On the design of a capillary flow phantom for the evaluation of ultrasound contrast agents at very low flow velocities

Quantitative imaging: systematic review of perfusion/flow phantoms

Background

We aimed at reviewing design and realisation of perfusion/flow phantoms for validating quantitative perfusion imaging (PI) applications to encourage best practices.

Methods

A systematic search was performed on the Scopus database for “perfusion”, “flow”, and “phantom”, limited to articles written in English published between January 1999 and December 2018. Information on phantom design, used PI and phantom applications was extracted.

Results

Of 463 retrieved articles, 397 were rejected after abstract screening and 32 after full-text reading. The 37 accepted articles resulted to address PI simulation in brain (n = 11), myocardial (n = 8), liver (n = 2), tumour (n = 1), finger (n = 1), and non-specific tissue (n = 14), with diverse modalities: ultrasound (n = 11), computed tomography (n = 11), magnetic resonance imaging (n = 17), and positron emission tomography (n = 2). Three phantom designs were described: basic (n = 6), aligned capillary (n = 22), and tissue-filled (n = 12). Microvasculature and tissue perfusion were combined in one compartment (n = 23) or in two separated compartments (n = 17). With the only exception of one study, inter-compartmental fluid exchange could not be controlled. Nine studies compared phantom results with human or animal perfusion data. Only one commercially available perfusion phantom was identified.

Conclusion

We provided insights into contemporary phantom approaches to PI, which can be used for ground truth evaluation of quantitative PI applications. Investigators are recommended to verify and validate whether assumptions underlying PI phantom modelling are justified for their intended phantom application.

Arterial Phantoms with Regional Variations in Wall Stiffness and Thickness

Regional wall stiffening and thickening are two common pathological features of arteries. To account for these two features, we developed a new arterial phantom design framework to facilitate the development of vessel models that contain a lesion segment whose wall stiffness and thickness differ from those of other segments. This new framework is based on multi-part injection molding principles that sequentially casted the lesion segment and the flank segments of the vessel model using molding parts devised with computer-aided design tools. The vessel-mimicking material is created from polyvinyl alcohol cryogel, and its acoustic properties are similar to those of arteries. As a case demonstration, we fabricated a stenosed three-segment phantom composed of a central lesion segment (5.1-mm diameter, 1.95-mm wall thickness, 212.6-kPa elastic modulus) and two flank segments (6.0-mm diameter, 1.5-mm wall thickness, 133.7-kPa elastic modulus). B-mode imaging confirmed the difference in thickness between the lesion segment and flank segments of the phantom. Also, Doppler-based vessel wall displacement analysis revealed that when pulsatile flow was fed through the phantom (carotid pulse; 27 mL/s peak flow rate), the lesion segment distended less compared with the flank segments. Specifically, the three-beat averaged peak wall displacement in the lesion segment was measured as 0.28 mm, and it was significantly smaller than that of the flank segments (0.60 mm). It is anticipated that this new multi-segment arterial phantom can serve as a performance testbed for the evaluation of local arterial stiffness estimation algorithms.

Toward a Standardization of Ultrasound Scanners for Dynamic Contrast-Enhanced Ultrasonography: Methodology and Phantoms

The standardization of ultrasound scanners for dynamic contrast-enhanced ultrasonography (DCE-US) is mandatory for evaluation of clinical multicenter studies. We propose a robust method using a phantom for measuring the variation of the harmonic signal intensity obtained from the area under the time-intensity curve versus various contrast-agent concentrations. The slope of this measured curve is the calibration parameter. We tested our method on two devices from the same manufacturer (AplioXV and Aplio500, Toshiba, Tokyo, Japan) using the same settings as defined for a French multicenter study. The Aplio500's settings were adjusted to match the slopes of the AplioXV, resulting in the following settings on the Aplio500: at 3.5 MHz: MI = 0.15; CG = 35 dB and at 8 MHz: MI = 0.10; CG = 32 dB. This calibration method is very important for future DCE-US multicenter studies.

