CT Physics & Scanner
Technology questions
with answers newest
edition
1. Increasing tube current (mA) primarily affects which image quality parameter?
A) Spatial resolution
B) Image noise
C) Temporal resolution
D) Beam hardening
Answer: B. Tube current (mA) is the primary determinant of the number of X-ray photons
produced. Increasing mA increases photon flux, which reduces quantum noise (image noise)
but does not directly improve spatial or temporal resolution .
2. The photoelectric effect is the primary mechanism of X-ray attenuation in which tissue?
A) Soft tissue
B) Fat
C) Calcium
D) Air
Answer: C. The photoelectric effect increases sharply with decreasing photon energy and
higher atomic number. Calcium (Z=20) attenuates low-energy X-rays more than soft tissue
due to its higher effective atomic number .
3. Which reconstruction algorithm most effectively reduces image noise in low-dose
cardiac CT while preserving spatial resolution?
A) Filtered back projection (FBP)
B) Standard iterative reconstruction (IR)
C) Model-based iterative reconstruction (MBIR)
D) Simple linear interpolation
Answer: C. MBIR models acquisition physics and noise statistics, achieving greater noise
reduction while preserving edge detail compared with FBP or basic IR .
4. In a 256-slice CT scanner, the maximum z-coverage per rotation is approximately:
A) 4 cm
,B) 8 cm
C) 12 cm
D) 16 cm
Answer: C. With detector rows approximately 0.5 mm each, 256 rows provide approximately
12 cm of z-coverage, allowing whole-heart coverage in a single rotation .
5. What is the primary advantage of dual-source CT regarding temporal resolution?
A) Temporal resolution remains unchanged at 165 ms
B) Temporal resolution improves to 83 ms (half the gantry rotation time)
C) Temporal resolution worsens to 330 ms
D) Temporal resolution is dependent on heart rate only
Answer: B. Dual-source CT uses two X-ray tubes and detectors offset by 90 degrees. The
standard quarter-scan reconstruction from a dual-source scanner rotating at 0.33 seconds
achieves a temporal resolution of 83 milliseconds at isocenter, which is half the gantry
rotation time .
6. Quantum noise is proportional to which of the following?
A) The square root of the signal (N)
B) The signal (N)
C) The square of the signal (N²)
D) The inverse of the signal (1/N)
Answer: A. Quantum noise is proportional to the square root of the signal (√N). Therefore,
the signal-to-noise ratio (SNR) is N/√N, which equals √N .
7. Increasing detector element size has what effect on spatial resolution?
A) Improves spatial resolution because more photons are captured
B) Decreases spatial resolution due to larger sampling intervals
C) Has no effect on spatial resolution
D) Only affects temporal resolution
Answer: B. Larger detector elements increase the minimum resolvable object size, thereby
reducing spatial resolution .
8. Which of the following best describes the "flash mode" (high-pitch) acquisition in dual-
source CT?
A) Continuous data acquisition over several heartbeats
B) A single-heartbeat scan with a pitch >3, providing ultra-low dose
C) Retrospective gating with ECG-based tube current modulation
D) A low-resolution scout scan only
Answer: B. Flash mode uses a very high pitch (>3) to acquire the entire heart in one rotation,
dramatically reducing radiation dose .
, 9. In virtual non-contrast imaging using dual-energy CT, iodine subtraction is based on:
A) Different photoelectric absorption at 80 and 140 kVp
B) The difference in Compton scattering between energies
C) The density of the material being imaged
D) The temporal resolution of the scanner
Answer: A. Dual-energy acquisition can separate iodine from calcium by exploiting the
different photoelectric absorption characteristics at two energy levels (e.g., 80 and 140 kVp),
providing virtual non-contrast images and iodine maps .
10. Which reconstruction kernel would be most appropriate for evaluating coronary stent
patency?
A) Smooth kernel
B) Standard kernel
C) Sharp/high-resolution kernel
D) Medium-smooth kernel
Answer: C. A sharp/high-resolution kernel, combined with metal artifact reduction and
curved MPR, best visualizes the stent lumen by improving spatial resolution at the cost of
increased noise .
Section 2: ECG Gating & Motion Control (ECG 门控与运动控制)
11. During a prospectively ECG-triggered axial scan, the heart rate variability exceeds the
padding window. Which adjustment best maintains image quality while limiting radiation
exposure?
A) Increase the padding window to cover the entire cardiac cycle
B) Switch to retrospective spiral with ECG-based tube current modulation
C) Lower the tube voltage to 100 kV and increase the padding
D) Proceed with the scan and accept potential motion artifacts
Answer: B. Prospective triggering freezes motion only within a narrow phase. If heart rate
variability is large, retrospective spiral with ECG modulation extends coverage across the
cycle while modulating dose, preserving diagnostic quality without excessive radiation .
12. What is the target heart rate for optimal coronary CTA image quality when using beta-
blockers?
