Essentials of Abdomino-Pelvic Sonography

A Handbook for Practitioners

Swati Goyal

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351261180
• Edition: 1
• Topic: Medicine
• Subtopic: Medical Theory, Practice & Reference

Sonography has emerged as a substantial diagnostic tool today. This handbook aims to cover ultrasound physics, abdominal and obstetric sonography, color Doppler, high resolution sonography and USG guided interventions with multiple choice questions and case reports for practical orientation.

PART I

USG Physics

1 Ultrasound Physics

1

Ultrasound Physics

INTRODUCTION

Ultrasound waves are defined as sound waves of high frequency that are inaudible to the ear. These are longitudinal waves that propel in a direction parallel to that of wave propagation in a medium.

High-frequency sound waves are inaudible to humans in the range of 2–20 million cycles per second (2–20 MHz)—this is the range of a diagnostic ultrasound.

Sound audible to humans is <20 KHz

Ultrasound is >20 KHz

Speed of sound in air is 330 meters per second

Speed of sound in fat is 1,450 meters per second

Speed of sound in soft tissue is 1,540–1,580 meters per second

Speed of sound in bone is 4,080 meters per second

Principle of sonography

BASED ON PULSE-ECHO PRINCIPLE

Pulses of high-frequency sound waves are transmitted to the patient. Echoes returning from various tissue boundaries are detected. The received echo produces an ultrasound image (Figure 1.1).

Electricity converted into sound—Pulse

Sound converted into electricity—Echo

If more sound is received back—suggestive of stronger reflector—whiter image

If less sound is received back—suggestive of weaker reflector—blacker image

Figure 1.1 Illustrating principle of ultrasound.

Frequency: The number of cycles per second; measured in Hz (Hertz).

Wavelength: The distance between two consecutive waves. It depends on the frequency of waves and speed of propagation in the medium through which it is passing. It is inversely proportional to frequency.

Bandwidth: Range of frequencies produced by the transducer.

Pulse length: Small number of cycles in a pulse.

INSTRUMENTATION

1. Transmitter: Sends voltage to energize the transducer.

2. Transducer:

3. Receiver: To detect and amplify weak signals and send them to display It controls the dynamic range and time-gain compensation (TGC).

4. Display: To present the USG image/data in a form suitable for analysis and interpretation.

The transducer’s input is communicated to scanner through a cable and the data can be visualized on the monitor.

Following are the ways through which spatial information can be displayed:

A mode: Amplitude mode; it is used for ophthalmic purposes

B mode: Brightness mode (gray scale, real time); it is used for routine sonography

M mode: Motion mode; it is used to measure the heart rate

ULTRASONOGRAPHY TRANSDUCER

Ultrasonography (USG) transducer is a device that converts electrical energy to mechanical energy and vice versa.

It has two functions:

1. Transmitter: Electrical energy is converted to acoustic pulse, which is transmitted to the patient.

2. Receiver: Receives reflected echoes. Weak pressure changes are converted to electrical signals for processing.

It is based on the principle of piezoelectricity.

Ultrasound pulses generated by transducer are propagated, reflected, refracted, and absorbed in tissues to provide useful clinical information.

Transducers (scanning probes) are the costliest part of any ultrasound unit.

Types of transducers

The shape of the scans from different transducers is different (Figure 1.2).

1. Curved array convex transducer: Wider fan-shaped image

Useful for all body parts except echocardiography

Large versions for general abdomino-pelvic and obstetrics scan

Small high-frequency curved array scanners for transvaginal, transrectal scans

2. Linear array: Rectangular shape

Most useful for small and superficial parts such as thyroid, testicle, and breast

Vascular, musculoskeletal, and obstetric applications

3. Phased array sector scanner: Triangular fan shaped

Used in cardiac examination through intercostal scanning

Selection of transducers

The thickness of transducer (usually 0.1–1.0 millimeters) determines its frequency (inversely proportional).

Each transducer is focused at a particular depth.

Penetration of the ultrasound diminishes with an increase in frequency.

Higher the frequency, shorter the wavelength, and better the resolution.

Frequencies from 7.5 to 15 MHz are used for superficial vessels and organs such as thyroid and breast lying within—1–3 centimeters of the surface.

Figure 1.2 Illustrating various types of transducers.

Frequencies of 2–5 MHz are required for deeper structures in abdomen and pelvis, that is, >12–15 centimeters from the surface.

High frequency—better spatial resolution, greater attenuation, and poor penetration.

High frequencies →

• Broadens the bandwidth

• Reduces the quality factor (Q)

• Shortens the spatial pulse length (SPL)

Specialized transducers

1. Endovaginal probes for early obstetric and gynecologic problems.

2. Endorectal probes for prostate imaging.

3. Intraoperative/laparoscopic—it is used to in...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• List of Abbreviations
• Preface
• Acknowledgments
• About the Author
• PART I USG PHYSICS
• PART II ABDOMINAL USG
• PART III OBSTETRICS USG
• PART IV COLOR DOPPLER
• PART V HIGH-RESOLUTION USG
• PART VI USG-GUIDED INTERVENTIONS
• PART VII RECENT ADVANCES IN SONOGRAPHY
• Sample Questions
• MCQs
• Answer Key
• Case Reports
• Glossary
• Index