Axial VS Helical Scanning

Question 1

Scanning mode where the table stops at the scanning position and the tube rotates around the patient?

Answer 1

Conventional / Axial / Regular

Question 2

Scanning mode where the patient is continuously moving in the z-axis direction while the tube rotates around?

Answer 2

Spiral / Helical Mode

Question 3

Earliest scanning mode?

Answer 3

Step-and-shoot method

Question 4

Alternative name for Step-and-shoot scanning?

Answer 4

Axial Scanning
Conventional / Regular Scanning
Serial Scanning
Sequence Scanning

Question 5

CT table moves to the desired location and remains stationary while the x-ray tube rotates within the gantry, collecting data

Answer 5

STEP-AND-SHOOT SCANNING

Question 6

Axial slices lie ___ to one another

Answer 6

parallel

Question 7

The slice beginning matches

Answer 7

exactly the slice end

Question 8

Perfect circles are formed that are ____ to z axis

Answer 8

perpendicular

Question 9

Used by both third- and fourth-generation scanners

Answer 9

STEP-AND-SHOOT SCANNING

Question 10

obtained data for one slice with each rotation (for early systems)

Answer 10

STEP-AND-SHOOT SCANNING

Question 11

How many degrees rotation did the third generation systems use for each acquisition for step and shoot scanning?

Answer 11

360 degrees

Question 12

How many degrees rotation did the fourth generation systems use for each acquisition for step and shoot scanning?

Answer 12

400 degrees

Question 13

In all types of scanners using this method there is a slight pause in scanning between data acquisitions as the table moves to the next location. , referred to as the

Answer 13

interscan delay

Question 14

In early scanners the time for a complete cycle allowed only a single scan to be acquired

Answer 14

each time the patient held her breath.

Question 15

Newer scanners shortened the cycle time dramatically, allowing axial scans to be

Answer 15

“clustered”

Question 16

Grouping scans in clusters reduces what problem

Answer 16

Slice misregistration

Question 17

Advantages of axial scanning mode?

Answer 17

Highest Image quality, superior to helical methods

Question 18

Why does step-and-shoot methods produces highest image quality

Answer 18

axial nature and the fact that the patient table remains stationary during data acquisition

Question 19

Disadvantages of axial scanning?

Answer 19

Adds to the total examination time
Less than 30 seconds
Not useful in contrast studies
Breathing creates motion artifact
Data reconstruction and reformation limited
Induce motion in patients organs
Misregistration

Question 20

Delay inherent in axial scan sequences which is caused by the differences in patients breathes with each data acquisition?

Answer 20

Misregistration

Question 21

When was helical scanning introduced?

Answer 21

late 1980s

Question 22

Alternative name for helical scanning?

Answer 22

Spiral or Continuous acquisition Scanning

Question 23

What did helical scanning eliminate?

Answer 23

Interscan delay

Question 24

three basic ingredients that define a helical scan process

Answer 24

1. a continually rotating x-ray tube,
2. constant x-ray output, and
3. uninterrupted table movement.

Question 25

Helical scanning is often referred to as

Answer 25

volumetric scanning

Question 26

Refers to the fact that the end result of such a scanning method is a block of data, not separate slices, as occurs in traditional axial scanning?

Answer 26

Volumetric scanning

Question 27

Increasing the scan speed results in improved image resolution owing to the ability to obtain images with:

Answer 27

Improved iodinated contrast concentration. Decreased respiratory and cardiac motion artifact. Superior multiplanar and three-dimensional (3-D) reformation capabilities.

Question 28

Other advantages of helical scanning

Answer 28

Improving diagnostic accuracy. Patient comfort. Department productivity.

Question 29

What major improvements lead to the development of the helical scan?

Answer 29

``` Slip ring design More Efficient Tube cooling Higher x-ray output More efficient detectors Smoother table movements Software improvements for table motion Improved raw data management ```

Question 30

allow the tube to move continually in the same direction

Answer 30

Newer systems slip rings

Question 31

eliminates cumbersome electrical cables and makes possible a data-gathering system using a continuous rotation of the x-ray source

Answer 31

Slip ring technology

Question 32

There is constant x-ray output throughout a helical scan acquisition that Can last more than 60 seconds without a pause for cooling.

Answer 32

More-Efficient Tube Cooling

Question 33

The tube makes a complete rotation in 1 second or less. | Overal decrease in mAs to one third (or less) compared to axial scan if the mA remained the same.

Answer 33

Higher X-ray Output

Question 34

allow the total radiation dose to be lower for both helical and axial scans done on the newer systems.

Answer 34

more-efficient detectors

Question 35

Motion artifact degrades images, and images are created while the table is in motion, helical scanning requires the table to move very smoothly.

Answer 35

Smoother Table Movement

Question 36

Manufacturers then since have created special software that adjusts for the smooth table motion

Answer 36

Special Software

Question 37

take the slant and blur out of are statistical methods that create images that closely resemble those acquired in a traditional axial mode

Answer 37

Interpolation

Question 38

Two most common schemes in interpolation

Answer 38

360° and the 180° linear interpolations (abbreviated 360LI and 180LI)

Question 39

Huge amounts of data are generated in a very short time

Answer 39

Improved Raw Data Management

Question 40

a parameter that is commonly used to describe the CT table movement

Answer 40

Pitch

Question 41

It is most commonly defined as the travel distance of the CT scan table per 360° rotation of the x-ray tube, divided by the x-ray beam collimation width

Answer 41

Pitch

Question 42

When the table feed and beam collimation are identical how much is the pitch?

Answer 42

1

Question 43

When the table feed is less than the beam collimation, pitch is?

Answer 43

Less than 1 and scan overlaps occur

Question 44

To maintain a pitch of 1, the table speed will vary according to

Answer 44

the slice thickness selected

Question 45

describes the relationship of the table speed to the slice thickness

Answer 45

Pitch

Question 46

As the pitch increases, so does the

Answer 46

slice angle

Question 47

is required to straighten the image and the effects of interpolation become more pronounced

Answer 47

More interpolation

Question 48

More interpolation effects to

Answer 48

image unsharpness and effective slice thickness blooming

Question 49

Increasing the pitch will result to

Answer 49

- a scan covering more anatomy lengthwise for a given total acquisition time - reduce the radiation dose to the patient

Question 50

A decrease in pitch will

Answer 50

slows down the table speed

Question 51

will result in overlapping slices and will decrease the amount of anatomy covered per unit time and increase the radiation dose to the patient

Answer 51

A pitch of less than 1

Question 52

A pitch that is not commonly used

Answer 52

pitch of less than 1

Question 53

A compromise is necessary when the pitch is

Answer 53

extended beyond 1

Question 54

exchange for the shortened examination time and the reduced patient radiation dose comes

Answer 54

comes the loss of image sharpness and a decrease in the SSP