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PubMed1990

A rapid method for standardization of the gated radionuclide left ventricular ejection fraction.

Radionuclide ventriculography has become the standard method for serially evaluating left ventricular ejection fraction (EF). The "gold standard" for evaluating EF is the contrast ventriculogram, which uses mathematical models to arrive at the volumes used to calculate EF. These models are subject to possible error. This paper reports the standardization of volume measurements of a digital angiographic camera system using a series of cardiac phantoms and the correlation of measurement of the EF of a series of patients whose EF was determined by digital angiography and radionuclide ventriculography.

Aged↗
PubMed1995

Continuous versus bolus thermodilution cardiac output measurements--a comparative study.

OBJECTIVE: To compare the methods for continuous and bolus thermodilution cardiac output measurements. DESIGN: In vivo and in vitro experimental studies. SETTING: Surgical research division in a university hospital. SUBJECTS: Eight calves and flow bench model. INTERVENTIONS: Data were collected in vivo from eight calves instrumented with pulmonary artery catheters, which allowed both continuous and bolus thermodilution measurements. The pulmonary artery catheter was placed through the external jugular vein. All in vitro measurements were performed using a flow bench model. MEASUREMENTS AND MAIN RESULTS: A total of 232 bolus and continuous thermodilution measurements were analysed in vivo to determine the degree of agreement between the two methods. The absolute measurement bias was 0.14 L/min with 95% confidence limits ranging from -0.83 to 1.15 L/min. In vitro analysis of 576 measurements at six different temperature points (range 31 degrees to 41 degrees C), using clinically relevant flows (2 to 9 L/min), showed overestimation of flow values using continuous and bolus thermodilution methods. However, the continuous method showed better accuracy by a lower degree of overestimation. Systematic error was 9.7 +/- 8.4 (SD) % for continuous and 11.1 +/- 6.3% for the bolus method (p < .001). This effect was especially evident at lower flow rates. The influence of various temperatures on the accuracy and reproducibility of both methods of measurement was statistically significant but not clinically relevant. The infusion of lactated Ringer's lactate solution (infusion rates 100 to 1000 mL/hr) affects both methods at a low flow rate of 2 L/min, without causing a significant effect on continuous measurement at a higher flow rate (4 L/min). Shunting of 50% of circulating volume to the distal part of the thermal filament of the pulmonary catheter impaired the accuracy of continuous measurement without affecting results from bolus measurements (systematic error -26.8 +/- 8.2% for continuous and -5.2 +/- 4.1% for bolus thermodilution). CONCLUSIONS: Continuous thermodilution cardiac output measurement provided higher accuracy and greater resistance to thermal noise than standard bolus measurements. The correct placement of the catheter is essential for precise measurements.

Analysis of Variance↗
PubMed1985

Flow determination using computed tomography: application to aortic dissection. Part I.

The CT method of flow determination evaluated in this study was based on the application of contrast enhancement dynamics. In order to characterize flow, such parameters as mean transit time, rise time, peak CT value, curve width and variance, and others were derived from the venoarterial indicator dilution curves using a perfect mixers-in-series model of curve fitting analysis and a bolus injection of contrast medium. The technique was first validated in a steady state phantom model that simulated in vivo conditions of right-sided mixing closely by the introduction of a number of mixers. A series of flows through small tubes was measured. Good correlation was obtained (r = .85). For a fixed number of mixers, the central second moment of the primary peak of the indicator dilution curve or variance decreased with increasing flow and peak CT value increased. Applied to the clinical situation, this method would allow characterization of blood flow using an intravenous bolus of contrast.

Aortic Dissection↗
PubMed1990

Quantitative dual-energy coronary arteriography.

Subtraction techniques for digital cardiac imaging have been hampered by misregistration artifacts. The use of dual-energy imaging is being evaluated as a means for reducing these artifacts. Results reported previously indicate that the dual-energy technique may be useful for applications such as exercise ventriculography and general quantification tasks. The purpose of the current study is to investigate the use of dual-energy subtraction imaging for quantitative coronary arteriography. In vivo coronary vessel phantoms (0.2 to 7 mm2 in cross-sectional area) were used to study the potential advantages of tissue suppressed energy subtracted images over unsubtracted images for quantification of absolute vessel cross-sectional area when cardiac motion is present. Estimates of lumen cross-sectional area (N = 20) were determined using videodensitometric analysis of selected energy subtracted and unsubtracted images. Linear regression analysis of measured and actual cross-sectional area showed energy subtracted image data (slope = 1.06, intercept = 0.48 mm2, r = 0.99) to have improved accuracy (P less than .05) and precision (P less than .05) over unsubtracted image data (slope = 1.24, intercept = 1.07 mm2, r = 0.95).

