Rationale and derivation of MI and TI--a review.

This review article provides a summary rationale and derivation for the mechanical index (MI) and thermal index (TI) formulas presented in the body of the "Standard for real-time display of thermal and mechanical acoustic output indices on diagnostic ultrasound equipment" (AIUM/NEMA 1998). For purposes of simplicity, this standard is referred to in this article by its colloquial "nickname," the "output display standard" or ODS. This review expands on the summary information provided in Appendix A of the ODS. Numerous references are made to the root publications from which the formulas were derived. As will be discussed in the derivation notes that follow, key parts of the MI and TI models rely heavily on experimental data. This document does not attempt to do any more than describe the relevant results of the experiments. A general overview is provided in the Introduction and Rationale for the nontechnical reader and the more rigorous Models and Derivation Notes provides a detailed mathematical review of the MI and TI models. A complete set of defined terms is provided in Appendix 1.