Quantitative Flow Measurements Research Articles

Aerodynamic efficiency explains flapping strategies used by birds

A faster cruising speed increases drag and thereby the thrust (T) needed to fly, while weight and lift (L) requirement remains constant. Birds can adjust their wingbeat in multiple ways to accommodate this change in aerodynamic force, but the relative costs of different strategies remain largely unknown. To evaluate the efficiency of several kinematic strategies, I used a robotic wing [E. Ajanic, A. Paolini, C. Coster, D. Floreano, C. Johansson, Adv. Intell. Syst. 5, 2200148 (2023)] and quantitative flow measurements. I found that, among the tested strategies, changing the mean wingbeat elevation provides the most efficient solution to changing thrust-to-lift ratio (T/L), offering insight into why birds tend to beat their wings with a greater ventral than dorsal excursion. I also found that although propulsive efficiency (ηp) may peak at a Strouhal number (St, measure of relative flapping speed) near 0.3, the overall efficiency of generating force decreases with St. This challenges the expectance of a specific optimal St for flapping flight and instead suggest the chosen St depends on T/L. This may explain variation in preferred St among birds and why bats prefer flying at higher St than birds [G. K. Taylor, R. L. Nudds, A. L. Thomas, Nature 425, 707-711 (2003)], since their body shape imposes relatively higher thrust requirements [F. T. Muijres, L. C. Johansson, M. S. Bowlin, Y. Winter, A. Hedenström, PLoS One 7, e37335 (2012)]. In addition to explaining flapping strategies used by birds, my results suggest alternative, efficient, flapping motions for drones to explore aiming to extend their flight range.

Capillary flow-MRI of micronized fat crystal dispersions: Effect of shear history on microstructure and flow

Micronized fat crystal (MFC) dispersions are a novel food ingredient enabling more efficient manufacturing of fat-based products as compared to established melt-cool processing. Yet, predicting rheological properties of MFC dispersions, remains a challenge. Here, we demonstrate how a capillary-flow Magnetic Resonance Imaging (MRI) platform provides quantitative measurements of local flow of MFC dispersions, inaccessible by global rheology. The measured 2D 1H MRI velocity maps unveiled a 5-fold velocity enhancement, and corresponding increase in wall slip, upon increasing the pre-shear time within 0–5 h, due to the 14 % increase in thickness of the crystalline nanoplatelets via recrystallization and aggregation of nanoplatelets. In the absence of pre-shearing, MFC dispersions exhibit an unsheared band at the walls of the capillary, likely arising from fouling and migration of thin nanoplatelets. In contrast to FCDs, flow cooperativity could not be observed for MFC dispersions due to the non-fractality of the fat crystal network. These results demonstrate that, by varying the pre-shear duration, the flow-microstructure properties of the MFC dispersions can be altered in a controlled manner. The approach presented here will allow for rapid assessment of shear-history dependence of flow properties of MFC dispersions under industrially relevant flow conditions.

Artificial intelligence-based extraction of quantitative ultra-widefield fluorescein angiography parameters in retinal vein occlusion

ObjectiveTo examine the association between quantitative vascular parameters extracted from intravenous fluorescein angiography (IVFA) and baseline clinical characteristics of patients with retinal vein occlusion (RVO). MethodsOur prospective single-centre study in Toronto, Canada, recruited patients with a diagnosis of macular edema secondary to RVO presenting with a central macular thickness (CMT) ≥310 μm from 2017 to 2023. IVFA images were captured using an ultra-widefield scanning laser ophthalmoscope and processed using the artificial intelligence-based RETICAD system to extract quantitative measurements of blood flow, perfusion, and blood–retinal barrier (BRB) permeability. Univariable and multivariable regression models were used to investigate associations between quantitative IVFA parameters and baseline best-corrected visual acuity (BCVA), CMT, and macular volume. ResultsThe study included 41 eyes from 41 RVO patients. In the multivariable analysis, BRB permeability was significantly associated with both CMT (p < 0.001) and macular volume (p = 0.005). Subgroup analyses revealed that in central RVO patients, central BRB permeability remained significantly associated with CMT (p = 0.022) and macular volume (p = 0.010); however, there was no association with BCVA (p = 0.921). In branch RVO patients, central BRB permeability was significantly associated with BCVA (p = 0.006) and CMT (p = 0.009), but not with macular volume (p = 0.723). Additionally, both central and peripheral BRB permeability were significantly higher in patients with RVO compared to healthy controls (p < 0.001). ConclusionsOur investigation reveals novel associations between baseline clinical characteristics and quantitative IVFA parameters in RVO patients, which may serve as clinically relevant biomarkers. Future studies should explore these associations in diverse RVO patient populations with extended follow-up.