Angiography, Digital Subtraction↗
PubMed1993

Enhancement of the echogenicity of flowing blood by the contrast agent perflubron.

RATIONALE AND OBJECTIVES: Perflubron, or perfluorooctylbromide, is an effective ultrasound and computed tomography contrast agent in a lecithin emulsion form. The authors studied acoustical properties of perflubron emulsion in static human and flowing porcine blood for concentrations from 0% to 30% weight per volume. METHODS: Propagation velocity (c), the intensity attenuation coefficient (mu), density (rho), and particle size were measured directly. Because the backscatter of flowing blood is dependent on shear rate, relative echogenicity was measured as a function of perflubron concentration in whole porcine blood, in a laminar flow system, at shear rates of 16.0 to 68.5 sec-1 for realtime sector scanner images obtained at 7.5 MHz. RESULTS: Neat perflubron is a colorless liquid with density of 1.93 g.mL-1 and velocity of 630 m.sec-1. The following values were obtained at 4.7 MHz in static human blood (hematocrit 44%) at expected human in vivo blood concentrations of 3.1% perflubron versus pure human blood: rho = 1.11 versus 1.05 g.mL-1, c = 1,480 versus 1,576 m.sec-1, mu = 1.00 versus 0.36 dB.cm-1. The mean echogenicity of whole porcine blood increased substantially with perflubron concentration and was inversely proportional to blood shear rate. CONCLUSION: Adding 3.1% concentration of perflubron increased image echogenicity at all shear rates studied, ranging from 70% at 68.5 sec-1 (16.3 cm.sec-1) up to 180% at 16.0 sec-1 (3.8 cm.sec-1). Perflubron enhancement of blood is marked and demonstrates shear rate dependence like that of whole blood.

Blood Flow Velocity↗
PubMed1994

Comparison of angiographic opacification of ioxaglate and iodixanol by digital region-of-interest processing technique in an experimental circulation model.

RATIONALE AND OBJECTIVES: By using digital ROI (region of interest) processing techniques, we measured and compared directly the angiographic opacification of ioxaglate and iodixanol in an experimental circulation model. METHODS: A pulsatile pump circulated water into a 2-mm plastic tube for digital subtraction angiography (DSA). Altogether, 90 digital imaging series were registered during injections of two contrast media with 320, 300, and 270 mg/mL iodine concentrations. By selecting a "vessel" ROI and a subtracted background ROI, a time-density curve (TDC) was created. From the TDC, the average density of contrast media and the appearance time of contrast media into the selected ROI were measured. RESULTS: The average density was statistically different (P < .01) among three various iodine concentrations of the contrast media, but no difference was found between the two contrast media. The appearance times of ioxaglate with 320 mg/mL iodine concentration were statistically shorter (P < .01) than those of iodixanol. In both contrast medium groups, the appearance times were statistically shorter (P < .05) with 270 mg/mL iodine concentration than with two higher iodine concentrations. CONCLUSION: The current experimental set-up facilitates reproducible measurement of angiographic opacification during the injection of contrast media. The average densities between ioxaglate and iodixanol are the same, but are significantly different among three iodine concentrations. The different appearance times of the two CM and the three iodine concentrations may be caused by the various viscosities of the contrast media.

Angiography, Digital Subtraction↗
PubMed1994

Validation of volume blood flow measurements using three-dimensional distance-concentration functions derived from digital x-ray angiograms.

