in describing the present invention , a variety of terms are used in the description . the term “ stent ” refers to a cylinder or scaffold made of metal or polymers that may be permanently implanted into a blood vessel following angioplasty procedure . reference may be had to u . s . pat . no . 6 , 190 , 393 , the ensure disclosure of which is hereby incorporated by reference . the term stent also refers to such a cylinder or scaffold used in lumens other than blood vessels . the term “ stenosis ” refers to the constriction or narrowing of a passage , duct , stricture , or lumen , such as a blood vessel . “ restenosis ” refers to the reoccurrence of stenosis in a lumen ( or implanted medical device ). the term “ baseline value ” refers to the measurement taken at specified period in time , which is later to be used as a reference point for comparison to a second measurement . baseline measurements are typically taken when the stent is in pristine condition . the baseline measurement allows the user to correct for energy reading variations due to the fluids that may fill the stent . a certain amount of deviation from the baseline reading is acceptable , as this may account for the inhomogeneity of many fluids . [ 0035 ] fig1 a is a cut away view of an apparatus that utilizes one embodiment of the instant invention . in the embodiment depicted in fig1 a , apparatus 10 comprises stent 14 is disposed within lumen 12 . in one embodiment , a fluid flows through lumen 12 in the direction of arrow 11 . in one embodiment , stent 14 is substantially flexible . in another embodiment , stent 14 is substantially inflexible . [ 0036 ] fig1 b is a cross sectional view of stent 14 . in the embodiment depicted in fig1 b , stent 14 comprises a cavity 20 , an outer wall 16 , and an inner wall 18 . in the embodiment depicted in fig1 c , stent 14 suffers from the buildup of plaque 22 . this restenosis causes the obstruction of cavity 20 . in one embodiment , inner wall 18 is optional . when the stent is implanted within a living organism , it is preferable that the tissue - contacting surfaces be biocompatible . in the embodiment depicted in fig1 b , outer wall 16 and inner wall 18 are biocompatible . in one embodiment , the wall is comprised of one or more of the biocompatible materials disclosed in u . s . pat . no . 6 , 124 , 523 , the contents of which are hereby incorporated by reference . in another embodiment , the wall is comprised of polytetrafluoroethylene . in additional embodiments , other fluorinated plastics are used . [ 0037 ] fig2 is a cross sectional view of another embodiment of the invention . in the embodiment depicted in fig2 stent 25 comprises cavity 20 , outer wall 28 , inner wall 30 , and middle layer 26 . disposed within middle layer 26 are elements 24 a to 24 e and 32 a to 32 e . in one embodiment , elements 24 a to 24 e function as transmitters of electromagnetic energy while elements 32 a to 32 e function as receivers of electromagnetic energy . in another embodiment , elements 24 a to 24 e and 32 a to 32 e function as both transmitters and receivers of electromagnetic energy . in one embodiment , the transmitters 24 and receivers 32 are comprised of one or more of the transmitters and receivers disclosed in u . s . pat . no . 6 , 488 , 704 . in another embodiment , transmitters 24 and receivers 32 are comprised of vcsel ( vertical cavity surface emitting lasers ). reference may had , for example , or u . s . pat . no . 6 , 686 , 216 (“ electro - optical transceiver system with controlled lateral leakage and method of making it ”). in one embodiment of the invention , elements 24 a to 24 e function as transmitters of vibrational energy . in another embodiment , both vibrational and electromagnetic energy is generated . in another embodiment , an energy wave is generated using a piezoelectric crystal . in this embodiment , the energy wave is a vibrational energy wave . in yet another embodiment , element 24 a emits a first type of energy while element 24 b emits a second type of energy . by way of illustration , and not limitation , element 24 a may emit light of a given wavelength , while element 24 b emits light of a second wavelength . alternatively or additionally , one such transmitting element may emit electromagnetic energy , while a second element emits vibrational energy . in one embodiment , the transmitting elements are activated simultaneously . in another embodiment , the elements are activated sequentially . receivers 32 may be comprised of a variety of materials . in one embodiment , the receiver element is a traditional antenna that is commonly utilized by one skilled in the art . in one embodiment , the receiver is a coil or circuit imposed on or within walls 26 , 28 , and / or 30 . reference may be had to u . s . pat . nos . 