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

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…

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

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 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

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

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

Distortion (Cont.)

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

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

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

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

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

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

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

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

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

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.

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

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

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

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.

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

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

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