ARRT ARRT CT Post-Processing and Reconstruction 1 — Questions and Answers
Question 1: Which CT post-processing technique displays only voxels above a selected threshold, making it useful for 3D visualization of bones and vascular structures?
- Multiplanar reformation (MPR)
- Volume rendering (VR)
- Surface shaded display (SSD)
- Maximum intensity projection (MIP) (Correct answer)
Correct answer: Maximum intensity projection (MIP)
Maximum intensity projection (MIP) selects and displays the highest attenuation voxel along each ray through the dataset, ideal for visualizing contrast-enhanced vessels or calcifications.
Question 2: Multiplanar reformation (MPR) in CT refers to:
- Generating 3D surface models from volumetric data
- Reconstructing axial images into coronal, sagittal, or oblique planes (Correct answer)
- Applying color to CT images based on Hounsfield units
- Subtracting pre-contrast from post-contrast images
Correct answer: Reconstructing axial images into coronal, sagittal, or oblique planes
MPR uses the volumetric CT dataset to create reformatted images in any anatomical plane without additional radiation exposure to the patient.
Question 3: In CT, the filtered back projection (FBP) reconstruction algorithm applies a mathematical filter primarily to:
- Remove quantum noise before reconstruction
- Correct for star artifacts inherent in simple back projection (Correct answer)
- Segment soft tissue from bone
- Align misregistered projection data
Correct answer: Correct for star artifacts inherent in simple back projection
FBP applies a ramp or other convolution filter to projection data before back-projecting to eliminate the blurring ('star artifact') produced by simple back projection.
Question 4: Iterative reconstruction (IR) techniques in CT offer which primary advantage over filtered back projection?
- Faster reconstruction speed
- Reduced image noise at the same or lower radiation dose (Correct answer)
- Higher spatial resolution
- Elimination of all artifacts
Correct answer: Reduced image noise at the same or lower radiation dose
IR algorithms use repeated mathematical modeling of the imaging process to suppress noise, allowing diagnostic image quality to be maintained at reduced mAs and dose.
Question 5: Curved planar reformation (CPR) in CT is most useful for:
- Generating endoscopic views of hollow organs
- Straightening and displaying tortuous structures such as vessels or the spine along their entire length (Correct answer)
- Creating color-coded perfusion maps
- Subtracting bone from CT angiography images
Correct answer: Straightening and displaying tortuous structures such as vessels or the spine along their entire length
CPR follows a user-defined curved path through the volume dataset to display a tortuous structure in a single unfolded plane, useful for coronary arteries or the aorta.
Question 6: Which post-processing technique is most appropriate for evaluating luminal stenosis of the carotid arteries on a CT angiogram?
- Minimum intensity projection (MinIP)
- Volume rendering alone
- Multiplanar reformation combined with MIP (Correct answer)
- Standard axial images only
Correct answer: Multiplanar reformation combined with MIP
Combining MPR (which shows vessel walls and plaques in cross-section) with MIP (which shows the lumen in projection) gives the most complete assessment of carotid stenosis.
ARRT ARRT CT Post-Processing and Reconstruction 1
Which CT post-processing technique displays only voxels above a selected threshold, making it useful for 3D visualization of bones and vascular structures?