5 , 737 , 699 and 5 , 627 , 552 (“ antenna structure for use in a timepiece ”), u . s . pat . no . 5 , 495 , 260 (“ printed circuit dipole antenna ”), u . s . pat . no . 5 , 206 , 657 (“ printed circuit radio frequency antenna ”), u . s . pat . no . 6 , 650 , 301 (“ electrically conductive patterns , antennas , and methods of manufacture ”), u . s . pat . no . 5 , 535 , 304 (“ optical transceiver unit ”), u . s . pat . no . 4 , 549 , 314 (“ optical communication apparatus ”), and the like . in another embodiment , the receiving elements are those described in u . s . pat . no . 5 , 602 , 647 (“ apparatus and method for optically measuring concentrations of components ”). the content of each of these patents is hereby incorporated by reference . in the embodiment shown in fig2 only ten such elements are shown . the embodiment has been illustrated as such only to simplify the illustration and prevent overcrowding of the drawing . as would be apparent to one skilled in the art , any number of transmitting and receiving elements may be used . in one embodiment , there is at least 1 such element per square centimeter surface area of inner wall 30 . in another embodiment , there is at least 1 such element per square millimeter surface area . it is advantageous to place enough transmitting and receiving elements within stent 38 to ensure that any restenosis that begins to occur is detected . in one embodiment , inner wall 30 further comprises a filtering element that is adapted to selectively filter the wavelength of the energy transmitted from elements 24 and 32 . by wall of illustration , and not limitation , transmitting element 24 may emit energy of wavelengths 400 nm to 750 nm and inner wall 30 may act as a filter such that only wavelengths of between 600 and 700 nm are allowed into cavity 20 . [ 0040 ] fig3 is a cross sectional view of one embodiment of the invention wherein stent 34 comprises elements 24 a to 24 e which transmit electromagnetic energy 36 to receiving elements 32 a to 32 e . stent 34 further comprises cavity 20 , outer wall 28 , inner wall 30 and middle layer 26 . in the embodiment depicted in fig3 the electromagnetic wave 36 is comprised of substantially parallel waves . in one embodiment , polarized light is used . in another embodiment , laser light is used . as is apparent from fig3 the transmitting and receiving elements are aligned such that they are opposite to each other . thus , in the embodiment depicted , transmitting element 24 a will transmit energy 36 to receiving element 32 a . the effect of the energy transmitted from transmitting element 24 a will have a minimal impact on receiving elements 32 b to 32 e . in one embodiment , transmitting elements 24 a to 24 e are activated simultaneously . in another embodiment , transmitting elements 24 a to 24 e are activated sequentially . in yet another embodiment , transmitting elements 24 a to 24 e are activated sequentially in groups . for example , transmitting elements 24 a and 24 e transmit an energy wave , and afterwards , elements 24 b and 24 d transmit an energy wave . in one embodiment of the invention , a baseline measurement is taken when cavity 20 is in its pristine state . when cavity 20 is filled with particles ( not shown ), these particles will absorb and / or scatter the energy 36 as energy 36 interacts with the particles . as such , the energy received by receiving element 32 will be less than the energy transmitted by transmitting element 24 . when the environment within cavity 20 is relatively constant , a baseline measurement can be taken and the amount of energy that is successfully received by receiving element 32 can be recorded . as would be appreciated by those skilled in the art , the environment of a dynamic lumen undergoes minor changes . by way of illustration , and not limitation , as blood flows through a stent , the exact composition of the blood may not be precisely constant . as such , the amount of energy received by receiving element 32 may not be constant . nevertheless , a sampling of data points over a period of time allows one to obtain a baseline measurement , as well as obtain a range of typical deviations from the baseline . such deviations may be caused by the change in blood flow due to the beating of the heart , localized concentrations of red blood cells or other particles , and the like . [ 0042 ] fig4 depicts an end view of another embodiment similar to that depicted in fig3 . in the embodiment depicted , stent 38 comprises an inner wall 30 , an outer wall 28 , and a middle layer 26 . disposed within middle layer 26 are transmitting elements , such as 24 a and receiving elements , such as 32 a . in the embodiment shown in fig4 transmitting element 24 a transmits energy 36 which is sensed by receiving