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Chapter 3: Understanding Ultrasound System Controls

Hillary B. Hrabak; Ashlee Davis; David B. Adams

INTRODUCTION

It is crucial for clinicians performing transesophageal echocardiographic (TEE) examinations to understand how the controls on an ultrasound machine alter the display. Without this knowledge, it is impossible to consistently optimize images, and unskilled manipulations may misrepresent diagnostic information and result in missed diagnoses. This chapter describes the controls found on most ultrasound machines, how they affect the image, and how they are used to optimize the ultrasound image. Table 3-1 presents the most commonly used controls for two-dimensional (2D) imaging.

Table 3–1.Commonly used controls for 2D imaging
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Table 3–1. Commonly used controls for 2D imaging
2D Variable Knob(s) Function
Gain Gain Amplifies returning signals before display
TGC/DGC TGC/DGC toggles Selectively amplifies returning signals before display (horizontally)
LGC LGC toggles Selectively amplifies returning signals before display (vertically)
Compression Compression Changes the difference between the highest and lowest received amplitudes (shades of gray)
Power Power (dB) Controls rate at which energy is propagated into an imaged medium
Frequency Dependent on probe Determines number of times/second a sound wave completes a cycle
Focal zone Focal zone Alters the placement of the narrowed region that designates an area of improved resolution
Depth Depth Selects how shallow or deep an area is imaged
Sector size Size, trackball Narrows or widens the image sector
Zoom Zoom Magnifies a particular area of interest within the sector
Freeze Freeze Stops or starts live imaging
Measurement Freeze, caliper, trace, enter, erase Quantifies features of a 2D image
Harmonics Harmonics Uses frequencies created by the tissues, rather than the fundamental frequency, to create an image
Annotation Annotation Adds text or picture to image

Abbreviations: 2D, two-dimensional; dB, decibel; DGC, depth gain compensation; LGC, lateral gain compensation; TGC, time gain compensation.

PREPARING THE MACHINE

After providing power to the machine itself, a TEE probe must be connected to the machine, register as compatible with the machine, and be selected from other possible transducer options. The basic parameters for the ultrasound examination may be defined by choosing an appropriate TEE preset. The preset provides a starting point for basic machine settings such as depth, gain, and image processing settings. The operator can adjust all the machine's variables from the initially fixed settings as needed. Adjustments to the preset can be saved permanently under a different name when desired. Patient identification (name and medical record number) and any other relevant information should be entered into the machine before beginning an exam. This includes date of birth, sex, the name of the person performing the examination, location, and a number of other qualifiers.

The five most common modes used during TEE examinations are 2D gray-scale imaging, color Doppler, pulsed-wave (PW) Doppler, continuous-wave (CW) Doppler, and three-dimensional (3D) imaging. The usual buttons to enable these modes are 2D, Color, PW, CW, and 3D, respectively. Other scanning ...

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