Contrast ultrasonography: necessity of linear data processing for the quantification of tumor vascularization.

PURPOSE: This study is intended to compare the value of uncompressed ultrasonic data, obtained after linear power detection of the ultrasonic radiofrequencies that we call linear data, with usual compressed video data for the quantification of tumor perfusion, particularly for monitoring antivascular therapy. MATERIALS AND METHODS: To form a clinically useful ultrasonic image, the detected power of the received signals (linear data) is compressed in a quasi-logarithmic fashion in order to match the limited dynamic range of the video monitor. The resulting reduced range of signals from an injected contrast agent may limit the sensitivity to changes in the time-intensity curves. Following a theoretical evaluation of the effects of compression on time-intensity curves and as an in vivo example, we measured at different times the effects of an antivascular drug administered to mice bearing melanoma tumors. The mean time-intensity curves within the tumors after bolus injection of a contrast agent were determined using both linear and video data. Linearized data was recovered using the inverse of the true scanner's compression law, which was experimentally determined. Three features were extracted from the time-intensity curves: peak intensity (PI), time to peak intensity (TPI) and area under the curve in the wash-in phase (AUC (wash-in)). When contrast reached its maximum value, the coefficient of variation reflecting the heterogeneity of the intensity of contrast uptake within the tumor, was computed using both data sets. RESULTS: TPI was found to be similar with either data set (r = 0.98, p < 0.05, factor of 1.09). Linear PI and AUC (wash-in) had significantly earlier decreases after drug administration than video data (p = 0.015 and p = 0.03, respectively). The coefficient of variation was significantly lower when using video rather than linear data (p < 10 (-4)). CONCLUSION: In conclusion, the use of linear data is the only mathematically valid methodology for determining a tumor's time-intensity curve and, in practice, it allows earlier demonstration of responses to antivascular drugs.

[Evaluation of early response to antiangiogenic treatment with dynamic contrast enhanced ultrasound]. / Evaluation précoce des traitements anti-angiogéniques par échographie dynamique de contraste.

Early functional imaging evaluation of targeted treatments in oncology is of major importance. Dynamic contrast enhanced US is now recognized as a functional imaging technique able to evaluate new antiangiogenic drugs targeting superficial and deep seated lesions. This evaluation is based on an analysis of the curve of signal intensity over time after injection of the contrast agent. The availability of quantification software allows objective quantification of tumor perfusion parameters from linear raw data, prior to logarithmic signal compression, including maximum intensity of enhancement, mean transit time, time to peak, and wash-in slope coefficient. Dynamic contrast enhanced US, a sensitive, reproducible and readily available technique, allows early prediction of tumor response to treatment based on changes in vascularity, before morphological changes (RECIST) become apparent.

[Validation of a new methodology for characterizing ultrasound contrast agents (UCA)]. / Validation d'un banc hydrodynamique pour la caractérisation de produits de contraste ultrasonores (PCUS).

PURPOSE: Validation of an experimental ultrasound system on erythrocyte suspensions with variable levels of aggregation and application to the echogenicity quantification of UCA under quasi-physiologic flow conditions. MATERIALS AND METHODS. The system is constituted with a Couette cell with variable applied shear rates, an ultrasound emitter/receiver and a digital scope for radio-frequency signal acquisition. Ultrasound indices (UI) were defined for the two experimental established protocols based on the gold standard laser methodology. Washed red cells with or without variable Dextran 70 kD concentrations were used to simulate a wide particle size range. A preliminary application to UCA was conducted with Levovist for calibration of the system. RESULTS: For each protocol, applied ten times on identical whole blood samples, a student t-test revealed no significant variation for all UI. Results on washed red cells were in good agreement with Rayleigh's theory of ultrasound backscattering. Significant correlations were obtained between laser and UI for washed red cells with different Dextran concentrations. An elevation of 12.13 dB in backscattered intensity was obtained after addition of Levovist. CONCLUSION: The constituted Couette system allowed reproducible and accurate echogenicity quantification of small scatterers such as UCA in quasi-physiologic blood flow conditions.

