Modeling the myocardial dilution curve of a pure intravascular indicator

1997 ◽  
Vol 273 (4) ◽  
pp. H2062-H2071 ◽  
Author(s):  
J. S. Lee ◽  
J. Karch ◽  
A. R. Jayaweera ◽  
J. R. Lindner ◽  
L. P. Lee ◽  
...  
Keyword(s):  
Contrast Medium ◽  
Present Model ◽  
Temporal Change ◽  
Mean Transit Time ◽  
Dilution Curve ◽  
Heterogeneous Flow ◽  
Myocardial Blood Volume ◽  
In Series ◽  
First Moment ◽  
Concentration Curves

The dispersion and dilution of contrast medium through the myocardial vasculature is examined first with a serial model comprised of arterial, capillary, and venous components in series to determine their time-concentration curves (TCC) and the myocardial dilution curve (MDC). Analysis of general characteristics shows that the first moment of the MDC, adjusted for that of the aortic TCC and mean transit time (MTT) from the aorta to the first intramyocardial artery, is one-half the MTT of the myocardial vasculature and that the ratio of the area of the MDC and aortic TCC is the fractional myocardial blood volume (MBV). The use of known coronary vascular morphometry and a set of transport functions indicates that the temporal change in MDC is primarily controlled by the MTT. An analysis of several models with heterogeneous flow distributions justifies the procedures to calculate MTT and MBV from the measured MDC. Compared with previously described models, the present model is more general and provides a physical basis for the effects of flow dispersion and heterogeneity on the characteristics of the MDC.

Dexamethasone and Enhancing Solitary Cerebral Mass Lesions: Alterations in Perfusion and Blood-tumor Barrier Kinetics Shown by Magnetic Resonance Imaging

Neurosurgery ◽  
2006 ◽  
Vol 58 (4) ◽  
pp. 640-646 ◽  
Author(s):  
Iain D. Wilkinson ◽  
David A. Jellineck ◽  
David Levy ◽  
Frederik L. Giesel ◽  
Charles A. J. Romanowski ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Blood Volume ◽  
Transit Time ◽  
Cerebral Blood Volume ◽  
Mean Transit Time ◽  
Resonance Imaging ◽  
Regional Cerebral Blood ◽  
Regional Cerebral Blood Volume ◽  
First Moment

Abstract OBJECTIVE: Glucocorticoid analogues are often administered to patients with intracranial space-occupying lesions. Clinical response can be dramatic, but the neurophysiological response is not well documented. This study sought to investigate the blood-lesion barrier, blood-brain barrier, and cerebral perfusion characteristics of patients who have undergone such therapy using magnetic resonance imaging. METHODS: Seventeen patients with intracranial mass-enhancing lesions underwent magnetic resonance imaging before and after 3 days of high-dose dexamethasone therapy. Assessments of blood-lesion barrier and blood-brain barrier integrity were based on a dynamic T1-weighted exogenous contrast technique that yielded the normalized maximal change in contrast uptake (T1-uptake). Perfusion was assessed using a dynamic T2*-weighted exogenous contrast technique to yield relative regional cerebral blood volume and first-moment mean transit time. Comparisons were made in T1-uptake, regional cerebral blood volume, and first-moment mean transit time of both enhancing lesion and contralateral normal-appearing white matter (CNAWM) obtained before and after dexamethasone. RESULTS: Significant reduction in T1-uptake was observed (19% decrease, P < 0.005) within enhancing pathological tissue, whereas no significant alteration was detected in CNAWM. Regional cerebral blood volume was significantly reduced in both enhancing tissue (28% decrease, P < 0.005) and in CNAWM (20% decrease, P < 0.001). Bolus first-moment mean transit time significantly increased (2.0 s prolongation, P < 0.05) in CNAWM, whereas there was no significant change (1.4 s prolongation, P > 0.05) within enhancing tissue. CONCLUSION: Glucocorticoid-analogue therapy not only affects the permeability of the blood-lesion barrier and lesion blood volume but also affects blood flow within normal-appearing contralateral parenchyma. There is a need for controls in steroid therapy in magnetic resonance imaging studies, which involve assessments of cerebrovascular function.

