ACUSON Sequoia™ Ultrasound System Slow Flow State
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White paper Slow flow state Lei Sui, Ph D. Michele Baillie, B. Sc, RDMS, RDCS Siemens Medical Solutions USA, Inc., Ultrasound Business Area Issaquah, Washington siemens-healthineers.com/ultrasound SIEMENS Healthineers White paper · Slow flow state Slow flow state Contents Introduction 3 The background principle behind Slow flow 4 Slow flow 5 Examples 7 Conclusion 7 2 siemens-healthineers.com/ultrasound Slow flow state · White paper Figure 1: Visualized kidney vasculature using conventional Doppler (left) and Slow flow (right). While conventional Doppler easily demonstrates the flow in larger vessels within the kidney parenchyma, it is unable to identify flow in the small lower velocity vessels in the periphery. When the Slow flow Doppler technology is enabled, the lower velocity microvascular branches are easily identified in the peripheral parenchyma. Introduction Color Doppler technology can allow a user to determine address conventional Doppler limitations. This new presence or absence of blood flow as well as direction technique is known as Slow flow Doppler state. Slow information and velocity. This technology, however, flow uses an intelligent algorithm combined with smart carries inherent limitations to sufficiently visualize system filters to detect and separate the weaker signals. smaller, low flow vessels. Small, weaker signals can be Once detected, these signals are amplified and used lost from the surrounding signal clutter or rejected as to help improve smaller, low flow vessel visualization. noise by filters within the system which remove this Compared to conventional color Doppler, Slow flow state information altogether. With these challenges in mind, allows users to easily visualize more vessels that are Siemens Healthineers developed a new color Doppler smaller and also see deeper into tissue1 (Figure 1). visualization technique that is specifically directed to 1 Siemens Healthineers user survey siemens-healthineers.com/ultrasound 3 White paper · Slow flow state Clutter filter HPF Clutter Blood signal Blood Clutter Power signal fclutter fD fblood Frequency –fa/2 0 fa/2 With microcirculation Figure 2: Conventional Doppler filters can successfully Figure 3: With microcirculation, weaker or slower blood distinguish and separate clutter and flow. flow signals may blend in with the surrounding stronger signals. When blended with clutter, these signals are not easily separated and can be lost or rejected as noise. The background principle behind Slow flow Medical ultrasound imaging is widely used in real Conventional Doppler filters work well when clutter and time to detect and display blood flow in the human flow are well separated (Figure 2). As flow becomes body. Ultrasound beams are transmitted into the body weaker or slower, it blends into clutter and becomes repeatedly at a predefined interval. The inverse of the more and more difficult to extract out of clutter (Figure 3). interval is called pulse repetition frequency (PRF). A If the signals are not identified and extracted, they can predefined number of the ultrasound pulses are grouped be rejected by the wall filter as being noise, thus the into a set of samples called ensembles. A wall filter is signal is lost from the image. The goal of the Slow flow applied to the ensembles to separate flow signal from state is to extend the capabilities of conventional Doppler clutter based on flow velocity derived from Doppler techniques to smaller vessels or slower blood flow in the phase shift. Conventional Doppler methods make use of Color Doppler Energy (CDE) mode where the strength of a wall filter to remove clutter from the Doppler image. flow signal is reported but not the velocity. 4 siemens-healthineers.com/ultrasound Slow flow state · White paper Moving Stational Signal intensity Signal range Figure 4: Separate moving signal from stationary signal. In this example, there are only two probability of being flow, 0 and 1. Slow flow Flow signals exist throughout a signal range, thus any The moving signal then passes through an adaptive filter. given signal could be a composite of moving signal and The adaptive filter selectively detects and amplifies smaller stationary signal. In order to accomplish the goal of or weaker flow signals to make them more pronounced extracting a flow signal out of clutter, smart filters have and thus more easily detected. At the same time, the to be in place to differentiate various flow from tissue. filter curbs motion artifacts and any overflowing stronger First, a novel self-constructive wall filter decouples flow signal (Figure 5). The results further go through motion signal from the stationary signal (Figure 4) over a stochastic process to suppress flashes and to sustain the entire signal range. This is