Paper 3 Exam Questions Flashcards
X ray tubes have an X ray spectrum for emission. Why does the spectrum have spikes at specific energy levels?
They are Specific the to anode element
Occur due to the Energy level transition
Why is the tungsten anode within an x ray tube rotating?
To spread heat equally across a larger area so that more energetic x rays are produced
State, in terms of active receptors, the conditions necessary for two separate images to be seen
(2 marks)
Cones must be stimulated
Cones stimulated by images must be separated by at least 1 unstimulated cone
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
Frequency is constant
Amplitude is reduced
Explain why the effective half life of a radionuclide in a biological system is always less than the physical half life
(2 marks)
The physical half life depends only on the properties of the radionuclide
Biological removal of the nuclide occurs
Describe how the rods and cones are distributed over the retina
(2 marks)
Only cones at the fovea
As you move away from the fovea, the number of cones decrease as rods increase
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
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
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)
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
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)
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
Explain the significance of the peak of intensity of a curve on an intensity level against frequency graph
It is the frequency at which the ear is most sensitive
State the purpose of the second fluorescent screen in a fluoroscopic image intensifier
(1 mark)
Converts energy of electrons into many light photons
Explain why a patient may need to swallow barium sulphate before x ray images are to be obtained
(2 marks)
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
State the use of of lead sheets
1 mark
Provides aperture through which x rays may pass, preventing scattering rays
OR
protects areas of the body not being scanned
State and explain the advantages of using an MR scanner to scan a patients brain compared with a CT scanner
(4 marks)
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
Explain why it is important to use a point source of X rays for imaging purposes
(1 mark)
Point source gives a sharp image
Why are short pulses used when making an A scan?
2 marks
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
What determines the proportion of waves reflected from an ultra sound prone?
(1 mark)
Tissue elasticity and density
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)
Ciliary muscles contract
Producing lens of great power/ shorter focal length
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)
Pupil constricts/ becomes smaller
Cones turn on and rods become inactive
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)
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
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)
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
What is the purpose of the backing block in an ultrasound probe?
(1 mark)
Heavily damps waves to produce short pulses and increase resolution
When does max energy transfer occur in an ultrasound probe?
1 mark
When voltage frequency is equal to the frequency of natural vibrations, causing resonance
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)
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