Flow capacity of a superficial temporal artery as a donor in a consecutive series of 100 patients with superficial temporal artery-middle cerebral artery bypass.

A superficial temporal artery-middle cerebral artery (STA-MCA) bypass is classically considered a low-flow bypass. It is known that the flow in the flow augmentation STA-MCA bypass is influenced by flow demand of the revascularized territory and can reach significantly higher values. The authors report their intraoperative flow measurement data in a consecutive series of 100 STA-MCA bypasses performed at their institution. Moreover, in a subanalysis, they show the postoperative bypass flow measured with quantitative MR angiography (qMRA) noninvasive optimal vessel analysis (NOVA). Between January 2013 and October 2023, 100 patients with acute, subacute, or chronic large-vessel occlusion (LVO) or moyamoya disease underwent a flow augmentation STA-MCA bypass revascularization at the authors' department with intraoperative bypass flow measurement. Patients with atherosclerotic LVO who underwent bypass surgery within a 6-week period following the onset of ischemic stroke symptoms were categorized into the acute bypass group, encompassing both acute and subacute LVO cases. Conversely, those who underwent bypass surgery > 6 weeks after the last occurrence of ischemic stroke were classified as the chronic group. Since May 2019, a consecutive subgroup of 37 patients received a postoperative (before discharge) bypass flow measurement with the qMRA-NOVA imaging tool. The mean ± SD intraoperative bypass flow in this consecutive series of 100 STA-MCA bypasses was 53.5 ± 28.8 ml/min (range 14-145 ml/min). In the subanalysis, there was no difference in the intraoperative flow capacity between the acute and chronic groups and between the moyamoya and acute groups. Patients in the moyamoya group showed a significantly higher flow rate in the STA-MCA bypass compared with the chronic group (63.0 ± 30.2 ml/min vs 48.4 ± 26.5 ml/min, p = 0.03). In a consecutive subanalysis of 37 STA-MCA bypass cases, postoperative flow measurements were also performed using qMRA-NOVA, showing a significant increase in the flow of STA-MCA bypasses after surgery compared with intraoperative flow measurements (mean intraoperative bypass flow rate vs qMRA-NOVA postoperative bypass flow rate: 73.4 ± 29.9 ml/min vs 111.3 ± 51.4 ml/min, p = 0.005). Using intraoperative and postoperative quantitative flow measurements of the STA, the data confirm that the flow in the flow augmentation STA-MCA bypass is influenced by the flow demand of the revascularized territory and can reach high values if needed. Moreover, the significant flow increase in the postoperative flow measurement using qMRA-NOVA demonstrates that the bypass can increase its flow over time.

Genome-wide quantification of RNA flow across subcellular compartments reveals determinants of the mammalian transcript life cycle

Dissecting the regulatory mechanisms controlling mammalian transcripts from production to degradation requires quantitative measurements of mRNA flow across the cell. We developed subcellular TimeLapse-seq to measure the rates at which RNAs are released from chromatin, exported from the nucleus, loaded onto polysomes, and degraded within the nucleus and cytoplasm in human and mouse cells. These rates varied substantially, yet transcripts from genes with related functions or targeted by the same transcription factors and RNA-binding proteins flowed across subcellular compartments with similar kinetics. Verifying these associations uncovered a link between DDX3X and nuclear export. For hundreds of RNA metabolism genes, most transcripts with retained introns were degraded by the nuclear exosome, while the remaining molecules were exported with stable cytoplasmic lifespans. Transcripts residing on chromatin for longer had extended poly(A) tails, whereas the reverse was observed for cytoplasmic mRNAs. Finally, machine learning identified molecular features that predicted the diverse life cycles of mRNAs.

