Transcript Medical Imaging and Biosignal Acquisitionx

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WEEK 4 PRACTICAL
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If possible, bring along a pair of headphones.
Practical focuses on editing sound files using a
program called Goldwave.
MEDICAL IMAGING AND
BIOSIGNAL ACQUISITION
Week 3
OVERVIEW
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Healthcare Technologies encompass all IT
solutions in healthcare ranging from software
systems which support patient management to
devices which support diagnosis and
management of disease.
Today, we want to focus on those devices which
are used for obtaining measurements from the
human body to assist with detection or absence of
disease.
HEALTHCARE TECHNOLOGY CATEGORIES
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Human beings are very complex, consisting of muscle,
bone, organs and transport vessels.
Healthcare technologies have emerged as a direct
need for examining the human body to provide
diagnosis and prognosis for a variety of different
complex ailments.
Healthcare technologies can be used to examine the:
Nervous System
 Cardiovascular System
 Respiratory System
 Skeletal System
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CURRENT HEALTHCARE TECHNOLOGIES
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What can we measure from the
human body?
Physical Structure
 Electrical Properties and
Behaviors
 Chemical Properties
 Acoustics
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Note. We often want to look at
things that are obvious on the
outside of the body, like
temperature. We look only at more
invasive applications here.
PHYSICAL STRUCTURE
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These are alterations
observed in the physical
structure of the body.
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E.g. A broken bone or
abnormal growth such as a
tumor.
http://upload.wikimedia.org/wikipedia/co
mmons/0/0e/Skeleton2.jpg
ELECTRICAL PROPERTIES AND BEHAVIORS
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Many of the body’s organs are
controlled by OR generate
electrical signals.
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E.g. The brain and muscles,
including the heart.
Changes observed in the typically
produced signals often indicate
changes to the physical /
mechanical structure of the
organs.
http://4.bp.blogspot.com/_U3vE-zSyfog/SKO0hRTNLfI/AAAAAAAAAAo/7dVSorEwczI/s320/port_brain.jpg
CHEMICAL PROPERTIES
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When organs become damaged or experience
shock or trauma they release chemicals into the
body’s blood stream.
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E.g. During a myocardial infarction (heart attack) the
chemical troponin is released into the blood stream.
The presence of such chemicals or elevated
concentrations of such chemicals can indicate
potential problems with the body’s organs.
ACOUSTICS
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The sounds generated by the body’s organs can
be reveal problems.
Auscultation is the technical term given to
listening to the internal sounds of the body,
usually using a stethoscope.
Typically performed for examining the
circulatory or respiratory system
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i.e. heart or lungs.
PHYSICAL MEASUREMENTS
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Many devices and techniques exist to measure the physical make up
of the body.
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Large portion of these devices are grouped under ‘medical imaging’.
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Main purpose of these devices is to non-invasively produce
images of internal aspects of the body:
Clinical rationale: examination, diagnosis, and prognosis.
 Medical science: assist with the study and understanding of the
anatomy.
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Different Medical Imaging devices include:
 X-ray
 Magnetic Resonance Imaging (MRI)
 Computed Axial Tomography (CAT) better known as CT
 Ultrasound
X-RAY
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Phrase coined in 1895 by a German Physicist.
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Wilhelm Rontgen
Widely used approach which is based on the usage of
electromagnetic radiation.
In diagnostic applications the X-rays are passed
through the body and detected on a photographic
plate or film.
More dense parts of the body absorb the x-rays while
less dense parts of the body allow the x-rays to pass
through.
This produces a shadow like image of the internal
part of the body which has been x-rayed.
X-RAY
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This approach can show up solid
items such as bones or tumours.
Very cheap, fast and relatively
safe.
Applications: Dentist, Broken
bones, mammography
Organs / blood vessels can also be
examined using contrast media to
more effectively absorb the x-ray
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Injected or swallowed.
SOURCE http://www.davidlnelson.md/Xrays_normal_hand_PA.htm
X-RAY VIDEO DESCRIPTION
http://video.about.com/orthopedics/How-Does-an-XRay-Work--.htm
http://en.wikipedia.org/wiki/File:X-ray3.jpg
ARE X-RAYS SAFE?
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X-rays can be harmful if exposed to for long periods.
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Radiation sickness can occur
X-rays are a form of ionizing radiation. When normal
light hits an atom, it can't change the atom in any
significant way. But when an X-ray hits an atom, it
can knock electrons off the atom to create an ion
(electrically-charged atom)
Free electrons then collide with other atoms to create more
ions.
 An ion's electrical charge can lead to unnatural chemical
reactions inside cells, such as the breaking of DNA chains,
leading to mutations such as cancer.
 Nevertheless, X-ray still safer than invasive surgery and
therefore regarded as one of the most useful medical
devices of all time.
