M y L a b
–
S A F E T Y A N D S T A N D A R D
2-7
The Output Display
The following table shows the indices used for each clinical application. Indices are
displayed in 0.1 increments.
Application
MI
TIS
TIB
TIC
OB/Fetal
Yes
Yes
Yes
No
Neonatal
5
Yes
Yes
Yes
Yes
Adult Cephalic
Yes
Yes
No
Yes
All others
Yes
Yes
Yes
6
No
The Output Default Settings
System default settings depend upon the probe, the mode of operation and the
application which is selected during the patient ID procedure. The
MyLab
defaults
the transmit power to obtain output levels that are below the historic Ispta limits
established by the FDA for the selected application.
Methodology and Accuracy of Display
The displayed indices values must be interpreted as relative information to help the
user to achieve the ALARA principle.
Initial data are derived from laboratory measurements based on the AIUM
standard. Then the indices are calculated beginning from these measurements
according to the AIUM/NEMA "Standard for Real-Time Display of Thermal and
Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment"
publication. Many of the assumptions used for measurements and calculation are
conservative in nature. The measured water tank values are derated using the
conservative attenuation coefficient established by the standard (0.3
dB/cm/MHz). Over-estimation of actual in-situ exposures is thus part of the
calculation process.
Accuracy:
14% for the MI,
30% for the TI A number of factors influence the
estimation of the accuracy of the displayed indices, the most significant ones being
the variability between probes and the laboratory measurements accuracy
(hydrophone, operator, algorithms, etc.) itself, while variability of the system pulser
and efficiency is a minor contributor.
The accuracy estimate, based on the variability range of probes and systems, and
on the inherent modeling and measurements errors, is 14% for the MI and 30%
for TI indices; this accuracy estimate does not consider errors in/or caused by
measuring with the AIUM standard.
5
Includes Neonatal Head studies
6
Only when TIB≠TIS
In combined modes
(ex.: 2D+Doppler),
the indices will show
the highest value
between the two
modes.
I N D I C E S
A C C U R A C Y
