Bio Medical
Content
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MEDICAL ELECTRONIC APPLICATIONS
INTRODUCTION
• Biomedical engineering is the application of engineering principles and techniques to the medical field. This field seeks to close the gap between engineering and medicine. It combines the design and problem solving skills of engineering with medical and biological sciences to improve healthcare diagnosis and treatment. Prominent biomedical engineering applications include the development of biocompatible prostheses, various diagnostic and therapeutic medical devices ranging from clinical equipment to micro-implants, common imaging equipment such as MRIs and EEGs, biotechnologies such as regenerative tissue growth, and pharmaceutical drugs and biopharmaceuticals.
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What is Biomedical? What are its common applications?
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GENERAL MEDICAL INSTRUMENTATION SYSTEM
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The sensor converts energy or information from the measurand to another form (usually electric). This signal is then processed and displayed so that humans can perceive the information.
GENERAL MEDICAL INSTRUMENTATION SYSTEM
MEASURAND • The physical quantity, property, or condition that the system measures is called measurand. Categories: • Biopotential • Pressure • Flow • Dimensions (imaging) • Displacement (velocity, acceleration, and force) • Impedance • Temperature • Chemical Concentrations • The measurand may be localized to a specific organ or anatomical structure.
FUNCTIONAL COMPONENTS OF THE INSTRUMENTATION SYSTEM
GENERAL MEDICAL INSTRUMENTATION SYSTEM
SENSOR • A sensor converts a physical measurand to an electric output. • It responds only to the form of energy present in the measurand. Primary sensing element Variable-conversion element How a sensor works? If a measurand is in the form of pressure, the primary sensing element should be a diaphragm – converts pressure to displacement; the variable-conversion element should be a strain gage – converts displacement to electric voltage.
FUNCTIONAL COMPONENTS OF THE INSTRUMENTATION SYSTEM
GENERAL MEDICAL INSTRUMENTATION SYSTEM
SIGNAL CONDITIONING • Signal conditioners amplify and filter the output signal from the sensor or merely match the impedance of the sensor to the display device. • For example, signal filtering may reduce undesirable sensor signals. It may also average repetitive signals to reduce noise, or it may convert information from the time domain to the frequency domain.
FUNCTIONAL COMPONENTS OF THE INSTRUMENTATION SYSTEM
OUTPUT DISPLAY • The results of the measurement process must be displayed in a form that a human operator can perceive. The forms for the display may be numerical or graphical, discrete or continuous, permanent or temporary, etc.
GENERAL MEDICAL INSTRUMENTATION SYSTEM
AUXILIARY ELEMENTS • Control and feedback • A calibration signal with the properties of the measurand should be applied to the sensor input or as early in the sensorprocessing chain as possible. • These elements are required to elicit the measurand, to adjust the sensor and signal conditioning, and to direct the flow of output for display, storage, or transmission.
FUNCTIONAL COMPONENTS OF THE INSTRUMENTATION SYSTEM
STETHOSCOPE
• Stethoscopes are used for listening to sounds from inside the body. Acoustic stethoscopes operate on the transmission of sound from the chest piece, via air-filled hollow tubes, to the listener's ears. The chestpiece usually consists of two sides that can be placed against the patient for sensing sound — a diaphragm (plastic disc) or bell (hollow cup). If the diaphragm is placed on the patient, body sounds vibrate the diaphragm, creating acoustic pressure waves which travel up the tubing to the listener's ears. If the bell is placed on the patient, the vibrations of the skin directly produce acoustic pressure waves traveling up to the listener's ears. The bell transmits low frequency sounds, while the diaphragm transmits higher frequency sounds.
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STETHOSCOPE
SPHYGMOMANOMETER
• Sphygmomanometer is used to check blood pressure.
How to use a sphygmomanometer? To check the blood pressure (BP), the cuff is wrap around the upper A normal blood arm first. Next, by using hand bulb, pumps air into the cuff, gently squeezing the arm and temporarily interrupting the flow of blood. The pressure is pressure gauge reaches a peak. This stop the blood flow to the artery. 120/80 Then the cuff is slowly deflated, letting blood flow again. As the cuff deflates and the pressure gauge gradually decreases, the return of the blood flow through the main artery in the arm can be heard using a stethoscope. The reading on the pressure gauge when the pulse is first heard is the systolic pressure (the peak pressure as the heart contracts). The reading when the pulse can first no longer be heard is the diastolic pressure (the lowest pressure as the heart relaxes between beats). A normal blood pressure is 120/80
SPHYGMOMANOMETER
• MEASUREMENT PROCESS
X-RAY GENERATOR
• An X-ray generator is a device used to generate X-rays. Xray machines are used in health care for visualizing bone structures and other dense tissues such as tumours.
