Digital Radiographic Imaging Formation and Quality Control

Question 1

describe differences in image formation between analog (film screen) and digital (CR and DDR/DR)

Answer 1

analog:
1. catches x-rays in cassettes with intensifying screens
2. need a dark room to handle, but is safe to work in there

digital:
1. can use conventional x-ray machines, just need housing of the new digital imaging system in the x-ray table
2. pixels are the picture elements, each pixel is assigned a shade of grey; the number of shades of grey available determines the CONTRAST resolution and the pixel size determines the SPATIAL resolution (size of the smallest detectable structure)
3. computed radiography (CR): the digital recording device is a cassette that contains a flexible imaging plate; takes more time in practice because need a CR image reader
4. direct digital radiography (DDR): digital recording device is a rigid imaging plate or chip; does not need an image reader so is quicker! meaning you can take more pics but also more pics means more radiation exposure for your team

Question 2

what is the image file format for radiographs? what is the storage?

Answer 2

DICOM: digital imaging and communications in medicine; has a bunch of info so is a legal document but is also a very large file

PACS: picture archiving and communication system: where electronic medical images are automatically archived and backed up; safe and secure

Question 3

compare and contrast the dynamic range of analog versus digital radiology

Answer 3

analog has a very narrow dynamic rage, meaning that you need to have the perfect technique for the specific body part you are analyzing to get a good image

digital detectors can correct the image post taking, so technique does not need to be perfect and you can evaluate multiple body parts in one image!

Question 4

what are the 6 advantages of digital radiography over analog?

Answer 4

1. reduced expendable supply cost and elimination of dark room maintenance
2. exposure latitude and contrast optimization; wide range of grey scale
3. image post-processing
4. consolidated image storage; won’t lose in a fire
5. enhanced image portability for consultation: enabled teleradiology
6. enhanced professionalism in eyes of consumer

Question 5

what are the 5 radiographic opacities?

Answer 5

1. air: least opaque, most luscent, and black
2. fat
3. soft tissue/fluid
4. bone
5. metal: most opaque, least luscent, white

Question 6

list and describe 3 image detail issues

Answer 6

1. geometric unsharpness:
   a. magnification and penumbra; size distortion due to sectorial geometry of x-ray beam; penumbra is when an object is far from the detector; objects farther from beam appear larger than actual size and blurry
   b. distortion: image misrepresent the true shape or position of the object from unequal magnification of different parts of the same object, some will occur in every radiograph
2. motion unsharpness
   a. subject/object motion: common in vet med bc patients don’t stay still
   b. can also have tube/detector motion with handheld machines or if disturb the detector
3. quantum mottle (noise): a decreased number of x-ray photons will decrease the quality of the radiograph and make it hard to distinguish structures

Question 7

describe loss of depth perception

Answer 7

lost in all radiographs! because we are taking 2D images of 3D objects; so always take 2 radiographic projections perpendicular to each other

Question 8

describe summation

Answer 8

results when parts of the patient in different planes (NOT in contact with each other) are superimposed; results in opacities added; occurs in every radiograph!

Question 9

describe border effacement/silhouetting

Answer 9

occurs when two structures of the same radiopacity are IN CONTACT, results in loss of individual margins; occurs in every radiograph!!