Minimize Patient Dose

Question 1

What are 4 CT System factors affecting patient dose?

Answer 1

X-ray tube to patient distance

Filtration

Pre-patient collimation

Multi row detector design along with noise reduction strategies

Question 2

The further the tube is situated from the patient, the ___ The absorb dose

Answer 2

Lower

Question 3

______ Removed some of the low energy photons from the x-ray beam

Answer 3

Filtration

Question 4

______ Determines the radiation penumbra and reduces scatter radiation and reduces dose.

Answer 4

Pre-patient collimation

Question 5

How does the software of the scanners automatically adjust the mA

Answer 5

1. The size of the anatomy and the attenuation of the x-ray beam by the anatomy are evaluated.
2. Once the size and density of the area is known, the MA is automatically adjusted for the body composition.
3. 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

Question 6

The manufacturers claim that the automated variation of the MA allows for dose reduction ranging from

Answer 6

15% to 55%

Question 7

How does the software, iterative Reconstruction reduce patient dose

Answer 7

1. Yields images with less noise

2. The scan can be run with a lower mA

Question 8

There is a _____ Relationship between MAS and Dose

Answer 8

Linear

If mAs is halved, then dose is halved

Question 9

With the average size patient, the kVp is Normally _____ for the purpose of decreasing the radiation dose.

Answer 9

Not reduced

Question 10

KVP is usually only decreased to minimize dose in what kind of patient.

Answer 10

Small patients and pediatric

Question 11

How can I reduce the patient dose for the scan?

Answer 11

By scanning shorter lengths of the body.

Question 12

Slice thickness Affects the dose to a patient on what type of scanners?

Answer 12

Single-row detector scanners

Question 13

When increasing the slice thickness to cover a given volume of anatomy, on a single-row detector scanner, _________ slices are used.

Answer 13

Fewer.

Question 14

On a single row detector scanner, why does choosing thicker Slices decrease patient dose?

Answer 14

Fewer slices means that there are fewer radiation penumbras that must be added into the CTDI.

Question 15

For MDCT scanners, why does not the slice thickness affect patient dose

Answer 15

There are no overlapping penumbras between individual slices.

Question 16

Why does increasing the table increment (for a given slice thickness) reduce dose?

Answer 16

It will reduce the number of slices needed to cover the area of interest; so fewer slices means fewer photons exposing the patient.

Question 17

Why does increasing the pitch, decrease dose?

Answer 17

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.

Question 18

Ways to reduce the need to repeat scans

Answer 18

1. Patient motion reduced by making pt comfortably
2. Artifacts removed
3. Helical to reduce motion artifact
4. Motion correction algorithm

Question 19

Other ways to minimize dose

Answer 19

Reformat rather than rescan

Reduce multiple scans

Use of prospective cardiac synchronization

Use of radiation shield

Question 20

When scanning the heart what technique must be used to avoid motion artifact

Answer 20

A synchronization Technique

Question 21

______ Synchronization is applied during the scan

Answer 21

Prospective

Question 22

When using prospective ECG triggering or gating, ______ scanning is used.

Answer 22

Serial/ axial

Question 23

When retrospective synchronization is used a _____ Scan is acquired throughout the entire cardiac cycle.

Answer 23

Helical

Question 24

____ gating Is frequently used for calcium scoring screening studies on seemingly healthy individuals

Answer 24

Prospective cardiac gating

Question 25

_______ is more accurate than _______ when the patient has an irregular heart beat, is typically used for exams of the coronary arteries.

Answer 25

1. Retrospective gating

2. Prospective techniques

Question 26

Radiation shields are often made of

Answer 26

Tungsten antimony

Bismuth