RATIONALE AND OBJECTIVES: The authors present phantom validation of a method for computing pulsatile flow waveforms in arterial vessels from high-frame-rate biplane x-ray angiograms. METHODS: The three-dimensional course of a blood vessel is constructed from biplane digital x-ray angiograms. A parametric image of contrast mass versus time and true three-dimensional path length is generated. Adjacent contrast mass-distance profiles are matched to compute instantaneous velocity, which is multiplied by cross-sectional area to yield volume flow. An electromagnetic flowmeter was used to validate flow estimates in a phantom consisting of 150-mm tubes 3, 4, and 6 mm in diameter, orientated 15 degrees, 30 degrees, and 35 degrees to the imaging plane, with flow rates and waveforms expected in vivo. RESULTS: Mean and peak flows were accurate to within 9% and 10%, respectively, for velocities of less than 1 meter/second at a frame rate of 25 frames per second. CONCLUSIONS: A practical method for computing highly pulsatile flow waveforms in vivo in tortuous vessels is presented.

Algorithms↗
PubMed1994

Functional properties of a prototype rheolytic catheter for percutaneous thrombectomy. In vitro investigations.

RATIONALE AND OBJECTIVES: The performance of a rheolytic catheter designed to provide rapid fragmentation and evacuation of debris was evaluated. Specifically, fragmentation and evacuation efficiency was investigated in vitro. METHODS: Fragmentation, aspiration, and recanalization of large thrombotic occlusions (8-cm length, 6-mm inner diameter) composed of clot (n = 11) or collagen gels (n = 20) of different stiffness were performed with different jet pressures at rates optimized by visual observation and were recorded on videotape for subsequent analysis. The size and number of the resulting particles in the evacuated fluid and those remaining in the artificial vessel were determined using filtration and laser light scattering techniques. The rate of fragmentation, mean particulate size, and efficiency of evacuation were evaluated as a function of operating parameters and "clot stiffness." RESULTS: Complete fragmentation of fresh thrombus occurred at 11,000 psi by direct action of the 6 radially disposed jets, which created a trapping vortex from which most of the particles (80%) were evacuated by suction. At lower pressure (5,500 psi), fragmentation efficiency was unchanged for fresh thrombus and softer 5% gels. Ninety-five percent of the thrombus was fragmented in very small particles with a mean diameter of 0.8 +/- 0.4 micron, while 5% of the mass of the fragmented thrombus was in particles > 40 microns. At 11,000 psi, the maximal rate of advancement associated with complete material fragmentation decreased with stiffness. For very stiff gels or heavily cross-linked old thrombus, complete fragmentation and removal of material was not achieved. CONCLUSION: The high-pressure rheolytic catheter rapidly fragmented and evacuated large thrombi much larger than the catheter diameter--features with potential for treating large thrombi, such as acute pulmonary emboli or deep vein thrombi. However, this rapid forceful disruption may damage vessel walls and invariably creates a broad range of particulate sizes, which makes evacuation of almost all of the particulate material imperative to minimize clinically relevant distal embolization.

Catheterization↗
PubMed1994

Influence of carbon dioxide gas perfusion to thermal distribution of sapphire probe. A comparative study with saline.

RATIONALE AND OBJECTIVES: A previous study confirmed that the direct laser-thermal conduction of the sapphire probe with carbon dioxide gas perfusion increased the width of the laser-recanalized channel. This caused us to further investigate the thermal distribution characteristics of the sapphire probe when lasing with CO2 gas perfusion. METHODS: The surface temperature of a sapphire probe in a circulation model using 37 degrees C flowing whole blood was measured. Two hundred and sixteen measurements were obtained by directly contacting a flexible thermocouple wire onto the sapphire probe at different sites: 1) metal connector; 2) lateral side of the sapphire crystal; 3) top of the sapphire crystal; and 4) 3 mm in front of the sapphire probe. During lasing with a neodymium-yttrium-aluminum garnet (Nd-YAG) laser, the CO2 gas or saline was infused through the sapphire probe at different flow rates. RESULTS: The lateral side of the sapphire crystal was heated up to 75 degrees C when lasing without any perfusion, but up to 220 degrees C when lasing with CO2 gas perfusion. At all four sites, the mean temperature increases were statistically higher (P < .01) with CO2 gas than with saline perfusion. The mean peak temperatures increased with increasing flows of CO2 gas perfusion and decreased with increasing flows of saline perfusion. CONCLUSIONS: The thermal conduction from the sapphire probe can be significantly enhanced by increasing flows of CO2 gas perfusion. This may play an important role in creating a greater diameter of the recanalized channel and in better delaying the formation of restenosis or re-occlusion after laser recanalization of atheromatous arteries.