accomplished by breaking the true flow signal (Figure 5). The combined effects of down the signal into components which are ranked those filters, together with longer ensembles and lower according to their possibilities of being clutters or flows. PRF, make it possible for the Slow flow state to detect By doing this, the novel wall filter optimally labels smaller flow, slower flow, and more vessel branches flow which could be mixed with clutter and would be into the tissue than conventional Color Doppler mode otherwise excluded by Doppler velocity cutoffs. (Figure 6, Figure 7). siemens-healthineers.com/ultrasound 5 White paper · Slow flow state Signal 8 8 Threshold 7 7 6 6 5 5 4 4 3 3 2 2 1 1 0 0 -2 0 2 4 6 8 10 12 14 -2 0 2 4 6 8 10 12 14 Figure 5: Moving signal (left) is further processed to amplify smaller flow, curb overflow and suppress flashes (right) with thresholds from adaptive algorithms. Signal clutter removed by Conventional Doppler Imaging wall filter Signal clutter Blood flow signal Signal intensity overlapping flow signal Flow velocity Blood flow signal Signal intensity Flow velocity Blood flow signal Signal intensity Slow flow Doppler Imaging Flow velocity Figure 6: Tissue motion artefacts result in clutter that overlies the low velocity component of the blood flow Doppler signal. Conventional Doppler imaging employs the use of wall filters that remove this clutter. This removal cleans up the displayed Doppler signal however it also results in a loss of the low velocity components buried in the clutter. Slow flow Doppler imaging uses smart filters that can differentiate the motion artefact from the low-velocity signal buried within it. The resulting blood flow signal contains both weak and strong echoes and thus displays smaller, low-flow vessels within the ultrasound image. 6 siemens-healthineers.com/ultrasound Slow flow state · White paper Sequoia Sequote Figure 7: Image of the kidney using conventional color Doppler (left) and Slow flow Doppler (right). Conclusion There is, of course, always challenges to overcome when Built on the advanced ACUSON Sequoia ultrasound processing a great number of signal components used system platform, the Slow flow state supplements to generate the ultrasound image. Longer ensembles conventional Doppler techniques to detect a broader and slower PRF increases observation time which helps range of flow signals. It employs sophisticated filters magnify flow signal. These longer ensembles, however, which extract flow out of clutter by motion filtering, adversely affect frame rate. The ACUSON Sequoia adaptive signal enhancement and flash suppression. ultrasound system’s powerful front-end compensates As a result of this advanced engineering technique, for the acquisition time with parallel receive channels Slow flow is able to visualize smaller, slower flow which yields good frame rates. Moreover, despite the vessels, as well as visualize these challenging vessels fact that the smart filters are very computation-intense, further into the tissue being imaged. the computation load is handled gracefully by the state-of-the-art computing engines on the ACUSON Sequoia ultrasound system. Overall, Slow flow provides information-rich images with a very good responsiveness to user operations. siemens-healthineers.com/ultrasound 7 Standalone clinical images may have been cropped At Siemens Healthineers, our purpose is to enable to better visualize pathology. The products/features healthcare providers to increase value by empowering mentioned in this document may not be commercially them on their journey towards expanding precision available in all countries. Due to regulatory reasons, medicine, transforming care delivery, and improving their future availability cannot be guaranteed. patient experience, all enabled by digitalizing healthcare. Please contact your local Siemens Healthineers An estimated five million patients worldwide everyday organization for further details. benefit from our innovative technologies and services in the areas of diagnostic and therapeutic imaging, ACUSON Sequoia is a trademark of Siemens Medical laboratory diagnostics and molecular medicine as well Solutions USA, Inc. as digital health and enterprise services. We’re a leading medical technology company with over 120 years of experience and 18,500 patents globally. With over 50,000 employees in more than 70 countries, we’ll continue to innovate and shape the future of healthcare. Siemens Healthineers Headquarters Legal Manufacturer Siemens Healthcare GmbH Siemens Medical Solutions USA, Inc. Henkestr. 127 Ultrasound 91052 Erlangen, Germany 22010 S.E. 51st Street Phone: +49 9131 84-0 Issaquah, WA 98029, USA siemens-healthineers.com Phone: 1-888-826-9702 siemens-healthineers.com/ultrasound Published by Siemens Medical Solutions USA, Inc. · 9258 1020 online · © Siemens Medical Solutions USA, Inc., 2020