JP7604230B2 - Blood Glucose Tracking System - Google Patents

Description

The present invention relates generally to non-invasive in vivo blood glucose measurement systems, and more particularly to a personalized subcutaneous blood glucose measurement and tracking system for instantaneous real-time readings of blood glucose levels.

For decades, attempts have been made to develop systems to directly read and non-invasively measure glucose levels in the bloodstream in "real time." However, to date, these attempts have been unsuccessful, primarily due to the inherent nature of glucose itself, which dissolves readily in blood, and the containment nature of the bloodstream in the human body, making it extremely difficult to directly and non-invasively measure glucose present in the bloodstream.

Historically, attempts to measure blood glucose levels have favored optical means, using visible or infrared light, or by detecting changes in polarized light due to variations in glucose levels in the blood. These attempts have repeatedly proven unsuccessful, as have other attempts to measure blood glucose levels directly and non-invasively.

Currently available continuous glucose monitoring systems actually measure interstitial fluid glucose levels rather than directly measuring blood glucose levels. As a result, such "blood glucose" systems and meters are unable to provide "real-time" blood glucose readings. Also, such systems inherently suffer from a substantial time lag, typically around 20 minutes, due to the correlation of interstitial fluid measurements to blood glucose readings.

It is generally recognized that blood glucose levels can be measured relatively accurately via microwave means in vitro under controlled laboratory conditions. However, prior art measurement devices have lacked the ability to perform these measurements in vivo. While clinically useful measurements may be possible under such fixed laboratory conditions, the automatic calibration mechanisms required to develop these simple laboratory measurement devices into systems suitable for routine use with real organisms that exhibit individual and mutually varying characteristics, as well as mechanisms and embodiments that allow for non-invasive blood glucose readings in the actual "field", have not previously existed.

In view of the above, there is a need for a true (direct read) blood glucose measurement system that is non-invasive and can be used in vivo without exhibiting the inherent measurement variability and time lag for determining blood glucose measurements typically associated with prior art "blood glucose" meters that are in fact "interstitial fluid" measurement devices. Accordingly, it is a general object of the present invention to provide a novel blood glucose tracking system that provides a novel, optimized and efficient approach to blood glucose measurement, tracking and monitoring that is non-invasive, measures blood glucose directly and can be performed in vivo without exhibiting measurement variability and time lag.

The present invention of a blood glucose tracking system and method operates differently than previous attempts at "blood glucose" meters and non-invasive measurement devices of the prior art. The present invention measures the total emitted microwave energy transmission and subsequent vascular reception within a defined and fixed target area, without replicating the specialized and optimized equipment required to measure glucose levels in solution under controlled laboratory conditions, and then compares this instantaneous measurement to a previous calibrated value to obtain an accurate calculation of said glucose value directly from the bloodstream. The difference between the instantaneous power reading measurement and the previous calibrated power reading measurement can be analyzed and calculated to determine the resulting blood glucose value. This can be further adapted through additional sensing values that compensate for various biological or ambient factors and changes to the individual patient. Additionally, the determined blood glucose value can be displayed for reading and/or transmitted and stored for record-keeping for future reference.

Unlike all currently available continuous "blood glucose" meters (which in fact measure interstitial fluid rather than directly measure blood glucose as discussed above), the blood glucose tracking system according to the present invention actually reads the instantaneous glucose concentration in the bloodstream. And unlike prior art meters that read interstitial fluid, the present system provides real-time blood glucose readings with no time lag between the measurement and the actual blood glucose reading. Moreover, such real-time measurements allow blood glucose levels to be measured and monitored in vivo, preferably utilizing a compact measurement unit that can be worn by an individual for in vivo use.

The systems and methods of the present invention differ substantially from other prior art systems and methods primarily in that the present invention is directed to a direct absorption measurement system and does not specifically rely on measuring transmitted energy transmitted from a transmitting element to a receiving element through a layer of skin and/or other parts of the body.

