SonoSite titan - Page 151

Chapter 6: Safety 145
Safety
TIB (Bone thermal index) is a thermal index for applications in which the
ultrasound beam passes through soft tissue and a focal region is in the
immediate vicinity of bone. TIB non-scan is the bone thermal index in the
non-autoscanning mode.
TIC (Cranial bone thermal index) is the thermal index for applications in which
the ultrasound beam passes through bone near the beam entrance into the
body.
A
aprt
Area of the active aperture measured in cm
2
.
P
r.3
Derated peak rarefactional pressure associated with the transmit pattern
giving rise to the value reported under MI (Megapascals).
Wo Ultrasonic power, except for TIS
scan
, in which case it is the ultrasonic power
passing through a one centimeter window in units of milliwatts.
W
.3
(z
1
) Derated ultrasonic power at axial distance z
1
in units of milliwatts.
I
SPTA.3
(z
1
) Derated spatial-peak temporal-average intensity at axial distance z
1
(milliwatts per square centimeter).
z
1
Axial distance corresponding to the location of maximum [min(W
.3
(z), I
TA.3
(z)
x 1 cm
2
)], where z > zbp in centimeters.
z
bp
1.69 in centimeters.
z
sp
For MI, it is the axial distance at which p
r.3
is measured. For TIB, it is the axial
distance at which TIB is a global maximum (i.e., z
sp
= z
b.3
) in centimeters.
d
eq
(z) Equivalent beam diameter as a function of axial distance z, and is equal to
, where I
TA
(z) is the temporal-average intensity as a
function of z in centimeters.
fc Center frequency in MHz.
Dim. of A
aprt
Active aperture dimensions for the azimuthal (x) and elevational (y) planes in
centimeters.
PD Pulse duration (microseconds) associated with the transmit pattern giving
rise to the reported value of MI.
PRF Pulse repetition frequency associated with the transmit pattern giving rise to
the reported value of MI in Hertz.
Table 4: Acoustic Output Terms and Definitions (Continued)
Term Definit ion
Aaprt()
4 π()⁄()Wo()ITA z()()⁄()