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Thorax and Abdomen

Abdomen

Anatomy

Students should be able to identify the following structures on radiographic images:

Lumbar spine (5 vertebrae), Anterior superior iliac spine (ASIS), Iliac crest, Psoas muscles, Kidneys, Diaphragms, Symphysis pubis, Liver, Spleen, Stomach, Small intestine, Large intestine (colon).

Routine Projections (ARRT Required)

AP Supine Abdomen (KUB)

CR Location & Positioning

  • SID: 40 inches
  • Patient position: Supine, MSP centered to table
  • Adjustments: Legs extended, pelvis not rotated, arms at sides
  • CR: Perpendicular at level of iliac crests to include symphysis pubis
  • Pt. Instructions: Suspend respiration at end expiration
  • Exposure: On expiration

Evaluation Criteria

  • Coverage (what anatomy must be included and how you verify it’s complete): Diaphragm may not be included, but symphysis pubis must be visible
  • Rotation checks (how symmetry or alignment tells you if positioning is correct): Iliac wings and obturator foramina symmetrical
  • Motion checks (how sharpness confirms patient cooperation/exposure timing): Sharp outlines of psoas muscles and spine
  • Technique checks (what contrast, density, soft tissue visibility, and artifacts to look for): Proper density to show kidneys and lumbar vertebrae
  • Clinical aim (what contrast, density, soft tissue visibility, and artifacts to look for): Baseline image for bowel gas pattern and urinary system survey

AP Upright Abdomen

CR Location & Positioning

  • SID: 40 inches
  • Patient position: Erect, back to IR, MSP centered
  • Adjustments: Weight evenly distributed, arms at sides
  • CR: Horizontal, 2 inches above iliac crests (to include diaphragms)
  • Pt. Instructions: Suspend respiration at end expiration
  • Exposure: On expiration

Evaluation Criteria

  • Coverage: Diaphragms must be included
  • Rotation checks: Iliac wings symmetrical
  • Motion checks: Clear diaphragm and bowel gas outlines
  • Technique checks: Appropriate contrast to show air-fluid levels
  • Clinical aim: Detect intraperitoneal air and fluid levels

Lateral Decubitus Abdomen (Left Side Down)

CR Location & Positioning

  • SID: 40 inches
  • Patient position: Lateral recumbent, side down (left preferred to show free air against liver)
  • Adjustments: Knees slightly flexed; arms above head; MSP parallel to IR
  • CR: Horizontal, 2 inches above iliac crests
  • Pt. Instructions: Suspend respiration at end expiration
  • Exposure: On expiration

Evaluation Criteria

  • Coverage: Diaphragms visible; lateral abdomen fully included
  • Rotation checks: Iliac wings nearly symmetrical
  • Motion checks: Sharp diaphragm borders, no motion
  • Technique checks: Adequate contrast to show free air along right lateral abdomen
  • Clinical aim: Detect free intraperitoneal air or fluid when upright not possible

Dorsal Decubitus Abdomen

CR Location & Positioning

  • SID: 40 inches
  • Patient position: Supine; MCP centered; arms raised above head
  • Adjustments: Legs extended; IR placed adjacent to right or left side
  • CR: Horizontal, 2 inches above iliac crests
  • Pt. Instructions: Suspend respiration at end expiration
  • Exposure: On expiration

Evaluation Criteria

  • Coverage: Diaphragms included; entire abdomen visualized
  • Rotation checks: Posterior ribs and iliac wings superimposed
  • Motion checks: Sharp organ outlines
  • Technique checks: Proper exposure for visualization of gas patterns and soft tissue
  • Clinical aim: Evaluate aneurysms, hernias, or air-fluid levels in immobile patients

Dorsal Decubitus Abdomen

CR Location & Positioning

SID: 40 inches (102 cm)
Patient position: Supine on cart or table; arms elevated to clear abdomen
Adjustments: Place IR vertically beside patient, centered at midcoronal plane; ensure long axis of IR aligns with midline of abdomen; support grid or detector upright against side of abdomen
CR: Horizontal beam, perpendicular to IR, entering at midcoronal plane 2 inches above iliac crest (to include diaphragm)
Pt. Instructions: Suspend respiration at end of expiration
Exposure: Grid required; use technique comparable to upright abdomen

