Flashcards in Viewing radiographs Deck (23)
How are conventional radiographs formed?
by variations in optical density of photographic emuslion on flexible film base
How are conventional radiographs viewed?
using a radiographic view/light box (can be large, heavy)
What are the 4 stages of film processing? 4
1.) DEVELOPMENT: makes the latent image on film visible
2.) FIXING: stops development and makes image permanent
3.) WASHING: removes chemicals from the film
4.) DRYING: necessary before handling and storage
Advantages- digital radiographs
- stored digitally so readily retrieved for review, linked ot parts of electronic patient record and can be sent b/w colleagues instantly
- no need for darkroom
How can digital radiography be described? 2
- computed radiography (CR)
- direct radiography (DR)
What are CR systems?
= computed radiography
- use storage-phosphor image plates that are exposed and then undergo a separate image readout process. In CR the storage-phosphor image plate is usually contained in a cassette that resembles the cassettes used for film-screen radiography
What are DR systems?
convert xrays into electrical charges more or less directly --> enables instant readout (i.e. no separate processing step)
What is fluoroscopy?
- instead o fusing the output of a a screen to expose radiographic film, it is possible to electronically amplify the screen image using an image intensifier and then deliver it to a TV monitor
- provides a moving radiographic image --> useful for observing moving structures
- images usually displayed as positive images (bones black)
Define photographic density
the degree of blackening of the image, i..e the black area of a radiograph may be described as having high photographic density. Range needed to distinguish structures
refers to teh range of grey shades in an image. High contrast means few grey shades b/w black and white; low contrast means many grey shages, producing a smooth gradation from black to white
refers to the ability of an image to render detail. a high resoluton image shows small structures clearly; low resolution images are often described as blurred. Blur may result from patient movement during exposure, excessive scattered radiation, fogging, damage to cassette and other technical factors
Picture Archiving and Communication System
List the 6 Rontgen signs
= ways an image can look abnormal (xray, ultrasound etc)
1. abnormal number
2. abnormal position
3. abnormal size
4. abnormal shape
5. abnormal opacity
6. abnormal margination
What might abnormal number suggest?
- congenital condiiton (polydactyly)
- acquired (tooth loss)
- may not be true (e.g. could be one complex structure that is multilobar, convoluted) or reduced number of structures if disease
Why might you have abnormal position on a radiograph?
- frequent sign of a mass
How do you evaluate radiographic position?
evaluate 2 or more radiographs made with xray beam at different orientation to body part - from these a 3D mental image of the structures visible on radiograph can be created.
How do you determine abnormal size of an organ?
frequently use a bone landmark as a reference point to account for magnification and variations in body size (canine kidney is 3 times L2) however breed variations make it difficult. very few measurements actually aid diagnosis
Why might an organ be enlarged? 4
- hypertrophy/ hyperplasia
Why might an organ be smaller? 4
What should you note when determining if an organ has an abnormal shape?
the silhouette of an irregular object varies greatly depending on its orientation whereas the silhoeutte of a rounded, regular object does not. pitted surface may be d/t scarring
Outline the order of opacities
air > fat > soft tissue (mm, parenchymal organs, blood, urine, bile, transudate, exudate) > bone > metal
Why are bones visible on a radiograph?
because they are more opaque than the adjacent tissues (cartilage, mm, ligament) d/t higher physical density and calcium content