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Running head: Instrumentation for Measuring Brain Function

Chapter 13Instrumentation for Measuring Anatomical

and Physiological ParametersMeasuring Structures and Functions

Prepared For:

Professor J. GreenBy:

Carlie R. Gilliard

D03137879

DeVry/DecaturSummer B

BMET312

10/09/2010


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Abstract

Instrumentation, in technology: The development and use of precise measuring equipment.

Although the sensory organs of the human body can be extremely sensitive and responsive,

modern science and technology rely on the development of much more precise measuring and

analytical tools for studying, monitoring, or controlling all kinds of phenomena. The brain fills

the top half of the head. The brain and the spinal cord form the central nervous system (CNS). It

is the coordination system for the entire body. It can store memories and is the site of the

thinking mind. Ideas, emotions, like and dislike, hopes, and dreams come from the brain. From

the brain millions of microscopically tiny nerve fibers like miniature cables carrying cables

throughout all parts of the body. Today we will discuss the biomedical instrumentation system:

The major difference between this system of medical instrumentation and conventional

instrumentation is that the source of the signals is living tissue or energy to living applied to

living tissue.


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Table of Contents


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Introduction

Instrumentation used to measure anatomical and physiological parameters of the brain

includes X-ray equipment, ultrasonic equipment, and electrophysiological equipment. The brain

and the spinal cord form the central nervous system (CNS). We can think of the central nervous

system as a central processing unit (CPU), much like a CPU: Sending, receiving, processing

pertinent information; and regulates and controls the locomotor system (Brown, Carr 2009).

Simply put, the human brain integrates as well as assimilates data from the outside world as

well as our internal organs. Messages are transmitted by a nerve signal which is small voltage

pulse (0.25mV) with duration of 0.33 msec. The signal travels along the outer skin of the cell

membrane. It is due to the Na+ and K+ ions. When the signal reaches from one cell to the

synapse or gap between the next cells which is

width of human hair, there is a released of

chemicals call neurotransmitters. Which flow into the cup-like receptors of the adjacent cell

(Campbell, Reece, Taylor, Simon, and Dickey 2009). Thus the signal passes from one cell to the

next cell. With biomedical instrumentation the structures and functions of the brand can be

measured. The physical quantity, property, or condition, that the system measure is called the

measurand. The accessibility of the measurand is imperative because it may emanate from the

body (infared radiation). Most medically important measurands can be grouped into the

following categories: Biopotential, pressure flow, dimensions (imaging), and chemical

concentrations. The measurand may be localized to a specific organ or anatomical structure

(Carr, Brown 2009).


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In Chapter 13 of the Carr Brown text describes the various and diverse types of

equipment used in measuring and diagnosing our brain. This chapter interest are on three basic

types of radiological equipment used in measuring the structures and functions of the brain: X-

Ray, ultrasonic, and electrophysiological devices. The equipment described in this chapter

conveys a thorough understanding of how these devices are used to diagnose problems within the

brain. It covers the differences of the equipment and how they are used with more detail focus

on the electroencephalography (EEG) system. It is based on six distributed contact electrodes

that measure brain signals on the scalp. The voltage produced is strong enough to reliably extract

EEG potentials in the microvolt range.

The EEG system topics cover the functions of the equipment to read low voltages picked

up from the scalp emitted by the brain as it functions. Frequency ranges and types of waveforms

received are then used to display patterns the lead to proper diagnosis of specific illnesses.


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Before measuring can be undertaken, ordinary EEG devices have to be mounted on the patients

head in a lengthy, time-consuming process. The single electrodes have to be filled with

electrolyte gel to achieve electrical contact with the scalp. Setting up such a device takes about

30 minutes

The last part of the chapter covers the actual amplification factors used in retrieving the

information and forming it into a readable form. The breakdown of the EEG system is explained

thoroughly with a simplified block diagram. S

ections 13-14 through 13-17, discuss the typical EEG recording artifacts, faults,

troubleshooting, and maintenance of an EEG system. It explains step by step procedures to

troubleshoot and correct errors that may occur while using an EEG. Three scenarios are giving,

which explains the symptoms, possible causes, and trouble shooting.


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Instrumentation for Measuring Brain Function

Instrumentation used to measure the brain consist of both anatomical (structure) and

physiological (function) parameters. They include X-ray, ultrasonic, and electrophysiological

types of equipment. X-ray equipment transmits a high-energy electromagnetic light waves in the

radioactive range to pass though the body and be picked up by a photographic plate. The denser

the tissue the less light passes though and results in a lighter area plate. X-rays can be used in

different functions to determine different diagnosis of the brain.

