Chest Radiography and Clinical Indications

Summary of Clinical Indications and Exposure Adjustments for Chest Radiography

• Aspiration (Mechanical Obstruction):

  • Most Common Radiographic Examinations: PA and lateral chest, lateral upper airway.
  • Possible Radiographic Appearance: Radiodense or radiopaque outline.
  • Exposure Factor Adjustment: Soft tissue technique for upper airway ($-$);

• Atelectasis (Collapse of All or Portion of Lung):

  • Most Common Radiographic Examinations: PA and lateral chest, PA inspiration/expiration.
  • Possible Radiographic Appearance: Radiodense lung regions with shift of heart and trachea in severe cases.
  • Exposure Factor Adjustment: Increase ($+$).

• Bronchiectasis:

  • Most Common Radiographic Examinations: PA and lateral chest with bronchogram or CT.
  • Possible Radiographic Appearance: Radiodense lower lungs.
  • Exposure Factor Adjustment: Generally none.

• Bronchitis:

  • Most Common Radiographic Examinations: PA and lateral chest.
  • Possible Radiographic Appearance: Hyperinflation (general radiolucency) and dominant lung markings of lower lungs.
  • Exposure Factor Adjustment: Generally none.

• Chronic Obstructive Pulmonary Disease (COPD):

  • Most Common Radiographic Examinations: PA and lateral chest.
  • Possible Radiographic Appearance: Depends on underlying cause.
  • Exposure Factor Adjustment: Changes in severe cases only.

• Cystic Fibrosis:

  • Most Common Radiographic Examinations: PA and lateral chest.
  • Possible Radiographic Appearance: Increased radiodensities in specific lung regions.
  • Exposure Factor Adjustment: Increase with severe condition ($+$).

• Dyspnea (Difficult Breathing):

  • Most Common Radiographic Examinations: PA and lateral chest.
  • Possible Radiographic Appearance: Depends on cause of dyspnea.
  • Exposure Factor Adjustment: Depends on cause.

• Emphysema:

  • Most Common Radiographic Examinations: PA and lateral chest.
  • Possible Radiographic Appearance: Increased lung dimensions, barrel chest, flattened diaphragm, radiolucent lungs.
  • Exposure Factor Adjustment: Significantly decreased, dependent on severity ($-$).

• Epiglottitis:

  • Most Common Radiographic Examinations: Soft tissue lateral upper airway.
  • Possible Radiographic Appearance: Narrowing of upper airway at epiglottic region.
  • Exposure Factor Adjustment: Soft tissue lateral technique ($-$).

• Lung Neoplasm (Benign - Hamartoma):

  • Most Common Radiographic Examinations: PA and lateral chest.
  • Possible Radiographic Appearance: Radiodensities with sharp outlines; mass may be calcified (radiopaque).
  • Exposure Factor Adjustment: Generally none.

• Lung Neoplasm (Malignant Types):

  • Most Common Radiographic Examinations: PA and lateral chest, CT scans.
  • Possible Radiographic Appearance: Slight shadows in early stages, larger defined radiopaque masses in advanced stages.
  • Exposure Factor Adjustment: Generally none.

• Pleural Effusion (Hydrothorax) in Pleural Cavity:

  • Subtypes:
  • Empyema: Fluid is pus.
  • Hemothorax: Fluid is blood.
  • Most Common Radiographic Examinations: Erect PA and lateral chest or horizontal beam lateral decubitus with affected side down.
  • Possible Radiographic Appearance: Increased radiodensity, air-fluid levels, possible mediastinal shift.
  • Exposure Factor Adjustment: Increase ($+$).

• Pleurisy:

  • Most Common Radiographic Examinations: Erect PA and lateral chest or lateral decubitus with affected side up, PA inspiration/expiration for small pneumothorax.
  • Possible Radiographic Appearance: Possible air-fluid levels, or none with "dry" pleurisy.
  • Exposure Factor Adjustment: Generally none.

