Absolute Flow Research Articles

A comparison of variability between absolute and relative blood flow restriction pressures.

Recommendations are that blood flow restriction (BFR) be applied relative to arterial occlusion pressure (AOP) to provide a similar stimulus. Compare variability of the change in blood flow, shear rateand discomfort between recommended relative pressures and an absolute pressure. During one visit, brachial arterial blood flow was measured in 91 participants using pulse-wave Doppler ultrasonography. After 5-min seated rest, AOP was measured. Following another 5-min rest, blood flow and discomfort were assessed twice before cuff inflation as controls (C1 and C2), then again with a cuff inflated to each BFR pressure (all measures separated by 1-min). Change scores from C1 to all subsequent measures were calculated (i.e., C2-C1; 40%AOP-C1; 80%AOP-C1; 100 mmHg-C1). Variability of the changes were compared via pairwise modified Pitman-Morgan tests (α = 0.008). Variance (95%CI) of the change for blood flow (ml/min), shear rate (1/s), and discomfort(AU) had similar trends. C2-C1 differed from all conditions (all p < 0.001), 40%AOP-C1 differed from 80% AOP-C1 and 100 mmHg-C1 (all p < 0.001), which did not differ (both p ≥ 0.117). Blood flow: C2-C1 = 469.79 (357.90, 644.07), 40%AOP-C1 = 1263.18 (962.34, 1731.80), 80%AOP-C1 = 1752.90 (1335.42, 2403.18), 100 mmHg-C1 = 1603.18 (1221.36, 2197.92); shear rate: C2-C1 = 6248.24 (4760.10, 8566.15), 40%AOP-C1 = 14 625.30 (11 142.06, 20 050.95), 80%AOP-C1 = 22 064.02 (16 809.13, 30 249.27), 100 mmHg-C1 = 20 778.76 (15 829.98, 28 487.21); discomfort: C2-C1 = 0.07 (0.05, 0.08), 40%AOP-C1 = 2.03 (1.55, 2.78), 80%AOP-C1 = 4.26 (3.25, 5.84), 100 mmHg-C1 = 4.50 (3.43, 6.17). Contrary to previous suggestions, applying relative pressures does not necessarily guarantee a similar stimulus. It seems that higher pressures produce more variable changes even if the external pressure applied is made relative to each individual.

Experimental analysis and deliverability calculation of abnormally pressured carbonate gas reservoir considering stress sensitivity

The stress sensitivity of abnormally pressured carbonate gas reservoirs is of great complexity and exerts much influence on gas well deliverability calculation. Fifty core samples from the AD Gas Reservoirs were selected in the experiment to study the effect of abnormally high pressure and fracture on the stress sensitivity of carbonate gas reservoir. The results show that the permeability decline mainly occurs in the abnormally high-pressure stage and is rather small in normal pressure stage. The existence of the fracture could substantially enhance the stress sensitivity. The higher fracture density could induce the stronger stress sensitivity. Furthermore, a mathematical model with the consideration of the variable permeability modulus was established to calculate gas well deliverability in the abnormally pressured carbonate gas reservoir with developed natural fractures. It is revealed that previous method assuming a fixed permeability modulus would lead to an overestimation of the real stress sensitivity and thus underestimating the absolute open flow of the gas well.

Coronary Flow Assessment Using 3-Dimensional Ultrafast Ultrasound Localization Microscopy

