Why is the temporal average intensity (Ita) considered the lowest measurement?

The temporal average intensity (Ita) is considered the lowest measurement because it takes into account both the receive time and the overall averaging over time. This means that Ita reflects the intensity of the ultrasound beam over an entire duty cycle, including both the 'on' and 'off' periods. During the 'on' time, the energy is being transmitted, while during the 'off' time, no energy is being transmitted.

Since Ita is an average of the intensity over the entire cycle, it yields a lower value than other measurements that might focus solely on the transmission periods or peaks of intensity. This comprehensive approach of incorporating the duration of the receive time along with the transmit time leads to a lower average intensity measurement compared to those that might consider only specific moments in time or specific processes, such as peak measurements or those focusing on shorter time frames.

By averaging over a longer period that includes receive times, Ita reflects a more inclusive and therefore typically lower intensity value, which holds significant importance in safeguarding against potential biological effects caused by ultrasound exposure.