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How does x-ray machine works? X-ray machines work by applying controlled voltage and current to the X-ray tube, which results in a beam of X-rays. The beam is projected on matter. Some of the X-ray beam will pass through the object, while some are absorbed. The resulting pattern of the radiation is then ultimately detected by a detection medium including rare earth screens (which surround photographic film), semiconductor detectors, or Xray image intensifiers.
X-RAY GENERATOR
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X-RAY TUBE Parts
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Diagram showing relationship of xray tube, patient, detector, and image reconstruction computer and display monitor.
COMPUTED TOMOGRAPHY SCAN
• Computed Tomography (CT) Scan is fast, patient friendly and has the unique ability to image a combination of soft tissue, bone, and blood vessels. It is based on the x-ray principle: as x-rays pass through the body, they are absorbed or attenuated (weakened) at differing levels creating a matrix or profile of x-ray beams of different strength. This x-ray profile is registered on film, thus creating an image.
Outside view of modern CT system showing the patient table and CT scanning patient aperture Inside view of modern CT system, the x-ray tube is on the top at the 1 o'clock position and the arc-shaped CT detector is on the bottom at the 7 o'clock position. The frame holding the x-ray tube and detector rotate around the patient as the data is gathered.
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COMPUTED TOMOGRAPHY SCAN
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CT SCAN Parts
CT image of the brain
MAGNETIC RESONANCE IMAGING
• MRI is primarily a noninvasive medical imaging technique used in radiology to visualize detailed internal structure and limited function of the body.
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MRI provides much greater contrast between the different soft tissues of the body than computed tomography (CT) does, making it especially useful in neurological (brain), musculoskeletal, cardiovascular, and oncological (cancer) imaging.
Unlike CT, MRI uses no ionizing radiation. Rather, it uses a powerful magnetic field to align the nuclear magnetization of (usually) hydrogen atoms in water in the body.
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MAGNETIC RESONANCE IMAGING
• MRI Parts and Block Diagram
MAGNETIC RESONANCE IMAGING
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HOW IT WORKS?
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In MRI, it is the unpaired nuclear spins of hydrogen protons that are of importance. When protons are placed in a magnetic field they behave like a magnet and become aligned with the external field. The frequency of the photon in MRI is in the radio frequency (RF) range. The tube contains a thick coil of wire that generates a very intense magnetic field. In order to generate a magnetic field of this strength the coil is cooled to near absolute zero with liquid helium. This very strong magnetic field is then used to align the hydrogen nuclei of the tissue to be imaged. The RF coil is used to both change the energy state of the hydrogen nuclei and to record the RF output of these perturbations.
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ULTRASONIC IMAGING
• Ultrasonography is an ultrasound-based diagnostic imaging technique used to visualize body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Obstetric sonography is commonly used during pregnancy and is widely recognized by the public. In physics, the term "ultrasound" applies to all acoustic energy (longitudinal, mechanical wave) with a frequency above the audible range of human hearing. The audible range of sound is 20 hertz-20 kilohertz. Ultrasound is frequency greater than 20 kilohertz.
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ULTRASONIC IMAGING
TYPICAL BLOCK DIAGRAM
Longitudinal waves (L-waves) compress and decompress the material in the direction of motion, much like sound waves in air. Shear waves (S-waves) vibrate particles at right angles compared to the motion of the ultrasonic wave. The velocity of shear waves through a material is approximately half that of the longitudinal waves.
The blank circles represent points of at which user control is introduced.
ULTRASONIC IMAGING
• TRANSDUCER It acts as a loudspeaker or a microphone, it converts electrical signals to ultrasound waves, and picks up the reflected waves, converting them back into electrical signals.
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
Simplest type of transducer used in ultrasonic imaging is called B-mode transducer. Other types are annular array, linear array, and curvilinear array transducers.
B-mode transducer is a circular single-element transducer with a fixed geometric focus. Annular array transducers are also circular but are composed of several (4 to 12) rings. Linear array transducers are built by dividing a piezoceramic strip into a large number of line-source-like elements. Curvilinear array transducers are built on a curved surface.
ULTRASONIC IMAGING
• PULSER Piezoceramic array elements are energized using a pulser. A pulse waveform is typically a short burst of one to three cycle duration.
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
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TRANSMITTER/RECEIVER (T/R) SWITCHES T/R switches are used to isolate the high voltages associated with pulsing from the sensitive amplification stage(s) associated with the variable gain stage. VARIABLE GAIN STAGE It is also called the TGC stage. The TGC stages supply the gain required to compensate for the attenuation brought by the propagation of sound tissue. The value of the gain is under user control. The dynamic range available from typical TGC amplifiers is in the order of 60dB.