Power Doppler signal calibration in the finger joint between two models of ultrasound machine: a pilot study using a phantom and joints in patients with rheumatoid arthritis

Background Despite the advantages of ultrasound (US) in the management of rheumatoid arthritis (RA) patients, power Doppler (PD) US may be highly dependent on the type of US machine used. Purpose To present a method to calibrate the PD signal of two models of US machines by use of a flow phantom and finger joints of patients with RA. Material and Methods For the phantom study, the PD signal count was measured in the flow phantom perfusing blood mimicking fluid at various injection rates and pulse repetition frequencies (PRFs). The quantitative PD index was calculated with ImageJ. For the clinical study, the second and third metacarpophalangeal joints of five consecutive patients with RA were examined. The quantitative PD index was measured at various PRFs by use of two models of machine (the same models as the phantom study). Results For the phantom and clinical studies, negative correlations were found between the PRF and the quantitative PD index when the flow velocity was constant and positive correlations between flow velocity and the quantitative PD index at constant PRF. There was a significant difference in the depiction performance of synovial blood flow between the two models, which can be calibrated by adjusting the PRF values derived from the phantom study in each model. Conclusion Signal calibration of pannus vascularity between US machines may be possible by adjusting the PRF value according to flow phantom data. Different US machines can thus provide equivalent examination results concerning the pannus vascularity.

Wall-less flow phantom for high-frequency ultrasound applications

There are currently very few test objects suitable for high-frequency ultrasound scanners that can be rapidly manufactured, have appropriate acoustic characteristics and are suitably robust. Here we describe techniques for the creation of a wall-less flow phantom using a physically robust konjac and carrageenan-based tissue-mimicking material. Vessel dimensions equivalent to those of mouse and rat arteries were achieved with steady flow, with the vessel at a depth of 1.0 mm. We then employed the phantom to briefly investigate velocity errors using pulsed wave Doppler with a commercial preclinical ultrasound system. This phantom will provide a useful tool for testing preclinical ultrasound imaging systems.

Power Doppler signal calibration between ultrasound machines by use of a capillary-flow phantom for pannus vascularity in rheumatoid finger joints: a basic study

Ultrasound allows the detection and grading of inflammation in rheumatology. Despite these advantages of ultrasound in the management of rheumatoid patients, it is well known that there are significant machine-to-machine disagreements regarding signal quantification. In this study, we tried to calibrate the power Doppler (PD) signal of two models of ultrasound machines by using a capillary-flow phantom. After flow velocity analysis in the perfusion cartridge at various injection rates (0.1-0.5 ml/s), we measured the signal count in the perfusion cartridge at various injection rates and pulse repetition frequencies (PRFs) by using PD, perfusing an ultrasound micro-bubble contrast agent diluted with normal saline simulating human blood. By use of the data from two models of ultrasound machines, Aplio 500 (Toshiba) and Avius (Hitachi Aloka), the quantitative PD (QPD) index [the summation of the colored pixels in a 1 cm × 1 cm rectangular region of interest (ROI)] was calculated via Image J (internet free software). We found a positive correlation between the injection rate and the flow velocity. In Aplio 500 and Avius, we found negative correlations between the PRF and the QPD index when the flow velocity was constant, and a positive correlation between flow velocity and the QPD index at constant PRF. The equation for the relationship of the PRF between Aplio 500 and Avius was: y = 0.023x + 0.36 [y = PRF of Avius (kHz), x = PRF of Aplio 500 (kHz)]. Our results suggested that the signal calibration of various models of ultrasound machines is possible by adjustment of the PRF setting.

Very different performance of the power Doppler modalities of several ultrasound machines ascertained by a microvessel flow phantom

Introduction

In many patients with rheumatoid arthritis (RA) subclinical disease activity can be detected with ultrasound (US), especially using power Doppler US (PDUS). However, PDUS may be highly dependent on the type of machine. This could create problems both in clinical trials and in daily clinical practice. To clarify how the PDUS signal differs between machines we created a microvessel flow phantom.

Methods

The flow phantom contained three microvessels (150, 1000, 2000 microns). A syringe pump was used to generate flows. Five US machines were used. Settings were optimised to assess the lowest detectable flow for each US machine.

Results

The minimal detectable flow velocities showed very large differences between the machines. Only two of the machines may be able to detect the very low flows in the capillaries of inflamed joints. There was no clear relation with price. One of the lower-end machines actually performed best in all three vessel sizes.

Conclusions

We created a flow phantom to test the sensitivity of US machines to very low flows in small vessels. The sensitivity of the power Doppler modalities of 5 different machines was very different. The differences found between the machines are probably caused by fundamental differences in processing of the PD signal or internal settings inaccessible to users. Machines considered for PDUS assessment of RA patients should be tested using a flow phantom similar to ours. Within studies, only a single machine type should be used.

