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Journal ArticleDOI

A complex flow phantom for medical imaging : ring vortex phantom design and technical specification

15 Jul 2019-Journal of Medical Engineering & Technology (Taylor & Francis)-Vol. 43, Iss: 3, pp 190-201

TL;DR: A novel, cost-effective, portable, complex flow phantom is proposed and the design specifications are provided, which employs a piston/cylinder system for vortex ring generation, coupled to an imaging tank full of fluid, for vortex propagation.

AbstractCardiovascular fluid dynamics exhibit complex flow patterns, such as recirculation and vortices. Quantitative analysis of these complexities supports diagnosis, leading to early prediction ...

Topics: Vortex ring (65%), Imaging phantom (60%), Vortex (57%)

Summary (4 min read)

1. Introduction

  • The fluid dynamics of the cardiovascular system are associated with many complexities and this has provoked interest from scientists for decades.
  • Magnetic Resonance angiography and Doppler Ultrasound are examples of technologies that offer valuable flow-based assessment of the cardiovascular system.
  • Blood speckle imaging is available on the GE Healthcare Vivid E95TM (GE Healthcare, Illinois, USA).
  • Manufacturers are not clear about tolerances and accuracy specifications [18] and the lack of well-defined protocols makes the Quality Control of scanners that measure flow and velocity challenging [15,16].
  • With its uniquely controllable characteristics, the ring vortex is a suitable flow reference for a flow test object.

2. Materials and Methods

  • The complex flow phantom design described here uses a piston to propel a slug of fluid along a cylindrical channel, through an orifice port that connects to an open tank of fluid (containing water, Blood-Mimicking Fluid etc.) where propagation of the ring may be observed and imaged.
  • A vortex ring naturally forms when a column of fluid is pushed through an orifice into a neighbouring expansive fluid environment.
  • The aノ┌キS ヮヴラヮWノノWS デエヴラ┌ェエ デエW ラヴキaキIW さヴラノノゲ ┌ヮざ デエW ラヴキaキIW face, forming a toroidal core of vorticity that may ultimately detach (at high enough Reynolds number) and propagates along the axisymmetric axis of the ring.
  • The whole process is managed by computer control of piston displacement that delivers the fluid slug with a precisely specified velocity/displacement profile.

2.1 Imaging Tank

  • The imaging tank is the principal component of the phantom since it is the environment in which the ring vortex propagates; it is the volume used to image the generated flow.
  • The tank is manufactured from clear poly(methyl methacrylate) (PMMA) which rests on four small screw feet.
  • These are adjustable to allow levelling of the system via two spirit levels placed on opposite walls of the tank box.
  • Several reference markers and a ruler are laser-cut into the surfaces of the tank walls to support positioning and measurement.
  • The top of the tank is open, offering easy access for Ultrasound imaging probes.

2.2 Piston Cylinder System

  • The generation of vortex rings relies on three components: a cylindrical channel, a plunger and an orifice that connects the channel to the imaging tank.
  • The cylindrical channel used here is of internal diameter 70+/-0.10 mm, reamed from a solid cylinder manufactured from PMMA .
  • One end of the chamber includes a screw thread for leak-proof coupling with the orifice and the imaging tank.
  • The piston head of the plunger incorporates an O-ring to provide a leak-proof seal between piston and the cylindrical chamber .
  • These generate rings of several centimetres diameter with characteristics that are relevant to human physiology.

2.3 Programmable Actuator

  • The nut/lead screw arrangement of the piston enables it to be driven by a linear stepper motor - this constitutes the actuator of the ring vortex generator.
  • A Nema 23 external linear stepper motor drives the threaded screw of length 150 mm (Nema 23 external linear actuator, OMC Corporation Limited, Nanjing, China).
  • Power is delivered through a digital stepper driver (OMC Corporation Limited, Nanjing, China) which has connections to a switching 150 W power supply (OMC Corporation Limited, Nanjing, China).
  • The digital system relies on CMOS logic (0-5V), with a square-wave signal of varying frequency (from 0.5 kHz to 1 kHz) but fixed duty cycle (50%) controlling the digital motor displacement.
  • The total cost of all the electronic components is less than one hundred Euros at the time of writing (2019).

