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

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

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

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

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

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

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

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

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

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

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

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

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

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

*Why are these used on larger areas on interest?

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)

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.

Interspace material degrades over time