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Title:
DEVICE IMPLANTABLE IN BIOLOGICAL DUCTS
Document Type and Number:
WIPO Patent Application WO/2011/121581
Kind Code:
A1
Abstract:
Medical device (200) that can be implanted in biological ducts in the human body having simultaneous functionalities of mechanical aid for biological ducts, sensor of the state of obstruction of the duct, radio transmitter and data storage unit. The device is made of biocompatible metal alloys and one or more microchips for radio- frequency identification (RFID) provided with a memory, able to monitor its own degree of endothelialization, detect the presence and the evolution of stenotic processes as well as locate the device, recognize it, evaluate its structural integrity and transmit the information collected to a suitable external reader by means of reflection of the electromagnetic field emitted by said external interrogator. The functionalities of the device further permit tracing of the entire history of the device and of the patient's medical data.

Inventors:
MARROCCO, Gaetano (Via Aldo Salvatori 14, Monte Compatri, I-00040, IT)
OCCHIUZZI, Cecilia (Via Carlopoli 6A, Roma, I-00178, IT)
Application Number:
IB2011/051436
Publication Date:
October 06, 2011
Filing Date:
April 04, 2011
Export Citation:
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Assignee:
UNIVERSITA' DEGLI STUDI DI ROMA "TOR VERGATA" (Via Orazio Raimondo 18, Roma, I-00173, IT)
MARROCCO, Gaetano (Via Aldo Salvatori 14, Monte Compatri, I-00040, IT)
OCCHIUZZI, Cecilia (Via Carlopoli 6A, Roma, I-00178, IT)
International Classes:
A61F2/82; A61F2/02; A61F2/90; A61F2/91; A61F2/915
Domestic Patent References:
2007-07-19
2003-06-05
2005-05-26
2001-02-22
Other References:
Pete Sorrells: "Application Note AN680. Passive RFID Basics", , 31 December 1998 (1998-12-31), pages 1-5, XP55001961, Retrieved from the Internet: URL:http://ww1.microchip.com/downloads/en/AppNotes/00680b.pdf [retrieved on 2011-07-05]
Attorney, Agent or Firm:
CINQUANTINI, Bruno et al. (Corso di Porta Vittoria 9, Milano, I-20122, IT)
Download PDF:
Claims:
CLAIMS

1 . Medical device (200) implantable in a biological duct, able to respond to an interrogating electromagnetic field emitted by a remote interrogator (100), said device being constituted of an at least partially electrically conducting implantable structure,

in which there are provided one or more digital modulators constituted of electrically passive RFID microchips (201 ) integral with the implantable structure, said RFID microchips (201 ) being able to cause the medical device (200) to reflect the interrogating electromagnetic field according to a digital modulation generating a respective unique identification code recognizable by the remote interrogator (100),

whereby said implantable structure is configured, in addition to performing the mechanical function of an aid for the biological duct once implanted therein, also for performing a function of antenna for transmitting a backscattered electromagnetic signal (SRFID) conditioned in amplitude and phase by the detected state of the biological duct, in response to an interrogating signal (Sread) coming from said remote interrogator (100), so that the device also acts as a sensor of the state of patency of said biological duct.

2. Device according to Claim 1 , wherein said RFID microchips (201 ) are provided with a respective memory for storing data regarding identification of the device, implantation of the device, dates and results of regular check-ups post- intervention, said data being updatable at each interaction with the remote interrogator (100).

3. Device according to one of the preceding claims, said device being a stent or a graft or a vascular prosthesis.

4. Device according to one of the preceding claims, wherein said structure is of biocompatible metallic or polymeric material.

5. Device according to Claim 4, in which said metallic material is a shape-memory metal alloy.

6. Device according to one of the preceding claims, wherein said structure has a continuous wall or has a wall with a mesh structure (224).

7. Device according to Claim 6 wherein, in the case of a wall with a mesh structure, said mesh structure (224) is constituted by assembling shaped metal wires (202) in closed contours stacked vertically, optionally with bifurcations, and optionally interconnected with one another with metal wires, and wherein said shaped metal wires can be supported by a surface of biocompatible dielectric material.

8. Device according to Claim 6 or 7, wherein each RFID microchip (201 ) is connected to a shaped metal wire (202) by interruption of said metal wire and connection of the two terminals of the RFID microchip (201 ) to the two terminations of the metal wire (202) by welding, gluing, mechanical pressing or crimping; or wherein each RFID microchip (201 ) is connected to a shaped metal wire (202) without causing interruption thereof by adding a stretch of shaped conductor (203), wherein one or both ends are fixed to said shaped metal wire (202); or wherein each RFID microchip (201 ) is connected to at least two closed wire conductors (202') by means of an additional conductor (204'), interrupted to incorporate said RFID microchip, the two ends of which are fixed to said closed wire conductors (202').

