Module 4 - CT Reconstruction and Imaging - Q&A Flashcards

A comprehensive set of 40 Q&A flashcards drawn from Module 4 slides to prep for exams on CT reconstruction, windowing, ROI, interpolation, MPR/VRT/SSD, and related concepts.

What system processes detector signals before reconstruction?

DAS (Data Acquisition System).

What is raw data?

Large temporary data files used for reconstruction.

How long is raw data usually stored?

24–48 hours before being overwritten or until deleted for extra space

What is image data?

Processed images used for diagnosis, review, and storage.

What happens if raw data is deleted?

No further reconstructions are possible.

Define prospective reconstruction.

Automatic reconstructions created during scanning.

Define retrospective reconstruction.

Reconstructions created later from raw data.

What reconstruction method has been historically dominant?

Filtered back-projection (FBP).

Main limitation of FBP?

High noise, requiring higher mA (dose).

Benefit of Iterative Reconstruction?

Dose reduction and improved noise/image quality.

Limitation of Iterative Reconstruction?

Slower processing and “plastic-y” appearance.

What does SFOV define?

The maximum circular scan area acquired.

Can DFOV exceed SFOV?

No, DFOV ≤ SFOV.

Why use a reduced DFOV?

To improve spatial resolution (smaller pixels).

Why is zoom inferior to target recon?

It enlarges pixels without improving detail.

What units quantify CT attenuation?

Hounsfield Units (HU).

HU of water?

0 HU.

HU of air?

−1000 HU.

HU of bone (dense cortical)?

Around +1000 HU.

1 HU equals what % attenuation difference?

0.1%.

How does kV affect attenuation?

Higher kV → lower attenuation.

What is window width (WW)?

HU range displayed. (shades of grey)

What is window level (WL)?

Center HU of tissue of interest. (brightness levels)

Typical WL/WW for lung?

WL –600, WW 1500.

Typical WL/WW for brain?

WL 30, WW 100.

What is an ROI used for?

Measuring attenuation (HU) in a selected region.

What are interpolation algorithms used for?

Correcting helical CT data to axial images.

Examples of interpolation methods?

180° LI, 360° LI.

What do MPRs provide?

Multi-planar views (coronal, sagittal, axial).

Why use overlapping recon slices?

Improve spatial and low-contrast resolution.

Example of overlapping slices?

3 mm slices every 1.5 mm.

SSD reconstruction is best for?

Bone (single tissue type).

VRT reconstruction is best for?

Multi-tissue display (bone + soft tissue).

What determines how long Iterative Reconstruction takes?

Number of processing iterations needed.

Why is FBP still used in trauma?

Speed (near real-time recon).

What is volume averaging?

Blending of tissue attenuation in one voxel.

How to reduce volume averaging?

Use thinner slices, small DFOV, small detector width.

What is the term for creating missing information between 2 known values?

Interpolation

Which of the following statements are true about retrospective reconstruction?

Uses raw data to generate new images after scanning

What determines the number of shades of gray that is represented on an image?

Window Width

After reviewing an images from abdomen CT, the radiologist wants to take a closer look at the spine. Which of the following options allows for enlarging the spine, yet maintaining good resolution? 

Reconstruct images with a smaller DFOV

You would like to find out the HU measurement of a suspicious looking mass. Which image display function will allow you to do that?

ROI measurement

Which of the following reconstruction methods offer the greatest dose reduction for the patient?

Adaptive Iterative Statistical Reconstruction

Filtered back projection uses which theory to supress noise?

Fourier Theory

What is the process of applying a filter to an attenuation profile called?

Convolution