PSV estimation variations following doppler ultrasound setting changes

Transcription

1 PSV estimation variations following doppler ultrasound setting changes Poster No.: C-3213 Congress: ECR 2010 Type: Scientific Exhibit Topic: Vascular Authors: S. Mirsadraee, A. Evans, D. O. Kessel; Leeds/UK Keywords: Doppler Phantom, Pulsatile phantom, Test objects DOI: /ecr2010/C-3213 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 8

2 Purpose Doppler ultrasound is regularly used to investigate vascular pathologies and plan treatment. Surrogate measures of stenosis and other haemodynamically important pathologies include peak systolic velocity and pulsatility parameters. There is scant evidence data on the reproducibility of these measures between operators or between machines. Aim of Study Aims of this study was to: 1.develop a portable phantom that simulates near physiological arterial flow in medium size vessels such as carotid arteries. 2.assess the effect of ultrasound equipment settings on velocity measurement reproducibility. Activities have been carried out in three phases: preliminary investigations and design of an example test object construction and validation of the example test object assessment of flow measurement by equipment setting changes Methods and Materials Fluid circuit & Blood mimicking solution A pulsatile blood pump was connected to a 500mls reservoir and the flow phantom. Natural latex rubber tubes were used to connect different components. The reservoir was used to avoid air bubbles within the circuit (Figure 2). Blood mimicking solution (BMS) Page 2 of 8

3 was made from nylon scattering particles (Orgasol) suspended in a fluid base of water, glycerol, dextran and surfactant (Ramnarine et al. 1998). Tissue mimicking material (TMM) The criteria for the selection of TMM included speed of sound, viscosity, safety, and availability. Materials tested were liquid and solid poly vinyl alcohol (PVA), natural latex rubber, and liquid glycerine. Final TMM material consisted of aluminium particles suspended in solid agar gel. Phantom (Figure 1) The blood vessel model was made from moulded latex tube (1-2mm thickness, 1.5mm diameter, 5 cm in length). The tube was connected to connecting tubes and then suspended in the tissue mimicking material (liquid PVA; agar based TMM) within a sealed container. To prevent dryness of TMM PVA and also protecting US probe, the TMM (2.5cm in depth above the tube) was topped with thin layers of latex (2-3mm in thickness) and air dried. Silicon sealant was used to seal potential areas of leak. Validation Ultrasound and computerised tomography were used to evaluate the physical properties of the phantom. Speed of sound, reflectivity, and ability to maintain vessel shape were evaluated in 3cm deep block of TMM and also moulded vessel tube. The BMS and flow were assessed with Duplex ultrasound. An experienced vascular sonographer made multiple peak velocity measurements on four different modern ultrasound machines. Assessment of velocity variations Phantom was perfused at constant flow volume (302+6ml/min) with BMS. A single experienced Doppler ultrasound operator performed multiple peak systolic (PSV) and end diastolic velocity (EDV) measurements (10 measurements per experiment). Measurements were performed with the operator blind to the results. The following parameters: PRF ( ), Doppler gain (35, 45, 55, and 65dB), and scanning angle (55 vs 65 degrees) were assessed. Statistical analysis of variance (ANOVA) was used to compare the velocity values. Images for this section: Page 3 of 8

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5 Fig. 1: PVA based phantom. Second image shows sagital CT reformat. 1=surface latex cover; 2=liquid PVA; 3=vessel wall Fig. 2: A: Images of the fluid circuit. P=pump; C=connector; Ph= phantom; R=reservoir. B: Colour Doppler signal and pulsatile flow measurements using pulsed Doppler. Page 5 of 8

6 Results Speed of sound in liquid glycerine, solid latex and PVA was significantly higher than in water (2-3 times higher in average). In contrary, the speed of sound in liquid PVA and agar based TMM was similar to that in water. The liquid PVA was relatively echo free unless contaminated with air bubbles. Pulsatile (multiphasic) Doppler flow signal was detected and the velocity was measured (Figure 1,2). Reproducible measurements of velocity were achieved. There was no significant statistical difference in the peak velocity measurements between ultrasound machines (n=4; ANOVA, p-value>0.3). Increasing Doppler gain resulted in significantly higher PSV and EDV (mean PSV values at 65dB 35% higher than at 35dB; 39 vs 56 cm/s; p <0.001). Changing PRF value resulted in significantly different velocity values but there was no linear correlation between these variables. Higher scanning angles (60 vs 55) resulted in significantly higher velocity estimation (38 vs 50 cm/s at 35dB; p<0.004)(figure 2). Images for this section: Fig. 1: A: Images of the fluid circuit. P=pump; C=connector; Ph= phantom; R=reservoir. B: Colour Doppler signal and pulsatile flow measurements using pulsed Doppler. Page 6 of 8

7 Fig. 2: Doppler signal from the flowing BMS. A: Measurement of PSV using different gains and PRF. Increasing gain resulted in significantly higher PSV measurement (ANOVA; P0.3). Page 7 of 8

8 Conclusion A pulsatile flow Doppler phantom has been developed and reproducible signals were detected. Different equipment demonstrated reproducible velocity measurements. Scanning technique can significantly alter the results of the ultrasound Doppler velocity measurements. Laboratories using velocity measurements to make management decisions should establish a measurement error range. Future directions: Carotid test objects that reproduce vascular stenoses are made to study flow dynamics. The test object is X-ray and MR compatible and will be used for multimodality assessment of luminal stenosis and flow restrictions. References Lubbers, K Ramnarine and PR Hoskins, Blood mimicking fluid for flow Doppler test object. Eur J Ultrasound 7 (1998) Volume 7, Supplement 1, February 1998, pp (1) Personal Information Mirsadraee S, Kessel D, Evans A Leeds Teaching Hospitals and University of Leeds, Leeds, United Kingdom This study has been supported by the 2007 BSIR Research and Educational Bursary. Page 8 of 8