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Chest Radiography Lecture Review

General Principles for Chest Radiography

Reasons for Erect Chest Imaging

When possible, chest imaging is preferred to be done erect (standing or seated upright) for four main reasons:

  • Air-fluid levels: Erect positioning allows gravity to demonstrate possible air-fluid levels within the lungs or pleural space more effectively.

  • Free air under the diaphragm: Free air, often indicative of a perforated viscus, will rise to the highest point when the patient is erect, making it visible under the diaphragm.

  • Organ displacement: Gravity causes the diaphragm and abdominal organs to fall, allowing for better assessment of the thoracic cavity (thorax) without compression or obscuration.

  • Reduced heart congestion: Blood tends to fall away from the heart due to gravity in an erect position, reducing vascular congestion in the heart and allowing for a clearer outline of the heart borders (less prominent vasculature).

Routine PA Chest Imaging

Patient Positioning

  • Feet: Spaced approximately shoulder-width apart.

  • Weight: Equally distributed on both feet.

  • Face/Chin: Patient's face should be looking straight up and forward; the chin must be elevated to prevent it from obscuring the lung apices.

  • Image Receptor (IR) Placement: The upper border of the IR is positioned approximately 1.5 to 2 inches above the patient's relaxed shoulders.

  • Midsagittal Plane: The patient's midsagittal plane must be perpendicular and centered to both the IR and the upright Bucky.

  • Rotation Check: No rotation of the patient's trunk; verified by checking the alignment of shoulders and hips.

  • Hands/Shoulders/Scapulae: The patient places the back of their hands on their hips. This action helps to roll the shoulders forward and rotate the scapulae out of the lung fields, allowing for better visualization of the apical portions of the lungs.

    • Guidance: If the patient struggles to achieve this position, gently guide their shoulders forward while instructing them.

Technical Factors and Setup

  • Source-to-Image Distance (SID): Typically 72 inches. This extended SID is used to minimize magnification of chest structures due to the object-to-image receptor distance (OID) within the chest and the Bucky.

  • Central Ray (CR): Perpendicular to the IR.

  • Centering Point: Level of T7 (seventh thoracic vertebra).

    • Methods for finding T7:

      • Vertebral Prominence: Locate the vertebral prominence (C7), the prominent spinous process at the base of the neck. Measure down approximately 7 inches for females and 8 inches for males.

      • Inferior Angle of Scapula: Locate the inferior angle of the scapula; T7 is generally at this level.

  • Patient Preparation: All necklaces, jewelry, bras, and clothing from the waist up should be removed. Patients should ideally wear a hospital gown.

    • Caution with Hair: Thick hair, wet hair, dreadlocks, or braids can sometimes obscure lung fields on modern radiographs and should be moved out of the way if possible.

  • Automatic Exposure Control (AEC): Typically used.

  • Kilovoltage (kVp): Generally in the 110 to 120 range.

  • Collimation: Must include the entire lung fields and exclude the upper arms as much as possible.

Breathing Instructions

  • Standard: "Hold your breath on the second inspiration."

    • Instruct the patient: "Take a big deep breath for me. Go ahead and blow that breath all the way out. Now I want you to take in another big deep breath for me. Hold that breath."

    • Ensure adequate time for the patient to take a full, deep breath to ensure sufficient air in the lungs for visualization of ribs and lung tissue.

  • Clinical Variation (Rule out Pneumothorax): Some orders, particularly for "rule out pneumothorax," may require suspended expiration instead. Always pay attention to the specific order.

Image Critique for PA Chest Radiographs

  • Motion: Assess for blur or unsharpness, indicating patient movement. Ensure the patient maintains position and follows breathing instructions fully.

  • Rotation: Evaluate alignment. A good indicator is the symmetry of the sternoclavicular (SC) joints relative to the tracheal air column or spinous processes.

    • SC Joint Assessment: If one SC joint is significantly further from the midline compared to the other, it indicates rotation. The clavicle further from the midline suggests the patient is rotated away from the receptor on that side.

