ABR Imaging Physics and Equipment Flashcards
6 cards from real ABR practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 ABR Imaging Physics and Equipment flashcards as text
In MRI, what phenomenon causes signal loss at tissue interfaces with different magnetic susceptibilities?
Answer: Susceptibility-induced T2* dephasing
Differences in magnetic susceptibility at tissue interfaces cause local field inhomogeneities that lead to rapid T2* dephasing and signal loss on gradient-echo sequences.
What is the purpose of the slice-select gradient in MRI pulse sequences?
Answer: Excites only the spins within a chosen slice by matching their resonant frequency
The slice-select gradient creates a linear variation in magnetic field strength so that only protons within a specific slice have the Larmor frequency matching the applied RF pulse.
In fluoroscopy, what is the automatic brightness control (ABC) system designed to do?
Answer: Maintain constant image brightness by adjusting kVp and/or mA as patient thickness changes
The ABC system automatically adjusts the x-ray generator's kVp and mA to compensate for changes in patient attenuation, keeping the image receptor input dose (and thus brightness) constant.
What is the primary advantage of a flat-panel detector over an image intensifier in fluoroscopy?
Answer: Larger field of view with less geometric distortion and better DQE uniformity
Flat-panel detectors provide a larger, geometrically undistorted field of view and more uniform DQE across the image compared to the pincushion distortion and veiling glare of image intensifiers.
In nuclear medicine, what is the purpose of a parallel-hole collimator on a gamma camera?
Answer: To accept only photons traveling perpendicular to the detector, providing spatial localization
The parallel-hole collimator accepts only photons traveling roughly perpendicular to its face, rejecting angled photons to provide spatial information about the source distribution.
What is the Nyquist theorem's implication for digital image sampling in radiology?
Answer: The sampling frequency must be at least twice the highest spatial frequency present to avoid aliasing
The Nyquist theorem states that to accurately digitize a signal, the sampling rate must be at least twice the highest frequency component, otherwise aliasing artifacts appear.