Aluminum Oxide↗
PubMed1994

Accuracy of quantifying coronary hydroxyapatite with electron beam tomography.

RATIONALE AND OBJECTIVES: The electron beam tomography coronary calcium score continues to be used without experimental validation. To determine its accuracy, a series of experiments was performed. METHODS: A chest phantom model was constructed with coronary arteries represented by cylindrical holes containing hydroxyapatite granules embedded in a gelatin matrix to simulate coronary arteries. Experiments were performed to determine the relationship between the mass of hydroxyapatite in each of these arteries, the coronary calcium score currently used in coronary screening, and an alternative method of estimating mass from the images. The model was scanned with equal amounts of hydroxyapatite in each artery: 1) when the cylindrical heart was rotated 36 degrees 10 times between scans, and 2) when the particle diameters varied from 0.1 mm to 4 mm. The scores were calculated, and a subtraction algorithm was applied to estimate the exact mass of hydroxyapatite in each artery. RESULTS: The hydroxyapatite scores varied by 42% with position and by 1.54 x 10(6)% with particle diameter. The estimated masses from the subtraction algorithm were more stable with position and particle size, with maximum percent errors of 10% and 14% for position and particle size, respectively. CONCLUSIONS: These results suggest that the coronary calcium score is invalid, and that more precise and clinically relevant methods, such as the arterial summation method, should be rigorously tested in clinical studies.

Algorithms↗
PubMed1994

Magnetic resonance measurement of volumes using a phantom. Application to the cardiac ventricles of infants and small children.

RATIONALE AND OBJECTIVES: Cine magnetic resonance (MR) is an established method for determining cardiac ventricular volumes in adults. The reported section slice thickness may be too thick for accurate measurement of ventricular volumes in infants and young children. In this article, acceptable slice thickness is established for cine MR in children. METHODS: Balloons filled with a dilute gadolinium solution were immersed in a water bath. The balloons were scanned using a fast scan technique to simulate cine MR. Scanning was performed using different slice thicknesses. Volumes were calculated using previously reported techniques. These calculated volumes were compared to direct measurement of the balloon volumes using graduated syringes. RESULTS: The balloons varied in volume from 0.9 mL to 27.3 mL. Measurements using 3- and 5-mm slice thickness sections were found to be significantly more accurate than 10-mm slice thickness sections. CONCLUSION: Section thickness should be less than 1-cm when performing cine MR in infants and small children for measurement of ventricular volumes.

Child↗
PubMed1997

A physiologic in vitro model of the inferior vena cava with a computer-controlled flow system for testing of inferior vena cava filters.

RATIONALE AND OBJECTIVES: The authors develop a physiologic in vitro model of the inferior vena cava (IVC) for testing of filters. METHODS: The model is driven by a centrifugal pump. A computer-controlled electromagnetic valve is used for generation of different flow patterns. Limitation of the pressure increase in case of IVC occlusion is achieved by a bypass circuit. A glycerin solution is used for perfusion. Artificial clots are made from polyacrylamide gel. Data acquisition includes continuous monitoring of flow and difference pressure over the filter and video recording of the testing events. RESULTS: The model can generate constant and pulsatile flows. The pressure increase can be limited to 70 mm Hg in case of occlusion. Calculation of the flow velocities in the IVC is possible. A classification of thrombus capturing is presented. The testing of most of the results are reproducible. CONCLUSIONS: The in vitro model simulates the physiologic conditions in the IVC. It can be used for comparative testing of different filters and the evaluation of new filter designs.

Blood Flow Velocity↗
PubMed1999

Enhancement of in vitro effectiveness for hydrodynamic thrombectomy devices. Simultaneous high-pressure rt-PA application.

