Filtered-Delay Multiply And Sum Research Articles

Experimental evaluation of ultrasound higher-order harmonic imaging with Filtered-Delay Multiply And Sum (F-DMAS) non-linear beamforming

Tissue Harmonic Imaging (THI) mode is currently one of the preferred choices by the clinicians for its ability to provide enhanced ultrasound images, thanks to the use of the second harmonic component of backscattered echoes. This paper aims at investigating whether the combination of THI with Filtered-Delay Multiply And Sum (F-DMAS) beamforming can provide further improvements in image quality. F-DMAS is a new non-linear beamformer, which, similarly to THI, is based on the use of the second harmonics of beamformed signals and is known to increase image contrast resolution and noise rejection. Thus, we have first compared the images obtained by using F-DMAS and the standard Delay And Sum (DAS) beamformers when only the second harmonics of the received signals was selected. Moreover, possible improvements brought about by other harmonic components generated by the combined use of the fundamental plus second harmonics and F-DMAS beamforming have been explored. Experimental results demonstrate that, as compared to standard harmonic imaging with DAS, THI and F-DMAS can be joined to improve the −20 dB lateral resolution up to 1 mm, the contrast ratio up to 12 dB on a cyst-phantom and up to 9 dB on in vivo images.

Ultrafast ultrasound imaging temporal resolution enhancement with filtered delay multiply and sum (FDMAS) beamforming

FDMAS beamforming technique have been employed with low number of steering angles and smaller lateral steps in order to improve the image quality for better cyst classification. Taking advantage of the autocorrelation process in FDMAS, lateral steps were reduced in order to calculate the time delay for the RF signal more accurately. The new beamforming technique has been tested on CIRS phantoms experimentally with the ultrasound array research platform version 2 (UARP II) using a 3-8 MHz 128 element clinical transducer. The point spread function (PSF) main lobes lateral resolution measured at 20 dB shows an improvement of 65.8% for lateral steps λ to λ/5. Meanwhile, the contrast ratio (CR) obtained for an anechoic cyst size 1 mm in diameter located at 15 mm depth with lateral steps of λ and λ/5 are -11.7 dB and -18.36 dB, respectively. The contrast to noise ratio (CNR) also shows improvement of 17.6% for the same lateral steps reduction. In conclusion, reducing lateral steps in FDMAS beamforming technique with low number of steering angles outperforms DAS with a high number of steering angles in laboratory experiments by narrowing its main lobes and increasing the image contrast thus improve the temporal resolution.

Depth-of-field enhancement in Filtered-Delay Multiply and Sum beamformed images using Synthetic Aperture Focusing

The Synthetic Aperture Focusing (SAF) technique makes it possible to achieve a higher and more uniform quality of ultrasound images throughout depth, as if both transmit and receive dynamic focusing were applied.In this work we combine a particular implementation of SAF, called Synthetic Transmit Aperture (STA) technique, in which a single element in turn transmits and all the array elements receive the ultrasound wave, with the Filtered-Delay Multiply and Sum (F-DMAS) non-linear beamforming algorithm that we presented in a previous paper. We show that using F-DMAS, which is based on a measure of backscattered signal spatial correlation, B-mode images have a higher contrast resolution but suffer from a loss of brightness away from the transmit focus, when a classical scan with receive-only dynamic focusing is performed. On the other hand, when synthetic transmit focusing is achieved by implementing STA, such a loss is compensated for and a higher depth of field is obtained, as signal coherence improves. A drawback of SAF/STA however is the reduced signal-to-noise ratio, due to single-element transmission; in the paper we also analyze how this influences F-DMAS images. Finally, a preliminary investigation on the use of the classical monostatic SAF technique with F-DMAS beamforming is also carried out to evaluate its potential performances.

High Frame-Rate, High Resolution Ultrasound Imaging With Multi-Line Transmission and Filtered-Delay Multiply And Sum Beamforming.

Multi-Line Transmission (MLT) was recently demonstrated as a valuable tool to increase the frame rate of ultrasound images. In this approach, the multiple beams that are simultaneously transmitted may determine cross-talk artifacts that are typically reduced, although not eliminated, by the use of Tukey apodization on both transmission and reception apertures, which unfortunately worsens the image lateral resolution. In this paper we investigate the combination, and related performance, of Filtered-Delay Multiply And Sum (F-DMAS) beamforming with MLT for high frame-rate ultrasound imaging. F-DMAS is a non-linear beamformer based on the computation of the receive aperture spatial autocorrelation, which was recently proposed for use in ultrasound B-mode imaging by some of the authors. The main advantages of such beamformer are the improved contrast resolution, obtained by lowering the beam side lobes and narrowing the main lobe, and the increased noise rejection. This study shows that in MLT images, compared to standard Delay And Sum (DAS) beamforming including Tukey apodization, F-DMAS beamforming yields better suppression of cross-talk and improved lateral resolution. The method's effectiveness is demonstrated by simulations and phantom experiments. Preliminary in vivo cardiac images also show that the frame rate can be improved up to 8-fold by combining F-DMAS and MLT without affecting the image quality.