ABR ABR Imaging Physics and Equipment 2

Question 1

In MRI, what phenomenon causes signal loss at tissue interfaces with different magnetic susceptibilities?

Accepted Answer

Susceptibility-induced T2* dephasing

Answer

T1 relaxation differences

Answer

Chemical shift artifact

Answer

Gibbs ringing artifact

Question 2

What is the purpose of the slice-select gradient in MRI pulse sequences?

Accepted Answer

Excites only the spins within a chosen slice by matching their resonant frequency

Answer

Encodes spatial information in the frequency direction

Answer

Encodes spatial information in the phase direction

Answer

Refocuses spin dephasing

Question 3

In fluoroscopy, what is the automatic brightness control (ABC) system designed to do?

Accepted Answer

Maintain constant image brightness by adjusting kVp and/or mA as patient thickness changes

Answer

Reduce patient entrance dose automatically

Answer

Filter scattered radiation

Answer

Improve spatial resolution

Question 4

What is the primary advantage of a flat-panel detector over an image intensifier in fluoroscopy?

Accepted Answer

Larger field of view with less geometric distortion and better DQE uniformity

Answer

Lower patient dose in all clinical scenarios

Answer

Higher frame rate capability

Answer

Lower cost of manufacture

Question 5

In nuclear medicine, what is the purpose of a parallel-hole collimator on a gamma camera?

Accepted Answer

To accept only photons traveling perpendicular to the detector, providing spatial localization

Answer

To focus photons from a point source onto the detector

Answer

To amplify photon signal

Answer

To filter out scattered photons by energy

Question 6

What is the Nyquist theorem's implication for digital image sampling in radiology?

Accepted Answer

The sampling frequency must be at least twice the highest spatial frequency present to avoid aliasing

Answer

Images must be sampled at equal intervals in both axes

Answer

Bit depth must exceed 12 bits for diagnostic quality

Answer

Pixel size equals the detector element size