Ribs Posterior AP is a radiography positioning projection of the Thorax. AP posterior ribs, erect above the diaphragm, supine below. SID 40". Breathing varies by location. The centering point is located above diaphragm: T7 on inspiration. Below diaphragm: midway between xiphoid and lower rib margin on expiration. The central ray is perpendicular to IR. T7 for ribs above the diaphragm; midway between the xiphoid and lower rib margin for ribs below it. Image-quality criteria include posterior ribs above the diaphragm (inspiration) or below it (expiration) demonstrated, per the area of interest, ribs 1-9 shown above the diaphragm, or at least ribs 10-12 below it (Bontrager). Merrill's lists ribs 1-10 above and 8-12 below. A sample technique is 81 kVp with DR 10 or CR 20 mAs, at the chart's 72 in SID. The working SID is 40 inches (102 cm).
Anatomy demonstrated
- Posterior ribs above or below the diaphragm, per the area of interest.
- Ribs 1-9 above the diaphragm, or ribs 10-12 below it (Bontrager); Merrill's: 1-10 above, 8-12 below.
- Ribs seen through the lungs and heart, or through the abdomen below the diaphragm.
Patient preparation
- Verify patient identity using two identifiers.
- Remove all radiopaque objects from the chest and trunk.
- Erect (facing the tube) for ribs above the diaphragm; supine for ribs below the diaphragm.
- Instruct: For upper ribs above diaphragm, breath on inspiration and hold.
- For lower ribs below diaphragm, breath on full expiration and hold.
Position & centering point
Above diaphragm: T7 on inspiration. Below diaphragm: midway between xiphoid and lower rib margin on expiration.
Central ray
Perpendicular to IR. T7 for ribs above the diaphragm; midway between the xiphoid and lower rib margin for ribs below it.
Exposure / technique
- kVp
- 81
- mAs
- DR 10 / CR 20
- Chart row
- kVp and mAs at the chart's 72 in SID
- Working SID
- 40" (102 cm)
- Notes
- Grid required. For ribs above diaphragm: full inspiration. For ribs below diaphragm: full expiration. Sample technique: DR 10 / CR 20 mAs at 81 kVp, 72 in SID, for a 21 cm part, above the diaphragm (Merrill's sample chart). Adjust for your equipment. The same chart below the diaphragm: DR 12.5 / CR 25 mAs at 85 kVp, 40 in SID. Bontrager prints digital 85 +/- 5 kV above and 80 +/- 5 kV below.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Posterior ribs above the diaphragm (inspiration) or below it (expiration) demonstrated, per the area of interest.
- Ribs 1-9 shown above the diaphragm, or at least ribs 10-12 below it (Bontrager). Merrill's lists ribs 1-10 above and 8-12 below.
- No rotation of the thorax; symmetry of the ribs.
Common errors
- 1 Rotation of the thorax evident.
- 2 Not suspending on inspiration for ribs above the diaphragm.
- 3 Not suspending on expiration for ribs below the diaphragm.
- 4 CR not at T7 (above diaphragm) or the xiphoid-to-rib-margin midpoint (below) clips ribs from the field.
Clinical indications
- Suspected rib fracture evaluation.
- Trauma assessment of the thoracic cage.
- Detection of rib metastases or lytic lesions.