How do I read an ultrasound (USG) image?

Guide to Reading Ultrasound (USG) Images

Fundamental Image Interpretation Principles

Start by understanding that ultrasound is a tomographic imaging modality where the appearance of structures changes based on transducer orientation and position, making standardized image acquisition and systematic interpretation essential. 1

Equipment Selection and Technical Setup

• Use high-frequency transducers (≥10 MHz) for superficial structures including tendons, ligaments, small joints, and synovial tissues to achieve optimal resolution 2
• 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 2
• Ensure the transducer footprint size matches your target—large footprints cannot adequately visualize small joints like metacarpophalangeal joints due to limited maneuverability 2

Standardized Image Orientation (Critical for Reproducibility)

Follow consistent transducer orientation to ensure you can interpret images correctly: 2

• Longitudinal scans: Proximal/cranial/upper structures appear on the LEFT side of the screen; distal/caudal/lower structures on the RIGHT side 2
• Transverse scans: Medial/ulnar/tibial structures appear on the LEFT side; lateral/radial/fibular structures on the RIGHT side 2

Systematic Approach to Image Reading

Always begin with conventional B-mode and Doppler techniques before switching to specialized imaging modes. 1

1. Identify the anatomical region and structures being examined—understand what tissue or organ you're looking at (synovium, bone, tendon, muscle, etc.) 1
2. Assess in two perpendicular planes for all pathological findings to confirm their presence and characteristics 2
3. Recognize the broad domain you're evaluating (inflammation vs. structural damage) and the specific target domain (synovitis, enthesitis, erosion) 1
4. Evaluate the operational definitions of what you're seeing—for example, synovial hypertrophy appears as hypoechoic thickening of the synovium, while synovial hyperaemia shows as increased Doppler signal within that hypertrophy 1

Understanding Image Quality Components

Image quality depends on multiple technical factors that you must recognize: 3

• Lateral and longitudinal resolution: How well you can distinguish adjacent structures 3
• Image uniformity: Consistent appearance across the field of view 3
• Sensitivity: Ability to detect subtle abnormalities 3
• Depth of penetration: How deep you can visualize structures clearly 4

Critical Pitfalls to Avoid

Never apply excessive transducer pressure—this eliminates synovial hypertrophy, compresses vessels, and removes Doppler signal, leading to false-negative findings 2

Avoid "seeing what you expect to see" based solely on clinical examination—maintain objectivity and consider obtaining a second opinion from an experienced sonographer when uncertain 2

Recognize that ultrasound operates on assumptions that can break down: 5

• The beam is assumed to be very narrow but actually has finite dimensions
• Energy is assumed to propagate in straight lines, but velocity variations in different tissues cause beam deviation
• These breakdowns create artifacts that must be appreciated during interpretation 5

Three Golden Rules for Image Interpretation

Follow these fundamental principles when reading any ultrasound: 5

1. Never make an interpretation on a single image—always obtain multiple views and planes 5
2. Just because a feature is displayed, do not assume it is necessarily real—consider artifacts and technical factors 5
3. Just because a feature is not displayed, do not assume it is necessarily absent—understand the limitations of sensitivity 5

Understanding Ultrasound Modalities

Recognize which ultrasound technique is being used, as each provides different information: 1

• Grey scale (B-mode): Basic anatomical imaging
• Doppler (color, power, pulse): Blood flow assessment
• Elastography: Tissue stiffness evaluation
• Contrast-enhanced ultrasound: Microvascular perfusion studies 1

Dynamic Examination Considerations

Understand that dynamic examinations involve moving the transducer along the anatomical region or moving the anatomical region itself (through muscle contraction or tendon movement), which provides additional diagnostic information not available in static images 1

Image Documentation Standards

Proper documentation requires: 2

• Standardized images that allow readers to easily recognize anatomical structures and target pathology 1
• Clear legends and points of reference on all images 1
• Removal of all patient information from images 1
• Use of drawings to facilitate interpretation for readers not experienced in ultrasound 1

Training and Competency Requirements

Recognize that ultrasound is highly operator-dependent, requiring: 2

• Detailed anatomical knowledge of all structures being examined 2
• Understanding of basic ultrasound physics and sound wave principles 2
• Proper training under experienced investigators rather than self-directed learning 2
• Continuous education due to the evolving nature of the technology 2

Context-Specific Applications

For emergency/trauma settings: 1

• Ultrasound serves resuscitative, diagnostic, symptom-based, procedure guidance, and therapeutic/monitoring purposes 1
• The FAST examination has specific sensitivity (79-87%) for detecting free intraperitoneal fluid but cannot identify the source of bleeding or specific organ injury 6
• Hemodynamically unstable patients with free fluid require immediate surgical intervention regardless of ultrasound findings 6, 7

For contrast-enhanced studies: 1

• The arterial phase occurs within 10-20 seconds and ends within 25-35 seconds after injection 1
• The portal venous phase begins within 30-45 seconds and finishes within 120 seconds 1
• The late phase (after 120 seconds) is most important for differentiating benign from malignant lesions—malignancy manifests as hypovascularity in this phase 1