Properties of swept FM waveforms in medical ultrasound imaging

For a given input noise level, an imager receiver´s signal-to-noise ratio (SNR) can only be increased by raising the energy contained in its transmit pulse. Given a fixed bandwidth pulse waveform energy can be raised only by increasing the transmit amplitude. For a linear swept frequency modulated (FM) waveform, both transmit amplitude and duration can be increased. For equal bandwidth signals and aperture size, the point spread function of pulse and swept waveforms is the same. It is shown that, because of receiver dynamic range limitations, aperture constraints, and transmit power regulations, use of swept FM waveforms may not translate into better medical ultrasound imager performance