Figure 4.

Raw transient signals reflected from the abdominal wall phantom at different IAP values. The reflection response between 181.5 and 182.5 ns is almost zero since there was a distance between the transmitter antenna and the front side of the abdominal wall phantom. Consequently, no reflection happened at this interval. At 182.7, however, the reflection response starts to increase, which means that the first group of reflected waves has been detected by the receiver antenna. Afterwards, more reflected waves from deeper layers of the abdominal wall phantom have been detected and the reflection response has increased progressively.