Computed Tomography Test Computed Tomography 4 — Questions and Answers
Question 1: During a CT pulmonary angiography (CTPA), the technologist observes the pulmonary arteries are not well opacified. What is the most likely cause?
- Excessive kVp causing beam hardening
- Scan initiated too early before contrast reaches the pulmonary arteries (Correct answer)
- The patient moved during acquisition
- The reconstruction kernel was set incorrectly
Correct answer: Scan initiated too early before contrast reaches the pulmonary arteries
CTPA timing is critical; scanning before contrast bolus reaches the pulmonary circulation results in non-diagnostic images — bolus tracking or test bolus timing is used to prevent this.
Question 2: What is the CTDI (Computed Tomography Dose Index) primarily used to measure?
- Patient effective dose in millisieverts
- Scanner radiation output for a single axial scan (Correct answer)
- Image noise level across a reconstructed slice
- Contrast-to-noise ratio of an image
Correct answer: Scanner radiation output for a single axial scan
CTDI measures the average absorbed dose within the scan volume from a single rotation and is used as a standardized descriptor of scanner output, not true patient effective dose.
Question 3: Which type of iodinated contrast agent has the lowest risk of adverse reactions?
- High-osmolality ionic monomers
- Low-osmolality ionic dimers
- Low-osmolality nonionic monomers (Correct answer)
- High-osmolality nonionic agents
Correct answer: Low-osmolality nonionic monomers
Low-osmolality nonionic monomers (e.g., iohexol, iopamidol) have the lowest rates of adverse reactions due to reduced chemotoxicity and near-physiologic osmolality.
Question 4: A patient's CT of the chest shows a focal area of ground-glass opacity (GGO). What does GGO characteristically represent?
- Complete airspace consolidation with no air bronchograms
- Partial filling of alveoli or interstitial thickening with preserved underlying architecture (Correct answer)
- Pleural fluid accumulation in the lung base
- Calcified lymph nodes in the hilum
Correct answer: Partial filling of alveoli or interstitial thickening with preserved underlying architecture
GGO appears as a hazy increased attenuation that does not obscure underlying vessels or bronchi, reflecting partial alveolar filling or thickened interstitium.
Question 5: Which of the following best describes 'iterative reconstruction' in modern CT?
- A method of acquiring projection data using multiple X-ray sources
- A computational algorithm that repeatedly refines the image to reduce noise while preserving spatial resolution (Correct answer)
- A technique for synchronizing image acquisition with cardiac cycles
- A post-processing filter applied only to bone windows
Correct answer: A computational algorithm that repeatedly refines the image to reduce noise while preserving spatial resolution
Iterative reconstruction algorithms model the CT acquisition process and iteratively update the image estimate to reduce noise, allowing diagnostic quality at lower radiation doses.
Question 6: What is the significance of a 'split-bolus' technique in contrast-enhanced CT?
- It doubles the contrast volume to improve enhancement
- It combines two contrast injection phases into a single acquisition to reduce radiation dose (Correct answer)
- It administers oral and IV contrast simultaneously
- It pre-mixes contrast with saline to reduce osmolality
Correct answer: It combines two contrast injection phases into a single acquisition to reduce radiation dose
The split-bolus technique injects contrast in two separated boluses so that a single scan acquisition captures both nephrographic and excretory phase opacification, reducing the number of scan passes and radiation dose.
Question 7: What is the appropriate action when a patient reports a previous moderate contrast reaction and requires contrast-enhanced CT today?
- Refuse the exam and refer back to the ordering physician without further action
- Premedicate with corticosteroids and antihistamines per protocol and notify the radiologist (Correct answer)
- Administer contrast immediately with double the dose to speed the exam
- Switch to a higher osmolality contrast agent
Correct answer: Premedicate with corticosteroids and antihistamines per protocol and notify the radiologist
Patients with prior moderate reactions are at increased risk and should receive premedication (typically oral prednisone plus diphenhydramine) with radiologist awareness before contrast administration.
Computed Tomography Test Computed Tomography 4
During a CT pulmonary angiography (CTPA), the technologist observes the pulmonary arteries are not well opacified.
What is the most likely cause?