  • Collimation: Verify tight collimation, including all lung fields while excluding the abdomen.

  • Scapulae: Confirm that both scapulae are completely out of the lung fields, rolled forward as intended during positioning.

    • Correction: If scapulae are in the lung field (e.g., left scapula visible over the lung apex), guide the patient to roll their shoulders further forward towards the IR.

  • Full Inspiration: Confirm sufficient lung inflation. Ideally, 10 posterior ribs should be visible above the diaphragm in their entirety. Clinically, with conditions like COVID, sometimes only 9 ribs may be achievable.

Rib and Anatomical Identification on PA Radiographs

  • Rib Counting: Start at the top, T1 articulates with the first rib, then proceed inferiorly (2^{nd}, 3^{rd}, 4^{th}, etc.).

  • Posterior vs. Anterior Ribs:

    • In a PA projection, the anterior ribs are closer to the receptor, appearing crisper and with less magnification. These are the portions running more horizontally near the sternum.

    • The posterior ribs curve around towards the spine, appearing wider and slightly less defined due to increased OID. These typically angle downwards from the spine.

  • Key Anatomy:

    • Spinous Process: Central vertebral midline structure.

    • Clavicle: Collarbone.

    • Scapula: Shoulder blade (should be projected out of lung field).

    • Anterior Ribs: Portions of ribs closer to the IR.

    • Trachea: Airway leading to lungs.

    • Bronchial Bifurcation (Carina): Point where the trachea divides into main bronchi.

    • Aortic Knob (Aortic Arch): Curvature of the aorta.

    • Left Bronchus: Airway to the left lung.

    • Hilum/Perihilar Region: Central area of each lung where blood vessels, bronchi, lymph vessels, and nerves enter and exit.

    • Descending Aorta: Portion of the aorta descending through the thorax.

    • Breast Tissue: Soft tissue shadows, typically overlying the inferior lung fields.

    • Gastric Air Bubble: Air collection in the stomach, usually seen below the left hemidiaphragm.

    • Liver: Dense organ visible below the right hemidiaphragm.

    • Right Atrium: Part of the heart on the right side.

    • Posterior Ribs: Portions of ribs further from the IR.

    • Costophrenic Angles: The acute angles formed by the conjunction of the diaphragm and the ribs (costo = ribs, phrenic = diaphragm). These should be sharp.

    • Cardiophrenic Angles: The angles formed by the conjunction of the heart and the diaphragm (cardio = heart).

Lateral Chest Imaging

Patient Positioning

  • True Left Lateral: Preferred to keep the heart closer to the IR, which helps reduce magnification of the heart shadow.

  • Shielding: Always shield the patient's gonadal region.

  • Midsagittal Plane: Parallel to the IR.

  • Shoulders: Positioned against the IR.

  • Centering: To the thorax itself, NOT the breast tissue. It's crucial to center for the lung field thickness.

  • Arms: Raised high above the head, ideally straight up if the patient can manage it (e.g., holding onto a Bucky bar). This moves them out of the lung field.

Technical Factors and Setup

  • SID: 72 inches (same as PA to minimize magnification).

  • Central Ray (CR): Perpendicular to the mid-coronal plane.

  • Centering Point: Level of T7 (same as PA).

  • Collimation: To include the lung fields.

  • Breathing Instructions: Suspended second inhalation (same as PA).

Beam Divergence in Lateral Chest Radiographs

  • Phenomenon: The X-ray beam diverges as it travels through the patient. This means structures at different distances from the central ray will be projected differently.

  • Effect on Lung Bases: Even if the lungs are at the same anatomical level, the divergence of the beam can cause a slight offset in the appearance of the lung bases (e.g., costophrenic angles) on a lateral radiograph. This small offset is considered normal and is not indicative of patient tilt.

  • Distinguishing from Rotation: A minimal differentiation between the two sets of posterior ribs (e.g., 1/2 inch or less) is often normal due to divergence. A more significant separation (e.g., 1 inch or more) suggests patient rotation.

