Sternum

Thorax and Abdomen

4 Sternum

Anatomy:

Landmarks & Levels:

CR Location & Positioning

SID: 60–72 inches (longer distance reduces magnification caused by large OID)
Patient position: Upright preferred; left side against IR
Adjustments: Arms drawn back with hands clasped to push chest outward, MSP parallel to IR
CR: Perpendicular to IR, midway between jugular notch and xiphoid process; top of IR about 1.5″ above jugular notch
Pt. Instructions: Suspend respiration on full inspiration (expands chest, moves sternum laterally away from spine)
Exposure: On full inspiration

Evaluation Criteria

Entire sternum visualized, free of superimposition from ribs, humeri, or soft tissues of arms
Posterior ribs directly superimposed (no rotation)
Sternum forms a sharp, clear anterior border

CR Location & Positioning

SID: 40 inches or less (shorter distance magnifies thoracic structures, making sternum more distinct)
Patient position: Upright or prone, rotated into RAO (right anterior chest closest to IR)
Adjustments: Rotate 15–20° (average), roll shoulders forward to bring sternum closer to IR
CR: Perpendicular to IR, centered midway between jugular notch and xiphoid process, 1″ left of MSP; top of IR about 1.5″ above jugular notch
Pt. Instructions: Suspend respiration on expiration; breathing technique may be used (low mA, 2–3 second exposure) to blur lung and rib markings if patient can cooperate
Exposure: On expiration or during breathing technique

Evaluation Criteria

Trauma/immobilized patients: If patient cannot be prone for RAO, perform LPO (upside sternum projects over heart).
Large body habitus: May need greater rotation (closer to 20°).
Thin body habitus: Less rotation (closer to 15°) to avoid superimposing sternum over spine.
Pediatrics: Lower exposure settings, immobilization if needed; shorter SID still used for RAO.

kVp: 70–80 for adequate contrast of sternum against thorax
mAs: Short exposure time for lateral; longer time with low mA for breathing technique (RAO)
Collimation: To sternum region only
Shielding: Gonadal shielding when possible without obscuring anatomy
Tube distance safety: Tube never closer than 12″ to patient

Anatomy & Landmarks

Positioning & Technique

Why should the sternum be imaged at distances of less than 40 inches (RAO)?
Shorter SID causes magnification and loss of detail in overlying thoracic structures, helping the sternum stand out.
Why should lateral sternum images be performed at 60–72 inches SID?
The long SID compensates for the large OID, reducing magnification and distortion.
Why is the sternum rotated into RAO position?
To project the sternum over the heart shadow, free from the spine.
Why might an LPO be used instead of RAO?
For trauma patients who cannot lie prone or be rotated forward; LPO projects sternum over heart shadow.
Why use a breathing technique for RAO sternum?
It blurs ribs and lung markings, making the sternum borders clearer.

Safety & Image Quality

How far should the tube be from the patient for safety?
At least 12 inches.
How do you know there’s no rotation on a lateral sternum?
Posterior ribs are superimposed.
How do you know exposure factors are correct?
Sternum margins are sharp, visible through heart shadow, and not obscured by noise or over-penetration.