BackgroundDirect assessment of the coronary microcirculation has long been hampered by the limited spatial and temporal resolutions of cardiac imaging modalities. ObjectivesThe purpose of this study was to demonstrate 3-dimensional (3D) coronary ultrasound localization microscopy (CorULM) of the whole heart beyond the acoustic diffraction limit (<20 μm resolution) at ultrafast frame rate (>1000 images/s). MethodsCorULM was performed in isolated beating rat hearts (N = 6) with ultrasound contrast agents (Sonovue, Bracco), using an ultrasonic matrix transducer connected to a high channel–count ultrafast electronics. We assessed the 3D coronary microvascular anatomy, flow velocity, and flow rate of beating hearts under normal conditions, during vasodilator adenosine infusion, and during coronary occlusion. The coronary vasculature was compared with micro-computed tomography performed on the fixed heart. In vivo transthoracic CorULM was eventually assessed on anaesthetized rats (N = 3). ResultsCorULM enables the 3D visualization of the coronary vasculature in beating hearts at a scale down to microvascular structures (<20 μm resolution). Absolute flow velocity estimates range from 10 mm/s in tiny arterioles up to more than 300 mm/s in large arteries. Fitting to a power law, the flow rate–radius relationship provides an exponent of 2.61 (r2 = 0.96; P < 0.001), which is consistent with theoretical predictions and experimental validations of scaling laws in vascular trees. A 2-fold increase of the microvascular coronary flow rate is found in response to adenosine, which is in good agreement with the overall perfusion flow rate measured in the aorta (control measurement) that increased from 8.80 ± 1.03 mL/min to 16.54 ± 2.35 mL/min (P < 0.001). The feasibility of CorULM was demonstrated in vivo for N = 3 rats. ConclusionsCorULM provides unprecedented insights into the anatomy and function of coronary arteries at the microvasculature level in beating hearts. This new technology is highly translational and has the potential to become a major tool for the clinical investigation of the coronary microcirculation.

Activity regimes for 82Rb cardiac PET: Effects on absolute MBF and MPI

BackgroundSelection of optimal tracer activity for 82Rb PET is based on a trade-off between necessary count-statistics in the late static phase and detector saturation in the early blood-pool phase. Administered tracer activity recommended in prescribing information differs substantially from recommendations in current literature. The present study examines the effect on both absolute myocardial blood flow (MBF), myocardial flow reserve (MFR) and relative myocardial perfusion imaging (MPI) of reducing dose. MethodsForty patients were scanned twice on a PMT-based PET/CT (GE D690): At recommended activity (1110 MBq) and at either 740 or 370 MBq. MBF, MFR, total perfusion deficit (TPD) and ejection fractions (EF) were quantified. Results were compared using linear regression and Bland–Altman plots. ResultsLinear correlation between MBF at 1110 MBq at either reduced activity had an R2 > 0.98. A small bias (± 5%-9%) was observed with opposite signs for 1110/740 and 1110/370. Limits of agreement for MBF were larger for 1110/370. MFR had a lower linear correlation (R2 = 0.96), but wide limits of agreement especially for 1110/370. TPD and EF correlated well at 1110/740 (R2 = 0.96 and 0.99, respectively), but large scatter was observed for 1110/370. ConclusionReduction of the tracer activity to 740 MBq, significantly reduced dead-time correction factors, while still producing reliable static and gated images. However, despite large dead-time at 1110 MBq, no systematic bias on absolute MBF was observed compared to reduced activities.

Nontraditional risk factors in chronic kidney disease: correlation between creatinine clearance, Framingham risk score, endothelial dysfunction, and inflammation

BackgroundChronic kidney disease became a public health problem increasing healthcare burden. Our aim was to detect the relationship between cardiovascular risk, endothelial dysfunction, inflammation, and kidney function in chronic kidney disease patients and to detect the nontraditional factors affecting the decline in kidney functions.MethodsA cross-sectional study including 30 male and female patients with chronic kidney disease stages 3–5. Creatinine clearance and Framingham risk score points were calculated. Carotid intimal medial thickness was measured as well as absolute flow mediated dilatation in brachial artery. Highly sensitive C-reactive protein, parathyroid hormone, kidney function tests, and lipid profile were measured.ResultsFramingham risk score points and carotid intimal medial thickness increased significantly with decreasing creatinine clearance (p 0.0025, 0.0285) respectively. A significant correlation was found between highly sensitive C-reactive protein and Framingham risk score points but not with carotid intimal medial thickness (p 0.0043, 0.2229) respectively. An inverse correlation was found between creatinine clearance and highly sensitive C-reactive protein (p 0.0174). Absolute flow mediated dilatation in brachial artery decreases with increasing Framingham risk score points and decreasing creatinine clearance (p 0.0044, 0.0269) respectively.ConclusionThere is correlation between chronic kidney disease and impaired vascular function, subclinical atherosclerosis, and heightened inflammatory response. Chronic kidney disease patients are at increased risk of cardiovascular events with higher [10-]year cardiovascular risk.

