Comparison of Spatial and Temporal Averaging on Ultrafast Imaging in Presence of Quantization Errors

In compound plane wave imaging (CPWI), multiple plane waves are used to insonify the imaging region with different steering angles. The compounding operation is effectively a spatial averaging filter that reduces the speckles of the image and increases the image contrast and its lateral resolution. Although spatial averaging often improves CPWI image quality, quantization errors which dependent on sampling frequency and element spacing (pitch), introduced during beam steering reduce this improvement. In this study, the effect of spatial and temporal averaging on speckle noise reduction, contrast resolution and spatial resolution in ultrafast ultrasound imaging is evaluated. The overall results from the simulations shows that the maximum effect of quantization errors on speckle noise is 0.18 dB, on the image contrast is 0.27 dB, on axial resolution is 2.38% and finally on lateral resolution is 1.44%. On the other hand, plane wave imaging (PWI) employing temporal averaging technique which is not bound with quantization errors relatively produces high contrast to noise ratio (CNR) and speckle signal to noise ratio (SSNR) at 40 MHz for both centre frequency compared to CPWI

Enhancement of contrast and resolution of B-mode plane wave imaging (PWI) with non-linear filtered delay multiply and sum (FDMAS) beamforming

FDMAS has been successfully used in microwave imaging for breast cancer detection. FDMAS gained its popularity due to its capability to produce results faster than any other adaptive beamforming technique such as minimum variance (MV) which requires higher computational complexity. The average computational time for single point spread function (PSF) at 40 mm depth for FDMAS is 87 times faster than MV. The new beamforming technique has been tested on PSF and cyst phantoms experimentally with the ultrasound array research platform version 2 (UARP II) using a 3-8 MHz 128 element clinical transducer. FDMAS is able to improve both imaging contrast and spatial resolution as compared to DAS. The wire phantom main lobes lateral resolution improved in FDMAS by 40.4% with square pulse excitation signal when compared to DAS. Meanwhile the contrast ratio (CR) obtained for an anechoic cyst located at 15 mm depth for PWI with DAS and FDMAS are -6.2 dB and -14.9 dB respectively. The ability to reduce noise from off axis with auto-correlation operation in FDMAS pave the way to display the B-mode image with high dynamic range. However, the contrast to noise ratio (CNR) measured at same cyst location for FDMAS give less reading compared to DAS. Nevertheless, this drawback can be compensated by applying compound plane wave imaging (CPWI) technique on FDMAS. In overall the new FDMAS beamforming technique outperforms DAS in laboratory experiments by narrowing its main lobes and increases the image contrast without sacrificing its frame rates

A New Nonlinear Compounding Technique for Ultrasound B-mode Medical Imaging

Compounding techniques have been used in ultra-fast ultrasound imaging to improve image quality by reducing clutter noise, smoothing speckle variance and enhancing its spatial resolution at the cost of reducing frame rate. However, the reduction of clutter noise and side lobes inside the anechoic regions is minimal when combining conventional spatial compounding and delay-and-sum (DAS) beamforming. Despite the availability of advanced beamforming algorithms such as filtered-delay-multiply-and-sum (FDMAS), its prevalence is hindered by relatively high computational cost. In this study, a new nonlinear compounding technique known as filtered multiply and sum (FMAS) was proposed to improve the B-mode image quality without increasing the overall computational complexity. With three compunding angles, the lateral resolution for DAS-FMAS was improved by 36% and 19% compared to DAS and FDMAS. The proposed DAS-FMAS technique also provided improvements of 14.1 dB and 7.29 dB in contrast ratio than DAS and FDMAS

A Novel Two-Dimensional Displacement Estimation for Angled Shear Wave Elastography

This study aimed to estimate angled tissue motion for shear wave compounding applications. Shear wave elastography produces the quantitative elasticity biomarker for assessing the health status of tissues. In sheer wave compounding, steered shear waves are generated with different angles, and individual angle elasticity maps are averaged to improve tissue stiffness reconstruction. When shear waves are steered and the tissue motion is generated in multiple directions, traditional one dimensional (1D) displacement estimation fails in capturing actual shear wave amplitude and direction. This study investigated the use of two dimensional (2D) kernel to track angular shear wave motion, which resulted in the underestimation of displacement values. Consequently, a new method named as 2D proposed (2D-P) was used to calculate both axial and lateral motion components separately using 1D axial and lateral kernels. Final results indicated that, the proposed scheme produced an average improvement of 2.01 μm and 4.4 μm compared with the 1D axial cross correlation and 2D cross correlation based methods, respectively

Optimizing the lateral beamforming step for filtered-delay multiply and sum beamforming to improve active contour segmentation using ultrafast ultrasound imaging

