ARRT Image Quality 2 — Questions and Answers
Question 1: Which CT parameter most directly controls the amount of radiation dose delivered to the patient?
- mAs (Correct answer)
- kVp
- Pitch
- Reconstruction kernel
Correct answer: mAs
mAs (milliampere-seconds) directly determines the number of X-ray photons produced and is the primary controller of patient dose.
Question 2: Increasing the reconstruction field of view (FOV) while keeping matrix size constant will:
- Increase pixel size and decrease spatial resolution (Correct answer)
- Decrease pixel size and increase spatial resolution
- Have no effect on spatial resolution
- Increase noise while improving contrast
Correct answer: Increase pixel size and decrease spatial resolution
Larger FOV with the same matrix means each pixel covers more area, increasing pixel size and reducing spatial resolution.
Question 3: A 'blooming artifact' in CT most commonly results from:
- High-density metallic objects causing overestimation of structure size (Correct answer)
- Patient motion during acquisition
- Undersampling of high-frequency data
- Incorrect HU calibration of the scanner
Correct answer: High-density metallic objects causing overestimation of structure size
Blooming occurs when high-attenuation objects like metals or calcifications appear larger than their true size due to beam hardening and partial volume effects.
Question 4: Which factor primarily determines the z-axis (longitudinal) resolution in a multislice CT scanner?
- Detector row width (Correct answer)
- Gantry rotation speed
- kVp setting
- Reconstruction matrix size
Correct answer: Detector row width
Z-axis resolution is primarily determined by detector row width (collimation), which defines slice thickness in the longitudinal direction.
Question 5: Quantum mottle in CT images is primarily caused by:
- An insufficient number of detected photons (Correct answer)
- Detector calibration errors
- High kVp beam hardening
- Excessive table speed
Correct answer: An insufficient number of detected photons
Quantum mottle (noise) occurs when too few photons reach the detector, causing statistical fluctuations that appear as grainy image texture.
Question 6: The Hounsfield unit (HU) value of pure water is:
- 0 (Correct answer)
- -1000
- +1000
- +100
Correct answer: 0
By definition, pure water is assigned an HU value of 0 on the Hounsfield scale used in CT imaging.
Question 7: When evaluating a CT image for streak artifacts emanating from a hip prosthesis, the BEST corrective technique is:
- Metal artifact reduction (MAR) reconstruction algorithm (Correct answer)
- Increasing the kVp to 140
- Decreasing the mAs by 50%
- Widening the reconstruction FOV
Correct answer: Metal artifact reduction (MAR) reconstruction algorithm
Metal artifact reduction algorithms use iterative or sinogram-based techniques to model and subtract metal-induced streaks from the image.
ARRT Image Quality 2
Which CT parameter most directly controls the amount of radiation dose delivered to the patient?