Study On Productivity Improvement Of Low Permeability Gas Reservoir By Hydraulic Fracturing

The C5 well completed in the LZ tight gas limestone reservoir of C field is considered very good candidate for stimulation by hydraulic fracturing for the following reasons. The reservoir gross thickness of 127 ft is thick enough. Long fractures can be created. Penetrated zone is far from lowest known gas. The permeability of 0.2973 mD and the absolute open flow potential of 2.3 MMscf are low. Estimated proven gas accumulation of 24.5 Bscf is significant. Crosslinked Gel + Hi Temp Stabilizer is used as fracturing fluid due to high temperature reservoir of 334oF. High-strength of Sintered Bauxite proppant with 20/40 mesh sand is selected for this high stress formation of reservoir rock. The desired propped fracture width is 0.1004 inch. The fracture height is approximately 62.5 ft based on the half height from the centre depth of reservoir upward and downward. The propped fracture halflengths are predicted by Perkins-Kern-Nordgren model. Prediction shows that to have the propped fracture half-gths of 1335, 1587, 1850, 2114, 2356, 2576 and 2640 ft for the propped fracture width of 0.1004 inch and the fracture height of 62.5 ft, the required proppant weight in one fracture wing are 139,167,195,221, 246, 271 and 278 Mlbs respectively. With the obtained propped fracture halflengths, the productivities improvement (J/Jo) are 13.8, 16.4, 19.2, 21.9, 24.4, 26.7 and 27.3

Prognostic Value of Coronary Sinus Flow Quantification by Cardiac Magnetic Resonance Imaging in Patients With Acute Myocardial Infarction.

BackgroundThis study aimed to evaluate the prognostic value of hyperemic coronary sinus flow (h‐CSF) and global coronary flow reserve (g‐CFR) obtained by phase‐contrast cine‐magnetic resonance imaging in patients with acute myocardial infarction (MI).Methods and ResultsThis retrospective study analyzed patients with acute MI (n=523) who underwent primary (ST‐segment–elevation MI) or urgent (non–ST‐segment–elevation MI) percutaneous coronary intervention. Absolute coronary sinus blood flow (CSF) at rest and during vasodilator stress hyperemia was quantified at 30 days (24–36 days) after the index infarct‐related lesion percutaneous coronary intervention and revascularization of functionally significant non–infarct‐related lesions. We used Cox proportional hazards regression modeling to examine the association between h‐CSF, g‐CFR, and major adverse cardiac events defined as all‐cause death, nonfatal MI, hospitalization for congestive heart failure, and stroke. Finally, 325 patients with ST‐segment–elevation MI (62.1%) and 198 patients with non–ST‐segment–elevation MI (37.9%) were studied over a median follow‐up of 2.5 years. The rest CSF, h‐CSF, and g‐CFR were 0.94 (0.68–1.26) mL/min per g, 2.05 (1.42–2.73) mL/min per g, and 2.17 (1.54–3.03), respectively. Major adverse cardiac events occurred in 62 patients, and Cox proportional hazards analysis showed that h‐CSF and g‐CFR were independent predictors of major adverse cardiac events (h‐CSF: hazard ratio [HR], 0.64; 95% CI, 0.47–0.88; P=0.005; g‐CFR: HR, 0.62; 95% CI, 0.47–0.82; P=0.001). When stratified by h‐CSF and g‐CFR, cardiac event‐free survival was the worst in patients with concordantly impaired h‐CSF (<1.6 mL/min per g) and g‐CFR (<1.7) (P<0.001).ConclusionsGlobal coronary sinus flow quantification using phase‐contrast cine‐magnetic resonance imaging provided significant prognostic information independent of infarction size and conventional risk factors in patients with acute MI undergoing revascularization.

