The Research of Sequential Images: Rebuilding of Gray (Position) ~ Time Function on Direction Lines and Their Applications

Contrasted with other information carriers, such as speech and text, images contains larger amount of information, especially in sequential images, that is waiting to be exploited, in particular the dynamic information of correlation, difference, and temporal relationship between different frames. This dynamic information contributes a great deal in analysis of 4D images. This paper proposes a method for detecting dynamic information from sequential images, based on the rebuilding of their gray (position)~time function on direction lines, an approach that has been analyzed and studied extensively on the setting of various direction lines. This method is based on motion that is presented on sequential images. In particular, the method, Omni directional M-mode Echocardiography system, which we have studied extensively, will be described leading to a robust way of diagnosing heart diseases

Adaptive windowing in contrast-enhanced intravascular ultrasound imaging

Intravascular ultrasound (IVUS) is one of the most commonly-used interventional imaging techniques and has seen recent innovations which attempt to characterize the risk posed by atherosclerotic plaques. One such development is the use of microbubble contrast agents to image vasa vasorum, fine vessels which supply oxygen and nutrients to the walls of coronary arteries and typically have diameters less than 200 µm. The degree of vasa vasorum neovascularization within plaques is positively correlated with plaque vulnerability. Having recently presented a prototype dual-frequency transducer for contrast agent-specific intravascular imaging, here we describe signal processing approaches based on minimum variance (MV) beamforming and the phase coherence factor (PCF) for improving the spatial resolution and contrast-to-tissue ratio (CTR) in IVUS imaging. These approaches are examined through simulations, phantom studies, ex vivo studies in porcine arteries, and in vivo studies in chicken embryos. In phantom studies, PCF processing improved CTR by a mean of 4.2 dB, while combined MV and PCF processing improved spatial resolution by 41.7%. Improvements of 2.2 dB in CTR and 37.2% in resolution were observed in vivo. Applying these processing strategies can enhance image quality in conventional B-mode IVUS or in contrast-enhanced IVUS, where signal-to-noise ratio is relatively low and resolution is at a premium

A transesophageal phased array transducer for ultrasonic imaging of the heart

In this thesis the development of a miniaturized phased array ultrasound transducer is described. The application of this transducer in the field of echocardiology is devoted to transesophageal cross-sectional scanning of the heart and its great vessels. The enormous increase in diagnostic applications of ultrasound over the last three decades is particularly due to the non-invasive character of this technique. Consequently the developments of transcutaneous scanning techniques have outnumbered all other possibilities, but researchers have continuously been investigating the alternatives of scanning organs from within the human body. In those patients in whom inhibiting factors preclude adequate diagnostic information to be obtained transcutaneously, alternative scanning techniques still may-provide vital information. For cardiac imaging two possibilities exist to enter the human body, invasively by means of a catheter or 'non-invasively' by means of an endoscope. In Chapter I, the introduction, our early experiences with a catheter-mounted scanning system are described. The limited possibilities of such a system combined with the inherent technological complications, as well as the invasive character of such a technique favoured the search for a different approach. The idea to advance in the catheter direction was never left but first the experience gained has been applied to transesophageal scanning with an endoscope-mounted transducer as described in this thesis

High-resolution sub-millimetre diameter side-viewing all-optical ultrasound transducer based on a single dual-clad optical fibre

All-optical ultrasound (OpUS), where ultrasound is both generated and received using light, has emerged as a modality well-suited to highly miniaturised applications. In this work we present a proof-of-concept OpUS transducer built onto a single optical fibre with a highly miniaturised lateral dimension (0.4 MPa and a corresponding bandwidth >27 MHz. Concurrent ultrasound generation and reception from the transducer enabled imaging via motorised pull-back allowing image acquisition times of 4 s for an aperture of 20 mm. Image resolution was as low as ~50 µm and 190 µm in the axial and lateral extents, respectively, without the need for image reconstruction. Porcine aorta was imaged ex vivo demonstrating detailed ultrasound images. The unprecedented level of miniaturisation along with the high image quality produced by this device represents a radical new paradigm for minimally invasive imaging

Boosting transducer matrix sensitivity for 3D large field ultrasound localization microscopy using a multi-lens diffracting layer: a simulation study

Mapping blood microflows of the whole brain is crucial for early diagnosis of cerebral diseases. Ultrasound localization microscopy (ULM) was recently applied to map and quantify blood microflows in 2D in the brain of adult patients down to the micron scale. Whole brain 3D clinical ULM remains challenging due to the transcranial energy loss which significantly reduces the imaging sensitivity. Large aperture probes with a large surface can increase both resolution and sensitivity. However, a large active surface implies thousands of acoustic elements, with limited clinical translation. In this study, we investigate via simulations a new high-sensitive 3D imaging approach based on large diverging elements, combined with an adapted beamforming with corrected delay laws, to increase sensitivity. First, pressure fields from single elements with different sizes and shapes were simulated. High directivity was measured for curved element while maintaining high transmit pressure. Matrix arrays of 256 elements with a dimension of 10x10 cm with small ( $\lambda$ /2), large (4 $\lambda$ ), and curved elements (4 $\lambda$ ) were compared through point spread functions analysis. A large synthetic microvessel phantom filled with 100 microbubbles per frame was imaged using the matrix arrays in a transcranial configuration. 93% of the bubbles were detected with the proposed approach demonstrating that the multi-lens diffracting layer has a strong potential to enable 3D ULM over a large field of view through the bones

Acoustic sizing of an ultrasound contrast agent

Because the properties of ultrasound contrast agent populations after administration to patients are largely unknown, methods able to study them noninvasively are required. In this study, we acoustically performed a size distribution measurement of the ultrasound contrast agent Definity®. Single lipid-shelled microbubbles were insonified at 25 MHz, which is considerably higher than their resonance frequency, so that their acoustic responses depended on their geometrical cross sections only. We calculated the size of each microbubble from their measured backscattered pressures. The acoustic size measurements were compared with optical reference size measurements to test their accuracy. Our acoustic sizing method was applied to 88 individual Definity® bubbles to derive a size distribution of this agent. The size distribution obtained acoustically showed a mean diameter (2.5 μm) and a standard deviation (0.9 μm) in agreement within 8% with the optical reference measurement. At 25 MHz, this method can be applied to bubble sizes larger than 1.2 μm in diameter. It was observed that similar sized bubbles can give different responses (up to a factor 1.5), probably because of shell differences. These limitations should be taken into account when implementing the method in vivo. This acoustic sizing method has potential for estimating the size distribution of an ultrasound contrast agent noninvasivel