Biomedical subjects

C L de Korte

Publications and source records attributed to C L de Korte.

17 recordsLinked to original sources

PubMed2000

Characterization of plaque components with intravascular ultrasound elastography in human femoral and coronary arteries in vitro.

BACKGROUND: The composition of plaque is a major determinant of coronary-related clinical syndromes. Intravascular ultrasound (IVUS) elastography has proven to be a technique capable of reflecting the mechanical properties of phantom material and the femoral arterial wall. The aim of this study was to investigate the capability of intravascular elastography to characterize different plaque components. METHODS AND RESULTS: Diseased human femoral (n=9) and coronary (n=4) arteries were studied in vitro. At each location (n=45), 2 IVUS images were acquired at different intraluminal pressures (80 and 100 mm Hg). With the use of cross-correlation analysis on the high-frequency (radiofrequency) ultrasound signal, the local strain in the tissue was determined. The strain was color-coded and plotted as an additional image to the IVUS echogram. The visualized segments were stained on the presence of collagen, smooth muscle cells, and macrophages. Matching of elastographic data and histology were performed with the use of the IVUS echogram. The cross sections were segmented in regions (n=125) that were based on the strain value on the elastogram. The dominant plaque types in these regions (fibrous, fibro-fatty, or fatty) were obtained from histology and correlated with the average strain and echo intensity. The strain for the 3 plaque types as determined by histology differed significantly (P=0.0002). This difference was mainly evident between fibrous and fatty tissue (P=0.0004). The plaque types did not reveal echo-intensity differences in the IVUS echogram (P=0.882). CONCLUSIONS: Different strain values are found between fibrous, fibro-fatty, and fatty plaque components, indicating the potential of intravascular elastography to distinguish different plaque morphologies.

Arteries↗

PubMed2000

Quantification of plaque volume, shear stress on the endothelium, and mechanical properties of the arterial wall with intravascular ultrasound imaging.

Present intravascular echographic imaging (IVUS) is based on either the mechanically rotated single element catheter or the multi-element phased array catheter principle. In both methods the ultrasonic beam is rotated through 360 degrees and the cross-sectional echo image of plaque and wall structures is visualised. A new development based on intravascular ultrasound is calculation of mechanical properties of the arterial wall. In this so-called elastographic approach, high frequency information obtained at identical positions in the arterial wall is compared under systolic and diastolic pressures. Minute shifts in the echo data indicate local compressibility. It thus becomes possible to indicate areas of high or low strain, which correspond to soft and hard material. Three-dimensional information can be obtained if the position of cross sectional slices is recorded with a pull-back device and slices are united into a 3D image. On the basis of such information it has become possible to view stents in 3D, and with interactive software, to calculate automatically plaque volume. With pull-back information only, the artery is reconstructed as a "straight pipe". Only when the biplane X-ray information is combined with the intravascular pull-back echo information can the true 3D reconstruction of the artery be constructed. Given the true geometric lumen information, it becomes possible, under certain assumptions, to derive the luminal fluid dynamics. From this, shear stress values close to the arterial wall can be calculated. Under the assumption that low values for local shear stress are areas prone to restenosis, predictions of endangered areas can be made.

Arteriosclerosis↗

PubMed2000

Vascular tissue characterisation with IVUS elastography.

Knowledge about the mechanical properties of the vessel wall and plaque is important for guiding intravascular interventional procedures and detection of plaque vulnerability. Rupture of atherosclerotic plaques is associated with acute myocardial infarction and unstable angina pectoris. In a plaque with a lipid core, the stress due to the arterial pulsation will be concentrated in the cap and a thin cap may be unable to bear this stress. In this study, the potential of intravascular elastography to characterise fibrous, fibro-fatty and fatty tissue based on their mechanical properties was investigated. Using a custom-made set-up, intravascular echograms and elastograms of excised human femoral arteries were determined. High frequency r.f. data (30 MHz) were acquired using an intravascular catheter. The tissue was compressed using intravascular pressures of 80 and 100 mmHg. The cross-sections of interest were marked with a needle for matching with histology. Using cross-correlation estimation of gated echosignals, elastograms (images of the local strain) were determined. After the intravascular experiments, the specimens were fixed in formaldehyde and processed for paraffin embedding. Sections were stained with picrosirius red and alpha-actin to counterstain collagen and smooth muscle cells (SMC), respectively. Results of vessel cross-sections with fibrous and fatty plaque regions will be presented. The elastograms of these specimens show that the strain in fatty tissue is higher than the strain in fibrous material. In conclusion, these in vitro experiments on human femoral arteries indicate the potential of intravascular elastography to characterise different plaque components.

Arteriosclerosis↗

PubMed2000

Angle matching in intravascular elastography.