AEC Selection (Control Panel)

  • For a lateral chest, the center chamber of the AEC should be selected and highlighted.

  • Always remember to set appropriate technical factors (kVp) regardless of AEC selection.

Image Critique for Lateral Chest Radiographs

  • Beam Divergence Offset: A small offset in the lung bases/costophrenic angles is normal.

  • Rotation: Evaluate the posterior ribs. A slight differentiation (e.g., less than 1/2 inch) is normal due to beam divergence. More significant separation (e.g., 1 inch or more) indicates patient rotation. Superimposed posterior ribs are ideal for demonstrating no rotation.

  • Arm Placement: Ensure arms are completely out of the lung field.

Anatomical Identification on Lateral Radiographs

  • Apices: Uppermost portions of the lungs.

  • Trachea: Dark, air-filled column descending anterior to the vertebral column.

  • Manubrium, Sternal Angle, Sternal Body: Parts of the sternum.

  • Scapulae: May be visible posteriorly if not fully pulled forward.

  • Spine and Posterior Ribs: Vertebral bodies and superimposed posterior ribs.

  • Heart Shadow: Large, dense shadow anterior to the spine.

  • Aortic Arch: Curved portion of the aorta superior to the heart.

  • Retrosternal Space: Air-filled space behind the sternum, anterior to the heart/great vessels.

  • Retrocardiac Space: Air-filled space behind the heart, anterior to the spine.

  • Hilum and Perihilar Region: Central lung area (vascular confluence).

  • Main Stem Bronchi: Major airways.

  • Breast Shadows: Overlying soft tissue.

  • Left Hemidiaphragm: Appears sharper and more defined because it is closer to the IR in a left lateral projection.

  • Right Hemidiaphragm: Appears slightly less defined or fuzzy due to greater OID.

  • Gastric Bubble: Air in the stomach, often visible below the left hemidiaphragm.

  • Costophrenic Angles: Angles at the lung bases, junction of ribs and diaphragm.

  • Interlobar Fissures: Thin lines representing the folds of the pleura between lung lobes (difficult to consistently identify).

Special Considerations and Adapted Chest Views

Not all patients can stand, hold their breath reliably, or sit upright. Adaptations are often necessary.

Supine AP Chest Imaging

Indications

  • Patients unable to sit or stand (e.g., broken hips, venous catheter in groin, unstable blood pressure, trauma).

Patient Positioning

  • Position: Patient laid straight down on the imaging board/table.

  • IR Placement: Upper border of the IR approximately 1.5 to 2 inches above the patient's shoulders.

  • SID: Often impossible to achieve 72 inches in a room or with mobile equipment. Use a standard distance like 40, 49, or 60 inches, and always document the SID on the image.

  • Centering Point: Approximately 3 inches inferior to the jugular notch (the indentation at the top of the sternum).

Mobile Imaging

General Considerations

  • Patient Identification: Always verify patient ID (last name, date of birth).

  • Patient Status: Patients requiring mobile imaging are often less cooperative or unable to be transported to the department (e.g., ICU, ER, post-op, trauma).

  • Upright/Seated Preference: Ideally, the patient should be sat upright if possible, but always confirm contraindications with nursing staff.

  • Disadvantage: Mobile imaging is typically performed AP, which results in increased heart magnification compared to a PA projection. Documentation of SID is crucial due to variable distances.

Positioning and Technical Factors

  • IR Placement: Behind the patient, with the top edge approximately 1.5 to 2 inches above the shoulders.

  • Central Ray (CR): Perpendicular to the film. Ensure the patient is lying flat against the film and the CR angle matches the film angle to avoid distortion.

  • Centering Point: Approximately 3 inches inferior to the jugular notch.

  • Shoulders: Encourage rolling shoulders forward if the patient is able.

  • Shielding: Always shield the gonadal region.

  • Horizontal CR Limitations: It's not always possible to achieve a horizontal CR with mobile AP chests, which can limit the ability to visualize air-fluid levels decisively. Sitting the patient as upright as possible helps if fluid levels are suspected.

