BS EN 61828:2002

INTRODUCTION
1 Scope
2 Normative references
3 General
   3.1 Focusing methods
   3.2 System and measurement requirements
   3.3 General focused field descriptions
4 Focusing definitions
   4.1 Background information
   4.2 Definitions
5 List of symbols
6 Measurement procedures
   6.1 General
   6.2 Finding the beam axis
   6.3 Determining if transducer is focusing
   6.4 Measuring other focal parameters of a focusing transducer
Annex A (informative) Background for the transmission/Characteristics
        of focusing transducers
Annex B (informative) Methods for determining the beam axis for
        well-behaved beams
   B.1 Comparisons of beam axis search methods
   B.2 Beamwidth midpoint method
Annex C (informative) Methods for determining the beam axis for beams
        that are not well-behaved
Annex ZA (normative) Normative references to international publications
         with their corresponding European publications
Figure 1 - Transducer options - Top: Transducer with a radius of
           curvature R and a focal length equal to R - Middle:
           Transducer with a plano-concave lens - Bottom: Transducer
           with a plano-convex lens
Figure 2 - Definitions for focusing measurements when the transducer
           geometry is unknown
Figure 3 - Field parameters for non-focusing and focusing transducers
Figure 4 - Beam contour plot - Contours at -6, -12, and -20 dB for
           a 5 MHz transducer with a diameter of 25 mm and a radius
           of curvature of 50 mm centred at location 0,0 (bottom
           centre of graph)
Figure 5 - Parameters for describing a focusing transducer of a known
           geometry
Figure 6 - Path difference parameters for describing a focusing
           transducer of a known geometry
Figure 7 - Beamwidth focus in a principal longitudinal plane
Figure 8 - Types of geometric focusing
Figure 9 - Pressure focus in a principal longitudinal plane
Figure B.1 - X-axis scan at 9 cm depth for the first focal zone with
           beam centre
Figure B.2 - X-axis scan at 4,4 cm depth for the second focal zone
Figure C.1 - Asymmetric beam showing beamwidth midpoint method
Table B.1 - Standard deviations for x and y scans using three
             methods of determining the centre of the beam
Table B.2 - -dB beamwidth levels for determining midpoints

Specifies the definitions for the transmitted field characteristics of focusing transducers for applications in medical ultrasound.

This International Standard - provides definitions for the transmitted field characteristics of focusing transducers for applications in medical ultrasound; - relates these definitions to theoretical descriptions, design, and measurement of the transmitted fields of focusing transducers; - gives measurement methods for obtaining defined characteristics of focusing transducers; - specifies beam axis alignment methods appropriate for focusing transducers. This International Standard relates to focusing ultrasonic transducers operating in the frequency range appropriate to medical ultrasound (0,5 MHz to 40 MHz) for both therapeutic and diagnostic applications. It shows how the characteristics of the transmitted field of transducers may be described from the point of view of design, as well as measured by someone with no prior knowledge of the construction details of a particular device. The radiated ultrasound field for a specified excitation is measured by a hydrophone in either a standard test medium (for example, water) or in a given medium. The standard applies only to media where the field behaviour is essentially like that in a fluid (i.e. where the influence of shear waves and elastic anisotropy is small), including soft tissues and tissue-mimicking gels. Any aspects of the field that affect their theoretical description or are important in design are also included. These definitions would have use in scientific communications, system design and description of the performance and safety of systems using these devices.