2.4 The Assembled System

  • The interconnection of these components provides the system depicted in Figure 5.
  • The actuator is programmed to deliver a preconfigured displacement profile (eg. top-hat) that moves the piston through the cylinder and propels a slug of fluid through the orifice (e.g. 3 cm3 of displaced fluid in 50 ms).
  • This results in a controlled, propagating ring vortex of an orificedependent size that travels steadily (with velocities < 1 ms-1) along the length of the tank .
  • Images captured by an imaging system can be referenced to the features of the flow, permitting characterisation of imaging system performance.
  • Bulk features (ring speed, size) are readily established through simple optical/video methods [20] whereas finer details of the flow benefit from technologies such as particle image velocimetry (PIV) or even computational fluid dynamics (CFD) [21].

3. Demonstration and Application

  • Reynolds number calculations are based on flow through the orifice generating the ring (Re = Vd/; - density, V-velocity, d-diameter, -viscosity).
  • In order to confirm the functionality of the phantom design, two different measurement methods were used to characterise the generated flows, namely optical/video measurements and Laser-PIV; details are provided in sections 3.1 and 3.2 below.
  • Optical/video measurements were accomplished on the premises of Leeds Test Objects Ltd (Leeds Test Objects Ltd, Boroughbridge, United Kingdom) as previously described by Ferrari et al [20].
  • The PIV methodology followed that described by Wieneke [24], with calibration procedures performed under the supervision of a LaVisionUK Ltd (LaVisionUK Ltd, Bicester, United Kingdom) application consultant.

3.1 Optical/video acquisition

  • Vortex progress was captured at 25 frames per second using a Sony camera HDR-PJ220E (Sony Corporation, Tokyo, Japan).
  • The camera was placed on a tripod at a distance of 3.8 m from the phantom, obtaining a clear view through the sides of the transparent tank.
  • This zone was chosen as the region of interest for all measurements (including PIV).
  • In addition, a 1/100sec universal counter-timer (RS Components Ltd, Stock No 612-445) was placed within the field of view of the images to provide visible timing data in support of the measurements.
  • Distance measurements from still frames enabled characterisation of vortex ring position and translational speed.

3.2 Laser-PIV acquisition

  • The Laser-PIV setup required neutrally buoyant scattering particles mixed throughout the tank/cylinder system to provide satisfactory conditions for flow capture using the stereo Laser-PIV technique.
  • Fluorescent particles of size 10-20 micron were mixed within the volume of water, which was illuminated by a laser sheet that cut the propagating ring through its centre in the vertical plane.
  • Reconstruction of particle displacement using two camera projections (stereoscopic view) and digital image correlation allowed the reconstruction of the flow field [24] at a spatial resolution of 0.4 mm and temporal steps of 0.071 s (14 Hz).
  • Accuracy of the instantaneous velocities of the PIV system is declared by LaVisionUK Ltd (LaVisionUK Ltd, Bicester, United Kingdom) to be better than +/-0.1%.
  • Mapping the flow field of the Vz components at each frame and knowing the frame rate of the acquisition (14 fps), the translational velocity of the ring was calculated.

4.1 Optical/Video measurements

  • Average vortex ring translational velocities (Vtrans with standard deviation expressed by the error bars) as a function of vortex ring position are plotted in figs 6,7 (see Table 1 for the configurations tested).
  • For improved clarity, results for the configurations that produced faster ring vortices (from 15 cm/s to 80 cm/s) are shown in Figure 6 while results from slower configurations (from 0 cm/s to 15 cm/s) are shown in Figure 7.
  • In order to compare the optical data directly with the Laser-PIV translational velocity measurements, each selected configuration (Table 1) corresponds to a specific colour and marker-shape combination.
  • In each case, variability within 10 runs is presented as +/-1SD on the plots and cited as coefficient of variation (%) within the text.
  • Such errors calculated with the optical/video method are always less than +/-10%.

