Ribs PA Oblique is a radiography positioning projection of the Thorax. PA oblique ribs, 45-degree. SID 40". Breathing varies by location. The centering point is located above diaphragm: level of T7. Below: midway between the xiphoid and lower rib margin. Midway between the spine and the lateral rib margin of the affected side, in a 45-degree anterior oblique (RAO/LAO), anterior chest toward the IR. The central ray is perpendicular to IR: T7 (7 to 8 inches below the vertebra prominens) above the diaphragm, midway between the xiphoid and lower rib margin below it. Image-quality criteria include axillary ribs of the affected side projected clear of the vertebral column, axillary ribs in profile, spine shifted away from the area of interest. A sample technique is 81 kVp with DR 16 or CR 36 mAs, at the chart's 72 in SID. The working SID is 40 inches (102 cm).
Anatomy demonstrated
- Axillary ribs, affected side: 1-9 above the diaphragm or 10-12 below (Bontrager); 1-10 above, 8-12 below (Merrill's).
- Axillary portion of the ribs without self-superimposition.
Patient preparation
- Verify patient identity using two identifiers.
- Remove all radiopaque objects from the chest and trunk.
- Position patient in 45-degree oblique facing away from tube (erect above the diaphragm, recumbent below).
- Affected side rotated away from the IR.
- Instruct: inspiration and hold for ribs above the diaphragm, expiration and hold for ribs below.
Position & centering point
Above diaphragm: level of T7. Below: midway between the xiphoid and lower rib margin. Midway between the spine and the lateral rib margin of the affected side, in a 45-degree anterior oblique (RAO/LAO), anterior chest toward the IR.
Central ray
Perpendicular to IR: T7 (7 to 8 inches below the vertebra prominens) above the diaphragm, midway between the xiphoid and lower rib margin below it.
Exposure / technique
- kVp
- 81
- mAs
- DR 16 / CR 36
- Chart row
- kVp and mAs at the chart's 72 in SID
- Working SID
- 40" (102 cm)
- Notes
- Grid required. Affected side rotated away from the IR. Full inspiration for ribs above the diaphragm, full expiration for ribs below. Sample technique: DR 16 / CR 36 mAs at 81 kVp, 72 in SID, for a 23 cm part (Merrill's sample chart). Adjust for your equipment. Bontrager prints digital 85 +/- 5 kV.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Axillary ribs of the affected side projected clear of the vertebral column.
- Axillary ribs in profile, spine shifted away from the area of interest.
- Ribs above the diaphragm demonstrated on an inspiration exposure, ribs below on expiration.
Common errors
- 1 Inadequate obliquity fails to project ribs clear of the spine.
- 2 Excessive obliquity foreshortens the ribs and distorts anatomy.
- 3 Affected side not raised prevents visualization of the axillary ribs.
- 4 Inadequate inspiration limits the rib and diaphragm visualization.
Clinical indications
- Evaluation of axillary rib fractures.
- Assessment of rib pathology not clearly visible on AP or PA.
- Follow-up imaging of axillary rib trauma.