Reichert IOPac Advanced, User Manual

Page: 29 / 38

16012-101 Rev. C 29
General Specifications (Continued)
Tissue Exposure To Ultrasound Energy
The ultrasound energy emitted by the IOPac is of low intensity and will have no adverse effects on the patient and/or
operator. However, the operator 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 probe against the eye or other tissue with the system activated except when making a
measurement. Do not make unnecessary measurements.
Ultrasonic Intensities
The IOPac has only one mode, and ultrasonic intensity settings are not under the control of the operator. Thus, the
values below are the values to be expected for a typical transducer.
In Water In the Eye
I SPTA, mw/cm
2
5.14 5.13
I SPPA, W/cm
2
10.23 10.22
MI(unitless) 0.171 0.170
Since the IOPac 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 probe to the transducer focus, which is the point of
measurement (1mm). The nominal frequency 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.