4.2 Laser-PIV

  • For consistency, average PIV vortex ring translational velocities with standard deviation are also plotted (dashed lines) as a function of vortex ring position .
  • These are calculated from 10 vortex ring acquisitions for each of the settings listed in Table 1 (as for the optical/video method).
  • Relative errors were calculated as for the optical/video experiment, and the varying configurations confirm very similar behaviour to the optical results.
  • Notably, the error increases for slower vortex ring configurations (e.g. Configuration 10, Table 1).

5. Discussion

  • Bulk flow performance has been assessed using two identical systems, undertaken at two different places (Leeds and Sheffield), two weeks apart.
  • In respect of ring vortex performance, Gharib observed that vortex ring generation depends on a non-dimensional parameter, described [25] as formation time or formation number.
  • Importantly, the measurement processes described in this paper indicate that realistic tolerances for these reproducible flows can be asserted に hence the utility of this design as a complex flow phantom.
  • With a longer-term ambition to compare flow imaging performance between different flow medical imaging modalities (Ultrasound, MRI and CT) - both for clinical and research purposes - the ring vortex phantom has been entirely manufactured from PMMA (except for the motor).
  • In an environment where the quality control of flow medical imaging scanners is still challenging and confusing, this technology offers support for both research and clinical imaging activities.

6. Conclusion

  • A technical specification for the design of a novel, cost-effective, portable complex flow test object currently compatible with ultrasound modalities has been provided.
  • Early experience indicates that the technology has the characteristics suited to basic and more advanced ultrasound quality control checks at research and clinical level.
  • The phantom as described, demonstrates that it can be reproducibly manufactured to deliver consistent performance within specified tolerances.
  • The authors report no conflict of interest.
  • This work is funded by the European Commission through the H2020 Marie Sklodowska-Curie European VPH-CaSE Training Network (www.vph-case.eu), GA No. 642612.

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This is a repository copy of A complex flow phantom for medical imaging : ring vortex
phantom design and technical specification.
White Rose Research Online URL for this paper:
http://eprints.whiterose.ac.uk/149487/
Version: Accepted Version
Article:
Ambrogio, S., Walker, A., Narracott, A. orcid.org/0000-0002-3068-6192 et al. (3 more
authors) (2019) A complex flow phantom for medical imaging : ring vortex phantom design
and technical specification. Journal of Medical Engineering & Technology, 43 (3). pp.
190-201. ISSN 0309-1902
https://doi.org/10.1080/03091902.2019.1640309
This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of
Medical Engineering and Technology on 15th July 2019, available online:
http://www.tandfonline.com/10.1080/03091902.2019.1640309
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A Complex Flow Phantom for Medical Imaging: Ring Vortex Phantom
Design and Technical Specification
1,2,3
Ambrogio Simone,
3
Walker Adrian,
1,2
Narracott Andrew,
1,2
Ferrari Simone,
4
Verma Prashant,
1,2
Fenner John
1
Medical Physics, Mathematical Modelling in Medicine Group, Department of Infection, Immunity and Cardiovascular Disease, University
of Sheffield, Sheffield, UK
2
Insigneo Institute for In Silico Medicine, University of Sheffield, Sheffield, UK
3
Leeds Test Objects Ltd., Boroughbridge, UK
4
Medical Imaging & Medical Physics, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK
Corresponding Author:
Simone Ambrogio
E-mail:
simoambr@gmail.com
(Orcid 0000-0003-1571-0016)
ABSTRACT
Cardiovascular fluid dynamics exhibit complex flow patterns, such as recirculation and vortices. Quantitative
analysis of these complexities supports diagnosis, leading to early prediction of pathologies. Quality Assurance
of technologies that image such flows is challenging but essential, and to this end, a novel, cost-effective,
portable, complex flow phantom is proposed and the design specifications are provided. The vortex ring is the
flow of choice because it offers patterns comparable to physiological flows and is stable, predictable,
reproducible and controllable. This design employs a piston/cylinder system for vortex ring generation, coupled
to an imaging tank full of fluid, for vortex propagation. The phantom is motor-driven and by varying piston speed,
piston displacement and orifice size, vortex rings with different characteristics can be produced. Two
measurement methods, namely Laser-PIV and an optical/video technique, were used to test the phantom under
a combination of configurations. Vortex rings with a range of travelling velocities (approximately 1-80cm/s) and
different output-orifice diameters (10-25mm) were produced with reproducibility typically better than +/-10%.
Although ultrasound compatibility has been demonstrated, longer-term ambitions include adapting the design
to support comparative studies with different modalities, such as MRA and X-ray-CTA.
Keywords: Medical Imaging Phantom, Doppler Ultrasound Quality Assurance, Vortex Ring, Complex Flow
Phantom, Laser PIV