Clinically viable myocardial CCTA segmentation for measuring vessel-specific myocardial blood flow from dynamic PET/CCTA hybrid fusion

BackgroundPositron emission tomography (PET)-derived LV MBF quantification is usually measured in standard anatomical vascular territories potentially averaging flow from normally perfused tissue with those from areas with abnormal flow supply. Previously we reported on an image-based tool to noninvasively measure absolute myocardial blood flow at locations just below individual epicardial vessel to help guide revascularization. The aim of this work is to determine the robustness of vessel-specific flow measurements (MBFvs) extracted from the fusion of dynamic PET (dPET) with coronary computed tomography angiography (CCTA) myocardial segmentations, using flow measured from the fusion with CCTA manual segmentation as the reference standard.MethodsForty-three patients’ 13NH3 dPET, CCTA image datasets were used to measure the agreement of the MBFvs profiles after the fusion of dPET data with three CCTA anatomical models: (1) a manual model, (2) a fully automated segmented model and (3) a corrected model, where major inaccuracies in the automated segmentation were briefly edited. Pairwise accuracy of the normality/abnormality agreement of flow values along differently extracted vessels was determined by comparing, on a point-by-point basis, each vessel’s flow to corresponding vessels’ normal limits using Dice coefficients (DC) as the metric.ResultsOf the 43 patients CCTA fully automated mask models, 27 patients’ borders required manual correction before dPET/CCTA image fusion, but this editing process was brief (2–3 min) allowing a 100% success rate of extracting MBFvs in clinically acceptable times. In total, 124 vessels were analyzed after dPET fusion with the manual and corrected CCTA mask models yielding 2225 stress and 2122 rest flow values. Forty-seven vessels were analyzed after fusion with the fully automatic masks producing 840 stress and 825 rest flow samples. All DC coefficients computed globally or by territory were ≥ 0.93. No statistical differences were found in the normal/abnormal flow classifications between manual and corrected or manual and fully automated CCTA masks.ConclusionFully automated and manually corrected myocardial CCTA segmentation provides anatomical masks in clinically acceptable times for vessel-specific myocardial blood flow measurements using dynamic PET/CCTA image fusion which are not significantly different in flow accuracy and within clinically acceptable processing times compared to fully manually segmented CCTA myocardial masks.

3D pCASL-perfusion in preoperative assessment of brain gliomas in large cohort of patients

The aim of the study was to evaluate the role of pseudocontinuous arterial spin labeling perfusion (pCASL-perfusion) in preoperative assessment of cerebral glioma grades. The study group consisted of 253 patients, aged 7–78 years with supratentorial gliomas (65 low-grade gliomas (LGG), 188 high-grade gliomas (HGG)). We used 3D pCASL-perfusion for each patient in order to calculate the tumor blood flow (TBF). We obtained maximal tumor blood flow (maxTBF) in small regions of interest (30 ± 10 mm2) and then normalized absolute maximum tumor blood flow (nTBF) to that of the contralateral normal-appearing white matter of the centrum semiovale. MaxTBF and nTBF values significantly differed between HGG and LGG groups (p < 0.001), as well as between patient groups separated by the grades (grade II vs. grade III) (p < 0.001). Moreover, we performed ROC-analysis which demonstrated high sensitivity and specificity in differentiating between HGG and LGG. We found significant differences for maxTBF and nTBF between grade III and IV gliomas, however, ROC-analysis showed low sensitivity and specificity. We did not observe a significant difference in TBF for astrocytomas and oligodendrogliomas. Our study demonstrates that 3D pCASL-perfusion as an effective diagnostic tool for preoperative differentiation of glioma grades.

