Signal processing techniques for operator independent Doppler ultrasound : potential for use in transcranial Doppler ultrasound

2D Doppler ultrasound can be used for continuous monitoring of vasospasm. However, the use of Doppler ultrasound suffers from operator dependence requiring a skilled ultrasonographer to make Doppler angle corrections. The aim of the research is to minimize the need of dedicated ultrasonographers for Doppler ultrasound monitoring of cerebral vasospasms. In this thesis, three studies including a steady flow phantom, pulsatile flow phantom and in vivo human internal carotid artery (ICA) were completed with the use of 3D Doppler ultrasound. The 3D vascular structure of the phantom and ICA were obtained using binary skeletonization from 3D power Doppler images. The vascular structure was used in combination with angle independent pulsed-wave Doppler to reconstruct the temporal blood velocity profiles at various parts of the vasculature. The results indicate that Doppler angle corrections can be minimized with the use of 3D Doppler ultrasound, and operator independent monitoring of blood flow is possible.

Signal processing techniques for operator independent Doppler ultrasound : potential for use in transcranial Doppler ultrasound

2D Doppler ultrasound can be used for continuous monitoring of vasospasm. However, the use of Doppler ultrasound suffers from operator dependence requiring a skilled ultrasonographer to make Doppler angle corrections. The aim of the research is to minimize the need of dedicated ultrasonographers for Doppler ultrasound monitoring of cerebral vasospasms. In this thesis, three studies including a steady flow phantom, pulsatile flow phantom and in vivo human internal carotid artery (ICA) were completed with the use of 3D Doppler ultrasound. The 3D vascular structure of the phantom and ICA were obtained using binary skeletonization from 3D power Doppler images. The vascular structure was used in combination with angle independent pulsed-wave Doppler to reconstruct the temporal blood velocity profiles at various parts of the vasculature. The results indicate that Doppler angle corrections can be minimized with the use of 3D Doppler ultrasound, and operator independent monitoring of blood flow is possible.

Common Doppler artefacts and pitfalls

Artefacts are spurious signals that do not represent true signals or physical structures. It is important to differentiate artefacts from genuine signals in ultrasound studies as this may help avoid misinterpretations and measurement errors. The nature of many Doppler ultrasound artefacts is similar to 2D echocardiography artefacts, including inappropriate gain settings, mirror artefacts, and reverberation artefacts. However, as Doppler ultrasound is used to detect blood flow and myocardial velocity, it is susceptible to insonation (Doppler) angle error, aliasing, and other velocity-related artefacts. These will be presented in this chapter as two main types of artefacts: one that is related to spectral Doppler, and the other related to colour-flow Doppler ultrasound.

Joint Range-Doppler-Angle Estimation for OFDM-Based RadCom System via Tensor Decomposition

Radar and communication (RadCom) systems have received increasing attention due to their high energy efficiency and spectral efficiency. They have been identified as green communications. This paper is concerned with a joint estimation of range-Doppler-angle parameters for an orthogonal frequency division multiplexing (OFDM) based RadCom system. The key idea of the proposed method is to derive different factor matrices by the tensor decomposition method and then extract parameters of the targets from these factor matrices. Different from the classical tensor decomposition method via alternating least squares or higher-order singular value decomposition, we adopt a greedy based method with each step constituted by a rank-1 approximation subproblem. To avoid local extremum, the rank-1 approximation is solved by using a multiple random initialized tensor power method with a comparison procedure followed. A parameterized rectification method is also proposed to incorporate the inherent structures of the factor matrices. The proposed algorithm can estimate all the parameters simultaneously without parameter pairing requirement. The numerical experiments demonstrate superior performance of the proposed algorithm compared with the existing methods.