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Fundamentals and Technology
Fundamentals and Technology
• Definition and Prevalence:
• Definition and Prevalence:
◦ The second most commonly used imaging modality in veterinary practice.
◦ The second most commonly used imaging modality in veterinary practice.
◦ Uses sound waves in the frequency range of 1.5–18 megahertz (MHz).
◦ Uses sound waves in the frequency range of 1.5–18 megahertz (MHz).
• Image Formation Mechanism:
• Image Formation Mechanism:
◦ A transducer makes contact with the patient via transmission gel to send ultrashort sound pulses.
◦ A transducer makes contact with the patient via transmission gel to send ultrashort sound pulses.
◦ Echoes are created as sound changes velocity when passing between tissues of different densities.
◦ Echoes are created as sound changes velocity when passing between tissues of different densities.
◦ The computer records the strength, time, and direction of returning echoes to create a cross-sectional image.
◦ The computer records the strength, time, and direction of returning echoes to create a cross-sectional image.
• Imaging Standards:
• Imaging Standards:
◦ Modern systems produce dynamic, real-time images.
◦ Modern systems produce dynamic, real-time images.
◦ The legal format for digital ultrasound images is the DICOM standard.
◦ The legal format for digital ultrasound images is the DICOM standard.
Image Formats
Image Formats
• B-mode (Brightness Mode):
• B-mode (Brightness Mode):
◦ The standard grayscale scanning used to create anatomical images.
◦ The standard grayscale scanning used to create anatomical images.
• M-mode (Motion Mode):
• M-mode (Motion Mode):
◦ Displays echo pattern and strength over time (x-axis is time; y-axis is depth).
◦ Displays echo pattern and strength over time (x-axis is time; y-axis is depth).
◦ Offers high temporal resolution, making it ideal for evaluating rapidly moving structures like heart valves.
◦ Offers high temporal resolution, making it ideal for evaluating rapidly moving structures like heart valves.
• Doppler Ultrasonography:
• Doppler Ultrasonography:
◦ Uses frequency shifts from moving RBCs to determine blood flow velocity and direction.
◦ Uses frequency shifts from moving RBCs to determine blood flow velocity and direction.
◦ Spectral Doppler: Evaluates a specific small volume; features high temporal resolution.
◦ Spectral Doppler: Evaluates a specific small volume; features high temporal resolution.
◦ Color Doppler: Depicts flow direction via color (conventionally Red = away; Blue = toward) and speed via color shade; features lower temporal resolution than spectral Doppler.
◦ Color Doppler: Depicts flow direction via color (conventionally Red = away; Blue = toward) and speed via color shade; features lower temporal resolution than spectral Doppler.
Clinical Applications
Clinical Applications
• Diagnostic Use:
• Diagnostic Use:
◦ Evaluation of soft tissue structures in the abdomen, musculoskeletal system, and thorax.
◦ Evaluation of soft tissue structures in the abdomen, musculoskeletal system, and thorax.
◦ Echocardiography: Quantitative evaluation of cardiac function (output, contractility, ejection fraction, and wall stiffness).
◦ Echocardiography: Quantitative evaluation of cardiac function (output, contractility, ejection fraction, and wall stiffness).
◦ Pancreatic Disease: A mainstay for assessment, though it may not always agree with clinicopathological findings.
◦ Pancreatic Disease: A mainstay for assessment, though it may not always agree with clinicopathological findings.
• Species-Specific Applications:
• Species-Specific Applications:
◦ Large Animals/Equids: Detecting tendon and ligament tears in legs; transrectal assessment of the reproductive system.
◦ Large Animals/Equids: Detecting tendon and ligament tears in legs; transrectal assessment of the reproductive system.
◦ Small Animals: Evaluating ligaments, tendons, joint capsules, and articular cartilage (specifically in the shoulder and stifle).
◦ Small Animals: Evaluating ligaments, tendons, joint capsules, and articular cartilage (specifically in the shoulder and stifle).
• Interventional Procedures:
• Interventional Procedures:
◦ Directs biopsy and aspiration instruments to specific lesions, which is safer and more diagnostic than "blind" biopsies.
◦ Directs biopsy and aspiration instruments to specific lesions, which is safer and more diagnostic than "blind" biopsies.
◦ Can often be performed under heavy sedation and analgesia rather than general anesthesia.
◦ Can often be performed under heavy sedation and analgesia rather than general anesthesia.
Interpretation Principles
Interpretation Principles
• Comparative Analysis: Evaluation is based on comparing the echo pattern (echogenicity) of organs and tissues against known normals.
• Comparative Analysis: Evaluation is based on comparing the echo pattern (echogenicity) of organs and tissues against known normals.
• Lesion Detection: Diseased organs may show uniform, focal, or multifocal changes.
• Lesion Detection: Diseased organs may show uniform, focal, or multifocal changes.
• Specificity Challenges: While sensitive for detecting disease, findings are often nonspecific for a single disease unless characteristic anatomical changes are present.
• Specificity Challenges: While sensitive for detecting disease, findings are often nonspecific for a single disease unless characteristic anatomical changes are present.
• Experience: The examiner must be familiar with normal anatomy and how pathological changes manifest on specific transducers.
• Experience: The examiner must be familiar with normal anatomy and how pathological changes manifest on specific transducers.
🛠️Limitations and Technical Challenges
🛠️Limitations and Technical Challenges
• Physical Barriers:
• Physical Barriers:
◦ Sound is totally reflected by gas and absorbed by bone, which "shadows" organs behind them.
◦ Sound is totally reflected by gas and absorbed by bone, which "shadows" organs behind them.
◦ Heart imaging must avoid the lungs (gas), and bowel gas can inhibit abdominal imaging.
◦ Heart imaging must avoid the lungs (gas), and bowel gas can inhibit abdominal imaging.
• Depth and Resolution:
• Depth and Resolution:
◦ Maximum scanning depth is approximately 30 cm.
◦ Maximum scanning depth is approximately 30 cm.
◦ Deep images are often "noisy" due to loss of beam intensity and background electronic noise.
◦ Deep images are often "noisy" due to loss of beam intensity and background electronic noise.
◦ Trade-off: Low-frequency transducers scan deeper but have decreased resolution.
◦ Trade-off: Low-frequency transducers scan deeper but have decreased resolution.
• Diagnostic Ambiguity:
• Diagnostic Ambiguity:
◦ In hyperadrenocorticism, adrenal glands may appear structurally normal if the issue is a pituitary adenoma, or benign adenomas may be present that have no clinical importance.
◦ In hyperadrenocorticism, adrenal glands may appear structurally normal if the issue is a pituitary adenoma, or benign adenomas may be present that have no clinical importance.
Advanced Modalities
Advanced Modalities
• Contrast Ultrasonography:
• Contrast Ultrasonography:
◦ Involves injecting microscopic bubbles into plasma to increase the reflectivity of blood and vascularized tissue.
◦ Involves injecting microscopic bubbles into plasma to increase the reflectivity of blood and vascularized tissue.
◦ Provides additional information about a lesion's vascularity.
◦ Provides additional information about a lesion's vascularity.
◦ Limited use due to high cost, typically reserved for special instances or funded research.
◦ Limited use due to high cost, typically reserved for special instances or funded research.
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