Diagnostic Imaging - Ultrasonography

How does an ultrasound machine create an image?

It sends high-frequency sound waves into the body and interprets the echoes that bounce back from internal structures.

What part of the ultrasound machine generates and receives sound waves?

The transducer — it emits high-frequency waves and also acts as a receiver to detect returning echoes.

How does the machine determine the position and brightness of a structure?

It measures the time delay for echoes to return and their strength, displaying this information as brightness on the image

What type of wave is sound in ultrasound?

A mechanical pressure wave that travels through a medium by alternating compression and rarefaction; it cannot travel through vacuum.

What is the frequency range for medical diagnostic ultrasound?

Typically 2–20 megahertz (MHz).

What is the relationship between frequency and wavelength?

They are inversely proportional — higher frequency = shorter wavelength = better resolution but less penetration depth.

What does amplitude represent in ultrasound?

The strength or intensity of the sound wave — proportional to image brightness

What is the approximate speed of sound in different materials?

Air: 330 m/s, Water: 1480 m/s, Tissue: 1540 m/s, Bone: 4080 m/s.

What is acoustic impedance (Z)?

The resistance a material offers to sound wave transmission, calculated as Z = density × speed of sound.

What happens when there is a mismatch in acoustic impedance between tissues?

It causes reflection, which appears as brightness on the image.

What are the four main interactions of ultrasound with tissues?

Absorption, Reflection, Scattering, and Refraction.

What is absorption in ultrasound?

The conversion of sound energy into heat, causing signal loss behind dense or reflective objects (e.g., bone → acoustic shadowing).

What is reflection and why is it important?

Reflection occurs at tissue boundaries with different impedance and forms the basis of image creation.

What factors affect reflection strength?

Differences in acoustic impedance, surface smoothness, size, and angle of the structure.

What is refraction in ultrasound?

A change in direction of the sound beam when it crosses tissues with different sound speeds — can cause misplaced anatomy.

What is scattering?

The redirection of sound waves in multiple directions when they hit small or irregular structures.

What causes ultrasound attenuation?

Absorption (the most), reflection, scattering, and refraction — all reduce the beam’s intensity as it travels through tissue.

How is depth of a structure calculated in ultrasound?

Using the formula D = (c × t) / 2, where c = speed of sound and t = round-trip travel time.

What are the key physical principles of ultrasound imaging?

Sound = mechanical energy transmitted as waves; echoes are reflected, scattered, refracted, or absorbed; depth depends on v × t / 2.

How is ultrasound used for pregnancy monitoring in humans?

To monitor fetal development, confirm viability, determine gestational age, and detect complications or abnormalities.

How is ultrasound used for pregnancy monitoring in animals?

To confirm and monitor pregnancies in species like horses and cattle.

How is ultrasound used in cardiac health for animals?

Echocardiography diagnoses congenital and acquired heart diseases such as valve disorders and cardiomyopathy.

How is ultrasound used for abdominal organs in animals?

To identify diseases like liver disease, kidney stones, and tumors.

How is ultrasound used for musculoskeletal issues in animals?

To diagnose tendon or ligament injuries, especially in athletic animals like racehorses and dogs

How is ultrasound used in emergency medicine for animals?

The FAST exam detects internal bleeding or chest/abdominal issues.

How is ultrasound used for interventional guidance in animals?

Assists in guided biopsies or injections, reducing the need for exploratory surgery.

Why can ultrasound not image structures behind bone?

Ultrasound waves cannot penetrate bone effectively, limiting imaging of the brain, spinal cord, or skeletal structures.

Why does air or gas interfere with ultrasound imaging?

Air scatters sound waves, making it ineffective for lungs or intestines; gas in the GI tract can obscure other organs.

What is the limitation of depth in ultrasound imaging?

High-frequency probes give better resolution but cannot image deep tissues effectively; low frequencies penetrate deeper but lose detail.

Why is ultrasound operator-dependent?

Image accuracy relies on the skill and training of the sonographer; poor technique can lead to inaccurate results.

Why can ultrasound not always diagnose specific diseases?

It detects anatomical changes but may not differentiate between benign and malignant masses without biopsy.

What are motion artifacts in ultrasound?

Blurring occurs when imaging fast-moving structures, reducing temporal resolution.

What are safety concerns with non-diagnostic ultrasound use?

While generally safe, unnecessary or prolonged exposure could cause tissue heating or biological effects.

What is an ultrasound artifact?

A false or misleading image feature caused by sound wave interactions or assumptions in image processing.

What causes a shadowing artifact in ultrasound?

A highly reflective object (like bone or gallstones) blocks the beam, creating a dark shadow behind it.

What does a shadowing artifact look like?

A dark, signal-free region deep to a reflective surface.

What causes an enhancement artifact in ultrasound?

A low-attenuation object (like a fluid-filled cyst) allows more sound to pass through, making deeper tissues appear brighter.

What does an enhancement artifact look like?

A bright region beneath a fluid-filled or weakly attenuating structure.

What causes a reverberation artifact?

Sound waves bounce repeatedly between two strong reflectors, creating multiple equally spaced echoes.

What does a reverberation artifact look like?

Multiple parallel lines appearing beneath a reflective surface.

What causes a mirroring artifact?

A highly reflective surface (like the diaphragm) creates a duplicate image on the opposite side of the reflector.

How does a mirroring artifact appear?

A duplicate structure appears deeper or opposite to the real one.

What causes a speed artifact in ultrasound?

Occurs when the beam travels through tissues with different sound speeds, causing structures to appear at incorrect depths.

What does a speed artifact look like?

The structure may appear shifted, curved, or misaligned on the image.

What are the main types of ultrasound transducers?

Linear (high resolution, shallow structures), curvilinear (wider field, deeper structures), and phased array (small footprint, for narrow spaces).

How does frequency affect image quality?

Higher frequency = better resolution, less depth. Lower frequency = greater depth, lower resolution.

What do “anechoic,” “hypoechoic,” and “hyperechoic” mean?

• Anechoic: no echoes (black, fluid-filled)

• Hypoechoic: few echoes (darker, soft tissues)

• Hyperechoic: many echoes (bright, dense tissue)

• Isoechoic: similar brightness to surrounding tissue