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E1766. Contrast Enhanced Ultrasound Guidance for Image-Guided Biopsy or Ablative Therapy
Authors
  1. Kimberly Coffman; Texas A&M University College of Medicine
  2. Mark Sultenfuss; Houston Methodist Hospital; Texas A&M University College of Medicine
  3. Nakul Gupta; Houston Methodist Hospital; Texas A&M University College of Medicine
  4. Nam Yu; Houston Methodist Hospital
Background
Contrast-enhanced ultrasound (CEUS) is an added tool in imaging to identify/characterize lesions in solid organs which are not readily visible on standard ultrasound imaging. Its utility in image-guided procedures is related to its ability to be performed multiple times during the procedure, as opposed to CT or MR contrast. Additionally, performing procedures under ultrasound allows better utilization of imaging resources, as CT-scanner time for procedures is oftentimes limited.

Educational Goals / Teaching Points
1. Review differences between first and second generation ultrasound contrast enhancement agents. 2. Describe the techniques of administering contrast agents for ultrasound, including agent preparation, administration, and image acquisition. 3. Discuss indications and contraindications to the administration of ultrasound contrast agents. 4. Review cases of contrast enhanced ultrasound used in image-guided biopsy and ablation, including examples where CEUS failed to identify the lesion.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Contrast Agents: Each agent has a different shell and gaseous core makeup. First generation agents have an air core, which dissolves when exposed to the US field. Second generation agents have cores made of gases other than air, and their shells are composed of phospholipids or proteins. Agent Preparation: All commercial agents must be agitated to create a homogeneous suspension of the microbubbles in solution. Administration: A dose of between 1mL and 5 mL is used prior to imaging, although detailed dosing guidelines will be discussed for each agent. A 5-10 mL normal saline flush is commonly administered after bolus injection of the UCA. However, infusion (as opposed to bolus) can be used to extend the useful imaging time. Imaging: CEUS requires switching to a low mechanical index (MI) to prevent disruption of the microbubbles, which can cause dangerous ventricular arrythmias. Arterial phase starts approximately 10-20 seconds after UCA injection, and ends at 35 seconds. Portal venous phase begins 30-35 seconds after injection and ends at 2 minutes. The late phase begins 120 seconds post-injection and lasts until the bubbles have dissipated (typically 5-7 minutes later). Examples of timing and lesion diagnosis will be discussed. Indications: 1. Patients unable to undergo contrast CT or MRI due to contrast allergy, etc. 2. Characterize solid organ lesions and further characterize lesions seen on CT/MRI. 3. Lesion visibility for biopsy and assessing tissue viability after ablation. Contraindications: 1. Allergy to contrast material 2. Right-to-left cardiac shunts. 3. Pregnancy is a relative contraindication.

Conclusion
Contrast-enhanced ultrasound is a safe, cost-effective and versatile imaging modality that is important for diagnosis and intervention of solid organ disease. Interventional and Diagnostic Radiologists using CEUS should familiarize themselves with indications/contraindications, administration techniques, and a basic understanding of CEUS characteristics of solid organ lesions in order to properly utilize this too in percutaneous biopsies and ablations.