According to a preferred embodiment of the present invention, the blood glucose measurement system and method utilizes a microwave energy source that preferably transmits radio frequency energy, with a short duty cycle, high impulse power, and very low average power. Blood composition as a whole contains, on average, about 92% water. It is a well-known fact that water containing glucose absorbs microwave energy more than water without glucose. By utilizing this phenomenon, practical methods exist that can ultimately detect and measure instantaneous glucose levels in the bloodstream non-invasively in vivo. According to a preferred embodiment, the microwave energy from the energy source is fed to an antenna assembly designed to focus and transmit the energy toward the appropriate subcutaneous blood vessels, i.e., the blood vessels closest to the surface of the skin. In a further preferred embodiment, the energy source and antenna assembly are provided in a housing that can be attached to a part of the body adjacent to the subcutaneous blood vessels of the patient, more preferably in a housing that can be attached to the patient's arm, and even more preferably as part of a bracelet or watch that can be attached to the patient's wrist, so as to measure the desired target area.

A unique and important feature of the blood glucose measurement system and method of the present invention is the use of a radio frequency (RF) mask that is individually tailored for each target patient and the individual's desired target area. Such an RF mask allows the transmitted microwave energy to reach only the exact target area, such as a specific portion of a blood vessel near the skin surface. By optimizing the antenna radiation lobe pattern, the selected transmission frequency, and the power level used, the microwave energy may be contained, shaped, and directed exclusively to a location and depth that conforms to a specifically defined area that includes the "close to the skin surface" blood vessels. The RF mask also limits the area where the RF energy can be directed and transmitted, essentially limiting the measurement of energy that may be absorbed outside of the desired target area. This greatly improves the accuracy of readings using the system and method of the present invention.

In one aspect of the invention, microwave energy is contained and shaped to a depth that conforms to a particular area, including subcutaneous blood vessels, and directed exclusively to the desired target area. Preferably, the antenna assembly is positioned adjacent the desired target area. In such an embodiment, the antenna radiation lobe pattern, transmission frequency and power level can be varied for a particular patient and that patient's target area.

In a preferred embodiment of the present invention, the power levels required to reach the target subcutaneous blood vessels are achieved by using pulsed radio emission similar to that used in radar transmitters.

According to an embodiment of the invention, for each calibration, a known glucose value and its corresponding delivered power value can be placed into a memory buffer. As the subject's glucose value changes, the average power level received into the bloodstream through the system will rise or fall relative to the power value associated with the last calibration value. With each subsequent periodic microwave emission, the measurement unit records all new data and calculates the blood glucose value based on an extrapolation of the change in delivered/received power level between the instantaneous power level and the previous calibration value.

The objects, features and advantages of the present invention will become apparent from the description of the illustrated embodiments and their features taken in conjunction with the accompanying drawings.
FIG. 1 shows a schematic embodiment of a blood glucose tracking system according to the present invention for non-invasive in-vivo blood glucose measurement. FIG. 1 illustrates another embodiment of a blood glucose tracking system according to the present invention integrated into a wristwatch. FIG. 13 shows yet another embodiment of a blood glucose tracking system according to the present invention in which an auxiliary housing containing an antenna is connected to a watch or bracelet containing a wireless transmitter, ideally worn on the wrist. FIG. 1 illustrates a schematic embodiment of a blood glucose tracking system that provides data relating to determined blood glucose levels to a computer, display, or memory buffer as appropriate. FIG. 1 illustrates another schematic embodiment of a blood glucose tracking system associated with two transmitters. FIG. 2 shows a mask that is applied to a patient to limit the area that can receive energy transmitted from a measurement device according to the present invention. 4 is a flow chart illustrating a test sequence according to a preferred embodiment of the present invention.

Referring to FIG. 1, a schematic embodiment of a blood glucose tracking system according to the present invention for non-invasive in-vivo blood glucose measurement is shown. The system generally comprises a measurement unit 10 having a microwave energy source (e.g., transmitter 12) operably connected to an antenna assembly 16 via a coaxial cable or waveguide, the antenna assembly comprising an antenna 14. The transmitter 12 and antenna 14 may be located within a common antenna housing 18 as shown, or may be located in separate units provided they are operably connected to each other. The antenna assembly also preferably comprises a controller/processor 24 used to measure the amount of power/energy delivered via the antenna 14. The transmitter 12 may also be in operative communication with the controller 24.

The transmitter 12 preferably comprises a microwave energy source that transmits radio frequency energy, and more preferably emits pulsed radio emissions similar to those used in radar transmitters, with a short duty cycle, high impulse power, and very low average power.
The transmitter 12 supplies microwave energy to an antenna 14 for focusing and transmitting toward an appropriate subcutaneous blood vessel 20 in a desired target area 50 of the patient. In use, the measurement device 10 measures microwave energy absorbed by nearby blood vessels 20 to assist in determining blood glucose levels within the target area 50. More specifically, the controller 24 determines how much of the energy generated by the transmitter 12 is output by the antenna 14 to measure the power delivered to the blood vessels 20. As shown in FIG. 1, the antenna housing 18 is placed on or near the patient's skin S in close proximity to the subcutaneous blood vessels 20 to be measured, such as on the patient's wrist.