1. Introduction
The fluid dynamics of the cardiovascular system are
associated with many complexities and this has
provoked interest from scientists for decades.
Recirculation, turbulence, jets and vortices are
observed both in healthy and pathophysiological
conditions [1,2]. Quantitative analysis of the
distribution of blood velocity patterns can support
diagnosis of the cardiovascular system, leading to
early prediction of pathologies, improvements of
surgical outcomes and evaluation of potential
therapies [2,3]. Magnetic Resonance angiography and
Doppler Ultrasound are examples of technologies that
offer valuable flow-based assessment of the
cardiovascular system. 4D Flow MRI is a powerful
technique that provides a time-resolved 3D velocity
field. Velocity is encoded along all three spatial
dimensions in the vessel of interest (4D = 3D + time).
Unfortunately, this technique is not clinically routine
because the acquisition time exceeds that demanded
by the clinical workflow [4]. Doppler Ultrasound is
portable, non-invasive, cost effective, does not involve
ionizing radiation and provides qualitative and
quantitative real-time information about volumes (i.e
stroke volume, ejection fraction), inferred pressures
(across heart valves) and flows (i.e. cardiac output)
[5,6]. For these reasons, Ultrasound is currently the
first choice as a diagnostic modality for the
assessment of several cardiovascular pathologies [7].
Recent developments include 2D and 3D real-time
angle independent Ultrasound Doppler imaging
techniques, based on Vector Flow Imaging (VFI), and
post-processing algorithms for particle velocimetry
tracking and volume quantification
[6,7,8,9,10,11,12,13]. A specific Ultrasound VFI
technique - Transverse Oscillation (TO) - has been FDA
approved (2013) and is clinically available on
commercial scanners (eg. BK Ultrasound, Nova Scotia,
Canada, and Carestream Health, Ontario, Canada) for
real-time analysis of complex flows in valves,
bifurcations and heart chambers [6,14]. A colour
Doppler based VFI technique is also commercially
available on clinical scanners manufactured by Hitachi
(Hitachi Ltd., Tokyo, Japan), GE Healthcare (GE
Healthcare, Illinois, USA) and Mindray (Mindray
Medical International Limited, Shenzen, China). Blood
speckle imaging is available on the GE Healthcare Vivid
E95
TM
(GE Healthcare, Illinois, USA). In this domain,
improved technologies for calibration of such medical
imaging techniques are essential. Complex flows are
needed as a standard reference for the validation of
innovative flow estimation algorithms.
Recent audits concerning Ultrasound Quality Control
protocols indicate that the current flow/velocity test
objects available on the market are rather limited,
expensive, and often fail to reproduce physiological
conditions and physiological waveforms
[15,16,17,18]. Manufacturers are not clear about
tolerances and accuracy specifications [18] and the
lack of well-defined protocols makes the Quality
Control of scanners that measure flow and velocity
challenging [15,16]. For example, experimental mean
velocity measurements using a commercial string
phantom (as recommended in IPEM Report 102,
Institute of Physics and Engineering in Medicine, 2010)
for linear, curvilinear and phased array probes
reported errors exceeding 20%, 50% and 40%,
respectively [17]. These values are considerably higher
than the recommended maximum error value of +/-
5%, as declared by BS EN 61685:2002-IEC 61685:2001,
a current International standard (stability date: 2020)
for the development of a flow Doppler test object [19].
It is this context that is the motivation for the
development of a novel phantom, designed to
produce complex flows that are stable, predictable,
controllable and reproducible. The particular flow
chosen as the basis for the design is the vortex ring.
This paper describes the salient features of a
prototype ring vortex phantom providing necessary
details for construction in a form suited to calibration
of Ultrasound flow imaging systems. With its uniquely
controllable characteristics, the ring vortex is a
suitable flow reference for a flow test object.