Evaluation of contrast-enhanced color Doppler ultrasound for the quantification of angiogenesis in vivo.

RATIONALE AND OBJECTIVES: To evaluate contrast-enhanced color Doppler ultrasonography (CDUS) aimed at quantifying angiogenesis in vivo. METHODS: Eight colon tumors xenografted into mice were studied with CDUS both without and after injection of SHU 508A. The number of intratumor vessels and pedicles visualized with CDUS and the value of the acoustic intensity quantified by computer were compared with the evaluation of angiogenesis by study of digitized histological slides. RESULTS: SHU 508A increased the number of intratumor vessels and pedicles depicted by CDUS, which could also be quantified by acoustic intensity. The comparison of CDUS and digitized histological slide studies showed that the detection threshold after SHU 508A administration allowed visualization of small vessels (40 microm in diameter). The "hot spots" seen on histology were superimposable onto vessels seen with CDUS. Regions in which no vessels were detected by CDUS corresponded to regions in which vascularization was absent by histological analysis. CONCLUSION: Injection of SHU 508A significantly increased vessel detection with CDUS.

Transfer of the murine interleukin-12 gene in vivo by a Semliki Forest virus vector induces B16 tumor regression through inhibition of tumor blood vessel formation monitored by Doppler ultrasonography.

To elucidate further the potential of a Semliki Forest virus (SFV) vector in vivo for gene therapy, we constructed a vector, SFV-IL12, to transfer murine IL-12 genes into tumors. A single intratumoral injection of established B16 murine melanoma with SFV-IL12 resulted in a significant inhibition of tumor growth, while injection with SFV-LacZ had no effect. This antitumoral activity correlated with an increase of IFN gamma production, MIG and IP-10 mRNA expression, both at the tumor site and at the periphery. In contrast, no increase in CTL- or NK cell-mediated cytotoxic response could be detected, ruling out the involvement of T and NK cell cytotoxicity. To determine how the transfer to IL-12 genes induced tumor regression, the antiangiogenic-activity of SFV-IL12 was investigated using Doppler ultrasonography (DUS). SFV-IL12 inhibited in situ neovascularization within the tumor, without affecting the resistance index of pre-existing intratumoral blood flows. In addition, histological analysis of SFV-IL12-treated tumors showed massive tumor necrosis induced by SFV-IL12 treatment. These data indicate that SFV-IL12 inhibits tumor growth through its antiangiogenic activity, demonstrated for the first time in vivo by DUS, and suggest that the SFV vector may be a novel valuable tool in tumor gene transfer.

New hemodynamic approach to angiogenesis: color and pulsed Doppler ultrasonography.

RATIONALE AND OBJECTIVES: To determine the capacity of color and spectral Doppler ultrasonography (US) to quantify angiogenesis in vivo and to characterize low-resistance intratumor blood flow. METHODS: Thirty-two tumors, xenografted into mice, were studied with Doppler US. The number of intratumor vessels visualized with color Doppler US was compared with the density of microvessels and the number of vessels >100 microm determined by histologic examination. The resistance index and the peak systolic velocities were evaluated. RESULTS: The number of intratumor vessels visualized by color Doppler US was correlated with the number of vessels >100 microm (P<0.001) determined histologically. When vessel density was >30, intratumor vessels were always detected by color Dopper US. The resistance index and peak systolic velocities were significantly lower in intratumor than in peritumor vessels. CONCLUSIONS: Color Doppler US evaluated tumor angiogenesis accurately. Spectral analysis confirmed the low resistance of intratumor blood flow.

Deconvolution process in measurement of arterial velocity profiles via an ultrasonic pulsed Doppler velocimeter for evaluation of the wall shear rate.

