Paper 3 Exam Questions

Question 1

X ray tubes have an X ray spectrum for emission. Why does the spectrum have spikes at specific energy levels?

Answer 1

They are Specific the to anode element

Occur due to the Energy level transition

Question 2

Why is the tungsten anode within an x ray tube rotating?

Answer 2

To spread heat equally across a larger area so that more energetic x rays are produced

Question 3

State, in terms of active receptors, the conditions necessary for two separate images to be seen

(2 marks)

Answer 3

Cones must be stimulated

Cones stimulated by images must be separated by at least 1 unstimulated cone

Question 4

Describe how the frequency and amplitude of the vibrations change as a wave is transmitted through the ear to the fluid in the inner ear

Answer 4

Frequency is constant

Amplitude is reduced

Question 5

Explain why the effective half life of a radionuclide in a biological system is always less than the physical half life

(2 marks)

Answer 5

The physical half life depends only on the properties of the radionuclide
Biological removal of the nuclide occurs

Question 6

Describe how the rods and cones are distributed over the retina

(2 marks)

Answer 6

Only cones at the fovea

As you move away from the fovea, the number of cones decrease as rods increase

Question 7

Explain how the resolution of the image of an object seen in very dim white light compares to that of the image of the same object seen in bright white light

Answer 7

Cones are used in bright light, rods used in dim light

Resolution in bright light is better because the size of cones are smaller than the size of the rod

Question 8

The unaided far point of the defective eye with short sightedness is 0.75m

Explain why the focal length of the correcting lens should be -0.75m

(1 mark)

Answer 8

So that rays from a distant object appear to come from the far point of the defective eye

OR

To form a virtual image at the unaided far point

Question 9

There are two lines on an intensity level against frequency graph, P and Q
P is a straight line graph where y=5
Q is a curved line
State and explain which sound meter scale is used for line P (2 marks)
State and explain which sound meter scale is used for line Q (2 marks)

Answer 9

P: dB scale because there is equal response at all frequencies (/intensity is independent of frequency)

Q: dBA scale because response depends upon FREQUENCY as EAR’S RESPONSE does

Question 10

Explain the significance of the peak of intensity of a curve on an intensity level against frequency graph

Answer 10

It is the frequency at which the ear is most sensitive

Question 11

State the purpose of the second fluorescent screen in a fluoroscopic image intensifier

(1 mark)

Answer 11

Converts energy of electrons into many light photons

Question 12

Explain why a patient may need to swallow barium sulphate before x ray images are to be obtained

(2 marks)

Answer 12

Without barium meal, poor contrast between area to be investigated and surrounding tissue
Barium meal provides high density material at sight to be investigated which provides much better contrast

Question 13

State the use of of lead sheets

1 mark

Answer 13

Provides aperture through which x rays may pass, preventing scattering rays

OR

protects areas of the body not being scanned

Question 14

State and explain the advantages of using an MR scanner to scan a patients brain compared with a CT scanner

(4 marks)

Answer 14

Non ionizing radiation

MR can give multi plane images from the same scan - CT needs new scan for every image

Better resolution for soft tissue

MR gives real time image whereas CT needed to rotate to produce the final image

Question 15

Explain why it is important to use a point source of X rays for imaging purposes

(1 mark)

Answer 15

Point source gives a sharp image

Question 16

Why are short pulses used when making an A scan?

2 marks

Answer 16

Transducer must stop oscillating before echo returns do that it can act as a receiver

Distance travelled is short so emitted pulse must cease before echo returns so that there is no overlapping

Question 17

What determines the proportion of waves reflected from an ultra sound prone?

(1 mark)

Answer 17

Tissue elasticity and density

Question 18

State the changes which occur in a normal eye when the eye changes from focusing on a distance object on a near object, both objects being viewed in bright light

(2 marks)

Answer 18

Ciliary muscles contract

Producing lens of great power/ shorter focal length

Question 19

State the changes which occur in a normal eye when the eye changes from viewing an object in very dim light to viewing the same object in bright light

(2 marks)

Answer 19

Pupil constricts/ becomes smaller

Cones turn on and rods become inactive

Question 20

State and explain what would happen to the reading on the dB and the dBA scale, that was originally set at 60dB/dBA, if the frequency of the sound was changed from 1000Hz to 500Hz

(2 marks)

Answer 20

dB remains at 60dB as it is not dependent on frequency

dBA reading would he less than 60dB because 500Hz had a higher threshold intensity/ ear is less sensitive

Question 21

A search coil is placed in a circular coil to measure voltage. It is connected to an oscilloscope to produce a vertical line
The frequency of the current in the circular coil is doubled
State and explain any changes that should be made to the oscilloscope when using this new setting

(3 marks) (4 possible points)

Answer 21

Adjust the y voltage gain to a less sensitive setting

Since voltage is increased beyond the range of the screen

Because induced emf is directly proportional to the rate of change of flux linkage

And rate of change of FL is doubled

Question 22

What is the purpose of the backing block in an ultrasound probe?

(1 mark)

Answer 22

Heavily damps waves to produce short pulses and increase resolution

Question 23

When does max energy transfer occur in an ultrasound probe?

1 mark

Answer 23

When voltage frequency is equal to the frequency of natural vibrations, causing resonance

Question 24

Explain how the image obtained using a gamma camera differs from that obtained using diagnostic x rays and why this difference can be an advantage in medical diagnosis

(2 marks)

Answer 24

Image in diagnostic X-ray is a shadow photograph

Image produced by gamma camera is image of actual emission points which can be used to monitor rapidly changing situations