Journal article
Frequency division transmission imaging and synthetic aperture reconstruction
In synthetic transmit aperture imaging only a few transducer elements are used in every transmission, which limits the signal-to-noise ratio (SNR). The penetration depth can be increased by using all transmitters in every transmission. In this paper, a method for exciting all transmitters in every transmission and separating them at the receiver is proposed.
The coding is done by designing narrow-band linearly frequency modulated signals, which are approximately disjointed in the frequency domain and assigning one waveform to each transmitter. By designing a filterbank consisting of the matched filters corresponding to the excitation waveforms, the different transmitters can be decoded at the receiver.
The matched filter of a specific waveform will allow information only from this waveform to pass through, thereby separating it from the other waveforms. This means that all transmitters can be used in every transmission, and the information from the different transmitters can be separated instantaneously.
Compared to traditional synthetic transmit aperture (STA) imaging, in which the different transmitters are excited sequentially, more energy is transmitted in every transmission, and a better signal-to-noise-ratio is attained. The method has been tested in simulation, in which the resolution arid contrast was compared to a standard synthetic transmit aperture system with a single sinusoid excitation.
The resolution and contrast was comparable for the two systems. The method also has been tested using the experimental ultrasound scanner RASMUS. The resolution was evaluated using a string phantom. The method was compared to a conventional STA using both sinusoidal excitation and linear frequency modulated (FM) signals as excitation.
The system using the FM signals and the frequency division approach yielded the same performance concerning both axial (of ap 3 lambda) and lateral resolution (of ap 4.5 lambda). A SNR measurement showed an increase in SNR of 6.5 dB compar- - ed to the system using the conventional STA method and FM signal excitation.
| Language: | English |
|---|---|
| Publisher: | IEEE |
| Year: | 2006 |
| Pages: | 900-911 |
| ISSN: | 15258955 and 08853010 |
| Types: | Journal article |
| DOI: | 10.1109/TUFFC.2006.1632681 |
| ORCIDs: | Jensen, Jørgen Arendt |
Algorithms Chirp modulation Energy resolution Frequency conversion Frequency modulation Image Enhancement Image Interpretation, Computer-Assisted Image reconstruction Information Storage and Retrieval Matched filters Radio Waves Signal resolution Signal to noise ratio Transducers Transmitters Ultrasonography axial resolution biomedical ultrasonics coding encoding filterbank frequency division transmission imaging image contrast image reconstruction image resolution lateral resolution linear frequency modulated signals matched filters medical image processing narrow-band linearly frequency modulated signals phantoms signal-to-noise ratio sinusoidal excitation string phantom synthetic aperture reconstruction synthetic transmit aperture imaging transducer elements ultrasound scanner RASMUS
