Intro to CT unit 4 Flashcards
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?
indirect
This effect is technologist controlled by increasing or decreasing dose to the patient?
direct
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?
mAs
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?
kVp
This technical factor defines the beam width for the examination and demonstrates the effective use of the x-ray beam at the detectors?
Collimation
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?
Justification
Optimization
Dose Limitation
Justification
Must be a benefit associated with every exposure
Optimization
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