Cerebrovascular Effects of Lower Body Negative Pressure at 3T MRI: Implications for Long‐Duration Space Travel

Optic disc edema develops in most astronauts during long-duration spaceflight. It is hypothesized to result from weightlessness-induced venous congestion of the head and neck and is an unresolved health risk of space travel. Determine if short-term application of lower body negative pressure (LBNP) could reduce internal jugular vein (IJV) expansion associated with the supine posture without negatively impacting cerebral perfusion or causing IJV flow stasis. Prospective. Nine healthy volunteers (six women). 3T/cine two-dimensional phase-contrast gradient echo; pseudo-continuous arterial spin labeling single-shot gradient echo echo-planar. The study was performed with two sequential conditions in randomized order: supine posture and supine posture with 25 mmHg LBNP (LBNP25 ). LBNP was achieved by enclosing the lower extremities in a semi-airtight acrylic chamber connected to a vacuum. Heart rate, bulk cerebrovasculature flow, IJV cross-sectional area, fractional IJV outflow relative to arterial inflow, and cerebral perfusion were assessed in each condition. Paired t-tests were used to compare measurement means across conditions. Significance was defined as P < 0.05. LBNP25 significantly increased heart rate from 64 ± 9 to 71 ± 8 beats per minute and significantly decreased IJV cross-sectional area, IJV outflow fraction, cerebral arterial flow rate, and cerebral arterial stroke volume from 1.28 ± 0.64 to 0.56 ± 0.31 cm2 , 0.75 ± 0.20 to 0.66 ± 0.28, 780 ± 154 to 708 ± 137 mL/min and 12.2 ± 2.8 to 9.7 ± 1.7mL/cycle, respectively. During LBNP25 , there was no significant change in gray or white matter cerebral perfusion (P=0.26 and P=0.24 respectively) and IJV absolute mean peak flow velocity remained ≥4cm/sec in all subjects. Short-term application of LBNP25 reduced IJV expansion without decreasing cerebral perfusion or inducing IJV flow stasis. 1 TECHNICAL EFFICACY STAGE: 1.

3D pseudo-continuous arterial spin labeling-MRI (3D PCASL-MRI) in the differential diagnosis between glioblastomas and primary central nervous system lymphomas.

The aim of the study was to compare the parameters of blood flow in glioblastomas and primary central nervous system lymphomas (PCNSLs), measured by pseudo-continuous arterial spin labeling MRI (3D PCASL), and to determine the informativeness of this method in the differential diagnosis between these lesions. The study included MRI data of 139 patients with PCNSL (n = 21) and glioblastomas (n = 118), performed in the Burdenko Neurosurgical Center. No patients received chemotherapy, hormone therapy, or radiation therapy prior to MRI. On the 3D PCASL perfusion map, the absolute and normalized values of tumor blood flow were calculated in the glioblastoma and PCNSL groups (maxTBFmean and nTBF). MaxTBFmean and nTBF in the glioblastoma group were significantly higher than those in the PCNSL group: 168.9ml/100g/min versus 65.6 and 9.3 versus 3.7, respectively (p < 0.001). Arterial spin labeling perfusion had high sensitivity (86% for maxTBFmean, 95% for nTBF) and specificity (77% for maxTBFmean, 73% for nTBF) in the differential diagnosis between PCNSL and glioblastomas. Blood flow thresholds were 98.9ml/100g/min using absolute blood flow values and 6.1 using normalized values, AUC > 0.88. The inclusion of 3D PCASL in the standard MRI protocol can increase the specificity of the differential diagnosis between glioblastomas and PCNSL.