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ULTRASONIC IMAGING
• BEAMFORMER (BEAM FORMATION) It is composed of two separate processes: beam steering and
focusing.
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
Focusing – is the modification of the localized phases of the acoustic beam so as to cause constructive interference at desired locations. Steering Three Methods: • Mechanical Steering – is the simplest method. It is used to reorient a transducer to predetermined set or orientations. • Element Selection Steering – this method doesn’t strictly steer the beam but rather changes the location of its origin. • Phased Arrays Steering –is achieved by adding an incremental delay to the firing time of each array elements that is linearly related to the element’s position.
ULTRASONIC IMAGING
• BEAMFORMER (BEAM FORMATION) Steering Focusing
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
ULTRASONIC IMAGING
• BEAMFORMER (BEAM FORMATION)
Steering Methods
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
(a) Mechanical (b and c) Phased Array (d) Element Selection
ULTRASONIC IMAGING
• COMPRESSION There is a logarithmic compression of the amplified signal after the beam formation. The goal of this is to emphasize the subtle gray level differences between the scatterers from the various types of tissues and from the diffuse disease conditions. DETECTION In purely analog approaches, simple full wave-rectification followed by a low pass filtering is considered to work well in envelope detection. It is also possible to digitize the RF signals earlier in the processing chain, perform compression and detection process digitally, and use quadrature detection to determine the signal envelope.
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
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ULTRASONIC IMAGING
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COMPONENTS OF ULTRASONIC IMAGING SYSTEM
SIGNAL PROCESS
ULTRASONIC IMAGING
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COMPONENTS OF ULTRASONIC IMAGING SYSTEM
DISPLAY OUTPUT
Using Linear Array
Using B-Mode
CARDIAC PACEMAKER
• A cardiac pacemaker is an electric stimulator that produces electric pulses that are conducted to electrodes normally located within the lining of the heart (the endocardium). The stimulus conducted to the heart causes it to contract – this effect can be used prosthetically in disease states in which the heart is not stimulated at a proper rate on its own (heart block). Cardiac pacemakers are either of the unipolar or the bipolar type. Unipolar type – a single electrode is in contact with the heart, and the negative-going pulses are connected to it from the generator. Bipolar type – two electrodes are placed within the heart, and the stimulus is applied across theses electrodes.
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CARDIAC PACEMAKER
• PARTS
1. 2. 3. 4. 5. 6. 7. 8.
Bundle Branches Purkinje Fibers Electrode Terminal (Front) Electrode Terminal (Rear) Electrode Tip Heart Pacemaker (Pulse Generator) Subclavian Vein
CARDIAC PACEMAKER
• Asynchronous pacemaker It is the first type of pacemaker that was developed. A cardiac pacemaker that is free running. It gives a fixed heart rate.
BLOCK DIAGRAM
The power supply is used to supply energy to the pacemaker circuit. The oscillator establishes the pulse rate for the pacemaker. It controls the pulse output circuit that provides the stimulating pulse to the heart. This pulse is conducted along lead wires to the cardiac electrodes.
CARDIAC PACEMAKER
• Synchronous pacemaker It is used when a human’s heart can establish a normal cardiac rhythm between periods of block. This means that it is not necessary to stimulates the ventricles continuously.
There are two general forms of synchronous pacemakers: the demand pacemaker and the arial-synchronous
pacemaker.
CARDIAC PACEMAKER
• Synchronous pacemaker The demand-type pacemaker BLOCK DIAGRAM
It consists of a timing circuit, an output circuit, electrodes, and a feedback loop. The timing circuit is set to run at a fixed rate, usually 60 to 80 beats/min. after each stimulus, the timing circuit resets itself, waits the appropriate interval to provide the next stimulus, and then generates the next pulse.
CARDIAC PACEMAKER
• Synchronous pacemaker The artial-synchronous pacemaker
BLOCK DIAGRAM
It is designed to replace the blocked conduction system of the heart. The heart’s physiological pacemaker, located at the SA node, initiates the cardiac cycle by stimulating the atria to contract and then providing a stimulus to the AV node, which, after appropriate delay, stimulates the ventricle. V1 is a pulse that corresponds to each beat. The atrial signal is then amplified and passed through a gate to a monostable multivibrator giving a pulse V2 of 120ms duration.