Intravascular elastography is a new technique to obtain mechanical properties of the vessel wall and plaque. Mechanical information of vascular tissue is important for characterisation of different plaque components, detection of plaque vulnerability and thus choosing the proper interventional technique. The feasibility of the technique is investigated using phantoms and diseased human arteries. These studies demonstrated that elastography reveals information that is unavailable or inconclusive from the echogram alone. The technique is based on the principle that tissue strain is directly related to its mechanical properties. In intravascular elastography, the tissue is compressed using different intravascular pressures. The strain is determined using cross-correlation techniques of the radio frequency (r.f.) signals. Reliable strain estimates are only obtained when signals of corresponding tissue are correlated. Owing to catheter motion, off-centre position and non-uniform rotation of the intravascular transducer, the r.f. traces at low and at high pressure may be misaligned. Four algorithms are tested to track the corresponding ultrasound signals. Three methods (l1norm, l2norm and cross-correlation) are applied on the r.f. signal and one (l1norm) on the envelope (speckle tracking). Simulations are performed to obtain a data set with a priori knowledge of the scattering particles positions in the tissue at high and low pressure. Different positions of the catheter in the lumen, compression levels of the material and signal-to-noise ratios (SNRs) are investigated. Finally, these findings are corroborated with a phantom experiment in a water tank. From the simulations, it can be concluded that the speckle tracking algorithm has the best performance, under all circumstances. The performance decreases with larger eccentricity of the catheter and larger compression of the material. The SNR is only of minor influence. The speckle tracking algorithm has also the best performance in the phantom experiment. The performance of the speckle tracking algorithm is better than the three r.f.-based algorithms. For intravascular elastography, implementation of this method may improve the quality of the elastogram.

Algorithms↗

PubMed2000

Intraluminal ultrasonic palpation: assessment of local and cross-sectional tissue stiffness.

Many intravascular therapeutic techniques for the treatment of significant atherosclerotic lesions are mechanical in nature: examples are angioplasty, stenting and atherectomy. The selection of the most adequate treatment would be advantageously aided by knowledge of the mechanical properties of the lesion and surrounding tissues. Based on the success of intravascular ultrasound (IVUS) in accurately depicting the morphology of atheromatous lesions, ultrasonic tissue characterisation has been proposed as a tool to determine the composition of atheroma. We describe the addition of local compliance information to the IVUS image in the form of a colour-coded line congruent with the lumen perimeter. The technique involves analysis of echo signals obtained at two or more states of incremental intravascular pressure. Using vessel phantoms and specimens, we demonstrate the utility of intravascular compliance imaging. The palpograms are able to identify lesions of different elasticity independently of the echogenicity contrast, because the information provided by the elastograms is generally independent of that obtained from the IVUS image. Thus, the palpogram can complement the characterisation of lesion from the IVUS image. We also describe cross-sectional measures of elasticity that are based on the elastogram. Finally, natural extensions of intravascular palpation to other endoluminal ultrasound applications are proposed.

Arteriosclerosis↗

PubMed2000

Characterization of plaque components and vulnerability with intravascular ultrasound elastography.

Intravascular ultrasound elastography is a method for measuring the local elastic properties using intravascular ultrasound (IVUS). The elastic properties of the different tissues within the atherosclerotic plaque are measured through the strain. Knowledge of these elastic properties is useful for guiding interventional procedures (balloon dilatation, ablation) and detection of the vulnerable plaque. In the last decade, several groups have applied elastography intravascularly with various levels of success. In this paper, the approaches of the different research groups will be discussed. The focus will be on our approach to the application of intravascular elastography. Elastograms were acquired in vitro and in vivo using the relative local displacements between IVUS images acquired at two levels of intravascular pressure with a 30 MHz mechanical or a 20 MHz array echo catheter. These displacements were estimated from the time shift between gated radiofrequency echo signals using cross-correlation algorithms with interpolation around the peak. Experiments on gel-based phantoms mimicking atherosclerotic vessels demonstrated the capability of elastography to identify soft and hard tissues independently of the echogenicity contrast. In vitro experiments on human arteries have demonstrated the potential of intravascular elastography to identify different plaque types based on their mechanical properties. These plaques could not be identified using the IVUS image alone. In vivo experiments revealed that reproducible elastograms could be obtained near end-diastole. Partial validation using the echogram was performed. Intravascular elastography provides information that is frequently unavailable or inconclusive from the IVUS image and which may therefore assist in the diagnosis and treatment of atherosclerotic disease.

Arteriosclerosis↗

PubMed1998

Intravascular imaging.