A numerically based simulation of pulsed Doppler ultrasound convolution and deconvolution of theoretical hemodynamic velocity profiles yields two major conclusions on performing a deconvolution process. First, the most important parameter to be accounted for is the size of the sample volume. Second, a deconvolution process with an overestimated sample volume size is revealed by high-frequency noise on the resulting profile. A deconvolution process is presented for in vivo arterial velocity profiles, which has the advantage of being systematic and not needing experimental testing for determining the size or the shape of the sample volume. It is also independent of the observation angle. Finally, an example of an application to in vivo human velocity profiles is given. Evaluation of the wall shear rate from the corrected deconvolved profiles shows a noticeable improvement with respect to that using the directly convolved Doppler profiles.

Pulse wave velocity measurement by cross-correlation of Doppler velocity signals. Application to elderly volunteers during training.

Pulse wave velocity (PWV) measurement is widely used for the indirect assessment of arterial wall distensibility. In order to improve its measurement technique, we built a system performing the calculation of the cross-correlation function of Doppler velocity signals. In 12 normal subjects and 10 patients, the mean difference between duplicate measurements was 0.7 +/- 7.8% (NS). We tested this technique in 15 elderly volunteers before and after a three months training period. Brachial and tibial systolic blood pressure decreased respectively from 18.1 +/- 2.2 kPa to 16.7 +/- 1.9 kPa (p = 0.008) and from 21.1 +/- 3.4 kPa to 18.4 +/- 2.5 kPa (p = 0.003), while lower limb PWV decreased from 8.96 +/- 1.26 to 7.92 +/- 1.22 m.s-1 (p = 0.016). Therefore, automatic PWV measurement using the cross-correlation technique allows to demonstrate training induced changes in PWV, although concomitant changes in blood pressure must be considered in their interpretation.

Quantification of erythrocyte aggregation by blood echogenicity: a preliminary study.

Many techniques were proposed to assess erythrocyte aggregation in clinical and experimental investigations in view of in vitro determination. However no methodology until now is available to measure erythrocyte aggregation in flowing blood in vivo. High resolution ultrasonography provides an original way to quantify erythrocyte aggregation using the echogenicity of blood. We have developed and A-mode ultrasound scanner coupled with an oscilloscope and a computer allowing the analysis of ultrasonic signals produced by erythrocytes. A closed measurement chamber connected to a calibrated roller-type blood pump where blood was perfused was used. The echogenicity of blood was determined at different shear rates. Dextran, fibrinogen and other high molecular weight substances were added to increase erythrocyte aggregation. Changes in red blood concentration was also tested. An increase in blood echogenicity rate was observed at low shear. At a given shear rate blood echogenicity increased when fibrinogen or dextran were added. Such determination of the echogenicity of flowing blood in vitro will provide an approach to the quantification of erythrocyte aggregation in vivo circulation, especially in the veins where low shear rates are observed.

Heterogeneity in migration of smooth muscle cells from normal and injured rat thoracic aorta in primary culture.

OBJECTIVE: Aside from proliferation, migration of smooth muscle cells is an essential component of the arterial sclerotic reaction. The aim of this study was to define a model to study migration. METHODS: Primary cultures of smooth muscle cells were derived from normal or injured rat thoracic aorta. An image analysis system was used to track cells migrating out of the explants and measure the displacement of their centre of gravity. RESULTS: Migration speeds for smooth muscle cells randomly sampled from the normal whole media were very heterogeneous. The media were therefore separated into three vertical segments. Cells from the middle third migrated faster than those from the upper and lower thirds, regardless of whether they originated from the anterior and posterior parts of the segment (P = 0.001). Heparin (10 micrograms.ml-1) only inhibited smooth muscle cell migration from the middle segment (P < 0.001). Migration of smooth muscle cells from explants of aorta 3 and 14 d after injury was also studied using a balloon catheter. Three days after injury, cell velocity varied widely among the segments of the same media. In contrast, 14 d after injury cells from neointimal explants migrated homogeneously and at a slower rate than those obtained from normal media. CONCLUSIONS: These experiments show migratory variations among smooth muscle cells depending upon their position in the normal aorta and their state of activation after arterial injury. This variability must be taken into account when planning experiments to study smooth muscle cell migration.

