Medical Lhyscis Flashcards
Explain how an A-scan could be used to measure the thickness of a patient’s eye lens.
You may draw a diagram to help with your answer.
(3) marks
Pulses of ultrasound sent into the eye
The reflections received by the transducer should produce an oscilloscope of emf of received against time
Find the two peaks for the reflection of the front AND back of the lens
Work out thr distanced to each of them using distance = speed x time / 2
Subtract the further distance from the closer one
For the X-ray tubes used in hospital, the X-ray photons have energy of about 105 eV.
State the attenuation mechanisms for these photons.
They give a graph and it says lg photon energy, what to do?
this means LOG BASE 10 OF ENERGY 😭
Just log and read the graph
Increasing the voltsge of 2nd circuit for x ray tube does what for the first ti it’s spectrum ?
Icnrease max frewuency for photon / wavelength
But the K lines stay the same because they are not due to pd …
Want to see faults between sorts in abdomen, which is better and why x ray or ultrasound (2) marks
Ultrasound as no ionising
Also better definition image apparently between tissue and blood
Why gamma trscer better than beta (2)
Key point about penetration
Less ionising = less damage done
More penetrating so actually CAN BE measured
Beta will be absorbed by the patient and cantbe detect etc
(Don’t think that beta can be detected snd gamma more easily, have to say beta not at all)
How to describe the graoh even tho if it looks linear but YOU KNOW IT MUST BE EXPONENTIAL
MSUT QUOTE DATA!!!
First say the trend
- as distance increases , intensity decreases
Say the type of change
- it is an exponential decrease due to the formula etc…
Say why it changes
- as the intensity rapidly decreases between 3 and 4 , it msut mean that bone has higher attenuation coeffeint than muscle
Talking about the scatters , don’t say an X-rays , must say
X ray photon interacts so tend to a 1 to 1 interactions
Also if confused if itsexponential or linear what to do?
Double check, use a ruler !
If you had to choose between fatter spaced lead tubes or thin in collimator which and WHY!
Proper answer
Thin
- because this increases the chance the gamma photon came directly beneath it, as for the fatter gaps, more range of angles can creep through without being absorbed
Proper answer
So REDUCES THE SPREAD OF ANGLE of gamma photons are detected
- this leads to a MORE SHARPER IMAGE of the scan as more certainty the photons came directly below the scintillator
(Blur comes from different photons arriving at different points, collimator can only sssume it came underneath )
Why is CAT high quality?
1) produces 3d Images
2) can offer high contrast between soft tissues of simialr atrnustion coeffeicmt
Why does intensity of reflection depend on physical properties?
(State quality and HOW that affects !)
Intrnsity is dependent on the acoustic impedances between two media, which is the product of density and speed of ultrasound of the material, which are both detrmineddue to inherent properties of the material
So now talk about HOW acoustic impedances chsnge the intesnsoty
- state equation
- this shows that the closer they are the less is reflected more different they are the more reflected
