Quantitative Detection of Circulating Embolic Materials With Doppler Ultrasound

Yang, Yi (1995) Quantitative Detection of Circulating Embolic Materials With Doppler Ultrasound. PhD thesis, University of Glasgow.

Abstract

1. Detection, quantification and differentiation of circulating embolic materials and other related heamodynamic phenomena was performed in middle cerebral artery (MCA) in vitro models using trancranial Doppler (TCD) ultrasonography. Signal intensity analysis was used as a major measurement method to quantify the Doppler signals in this study. The validity of this method was also examined in experimental and clinical settings 2. In an MCA in vitro model, the ability of TCD to detect microbubbles was initially evaluated. Two sizes of microbubbles (5 mum and 30 mum) were prepared in Ultravist 370 (a contrast medium) and 5% albumin respectively. TCD proved to be sensitive to detect microbubbles as small as 5 mum in diameter. The correlation between embolic signal intensity and the number of microbubbles was investigated in twoconcentrations of microbubbles with signal intensity analysis. It was found that embolic signal intensity was proportional to the increase in the number of microbubbles present in the Doppler sample volume. However, this relationship tended to weaken at higher concentrations of microbubbles. 3. In the same model, the relationship between embolic signal intensity and the size of emboli of different sources was examined and the signal intensities caused by different embolic materials were compared. Seven types of embolic material were prepared and studied in this test. A quantitative relationship existed between the embolic signal intensity and the size of all the types of emboli tested. Air bubble emboli caused higher signal intensity than that caused by any solid embolic materials. Among the solid emboli at an average size of 100 mum, platelet-rich thrombin produced the highest signal intensity. Further, the suitability of using total embolic signal intensity to differentiate the different sources of embolic was studied. It was found that an assigned embolic signal intensity could be produced by a small but highly reflective type of embolus or a larger but less reflective type of embolus. 4. In an modified MCA model, spontaneous contrast echo was reproduced in a expansion chamber under low flow conditions. With a two-dimensional cardiosonography system and TCD, the differentiation of spontaneous contrast from emboli was carried out by both visual observation of the echo images and Doppler signal intensity analysis. Spontaneous contrast was distinct from emboli (whole blood clots, platelet-rich thrombin, and microbubbles) in echographic appearances and Doppler signal intensity. 5. The relationship between average signal intensity and the degree of stenosis of the MCA and the differentiation of turbulence from embolic signals were examined in a stenotic in vitro MCA model. A series of short, asymmetric stenoses were prepared in this test. Transition of turbulence from the laminar flow began to occur at a moderate degree of stenosis (55%) but became dump at the high degrees of stenoses (75% and 85%). Turbulence caused a significant increase in Doppler signal intensity. However, The degree of stenosis was not associated with signal intensity at the region of the turbulence but was related to the mean flow velocity through the narrowed region. Air bubbles (30 mum) and platelet-rich clots (100 mum) had a significantly higher signal intensity than the signal intensity through areas of turbulence. All the tested embolic signals showed different Doppler characteristics from the signals associated with turbulent flow. 6. The effect of transmitting frequency and flow velocity on ultrasonic quantification of emboli was investigated in an modified MCA model. A measured platelet-rich clot (2 x 2 x 2 mm for flow velocity test and l x l x l mm for transmitting frequency test) was repeatedly introduced into the model at different settings (23 cm/sec and 40 cm/sec for mean velocity settings; 2 MHz, 4 MHz, and 8 MHz for transmitting frequency settings). An embolus floating at a high flow velocity had a lower increase in total signal intensity and shorter duration of passage than an embolus passing at low flow velocity. The intensity of embolic signals recorded from a probe with lower transmitting frequency was significantly higher than that by a probe with higher frequency. Similarly, the duration of embolic signal was inversely proportional to the transmitting frequency of the probe. 7. Quantitative detection of cerebral emboli from the MCA was studied in 16 patients undergoing cardiac catheterisation. A continuous TCD recording was made throughout the procedure and the occurrence and intensity of embolic signals were examined in relation to different steps of the catheerisation. Embolic signal intensity was also correlated to the in vitro findings. In descending order of frequency, ventriculogram, change of the catheter guidewire, and catheter manipulation contributed to the highest incidence of cerebral emboli and to the highest embolic signal intensities. Embolic signals occurring during catheter insertion and catheter manipulation often showed lower intensities compared to those generated by the injection of normal saline at the level of the ascending aorta or within the left ventricle. The intensities from the former were equal to the intensities caused by atheroma materials (100 mum) in vitro and the intensities from the latter were similar to the intensities produced by microbubbles (30 mum) in vitro.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Donald G Grosset
• Keywords: Biomedical engineering, Acoustics
• Date of Award: 1995
• Depositing User: Enlighten Team
• Unique ID: glathesis:1995-75556
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 19:28
• Last Modified: 19 Nov 2019 19:28
• URI: https://theses.gla.ac.uk/id/eprint/75556