Mobile Radiography Notes

Mobile Radiography

Factors Contributing to Difficulty

  • Geometrical positioning factors: Accurate positioning is challenging in mobile radiography due to various constraints.
  • Distance considerations:
    • Traction devices, isolettes, and other equipment can affect the source-to-image receptor distance (SID).
  • Alignment of tube:
    • Side-to-side alignment and angulation of the X-ray tube must be carefully considered.
  • Grids: Using grids in mobile radiography can be tricky due to alignment and distance issues.

Communication Methods

  • Exposure announcement: Always announce the exposure to alert individuals in the vicinity.
  • Help from clinical staff: Collaborate with nurses and other clinical staff for assistance.

Arranging the Patient Room

  • Patient ancillary devices: Be mindful of IV lines, oxygen tubing, catheters, etc.
  • Room furniture: Arrange furniture to allow for safe and efficient mobile radiography.

Radiation Protection

  • Shielding: Use appropriate shielding for patient and personnel protection.
  • Shared room considerations: Take extra precautions in shared rooms to protect other patients.
  • Collimation: Use tight collimation to reduce scatter radiation.

Grids

  • Select appropriate grids for mobile examinations, considering their ratio and focal range.

Communication Protocol

  • Park the mobile unit outside the patient's room.
  • Identify the patient using two identifiers.
  • Establish rapport with the patient.
  • Obtain the patient's permission to perform the exam.
  • Explain the procedure to the patient.
  • Move any items that may obstruct the examination.
  • Considerations for incognizant patients, surgery, emergency room, and ICU settings.
  • Important Reminder: Patients often change rooms, so always double-check!

Equipment Manipulation

  • Be cautious of:
    • Equipment power supplies
    • Oxygen tubing
    • Intravenous lines
    • Catheters
  • Nurses can provide valuable assistance.

Equipment Handling

  • Avoid bumping the bed or your head.
  • It is the radiographer's responsibility to return all items to their original locations.
    • Beside tables and personal items
    • Side rails and restraints (if in use)

Positioning and Pathology Considerations

  • Maintain typical positioning techniques whenever possible.
  • Perform chest radiography in a semi-erect position when feasible.

Artifacts

  • Increased possibility of artifacts in mobile radiography.
    • Remove all radiopaque objects from the imaging field.
    • Move lines and tubes out of the imaging field if possible.
    • Limit coverings to a single, smoothed layer.

Air-Fluid Levels

  • Air-fluid levels can be visualized using specific positioning techniques.

Portable AP Chest in the ICU

  • Common devices seen on portable AP chest radiographs in the ICU include:
    • Intraaortic balloon pump catheter
    • Swan-Ganz catheter
    • Endotracheal tube
    • Mediastinal drain
    • Electrocardiographic leads
    • Nasogastric (NG) tube

Air-Fluid Level Question

  • To achieve a sharply delineated air-fluid level, the best positions are:
    • AP Erect
    • PA decubitus
    • Therefore, the answer is both 1 and 4.

Types of Mobile Equipment

  • Power supplies
  • Generators
  • Power drive

Power Supplies

  • Portable light duty units
    • Used for nursing home service, etc.
    • Operate on 220V or 110V outlet.
  • Full power mobile institutional units
    • Constant potential generators (CPGs)
    • Battery operated

Mobile Generators

  • Constant Potential Generators (CPGs):
    • Battery-powered: Require regular charging to maintain technique availability.
    • High voltage efficiency: Minimal ripple effect.
    • Require 8-10 kVp less than a typical 3-phase generator.
    • Usually have single mAs control.
    • Automatically engages highest mA available, varying time.

Mobile Generators Efficiency

  • More efficient than 3-Phase, 12 pulse generators.
  • Typically require a reduction of at least 8 kVp when compared to 3-Phase, 6 pulse generators.

Power Drive Features

  • Self-propulsion for mobile unit.
  • Dead-man switch for safety.
  • Bumper brake to prevent collisions.
  • Use caution when piloting equipment, especially using corner mirrors.

Technical Factor Selection

  • Kilovoltage (kVp)
  • Milliampere-seconds (mAs)
  • Distance (SID)
  • Grids

Milliampere-Seconds Considerations

  • Low power units may not be capable of high mAs techniques needed for grid radiography.
  • Double or triple exposures may be required for patients with large body mass (> 300 lbs).
    • This can be compromised by motion unsharpness.
    • Be careful not to overload the tube (increase heat units).

High kVp Techniques

  • Using high kVp techniques can help minimize motion unsharpness.
  • Example: Crosswise 14 x 17 Overlap at L4, 100 – 125 kVp, 5:1 Grid

Distance Management

  • SID must be measured or accurately replicated uniformly when using manually set technical factors.
  • Common SIDs:
    • 40 inches
    • 56 inches
    • 72 inches
    • 85 inches (foot of the bed!)

Distance Compensations

  • From 100 cm (40 inches):
    • 125 cm (50 inches): 50% increase in technique
    • 150 cm (60 inches): Double technique
    • 180 cm (72 inches): Triple technique
    • Change between 100 cm (40 inches) and 180 cm (72 inches) = FACTOR OF 3 adjustment in overall technique.
    • Mobile units: Adjust one “step” in mAs (approximately 50%) for every 25 cm (10 inches) change in SID.

Estimating Distance (SID)

  • Diagram provided to visually estimate distance.

Geometrical Factors Explained

  • Distances:
    • Fingertip-to-fingertip distance is usually equal to one’s height. For example, 180cm180 cm (6 ft) tall = 180cm180 cm (72 inches) “wingspan”.
    • 158cm158 cm tall: Can extend arms to collimator rather than tube.
    • For 100cm100 cm (40 inches), average person can use fingertip-to-opposite axilla.
  • Minimize object-to-image receptor distance (OID) when possible.
  • When OID gap is unavoidable, compensate with a proportionate increase in SID when possible.
  • Any change in SID > 1515 % requires compensation in technique.
  • Angles > 15°15° require compensation in technique (due to the effect on distance).

SID and Magnification

  • Question: On portable rotations, which SID will deliver an image with the least magnification?
  • Answer: 72’ Erect. Longer SID results in less magnification.

Alignment Considerations

  • When long bones or extremities cannot be positioned parallel to the cassette or IR, use Ceiszynski’s law of isometry (Chapter 24), splitting the difference between the two angles to minimize distortion.
  • If the anatomy of interest includes joint spaces, it is always more important to keep the CR perpendicular to the anatomy rather than to the cassette or IR.

Grid Alignment

  • Whenever crosswise orientation of the grid is in use, the CR must be directed perpendicular to the plane of the imaging plate!

Virtual Grid Software

  • The advent of virtual grid software has precluded the need for conventional grids in many cases.
  • A great advantage, especially for trauma patients, is not using conventional grids allows us to work around the patient “as they lie” by eliminating the possibility of grid cut-off from:
    • Orienting the IR crosswise or lengthwise
    • Intentional or accidental off-centering
    • Slight tilt of the IR
  • Added benefit: 50-70% savings in patient dose through technique reduction to non-grid levels

Virtual Grid Recommendation

  • Strongly Recommended for All Mobile Procedures: Virtual Grid Software
  • Pelvis and skull exposures without conventional grids benefit greatly from virtual grid software.

Digital Mobile Radiography

  • Fuji DR Mobile Radiography example.

Technique Combinations Question

  • Which combination of factors has wider exposure latitude?
  • 12 mAs at 75 kVp OR 2 mAs at 115 kVp?

Mobile C-Arm Fluoroscope

  • Description of Mobile C-Arm Fluoroscopy; Youtube video links Provided.

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