Sensors Used In Medical Field 4y4l44

SENSORS USED IN MEDICAL FIELD  1 Temperature Sensor Technology  2 Flow Sensors for Liquids  3 Flow Sensors for Respiratory Gases  4 Biomedical Sensors of Ionizing Radiation  5 Sensors for Radiometric and Photometric Measurements  6 Medical Ultrasound Sensors  7 Chemical Sensors for Biomedical Applications  8 Biosensors  9 Sensors for Medical Thermography and Infrared Radiation Measurements

TEMPERATURE SENSORS  Many different kinds of temperature sensors are currently used in different types of probes (surface, indwelling), catheters, or needles making with or introduced to the object site of the body  Types : 1) Resistance based a. Resistance Temperature Devices b. Thermistors 2) Thermoelectric – Thermocouples 3) Radiation Thermometry

1) RTD :  RTDs are made of materials whose resistance changes in accordance with temperature  Metals such as platinum, nickel and copper are commonly used.  They exhibit a positive temperature coefficient.  Resistance thermometers are slowly replacing thermocouples in many industrial applications because they have greater stability, accuracy, and repeatability.

THERMOCOUPLE :  Thermocouples are one of the most popular temperature sensors.  temperature sensors measure their own temperature  When a pair of dissimilar metals are ed at one end, and there is a temperature difference between the ed ends and the open ends, thermal emf is generated, which can be measured in the open ends.(SEEBECK EFFECT)  Because of their physical characteristics, thermocouples are the preferred method of temperature measurement in many applications, including clinical applications. No other temperature sensor provides this degree of versatility.

THERMISTORS :  Thermistors are made from semiconductor material.  Generally, they have a negative temperature coefficient (NTC)  Thermistors are used in digital thermometers  Generally, they have a negative temperature coefficient (NTC) SEMICONDUCTOR THERMOMETERS:  Semiconductor thermometers are produced in many types and shapes in the form of ICs  A typical example is the LM35 series (National Semiconductor, Santa Clara, CA) precision IC

ULTRASONIC SENSORS :  Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor.  Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object  Since ultrasonic sensors can visualize the internal condition of the human body without damaging them, they are widely used in various medical inspections including prenatal examinations to which radiography cannot be applied.  Because of it's ability of real-time visualization, the sensors can also be used for tissue biopsy sampling or therapeutics while locating the target organ.

 Ultrasonic sensors are used for diagnosis of internal organs including liver, kidneys, pancreas and gallbladder or watching fetal growth and health condition of the pregnant women.  Ultrasonic sensors are used for breast cancer check-ups to detect the presence of lumps under breasts or any changes in their shape, and for thyroid gland examinations to detect the presence of lumps inside the neck.  Ultrasonic scanners are used for cardiac diagnosis to capture the size of the heart and to check it for shape or movement abnormality as well as to determine the heart blood flow condition.  Ultrasonic sensors are used to check the blood flow, initimal thickness measurement (IMT) and endothelical function test (FMD), helping detection of arteriosclerosis. (yet to : glucose,pH,piezo,EEG/ECG,piezo)

GLUCOSE SENSORS :

Glu cos e  O2  GluconicAcid  H2 O2 Glu cos eOxidase

 Makes use of catalytic (enzymatic) oxidation of glucose  The setup contains an enzyme electrode and an oxygen electrode and the difference in the readings indicates the glucose level.  The enzyme electrode has glucose oxidase immobilized on a membrane or a gel matrix.

BIOSENSORS :  A biosensor is an analytical device which converts a biological response into an electrical signal  The term 'biosensor' is often used to cover sensor devices used in order to determine the concentration of substances and other parameters of biological interest

Figure 6.1. Schematic diagram showing the main components of a biosensor. The biocatalyst (a) converts the substrate to product. This reaction is determined by the transducer (b) which converts it to an electrical signal. The output from the transducer is amplified (c), processed (d) and displayed (e).

The key part of a biosensor is the transducer (shown as the 'black box' in Figure 6.1) which makes use of a physical change accompanying the reaction. This may be 1. the heat output (or absorbed) by the reaction (calorimetric biosensors), 2. changes in the distribution of charges causing an electrical potential to be produced (potentiometric biosensors), 3. movement of electrons produced in a redox reaction (amperometric biosensors), 4. light output during the reaction or a light absorbance difference between the reactants and products (optical biosensors), or 5. effects due to the mass of the reactants or products (piezo-electric biosensors).  The electrical signal from the transducer is often low and superimposed upon a relatively high and noisy (i.e. containing a high frequency signal component of an apparently random nature, due to electrical interference or generated within the electronic components of the transducer) baseline.  The signal processing normally involves subtracting a 'reference' baseline signal, derived from a similar transducer without any biocatalytic membrane,

BLOOD GLUCOSE METER :

 The most important application of bio-sensors is the blood glucose meter  A glucose meter (or glucometer) is a medical device for determining the approximate concentration of glucose in the blood. It can also be a strip of glucose paper dipped into a substance and measured to the glucose chart.  A small drop of blood, obtained by pricking the skin with a lancet, is placed on a disposable test strip that the meter reads and uses to calculate the blood glucose level. The meter then displays the level in mg/dl or mmol/l.

 Glucose meters require a precision analog front end to interface to the optical or bio-sensor based glucose sensor.  The sensor detects the optical properties of the chemical strip as it reacts with a blood sample.  The analog front end includes up to four channels of trans impedance amplifiers with a gain stage, a precision ADC, and a very accurate voltage reference.  Multiple precision DACs are also required to properly bias the sensor. Other design requirements include LCD drive, Real time Clock (RTC), very low power consumption and interface. Consistent performance across temperature (0-50C) is also essential to ensure accurate diagnosis of unsafe blood glucose levels.

IMPLANTABLE SENSORS :  Implantable sensors need to be small, lightweight and compatible with body mass as well as require very little power to operate.  Most importantly, they must not decay over time  The power requirement is one of the major challenges for implantable sensors  Piezoelectric polymer sensors are well suited for vibration detection since they are small, reliable, durable and require no power.  Such sensors can be used in pacemakers that monitor activities of the patient.  This Piezo sensor is in the shape of a tiny cantilever beam with weight attached on one end that flops with body movement. Every time the patient moves, the sensor generates a signal. Using a pacemaker as an example, the pacemaker then receives this signal and makes the heart beat at the desired pace.

 The sensor can differentiate between various activities such as walking, running, or other physical activities.  For instance, if the patient is resting, the signal will be zero and the pacemaker will make the heart beat at a minimal rate. In this way, the sensor signal is proportional to the level of activity  Implanted sensors can also be powered by external sources. For example, an RF (radiofrequency) energy wand when placed near a sensor located inside the body will power the sensor up. The sensor will then record patient measurements, transmit the data back to the wand via RF link and return to hibernation.  Another example of using an implanted sensor in this way is that of a post abdominal aortic aneurysm procedure where an implanted sensor can monitor the pressure leaks at the surgical location