Name: blood flow imaging with ultrafast doppler
Uploaded: 2020-10-14T13:00:00.000+00:00
Duration: 5 min 57 s
Description: Watch this Scientific Journal Video about Blood Flow Imaging with Ultrafast Doppler at JoVE.com

We would like to thank Shreya Shah for her proofreading and advice.

1. Doppler phantom preparation setup (Figure 2A)
<ol>
	<li>Connect the peristaltic pump, the blood mimicking fluid reservoir, the pulse dampener and the Doppler flow phantom with the plastic tubes.</li>
	<li>Choose the canal with a 4 mm diameter.</li>
	<li>Program the pump to eject 720 mL/min of fluid for 0.3 s and then to eject 50 mL/min for 0.7 s to respectively mimic the systole and diastole cardiac phases</li>
	<li>Run the pump and gently shake the pipes to expel potential air bubbles. 
	NOTE: The operator can choose a different canal diameter and different pump rate but will have to ensure that the ultrasound sequence is fast enough to acquire the fastest flow velocities. Eq. 3 presented later can help to design the sequence.</li>
</ol>
2. Ultrafast ultrasound scanner setup (Figure 2A)
<ol>
	<li>Connect the ultrafast-enabled research scanner to the host computer with the PCI express link.</li>
	<li>Change the transducer adapter on the ultrasound scanner to match the probe connector, then connect the probe.</li>
	<li>Run Matlab and activate the ultrasound scanner license. 
	NOTE: This section and the following implicitly assume the use of a Verasonics Vantage system.</li>
</ol>
3. Ultrasound sequence programming
<ol>
	<li>Using the examples scripts, design a conventional focused &#8220;B-Mode&#8221; (i.e., echography) sequence that will be used for probe positioning.
	<ol>
		<li>Set the imaging depth to 50 mm.</li>
		<li>Set the focal depth to 35 mm.</li>
	</ol>
	</li>
	<li>Using the examples scripts, design an ultrafast ultrasound sequence.
	<ol>
		<li>Set the imaging depth to 50 mm.</li>
		<li>Program 3 tilted plane-waves at [-3,0,3] degree.</li>
		<li>Set the pulse repetition frequency (PRF) to 12 kHz.</li>
		<li>Use 4 half-cycles for the ultrasound waveform, with a center frequency depending on the probe used. A center frequency of 5.2 MHz is assumed here.</li>
		<li>Set the total duration to 1 s.</li>
	</ol>
	</li>
</ol>
4. Probe positioning and data acquisition
<ol>
	<li>Apply ultrasound gel on the probe&#8217;s lens.</li>
	<li>Place the probe on the phantom and launch the B-Mode ultrasound sequence.</li>
	<li>Locate the canal of interest. The fluid appears darker than the surrounding tissue. Place the probe in longitudinal view.</li>
	<li>Manually maintain the probe in the position of interest.</li>
	<li>End the B-Mode sequence and launch the ultrafast sequence acquisition script.</li>
</ol>
5. Image reconstruction (Figure 2B)
<ol>
	<li>Once the sequence is over, save the raw data (also called Radio-Frequency data, &#8220;RF&#8221;).</li>