CARDIAC PACEMAKER
• Synchronous pacemaker The artial-synchronous pacemaker
BLOCK DIAGRAM (continuation)
Another monostable multivibrator giving a pulse duration of 500ms is also triggered by the atrial pulse. It produces V4, which causes the gate to block any signals from the atrial electrodes for a period of 500ms following contraction. This eliminates any artifact caused by the ventricular contraction from stimulating additional ventricular contractions. The falling edge of the 120ms duration pulse, V2, is used to trigger a monostable multivibrator of 2ms duration. Then V3 controls an output circuit that applies the stimulus to appropriate ventricular electrodes.
MUSCLE STIMULATOR
• Stimulators can be used in physical therapy to determine whether muscle groups are able to contract by applying external stimuli to these muscles and observing the results.
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Stimulators are especially useful in cases in which temporary paralysis can result from atrophy of the muscle caused by disuse, which significantly reduces the mass of the muscle.
Electric stimulation of muscle can regain function of paralyzed muscles when the paralysis is a result of neurological injury.
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MUSCLE STIMULATOR
• Muscle stimulator --- problems in stroke victims Stroke victims encounter gait problems that are evidenced in a condition known as drop foot. A Drop Foot Prosthesis
It consists of a switch in the heel of the patient’s shoe. The contacts of the switch close when the patient takes weight off his foot. This switch controls a stimulator that continuously stimulates the muscles responsible for lifting the foot. When the individual again places weight on the foot, the switch contacts are opened and the stimulus is stopped.
NERVE STIMULATOR
• A nerve stimulator supplies electrons to depolarise a nerve. The number of electrons supplied per stimulus equals the current. To make sure that the nerve is completely depolarised, continuous winding up of the stimulating current should be done until the muscular response does not increase any more, then add another 10%. As a result the muscle must be maximally stimulated by the nerve. The muscle contraction that results must also be maximal. The contraction is also called a twitch. The muscle response to the stimulus is called a twitch. The amount or strength of movement is called the twitch height. To allow comparison of twitches it is essential that this current remains constant to ensure the nerve is always completely depolarised.
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NERVE STIMULATOR
• PLACEMENT OF ELECTRODES The outside of a 'resting' the nerve is charged positive. It is 'polarised'. If negative electrons are added to the outside they will neutralise the charge. This will cause that wave of depolarisation to wash down the nerve. The negative electrode should be attached as near as possible to a nerve, commonly the ulnar nerve at the wrist or the elbow. The other electrode can be placed anywhere else along the line of the nerve, commonly half way along the forearm.
NERVE STIMULATOR
• TYPES OF NERVE STIMULATORS
Changing resistance
The connection between the electrodes and the skin is not constant. If the electrodes dry out or come a bit loose from the skin their resistance will increase. There are two ways a nerve stimulator can respond to this change...with a constant voltage or a constant current. Voltage = Current x Resistance
Constant Voltage Nerve Stimulators
Constant voltage nerve stimulators are relatively easy and cheap to make. Unfortunately if the voltage remains constant when resistance increases then the current must decrease. As a result the nerve may not be completely stimulated. The muscle contraction will then be depressed. Some constant voltage nerve stimulators will display the current actually delivered and will alarm if it falls below some predefined threshold.
NERVE STIMULATOR
• TYPES OF NERVE STIMULATORS
Constant Current Nerve Stimulators
Constant current nerve stimulators are the safest but also the most expensive to build. As the resistance of the electrodes goes up they compensate by increasing their voltage. As a result the current stays constant. The stimulation of the nerve remains constant. Any change in response is occurring at the neuromuscular junction or in the muscle itself. There is a limit to how high the nerve stimulator can raise the voltage. At this point the stimulator should give an audible and visual alarm that the stimulating current has not been reached
ELECTROCARDIOGRAM
• • Electrocardiogram is commonly known as ECG. The ECG is the most commonly performed cardiac test. This is because the ECG is a useful screening tool for a variety of cardiac abnormalities; ECG machines are readily available in most medical facilities; and the test is simple to perform, risk-free and inexpensive.
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How is the ECG performed? The patient will lie on an examination table, and 10 electrodes (or leads) are attached to his arms, legs, and chest. The electrodes detect the electrical impulses generated by his heart, and transmit them to the ECG machine. The ECG machine produces a graph (the ECG tracing) of those cardiac electrical impulses. The electrodes are then removed. The test takes less than 5 minutes to perform.