RATIONALE AND OBJECTIVES: To determine the efficacy of simultaneous high-pressure recombinant tissue plasminogen activator (rt-PA) application for clot removal and procedure-related peripheral particle embolization for the hydrodynamic thrombectomy devices LF 140 AngioJet (LF 140) and triplelumen Hydrolyser (triple HL) in an in vitro flow model. METHODS: Thrombectomy of clots (n = 47) from 5-day-old human blood (8.9-9.7 g) was performed with the LF 140 and the triple HL, each with and without simultaneous rt-PA (9.97-12.59 g) application in a flow model (flow 1 liter/min) made of silicone tubes (7 mm inner tube diameter). All catheters were used according to the manufacturer's recommendations. RESULTS: The triple HL revealed no statistically significant performance differences with additional rt-PA. For the LF 140, mean thrombectomy time ranged from 23.5 sec (with rt-PA) to 33.5 sec (P = 0.05). The ratio of peripheral embolus weight to thrombus weight was reduced from 2.12% to 0.46% (rt-PA; P = 0.05). None of the tested devices had an isovolumetric performance; the mean ratio of applied saline to aspirated fluid for the devices were different from one, ranging from 0.89 to 0.92 (rt-PA) for the triple HL and from 0.43 to 0.52 (rt-PA) for the LF 140. No significant differences for remaining thrombus within the tubes were found. CONCLUSIONS: Simultaneous rt-PA-enhanced hydrodynamic thrombectomy is feasible in vitro. This combination reduces the time for thrombectomy and procedure-related peripheral particle embolization for the LF 140. No effect could be demonstrated for the triple HL in an in vitro flow model. It remains unclear whether this procedure is effective in vivo. It seems likely that the incidence of fibrinolysis-associated complications may increase in vivo.

Humans↗
PubMed2001

Comparison of the mechanical thrombectomy efficacy of the Amplatz thrombectomy device and the Cragg thrombolytic brush in vitro.

RATIONALE AND OBJECTIVES: To determine the efficacy of thrombectomy (without thrombolytic agents) for the Amplatz thrombectomy device (ATD) and the Cragg thrombolytic brush catheter (CBC) in vitro. METHODS: Thrombectomy was performed with the ATD or CBC (6F) in a flow model. Embolus sizes, weight, remaining thrombus, and activation time were evaluated. RESULTS: No significant difference in the activation time was found. The CBC produced significantly less embolism (3.3% vs. 0.03% in the 5-mm and 89% vs. 0.5% in the 7-mm model), but also much more thrombus remained in the system than with the ATD (1% vs. 41% in the 5-mm and 0.1% vs. 62% in the 7-mm model). CONCLUSIONS: The ATD can remove almost all thrombus (99%), whereas the CBC removes only up to 60%, producing fewer emboli than the ATD. This might be due to the lower rotational speed of the CBC compared with the ATD, which is 20 times greater. The soft nylon brush offers less resistance and shear force toward the thrombus than the stainless-steel impeller of the ATD. Because of the large amount of remaining thrombus, the CBC should not be used without lytic agents.

Catheterization↗
PubMed1998

Distribution volume of radiolabeled large neutral amino acids in brain tissue.

Variations in the cerebellum to plasma ratio at late times in 6-[18F]fluoro-L-DOPA studies are shown to be consistent with competitive binding of large neutral amino acids for a common transporter in the blood-brain barrier and the stability of brain tissue large neutral amino acid level in the presence of plasma level changes. The distribution volume of an inert large neutral amino acid can be estimated from plasma and tissue large neutral amino acid levels and apparent half-saturation concentrations (Km) of the transporter in the blood-brain barrier. Stability of brain large neutral amino acid levels is supported by literature findings and can be explained by high saturation of the large neutral amino acid transporter at physiologic conditions.

Amino Acids↗
PubMed1999

Bolus injection versus slow infusion of [15O]water for positron emission tomography activation studies.

In positron emission tomography studies using bolus injection of [15O]water, activation responses reflect underlying CBF changes during a short time (15 to 20 seconds) after arrival of the bolus in the brain. This CBF sensitivity window may be too short for complex activation paradigms, however, particularly those of longer duration. To perform such paradigms, we used a slow infusion method of tracer administration to lengthen the CBF sensitivity window. The present study was designed to determine if this slow infusion technique yields similar results to a bolus injection with a short activation task involving memory for faces. When analyzed using statistical parametric mapping, scanning durations of either 90 or 120 seconds and a 90-second slow infusion schedule produced very similar results to a standard 60-second scan collected after bolus injection, indicating that statistically similar brain activation maps can be produced with the two infusion techniques. This slow infusion approach allows for increased flexibility in designing future studies in which a short CBF sensitivity window is a limiting factor.