Value of SiPM PET in myocardial perfusion imaging using Rubidium-82

BackgroundPET scanners using silicon photomultipliers with digital readout (SiPM PET) have an improved temporal and spatial resolution compared to PET scanners using conventional photomultiplier tubes (PMT PET). However, the effect on image quality and visibility of perfusion defects in myocardial perfusion imaging (MPI) is unknown. Our aim was to determine the value of a SiPM PET scanner in MPI. MethodsWe prospectively included 30 patients who underwent rest and regadenoson-induced stress Rubidium-82 (Rb-82) MPI on the D690 PMT PET (GE Healthcare) and within three weeks on the Vereos SiPM PET (Philips Healthcare). Two expert readers scored the image quality and assessed the existence of possible defects. In addition, interpreter’s confidence, myocardial blood flow (MBF), and myocardial flow reserve (MFR) values were compared. ResultsImage quality improved (P = 0.03) using the Vereos as compared to the D690. Image quality of the Vereos and the D690 was graded fair in 20% and 10%, good in 60% and 50%, and excellent in 20% and 40%, respectively. Defect interpretation and interpreter’s confidence did not differ between the D690 and the Vereos (P > 0.50). There were no significant differences in rest MBF (P ≥ 0.29), stress MBF (P ≥ 0.11), and MFR (P ≥ 0.51). ConclusionSiPM PET provides an improved image quality in comparison with PMT PET. Defect interpretation, interpreter’s confidence, and absolute blood flow measurements were comparable between both systems. SiPM PET is therefore a reliable technique for MPI using Rb-82. Trial registrationToetsingOnline NL63853.075.17. Registered 13 November, 2017.

A new comprehensive dimensionless inflow performance relationship for gas wells

Prediction of gas well deliverability is important for reservoir management. Conventional flow after flow, isochronal or modified isochronal tests are common methods for calculation of well deliverability. Single-point test using Vogel-type dimensionless inflow performance relationships (IPR) was also proposed to overcome the need for multi-point tests. However, analysis of field data showed that existing dimensionless IPR correlations fail to accurately predict well deliverability for some reservoir conditions. In this study, a wide range of reservoir rock and fluid data was used to develop a comprehensive dimensionless IPR correlation for calculation of gas well deliverability from single-point test data. Multi-point well test data from 61 different gas wells of 15 fields were used to compare predicted absolute open flow (AOF) and calculated AOF from multi-point test data. The data used for validation of the proposed dimensionless IPR cover a wide range of actual AOFs (2.1–1411 MMSCF/D). Good agreement between predicted well deliverability from new dimensionless IPR and that from multi-point test was achieved. In addition, superiority of the new dimensionless IPR to previous correlations was confirmed for a wide range of reservoir conditions through error analysis. The average absolute error for new model is 11.6% (standard deviation of 8.5%) while for the other models are 85.9% (standard deviation of 148.1%) and 68.6% (standard deviation of 115.3%) for a wide range of field data.

Absolute flow measurement in chicken embryo based on optical coherence tomography with direct Doppler angle measuring

Abnormal blood flow in the early stage of embryonic heart can lead to cardiac defects. Thus, accurate flow measurement in the embryonic heart is important for related studies. Optical coherence tomography (OCT) is a noninvasive imaging approach which can provide flow velocity distribution information with high spatial and temporal resolution. However, OCT is only sensitive to velocity components parallel to the probing beam. To measure absolute flow velocity, additional information, such as Doppler angle, is required. Here, we propose a practical method to measure Doppler angle by introducing a dividing head to probe the arm of OCT. The incident angle of the probe beam can be controlled by rotating the dividing head. With the scale of the dividing head, rotating angle can be obtained. In each measurement, probe beam is adjusted to a proper angle by real time flow monitoring. Then, the probe beam is rotated perpendicularly to the flow velocity, i.e. Doppler angle is π/2, and the Doppler angle can be calculated. This method is validated by capillary phantom. Last, blood flow in the early stage of chicken embryo is measured in vivo by the proposed method.

Exercise-dependent changes in ventricular-arterial coupling and aortopulmonary collateral flow in Fontan patients: a real-time CMR study.

