Minimize Patient Dose Flashcards
What are 4 CT System factors affecting patient dose?
X-ray tube to patient distance
Filtration
Pre-patient collimation
Multi row detector design along with noise reduction strategies
The further the tube is situated from the patient, the ___ The absorb dose
Lower
______ Removed some of the low energy photons from the x-ray beam
Filtration
______ Determines the radiation penumbra and reduces scatter radiation and reduces dose.
Pre-patient collimation
How does the software of the scanners automatically adjust the mA
- The size of the anatomy and the attenuation of the x-ray beam by the anatomy are evaluated.
- Once the size and density of the area is known, the MA is automatically adjusted for the body composition.
- This information is updated dozens of times per second, varying the tube current as the x-ray beam continues to encircle the patient’s body
The manufacturers claim that the automated variation of the MA allows for dose reduction ranging from
15% to 55%
How does the software, iterative Reconstruction reduce patient dose
- Yields images with less noise
2. The scan can be run with a lower mA
There is a _____ Relationship between MAS and Dose
Linear
If mAs is halved, then dose is halved
With the average size patient, the kVp is Normally _____ for the purpose of decreasing the radiation dose.
Not reduced
KVP is usually only decreased to minimize dose in what kind of patient.
Small patients and pediatric
How can I reduce the patient dose for the scan?
By scanning shorter lengths of the body.
Slice thickness Affects the dose to a patient on what type of scanners?
Single-row detector scanners
When increasing the slice thickness to cover a given volume of anatomy, on a single-row detector scanner, _________ slices are used.
Fewer.
On a single row detector scanner, why does choosing thicker Slices decrease patient dose?
Fewer slices means that there are fewer radiation penumbras that must be added into the CTDI.
For MDCT scanners, why does not the slice thickness affect patient dose
There are no overlapping penumbras between individual slices.
Why does increasing the table increment (for a given slice thickness) reduce dose?
It will reduce the number of slices needed to cover the area of interest; so fewer slices means fewer photons exposing the patient.
Why does increasing the pitch, decrease dose?
Each loop of the X-ray helix will be stretched out.
This decreases the number of photons required to cover the anatomical region of interest, as well as dose.
Ways to reduce the need to repeat scans
- Patient motion reduced by making pt comfortably
- Artifacts removed
- Helical to reduce motion artifact
- Motion correction algorithm
Other ways to minimize dose
Reformat rather than rescan
Reduce multiple scans
Use of prospective cardiac synchronization
Use of radiation shield
When scanning the heart what technique must be used to avoid motion artifact
A synchronization Technique
______ Synchronization is applied during the scan
Prospective
When using prospective ECG triggering or gating, ______ scanning is used.
Serial/ axial
When retrospective synchronization is used a _____ Scan is acquired throughout the entire cardiac cycle.
Helical
____ gating Is frequently used for calcium scoring screening studies on seemingly healthy individuals
Prospective cardiac gating
