Week 5 - Acquisition

Question 1

-Determines the area within the gantry from which the raw data is acquired
-determines the number of detector cells collecting data
*isocentering crucial
*should come close to just encompassing the patient

Answer 1

Scan field of view (SFOV)

Question 2

T/F
Anything outside the SFOV is not imaged

Answer 2

True

Question 3

Artifacts from outside the FOV

Answer 3

Out of field artifacts
Ex. Arms on abdomen scan

Question 4

-determines how much of the collected raw data is used to create the image
-acts like a digital zoom on a camera
-affects image quality by changing the pixel size
*cannot be larger than SFOV

Answer 4

Display field of view (DFOV)

Question 5

T/F
DFOV is always smaller than SFOV

Answer 5

True

Question 6

What are the 2 methods of data acquisition?

Answer 6

Slice by slice - axial

Volume - spiral/helical

Question 7

What 3 steps contribute to interscan delay in slice by slice CT scan?

Answer 7

1. Tube and detectors accelerate to a constant speed
   2.
2. Tube and detectors slow down and come to a stop
3. Table and patient indexed to the next scanning position

Question 8

What is an advantage of step and shoot scanning? (Slice by slice)

Answer 8

-When breathing movement is not seen, image quality is slightly superior to that of helical scanning
-slices are axial in nature

Question 9

What are some limitations of slice by slice scanning? (Axial)

Answer 9

-longer exam times because of start-stop action, table indexing, cable unwinding

Question 10

T/F
A limitation of axial scanning is certain portions of anatomy are omitted because patient respiration phase may not be consistent each time

Answer 10

True

Question 11

Why does axial (slice by slice) acquisition misregistration occur?

Answer 11

Occurs because of different breathing patterns between scans

Question 12

What causes a “steplike” contour appearance in 3D images in axial (slice by slice) scanning?

Answer 12

Inconsistent levels of inspiration

Question 13

What are the applications of volume scanning, and could not be done without it?

Answer 13

1. CT fluoroscopy
2. CT perfusion
3. 3D imaging
4. CT angiography
5. CT endoscopy: Virtual reality
6. Cardiac CT imaging
7. Artificial Intelligence in CT

Question 14

T/F
The 7 applications of volume scanning could not be done with axial scanning

Answer 14

True

Question 15

T/F
Not all CT are done supine

Answer 15

True

Question 16

-allows for reconstruction and display of images in real time with variable frame rates
-used when doing CT biopsies

Answer 16

CT fluoroscopy

Question 17

What 3 advantages is CT fluoroscopy based on?

Answer 17

1. Fast, continuous scanning made possible by spiral/helical scanning
2. Fast image reconstruction made possible by special hardware performing quick calculations and a new image reconstruction algorithm
3. Continuous image display by use of cine mode at frame rates of 2-8 images per second

Question 18

Used to evaluate strokes, vasospasms, neurovascular disorders
Determined the extent of irreversible infarcted brain tissue
Generates map of the cerebral blood flow, cerebral blood volume, and mean transit time

Answer 18

CT perfusions

Question 19

What needs to be performed before a CT perfusion?

Answer 19

CT angiogram

Question 20

Used in radiation treatment planning, cranial imaging, surgical planning, and orthopaedics
Transforms transaxial CT data into simulated 3D images

Answer 20

3D imaging

Question 21

CT imaging of blood vessels pacified by contrast media

Answer 21

CT angiography

Question 22

The creation of inner views of tubular structures is called virtual endoscopy

Answer 22

CT virtual reality

Question 23

To image the beating heart with the goal of reducing motion artifacts and a loss of both spatial and contrast resolution

Answer 23

CT cardiac imaging
*ECG is used when doing cardiac scanning

Question 24

What is the goal of DLR (deep learning reconstruction) (artificial intelligence in CT)

Answer 24

1. Provide improved image quality
2. Dose performance
3. Reconstruction speed

Question 25

What are the requirements for volume scanning?

Answer 25

-continuously rotating scanner based on slip ring technology -continuous table movement -increased heat loading (min. 200mA per revolution) -increased cooling capacity of xray tube -spiral/helical weighing algorithm -mass memory to store the vast amount of data collected

Question 26

What is the first step in data acquisition?

Answer 26

Scanning

Question 27

Why is holding the breath required in a volume scan?

Answer 27

Eliminates artifacts, misregistration, motion

Question 28

T/F There is no defined slice in volume scanning, so localization of a particular slice is difficult

Answer 28

True (Not a true perpendicular slice)

Question 29

T/F Volume scanning uses non planar geometry, meaning the slices are not true parallel as in slice by slice

Answer 29

True

Question 30

T/F Axial scanning uses planar geometry (parallel slices)

Answer 30

True

Question 31

T/F Effective slice thickness increases in volume scanning because it is influenced by the width of the fan beam and the speed of the table

Answer 31

True

Question 32

T/F When inconsistent projection data is used with standard reconstruction process, streak artifacts akin to motion artifacts are clearly apparent on the image

Answer 32

True

Question 33

What post processing technique is used to solve the problems of volume scanning?

Answer 33

Interpolation

Question 34

What algorithm is used in the reconstruction of images?

Answer 34

Filtered back-projection algorithm

Question 35

How is motion eliminated in volume scanning?

Answer 35

1. Calculation (interpolation) of planar dataset from the tissue volume data set for every image 2. Reconstruction of images similar to conventional CT by use of the filtered back-projection algorithm

Question 36

T/F Contrast resolution is improved with thicker slices

Answer 36

True

Question 37

-2 xray tubes and 2 corresponding detectors positioned 90 degrees from eachother -temporal resolution improved -increased scan speed is useful in cardiac imaging

Answer 37

DSCT Dual source

Question 38

-acquisition of data using 2 different kvp settings simultaneously -can be performed using DSCT or SSCT

Answer 38

DECT Dual energy

Question 39

Used when doing CT biopsies

Answer 39

CT fluoroscopy

Question 40

-the planar slice is interpolated by using points that are 360 degrees apart -degrades image quality

Answer 40

360 degree linear interpolation algorithm -SSCT

Question 42

-LI algorithm improves image quality by using points that are closer to the planar slice to be interpolated -a second spiral is calculated from the measured spiral/helical and offset by 180 degrees

Answer 42

180 degree linear interpolation algorithm *higher/better interpolation *detail is improved, but produces more noise

Question 43

T/F In SSCT scanners, a higher pitch ratio degrades image quality and produces artifacts

Answer 43

True

Question 44

In MSCT, as beam width increases, scatter also increases. Postpatient collimators are used to remove scatter

Answer 44

True