9. Device according to Claim 6 wherein, in the case of a continuous wall, the RFID microchips (201 ) are inserted in at least one slot (205) of the structure with continuous wall, fixing them to the edges of the slot by welding or gluing or crimping.

10. Monitoring system comprising:

- a medical device (200) implantable in biological ducts according to Claim 1 ;

- a remote interrogator ( 100) having a radio-frequency or microwave radio transmitter (102) and a control logic ( 103), configured for acquiring the identification codes, transmitted by the respective one or more RFID microchips (201 ), and the backscattered electromagnetic signals (SRFID) associated with said codes, and for processing said backscattered electromagnetic signals (SRFID) SO as to produce at the output at least one indicating parameter that is a function of the state of said device.

1 1 . Monitoring system according to Claim 10, wherein the remote interrogator ( 1 00) comprises a first electronic subsystem ( 1 04) configured for interrogating the medical device (200) with power of emission increasing until it identifies the minimum turn-on power of each of the RFID microchips (201 ) integrated in the implantable structure.

12. Monitoring system according to Claim 1 1 , wherein the remote interrogator (100) is configured for associating the state of the device implanted in a biological duct with the minimum turn-on powers of the RFID microchips (201 ).

13. Monitoring system according to Claim 10, wherein the remote interrogator (100) comprises a second electronic subsystem (105) configured for storing the power backscattered by each of the RFID microchips (201 ) in a condition of maximum allowed power of emission.

14. Monitoring system according to Claim 1 1 , wherein the remote interrogator (100) comprises a second electronic subsystem (105) configured for storing the power backscattered by each of the RFID microchips (201 ) in a condition of minimum turn-on power of said RFID microchips.

15. Monitoring system according to Claim 13 or 14, wherein the remote interrogator (100) is configured for associating the state of the device implanted in a biological duct with the powers backscattered by the RFID microchips (201 ). 16. Monitoring system according to Claim 14, wherein the remote interrogator (100) comprises a third electronic subsystem (106) configured for processing the minimum turn-on power of the RFID microchips and the corresponding backscattered powers in order to obtain a measurement indicating parameter independent from the orientation between the interrogator and the medical device and that can be correlated with the state of health of the biological duct.

1 7. Process for monitoring the state of a biological duct in which a medical device (200) according to Claim 1 is implanted, said process comprising the following stages:

- identifying the RFID microchips (201 ) present in the device (200) by interrogation and acquisition of the identification codes, transmitted from the respective one or more RFID microchips (201 ), by the interrogator (100);

- at a first time (tO) selectively interrogating each RFID microchip (201 ) with an electromagnetic signal (Sread) emitted by the interrogator (100) and processing the backscattered electromagnetic signal (SRFID) SO as to produce at the output a first indicating parameter p(t0) that is a function at least of the input impedance evaluated at the terminals of the device (200) where the respective RFID microchip is placed, - at a second time (tk) selectively interrogating each RFI D microchip (201 ) with a further electromagnetic signal (Sread) emitted by the interrogator (100) and processing the corresponding backscattered electromagnetic signal (SRFID) SO as to produce at the output a second indicating parameter p(tk) that is a function at least of the input impedance evaluated at the terminals of the device (200) where the respective RFI D microchip is placed ,

- comparing said second indicating parameter p(tk) and said first indicating parameter p(t0) to assess any change in the state of said biological duct.

Description:
DEVICE IMPLANTABLE IN BIOLOGICAL DUCTS

Field of the invention

The present invention relates to a medical device implantable in biological ducts of the human body with enhanced functions.

Prior art

Medical devices that are implantable in biological ducts, such as stents, prostheses or more generally intravascular devices, are used in treatments for correcting changes of coronaries, central and peripheral arteries, veins, biliary ducts, oesophagus, colon, trachea, bronchi, ureter, urethra and for central and peripheral neurosurgical applications. The main aim of these devices is to correct significant changes in the diameter of a blood vessel or of a duct. They are often used for increasing the diminished flow of blood, or some other fluid, to organs downstream of an obstruction or for mechanically supporting the walls of vessels weakened and deformed by age, diseases or injuries.

As with all implanted devices, there is an increasingly evident demand for integrated systems for remote monitoring of their state, functioning and conditions of the biological compartment in which they are placed. Such systems should, moreover, guarantee the localization and identification of the device itself and store information, also regarding the patient and his clinical history.

Continuous follow-up is essential for patients subjected to implantation of intravascular devices in the period following the intervention, within one month and then, in the absence of changes, at three months, six months, at one year and annually thereafter. In the initial period it is moreover of particular clinical importance to monitor the process of endothelialization of the device, i.e. its total incorporation in the vessel wall through hyperproliferation of the inner endothelial layer. When said growth, which is desirable for correct implanting of the device, degenerates into uncontrolled hyperproliferation with production of a thick layer of smooth muscle tissue within the lumen, called neointima, the phenomenon of restenosis occurs. The development of neointima is variable but can be so substantial that it completely occludes the lumen of the duct, especially in the case of vessels of small diameter, often necessitating a new intervention. In the long term the commonest problems are formation of new occlusions, as well as degradation of the structural integrity of the device and possible migration of all or parts of the structure from the place of implantation.