	<li>Launch the image reconstruction script using the ultrasound system default software. At the end of the process, the IQ data matrix should be created. 
	NOTE: The ultrasound echoes are recorded on each element of the probe and for each emission/reception, then stored in the RF data matrix. The image reconstruction applied the appropriate delay law to each channel and results in the so-called &#8220;IQ&#8221; (In-Phase/Quadrature) matrix. The complex IQ matrix has three dimensions: two for space (image depth and width) and one for time</li>
</ol>
6. Clutter filtering (Figure 2C)
NOTE: For steps 6-7, see the Matlab script provided in the Supplementary Material.
<ol>
	<li>Reshape the 3D (space x space x time) IQ matrix into a 2D (space x time) Casorati matrix, named IQr.</li>
	<li>Compute the singular value decomposition15 of IQr (Eq. 1). 
	<img alt="Equation 1" src="/files/ftp_upload/61838/61838equ01v3.jpg" /> Eq. 1</li>
	<li>Compute the Spatial Similarity Matrix C using the spatial singular vectors U as described by Baranger et al.18 (II, D), and identify the blood subspace boundaries N.</li>
	<li>Use this cutoff N to filter the IQ data as described in Demene et al.15 (II,C).</li>
</ol>
7. Flow visualization and velocity measurements (Figure 2C)
<ol>
	<li>Compute power Doppler map PD by integrating the envelope of the filtered data IQt along the temporal dimension (Eq. 2). The 3D coordinates z, x and t are respectively the depth, width and temporal dimension, nt and is the number of frames acquired. 
	<img alt="Equation 2" src="/files/ftp_upload/61838/61838equ02v5.jpg" /> Eq. 2</li>
	<li>Display the PD map in logarithm scale. To set the dynamic range, compute the mean PD in a region outside the canal and use this value in dB as the lower bound of the dynamic range. A typical dynamic range is [-30, 0] dB.</li>
	<li>Define a circular region of interest (ROI) on the image, containing 1 to 30 pixels.</li>
	<li>Average the IQf signal over the pixels of that ROI, to obtain a vector <img alt="Equation 3" src="/files/ftp_upload/61838/61838equ03v2.jpg" /> of nt time points.</li>
	<li>Compute and display the Doppler spectrogram of <img alt="Equation 4" src="/files/ftp_upload/61838/61838equ04v2.jpg" />, using the square magnitude of the Short-Time Fourier Transform (STFT).
	<ol>
		<li>Set the STFT window to a 60-samples Hann window.</li>
		<li>Set the STFT overlap to 90% of the window length.</li>
	</ol>
	</li>
	<li>Overlay the center frequency at each time point of the spectrogram.</li>
	<li>Convert the frequency f values into blood axial velocities vz using the Doppler formula (Eq. 3). c0 is the speed of sound in the medium and fTW the center frequency of the transmitted ultrasound waveform (here 5.2 MHz). 
	<img alt="Equation 5" src="/files/ftp_upload/61838/61838equ05v4.jpg" /> Eq. 3</li>
</ol>