Referring to the schematic diagram shown in FIG. 7, the system can accurately calculate the patient's blood glucose level in a defined and fixed target area 50 by measuring the total amount of radiated microwave energy transmitted and preferably absorbed by the subcutaneous blood vessels 20 in the target area 50, i.e., the blood vessels 20 "close to the skin surface." Instantaneous real-time measurements taken directly from the blood flow can be compared to a predetermined calibration value. The difference between the measurement and the calibration value, i.e., the "delta" value, can provide the resultant blood glucose value through analysis and calculation. In a preferred embodiment, an algorithm is used to correlate the power energy value to the blood glucose value to determine the resultant blood glucose value. Such an algorithm is preferably stored in the controller 24. The calibration value can be stored in a memory buffer 22 provided as part of the controller 24.

The location for accurate measurement of subcutaneous blood vessels 20 according to the present invention is generally preferred near an individual's wrist. However, the system of the present invention may be used at other locations on the body without departing from the spirit and scope of the present invention. Thus, the antenna 14 is preferably positioned adjacent to the desired target area 50, preferably by placing the antenna housing 18 on the skin surface S proximate the desired target area 50. A unique and important feature of the system of the present invention is the use of an RF mask 52, generally shown in FIG. 6, that is individually tailored for each target patient and the desired target location 50. This allows the microwave energy delivered by the antenna 14 to precisely reach only the target area, such as a specific portion of the blood vessel 20 near the skin surface. By further optimizing the antenna radiation lobe pattern, the selected transmission frequency, and the power level used, the microwave energy can be further contained, shaped, and exclusively directed to a depth that is consistent with the specific area, including the blood vessel 20 "close to the skin surface." Note that the skin S in these areas is very thin, making it easier to actually see the location of the blood vessel, and that in these areas there is little in the path between the antenna 14 and the target blood vessel 20 to unduly attenuate or interfere with the transmission path.

The system and method of the present invention differs substantially from other prior art systems and methods in that the present invention is a direct absorption measurement system and does not specifically rely on measuring transmitted energy transmitted from a transmitting element to a receiving element through a layer of skin and/or other parts of the body.

As generally shown in FIG. 6, in use, an RF mask 52 is created for an individual patient, then laid and temporarily attached to the patient's skin S over the desired target area 50, and then used with the measurement unit 10 described herein for blood glucose measurement and tracking. The RF mask 52 also limits the area into which RF energy can be transmitted, essentially limiting the measurement of energy that can be absorbed outside of the target area 50. This greatly improves the accuracy of the reading. A preferred method for creating an individually tailored RF mask 52 is described in more detail below.

As mentioned above, the power levels required to reach the target subcutaneous blood vessels 20 are achieved by using pulsed radio radiation similar to that used in radar transmitters. Although the "peak" power levels may be relatively high (to penetrate the skin to the required depth), the duty cycle of these radiations is very low, resulting in very low "average" power levels. This makes such radio transmitters 12 very energy efficient, and such radiation, in contrast to the continuous wave radiation commonly used in laboratory equipment, does not result in a temperature rise that is perceptible by the individual wearing the system.

The extrapolation process to determine the amount of energy absorbed (e.g., power reading measurements) may utilize one or more of the following processes, either alone or in combination:

In the first approach, the antenna assembly measures one of the forward radiation peak power level and/or average power level delivered at a particular radio frequency over a particular time frame. More specifically, as a microwave pulse is emitted from the antenna 14, its peak transmit power level and/or average power level is measured by the controller 24. A "delta" value is then determined by comparing the measured transmit energy power level with the calibration value recorded during the last calibration reading/measurement. The system, via an algorithm, identifies a newly calculated blood glucose reading that corresponds to the measured energy power level. More specifically, the algorithm correlates the particular blood glucose reading to the energy absorption data. The calculated/determined blood glucose reading may be provided to a display and/or memory buffer as needed.

