Reconstruction & Data Manipulation

Question 1

What is a ray?

Answer 1

Path of the x-ray beam from the tube to the detector

Question 2

What is ray sum?

Answer 2

The detector senses the arriving ray and measures the attenuated beam

Question 3

What are attenuation profiles?

Answer 3

A row of voxels and their attenuation properties that form a line from one side of the images space to the other

Question 4

What is back projection?

Answer 4

Process of mathematically mapping the attenuation pathway at every angle and measured through a scan to locate where in a patient attenuation is occurring and to what degree

Question 5

What is a disadvantage of back projection?

Answer 5

Streaking artefact or star projection

Question 6

What is FILTERED back projection?

Answer 6

Complex mathematical equations that are applied to attenuation profile BEFORE back projection is done

Question 7

How is back projection done?

Answer 7

1. The path of the x-ray beam from the tube is detected by the detector
2. The detector senses the arriving ray that measures the beam that is attenuated
3. The complete set of rays are summed up
4. The attenuation properties of each ray are correlated to their position to create a map
5. This is done at all angles around the body to identify locations of attenuated objects

Question 8

What is the smoothing algorithm?

Answer 8

A decrease of difference in HU pixel values

Decreased spatial resolution
Increased low contrast resolution

Question 9

What is a bone algorithm?

Answer 9

An increase in difference between HU values of pixels

Increased spatial resolution
Decreased low contrast resolution

Question 10

What is iterative reconstruction?

Answer 10

Repetitive process that starts with a back projection as an estimate of the true data set and then compared to the scan data to see how close it is to the true data

This is done repeatedly many times until it resembles very closely to a true data representation

Question 11

What are advantages of iterative reconstruction over filtered back projection?

Answer 11

1. Reduced patient dose
2. Improved low contrast resolution
3. Reduced image noise

Question 12

What is volume averaging?

Answer 12

Mean density of voxels from a few slices to generate a thicker slice

Question 13

What is MIP?

Answer 13

Maximum Intensity Projection

Applying the highest value of voxels within a few slices only to a slice

Useful for bone and contrast usage

Question 14

What is MinIP?

Answer 14

Minimum Intensity Projections

Applying the lowest voxel value within a few slices only to a slice

Useful for the bronchial tree

Question 15

What is MPR?

Answer 15

Multi Planar Reformatting

Combining data to be able to view it from different orientations

Question 16

What happens if the axial slices used for MPR are too thick?

Answer 16

Coronal and sagittal slices will have a stair step artefact

Question 17

What is VRT?

Answer 17

Volume Rendering Technique

3D model that displays only a desired anatomical feature

Used in Angio, surgical planning, and strokes

Question 18

What is SSD?

Answer 18

Surface Shading Display

Surface rendered image that provides a realistic appearance of anatomy on VRT