Comparison and evaluation of indicator dilution models for bolus of ultrasound contrast agents

Dynamic contrast-enhanced ultrasound (DCE-US) imaging is a promising diagnostic method, which enables the evaluation of tissue perfusion via different parameters. The mean transit time and time-to-peak parameters are the main time parameters and their values depend on the model used for the approximation of the noisy perfusion curves. In this paper, we described a new comparison of different perfusion models using a tissue mimicking phantom. The following models were compared: log-normal, lagged, Erlang, Gamma and the local density random walk model. We discovered that the mean-square error is not the best criterion for model evaluation. More important is the comparison between the estimated time perfusion parameters and the physical parameters of the developed tissue mimicking phantom. Based on the statistical analysis, we can suggest that for the DCE-US perfusion analysis more models should be used, excluding the log-normal model, which gives the highest error of mean transit time value.

Improved flow measurement using microbubble contrast agents and disruption-replenishment: clinical application to tumour monitoring

Dynamic contrast-enhanced ultrasound (DCE-US) and the method of disruption replenishment has been used for the past 10 years to measure flow noninvasively in the microcirculation. However, the method's perceived poor reproducibility remains a major impediment to widespread clinical acceptance. Poor reproducibility can be attributed, in part, to the curve fitting model that is used to quantify microbubble enhancement. Flow measurement in tumours is further complicated by the spatial and temporal heterogeneity of tumour blood flow. In this work, we evaluate three models of microbubble disruption and replenishment (mono-exponential, a simplified multivessel model by Krix and the lognormal perfusion model) using clinical data (11 patients, 41 sessions) from an antiangiogenic drug trial for metastatic renal cell carcinoma (RCC) and evaluate their contribution to the measurement's variability. Compared with the mono-exponential model, the lognormal perfusion model decreased the variability of intra-session velocity and blood volume measurements by 33% and 34%, respectively. Blood volume assessment using the lognormal perfusion model was comparable to Krix's mutlivessel model. Flow velocity measurement was 18% less variable for the lognormal perfusion model compared with the multivessel model. To further decrease flow measurement variability, we examine a method that exploits microbubble flow dynamics to discard the contribution of flow in large arteries and isolate the portion of the tumour microvasculature that is most sensitive to vessel targeting therapies. The method is validated with an in vitro phantom study prior to its application to the RCC clinical data set. Combined with the lognormal perfusion model, this method decreased the inter-plane variability of clinical measurements of relative tumour blood volume, in some cases by up to 20%.

Estimation of intra-operator variability in perfusion parameter measurements using DCE-US

AIM: To investigate intra-operator variability of semi-quantitative perfusion parameters using dynamic contrast-enhanced ultrasonography (DCE-US), following bolus injections of SonoVue^®.

METHODS: The in vitro experiments were conducted using three in-house sets up based on pumping a fluid through a phantom placed in a water tank. In the in vivo experiments, B16F10 melanoma cells were xenografted to five nude mice. Both in vitro and in vivo, images were acquired following bolus injections of the ultrasound contrast agent SonoVue^® (Bracco, Milan, Italy) and using a Toshiba Aplio^® ultrasound scanner connected to a 2.9-5.8 MHz linear transducer (PZT, PLT 604AT probe) (Toshiba, Japan) allowing harmonic imaging (“Vascular Recognition Imaging”) involving linear raw data. A mathematical model based on the dye-dilution theory was developed by the Gustave Roussy Institute, Villejuif, France and used to evaluate seven perfusion parameters from time-intensity curves. Intra-operator variability analyses were based on determining perfusion parameter coefficients of variation (CV).

RESULTS: In vitro, different volumes of SonoVue^® were tested with the three phantoms: intra-operator variability was found to range from 2.33% to 23.72%. In vivo, experiments were performed on tumor tissues and perfusion parameters exhibited values ranging from 1.48% to 29.97%. In addition, the area under the curve (AUC) and the area under the wash-out (AUWO) were two of the parameters of great interest since throughout in vitro and in vivo experiments their variability was lower than 15.79%.

CONCLUSION: AUC and AUWO appear to be the most reliable parameters for assessing tumor perfusion using DCE-US as they exhibited the lowest CV values.

