Emergency imaging protocols

Foundations - Imaging Fast & Smart

• First-line FAST scans: Bedside ultrasound (eFAST) for trauma, fluid, or procedural guidance. Portable X-ray for lines, tubes, and initial fracture assessment.
• Contrast Essentials:
  • IV Iodinated: For CT. Risk: Contrast-Induced Nephropathy (CIN). Hold if eGFR < 30.
  • IV Gadolinium: For MRI. Risk: Nephrogenic Systemic Fibrosis (NSF).
• Radiation Hierarchy: CT (high) > X-ray (low) > US/MRI (none).
• 📌 ALARA Principle: As Low As Reasonably Achievable. Justify high-radiation studies.

⭐ For suspected acute appendicitis in children and pregnant women, ultrasound or MRI is preferred over CT to minimize radiation exposure.

Neuro Emergencies - Brain Under Attack

• Initial Protocol: Immediate Non-Contrast CT (NCCT) is the critical first step to differentiate ischemic vs. hemorrhagic stroke. "Time is brain."

• Ischemic Stroke:

  • NCCT is often normal in the first few hours but rules out a bleed before giving tPA. May show a hyperdense MCA sign.
  • MRI with DWI is the most sensitive test for acute infarction.
  • CTA/CTP is used to detect Large Vessel Occlusion (LVO) and assess the ischemic penumbra, guiding thrombectomy.

• Hemorrhagic Stroke:

  • Intracerebral (ICH): NCCT shows a hyperdense collection of blood.
  • Subarachnoid (SAH): NCCT may show blood in sulci/cisterns. If negative but suspicion is high, a lumbar puncture (LP) showing xanthochromia is diagnostic.

⭐ The ASPECTS score (0-10) on initial NCCT helps quantify early ischemic changes in the MCA territory to predict outcomes and guide therapy.

Cardiothoracic Crises - Heart & Lung SOS

• Pulmonary Embolism (PE):

  • CTA chest (PE protocol) is the primary diagnostic test.
  • V/Q scan if contrast is contraindicated (e.g., renal failure, allergy).
  • Bedside echo may show signs of right heart strain (McConnell's sign).

• Aortic Dissection:

  • CTA chest/abdomen/pelvis is the gold standard, identifying the intimal flap.
  • Transesophageal echo (TEE) is excellent for unstable patients.

• Cardiac Tamponade:

  • Diagnosed with echocardiography (part of FAST/RUSH exam).
  • Shows pericardial effusion, diastolic right ventricular collapse.
  • 📌 Beck's Triad: Hypotension, JVD, Muffled Heart Sounds.

• Tension Pneumothorax:

  • Clinical diagnosis! Do not delay treatment for imaging.
  • CXR/eFAST confirms: shows contralateral mediastinal shift.

⭐ High-Yield: Aortic dissection management hinges on location. Stanford Type A (involving ascending aorta) is a surgical emergency, while Type B (descending aorta only) is often managed medically.

Abdominal Catastrophes - Gut Feelings

• AAA Rupture:
  • Unstable: Bedside US (FAST).
  • Stable: CT Angiography (CTA).
• Aortic Dissection:
  • CTA is the gold standard for diagnosis and classification.
• Acute Mesenteric Ischemia:
  • CTA is the primary modality.
  • Look for: arterial filling defects, bowel wall thickening, pneumatosis.
  • 💡 Classic: "Pain out of proportion to exam."
• Bowel Obstruction:
  • Initial: X-ray (dilated loops, air-fluid levels).
  • Definitive: CT A/P with contrast.
• Visceral Perforation:
  • Initial: Upright Chest X-ray (pneumoperitoneum).
  • Most sensitive: CT scan for free air and source.

⭐ In suspected bowel perforation, an upright CXR is the fastest screen for pneumoperitoneum, but an abdominal CT is the most sensitive test and can locate the source.

High-Yield Points - ⚡ Biggest Takeaways

• Non-contrast CT is the first-line for suspected acute stroke to exclude hemorrhage before tPA.
• CT angiography (CTA) is the gold standard for diagnosing pulmonary embolism and aortic dissection.
• The FAST exam (ultrasound) is the initial imaging modality in blunt abdominal trauma to detect free fluid.
• Upright chest/abdominal X-ray is critical for suspected bowel perforation (free air) or obstruction.
• Doppler ultrasound is essential for ruling out testicular or ovarian torsion.
• CT with IV contrast is the preferred study for suspected appendicitis in non-pregnant adults.