The technology of the prior art focuses mainly on reduction of growth of neointima after placement of the device: the use of biocompatible materials, the use of special drugs released from the device itself (drug-eluting device) and absorbable implants have produced notable improvements but so far have not solved the problem.

The diagnosis of the state of implanted intravascular devices is entrusted to echo(colour)-Doppler, which is able, in the vast majority of cases, to perform a diagnosis not only of the degree of restenosis, based essentially on the increase in flow velocity in the stretch of interest, but also of the typology and morphology of the restenotic plaque. The other diagnostic techniques, such as IVUS, TC or angio-RM with contrast medium (in exceptional cases traditional angiography) are reserved for doubtful and symptomatic cases in which surgical correction of restenosis is presumed to be suitable.

To date, however, no integrated implantable systems are available that, in addition to the own medical functions, are also capable of effectively and efficiently monitoring the state of endothelialization and patency of the vessel and of tracking chemical and physical changes of the duct over time. Application in highly sensitive contexts, such as biological ducts, makes it difficult and in some cases prohibitive to use powered sensors and communication structures associated with the device itself. Solutions that are completely passive and have no sensors, based essentially on the different response of the device (generally of the stent type) to external stresses such as acoustic or electromagnetic waves in relation to the degree of restenosis, have not found clinical application because they are not sufficiently sensitive and the results produced are highly variable.

Document WO2005/046467 describes a telemetry system for monitoring the state of a biological duct based on a stent, one or more dedicated sensors (optionally active) and a system for communicating with the exterior, which in particular embodiments is an RFID tag but different from the implantable medical device, said RFID tag including two separate elements such as a microchip and an antenna. This RFID tag can perform functions of localization, identification and storage of data relating to the medical device and to the patient in whom it is implanted. The aforementioned tag can also perform sensory functions only if suitably integrated with active sensors and provided with a power supply. While meeting the requirements of identification and labelling of the implantable medical device, the system described necessarily requires an autonomous power source which must be replenished from outside at regular time intervals, or which imposes various time limits on the use of said device, and moreover it must be provided with additional control electronics, increasing its invasiveness. The foregoing therefore precludes its application in particularly sensitive biological contexts, such as those relating to cardiology and neurology.

Alternative solutions, which reduce the need for additional electronic components, are described in WO01/12092. That document describes a stent that is suitably modified for housing a passive sensing circuit that has a wireless link to an external reader and is able to transmit the status of the stent and of the vessel in which the latter is placed (degree of restenosis). The sensory information is transformed into a variable impedance, which is detected by an external reader from the variation in resonance frequency of the circuit, describing the magnetostatic coupling between reader and stent.

A disadvantage of this solution is that it does not permit easy, unambiguous identification of the implanted device, because the response signal of the device is not immediately identifiable, especially when several stents are present.

It also proves difficult to trace the state of health of a particular portion of the duct in which the stent is placed, i.e. locate the position of restenosis inside intravascular devices of large dimensions.

Furthermore, this solution does not allow information regarding said device, the patient, the implantation surgery and its follow-up to be stored in the medical device.

The magnetostatic nature of the interaction between reader and device finally imposes severe restrictions on the maximum reading distance allowed, typically of a few centimetres.

There is therefore a need to provide a device that can be implanted in biological ducts and makes it possible to overcome the aforementioned drawbacks. Summary of the invention

The primary aim of the present invention is to provide a device that is implantable in biological ducts and has additional functionalities of identification and monitoring of the device itself, monitoring of the state of health of the duct in which it is implanted, localization and data storage, with a minimum number of electronic components and without local sources of power.

A further aim of the present invention is to provide an implantable device that is completely passive from the energy standpoint, which requires minimal variations in geometry with respect to a standard implantable device, so that it can be used with the normal implantation procedures.

Another aim of the invention is to provide a monitoring system and an associated process for monitoring the state of endothelialization and patency of biological ducts by means of said device.

The present invention proposes to achieve the aims discussed above by providing a device implantable in biological ducts having the features of claim 1 , a monitoring system having the features of claim 10, and a monitoring process comprising the stages of claim 17.

The medical device of the invention performs simultaneously the function of intravascular aid by virtue of its geometry, the function of radio transmitter for transmitting signals responding to interrogating signals sent from a remote interrogator, the function of sensor of the state of the duct and the function of data storage unit by means of suitable integration of one or more microchips for radio- frequency identification (RFID) in the structure of said device. The device is totally passive and does not require local sources of energy and additional sensors and dedicated electronics.

