Forming CT Images

Question 1

What do you need to measure in order to produce a cross-sectional image?

Answer 1

Attenuation information through many projections

Question 2

What are the three scanning methods used in CT?

Answer 2

Localizer
Conventional (Serial)
Helical

Question 3

When would a localizer image (single projection image) be used?

Answer 3

To position the slices at the location where we want to collect the cross-sectional images

Question 4

Which of the scanning methods used in CT produces cross-sectional images?

Answer 4

Conventional & Helical Scan

Question 5

What is another term used for helical scans?

Answer 5

Spiral or Volumetric CT

Question 6

What views may be collected in a localizer scan?

Answer 6

Lateral
Anterior/Posterior
Oblique

Question 7

When would an AP localizer image be collected?

Answer 7

To specify transverse slices

Question 8

When would a lateral localizer image be collected?

Answer 8

To specify oblique slices when the gantry is angle

Question 9

What is the length of anatomical coverage of the localizer image dependent upon?

Answer 9

Speed of the patient table and amount of time the x-ray tube is on

Question 10

What are the reasons as to why helical CT is most often used in CT studies performed today?

Answer 10

Speed
Ease of use
Ability to reconstruct images

Question 11

Conventional CT yields the best image quality which is free from:

Answer 11

Helical artifacts

Question 12

What are some reasons as to why conventional CT scans may be chosen over helical CT?

Answer 12

Neurological work involving fine detail
Obese patients
Cardiac calcium scoring

Question 13

When performing a conventional scan on a single-row detector scanner, how is raw data obtained?

Answer 13

By a single rotation of the gantry from only one cross-sectional slice location

Question 14

Why does a helical scan’s x-ray beam take on a helical path?

Answer 14

The patient table is moved through the gantry at the same time that the x-ray tube rotates around the patient’s body

Question 15

Why would a patient be required to refrain from breathing in CT?

Answer 15

To minimize motion artifacts

To avoid skipping anatomy

Question 16

What are some advantages of helical scanning?

Answer 16

Faster studies
More coverage in a breath-hold
No missed anatomy
Less contrast injection needed
Arbitrary slice positioning
Ideal data for post-processing

Question 17

In a helical scan, how is the path of the x-ray beam defined?

Answer 17

Thickness of the x-ray bream

Speed of the patient table

Question 18

How is the thickness of the x-ray beam determined on a single-row detector scanner?

Answer 18

It equals the slice thickness of the final image

Question 19

How is the thickness of the x-ray bream determined on a multi-row detector scanner?

Answer 19

It is divided by the number of rows of detectors being used

Question 20

In which scanning method used in CT does not collect images in a single slice plane?

Answer 20

Helical

Question 21

What must be done to the attenuation information in a helical scan?

Answer 21

It must be divided into raw data files for individual, planar slices

Question 22

What are sharp reconstruction filters often used for?

Answer 22

Visualizing musculoskeletal detail

Question 23

What are smooth reconstruction filters often used for?

Answer 23

Visualizing soft tissue contrast

Question 24

On what kind of scanners would back projection be used?

Answer 24

Single-row detector

Multi-row detector

Question 25

Why would retrospective reconstruction be commonly performed?

Answer 25

To apply a different reconstruction filter

Question 26

Why might retrospective reconstruction be performed on MDCT scanners?

Answer 26

To vary the reconstructed slice thickness

Question 27

Multiplanar reconstruction requires only the _____ data.

Answer 27

Image

Question 28

3D surface rendering is performed on the _____ data.

Answer 28

Image

Question 29

In which orientation would we position the scanner if we want to angle the slice away from the transverse plane and toward the coronal plane?

Answer 29

Lateral

Question 30

What is used to store the actual attenuation data measured by the detectors prior to image reconstruction?

Answer 30

Raw data file

Question 31

What is another term used for reconstruction filter?

Answer 31

“Kernel”

Question 32

On scanners that are capable of collecting 64 slices in one rotation, which reconstruction is used?

Answer 32

Cone beam

Question 33

On scanners that do not collect more than four slices per rotation, which reconstruction method is best to be used?

Answer 33

Back-projection

Question 34

When performing retrospective reconstruction, what kind of data is needed?

Answer 34

Raw data

Question 35

On a single-row detector, how is the slice thickness determined?

Answer 35

By the collimation of the x-ray beam

Question 36

Which reconstruction process is used to reconstruct images in orientations other than the one in which they were acquired?

Answer 36

Multiplanar reconstruction

Question 37

Overlapping slices with no gaps in-between generates the most diagnostic _____ reconstruction

Answer 37

Multi-planar

Question 40

Which reconstruction method allows us to reconstruct images using different parameters than those that were originally reconstructed?

Answer 40

Retrospective reconstruction

Question 41

Which reconstruction process is used to reconstruct cross-sectional CT images from the raw data?

Answer 41

Back-projection