medicine

Question 1

what is a photon

Answer 1

packet of electromagnetic energy

Question 2

what are a photon’s main properties

Answer 2

travels at 3 x 10^8 in a vacuum; has no charge; causes ionisation

Question 3

an x-ray of soft tissues shows poor contrast; explain a technique to deal with this

Answer 3

inject contrast material into the patient; it has large attenuation coefficient; this reveals the tissue’s outline on the x-ray image

Question 4

why do we use gamma emitters as medical tracers and not beta emitters

Answer 4

gamma can pass through the patient; gamma is less ionising so causes less cell damage

Question 5

how does a CAT scanner produce a 3D image

Answer 5

x-ray tube rotates around patient; thin x-ray beam is used, producing cross section images; x-ray tube moves along the patient; 3D image is produced by computer using data from detectors

Question 6

what is the doppler effect

Answer 6

change in wavelength due to movement of the source

Question 7

how can ultrasound be used to determine the speed of blood through an artery (using the doppler effect)

Answer 7

ultrasound transducer used to emit and detect ultrasound; ultrasound is reflected by the blood; change in wavelength is related to the speed of blood

Question 8

for an ultrasound scan, most of the ultrasound should be transmitted into the patient; explain how this is achieved

Answer 8

gel is used between transducer and skin; gel has similar acoustic impedance to skin so less reflection

Question 9

what is an energy level of an atom

Answer 9

discrete amount of energy that an electron can have

Question 10

explain how ultrasound scanning is used for medical purposes; include the difference between A-scans and B-scans

Answer 10

ultrasound is reflected at boundaries between materials; time delay of reflection used to determine depth; fraction reflected used to identify tissue; A-scan is taken in a straight line; B-scan is taken from different angles, making a 2D image

Question 11

explain how a PET scan works, including how fluorine-18 is used as a tracer

Answer 11

positrons from F-18 annihilate electrons; two gamma photons are formed, going in opposite directions; patient is surrounded by gamma detectors; delay between the two photons reveals location of F-18

Question 12

what does PET scan stand for

Answer 12

positron emission tomography

Question 13

advantages of CAT scan over normal x-ray

Answer 13

produces a 3D image; more detail (soft tissues can be seen)

Question 14

what is the piezoelectric effect

Answer 14

p.d. causes a material to change shape

Question 15

examples of contrast materials

Answer 15

barium, iodine

Question 16

what is technetium-99m used for

Answer 16

tracer for gamma cameras

Question 17

what is fluorine-18 used for

Answer 17

tracer for PET scans

Question 18

explain the functions of the main components of a gamma camera

Answer 18

collimator: gamma travels along the axis of lead tubes; scintillator: gamma converted to visible light photons; photocathode: photons converted to electrical signal; computer: signals converted to an image

Question 19

how to improve quality of a gamma camera image

Answer 19

use thinner / longer collimator

Question 20

describe how a medical tracer is used to diagnose an organ

Answer 20

tracer injected into patient; organ absorbs it; gamma camera detects radiation from tracer

Question 21

how are x-rays produced in an x-ray tube

Answer 21

fast-moving electrons hit a metal anode; their kinetic energy is converted into x-ray photons