• Pneumonia (Pneumonitis):

  • Subtypes: Aspiration pneumonia, Bronchopneumonia, Lobar (pneumococcal), Viral (interstitial).
  • Most Common Radiographic Examinations: PA and lateral chest.
  • Possible Radiographic Appearance: Patchy infiltrate with increased radiodensity.
  • Exposure Factor Adjustment: Generally none.

• Pneumothorax:

  • Most Common Radiographic Examinations: Erect PA and lateral chest or lateral decubitus with affected side up, PA inspiration/expiration for small pneumothorax.
  • Possible Radiographic Appearance: Lung seen displaced from chest wall, no lung markings.
  • Exposure Factor Adjustment: Generally none.

• Pulmonary Edema (Fluid Within Lungs):

  • Most Common Radiographic Examinations: PA and lateral chest; horizontal beam projection for air-fluid levels.
  • Possible Radiographic Appearance: Increased diffuse radiodensity in hilar regions; air-fluid levels.
  • Exposure Factor Adjustment: Increase ($+$) in severe cases.

• Pulmonary Emboli (Sudden Blockage of Artery in Lung):

  • Most Common Radiographic Examinations: PA and lateral chest and perfusion scans (nuclear medicine), CT scans.
  • Possible Radiographic Appearance: Rarely demonstrated on chest radiographs except for possible wedge-shaped opacity (Hampton hump).
  • Exposure Factor Adjustment: Generally none.

• Respiratory Distress Syndrome (RDS) / Hyaline Membrane Disease (HMD in Children):

  • Most Common Radiographic Examinations: PA and lateral erect chest.
  • Possible Radiographic Appearance: Granular pattern of increased radiodensity throughout lungs, possible air-fluid levels.
  • Exposure Factor Adjustment: Increase ($+$) without obscuring pathology.

• Tuberculosis (Primary Tuberculosis):

  • Most Common Radiographic Examinations: PA and lateral chest.
  • Possible Radiographic Appearance: Small opaque spots throughout lungs; enlargement of hilar region in early stages.
  • Exposure Factor Adjustment: Generally none.

• Tuberculosis (Reactivation / Secondary Tuberculosis):

  • Most Common Radiographic Examinations: PA and lateral chest and AP lordotic chest, tomograms.
  • Possible Radiographic Appearance: Regions of calcification with cavitations, frequently in area of upper lobes and apices with upward retraction of hila.
  • Exposure Factor Adjustment: None or increase slightly ($+$).

• Occupational Lung Diseases (Forms of Pneumoconiosis):

  • Anthracosis (Black Lung):
  • Radiographic Examination: PA and lateral chest.
  • Appearance: Small opaque spots throughout lungs.
  • Exposure Adjustment: Generally none.
  • Asbestosis:
  • Radiographic Examination: PA and lateral chest.
  • Appearance: Calcifications (radiodensities) involving the pleura.
  • Exposure Adjustment: Generally none.
  • Silicosis:
  • Radiographic Examination: PA and lateral chest.
  • Appearance: Distinctive pattern of scarring and dense nodules.
  • Exposure Adjustment: Generally none.

• Automatic Exposure Control (AEC) and Exposure Factors Note:

  • AEC systems are specifically designed to optimize mAs.
  • Digital radiographic systems automatically correct exposure brightness for patient size variances and pathologic conditions through specialized processing algorithms; manual adjustments generally are not required when AEC is correctly calibrated and used as intended.
  • Manual exposure adjustments may be required for extreme cases or repeat exposures, even when using AEC.
  • Manual exposure adjustments are essential when manual exposure techniques (e.g., tabletop or mobile examinations) are set without AEC.

PA Projection: Chest (Ambulatory Patient)

• Clinical Indications:

  • Performed erect to demonstrate pleural effusion, pneumothorax, atelectasis, and signs of infection.

• Technical Factors:

  • Minimum SID: $72\,\text{inches}$ ($180\,\text{cm}$).
  • Recommended Field Size: $14 \times 17\,\text{inches}$ ($35 \times 43\,\text{cm}$), portrait or landscape.
  • Grid: Required.
  • kVp Range: $110-125\,\text{kVp}$.
  • Shielding: Follow local regulations, department policy, and departmental protocol.

