2
HD11 XE Getting Started
4535 612 62651
35
Safety
Mechanical and Thermal Indices Display Precision and Accuracy
The MI and TI precision is 0.1 unit on the system.
For system MI and TI display accuracy estimates, see the HD11 XE Acoustic Output
Tab le s. These accuracy estimates are based on the variability range of transducers
and systems, inherent acoustic output modeling errors and measurement variabil-
ity, as discussed below.
The displayed values should be interpreted as relative information to help the sys-
tem operator achieve the ALARA principle through prudent use of the system.
The values should not be interpreted as actual physical values in interrogated tis-
sue or organs. The initial data that is used to support the output display is derived
from laboratory measurements based on the American Institute of Ultrasound in
Medicine (AIUM) measurement standard. The measurements are then put into
algorithms for calculating the displayed output values.
Many of the assumptions used in the process of measurement and calculation are
conservative in nature. Over-estimation of actual in situ intensity exposure, for
the vast majority of tissue paths, is built into the measurement and calculation
process. For example:
• The measured water tank values are derated using a conservative, industry
standard, attenuation coefficient of 0.3 dB/cm-MHz.
• Conservative values for tissue characteristics were selected for use in the TI
models. Conservative values for tissue or bone absorption rates, blood perfu-
sion rates, blood heat capacity, and tissue thermal conductivity were selected.
• Steady State temperature rise is assumed in the industry standard TI models,
and the assumption is made that the ultrasound transducer is held steady in
one position long enough for steady state to be reached.
A number of factors are considered when estimating the accuracy of the displayed
values: hardware variations, estimation algorithm accuracy, and measurement
variability. Variability among transducers and systems is a significant factor. Trans-
ducer variability results from piezoelectric crystal efficiencies, process-related
impedance differences, and sensitive lens focusing parameter variations. Differ-
ences in system pulser voltage control and efficiencies is also a contributor to
variability. There are inherent uncertainties in the algorithms used to estimate
acoustic output values over the range of possible system operating conditions and
pulser voltages. Inaccuracies in laboratory measurements are related to, among
To Next Page
Loading...