Imaging-Richard Flashcards
what does CAT stand for?
Computerised Axial Tomography
what does MRI stand for?
Magnetic Resonance Imaging
X-ray
electromagnetic wave of high enough energy to penetrate solid objects
may be absorbed or attenuated when encounter objects of high density
enables production of shadow image or skiagraph which can be used to see organs of the body, disease or foreign objects
X-Ray imaging
X-Rays are produced using an X-Ray gun which accelerates into a metal target and thus produces characteristic Bremsstrahlung X rays
allows the user to tune the energy of the X-rays produced to create hard or soft x rays.
hard x rays have greater penetrating power and can be used for imaging of dense metal objects
digital detection
images produced via flat panel detectors
film detection
an x-ray sensitive phosphor screen is placed under the object or patient behind which is x-ray film sensitive to x rays.
CAT scan
consists of a x ray source and detector normally housed in a toroid unit
unit can take x rays from multiple angles and these can be combined to form 3D images
systems such as SPECT use gamma irradiation
PET uses no external irradtion, relying on the breakdown of radioactive tracer isotopes
MRI
place body in strong oscillating magnetic field at a specific frequency, this excited hydrogen atoms in the body
the excited atoms return to an equilibrium state and in doing so emit a RF signal which can be measured using a ‘receiving coil’
drawbacks of MRI
magnetic field is enormous
anything ferromagnetic is a big no
cooling a super conducting magnet with liquid helium is expensive
Ultrasound (sonography)
can be used to image internal structures within the body
involves sending sound waves with a wavelength above 20,000Hz into tissue
sound echos from tissue with different structures reflecting varying amounts of the incident sounds - can be translated into an image
