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What is radiographic technique?
- Combination of settings on the control panel to produce a quality image.
- The geometry and position of the x-ray tube, the patient, and the image receptor must be taken into account.
What three groups of factors influence radiographic technique?
- Patient factors
- Image Quality factors
- Exposure Technique Factors
Which of the three groups of factors influence radiographic technique is the most difficult to evaluate?
When determining patient factors, what three evaluation steps should you take as a RT to assist you in setting
- Size and Shape of patient
- Thickness and Composition of body part being examined
- Pathology type, Size, and Composition
What are the four classifications of body habitus?
- Sthenic –average, healthy
- Hyposthenic – thin, healthy
- Hypersthenic – big frame, overweight
- Asthenic – small, frail, emaciated
Whate are some destructive pathologies that can affect radiographic technique settings?
- See Box
- 20-1 on page 300 in Bushong
Whart are some constructive pathologies that can affect radiographic technique settings?
- See Box
- 20-1 on page 300 in Bushong
What are the image quality factors?
- Optical Density
What is the primary control of optical density in the analog environment?
If a change in density is determined to be needed, what is the minimum percentage of change required in order tosee it?
What actual change should you make? Again, this applies only to analog
What percentage of change of kVp equals doubling or halving the mAs?
30%, double or halve
Besides being a means of altering optical density, what else does changing kVp effect?
- Scatter Radiation
- Patient Dose
If the only change of a radiograph that is needed is density, what should you do?
Change the mAs
What is the primary control of contrast in analog radiography?
What is a short gray scale?
- High Contrast
- Few steps from white to black
What is a long gray scale?
- Low Contrast
- Many steps from white to black
How would you decrease contrast?
Increase kVp (and lower mAs if you want to maintain the same density).
When working with the most used range of kVp (50-90), what change of kVp is needed to affect the scale of contrast?
Besides kVp, what secondary factors can increase contrast?
- Intensifying Screen
If the goal is to change contrast but maintain the same density, what should you do? (analog only)
Increase/Decrease kVp by 15% while making corresponding opposite doubling/halving of mAs.
What factors control the sharpness of detail?
What should you do to gain the shaprest detail?
- Use small focal spot
- Long SID
- Short OID
What should you do to improve visibility of detail?
- Use Collimation
- And other means of reducing scatter.
What is distortion?
Misrepresentation of object size and/or shape.
What causes shape distortion?
- Improper Alignment of Tube
- Image Receptor
What causes size distortion?
Changes in SID/OID
What principal exposure factors are taken into account when developing technique charts?
What are the four types of technique charts? What are their characteristics?
- Variable kVp
- - short scale of contrast
- - higher patient dose
- - less exposure latitude
- - must measure part very accurately
- Fixed kVp
- -Longer scale of contrast
- -Lower patient dose
- -More exposure lattitude
- -Accurate measurement not as critcal
- High kVp
- - kVp settings greater than 100
- - Ideal for barium studies and CXR
- Automatic Exposure
- -Computer assisted/Electronic exposure timer
- -Uses Photocell or ionization chamber
- -Patient position critical
What is automatic exposure control?
- Mechanism for controlling automatic exposure
- Uses 2-3 photocells
- Can adjust OD
What is automatically programmed radiography?
- Uses graphics on console or touch screen
- Computer sets kVp/mAs,