Quantitative Flow Measurements Research Articles

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.

Single-shot temporal speckle correlation imaging using rolling shutter image sensors

We propose a single-shot wide-field imaging method that maps local temporal intensity decorrelations of dynamic speckle fields. Our method, named rolling shutter speckle imaging (RSSI), utilizes short time intervals between each row of a rolling shutter complementary metal–oxide–semiconductor (RS-CMOS) image sensor to discern fast temporal changes in the speckle field, which otherwise requires sequential measurements with high-speed cameras. RSSI generates elongated speckle patterns on an RS-CMOS image sensor and quantifies temporal decorrelations of speckle fields from row-by-row intensity correlations (RICs) within a single image. To quantify the local speckle decorrelation times of dynamic scattering media, we derived a theoretical model for RIC and verified the model using numerical simulations and flow-phantom experiments. Further, our in vivo imaging results show that RSSI can map the flow rate distributions in cerebral blood vessels with the correction of static scattering in the tissue, demonstrating that RSSI is a powerful and cost-effective imaging tool for in vivo quantitative blood flow measurements.

Influence of Respiration on Collateral Flow in the Fontan Population Using Real-time Phase-contrast Cardiovascular Magnetic Resonance: Collateral Flow Does Not Protect the Ventricle From Volume Deficiency and Diastolic Dysfunction.

The clinical significance of collateral flow for the ventricular function of patients with univentricular hearts is often debated. This study evaluates the impact of collateral flow on respiration-dependent preload modification and diastolic function in Fontan patients assessed by systemic and pulmonary vein (PV) flow patterns. Real-time phase-contrast cardiovascular magnetic resonance was performed in the right upper PV, ascending aorta, superior, and inferior vena cava (IVC) in 21 Fontan patients and 11 healthy individuals. The patients' respiratory cycle was divided into 4 periods to generate respiratory-dependent stroke volumes (SV i ). Conventional quantitative blood flow measurements were used to quantify and differentiate between low (group A) and high (group B) collateral flow. Group B showed significantly lower SV i IVC in inspiration, end-inspiration, expiration, and SV i ΔIVC compared with group A (23.6±4.8mL/m 2 to 33.4±8.0; P =0.005). PV flow resulted in a lower mean SV i PV (11.6±7.6mL/m 2 , vs. 14.0±11.4mL/m 2 ) as well as a significantly lower peak systolic S-wave velocity (S max ) ( P =0.005), S/D-ratio (S max /peak diastolic wave velocity) ( P =0.015), and shorter diastolic deceleration time (DT D ; P =0.030; median DT D =134ms) compared with group A (DT D =202ms). This study demonstrates the incapability of Fontan patients to properly increase preload by inspiration in the presence of significant collateral flow. The results further show that collateral flow is associated with a volume-deprived ventricle and impaired diastolic function.

Quantitative regional cerebral blood flow measurement using near-infrared spectroscopy and indocyanine green in patients undergoing superficial temporal to middle cerebral artery bypass for moyamoya disease: a novel method using a frequency filter.

Measuring regional cerebral blood flow (rCBF) after revascularization for moyamoya disease, as a type of ischemic cerebrovascular disease, is crucial. This study aims to validate our novel technology that combines near-infrared spectroscopy (NIRS) with a frequency filter to extract the arterial component. We measured rCBF before and after revascularization for moyamoya disease and at the end of the surgery using NIRO-200NX (Hamamatsu Photonics, Japan) and indocyanine green (ICG). rCBF was calculated using Fick's principle, change in arterial ICG concentrations, and maximum arterial ICG concentration. rCBF measured with NIRS (rCBF_N) was compared with pre- and postoperative rCBF measured with SPECT (rCBF_S). Thirty-four procedures were analyzed. rCBF_N increased from baseline to end of the surgery (mean difference (MD), 2.99ml/min/100g; 95% confidence interval (CI), 0.40-5.57ml/min/100g on the diseased side; MD, 4.94ml/min/100g; 95% CI, 2.35-7.52ml/min/100g on the non-diseased side). Similar trends were observed for rCBF_S (MD, 3.98ml/min/100g; 95% CI, 2.30-5.67ml/min/100g on the diseased side; MD, 2.77ml/min/100g; 95% CI, 1.09-4.45ml/min/100g on the non-diseased side). Intraclass correlations 3 (ICC3s) between rCBF_N and rCBF_S were weak on the diseased side (ICC3, 0.25; 95% CI, -0.03-0.5; p = 0.07) and the non-diseased side (ICC3, 0.24; 95% CI, -0.05-0.5; p = 0.08). rCBF measurements based on this novel method were weakly correlated with rCBF measurements with SPECT.

