SonoSite iLook - Page 59

Chapter 5: Safety 51
Safety
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 milliwatts.
W
.3
(z
1
) Derated ultrasonic power at axial distance z1 in 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.
pr@PII
max
Peak rarefactional pressure at the point where the free-field, spatial-peak
pulse intensity integral is a maximum in Megapascals.
d
eq
@PII
max
Equivalent beam diameter at the point where the free-field, spatial-peak
pulse intensity integral is a maximum in centimeters.
FL Focal length, or azimuthal (x) and elevational (y) lengths, if different
measured in centimeters.
Table 1: Acoustic Output Terms and Definitions (Continued)
Term Defin ition
Aaprt()
4 π()⁄()Wo()ITA z()()⁄()