Test 2

Question 1

What is data acquisition

Answer 1

method of how patient is scanned to obtain data for image reconstruction

Question 2

What factors affect data acquisition

Answer 2

beam geometry
components

Question 3

size, shape, and motion of incident x-ray beam
A. Beam geometry
B. Components
C. Single slice

Answer 3

A. beam geometry

Question 4

what is a component fact for CT scanning

Answer 4

physical devices that shape and define the beam, measure transmission through patient, converts into digital data

Question 5

what are the types of CT image acquisition

Answer 5

single slice CT (conventional)
multi-slice CT (recent)
spiral scan CT (cutting edge)

Question 6

scanner moves along x-ray tube in straight line across patient’s body
A. Multi-slice
B. Spiral scan
C. Single Slice

Answer 6

C. single slice

Question 7

creates single 3D slice from x-ray tube getting multiple slices at a time
A. Multi-slice
B. Spiral scan
C. Single Slice

Answer 7

A. multi-slice

Question 8

array of multiple detectors used to improve image resolution and reduce dose
A. Multi-slice
B. Spiral scan
C. Single Slice

Answer 8

B. spiral scan

Question 9

Why do we use multislice detectors?

Answer 9

reduce number of elements needed for thicker slices
reduce dead space/gap between elements

Question 10

what is pitch

Answer 10

table movement per rotation divided by slice thickness - determined by collimation
aka. how far apart helical spiral gaps are

Question 11

pitch = 1
A. Overlapping spiral
B. Contiguous spiral
C. Extended spiral

Answer 11

B

Question 12

pitch > 1
A. Overlapping spiral
B. Contiguous spiral
C. Extended spiral

Answer 12

C

Question 13

pitch < 1
A. Overlapping spiral
B. Contiguous spiral
C. Extended spiral

Answer 13

A

Question 14

if pitch increases = gap _____

Answer 14

increases

Question 15

what has higher radiation dose
A. Overlapping spiral
B. Contiguous spiral
C. Extended spiral

Answer 15

A

Question 16

pitch ratio equation

Answer 16

pitch ration = mm traveled during 1 revolution / slice thickness

Question 17

patient dose is _____ proportional to pitch

Answer 17

inversely

Question 18

if pitch increases = dose _____

Answer 18

decreases

Question 19

what is used to reconstruct missing data

Answer 19

interpolation

Question 20

what is interpolation

Answer 20

computation of unknown value using known values on either side

Question 21

how does interpolation work?

Answer 21

• calculates planar data set from volume data set
• reconstructs image similar to conventional CT

Question 22

Advantages of helical CT (10)

Answer 22

1. complete organs scanned in short time
2. short scan times
3. gapless scanning since volume is scanned
4. reduced motion artifact
5. slices can be obtained for any position within volume
6. no slice shifting due to respiration
7. contrast given times are shorter and smaller amounts needed
8. contrast enhancement more uniform, lesion detection enhanced
9. greater multi-planar reconstruction accuracy
10. multiplanar imaging in fluoroscopy, angiography, endoscopy

Question 23

Limitations of CT

Answer 23

1. additional x-ray tube demands - tungsten expensive
2. interpolation removes streak artifacts but blurry images more likely to appear in low contrast regions of soft tissue = partial volume imaging

Question 24

what is considered a complementary view

Answer 24

views 180 degrees across from each other - corkscrew

Question 25

pro vs cons of MSCT (multislice CT)

Answer 25

pro: reduced scan time full body 30 sec very good spatial resolution easier to reconstruct 3D views con: powerful computing power needed longer processing time potential for increased patient dose

Question 26

what are the differences between CT scanner generations

Answer 26

scanning geometry scanning motion x-ray sources detectors

Question 27

why was the fifth generation developed for?

Answer 27

cardiac tomographic imaging

Question 28

what type of scanner does a fifth generation CT use?

Answer 28

electron beam scanner

Question 29

why would an electron beam scanner be used?

Answer 29

produces fast frame rate CT movies of heart beating

Question 30

how is spiral-helical CT made possible?

Answer 30

disk and cylinder --> design

Question 31

what is interscan delay time (ISD)

Answer 31

time to scan, collect data, and index the table and patient to next scanning position

Question 32

Limitations of conventional CT scanning

Answer 32

1. longer exam times for table indexing a inter-breath scanning 2. inaccurate 3D image creation --> missed anatomy from inconsistent levels of respiration 3. only a few slices can be scanned when max contrast enhancement technique is possible

Question 33

scanning time of patients A. 5 mm/sec B. 10 mm/sec C. 15 mm/sec D. 20 mm/sec

Answer 33

B

Question 34

Data acquisition problems with conventional CT

Answer 34

1. data collect in nonplanar geometry = different regions of volume and not through particular plane 2. no defined slice = localization of voxels within a planar slice is difficult 3. increased effective slice thickness