Experimental Investigation of Simple-Built and Low-Speed Water Tunnel as a Platform for Studying Fluid Flow Using PIV Measurements

We present a thorough experimental investigation of a simple-built low-speed water tunnel that could facilitate the study of some of the primary fluid dynamic concepts based on quantitative flow measurements using Particle Image Velocimetry (PIV). The water tunnel system is designed and built using a simple arrangement of a double reservoir tank and a centrifugal pump that drives the fluid flow at low speed into a square cross-sectional and relatively short test section. The study shows that the system reasonably and steadily generates fully developed flows inside the test section with <20% of point velocity variations. Based on the fluid-structure tests, it is also observed that the system could produce moderately consistent boundary layer separation phenomena with the variance of the area mean vorticity within 25%. With this performance, we show that the system fulfills the essential requirement to be used as a simple, easy-to-operate, and easy-to-maintain educational platform to study fluid dynamic phenomena related to the interaction of a static sub-merged object and fluid flow.

Acute effect of resistance exercise at different velocities on stiffness and vascularity of the biceps brachii muscle: a preliminary study.

Resistance exercise can be defined as the percentage of maximal strength (%1 repetition maximum) used for a particular exercise. Shear wave elastography (SWE) is a robust and novelty imaging technique that provides information regarding tissue stiffness. Superb microvascular imaging (SMI) is a non-irradiating technique that can provide quantitative measurement of muscle blood flow non-invasively. To compare the acute effects of low- and high-velocity resistance exercise on stiffness and blood flow in the biceps brachii muscle (BBM) using SWE and SMI. This prospective study included 60 healthy men (mean age=28.9 years; age range=26-34 years). BBM stiffness was measured by using SWE at rest, after low- and high-velocity resistance exercise, and muscle blood flow was also evaluated by SMI. Resistance exercise was performed using a dumbbell with a mass adjusted to 70%-80% of one-repetition maximum. The stiffness values increased significantly from resting to high- and low-velocity resistance exercises. There was no significant difference between the elastography values of the BBM after the high- and low-velocity resistance exercise. The blood flow increased significantly from resting to high- and low-velocity resistance exercises. Blood flow increase after low-velocity exercise was significantly higher compared to high-velocity exercise. While muscle stiffness parameters and blood flow significantly increased from resting after both high- and low-velocity resistance exercises, blood flow significantly increased after low-velocity exercise compared to high-velocity exercise. This can mean that metabolic stress, an important trigger for muscle development, is more likely to occur in low-velocity exercise.

Accelerated two-dimensional phase-contrast for cardiovascular MRI using deep learning-based reconstruction with complex difference estimation.

