Intro to CT unit 4 Flashcards Preview

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Flashcards in Intro to CT unit 4 Deck (41)
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The range of CT numbers used to map signals into shades of gray can be used to describe?

Window width


Pitch is defined as?

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


What is the definition of High Reproducibility?

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


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?

Window level


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?

Absorption efficiency


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

Increasing pixel size, size thickness, mAs
Noise- grainy appearance/mottle


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

Quantum detection efficiency


Detector dose efficiency affects the following factors by increasing signal to noise ratio:
a. Patient Dose =
b. Scanning (Imaging) Times =
c. Image Quality =

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


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



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



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

ATCM-Automatic tube current modulation


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

Directly proportional


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



How does mAs affect dose?

Increase mAs, increase dose DIRECT


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

mAs must be increased


How is radiation dose affected by kVp²?

Radiation dose is proportional to the square of the kVp


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



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



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

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


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

1 typical; 2 ct angiography


How does pitch affect dose?

Increasing pitch decreases dose


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

Increase pitch


More detectors have what affect on patient dose?

Decrease dose (inverse)


Why is patient centering so crucial in computed tomography?

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


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

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


How does time of exposure relate to patient dose?

Increased time increased dose (Directly)


How is distance related to patient dose?

Inversely proportional to the square of distance


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

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


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

Dose Limitation



Must be a benefit associated with every exposure



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


dose limitation

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


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

5 rem or 50 mrem


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

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


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

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


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

“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)


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

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


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

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


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

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


When should a patient be immobilized for a CT Examination?

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


What is the three Cardinal Rules for Radiation Protection?

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