Exposure Technique Selection

What is known as pre-established guidelines used by the radiographer to select standardized manual or exposure factors for exams

exposure technique charts

What is the overall goal of having a technique chart?

to produce consistent radiographs, reduce the amount of repeats, and reduce patient dose

Technique cahrts re accurate for what percent of patients?

90%

What are technique charts based on?

the average patient (sthenic)

T/F: each x-ray tube requires its own technique chart

True

T/F: measurement of part thickness is critical for the use of technique charts

True

What tool is used to measure part thickness?

calipers

What types of things are often found on a technique chart?

• anatomy

• AEC selection

• CR location

• FFS

• Type of IR

• Grid ratio

• kVp

• mAs

• Part thickness

• Position/projection

• SID

What are the 2 types of technique charts?

1. variable kVp - fixed mAS

2. fixed kVp - variable mAs

Which type of technique chart is based on the concept that kVp can be increased as the anatomic part size increases

variable kVp - fixed mAs

For a variable kVp - fixed mAs technique chart, kVp is increased by __ for every __ cm increase in part thickness

increased by 2 for every 1 cm

T/F: in a variable kVp-fixed mAs technique chart, part measurement is critical

True

When is a variable kVp-fixed mAs technique chart most effective?

with pediatric patients or small extremities

What are the disadvantages to a variable kVp-fixed mAs technique chart?

• subject contrast varies

• less accurate for part size extremes

• adequate penetration of the part is not assured

If a knee radiograph at 10 cm thick using a 63 kVp and 8 mAs is taken using a variable kVp-fixed mAs technique chart, what will the new technique be if the part measures to be 14 cm?

71 kVp 8 mAs

What is the goal of a fixed kVp-variable mAs technique chart?

to determine the kVp that will penetrate the part without compromising subject contrast

When using a fixed kVp-variable mAs, for every ___ to ___ cm change in part thickness, the mAs should be adjusted by a factor of ___

4 to 5 and 2

What are the advantages of using a fixed kVp-variable mAs technique chart?

• patient thickness groups

• more consistency in quality

• greater assurance of adequate penetration

• uniform subject contrast

• increased accuracy with extreme variation in part size

If an AP knee radiograph is taken with 12cm at 73 kVp and 4 mAs. If using a fixed kVp-variable mAs technique chart, what is the new technique if the part size increased to 20cm?

73 kVp at 16 mAs

T/F: when using a fixed kVp-variable mAs technique chart, part measurement is less critical

true

Which type of technique chart requires higher patient dose?

variable kVp - fixed mAs

What tools are needed to create a technique chart?

• phantoms

• calipers

• calculator

What does the concept of comparative anatomy state?

different parts of the same size can be radiographed using the same exposure factors

What are the 4 steps in developing a technique chart?

1. using phantoms, select kVp and determine appropriate mAs for the desired exposure

2. extrapolate the exposure techniques for changes in part thickness

3. use comparative anatomy

4. test the chart for accuracy