To develop and validate a deep learning-based reconstruction framework for highly accelerated two-dimensional (2D) phase contrast (PC-MRI) data with accurate and precise quantitative measurements. We propose a modified DL-ESPIRiT reconstruction framework for 2D PC-MRI, comprised of an unrolled neural network architecture with a Complex Difference estimation (CD-DL). CD-DL was trained on 155 fully sampled 2D PC-MRI pediatric clinical datasets. The fully sampled data ( ) was retrospectively undersampled (6-11 ) and reconstructed using CD-DL and a parallel imaging and compressed sensing method (PICS). Measurements of peak velocity and total flow were compared to determine the highest acceleration rate that provided accuracy and precision within . Feasibility of CD-DL was demonstrated on prospectively undersampled datasets acquired in pediatric clinical patients ( ) and compared to traditional parallel imaging (PI) and PICS. The retrospective evaluation showed that 9 accelerated 2D PC-MRI images reconstructed with CD-DL provided accuracy and precision (bias, [95 confidence intervals]) within . CD-DL showed higher accuracy and precision compared to PICS for measurements of peak velocity (2.8 [ , 4.5] vs. 3.9 [ , 4.9]) and total flow (1.8 [ , 3.4] vs. 2.9 [ , 6.9]). The prospective feasibility study showed that CD-DL provided higher accuracy and precision than PICS for measurements of peak velocity and total flow. In a retrospective evaluation, CD-DL produced quantitative measurements of 2D PC-MRI peak velocity and total flow with error in both accuracy and precision for up to 9 acceleration. Clinical feasibility was demonstrated using a prospective clinical deployment of our 8 undersampled acquisition and CD-DL reconstruction in a cohort of pediatric patients.

Pseudocontinuous Arterial Spin Labeling: Clinical Applications and Usefulness in Head and Neck Entities.

Simple SummaryConventional imaging methods, such as ultrasonography, computed tomography, and magnetic resonance imaging may be inadequate to accurately diagnose lesions of the head and neck because they vary widely. Recently, the arterial spin labeling technique, especially pseudocontinuous arterial spin labeling (pCASL) with the three-dimensional (3D) readout method, has been dramatically developed to improve diagnostic performance for lesion differentiation, which can show prominent blood flow characteristics. Here, we demonstrate the clinical usefulness of 3D pCASL for diagnosing various entities, including inflammatory lesions, hypervascular lesions, and neoplasms in the head and neck, for evaluating squamous cell carcinoma (SCC) treatment responses, and for predicting SCC prognosis.As functional magnetic resonance imaging, arterial spin labeling (ASL) techniques have been developed to provide quantitative tissue blood flow measurements, which can improve the performance of lesion diagnosis. ASL does not require contrast agents, thus, it can be applied to a variety of patients regardless of renal impairments and contrast agent allergic reactions. The clinical implementation of head and neck lesions is limited, although, in recent years, ASL has been increasingly utilized in brain lesions. Here, we review the development of the ASL techniques, including pseudocontinuous ASL (pCASL). We compare readout methods between three-dimensional (3D) turbo spin-echo and 2D echo planar pCASL for the clinical applications of pCASL to head and neck lesions. We demonstrate the clinical usefulness of 3D pCASL for diagnosing various entities, including inflammatory lesions, hypervascular lesions, and neoplasms; for evaluating squamous cell carcinoma (SCC) treatment responses, and for predicting SCC prognosis.

Effects of surfactant size and concentration on the internal flow fields of moving slug and Disk-like droplets via μ-PIV

• • A laser-based phase-locking system is developed and integrated with a Micro Particle Image Velocimetry system enabling quantitative measurement of the internal velocity of moving droplets. • • Effects of surfactant size on the flow field of moving droplets are investigated by choosing two surfactants, Sodium Dodecyl Sulphate (SDS) and Tween 20, which have a large difference in adsorption timesale. • • Effects of surfactant concentration (zero to 10X) on the internal flow field of moving droplets are evaluated and discussed. • • Effects of droplet shape (slug and spherical) and droplet generation regimes on the internal flow field of moving droplets with surfactant are investigated and discussed. • • It is revealed that achievement of complete remobilisation in the internal flow depends on surfactant type, concentration, and droplet operating regime. Understanding the effects of surfactant on the internal flow field of moving droplets is of fundamental and practical importance. A laser-based phase-locking system was developed and coupled with a micro particle image velocimetry system enabling quantitative measurement of the internal droplet flow filed. Five concentrations (zero to 10X critical micelle concentration) of each of the two surfactants, Sodium Dodecyl Sulphate (SDS) and Tween 20, which present a large difference in adsorption timescale, were evaluated. Slug- and disk-shaped droplets were considered because of their different contact area with channel walls and thus the resulted friction. Squeezing and transition droplet formation regimes which normally yield monodispersed droplets were evaluated using SDS. Flow retardation was observed at low surfactant concentrations for slug droplets, which was primarily attributed to the induced Marangoni flow opposing the internal flow. Achievement of complete remobilisation in the internal flow depends on surfactant type, concentration, and droplet operating regime.