2. Materials and Methods
The complex flow phantom design described here
uses a piston to propel a slug of fluid along a cylindrical
channel, through an orifice port that connects to an
open tank of fluid (containing water, Blood-Mimicking
Fluid etc.) where propagation of the ring may be
observed and imaged. A vortex ring naturally forms
when a column of fluid is pushed through an orifice
into a neighbouring expansive fluid environment. The
        
face, forming a toroidal core of vorticity that may
ultimately detach (at high enough Reynolds number)
and propagates along the axisymmetric axis of the
ring. The whole process is managed by computer
control of piston displacement that delivers the fluid
slug with a precisely specified velocity/displacement
profile. Each component of the phantom is presented
below followed by description of the functioning unit
as a whole.
2.1 Imaging Tank
The imaging tank (Figure 1) is the principal component
of the phantom since it is the environment in which
the ring vortex propagates; it is the volume used to
image the generated flow. The tank is manufactured
from clear poly(methyl methacrylate) (PMMA) which
rests on four small screw feet. These are adjustable to
allow levelling of the system via two spirit levels
placed on opposite walls of the tank box. The tank has
internal dimensions of 15 cm (W) x 35 cm (L) x 16.5 cm
(H) (Figure 1), chosen to be sufficiently large that the
walls do not influence ring vortex propagation.
Several reference markers and a ruler are laser-cut
into the surfaces of the tank walls to support
Figure 1. CAD drawing of the ring vortex tank.

Figure 2. CAD drawing of the piston cylinder system.
Figure 3. CAD drawing of the attachable/detachable orifices.

Figures (11)
Citations
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01 Nov 2017
Abstract: The evolution of vortex rings in isodensity and isoviscosity fluid has been studied analytically using a novel mathematical model. The model predicts the spatiotemporal variation in peak vorticity, circulation, vortex size and spacing based on instantaneous vortex parameters. This proposed model is quantitatively verified using experimental measurements. Experiments are conducted using high-speed particle image velocimetry (PIV) and laser induced fluorescence (LIF) techniques. Non-buoyant vortex rings are generated from a nozzle using a constant hydrostatic pressure tank. The vortex Reynolds number based on circulation is varied in the range 100–1500 to account for a large range of operating conditions. Experimental results show good agreement with theoretical predictions. However, it is observed that neither Saffman’s thin-core model nor the thick-core equations could correctly explain vortex evolution for all initial conditions. Therefore, a transitional theory is framed using force balance equations which seamlessly integrate short- and long-time asymptotic theories. It is found that the parameter , where is the vortex half-spacing and denotes the standard deviation of the Gaussian vorticity profile, governs the regime of vortex evolution. For higher values of , evolution follows short-time behaviour, while for , long-time behaviour is prominent. Using this theory, many reported anomalous observations have been explained.

