Topic Option: Medical Physics

Question 1

Outer Ear

Answer 1

shaped to channel air vibrations (sound) to the tympanic membrane

Question 2

Tympanic Membrane

Answer 2

ear drum

Question 3

Middle Ear

Answer 3

converts the oscillations of the ear drum into oscillations in the fluid of the inner ear at the oval window

Question 4

Ossicles

Answer 4

three small bones in the inner ear – malleus, incus and stapes

Question 5

Inner Ear (especially Cochlea)

Answer 5

converts the oscillations in the fluid of the inner ear into electrical signals that are sent along the auditory nerve to the brain

Question 6

Impedance Matching

Answer 6

a mechanism for transmitting, rather than reflecting, as much of the sound energy from the air to the cochlea as possible – without this mechanism for pressure transformation between media of different densities (air and fluid), most sound would be reflected rather than transmitted into the cochlear fluid

Question 7

Sound Intensity

Answer 7

Power per unit area of a sound wave(NOTE: Intensity depends on the square of the amplitude of the sound wave.) (NOTE: There is a logarithmic response of the ear to intensity.)

Question 8

Loudness

Answer 8

The response of the ear to intensity

Question 9

Sound Intensity Level (IL)

Answer 9

ten times the common logarithm of the ratio of the intensity of a sound to the sound intensity at the threshold of hearing (measured in decibels (dB))

Question 10

Selective Frequency Loss

Answer 10

conductive loss of hearing for a particular range of frequencies

Question 11

Tinnitus

Answer 11

temporary deafness across the frequency range due to short-term exposure to loud sounds (“ringing” in the ears)

Question 12

Attenuation

Answer 12

Absorption of energy from beam

Question 13

Half-Value Thickness (x1/2)

Answer 13

the thickness of a material needed for a beam (of X-rays) to be attenuated (reduced in intensity) by 50%

Question 14

Attenuation Coefficient (μ)

Answer 14

Probability of a single photon being absorbed in 1m of a material

Question 15

Computed Tomography (CT) Scan

Answer 15

an X-ray imaging technique – X-rays and detectors are rotated around a patient and a computer combines the information to produce a 3-D interior picture

Question 16

Ultrasound Scan

Answer 16

medical imaging technique in which high frequency (20kHz) sound waves are transmitted and reflected from soft tissue

Question 17

Piezoelectric Crystals

Answer 17

quartz crystals that change shape when an electric current flows and can be used with AC voltage to produce and detect ultrasound

Question 18

Acoustic Impedance (Z)

Answer 18

the product of the density of a substance and the speed of sound in that substance

Question 19

A-scan

Answer 19

amplitude modulated scan – presents the information from an ultrasound probe as a graph of returned intensity versus time

Question 20

B-scan

Answer 20

brightness modulated scan – Operator moves ultrasound generator and computer records echo returns.

Question 21

Nuclear Magnetic Resonance (NMR) Imaging

Answer 21

medical imaging technique that involves the use of a non-uniform magnetic field in conjunction with a large uniform field to cause nuclei to broadcast radio waves used to image the patient

Question 22

Pulse Oximetry

Answer 22

laser technique for measuring the oxygen content of the blood by shining red or infrared light through a thin part of a patient’s anatomy

Question 23

Endoscope

Answer 23

tube with a collection of optical fibers using lasers to look inside the human body

Question 24

Radiation Dosimetry

Answer 24

techniques for measuring the amount of ionizing radiation

Question 25

Exposure (X)

Answer 25

charge per unit mass produced as a result of ionization

Question 26

Absorbed Dose (D)

Answer 26

Energy absorbed per unit mass of tissue

Question 27

Quality Factor

Answer 27

for the same absorbed dose, this measures the relative effectiveness of different radiations in destroying cells

Question 28

Dose Equivalent (H)

Answer 28

product of quality factor and absorbed dose which is an attempt to measure the radiation damage that actually occurs in tissues

Question 29

Balanced Risk

Answer 29

an attempt to balance the risk of exposure to ionizing radiation with the benefits of its use in diagnosis and treatment of illness

Question 30

Physical Half-life (TP) (same as T1/2)

Answer 30

Time taken for the activity of a sample to decrease to ½ its initial value

Question 31

Biological Half-life (TB)

Answer 31

time taken for half the number of ingested radioactive nuclei in the body to be removed by natural bodily (chemical) processes

Question 32

Effective Half-life (TE)

Answer 32

the time for the activity to halve due to physical and biological processes (USE equation)

Question 33

Threshold intensity

Answer 33

10^-12 Wm^-2. Minimum intensity at which sound is heard