1. Lavin: Chapter 7 CTVT: pp. 539-541
Optimizing The Image
Lavin: Chapter 7
CTVT: pp

2. Blue vs Green Technology
Blue light technology
Only type until 1981
Screens emit ultraviolet blue light
Require blue receiving film
Being phased out
Green light technology
Since 1981
Superior imaging system
Emits green or blue-green light
Require green receiving film
If a problem with an image, check the film/screen combination…

3. Radiographic Record-keeping
A radiographic log should always be completed following a radiograph.

4. Learning Objectives: Chapter 7
Define motion, distortion, magnification, and blur and understand the ways they can impact a radiographic image.
Understand the purpose of filters
Define collimation, and understand its impact on secondary/scatter radiation
Know how and when to use grids
Finished the science – Now to the “art” of radiography
Radiographic detail = degree of sharpness that defines edges of anatomic structure

5. Factors Impacting Radiographic Quality
Distortion - Misrepresentation of the anatomical part by size or shape
Magnification – A form of distortion that magnifies size
Motion – A lack of image sharpness caused by overall patient movement
Blur - Movement of a particular part that reduces the visibility of details such as small objects and structures
Shorter WL’s have higher energy, and penetrate farther

6. Distortion Misrepresentation of the anatomical part by size or shape
Occurs when the x-ray beam is not perpendicular to the cassette
Can be shape, size, elongation, or foreshortening
Not desired
Central ray
Sandbags and rolled towels can be used
Can be angel of body part or centering of beam on wrong area

7. Use bone against light to demonstrate:
Mangification – Closer to light
Foreshortening – one end closer
Elongation – one end away from light

8. Distortion (Cont.)

9. Magnification A form of distortion
Magnifies size with area of interest closer than normal to the source
Position of the structure in the body influences
Minimizing magnification is “normally” desired.
Farther away from receptor = the more magnified
Closer to tube than receptor = magnification + increased fuzziness
Place part to be x-rayed as close to the film as possible
Based on the principle that a larger image can be obtained if the distance between the object & film is increased

10. Magnification SID = Focal Film Distance SID = 40 SOD = 25
40/25 = 1.6 MF
SOD = 30
40/30 = 1.5 MF

11. Magnification SID is…? SID = Source to image receptor distance
Magnified image is fuzzier
SID is…?

12. Motion Not a form of distortion but an enemy of resolution
Overall patient movement = lack of image sharpness
Voluntary or involuntary
Controlled with short exposure times
Immobilization devices
Distortion always involves foreshortening, elongation, or shape change

13. Blur Movement of a part that reduces the visibility of details
Can be used to advantage by timing a radiograph for a point where something is moving and blurred, allowing a clear picture of a stationary structure behind it
Types:
Involuntary - cardiac, peristalsis, spasm, tremor
Voluntary - patient movement
Equipment – rotor activation, x-ray tube lock failure, cassette movement

14. Motion vs Blur
Motion:
Any unwanted movement or restlessness of the patient during an x-ray exposure
May be prevented by immobilization devices, sedation, or effective restraint
Blur:
May be intentional, as in computerized tomography
Uses patient movement (like breathing) to blur body parts outside the level of interest so the intended anatomy images clearly

15. Filtration Some emitted radiation is not useful
Aluminum filtration - Placed in the beam to absorb lower-energy “extra” x-ray photons before they reach the target
Produces a clearer image
Can be:
Inherent - Filters the beam before it leaves the tube
Added – Inserted outside the x-ray tube but within the beam to even out discrepancies between body part sizes
Photons of varying energy & scatter radiation
Usually attached to the collimator

16. Filtration Inherent filtration Part of the tube
Includes the envelope, the oil in the tube, and the collimation mirror
Added filtration:
Put into place by the installer to meet governmental regulations
Special filters:
Added to the primary beam to enhance imaging
Can use saline or rice bags to absorb scatter

17. Wedge Filter A type of special filter
Also called a compensating filter
Evens out the difference in tissue measurement
Attached to the collimator with the thickest end at the thinnest part of the patient

18. Collimation
Focuses the x-ray beam to reduce scattered and extrafocal radiation
Produces a light beam that shows the area to be irradiated during the exposure
Decreased collimation = field size increases
Brown: Lavin’s Radiography for Veterinary Technicians Copyright © 2014, 2007, 2003, 1999, 1994 by Saunders, an imprint of Elsevier Inc.

19. Collimation Final filtration of the x-ray beam
Defines the area of interest
Knobs elongate or close the shutters
Collimate before placing the animal on the table
Reduces scattered radiation

20. Grids & Grid Trays Previously called Potter-Bucky diaphragm
Controls scatter radiation before it reaches the cassette
Allows only the primary x-ray beam to pass through
Made of lead strips interfaced with radiolucent spacers
Placed directly under the table between the animal and cassette
Grid tray holds cassette in place
Can deteriorate over time

21. Grids (cont.) Identified by “grid ratio” Too low = don’t filter
Too high = eliminates some of useful beam
Most useful is 8:1 or 10:1
Absorbs some primary radiation, so greater exposure times needed
Intensifying screens vs grid

22. Parallel vs Focused Grid
Parallel Focused
Parallel:
Strips are parallel or vertical
Never fully aligns with beam
Can angle cranial or caudal without visible gridlines
Great for portable units
Focused:
Newer
Allows more radiation to reach the film
Most effective for reducing scattered radiation
Lead strips are tilted progressively as they move away from center
Follows the beam more cleanly
Focused grids allow more primary radiation to reach the film.

23. Grid Deterioration
Over time, projects an image of itself on every radiograph
Can appear as gridlines

24. Decreasing Scatter Radiation
Decreasing exposure to scattered radiation:
Careful collimation
Setting accurate technical factors
Reducing retakes
Decreasing scatter radiation impacts on the radiograph:
Beam-limiting devices
Correct kVp settings
Filtering
Grids

25. Illumination of the Radiograph
Illuminators:
Used to transmit light evenly through a specially produced glass in order to identify and interpret radiographic images
Must be maintained at optimal brightness
Glass should be cleaned regularly
Should be positioned in a room that can be dimmed