Inefficient ventricular-arterial (V-A) coupling has been described in Fontan patients and may result in adverse haemodynamics. A varying amount of aortopulmonary collateral (APC) flow is also frequently present that increases volume load of the single ventricle. The aim of the study was to assess changes in V-A coupling and APC flow during exercise CMR. Eighteen Fontan patients (age 24 ± 3 years) and 14 controls (age 23 ± 4 years) underwent exercise CMR using a cycle ergometer. Ventricular volumetry and flow measurements in the ascending aorta (AAO), inferior (IVC), and superior (SVC) vena cava were assessed using real-time sequences during stepwise increases in work load. Measures of systemic arterial elastance Ea, ventricular elastance Ees, and V-A coupling (Ea/Ees) were assessed. APC flow was quantified as AAO - (SVC + IVC). Ea remained unchanged during all levels of exercise in both groups (P = 0.39 and P = 0.11). Ees increased in both groups (P = 0.001 and P < 0.001) with exercise but was lower in the Fontan group (P = 0.04). V-A coupling was impaired in Fontan patients at baseline (P = 0.04). Despite improvement during exercise (P = 0.002) V-A coupling remained impaired compared with controls (P = 0.001). Absolute APC flow in Fontan patients did not change during exercise even at maximum work load (P = 0.98). Inefficient V-A coupling was already present at rest in Fontan patients and aggravated during exercise due to a limited increase in ventricular contractility which demonstrates the importance of a limited functional reserve of the single ventricle. APC flow remained unchanged suggesting no further increase in volume load during exercise.

Can nuclear imaging accurately detect scar in ischemic cardiac resynchronization therapy candidates?

Accurate scar assessment is crucial in cardiac resynchronization therapy (CRT) candidates, since its presence is a negative predictor for CRT response. Therefore, we assessed the performance of different PET parameters to detect scar in CRT candidates. Twenty-nine CRT candidates underwent 18F-fluorodeoxyglucose (18F-FDG)-PET/computed tomography (CT), resting 13N-NH3-PET/CT and cardiac magnetic resonance (CMR) prior to CRT implantation. Segmental 18F-FDG uptake, late 13N-NH3 uptake and absolute myocardial blood flow (MBF) were evaluated for scar detection using late gadolinium enhancement (LGE) CMR as reference. A receiver operator characteristic (ROC) area under the curve (AUC) ≥0.8 indicated a good accuracy of the methods evaluated. Scar was present in 111 of 464 segments. None of the approaches could reliably identify segments with nontransmural scar, except for 18F-FDG uptake in the lateral wall (AUC 0.83). Segmental transmural scars could be detected with all methods (AUC ≥ 0.8), except for septal 18F-FDG uptake and MBF in the inferior wall (AUC < 0.8). Late 13N-NH3 uptake was the best parameter for transmural scar detection, independent of its location, with a sensitivity of 80% and specificity of 92% using a cutoff of 66% of the maximum tracer activity. Late 13N-NH3 uptake is superior to 13N-NH3 MBF and 18F-FDG in detecting transmural scar, independently of its location. However, none of the tested PET parameters was able to accurately detect nontransmural scar.

Pulsed Arterial Spin Labeling and Segmented Brain Volumetry in the Diagnostic Evaluation of Frontotemporal Dementia, Alzheimer’s Disease and Mild Cognitive Impairment