element 32 a . [ 0043 ] fig5 is a cross section view of stent 34 depicting the restenosis of the stent . in the embodiment depicted , stent 34 comprises cavity 20 , inner wall 30 , outer wall 28 , middle layer 26 . disposed within middle layer 26 are transmitting elements 24 a to 24 e and receiving elements 32 a to 32 e . as depicted in fig5 stent 34 further comprises plaque 22 and 23 . it is clear from the figure that the energy 36 that is transmitted from transmitting element 24 a to receiving element 32 a is not obstructed by plaque 22 . as such , the intensity of energy 36 detected at 32 a is equal to the intensity of the energy transmitted from 24 a , minus the energy lost to the environment in cavity 20 ( for example , scattering of energy due to the presence of blood in the cavity 20 ). the energy received by 32 a is then compared to the baseline measurements taken when stent 38 was in pristine condition . in the embodiment depicted in fig5 the energy received by 32 a would be within the acceptable deviation limits as compared to the baseline measurements . in comparison , it is clear that the energy received by receiving element 32 b is outside of the deviations expected , relative to the previously measured baseline . this is due to the additional scattering due to plaque 22 . similarly , element 32 b would receive somewhat less energy , as compared to the baseline , due to the thin layer of plaque . the plaque need not be present at the receiving elements . for example , plaque 23 diminishes the energy received at receiving element 32 d , even though it is at least partially covering transmitting element 24 d . [ 0044 ] fig6 . depicts an end view of an embodiment similar to that shown in fig5 . stent 38 comprises an inner wall 30 , an outer wall 28 , a middle layer 26 , and plaque 22 . disposed within middle layer 26 are transmitting elements , such as 24 a and receiving elements , such as 32 a . in the embodiment shown in fig6 transmitting element 24 a transmits energy 36 which is sensed by receiving element 32 a . it is clear from fig6 that the energy received by receiving element 32 a is less than the baseline due to the presence of plaque 22 . similarly , the energy received by receiving element 32 b is less than the baseline , due to the thin layer of plaque 22 . by contrast , the energy received at receiving element 32 c would be within the typical deviation of the baseline value , as there is no significant scattering or absorbance of the energy due to a foreign body . [ 0045 ] fig7 is a cross sectional view of another embodiment of the invention which is similar that depicted in fig3 . in this embodiment , elements 24 a to 24 e and elements 32 a to 32 e function both as transmitting and receiving elements . thus energy 36 may be transmitted in two directions . [ 0046 ] fig8 is an end view of an embodiment similar to that depicted in fig7 . elements 24 a and 32 a function as both transmitters and receivers of electromagnetic energy . in the embodiment depicted , the energy used comprises substantially parallel waves of energy . in another embodiment , the waves are non - parallel . [ 0047 ] fig9 is a cross sectional view of another embodiment of the invention which employs non - parallel waves of energy . in the embodiment depicted in fig9 elements 24 a to 24 e and 32 a to 32 e are adapted to both transmit and receive energy . as shown in fig9 element 24 b broadcasts a wave of non - parallel wave energy , which is detected by receiving elements 32 a to 32 e . as would be apparent to one skilled in the art , the energy at receiving element 32 b is most intense , but a certain portion of the energy is detected at the other receiving elements . in one embodiment , a portion of the energy is reflected off of the surface of the elements 32 , and redirected back to elements 24 . in one embodiment , none of the energy is redirected . in another embodiment , between 0 . 01 % and 10 % of the light is redirected . in another embodiment , between 10 % and 50 % of the light is redirected . in yet another embodiment , between 50 % and 90 % of the light is redirected . in the embodiment depicted , element 24 b is functioning as a transmitter , while elements 24 a , 24 c to 24 e , and 32 a to 32 e are all in “ receive mode .” at another point in time , element 32 d , for example , may be in “ transmit mode ” and the other elements in “ receive mode .” in a similar manner , the elements can be sequentially activated and a map of the inner surface of stent 34 may be constructed . by conducting such measurements when the stent is in pristine condition , a baseline measurement may be obtained . [ 0048 ] fig1 is an end view of an embodiment of the device similar to that depicted in fig9 . stent 38 comprises an inner wall 30 , an outer