In vivo comparison of two through-plane MR velocity mapping methods: fast Fourier encoding and phase mapping.

Magnetic resonance imaging maps of velocity were acquired with a 1.5-T system in 10 subjects in a plane perpendicular to the main pulmonary artery. Velocity images were successively acquired with a method developed from Fourier-encoding velocity imaging (FEVI) principles with eight gradient steps and one excitation, and with two-point phase-subtraction mapping. Reconstruction in FEVI was implemented by zero-filling interpolation around the eight gradient steps and then around the four central steps. The methods were compared by using estimates of noise in velocity measurements based on the difference between the experimental map and a smooth fitted map. For the same acquisition time, FEVI with four encoding steps was more precise in velocity measurements than phase mapping. Precision was further increased by the use of eight encoding steps, but acquisition time was doubled.

Animal evaluation of the prototype omnicath atherectomy catheter.

A prototype directional atherectomy catheter (Omnicath) was evaluated in four Yucatan microswines. Atherectomy was performed on iliac or aortic target lesions. After control angiography, the animals were sacrificed and the target arteries were examined histologically. Atherectomy resulted in arterial ruptures in three cases, and the track of the blade was measured to be of an average depth of 0.38 mm. Maneuverability was satisfactory but aspiration was not efficient. Precise localization of the atherectomy window was difficult. We conclude that modification of the catheter seems mandatory before use in humans.

A 3D reconstruction of vascular structures from two X-ray angiograms using an adapted simulated annealing algorithm.

A three-dimensional (3D) reconstruction of the vessel lumen from two angiographic views, based on the reconstruction of a series of cross-sections, is proposed. Assuming uniform mixing of contrast medium and background subtraction, the cross-section of each vessel is reconstructed through a binary representation. A priori information about both the slice to be reconstructed and the relationships between adjacent slices are incorporated to lessen ambiguities on the reconstruction. Taking into account the knowledge of normal vessel geometry, an initial solution of each slice is created using an elliptic model-based method. This initial solution is then deformed to be made consistent with projection data while being constrained into a connected realistic shape. For that purpose, properties on the expected optimal solution are described through a Markov random field. To find an optimal solution, a specific optimization algorithm based on simulated annealing is used. The method performs well both on single vessels and on branching vessels possessing an additional inherent ambiguity when viewed at oblique angles. Results on 2D slice independent reconstruction and 3D reconstruction of a stack of spatially continuous 2D slices are presented for single vessels and bifurcations.

High-precision MR velocity mapping by 3D-Fourier phase encoding with a small number of encoding steps.

The final result of Fourier velocity mapping is a set of images, each representing the spatial distribution of spins at a given velocity. To acquire data in a short time, the number of encoding gradient steps must be as small as possible, but this can mean sacrificing velocity resolution. We used interpolation methods to obtain high velocity resolution with a small number of encoding steps involving linear interpolation from 16 encoding steps or more and zero-filling interpolation from two to eight encoding steps. Velocity measured by interpolated Fourier-flow encoding agreed well with values obtained using a calibrated phantom. A simulation of noise on the images of the phantom showed that, for a given acquisition time, increasing number of encoding steps in the Fourier flow encoding gave better precision for velocity measurement than did averaging identical signals in phase-mapping methods.

Segmentation, modelling and reconstruction of arterial bifurcations in digital angiography.

The paper presents a method to model an arterial bifurcation from a pair of X-ray angiographic images. It is the initial step of a reconstruction process aiming at detecting and quantifying abnormal sites located on bifurcations. The method proposed consists of two steps. First, each image is independently segmented to extract the vessels in the images. The algorithm uses dynamic programming first to find the bifurcation centrelines from the original images, and secondly to extract vessel edges from the morphological gradient images, under a constraint of parallelism with the previously detected centrelines. Then, a three-dimensional bifurcation model is built by adapting cylinders around the three-dimensional bifurcation centrelines. These cylinders are obtained as a stack of binary orientable ellipses fitted to the projection densities in the corresponding cross-sections. Results obtained on simulated data, phantom and femoral bifurcations are displayed.

