Why digital over film-based radiography?
- Lower patient dose
- Greater manipulation of image post processing
- image enhancement allows for improved diagnosis
- better contrast resolution and image enhancement produces more information compared to film
- Eliminates need for a dark room
- Eliminates the need for a film processor as well as the storage, use, and disposal of toxic processor chemicals. Also no risk for processor damage to film which would require retakes.
- Significantly smaller office footprint for film storage
- Simpler image retrieval and image sharing
- No image degradation over time
CR (Computed Radiology)
- Film-less, uses a flexible phosphor plate in an x-ray cassette.
- Film x-ray processor is replaced with a digital plate reader
- Once the image is read off the plate the image is erased by exposing the plate to a bright light
Advantages:
- Easiest method to retrofit or upgrade an existing film-based x-ray system
- Lower cost than DR
- Smaller office footprint than a film-based system
- Larger office footprint than DR due to the need for a plate reader
- Slower results due to need to scan and process the phosphor plate in the reader
- Incomplete or inadequate erasing of an image from the plate can result in a double image requiring retakes
- Dust and dirt may accumulate between the phosphor plate and the cassettes as it may with film-based, requires cassette cleaning and maintenance
DR (Digital Radiography)
- Digital receptor, therefore, no need for cassettes or special plate
- Highest resolution and image quality
- Uses wired or wireless flat panel digital plate detectors
- Wired has a direct line for power to the plate and LAN communication to the DR console
- Wireless uses a rechargeable battery to power the plate and a wireless connection to transmit the image to the console
- Wireless offers greater freedom to position the digital plate detector but need for recharging the battery may make the system unusable for some periods of time
Advantages:
- Lowest patient dose - up to 4x lower dose than CR
- Images are produced instantaneously
- More technique independent, gives higher quality images than CR or film-based
- Greater ability to manipulate the image compared to CR and film (DX) cannot be manipulated
- Higher initial costs versus CR or film based systems
- Digital receptors faults may occur. This produces a black spot or line in the region of the faulty receptor
- Low exposures can produce grainy or pixelated images which can hide subtle abnormalities
Key Terms
Some key terms you may come across which describe the quality of the system:
Detective Quantum Efficiency (DQE) - represents a measure of image quality vs dose. A high value represents higher quality images at lower patient doses
Pixel Size - a representation of the amount of information that can be stored in each pixel or picture element. A smaller pixel size means more pixels in the field of view and therefore a higher quality image
Pixel Bit Depth - A fixed value by the manufacturer. A greater the pixel depth means a wider range of shades of gray which improves the image contrast resolution. This is calculated 2 to the power of n where n represents the pixel bit depth.
examples of bit depth: 8 = 256 shades of gray
12 = 4096 shades of gray
14 = 16.384 shades of gray
16 = 65, 536 shades of gray
Matrix - arrangement of the columns and rows of pixels. eg. of matrix size 64x64, 215x215, 1024x1024, and largest matrix - 2048x2048. A larger matrix means a greater number of smaller pixels. 1024x1024 matrix has 1,048, 576 individual pixels. 2048x2048 matrix has 4,194,304 pixels.
Dynamic Range - Range of doses over which an x-ray image receptor can properly reproduce an x-ray image. A wide range means a wide range of doses can be used for x-ray imaging. X-ray film has a narrow dynamic range.
Detector Element Size (DEL) - term used for DR detector panels, represents the image receptor type and size and the space between adjacent pixels. A smaller DEL is equivalent to more pixels and therefore better spatial resolution
Detective Quantum Efficiency (DQE) - represents a measure of image quality vs dose. A high value represents higher quality images at lower patient doses
Pixel Size - a representation of the amount of information that can be stored in each pixel or picture element. A smaller pixel size means more pixels in the field of view and therefore a higher quality image
Pixel Bit Depth - A fixed value by the manufacturer. A greater the pixel depth means a wider range of shades of gray which improves the image contrast resolution. This is calculated 2 to the power of n where n represents the pixel bit depth.
examples of bit depth: 8 = 256 shades of gray
12 = 4096 shades of gray
14 = 16.384 shades of gray
16 = 65, 536 shades of gray
Matrix - arrangement of the columns and rows of pixels. eg. of matrix size 64x64, 215x215, 1024x1024, and largest matrix - 2048x2048. A larger matrix means a greater number of smaller pixels. 1024x1024 matrix has 1,048, 576 individual pixels. 2048x2048 matrix has 4,194,304 pixels.
Dynamic Range - Range of doses over which an x-ray image receptor can properly reproduce an x-ray image. A wide range means a wide range of doses can be used for x-ray imaging. X-ray film has a narrow dynamic range.
Detector Element Size (DEL) - term used for DR detector panels, represents the image receptor type and size and the space between adjacent pixels. A smaller DEL is equivalent to more pixels and therefore better spatial resolution
Important Questions
What is included in the package?
What are the service terms?
- Computer workstation, software to view and process the images, appropriate high resolution display monitors
- Plate reader if CR
- Onsite or offsite image backup
- If wireless DR plate - what is the battery life? time to recharge the plate? Warranty if the battery is faulty and time to service/replace?
- Detector size, how many megapixels and pixel bit depth, dynamic range
- Image sharing features - burning CDs, send to radiologist/PACS, remote access for the patient, radiologist, or sharing with another site
- Hidden or additional recurrent fees? For instance, image sharing or image backup may require an upgrade fee
What are the service terms?
- Who services/maintains the unit - the company? subcontractor? Who maintains the warranty if the company that is selling the unit goes out of business
- Length of warranty for the different components - may vary fo the computer workstation, consoles, plate readers and cassettes/plates