Medical Imaging (C27) Flashcards
How do you produce x-rays
thermionic emission of electron
electron is accelerated
hit target metal and emit photons
max energy of x-ray photon =
max KE of electron
define attenuation
decrease in intensity as EM radiation passes through matter
4 possibilities when an x-ray collides with an atom
simple scatter
Photoelectric effect
Compton scattering
Pair production
What is Compton scattering
Incident X-ray collides with electron and removes it and a lower energy EM photon is also emitted
Why is simple scatter bad for hospitals
Creates blurriness
What is a CAT scan in simple terms
3D X-ray
Describe a cat scan
360 rotation
X-ray
Computer stitches together images
Advantage of a CAT scan
allows you to determine foreground and background
What does PET stand for
Positron emission Tomography
How does PET work
Uses a beta plus source
emitted positron annihilates with electron giving off antiparallel gamma rays
these are recorded and time delay can be used to find location.
How does the scanner work in PET
Incident photon hits scintillator (which amplifies signal) and then photomultiplier produces a voltage
Advantages of PET scanning
Non-invasive
Can see where respiration is occurring
disadvantages of PET scanning
very expensive
high radiation dose
What device is used in PET
radiopharmaceutical or medical tracer
what method of medical imaging is non-invasive and non-ionising
ultrasound
What is the name of the device that makes and receives ultrasound
transducer
What is the piezoelectric effect
Crystals that change shape under voltage (or the reverse)
How does a transducer make ultrasound
alternating p.d. causing crystal to vibrate via the piezoelectric effect
What is an A-scan
records ultrasound reflections in a line
What is a B-scan
Creates 2d images by plotting intensity as brightness
what is Z
acoustic impedance
what is acoustic impedence
a material propety that affects how much sound is reflected and refracted
what must be true to get a small proportion reflected
z1 ~ z2
What is used in ultrasound
coupling gel
why is a coupling gel used
ensures acoustic matching which reduces reflection
What can be said between the air skin boundary compared to the skin gel boundary
there is impedance matching in the skin gel, whereas almost all the sound would be reflected at the air skin
What is the intensity reflection coeffecient
ratio of the reflected to the initial intensities
what effect is used to measure blood flow
doppler effect
what happens to the frequency if the blood is moving towards the transducer
the frequency is high, the wavelength is lower
what happens to the ultrasound if the blood is moving away
the frequency lowers the wavelength is larger
what does a blood flow scan look like
different colours for different directions
What medical tracer is used in PET
Fluorine 18 attached to fluorodeoxyglucose (FDG)
what tracer is used in the gamma camera
Technetium-99m (Tc-99m)
half life of Tc-99m
6 hours
What does tc-99m emit
gamma radiation
What is a key advantage of Tc-99m as a tracer
decays into a stable isotope
Five key parts of a gamma camera
Source in organ collimator scintillator photomultiplier computer
What is a collimator
long thin lead tubes
what does a scintillator do
turns gamma photon into many visible photons
What does a photomultiplier do
turns photon into an electric pulse
Why does a gamma camera use a collimator
means only radiation travelling along axis of lead tubes is recorded, giving a clear image
What is a gamma camera used for
Used to measure the function of organs like the kidney