A New Adaptive Imaging Technique Using Generalized Delay Multiply and Sum Factor

Coherent multi-transducer ultrasound (CoMTUS) imaging enables the use of multiple arrays as one large effective aperture. This yields images with enlarged field-of-view, improved resolution, and higher SNR. However, creating a large but discontinuous effective aperture increases the grating and side lobe levels and generates cross-talk artifacts from the direct transmissions between arrays. These additional challenges can degrade the contrast of the images obtained through the classic Delay and Sum (DAS) beamforming algorithm. This study investigates the use of an alternative nonlinear beamforming algorithm, the Delay Multiply and Sum (DMAS), to improve contrast and reduce cross-talk artifacts in CoMTUS. We adapted the original DMAS beamforming algorithm to the specific effective aperture of CoMTUS and tested its performance in a coherent dual-array system for both 2-D and 3-D imaging. The comparison between images obtained through CoMTUS DMAS and DAS was investigated by both 2-D and 3-D simulations and experiments. DMAS was shown effective to lower the side lobes and the noise floor, thus improving the detectability of cystic lesions.

In this research work, a novel framework is proposed as an efficient successor to traditional imaging methods for breast cancer detection in order to decrease the computational complexity. In this framework, the breast is divided into segments in an iterative process and in each iteration, the one having the most probability of containing tumor with lowest possible resolution is selected by using suitable decision metrics. After finding the smallest tumor-containing segment, the resolution is increased in the detected tumor-containing segment, leaving the other parts of the breast image with low resolution. Our framework is applied on the most common used beamforming techniques, such as delay and sum (DAS) and delay multiply and sum (DMAS) and according to simulation results, our framework can decrease the computational complexity significantly for both DAS and DMAS without imposing any degradation on accuracy of basic algorithms. The amount of complexity reduction can be determined manually or automatically based on two proposed methods that are described in this framework.

In photoacoustic imaging, delay-and-sum (DAS) beamformer is a common beamforming algorithm having a simple implementation. However, it results in a poor resolution and high sidelobes. To address these challenges, a new algorithm namely delay-multiply-and-sum (DMAS) was introduced having lower sidelobes compared to DAS. To improve the resolution of DMAS, a beamformer is introduced using minimum variance (MV) adaptive beamforming combined with DMAS, so-called minimum variance-based DMAS (MVB-DMAS). It is shown that expanding the DMAS equation results in multiple terms representing a DAS algebra. It is proposed to use the MV adaptive beamformer instead of the existing DAS. MVB-DMAS is evaluated numerically and experimentally. In particular, at the depth of 45mm MVB-DMAS results in about 31, 18, and 8dB sidelobes reduction compared to DAS, MV, and DMAS, respectively. The quantitative results of the simulations show that MVB-DMAS leads to improvement in full-width-half-maximum about 96%, 94%, and 45% and signal-to-noise ratio about 89%, 15%, and 35% compared to DAS, DMAS, MV, respectively. In particular, at the depth of 33mm of the experimental images, MVB-DMAS results in about 20dB sidelobes reduction in comparison with other beamformers.

Ultrasound-induced cavitation is a fundamental physical phenomenon for histotripsy, lithotripsy, and local drug delivery. Magnetic nanoparticles (MNPs) enable magnetically assisted cancer therapy (Magnetic Drug Targeting, MDT) and can be used as cavitation nuclei. While MDT has shown promising results in preclinical studies, there remains a need for a real-time monitoring system. Here, we introduce a GPU-accelerated passive cavitation mapping (PCM) method that pairs a third-degree delay-multiply-and-sum beamformer (DMAS3) with coherence-factor weighting (CFwDMAS3) to enhance spatial localization and suppress off-axis incoherent emissions. We evaluated the approach in a flow-channel phantom perfused with lauric-acid–coated MNPs under pulsed focused ultrasound, and complemented the experiments with simulations based on Vokurka’s bubble-dynamics model. Reconstructions using Delay and Sum (DAS), Delay Multiply and Sum (DMAS), and DMAS3, each with and without CF weighting, were assessed using ROC metrics (AUROC, sensitivity, specificity) and precision measures (PPV, F1-score). CF weighting consistently produced sharper maps and higher specificity; CFwDMAS3 achieved the best overall balance and supported real-time visualization (approximately 0.1 s per frame) on a GPU. These results indicate that CFwDMAS3 PCM is a practical solution for monitoring MNP-mediated cavitation during MDT and related therapeutic ultrasound procedures.

