How do I interpret an ultrasound image?

How to Interpret Ultrasound Images

Ultrasound interpretation requires understanding that it is a tomographic imaging modality where structures change appearance based on transducer orientation and position, making systematic evaluation in multiple planes essential for accurate diagnosis. 1

Fundamental Interpretation Framework

Identify What You're Looking At

• Determine the anatomical region and specific structures being examined (synovium, bone, tendon, muscle, organ) before attempting to identify pathology 1
• Recognize which ultrasound technique is being used, as each provides different information: grey scale (B-mode) for anatomical imaging, Doppler for blood flow, elastography for tissue stiffness, and contrast-enhanced ultrasound for microvascular perfusion 1
• Understand the clinical context: resuscitative, diagnostic, symptom-based, or procedure guidance purposes 1

Apply the Three Golden Rules

Never make an interpretation on a single image alone - ultrasound is dynamic and requires real-time evaluation through all tissue planes 2

Just because a feature is displayed does not mean it is necessarily real - artifacts are common and must be recognized 2

Just because a feature is not displayed does not mean it is necessarily absent - technical factors and operator skill significantly affect what is visualized 2

Systematic Scanning Approach

Two-Plane Confirmation

• Always assess pathological findings in two perpendicular planes to confirm their presence and characteristics 1
• Identification of structures in a single still image or plane will result in early injuries or small volumes of pathology being overlooked 3
• Scan methodically in real-time through all tissue planes rather than relying on static images 3

Equipment Selection Based on Depth

• Use high-frequency transducers (≥10 MHz) for superficial structures including tendons, ligaments, small joints, and synovial tissues to achieve optimal resolution 1
• Switch to lower frequency transducers (3.5-5 MHz) for deeper structures like the shoulder or hip, accepting the trade-off between resolution and penetration depth 1

Technical Optimization

Machine Settings Matter

• Adjust gain settings appropriately for each view - posterior acoustic enhancement from fluid-filled structures (like the bladder) can cause pathology to be overlooked if gain is not decreased 3
• Optimize frequency, depth, focus, and gain settings for the specific structures being examined, particularly for superficial structures like the pleura 3
• Minimize rib shadowing by adjusting transducer position when scanning intercostal spaces 3

Dynamic Real-Time Evaluation

• Ultrasound appearance varies with probe position, orientation, and contact force - static images alone are insufficient 4
• Anatomical structures are most distinctively characterized by the variation of their appearance as the transducer moves, not by their appearance in a single image 5
• Rock, tilt, and rotate the transducer to allow real-time imaging of underlying potential spaces 3

Common Pitfalls to Avoid

False Positives

• Pericardial fat pads, pericardial cysts, and the descending aorta can be mistaken for free fluid 3
• Echogenic clot may be isoechoic to unclotted blood, so failure to see echogenic material does not exclude thrombosis 3

False Negatives

• Patients with peritoneal or pleural adhesions may not develop free fluid in normal locations despite significant hemorrhage 3
• Small volumes of pathology require Trendelenburg or sitting positions to increase sensitivity in specific regions 3
• Serial examinations may be necessary to detect previously undetectable volumes of fluid as they accumulate 3

Documentation Requirements

Interpretations must be documented in real-time as they guide contemporaneous clinical decisions 3

Documentation should include:

• Indication for the procedure 3
• Views obtained and structures studied 3
• Interpretation of findings 3
• Limitations of the exam and impediments to performing a complete examination 3
• Representative images stored as part of the medical record when feasible, though timely care should not be delayed by image archiving 3