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COMPUTED (AXIAL) TOMOGRAPHY
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A major drawback of X-Ray is that it can only represent the
internal system on one axis at a time .
CAT scan or CT scan overcomes this drawback by capturing a
series of 2D X-ray images which are processed to provide 3D
projections.
CT used to separate anatomical structures at different depths.
The computer varies the intensity of the X-rays in order to
scan each type of tissue with the optimum power.
 Especially good for scanning bone structure!
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Contrast materials are used to allow the viewing of some
structures like vessels.
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Images are typically rendered on a computer.
CT SCAN
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CT uses x-rays but instead of passing the
x-rays through the body from one angle the
x-rays are passed into the body from
numerous locations and angles.
With the aid of a special computer the
resulting patterns can be captured and
pieced together to form a cross-sectional
image of inside the body.
This technique can also produce 3d images.
Excessive exposure to x-rays does produce
a risk to the patient’s health.
This applies to both conventional x-ray
machines and CT scans.
Source http://www.radiology-equipment.com/instrumentpics/ACFFA27.jpg
CT SCAN – OVERCOMING THE 2D
PERSPECTIVE
Source: http://health.howstuffworks.com/cat-scan1.htm
CT SCAN VIDEO DESCRIPTION
http://video.about.com/orthopedics/CAT-Scans.htm
http://www.youtube.com/watch?v=Tx-0emi4m8s
Source: http://health.howstuffworks.com/cat-scan2.htm
MAGNETIC RESONANCE IMAGING (MRI)
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MRI works in a different way from X-ray.
This technique relies on a strong magnetic field (effectively a large magnet)
and radio waves.
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No metals allowed in an MRI room.
Small metal object such as paperclips or pens can be lethal!
Magnetic coding on Credit cards wiped!
Cardiac pacemakers!
Orthopaedics are typically ok
These waves can pass through the body and produce an image which
represents a 2d slice of the body.
MRI can generate cross-sectional images in any plane.
These 2d slices can then be put together to produce a 3d image of what ever
organ is under investigation.
MRI VIDEO DESCRIPTION
http://video.about.com/orthopedics/MRI.htm
 http://www.youtube.com/watch?v=ctwXQ5xK4PU&NR=
1
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MRI (2)
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Useful in the diagnosis of neurological, musculoskeletal,
cardiovascular, and oncological (tumors) diseases.
An advantage of MRI over X-ray is that there is no reliance
between soft and hard tissue so non-solid parts of the body
can be imaged
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E.g. the brain
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Unlike CT, the entire scanner does not need to be rotated.
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A further advantage is that MRI is deemed not to be as
harmful.
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Pregnant women not scanned.
Because MRI scanners consist of a large magnet, this
approach is not always suitable to people who have some
sort of metal inside their body.
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For example, a pace maker
http://www.youtube.com/watch?v=_lBxYtkh4ts&feature=relat
ed
MRI (3)
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MRI can cause claustrophobia.
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MRI machines are VERY noisy.
(http://www.youtube.com/watch?v=8oI9YnhPNcQ&NR=1)
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Similar dbs to a jet engine.
Ear plugs and headphones usually worn.
Patient must remain VERY still during the examination.
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20 – 90 minutes in duration.
Any movement requires the section to be rescanned.
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Orthopedic implants can cause artifact if present in the
area being scanned.
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MRI machines are very expensive, therefore examination is
expensive.
MRI (4)
Source: http://en.wikipedia.org/wiki/
Magnetic_resonance_imaging
Source:://health.howstuffworks.com/mri-pictures1.htm
Source:
http://health.howstuffworks.com/mri5.ht
m
MRI VS X-RAY VS CT SCAN
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Xray more clearly shows the difference between soft and hard tissue.
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MRI more clearly shows a better contrast between different types of
soft tissue.
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MRI contains no radiation (no known biological harm)
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Noisy though and patients have to remain very still.
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Patients with pacemakers cant be scanned using MRI.
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Very obese people cannot be scanned in an MRI machine.
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X-ray contains a minimal amount of radiation.
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CT scan contains a considerable amount of radiation. Requires
injection prior to SCANS.
ULTRASOUND
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Ultrasound imaging is a process
where sound waves are sent into
the body and the reflection of
these sound waves is measured.
The technique relies on the
principle that tissues of varying
density will reflect sound waves
in a different way.
In most cases a hand held device
(transducer) is placed against the
skin to transmit and measure the
ultrasound waves.
A gel is used to ensure that this
device makes a good mechanical
contact with the skin.
http://www.nlm.nih.gov/medlineplus/ency/imagepages/18058.htm
ULTRASOUND (2)
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It is very effective for imaging soft tissues.
The patterns of reflection of the sound from within
the body can be converted into images and be
displayed on a monitor.