• Patient Position:

  • Patient erect, feet spread slightly, weight equally distributed on both feet.
  • Chin raised, resting against the image receptor (IR).
  • Hands placed on lower hips, palms facing out, elbows partially flexed.
  • Shoulders rotated forward against the IR to allow the scapulae to move laterally clear of the lung fields.
  • Shoulders depressed downward to move the clavicles below the apices.

• Part Position:

  • Align the midsagittal plane with the central ray (CR) and with the midline of the IR, maintaining equal margins between the lateral thorax and the sides of the IR.
  • Ensure no rotation of the thorax by placing the midcoronal plane parallel to the IR.

• Central Ray (CR):

  • Raise or lower CR and IR as needed to the level of T7 for an average patient (top of IR is approximately $1.5\,\text{inches}$ to $2\,\text{inches}$ [$4\,\text{cm}$ to $5\,\text{cm}$] above shoulders on average patients).
  • CR perpendicular to IR and centered to midsagittal plane at level of T7 ($7\,\text{inches}$ to $8\,\text{inches}$ [$18\,\text{cm}$ to $20\,\text{cm}$] below vertebra prominens, or to the inferior angle of the scapula).
  • IR centered directly to CR.

• Recommended Collimation:

  • Collimate on four sides to the area of the lung fields (top border of illuminated field to level of vertebra prominens, lateral border to outer skin margins).

• Respiration:

  • Exposure is made at the end of the second full inspiration.

• Positioning and Alignment Notes:

  • NOTE 1: For hypersthenic and broad-chested patients, place the $14 \times 17\,\text{inches}$ ($35 \times 43\,\text{cm}$) IR landscape (or collimate to at least this size when possible with larger digital receptors).
  • NOTE 2: Scoliosis and kyphosis may cause asymmetry of sternoclavicular joints and rib cage margins, as evidenced by right-to-left spinal curvature.

• Evaluation Criteria:

  • Anatomy Demonstrated: Includes both lungs from apices to costophrenic angles and the air-filled trachea from T1 down. Hilum region markings, heart, great vessels, and bony thorax are demonstrated. Visualized structures include apex, clavicle, hilum, right hemidiaphragm, right costophrenic angle, air-filled trachea, 4th rib, aortic arch, and heart.
  • Position: Chin sufficiently elevated to prevent superimposing apices. Sufficient forward shoulder rotation to prevent superimposition of scapulae over lung fields. Larger breast shadows (if present) primarily lateral to lung fields. No rotation demonstrated: both sternoclavicular joints are the same distance from the center line of the spine; distance from lateral rib margins to vertebral column is the same on each side from upper to lower rib cage. Collimation margins near equal on top and bottom with center of collimation field (CR) to T7 region on most patients. Full inspiration with no motion visualizes a minimum of 10 posterior ribs above the diaphragm (11 on many patients).
  • Exposure: No motion, as evidenced by sharp outlines of rib margins, diaphragm, and heart borders, as well as sharp lung markings in the hilar region and throughout the lungs. Optimal image receptor exposure with sufficient long-scale contrast for visualization of fine vascular markings within lungs. Faint outlines of at least midthoracic and upper thoracic vertebrae and posterior ribs visible through heart and mediastinal structures.

Lateral Position: Chest (Ambulatory Patient)

• Clinical Indications:

  • A $90^\circ$ perspective from the PA projection may demonstrate pathology situated posterior to the heart, great vessels, and sternum.

• Technical Factors:

  • Minimum SID: $72\,\text{inches}$ ($180\,\text{cm}$).
  • Recommended Field Size: $14 \times 17\,\text{inches}$ ($35 \times 43\,\text{cm}$), portrait.
  • Grid: Required.
  • kVp Range: $110-125\,\text{kVp}$.
  • Shielding: Follow local regulations, department policy, and protocol.

• Patient Position:

  • Patient erect, left side against IR unless patient complaint involves the right side (in that case, perform a right lateral if departmental protocol includes this option).
  • Weight evenly distributed on both feet.
  • Arms raised above head, chin up.

• Part Position:

  • Center patient to CR and to IR anteriorly and posteriorly.
  • Position in a true lateral position (coronal plane is perpendicular and sagittal plane is parallel to IR).
  • Lower CR and IR slightly from PA if needed.