Adult↗
PubMed2000

Dependence of oxygen delivery on blood flow in rat brain: a 7 tesla nuclear magnetic resonance study.

Magnetic resonance imaging (MRI) and spectroscopy (MRS) were used at a magnetic field strength of 7 T to measure CBF and CMRO2 in the sensorimotor cortex of mature rats at different levels of cortical activity. In rats maintained on morphine anesthesia, transitions to lower activity and higher activity states were produced by administration of pentobarbital and nicotine, respectively. Under basal conditions of morphine sulfate anesthesia, CBF was 0.75 +/- 0.09 mL x g(-1) x min(-1) and CMRO2 was 3.15 +/- 0.18 micromol x g(-1) x min(-1). Administration of sodium pentobarbital reduced CBF and CMRO2 by 66% +/- 16% and 61% +/- 6%, respectively (i.e., "deactivation"). In contrast, administration of nicotine hydrogen tartrate increased CBF and CMRO2 by 41% +/- 5% and 30% +/- 3%, respectively (i.e., "activation"). The resting values of CBF and CMRO2 for alpha-chloralose anesthetized rats were 0.40 +/- 0.09 mL x g(-1) x min(-1) and 1.51 +/- 0.06 micromol x g(-1) x min(-1), respectively. Upon forepaw stimulation, CBF and CMRO2 were focally increased by 34% +/- 10% and 26% +/- 12%, respectively, above the resting nonanesthetized values (i.e., "activation"). Incremental changes in CBF and CMRO2, when expressed as a percentage change for "deactivation" and "activation" from the respective control conditions, were linear (R2 = 0.997) over the entire range examined with the global and local perturbations. This tight correlation for cerebral oxygen delivery in vivo is supported by a recent model where the consequence of a changing effective diffusivity of the capillary bed for oxygen, D, has been hypothetically shown to be linked to alterations in CMRO2 and CBF. This assumed functional characteristic of the capillary bed can be theoretically assessed by the ratio of fractional changes in D with respect to changes in CBF, signified by omega. A value 0.81 +/- 0.23 was calculated for omega with the in vivo data presented here, which in turn corresponds to a supposition that the effective oxygen diffusivity of the capillary bed is not constant but presumably varies to meet local requirements in oxygen demand in a similar manner with both "deactivation" and "activation."

Animals↗
PubMed2000

Model of blood-brain transfer of oxygen explains nonlinear flow-metabolism coupling during stimulation of visual cortex.

The coupling between cerebral metabolic rate of oxygen (CMRO2) and blood flow (CBF) in response to visual stimulation was evaluated by means of a model of oxygen delivery. The model predicted a nonlinear relationship between stimulus-evoked changes of oxygen consumption and blood flow. The magnitude of the CMRO2/CBF ratio index (IO2) was used to indicate the degree of flow-metabolism coupling prevailing in specific areas of the brain during physiological stimulation. Therefore, the index provided a measure of the blood oxygenation level dependent (BOLD) magnetic resonance contrast. To evaluate the changes of IO2 in response to visual stimulation, the model was applied to the effect of a changing flicker rate of a visual stimulus on the magnitudes of CBF, CMRO2, and oxygen diffusion capacity, in the human brain. Positron emission tomography (PET) was used to measure the CBF and the CMRO2 in 12 healthy volunteers who viewed a cross-hair (baseline) or a yellow-blue annular checkerboard reversing at frequencies of 1, 4, or 8 Hz. The magnitude of CBF in the primary visual cortex increased as a function of the checkerboard reversal rate and reached a maximum at the frequency of 8 Hz (z=16.0), while the magnitude of CMRO2 reached a maximum at 4 Hz (z=4.0). Therefore, the calculated IO2 was lower at 8 Hz than at 1 and 4 Hz, in contrast to the oxidative metabolic rate that reached its maximum at 4 Hz. The model explained the increase of oxygen consumption as the combined effect of increased blood flow and increased oxygen diffusion capacity in the region of visual activation.

Adult↗