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Image Quality
Published in Kwan Hoong Ng, Jeannie Hsiu Ding Wong, Geoffrey D. Clarke, Problems and Solutions in Medical Physics, 2018
Kwan Hoong Ng, Jeannie Hsiu Ding Wong, Geoffrey D. Clarke
Some examples: In MRI, aliasing causes the appearance of wrap-around, translocation of anatomy from one side of the image to the other.In CT, the body section is sampled by a fan beam consisting of a limited number of X-ray pencil beams, coming from a limited number of directions. If these are too few, the system does not have the information to reproduce sharp high-contrast boundaries, instead ‘low frequency’ streak artefacts are produced.In pulsed Doppler ultrasound, the flow of blood cells is sampled by a series of ultrasound pulses. If the pulse repetition rate is not fast enough, fast flow in one direction will be interpreted as a slower flow in the opposite direction.
Predicting the Biomechanics of the Aorta Using Ultrasound
Published in Ayman El-Baz, Jasjit S. Suri, Cardiovascular Imaging and Image Analysis, 2018
Mansour AlOmran, Alexander Emmott, Richard L. Leask, Kevin Lachapelle
Lastly, Doppler ultrasound technology has also been employed to assess tissue strain. Traditionally, Doppler ultrasound is used to determine the velocity and direction of blood flow by measuring changes in frequency of sound wave reflection off of red blood cells [48]. This same principle was applied to cardiac tissue; most commonly to assess ventricular function by measuring the velocity of the mitral annulus by analyzing the sound waves reflected off of the annulus itself [48]. More recently, aortic wall tissue mechanics were studied using Doppler technology to measure its velocity and direction to estimate the aortic systolic radial strain [57]. Doppler ultrasound technology is highly angle dependent [48], which limits its use only to specific areas of the arterial tree.
Time–Frequency Signal Representations for Biomedical Signals
Published in Hualou Liang, Joseph D. Bronzino, Donald R. Peterson, Biosignal Processing, 2012
G. Faye Boudreaux-Bartels, Robin Murray
The Doppler ultrasound signal is the reflection of an ultrasonic beam due to moving red blood cells and provides information regarding blood vessels and heart chambers. Doppler ultrasound signals in patients with narrowing of the aortic valve were analyzed using the spectrogram by Cloutier et al. (1991). Guo and colleagues (1994) examined and compared the application of five different time-frequency representations (the spectrogram, short-time AR model, CWD, RID, and Bessel distributions) with simulated Doppler ultrasound signals of the femoral artery. Promising results were obtained from the Bessel distribution, the CWD, and the short-time AR model.
Patient-specific hemodynamics simulations: model parameterization from clinical data to enable interventional planning
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Irene E. Vignon-Clementel, Sanjay Pant
Depending on the considered application, available measurements besides imaging data to build the 3D geometry vary. Direct or surrogate measurements of flow and/or pressure are considered:phase-contrast magnetic resonance imaging provides flow rate over time on a surface and if the spatial resolution is fine enough even a velocity profile and its time evolution,catheterization leads to pressure over time at a given location (direct or wedge as a surrogate),Doppler ultrasound can provide maximum (in a small volume) velocity over time, typically interpreted as a flow rate over time assuming a certain flow profile on a surface or by direct integration of the machine.
Recent developments on foaming mechanical and electronic techniques for the management of varicose veins
Published in Expert Review of Medical Devices, 2019
C. Davide Critello, Salvatore A. Pullano, Thomas J. Matula, Stefano De Franciscis, Raffaele Serra, Antonino S. Fiorillo
Sclerotherapy is a common approach for treatment of varicose disease. Its increasing use over other minimally invasive procedures is likely due to its mild effect, good esthetic results, good tolerance, and economic advantage in the short term. As regards the efficacy of foam treatment, several randomized controlled studies showed that foam is inferior to the endovenous ablation and surgical procedures, especially in the long term [95,96]. However, these results could be improved if foam would have been produced according to the usual consensus (1:4 liquid-to-gas ratio) or with further re-treatments. In the past two decades, foam sclerotherapy has acquired a significant role versus the traditional liquid sclerotherapy mainly because of its superior efficacy, especially in large veins (or other venous malformations [97]). Maximum sclerosing action can be obtained at lesser concentration and quantity. Although the first attempt to create sclerosing foam for vein injections dates back in 1939, the treatment became increasingly popular after Cabrera proved the successful efficacy of foams prepared with physiological gas using a rotating brush method. Successively, the introduction of easy, fast and extemporary techniques (Tessari and DSS methods) for foam preparation has increased the use of foam for vascular treatment. Although the Tessari and DSS techniques are in common clinical use, the lack of standardization has always been somewhat controversial. Foam properties can differ because of the manual act of preparation, causing inevitable discrepancies in the efficacy of the treatment. The cause of neurological complications during treatment is probably due to the circulation of bubbles after foam injections, which acting as gas emboli create a temporary mechanical block in cerebral vessels. The clinical outcome of gas embolism depends on bubble size and bubble location in the circulatory system. Researchers have found that venous embolism in some animal models caused by the injection of microbubbles from 60 up to 500 µm in diameter could provoke significant changes in the lungs [98]. Chung et al. [99] evaluated the importance of bubble size on the ability to trigger ischemic events in the brain during cardiac surgery, implementing a computational method for estimating bubble size based on the analysis of Transcranial Doppler ultrasound recordings. Simulated results on gas emboli, moving through a model of arterial vascular system, have shown that bubbles less than 38 μm did not generate any relevant obstruction while those greater than 100 µm would affect partially (up to 2.2%) the circulation for several hours [99]. Therefore, the size of microbubbles constitutes a threat of embolization. While large bubbles have been implicated in risk, small microbubbles are safe since they can pass through the microcirculation, as evidenced in the clinically–approved microbubbles used as contrast agents in CEUS procedures.