion integral with said needle unit and a control utility for operating said probing portion, said tissue affecting system being adapted for carrying out at least one of tissue identification and stimulation.

2. A device according to claim 1, comprising a housing, the needle unit being removably mountable to said housing.

3. A device according to claim 2, wherein said housing is configured as a hand held housing.

4. A device according to claim 2 or 3, wherein said housing is disposable.

5. A device according to any one of the preceding claims, wherein the needle unit has a connection port linked to the lumen of the needle and serving for inserting the forward portion of the medical tool thereinto.

6. A device according to any one of the preceding claims, wherein the probing portion is at least partially incorporated in the needle unit or in the medical tool.

7. A device according to claim 6, wherein the probing portion comprises at least one element in the forward portion of the medical tool and at least one element in the needle.

8. A device according to claim 6, wherein the probing portion is incorporated in the medical tool.

9. A device according to any one of the preceding claims, wherein the medical tool comprises a catheter.

10. A device according to any one of the preceding claims, wherein the medical tool comprises a stylet.

11. A device according to any one of the preceding claims, wherein the tissue affecting system comprises an electrical system.

12. A device according to claim 11, wherein the tissue affecting system is configured and operable for real-time bio-impedance measurements thereby enabling tissue identification.

13. A device according to claim 11 or 12, wherein the medical tool comprises a catheter having at least one pair of electrodes embedded within the catheter walls.

14. A device according to claim 13, wherein the electrodes extend along the catheter.

15. A device according to any one of claims 12 to 14, wherein the needle is configured and operable to record a bio-impedance signal.

16. A device according to any one of the preceding claims, comprising window for controlling a length of said medical tool to be located within a body during the device operation.

17. A device according to any one of the preceding claims, wherein said control utility is configured and operable to localize in real-time a distal end of the needle unit position within a body portion of a subject.

18. A device according to any one of the preceding claims, wherein said control utility is configured and operable to identify in real-time a tissue type interacting with a distal end of the needle unit within a body portion of a subject.

19. A device according to any one of the preceding claims, wherein said control utility is configured and operable to localize in real-time transition between different tissues interacting with a distal end of the needle unit while propagating through the body portion of a subject.

20. A device according to claim 10, wherein the stylet is or carries an electrode which is an element of said probing portion.

21. A system for controlling local anesthesia, the system comprising: a needle unit comprising: a needle having a lumen and configured for penetrating body tissue, and a catheter configured for passing by its forward portion through said lumen of the needle; and a tissue characterization system comprising a probing portion integral with said needle unit and a control utility for operating said probing portion.

22. A blood vessel catheterization system, comprising: a needle unit comprising: a needle having a lumen and configured for penetrating the blood vessel, and a catheter configured for passing by its forward portion through said lumen of the needle; and; a tissue affecting system comprising a probing portion integral with said needle unit and a control utility for operating said probing portion and generating a signal indicative of the penetration of said needle into the blood vessel.

23. A needle unit comprising: a body; a needle with a lumen projecting from the body; a connection port for introducing a forward portion of a medical tool and allowing its passage through the lumen; an electrical coupler for coupling the needle or an electrode embedded in or carried by the needle to an electrical unit.

24. A needle unit according to claim 23, comprising a control mechanism for controlling a length of said forward portion of the medical tool interacting with the body.

25. A needle unit according to claim 24, wherein said control mechanism comprises a window made in said body to enable visual observation of the medical tool displacement with respect to the body.

26. A needle unit according to claim 25, wherein at least one of the window and the medical tool viewed through the window is formed with a scale.

27. A method for monitoring the position of a needle within the body comprising: performing continuous impedance measurements at different operating frequencies to obtain an impedance profile; and analyzing impedance profile variations between different frequencies to characterize the tissue and thereby determine position.

28. A method according to claim 27, comprising propagating the needle within a body portion and concurrently determining an impedance profile.

29. A method according to claim 28, wherein a change in the impedance profile while propagating the needle through a body portion, is indicative of passage between one tissue to another.

30. The method of claim 29, comprising identifying the epidural space.

31. The method of claim 30, comprising detecting a blood vessel.

32. The method of claim30, comprising predicting upcoming of a certain impedance zone.