Ch23+Technical+Considerations

Chapter 23: Technical Considerations in Digital Imaging

Introduction

  • Discusses the critical aspects of digital imaging in radiography.

  • Highlights key considerations for maintaining image quality and efficiency.

Objectives

  • Technical Factor Selection: Explain principles of selecting technical factors for digital receptors.

  • Deviation Index Values: Understand the scale of deviation index values and their significance.

  • Digital Imaging Artifacts: Identify causes of common digital imaging artifacts.

CR vs. DR Imaging Systems

Advantages of Digital Radiography (DR)

  • Lower Patient Dose: Reduced radiation exposure for patients.

  • Improved Efficiency: Faster imaging process and workflow.

  • Cost-Effective: Lower initial costs compared to some traditional modalities.

  • Higher Detective Quantum Efficiency (DQE): Enhanced image quality at lower doses.

Advantages of Computed Radiography (CR)

  • Lightweight Receptors: Easy handling of image receptors.

  • Positioning Adaptability: Flexible positioning options.

  • Variety of Sizes: Availability in different sizes to suit various needs.

Image Quality Factors

  • Traditional parameters still apply for assessing image quality:

    • SID (Source-to-Image Distance): Affects the intensity of the radiation received by the detector.

    • OID (Object-to-Image Distance): Impact on magnification and image blur.

    • Focal Spot Size: Influences spatial resolution.

    • kVp (Kilovolt Peak): Affects image contrast and exposure. In DR using lower kVp values decreases image quality.

    • mAs (Milliampere-seconds): Controls the quantity of radiation.

    • Collimation: Reduces scatter and improves image quality.

    • Grids: Help eliminate scatter radiation, enhancing image clarity.

Digital Exposure Considerations

  • Old Exposure Rules: They no longer apply in digital imaging.

  • kVp and Image Contrast: The relationship is not as straightforward as in film imaging.

  • mAs and Brightness: mAs levels don't dictate image brightness in digital imaging.

  • Total Exposure: The overall exposure impact on the receptor must be carefully assessed.

  • Exposure Indicators: Assessment tools for evaluating image quality.

Total Exposure to Image Receptor

  • Influenced by:

    • mAs: Quantity of radiation.

    • kVp: Energy level of radiation.

    • SID and OID: Distance factors affecting image quality.

    • Collimation: Improves clarity by reducing scatter.

    • Patient Thickness and Tissue Composition: Variations in body anatomy impact absorption.

    • Filters: Enhance quality by absorbing unnecessary radiation.

  • Higher kVp Usage: Results in less entrance skin exposure (ESE).

  • Noise Consideration: Low mAs can introduce quantum mottle (noise) into images. DR detectors did not receive enough exposure.

Digital Exposure Technique Systems

  • Technique Systems Development: Established originally by Ed. C. Jerman, refined by Arthur W. Fuchs.

    • Fixed-kVp, Variable mAs: Adjusts mAs according to body part thickness.

    • Variable kVp, Fixed mAs: Adjusts kVp based on thickness with a base kVp.

    • Fixed kVp System: Better suited for digital receptors, optimizing exposure settings.

Assessing Digital Exposure Technique

  • Exposure Indicators: Important for feedback on image quality.

  • Image Noise: Relates directly to exposure levels, higher mAs lowers noise.

  • Digital Processing Tolerance: More forgiving of overexposure than underexposure leads to dose creep.

Dose Creep

  • Best practices recommend maximizing kVp and minimizing mAs to optimize image quality while adhering to radiation safety standards (ALARA principle).

Addressing Unacceptable DI Numbers

  • Establish acceptable ranges for exposure indicator variances:

    • +25% for overexposure.

    • -20% for underexposure.

Digital Processing Considerations

  • Relies upon advanced computing to enhance images.

  • Utilizes initial images with low contrast, adjusted by algorithms to achieve desired contrast levels through techniques like LUT application.

Post-Processing Techniques

Electronic Masking/Shuttering

Intended to eliminate extraneous Brightness from image edges to minimize veil glare.

  • Cropping Methods: Can be manual or automatic to reduce image glare without affecting resolution.

  • Collimation: Manual masking is not a substitute for proper collimation practices.

  • Not related to spatial resolution

Electronic Annotation

  • Involves labeling certain aspects of imaging for clarity and context (e.g., labeling laterality, upright stance).

  • Careful use of lead markers during acquisition is recommended for accuracy.

Tenets of Radiologic Images

  • Radiographs serve as legal documents that document anatomical and medical conditions.

  • Quality is essential for accurate interpretation; departments must follow standard practices ensuring ALARA compliance.

Common CR Artifacts

  • Phantom Images: Resulting from incomplete erasure.

  • Scratches/Tears: Indicate permanent damage to the imaging plate.

  • Opaque Spots: Caused by foreign materials on the imaging plate.

  • Dropouts: Arising from dust interference in the image receptor.

  • Fogging: Scatter radiation leading to blurred images.

Common CR/DR Artifacts

  • Quantum Mottle: Insufficient mAs.

  • Histogram Analysis Errors: Processing mishaps due to algorithm faults.

  • Moire Artifact: A pattern artifact resulting from grid misalignment or scanning errors.

  • Laser Transport Artifacts: Issues during image printing related to transport errors.

  • Electronic artifacts: only happens in DR due to motor or rotor interference.

Data Drop Artifacts

  • Occurs from detector saturation, leading to image quality artifacts.

  • Prevention and Correction:

    • Use of tissue bolusing, collimation, and compensating filtration to mitigate issues.

    • Post-processing recovery methods are essential for correcting data dropouts.