Although ultrasound relies on measuring acoustics
these are not sounds that are actively generated by
the body (i.e. they are merely passed through the
body from an external source – a transducer).
Very safe procedure
ULTRASOUND (3) – DIFFERENT TYPES
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The ultrasound that we have described so far
presents a 2d image, or "slice," of a 2d object (fetus,
organ).
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Two other types of ultrasound are currently in use
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3D ultrasound imaging
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In 3D Ultrasound, series of 2D images are
acquired by moving the probes across the body
surface or rotating inserted probes.
The two-dimensional scans are then processed
digitally to produce 3D models
3-D imaging provides enhanced view of
organs.
Particularly beneficial for early detection of
cancerous and benign tumors, and for
visualizing a fetus to assess its development.
http://www.youtube.com/watch?v=-
Source: http://news.bbc.co.uk/1/hi/health/3846525.stm
ULTRASOUND (4) – DIFFERENT TYPES
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Doppler imaging
 Based on Doppler effect
 Visualizing blood flow in various organs or a fetus
 Moving objects reflect ultrasound waves at
different frequency.
 Higher frequency if object moving towards the
probes and lower freq. if object moving away from
probe.
 Variance in frequency is proportional to speed of
object.
 Doppler ultrasound most used to measure rate of
blood flow through the heart and blood vessels.
BIOSIGNALS…
BIOSIGNAL ACQUISITION
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As stated various organs and systems within the body can
produce or rely on electrical impulses and electrical
activity.
There are many such systems within the body. Here we
focus on some of the most commonly measured.
These include:
Electrocardiogram (ECG)
Electroencephalogram (EEG)
Electromyogram (EMG)
Electrooculogram (EOG)
ELECTROCARDIOGRAM (ECG)
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The ECG is the result of measuring
the electrical activity of the heart as
projected from inside the body onto
the body’s surface.
The heart is essentially a collection
of muscles which rely on an
electrical signal to make them
contract and push blood out.
These electrical signals are
generated and travel to the surface
of the body each time the heart
beats.
ECG (2)
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The ECG is measured by placing
electrodes in contact with the skin.
Several recording configurations
exist but the most common is the 12
lead ECG.
This approach records 12 signals
and a clinician will view these and
look for changes in the waveforms
which might signal abnormality.
ECGs can be recorded when the
patient is at rest or when the
patient is exercising to assess
different effects of physical activity
on the heart.
Normal
Abnormal
ECG (3)
http://arrhythmiacenter.idsutcliffe.com/Pt%20Resources%20Dx%20of%20Arrhythmias.htm
http://www.corscience.de/en/medical-engineering/oemodm-solutions/odm-products/24h-holter-2-lead.html
http://www.mdconsult.com/das/stat/images/imng/0c039bbb2reduced_us.jpg
http://rudylab.wustl.edu/overview/index.htm
http://www.bioeng.auckland.ac.nz/physiome/movies/movies_display.php?type_id=4
http://www.ecglibrary.com/norm.html
http://www.medcatalog.com
http://homepages.cae.wisc.edu/~bme300/ecg_trainer_s09/images/12lead.jpg
millivolts (mV)
millivolts (mV)
ELECTROENCEPHALOGRAM (EEG)
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The EEG is a measurement of the brain’s electrical activity.
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Similar to the heart, the brain produces electrical patterns which can
be measured on the scalp.
The measurement process involves putting numerous (16 – 25)
electrodes on the scalp
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Brain cells communicate by producing small electrical impulses.
these can be part of a cap like structure.
Like in the ECG the resulting signals can be analysed to look for
abnormal patterns in brain activity.
It should be noted that the signal produced and the origin of the
signal is very different between the EEG and the ECG.
EEG
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In deep sleep the EEG pattern produces large
slow waves.
When relaxing the waves being faster.
When active the EEG is described as being very
dense with a low voltage and a high frequency
which produce a fast wave
EEG (2)
 The auditory brainstem response is the
recording of signals from the brain in
response to a form of external audible
stimulus.
Temporal representation of
the ABR signals show clear
differences between the
waveforms with and without
a response.
EEG (3)
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EEG is commonly used to detect:
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Presence and type of seizures (epilepsy, convulsions)
Cause of confusion
Effects of head injury
Tumors
Infections
Degenerative Diseases
Brain activity in coma
Brain activity during sleep (narcolepsy)
As with the ECG the recording of EEG is VERY
safe.
EEG (4)
http://archlab.gmu.edu/people/cbaldwi4/ARG_People.html
http://people.brandeis.edu/~sekuler/eegERP.html
http://www.umsl.edu/~neurodyn/projects/eeg.html
BRAIN COMPUTER INTERFACES (BCI)
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In recent years EEG has been used to acquire brain activity
for the purposes of controlling machines.