Differentiation Between High-Grade Glioma and Brain Metastasis Using Cerebral Perfusion-Related Parameters (Cerebral Blood Volume and Cerebral Blood Flow): A Systematic Review and Meta-Analysis of Perfusion-weighted MRI Techniques.

Distinguishing high-grade gliomas (HGGs) from brain metastases (BMs) using perfusion-weighted imaging (PWI) remains challenging. PWI offers quantitative measurements of cerebral blood flow (CBF) and cerebral blood volume (CBV), but optimal PWI parameters for differentiation are unclear. To compare CBF and CBV derived from PWIs in HGGs and BMs, and to identify the most effective PWI parameters and techniques for differentiation. Systematic review and meta-analysis. Twenty-four studies compared CBF and CBV between HGGs (n = 704) and BMs (n = 488). Arterial spin labeling (ASL), dynamic susceptibility contrast (DSC), dynamic contrast-enhanced (DCE), and dynamic susceptibility contrast-enhanced (DSCE) sequences at 1.5 T and 3.0 T. Following the PRISMA guidelines, four major databases were searched from 2000 to 2024 for studies evaluating CBF or CBV using PWI in HGGs and BMs. Standardized mean difference (SMD) with 95% CIs was used. Risk of bias (ROB) and publication bias were assessed, and I2 statistic was used to assess statistical heterogeneity. A P-value<0.05 was considered significant. HGGs showed a significant modest increase in CBF (SMD = 0.37, 95% CI: 0.05-0.69) and CBV (SMD = 0.26, 95% CI: 0.01-0.51) compared with BMs. Subgroup analysis based on region, sequence, ROB, and field strength for CBF (HGGs: 375 and BMs: 222) and CBV (HGGs: 493 and BMs: 378) values were conducted. ASL showed a considerable moderate increase (50% overlapping CI) in CBF for HGGs compared with BMs. However, no significant difference was found between ASL and DSC (P = 0.08). ASL-derived CBF may be more useful than DSC-derived CBF in differentiating HGGs from BMs. This suggests that ASL may be used as an alternative to DSC when contrast medium is contraindicated or when intravenous injection is not feasible. Stage 2.

Quantitative noninvasive measurement of cerebrospinal fluid flow in shunted hydrocephalus.

Standard MRI protocols lack a quantitative sequence that can be used to evaluate shunt-treated patients with a history of hydrocephalus. The objective of this study was to investigate the use of phase-contrast MRI (PC-MRI), a quantitative MR sequence, to measure CSF flow through the shunt and demonstrate PC-MRI as a useful adjunct in the clinical monitoring of shunt-treated patients. The rapid (96 seconds) PC-MRI sequence was calibrated using a flow phantom with known flow rates ranging from 0 to 24 mL/hr. Following phantom calibration, 21 patients were scanned with the PC-MRI sequence. Multiple, successive proximal and distal measurements were gathered in 5 patients to test for measurement error in different portions of the shunt system and to determine intrapatient CSF flow variability. The study also includes the first in vivo validations of PC-MRI for CSF shunt flow by comparing phase-contrast-measured flow rate with CSF accumulation in a collection burette obtained in patients with externalized distal shunts. The PC-MRI sequence successfully measured CSF flow rates ranging from 6 to 54 mL/hr in 21 consecutive pediatric patients. Comparison of PC-MRI flow measurement and CSF volume collected in a bedside burette showed good agreement in a patient with an externalized distal shunt. Notably, the distal portion of the shunt demonstrated lower measurement error when compared with PC-MRI measurements acquired in the proximal catheter. The PC-MRI sequence provided accurate and reliable clinical measurements of CSF flow in shunt-treated patients. This work provides the necessary framework to include PC-MRI as an immediate addition to the clinical setting in the noninvasive evaluation of shunt function and in future clinical investigations of CSF physiology.

Inline automatic quality control of 2D phase-contrast flow MRI for subject-specific scan time adaptation.

