1. Optimizing The Image RVT: Chapter 7
The “art” of taking great radiographs.

2. 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

3. Factors Impacting Radiographic Quality: Distortion
Misrepresentation of the anatomical part by size or shape
Occurs when the x-ray beam is not perpendicular to the cassette
Can be: elongation, foreshortening, or magnification
Not desired! Except sometimes….
Can be angel of body part or centering of beam on wrong area
Used in dental imaging

4. Magnification Occurs when anatomy is moved closer to the tube
Leads to fuzzy image on the radiograph
Farther away from image receptor = the more magnified
What piece of positioning equipment might cause patient to be further from the cassette?
Good thing is…
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

5. Factors Impacting Radiographic Quality: Motion
Not a form of distortion but decreases resolution of the image
Overall patient movement = lack of image sharpness
Voluntary or involuntary?
Controlled with ___________ exposure times
Immobilization devices?
Distortion always involves foreshortening, elongation, or shape change
Chemicals, tape, sand bags, leashes

6. Factors Impacting Radiographic Quality: Blur
Movement of an anatomical part that reduces the visibility of anatomic detail of that part
Can be purposeful!
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, breathing, peristalsis, spasm, tremor
Voluntary – discomfort, fear
Equipment –cassette movement

7. Motion vs Blur Motion: Blur:
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

8. Decreasing Scatter Radiation: Filtration
Radiation produces a beam that contains photons of varying amounts of energy
Some of those low energy photons are not useful radiation
They are scattered from the patient (secondary radiation)
Scatter radiation ____________clarity of the image
It can be filtered before or after entering the patient
The best way is before via aluminum filtration
Central beam is applying your determined kilovolts AND more!
Usually attached to the collimator

9. Aluminum Filtration Installed by the manufacturer
Regulated by the government
Placed in the beam to absorb lower-energy “extra” x-ray photons before they reach the target
2.5 mm thickness of
aluminum required e

10. Other Types of Filtration
Inherent filtration
Filters the beam before it leaves the tube
Includes: the glass envelope, the oil in the tube, and the collimation mirror
Compensating filters
Added to the primary beam to enhance imaging
Example: Wedge filter
Used when there is a significant variation in thickness of the patient
Other filters: fluid bags, rice socks, leaded rubber
Collimation = beam restriction
WEDGE: Thicker part goes over the thin part of the animal ; settings are for thick part

11. The final filtration: Collimation
Found directly below the x-ray tube
Produces a light beam that shows the area to be irradiated during the exposure
Must be centered within 1 cm of the primary beam
Allows technician to see exactly what will be included in the image
Focuses the x-ray beam to match cassette and patient size
Works by opening and closing shutters

12. Collimation Knobs open or close the shutters
Collimate to the cassette size before placing the animal on the table
Goal: reduce primary beam to exactly as big or small as we need it
Reduces scattered radiation
*Replacing the light bulb is the only maintenance you should do
Must match voltage and wattage
Must turn off generator at the ________ ___________.
Defines the area of interest

13. Collimator Issue vs. Scatter
Anatomy is shown on the image, outside of the collimation
If only happens when radiographing large patients, it’s due to ________________.
If happens consistently, it’s due to _______________
_____________.
EXTRA-FOCAL or OFF FOCUS radiation: Photons created outside of the actual focal spot size

14. Grids & Grid Trays Previously called Potter-Bucky diaphragm
Grid tray is housed under the table top
The table top allows x-rays to readily pass through making it _____________.
Holds the cassette
The grid is housed directly under the table top
Allows only the primary x-ray beam to pass through to the cassette
Controls scatter radiation before it reaches the cassette
Enhances contrast of the image
Radiolucent

15. *Why are these used on larger areas on interest?

16. Grid Made of lead strips interfaced with radiolucent spacers
Identified by grid ratio
Too low = don’t filter scattered photons at all
Too high = absorbs some of useful primary beam
Most useful is 8:1 or 10:1
103 lp/inch is best
Line pairs
16:1 = height is too tall
5:1 = too short
**Absorbs some primary radiation, so greater exposure times needed
Grid factor = 10 (kVp)

17. Parallel vs Focused Grid
Parallel Focused
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.

18. Interspace material degrades over time