ABR ABR Imaging Physics and Equipment 1

Question 1

What is the primary source of image noise in computed tomography (CT) imaging?

Accepted Answer

Quantum noise from limited photon statistics

Answer

Quantum noise, arising from statistical fluctuations in the number of x-ray photons detected, is the dominant source of image noise in CT.

Question 2

In CT imaging, what does the CT number (Hounsfield unit) of water equal?

Accepted Answer

0 HU

Answer

By definition, water has a CT number of 0 Hounsfield units (HU), with air at −1000 HU and dense bone typically above +400 HU.

Question 3

Which parameter most directly controls spatial resolution in a CT scanner?

Accepted Answer

Detector aperture and reconstruction kernel

Answer

Spatial resolution in CT is primarily determined by the detector aperture size and the reconstruction (convolution) kernel used in filtered back-projection.

Question 4

What is the purpose of the modulation transfer function (MTF) in evaluating imaging system performance?

Accepted Answer

Quantifies spatial resolution by measuring how faithfully a system reproduces contrast at different spatial frequencies

Answer

The MTF describes how well a system transfers contrast from the object to the image as a function of spatial frequency, with higher MTF values indicating better resolution.

Question 5

In digital radiography, what is the Detective Quantum Efficiency (DQE) a measure of?

Accepted Answer

How efficiently a detector converts incident x-ray quanta into useful image signal relative to an ideal detector

Answer

DQE measures the efficiency with which a detector uses the available x-ray quanta for image formation, accounting for both sensitivity and noise added by the detector.

ABR - American Board of Radiology Medical Physics Exam Practice Test

ABR - American Board of Radiology Medical Physics Exam Practice Test

ABR ABR Imaging Physics and Equipment 1