To develop an inline automatic quality control to achieve consistent diagnostic image quality with subject-specific scan time, and to demonstrate this method for 2D phase-contrast flow MRI to reach a predetermined SNR. We designed a closed-loop feedback framework between image reconstruction and data acquisition to intermittently check SNR (every 20 s) and automatically stop the acquisition when a target SNR is achieved. A free-breathing 2D pseudo-golden-angle spiral phase-contrast sequence was modified to listen for image-quality messages from the reconstructions. Ten healthy volunteers and 1 patient were imaged at 0.55 T. Target SNR was selected based on retrospective analysis of cardiac output error, and performance of the automatic SNR-driven "stop" was assessed inline. SNR calculation and automated segmentation was feasible within 20 s with inline deployment. The SNR-driven acquisition time was 2 min 39 s ± 67 s (aorta) and 3 min ± 80 s (main pulmonary artery) with a min/max acquisition time of 1 min 43 s/4 min 52 s (aorta) and 1 min 43 s/5 min 50 s (main pulmonary artery) across 6 healthy volunteers, while ensuring a diagnostic measurement with relative absolute error in quantitative flow measurement lower than 2.1% (aorta) and 6.3% (main pulmonary artery). The inline quality control enables subject-specific optimized scan times while ensuring consistent diagnostic image quality. The distribution of automated stopping times across the population revealed the value of a subject-specific scan time.

Water tunnel testing of downwind yacht sails

Downwind yacht sails, such as spinnakers, are low-aspect-ratio highly cambered wings with a sharp leading edge. They are characterised by substantial three-dimensional flow separation and are thus modelled with difficulty with numerical simulations. Furthermore, accurate full-scale validation data are not available. The first quantitative flow measurements have only recently been achieved in water tunnels. In this study, we aim to provide guidelines on this emerging sail testing methodology. We consider six model-scale rigid models at average-chord-based Reynolds numbers ranging from 5 870 to 61 870. A critical Reynolds number is identified, below which relaminarisation of the reattached boundary layer downstream of the leading edge separation bubble occurs. Both lift and drag increase monotonically at subcritical Reynolds numbers while remaining about constant at transcritical Reynolds numbers. The critical Reynolds number decreases with increasing incidence and is insensitive to the blockage ratio. Spinnakers are normally sailed in front of the mainsail, whose circulation is found to generate an approximately 3∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3^{\\circ }$$\\end{document} upwash on the spinnaker and higher flow velocity on both sides of it. These findings provide guidelines for the experimental testing of spinnaker-like wings in water tunnels and provide new insights into the flow and experimental testing of highly cambered wings with massive flow separation at low Reynolds numbers.

Non-invasive low-cost deep tissue blood flow measurement with integrated Diffuse Speckle Contrast Spectroscopy.

Diffuse Correlation Spectroscopy (DCS) is a widely used non-invasive measurement technique to quantitatively measure deep tissue blood flow. Conventional implementations of DCS use expensive single photon counters as detecting elements and optical probes with bulky fiber optic cables. In recent years, newer approaches to blood flow measurement such as Diffuse Speckle Contrast Analysis (DSCA) and Speckle Contrast Optical Spectroscopy (SCOS), have adapted speckle contrast analysis methods to simplify deep tissue blood flow measurements using cameras and single photon counting avalanche detector arrays as detectors. Here, we introduce and demonstrate integrated Diffuse Speckle Contrast Spectroscopy (iDSCS), a novel optical sensor setup which leverages diffuse speckle contrast analysis for probe-level quantitative measurement of tissue blood flow. iDSCS uses a standard photodiode configured in photovoltaic mode to integrate photon intensity fluctuations over multiple integration durations using a custom electronic circuit, as opposed to the high frequency sampling of photon counts with DCS. We show that the iDSCS device is sensitive to deep-tissue blood flow measurements with experiments on a human forearm and compare the sensitivity and dynamic range of the device to a conventional DCS instrument. The iDSCS device features a low-cost, low-power, small form factor instrument design that will enable wireless probe-level measurements of deep tissue blood flow.

Development of an automated region-of-interest-setting method based on a deep neural network for brain perfusion single photon emission computed tomography quantification methods.

