Computed Tomography Test Computed Tomography Knowledge Questions and An 4 — Questions and Answers
Question 1: What is the primary safety concern when scanning a patient with a pacemaker using CT?
- Radiofrequency interference causing pacemaker malfunction
- Excessive radiation dose to the cardiac device
- Potential image artifacts affecting diagnostic quality (Correct answer)
- Gadolinium contrast nephrotoxicity
Correct answer: Potential image artifacts affecting diagnostic quality
While CT does not emit RF waves that affect pacemaker function, metallic pacemaker components cause streak artifacts that can limit evaluation of surrounding cardiac and mediastinal structures.
Question 2: What is meant by 'isotropic voxels' in CT imaging?
- Voxels with identical attenuation values in all directions
- Voxels with equal dimensions in all three spatial planes (x, y, z) (Correct answer)
- Voxels that contain only a single tissue type
- Voxels with zero noise contribution
Correct answer: Voxels with equal dimensions in all three spatial planes (x, y, z)
Isotropic voxels have equal length, width, and height, enabling high-quality multiplanar and 3D reconstructions without resolution loss in any plane.
Question 3: A technologist notes that a CT image has a mottled, grainy appearance. Which adjustment would most directly improve this?
- Increase kVp
- Decrease pitch
- Increase mAs (Correct answer)
- Widen the window width
Correct answer: Increase mAs
Increasing mAs increases X-ray photon flux, reducing quantum (photon) noise and improving the signal-to-noise ratio of the image.
Question 4: Which structure should be visible in a CT scan performed at the level of the carina?
- Aortic arch bifurcation only
- Bifurcation of the trachea into the left and right main bronchi (Correct answer)
- Aortic valve and cardiac chambers
- Renal hila
Correct answer: Bifurcation of the trachea into the left and right main bronchi
The carina is the cartilaginous ridge at the inferior end of the trachea marking its bifurcation into the left and right main bronchi, located at approximately T4–T5.
Question 5: What is the role of iterative reconstruction (IR) in modern CT imaging?
- To increase spatial resolution beyond hardware limitations
- To reduce image noise at lower radiation doses compared to filtered back projection (Correct answer)
- To eliminate all metallic streak artifacts
- To automatically segment anatomical structures
Correct answer: To reduce image noise at lower radiation doses compared to filtered back projection
Iterative reconstruction algorithms model the acquisition process and iteratively correct image data, enabling diagnostic image quality at significantly reduced radiation doses.
Question 6: In CT, what does the acronym 'FOV' stand for and what does it control?
- Field of Voltage — controls kVp selection
- Field of View — controls the size of the reconstructed image area (Correct answer)
- Frequency of Viewing — determines display refresh rate
- Focus of Vision — adjusts detector sensitivity
Correct answer: Field of View — controls the size of the reconstructed image area
Field of View (FOV) defines the diameter of the reconstructed image; a smaller FOV zooms in on a region of interest and improves apparent spatial resolution.
Question 7: What is the typical HU range for simple fluid (such as pleural effusion or ascites) on CT?
- -100 to -50 HU
- 0 to 20 HU (Correct answer)
- 30 to 70 HU
- 80 to 120 HU
Correct answer: 0 to 20 HU
Simple transudative fluid (water-density) typically measures 0–20 HU, as it is close to pure water (0 HU) in composition.
Computed Tomography Test Computed Tomography Knowledge Questions and An 4
What is the primary safety concern when scanning a patient with a pacemaker using CT?