Objective selection of high-frequency power Doppler wall filter cutoff velocity for regions of interest containing multiple small vessels

High-frequency (> 20 MHz) power Doppler ultrasound is frequently used to quantify vascularity in preclinical studies of small animal angiogenic models, but quantitative images can be difficult to obtain in the presence of flow artifacts. To improve flow quantification, color pixel density (CPD) can be plotted as a function of wall filter cutoff velocity to produce a wall-filter selection curve that can be used to estimate actual vascular volume fraction. A mathematical model based on receiver operating characteristic statistics is developed to study the behavior of wall-filter selection curves. The model is compared to experimental data acquired with a 30-MHz transducer and a custom-designed multiple-vessel flow phantom capable of mimicking a range of blood vessel sizes (200-300 microm), blood flow velocities (1-10 mm/s), and blood vessel orientations. At high flow rates, wall-filter selection curves for multiple-vessel regions include a plateau whose CPD corresponds with the total vascular volume fraction. Conversely, the vascular volume fraction of a subset of vessels is obtained at low flow rates. Detection of the volume fraction of all vessels is ensured when a plateau is > 0.5 mm/s in length and begins at a wall filter cutoff < 2 mm/s.

Quantification of flow using ultrasound and microbubbles: a disruption replenishment model based on physical principles

Contrast-enhanced ultrasound (CEUS) is a promising clinical tool capable of noninvasively quantifying flow and relative vascular volume within the microcirculation. Quantification can be performed by recording the replenishment intensity time course of the imaging plane after the local disruption of agent during a constant infusion. Traditional analyses of the time-intensity curves have relied on mathematical functions (e.g., mono-exponential) that fail to consider the underlying physical principles of the flow system and the influence of the measurement device. In reality, the time-intensity curve reflects the hemodynamics and morphology of the vascular system being measured, the ultrasound field distribution and microbubble properties. We introduce a general analytic disruption replenishment model that attempts to account for these parameters and compare its performance to the established model in a flow phantom. Specifically, the proposed model incorporates the hemodynamic properties of the flow system (velocity distribution and vascular cross section); includes the elevation and axial plane pressure distributions; and accounts for the distinct high and low mechanical index (MI) disruption and detection boundaries. In addition, we demonstrated the importance of the ultrasound beam profile for accurate velocity quantification. It was shown that velocity estimates vary by up to 56% if the depth-dependent elevation thickness is not properly accounted for. Compared with the currently accepted mono-exponential model, the presented formalism was shown to be more robust in the presence of simulated motion artifacts and demonstrated better agreement in both the quality of the fit and estimation of velocity (approximately 3 to 10% vs. 90% error) for the same flow and acoustic conditions.

Simulation and validation of arterial ultrasound imaging and blood flow

We reviewed the simulation and validation of arterial ultrasound imaging and blood flow assessment. The physical process of ultrasound imaging and measurement is complex, especially in disease. Simulation of physiological flow in a phantom with tissue equivalence of soft tissue, vessel wall and blood is now achievable. Outstanding issues are concerned with production of anatomical models, simulation of arterial disease, refinement of blood mimics to account for non-Newtonian behavior and validation of velocity measurements against an independent technique such as particle image velocimetry. String and belt phantoms offer simplicity of design, especially for evaluation of velocity estimators, and have a role as portable test objects. Electronic injection and vibrating test objects produce nonphysiologic Doppler signals, and their role is limited. Computational models of the ultrasound imaging and measurement process offer considerable flexibility in their ability to alter multiple parameters of both the propagation medium and ultrasound instrument. For these models, outstanding issues are concerned with the inclusion of different tissue types, multilayer arteries, inhomogeneous tissues and diseased tissues.

Methodology for quantifying interactions between perfusion evaluated by DCE-US and hypoxia throughout tumor growth

The objective was to validate a combination of two new technologies to depict tumor physiology both temporally and spatially with dynamic contrast-enhanced sonography and an oximeter. Human cancer prostate tumors xenografted onto mice were followed for three weeks using dynamic contrast-enhanced ultrasonography (DCE-US) to detect tumor perfusion. Time intensity curves in linear data were quantified on four regions-of-interest (ROI, main tumor section and its anterior, central and posterior intra-tumoral areas) to extract three indices of perfusion. An oxygen sensor was guided by sonography to obtain accurate pO(2) measurements in the three predefined areas of tumors during their development. No impact on tumor growth of subsequent pO(2) probe insertion was detected. Among the four ROIs studied, the local central tumor showed significant perfusion and oxygenation variations throughout the experiment. A correlation was observed between local central tumor perfusion and pO(2), both of them decreasing through time (p = 0.0068; r = 0.66). The methodology which we developed demonstrated the potential of combining DCE-US with direct tissue pO(2) measurements, improving the description of complex intratumoral dynamic behavior.