ELECTROCARDIOGRAM
• What information can be gained from the ECG? From the ECG tracing, the following information can be determined: the heart rate the heart rhythm whether there are ―conduction abnormalities‖ (abnormalities in how the electrical impulse spreads across the heart) whether there has been a prior heart attack whether there may be coronary artery disease whether the heart muscle has become abnormally thickened
ELECTROCARDIOGRAM
• ECG BLOCK DIAGRAM
MEDICAL ELECTRONIC APPLICATIONS
INTRODUCTION
• Biomedical engineering is the application of engineering principles and techniques to the medical field. This field seeks to close the gap between engineering and medicine. It combines the design and problem solving skills of engineering with medical and biological sciences to improve healthcare diagnosis and treatment. Prominent biomedical engineering applications include the development of biocompatible prostheses, various diagnostic and therapeutic medical devices ranging from clinical equipment to micro-implants, common imaging equipment such as MRIs and EEGs, biotechnologies such as regenerative tissue growth, and pharmaceutical drugs and biopharmaceuticals.
•
What is Biomedical? What are its common applications?
•
•
GENERAL MEDICAL INSTRUMENTATION SYSTEM
•
The sensor converts energy or information from the measurand to another form (usually electric). This signal is then processed and displayed so that humans can perceive the information.
GENERAL MEDICAL INSTRUMENTATION SYSTEM
MEASURAND • The physical quantity, property, or condition that the system measures is called measurand. Categories: • Biopotential • Pressure • Flow • Dimensions (imaging) • Displacement (velocity, acceleration, and force) • Impedance • Temperature • Chemical Concentrations • The measurand may be localized to a specific organ or anatomical structure.
FUNCTIONAL COMPONENTS OF THE INSTRUMENTATION SYSTEM
GENERAL MEDICAL INSTRUMENTATION SYSTEM
SENSOR • A sensor converts a physical measurand to an electric output. • It responds only to the form of energy present in the measurand. Primary sensing element Variable-conversion element How a sensor works? If a measurand is in the form of pressure, the primary sensing element should be a diaphragm – converts pressure to displacement; the variable-conversion element should be a strain gage – converts displacement to electric voltage.
FUNCTIONAL COMPONENTS OF THE INSTRUMENTATION SYSTEM
GENERAL MEDICAL INSTRUMENTATION SYSTEM
SIGNAL CONDITIONING • Signal conditioners amplify and filter the output signal from the sensor or merely match the impedance of the sensor to the display device. • For example, signal filtering may reduce undesirable sensor signals. It may also average repetitive signals to reduce noise, or it may convert information from the time domain to the frequency domain.
FUNCTIONAL COMPONENTS OF THE INSTRUMENTATION SYSTEM
OUTPUT DISPLAY • The results of the measurement process must be displayed in a form that a human operator can perceive. The forms for the display may be numerical or graphical, discrete or continuous, permanent or temporary, etc.
GENERAL MEDICAL INSTRUMENTATION SYSTEM
AUXILIARY ELEMENTS • Control and feedback • A calibration signal with the properties of the measurand should be applied to the sensor input or as early in the sensorprocessing chain as possible. • These elements are required to elicit the measurand, to adjust the sensor and signal conditioning, and to direct the flow of output for display, storage, or transmission.
FUNCTIONAL COMPONENTS OF THE INSTRUMENTATION SYSTEM
STETHOSCOPE
• Stethoscopes are used for listening to sounds from inside the body. Acoustic stethoscopes operate on the transmission of sound from the chest piece, via air-filled hollow tubes, to the listener's ears. The chestpiece usually consists of two sides that can be placed against the patient for sensing sound — a diaphragm (plastic disc) or bell (hollow cup). If the diaphragm is placed on the patient, body sounds vibrate the diaphragm, creating acoustic pressure waves which travel up the tubing to the listener's ears. If the bell is placed on the patient, the vibrations of the skin directly produce acoustic pressure waves traveling up to the listener's ears. The bell transmits low frequency sounds, while the diaphragm transmits higher frequency sounds.
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STETHOSCOPE
SPHYGMOMANOMETER
• Sphygmomanometer is used to check blood pressure.
How to use a sphygmomanometer? To check the blood pressure (BP), the cuff is wrap around the upper A normal blood arm first. Next, by using hand bulb, pumps air into the cuff, gently squeezing the arm and temporarily interrupting the flow of blood. The pressure is pressure gauge reaches a peak. This stop the blood flow to the artery. 120/80 Then the cuff is slowly deflated, letting blood flow again. As the cuff deflates and the pressure gauge gradually decreases, the return of the blood flow through the main artery in the arm can be heard using a stethoscope. The reading on the pressure gauge when the pulse is first heard is the systolic pressure (the peak pressure as the heart contracts). The reading when the pulse can first no longer be heard is the diastolic pressure (the lowest pressure as the heart relaxes between beats). A normal blood pressure is 120/80
SPHYGMOMANOMETER
• MEASUREMENT PROCESS
X-RAY GENERATOR
• An X-ray generator is a device used to generate X-rays. Xray machines are used in health care for visualizing bone structures and other dense tissues such as tumours.
