Ultrasonography – BCSE Study Guide

Overview and Clinical Importance

Ultrasonography is one of the most valuable non-invasive diagnostic imaging modalities in veterinary medicine. It uses high-frequency sound waves to create real-time images of internal structures, making it indispensable for evaluating abdominal organs, cardiac function, and reproductive status. Unlike radiography, ultrasound provides dynamic imaging without ionizing radiation, making it safe for repeated examinations and use during pregnancy.

The BCSE examination tests candidates on ultrasound physics (understanding how images are formed), artifact recognition (distinguishing real findings from imaging artifacts), and clinical applications across multiple organ systems. Mastery of ultrasonography fundamentals is essential for accurate diagnosis and patient management.

Section 1: Ultrasound Physics and Instrumentation

Basic Physics Principles

Ultrasound imaging uses mechanical sound waves at frequencies above the human audible range (greater than 20 kHz). Medical diagnostic ultrasound typically operates between 2-18 MHz. The transducer contains piezoelectric crystals that convert electrical energy to mechanical energy (sound waves) and vice versa.

Key Physics Concepts

[Include Image: Figure 1. Diagram showing ultrasound wave properties including frequency, wavelength, and amplitude]

Transducer Types and Selection

Transducer selection is critical for optimal image quality. The choice depends on patient size, depth of structures to be examined, and required field of view.

Image Display Modes

Section 2: Ultrasound Artifacts

Artifacts are features in ultrasound images that do not accurately represent the examined structures. They occur because the ultrasound machine makes certain assumptions about sound wave behavior. Understanding artifacts is essential for accurate image interpretation and to avoid misdiagnosis. Artifacts can be classified as either useful (providing diagnostic information) or non-useful (interfering with interpretation).

Useful Artifacts

Acoustic Shadowing

Acoustic shadowing occurs when sound waves are blocked or strongly attenuated by dense structures, creating a dark (anechoic) region distal to the structure. This is caused by highly reflective or absorptive materials such as bone, calculi (stones), gas, or mineral deposits.

[Include Image: Figure 2. Ultrasound image showing acoustic shadowing posterior to a gallstone]

Acoustic Enhancement (Posterior Enhancement)

Acoustic enhancement (also called through transmission or distal acoustic enhancement) occurs when sound waves pass through a fluid-filled structure with low attenuation. The tissue deep to the fluid appears brighter than adjacent tissue at the same depth because more sound energy reaches and returns from that region.

Clinical Significance: Acoustic enhancement helps confirm the fluid nature of a structure. A cyst will show posterior enhancement, while a solid mass typically will not. This artifact is useful for differentiating cystic from solid lesions.

Common Examples: Urinary bladder (tissues deep to bladder appear brighter), gallbladder, cysts, abscesses, ascites.

[Include Image: Figure 3. Ultrasound image demonstrating acoustic enhancement deep to the urinary bladder]

Non-Useful (Misleading) Artifacts

Reverberation Artifacts

Reverberation occurs when sound waves bounce back and forth between two highly reflective parallel surfaces (such as between the transducer face and a strong reflector). This creates multiple equally-spaced parallel lines that appear progressively deeper in the image with decreasing amplitude.

Comet Tail Artifact: A special form of reverberation occurring between two closely spaced reflectors. Appears as a bright tapering line extending from the structure. Commonly seen with gas bubbles, metallic foreign bodies, and crystalline structures.

Mirror Image Artifact

Mirror image artifact occurs when sound reflects off a highly reflective curved surface (like the diaphragm), creating a duplicate image of a structure on the opposite side of the reflector. The duplicated image appears equidistant from the reflector as the real structure but on the wrong side.

Clinical Significance: The liver may appear to be duplicated across the diaphragm, mimicking a mass in the thorax. Recognize this by noting the identical echogenicity and pattern of the duplicated structure.

Edge Shadowing (Refraction Artifact)

Edge shadowing occurs at the curved edges of round structures where sound waves are refracted away from the transducer, creating narrow shadow areas at the margins. This is commonly seen at the edges of the gallbladder, urinary bladder, or rounded organs.

Side Lobe Artifact

Side lobes are weaker sound beams emitted at angles to the main beam. Echoes from side lobes are incorrectly displayed as if coming from the main beam, potentially creating false echoes within anechoic structures (like pseudosludge in the bladder or gallbladder).

Artifact Recognition Summary Table

Section 3: Abdominal Ultrasound

Patient Preparation and Technique

Proper patient preparation optimizes image quality. Clip hair over the abdomen (ventral abdomen from xiphoid to pubis and laterally to the flanks). Apply coupling gel liberally to eliminate air between the transducer and skin. Position the patient in dorsal or lateral recumbency depending on the organ being examined.

Fasting: Fasting for 12 hours is ideal to reduce gastric gas and allow gallbladder distension. However, do not delay emergency examinations for fasting.

Bladder: A moderately distended urinary bladder serves as an acoustic window for evaluating pelvic structures and improves visualization of the sublumbar region.