Every time we move, think, feel or remember our brain fires
electrical activity.
By placing electrodes on the surface of the scalp it is possible to
capture some of this electrical activity.
 Some of the electrical activity is distorted as it passes through the
brain tissue and bone of the skull.
 Implantable electrodes in also an option.
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Rationale
Sensory OUTPUT BCI can be used to control some external device or
prosthetic.
 An MRI can help with profiling the activity.
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Computer Screen
Artificial limb
Sensory INPUT BCI can be used to ‘feed’ signals INTO the brain
(implant) to bypass some damaged section of it.
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Allowing a blind person to see!
BCI (2) - APPLICATIONS
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Controlling external device with you mind.
 Controlling an onscreen mouse via mental commands to
assist with communication.
 Severely disabled persons.
Controlling an artificial limb.
 Often requires training – ‘imagine’ closing your fist or
moving your arm.
BCI – APPLICATIONS (2)
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Sensory input from
spectacle mounted
cameras to allow sight
for blind people.
To date, only limited
sights can be restored.
 Basic shapes
represented as a
series of dots.
ELECTROMYOGRAPHY (EMG) (1)
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EMG is the discipline that deals with the detection,
analysis, and use of the electrical signals that
emanates from the muscles. In the words of De Luca
(1997)
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“…it provides easy access to physiological processes that
cause the muscle to generate force, produce movement and
accomplish functions which allow us to interact with the
world around us”
The origin of these signals is similar in principle to
that of the ECG as the heart is in effect a muscle.
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Nerves cells (Motor neurons) connect to our muscles from
the spinal cord.
ELECTROMYOGRAPHY (EMG) (2)
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The technique can be used to study muscle function
and activity.
The EMG can be recorded by placing needle
electrodes in the muscle or by placing (gel) electrodes
on the surface of the skin.
The former provides a more specific measurement
whilst the latter provides a more general picture of
the operation of the muscles in the area under
interrogation.
EMG - APPLICATION
Figure 2.2 Amplitude and Frequency spectrum of
the EMG signal
http://www.hhdev.psu.edu/atl
ab/EMG.jpg
Figure 5.5 Screen shot of Animation Program
Figure 5.4 Screen shot of Analysis Program
ELECTROOCULOGRAM (EOG)
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EOG is a technique for measuring the resting
potentials of the retina.
Electrode pairs are placed either above and below
the eye or to the left and right of it.
http://www.youtube.com/watch?v=jJ2BKq0fadQ
ACOUSTIC MEASUREMENTS (1)
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Sounds emanating from various organs
can be measured.
The two organs which are most
commonly interrogated in this way are
the lungs and the heart.
Sounds from these organs are typically
measured using a stethoscope.
The classical stethoscope consists of a
chestpiece which is placed against the
body.
http://www.waldosworld.org/gall
ery04/stethoscope.jpg
ACOUSTIC MEASUREMENTS (2)
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Vibrations are picked up by this chestpiece and
transmitted along a hollow tube to a set of ear buds.
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When auscultating (listening to) the heart, doctors listen
for heart murmurs, gallops and heart rate.
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When examining the lungs, doctors listen for wheezes or
crackles.
More recently electronic stethoscopes have been
invented which use a sensor inside the chest piece (in
some cases a microphone).
Information from this sensor can be processed and
enhanced before being transmitted to a headset.
Noise reduction / filtering and signal enhancement.
 Digitized sounds can be stored and shared.
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CHEMICAL PROPERTIES
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Changes in the conditions of various organs and body
systems can also be reflected in chemical changes.
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For example if muscles are damaged i.e. if muscle tissue
dies, enzymes can be released into the blood.
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A particular case where this is used as a diagnostic test is
in the case of cardiac patients.
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The heart can be considered as a muscular organ, and
when someone has a heart attack, this muscle releases
various chemicals into the blood.
One such chemical is troponin-t (a protein). This is often
used to diagnose if someone has had a a heart attack.
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Takes time to conduct test thus why ECG is so important.
SUMMARY
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We have studied (briefly) how various signals /
images can be measured from the body.
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Changes in these signals allow a specialist to make a
diagnosis.
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We have thought exclusively about diagnostic
applications.
o
There also the reverse of this where we push signals
into the body:
o Therapeutic radiography
o Implantable devices
o
Cardiac pacemakers, defibrillators, vascular pumps
NEXT WEEK
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Lectures – running!
Medical data
 Processing
 PACS
 Security
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Tutorial and Practical Sessions
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Use this time wisely to work on your assignment!
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3 hours.
This is a really good opportunity to produce a draft of your
assignment.
 Visit the library, do a literature review etc…
 This should ensure that everyone is able to submit a good
piece of work in week 7.
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