A) <50 bpm
B) <65 bpm
C) <80 bpm
D) <100 bpm
Technology questions
with answers newest
edition
1. Increasing tube current (mA) primarily affects which image quality parameter?
A) Spatial resolution
B) Image noise
C) Temporal resolution
D) Beam hardening
Answer: B. Tube current (mA) is the primary determinant of the number of X-ray photons
produced. Increasing mA increases photon flux, which reduces quantum noise (image noise)
but does not directly improve spatial or temporal resolution .
2. The photoelectric effect is the primary mechanism of X-ray attenuation in which tissue?
A) Soft tissue
B) Fat
C) Calcium
D) Air
Answer: C. The photoelectric effect increases sharply with decreasing photon energy and
higher atomic number. Calcium (Z=20) attenuates low-energy X-rays more than soft tissue
due to its higher effective atomic number .
3. Which reconstruction algorithm most effectively reduces image noise in low-dose
cardiac CT while preserving spatial resolution?
A) Filtered back projection (FBP)
B) Standard iterative reconstruction (IR)
C) Model-based iterative reconstruction (MBIR)
D) Simple linear interpolation
Answer: C. MBIR models acquisition physics and noise statistics, achieving greater noise
reduction while preserving edge detail compared with FBP or basic IR .
4. In a 256-slice CT scanner, the maximum z-coverage per rotation is approximately:
A) 4 cm
,B) 8 cm
C) 12 cm
D) 16 cm
Answer: C. With detector rows approximately 0.5 mm each, 256 rows provide approximately
12 cm of z-coverage, allowing whole-heart coverage in a single rotation .
5. What is the primary advantage of dual-source CT regarding temporal resolution?
A) Temporal resolution remains unchanged at 165 ms
B) Temporal resolution improves to 83 ms (half the gantry rotation time)
C) Temporal resolution worsens to 330 ms
D) Temporal resolution is dependent on heart rate only
Answer: B. Dual-source CT uses two X-ray tubes and detectors offset by 90 degrees. The
standard quarter-scan reconstruction from a dual-source scanner rotating at 0.33 seconds
achieves a temporal resolution of 83 milliseconds at isocenter, which is half the gantry
rotation time .
6. Quantum noise is proportional to which of the following?
A) The square root of the signal (N)
B) The signal (N)
C) The square of the signal (N²)
D) The inverse of the signal (1/N)
Answer: A. Quantum noise is proportional to the square root of the signal (√N). Therefore,
the signal-to-noise ratio (SNR) is N/√N, which equals √N .
7. Increasing detector element size has what effect on spatial resolution?
A) Improves spatial resolution because more photons are captured
B) Decreases spatial resolution due to larger sampling intervals
C) Has no effect on spatial resolution
D) Only affects temporal resolution
Answer: B. Larger detector elements increase the minimum resolvable object size, thereby
reducing spatial resolution .
8. Which of the following best describes the "flash mode" (high-pitch) acquisition in dual-
source CT?
A) Continuous data acquisition over several heartbeats
B) A single-heartbeat scan with a pitch >3, providing ultra-low dose
C) Retrospective gating with ECG-based tube current modulation
D) A low-resolution scout scan only
Answer: B. Flash mode uses a very high pitch (>3) to acquire the entire heart in one rotation,
dramatically reducing radiation dose .
, 9. In virtual non-contrast imaging using dual-energy CT, iodine subtraction is based on:
A) Different photoelectric absorption at 80 and 140 kVp
B) The difference in Compton scattering between energies
C) The density of the material being imaged
D) The temporal resolution of the scanner
Answer: A. Dual-energy acquisition can separate iodine from calcium by exploiting the
different photoelectric absorption characteristics at two energy levels (e.g., 80 and 140 kVp),
providing virtual non-contrast images and iodine maps .
10. Which reconstruction kernel would be most appropriate for evaluating coronary stent
patency?
A) Smooth kernel
B) Standard kernel
C) Sharp/high-resolution kernel
D) Medium-smooth kernel
Answer: C. A sharp/high-resolution kernel, combined with metal artifact reduction and
curved MPR, best visualizes the stent lumen by improving spatial resolution at the cost of
increased noise .
Section 2: ECG Gating & Motion Control (ECG 门控与运动控制)
11. During a prospectively ECG-triggered axial scan, the heart rate variability exceeds the
padding window. Which adjustment best maintains image quality while limiting radiation
exposure?
A) Increase the padding window to cover the entire cardiac cycle
B) Switch to retrospective spiral with ECG-based tube current modulation
C) Lower the tube voltage to 100 kV and increase the padding
D) Proceed with the scan and accept potential motion artifacts
Answer: B. Prospective triggering freezes motion only within a narrow phase. If heart rate
variability is large, retrospective spiral with ECG modulation extends coverage across the
cycle while modulating dose, preserving diagnostic quality without excessive radiation .
12. What is the target heart rate for optimal coronary CTA image quality when using beta-
blockers?
A) <50 bpm
B) <65 bpm
C) <80 bpm
D) <100 bpm