The presence of digital modulators with RFID microchips allows easy, unambiguous identification of the implanted device, localization of the position of restenosis and/or of the layer of endothelium inside said device and the storage, in the medical device, of information regarding the device, the patient, the surgical intervention and its follow-up.

Advantageously, the proposed invention applies RFID technology to the problem of monitoring the endothelialization of intravascular devices and restenosis. It consists of a new class of medical devices made with biocompatible materials and conventional shapes, but integrated with one or more digital modulators of the RFID microchip type, having simultaneously mechanical, sensory and transmission functionalities, without the addition of specific sensors, batteries or antennas. In other words, the conductive structure, whether it is metallic or polymeric, which performs the true functions of a stent or of a general vascular support, is designed so that it also acts as an antenna.

When interrogated from the outside by a reader, which can be of portable or fixed type, but not necessarily placed just a few centimetres from the human body, the device of the invention supplies a response that is correlated with the variation in dimensions of the lumen in question, optionally also discriminating the nature of the neoformation.

The absence of a power supply and of dedicated sensors means there are no time limits to its fault-free operation.

This new family of implantable devices therefore allows various innovative functionalities to be performed, in addition to the therapeutic functionalities, which currently are not possible by means of a single device, namely:

- unambiguous identification of the device by means of the identification codes contained in the RFID microchip of the device throughout its life, thus making it possible to trace, for example, the manufacturer, the distributor, the date of implantation, references of the doctor and of the surgical team that performed the intervention, the dates of check-ups, etc.;

- monitoring the state of the lumen, of its endothelialization, of any phenomena of restenosis and determination of their position and typology also within said device;

- localization of the device during the procedure for positioning in the biological duct by minimally invasive techniques (percutaneous surgery), producing information for indicating, interactively with the medical team, the path to follow to reach the correct site of implantation;

- localization of the device at its site of implantation, identifying any displacements and distinguishing it unambiguously from any other implanted devices.

The device makes it possible to extend the safety of the medical procedure beyond the existing limits and in particular to monitor, simply and inexpensively, the post-implantation course, even away from hospital facilities (pharmacies, consulting rooms and private dwellings), providing the doctor with useful information for a targeted planning of any analyses and/or adjustment of drug therapy.

The proposed invention offers additional functionalities of identification, monitoring and localization, which moreover make it possible to extend the market potential of intravascular devices also to the fields of diagnosis and of health service logistics.

The dependent claims describe preferred embodiments of the invention.

Brief description of the drawings

Further features and advantages of the invention will become clearer from the detailed description of preferred, but not exclusive, embodiments of a device implantable in biological ducts, as illustrated, as non-limiting examples, by means of the appended drawings, in which:

Fig. 1 shows a schematic diagram in which the device of the invention is implanted in a human body;

Fig. 2 shows an enlarged detail of a first preferred embodiment of the device;

Fig. 3 shows an enlarged detail of a second embodiment of the device of the invention;

Fig. 4 shows an enlarged detail of a third embodiment of the device of the invention;

Fig. 5 shows an enlarged detail of a fourth embodiment of the device of the invention;

Fig. 6 shows an enlarged detail of a fifth embodiment of the device of the invention;

Fig. 7 shows a schematic diagram of the main components of an external interrogator;

Fig. 8 shows a schematic diagram of the principle of operation of the device of the invention;

Fig. 9 is a graph showing the variation of the signal received from the device in various situations of the biological duct;

Fig. 10 shows a schematic diagram of a further manner of operation of the device of the invention;

Fig. 1 1 shows a schematic diagram of a further situation of operation of the device of the invention; Fig. 1 2 shows a schematic diagram of a further manner of operation of the device of the invention;

Fig. 1 3 shows an example of organization of the information contained in the memory of the device of the invention.

The same reference numbers in the figures identify the same elements or components.