A new formalism for the quantification of tissue perfusion by the destruction-replenishment method in contrast ultrasound imaging

A new formalism is presented for the destruction-replenishment perfusion quantification approach at low mechanical index. On the basis of physical considerations, best-fit methods should be applied using perfusion functions with S-shape characteristics. These functions are first described for the case of a geometry with a single flow velocity, then extended to the case of vascular beds with blood vessels having multiple flow velocity values and directions. The principles guiding the analysis are, on one hand, a linearization of video echo signals to overcome the log-compression of the imaging instrument, and, on the other hand, the spatial distribution of the transmit-receive ultrasound beam in the elevation direction. An in vitro model also is described; it was used to confirm experimentally the validity of the approach using a commercial contrast agent. The approach was implemented in the form of a computer program, taking as input a sequence of contrast-specific images, as well as parameters related to the ultrasound imaging equipment used. The generated output is either flow-parameter values computed in regions-of-interest, or parametric flow-images (e.g., mean velocity, mean transit time, mean flow, flow variance, or skewness). This approach thus establishes a base for extracting information about the morphology of vascular beds in vivo, and could allow absolute quantification provided that appropriate instrument calibration is implemented.

The quantification of absolute myocardial perfusion in humans by contrast echocardiography: algorithm and validation

OBJECTIVES

We sought to test whether myocardial blood flow (MBF) can be quantified by myocardial contrast echocardiography (MCE) using a volumetric model of ultrasound contrast agent (UCA) kinetics for the description of refill curves after ultrasound-induced microsphere destruction.

BACKGROUND

Absolute myocardial perfusion or MBF (ml.min(-1).g(-1)) is the gold standard to assess myocardial blood supply, and so far it could not be obtained by ultrasound.

METHODS

The volumetric model yielded MBF = rBV.beta/rho(T), where rho(T) equals tissue density. The relative myocardial blood volume rBV and its exchange frequency beta were derived from UCA refill sequences. Healthy volunteers underwent MCE and positron emission tomography (PET) at rest (group I: n = 15; group II: n = 5) and during adenosine-induced hyperemia (group II). Fifteen patients with coronary artery disease underwent simultaneous MCE and intracoronary Doppler measurements before and during intracoronary adenosine injection.

RESULTS

In vitro experiments confirmed the volumetric model and the reliable determination of rBV and beta for physiologic flow velocities. In group I, 187 of 240 segments were analyzable by MCE, and a linear relation was found between MCE and PET perfusion data (y = 0.899x + 0.079; r(2) = 0.88). In group II, resting and hyperemic perfusion data showed good agreement between MCE and PET (y = 1.011x + 0.124; r(2) = 0.92). In patients, coronary stenosis varied between 0% to 89%, and myocardial perfusion reserve was in good agreement with coronary flow velocity reserve (y = 0.92x + 0.14; r(2) = 0.73).

CONCLUSIONS

The volumetric model of UCA kinetics allows the quantification of MBF in humans using MCE and provides the basis for the noninvasive and quantitative assessment of coronary artery disease.

Comparison of different mathematical models to analyze diminution kinetics of ultrasound contrast enhancement in a flow phantom

Ultrasound (US) energy leads to intensity- and frequency-dependent destruction of US contrast agent (UCA) microbubbles. When applying repeated US pulses, this phenomenon can be detected as contrast diminution over time. Contrast diminution kinetics depend on the replenishment of UCA into the sample volume. Thus, it is related to organ perfusion. To analyze the contrast diminution kinetics following pulsed harmonic US application (SONOS 5500, 1.8-3.6 MHz, MI: 1.6, frame rates: 2, 4, and 6.67 Hz), we performed an in vitro study using SonoVue continuous infusion. Seven flow rates (4.5, 9, 13.5, 18, 22.5, 27 and 36 mL/min) were tested. Based on our results, three mathematical models (linear intensity decrease, exponential decay, and an exponential destruction/reperfusion model) describing diminution kinetics were compared. In 113 (89.7%) of 126 trials, a signal decrease was observed after US application. At higher flow rates (18 to 36 mL/min), curve fitting was not possible for the exponential models. For the linear model, intensity decrease depended significantly on the flow rate (p < or = 0.005, n = 7). A logistic model was fitted to the data, defining the slope in the dynamic range of quasilinear dependence for the different frame rates, as well as the inflection point: The higher the frame rate, the higher the flow rate at the point of inflection. For the exponential model, the contrast half-life was dependent on the flow rate (r = 0.95, p = 0.03, n = 6) only at the highest frame rate (6.67 Hz). The perfusion coefficient derived from the destruction/reperfusion model was not significantly related to the flow rate. In conclusion, the linear intensity decrease correlates well with the flow rate (i.e., flow velocity) and defines optimum frame rates for diminution imaging at different flow velocities. The exponential models, which required curve-fitting procedures, were determined to be inappropriate to describe flow in our phantom.