A simple noninvasive microsphere (SIMS) method using 123I-IMP and an improved brain uptake ratio (IBUR) method using 99mTc-ECD for the quantitative measurement of regional cerebral blood flow have been recently reported. The input functions of these methods were determined using the administered dose, which was obtained by analyzing the time activity curve of the pulmonary artery (PA) for SIMS and the ascending aorta (AAo) for the IBUR methods for dynamic chest images. If the PA and AAo regions of interest (ROIs) can be determined using deep convolutional neural networks (DCNN) for segmentation, the accuracy of these ROI-setting methods can be improved through simple analytical operations to ensure repeatability and reproducibility. The purpose of this study was to develop new PA and AAo-ROI setting methods using a DCNN (DCNN-ROI method). A U-Net architecture based on convolutional neural networks was used to determine the PA and AAo candidate regions. Images of 290 patients who underwent 123I-IMP RI-angiography and 108 patients who underwent 99mTc-ECD RI-angiography were used. The PA and AAo-ROI results for the DCNN-ROI method were compared to those obtained using manual methods. The counts for the input function on the PA and AAo-ROI were determined by integrating the area under the curve (AUC) counts of the time-activity curve of PA and AAo-ROI, respectively. The effectiveness of the DCNN-ROI method was elucidated through a comparison with the integrated AUC counts of the DCNN-ROI and the manual ROI. The coincidence ratio for the locations of the PA and AAo-ROI obtained using the DCNN method and that for the manual method was 100%. Strong correlations were observed between the AUC counts using the DCNN and manual methods. New ROI- setting programs were developed using a deep convolution neural network DCNN to determine the input functions for the SIMS and IBUR methods. The accuracy of these methods is comparable to that of the manual method.

On the multiple tones in trailing edge noise of an aerofoil at low-to-moderate Reynolds number flows

In this work, the aeroacoustics of a NACA 0012 airfoil are studied at the Reynolds number ranges from 3.2×10^4 to 3.2×10^5, in which region there are controversies of tonal noise generation, especially for multiple tones. Particle image velocimetry and acoustic measurements are simultaneously performed in an anechoic wind tunnel. A dynamic acoustic feedback loop in different flow regimes is proposed to explain the noise generation mechanism. At the low Reynolds number, the existing tonal noise acts as an external force, trigging the upstream flow structures that will interact with the shedding vortices aft the trailing edge. Consequently, this vortex interaction at the hydrodynamic region can modulate the tonal noise amplitude, resulting in the observed secondary tonal noise. Intermittency of vortex dynamics occurs due to tonal noise amplitudes variation. With the increase of Reynolds number, the boundary-layer transition on the suction side leads to a weak tonal noise. If the Reynolds number is higher, the boundary-layer flow on the suction side is turbulent, leading to the dominance of broadband noise. However, flow instability on the pressure side is triggered by the acoustic waves such that the modulation process takes place again. The quantitative measurements of the boundary layer flow and acoustic signals provide insight into understanding the aeroacoustics of airfoils at low-to-moderate Reynolds number.

Low-dose quantitative CT myocardial flow measurement using a single volume scan: phantom and animal validation.

To validate a low-dose, single-volume quantitative CT myocardial flow technique in a cardiovascular flow phantom and a swine animal model of coronary artery disease. A cardiovascular flow phantom was imaged dynamically over different flow rates (0.97 to ) using 15mL of contrast per injection. Six swine () were also imaged dynamically, with different left anterior descending coronary artery balloon stenoses assessed under intracoronary adenosine stress, using of contrast per injection. The resulting images were used to simulate dynamic bolus tracking and peak volume scan acquisition. After which, first-pass single-compartment modeling was performed to derive quantitative flow, where the pre-contrast myocardial attenuation was assumed to be spatially uniform. The accuracy of CT flow was then assessed versus ultrasound and microsphere flow in the phantom and animal models, respectively, using regression analysis. Single-volume quantitative CT flow measurements in the phantom () were related to reference ultrasound flow measurements () by (Pearson's ; ). In the animal model (), they were related to reference microsphere flow measurements () by (Pearson's ; ). The effective dose per CT measurement was 1.21mSv. The single-volume quantitative CT flow technique only requires bolus tracking data, spatially uniform pre-contrast myocardial attenuation, and a single volume scan acquired near the peak aortic enhancement for accurate, low-dose, myocardial flow measurement (in mL/min/g) under rest and adenosine stress conditions.

Quantitative hemodynamic imaging: a method to correct the effects of optical properties on laser speckle imaging.