6 citations


Journal ArticleDOI
Abstract: The medical physics community has hitherto lacked an effective calibration phantom to holistically evaluate the performance of three-dimensional (3-D) flow imaging techniques. Here, we present the design of a new omnidirectional, three-component (3-C) flow phantom whose lumen is consisted of a helical toroid structure (4 mm lumen diameter; helically winded for 5 revolutions over a torus with 10 mm radius; 5 mm helix radius). This phantom's intraluminal flow trajectory embraces all combinations of x, y, and z directional components, as confirmed using computational fluid dynamics (CFD) simulations. The phantom was physically fabricated via lost-core casting with polyvinyl alcohol cryogel (PVA) as the tissue mimic. 3-D ultrasound confirmed that the phantom lumen expectedly resembled a helical toroid geometry. Pulsed Doppler measurements showed that the phantom, when operating under steady flow conditions (3 mL/s flow rate), yielded flow velocity magnitudes that agreed well with those derived from CFD at both the inner torus (-47.6 ± 5.7 versus -52.0 ± 2.2 cm/s; mean ± 1 S.D.) and the outer torus (49.5 ± 4.2 versus 48.0 ± 1.7 cm/s). Additionally, 3-C velocity vectors acquired from multi-angle pulsed Doppler showed good agreement with CFD-derived velocity vectors (<7% and 10˚ difference in magnitude and flow angle, respectively). Ultrasound color flow imaging (CFI) further revealed that the phantom's axial flow pattern was aligned with the CFD-derived flow profile. Overall, the helical toroid phantom has strong potential as an investigative tool in 3-D flow imaging innovation endeavors, such as the development of flow vector estimators and visualization algorithms.

Journal ArticleDOI
Abstract: Flow phantoms are used in experimental settings to aid in the simulation of blood flow. Custom geometries are available, but current phantom materials present issues with degradability and/or mimicking the mechanical properties of human tissue. In this study, a method of fabricating custom wall-less flow phantoms from a tissue-mimicking gel using 3D printed inserts is developed. A 3D blood vessel geometry example of a bifurcated artery model was 3D printed in polyvinyl alcohol, embedded in tissue-mimicking gel, and subsequently dissolved to create a phantom. Uniaxial compression testing was performed to determine the Young’s moduli of the five gel types. Angle-independent, ultrasound-based imaging modalities, Vector Flow Imaging (VFI) and Blood Speckle Imaging (BSI), were utilized for flow visualization of a straight channel phantom. A wall-less phantom of the bifurcated artery was fabricated with minimal bubbles and continuous flow demonstrated. Additionally, flow was visualized through a straight channel phantom by VFI and BSI. The available gel types are suitable for mimicking a variety of tissue types, including cardiac tissue and blood vessels. Custom, tissue-mimicking flow phantoms can be fabricated using the developed methodology and have potential for use in a variety of applications, including ultrasound-based imaging methods. This is the first reported use of BSI with an in vitro flow phantom.

References
More filters

Journal ArticleDOI
Abstract: The formation of vortex rings generated through impulsively started jets is studied experimentally. Utilizing a piston/cylinder arrangement in a water tank, the velocity and vorticity fields of vortex rings are obtained using digital particle image velocimetry (DPIV) for a wide range of piston stroke to diameter (L/D) ratios. The results indicate that the flow field generated by large L/D consists of a leading vortex ring followed by a trailing jet. The vorticity field of the leading vortex ring formed is disconnected from that of the trailing jet. On the other hand, flow fields generated by small stroke ratios show only a single vortex ring. The transition between these two distinct states is observed to occur at a stroke ratio of approximately 4, which, in this paper, is referred to as the ‘formation number’. In all cases, the maximum circulation that a vortex ring can attain during its formation is reached at this non-dimensional time or formation number. The universality of this number was tested by generating vortex rings with different jet exit diameters and boundaries, as well as with various non-impulsive piston velocities. It is shown that the ‘formation number’ lies in the range of 3.6–4.5 for a broad range of flow conditions. An explanation is provided for the existence of the formation number based on the Kelvin–Benjamin variational principle for steady axis-touching vortex rings. It is shown that based on the measured impulse, circulation and energy of the observed vortex rings, the Kelvin–Benjamin principle correctly predicts the range of observed formation numbers.

