What values of TI and MI are recommended for fetal Ultrasound studies?
TI and MI recommendations for fetal studies include:
- • TIs values are used for first trimester studies.
- • TIb values are used for second and third trimester studies.
- • TI <0.5 should be used particularly for first trimester studies.
- • TI <0.5 may likely be used for extended scan times.
- • TI >0.5 and <1.0 should be limited to scan times of less than 30 minutes.
- • TI >2.5 should be limited to scan times of less than one minute.
- • MI ≤1.9 (the current FDA limit) can be used as needed in the absence of gas bodies.
In general, as for ionizing radiation, the principle of “as low as reasonably achievable (ALARA)” should be employed for ultrasound, particularly for obstetric studies.