Imaging Technologies 2 Flashcards
What is alpha decay comprised of?
What is its charge?
What is its RAM?
What does this mean in terms of deflection in a magnetic field?
It is a helium nucleus(He2+) consisting of X2 proteins and X2 neutrons (zero electrons).
It has a +2 charge and high RAM, meaning it is weakly deflected in an electromagnetic field.
What is beta decay comprised of?
What is its charge?
What is its RAM?
What does this mean in terms of deflection in a magnetic field?
High energy electron from the nucleus of a neutron as it decays to a proton.
Neutron —> Proton(+) & e(-)
It has a -1 charge and a small mass meaning it is deflected strongly in an electromagnetic field.
What is the name of the process from which gamma radiation is produced?
How are gamma rays produced in this process?
Positron annihilation.
1) A radioactive tracer decays and emits a positron (e+)
2) positron travels 1-3mm and joins with an electron
3) annihilation occurs and X2 equal 511KeV photons of gamma radiation is emitted 180 degrees apart from each other
What is the formula for decay rate?
Decay rate = ΔN / Δt
N = number of emissions t = time
What does the symbol λ stand for and what does this mean?
λ = decay constant = the probability that an individual nuclei will decay (per unit time)
What is the formula for the activity of a sample?
A = λ N
(Where N =number of undecayed atoms)
OR
A = A(o) x e^(-λt)
What is meant by the half life of a sample?
What is the formula for calculating half life?
The time taken for half the nuclei within an active sample to decay.
T1/2 = ln(2) / λ
What stops alpha, beta and gamma radiation?
Which is most harmful to the body:
1) inside
2) outside
Alpha = soft tissue Beta = Perspex Gamma = lead
Inside = alpha Outsize = gamma
Which element is commonly used in medical imaging?
What is it formed by?
Technetium-99m
Formed by molybdenum decay
What does PET stand for and how are PET scans performed?
Positron Emission Tomography
1) Glucose is given with a tracer, which spreads to the area of disease/tumour due to its high level of metabolism
2) positive beta decay occurs which causes gamma radiation to be emitted
3) the gamma radiation is detected by a ring of detectors which can pinpoint the source due to the 2 gamma photos being at 180 degrees from each other
How does MRI scanning work?
The water in our body acts as tiny magnets which align when we are in the scanner (which acts as a strong magnetic field). A radio frequency is applied which turns the atoms 90 degrees, and when this is turned off the protons realign and release radio waves in the process. These radio waves are monitored and the speed at which the atoms realign allows for tissue differentiation.
How does ultrasound work?
A piezoelectric crystal changes its shape based on current passing through it, which vibrates the air molecules around it forming ‘ultrasound’. These are emitted from a probe and the time taken for a pulse to be emitted and received can tell us the distance of a structure (the echo principle).
What is the average propagation or sound in body tissue?
1540ms
What formula is used to identify the depth of a structure?
Speed = distance / time
Therefore distance = (speed X time) / 2«
What determines the boundaries based on the amount of sound reflected back?
The acoustic impedance of tissues.