• Central Ray (CR):

  • CR perpendicular, directed to midthorax at level of T7 ($3\,\text{inches}$ to $4\,\text{inches}$ [$7.5\,\text{cm}$ to $10\,\text{cm}$] below level of jugular notch).
  • IR centered to CR.

• Recommended Collimation:

  • Collimate on four sides to area of lung fields (top border of light field to level of vertebra prominens).

• Respiration:

  • Make exposure at end of second full inspiration.

• Positioning Notes:

  • NOTE 1: Ensure that the midsagittal plane is parallel to the IR; for slender but broad-shouldered patients, this results in hips and lower thorax not being against the IR.
  • NOTE 2: This increase in object-to-image distance (OID) of the lower chest results in the costophrenic angles of the lungs being projected lower because of divergence of the x-ray beam. Therefore, CR and IR should be lowered a minimum of $1\,\text{inch}$ ($2.5\,\text{cm}$) from the PA on this type of patient to prevent cutoff of costophrenic angles.

• Evaluation Criteria:

  • Anatomy Demonstrated: Included are the entire lungs from apices to the costophrenic angles and from the sternum anteriorly to the posterior ribs and thorax posteriorly. Anatomical structures identified include apices, thoracic vertebrae, posterior ribs, costophrenic angles, body of sternum, heart, and diaphragm.
  • Position: Chin and arms elevated sufficiently to prevent excessive soft tissues from superimposing apices. No rotation: posterior ribs and costophrenic angle on side away from IR projected slightly ($\frac{1}{4}\,\text{inch}$ to $\frac{1}{2}\,\text{inch}$ [or about $1\,\text{cm}$]) posterior because of divergent rays. The hilar region should be in the approximate center of the IR.
  • Exposure: No motion, as evidenced by sharp outlines of the diaphragm and lung markings. Optimal image receptor exposure with sufficient exposure and long-scale contrast for visualization of rib outlines and lung markings through the heart shadow and upper lung areas without overexposing other regions of the lungs.

AP Projection: Chest (Supine, Upright, or Semierect - Bedside Portable)

• Clinical Indications:

  • Demonstrates pathology involving the lungs, diaphragm, and mediastinum.
  • Determining air-fluid levels (pleural effusion) requires a completely erect position with a horizontal CR, as in a PA, AP, or decubitus chest projection.

• Technical Factors:

  • Minimum SID: $72\,\text{inches}$ ($180\,\text{cm}$) for semierect.
  • Recommended Field Size: $14 \times 17\,\text{inches}$ ($35 \times 43\,\text{cm}$), portrait or landscape.
  • Grid: Due to higher kVp, the use of a grid is strongly recommended.
  • kVp Range: $110-125\,\text{kVp}$.
  • Shielding: Follow local regulations, department policy, and protocol.

• Patient Position:

  • Patient is supine on cart; if possible, the head end of the cart or bed should be raised into a semierect position.
  • Alternatively, patient may be seated erect, legs over the edge, back against the IR.
  • Roll patient's shoulders forward by rotating arms medially or internally.

• Part Position:

  • Place IR under or behind patient; align center of IR to CR (top of IR about $1.5\,\text{inches}$ [$4\,\text{cm}$ to $5\,\text{cm}$] above shoulders).
  • Center patient to CR and to IR.
  • Ensure no rotation of the thorax by placing the midcoronal plane parallel to IR.

• Central Ray (CR):

  • CR angled caudad to be perpendicular to long axis of sternum (generally requires $+5^\circ$ caudad angle, to prevent clavicles from obscuring the apices).
  • CR to level of T7, $3\,\text{inches}$ to $4\,\text{inches}$ ($8\,\text{cm}$ to $10\,\text{cm}$) below jugular notch.

• Recommended Collimation:

  • Collimate on four sides to area of lung fields (top border of light field to level of vertebra prominens).

• Respiration:

  • Make exposure at end of second full inspiration.

