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Background
Ultrasound (US) is the most common imaging modality used to guide abdominopelvic biopsies, in part due to its ability to obtain real-time imaging, flexibility in biopsy approach, and lack of ionizing radiation. However, isoechoic soft tissue lesions can be difficult to differentiate from normal parenchyma and the inability to discriminate target from background is one of the main reasons for a failed US procedure. Although use outside of the liver is off label, contrast enhanced ultrasound (CEUS) is being studied and utilized in the depiction and characterization of a wide range of pathology in the chest, abdomen, and pelvis, and can be a valuable tool when performed in adjunct with US guided interventions. The purpose of this exhibit is to familiarize imagers with CEUS biopsy technique and advantages of CEUS in the planning and execution of image-guided biopsies.

Educational Goals / Teaching Points
Gain confidence in CEUS technique to enable integration into typical procedural workflow. Appreciate the ability of CEUS to augment lesion detection, aid in target selection, and optimize sample quality. Recognize CEUS imaging characteristics that denote benignity and may make intervention unnecessary.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
US contrast is a purely intravascular agent composed of microbubbles of inert gas surrounded by a biomaterial shell. The main advantages of CEUS include its strong safety profile, including lack of nephrotoxicity, ability to administer multiple doses over the course of an examination, and multiplanar flexibility in approaching a lesion with the same transducer and apparatus used during a procedure. Limitations, shared by CEUS and noncontrast US, include difficulty in assessing lesions in patients with large body habitus, through poor acoustic windows, or more than 10cm deep from the transducer. Additional limitations, specific to CEUS, include the need for IV access, addition of personnel, and CEUS specific software; however, some of these requirements may already be met within the typical procedural workflow. CEUS can demonstrate differential perfusion in a target lesion relative to background, increasing conspicuity. If several lesions are present, CEUS may demonstrate differences in accessibility, enhancement, or composition that make a particular target lesion preferential to another. Within a lesion, CEUS can discriminate vascularized tissue from nonenhancing necrotic debris or cystic change. By preferentially targeting enhancing tissue, CEUS guided biopsy can improve diagnostic accuracy and reduce number of puncture attempts compared to using grayscale US alone. Finally, CEUS can prevent unnecessary biopsy in instances where interrogation reveals findings consistent with a benign diagnosis.

Conclusion
When utilized in the appropriate clinical context, CEUS can be a safe and efficient way to add value to percutaneous US guided biopsy by improving lesion detection, increasing diagnostic yield, and preventing unnecessary biopsies.