Radiographic Exposure, Processing and Quality Control Notes

Optimum kVp for Different Procedures

  • Hand / Wrist: 54 kVp
    The relatively low kVp used for imaging the hand and wrist allows for the appropriate penetration of soft tissues while still detailing the bony structures. This setting helps in reducing exposure while ensuring good image quality.

  • Elbow / Foot: 60 kVp
    This optimal kVp balances the need for clarity in bony landmarks while minimizing radiation exposure.

  • Ankle: 64 kVp
    The increased kVp helps to penetrate the thicker soft tissue surrounding the ankle joint, providing a clearer image of the bony structures.

  • Knee: 70 kVp
    Here, the kVp is elevated to ensure that both soft tissue and bony anatomy are adequately visualized, considering the thickness of the overlying soft tissue.

  • Femur / Shoulder / Sinus / Ribs: 76 kVp
    This level is optimal for larger structures and areas with denser tissue, allowing for effective differentiation between anatomical features.

  • Cervical / Thoracic Spine (all views): 76 kVp
    A higher kVp is essential to visualize both the bony anatomy and any potential pathologies in the spine effectively.

  • General Torso Anatomy (Pelvis, Abdomen, Lumbar Spine): 80 kVp
    Used for comprehensive imaging of the torso, this setting balances penetration and contrast, particularly for vascular studies or examinations requiring contrast agents.

  • All Iodine Procedures (IVP, Cystogram, etc.): 80 kVp
    The optimal kVp ensures sufficient penetration of the iodine-based contrast agents, facilitating clear imaging of organ structures.

  • Non-Grid Chest: 80 kVp
    This setting allows visualization of lung structures while reducing scatter, providing a clean image.

  • Air Contrast / Barium Studies: 90 kVp
    The higher kVp allows for adequate penetration to reveal air and contrast differences when examining gastrointestinal structures.

  • Esophagram: 90 kVp
    Used specifically to visualize the esophagus, accommodating for the contrast differences present during studies.

  • Solid - Column Barium Studies: 110 kVp
    This requires high penetration power due to the dense barium; effective for detailed imaging of the gastrointestinal tract.

  • Grid Chest: 110-120 kVp
    This range is required for grid-assisted imaging, increasing the contrast resolution significantly, crucial for detailed chest assessments.

Patient Status & Contrast Agents

  • Tissue composition and thickness greatly influence radiation traversing:

    • Bone: Less penetrable than soft tissues, meaning higher exposure is needed for imaging bones properly.

    • Body fluids: Absorption characteristics similar to soft tissue, requiring careful consideration when adjusting kVp and mAs.

Somatotypes (Body Habitus)

  1. Hypersthenic (Massive): 5% of the population; characterized by heavy musculature and larger bones, necessitating modifications in standard imaging protocols due to increased density.

  2. Sthenic (Average): 50% of the population; moderate build commonly encountered, requiring average technique adjustments based on typical anatomy.

  3. Hyposthenic (Slender): 35% of the population; falls between sthenic and asthenic, often posing a challenge for accurate classification in imaging paradigms.

  4. Asthenic (Very Slender): 10% of the population; individuals require special adaptations in imaging techniques due to their very light build, which can increase image quality concerns.

Anthropological Factors

  • Variations in bone density due to race necessitate tailored adjustments in radiographic techniques.

    • Skull types affecting techniques:

    1. Mesocephalic: The average skull shape found in many individuals, typically requires standard settings.

    2. Dolichocephalic: A longer skull shape with a 40° angle that may require alterations in imaging due to its dimensions.

    3. Brachycephalic: Broad and round skull shape (54° angle), typically necessitating increased mAs for optimal imaging.

Measuring Body Thickness

  • Calipers should be used rigorously to measure body thickness accurately, avoiding any compression to obtain true dimensions.

  • Thickness Ranges are established for young adults to derive standard thickness benchmarks, imperative for effective exposure calculations.

Average Thickness Ranges

  • Significant data show a high correlation between patient dimensions and average thickness ranges:

    • Average torso thickness: 22 cm in AP (anterior-posterior) view, and up to 30 cm in lateral view.

    • Adjust techniques based on deviations from these averages, with every 4 cm change in thickness affecting mAs density by a factor of 2, necessitating careful consideration in adjustment calculations.

Use of Contrast Agents

  • Iodine and Barium: High atomic number materials enhancing subject contrast, each requiring specific kVp to ensure adequate penetration and visibility:

    • Iodine: Minimum of 80 kVp to effectively reveal anatomical structures.

    • Barium: Minimum of 110 kVp (90 kVp for esophagram) to provide clear images in gastrointestinal studies.

Influence of Respiration on Density

  • It is vital to instruct patients on proper breath-holding techniques during radiographs to achieve accurate results:

    • Full inspiration is preferred to avoid risks of underexposure, ensuring the visibility of potentially obscured anatomical structures.

Pathologies and Technique Adjustments

  1. Additive Diseases (e.g., pleural effusion): These pathologies necessitate an increase in exposure techniques by 35%-100% to adequately visualize the affected areas.

  2. Destructive Diseases (e.g., conditions emphasizing air or fat increase): These typically require a reduction in exposure techniques by 30%-50% to avoid overexposure of the affected areas.

Casts and Splints

  • Full plaster casts generally require doubling the mAs or an increase in kVp by 15%, especially concerning wet plaster, which may need additional adjustments.

  • Fiberglass casts are generally radiolucent but could require slight mAs adjustments depending on the density of the materials used in the cast.

Grids in Radiography

  • Grid Ratios are defined by the relationship of lead strip height to the distance between them, significantly influencing the absorption efficiency of scatter radiation.

  • Utilizing grids can substantially improve image contrast but necessitates mAs adjustments to compensate for the primary radiation that is absorbed by the grid, ensuring optimal image quality.

Intensifying Screens

  • Essential in imaging since they reduce patient exposure while enhancing image density. The screen speed dramatically influences the necessary adjustments in mAs.

  • Traditional screens compared to rare earth screens differ in efficiency and speed, which can significantly dictate the modifications necessary to maintain appropriate density in final images.

Effect of Fog and Scatter Radiation

  • Fog results from scatter radiation, which can detrimentally affect image quality, contrast, and overall resolution. Employing grids and techniques specifically designed to minimize scatter are crucial during exposure to enhance the final imaging results.