Intro to CT unit 4

Question 1

The range of CT numbers used to map signals into shades of gray can be used to describe?

Answer 1

Window width

Question 2

Pitch is defined as?

Answer 2

The distance the CT table moves during one complete revolution (360) of the xray tube

Question 3

What is the definition of High Reproducibility?

Answer 3

The product of capture efficiency, absorption efficiency, and conversion efficiency. It produces the total detector efficiency or dose efficiency.

Question 4

The location of a CT number scale at which levels of gray are represented by the sample, regulating the optical density of a displayed image. This is the definition of what CT term?

Answer 4

Window level

Question 5

This efficiency detector principle determines how well the detectors convert incoming x-ray photons by the type of tube material used and the thickness of the detectors is termed as which efficiency factor?

Answer 5

Absorption efficiency

Question 6

When increasing these 3 common factors it will reduce image noise and what does noise look like on a CT Image?

Answer 6

Increasing pixel size, size thickness, mAs

Noise- grainy appearance/mottle

Question 7

The relative number of x-ray that interacts with a detector can be defined as?

Answer 7

Quantum detection efficiency

Question 8

Detector dose efficiency affects the following factors by increasing signal to noise ratio:

a. Patient Dose =
b. Scanning (Imaging) Times =
c. Image Quality =

Answer 8

a. Patient Dose = reduce
b. Scanning (Imaging) Times =increase
c. Image Quality =increase

Question 9

This effect improves image quality without the influence of radiation exposure?

Answer 9

indirect

Question 10

This effect is technologist controlled by increasing or decreasing dose to the patient?

Answer 10

direct

Question 11

What is considered the most important technique for maintain constant image quality while optimizing radiation dose?

Answer 11

ATCM-Automatic tube current modulation

Question 12

What is the correlation between the use of mA for slice thickness size?

Answer 12

Directly proportional

Question 13

This technical factor determines the quantity of photons incident on the patient for the duration of the exposure?

Answer 13

mAs

Question 14

How does mAs affect dose?

Answer 14

Increase mAs, increase dose DIRECT

Question 15

When pitch increases what should happen to mAs in order to keep the Computed Tomography Dose Index (CTDI) constant?

Answer 15

mAs must be increased

Question 16

How is radiation dose affected by kVp²?

Answer 16

Radiation dose is proportional to the square of the kVp

Question 17

This technical factor determines the penetrating power of the photons coming from the x-ray tube?

Answer 17

kVp

Question 18

This technical factor defines the beam width for the examination and demonstrates the effective use of the x-ray beam at the detectors?

Answer 18

Collimation

Question 19

What is the difference between Translation (Rotation) and Pitch?

Answer 19

Pitch is the distance the CT table moves during one complete revolution of the xray tube, while translation is the distance the table travels between slices during the actual scanning of the pt

Question 20

What is the typical pitch used in CT & CT Angiography?

Answer 20

1 typical; 2 ct angiography

Question 21

How does pitch affect dose?

Answer 21

Increasing pitch decreases dose

Question 22

To increase patient scanning & volume scanning what should happen to pitch?

Answer 22

Increase pitch

Question 23

More detectors have what affect on patient dose?

Answer 23

Decrease dose (inverse)

Question 24

Why is patient centering so crucial in computed tomography?

Answer 24

Inadequate positioning results in a reduction in imaging quality and increases the pt dose also inadequate pt positioning results in the bowtie filter not to work properly

Question 25

What is the purpose of a “Bow Tie” filter?

Answer 25

Reduce the beam intensity at the periphery of the beam corresponding to the thinner area of the pts anatomy—started in the second generation

Question 26

How does time of exposure relate to patient dose?

Answer 26

Increased time increased dose (Directly)

Question 27

How is distance related to patient dose?

Answer 27

Inversely proportional to the square of distance

Question 28

For a technologist to receive the least amount of radiation dose when holding a patient, the technologist should stand where?

Answer 28

Stand in a straight line at a right angle with the ct gantry the individual will receive the least amount of radiation dose if individual has to be in the room

Question 29

What are the 3 Principles that are vital to radiation protection?

Answer 29

Justification Optimization Dose Limitation

Question 30

Justification

Answer 30

Must be a benefit associated with every exposure

Question 31

Optimization

Answer 31

ensure that doses delivered to pt are kept with ALARA, economic & social factors being taken into account

Question 32

dose limitation

Answer 32

dose that an individual receives annually or accumulates over a working lifetime should be within the limits established by the ICRP

Question 33

30) The amount of radiation dose a technologist should not exceed is?

Answer 33

5 rem or 50 mrem

Question 34

Explain the importance for a technologist to have good communication skills when explaining procedures to their patients?

Answer 34

Good communication skills ensure that the patient understands what you want them to do and this could prevent repeats having to be taken

Question 35

What should a technologist do if a patient asks a question that is above their scope of practice?

Answer 35

Refer them to the radiologist or the ordering physician – make sure the pt fully understands

Question 36

How should a technologist treat a patient that has a mental handicap when asking questions for a CT procedure?

Answer 36

“treat them how you want to be treated” have patience and treat them as you would treat your own family members or treat them just like any other patient. Do they have guardian? (if just a caregiver they can’t sign for contrast media)

Question 37

If a technologist is scanning a young pediatric patient, who should hold the patient while the scan is being preformed?

Answer 37

Order of holding Dad, Grandparents, mom, other health care professional, last resort tech

Question 38

How should a technologist approach a pediatric patient for a CT Examination?

Answer 38

Explain procedure to the parent if patient is old enough to understand explain to them what you are doing on their terms. For very young pt keep them warm and talk soothingly. Always have everything ready, answer all questions, never lie, rewards

Question 39

What precautions should a technologist perform when performing a CT Examination on a neonatal patient?

Answer 39

Maintain neonatal body temperature. Have the room ready beforehand, increase the room temperature, have a nurse measure the infants vitals and body temperature

Question 40

When should a patient be immobilized for a CT Examination?

Answer 40

When a pt wont stop moving to avoid motion artifacts and for their safety. Also, when physician deems necessary

Question 41

What is the three Cardinal Rules for Radiation Protection?

Answer 41

Time- spend as little time in the room with the xray as possible Distance- is inversely proportional to the square of distance-stand far away Shielding- if in room where scatter radiation is use lead protection