wall 28 , and a middle layer 26 . disposed within middle layer 26 are transmitting elements , such as 24 a and receiving elements , such as 32 a . in the embodiment shown in fig1 , transmitting element 24 a transmits non - parallel energy 36 which is sensed most strongly by receiving element 32 a , but is also sensed by the other receiving elements . a portion of the energy 36 is reflected off of inner wall 30 and detected by other elements . it is clear from the previous discussions that any obstructions , such as plaque depositions during restenosis , would be detected when a comparison is made to the baseline energy values . [ 0049 ] fig1 is an end view of yet another embodiment of the invention , wherein power source 40 is shown . in the embodiment depicted , stent 38 comprises an inner wall 30 , an outer wall 28 , and a middle layer 26 . disposed within middle layer 26 are transmitting elements , such as 24 a and receiving elements , such as 32 a . in the embodiment shown in fig1 , transmitting element 24 a transmits energy 36 which is sensed by receiving element 32 a . in one embodiment , power source 40 is a convention power supply . power source 40 provides a source of electrical power to elements 24 and 32 . thus , by way of illustration , one may use a lithium - iodine battery , and / or a battery that is chemically equivalent thereto . the battery used may , for example , have an anode of lithium or carbon and a cathode of iodine , carbon , or of silver vanadium oxide , and the like . by way of further illustration , one may use one or more of the batteries disclosed in u . s . pat . no . 5 , 658 , 688 , “ lithium - silver oxide battery and lithium - mercuric oxide battery ,” u . s . pat . no . 4 , 117 , 212 , “ lithium - iodine battery ,” and the like . in fig1 , power source 40 is disposed within middle layer 26 . it is clear to those skilled in the art that the power source may be disposed elsewhere without deviating from the teaching of this invention . [ 0050 ] fig1 . depicts an embodiment wherein remote unit 44 communicates with antenna 42 . antenna 42 is adapted to both transmit and receive signals from remote unit 44 . in the embodiment shown , antenna 42 is disposed within middle layer 26 . in another embodiment , the antenna is disposed in outer wall 28 . in one embodiment , stent 38 comprises a microprocessor 43 that is operatively connected to transmitting element 24 , receiving element 32 , power source 40 , and antenna 42 . in one embodiment , the remote unit 44 is a data acquisition unit . in another embodiment , the remote unit 44 is a control unit . in yet another embodiment , the remote unit 44 is both a data acquisition unit and a control unit . for example , one may use the telemetry system disclosed in u . s . pat . no . 5 , 843 , 139 , “ remotely operable stent .” by way of further illustration , one may use the remote system disclosed in u . s . pat . no . 5 , 843 , 139 and the like . acoustic energy may also be employed . see , for example , u . s . pat . no . 6 , 170 , 488 , “ acoustic - based remotely interrogated diagnostic implant device and system .” [ 0051 ] fig1 is a flowchart that illustrates one process of the invention . in steps 46 to 54 , a baseline measurement is obtained . in step 46 , the stent is exposed to the conditions of operation . by way of illustration , if the stent is to be disposed in a blood vessel , then blood is allowed to flow through the stent . in step 48 , a wave is transmitted across the lumen of the stent . the intensity of the wave is recorded in the microprocessor of the stent . in step 50 , the energy wave is received . step 52 then compares the intensity of the wave received in step 50 to the intensity of the wave transmitted in step 48 . in step 54 , this comparison value ( i . e . the baseline value ) is recorded in the stent &# 39 ; s microchip . alternatively or additionally , the recorded value may be transmitted to a remote unit ( see , for example , fig1 ). in one embodiment , several baseline values are recorded , and an acceptable “ baseline range ” is obtained . in steps 56 to 66 illustrated in fig1 , the stent performs a diagnostic procedure to detect any possible restenosis that may have occurred since the baseline measurement was recorded . in step 56 , the stent is allowed to operate normally for a period of time . in step 58 , a wave is transmitted across the lumen of the stent . the intensity of the wave is recorded in the microprocessor of the stent . in step 60 , the energy wave is received . step 62 then compares the intensity of the wave received in step 60 to the intensity of the wave transmitted in step 58 . step 64 compares the value obtained from step 62 to the baseline ( or baseline range ). step 66 , which is optional , is a step the