In the second approach, instead of reading the forward power level actually delivered and/or received by the target vessel 20, the system measures the reflected energy power level in the vessel 20 of the desired target area 50 and compares it to a calibrated value to determine a "delta" value. In this case, a lower reflected power reading indicates more energy received within the target area 50, which represents a higher glucose level. The higher the glucose level in the blood, the more the blood tries to absorb the energy, resulting in a lower reflected power. Similar to the calculated "delta" value in the first approach, the system identifies a newly calculated blood glucose reading via an algorithm. The calculated/determined blood glucose reading may be provided to a display and/or memory buffer as needed.

In a third approach, the system measures standing wave ratio (SWR) readings from the transmitter 12 at a particular radio frequency and calculates from such measurements a "delta" value related to the calibration reading. In this case, the SWR reading generally tracks the blood glucose level. The SWR reading increases when the blood glucose level is low and decreases when the blood glucose level is high. Through an algorithm, the calculated "delta" value is again used to determine the appropriate blood glucose reading. This may be provided to a display and/or memory buffer as desired.

In the various processes described above, all power measurements are made at a fixed frequency. According to a fourth approach, the transmitter 12 is instructed to sequentially vary the transmission frequency in a predetermined manner, such that the frequency steps are repeated from low to high or high to low within a predetermined frequency range. The energy acceptance from each of the utilized individually transmitted radio frequencies is measured for peak or average power delivered and then compared to the other frequencies in the same measurement cycle. The shift in absorption rate between frequencies is tracked with the changing glucose value and extrapolated to a blood glucose value using one or more extrapolation methods. One embodiment that can be used in the method dynamically analyzes the location of the frequency that received the maximum energy absorption. This then becomes the "center" or "index" frequency. This "index" frequency is compared to the last calibrated "index" frequency to generate an offset value. This offset value is applied to a scaling algorithm to determine the calculated blood glucose value. This can then be provided to a display and/or memory buffer as required.

A similar approach can utilize the frequency hopping method of the fourth approach. However, rather than resolving and analyzing a "center" or "index" frequency, this approach analyzes all the energy changes at the various transmit frequencies to identify the "spread" or bandwidth of frequencies that exhibit microwave energy absorption activity above a predefined threshold, and then compares that instantaneous spread of frequencies above the threshold to the spread of readings obtained at the last calibration. An algorithm analyzes this increase or decrease in spread to derive a difference value. This value is applied to the algorithm to calculate the blood glucose reading, which can then be provided to a display and/or memory buffer as desired.

The measurement unit 10 records all new data for each subsequent periodic microwave emission and determines the blood glucose level based on an extrapolation of the change in delivered/accepted power level between the instantaneous power level and the previous calibration value. For example, if the calibration entry resulted in a direct blood glucose reading of 100 (assuming the system uses a 1:1 algorithm) and blood at that blood glucose level received 100 milliwatts of power from the transmitter 12, a new test reading indicating a 10% increase in power delivered to the target area 50 (i.e., to 110 milliwatts) would indicate a blood glucose level of 110 mg/dl.

In addition to power sensing via the base transmitter 12 and antenna assembly, the blood glucose tracking system and method according to the present invention may utilize additional optional compensation measures to improve the accuracy of blood glucose readings. Among these measures are the following:
(A) A pulse sensor is incorporated to compensate for changes in the rate of blood flow through the blood vessel 20. As blood flows faster or slower, the rate of energy acceptance changes and can detrimentally skew the results of calculations. To compensate for this, a pulse sensor is optionally incorporated to dynamically compensate for the variations.
(B) With a skin temperature sensor proximate the desired target area 50, temperature compensation is applied to optimize changes in vessel diameter (eg, vasodilation, vasoconstriction) due to variations in core temperature.
(C) Measuring the galvanic skin response, preferably in conjunction with skin temperature monitoring, can determine the level of sweating in the area of the measurement unit 10 that can distort microwave absorption rates, so that the system can compensate for sweating based on the measurement of the galvanic skin data.
(D) Although blood is typically 92% water on average, a patient's moisture level may vary widely. By using periodic microwave energy measurements at a frequency more resonant with water (as opposed to a frequency more resonant with glucose), the measurement unit 10 can be continuously calibrated to account for fluctuations in a patient's moisture level. By using either a dual band microwave transmitter, or a wideband single band transmitter capable of operating with a wide frequency variation, one of the frequencies or transmitters can be dedicated to monitoring water levels while the other is optimized for glucose detection, as described above.

