Content Pertaining to CT NMTCB
Automatic Tube Current Modulation - ANSWER-regulates optical density by adjusting mA to the xray tube thus sustaining the same density (area) being scanned.
Angular Modulation - ANSWER-within the scanning field of view, automatic modulation occurs by mA adjustment in the x-y axis
reducing the amount of radiation exposure which is based on the level of attenuation
AEC application - automatic exposure control - ANSWER-variation fo mAs are noted as the optical density varies from the head to neck to chest
the scout film defines the appropriate adjustments
technologist defines the image noise target value which should remain constant throughout the variations in density with the patient's body
Fourier Transform - ANSWER-The projection -slice theorem, which states that the one- dimensional Fourier Transform of the projection of a two-dimensional signal is equal to the slice of its two dimensional at the same angle
Poly-energetic X-ray - ANSWER-produced in a range of keV as the electron beam sticks and strikes the tungston anode
Increasing the voltage (kVp) to the tube - ANSWER-generates greater energized poly- energetic x-ray energy
As kVp increases - ANSWER-K and L characteristic x-rays are produced
Brumsstrahlung - ANSWER-occurs at all levels of kVp
Shielding - ANSWER-The lead housing that surrounds the x-ray tubes because xrays occur in every direction and to absorb secondary xrays
milli-amperes per second (mAs) - ANSWER-the quantity of xrays produced
the greater the current - ANSWER-more xrays produced within a preset kVp
the greater the mAs - ANSWER-the greater the dose to the patient
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kVp - ANSWER-applied to increase the xrays penetration
mAs - ANSWER-defines the amount of xrays
Detecting the xrays - ANSWER-Gas Xenon detectors Scintallation detectors
Gas Xenon detectors - ANSWER-Xrays are absorbed with chambers, genreating postive and negative ions, image represents a single row of detectors
X-ray Production - ANSWER-produced by accelerating elec trons with a high voltage and allowing them to collide with the focal spot.
The opening collimates the beam but must first pass through - ANSWER-a layer of aluminum
Aluminum - ANSWER-Filters out low energy x-rays
Computed Tomography - ANSWER-machine that uses xrays, a powerful form of electromagnetic energy
combines x radiation and radiation detectors coupled with a computer to create cross sectional image of any part of the body
Quantum detection efficiency (QDE) is not as efficient as solid state detectors
Scintillation Detection - ANSWER-Similar to a gamma camera, xrays are absorbed by a NaI crystal, scintillation occurs and a PMT converts the light to an electron event
Issue with scintillation detection - ANSWER-dead time (afterglow)
Solid state detector crystals - ANSWER-either cadium tungstate or ceramic rare earth oxide
solid state detectors - ANSWER-silicon based semiconductor has greater absorption based on its density
xrays absorbed causing scintillation where a lens focuses the light
electrons pairs passing from positve to negative side generating a pulse
system contains proportionality
The Transmission Data - ANSWER-as the beam passes through an object it becomes attenuated by the type of object it encounters
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