Detailed description of preferred embodiments of the invention

The physical principle on which the operation of the device of the invention is based requires making said device, completely or partially, of a metal alloy with good characteristics of electrical conduction. Referring in particular to Fig. 1 , when it is exposed to electromagnetic radiation emitted by a remote radio-frequency device, conventionally called interrogator 100, the implanted device 200, for example in the form of a stent or graft or vascular prosthesis, produces, like any metallic conductor, a backscattered electromagnetic field. The characteristics of intensity and spatial distribution of the backscattered field depend on the shape of the device, the material of which it is composed and the surrounding region of the body, indicated as parameters {Ψ-ι , Ψ2 · · . ΨΜ) in Fig. 1 . The quantity used for describing the electromagnetic field backscattered by a general object is its radar cross-section, as it is commonly defined in English. If the site of implantation of the device undergoes, over time, chemical and physical changes with respect to an initial condition, as a result of phenomena of plaque formation or of regrowth of tissue, which lead to a change in the patency of the duct, which can be indicated with the parameters {Ψ'ι, Ψ'2 · .. Ψ'Μ)≠ { Ψ 1 . Ψ2 · · · Ψ Μ) in Fig. 1 , the radar cross- section of the implanted device 200 will undergo corresponding changes. Consequently, the intensity or the phase of the backscattered field collected by the interrogator 100 will incorporate information on the state of the duct, making it possible, in theory, to perform remote monitoring of changes in the state of the duct, for example remote monitoring of the degree of endothelialization of the device or remote monitoring of a phenomenon of restenosis if the device is a stent. The intravascular device of the invention, in this form, can then also be regarded as a sensor of the change in the state of the duct in which it is implanted. The therapeutic and diagnostic functionalities are not separable since they are performed by a single physical object. In the devices of the prior art, remote monitoring of this kind cannot be achieved, for the following physical reasons:

- the electromagnetic field backscattered by the device is a function of the inclination and of the distance of the implanted device with respect to the interrogator; therefore to evaluate a change in the state of the site of implantation it would be necessary to reproduce, in successive measurements, the identical mutual position between interrogator and site of implantation, the latter not being easily mappable on the outside surface of the patient's body; (in reality this problem is only overcome with the impedance interrogator but not with the other two)

- the field backscattered by the device is superimposed on that produced by the body and by the surroundings, tending to mask it completely.

To overcome the aforementioned physical limitations and make it possible to extract information parameters from the electromagnetic field backscattered by the device 200 and collected by the interrogator 100, in accordance with the invention, one or more microchips for radio-frequency identification, commonly called RFID microchips, which cause the device to reflect the interrogating electromagnetic field according to digital modulation, i.e. generating an unambiguous and recognizable code, are suitably integrated in the structure of the implantable device, for example a stent. At this point the interrogator will, by means of demodulation and decoding, be able to identify unambiguously the specific contribution of the device itself, independently of the conditions of measurement and of the variation of the outside environment, which instead induce variations in the backscattered electromagnetic field that are unmodulated, and so can easily be eliminated.

The radar cross-section of this implantable device can be likened to that of an antenna connected to a network of variable impedances and depends on the gain of said antenna and on matching the impedances of the various RFID microchips with the impedances of the conducting structure, taken at the points of interruption and insertion of the RFID microchips.

Both the gain and the input impedances of the implantable device of the invention, being macroscopic characteristics, will also be determined by the state of the duct in which the device is implanted and will in their turn influence the electromagnetic field backscattered by said device.

In particular, from the theory of antennas loaded with RFID microchips it is known that the intensity of the backscattered field decreases with worsening of the aforementioned impedance matching until it disappears completely when the mismatching diminishes beyond a certain threshold.

In this meaning, the device of the invention, in addition to the functions of medical device and of sensor, also incorporates the function of a radio, which is able to establish communication with the interrogator, in accordance with suitable protocols. There are no structural and/or logical distinctions between said parts (medical device, for example a stent, sensor and radio antenna) and functionalities.

In more detail, the operation of the device of the invention envisages that the interrogator 100 emits an electromagnetic interrogating signal S read . Via this signal, the implantable device 200 receives the energy required for activation of one or more RFID -microchips that are incorporated therein and retransmits an electromagnetic signal S RFID (t.,), modulated by said RFID microchips supplying the identification code of the device. The backscattered signal at time t v S RFID (t.,), will be conditioned in amplitude and phase by the detected state of the duct, indicated by the sequence of parameters {Ψι , Ψ2·· . ΨΜ}·

If the interrogation by the interrogator 100 is carried out at a time t2, at which the biological duct has undergone changes so that the parameters {ΨΊ , Ψ' 2 ... Ψ'Μ} are different from {Ψ-ι, Ψ 2 ... Ψ Μ }, the chemical, physical and geometric characteristics of the implanted device will be altered in relation to said changes, so that the retransmitted signal, S RFID (t 2 ), will be different from the previously backscattered signal S^^t.,). Said changes, suitably processed by the interrogating unit, will supply information on the state of the duct detected by the device itself.

In particular the device of the invention is an intravascular device made partially or completely with wires made of electrically conducting metal alloys, optionally with shape memory properties such as Nitinol, produced in a continuous form or as a mesh, namely by assembly of wires that can also be shaped in a base form such as rings with a profile of uniform or variable section and segments of wires interconnected in conventional ways, specific for the anatomical site of the implant. In particular the base forms, for example rings, can be stacked vertically optionally along bifurcations for adapting to particular biological ducts, for example the oesophagus or the abdominal aorta. The metallic structure constituted of the wires can moreover be supported by a surface of biocompatible dielectric material. As an alternative to metal alloys, it is possible to use electrically conducting polymers or conductors that are bioabsorbable by the human body.

