RADIOLOGY - other modalities Flashcards
what are the other modalities in radiology?
CT
MRI
ultrasound
nuclear medicine
combination - PET-CT/ PET MRI
what may be used to increase soft tissue contrast when taking a CT scan?
iodinated contrast intra-venously
what shape is the beam for a CT scan?
fan shaped
what position is the patient for a CT scan?
lying horizontal
what do newer CT units use instead of normal voxels? and what are the advantages of these?
isotropic voxels
allow for manipulation of images in all 3 planes with no distortion
what value is given to CT voxels?
Hounsfield units
what are the hounsfield numbers for the tissues a CT scans?
air -1000
fat -100 to -60
water 0
dense bone +1000
how do hounsfield numbers correlate with colour?
-1000 black
+1000 white
what is windowing in CT scan?
alters levels of densities visualised in scan to optimally look at specific tissues
window level: value at centre of range
window width: range of values selected to view tissues
what is the equivalent of radiation dose from a bitewing to natural background?
less than 1.5 days
what is the equivalent of radiation dose from a CT head to natural background?
1 year
how is an MRI taken?
whole room is a magnetic field
imaging coil is placed over a region of interest to gain higher resolution
what colour is cortical bone, fat, and fluid in an MRI?
cortical bone - black
fat - white
fluid - white
what are the advantages of an MRI?
no ionising radiation
very good imaging of soft tissues and early changes in bone marrow
what are the disadvantages of an MRI?
multiple contraindications
lengthy scans
claustrophobia
cost