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No conflict of interest

Several variations are possible around the main frame of this protocol.
Hardware concerns 
If the user supplies its custom host computer, the motherboard and the computer&#8217;s case must have an available PCI express slot. The CPU must also have enough PCIe lanes to handle all the devices.
Probe selection 
The ultrasound probe (also named transducer) is chosen according to the spatial resolution needed and to the geometr...

Ultrasound imaging is one of the most commonly used imaging techniques in clinical practice and research activities. The combination of ultrasound wave emission in the biological tissues followed by the recording of the backscattered echoes allows the reconstruction of anatomical images, the so-called &#8220;B-Mode&#8221;. This method is perfectly adapted for soft tissue imaging, such as biological tissues, which typically permit the penetration of ultrasound over several centimeters, with a propagation speed of &#8776;1540 m/s. Depending on the center frequency of the ultrasound probe, images with a resolution from 30 &#181;m to 1 mm are obtained. Furthermore, it is well known that the motion of an acoustic source, affects the physical characteristics of the associated waves. Particularly, the link between the frequency shifts of a wave relative to the speed of its source is described as the Doppler effect1, whose simplest manifestation is the changing siren&#8217;s pitch of a moving ambulance. Ultrasound imaging has long used this physical effect to observe the moving red blood cells2, and it proposes a variety of imaging modes commonly labelled &#8220;Doppler imaging&#8221;. These modes enable the assessment of blood flows in very different applications and organs, such as brain, heart, kidney or peripheral arteries.
Remarkably, most of the currently available ultrasound systems rely on the same technology, referred to as conventional ultrasound. The underlying principles are the following: an acoustic beam insonifies the field of view and is swept along the ultrasound transducer aperture. For each position of the beam, the echoes are recorded and converted into a line of the final image. By progressively moving the beam along the transducer, the whole field of view can be imaged line-per-line (Figure 1, left panel). This strategy was well adapted to the electrical constraints and computing power prevailing until the beginning of the 21st century. Nonetheless, it has several drawbacks. Among these, the final framerate is limited to a few hundred images per second by the beam scanning process. In terms of blood flow, this relatively low framerate affects the maximum flow velocities that can be detected, which is dictated by the sampling criteria of Shannon-Nyquist3. Moreover, conventional Doppler must deal with a complex tradeoff. In order to assess the blood flow velocity in a particular region of interest (ROI), several echoes coming from that ROI have to be successively recorded. This implies that the ultrasound beam is temporarily maintained in a fixed position. The longer the echo ensemble, the better the velocity estimation will be for that ROI. However, to produce a complete image of the field of view, the beam must scan the medium. Therefore, one can sense the conflict between these two constraints: holding the beam to precisely assess the velocity along one line, or moving the beam to produce an image. The different conventional Doppler modes (i.e., Color Doppler or Pulse Wave Doppler) directly reflect this tradeoff. Typically, the Color Doppler produces a low-fidelity flow map used for localizing the vessels4, and the Pulse Wave Doppler is then used to accurately quantify the flow in a previously identified vessel5.
These two limitations (low framerate and localization/quantification tradeoff) are overcome with very high-framerate emerging techniques. Among these, the synthetic aperture approach6 or the multiline transmit technique can be cited7. In this study, we focus on the so-called Ultrafast ultrasound method. Introduced two decades ago8,9,10, this method also relies on the emission/reception of ultrasounds, but with a radically different pattern. Indeed, instead of using a scanning focused beam, ultrafast imaging uses plane wave or diverging waves, which are able to insonify the field of view with a single emission. Following that single emission, the associated electronics is also able to receive and process the huge number of echoes originating from the whole field of view. At the end, an image can be reconstructed from a single emission/reception pattern11 (Figure 1, right panel). These unfocused emissions can have a low signal to noise ratio (SNR) due to the spread of the acoustical energy. This can be tackled by emitting several titled plane-waves (or diverging waves with different sources) and by adding the resulting images. This method is named &#8220;coherent compounding&#8221;12. Two major consequences arise. Firstly, the framerate only depends on the ultrasound time of flight and can reach typical values from 1 to 10 kHz. Secondly, this ensures the data continuity in both spatial and temporal dimensions, also referred to as spatiotemporal coherence. The conventional localization/quantification tradeoff is thus broken. This combination of a high framerate and spatiotemporal coherence has a tremendous impact on the ability to detect blood flows with ultrasound. As compared to conventional ultrasound, ultrafast ultrasound provides full characterization of the blood flow3. Practically, the user has access to the velocity time course in every pixel of the image, for the whole duration of the acquisition (typically &#8776;1 s), with a timescale given by the framerate (typically, a framerate of 5 kHz for a temporal resolution of 200 &#181;s). This high framerate makes the method suitable for a wide range of application such as fast flow in moving organs like heart chambers13 or myocardium with the coronary micro-perfusion14. Furthermore, it has been shown that its spatiotemporal coherence strongly improves its ability to separate slow blood flow from background moving tissues, therefore increasing the sensitivity to micro-vascular flow15. This capacity gives access to the micro vasculature of the brain in both animals16 and humans17.
Hence, ultrafast ultrasound is well suited to image blood flow in a variety of situations. It is restricted to soft biological tissues and will be strongly affected by the presence of hard interfaces such as bones, or gas cavity such as the lung. The tuning of the physical parameters of the ultrasound sequence allows the study of both slow (down to 1 mm/s11,16) and fast flows (up to several m/s). A tradeoff exists between the spatial resolution and the depth of penetration. Typically, a resolution of 50 &#181;m can be achieved at the cost of a penetration around 5 mm. Conversely, the penetration can be extended to 15-20 cm at the cost of a resolution of 1 mm. It is worth noting that most ultrafast scanners such as the one used in this article only provide 2D images.
Here, we propose a simple protocol to introduce the concept of Ultrafast Doppler imaging, using a programmable research ultrasound scanner and Doppler phantom mimicking a vessel (artery or vein) embedded in biological tissue.

