Ch. 21 Carlton

When did Computed Radiography (CR) evolve?

1980s, utilizing storage phosphors.

Who were the early developers of CR?

Eastman Kodak and Fuji Medical Systems.

CR market is affected by

several vendors & decreasing reimbursement.

How did CR transition to Digital Radiography (DR)?

Affordable transition

What is the two step process of CR Systems?

Acquisition, image processing and display.

What imaging technology do CR Systems use?

Photostimulable imaging plates (PSP).

What are the key steps in CR Systems?

Image acquisition, latent image production & reading CR data.

What are Photostimulable Imaging Plates (PSP)?

Reusable, multi-layered rigid sheets.

What is the main function of PSPs?

Record and transmit image information.

How are PSP's processed?

Filmless cassettes and Reader assembly.

What are common PSP Phosphors?

Barium fluorohalide Bromides (BaFBr:Eu).

What is another common PSP Phosphor?

Barium fluorohalide Iodides (BaFI:Eu).

What is the role of Europium (Eu) in PSPs?

An activator, maintaining electron holes.

What is the optimal range for K-Edge Attenuation?

35 and 50 keV

What is the relationship between K-Edge and kVp?

Average energy of 80 kVp beam.

PSPs Absorb more

Low-energy radiation than film.

kVp Requires more exposure if

kVp is outside the optimal range.

PSPs are more sensitive to

Scatter before and after exposure.

What is the PSPs sensitivity to energy?

Low levels of radiation energy.

What is the Image Acquisition Process?

X-rays expose cassettes, storing the latent image in the IP.

What are the usage options for PSPs?

Tabletop or with a grid.

Rules do what when using CR

Stay the same.

Wider exposure latitude than film avoid

Overexposure (More room for error in selection of kvp).

What is latent image production?

Electron pattern stored in the active layer of IP, creating electron traps or F-centers.

Fluorohalide absorb the beam through

Photoelectric interactions.

Energy transfers to

Photoelectrons.

What occurs during photoelectron liberation?

Several photoelectrons liberated.

What is the result of Secondary Electron Liberation?

More electrons freed by photoelectrons.

Liberated electrons have

Extra energy.

Fluorohalides trap electrons to

Create holes at Europium sites.

Latent image consists of millions of

trapped electron holes.

CR plates are highly sensitive to

Post-exposure radiation.

Latent image loses

25% of its energy in 8 hours; process right after exposure.

Trapped electrons are freed by

Exposure to a laser beam, allows stored energy to be released as light.

Electrons return to a lower energy state, emitting

Blue-purple light (Photostimulable Luminescence).

What happens during signal conversion?

Light captured by photomultiplier (PM) tubes, converted to an analog signal.

What occurs during digital conversion?

Analog signal converted to digital data by ADC for processing.

Plate erasure occurs in

intense light exposure.

Type of IP processing?

Point-by-point.

What is another type of IP processing?

Line-by-line readout.

What is the relationship between Pixel Pitch and Size?

Inversely related to spatial resolution.

Sampling frequency is expressed as

Pixels/mm (Nyquist frequency).

What factors affect sampling frequency?

Matrix size and image receptor size.

Higher sampling frequencies

Increase resolution.

How does pixel bit depth impact images?

Determines the number of density values, affecting density and contrast.

Bit Depth is controlled by

ADC.

What is matrix size dependent on?

Sampling frequency and plate size.

What factors affect file size?

Pixel size, matrix, and bit depth.

What does Data Manipulation (Preprocessing) refer to?

Raw data is located and prepared.

What do preprocessing steps include?

Anatomical part selection, orientation on IP, and number of projections.

What are CR Image Processing Steps?

Pre-processing and post-processing.

What does Pre-Processing include?

Exposure field recognition, histogram analysis, and grayscale analysis.

What does Post-Processing include?

Frequency processing and spatial location processing.

What is Exposure Field Recognition also known as?

Exposure data recognition (EDR).

What does Computer Analysis involve?

Exposure distribution, collimation edges, orientation, and multiple images.

Improper placement leads to

Histogram analysis errors.

What are Histogram Analysis Errors?

Obtained data does not match the reference histogram.

What causes Histogram Analysis Errors?

Inability to find collimated edges, prosthetic devices, or abnormal attenuation areas.

What is Data Clipping?

Clinically irrelevant data is excluded from image display based on VOI.

Body Part Specificity is

Different for each body part.

LUT has appropriate

Contrast for each body part.

What are Look-Up Table Adjustments?

Changing optical density or contrast. Graph of processed pixel values

What is Pathology Enhancement?

Changing the DlogE curve of film emulsion.

What are Histogram Equalization Examples?

Normal chest x-ray, bone-enhanced, and soft tissue images.

What standards should practices adhere to?

American College of Radiology (ACR) standards.

What Post-Processing Methods are there?

Spatial Location Processing and Frequency Processing.

Edge Enhancement Enhances

Cortical margins of bone, micro-calcifications, trabeculae (High band-pass filtering).

What does Image Smoothing do?

Suppresses visible image noise (Low band-pass filtering).

What is Image Stitching used for?

Scoliosis or leg length studies.

What is one Technical Consideration?

Higher kVp's suggested.

Suboptimum mAs exposures create

Quantum noise.

CR plate response to radiation

Linear and non-limiting.

How is grid usage vendor dependent?

Indirect and Direct with exposure

Grids should be used more often due to

Increased sensitivity to scatter.

Chest greater than 24-26cm should use

grid

With grid use you should avoid

Moire effect

Kvp outside suggest range can produce too much

Compton for CR