Studying cerebral hemodynamics may provide diagnostic information on neurological conditions. Wide-field imaging techniques, such as laser speckle imaging (LSI) and optical intrinsic signal imaging, are commonly used to study cerebral hemodynamics. However, they often do not account appropriately for the optical properties of the brain that can vary among subjects and even during a single measurement. Here, we describe the combination of LSI and spatial-frequency domain imaging (SFDI) into a wide-field quantitative hemodynamic imaging (QHI) system that can correct the effects of optical properties on LSI measurements to achieve a quantitative measurement of cerebral blood flow (CBF). We describe the design, fabrication, and testing of QHI. The QHI hardware combines LSI and SFDI with spatial and temporal synchronization. We characterized system sensitivity, accuracy, and precision with tissue-mimicking phantoms. With SFDI optical property measurements, we describe a method derived from dynamic light scattering to obtain absolute CBF values from LSI and SFDI measurements. We illustrate the potential benefits of absolute CBF measurements in resting-state and dynamic experiments. QHI achieved a 50-Hz raw acquisition frame rate with a field of view and flow sensitivity up to . The extracted SFDI optical properties agreed well with a commercial system (). The system showed high stability with low coefficients of variations over multiple sessions within the same day () and over multiple days (). When optical properties were considered, the in-vivo hypercapnia gas challenge showed a slight difference in CBF ( to 0.5% difference). The in-vivo resting-state experiment showed a change in CBF ranking for nine out of 13 animals when the correction method was applied to LSI CBF measurements. We developed a wide-field QHI system to account for the confounding effects of optical properties on CBF LSI measurements using the information obtained from SFDI.

Assessment of the Microcirculation in Superficial and Deep Biotissue with Photobiomodulation

Background Quantitative measurement of blood flow in specific biotissue targets is crucial for photobiomodulation therapy (PBMT). PBMT has been applied on many clinical applications. However, the conclusive confirmation of its effects on microcirculation and laser wavelength dependency in superficial and deep tissues is lacking. Objective This study examines the microcirculatory response and laser wavelength dependency of red and near infrared (NIR) lasers in biotissue. Laser Doppler flowmetry (LDF) was used to assess the flux and velocity of erythrocytes in buccal tissue when exposed to 660 nm and 830 nm laser radiation. Discussion The microcirculatory response of subjects during and after laser radiation were analyzed. Each laser has an energy density of 73.17 J/cm2 . Both the 660 nm and 830 nm lasers demonstrated the capability to enhance microcirculation in both superficial and deep tissues. Furthermore, we observed that laser wavelengths at 660 nm and 830 nm respectively enhanced the microcirculatory response in superficial and deep tissues. Importantly, this cumulative effect persisted for at least 10 minutes. Conclusions The present results indicate that PBM can effectively improve local blood perfusion in specific target areas and peripheral biotissues. These findings have potential applications in enhancing wound healing and local microcirculation within the target areas.

Quantitative Flow Measurements of Pelvic Venous Vasculature Using 4D Flow MRI

To evaluate 4D Flow magnetic resonance imaging (MRI) sequences for quantitative flow measurements of the pelvic venous vasculature. A prospective study of healthy volunteers was performed. After informed consent all subjects underwent 4D flow sequences at a 3 T MRI scanner with different isotropic resolution and different velocity encoding (Venc) settings: (sequence #1) voxel size (VS) 1.63 mm3, Venc 50cm/s; (sequence #2) VS 1.63 mm3, Venc 100cm/s and (sequence #3) VS 2.03 mm3, Venc 50cm/s. Perfusion parameters were calculated for all venous vessel segments starting at the level of the inferior vena cava and extending caudally to the level of the common femoral vein. For reference, arterial flow was calculated using 1.63 mm3 isotropic resolution with a Venc of 100cm/s. Ten healthy subjects (median age 28 years, interquartile range [IQR]: 26.25-28 years) were enrolled in this study. Median scanning time was 12:12 minutes (IQR 10:22-13:32 minutes) for sequence #1, 11:02 minutes (IQR 9:57-11:19 minutes) for sequence #2 and 6:10 minutes (IQR 5:44-6:47 minutes) for sequence #3. Flow measurements were derived from all sequences. The venous pelvic vasculature showed similar perfusion parameters compared to its arterial counterpart, for example the right common iliac arterial segment showed a perfusion of 8.32ml/s (IQR: 6.94-10.68ml/s) versus 7.29ml/s (IQR: 4.70-8.90ml/s) in the corresponding venous segment (P=0.218). The venous flow measurements obtained from the three investigated sequences did not reveal significant differences. 4D Flow MRI is suitable for quantitative flow measurement of the venous pelvic vasculature. To reduce the scanning time without compromising quantitative results, the resolution can be decreased while increasing the Venc. This technique may be utilized in the future for the diagnosis and treatment response assessment of iliac vein compression syndromes.

