Positioning 1

Respiratory System Anatomy and Radiographic Density

• Anatomical components of the respiratory system:

  • Pharynx

  • Trachea

  • Bronchi

  • Two lungs

• Structural characteristics of the trachea:

  • Composed of fibrous tissue and C-shaped cartilaginous rings.

  • Contains exactly $16$ to $20$ cartilaginous rings.

  • Measures approximately $4.5\,\text{inches}$ in total length.

  • Flat on its posterior (back) surface.

• Radiographic appearance and density:

  • Air within the trachea appears black on the image receptor.

  • Barium products consist of liquid metal material that attenuates X-rays and appears bright white.

  • Aspiration occurs when liquid barium enters the trachea, occupying the space intended for air.

Patient Body Habitus and Image Receptor Orientation

• Image receptor ($IR$) setup criteria:

  • Patient body habitus dictates whether the image receptor is oriented crosswise or lengthwise.

  • For patients who are very wide and experiencing severe breathing difficulty, the image receptor must be placed crosswise.

• Evaluation of cardiac size:

  • Every heart has an established baseline average size.

  • Any visual deviation exceeding the average heart size must be interpreted relative to the patient's specific body habitus.

Central Ray Alignment and Technical Positioning

• Central Ray ($CR$) specification:

  • Abbreviated as $CR$.

  • Designated by the precise intersection point of the longitudinal and transverse dark lines within the collimated light field.

  • Pinpoints the specific entrance or exit location on the anatomical body part being imaged.

• Anteroposterior (AP) Projection alignment:

  • The central ray is directed perpendicularly with no angular tilt.

  • Entrance point is perpendicular through the midsacral plane at the level of the laryngeal prominence (last angle/thyroid cartilage level).

  • The midline of the patient's neck must be centered directly to the midline of the grid and image receptor.

• Lateral / Opposing Projection alignment:

  • Involves positioning along the coronal plane rather than the sagittal plane.

  • The central ray enters perpendicularly at the midcoronal plane at the level of the laryngeal prominence.

Respiration Protocols and Motion Control

• Patient respiration instructions:

  • The patient must keep their mouth completely closed.

  • The patient is instructed to inhale slowly through the nose (slow inspiration).

• Radiographer exposure timing:

  • The rotor switch is depressed to trigger the exposure during the patient's active slow inspiration.

• Motion blur artifacts:

  • Respiration during image acquisition creates motion artifacts, producing image blurriness equivalent to capturing a fast-moving subject with a camera.

• Visualized anatomy during slow inspiration:

  • Provides clear diagnostic visualization of the air-filled trachea and the superior mediastinum.

Image Evaluation, Collimation, and Multi-Projection Requirements

• Collimation field dimensions:

  • Standard field size collimation is $10 \times 12\,\text{inches}$.

  • The collimation field size remains identical across primary and opposing views, as tracheal anatomical dimensions do not change.

  • The collimated light field displays a distinct shadow outlining the patient's skin line against the bright light.

• Image receptor density visual criteria:

  • Black regions indicate unattenuated air on the image receptor.

  • White regions indicate dense osseous structures (bone) or contrast media.

  • Soft tissue skin lines are visible along the perimeter of the primary exposure field.

• Multi-projection imaging requirement:

  • Standard diagnostic radiography requires a minimum of two opposing projections for proper evaluation.

• Competency and image verification:

  • Images must be thoroughly reviewed following exposure to confirm that positional alignment, plane orientation, and visual criteria meet clinical standards.