Photoacoustic imaging (PAI), is a promising medical imaging technique that\nprovides the high contrast of the optical imaging and the resolution of\nultrasound (US) imaging. Among all the methods, Three-dimensional (3D) PAI\nprovides a high resolution and accuracy. One of the most common algorithms for\n3D PA image reconstruction is delay-and-sum (DAS). However, the quality of the\nreconstructed image obtained from this algorithm is not satisfying, having high\nlevel of sidelobes and a wide mainlobe. In this paper, delay-multiply-and-sum\n(DMAS) algorithm is suggested to overcome these limitations in 3D PAI. It is\nshown that DMAS algorithm is an appropriate reconstruction technique for 3D PAI\nand the reconstructed images using this algorithm are improved in the terms of\nthe width of mainlobe and sidelobes, compared to DAS. Also, the quantitative\nresults show that DMAS improves signal-to-noise ratio (SNR) and\nfull-width-half-maximum (FWHM) for about 25 dB and 0.2 mm, respectively,\ncompared to DAS.\n

Various methods have been proposed to estimate the tissue speed of sound (SOS) of propagating medium using the curvature of received channel waveform or the analysis of resultant image quality. In our previous study, baseband delay-multiply-and-sum (DMAS) beamforming methods have been developed for multi-angle plane-wave (PW) imaging which relies on signal coherence among transmit events (Tx-DMAS) or receive channel (Rx-DMAS) or both (2D-DMAS) to suppress low-coherence clutters. In this study, we further extend our DMAS beamforming to quantify the level of signal coherence for determining the average SOS in multi-angle PW imaging. The signal coherence in multi-angle PW imaging is represented as the phase coherence factor (PCF) which can be easily estimated from the magnitude ratio of the pixel value of DMAS image to that of DAS image. By searching the beamforming velocity that provides the highest signal coherence of echo matrix, the averaged tissue SOS of the image object can be determined. For the PICMUS experimental dataset, the optimal beamforming velocity $(C_{opt})$ estimated by the proposed PCF method does provide the best image quality. For the Prodigy dataset, the estimated tissue SOS is 1426±6 m/s which is very close to the actual tissue SOS of 1427 m/s and the estimated SOS also corresponds to the $C_{opt}$ with the minimal −6-dB LW and the maximal CR within an error of 10 m/s.

Photoacoustic imaging (PAI) is a promising medical imaging modality providing the spatial resolution of ultrasound imaging and the contrast of optical imaging. For linear-array PAI, a beamformer can be used as the reconstruction algorithm. Delay-and-sum (DAS) is the most prevalent beamforming algorithm in PAI. However, using DAS beamformer leads to low-resolution images as well as high sidelobes due to nondesired contribution of off-axis signals. Coherence factor (CF) is a weighting method in which each pixel of the reconstructed image is weighted, based on the spatial spectrum of the aperture, to mainly improve the contrast. We demonstrate that the numerator of the formula of CF contains a DAS algebra and propose the use of a delay-multiply-and-sum beamformer instead of the available DAS on the numerator. The proposed weighting technique, modified CF (MCF), has been evaluated numerically and experimentally compared to CF. It was shown that MCF leads to lower sidelobes and better detectable targets. The quantitative results of the experiment (using wire targets) show that MCF leads to for about 45% and 40% improvement, in comparison with CF, in the terms of signal-to-noise ratio and full-width-half-maximum, respectively.

Effects of Phase Aberration and Noise on Extended High Frame Rate Imaging

To prospectively compare iopamidol 370, which is a low-osmolar contrast medium and iodixanol 320, which is an iso-osmolar contrast medium, in terms of image quality and nonserious adverse effects that have the potential to influence the image quality in a 16-slice multi-detector row computed tomography coronary angiography. Sixty patients were divided into two groups to receive iodixanol 320 or iopamidol 370. Image quality was assessed, using a five-point grading scale. Differences in the mean attenuation (Hounsfield units) at the origin of the coronary arteries and on the ascending aorta in both the groups were compared. The number and intensity of adverse effects were compared between the two groups. The mean attenuation values of the ascending aorta and the origins of the coronary arteries for the two groups showed no significant difference (P≥0.41). There was no significant difference in terms of image quality between the two groups on all evaluated segments. There was a statistically significant difference in the number of adverse effects (P=0.001) between the two groups. However, in both the iodixanol group and the iopamidol group, there was no significant difference in terms of image quality between the patients with and without adverse effects. The frequency of adverse effects is lower in the iodixanol group than the iopamidol group. Iodixanol 320 can provide both vascular enhancement and image quality, which is similar to iopamidol 370 in a 16-slice multi-detector row computed tomography coronary angiography. There was no significant difference in terms of overall image quality between the patients with and without adverse effects in either of the groups.

Plane wave ultrasound imaging using compressive sensing and minimum variance beamforming

In this paper, we report the design and development of a metamaterial (MTM)-based directional coplanar waveguide (CPW)-fed reconfigurable textile antenna using radiofrequency (RF) varactor diodes for microwave breast imaging. Both simulation and measurement results of the proposed MTM-based CPW-fed reconfigurable textile antenna revealed a continuous frequency reconfiguration to a distinct frequency band between 2.42 GHz and 3.2 GHz with a frequency ratio of 2.33:1, and with a static bandwidth at 4–15 GHz. The results also indicated that directional radiation pattern could be produced at the frequency reconfigurable region and the antenna had a peak gain of 7.56 dBi with an average efficiency of more than 67%. The MTM-based reconfigurable antenna was also tested under the deformed condition and analysed in the vicinity of the breast phantom. This microwave imaging system was used to perform simulation and measurement experiments on a custom-fabricated realistic breast phantom with heterogeneous tissue composition with image reconstruction using delay-and-sum (DAS) and delay-multiply-and-sum (DMAS) algorithms. Given that the MWI system was capable of detecting a cancer as small as 10 mm in the breast phantom, we propose that this technique may be used clinically for the detection of breast cancer.