<table><tbody><tr><td>Blood-mimicking fluid</td><td>CIRS Inc, Norfolk, Virginia, USA</td><td>069DTF</td><td></td></tr><tr><td>Doppler flow phantom</td><td>CIRS Inc, Norfolk, Virginia, USA</td><td>ATS523A</td><td></td></tr><tr><td>Matlab</td><td>MathWorks, Natick, Massachusetts, United States</td><td></td><td></td></tr><tr><td>Peristaltic pump / Doppler flow pump</td><td>CIRS Inc, Norfolk, Virginia, USA</td><td>769</td><td>Include tubings and pulse dampener</td></tr><tr><td>Transducer adpter</td><td>Verasonics, Kirkland, Washington, USA</td><td>UTA 408-GE</td><td></td></tr><tr><td>Ultrafast ultrasound research scanner</td><td>Verasonics, Kirkland, Washington, USA</td><td>Vantage 256</td><td></td></tr><tr><td>Ultrasound probe/transducer</td><td>GE Healthcare</td><td>GE 9L-D</td><td></td></tr></tbody></table>

blood flow imaging with ultrafast doppler

The pulsed-Doppler effect is the main technique used in clinical echography to assess blood flow. Applied with conventional focused ultrasound Doppler modes, it has several limits. Firstly, a finely tuned signal filtering operation is needed to distinguish blood flows from surrounding moving tissues. Secondly, the operator must choose between localizing the blood flows or quantifying them. In the last two decades, ultrasound imaging has undergone a paradigm shift with the emergence of ultrafast ultrasound using unfocused waves. In addition to a hundredfold increase in framerate (up to 10000 Hz), this new technique also breaks the conventional quantification/localization trade-off, offering a complete blood flow mapping of the field of view and a simultaneous access to fine velocities measurements at the single-pixel level (down to 50 &#181;m). This data continuity in both spatial and temporal dimensions strongly improves the tissue/blood filtering process, which results in an increase sensitivity to small blood flow velocities (down to 1 mm/s). In this method paper, we aim to introduce the concept of ultrafast Doppler as well as its main parameters. Firstly, we summarize the physical principles of unfocused wave imaging. Then, we present the Doppler signal processing main steps. Particularly, we explain the practical implementation of the critical tissue/blood flow separation algorithms and on the extraction of velocities from these filtered data. This theoretical description is supplemented by in vitro experiences. A tissue phantom embedding a canal with flowing blood-mimicking fluid is imaged with a research programmable ultrasound system. A blood flow image is obtained and the flow characteristics are displayed for several pixels in the canal. Finally, a review of in vivo applications is proposed, showing examples in several organs such as carotids, kidney, thyroid, brain and heart.

The quality of the acquisition and the post-processing is firstly assessed by visual inspection. The shape of the canal must be clearly visible in the power Doppler image, and the tissue area must appear dark. If the power Doppler signal is not restricted to the canal, it can mean that either the clutter filter step went wrong (SVD threshold is too low), or the probe experienced a strong movement during the acquisition.
After visual inspection, the study of the spectrogram inside the canal can...

Watch this Scientific Journal Video about Blood Flow Imaging with Ultrafast Doppler at JoVE.com

Blood Flow Imaging with Ultrafast Doppler

This protocol shows how to apply ultrafast ultrasound Doppler imaging to quantify blood flows. After a 1 s long acquisition, the experimenter has access to a movie of the full field of view with axial velocity values for each pixel every &#8776;0.3 ms (depending on the ultrasound time of flight).

The pulsed-Doppler effect is the main technique used in clinical echography to assess blood flow. Applied with conventional focused ultrasound Doppler ...

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7.4K Views.  The Hospital for Sick Children, PGCRL Research Institute. This protocol shows how to apply ultrafast ultrasound Doppler imaging to quantify blood flows. After a 1 s long acquisition, the experimenter has access to a movie of the full field of view with axial velocity values for each pixel every ≈0.3 ms (depending on the ultrasound time of flight).

