Ultrasound Image Quality and Modes

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Questions and Answers

What determines the choice of an ultrasound?

Neither good resolution nor deep penetration

Only good resolution

Good resolution and deep penetration (correct)

Only deep penetration

What type of reflection originates the echo signal?

Parallel reflection

Non-perpendicular reflection

Perpendicular reflection (correct)

Oblique reflection

What happens to the echo signal when the surface is rough?

The echo signal remains the same

The echo signal increases

The echo signal decreases (correct)

The echo signal is inverted

What does a smooth surface result in?

Low scattering and good image Signup and view all the answers

What is the mode of ultrasound imaging used to obtain diagnostic information about the depth of a structure?

A-Mode Signup and view all the answers

What is the formula to calculate the depth of an interface?

Depth = Velocity x time Signup and view all the answers

What is the average speed of sound in soft tissue?

1540 m/sec Signup and view all the answers

What is the application of A-Mode scan in ophthalmology?

Biometry and diagnosis of eye diseases Signup and view all the answers

What is the shift in the middle structure considered abnormal in an adult?

More than 3 mm Signup and view all the answers

What is the application of A-Mode scan in echo encephalography?

Detection of brain tumors Signup and view all the answers

What is the advantage of using high frequency ultrasound in the eye?

Better resolution due to less absorption Signup and view all the answers

What type of ultrasound mode is used to study motion such as heart and heart valves?

M-mode Signup and view all the answers

What is the effect of continued ultrasound at an intensity of 1 W/cm²?

Deep heating effect and temperature rise Signup and view all the answers

What is the purpose of B-mode ultrasound?

To obtain 2D images of the body Signup and view all the answers

What is the effect of focused ultrasound at an intensity of 10³ W/cm²?

Selective destroying of deep tissue Signup and view all the answers

What is the advantage of using ultrasound frequencies of up to 20 MHz in the eye?

Better resolution due to less absorption Signup and view all the answers

What type of ultrasound mode is used to obtain 3D images with motion?

D-mode Signup and view all the answers

What is the effect of continued ultrasound at an intensity of 0.01 W/cm²?

No harmful effects are observed Signup and view all the answers

What is the purpose of A-mode ultrasound?

To study internal structure of the eye Signup and view all the answers

What is the effect of continued ultrasound at an intensity of 35 W/cm²?

Tissue destroying effect Signup and view all the answers

What is the frequency range of ultrasound waves used in medical applications?

20 kHz to 1 GHz Signup and view all the answers

What is the principle behind the generation and detection of ultrasound signals?

Piezoelectric principle Signup and view all the answers

What is the purpose of using water or a jelly paste in medical ultrasound diagnosis?

To create a good impedance matching between the transducer and skin Signup and view all the answers

What is the term for the device that uses ultrasound waves to generate an image of a particular soft tissue structure in the body?

SONAR Signup and view all the answers

What is the focal zone related to in ultrasound image production?

Resolution of the image Signup and view all the answers

What is the purpose of the transducer in medical ultrasound diagnosis?

To convert electrical energy to mechanical energy and vice versa Signup and view all the answers

What is the effect of applying an electric potential difference between the faces of a piezoelectric crystal?

The crystal will vibrate and produce an ultrasound wave Signup and view all the answers

What is the term for the conversion of electrical energy to mechanical energy and vice versa?

Transduction Signup and view all the answers

What is affected by the acoustic impedance in ultrasound image production?

Image quality Signup and view all the answers

What is the result of the push-pull action of the transducer in medical ultrasound diagnosis?

Regions of compression and rarefaction Signup and view all the answers

What happens when an ultrasound wave encounters a boundary between two tissues with different acoustic impedance values?

A certain fraction of the wave energy is backscattered towards the transducer Signup and view all the answers

Why is a thick liquid (jelly) used between the transducer and the patient's skin?

To help eliminate air bubbles and facilitate easy passage of the ultrasound waves Signup and view all the answers

What is refraction in the context of ultrasound imaging?

A change in direction of the sound wave as it passes from one tissue to another Signup and view all the answers

What determines the quality of ultrasound imaging?

