What is a guide to reading Ultrasound (USG) images?

A Guide to Reading Ultrasound (USG) Images

Ultrasound is the most operator-dependent imaging modality, requiring systematic training under experienced supervision, detailed anatomical knowledge, and standardized scanning protocols to avoid misinterpretation that can lead to patient harm. 1

Fundamental Principles for Image Interpretation

Understanding Equipment and Image Quality

• Use high-frequency transducers (≥10 MHz) for superficial structures including tendons, ligaments, small joints, and synovial tissues to achieve optimal resolution 2
• Lower frequency transducers (3.5-5 MHz) are appropriate for deeper structures like the shoulder or hip, recognizing the trade-off between resolution and penetration depth 1
• Test your equipment's capability before clinical use by visualizing fine structures such as small extensor tendon insertions or tiny amounts of fluid in the pre-Achilles bursa 2
• Select transducers with appropriate footprint size; large footprints cannot adequately visualize small joints like metacarpophalangeal joints due to limited maneuverability 2

Standardized Image Orientation

Follow consistent transducer orientation to ensure reproducibility: 1

• Longitudinal scans: Left side of screen shows proximal/cranial/upper structures; right side shows distal/caudal/lower structures
• Transverse scans: Left side shows medial/ulnar/tibial structures; right side shows lateral/radial/fibular structures

Critical Scanning Technique

• Document all pathological findings in two perpendicular planes to ensure complete characterization 2
• Avoid excessive transducer pressure, which can compress synovial tissue, eliminate Doppler signal, or distort anatomy 2
• Integrate ultrasound findings with clinical history and physical examination rather than interpreting images in isolation 1

Clinical Application Categories

Emergency and Critical Care Settings

Ultrasound in acute settings serves five functional categories: 1

1. Resuscitative: Direct use during acute resuscitation
2. Diagnostic: Emergent diagnostic imaging capacity
3. Symptom-based: Clinical pathways based on patient presentation (e.g., shortness of breath)
4. Procedure guidance: Aid for invasive procedures
5. Therapeutic/Monitoring: Therapeutics or physiological monitoring

Core Emergency Applications

The following represent essential bedside skills with strong evidence bases: 1

• Trauma assessment (FAST examination)
• Intrauterine pregnancy evaluation
• Abdominal aortic aneurysm detection
• Cardiac assessment
• Biliary system evaluation
• Urinary tract examination
• Deep venous thrombosis screening
• Soft-tissue/musculoskeletal assessment
• Thoracic evaluation
• Ocular examination
• Procedural guidance

Intensive Care Basic Skills

For vascular access, the European Society of Intensive Care Medicine strongly recommends: 1

• Anatomical evaluation under ultrasound guidance for arterial cannulation when pulse is not palpable or after multiple failed attempts
• Continuous visualization of the needle tip during trajectory using both in-plane and out-of-plane techniques to avoid posterior wall penetration
• Scanning vessels to detect size, position, patency via compression ultrasonography, and assess surrounding vital structures
• Post-procedural verification of tip position and exclusion of immediate life-threatening complications

For DVT detection: 1

• Apply compression technique from common femoral vein at the groin to popliteal vein at the popliteal fossa
• This provides rapid, accurate diagnosis of proximal lower extremity DVT at the bedside

Training Requirements and Competency

Essential Knowledge Base

Operators must possess: 1, 2

• Detailed anatomical knowledge of all structures being examined
• Understanding of basic ultrasound physics and sound wave principles
• Recognition that musculoskeletal ultrasound cannot be learned at conferences over a few days

Structured Training Pathway

• Seek proper training under guidance of experienced investigators rather than attempting self-directed learning 2
• Utilize national and international society training guidelines (e.g., EULAR for musculoskeletal ultrasound) 2
• Engage in continuous training and education due to the operator-dependent nature of ultrasound 2
• Obtain hands-on experience through local expertise when available 1

Common Pitfalls and How to Avoid Them

Technical Errors

• Never apply excessive transducer pressure as this eliminates synovial hypertrophy, compresses vessels, or removes Doppler signal 2
• Avoid flexing the elbow beyond 90° during examination to prevent ulnar nerve compression 2
• Do not apply pressure on the postcondylar groove (ulnar groove) during elbow assessment 2

Interpretation Errors

• Recognize that operator inexperience leads to incorrect image acquisition and interpretation, potentially causing patient harm through misdiagnosis 2
• Avoid "seeing what you expect to see" from clinical examination alone; consider obtaining a second opinion from an experienced sonographer for scientific analysis 1
• Never make management decisions based on a single ultrasound or single measurement in hemodynamically stable patients 3

Clinical Context Errors

• In pregnancy with vaginal bleeding, always perform ultrasound before digital pelvic examination to avoid catastrophic hemorrhage from placenta previa or vasa previa 4
• Remember that ultrasound misses up to 50% of placental abruptions, requiring clinical correlation 4
• In pregnancy of unknown location, recognize that 7-20% will be ectopic pregnancies requiring close follow-up 4

Documentation Standards

Image Recording

Document every examination carefully using: 1

• Paper, films, video cassettes, laser-printed acetates, optical discs, or digital storage systems
• Standardized format to ensure reproducibility
• Two perpendicular planes for all pathological findings

Reporting Requirements

For research or quality assurance purposes, the EULAR recommendations specify: 1

• Ultrasound modalities and settings used (grey scale, Doppler, other)
• Brand and model of ultrasound device and transducer type
• Whether acquisition and reading were performed simultaneously or separately
• Number of sonographers/readers and their experience level
• Transducer position (transverse, longitudinal) and whether examination was dynamic