Video: Blood Flow Imaging with Ultrafast Doppler

Doppler Optical Coherence Tomography of Retinal Circulation

Noncontact retinal blood flow measurements are performed with a Fourier domain optical coherence tomography (OCT) system using a circumpapillary double circular scan (CDCS) that scans around the optic nerve head at 3.40 mm and 3.75 mm diameters. The double concentric circles are performed 6 times consecutively over 2 sec. The CDCS scan is saved with Doppler shift information from which flow can be calculated. The standard clinical protocol calls for 3 CDCS scans made with the OCT beam passing through the superonasal edge of the pupil and 3 CDCS scan through the inferonal pupil. This double-angle protocol ensures that acceptable Doppler angle is obtained on each retinal branch vessel in at least 1 scan. The CDCS scan data, a 3-dimensional volumetric OCT scan of the optic disc scan, and a color photograph of the optic disc are used together to obtain retinal blood flow measurement on an eye. We have developed a blood flow measurement software called "Doppler optical coherence tomography of retinal circulation" (DOCTORC). This semi-automated software is used to measure total retinal blood flow, vessel cross section area, and average blood velocity. The flow of each vessel is calculated from the Doppler shift in the vessel cross-sectional area and the Doppler angle between the vessel and the OCT beam. Total retinal blood flow measurement is summed from the veins around the optic disc. The results obtained at our Doppler OCT reading center showed good reproducibility between graders and methods (&lt;10%). Total retinal blood flow could be useful in the management of glaucoma, other retinal diseases, and retinal diseases. In glaucoma patients, OCT retinal blood flow measurement was highly correlated with visual field loss (R2&gt;0.57 with visual field pattern deviation). Doppler OCT is a new method to perform rapid, noncontact, and repeatable measurement of total retinal blood flow using widely available Fourier-domain OCT instrumentation. This new technology may improve the practicality of making these measurements in clinical studies and routine clinical practice.

Total retinal blood flow is measured by Doppler optical coherence tomography and semi-automated grading software.

Noncontact retinal blood flow measurements are performed with a Fourier domain optical coherence tomography (OCT) system using a circumpapillary double ...

Medicine

Micro-particle Image Velocimetry for Velocity Profile Measurements of Micro Blood Flows

Micro-particle image velocimetry (&mu;PIV) is used to visualize paired images of micro particles seeded in blood flows. The images are cross-correlated to give an accurate velocity profile. A protocol is presented for &mu;PIV measurements of blood flows in microchannels. At the scale of the microcirculation, blood cannot be considered a homogeneous fluid, as it is a suspension of flexible particles suspended in plasma, a Newtonian fluid. Shear rate, maximum velocity, velocity profile shape, and flow rate can be derived from these measurements. Several key parameters such as focal depth, particle concentration, and system compliance, are presented in order to ensure accurate, useful data along with examples and representative results for various hematocrits and flow conditions.

Micro-particle image velocimetry (&mu;PIV) is used to visualize paired images of micro particles seeded in blood flows which are cross-correlated to give an accurate velocity profile. Shear rate, maximum velocity, velocity profile shape, and flow rate, each of which has clinical applications, can be derived from these measurements.

Micro-particle image velocimetry (&mu;PIV) is used to visualize paired images of micro particles seeded in blood flows. The images are cross-correlated to ...

Using Laser Doppler Imaging and Monitoring to Analyze Spinal Cord Microcirculation in Rat

Laser Doppler flowmetry (LDF) is a noninvasive method for blood flow (BF) measurement, which makes it preferable for measuring microcirculatory alterations of the spinal cord. In this article, our goal was to use both Laser Doppler imaging and monitoring to analyze the change of BF after spinal cord injury. Both the laser Doppler image scanner and the probe/monitor were being employed to obtain each readout. The data of LDPI provided a local distribution of BF, which gave an overview of perfusion around the injury site and made it accessible for comparative analysis of BF among different locations. By intensely measuring the probing area over a period of time, a combined probe was used to simultaneously measure the BF and oxygen saturation of the spinal cord, showing overall spinal cord perfusion and oxygen supply. LDF itself has a few limitations, such as relative flux, sensitivity to movement, and biological zero signal. However, the technology has been applied in clinical and experimental study due to its simple setup and rapid measurement of BF.