In a first embodiment the introduction of one or more RFID microchips 201 in the conducting structure that constitutes an intravascular device 200, for example a stent represented in Fig. 2 for simplicity as a sequence of rings 202 of any shape, interrupts the conducting ring locally at one or more points. One or more RFID microchips 201 are introduced on said conducting rings or wires 202, by welding or gluing or mechanically pressing or crimping the two terminals of the RFID microchip near the interruption, in order to restore the mechanical and functional continuity of the structure, as illustrated in Fig. 2.

Alternatively, another embodiment envisages that each RFID microchip 201 is connected to the closed conducting wire or ring 202, without causing its interruption by adding, in parallel, a stretch of a further shaped conducting wire 203, interrupted by interconnecting a respective RFID microchip 201 as described above, one end of which 204 or both ends are fixed by welding, gluing or crimping to said closed conducting wire 202, as illustrated in Fig. 3. The features of the embodiment in Fig. 3 can be combined with the features of Fig. 2.

In another advantageous embodiment of the device of the invention 200, the single RFID microchip 201 is connected to two or more closed conducting wires 202 by means of an additional conductor 204', transverse with respect to the closed wire conductors 202, interrupted by interconnecting the RFID microchip, the two ends of which are fixed by welding, gluing or crimping to said closed wire conductors. This variant is illustrated in Fig. 4. The features of the variant in Fig. 4 can be combined with the features of Figs. 2 and 3.

Another variant alternative to the foregoing variants envisages that the device of the invention 200 is obtained by processing a single block of metal alloy and the various RFID microchips 201 are housed in slots or slits 205 that are more or less articulated, pre-existing or created suitably in the device; this variant is illustrated in Fig. 5. Fig. 6, finally, illustrates a further variant of the device of the invention, in the form of a stent 200 having a tubular mesh structure. At predetermined points of the mesh 224, one or more RFID microchips 201 are introduced, welding or gluing or mechanically pressing or crimping the two terminals of the RFID microchip near the interruption, in order to restore the mechanical and functional continuity of the structure.

The RFID microchips are identified by different identification codes, established on initialization of the device of the invention, and stored in their internal memory. The internal memories of the RFID microchips can in addition contain logistic information about the life of the device, about the patient, about the surgical intervention and about the post-implant diagnostic tests.

The mechanical (shape) and electrical (position of the microchips) design of the device of the invention must ensure appropriate sensitivity of the radar cross- section of said device to variation of the state of patency of the duct. The shape of the implantable device and the positioning of the microchips are optimized with instruments for electromagnetic simulation, having, as the desired result, the variation of the input impedance at the various points of interruption of the conductor with variation of the state of patency of the duct. This variation in impedance is fixed by the designer following simulations for reference cases and experimental studies on biological models.

In the case when several RFID microchips are provided, the implantable device is designed so that at least one microchip is always sufficiently matched, regardless of the condition of the state of patency of the duct, and the code transmitted by it constitutes the unique identifier of the device. The remaining RFID microchips may or may not be able to transmit the own digital code in relation to the state of the duct. The subset of codes transmitted is part of the information processed by the interrogator in the diagnostic procedure.

A monitoring system according to the present invention comprises the medical device 200 and the external interrogator or reader 100.

The interrogator 100 supplies energy to the implantable device by means of electromagnetic waves, as well as supplying the carrier for the modulation introduced by the RFID microchip. The interrogator interrogates the various RFID microchips, acquires the codes transmitted by the microchips and the signals associated with them, processes one or more parameters to be correlated with the state of the device and optionally stores information in the RFID microchips' own memory.

Fig. 7 shows a schematic representation of the main components of the external interrogator 00. This includes a radio-frequency or microwave radio transmitter 102, a control logic 103, one or more antennas 101 and a series of components dedicated to implementation of the sensing algorithm. The interrogator is capable of performing the task of processing the responses of the device 200 (producing specific diagnostic indicators) and of writing the results of the periodical checks of the state of health of the biological duct in the memories of the RFID microchips 201. The electronic blocks that permit execution of acquisition and processing of the sensory data are:

- a first electronic subsystem 104 that interrogates the implantable device 200 with increasing power of emission until the minimum power is identified for turn-on of each of the RFID microchips 201 integrated in the implantable device. This first electronic subsystem 104 is able to perform said interrogation at a multiplicity of different frequencies and to store the values of said frequencies. Moreover, it is configured so as to associate with the minimum turn-on powers of the RFID microchips, integrated in the implantable device, the state of health of the biological vessel by means of conversion tables or graphs stored in the reader;

- a second electronic subsystem 105 that stores the power backscattered by each of the RFID microchips 201 , integrated in the implantable device 200, in the condition of minimum turn-on power of said microchips or in the condition of maximum allowed power of emission. This second electronic subsystem 105 is able to store these powers backscattered at different frequencies. Furthermore it is able to store separately the powers backscattered by the RFID microchips for a fixed value of power of emission. Lastly, it is configured so as to correlate these backscattered powers with the state of health of the biological duct by means of conversion tables or graphs stored in the reader;

- a third electronic subsystem 106 configured for combining and processing the minimum turn-on powers of each of the RFID microchips and the powers backscattered from each of said RFID microchip at the various frequencies used for obtaining a measurement indicator independent of the spatial orientation between reader and implantable device and that can be correlated with the state of health of the biological duct by means of conversion tables or graphs stored in the reader.