Diagnostic efficiency and incremental value of myocardial blood flow quantification by CZT SPECT for patients with coronary artery disease

Objective: To investigate the diagnostic efficiency and incremental value of quantitative myocardial blood flow measurements by Cadmium-Zine-Telluride (CZT) single photon emission computed tomography (SPECT) dynamic myocardial perfusion imaging (MPI) in patients with coronary artery disease (CAD) compared with traditional semi-quantitative measurements by MPI. Methods: This is a retrospective, cross-sectional study. We retrospectively analyzed clinical data of patients with suspected or known CAD, who underwent the dynamic MPI quantitative blood flow measurement of CZT SPECT in TEDA International Cardiovascular Hospital from October 2018 to December 2020. Clinical data, semi-quantitative parameters (stress score (SS), rest score (RS) and different score (DS)) and myocardial quantitative blood flow parameters (rest myocardial blood flow (rMBF), stress myocardial blood flow (sMBF) and myocardial flow reserve (MFR)) were analyzed. According to the results of coronary angiography, patients were divided into the stenosis group and the control group with coronary artery stenosis ≥50% or ≥75% as the diagnosis criteria. The differences of quantitative and semi-quantitative parameters between the two groups were compared, and the diagnostic efficacy was compared by receiver operating characteristic(ROC) curve. Results: A total of 98 patients with a mean age of (62.1±8.7) years were included in the study, including 66 males (67%). At the patient level, with the positive standard of coronary artery stenosis≥50%, the left ventricle (LV) stress MBF (LV-sMBF) ((1.36±0.45) ml·min-1·g-1) and LV-MFR (1.45±0.43) of the stenosis group were lower than the LV-sMBF ((2.09±0.64) ml·min-1·g-1) and LV-MFR (2.17±0.54) of control group; summed SS and summed DS were higher than control group (all P<0.05). With the positive standard of coronary artery stenosis ≥75%, the LV-sMBF ((1.19±0.34) ml·min-1·g-1) and LV-MFR (1.34±0.35) of stenosis group were lower than the LV-sMBF ((1.94±0.63) ml·min-1·g-1) and MFR (2.00±0.58) of control group; all semi-quantitative parameters were higher than control group (all P<0.05). At the vascular level, with coronary artery stenosis ≥50% as the diagnosis criteria, the sMBF ((1.26±0.49) ml·min-1·g-1) and MFR (1.35±0.46) of stenosis group were lower than the sMBF ((1.95±0.70) ml·min-1·g-1) and MFR (2.05±0.65) of control group; SS and DS were higher than control group (all P<0.05). With coronary artery stenosis≥75% as the diagnosis criteria, the sMBF ((1.12±0.41) ml·min-1·g-1) and MFR (1.25±0.38) of stenosis group were lower than the sMBF ((1.84±0.70) ml·min-1·g-1) and MFR (1.93±0.66) of control group; all semi-quantitative parameters were higher than control group (all P<0.05). With coronary artery stenosis≥50% as the diagnosis criteria and CAG as the reference standard, the AUC and 95%CI of myocardial quantitative blood flow parameters indicated by ROC curve for diagnosis of CAD were 0.830 (0.783-0.877). The sensitivity (86.1% vs. 61.5%), specificity (82.6% vs. 73.8%), positive predictive value (77.8% vs. 62.5%), negative predictive value (89.3% vs. 73.0%) and accuracy (84.0% vs. 68.7%) were all higher than the semi-quantitative parameters (all P<0.05). With coronary artery stenosis≥75% as the diagnosis criteria, the AUC and 95%CI of myocardial quantitative blood flow parameters indicated by ROC curve for diagnosis of CAD were 0.832(0.785-0.879). The sensitivity (89.2% vs. 67.6%), negative predictive value (95.5% vs. 86.2%) and accuracy (80.6% vs. 68.0%) were all higher than semi-quantitative parameters (all P<0.05). Conclusion: Compared with traditional SPECT MPI derived semi-quantitative parameters, diagnostic efficacy for CAD is higher using CZT SPECT quantitative myocardial blood flow parameters, this strategy thus has additional diagnostic benefits and incremental value on the diagnosis of CAD.