Evaluation Criteria

Coverage: Entire abdomen from diaphragm to symphysis pubis, including lateral abdominal walls
Rotation checks: Spinous processes and iliac wings symmetric; no rotation of spine or pelvis
Motion checks: Sharp bowel gas patterns; no breathing blur
Technique checks: Adequate penetration to demonstrate soft tissue structures, free intraperitoneal air, and air–fluid levels if present
Clinical aim: Demonstrates air–fluid levels and free intraperitoneal air when patient cannot stand or be placed in lateral decubitus position

Clinical Context:  Although rarely performed in modern practice, the dorsal decubitus projection remains part of ARRT-required competencies because it demonstrates a technologist’s ability to adapt positioning for critically ill or immobilized patients. In situations such as trauma, postoperative, or ICU care, this view allows evaluation of air–fluid levels and free air using a horizontal beam when upright or lateral decubitus imaging is not feasible.

Acute Abdominal Series (Three-View Abdomen)

Projections:

  1. AP Supine Abdomen (KUB)

  2. AP Upright Abdomen (or Left Lateral Decubitus if non-ambulatory)

  3. PA Upright Chest

CR Location & Positioning (Summary):
Supine – Perpendicular at iliac crest (include symphysis pubis)
Upright – Horizontal 2″ above iliac crest (include diaphragms)
Chest – Perpendicular at T7 (include apices through costophrenic angles)

Evaluation Criteria:
All three images demonstrate proper inspiration/expiration, no rotation, and complete coverage of abdominal and thoracic structures relevant to the patient’s complaint.

Hows & Whys of Abdominal Radiography

Anatomy

  • How many quadrants divide the abdomen, and why?
    Four quadrants (RUQ, LUQ, RLQ, LLQ) — used for localizing pain and correlating organ position.
  • How are the psoas muscles useful on an abdominal radiograph?
    Their visibility confirms correct exposure and proper soft-tissue contrast.
  • How can you tell the kidneys are correctly visualized?
    Each kidney should appear faintly outlined lateral to the spine at the T12–L3 level.

Positioning

  • Why are some abdominal images performed upright?
    To demonstrate air-fluid levels and free intraperitoneal air.
  • Which side is down for a decubitus abdomen, and why?
    Left side down — so free air rises over the liver margin, not the gastric bubble.
  • Why must the symphysis pubis be included on supine KUB?
    To confirm bladder inclusion and complete urinary tract coverage.
  • Why is the CR placed 2 inches above the iliac crest for upright and decubitus views?
    To ensure diaphragms are included for detection of free air.
  • Why perform all abdominal projections on expiration?
    Expiration elevates the diaphragm, spreading abdominal organs for better visualization.

Technique & Image Evaluation

  • How do you check for rotation on a KUB?
    Symmetric iliac wings and obturator foramina indicate true AP alignment.
  • How do you confirm adequate exposure on an abdomen?
    The outlines of the psoas muscles, kidneys, and lower liver margin should be visible without overexposure.
  • How do you evaluate motion?
    Bowel gas margins and diaphragm edges should appear sharp.
  • How do you adjust technique for obese or fluid-filled abdomens?
    Increase kVp or mAs moderately to penetrate denser tissue.
  • How do you adjust technique for bowel obstruction or ileus?
    Decrease mAs or kVp slightly to improve contrast between air and tissue.

Clinical Applications

  • Why is the upright abdomen essential in an acute abdominal series?
    It shows free air and fluid levels not visible on supine images.
  • Why include a chest radiograph in the acute series?
    To detect free air beneath the diaphragm and rule out thoracic causes of abdominal pain.
  • Why use the left lateral decubitus when upright imaging is not possible?
    It keeps free air adjacent to the liver, away from the gastric bubble.
  • Why might a dorsal decubitus projection be requested?
    To assess aneurysms, hernias, or air-fluid levels when the patient cannot be turned.
  • Why is precise centering critical in abdominal radiography?
    Improper centering may exclude key anatomy such as the symphysis pubis or diaphragms, requiring repeats and added dose.

 

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Clinical Preceptor Reference Guide for Student Competencies Copyright © 2025 by Carla M. Allen is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.

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