Systematic Approach to Abdominal Scanning

A consistent systematic approach ensures complete evaluation and prevents missed abnormalities. The examination should include all major abdominal organs regardless of the suspected disease.

Normal Organ Echogenicity

Understanding relative organ echogenicity is fundamental for identifying pathology. The BCSE frequently tests knowledge of normal echogenicity relationships.

[Include Image: Figure 4. Ultrasound image showing normal relative echogenicity of liver and spleen in a dog]

Key Abdominal Ultrasound Findings

Liver Findings

Urinary Bladder Findings

FAST (Focused Assessment with Sonography for Trauma)

AFAST (Abdominal FAST) is a rapid point-of-care ultrasound technique used in emergency settings to detect free abdominal fluid. The examination evaluates four standardized sites and assigns an Abdominal Fluid Score (AFS) from 0 to 4 based on the number of positive sites.

Section 4: Echocardiography Basics

Introduction to Cardiac Ultrasound

Echocardiography is the gold standard non-invasive method for evaluating cardiac structure and function. It allows real-time assessment of chamber size, wall thickness, valve function, and blood flow. The technique requires specialized training and uses phased-array transducers with small footprints to fit between the ribs.

Patient Positioning and Acoustic Windows

Dogs and cats are typically positioned in lateral recumbency on a specialized table with a cutout allowing transducer access from below. The right parasternal window (between ribs 3-6) provides long-axis and short-axis views. The left apical window allows evaluation of all four chambers and Doppler assessment of valvular flow.

Standard Echocardiographic Views

[Include Image: Figure 5. Diagram showing standard echocardiographic imaging planes in a dog]

Key Echocardiographic Measurements

Common Cardiac Abnormalities

Section 5: Reproductive Ultrasound

Introduction

Reproductive ultrasound is essential for pregnancy diagnosis, fetal viability assessment, gestational aging, and evaluation of reproductive pathology. The technique and timing of examination vary considerably among species.

Canine and Feline Pregnancy

In dogs and cats, pregnancy can be detected as early as 20-25 days post-breeding (gestational sacs visible), with fetal heartbeats detectable by 22-25 days and embryonic structures by 28-35 days. Ultrasound is the preferred method for early pregnancy diagnosis and fetal viability assessment.

Gestational Aging Formulas

Several measurements can estimate gestational age and predict parturition date. These formulas have varying accuracy depending on stage of pregnancy and breed.

• Gestational Sac Diameter (GSD): Useful early (days 20-35)
• Crown-Rump Length (CRL): Useful mid-pregnancy
• Biparietal Diameter (BPD): Head width; useful later in pregnancy
• Body Diameter (BD): Trunk measurement at stomach level

[Include Image: Figure 6. Ultrasound image of a canine gestational sac at approximately 25 days showing early embryo with heartbeat]

Equine Reproductive Ultrasound

Transrectal ultrasonography revolutionized equine reproductive management. It allows detailed evaluation of ovarian follicles, corpus luteum, and early pregnancy detection. A linear rectal probe (5-10 MHz) is standard.

Bovine Reproductive Ultrasound

Transrectal ultrasound is the standard for bovine pregnancy diagnosis, allowing earlier detection than manual palpation. Pregnancy can be detected as early as day 26-28 post-breeding, though day 30-35 is more practical for routine diagnosis.

Reproductive Pathology

[Include Image: Figure 7. Ultrasound image of canine pyometra showing fluid-filled uterine horns]

Ultrasound Physics

• Higher frequency = better resolution but shallower penetration; Lower frequency = deeper penetration but lower resolution
• Reflection occurs at interfaces between tissues with different acoustic impedances
• Select transducer based on application: phased array for cardiac, curvilinear for general abdomen, linear for superficial structures

Critical Artifacts

• Useful artifacts: Acoustic shadowing (confirms stones/calcifications) and acoustic enhancement (confirms fluid)
• Misleading artifacts: Reverberation, mirror image, side lobe artifacts - recognize to avoid misdiagnosis
• Dirty shadow (gas) vs clean shadow (mineral/bone) - important differentiation

Abdominal Ultrasound

• Normal echogenicity in dogs: Spleen > Liver > Renal cortex (SLiCK)
• Cats differ: renal cortex may be iso- to hyperechoic compared to liver
• AFAST uses 4 views (DH, HR, SR, CC) to detect free abdominal fluid in emergency patients

Echocardiography

• Key measurements: FS% (25-45% normal), LA:Ao ratio (< 1.6 normal), EPSS
• MMVD: thickened valve, prolapse, MR jet, LA enlargement - most common acquired heart disease in dogs
• DCM: dilated chambers, decreased FS, thin walls. HCM (cats): thickened walls

Reproductive Ultrasound

• Canine pregnancy: detectable ~20-25 days; heartbeat by 22-28 days; optimal counting at days 28-35
• Equine: earliest detection day 10-11; check for twins day 14-16 before fixation
• Bovine: transrectal US day 28-30+; transcutaneous after day 90
• Fetal viability: monitor heartbeat (normal >180-200 bpm); decreased rate suggests distress