Intracranial-Intracranial Bypass for Aneurysms: Quantitative Intraoperative Assessment of Flow Preservation.

Intraoperative flow measurement has proven utility in extracranial-intracranial bypass, particularly in assessing the adequacy of donors by measurement of cut flow. The nature of intracranial-intracranial (IC-IC) bypass precludes cut flow measurement, but quantitative intraoperative flow measurements may evaluate augment assessment of the bypass. To retrospectively evaluate flow measurements performed in IC-IC bypass to determine the adequacy of the constructs in preserving flow. With institutional review board approval, we performed a retrospective review of our bypass database from 2001 to 2021 for aneurysms treated with IC-IC bypass and with intraoperative flow measurements. Patients' preoperative characteristics, bypass indications, prebypass and postbypass intraoperative flow measurements, and patient outcomes were recorded. Of 346 bypasses, 21 cases using 22 IC-IC bypasses were included. The median age was 55 years; 13 of 21 cases were ruptured aneurysms. Aneurysms involved posterior inferior cerebellar artery (n = 7), middle cerebral artery (n = 6), distal anterior cerebral artery (n = 5), and anterior communicating artery (n = 3). Six bypasses were end-to-side (ETS), 10 were side-to-side (STS), and 6 were excisional with reanastomosis (end-to-end, ETE). Intraoperatively, 21 of the bypasses were patent; the postbypass/prebypass flow index averaged 1.15 (±0.32): ETE (n = 6) 1.22 ± 0.34 and ETS/STS bypasses (n = 15) 1.11 ± 0.32. All intraoperatively patent bypasses were patent on postoperative angiography. One occluded on delayed angiography without clinical sequelae. Despite advances in endovascular therapy, IC-IC bypass remains essential to the treatment of large and fusiform aneurysms. We demonstrate quantitatively that IC-IC donors provide adequate direct (ETE) and redistributed (STS ETS) flow to the recipient territory. Flow measurement provides valuable information regarding the patency and adequacy of IC-IC bypass for flow preservation.

Impact of signal strength on quantitative retinal and choriocapillaris flow measurement from optical coherence tomography angiography

We evaluated the impact of signal strength (SS) on quantitative measurements from optical coherence tomography (OCTA). Twenty healthy-volunteers were included. A neutral density filter (NDF) was attached to spectral-domain OCTA (SD-OCTA) and swept-source OCTA (SS-OCTA). All subjects were imaged with both devices three times using three different conditions: no filter, NDF0.3, and NDF0.6. For SD-OCTA, SS decreased from 10.0 to 8.2 and 4.0 with the NDF0.3 and 0.6, respectively. The vessel density (VD) and vessel length density (VLD) of the superficial capillary plexus (SCP) decreased when SS decreased from 10 to 8.2, but no further decrease when SS changed from 8.2 to 4.0. The flow metrics of the deep capillary plexus (DCP) did not change. For SS-OCTA, SS decreased from 10 to 9.5 and 7.2. The VD and VLD of the SCP and DCP decreased when SS decreased, except for the VD of the DCP when SS changed from 10 to 9.5. The choriocapillaris flow deficits significantly increased along with the decrease in SS. Quantitative flow parameters were significantly affected by a small change in SS and were most conspicuous in the SCP and choriocapillaris. These finding highlight the importance of high and consistent SS in quantitative OCTA studies.