Background: Previous studies suggest that brain atrophy can not only be defined by its morphological extent, but also by the cerebral blood flow (CBF) within a certain area of the brain, including white and gray matter. The aim of this study is to investigate known atrophy patterns in different forms of dementia and to compare segmented brain volumetrics and pulsed arterial spin labeling (pASL) data to explore the correlation between brain maps with atrophy and this non-contrast-enhanced brain-perfusion method. Methods: Our study comprised 17 patients with diagnosed cognitive impairment (five Alzheimer’s disease = AD, five frontotemporal dementia = FTD, seven mild cognitive impairment = MCI) and 19 healthy control subjects (CO). All patients and controls underwent 4D-pASL brain-perfusion MR imaging and T1w MPRAGE. The data were assessed regarding relative brain volume on the basis of 286 brain regions, and absolute and relative cerebral blood flow (CBF/rCBF) were derived from pASL data in the corresponding brain regions. Mini-Mental State Examination (MMSE) was performed to assess cognitive functions. Results: FTD patients demonstrated significant brain atrophy in 43 brain regions compared to CO. Patients with MCI showed significant brain atrophy in 18 brain regions compared to CO, whereas AD patients only showed six brain regions with significant brain atrophy compared to CO. There was good correlation of brain atrophy and pASL perfusion data in five brain regions of patients with diagnosed FTD, especially in the superior temporal gyrus (r = 0.900, p = 0.037), the inferior frontal white matter (pars orbitalis; r = 0.968, p = 0.007) and the thalami (r = 0.810, p = 0.015). Patients with MCI demonstrated a correlation in one brain region (left inferior fronto-occipital fasciculus; r = 0.786, p = 0.036), whereas patients with diagnosed AD revealed no correlation. Conclusions: pASL can detect affected brain regions in cognitive impairment and corresponds with brain atrophy, especially for patients suffering from FTD and MCI. However, there was no correlation of perfusion alterations and brain atrophy in AD. pASL perfusion might thus represent a promising tool for noninvasive brain-perfusion evaluation in specific dementia subtypes as a complimentary imaging-based bio marker in addition to brain volumetry.

Correlation between the Internal Flow Pattern and the Blade Load Distribution of the Centrifugal Impeller

The blade load distributions reflect the working characteristics of centrifugal impellers, and the vortexes in the impeller channel affect the blade load distribution, but the mechanism of this phenomenon is still unclear. In this study, particle image velocimetry (PIV) was adopted to clarify the correlation between the internal flow pattern and the blade load distribution. The internal flow pattern and the blade load distribution were presented under different working conditions to study the influence of the internal flow pattern on the blade load. Results showed that the vortexes in the flow channel redistributed the blade load. The clockwise vortex made the position of the maximum blade load closer to the outlet, while the counterclockwise vortex had the opposite effect. Meanwhile, the vortexes caused the blade load distribution to be steeper, which reduced energy conversion efficiency. Moreover, the mean absolute flow angle was introduced to explain the mechanism of the effects of vortexes on blade load. The results can be used as a theoretical basis for the design of high-performance impellers.

Influence of geometric factors at runner outlet on the hump characteristics of a pump-turbine

In order to investigate the influence of geometric factors at runner outlet on the hump characteristic of pump-turbines, three different distribution plans of geometric factors at runner outlet are proposed and numerical simulated using the SST (shear stress transport) k-ω turbulence model. Numerical results show good agreement with the experimental data. Different distribution plans show large difference at the hump region and of which the plan with large radius and small outlet angle near the shroud can improve the hump safety margin from 4% to 5.82%. The causes are analyzed through the input energy (the Euler head) and the hydraulic loss respectively. The analysis results show that the best distribution plan can provide small absolute flow angle near the hub and the middle spanwise at the runner outlet, leading to the increase of the Euler head. Moreover, for the best distribution plan, the hydraulic loss distribute more evenly at part load operating points, resulting in the movement of the hump region to smaller discharge operating points and the increase of the hump safety margin. Detailed local entropy production rate (LEPR) analyses reveal that when the pump-turbine operates in hump region, the hydraulic loss is concentrate in vaneless region and show different variation rules in discharge varying direction.

The Application of Conditional Probability to Harmonize Nuclear Cardiology Test Results.

Both exercise single photon emission computed tomography (SPECT) imaging and myocardial perfusion imaging with positron emission tomography produce multiple outcome variables. These include the stress electrocardiogram (ECG), visual perfusion assessment and quantitative myocardial blood flow. Bayes' analysis using conditional probability allows the distillation of multiple test results into a single probability of disease for individual patients. This paper examines the application of conditional probability analysis to two noninvasive modalities that generate multiple outcome results: exercise ECG combined with SPECT imaging and vasodilator RB-82 positron emission tomography perfusion imaging combined with quantitative measure of absolute myocardial blood flow. In this manner, a single probability of disease incorporating all the available data is generated for an individual patient.