Page 273 - Biomedical Engineering and Design Handbook Volume 2, Applications

INSTRUMENTATION DESIGN FOR ULTRASONIC IMAGING 251

Obstetrics Fetal growth, congenital malformations
Peripheral vasculature Extent of plaque, blood vessel tortuosity
Many of these diagnoses are based on relatively gross anatomical information that is available
from the ultrasound image. In addition there is a large amount of additional information imparted to
the echoes by the scattering process. Some of this information is displayed on B-mode images and
is of major value to the clinician. This information is critical to diagnoses such as diffuse disease
processes, the identification of tumors, quality of myocardial dynamics, and so forth. It is for these
reasons the signal integrity and retention of maximum dynamic range is of key value in the image
formation process.
Sales of ultrasound instruments are divided among the four areas listed above roughly as follows
(source: Klein Biomedical Consultants):
Radiology 39%
Cardiology 35%
Obstetrics/gynecology 16%
Peripheral vasculature 5%

This gives a rough idea of the level of utilization in the several areas; however, it also should be
noted that the marketplace is currently undergoing significant changes with the health-care reform
activity. Also, there is much overlap between the segments. For example, many radiologists do
perform obstetric or peripheral vascular examinations and echocardiologists perform increasing
amounts of peripheral vascular work. In terms of instrumentation sales, these are believed to be
approximately $4.0 billion in year 2008. The growth of the total revenues has flattened of the last
decade; however, there are areas such as highly miniaturized systems that are experiencing
double digit growth rates as new markets are opening up. Ultrasound is also seen as a likely ben-
eficiary of the reduced spending in the very high-end of imagers such as CT, PET, SPECT, and
MRI scanners.

9.2.4 Classifications of Ultrasound Instruments
Ultrasonic instruments can be classified in many of different ways (Christensen, 1988). Among
these are

Types of electronic beam steering Phased arrays versus steering by element selection
Clinical applications See Sec. 9.2.3
Nature of beam formation Analog versus digital
Portability Console-based systems versus handhelds
With respect to steering methods, the huge majority of instruments (perhaps more than 99 percent)
sold today are electronically (as opposed to mechanically) steered. Phased-array systems are domi-
nant in echocardiographic applications where aperture size is limited by rib spacings, while the other
beam-steering methods are more often used in radiologic and obstetric and gynecological examina-
tions. The latter grouping is sometimes referred to as general imaging ultrasound. The shift to digital
beam formation is accelerating, and it is likely that today nearly all instruments sold will have digital
beam formers. This is true even for the lower-price points.

9.3 TYPICAL SYSTEM BLOCK DIAGRAM

The block diagram in Fig. 9.1 shows the signal-processing steps required for B-mode image forma-
tion. The actual implementations vary considerably among manufacturers and the types of systems.
For example, the grouping of functions might be different from one system to the next, depending