Quantitative Blood Flow Measurements in the Common Carotid Artery: A Comparative Study of High-Frame-Rate Ultrasound Vector Flow Imaging, Pulsed Wave Doppler, and Phase Contrast Magnetic Resonance Imaging.

V Flow is commercially developed by high-frame-rate ultrasound vector flow imaging. Compared to conventional color Doppler, V Flow is angle-independent and is capable of measuring both the magnitude and the direction of blood flow velocities. This paper aims to investigate the differences between V Flow and pulsed wave Doppler (PW) relative to phase contrast magnetic resonance imaging (PC-MRI), for the quantitative measurements of blood flow in common carotid arteries (CCA) and, consequently, to evaluate the accuracy of the new technique, V Flow. Sixty-four CCAs were measured using V Flow, PW, and PC-MRI. The maximum velocities, time-averaged mean (TAMEAN) velocities, and volume flow were measured using different imaging technologies. The mean error with standard deviation (Std), the median of absolute errors, and the r-values between V Flow and PC-MRI results for the maximum velocity, the TAMEAN velocity, and the volume flow measurements are {9.40% ± 14.91%; 11.84%; 0.84}, {21.52% ± 14.46%; 19.28%; 0.86}, and {−2.80% ± 14.01%; 10.38%; 0.7}, respectively, and are {53.44% ± 29.68%; 49.79%; 0.74}, {27.83% ± 31.60%; 23.83; 0.71}, and {21.01% ± 29.64%; 25.48%; 0.34}, respectively, for those between PW and PC-MRI. The boxplot, linear regression and Bland–Altman plots were performed for each comparison, which illustrated that the results measured via V Flow rather than via PW agreed more closely with those measured via PC-MRI.

From Fluid Flow to Coupled Processes in Fractured Rock: Recent Advances and New Frontiers

AbstractQuantitative predictions of natural and induced phenomena in fractured rock is one of the great challenges in the Earth and Energy Sciences with far‐reaching economic and environmental impacts. Fractures occupy a very small volume of a subsurface formation but often dominate fluid flow, solute transport and mechanical deformation behavior. They play a central role in CO2 sequestration, nuclear waste disposal, hydrogen storage, geothermal energy production, nuclear nonproliferation, and hydrocarbon extraction. These applications require predictions of fracture‐dependent quantities of interest such as CO2 leakage rate, hydrocarbon production, radionuclide plume migration, and seismicity; to be useful, these predictions must account for uncertainty inherent in subsurface systems. Here, we review recent advances in fractured rock research covering field‐ and laboratory‐scale experimentation, numerical simulations, and uncertainty quantification. We discuss how these have greatly improved the fundamental understanding of fractures and one's ability to predict flow and transport in fractured systems. Dedicated field sites provide quantitative measurements of fracture flow that can be used to identify dominant coupled processes and to validate models. Laboratory‐scale experiments fill critical knowledge gaps by providing direct observations and measurements of fracture geometry and flow under controlled conditions that cannot be obtained in the field. Physics‐based simulation of flow and transport provide a bridge in understanding between controlled simple laboratory experiments and the massively complex field‐scale fracture systems. Finally, we review the use of machine learning‐based emulators to rapidly investigate different fracture property scenarios and accelerate physics‐based models by orders of magnitude to enable uncertainty quantification and near real‐time analysis.

Quantitative angiographic haemodynamic evaluation of bypasses for complex aneurysms: a preliminary study

ObjectiveOpen microsurgery, often with bypass techniques, is indispensable for complex aneurysms. To date, it remains unknown whether arterial anatomy or quantitative blood flow measurements can predict insufficient flow-related stroke (IRS)....