•
How does x-ray machine works? X-ray machines work by applying controlled voltage and current to the X-ray tube, which results in a beam of X-rays. The beam is projected on matter. Some of the X-ray beam will pass through the object, while some are absorbed. The resulting pattern of the radiation is then ultimately detected by a detection medium including rare earth screens (which surround photographic film), semiconductor detectors, or Xray image intensifiers.
X-RAY GENERATOR
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X-RAY TUBE Parts
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Diagram showing relationship of xray tube, patient, detector, and image reconstruction computer and display monitor.
COMPUTED TOMOGRAPHY SCAN
• Computed Tomography (CT) Scan is fast, patient friendly and has the unique ability to image a combination of soft tissue, bone, and blood vessels. It is based on the x-ray principle: as x-rays pass through the body, they are absorbed or attenuated (weakened) at differing levels creating a matrix or profile of x-ray beams of different strength. This x-ray profile is registered on film, thus creating an image.
Outside view of modern CT system showing the patient table and CT scanning patient aperture Inside view of modern CT system, the x-ray tube is on the top at the 1 o'clock position and the arc-shaped CT detector is on the bottom at the 7 o'clock position. The frame holding the x-ray tube and detector rotate around the patient as the data is gathered.
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COMPUTED TOMOGRAPHY SCAN
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CT SCAN Parts
CT image of the brain
MAGNETIC RESONANCE IMAGING
• MRI is primarily a noninvasive medical imaging technique used in radiology to visualize detailed internal structure and limited function of the body.
•
MRI provides much greater contrast between the different soft tissues of the body than computed tomography (CT) does, making it especially useful in neurological (brain), musculoskeletal, cardiovascular, and oncological (cancer) imaging.
Unlike CT, MRI uses no ionizing radiation. Rather, it uses a powerful magnetic field to align the nuclear magnetization of (usually) hydrogen atoms in water in the body.
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MAGNETIC RESONANCE IMAGING
• MRI Parts and Block Diagram
MAGNETIC RESONANCE IMAGING
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HOW IT WORKS?
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In MRI, it is the unpaired nuclear spins of hydrogen protons that are of importance. When protons are placed in a magnetic field they behave like a magnet and become aligned with the external field. The frequency of the photon in MRI is in the radio frequency (RF) range. The tube contains a thick coil of wire that generates a very intense magnetic field. In order to generate a magnetic field of this strength the coil is cooled to near absolute zero with liquid helium. This very strong magnetic field is then used to align the hydrogen nuclei of the tissue to be imaged. The RF coil is used to both change the energy state of the hydrogen nuclei and to record the RF output of these perturbations.
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ULTRASONIC IMAGING
• Ultrasonography is an ultrasound-based diagnostic imaging technique used to visualize body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Obstetric sonography is commonly used during pregnancy and is widely recognized by the public. In physics, the term "ultrasound" applies to all acoustic energy (longitudinal, mechanical wave) with a frequency above the audible range of human hearing. The audible range of sound is 20 hertz-20 kilohertz. Ultrasound is frequency greater than 20 kilohertz.
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ULTRASONIC IMAGING
TYPICAL BLOCK DIAGRAM
Longitudinal waves (L-waves) compress and decompress the material in the direction of motion, much like sound waves in air. Shear waves (S-waves) vibrate particles at right angles compared to the motion of the ultrasonic wave. The velocity of shear waves through a material is approximately half that of the longitudinal waves.
The blank circles represent points of at which user control is introduced.
ULTRASONIC IMAGING
• TRANSDUCER It acts as a loudspeaker or a microphone, it converts electrical signals to ultrasound waves, and picks up the reflected waves, converting them back into electrical signals.
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
Simplest type of transducer used in ultrasonic imaging is called B-mode transducer. Other types are annular array, linear array, and curvilinear array transducers.
B-mode transducer is a circular single-element transducer with a fixed geometric focus. Annular array transducers are also circular but are composed of several (4 to 12) rings. Linear array transducers are built by dividing a piezoceramic strip into a large number of line-source-like elements. Curvilinear array transducers are built on a curved surface.
ULTRASONIC IMAGING
• PULSER Piezoceramic array elements are energized using a pulser. A pulse waveform is typically a short burst of one to three cycle duration.
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
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TRANSMITTER/RECEIVER (T/R) SWITCHES T/R switches are used to isolate the high voltages associated with pulsing from the sensitive amplification stage(s) associated with the variable gain stage. VARIABLE GAIN STAGE It is also called the TGC stage. The TGC stages supply the gain required to compensate for the attenuation brought by the propagation of sound tissue. The value of the gain is under user control. The dynamic range available from typical TGC amplifiers is in the order of 60dB.
