Ametek iPac User Manual page 39

Acoustic Output
(continued)
Definitions (Continued)
PD - pulse duration (microseconds)
PRF - pulse repetition frequency (Hz)
EBD - entrance beam dimensions for the azimuthal and elevational planes (centimeters).
Tissue Exposure To Ultrasound Energy
The ultrasound energy emitted by the iPac is of low intensity and will have no adverse effects
on the patient and/or user. However, the user is still cautioned to perform examinations using
the principle of ALARA (As Low As Reasonably Achievable). All examinations should be done
so that the patient receives as little ultrasound radiation as possible. Do not hold the mea-
surement tip against the eye or other tissue with the system activated except when making a
measurement. Do not make unnecessary measurements.
Ultrasonic Intensities
The iPac has only one mode, and ultrasonic intensity settings are not under the control of the
user. Thus, the values below are the values to be expected for a typical transducer.
In Water In the Eye
I SPTA, mw/cm2 5.14 5.13
I SPPA, W/cm2 10.23 10.22
MI(unitless) 0.171 0.170
Since the iPac is a contact instrument, the energy will always be attenuated by the tissue when
used as recommended. However, since the focal length (point of maximum intensity) is very
short (1 mm), and thus penetration into the eye is limited, the water values are effectively the
same as the tissue values, for all practical purposes. If more accuracy is desired, the intensity
in the eye at the transducer focus (corresponding to maximum intensity) may be calculated
according to the formula recommended by the FDA:
It=Iw x e(-0.069 x f x z)
where It is the estimated in situ intensity, Iw is the measured intensity in water at the focus of
the transducer, f is the ultrasonic frequency, and z is the distance from the face of the measure-
ment tip to the transducer focus, which is the point of measurement (1mm). The nominal fre-
quency of these transducers is 20 MHz. The actual frequency of a particular transducer may
vary from this value. The tissue calculations above were done with the measured frequency
of the transducer used for the tests.
16040-101 Rev. J 39