Additional measuring and display means may be provided together with the measuring unit 10. For example, a display screen 26 may be provided on the antenna housing 18, as shown in Figs. 2 and 4. The measuring unit 10 may also be part of or in the form of a bracelet or watch 28 worn on the wrist, and may comprise a local unit attached to the skin S, for example by adhesive. As shown diagrammatically in Fig. 5, it may further comprise additional transmitter means 30 for transmitting data from the measuring unit 10 to another unit 32, such as a computer, tablet or smartphone. This allows the blood glucose measurements obtained by the measuring unit 10 to be displayed and/or recorded. For example, the measuring unit 10 in the form of a bracelet or watch 28 may store the measured data and then synchronize with the computer 32 to further store, monitor and analyze the blood glucose measurements of the patient.

As mentioned above and shown in FIG. 1, the blood glucose tracking system according to the present invention may be a separate "stand-alone" system or may be incorporated into an unrelated article worn on the wrist (such as a watch or jewelry). This allows for unobtrusive access to blood vessels 20 close to the skin surface of the wrist. In the case of a watch 28 containing a transmitter 12 and associated control elements, a small fixed or flexible portion of a miniature waveguide 34 is attached to the body of the watch 28, and the other end is connected to a removable auxiliary "sidecar" antenna housing 36 that is placed over the desired target area for measurement. Such an auxiliary antenna housing 36, containing an antenna 14 and associated control elements 24, is attached to the watch 28 when a measurement is made and is removed when not needed. Once the housings 18 and 36 are attached, the antenna 14 may be connected to the transmitter 12 via a waveguide or coaxial cable 34 that runs through the band of the watch 28. In the case of a wristwatch or "smartwatch" as shown in FIG. 2, in which the blood glucose tracking system of the present system is integrated, the existing digital readout 26 of the wristwatch 28 can be used to display instantaneous blood glucose readings.

Also, many other creative physical embodiments may be utilized without departing from the spirit and intent of the present invention, for example, by incorporating a metal shield to confine the antenna energy toward the adjacent desired target area 50, or by incorporating a battery to power the RF transmitter 12 or other device located within the watch band portion.

The system may also incorporate a separate data transmitter 30 (in addition to the sampling transmitter 12 as described above) that allows the output of raw or calculated data to be relayed to a separate display 32 or storage device 38, such as a computer, tablet or smart phone, or to a device such as an insulin pump 40. Depending on the make or model of these devices, the data output may be transmitted in a suitable proprietary format for display and/or storage, as described above.

The system and method according to the present invention derives an instantaneous glucose reading by comparing the difference between a "control" reading, where the glucose level is known, and an instantaneous reading, where the glucose level is not known and needs to be determined. The "control" reading may be a calibration value, which may be adjusted each time such a calibration measurement is made using the system (e.g., the new control measurement becomes the calibration value for the next measurement). To accurately extrapolate the instantaneous glucose reading at the level of microwave energy accepted, periodic calibration is performed using an appropriate measurement method, including traditional "finger stick" glucose measurement or other means of accurately determining the actual glucose level. This data provides the measurement unit 10 with a standard reference measurement, which is then used to compare with subsequent readings at the individual's specific body and target body location (such as a specific vein on the wrist), allowing subsequent glucose readings to be provided and tracked.

To create a unique, individually tailored RF antenna mask 52 as shown in FIG. 6, two preferred methods of mask creation can be utilized. The first "manual" method utilizes a thin strip of Mylar or other flexible transparent material that is temporarily wrapped around the individual's wrist or other area associated with the desired target area 50 and held in place. A marking pen is utilized to outline the exact target area 50 for the antenna 14 along the width of the subject's arm or other body area, which can provide subsequent positioning reference guidance. Once removed, a flexible sheet can be laid over the antenna mask blank and used to assist in cutting the mask opening. Once the RF mask 52 is created, it can be laid and temporarily attached over the patient's skin S in the desired target area 50 and used with the measurement unit 10 described herein for measuring and tracking blood glucose levels.

A second preferred RF mask fabrication method is an "automatic" method, where the desired target area 50 is photographed or scanned in the visible and/or thermal infrared spectrum. The thermal data can be further used to establish the optimal sensing area. Physical measurements of the general area surrounding the desired target area 50 are also taken. The resulting photographic data is fed to a laser cutting or CNC machine which scales the cutting information based on the measurements to automatically select and outline the unmasked areas to correspond to the optimized target area. The cutting machine can form the mask openings directly on the sheet of non-RF transparent material. This automatic selection process may occur as a result of either or both of the collected visible information or the collected thermal infrared information.

