M y L a b
–
S A F E T Y A N D S T A N D A R D
2-11
may increase the MI, but because of the enhanced sensitivity, you may be able to
reduce the transmit power, thus reducing the MI. Decreasing the imaging depth as
low as possible may allow the system to increase the PRF and thus reduce the MI.
In Doppler modes, if you are working with a 2D + Doppler display, the MI will
show the 2D value (because it is higher than the Doppler one) and the Doppler
TIS; the latter parameter should be your primary concern: the MI value reflects the
energy to which the patient is exposed only for a minimal time, i.e. between every
sweep. You may want however to remember that whenever varying the Doppler
speed: increasing the speed will cause the 2D to be refreshed more often. You may
eventually freeze the 2D or switch to a full screen mode; however, this will
probably increase the time to actually find the desired signal, and therefore the
exposure time.
In
OB
exams, this system displays both the MI and the TIB in imaging and CFM
modes. While the MI will remain your primary concern in those modes, you
should also consider the TIB in imaging a second or third trimester fetus as a
conservative estimate of the actual temperature rise. In PW Doppler, the latter
value is the primary parameter to consider for second or third trimesters
pregnancies while the TIS is a more reliable indicator for earlier exams. The general
guidelines already expressed for the previous exams remain valid.
For
Neonatal Head
studies, the MI and the TIB may be significant in imaging
and CFM modes, while the MI and both TIS and TIB are displayed for Doppler
modes. Because of the chance of focusing near the base of the skull, the TIB
should be conservatively considered the ideal thermal index. As usual the MI is the
primary concern in imaging modes, and the TIB in Doppler. The general
guidelines expressed above are valid. In
Adult Cephalic
, because of the skull, the
TIC is considered the most significant index for this application. The general
guidelines expressed above are valid.
Acoustic Output Tables
According to the IEC61157 and EN 60601-2-37, the acoustic output tables give
the acoustic output data for each probe in every operating mode. These tables are
located in the
MyLab
Operator Manual CD.
In OB, the TIB
should be considered
when scanning a
second or third
trimester fetus, while
the TIS is more
reliable for earlier
exams.
The TIB is a better
predictor during
neonatal head studies,
while the TIC is
more significant in
adult transcranial
studies.