Based on three-dimensional (3D) information, quantitative data such as plaque volume can be calculated. The procedure includes automatic contour detection based in image segmentation methods and greatly speeds up clinical evaluation. With the use of additional X-ray information, the true tortuous vessel geometry can be reconstructed in 3D. This allows, by numerical modelling techniques, to calculate endothelial shear stress values which in turn may indicate sites prone to stenosis. With a decorrelation technique for radio frequency (RF) echo information from sequential data in the same beam direction and integration method over the entire cross section, blood velocity can be shown colour-coded during the cardiac cycle, while even blood flow quantification seems to be possible. In vitro as well as animal experiments have shown the feasibility of the method. Intravascular imaging can be used to study the biomechanical properties of atheroma components. Local radial strain as a measure of local tissue hardness can be estimated in principle. Hard or soft plaques can be identified from the strain images independently of the echogenic contrast between plaque and vessel wall.

Angiography↗

PubMed1998

Intravascular ultrasound elastography in human arteries: initial experience in vitro.

Intravascular elastography is a new technique to obtain the local mechanical properties of the vessel wall and its pathology using intravascular ultrasound (IVUS). Knowledge of these mechanical properties may be useful for guiding interventional procedures. An experimental set-up is described for assessment of the strain data of arteries. Using a 30-MHz IVUS catheter, radio frequency data are acquired with a custom-made high-performance data acquisition system. High-resolution, local tissue displacement estimation by cross-correlation is followed by computation of local strain. An algorithm that uses a priori knowledge of the correlation coefficient function was applied to filter the obtained strain data. With this experimental set-up, intravascular elastograms containing 400 angles/revolution with a radial resolution of 200 microns can be produced. The feasibility of intravascular elastography with this experimental set-up is demonstrated using two diseased human femoral arteries. Qualitative comparison of the elastograms with the echograms and the histology demonstrates the potential of intravascular elastography to obtain mechanical information from the vessel wall and from plaque.

Algorithms↗

PubMed1998

New developments in intravascular ultrasound imaging.

IntraVascular Ultrasound Imaging (IVUS) has already been proposed in the early days of diagnostic ultrasound. Today, it has come under further full attention as a result of minimal invasive techniques. Not only excellent intravascular two-dimensional (2D) images are presently obtained, also three-dimensional (3D) reconstructed images show their diagnostic value. Based on 3D information, quantitative data such as plaque volume can be calculated. The procedure includes automatic contour detection based on image segmentation methods and greatly speeds up clinical evaluation. With the use of additional X-ray information, the true tortuous vessel geometry can be reconstructed in 3D. This allows, by numerical modelling techniques, to calculate endothelial shear stress values, which in turn may indicate sites prone to stenosis. With a decorrelation technique for radiofrequency (RF) echo information from sequential data in the same beam direction and integration method over the entire cross section, blood velocity can be shown colour-coded during the cardiac cycle, while even blood flow quantification seems to be possible. In vitro as well as in vivo experiments have shown the feasibility of the method. Intravascular imaging can be used to study the biomechanical properties of atheroma components. Local radial strain, used as a measure of local tissue hardness, can be estimated to identify hard or soft plaques independently of the echogenicity contrast between plaque and vessel wall.

Blood Flow Velocity↗

PubMed1998

Intravascular ultrasound elastography: assessment and imaging of elastic properties of diseased arteries and vulnerable plaque.

OBJECTIVE: Intravascular elastography is concerned with methods for measuring the local elastic properties using intravascular ultrasound (IVUS). The elastic properties of the vessel wall and atheroma can be measured through the strain. Knowledge of these mechanical properties is useful for guiding interventional procedures (balloon dilatation, ablation) and detection of plaque vulnerability. METHODS: Elastograms and palpograms (images of strain) were constructed using the relative local displacements between IVUS images acquired at two levels of intravascular pressure with a 30-MHz echo catheter. These displacements were estimated from the time shift between gated radio-frequency echo signals using cross-correlation algorithms with interpolation around the peak. RESULTS: Experiments on gel-based phantoms mimicking atherosclerotic vessels demonstrated the capability of elastography to identify soft and hard plaques independently of the echogenicity contrast. In vitro experiments on human arteries have demonstrated the potential of intravascular elastography to identify different plaque types based on the mechanical properties. These plaques could not be identified using the IVUS image alone. Regions with elevated mechanical stress could also be detected. These stress concentrations are related to plaque fracture. CONCLUSION: Intravascular elastography provides information that is frequently unavailable or inconclusive from the IVUS image and therefore may assist in the diagnosis and treatment of atherosclerotic disease.

Algorithms↗

PubMed1998

Intravascular ultrasound elastography.

