Unit 3: Week 3 Flashcards
What are the two parameters to adjust for an xray?
Voltage- relates to what energy the x ray photon has
Current- relates to how many X-ray photons there are
What does altering the voltage do?
Voltage means that electrons have more energy leaving the cathode and striking the anode.
If there is not enough voltage than only continuous X-rays are produced- transitions occur at a certain energies.
As voltage increases more energy is available for electrons to transition so more characteristic x rays (lines appear) with the same energy- as transitions are fixed. (The lines keep the same horizontal position). They have the same length- each electron has more energy proportionally there are the same electrons with the right energy.
The continuous x rays right of the characteristic line have more energy therefore increase penetration.
It would move the graph up&right(peak increases). Increase intensity area under graph. Range increased which is better for contrast. Due to higher range of energies in electrons more are slowed to give the continuous X-rays and more electrons can cause transitions.
High voltage increase penetration and image too dark because not enough absorb. voltage effects contrast
Increasing V means that there is more energy when the electron and nucleus interact and therefore more x ray photons would be generated compared to energy wasted, making the process more efficient and increasing intensity
What does altering the current do?
Current changes the amount of electrons released by the cathode so more electrons of sufficient energy may cause transitions and continuous x rays.
They energy wouldn’t be effected but this would increase the amount of X-rays which is an increase in intensity area under graph (peak moves up). Characteristic lines will get longer- more electrons have the right energy to cause transition.
Increase the current may cause too many x ray photons to be produced and are able to pass through the tissue without being absorbed making the final image darker current effects brightness
What is a filter and what can it be used for?
Thin sheet of aluminium to improve resolution as it blocks out soft low energy x rays that would just be absorbed by the dead layer of skin resulting in hard penetrating x rays passing through.
Since energy is needed to overcome the filter the characteristic lines get shorter as lower energy transitions are blocked. There are less photons passing though so intensity decreases (peak moves down). minimises dose absorbed by patient.
Can improve contrast
What are advantages to x rays
Good for hard tissue scans Can be used for soft tissue scans Can treat some cancers- non medical imaging Minimal invasive Good resolution compared to ultrasound
What are some disadvantages of X-rays
Ionising radiation Allergy risk to contrast Expensive Cooling need Bulky equipment Not suitable in pregnancy or people with previously high doses of radiation (eg radiotherapy)
What are there three main tracers?
Iodine 131- gamma and beta radiation- primarily used for treatment of an overactive thyroid or cancer as it mimics dietary iodine who which is absorbed and and can beta short range helps destroy thyroid cells- mainly for treatment and not medical imaging but does produce gamma radiation that can be picked up
Iodine 123- similar to iodine 131 but i used primarily for imaging as it penetrates out of the body. The thyroid mainly uses iodine to make hormones that regulate metabolism
Technetium 99m can be chemically attached to drugs/compound (calcium) to be absorbed by bone which can be picked up by gamma cameras to see abnormalities
How are tracers used?
- Patient given tracer. wait for absorption. Gamma rays exit the patients body
- The collimator is a lead grid that only allows gamma rays in at a frontward angle. This is so the computer only processes data at the body part directly beneath it.
- The gamma rays hit the detection crystals causing them to scintillate
- Photomultiplier tubes electronically increase the intensity of light
- The light exiting is picked up by light sensors for data is processed by the computer
What can tracers be used for?
Structural and functional images of organs Whole body scans Identify blockages (gallbladder) Evaluate bone fractures infection arthritis Image bleeding or flow of blood Image function of heart Locate infections Thyroid function Enzyme levels in kidneys
What are advantages of using tracers?
Assess bodily functions
Don’t have to wait for physical signs of deterioration
Some results can’t be replicated by other imaging techniques
Can scan whole body
What are some disadvantages of tracers?
Use of radioisotopes Poor resolution Slightly invasive Radioactive waste (human waste) Expensive to prepare use and dispose Time consuming- have to wait for absorption
What factors determine the use of tracers?
Range- able to penetrate out of the body
Activity- enough to be picked up by gamma camera but not enough to damage
Half life- enough to complete the scan but short enough to exit the body soon after
What are MRI scans?
Magnetic resonance imaging uses powerful magnets to produce images using resonance- the input frequency matches the natural frequency of the object to overall increase energy- and precession- change in orientation of the rotational axis.
How are MRI scan produced?
- An electromagnet causes a large electromagnetic feild to form. This
causes the direction of spin in the proton of the hydrogen atoms in H2O to align with the magnetic feild. - Radio frequency causes the protons to resonate and precess further-the frequency uses is specific to P in H2O at 90DEGREES
- When the radio frequency stops the proton de excite to their original precession and release a radio signal
- The time of relaxation and direction of signal is picked up by receiver coils
What are advantages to using MRI?
Safe- no ionising radiation
Detailed images produced
Images can be produced in any plane
Images can be manipulated to enhance certain areas/tissues
Setting can be adjusted for soft tissue fat water
Can be used to investigate biochemistry and function was well
What are disadvantages to MRI?
Expensive
High level of expertise needed to operate
Process for patient can be difficult as it can take a long time to produce images
Problems associated with the use of a strong magnet- tattoo witch heavy metals- replacement joints/bone- work in metal factory