Here we present a combination of laser Doppler perfusion imaging (LDPI) and laser Doppler perfusion monitoring (LDPM) to measure spinal cord local blood flows and oxygen saturation (SO2), as well as a standardized procedure for introducing spinal cord trauma on rat.

Laser Doppler flowmetry (LDF) is a noninvasive method for blood flow (BF) measurement, which makes it preferable for measuring microcirculatory ...

Behavior

A Novel Application of Musculoskeletal Ultrasound Imaging

Ultrasound is an attractive modality for imaging muscle and tendon motion during dynamic tasks and can provide a complementary methodological approach for biomechanical studies in a clinical or laboratory setting. Towards this goal, methods for quantification of muscle kinematics from ultrasound imagery are being developed based on image processing. The temporal resolution of these methods is typically not sufficient for highly dynamic tasks, such as drop-landing. We propose a new approach that utilizes a Doppler method for quantifying muscle kinematics. We have developed a novel vector tissue Doppler imaging (vTDI) technique that can be used to measure musculoskeletal contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities using ultrasound. The goal of this preliminary study was to investigate the repeatability and potential applicability of the vTDI technique in measuring musculoskeletal velocities during a drop-landing task, in healthy subjects. The vTDI measurements can be performed concurrently with other biomechanical techniques, such as 3D motion capture for joint kinematics and kinetics, electromyography for timing of muscle activation and force plates for ground reaction force. Integration of these complementary techniques could lead to a better understanding of dynamic muscle function and dysfunction underlying the pathogenesis and pathophysiology of musculoskeletal disorders.

We describe a new ultrasound-based vector tissue Doppler imaging technique to measure muscle contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities. This approach provides complementary measurements of dynamic muscle function and could lead to a better understanding of mechanisms underlying musculoskeletal disorders.

Ultrasound is an attractive modality for imaging muscle and tendon  motion during dynamic tasks and can provide a complementary methodological  approach ...

Ultrasound Assessment of Flow-Mediated Dilation of the Brachial and Superficial Femoral Arteries in Rats

Arterial vasodilation to increases in wall shear rate is indicative of vascular endothelial function. In humans, the non-invasive measurement of endothelial function can be achieved by employing the flow-mediated dilation technique, typically performed in the brachial or superficial femoral artery. Briefly, a blood pressure cuff placed distal to an ultrasound probe is inflated to a suprasystolic pressure, which results in limb ischemia. After 5 min of occlusion the cuff is deflated, resulting in reactive hyperemia and increases in wall shear rate that signal vasodilatory molecules to be released from the endothelium eliciting vasodilation. Despite the thousands of studies performing flow-mediated dilation in humans, surprisingly, no studies have performed this technique non-invasively in living rats. Considering the recent shift in focus to translational research, the establishment of guidelines for non-invasive measurement of flow-mediated dilation in rats and other rodents would be extremely valuable. In the following article, a protocol is presented for the non-invasive measurement of flow-mediated dilation in brachial and superficial femoral arteries of rats, as those sites are most commonly measured in humans.

Non-invasive assessment of endothelial function in humans can be determined by the flow-mediated dilation technique. Although thousands of studies have used this technique, no study has performed this technique non-invasively in rats. The following article describes non-invasive measurement of flow-mediated dilation in the brachial and superficial femoral arteries of rats.

Arterial vasodilation to increases in wall shear rate is indicative of vascular endothelial function. In humans, the non-invasive measurement of ...

