instrumentation 2/22/00. magnetic resonance imaging magnetic field through tissue pass radio waves...

Instrumentation

2/22/00

Magnetic Resonance Imaging

• Magnetic field through tissue

• Pass radio waves through tissue

– Protons absorb some energy & change direction

– They then move back to the original position when the

charge is shut off

• Release absorbed energy to create an image

• Tissues have different densities (absorb different amounts of

protons)

MRI

• Purpose:

• Acquiring images inside body- no radiation

• Detailed information about anatomical structures

• Speech:

– Precise measurements of the entire vocal tract without

radiation effects

– Well defined pharyngeal cavity- measurements

– Central control and the actual speech events that result

Electromyography (EMG)

• Purpose: Record the action potential of muscles

during contraction

• Investigation in pathology of muscles

• Speech:

– Provide information about speech control mechanisms

& speech gestures in natural units

– Central nervous system control of muscles

Auditory System

Hearing: Mechanoreceptors

• Hearing = sensitivity to mechanical vibrations transmitted through air.

• Mechanoreceptors= mechanical sensitivity; monitor mechanical stimuli such as pressure, position & movement.

– Hair cell= sensory receptor for audition & balance– Site of mechanoelectric transduction

Ear: Three Parts

• Outer Ear– Visible externally– Captures vibrations in the air & funnels them into the

ear canal (External Auditory Meatus)

• Middle Ear– Starts at the ear drum (Tympanic Membrane)– Contains ossicles (Stapes, Incus, Malleus)

• Inner Ear– Sensory end organ of hearing (Cochlea)– Fluid filled

Outer ear

Pinna

Outer Ear Middle Ear

Eustachian Tube

External Auditory Meatus

Inner Ear

Auditory Nerve

Ear Anatomy

Electrical Events

• Bending hair cells are responsible for the generation of neural impulses– Transmits signal to brain

– Signals can be recorded

• Otoacoustic Emission– Faint sounds produced by the cochlea as it

responds to acoustic stimuli

– Emissions recorded in the human ear

– Miniature probe placed in EAM

Otoacoustic Emission

• Two types of emission:– 1. Spontaneous otoacoustic emission-

• weak tonal signals that occur naturally, without acoustic stimuli

– 2. Evoked otoacoustic emission-• occur in almost everyone; elicited with low to

moderate level test sounds

• Clinical application

Otoacoustic Emission

• Reflect the biomechanical activity of the outer hair cells– outer hair cells are susceptible to: 1) Disease, 2)

Damage due to loud sounds,

• Provides a means to test hearing in infants & subjects who cannot complete behavioral tests of auditory function

• Otoacoustic emissions are absent in some disorders of the cochlea

Energy & Information Flow in the Auditory System

• Both energy & information have two paths of travel

• Acoustic stimulation in the environment = flow of energy from the outer ear to inner ear

• Reverse flow= otoacoustic emission– Allows the brainstem to influence actions in the inner

ear

Inner Hair cells

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AuditoryCortex

Middle ear

Nerve Fibers

Brain Stem Center

Outer ear

Inner Ear

Flow of Information & Energy in the Auditory System

Auditory Function: Comparative

• Frequency range– Humans: 20-20,000 Hz

• Greatest sensitivity at 1000 Hz

– Dogs: 20-60,000 Hz

– Elephants: better low frequency range• as low as 12 Hz

• Auditory frequencies most important to humans– 100 Hz-5000Hz (Speech frequencies)

Life Course Considerations

• Auditory system development:– 5 1/2 months after conception– Cochlea is the last structure to reach maturity – Auditory function in the fetus (Heper & Shahidullah,

1994):• Fetuses: 19-35 weeks gestation

• Pure tones (100, 250, 500, 1000, 5000) presented with speaker

• Fetal response: ultrasound of movement

• 19 weeks- Response to 500 Hz

• With maturation: response spread to low frequencies (27 weeks) than high (33-35 weeks)

Audition: Age

• Hearing high frequencies: Decline after the age of 20 years

• 30 Years: Hearing in men declines 2x as rapidly as women’s

• Hearing low frequencies: Declines in the 7th decade

• Older women have more sensitive hearing than older men

Risk factors: Hearing Loss

• Industrial noise

• Aging

• Combination of aging and noise exposure

• Diet

• Medications (ototoxic drugs)– Aspirin– Some antibiotics (Streptomyocin)– Alcohol

• Cardiovascular disease