Chest AP is a radiography positioning projection of the Chest. Anteroposterior chest. Used when patient cannot stand for PA. The centering point is located level of t7. cr perpendicular to ir. sid 40" (102 cm) for portable; 72" if upright unit available.. The central ray is horizontal, perpendicular to ir. centered to t7.. Image-quality criteria include both lungs visualized in entirety., heart shadow is wider than pa (cardiothoracic ratio not assessable on ap).. Standard exposure ranges from 80 to 100 kVp, 2 to 6 mAs, at an SID of 40 inches (102 cm).
Patient preparation
- Verify patient identity using two identifiers.
- Remove radiopaque objects (ECG leads if possible, jewelry, gowns with snaps).
- Confirm pregnancy status for female patients of child-bearing age.
- For supine AP: patient lies flat; for upright AP: patient sits/stands with back to upright Bucky.
- Instruct full inspiration and breath-hold on second breath in.
Position & centering point
Level of T7. CR perpendicular to IR. SID 40" (102 cm) for portable; 72" if upright unit available.
Central ray
Horizontal, perpendicular to IR. Centered to T7.
Exposure / technique
- kVp
- 80–100
- mAs
- 2–6
- SID
- 40" (102 cm)
- Notes
- AP/portable chests commonly use a lower kVp than the high-kVp 72-inch PA technique (practical and contrast reasons). The shorter SID is compensated with mAs via the inverse-square law, not by kVp. The heart appears larger from magnification at the shorter SID, expect roughly 15% more cardiac silhouette than a PA on the same patient.
Image-quality criteria
- Both lungs visualized in entirety.
- Heart shadow is wider than PA (cardiothoracic ratio not assessable on AP).
- Clavicles project higher and more horizontal than PA (above lung apices).
- Scapulae overlap the lung fields (cannot be rotated out as in PA).
- A minimum of 8-10 posterior ribs visible above the diaphragm if good inspiration.
- No rotation: spinous processes equidistant between sternoclavicular joints.
Clinical indications
- Patient cannot stand or tolerate PA (ICU, trauma, post-op).
- Bedside chest for line/tube placement check (NG, ET, central line).
- Pneumothorax assessment in supine patient (look for deep sulcus sign).
- Routine ICU follow-up of cardiopulmonary status.
Aligned to the 2025 ARRT Content Specifications.