Microvessel mean transit time and blood flow velocity of sulfhemoglobin-RBC

1980 ◽  
Vol 238 (5) ◽  
pp. H745-H749 ◽  
Author(s):  
C. H. Baker ◽  
E. T. Sutton ◽  
D. L. Davis
Keyword(s):  
Blood Flow ◽  
Red Blood Cells ◽  
Flow Velocity ◽  
Transit Time ◽  
Blood Flow Velocity ◽  
Blood Cells ◽  
Optical Measurement ◽  
Mean Transit Time ◽  
The Mean ◽  
Concentration Curves

An indicator dilution technique is described for obtaining time-concentration curves subsequent to bolus injections of sulfhemoglobin red blood cells (SH-RBC), which have a deep greenish-brown color (absorption peak 620 nm vs. 542 and 564 nm for normal red cells). The series- and parallel-coupled microvessels of cat mesentery were studied. This is accomplished by means of video microscopy with a two-window intensity-sensitive video sampler system. The relationship between SH-RBC concentration in blood and optical measurement is linear. Blood flow velocities were calculated from the difference in mean transit times between two points along a vessel. When this technique is used in association with the previously reported method for determining time-concentration curves for the plasma indicator FITC-dextran the mean transit time (t) for red blood cells was less than for plasma in arterioles. The reproducibility of t and flow velocity for both SH-RBC and FITC-dextran from successive injections were reported. The mean transit time ratio of arteriolar SH-RBC to FITC-dextran averages 0.89. Blood flow velocity calculated from SH-RBC is greater than that calculated from FITC-dextran in these same arterioles. The ratio of the velocities averages 1.29.

Regional perfusion parameters from pulmonary microfocal angiograms

1997 ◽  
Vol 272 (3) ◽  
pp. H1537-H1548 ◽  
Author(s):  
A. V. Clough ◽  
J. H. Linehan ◽  
C. A. Dawson
Keyword(s):  
Contrast Medium ◽  
Transit Time ◽  
Regional Blood Flow ◽  
Mean Transit Time ◽  
Random Noise ◽  
Concentration Curve ◽  
Estimation Methods ◽  
Pulmonary Vasculature ◽  
Parameter Estimates ◽  
Inlet Concentration

An indicator-dilution model was developed to describe transport of vascular contrast medium through an organ during acquisition of vascular dynamic contrast images. The model provides the theoretical basis for methods of determining regional blood flow, blood volume, and mean transit time from time-absorbance curves acquired from the images of tissue regions of interest (ROI) distal from the inlet site. The robustness of these methods was evaluated using a computer-simulated vessel network, which simulated the passage of a bolus of contrast medium through arterioles, networks of capillaries, and venules. The network was used to evaluate the reliability of ROI parameter estimation methods when the underlying model assumptions are violated. The shape of the ROI inlet concentration curve and moderate amounts of random noise did not affect the ability of the method to recover accurate parameter estimates. The estimates of ROI flow and transit time were degraded in the presence of significant dispersion of the inlet concentration curve as it traveled through arteries upstream from the microvascular ROI or when the flow was redistributed within the ROI. The estimates of ROI volume were relatively robust. The method was applied to image data of the dog pulmonary vasculature obtained using microfocal X-ray angiography to show that the results obtained from the simulations are consistent with actual data.

scholarly journals Analysis of Mean Transit Time of Contrast Medium in Ruptured and Unruptured Arteriovenous Malformations

Stroke ◽  
2003 ◽  
Vol 34 (10) ◽  
pp. 2410-2414 ◽  
Author(s):  
Tatemi Todaka ◽  
Jun-ichiro Hamada ◽  
Yutaka Kai ◽  
Motohiro Morioka ◽  
Yukitaka Ushio
Keyword(s):  
Contrast Medium ◽  
Transit Time ◽  
Arteriovenous Malformations ◽  
Mean Transit Time

scholarly journals Sound Attenuation of Membranes Loaded with Square Frame-Shaped Masses

