Thorax and Abdomen
2 Abdomen Series
Anatomy
- Lumbar spine (5 vertebrae)
- Anterior superior iliac spine (ASIS)
- Iliac crest
- Psoas muscles (triangular on either side of spine)
- Kidneys
- Diaphragms
- Symphysis pubis
Projections
Abdomen, AP supine (KUB)
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine, MSP aligned to IR, arms at sides
- Adjustments: Legs extended, pelvis not rotated
- CR: Perpendicular to IR at level of iliac crest; center to MSP
- Pt. Instructions: Hold breath after expiration
- Exposure: On expiration
Evaluation Criteria
- Symphysis pubis included (entire bladder visualized)
- Outer rib margins equal distance from spine; iliac wings symmetrical (no rotation)
- Spine straight and centered
- Proper exposure to show psoas muscles, kidneys, and lumbar vertebrae
Abdomen, AP upright
CR Location & Positioning
- SID: 40 inches
- Patient position: Erect, MSP centered to IR, arms at sides
- Adjustments: Weight evenly distributed on feet
- CR: Horizontal, centered to IR about 2 inches above iliac crest (to include diaphragms); top of IR near axilla
- Pt. Instructions: Hold breath after expiration
- Exposure: On expiration
Evaluation Criteria
- Diaphragms included (must be visualized)
- Outer rib margins equidistant from spine; iliac wings symmetrical
- Spine straight and aligned to IR center
Abdomen, Lateral Decubitus
CR Location & Positioning
- SID: 40 inches
- Patient position: Lateral recumbent, side down on table (usually left side down to show free air against liver)
- Adjustments: Knees flexed slightly for stability; MSP parallel to table
- CR: Horizontal, centered about 2 inches above iliac crest; center to MSP
- Pt. Instructions: Hold breath after expiration
- Exposure: On expiration
Evaluation Criteria
- Diaphragms included
- Iliac wings symmetrical; no rotation
- Spine straight and centered
- Free air demonstrated on right side if present
Abdomen, Dorsal Decubitus
Indications
- Abnormal masses
- Gas/air-fluid levels
- Aneurysms (dilated vessels)
- Calcifications of aorta or vessels
- Umbilical hernia
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine, MCP centered to IR, arms elevated out of field
- Adjustments: Legs extended, MSP perpendicular to table
- CR: Horizontal, 2 inches above iliac crest, centered to MCP
- Pt. Instructions: Hold breath after expiration
- Exposure: On expiration
Evaluation Criteria
- Posterior ribs and posterior iliac wings superimposed (no rotation)
- Bilateral ASIS symmetric
- Diaphragms included
- Appropriate exposure to show abdominal contents
Acute Abdominal Series (3-View Abdomen)
Projections included:
- AP supine abdomen (KUB)
- AP upright abdomen – or left lateral decubitus abdomen if patient cannot stand
- PA chest (upright if possible)
CR Location & Positioning (summary):
- Supine abdomen: CR perpendicular to iliac crest, include symphysis pubis.
- Upright abdomen: CR horizontal, 2″ above iliac crest, include diaphragms.
- PA chest: CR perpendicular at T7, top of IR 1.5–2″ above shoulders.
Pt. Instructions:
- Supine/upright/decubitus abdomen → expose on expiration.
- PA chest → expose on full inspiration.
Evaluation Criteria:
- Supine: Symphysis pubis included, no rotation.
- Upright/decubitus: Diaphragms included, no rotation.
- PA chest: Full lung expansion with diaphragms visible, no rotation.
Procedure Adaptation
- Pediatrics: Lower kVp/mAs, immobilization may be required
- Trauma/immobilized: Use horizontal beam (decubitus or dorsal) for free air/fluid
- Obese patients: Palpate carefully for landmarks; may require increased kVp for penetration
- Localization: Place markers over palpable lumps, pain sites, or surgical scars to assist radiologist
Exposure Factors & Technical Considerations
- kVp: 70–85 (higher for larger patients to penetrate abdomen)
- mAs: Adequate for abdominal density, short exposure time to reduce motion
- Collimation: To abdominal margins, include diaphragm (upright/decubitus) or symphysis pubis (supine)
- Shielding: Gonadal shielding when it does not obscure anatomy of interest
- Breathing phase: Always expose on expiration (reduces diaphragm, spreads abdominal organs)
Hows & Whys of Abdominal Radiography
Projections & Indications
-
Why are some abdominal images performed upright?
To look for free air and fluid levels. -
Which side will free air rise to on an upright abdomen? Why?
The right side — the liver is higher, so free air collects beneath the diaphragm. -
What structures must be included on an upright abdomen image?
Diaphragms. -
What is the supine abdomen commonly called?
KUB (Kidneys, Ureters, Bladder). -
What structure must be included on supine abdomen image? Why?
Symphysis pubis — to confirm bladder inclusion. -
Why use a lateral decubitus view?
To show free intraperitoneal air when upright imaging is not possible. -
Why might you do a dorsal decubitus abdomen?
For aneurysms, calcifications, hernias, or air-fluid levels in immobile patients.
Breathing & Technique
-
Why perform abdominal images on expiration?
Expiration raises the diaphragm and spreads abdominal organs for clearer visualization. -
What are the two triangular-shaped muscles visible on some abdominal images?
The psoas muscles.
Acute Abdominal Series
-
Why is the supine abdomen included?
Demonstrates bowel gas pattern, kidneys, ureters, bladder, and possible calcifications. -
Why must the symphysis pubis be included on the supine view?
To confirm that the bladder region is fully visualized. -
Why is the upright abdomen important?
Shows free intraperitoneal air and air-fluid levels that cannot be seen on supine images. -
Why might a lateral decubitus abdomen be substituted for upright?
For patients who cannot stand; left lateral is preferred so free air rises along the liver margin, not over the gastric bubble. -
Why is the PA chest included in an acute abdominal series?
To detect free air beneath the diaphragm and evaluate for thoracic causes of abdominal pain. -
Why is PA preferred over AP chest?
PA reduces radiation dose to breast tissue and provides better visualization of free air. -
Why is expiration used for abdominal images?
Expiration raises the diaphragm and spreads abdominal organs for clearer visualization. -
Why is inspiration used for the chest image?
To expand lungs fully and show free air beneath the diaphragm.