Measurement of relative blood flow, transit-time distributions and transport-model parameters by residue detection when radiotracer recirculates

Hepatic function can be characterized by the activity/time curves obtained by imaging the aorta, spleen, and liver. Nonparametric deconvolution of the activity/time curves is clinically useful as a diagnostic tool in determining organ transit times and flow fractions. The use of this technique is limited, however, because of numerical and noise problems in performing deconvolution. Furthermore, the interaction of part of the tracer with the spleen and gastrointestinal tract, before it enters the liver, further obscures physiological information in the deconvolved liver curve. In this paper, a mathematical relationship is derived relating the liver activity/time curve to portal and hepatic behavior. The mathematical relationship is derived by using transit time spectrum/residence time density theory. Based on this theory, it is shown that the deconvolution of liver activity/time curves gives rise to a complex combination of splenic, gastrointestinal, and liver dependencies. An anatomically and physiologically plausible parametric model of the hepatic vascular system has been developed. This model is used in conjunction with experimental data to estimate portal, splenic, and hepatic physiological blood flow parameters for eight normal volunteers. These calculated parameters, which include the portal flow fraction, the splenic blood flow fraction, and blood transit times are shown to adequately correspond to published values. In particular, the model of the hepatic vascular system identifies the portal flow fraction as 0.752 +/- 0.022, the splenic blood flow fraction as 0.180 +/- 0.023, and the liver mean transit time as 13.4 +/- 1.71 s. The model has also been applied to two portal hypertensive patients. The variation in some of the model parameters is beyond normal limits and is consistent with the observed pathology.

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Parameter Determination for Chloride and Tritium Transport in Undisturbed Lysimeters during Steady Flow

Hydrology Research ◽

10.2166/nh.1992.0007 ◽

1992 ◽

Vol 23 (2) ◽

pp. 89-104 ◽

Cited By ~ 30

Author(s):

Ole H. Jacobsen ◽

Feike J. Leij ◽

Martinus Th. van Genuchten

Keyword(s):

Experimental Data ◽

Unsaturated Flow ◽

Transport Model ◽

Time Moment ◽

Breakthrough Curves ◽

Coarse Sand ◽

Retardation Factor ◽

Parameter Determination ◽

Model Parameters ◽

Water Fraction

Breakthrough curves of Cl and 3H2O were obtained during steady unsaturated flow in five lysimeters containing an undisturbed coarse sand (Orthic Haplohumod). The experimental data were analyzed in terms of the classical two-parameter convection-dispersion equation and a four-parameter two-region type physical nonequilibrium solute transport model. Model parameters were obtained by both curve fitting and time moment analysis. The four-parameter model provided a much better fit to the data for three soil columns, but performed only slightly better for the two remaining columns. The retardation factor for Cl was about 10 % less than for 3H2O, indicating some anion exclusion. For the four-parameter model the average immobile water fraction was 0.14 and the Peclet numbers of the mobile region varied between 50 and 200. Time moments analysis proved to be a useful tool for quantifying the break through curve (BTC) although the moments were found to be sensitive to experimental scattering in the measured data at larger times. Also, fitted parameters described the experimental data better than moment generated parameter values.

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Application of Dynamically Constrained Interpolation Methodology in Simulating National-Scale Spatial Distribution of PM2.5 Concentrations in China

Atmosphere ◽

10.3390/atmos12020272 ◽

2021 ◽

Vol 12 (2) ◽

pp. 272

Author(s):

Ning Li ◽

Junli Xu ◽

Xianqing Lv

Keyword(s):

Transport Model ◽

Ground Level ◽

Kriging Interpolation ◽

Model Parameters ◽

National Scale ◽

Constrained Interpolation ◽

Simulation Accuracy ◽

Interpolation Accuracy ◽

Geographical Regions ◽

The Right

Numerous studies have revealed that the sparse spatiotemporal distributions of ground-level PM2.5 measurements affect the accuracy of PM2.5 simulation, especially in large geographical regions. However, the high precision and stability of ground-level PM2.5 measurements make their role irreplaceable in PM2.5 simulations. This article applies a dynamically constrained interpolation methodology (DCIM) to evaluate sparse PM2.5 measurements captured at scattered monitoring sites for national-scale PM2.5 simulations and spatial distributions. The DCIM takes a PM2.5 transport model as a dynamic constraint and provides the characteristics of the spatiotemporal variations of key model parameters using the adjoint method to improve the accuracy of PM2.5 simulations. From the perspective of interpolation accuracy and effect, kriging interpolation and orthogonal polynomial fitting using Chebyshev basis functions (COPF), which have been proved to have high PM2.5 simulation accuracy, were adopted to make a comparative assessment of DCIM performance and accuracy. Results of the cross validation confirm the feasibility of the DCIM. A comparison between the final interpolated values and observations show that the DCIM is better for national-scale simulations than kriging or COPF. Furthermore, the DCIM presents smoother spatially interpolated distributions of the PM2.5 simulations with smaller simulation errors than the other two methods. Admittedly, the sparse PM2.5 measurements in a highly polluted region have a certain degree of influence on the interpolated distribution accuracy and rationality. To some extent, adding the right amount of observations can improve the effectiveness of the DCIM around existing monitoring sites. Compared with the kriging interpolation and COPF, the results show that the DCIM used in this study would be more helpful for providing reasonable information for monitoring PM2.5 pollution in China.

