Ch 8 Computerized Radiography and Digital Imaging PP

Storage Capabilities:
- Images and data utilized in hospitals and clinics can be stored on personal computers equipped with exchangeable hard drives.
- Backup images are frequently stored in data banks globally, indicating that the future of imaging has extensive potential for growth and advancement.
- A consistent aspect of any imaging system is the x-ray unit; any correctly calibrated x-ray unit is compatible with any digital imaging system.

Transition from traditional to digital imaging involves the following systems:
- CR (Computed Radiology, Indirect): Involves the indirect capturing of x-ray images via imaging plates.
- DR (Direct Digital Imaging, Direct Capture Radiology): Involves direct capture of digital images without the need for film.

Overview:
- Computerized radiography (CR) marked the initial evolution towards digital imaging in veterinary medicine.
- Key similarities with traditional imaging:
- Both utilize a cassette for image capture, which must be processed in a separate unit.
- Imaging plates are coated with photostimulable phosphors (PSPs), which the cassettes protect from light exposure and physical damage.
- The only traditional imaging step excluded by CR is reloading film into the cassette.
- Each imaging plate (IP) within a CR cassette can acquire and store the image, removing the necessity for film altogether.
- Differences between traditional and CR:
- How images are acquired, processed, and viewed varies significantly between these two methodologies.

Inside the CR cassette:
- Contains a single intensifying screen capable of trapping images via the use of photo-stimulable phosphors (PSPs).
- Imaging Plate (IP): The front is coated with a PSP, usually barium fluorohalide, which reacts to the x-ray beam and light.
- Image Retention:
- If the IP is not inserted into a reader unit promptly, the image will begin to fade within 6 to 8 hours as electrons revert to their original state.

Noise Issues:
- Highest levels of noise in CR occur at lower exposure levels, primarily due to:
- Background fog.
- Scattered radiation affecting image clarity.

Advantages:
- Elimination of wet processing and the chemical hazardous processes associated with traditional film development.
- Provides a wide latitude concerning technical factors involved in imaging.
- Quick wait time for image display following acquisition.
Disadvantages:
- Imaging plates (IPs) are consumables; they must be frequently serviced and replaced when worn or incapable of erasing ghost images from previous captures.
- Susceptibility to issues from scattered radiation.
- The necessity to flash the IP before each use if imaging is limited within clinics or hospitals.
- Noise at low radiation levels can be problematic, although improvements in technology aim to mitigate this.
- Requirement for processing images in a laser reader as an intermediate step.

Overview:
- Direct digital radiography evolved as an enhancement from the CR model.
- Key features include:
- Direct acquisition of images effectively removes several steps associated with film/screen imaging:
  - Entire processing and hanging steps as well as cassette preparation are eliminated.
  - Only requires entering the patient’s information into the computer and transmitting the requisition back to the operators, with subsequent actions handled by computer systems as needed.
- Similar to CR, postprocessing remains available as an additional option.

System Architecture:
- The digital systems deploy a detector consisting of scintillation phosphor situated atop a supportive plate resting on a Thin Film Transistor (TFT).
- This plate conveys radiation signals to the digital receptor (DR).
- The DR contains individual pixels that convert radiation input into electronic signals and transmit data to software through data lines emerging from each pixel.

Resolution Limitation:
- Pixel size limits resolution in digital imaging.
- Capture element contributes approximately 80% of each pixel, while the remaining 20% encompasses the TFT and data lines, which do not add to the image quality and must be artificially filled by the computer during image processing.

Concerns:
- Technique charts offered by vendors can sometimes reflect poor understanding, raising concerns.
- Example: Setting technical parameters—85 kilovolts (kV), 300 milliamperes (mA), for a kitten's paw or a cat's 10-cm abdomen—illustrates vendor deficiencies.
- Problems arise when reliance is placed on these charts, necessitating postprocessing of every image, which:
- Adds to original examination durations and results in data loss.
- Requires adjustment of windowing and leveling (altering brightness and contrast), which compromises image data accuracy.

Digital Imaging Optimization:
- Best diagnostic images are achieved when parameters closely align with those of the animal being radiographed.
- Typically, smaller body parts yield a higher technique due to the required radiation level for image acquisition, although this requirement decreases as technology advances.

Distance Impact:
- Distance has minimal significance in small-animal imaging but is crucial in large-animal imaging contexts, requiring an exact distance from the x-ray unit to the detector consistently for reliable results.

Resolution Metrics:
- Spatial Resolution: Expressed in line pairs per millimeter, determining the detail level in the image.
- Contrast Resolution: Associated with the black and white values in the image, measured by dynamic range. The ultimate objective of digital imaging lies in producing high-resolution imagery.
Contrast and Brightness Adjustments:
- Windowing: Refers to manipulating the contrast range of densities.
- Leveling: Pertains to adjustments of density or brightness. The window level sets the average midpoint of visible densities in a digital image.

Exploitability of Digital Processes:
- Digital images utilize the capacity of digital mechanisms to create a significantly broader array of gray shades.
- The human eye can discern a maximum of 30 shades of gray, meaning digital images tend to present enhanced visual quality compared to film images due to the greater detail and gradation within images.

Image Archiving Necessities:
- Post-image production, archiving is necessary, mandating that systems include redundancy.
- Data must be stored in multiple locations to ensure accessibility and security of imaging data over time.