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
J. S. Chen ◽  
D. W. Kao
Keyword(s):  
Effective Mass ◽  
Sound Wave ◽  
Present Model ◽  
Transmission Loss ◽  
Mass Density ◽  
Sound Attenuation ◽  
Loss Peak ◽  
In Series ◽  
Thin Membranes ◽  
Multiple Transmission

This study examines sound transmission of thin membranes with square frame-shaped masses. Numerical results indicate that multiple transmission loss peaks can be generated by adding more frame mass inclusions. The number and the location of the peaks are controlled by the number of frames, the frame distribution, and the frame width. Near the transmission loss peak frequencies, the dynamic effective mass density turns from positive to negative. The validity of the present model has been verified by comparing the analytical results with FE results. Two types of cell arrangements are also considered in this study, namely, cells in series and cells in array. It is seen that either the stacked or array configurations can produce better sound attenuation than single-celled structures. Moreover, the frequency band where sound wave is blocked can be broadened by stacking more layers with different mass magnitudes. Furthermore, additional frequency bands due to the periodicity of the structure are found in the stacked configurations.

Isotope external counting method for cardiac output analyzed in glass model circulation

1961 ◽  
Vol 16 (2) ◽  
pp. 266-270 ◽  
Author(s):  
Ralph Gorten ◽  
J. Caulie Gunnells
Keyword(s):  
Cardiac Output ◽  
Mean Transit Time ◽  
Dilution Curve ◽  
Counting Method ◽  
Recording Time ◽  
Sources Of Error ◽  
Glass Model ◽  
Chamber Size ◽  
Central Circulation

Certain aspects regarding degree of accuracy and some of the theoretical sources of error of the isotope-external counting method for determination of cardiac output have been further evaluated by the use of a glass model central circulation. By comparing calculated flow with actually timed flow, and by observing the constant relationship between dilution curve area and flow, it was found that single as well as multichambered systems could be used for this method with valid and reproducible results. Variations in chamber size, rate of flow, isotope dosage and instrument settings were used to evaluate some of the possible sources of error. Variable mixing was the most important factor responsible for discrepancies. Errors in extrapolation of the primary dilution curve to zero and instrumental lag were considered to be of less importance and can most often be avoided. A change in the recording time constant altered the curve shape, and therefore the calculated mean transit time, but not curve area and calculated flow. Submitted on July 6, 1960

scholarly journals A vascular transport operator

1993 ◽  
Vol 265 (6) ◽  
pp. H2196-H2208 ◽  
Author(s):  
R. B. King ◽  
A. Deussen ◽  
G. M. Raymond ◽  
J. B. Bassingthwaighte
Keyword(s):  
Differential Operator ◽  
Velocity Profile ◽  
Linear Differential Operator ◽  
Mean Transit Time ◽  
Arterial System ◽  
Relative Dispersion ◽  
Transport Function ◽  
Mean Velocity ◽  
In Series ◽  
Linear Differential

A pulse or a sharp front in concentration of a tracer or a substrate in the blood within a vessel becomes dispersed while being transported along a vessel. Cross-stream mixing and pulsations in flow with the heartbeat cause the dispersion to be less than would occur with a parabolic velocity profile (Newtonian flow). These characteristics allow intravascular mass transport to be described well by a simple two-parameter differential operator, which is a one-dimensional representation of the rather complex real situation. The operator consists of two components in series, a pure delay and a fourth-order linear differential operator. The latter is merely two underdamped second-order operators in series, with fixed relationships between the natural frequencies and damping coefficients. The operator is useful because it provides a transport function with skewness and kurtosis suitable to intravascular transport where the mean velocity profile is blunter than in Newtonian parabolic flow. The parameters of the operator are its mean transit time, t, and its relative dispersion, RD, which is the standard deviation of the response impulse divided by t. The operator transport function describes blood transport through the human leg arterial system, where the RD values are approximately 15–20%.