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Abstract: A stereo-PIV (stereo particle image velocimetry) calibration procedure has been developed based on fitting a camera pinhole model to the two cameras using single or multiple views of a 3D calibration plate. A disparity vector map is computed on the real particle images by cross-correlation of the images from cameras 1 and 2 to determine if the calibration plate coincides with the light sheet. From the disparity vectors, the true position of the light sheet in space is fitted and the mapping functions are corrected accordingly. It is shown that it is possible to derive accurate mapping functions, even if the calibration plate is quite far away from the light sheet, making the calibration procedure much easier. A modified 3-media camera pinhole model has been implemented to account for index-of-refraction changes along the optical path. It is then possible to calibrate outside closed flow cells and self-calibrate onto the recordings. This method allows stereo-PIV measurements to be taken inside closed measurement volumes, which was not previously possible. From the computed correlation maps, the position and thickness of the two laser light sheets can be derived to determine the thickness, degree of overlap and the flatness of the two sheets.

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"A complex flow phantom for medical ..." refers methods in this paper

  • ...The PIV methodology followed that described by Wieneke [24], with calibration procedures performed under the supervision of a LaVisionUK Ltd (LaVisionUK Ltd, Bicester, UK) application consultant....

    [...]

  • ...Reconstruction of particle displacement using two camera projections (stereoscopic view) and digital image correlation allowed the reconstruction of the flow field [24] at a spatial resolution of 0....

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Abstract: Particle image velocimetry (PIV) has evolved to be the dominant method for velocimetry in experimental fluid mechanics and has contributed to many advances in our understanding of turbulent and complex flows. In this article we review the achievements of PIV and its latest implementations: time-resolved PIV for the rapid capture of sequences of vector fields; tomographic PIV for the capture of fully resolved volumetric data; and statistical PIV, designed to optimize measurements of mean statistical quantities rather than instantaneous fields. In each implementation, the accuracy and spatial resolution are limited. To advance the method to the next level, we need a completely new approach. We consider the fundamental limitations of two-pulse PIV in terms of its dynamic ranges. We then discuss new paths and developments that hold the promise of achieving a fundamental reduction in uncertainty.

329 citations


"A complex flow phantom for medical ..." refers methods in this paper

  • ...A complementary method – Laser-PIV – was also employed, which is a well-established technique for quantitative measurement of complex flow velocity fields [22,23]....

    [...]


Journal ArticleDOI
Ian Grant1
01 Jan 1997
Abstract: The evolution of particle image velocimetry (PIV) from its various roots is discussed. The importance of these roots and their influence on different trends in the speciality are described. The state-of-the-art of the technique today is overviewed and illustrated by reference to recent, seminal publications describing both the development and application of PIV.

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"A complex flow phantom for medical ..." refers methods in this paper

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TL;DR: This document provides a descriptive outline of the relevant concepts in cardiac fluid mechanics, including the emergence of rotation in flow and the variables that delineate vortical structures, and elaborate on the main methods developed to image and visualize multidirectional cardiovascular flow.
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Frequently Asked Questions (2)
Q1. What have the authors contributed in "A complex flow phantom for medical imaging: ring vortex phantom design and technical specification" ?

Quality Assurance of technologies that image such flows is challenging but essential, and to this end, a novel, cost-effective, portable, complex flow phantom is proposed and the design specifications are provided. 

It is worth noting that their analysis has focussed on bulk flow characteristics ( eg. translational vortex ring speed Vtrans ) but for completeness, further work is needed to assess the micro-flow environment in addition to the macro-flow characteristics described here. Future work will extend the assessment presented here to include comparative studies between medical imaging modalities ( Ultrasound, CT, and with some adaptation MRI ) and optical modalities ( Laser-PIV, Laser-diode ) to further assess reliability, long-term stability and detailed flow performance. Currently, four identical phantom systems have been manufactured and are currently being evaluated in the United Kingdom and France within both research and clinical environments, in order to identify potential improvements to the design.