Spatial Temporal Analysis of Fieldwise Flow in Microvasculature

Changes in blood flow velocity and distribution are vital in maintaining tissue and organ perfusion in response to varying cellular needs. Further, appearance of defects in microcirculation can be a primary indicator in the development of multiple pathologies. Advances in optical imaging have made intravital microscopy (IVM) a practical approach, permitting imaging at the cellular and subcellular level in live animals at high-speed over time. Yet, despite the importance of maintaining adequate tissue perfusion, spatial and temporal variability in capillary flow is seldom documented. In the standard approach, a small number of capillary segments are chosen for imaging over a limited time. To comprehensively quantify capillary flow in an unbiased way we developed Spatial Temporal Analysis of Fieldwise Flow (STAFF), a macro for FIJI open-source&#160;image analysis software. Using high-speed image sequences of full fields of blood flow within capillaries, STAFF produces&#160;images that represent motion over time called kymographs for every time interval for every vascular segment. From the kymographs STAFF calculates velocities from the distance that red blood cells move over time, and outputs the velocity data as a sequence of color-coded spatial maps for visualization and tabular output for quantitative analyses. In normal mouse livers, STAFF analyses quantified profound differences in flow velocity between pericentral and periportal regions within lobules. Even more unexpected are the differences in flow velocity seen between sinusoids&#160;that are side by side and fluctuations seen within individual vascular segments over seconds. STAFF is a powerful new tool capable of providing novel insights by enabling measurement of the complex spatiotemporal dynamics of capillary flow.

To quantify microvascular flow from high speed capillary flow image sequences, we developed STAFF (Spatial Temporal Analysis of Fieldwise Flow) software. Across the full image field and over time, STAFF evaluates flow velocities and generates a sequence of color-coded spatial maps for visualization and tabular output for quantitative analyses.

Changes in blood flow velocity and distribution are vital in maintaining tissue and organ perfusion in response to varying cellular needs. Further, ...

A Novel Approach to Overcome Movement Artifact When Using a Laser Speckle Contrast Imaging System for Alternating Speeds of Blood Microcirculation

The laser speckle contrast imager (LSCI) provides a powerful yet simple technique for measuring microcirculatory blood flow. Ideal for blood dynamic responses, the LSCI is used in the same way as a conventional Laser Doppler Imager (LDI). However, with a maximum skin depth of approximately 1 mm, the LSCI is designed to focus on mainly superficial blood flow. It is used to measure skin surface areas of up to 15 cm x 20 cm. The new technique introduced in this paper accounts for alternating speeds of microcirculations; i.e. both slow and fast flow flux measurement using the LSCI. The novel technique also overcomes LSCI&#39;s biggest shortcoming, which is high sensitivity to artifact movement. An adhesive opaque patch (AOP) is introduced for satisfactory recording of microcirculatory blood flow, by subtracting the LSCI signal from the AOP from the laser speckle skin signal. The optimal setting is also defined because the LSCI is most powerful when flux changes are measured relative to a reference baseline, with blood microcirculatory flux expressed as a percentage change from the baseline. These changes may be used for analyzing the status of the blood flow system.

This study introduces a novel technique for the measurement and analysis of alternating speeds of blood microcirculation in a single experiment using a laser speckle contrast imager.

The laser speckle contrast imager (LSCI) provides a powerful yet simple technique for measuring microcirculatory blood flow. Ideal for blood dynamic ...

Human Fetal Blood Flow Quantification with Magnetic Resonance Imaging and Motion Compensation

Magnetic resonance imaging (MRI) is an important tool for the clinical assessment of cardiovascular morphology and heart function. It is also the recognized standard-of-care for blood flow quantification based on phase contrast MRI. While such measurement of blood flow has been possible in adults for decades, methods to extend this capability to fetal blood flow have only recently been developed.
Fetal blood flow quantification in major vessels is important for monitoring fetal pathologies such as congenital heart disease (CHD) and fetal growth restriction (FGR). CHD causes alterations in the cardiac structure and vasculature that change the course of blood in the fetus. In FGR, the path of blood flow is altered through the dilation of shunts such that the oxygenated blood supply to the brain is increased. Blood flow quantification enables assessment of the severity of the fetal pathology, which in turn allows for suitable&#160;in utero&#160;patient management and planning for postnatal care.
The primary challenges of applying phase contrast MRI to the human fetus include small blood vessel size, high fetal heart rate, potential MRI data corruption due to maternal respiration, unpredictable fetal movements, and lack of conventional cardiac gating methods to synchronize data acquisition. Here, we describe recent technical developments from our lab that have enabled the quantification of fetal blood flow using phase contrast MRI, including advances in accelerated imaging, motion compensation, and cardiac gating.