The above embodiments of the present invention have been described for the purpose of illustration and description. The above description is not intended to be exhaustive or to limit the present invention to the described form. Obvious modifications and variations are possible based on the above description. The embodiments described herein have been selected to best explain the principles and application methods of the present invention, and those skilled in the art can utilize the present invention in various embodiments and various modifications suitable for specific applications.

Claims (23)

A blood glucose measuring device, comprising:
an antenna housing having an antenna assembly with an antenna, the antenna housing configured to be placed on or near the patient's skin adjacent a desired target area that includes a blood vessel to be measured;
a transmitter operatively connected to the antenna for transmitting microwave energy through the antenna into a blood vessel in the target area;
the antenna assembly determines the microwave energy absorbed in blood vessels within the target area without the use of a receiving element to receive microwave energy transmitted within the target area, determining an absorbed microwave energy measurement that can be correlated to a blood glucose level of the patient.
Blood glucose measuring device. a controller for comparing the absorbed microwave energy measurement to a calibration value to identify a difference between the values and then determining a blood glucose level based on the difference.
The blood glucose measuring device according to claim 1 . The blood vessels in the desired target area are subcutaneous blood vessels.
The blood glucose measuring device according to claim 1 . configured to be placed on the patient's arm proximate the desired target area;
The blood glucose measuring device according to claim 1 . configured to be placed on the patient's wrist;
The blood glucose measuring device according to claim 4. and further comprising a strap to which the antenna housing is attached, the strap being configured to be wrapped around an arm of the patient.
The blood glucose measuring device according to claim 4. and a visual display for displaying measurement data corresponding to the absorbed microwave energy measurements.
The blood glucose measuring device according to claim 1 . and a second transmitter for transmitting the measurement data to an external device for at least one of displaying and storing the measurement data .
The blood glucose measuring device according to claim 1 . The microwave energy is in the form of microwave pulses.
The blood glucose measuring device according to claim 1 . The blood glucose measuring device of claim 1, wherein the antenna assembly measures an actual energy power level delivered to a blood vessel in the target area. 1. A method for measuring blood glucose in a patient, comprising:
establishing a calibration value for microwave absorption in blood vessels within a desired target area of said patient in relation to a known blood glucose level;
transmitting microwave energy into a blood vessel in the target area;
determining an amount of transmitted microwave energy absorbed by blood vessels within a target area without the use of a receiving element to receive the transmitted microwave energy within the target area to determine a measurement;
comparing the measured value to the calibration value to generate a calculated power difference value;
determining a blood glucose value representative of the calculated power difference value. The method of claim 11 , wherein the blood glucose level is determined by extrapolating a value from a measured power level absorbed in blood vessels within the target area. The method of claim 11 , wherein the power values associated with the known glucose values are used to generate calibration values for further blood glucose measurements of the patient. 12. The method of claim 11 , further comprising adjusting the calculated blood glucose value based on additional sensed values related to the patient's condition. The method of claim 14 , wherein the additional sensed values include at least one of the patient's pulse rate, skin temperature, galvanic skin response, and moisture level. The method of claim 11 further comprising the step of displaying the calculated blood glucose value. The method of claim 11 , further comprising storing the calculated blood glucose value and the calculated power delta value associated therewith. The method of claim 11 , further comprising the step of varying the transmission frequency of the microwave energy over a predetermined frequency range. The method of claim 11 , wherein the blood vessels in the desired target area are subcutaneous blood vessels. 12. The method of claim 11, further comprising the step of locating a measurement device on or near the patient's skin proximate the desired target area, the measurement device comprising an antenna housing having an antenna and a transmitter operatively connected to the antenna for transmitting the microwave energy via the antenna into a blood vessel in the target area . 21. The method of claim 20 , wherein the measurement device is placed on the patient's arm proximate the desired target area. The method of claim 21 , wherein the measurement device is placed on the patient's wrist. 21. The method of claim 20, further comprising the steps of creating a radio frequency mask correlating to the size, shape and location of the desired target area and placing the radio frequency mask on the patient's skin proximate to the desired target area prior to locating the measurement device.

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