Contribution of the high amplitude electrocardiography to the detection of ventricular late potentials in several cardiovascular diseases.

The criteria for detection of ventricular late potentials (VLP) by high amplitude electrocardiography (ECG) in the frequency domain were evaluated in 75 patients with cardiovascular diseases, mostly men (85%), with a mean age of 57 years, distributed by disease type into three subgroups: (1) with a history of myocardial infarction (MI)--53 cases; (2) with syncopes, episodes of prolonged ventricular arrhythmias--18 cases; (3) with unobstructive, primary cardiomyopathies--4 cases. Complete clinical examination, standard ECG, continuous 24 hr Holter ECG, high amplitude ECG (Corazonix system) for detection of VLP by analyses in the time domain (TD) and in the frequency one (FD) were performed in all the cases. The VLP incidence was evidently high in all the cases. By association of the analyses in TD and FD, the accuracy of VLP detection increased by 17.3% in the whole group (from 64% to 81.3%). The incidence of severe ventricular arrhythmias (class 4-5 Lown, i.e., doubled and/or trebled ventricular extrasystoles, salvos of unsustained ventricular tachycardia) was evidently higher in the patients with VLP (88% compared with 77% in the absence of VLP), thus demonstrating the presence, in most of the patients studied, of an arrhythmogenic mechanism by ventricular reentry.

[Use of extracorporeal circulation oxygenators (CEC) in the European Economic Community (EEC)]. / Utilisation des oxygénateurs en circulation extra-corporelle (CEC) dans la Communauté Economique Européenne (CEE).

This study analyses the growth of CPB in the EEC. The study situates its position in the world taking into account several indexes such as the Gross National Product and its growth the life expectancy and other technical or economic factors. Only a broad analysis could be performed for Europe to the irregular development of CPB. A more detailed analysis was performed for France thanks to a greater number of data. In this type of study the most important problem is to estimate the relevance and consistency of the data provided either by companies or by other organizations because they can change very quickly.

[Thrombosis of atrioventricular prosthesis. Contribution of transesophageal echocardiography]. / Thromboses de prothèses en position auriculo-ventriculaire. Apport de l'échocardiographie transoesophagienne.

The aim of this study was to assess the diagnostic value of transesophageal echocardiography for the detection of thrombosis of a mechanical mitral or tricuspid valve prosthesis. Twelve patients (mean age 54 +/- 12 years) out of a series of 39 patients operated between April 1988 and June 1989 for prosthetic valve dysfunction had valve thrombosis at operation (11 mitral and 1 tricuspid valve prosthesis). Transesophageal echocardiography was routinely performed preoperatively in addition to transthoracic Doppler echocardiography to search for an abdominal mass on the prosthetic valves. The largest diameter of the diastolic jet at the level of the prosthetic valve annulus was measured using transesophageal color flow Doppler in the 8 Starr-Edwards mitral valve prostheses and compared with 5 control valves. The results of transthoracic Doppler echocardiography and transesophageal echocardiography were compared with the operative findings. The specificity of transthoracic echocardiography for the positive diagnosis of prosthetic valve thrombosis was 18%. A thrombosis could be suspected in 10 of the 12 cases by transthoracic echocardiography giving a sensitivity of 83%. Eleven of the 12 abnormal masses on the prostheses were visualised by transesophageal echocardiography, a sensitivity of 91%. Detection of the masses on the arterial side was possible in all cases (10/10) but 5 of the 6 extensions of the thrombus into the ventricle could not be visualised. The diameter of the transprosthetic jet was less than 12 mm in 7 of the 8 thrombosed valves compared with greater than 15 mm in the 5 normal control prostheses.(ABSTRACT TRUNCATED AT 250 WORDS)