Mechanical index

Mechanical index (MI) is an ultrasound metric. It is defined as

$MI = \frac{PNP}{\sqrt(F_c)}$^[1]

where:

• PNP is the peak negative pressure of the ultrasound wave (MPa)
• F_c is the center frequency of the ultrasound wave (MHz)

Mechanical index can be used as an estimate for the degree of bio-effects a given set of ultrasound parameters will induce. A higher mechanical index means a larger bio-effect. Currently the FDA stipulates that diagnostic ultrasound scanners cannot exceed a mechanical index of 1.9.^[2]

References

1. ^ Thomas Szabo (2004). Diagnostic Ultrasound Imaging: Inside Out (Biomedical Engineering). ISBN 978-0126801453
2. ^ http://www.accessdata.fda.gov/cdrh_docs/pdf9/K091970.pdf (accessed July 2010)