Cerebral angiography is a function of the use of x-rays which uses contrast, a radiopaque

dye injected into a patient. The contrast blocks the light and can be used to highlight brain

structures and blood vessels. Nuclear medicine is a different type of contrast that is much safer

because it is short lived in the body. As the body absorbs the contrast x-rays are taken and can

show gland function. Another function is the cranial x-rays. This two dimensional x-ray is used

to find fractures, blood clots and tumors in the brain. One disadvantage is that the contrast of the


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density of the tissue must be high in order to easily read the x-ray. X-rays can also be used by

successive scanning of the brain and using a highly collimated x-ray beams call brain scans.

This provides a better contrast of tissue in the brains and is easier to read than cranial x-rays.

Computed tomography (CT) scans take images in thin layers with a pencil beam. By

taking many layers in concession a computer can reconstruct the images into a three dimensional

image. But one of the best x-ray functions is the whole body scanner. It gives more detail and

resolution for better diagnostic quality but it is very costly.

Ultrasonic equipment transmits high-frequency sound waves into the body that are

reflected back to form an image. Reflection speed of the sound depends on the density of the

tissue and recording this speed in a computer creates an internal image of the brain. Diagnostic

ultrasonography is covered in more detail in chapter 17. This chapter covers

echoencephalography which is a sonogram of the brain used to quickly detect tumors, dilated

brain ventricles and hemorrhages. The principles of the sonogram work like that of a radar or

sonar. It emits short burst of sound at pulse frequencies at or near 2.5 MHz. The echo back

indicates the distance. Unlike an image it is shown in a graph form and pecks may indicate a

tumor or swelling.


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The Electroencephalography system uses electrodes attached to the scalp to read the low

voltages emitted by the firing of the neurons within the brain. These small voltages are

amplified and filtered to provide a waveform on paper or a computer screen. It is used to help

and assist physicals and neurologist localize cerebral brain lesions, study epilepsy, mental

disorders, sleep patterns, and brain activity during sensory stimuli. There are five types of

electrodes typically used.

1. Scalpsilver pads, discs, or cups; stainless steel rods; and chloride silver wires.


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2. Sphenoid - alternating insulated silver and bare wire and chloride tip inserted thoughmuscle tissue by a needle.

3. Nasopharyngealsilver rod with silver ball at the tip inserted though the nostrils.4. Electrocorticographiccotton wicks soaked in saline solution that rest on the brain

surface (removes artifacts generated in the cerebrum by each heartbeat).

5. Intracerebralsheaves of Teflon-coated gold or platinum wires cut at variousdistances from the sheaf tip and used to electrically stimulate the brain.

(Carr & Brown, 2001)

Waveforms:

Alpharelaxed BetaAlert (excited) ThetaDrowsy DeltaDeep sleep Gamma - attention

rt


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The EEG and the 10-20 system refer to the placement of the electrodes on the scalp at

and 10% to 20% distance across the cranium. The placement of the electrode corresponds to

areas of the brains different functions. A total of nineteen electrodes are used with one used for

reference. The patterns are distinguished by location, frequency, amplitude, form, periodicity,

and functional properties. (Carr & Brown, 2001) The earlobe is used as a common to supply the

differential amplifier input with an inactive reference. Two types of recording are made unipolar

and bipolar. Unipolar is the difference between active and inactive sites where bipolar is

recorded between active to active sites.

EEG frequency bands are classified into five categories: Delta (0.5-4 Hz), Theta (4-8 Hz),

Alpha (8-13 Hz), Beta (13-22 Hz), and Gamma (22-30 Hz). Delta wave usually has the highest

amplitude, and occurs when the user is asleep. Theta waves are usually seen when the individual

is drowse. Alpha waves occur by closing the eye lids and by relaxation. Beta waves are

attenuated during active moments. The Gamma represents the binding of different populations of

neurons together into a network for the purpose of carrying out motor function. The EEG can

help us determine if patients have a sleep disorder. The dramatic changes in the amplitude and

frequencies can determine which sleep disorder is occurring.

Clinical EEG machines consist of 8, 16, or 32 channels. The most common is the 8

channel device which has 20 cranial electrodes. The EEG machines have been improved over

the years, making them small and more accurate.

An EEG system Simplified Block Diagram can explain an EEG systems operation. The

principal parts and functions are represented by blocks connected by lines which are aimed more

at understanding the overall concept of implementation.


