CT Flashcards by Squidward Tentacles

what is the scientific unit of measurement for radiation (effective dose - refers to radiation risk averaged over entire body)?

mSv (millisievert)

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what is the effective radiation dose in the ankle CT?

0.07 mSv

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effective dose of radiation ina dults for extremity x rayu

o0.0001 mSv

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digital image consists of a square matrix of

pixels, each a voxel of tissue

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CT image is

map of measured average linear voxels of a section of teh body

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how many hounsfield units is air?

-1000

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fat?

-60 to -120

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water

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compact bon

+1000

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what is the tissue density calculated from, uses transmission to calculate?

attenuation coefficient

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what method is used to calculate attenuation coefficient of each pixel?

filtered back projection

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what is term for midpoint of CT number range?

window level WL

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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

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what is term for band of CT numbers centered about WL (window level)?

WW, window woidth

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if WW (window width) is large, will contrast be more or less?

less

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if WW (window width) is small, will contrast be more or less?

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Which of the following would have the greatest Hounsfield units?

Air
Fat
Water
Compact bone

compact bone

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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

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2nd generation: Helical, spiral
3rd generation: Multidetector (MDCT)

type of scanning methid?

volumetric

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what scanning method?

Scout topogram
Scanogram (e.g. leg length)

digital projection

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what generation CT scanner has single detector, pencil-like X-ray beam, 25-30 min scan?

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1st gen

what generation CT scanner has up to 30 detectors, fan shape, >90 sec scan?

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2nd gen

what generation CT scanner 700->2000 detectors, fan-shaped beam, <5 sec scan?

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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?

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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?