As an alternative to delay-and-sum beamforming, a novel beamforming technique called filtered-delay multiply and sum (FDMAS) was introduced recently to improve ultrasound B-mode image quality. Although a considerable amount of work has been performed to evaluate FDMAS performance, no study has yet focused on the beamforming step size, , in the lateral direction. Accordingly, the performance of FDMAS was evaluated in this study by fine-tuning to find its optimal value and improve boundary definition when balloon snake active contour (BSAC) segmentation was applied to a B-mode image in ultrafast imaging. To demonstrate the effect of altering in the lateral direction on FDMAS, measurements were performed on point targets, a tissue-mimicking phantom and in vivo carotid artery, by using the ultrasound array research platform II equipped with one 128-element linear array transducer, which was excited by 2-cycle sinusoidal signals. With 9-angle compounding, results showed that the lateral resolution (LR) of the point target was improved by 67.9% and 81.2%, when measured at −6 dB and −20 dB respectively, when was reduced from to . Meanwhile the image contrast ratio (CR) measured on the CIRS phantom was improved by 10.38 dB at the same reduction and the same number of compounding angles. The enhanced FDMAS results with lower side lobes and less clutter noise in the anechoic regions provides a means to improve boundary definition on a B-mode image when BSAC segmentation is applied

New improved unsharp masking methods compatible with ultrasound B-mode imaging

© 2017 IEEE. In medical ultrasound B-mode imaging, by increasing the image contrast, spatial and temporal resolution, it will help to improve the diagnostic and decision making process. Previously the unsharp masking (UM) techniques have been successfully implemented for digital image processing as edge enhancement techniques. However, the outcomes of the method are limited and influenced by the image formats conversion and lower dynamic range. Moreover the conventional UM technique sensitive to noise due to the presence of linear high pass filter which cannot discriminate signal from noise. Furthermore, the technique only enhances the image in darker compared to lighter regions. To overcome those issues, a new improved UM method compatible with ultrasound B-mode imaging was applied to compound plane wave imaging (CPWI). The received radio frequency (RF) signal was beamformed with delay and sum (DAS) and filtered delay and sum (FDMAS). Results show that the proposed techniques are not only able to improve the image contrast but also the spatial resolution. The UM technique manages to improve the B-mode image lateral resolution (LR) by 18.36% and 10.25% as well as reduced the peak side lobes (PSL) by 16.67 dB and 21.24 dB on DAS and FDMAS respectively when compounded with CPWI, N=13. For the same number of compounding and beamforming order, the image contrast ratio (CR) has been improved by 10.35 dB and 7.39 dB accordingly

New Denoising Unsharp Masking Method for Improved Intima Media Thickness Measurements with Active Contour Segmentation

The semi-automated balloon snake active contour (BSAC) based segmentations play a vital role in determining the intima-media thickness (IMT) for accessing the risk related to cardio vascular diseases (CVD). However, the speckle and clutter noise in the ultrasound B-mode images are known to interfere with the contour formation during segmentation. Both noise sources act as false external energy in BSAC and thus influence the resulting boundary definition. A large number of iterations are required for the BSAC to accurately detect the boundary and in the presence of high noise the segmentation algorithm can result in false detections. Thus in this work we have applied the new denoising unsharp masking (UM) method on human common carotid artery in order to reduce clutter noise in the B-mode image before the segmentation process takes place for faster and accurate IMT measurement. The resuts show the number of iterations needed for BSAC to settle on the final intima-media border is less with UM-DAS (100 iterations) compared to that without the denoising technique, DAS (200 iterations). Thus the proposed UM techniques is able to provide better results with less time in measuring the IMT compared to that using DAS

New improved unsharp masking methods compatible with ultrasound B-mode imaging

In medical ultrasound B-mode imaging, by increasing the image contrast, spatial and temporal resolution, it will help to improve the diagnostic and decision making process. Previously the unsharp masking (UM) techniques have been successfully implemented for digital image processing as edge enhancement techniques. However, the outcomes of the method are limited and influenced by the image formats conversion and lower dynamic range. Moreover the conventional UM technique sensitive to noise due to the presence of linear high pass filter which cannot discriminate signal from noise. Furthermore, the technique only enhances the image in darker compared to lighter regions. To overcome those issues, a new improved UM method compatible with ultrasound B-mode imaging was applied to compound plane wave imaging (CPWI). The received radio frequency (RF) signal was beamformed with delay and sum (DAS) and filtered delay and sum (FDMAS). Results show that the proposed techniques are not only able to improve the image contrast but also the spatial resolution. The UM technique manages to improve the B-mode image lateral resolution (LR) by 18.36% and 10.25% as well as reduced the peak side lobes (PSL) by 16.67 dB and 21.24 dB on DAS and FDMAS respectively when compounded with CPWI, N=13. For the same number of compounding and beamforming order, the image contrast ratio (CR) has been improved by 10.35 dB and 7.39 dB accordingly

Resolving the Effect of Phase Errors on Ultrafast Ultrasound Plane Wave Imaging

The phase error caused by non-ideal physical transducer characteristics can affect the ultrasonic wave front during beamforming. If not compensated, the phase error can degrade the focusing capability and reduce the B-mode image spatial resolution. In this paper, the effect of the phase error on ultrafast coherent plane wave imaging (CPWI) was investigated using a bespoke ultrasound imaging system, ultrasound array research platform II (UARP II). The phase deviations between the aligned radio frequency (RF) signals from all active elements were calculated by applying cross-correlation techniques with the RF signal from the first active element as the registration reference. A sign-reversed lag technique has been applied to the RF signals to encounter the phase error. When the phase error was corrected, the lateral resolution at -6 dB and -20 dB showed improvements from 0.42 mm to 0.34 mm and from 1.18 mm to 0.56 mm, respectively. No significant changes occurred for the axial main lobe