Managing External Obstructions

  • Wires/Lines: Patients, especially in ICU/ER, will have numerous wires, tubing, and monitoring devices. Move as many as possible out of the lung fields without disconnecting or disrupting critical care.

AP Lordotic Chest (Axial Lordotic Chest)

Indications

  • Non-routine and primarily requested by specialists.

  • Most commonly performed to rule out tuberculosis (TB) or to visualize apical lesions (tumors) in the lung apices.

Patient Positioning

  • Position: Upright, facing the X-ray tube.

  • Feet: One foot placed forward.

  • Body Lean: Patient leans back against the IR, arching their spine. Shoulders go back, and hips/pelvis move forward.

  • IR Placement: Approximately 3 inches above the shoulders.

  • SID: Still 72 inches.

  • Centering Point: Approximately 3 inches inferior to the jugular notch.

  • Shoulders: Rolled forward (even with the lordotic arch) to prevent obscuring the upper lung fields.

Purpose of the View

  • This projection is designed to throw the clavicles up and out of the way of the lung apices, allowing for unobstructed visualization of the upper lung portions, which are often obscured in standard views.

Decubitus Chest (Lateral Decubitus Chest)

Indications

  • Fluid Accumulation: Essential for diagnosing fluid (pleural effusion) in the pleural space, especially when the patient cannot be erect.

  • Bilateral Assessment: If the disease process affects both lungs, bilateral decubitus views may be performed.

  • Affected Side Down: The patient is positioned with the affected (or suspected affected) side down to allow gravity to pool the fluid in that area, making it more visible.

  • Pre/Post Thoracentesis: May be performed before or after fluid drainage procedures.

  • Challenging Patients: Useful for very sick patients or those unable to stand.

Patient Positioning and Setup

  • Setup Time: Allow at least 5 minutes in position for fluid to settle due to gravity before exposure.

  • Support: Use a radiolucent sponge under the patient's thoracic cavity to elevate them off the bed/cart. This prevents the bed from appearing in the image and obscuring lateral lung tissue.

  • Arms: Raised above the head if possible.

  • True Lateral: Hips and shoulders should be superimposed (stacked) to ensure a straight spine and prevent rotation.

  • Proximity to IR: Patient should be as close to the IR as possible.

  • Coverage: Ensure the entire chest is included on the film.

  • Central Ray (CR): Horizontal and centered to the film.

Image Marking

  • Naming: Decubitus views are named by the side that is DOWN (e.g., Left Lateral Decubitus means the left side is down).

  • Marker Placement: Typically, mark the side that is UP on the film (e.g., for a Left Lateral Decubitus, place a RIGHT marker with a decubitus indicator).

  • Decubitus Marker: Always include a specific decubitus marker on the film.

Technical Factors and Centering

  • Centering Point: Still approximately 3 inches inferior to the jugular notch.

  • Shielding: Apply gonadal shielding.

  • Breathing Instructions: Suspended second inhalation, if the patient is able.

Clinical Priority and Lab Setup Suggestion

  • Priority: The side that is DOWN is the priority for clear visualization, as gravity will draw the fluid to this dependent aspect of the lung. This side must be built up with a sponge and clearly seen.

  • Lab Suggestion: Line up the tube (source) and IR first. Then, bring the patient's cart into position and adjust the cart to align with the pre-arranged tube and IR setup.

Image Interpretation

  • Fluid accumulation: Appears as a dense, horizontal line or layering along the dependent side, pushing the lung away from the ribs.

  • Critique for rotation: Assessed by checking the sternoclavicular joints, similar to other views.

Additional, Non-Routine Projections

  • Obliques: Rarely performed, but may include 60^{\circ} or 45^{\circ} views, such as Left Anterior Oblique (LAO) or Right Anterior Oblique (RAO).

  • Nipple Markers: For shallower obliques, nipple markers may be used to identify breast tissue and assess rotation, often requiring additional 10-15^{\circ} rotations to remove from lung field.