47 terms

Formaulating x-ray techniques Ch 12

A technique chart provides the following information
1. MA
2. kVp
3. source-image distance (SID)
Manual technique charts are based on patient part measurements obtained using an x-ray caliper
thickness, in centimeters
The kVp that is sufficient to penetrate the body part adequately without excess exposure to the patient is called
Optinmum kVp
What factors need to be considered when selecting the mA station
Exposure time and focal spot size
When selecting a low mA station (100 mA) you should use
the small focal spot.
The advantage of using a variable kVp technique chart are
Lower overall image contrast. Improved visibility of detail. ability to make small incremental changes in exposure technique.
Why should a small focal spot be used as much as possible.
It provides better image sharpness
How should a exposure factors be adjusted when there is the likelihood of motion?
increase mA , decrease exposure time
A satisfactory radiograph is made using 5 mAs with an image receptor relative speed (RS) of 400. How many mAs would be necessary to produce a radiographih of similar density if an RS 100 screen is used?
20 mAs
Which mA station can be used for the most average size patients to take advantage of the small focal spot?
If 10 mAs produces satisfactory results with a 5:1 ratio grid, what mAs would be needed if a 16:1 ratio grid is used?
Radiography of a wet plaster cast will require an increase in mAs of how much?
A fiberglass cast will require an increase in mAs of how much?
No change is required.
What x-ray projections can benefit from the use of compensating filters?
Ateroposterior (AP) thoracic spine
axiolateral hip
Indicates the need for increased techniue
Paget disease
Pleural effusion
Indicates a decrease technique
Chronic obstructive pulmonary disease (COPD)
Degenerative arthritis
Advanced age
Bowe; obstruction
Which tool and which unit is used to measure body part thickness for radiography?
caliper - centimeters
Optimum kVp range for AP projection of the cervical spine
70 to 80 kVp
Optimum kVp for AP projection of the thoracic spine
80 to 90 kVp
Optimum kVp range for AP projection of the lumber spine
74 to 88 kVp
mA setting setting for Elbow
50 or 100 mAs with small focal spot
mA setting lumber spine
200 mAs
mA setting for chest
300 mAs with the shortest time possible involunteer movement
4 factors primary radiographic
1. mA
2. Time
3. kVp
4. distance SID
4 primary factors responsible for density
1. mA
2. Time
3. Distance
4. kVp contrast
target object distance
Make change in mAs you need to go at least
25 - 35 %
Record detail
refers to image clarity
Record detail - image clarity affected by
quantum mottle
focal spot size
intensifying screen and film speed
film/screen contact
Also refered to as resolution
sharpness, definition, or detail
how much information you get
Gemetric Factors
Focal spot size
overall blackness
compensating filter
devices that can be placed between the radiographic tube and IR to compensate for variations in tissue density. (attenuating devices)
Fixed kVp chart
optimum KvP vaule is established for each projection and the mAs is varied according to the patient/part thickness
optimum kVp
the highest kVp setting that produces sufficient contrast for acceptable image quality.
Technique Chart
A listing of varies radiograp[hic examinations performed in the facility. It provides exposure factors for each body part according to its thickness.
variable kVp chart
Chart based on a specific mAs vaule for each projection and to vary the kVp by 2 to 3 kVp/cm for changes in the patient/part size.
High contrast
Is called short scale contrast
High kVp
Is called long scale contrast
Long scale
Is called low contrast.
Small focal spot
provides better image sharpness for all body parts.
200 mA station and small focal spot
Can be used for nearly all small to average size patients
To decrease contrast
increase kVp by 15% and divide the mAs by 2
compensaring filter
attenuating device
short exposure time
highest mAs is used.
Exposure times
are determine by calculation, based on the required mAs and the desired mA.