Medical Physics Flashcards
Collimated Beam
parallel rays so minimal spread of rays as the beam propagates
Attenuation
the process by which the number of particles or photons entering a body of matter is reduced by absorption and scattering
Simple Scattering
photon energy less than work function, enters atom and scatters, doesn’t lose energy
Compton Scattering
excess energy, x-ray photon absorbed by an electron which is released then a new x-ray photon is scattered due to the excess energy
Photoelectric Effect
x-ray absorbed by an electron, electron uses this energy to escape with some kinetic energy
CAT Scan
-x-ray tube rotates in a ring around patient
-thin fan-shaped beam of x-rays
-different tissues absorb x-rays differently, intensity is recorded by a detector directly opposite the tube
-produces images of “slices” (cross-sections) of patients
-x-ray tube moves along patient
-computer software produces 3D image
Gamma Camera
-radiopharmaceuticals e.g. flourine-18, technitium 99m give off gamma radiation
-collimator consist of thin lead tubes, only receives gamma rays travelling parallel to the tubes rest are absorbed
-collimated beam of gamma rays goes to sodium-iodide crystal (scintillator) that converts each gamma ray into visible light photons
-photomultiplier tube converts a single light photon into an electrical signal i.e. voltage
-signal used to create a 3D image
PET Scan
-patient lies in a ring of gamma detectors
-radioisotope produces a positron through beta+ emission
-positron collides with an electron and is annihilated, produces two gamma photons diametrically opposite to each other
-received by the gamma detectors, lag time is used to position the interaction
-computer connected to detectors produces a “slice”, gradually builds a 3D image
Piezoelectric Effect
when certain crystals produce a p.d. when compressed and vice versa
Transducer
crystal under the piezoelectric effect, sends ultrasound then receives the reflected waves