The interaction of the acoustic wave with the body tissue Signup and view all the answers

What is the main cause of attenuation of the ultrasound beam as it propagates through tissue?

All of the above Signup and view all the answers

What is the characteristic of the attenuation of the ultrasound beam as it propagates through tissue?

An exponential decrease in intensity Signup and view all the answers

What is the purpose of aligning the US transducer perpendicular to the interface between two media?

To minimize refraction artifacts in the ultrasound image Signup and view all the answers

What is spatial resolution in the context of ultrasound imaging?

The ability to distinguish between two structures at a certain distance Signup and view all the answers

What happens to the intensity of the ultrasound wave as it passes through tissue?

It decreases exponentially Signup and view all the answers

What is the effect of refraction on the ultrasound image?

It causes artifacts in the ultrasound image Signup and view all the answers

Study Notes

Ultrasound Imaging

Ultrasound image quality is determined by a compromise between good resolution and deep penetration.

Reflection

Perpendicular reflection originates the echo signal, while non-perpendicular reflection causes an intensity loss in the echo signal.
Smooth surface → low scattering → good image
Rough surface → high scattering → bad image

A-Mode (1D)

Used to obtain diagnostic information about the depth of structures (image with 1-dimension).
Sends US waves into the body and measures the time required to receive the reflected sound (echoes) from the interface between different tissues.
Depth = Velocity x time
Used to detect brain tumors and eye diseases.

Applications of A-Mode Scan

Echo Encephalography: • Used in the detection of brain tumors. • Pulses of ultrasound are sent to a thin region of the skull above the ear, and the echoes from different structures are displayed on the oscilloscope. • Compare the echoes from the left side of the head to the right side, and find the shift in the middle structure. • If the shift > 3 mm for an adult (abnormal) or > 2 mm for a child (abnormal).
Ophthalmology: • Used in diagnosis of eye diseases. • Used in biometry (measurement of distance in the eye, such as lens thickness, depth from cornea to lens, distance to the retina, and thickness of the vitreous tumor).

US Image Modes

B-Mode (2D): • Used to obtain 2D images of the body. • Principle is the same as in A-mode, except that the transducer is moving. • Provides information about the internal structure of the body, such as size, location, and change with time of the eye, liver, breast, heart, and fetus.
M-Mode (2D + motion): • Used to study motion, such as that of the heart and heart valves (image with 2D + motion). • Combines features of A- and B-mode. • Used in diagnostic information about the heart (mitral valve) and detection of pericardial effusion.
D-Mode (3D + motion; or 4D): • Takes 3-dimensional US images and adds the element of time to the process (image with 3D with motion).

Physiological Effects of Ultrasound

Various physiological and chemical effects occur when ultrasonic waves pass through the body, and they can cause physiological effects.
The magnitude of physiological effects depends on the frequency and amplitude of the sound.

Low Intensity US (~ 0.01 W/cm²)

No harmful effects are observed → used for diagnostic work (as in sonar).

Continues US (~1 W/cm²)

Deep heating effect (diathermy) → temperature rise due to the absorption of acoustic energy in the tissue.

Continues US (1-10 W/cm²)

Sound moves through → region of compression and rarefactions → pressure differences in adjacent regions of tissues (micromassage).

Continues US (~ 35 W/cm²)

Tissue destroying effect → rupture DNA molecules.

Continues and focused US (~ 10³ W/cm²)

Selective destroying of deep tissue using a focused ultrasound beam.

Ultrasound Generation

Ultrasound is sound with a frequency of 20 kHz to 1 GHz (for medical applications).
It is greater than the upper limit of human hearing.

Piezoelectric Principle

The ultrasound signal is generated and detected by the sensor.
The transducer is based on the piezoelectric principle.
Many crystals can be used so that AC voltage (electrical energy) across the crystal will produce a vibration of the crystal (mechanical energy), thus generating an ultrasound wave and vice versa.

SONAR

It is a device that uses an US wave to generate an image of a particular soft tissue structure in the body.

Image Production

Three concepts that affect US image production: • Focal zone • Acoustic impedance • Refraction

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Description

Learn about the factors affecting image quality in ultrasound imaging, including perpendicular and non-perpendicular reflection, and the different types of ultrasound image modes, including A-mode.