Time–frequency analysis of laser speckle contrast for transcranial assessment of cerebral blood flow

Improving noninvasive approaches to monitoring blood microcirculation is an urgent topic in modern biomedical engineering. One of the actively developing methods is laser speckle contrast imaging (LSCI), which allows not only the visualization of microvessels but also the quantitative measurements of microcirculatory blood flow. This work shows the application of LSCI for mapping the cerebral vessels of a laboratory animal, and also presents the time–frequency processing of the registered signal. Thus, we expand the capabilities of the existing LSCI approach and demonstrate spatial mapping of blood flow rhythms. The proposed technology makes it possible not only to measure the relative cerebral blood flow but also to expand diagnostic capabilities for a detailed analysis of the physiological mechanisms of changes in blood flow.

Malperfusion in dilated cardiomyopathy: One more link in the pathologic chain?

Dilated cardiomyopathy (DCM) is considered the primary non-ischemic heart disease, but there are controversial data regarding the microcirculatory disturbance in these patients. While the major epicardial vessels are always intact in these patients, the malperfusion of the myocardium of the left ventricle (LV) may be present, and the role of this malperfusion in the progression of the disease is not clear. The non-invasive echocardiographic assessment of the coronary blood flow reveals that it may be increased at rest and decreased during pharmacological stress, leading to a decreased coronary flow reserve.1 Beyond echocardiographic studies, microvascular dysfunction in DCM has been previously investigated with various imaging modalities. Bietenbeck M. et al. performed the quantitative myocardial first-pass perfusion cardiovascular magnetic resonance (CMR) imaging and coronary sinus flow measurements at rest and during maximal vasodilatation which is a well-validated approach for the quantification of global myocardial blood flow in CMR. The blood flow parameters were reduced at rest and during stress in both groups of patients with DCM and hypertrophic cardiomyopathy.2 Interestingly, in another study, it was shown that myocardial blood flow assessed by the CMR in DCM could be elevated at rest with a substantial decrease during the stress-test with adenosine. This corresponds well with the previous echocardiographic findings and also can reflect the possible stress-induced stunning instead of chronic hypoperfusion in DCM.3 Another promising in microcirculation evaluation, though not a fully available modality, is PET. In a study by Yamaguchi et al., the authors observed the regional 18-fluorodesoxiglucose uptake in all patients with ischemic cardiomyopathy in the fasting state, while patients with DCM showed variable patterns of uptake. Nevertheless, when going to glucose loading state, the DCM patients demonstrated mostly non-reversing patterns of uptake, which allows PET to distinguish DCM from ischemic cardiomyopathy.4 (99 m)Tc-methoxy-isobutyl-isonitrile and (123)I-15-(p-iodophenyl)-3(R,S)-methylpentadecanoic acid dual single photon emission computed tomography also provides valuable data on perfusion-metabolism mismatches, which carry the prognostic role in DCM.5 Myocardial contrast echocardiography (MCE) being a more simple, bedside method has been previously found to be helpful in differentiating the DCM and ischemic heart disease in patients with acute onset of heart failure.6 However, another group of authors has the confronting results: the contrast replenishment rate was similar in patients with coronary artery disease and without it.7 In this issue of the Journal of Clinical Ultrasound Sha Tang et al, for the first time the MCE was combined with speckle tracking strain analysis in a layer-specific manner in patients with DCM and compared with the same parameters in healthy volunteers.8 While the poor global and regional LV systolic function assessed by speckle tracking strain in DCM patients in comparison to healthy subjects is awaited, the authors performed the comprehensive analysis of the interaction between segmental parameters by dividing the myocardium into standard segments plus three layers in each segment. Therefore, the data on gradients in strain and perfusion parameters becomes the mainstay of this study. The idea of layer-specific strain analysis is not new, but still can be regarded as a pure experimental method with no clinical implication. For example, in the work by Nagata Y et al. the authors offer Endo/Epi strain ratio for gradient assessment.9 Therefore, the authors demonstrated an interesting correlation between MCE perfusion and longitudinal function at rest in DCM patients with the diffuse pattern of impairment in all segments and layers. Considering the aforementioned CMR-based and PET-based studies, which showed a substantial decrease in coronary flow reserve between rest and stress, the MCE with pharmacological stress could be the rational development of basic ideas, presented in this study. Moreover, the dynamic nature of MCE can give the opportunity for dynamic malperfusion assessment in patients with DCM during stress. In addition, new insights into the pathophysiology of DCM may provide the basis for new clinical trials of various agents, intended to restore the damaged microcirculatory link in the chain of global LV deterioration. The authors have nothing to disclosure. Open Access funding enabled and organized by Projekt DEAL. Not applicable.

