Extended Pure Harmonic Detection (ExPHD) - a specific contrast harmonic enhanced technology
The purpose of contrast harmonic enhanced imaging based on ExPHD mode is to clearly detect the microbubbles signal when injected into patient’s body. When the tissue and the microbubbles receive a transmitted low acoustic pressure ultrasound waves, harmonic components that are integer multiples of the fundamental frequency are produced.
The two transmitted pulse reach the microbubble in sequence, collecting a phase shifting (delay by phase) between the two received waves. More specific, when the second pulse insonate the microbubble, the bubble is under a strong deformation (vibration). This means the diameter of the bubble is continuously changing, providing a phase delay between the first and the second received wave.
Standard contrast harmonic imaging more intensively depicts signals from the microbubbles than those from the tissue by selectively detecting the second harmonic components. However, standard contrast harmonic imaging is not able to filter the signals from the tissue.
The ExPHD mode selectively depicts signals from the microbubbles, filtering harmonic component from the tissue by synthesizing the phase-shift signals with the second harmonic components.
Signals from the contrast agent provide a wider phase shifting with no relation to its motion even more when compared to the tissue phase shifting.
This processing is capable of enhancing the signals from contrast agents. In ExPHD mode different low Mechanical Index transmits frequencies for various transducers are available to match the specific target. The gain and dynamic range are adjusted to avoid signal saturation.