CT Flashcards
what is the scientific unit of measurement for radiation (effective dose - refers to radiation risk averaged over entire body)?
mSv (millisievert)
what is the effective radiation dose in the ankle CT?
0.07 mSv
effective dose of radiation ina dults for extremity x rayu
o0.0001 mSv
digital image consists of a square matrix of
pixels, each a voxel of tissue
CT image is
map of measured average linear voxels of a section of teh body
how many hounsfield units is air?
-1000
fat?
-60 to -120
water
0
compact bon
+1000
what is the tissue density calculated from, uses transmission to calculate?
attenuation coefficient
what method is used to calculate attenuation coefficient of each pixel?
filtered back projection
what is term for midpoint of CT number range?
window level WL
Attenuation of each voxel is represented by CT number or ___________ number, which is a linear transformation of the original linear attenuation coefficients, represented by a shade of grey determined by window level and width controls, and actual number by defining a ROI (region of interest)?
hounsfield
what is term for band of CT numbers centered about WL (window level)?
WW, window woidth
if WW (window width) is large, will contrast be more or less?
less
if WW (window width) is small, will contrast be more or less?
more
Which of the following would have the greatest Hounsfield units?
Air
Fat
Water
Compact bone
compact bone
what determines image quality in CT?
Bone: high frequency “edge-enhanced”
ST: low frequency “smoothing”
Trade-off between spatial resolution and noise
slice thickness
reconstruction kernel
2nd generation: Helical, spiral
3rd generation: Multidetector (MDCT)
type of scanning methid?
volumetric
what scanning method?
Scout topogram
Scanogram (e.g. leg length)
digital projection
what generation CT scanner has single detector, pencil-like X-ray beam, 25-30 min scan?
1st gen
what generation CT scanner has up to 30 detectors, fan shape, >90 sec scan?
2nd gen
what generation CT scanner 700->2000 detectors, fan-shaped beam, <5 sec scan?
3rd/4th
what kind of CT uses Shorter time-less motion, Reconstruction in different slice widths, Increasing slices increases efficiency of X-ray beam use (4-slice-80%, 64 slice-97%), Reduced radiation dose, Tube current is automatically adjusted to patient size, Improved spatial resolution, Isotropic imaging, Better multiplanar recon and 3D?
MDCT
what tissue type uses high frequency, endge enhanced?
Bone
what tissue type uses low frequency, smoothing?
soft tissue
what type of CT do Substances have different attenuation coefficients at different energies (K-edge)
New CT systems can acquire images at 2 different energies near simultaneously
Typically 80kVp and 140 kVp
Can distinguish iodine, Ca++ and UA crystals from ST?
dual energy CT
what type of CT allows for 3-D weightbearing CT, uses cone-shaped X-ray beam
Reduced radiation dose
Standing or sitting
48 seconds for bilateral scan
Used in biomechanical evaluation, pre-op planning and post-op evaluation?
WB pedCT
what type of CT is Fusion of CT and PET (positron emission tomography) using radioactive isotope of FDG (fluorodeoxyglucose)
PET provides tumor specificity
CT provides anatomic localization?
PET CT
what CT artifact is inconsistency in a single measurement?
streaking
what CT artifact is groups of views deviating gradually from true measurement?
shading
what CT artifact are errors in individual detector calibration?
rings
what CT artifacts are due to helical reconstruction?
distortion
what origin of CT artifact are the following?
Beam hardening: Beam becomes “harder” (i.e. its mean energy increases) as it passes through the object because lower energy photons are absorbed more rapidly than high energy photons
Produces streaks and dark bands
Manufacturer correction: filtration, calibration, special software
Operator: tilt gantry, filter selection
Partial volume: off-center dense object protrudes into the beam path
Use thin acquisition width
Photon starvation
Undersampling
physics based
what origin of CT artifact are the following?
Metallic materials: Severe streaking due to high density of metal
Manufacturers: interpolation techniques
Operator: remove jewelry etc.
Motion: misregistration artifact
Incomplete projection: parts of patient outside FOV degrade the image
Operator: patient positioning inside scanner
Manufacturers: large bore scanner (up to 70 cm)
patient based
what type of artifact is More common in the skull due to thickness of calvarium?
Beam-hardening artifact
what type of CT is used for Gout?
Dual energy
what type of fracture?
Pylon
?
OCD lesion
PED CAT
3D weightbearing CT, for biomechanical,
PED shows utility in
staging and classifying PT dysfunction and pes planus
PET CT
tumor imaging, pet amd ct in one using FDG isotope
Infications for foot ankle CT
Fx
surgical planning
Post op, healing comps or non unions
tarsal soalitions
cortical tumors
gout
fx?
calc
fx?
talar fx
lisfranc
??
tarsal coalition
trauma with ST entrapment
ST infection
healing related complications
wat is gantry
donut looking thing