The remote interrogator 100 provides for interrogation of the implanted device 200 in three modalities.

The interrogation procedure of the monitoring process according to the invention envisages the steps of:

a) defining a reference distance di between interrogator 100 and device 200 and a particular spatial orientation between the two aforementioned components;

b) identifying, by means of the interrogator, the RFID microchips 201 present in the implanted device 200 or in several implanted devices placed in the reading volume of the interrogator 100, by interrogation and subsequent acquisition of the identification codes transmitted by the RFID microchips;

c') in a first interrogation modality, the reader 100 interrogates selectively each n-th RFID microchip with an electromagnetic signal equal to the maximum power of emission allowed, and stores, by means of the second electronic subsystem 105, the value of the power backscattered by said microchip, SRFiD,n=S maX RFiD,n(t), in the memory of the reader. Said second electronic subsystem 105 calculates the ratio of said backscattered power to the interrogation power Pbs,n(t)= SRFiD,n S max read that constitutes a first sensory indicator called "backscattering indicator" which is found to depend on the distance d-i, on the input impedance evaluated at the terminals of the implantable device where said microchip is placed, and on the gain of radiation of the implantable device along the spatial orientation. Therefore this backscattering indicator is correlated with the state of the device and of the duct in which it is implanted. For each RFID microchip interrogated, the reader stores the respective backscattering indicator at time t;

c") in a second interrogation modality the reader interrogates selectively, by means of the first electronic subsystem 104, each n-th RFID microchip with an electromagnetic signal S rea d at increasing power of emission until said n-th RFID microchip is activated and transmits back its identification code. The minimum power of emission S to re ad,n(t) for which the reader 100 is able to receive the response of the n-th RFID microchip is stored and is defined as "turn-on indicator" Pto,n(t)=S read,n(t)/S' n of the n-th RFID microchip, where S' n is the sensitivity of the n-th RFID microchip, and depends on the distance di , on the input impedance evaluated at the terminals of the implantable device where said microchip is placed, and on the radiation gain of the implantable device along the spatial orientation. Therefore this turn-on indicator is also correlated with the state of the device and of the duct in which it is implanted. For each RFID microchip interrogated, the reader stores the respective turn-on indicator at time t;

c"') in a third interrogation modality, the reader detects for each RFID microchip its own turn-on indicator Pto,n(t)=S t0 read,n(t)/S' n , as described in point c"); it also detects the corresponding backscattering indicator Pbs,n(t)= S R FiD,n/S t0 read,n(t), as described in point c') with the only difference that detection is carried out in the condition of minimum turn-on power and not in the condition of maximum power of emission allowed by the reader; and it combines, by means of the third electronic subs stem 106, these two indicators according to the algorithm p t)≡ 1

thus obtaining a third indicator, called "impedance indicator" p,, n of the n-th RFID microchip, which depends solely on the input impedance evaluated at the terminals of the implantable device where the n-th RFID microchip is placed, and therefore is completely insensitive to the position of the interrogator with respect to the implanted device. Therefore this impedance indicator is also correlated with the state of the device and of the duct in which it is implanted. For each RFID microchip interrogated, the reader stores the respective power indicator at time t; d) the reader 100 repeats the steps from a) to c'), from a) to c") or from a) to c'") at increasing frequency until the entire operating range of the RFID microchips is covered.

The whole procedure for interrogation and correlation of the measured indicator with the evolution of the state of the biological duct can be outlined as follows: - once the medical device 200 has been implanted in the biological duct, the external reader 100 executes the steps from a) to d) following one of the three interrogation modalities, storing their data as initial reference condition in the memory of the reader and/or in the memory of the RFID microchips integrated in the implanted device. Furthermore, the reader can store the registration data of the device and information relating to the intervention;

- at each check-up at time t k , following implantation of the device (hours, days, weeks or months) the reader 100 performs the following operations:

- repetition of the steps from a) to d) following the interrogation modality selected in the initial reference condition (to), until the identification codes of the RFID microchips are acquired and the respective new indicators {Pbs.n(tk), Pto.n(tk), pi,n(tk)} are obtained for each RFID microchip;