Dynamic MR imaging of cerebral perfusion during bicycling exercise

Habitual physical activity is beneficial for cerebrovascular health and cognitive function. Physical exercise therefore constitutes a clinically relevant cerebrovascular stimulus. This study demonstrates the feasibility of quantitative cerebral blood flow (CBF) measurements during supine bicycling exercise with pseudo-continuous arterial spin labeling (pCASL) magnetic resonance imaging (MRI) at 3 Tesla.Twelve healthy volunteers performed a steady-state exercise-recovery protocol on an MR-compatible bicycle ergometer, while dynamic pCASL data were acquired at rest, during moderate (60% of the age-predicted supine maximal heart rate (HRmax)) and vigorous (80% of supine HRmax) exercise, and subsequent recovery. These CBF measurements were compared with 2D phase-contrast MRI measurements of blood flow through the carotid arteries. Procedures were repeated on a separate day for an assessment of measurement repeatability.Whole-brain (WB) CBF was 41.2 ± 6.9 mL/100 g/min at rest (heart rate 63 [57-71] beats/min), remained similar at moderate exercise (102 [97-107] beats/min), decreased by 10% to 37.1 ± 5.7 mL/100 g/min (p = 0.001) during vigorous exercise (139 [136-142] beats/min) and decreased further to 34.2 ± 6.0 mL/100 g/min (p < 0.001) during recovery. Hippocampus CBF decreased by 12% (p = 0.001) during moderate exercise, decreased further during vigorous exercise (-21%; p < 0.001) and was even lower during recovery (-31%; p < 0.001). In contrast, motor cortex CBF increased by 12% (p = 0.027) during moderate exercise, returned to resting-state values during vigorous exercise, and decreased by 17% (p = 0.006) during recovery. The inter-session repeatability coefficients for WB CBF were approximately 20% for all stages of the exercise-recovery protocol. Phase-contrast blood flow measurements through the common carotid arteries overestimated the WB CBF because of flow directed to the face and scalp. This bias increased with exercise.We have demonstrated the feasibility of dynamic pCASL-MRI of the human brain for a quantitative evaluation of cerebral perfusion during bicycling exercise. Our spatially resolved measurements revealed a differential response of CBF in the motor cortex as well as the hippocampus compared with the brain as a whole. Caution is warranted when using flow through the common carotid arteries as a surrogate measure for cerebral perfusion.

Assessment of Retinal Capillary Dropout after Transcatheter Aortic Valve Implantation by Optical Coherence Tomography Angiography

Transcatheter aortic valve implantation (TAVI) is an alternative to open heart surgery in the treatment of symptomatic aortic valve stenosis, which is often the treatment of choice in elderly and frail patients. It carries a risk of embolic complications in the whole cerebral vascular bed, which includes the retinal vasculature. The main objective was the evaluation of retinal emboli visible on optical coherence tomography angiography (OCTA) following TAVI. This is a prospective, single center, observational study enrolling consecutive patients over two years. Patients were assessed pre- and post-TAVI. Twenty-eight patients were included in the final analysis, 82.1% were male, median age was 79.5 (range 52–88), median BCVA was 82.5 letters (range 75–93). Eight patients (28.6%) presented new capillary dropout lesions in their post-TAVI OCTA scans. There was no statistically significant change in BCVA. Quantitative analysis of macular or peripapillary OCTA parameters did not show any statistically significant difference in pre- and post-intervention. In conclusion, capillary dropout lesions could frequently be found in patients after TAVI. Quantitative measurements of macular and peripapillary flow remained stable, possibly indicating effective ocular blood flow regulation within the range of left ventricular ejection fraction in our cohort.

