Academic literature on the topic 'Transcranial Doppler ultrasound (TCD)'

Background: Stroke is a leading cause of significant physical, cognitive, and psychiatric morbidity. One risk factor for stroke is paradoxical embolization through a patent foramen ovale (PFO). In cardiac clinical practice, power M-mode Transcranial Doppler (TCD) evaluation is the gold standard for diagnosis of PFO, or right-to-left cardiac shunt (RLS). Brain micro-embolization due to diagnostic bubble contrast echocardiography may cause neurological symptoms in patients with PFO. However, the neurocognitive effects of TCD have not been studied. Objective: The purpose of this study was to evaluate cognitive outcomes in patients who undergo routine diagnostic bubble contrast TCD. The aims of the study were (1) to determine if cognitive function declines pre- to post-TCD evaluation and, (2) to assess the relationship between cognitive function and severity of the RLS measured using the Spencer Grading System. Methods: One hundred and four participants referred to Sorensen Cardiovascular Group for diagnosis of RLS were evaluated for changes in cognitive functioning at three time points. A dual baseline (pre-test and baseline test) was administered to mitigate practice effects between the first and second administrations. All pre and post-TCD comparisons were analyzed using the baseline test and post-TCD test, controlling for the effects of practice, if present. Results: Practice effects were observed for the working memory task, with significant improvement in working memory scores occurring between the first (pre-test) and second (baseline) administrations. The main effect for shunt group (no shunt vs. moderate-to-severe shunt) and the shunt group by time interactions were not significant for processing speed, attention, or working memory, adjusting for practice effects, age, and education. Migraine did not predict group status for mood or shunt variables. Conclusion: Cardiac patients with both small and large RLS did not experience a decline in processing speed, attention, or working memory ability following TCD, suggesting that TCD-induced microemboli do not result in immediate cognitive deficits in these domains. These findings support the use of TCD for routine evaluation of PFO, even in patients with severe RLS, although findings are limited to young (30s), medically healthy, predominately Caucasian individuals assessed immediately following TCD. Results do not exclude the possibility of cognitive impairment at follow-up, on other cognitive tests, or in other cognitive domains.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (pages 183-190).<br>Transcranial Doppler (TCD) sonography is a specialized ultrasound technique that enables measurement of blood ow velocity from the basal intracerebral vessels. Use of TCD sonography is highly compelling as a diagnostic modality due to its safety in prolonged studies, high temporal resolution, and relative portability. Although TCD methods have been clinically indicated in a variety of cerebrovascular diagnostic applications, general acceptance by the medical community has been impeded by several critical deficiencies { including the need for a highly-trained TCD operator, operator dependent measurement results, and severe patient movement restrictions. This thesis seeks to mitigate such limitations through the development of a compact, wearable TCD ultrasound system, permitting untethered cerebrovascular monitoring with limited operator interaction. The prototype system incorporates a custom two-dimensional transducer array and multi-channel transceiver electronics, thereby facilitating acoustic focusing via phased array operation. Algorithmic vessel search and tracking further reduce operator dependencies by expediting vessel localization, systematizing vessel identification, and dynamically adapting to relative vessel position. Additionally, focal correction methods are presented, which improve acoustic beamformation capabilities in the presence of tissue inhomogeneities. Validation of the prototype hardware and embedded signal processing implementations under flow phantom and human subject testing yields high correlation with accepted velocimetry methods. Vessel search and tracking functionality are also verified experimentally. Circuit integration is explored to further reduce instrumentation dimensions and power consumption.<br>by Sabino Joseph Pietrangelo.<br>Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 137-144).<br>This thesis details the design of a transcranial Doppler (TCD) ultrasound system to measure cerebral blood flow velocity (CBFV) at the middle cerebral artery (MCA). TCD sonography has been clinically indicated in a variety of neurovascular diagnostic applications. Acceptance of conventional TCD methods, however, has been primarily impeded by several constraints, including restrictive system form factors, measurement reliability concerns, and the need for a highly-skilled operator. The goal of this work is to reduce the effects of such limitations through the development of a highly-compact, wearable TCD ultrasound system for autonomous CBFV measurement. A first-generation, eight channel printed circuit board prototype system has been designed, fabricated, and experimentally tested. Characterization of the prototype system using a Doppler flow phantom resulted in a normalized root-mean-square error of < 3.5% over the range of expected in vivo MCA flow velocities. Extension of the initial prototype to higher channel count systems and the development of phased array beamformation and algorithmic vessel location are also examined in this work. The emergence of simple, robust, and non-invasive neurovascular diagnostic methods presents an enormous opportunity for the advancement of neurovascular monitoring, particularly in applications where - due to restrictions in current diagnostic modalities - standard monitoring procedures have not yet been established.<br>by Sabino Joseph Pietrangelo.<br>S.M.

The detection of micro-embolic signals (MES) is a mature application of transcranial Doppler (TCD) ultrasound. It involves the identification of abnormally highpitched signals within the arterial waveform as a method of diagnosis and prediction of embolic complications in stroke patients. More recently, algorithms have been developed to help characterise and classify MES using advanced signal processing techniques. These advances aim to improve our understanding of the causes of cereberovascular disease, helping to target the most appropriate interventions and quantifying the risk to patients of further stroke events. However, there are a number of limitations with current TCD systems which reduce their effectiveness. In particular, improvements in our understanding of the scattering effects in TCD ultrasound propagation channels will benefit our ability to develop algorithms that more robustly and reliably identify the consistency and material make-up of MES. This thesis explores TCD propagation channels in three related research areas. Firstly, a method of characterising TCD ultrasound propagation channels is proposed. Isotropic and non-isotropic three dimensional space (3-D) spherical scattering channel models are described in terms of theoretical reference models, simulation models, and sum of sinusoids (SoS) simulators, allowing the statistical properties to be analysed and reported. Secondly, a TCD ultrasound medical blood flow phantom is described. The phantom, designed to replicate blood flow in the middle cerebral arteries (MCA) for TCD ultrasound studies, is discussed in terms of material selection, physical construction and acoustic characteristics, including acoustic velocity, attenuation and backscatter coefficients. Finally, verification analysis is performed on the non-isotropic models against firstly, the blood flow phantom, and secondly, a patient recordings database. This analysis expands on areas of agreement and disagreement before assessing the usefulness of the models and describing their potential to improve signal processing approaches for detection of MES. The proposed non-isotropic channel reference model, simulation model, SoS simulator, and blood flow phantom are expected to contribute to improvements in the design, testing, and performance evaluation of future TCD ultrasound systems.

Estimates of the capacity of visuospatial short-term memory (VSTM) have ranged from less than 1 item to 4 +/- 1 items. The purpose of the present study was to find the capacity of VSTM by looking at the contribution of the other working memory systems (phonological loop and central executive) and determine the factor that limits VSTM capacity (either number of objects or object complexity). In this study, the psychophysiological measure of cerebral blood flow velocity also was incorporated to determine whether changes in cerebral blood flow velocity were indicative of VSTM performance and capacity. Both performance measures and cerebral blood flow velocity indicate that capacity for random polygons is approximately one object. Complexity of the objects affected capacity, such that simple objects had higher capacities and lower cerebral blood flow velocity than complex objects. Other working memory systems were not found to have an effect on performance.