• Technical Notes:

  • Crosswise IR placement is recommended for large or hypersthenic or broad-chested patients to minimize chance of lateral cutoff. This requires accurate CR alignment with center of IR with only minimal caudal angle to prevent grid cutoff if grid is used.
  • For semierect position, use $72\,\text{inch}$ ($180\,\text{cm}$) SID if possible. Always place markers on the IR or label the image to indicate the SID used; also indicate the projections obtained, such as AP semierect or AP upright.

• Evaluation Criteria:

  • Criteria for chest radiographs taken in semierect or upright positions should be similar to criteria for PA projection, with three exceptions:
  1. The heart appears larger as a result of increased magnification from a shorter SID and increased OID of the heart.
  2. For the semierect patient, possible pleural effusion often obscures vascular lung markings compared with a fully erect PA chest projection. Without a horizontal beam, fluid levels may not be demonstrated.
  3. Usually, inspiration is not as full, and only eight or nine posterior ribs are visualized above the diaphragm. The lungs may appear denser because they are not as fully aerated.
  • Correct CR Angle: The clavicles should be in the same horizontal plane with an unobstructed view of the apical region.

Anterior Oblique Positions: RAO and LAO - Chest

• Clinical Indications:

  • Investigate pathology involving the lung fields, trachea, and mediastinal structures.
  • Determine the size and contours of the heart and great vessels.

• Technical Factors:

  • Minimum SID: $72\,\text{inches}$ ($180\,\text{cm}$).
  • Recommended Field Size: $14 \times 17\,\text{inches}$ ($35 \times 43\,\text{cm}$), portrait.
  • Grid: Required.
  • kVp Range: $110-125\,\text{kVp}$.
  • Shielding: Follow local regulations, department policy, and protocol.

• Patient Position:

  • Patient erect, rotated $45^\circ$ with right anterior shoulder against IR for RAO and $45^\circ$ with left anterior shoulder against IR for LAO.
  • Patient's arm flexed nearest IR and hand placed on hip, palm out.
  • Opposite arm raised to clear lung field and hand rested on head or on chest unit for support, keeping arm raised as high as possible.
  • Patient looking straight ahead; chin raised.

• Part Position:

  • As viewed from the x-ray tube, center the patient to CR and to IR, with top of IR about $1\,\text{inch}$ ($2.5\,\text{cm}$) above vertebra prominens.

• Central Ray (CR):

  • CR perpendicular, directed to level of T7 ($7\,\text{inches}$ to $8\,\text{inches}$ [$8\,\text{cm}$ to $10\,\text{cm}$] below level of vertebra prominens).
  • CR midway between midsagittal plane and lateral margin of thorax.

• Recommended Collimation:

  • Collimate on four sides to area of lung fields (top border of light field to level of vertebra prominens).

• Respiration:

  • Make exposure at end of second full inspiration.

• Technical Notes:

  • For anterior oblique, the side of interest generally is the side farthest from the IR. Thus, the RAO provides the best visualization of the left lung.
  • Certain positions for studies of the heart and great vessels require oblique positions with an increase in rotation of $45^\circ$ to $60^\circ$.
  • Less rotation ($15^\circ$ to $20^\circ$) may be valuable for better visualization of the various areas of the lungs for possible pulmonary disease.
  • Exception: Either erect or recumbent posterior oblique projections can be taken if the patient cannot assume an erect position for anterior oblique, or if supplementary projections are required.

• Evaluation Criteria:

  • Anatomy Demonstrated: Both lungs from the apices to the costophrenic angles should be included. Air-filled trachea, great vessels, and heart outlines are best visualized with $60^\circ$ LAO position.
  • Position: To evaluate for a $45^\circ$ rotation, the distance from the outer margin of the ribs to the vertebral column on the side farthest from the IR should be approximately two times the distance of the side closest to the IR. CR centered at level of T7.
  • Exposure: No motion; outline of the diaphragm and heart should appear sharp. Optimal exposure and contrast allow visualization of vascular markings throughout the lungs and rib outlines except through the densest regions of the heart.

Posterior Oblique Positions: RPO and LPO - Chest

• Clinical Indications:

  • Investigate pathology involving the lung fields, trachea, and mediastinal structures.
  • Determine the size and contours of the heart and great vessels.