- comparison of said new indicators {p bs ,n(tk), Pto.n(tk), Pi.n(tk)} with the indicators recorded at the previous times (to,... t k- i );

- production of an assessment of the state of the implanted device or of the biological duct starting from at least one of the three indicators acquired at different moments of time, or by means of a subset or composition thereof, making use of conversion tables and/or reference graphs (e.g. Fig. 9), obtained starting from a significant sample of digital simulations, in-vitro experiments on equivalent electromagnetic models, in-vivo experiments on animals, experimental data obtained from conventional diagnostic techniques or from the clinical experience of qualified operators. Based on the specific biological duct, the patient's age and sex, their build and their medical history, the data produced at time t k find a classification in the reference graphs and/or in the conversion tables and determine the state of the device and of the biological duct in which it is implanted;

- storage of the information thus generated about the state of the implanted device in the internal memory of the RFID microchips and/or of the external reader.

Being known the number of RFID microchips present in the device of the invention, the state of the implanted device or of the biological duct can also be assessed based on the effective number of microchips that respond to interrogation by the reader 100, making use of conversion tables and/or reference graphs (e.g. Fig. 9).

EXAMPLES

In a first example of practical application, the device of the invention 200 gives information, as illustrated in Fig. 8, about the variations in patency of the duct, in particular the change in longitudinal extension H of the layer 210 of endothelialization and/or restenosis and the change in radius R of portion 220 of the biological duct not occupied by said layer 210 (see Ri and Hi on the left and R 2 and H2 on the right in Fig. 8), as a change in its dimension and electrical form and reacts by changes of its radar cross-section and of the signal backscattered to the interrogator.

An example of signal received by the interrogator, with variation of the degree of endothelialization and/or of restenosis, is shown in Fig. 9. This signal is obtained from a computer simulation of a device implanted in a tubular duct of dimensions comparable to a carotid artery. The device of the invention, implanted, is interrogated at a frequency of 870 MHz, which is allocated in Europe to UHF RFID communications. The graph shows the variation of the signal received by the external interrogator on increasing the degree of shrinkage of the lumen or portion of duct 220, defined as (Ro-R)/Ro, where R 0 is the radius of the duct in the initial conditions post-intervention and R is the radius of the duct in the various detections, for two different types of process, neointimal and atherosclerotic. This curve, which is found to be monotonic and increasing, has the direction of an inversion curve, in the sense that it makes it possible to associate, unambiguously, a change in the degree of occlusion of the duct with the variation of the signal received. Moreover, the curves associated with the two processes - neointimal and atherosclerotic - have a different slope and therefore processing of the signal received, in successive measurements, would also make it possible to distinguish the type of restenosis.

In a second example of application, the device of the invention 200 reacts to the variations of the state of the duct 250 in which it is placed, indicated by the sequence of parameters {Ψ 1 , 4 , ΨΜ}. by change of shape, and in the specific case passing from a radius R 3 to a radius R of duct 250, and finally altering its radius of curvature as illustrated in Fig. 10. The change in shape leads to a change of the radar cross-section of the device and therefore of the signal backscattered to the interrogator.

In a third example, illustrated in Fig. 1 1 , the device of the invention 200, implanted in a biological duct, has suffered, in the operating conditions, a disconnection between the modules of which it is composed. This deformation will produce a 2011/051436

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change of the gain and of the condition of matching of one or more RFID microchips 201 and consequently of the radar cross-section of the device. This change is evaluated by processing the field backscattered by the device, which will therefore carry information about the structural integrity of the device itself. In a fourth example, illustrated in Fig. 12, the device of the invention is a Y-shaped stent 200 to match the bifurcation of a long biological duct. The device contains a multiplicity of RFID microchips 201 spatially arranged, making it possible to monitor each portion of the device independently.

Fig. 12 also shows, on the right, a possible temporal variation of the signal arriving from the aforementioned Y-shaped stent 200 and collected by the external interrogator 100. The implanted device involves the terminal portion of the abdominal aorta and its final bifurcation into the two iliac arteries. The RFID microchips 201 are arranged so as to monitor the three anatomical compartments independently, supplying at each control time {TO, T1 , T2....} specific information on their degree of endothelialization and/or restenosis (expressed as percentages) and consequently to locate the position of obstructions and/or absence of endothelial proliferation. In particular the graph clearly shows the different evolution of the obstruction of the abdominal aorta and of the left common iliac artery.

A fifth example (Fig. 13) shows a possible organization of the memory of the. RFID microchips 201 placed in the device of the invention so as to contain the registration data of the device, the manufacturer, the distributor, the date of implantation, the references of the doctor and of the surgical team that carried out the intervention and the dates and results of regular check-ups, these functioning as the pedigree of the device and the patient's medical record card, which can be updated instantly at each interaction with the interrogator 100, even outside of the medical facility.