Computed Tomography Test Computed Tomography 5 — Questions and Answers
Question 1: Which CT acquisition mode collects data continuously as the table moves through the gantry?
- Sequential (axial) mode
- Helical (spiral) mode (Correct answer)
- Cine mode
- Scout (topogram) mode
Correct answer: Helical (spiral) mode
Helical CT rotates the X-ray tube continuously while the table advances, creating a spiral data set that allows retrospective reconstruction at any slice position.
Question 2: What is the primary advantage of dual-energy CT (DECT) over single-energy CT?
- Faster gantry rotation speed
- Material decomposition enabling differentiation of tissues with similar HU values (Correct answer)
- Higher spatial resolution in the z-axis
- Reduced contrast volume requirements in all body regions
Correct answer: Material decomposition enabling differentiation of tissues with similar HU values
DECT acquires data at two kVp settings, enabling material decomposition algorithms that distinguish substances like iodine, uric acid, and calcium that may overlap in attenuation at single energy.
Question 3: Which structure is best identified on a CT image using a bone window with a window level of approximately 300–700 HU?
- Brain white matter
- Liver parenchyma
- Cortical bone and fracture lines (Correct answer)
- Pulmonary vessels
Correct answer: Cortical bone and fracture lines
Bone windows use high window levels centered on dense cortical bone (≈400–1000 HU), which optimizes visualization of fractures, bony trabecular detail, and periosteal changes.
Question 4: A pregnant patient requires abdominal CT for suspected appendicitis. Which statement about fetal radiation risk is most accurate?
- CT is absolutely contraindicated in all trimesters
- Fetal risk is negligible at typical diagnostic doses below 50 mGy, but benefits must outweigh risks (Correct answer)
- The fetus is fully shielded by the uterus and receives no radiation dose
- Radiation risk is identical regardless of gestational age
Correct answer: Fetal risk is negligible at typical diagnostic doses below 50 mGy, but benefits must outweigh risks
At diagnostic CT doses typically below 25 mGy, deterministic fetal effects are extremely unlikely; however, the ALARA principle still applies and clinical benefit must justify the exposure.
Question 5: What does 'multiplanar reformation' (MPR) allow in CT post-processing?
- Reconstruction of 3D surface-rendered models for printing
- Display of axial raw data in coronal, sagittal, or oblique planes (Correct answer)
- Subtraction of pre-contrast from post-contrast images
- Automated segmentation of lung nodules for volumetry
Correct answer: Display of axial raw data in coronal, sagittal, or oblique planes
MPR resamples the volumetric CT dataset to display images in any desired plane, allowing evaluation of anatomy that is difficult to assess on axial images alone.
Question 6: Which factor most significantly increases the risk of contrast extravasation during CT power injection?
- Using a 20-gauge antecubital IV catheter
- Injecting at a rate of 2 mL/s
- Using a small-gauge hand or wrist vein at high flow rates (Correct answer)
- Warming the contrast agent to body temperature
Correct answer: Using a small-gauge hand or wrist vein at high flow rates
Small, fragile distal veins of the hand or wrist are more prone to rupture at high injection rates, and extravasation of large volumes of contrast can cause tissue necrosis.
Question 7: What is the main clinical application of CT fluoroscopy?
- Cardiac stress perfusion imaging
- Real-time guidance for percutaneous biopsies and drainage procedures (Correct answer)
- Dynamic assessment of swallowing disorders
- Whole-body oncologic staging
Correct answer: Real-time guidance for percutaneous biopsies and drainage procedures
CT fluoroscopy provides continuous or near-continuous CT imaging to guide needle placement during interventional procedures such as lung biopsies or abscess drainage.
Computed Tomography Test Computed Tomography 5
Which CT acquisition mode collects data continuously as the table moves through the gantry?