30 - Medical imaging

Question 1

Define attenuation

Answer 1

the gradual decrease of intensity of radiation as it passes through a medium

Question 2

Define attenuation coefficient (μ)

Answer 2

a constant that depends on the material and the frequency of the X-rays (μ)

Question 3

Define contrast of an image

Answer 3

the difference in brightness between the brightest and the dark areas

Question 4

Define contrast media

Answer 4

material,which are good absorbers of X-rays; they are used to show the edges of soft tissues in X-ray images

Question 5

Define computerised axial tomography (CAT)

Answer 5

a technique in which X-rays are used to image the body in order to produce a three dimensional image

Question 6

Define piezo-electric crystal

Answer 6

a material that produces an e.m.f. when it is stressed, causing its shape to change. Also, when a voltage is applied across it in one direction, it changes its dimensions slightly

Question 7

Define piezo-electric effect

Answer 7

the production of an e.m.f across a crystal by putting the crystal under stress. the opposiet effect is applysing a p.d. across the crystal causing it to chnage shape

Question 8

Define acoustic impedance

Answer 8

the product of the density of the substance and the speed of the ultrasound in the substance

Question 9

Acoustic impedance equation

Answer 9

acoustic imepdance = density x speed of sound
Z = ρc

Question 10

Define impedance matching

Answer 10

the use of a gel to reduce the intensity of unwanted, reflected ultrasound between two materials. The gel has a similar acoustic impedence to the reflecting material

Question 11

Define radiotracer

Answer 11

a substance that consists of radioactive material that is attached to a natural chemical, such as gluose

Question 12

Define line of response

Answer 12

a line drawn from PET detector triggered by one gamma-ray to the opposite detector that was triggered by the second gamma-ray