Laminar perfusion imaging with zoomed arterial spin labeling at 7 Tesla

Laminar fMRI based on BOLD and CBV contrast at ultrahigh magnetic fields has been applied for studying the dynamics of mesoscopic brain networks. However, the quantitative interpretations of BOLD/CBV fMRI results are confounded by different baseline physiology across cortical layers. Here we introduce a novel 3D zoomed pseudo-continuous arterial spin labeling (pCASL) technique at 7T that offers the capability for quantitative measurements of laminar cerebral blood flow (CBF) both at rest and during task activation with high spatial specificity and sensitivity. We found arterial transit time in superficial layers is ∼100 ms shorter than in middle/deep layers revealing the time course of labeled blood flowing from pial arteries to downstream microvasculature. Resting state CBF peaked in the middle layers which is highly consistent with microvascular density measured from human cortex specimens. Finger tapping induced a robust two-peak laminar profile of CBF increases in the superficial (somatosensory and premotor input) and deep (spinal output) layers of M1, while finger brushing task induced a weaker CBF increase in superficial layers (somatosensory input). This observation is highly consistent with reported laminar profiles of CBV activation on M1. We further demonstrated that visuospatial attention induced a predominant CBF increase in deep layers and a smaller CBF increase on top of the lower baseline CBF in superficial layers of V1 (feedback cortical input), while stimulus driven activity peaked in the middle layers (feedforward thalamic input). With the capability for quantitative CBF measurements both at baseline and during task activation, high-resolution ASL perfusion fMRI at 7T provides an important tool for in vivo assessment of neurovascular function and metabolic activities of neural circuits across cortical layers.

Relationship Between Plasma Total Homocysteine Levels and Mean Corrected TIMI Frame Count in Patients with Acute Myocardial Infarction.

ObjectiveTo explore the relationship between the plasma total homocysteine (tHcy) levels and slow coronary flow (SCF) measured by mean corrected TIMI frame count (CTFC) in patients with acute myocardial infarction (AMI).MethodsNinety-one patients with primary myocardial infarction were enrolled in this study. The quantitative measurement of coronary blood flow was performed using the mean CTFC method. Plasma tHcy levels were determined using enzymatic assay from venous blood samples. Multivariable linear regression models indicated were used to estimate the effect size (β) of plasma tHcy levels on mean CTFC levels.ResultsCompared with patients with the mean CTFC ≤23.61 frames per second (FPS) group, there were increased plasma tHcy levels in patients of the second, third and highest mean CTFC quartiles (P < 0.001). Linear regression models indicated that plasma tHcy levels were positively associated with mean CTFC levels (adjusted-β per SD increase: 1.96, 95% CI 1.20 to 2.73, P < 0.001). Compared to the tHcy ≤12.30 μmol/L group, the third and highest tHcy-quartile groups had higher mean CTFC levels (adjusted-β: 2.52, 95% CI 0.39 to 4.65, P = 0.023; adjusted-β: 5.07, 95% CI 2.98 to 7.16, P < 0.001, respectively; P for trend <0.001). Moreover, this positive relationship was modified by diabetes mellitus (P-value for interaction was 0.046).ConclusionWe found a positive relationship between plasma tHcy levels and mean CTFC levels in patients with AMI. Moreover, diabetes mellitus played an interactive role in this positive association between the plasma tHcy levels and mean CTFC levels.

Quantitative Measurement of Two-Phase Flow by Electrical Capacitance Tomography Based on 3D Coupling Field Simulation

Measurement of oil-gas two-phase flow parameters such as Gas Void Fraction (GVF) and phase distribution plays a vital role in oil and gas industries. To quantitatively evaluate the performance of Electrical Capacitance Tomography (ECT) for measuring the complex dynamic oil-gas two-phase flows, a three-dimensional fluid dynamics-electrostatic field coupling model (3D-FECM) is proposed in this paper. Coupling simulation are carried out with a 12-electrode ECT sensor. Utilizing the 3D-FECM, the dynamic oil-gas two-phase flows and instantaneous ECT measurements are simultaneously obtained. Two GVF measurement approaches, i.e. the capacitance-based method and the image-based method, are used to calculate GVF. The permittivity distribution is reconstructed by using Linear Back Projection (LBP) and Landweber iteration. The capacitances with signal-noise ratios (SNRs) of 40 and 60 dB are generated for comparison and verification. Evaluation results show that the structural similarity between the ground truth and the reconstructed images using noise-free data by Landweber iteration are better than 0.765, while those by LBP are higher than 0.754, the noise with SNR of 60 dB has no obvious effect on the performance of image reconstruction, and the full-scale error of the image-based GVF prediction using 60 dB noisy data is within -0.82% to +6.09%, slightly better than that of the capacitance-based GVF results (i.e. −1.16% to +7.63%).