stent performs depending on the value obtained in step 64 . [ 0053 ] fig1 is a flow chart that depicts step 64 in more detail . in step 68 , the value obtained from step 64 is compared to the baseline obtained in step 54 . if the value is within an acceptable range , then path 78 will be followed . in one embodiment , step 70 is executed , wherein no action is taken . in another embodiment , step 72 is followed , wherein the value obtained in step 64 is transmitted to a remote unit . if the value obtained in step 64 is outside of an acceptable range , then path 80 is followed . in one embodiment , not shown , no action is taken . in another embodiment , step 74 is taken , wherein the value obtained in step 64 is transmitted to a remote unit ( step 74 ). in another embodiment , a therapeutic response is triggered ( step 76 ). in yet another embodiment , both step 74 and 76 are executed . a number of therapeutic responses may be triggered . in one embodiment , an anticoagulant is released to counteract restenosis . in another embodiment , a therapeutic agent is released . in another embodiment , the therapeutic agent released acts to counteract restenosis . reference may be had , for example , to u . s . pat . nos . 5 , 865 , 814 ; 6 , 613 , 084 ; 6 , 613 , 082 ; 6 , 656 , 162 ; 6 , 589 , 546 ; 6 , 545 , 097 ; 6 , 491 , 666 ; 6 , 379 , 382 ; 6 , 344 , 028 ; 5 , 865 , 814 and the like . the content of each of these patents is hereby incorporated by reference . as would be apparent to one skilled in the art , the release of the agent may be triggered remotely by remote unit 44 , and need not necessarily be coupled to the value obtained in step 64 . in another embodiment , the therapeutic response comprises a release of energy of sufficient intensity to counteract restenosis . reference may be had to u . s . pat . nos . 6 , 709 , 693 ; 6 , 200 , 307 ; 5 , 964 , 751 and the like . the content of each of these patents is hereby incorporated by reference . the telemetry means taught above may also be used to reprogram microprocessor 43 in vivo . thus , it is possible to trigger the remote activation of steps 46 to 54 without removing the stent from the body . additionally or alternative , a range of acceptable deviation values may be remotely programmed or reprogrammed via remote unit 44 . as would be apparent to one skilled in the art , a variety of forms of energy may be used with the instant invention . in one embodiment , vibrational energy is used . in another embodiment , acoustic energy is used . in one embodiment , a piezoelectric crystal is used to generate the acoustic energy . in another embodiment electromagnetic radiation is used . in one embodiment , the electromagnetic energy used is vacuum uv radiation . in another embodiment , the energy used is near uv energy . in another embodiment the energy used is visible light . in another embodiment the energy used is infrared radiation . in yet another embodiment , the energy used is radio frequency energy . in one embodiment , the energy used has a wavelength between about 400 nm and about 750 nm . in another embodiment , the energy used has a wavelength between about 600 nm and about 700 nm . in another embodiment , the wavelength of the energy is between about 1 nm and about 400 nm . in another embodiment , the wavelength of energy used is between about 750 nm and about 3 μm . in yet another embodiment , the wavelength of energy used is between about 3 μm and 30 μm . in yet still another embodiment , the wavelength of energy used is between 30 μm and 1 mm . in another embodiment , the wavelength of energy used is between about 1 m and about 10 5 m , and preferably between 1 m and 10 3 m . in yet another embodiment , the wavelength of energy used is between 10 − 3 m and 1 m . numerous methods for the manufacturing and implantation of stents and modified stents are well known to those skilled in the art . reference may be had to u . s . pat . nos . 6 , 527 , 919 ; 6 , 190 , 393 ; 6 , 124 , 523 ; 6 , 096 , 175 and the like . it is , therefore , apparent that there has been provided , in accordance with the present invention , a method and apparatus for the detection of restenosis within a stent . while this invention has been described in conjunction with preferred embodiments thereof , it is evident that many alternatives , modifications , and variations will be apparent to those skilled in the art . accordingly , it is intended to embrace all such alternatives , modifications and variations that fall within the spirit and broad scope of the appended claims .
a medical apparatus is disclosed for determining the degree of restenosis of a stent comprising a stent , an energy transmitter , an energy receiver , and a processor to compare the transmitted energy and the received energy .