In this paper, a novel processing framework is introduced for Fourier-domain beamforming of plane-wave ultrasound data, which incorporates coherent compounding and angular weighting in the Fourier domain. Angular weighting implies spectral weighting by a 2-D steering-angle-dependent filtering template. The design of this filter is also optimized as part of this paper. Two widely used Fourier-domain plane-wave ultrasound beamforming methods, i.e., Lu's f-k and Stolt's f-k methods, were integrated in the framework. To enable coherent compounding in Fourier domain for the Stolt's f-k method, the original Stolt's f-k method was modified to achieve alignment of the spectra for different steering angles in k-space. The performance of the framework was compared for both methods with and without angular weighting using experimentally obtained data sets (phantom and in vivo), and data sets (phantom) provided by the IEEE IUS 2016 plane-wave beamforming challenge. The addition of angular weighting enhanced the image contrast while preserving image resolution. This resulted in images of equal quality as those obtained by conventionally used delay-and-sum (DAS) beamforming with apodization and coherent compounding. Given the lower computational load of the proposed framework compared to DAS, to our knowledge it can, therefore, be concluded that it outperforms commonly used beamforming methods such as Stolt's f-k, Lu's f-k, and DAS.

Based on the high frame rate (HFR) imaging method developed in our lab, an extended high frame rate imaging method with various transmission schemes was developed recently. In this method, multiple, limited-diffraction array beams or steered plane wave transmissions are used to increase image resolution and field of view as well as to reduce sidelobes. Furthermore, the multiple, limited-diffraction array beam transmissions can be approximated with square-wave aperture weightings, allowing one or two transmitters to be used with a multielement array transducer to simplify imaging systems. By varying the number of transmissions, the extended HFR imaging method allows a continuous trade-off between image quality and frame rate. Because multiple transmissions are needed to obtain one frame of image for the method, motion could cause phase misalignment and thus produce artifacts, reducing image contrast and resolution and leading to an inaccurate clinical interpretation of images. Therefore, it is important to study how motion affects the method and provide a useful guidance of using the method properly in various applications. In this paper, computer simulations, in vitro and in vivo experiments were performed to study the effects of motion on the method in different conditions. Results show that a number of factors may affect the motion effects. However, it was found that the extended HFR imaging method is not sensitive to the motions commonly encountered in the clinical applications, as is demonstrated by an in vivo heart experiment, unless the number of transmissions is large and objects are moving at a high velocity near the surface of a transducer.

Magnetic Resonance Imaging (MRI) is known to be significantly affected by a number of acquisition artifacts, such as intensity non-standardness, bias field, and Gaussian noise. These artifacts degrade MR image quality significantly, obfuscating anatomical and physiological detail and hence need to be corrected for to facilitate application of computerized analysis techniques such as segmentation, registration, and classification. Specifically, algorithms are required to correct for bias field (intensity inhomogeneity), intensity non-standardness (drift in tissue intensities across patient acquisitions), and Gaussian noise, an artifact that significantly affects and blurs tissue boundaries (resulting in poor gradients). While clearly one needs to correct for all these artifacts, the exact sequence in which all three operations need to be applied in order to maximize MR image quality has not been explored. In this paper, we empirically evaluate the interplay between distinct algorithms for bias field correction (BFC), intensity standardization (IS), and noise filtering (NF) to study the effect of these operations on image quality in the context of 3 Tesla T2-weighted (T2w) prostate MRI. 7 different sequences comprising combinations of BFC, IS, and NF were quantitatively evaluated in terms of the percent coefficient of variation (%CV), a statistic which attempts to quantify the intensity inhomogeneity within a region of interest (prostate). The different combinations were also independently evaluated in the context of a classifier scheme for detection of prostate cancer on high resolution in vivo T2w prostate MRI. A secondary contribution of this work is a novel evaluation measure for quantifying the level of intensity non-standardness, called difference of modes (DoM). Experimental evaluation of the different sequences of operations across 22 patient datasets revealed that the sequence of BFC, followed by NF, and IS provided the best image quality in terms of %CV as well as classifier accuracy. The DoM measure was able to accurately capture the level of intensity non-standardness present in the images resulting from the different sequences of operations.

Controlled experiments were designed to evaluate the high frame rate (HFR) imaging method and compare it with the conventional D&S method on sidelobe, spatial resolution, contrast resolution, and detectability. A point object or modified ATS512 contrast-detail tissue-mimicking phantom was placed in a water tank, and a modified Acuson V2 array transducer was used. RF echoes were obtained with a homemade HFR imaging system. Data were constructed with both the Fourier-based method (with 1, 11, 19, and 91 transmissions) and the D&S method of 91 transmissions. The Fourier-based method provides a continuous compromise between image frame rate and image quality. At the same frame rate (91 transmissions), the Fourier-based method has a higher resolution and lower sidelobe than the D&S method, even at its transmission focal distance.