Long-Term Prognostic Value of 82Rb PET/CT-Determined Myocardial Perfusion and Flow Reserve in Cancer Patients.

Myocardial flow reserve (MFR), derived from quantitative measurements of myocardial blood flow during PET imaging, provides prognostic information on patients with coronary artery disease (CAD), but it is not known if this also applies to cancer patients with a competing risk for mortality. Methods: To determine the prognostic value of MFR in patients with cancer, we designed a retrospective cohort study comprising 221 patients with known or suspected CAD (median age, 71 y; range, 41-92 y) enrolled between June 2009 and January 2011. Most patients were referred for perioperative risk assessment. Patients underwent measurement of myocardial blood flow at rest and during pharmacologic stress, using quantitative 82Rb PET imaging. They were divided into early-stage versus advanced-stage cancer groups based on cancer histopathology and clinical state and were further stratified by myocardial perfusion summed stress score, summed difference score, and calculated MFR. Overall survival (OS) was assessed using the Kaplan-Meier estimator, and Cox proportional-hazards regression helped identify independent predictors for OS. Results: During a follow-up of 85.6 mo, 120 deaths occurred. MFR, summed difference score, and cancer stage were significantly associated with OS. In the age-adjusted Cox hazard multivariable analysis, MFR and cancer stage remained independent prognostic factors. MFR combined with cancer stage enhanced OS discrimination. The groups had significantly different outcomes (P < 0.001), with 5-y OS of 88% (MFR ≥ 1.97 and early-stage), 53% (MFR < 1.97 and early-stage), 33% (MFR ≥ 1.97 and advanced-stage), and 13% (MFR < 1.97 and advanced-stage). Conclusion: Independent of cancer stage, MFR derived from quantitative PET was prognostic of OS in our cohort of cancer patients with known or suspected CAD. Combining these 2 parameters enhanced discrimination of OS, suggesting that MFR improves risk stratification and may serve as a treatment target to increase survival in cancer patients.

Improving Detection of CAD and Prognosis with PET/CT Quantitative Absolute Myocardial Blood Flow Measurements.

The purpose of this review is to provide an overview of the role of PET MPI in the detection of CAD, focussing on the added value of MBF for diagnosis and prognostication. Positron emission tomography (PET) myocardial perfusion imaging (MPI) is increasingly used for the risk stratification of patients with suspected or established coronary artery disease (CAD). PET MPI provides accurate and reproducible non-invasive quantification of myocardial blood flow (MBF) at rest and during hyperemia, providing incremental information over conventional myocardial perfusion alone. Inclusion of MBF in PET MPI interpretation improves both its sensitivity and specificity. Moreover, quantitative MBF measurements have repeatedly been shown to offer incremental and independent prognostic information over conventional clinical markers in a broad range of conditions, including in CAD. Quantitative MBF measurement is now an established and powerful tool enabling accurate risk stratification and guiding patients' management. The role of PET MPI and flow quantification in cardiac allograft vasculopathy (CAV), which represents a particular form of CAD, will also be reviewed.