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ULTRASONIC IMAGING
• BEAMFORMER (BEAM FORMATION) It is composed of two separate processes: beam steering and
focusing.
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
Focusing – is the modification of the localized phases of the acoustic beam so as to cause constructive interference at desired locations. Steering Three Methods: • Mechanical Steering – is the simplest method. It is used to reorient a transducer to predetermined set or orientations. • Element Selection Steering – this method doesn’t strictly steer the beam but rather changes the location of its origin. • Phased Arrays Steering –is achieved by adding an incremental delay to the firing time of each array elements that is linearly related to the element’s position.
ULTRASONIC IMAGING
• BEAMFORMER (BEAM FORMATION) Steering Focusing
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
ULTRASONIC IMAGING
• BEAMFORMER (BEAM FORMATION)
Steering Methods
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
(a) Mechanical (b and c) Phased Array (d) Element Selection
ULTRASONIC IMAGING
• COMPRESSION There is a logarithmic compression of the amplified signal after the beam formation. The goal of this is to emphasize the subtle gray level differences between the scatterers from the various types of tissues and from the diffuse disease conditions. DETECTION In purely analog approaches, simple full wave-rectification followed by a low pass filtering is considered to work well in envelope detection. It is also possible to digitize the RF signals earlier in the processing chain, perform compression and detection process digitally, and use quadrature detection to determine the signal envelope.
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
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ULTRASONIC IMAGING
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COMPONENTS OF ULTRASONIC IMAGING SYSTEM
SIGNAL PROCESS
ULTRASONIC IMAGING
•
COMPONENTS OF ULTRASONIC IMAGING SYSTEM
DISPLAY OUTPUT
Using Linear Array
Using B-Mode
CARDIAC PACEMAKER
• A cardiac pacemaker is an electric stimulator that produces electric pulses that are conducted to electrodes normally located within the lining of the heart (the endocardium). The stimulus conducted to the heart causes it to contract – this effect can be used prosthetically in disease states in which the heart is not stimulated at a proper rate on its own (heart block). Cardiac pacemakers are either of the unipolar or the bipolar type. Unipolar type – a single electrode is in contact with the heart, and the negative-going pulses are connected to it from the generator. Bipolar type – two electrodes are placed within the heart, and the stimulus is applied across theses electrodes.
•
•
CARDIAC PACEMAKER
• PARTS
1. 2. 3. 4. 5. 6. 7. 8.
Bundle Branches Purkinje Fibers Electrode Terminal (Front) Electrode Terminal (Rear) Electrode Tip Heart Pacemaker (Pulse Generator) Subclavian Vein
CARDIAC PACEMAKER
• Asynchronous pacemaker It is the first type of pacemaker that was developed. A cardiac pacemaker that is free running. It gives a fixed heart rate.
BLOCK DIAGRAM
The power supply is used to supply energy to the pacemaker circuit. The oscillator establishes the pulse rate for the pacemaker. It controls the pulse output circuit that provides the stimulating pulse to the heart. This pulse is conducted along lead wires to the cardiac electrodes.
CARDIAC PACEMAKER
• Synchronous pacemaker It is used when a human’s heart can establish a normal cardiac rhythm between periods of block. This means that it is not necessary to stimulates the ventricles continuously.
There are two general forms of synchronous pacemakers: the demand pacemaker and the arial-synchronous
pacemaker.
CARDIAC PACEMAKER
• Synchronous pacemaker The demand-type pacemaker BLOCK DIAGRAM
It consists of a timing circuit, an output circuit, electrodes, and a feedback loop. The timing circuit is set to run at a fixed rate, usually 60 to 80 beats/min. after each stimulus, the timing circuit resets itself, waits the appropriate interval to provide the next stimulus, and then generates the next pulse.
CARDIAC PACEMAKER
• Synchronous pacemaker The artial-synchronous pacemaker
BLOCK DIAGRAM
It is designed to replace the blocked conduction system of the heart. The heart’s physiological pacemaker, located at the SA node, initiates the cardiac cycle by stimulating the atria to contract and then providing a stimulus to the AV node, which, after appropriate delay, stimulates the ventricle. V1 is a pulse that corresponds to each beat. The atrial signal is then amplified and passed through a gate to a monostable multivibrator giving a pulse V2 of 120ms duration.