• Technical Factors:

  • Minimum SID: $72\,\text{inches}$ ($180\,\text{cm}$).
  • Recommended Field Size: $14 \times 17\,\text{inches}$ ($35 \times 43\,\text{cm}$), portrait.
  • Grid: Required.
  • kVp Range: $110-125\,\text{kVp}$.
  • Shielding: Follow local regulations, department policy, and protocol.

• Patient Position (Erect):

  • Patient erect, rotated $45^\circ$ (up to $60^\circ$) with right posterior shoulder against IR for RPO and $45^\circ$ (up to $60^\circ$) with left posterior shoulder against IR for LPO.
  • Arm closest to the IR raised, resting on head; other arm placed on hip with palm out.
  • Patient looking straight ahead.

• Patient Position (Recumbent):

  • If patient cannot stand or sit, perform posterior oblique projections on table.
  • Place supports under patient's head and under elevated hip and shoulder.

• Part Position:

  • Top of IR about $1\,\text{inch}$ ($2\,\text{cm}$) above vertebra prominens or about $5\,\text{inches}$ ($12\,\text{cm}$) above level of jugular notch ($2\,\text{inches}$ [$5\,\text{cm}$] above shoulders).
  • Thorax centered to CR and to IR.

• Central Ray (CR):

  • CR perpendicular, to level of T7.
  • CR midway between midsagittal plane and lateral margin of thorax.

• Recommended Collimation:

  • Collimate on four sides to area of lung fields (top border of light field to level of vertebra prominens).

• Respiration:

  • Make exposure after second full inspiration.

• Technical Notes:

  • Posterior oblique projections provide best visualization of the side closest to the IR.
  • Posterior positions show the same anatomy as the opposite anterior oblique positions. Thus, the RPO corresponds to the LAO position and the LPO corresponds to the RAO position.

• Evaluation Criteria:

  • Evaluation criteria are similar to criteria for anterior oblique positions.
  • However, because of increased magnification of the anterior diaphragm, lung fields usually appear shorter on posterior oblique than on anterior oblique projections.
  • The heart and great vessels also appear larger on posterior oblique because they are farther from the IR.
  • Identified anatomical callouts in images: trachea, carina, heart, left clavicle, left costophrenic angle, right clavicle, left apex, scapula, right lung.

Lateral Position: Upper Airway

• Clinical Indications:

  • Investigate pathology of the air-filled larynx and trachea, including the region of thyroid and thymus glands and upper esophagus, for opaque foreign object or if contrast medium is present.
  • Rule out epiglottitis, which may be life-threatening for a young child.

• Technical Factors:

  • Minimum SID: $72\,\text{inches}$ ($180\,\text{cm}$) to minimize magnification.
  • Recommended Field Size: $10 \times 12\,\text{inches}$ ($24 \times 30\,\text{cm}$), portrait.
  • Grid: Required.
  • kVp Range: $75-85\,\text{kVp}$.
  • Shielding: Follow local regulations, department policy, and protocol.

• Patient Position:

  • Patient should be upright if possible, seated, or standing in a lateral position (may be taken in R or L lateral and may be taken recumbent tabletop if necessary).

• Part Position:

  • Position patient to center upper airway to CR and to center of IR (larynx and trachea lie anterior to cervical and thoracic vertebrae).
  • Rotate shoulders posteriorly with arms hanging down and hands clasped behind back.
  • Raise chin slightly and have patient look directly ahead.
  • Adjust IR height to place top of IR at level of external auditory meatus (EAM), which is the opening of the external ear canal.

• Central Ray (CR):

  • CR perpendicular to center of IR at level of C6 or C7, midway between the laryngeal prominence of the thyroid cartilage and the jugular notch.

• Recommended Collimation:

  • Collimate to region of soft tissue of the neck.

• Respiration:

  • Make exposure during a slow, deep inspiration to ensure filling trachea and upper airway with air.

