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ALARA means exposing the patient to the lowest ultrasound exposure that can be used to obtain the required clinical information. This is the guiding principle for our use of diagnostic ultrasound energy.
Adherence to the ALARA principle requires, at a minimum, the following:
Use the correct preset (e.g. do NOT use an adult cardiac preset to scan a fetal heart)
Adjust the transmit power to the lowest setting that will produce a diagnostic study
Reduce the acoustic power at the end of the study in preparation for the next study
Monitor the Output Display Standard (MI & TI) throughout the scan
Know and use the recommended maximum scan times for specific TI values
Move/lift the transducer when stationary imaging is not needed to reduce dwell time
When possible avoid sensitive tissues such as eyes, gas-filled tissues, and fetal calcified structures
Minimize exposure time by performing exams as efficiently as possible
Table 1. Pertains to obstetric (including gynecologic when pregnancy is possible), neonatal transcranial, and neonatal spinal examinations.
From this table, we can see that the higher the TI, the shorter the recommended dwell time. We can also see that if the TI can be kept at or below 0.7, there is no time limit to the recommended dwell time.
Table 2. Pertains to adult transcranial, general abdominal, peripheral vascular, neonatal (except head and spine), and other scanning examinations (except the eye).
From this table, we can see that for these less sensitive procedures, the TI values can be higher, and that if the TI can be maintained at or below 1.5, there is no time limit.
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