In vitro and in vivo studies on continuous echo-contrast application strategies using SonoVue in a newly developed rotating pump setup

With emerging imaging strategies for contrast sonography (CS), there is a rising demand for the precise control of ultrasound (US) contrast agent delivery. Constant delivery minimizes artefacts and improves efficacy. The aim of this study was to evaluate the physical properties of the new contrast agent SonoVue and to evaluate the feasibility and accuracy of a new infusion approach using an automated infusion system for contrast agitation and delivery of echo-contrast agents. In vitro testing of infusion properties of SonoVue were performed in a capillary phantom mimicking tissue perfusion. Nonagitated standard infusion setups were compared with hand agitation and the new pump system with respect to possible artefacts, constancy of contrast effect and efficacy. In three volunteers, the new pump system was tested for constancy of contrast in large vessels. Without continuous agitation, continuous infusion of SonoVue resulted in bolus-like signal-intensity curves, along with substantial imaging artefacts. Additionally, homogenization of SonoVue significantly improved efficacy (p < 0.0001). No significant differences were found between hand agitation and homogenization by the new pump. In clinical settings, constant agitation using the new pump resulted in constant signal conditions in the carotid artery 3.72 +/- 0.46 units (U) after 5 min. Continuous agitation of SonoVue is mandatory for quantitative approaches. By the new infusion technique, CS could be performed for a reasonably long time period and efficacy is significantly improved (p < 0.0001). The new infusion technique might thereby allow routine application of constant infusion scenarios in clinical CS.

Subharmonic signal generation from contrast agents in simulated neovessels

Detection and measurement of blood flow in neovessels around a tumor can yield prognostic information about the tumor. Early detection and classification may help differentiate benign and malignant tumors; thus, improving patient management. This can be accomplished by injecting ultrasonic contrast agents and measuring the backscattered signals from them. Use of the subharmonic backscattered signals from these agents may be better than fundamental or second harmonic components because of the negligible subharmonics generated by the surrounding tissue. Preliminary results on the detection and measurement of subharmonic signal components up to 12 dB (at increasing pressures) from very small tubes (200 to 300 microm diameter) are reported, demonstrating the possibility and potential application of subharmonic imaging in detecting tumor angiogenesis.

A multivessel model describing replenishment kinetics of ultrasound contrast agent for quantification of tissue perfusion

To improve the quantification of tissue perfusion using intermittent sonography, a new model describing replenishment kinetics of microbubbles is proposed. The new approach takes into account the variability of blood flow velocities found in vivo, especially in tumors, and consistently describes the refilling process of microbubbles. Based upon this model, blood volume, blood velocity, blood flow and perfusion in 17 experimental tumors were calculated, and compared with the results obtained with the established, phenomenologically derived exponential kinetic model. In contrast to the existing model, our approach describes tissue vascularization more physiologically and allows deduction of a consistent new hyperbolic model for quantification of intermittent sonography. Blood volume and mean blood velocity did significantly correlate between both the new and the established model (k=0.99; k=0.94, both p<0.001). However, mean tumor blood velocity was lower (-19%, p<0.01) with the established model compared to the newly developed model. In addition, the range and distribution of blood flow velocities found in vivo can be estimated with the new model. Furthermore, it uses simpler mathematical fitting routines and allows easier data acquisition, which may allow a more practicable clinical application of intermittent sonography. In conclusion, a more valid, detailed and accurate calculation of perfusion parameters, especially of tumors, can be derived in vivo with the new multivessel model of intermittent sonography.