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Hyperacute Stroke: Simultaneous Measurement of Relative Cerebral Blood Volume, Relative Cerebral Blood Flow, and Mean Tissue Transit Time

Radiology ◽

10.1148/radiology.210.2.r99fe06519 ◽

1999 ◽

Vol 210 (2) ◽

pp. 519-527 ◽

Cited By ~ 310

Author(s):

A. Gregory Sorensen ◽

William A. Copen ◽

Leif Østergaard ◽

Ferdinando S. Buonanno ◽

R. Gilberto Gonzalez ◽

...

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Blood Volume ◽

Transit Time ◽

Simultaneous Measurement ◽

Cerebral Blood Volume ◽

Hyperacute Stroke ◽

Relative Cerebral Blood Volume

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Measurement of arterial transit time and renal blood flow using pseudocontinuous ASL MRI with multiple post-labeling delays: Feasibility, reproducibility, and variation

Journal of Magnetic Resonance Imaging ◽

10.1002/jmri.25634 ◽

2017 ◽

Vol 46 (3) ◽

pp. 813-819 ◽

Cited By ~ 15

Author(s):

Dong Won Kim ◽

Woo Hyun Shim ◽

Seong Kuk Yoon ◽

Jong Yeong Oh ◽

Jeong Kon Kim ◽

...

Keyword(s):

Blood Flow ◽

Renal Blood Flow ◽

Transit Time ◽

Arterial Transit Time

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Blood Flow to Hindquarters of Steers Measured by Transit Time Ultrasound and Indicator Dilution

Journal of Dairy Science ◽

10.3168/jds.s0022-0302(87)80160-1 ◽

1987 ◽

Vol 70 (7) ◽

pp. 1385-1390 ◽

Cited By ~ 15

Author(s):

J.H. Eisemann ◽

G.B. Huntington ◽

C.L. Ferrell

Keyword(s):

Blood Flow ◽

Transit Time ◽

Indicator Dilution

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Blood flow, volume, and transit time in the pulmonary microvasculature using laser-Doppler

Journal of Applied Physiology ◽

10.1152/jappl.1994.76.6.2643 ◽

1994 ◽

Vol 76 (6) ◽

pp. 2643-2650 ◽

Cited By ~ 2

Author(s):

T. S. Hakim ◽

E. Gilbert ◽

E. M. Camporesi

Keyword(s):

Blood Flow ◽

Blood Volume ◽

Transit Time ◽

Flow Rate ◽

Venous Pressure ◽

Laser Doppler ◽

Flow Volume ◽

Doppler Flowmetry ◽

Blood Flow Volume ◽

Wide Range

Capillary transit time is determined by the ratio of capillary volume to flow rate. Exercise-induced hypoxemia is thought to occur because of the short transit time of erythrocytes in capillaries. The effect of flow rate on capillary volume (recruitment vs. distension) is controversial. In a perfused left lower lobe preparation in canine lungs, we used laser-Doppler flowmetry (model ALF21R) to monitor changes in blood flow, volume, and transit time in the microvasculature near the subpleural surface. Changes in total flow, blood volume, and total transit time (tt) were also measured. The results showed that microvascular volume approached maximum when flow rate was at resting value (0.4 l/min) and pressure in the pulmonary artery was > 6 mmHg relative to the level of the capillaries. In contrast, the total blood volume increased gradually over a wide range of flow rates. When flow increased 4.2 times (from 155 to 650 ml/min), tt decreased from 7.32 to 3.53 s; meanwhile, microvascular flow increased from 6.0 to 12.7 units and microvascular transit time decreased from 3.14 to 1.81 units. The changes in microvascular volume and transit time were essentially independent of whether the venous pressure was higher or lower than alveolar pressure. At very high flow (6–10 times resting value), tt fell gradually to approximately 1 s. Direct monitoring of transit time with the laser-Doppler also revealed a gradual decline in microvascular transit time as flow rate increased from 2 to 10 times the normal flow. (ABSTRACT TRUNCATED AT 250 WORDS)

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