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An example of an EEG system is on page 383 (Carr, Joseph J., Introduction to the

Biomedical Equipment Technology Fourth Edition). This Simplified Block Diagram illustrates

an eight channel EEG System. Twenty electrodes are placed on the patients head, and these are

switchselected to the input of eight differential input, single ended output. The eight outputs

are further amplified and presented to eight driver or power amplifiers that supply sufficient

current to drive the pen deflectors. A calibration signal Generator is usually connected to the

electrode switch selector box to check the system operation. The amplitude of the calibration

signal gives an indication of the correct sensitivity settings. The amplifier can be adjusted if the

readings are not within specifications. Also a low voltage power supply is important in a EEG

system because the low-level input signals can easily pick 60 Hz noise as well as external noise.

The EEG output signal can be converter in an analog to digital converter and then analyzed by a

computer or store.

Preamplifiers and EEG system specification

The most important component of an EEG system is the preamplifiers (differential

amplifiers).

The characteristics of an EEG differential amplifier: low internal noise, high gain, high common-

mode rejection ratio, low-frequency ac-coupled operation, low dc drift, and high input

impedance. The single-ended amplifier simply provides a ground for the one head electrode and

uses the other as an active site. The equation for finding the current resulting from the cranial

voltage source is:


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e is the cranial voltage source acting through cranial impedance, r represent equivalent electrode head resistance is the input impedance of the electronic amplifier impedance

current

To avoid signal attenuation and reduce possible shock hazard is to have high input

impedance in the EEG preamplifiers. The single-ended input operational amplifier has a serious

disadvantage compare to the differential amplifier. It will amplify noise voltages induced from

lights or power equipment by the same amount as the signal. When the noise amplitude is larger

than the EEG signal, the EEG recordings will be obscured. The differential input amplifier stops

most of the noise pickup problem. Noise is usually capacitive coupled into both inputs (C 1 and

C2). When the Gain (G1) equals the Gain (G2) the noise signals will be cancelled. The amplifier

gain equals G1- G2 and amplified noise equals (e1noisee2noise) * G. G equal total gain, and e1noise

e2noise equals zero. But e1EEG is not equal to e2EEG, so the difference is not equal. The

differential amplifier subtracts the two unequal input EEG signals to produce an amplified EEG

output. It also subtracts the equal noise signals to produce zero noise output or a very small

output.

EEG preamplifiers are the predominant stage that influences EEG machine specifications.

EEG machine specifications typically include:

1. Input impedance: 12 M min. at 10 Hz.2. Sensitivity: 0.5 V/mm max.3. Sensitivity controls: 10-position master (2 to 75 V/mm), six-position individual

channel (200.25), and individual-channel gain equalizer.


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4. Calibration voltages: 5 to 1000 V.5. CMRR: 2000 or 66 dB min at 60 Hz and 10,000 or 80 dB min at 10 Hz.6. Noise: 1 VRMS with input shorted.7. Low frequency: 30% attenuation0.16 through 5.3 Hz, at time constants of one

through 0.03 s, respectively.

8. Low frequency response: 30% attenuation at 1 to 1000 Hz.9. 60 Hz filter: 50 dB down at 60 Hz.10.Chart speeds: 10 to 60 mm/s.

Visual and auditory evoked potential recordings

Early EEG investigators discovered that cortical potentials could be evoked from sensory

stimulus of some sort (visual, auditory, etc.). Cortical potential is the rapid fluctuations of

voltage between parts of the cerebral cortex that are detectable with an EEG. Most evoked

responses on the scalp are too small to be recorded by typical EEG machines. Small evoked

signals are very small to read so a technique called Averaging Repetitive EEG Signals is used to

separate the evoked signals from the background EEG.


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Conclusion

X-ray, ultrasonic, and electrophysiological equipment help physicians and neurologist

study and diagnose illnesses in the brain. This chapter focuses on the understanding the basic

functionality of the different types of systems used to measure the brain. By use of these types

of equipment both anatomical and physiological functions can be observed. Also the proper

maintenance of these machines will help keep them running efficiently. Routine inspections must

be done daily. Knowing how to troubleshoot will greatly prepare the user for any situation that

maybe encounter.


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References

Carr, J. J., & Brown, J. M. (2001).Introduction to Biomedical Equipment Technology.

Columbus, Ohio: Prentice Hall.

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Instrumentation for Measuring Brain Function[1] Rev1 Auto Saved)