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pinna to ear drum
filled with air
ear drum to oval window(cochlea)
filed with air
cochlea (oval window to auditory nerves)
filled with fluid
channel sound wave (variations in air pressure) to ear drum
vibrate in resonance with sound wave to drive the ossicles
Equalize pressure on both sides of eardrum
d)
hammer anvil and stirrup – malleus, incus, and stapes
vibrate the oval window causing fluid in cochlea to vibrate
e)
vibration of cochlear fluid causes hairs (cilia) to vibrate which creates electrical impulse
different hairs resonate with different frequencies
transform vibrations of fluid into electrical impulses
f)
send electrical impulses to brain to allow sound to be interpreted
April 26, 2012
Longitudinal, mechanical wave – variations in pressure (eg. Air)
Produced by vibration of object producing sound
Frequency of sound is frequency of object’s vibration – forced oscillation – driving
frequency
force per unit area
\
mechanical advantage that turns a small force at tympanic membrane
into a larger force at oval window (1.5:1) – force multiplier
small area of eardrum and smaller area of oval window (20:1)
Lever action of ossicles increases force which then acts on a smaller area
Sound pressure is amplified by inner ear
PO > P T since F increases and A decreases
(30:1)
Transmission not reflection
Mechanism for pressure transformation between media of different densities (air and fluid)
Without it, most sound would be reflected from cochlear fluid rather transmitted – when densities
are very different at a boundary (impedance matching)
April 26, 2012
response of the ear to intensity
response of ear to intensity is logarithmic – doubling intensity
does not double loudness – relationship is logarithmic
Intensity is well-defined
Loudness is not well-defined
Same intensity does not seem as loud at different frequencies
– perceived loudness varies from person to person and frequency to frequency
April 26, 2012
ten times the common logarithm of the ratio of the sound intensity
of a sound to the sound intensity at the threshold of hearing
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10 dB
for every factor of 10 in intensity,
an increase of 10 dB logarithmic response –
approx. doubles the perceived loudness
threshold of pain = approx 120 dB
I/I0 = 1012 = twelve orders of magnitude more intense
April 26, 2012
Reduced frequency range – greater loss at higher frequencies –
increased intensity needed at all frequencies
April 26, 2012
electrons boiled off a filament due to heating
electrons accelerated through a high potential difference
strike a metal target – tungsten
inner shell target electrons jump to high energy
level and emit x-ray photons when relax
X-rays pass through person and fall on a
photographic film which darkens when x-rays hit it
Bone absorbs more of x-rays than soft
tissue so tissue is darker and bone is lighter
fluorescent screens surround
photographic plate to intensify image
Scattered x-rays are absorbed
by lead plates before photographic film –
reduces blurring – increases sharpness
April 26, 2012
lessening of radiation in intensity
spreading out of beam – we only look at parallel beams
being absorbed by a material (eg. Bone)
thickness of material needed for a beam of X-rays to
be attenuated (reduced in intensity) by 50%
ratio of the natural log of 2 to the half-value thickness
April 26, 2012
attenuation coefficient greater for bone than for muscle/tissue
so intensity of X-ray less for section of film where bone is =lighter image for bone
good contrast to darker image for muscle
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an attempt to balance the risk of exposure to ionizing radiation with
the benefits of its use in diagnosis and treatment of illness
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a quartz crystal that changes shape when
a potential difference is applied across it
apply an AC voltage to generate
a vibration at desired frequency
received sound wave causes it to vibrate and
generate an AC voltage that can be measured
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size of smallest object that can be imaged. Ultrasound is a wave so
diffraction effects must be minimized. Use smallest wavelength possible
absorption of signal. Attenuation increases as frequency increases. High
frequency ultrasound will be absorbed and not reflected back to receiver.
High frequency can’t scan organs deep in body – poor depth penetration
between two extremes – choose frequency so body part being
imaged is about 200 wavelengths from probe
product of the density of a substance and
the speed of sound in that substance
April 26, 2012
the greater the difference between the
two media, the more reflection occurs
Prevents reflections of ultrasound at skin surface because
most reflection occurs at air/skin boundary
amplitude-modulated scan –
one-dimensional – not usually used
graph of signal
strength versus time
April 26, 2012
brightness-modulated scan –
two-dimensional – most frequent –
uses the signal strength to affect the brightness of a dot
on the screen many B-scans are combined to give an
image of the internal organs/baby
nuclear magnetic resonance
magnetic resonance imaging
low-energy radiation in radio region of EM spectrum
magnetic fields
imaging blood flow and soft tissue in the body
Preferred for the brain and central nervous system
Detecting tumors, strokes, infections in brain, spine, joints
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radiation used for imaging
radiation used for treatment
techniques for the measurement of amounts of ionizing radiation
ratio of total charge of air
ionized by radiation to mass of air
attempt to measure total amount of ionization produced
by radiation – limited application since doesn’t
measure ability of body tissue to absorb radiation
total energy absorbed per unit mass of tissue
difficult to measure directly – attempts to
measure amount of radiation tissue absorbs
type, intensity, time
roentgen
April 26, 2012
for the same absorbed dose, this measures the relative
effectiveness of different radiations in destroying cells
other radiations measured against X-rays– alpha particles
are 10 times more damaging per dose than X rays
product of quality factor and absorbed dose
attempts to measure the radiation damage that actually occurs in tissues
Effect depends on amount of ionization
Alpha causes more ionization per unit length of its track
Takes into account density of ionization/deposition of energy
April 26, 2012
quality factor
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time taken for half the number of ingested radioactive
nuclei in the body to be removed by natural bodily (chemical) processes
time taken for the number of radioactive nuclei present in the body to halve
April 26, 2012