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Chapter 7
Optimizing the scan
75
CHAPTER CONTENTS
Introduction 75
The patient 76
Starting the scan 76 B-mode controls 76 Imaging artifacts 76 Color Doppler controls 78
Color pulse repetition frequency 78
Color box angle and size 79
Color imaging artifacts 80
Spectral Doppler optimization 81 Repetitive strain injury and occupational
hazards 82
Safety of diagnostic ultrasound 82
Ultrasound intensity 82 Mechanical and thermal indices 82 User’s responsibility 83
Infection control 83
INTRODUCTION
The preceding chapters have covered some of the basic scientific principles behind ultrasound, the Doppler effect and hemodynamics. The sonographer should now have a clearer understanding of how a B-mode image is created and how color flow imaging can be used to rapidly interrogate blood flow in ves- sels, allowing the blood flow in selected areas to be assessed with spectral Doppler. This has made duplex scanning a powerful technique for the investiga- tion of patients with vascular diseases, and many vascular surgeons are making clinical decisions on the basis of duplex scanning alone. It is therefore vitally important that the operator understands the use of the scanner controls and the limitations of the technique. Some manufacturers have introduced auto-optimization controls, but there are still many situations in which the controls will need to be adjusted manually. Manufacturers often use different names or terms for the same scanner control or func- tion, such as power imaging and color angiography, both of which relate to power Doppler imaging. It is important to consult the operator’s manual or ask the manufacturer if the function of any control is not clear.
Contemporary duplex scanners have a range of examination-specific presets that optimize the sys- tem for a particular examination. However, in many instances the scanner controls need adjusting, or optimizing, to demonstrate pathology. In addition, a number of imaging and Doppler artifacts may be confused or misinterpreted as significant disease, leading to serious diagnostic errors. The aim of