• Centering & Exposure Notes:

  • Neck Region: Centering should be to laryngeal prominence (C5) with exposure factors for a soft tissue lateral neck if the area of interest is primarily the larynx and upper trachea.
  • Distal Larynx and Trachea Region: If the distal larynx and upper trachea and midtrachea are the primary areas of interest, the IR and CR should be lowered to place the CR at the upper jugular notch (T1-T2) with exposure factors approximately those for a lateral chest.

• Evaluation Criteria:

  • Anatomy Demonstrated: The larynx and trachea should be filled with air and well visualized. Structures identified include epiglottis, larynx, and trachea.
  • Position: Centering for the neck region (larynx and proximal trachea) should include the EAM at the upper border of the image and T2 or T3 on the lower border. If the distal larynx and trachea is the primary area of interest, centering should be lower to include the area from C3 to T4 or T5 on the image. The shadows of the shoulders should be primarily posterior to and should not superimpose the area of the trachea. Collimation borders should appear on both sides with ideally only minimal ($< \frac{1}{4}\,\text{inch}$) borders on top and bottom.
  • Exposure: Optimal exposure includes a soft tissue technique and processing algorithm wherein the air-filled larynx and upper trachea are not overexposed, but well visualized. Cervical vertebrae appear underexposed.

AP Projection: Upper Airway

• Clinical Indications:

  • Investigate pathology of the air-filled larynx and trachea, including the region of the thyroid and thymus glands and upper esophagus for opaque foreign object or if contrast medium is present.

• Technical Factors:

  • Minimum SID: $40\,\text{inches}$ ($100\,\text{cm}$) if possible, to minimize magnification.
  • Recommended Field Size: $10 \times 12\,\text{inches}$ ($24 \times 30\,\text{cm}$), portrait.
  • Grid: Required.
  • kVp Range: $75-85\,\text{kVp}$.
  • Shielding: Follow local regulations, department policy, and protocol.

• Patient Position:

  • Patient should be upright if possible, seated or standing with back of head and shoulders against IR (may be taken recumbent tabletop if necessary).

• Part Position:

  • Align midsagittal plane with CR and with midline of grid or table.
  • Raise chin so that acanthiomeatal line is perpendicular to the IR (line from the acanthion or area directly under the nose and the meatus or EAM); have patient look directly ahead.

• Central Ray (CR):

  • Adjust the IR height to place top of IR about $1\,\text{inch}$ to $1.5\,\text{inches}$ ($3\,\text{cm}$ to $4\,\text{cm}$) below EAM.
  • CR perpendicular to center of IR at level of T1-T2, about $1\,\text{inch}$ ($2.5\,\text{cm}$) above the jugular notch.

• Recommended Collimation:

  • Collimate to region of soft tissue of the neck.

• Respiration:

  • Make exposure during a slow, deep inspiration to ensure filling of trachea and upper airway with air.

• Technical Notes:

  • Exposure: Exposure for this AP projection should be approximately that of an AP of the cervical or thoracic spine.
  • Centering for Upper Airway and Trachea: Centering for this AP projection is similar to that of the lateral distal larynx and upper trachea position because the most proximal area of the larynx is not visualized on the AP as a result of the superimposed base of the skull and mandible. Therefore, more of the trachea can be visualized.

• Evaluation Criteria:

  • Anatomy Demonstrated: The larynx and trachea from C3 to T4 should be filled with air and visualized through the spine. The area of the proximal cervical vertebrae (the lower margin of the shadow of the superimposed mandible and base of skull) to the midthoracic region should be included.
  • Position: No rotation should occur, as evidenced by the symmetric appearance of the sternoclavicular joints. The mandible should superimpose the base of the skull with the spine aligned with the center of the film. Collimation borders should appear on both sides with ideally only minimal ($\le \frac{1}{4}\,\text{inch}$) borders on top and bottom. The collimation field (CR) should be centered to the area of T1-T2.
  • Exposure: Optimal exposure and processing algorithm should allow visualization of the air-filled trachea through the cervical and thoracic vertebrae.

• Pathology Manifestation (Croup):

  • Radiographic image of croup demonstrates smooth, tapered narrowing of the subglottic portion of the trachea, known as the "Gothic arch sign", compared to a normal trachea which possesses a broad subglottic region.