How countercurrent blood flow and uneven perfusion affect the motion of inert gas

1990 ◽  
Vol 69 (1) ◽  
pp. 162-170 ◽  
Author(s):  
L. D. Homer ◽  
P. K. Weathersby ◽  
S. Survanshi
Keyword(s):  
Mean Transit Time ◽  
High Flow ◽  
Inert Gas ◽  
Low Flow ◽  
Relative Dispersion ◽  
Heterogeneous Flow ◽  
Small Vessels ◽  
Transit Times ◽  
Flow Through ◽  
Washout Curves

Monte Carlo simulations of the passage of inert gas through muscle tissue reveal that countercurrent gas exchange is more important than heterogeneity of flow in determination of the shape of inert gas washout curves. Semilog plots of inert gas washout are usually curved rather than straight. Two explanations often offered are that countercurrent flow may distort the shape and that uneven perfusion of the tissue gives rise to nonuniform washout. The curvature of the semilog plot may be summarized by the relative dispersion (RD), which is the ratio of the standard deviation of transit times to the mean transit time. For straight semilog plots, RD is 1. Semilog plots of data showing xenon washout from dog tissues are curved and have and RD of approximately 2. We have simulated the transit of gas particles through a vascular bed composed of repeating units of 100 mg of tissue perfused by three small vessels 80 microns in diameter and several levels of branching that direct flow through 190,000 capillaries. Geometric distribution of flow is important. Similar degrees of flow heterogeneity affect the curvature of the washout curve more if regions of heterogeneous flow are widely spaced than if they are close together. Diffusion blunts the effects of heterogeneous flow by mixing particles in high-flow regions with particles in low-flow regions. Because of this mixing, alternating regions of high flow and low flow spaced at intervals of less than 0.5 cm are unlikely explanations for the curved semilog plots.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Clinically Meaningful MRI Perfusion Abnormalities in Acute Stroke: Comparison of Analytic Techniques

Stroke ◽  
2001 ◽  
Vol 32 (suppl_1) ◽  
pp. 339-339
Author(s):  
Chen-Sen Wu ◽  
Lawrence L Latour ◽  
Steven Warach
Keyword(s):  
At Risk ◽  
Acute Stroke ◽  
Moment Method ◽  
Cerebral Blood Volume ◽  
Mean Transit Time ◽  
Clinical Severity ◽  
Perfusion Parameter ◽  
Time Curve ◽  
Time To Peak ◽  
First Moment

P2 Background: MRI perfusion imaging (PWI) can demonstrate hemodynamic abnormalities in acute stroke. The volume of hypoperfusion derived from calculated perfusion parameter maps has been used to predict tissue at risk for infarction and to identify presumptive ischemic penumbra. It is unclear how best to distinguish true tissue at risk from benign hypoperfusion. A first step toward this goal is identifying clinically significant PWI abnormalities in stroke patients. Our purpose was to evaluate four different perfusion parameter maps to determine which algorithm best correlates with clinical severity. Methods: Twenty patients were retrospectively selected from our database. Selection criteria included 1) acute hemispheric lesion, 2) MRI within 24 hours of symptom onset, and 3) no history of prior stroke. Perfusion maps were derived using four different algorithms to estimate relative mean transit time (rMTT): 1) cerebral blood volume (CBV) / cerebral blood flow (CBF), 2) CBV / peak of the concentration-time curve, 3) time to peak (TTP), and 4) ratio of the 1 st / 0 th moment of the transfer function (first moment method). Abnormal perfusion volumes were derived from ever-increasing thresholds of rMTT delay relative to normal contralateral tissue. The volumes at each delay threshold were correlated with National Institutes of Health Stroke Scale (NIHSS) for each algorithm. Results: Significant correlations between hypoperfusion volumes and NIHSS were found for all algorithms. The first moment method had the highest correlation (r = 0.76) and the correlations for this method were independent of the delay threshold used to derive the volumes. For the other algorithms, the best correlations were observed for volumes including only voxels with delays of 4 seconds or greater. Conclusions: This analysis suggests that the first moment method may have advantages over the others in determining the correlation of hypoperfusion volume to NIHSS. Further analyses correlating acute hypoperfusion volumes to final infarct volumes may help refine the choice of best analytic method for determining clinically relevant PWI abnormalities.

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