Computed Tomography Test Computed Tomography 2 — Questions and Answers
Question 1: Which CT artifact is caused by two high-density objects lying in the same scan plane?
- Motion artifact
- Beam hardening artifact (Correct answer)
- Partial volume artifact
- Ring artifact
Correct answer: Beam hardening artifact
Beam hardening occurs when polychromatic X-rays are differentially absorbed, causing dark streaks between dense structures like metal implants or dense bone.
Question 2: What does the term 'pitch' refer to in helical CT scanning?
- The number of detector rows
- The table distance traveled per gantry rotation divided by beam collimation (Correct answer)
- The speed of gantry rotation in RPM
- The angle of the X-ray beam relative to the patient
Correct answer: The table distance traveled per gantry rotation divided by beam collimation
Pitch is calculated as table feed per rotation divided by total beam collimation width; a pitch of 1 means the table moves exactly one beam width per rotation.
Question 3: Which window setting is most appropriate for evaluating pulmonary nodules?
- Bone window (WW 2000, WL 500)
- Lung window (WW 1500, WL -600) (Correct answer)
- Brain window (WW 80, WL 40)
- Soft tissue window (WW 400, WL 40)
Correct answer: Lung window (WW 1500, WL -600)
The lung window uses a wide window width and low window level to optimize contrast between air-filled lung parenchyma and soft tissue nodules.
Question 4: What is the primary purpose of a bow-tie filter in a CT scanner?
- To reduce image noise at the center of the scan field
- To shape the X-ray beam and reduce dose to peripheral tissues (Correct answer)
- To increase contrast resolution throughout the image
- To correct for detector calibration errors
Correct answer: To shape the X-ray beam and reduce dose to peripheral tissues
A bow-tie (wedge) filter is thicker at the edges to attenuate X-rays where the patient cross-section is thinner, reducing peripheral skin dose and detector saturation.
Question 5: A patient with a creatinine level of 2.8 mg/dL is scheduled for contrast-enhanced CT. What is the most appropriate next step?
- Proceed with full contrast dose as ordered
- Administer contrast and monitor vitals closely
- Consult with the ordering physician regarding contrast risk and alternatives (Correct answer)
- Automatically cancel the exam without notifying the physician
Correct answer: Consult with the ordering physician regarding contrast risk and alternatives
Elevated creatinine indicates reduced renal function and significant risk of contrast-induced nephropathy; the ordering physician must be consulted to weigh risk versus benefit.
Question 6: Which reconstruction algorithm produces the sharpest bone detail in CT imaging?
- Soft tissue (smooth) kernel
- Standard kernel
- High-frequency (edge-enhancing) kernel (Correct answer)
- Low-frequency kernel
Correct answer: High-frequency (edge-enhancing) kernel
High-frequency or bone kernels accentuate edge transitions, producing sharper images ideal for cortical bone and temporal bone detail, though they increase image noise.
Question 7: What is the typical Hounsfield Unit (HU) value for simple (non-hemorrhagic) cerebrospinal fluid?
- 0 HU (Correct answer)
- −100 HU
- 35–45 HU
- 80–100 HU
Correct answer: 0 HU
Simple CSF measures approximately 0–15 HU, close to the value of water, allowing differentiation from higher-density hemorrhage or proteinaceous fluid.
Computed Tomography Test Computed Tomography 2
Which CT artifact is caused by two high-density objects lying in the same scan plane?