Here we present a protocol for measuring fetal blood flow rapidly with MRI and retrospectively performing motion correction and cardiac gating.

Magnetic resonance imaging (MRI) is an important tool for the clinical assessment of cardiovascular morphology and heart function. It is also the ...

Ultrafast Doppler Ultrasound for Hepatic Microvasculature Analysis in Mice

Imaging and Quantification of the Hepatic Vasculature of Mice Using Ultrafast Doppler Ultrasound

Non-invasive in vivo imaging of the vasculature is a powerful tool for studying disease mechanisms in rodents. To achieve high sensitivity imaging of the microvasculature using Doppler ultrasound methods, imaging modalities employing the concept of ultrafast imaging are preferred. By increasing the frame rate of the ultrasound scanner to thousands of frames per second, it becomes possible to improve the sensitivity of the blood flow down to 2 mm/s and to obtain functional information about the microcirculation in comparison to a sensitivity of around 1 cm/s in conventional Doppler modes. While Ultrafast Doppler ultrasound (UFUS) imaging has become adopted in neuroscience, where it can capture brain activity through neurovascular coupling, it presents greater challenges when imaging the vasculature of abdominal organs due to larger motions linked to breathing. The liver, positioned anatomically under the diaphragm, is particularly susceptible to out-of-plane movement and oscillating respiratory motion. These artifacts not only adversely affect Doppler imaging but also complicate the anatomical analysis of vascular structures and the computation of vascular parameters. Here, we present a qualitative and quantitative imaging analysis of the hepatic vasculature in mice by UFUS. We identify major anatomical vascular structures and provide graphical illustrations of the hepatic macroscopical anatomy, comparing it to an in-depth anatomical assessment of the hepatic vasculature based on Doppler readouts. Additionally, we have developed a quantification protocol for robust measurements of hepatic blood volume of the microvasculature over time. To contemplate further research, qualitative vascular analysis provides a comprehensive overview and suggests a standardized terminology for researchers working with mouse models of liver disease. Furthermore, it offers the opportunity to apply ultrasound as a non-invasive complementary method to inspect hepatic vascular defects in vivo and measure functional microvascular alterations deep within the organ before unraveling blood vessel anomalies at the micron scale levels using ex vivo staining on tissue sections.

Ultrafast Doppler ultrasound (UFUS) with high spatial resolution (100 &#956;m) and sensitivity represents a suitable noninvasive imaging modality for obtaining a comprehensive qualitative overview of the hepatic vasculature. UFUS also facilitates quantitative measurements of the microvasculature, aiming to enhance our understanding of vascular disease mechanisms.

Non-invasive in vivo imaging of the vasculature is a powerful tool for studying disease mechanisms in rodents. To achieve high sensitivity imaging of the ...

Deep Vascular Imaging in the Eye with Flow-Enhanced Ultrasound

The retina within the eye is one of the most energy-demanding tissues in the body and thus requires high rates of oxygen delivery from a rich blood supply. The capillary lamina of the choroid lines the outer surface of the retina and is the dominating source of oxygen in most vertebrate retinas. However, this vascular bed is challenging to image with traditional optical techniques due to its position behind the highly light-absorbing retina. Here we describe a high-frequency ultrasound technique with subsequent flow-enhancement to image deep vascular beds (0.5-3 cm) of the eye with a high spatiotemporal resolution. This non-invasive method works well in species with nucleated red blood cells (non-mammalian and fetal animal models). It allows for the generation of non-invasive three-dimensional angiographies without the use of contrast agents, and it is independent of blood flow angles with a higher sensitivity than Doppler-based ultrasound imaging techniques.

We present a non-invasive ultrasound technique for generating three-dimensional angiographies in the eye without the use of contrast agents.

The retina within the eye is one of the most energy-demanding tissues in the body and thus requires high rates of oxygen delivery from a rich blood ...