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
what are the contraindications for MRI?
pacemakers
orbital foreign bodies
artificial heart valves
surgical clips
what can MRI be used for in dentistry?
TMJ degeneration
salivary glands
sinuses for malignancies
how does an ultrasound produce image?
high frequency sounds waves
transducer placed on skin surface with coupling agent between probe and skin to penetrate waves
length of time it takes for sound waves to return will create level of depth
what can sound waves not penetrate?
dense bone
what are the advantages of ultrasound?
no ionising radiation
good for superficial structures
real time imaging
can be used in adjunct to biopsy/ aspirates
blood flow
what are the disadvantages of ultrasound?
operator dependent
cant penetrate bone
can be difficult to interpret
only superficial structures seen
what are examples of ultrasound use in the head and neck?
neck lumps
salivary glands
vascular
what type of neck lumps may you want to ultrasound?
cysts
tumours
lymph nodes
what salivary gland disorders may you want to ultrasound?
sjogrens
neoplasia
sialadenitis
sialoliths
what type of vascular diseases may you want to ultrasound?
carotid artery stenosis
vascular lesions
what are the types of nuclear medicine?
PET
SPECT
Scintigraphy
what is nuclear medicine?
patient is injected intra-venously with radiopharmaceutical which when it decays emits particles that are picked up on a gamma camera
increased activity - hot spot
reduced/ no activity - cold spot
what are the advantages of NM scans?
can be superimposed over other cross sectional imaging
highly sensitive
can assess function
what are disadvantages of NM scans?
poor resolution
poor specificity
very high radiation dose
what are the 2 types of rasioisotopes?
TECHNETIUM-99M
18-FDG
what is a PET-CT?
type of nuclear medicine scan superimposed over conventional CT
what are PET CTs used for?
cancer diagnosis