CARDIAC PACEMAKER
• Synchronous pacemaker The artial-synchronous pacemaker
BLOCK DIAGRAM (continuation)
Another monostable multivibrator giving a pulse duration of 500ms is also triggered by the atrial pulse. It produces V4, which causes the gate to block any signals from the atrial electrodes for a period of 500ms following contraction. This eliminates any artifact caused by the ventricular contraction from stimulating additional ventricular contractions. The falling edge of the 120ms duration pulse, V2, is used to trigger a monostable multivibrator of 2ms duration. Then V3 controls an output circuit that applies the stimulus to appropriate ventricular electrodes.
MUSCLE STIMULATOR
• Stimulators can be used in physical therapy to determine whether muscle groups are able to contract by applying external stimuli to these muscles and observing the results.
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Stimulators are especially useful in cases in which temporary paralysis can result from atrophy of the muscle caused by disuse, which significantly reduces the mass of the muscle.
Electric stimulation of muscle can regain function of paralyzed muscles when the paralysis is a result of neurological injury.
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MUSCLE STIMULATOR
• Muscle stimulator --- problems in stroke victims Stroke victims encounter gait problems that are evidenced in a condition known as drop foot. A Drop Foot Prosthesis
It consists of a switch in the heel of the patient’s shoe. The contacts of the switch close when the patient takes weight off his foot. This switch controls a stimulator that continuously stimulates the muscles responsible for lifting the foot. When the individual again places weight on the foot, the switch contacts are opened and the stimulus is stopped.
NERVE STIMULATOR
• A nerve stimulator supplies electrons to depolarise a nerve. The number of electrons supplied per stimulus equals the current. To make sure that the nerve is completely depolarised, continuous winding up of the stimulating current should be done until the muscular response does not increase any more, then add another 10%. As a result the muscle must be maximally stimulated by the nerve. The muscle contraction that results must also be maximal. The contraction is also called a twitch. The muscle response to the stimulus is called a twitch. The amount or strength of movement is called the twitch height. To allow comparison of twitches it is essential that this current remains constant to ensure the nerve is always completely depolarised.
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NERVE STIMULATOR
• PLACEMENT OF ELECTRODES The outside of a 'resting' the nerve is charged positive. It is 'polarised'. If negative electrons are added to the outside they will neutralise the charge. This will cause that wave of depolarisation to wash down the nerve. The negative electrode should be attached as near as possible to a nerve, commonly the ulnar nerve at the wrist or the elbow. The other electrode can be placed anywhere else along the line of the nerve, commonly half way along the forearm.
NERVE STIMULATOR
• TYPES OF NERVE STIMULATORS
Changing resistance
The connection between the electrodes and the skin is not constant. If the electrodes dry out or come a bit loose from the skin their resistance will increase. There are two ways a nerve stimulator can respond to this change...with a constant voltage or a constant current. Voltage = Current x Resistance
Constant Voltage Nerve Stimulators
Constant voltage nerve stimulators are relatively easy and cheap to make. Unfortunately if the voltage remains constant when resistance increases then the current must decrease. As a result the nerve may not be completely stimulated. The muscle contraction will then be depressed. Some constant voltage nerve stimulators will display the current actually delivered and will alarm if it falls below some predefined threshold.
NERVE STIMULATOR
• TYPES OF NERVE STIMULATORS
Constant Current Nerve Stimulators
Constant current nerve stimulators are the safest but also the most expensive to build. As the resistance of the electrodes goes up they compensate by increasing their voltage. As a result the current stays constant. The stimulation of the nerve remains constant. Any change in response is occurring at the neuromuscular junction or in the muscle itself. There is a limit to how high the nerve stimulator can raise the voltage. At this point the stimulator should give an audible and visual alarm that the stimulating current has not been reached
ELECTROCARDIOGRAM
• • Electrocardiogram is commonly known as ECG. The ECG is the most commonly performed cardiac test. This is because the ECG is a useful screening tool for a variety of cardiac abnormalities; ECG machines are readily available in most medical facilities; and the test is simple to perform, risk-free and inexpensive.
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How is the ECG performed? The patient will lie on an examination table, and 10 electrodes (or leads) are attached to his arms, legs, and chest. The electrodes detect the electrical impulses generated by his heart, and transmit them to the ECG machine. The ECG machine produces a graph (the ECG tracing) of those cardiac electrical impulses. The electrodes are then removed. The test takes less than 5 minutes to perform.
ELECTROCARDIOGRAM
• What information can be gained from the ECG? From the ECG tracing, the following information can be determined: the heart rate the heart rhythm whether there are ―conduction abnormalities‖ (abnormalities in how the electrical impulse spreads across the heart) whether there has been a prior heart attack whether there may be coronary artery disease whether the heart muscle has become abnormally thickened
ELECTROCARDIOGRAM
• ECG BLOCK DIAGRAM