Intravascular Ultrasound Blastography. The response of a tissue to mechanical excitation is a function of its mechanical properties. Excitation can be dynamic or quasistatic in nature. The response (e.g. displacement, velocity, compression) can be measured via ultrasound. This is the main principle underlying ultrasound elasticity imaging, sonoelasticity imaging, or ultrasound elastography. It is of great interest to know the local hardness of vessel wall and plaques. Intravascular elastography yields information unavailable or inconclusive if obtained from IVUS alone and thus contributes to more correct diagnosis. Potentially it can be used for therapy guidance. During the last decade several working groups used elastography in intravascular applications with varying success. In this paper we discuss the various approaches by different working groups. Focus will be on the approach of the Rotterdam group. Using a 30 MHz IVUS catheter, RF data are acquired from vessels in vitro at different intraluminal pressures. Local tissue displacement estimation by cross-correlation is followed by computation of the local strain. The resulting image supplies local information on the elastic properties of the vessel and plaque with high spatial resolution. Feasibility and usefulness are shown by means of phantom measurements. Furthermore, initial in vitro results of femoral arteries and correlation with histology are discussed. Phantom data show that the elastograms reveal information not presented by the echogram. In vitro artery data prove that in principle elastography is capable of identifying plaque composition where echography fails.

Arteriosclerosis↗

PubMed1997

Performance of time delay estimation methods for small time shifts in ultrasonic signals.

In this study several time delay estimation (TDE) methods were investigated for estimation of time shifts of less than 10 ns at a frequency of 30 MHz. Using simulated and experimental echosignals we investigated the performance of five methods: two phase related methods (phase shift and phase difference method); two correlation methods (cross-correlation and correlation interpolation method); and a demodulation method. The results showed that the correlation interpolation method is by far the most accurate for all time delays. With this method, estimation errors of about 200 ps are achievable with an signal-to-noise ratio (SNR) of 40 dB (f0 = 30 MHz, bandwidth = 20 MHz) for time shifts of up to 10 ns.

Computer Simulation↗

PubMed1997

Intravascular elasticity imaging using ultrasound: feasibility studies in phantoms.

A technique is described for measuring the local hardness of the vessel wall and atheroma using intravascular ultrasound. Strain images were constructed using the relative local displacements, which are estimated from the time shifts between gated echo signals acquired at two levels of intravascular pressure. Time shifts were estimated using one-dimensional correlation with bandlimited interpolation around the peak. Tissue-mimicking phantoms with typical morphology and hardness topology of some atherosclerotic vessels were constructed. Hard and soft regions could be distinguished on the strain image, independently of their contrast in echogenicity. Thus, the potential of ultrasonic hardness imaging to provide information that may be unavailable from the echogram alone was demonstrated. The strain images of the homogeneous and layered phantoms showed some artifacts that need to be corrected for, to obtain images of the modulus of elasticity. For in vitro and in vivo experiments, the spatial resolution of the technique needs to be improved. Furthermore, two-dimensional correlation techniques may be necessary in case of nonradial expansion and an off-centre catheter position.

Arteriosclerosis↗

PubMed1997

Elastic and acoustic properties of vessel mimicking material for elasticity imaging.

The mechanical and acoustic properties of agar-gelatin gels, used to construct vessel mimicking phantoms for ultrasonic elasticity studies, were investigated. Gels with varying compression moduli were made using a gelatin solution (8% by weight) with a variable amount of agar (1%-3% by weight). Carborundum particles were added as scattering material. The compression modulus was determined using a dynamic mechanical analyzer. The dependence of the compression modulus and the acoustic parameters on the agar concentration, as well as on the age and the temperature of the samples, was investigated. The results show that the compression modulus is strongly influenced by these factors, while the effect on the acoustic parameters is less. Compression moduli spanning a useful range for vascular phantom construction with realistic acoustic parameters can be achieved by varying the amount of agar. Phantoms constructed from these gels are well suited to serve as a model for plaque containing vessels.

Agar↗

PubMed1997

Intravascular elastography: principles and potentials.

Many intravascular therapeutic techniques for the treatment of significant atherosclerotic lesions are mechanical in nature: angioplasty, stenting and atherectomy. The selection of the most adequate treatment would be advantageously aided by knowledge of the mechanical properties of the lesion. Based on the success of conventional intravascular ultrasound (IVUS) imaging in accurately depicting the morphology of atheromatous lesions, ultrasonic tissue characterization has been proposed to determine the composition of atherosclerotic plaques. Elastography is an ultrasound-based imaging technique capable of producing cross-sectional elasticity images called elastograms. The technique involves analysis of echo signals obtained at two states of incremental intravascular pressure. High resolution, local tissue displacement estimation by cross-correlation is followed by computation of local strain. Strain is utilized as an indicator of the local compliance of tissue under the assumption of constant stress within the scan plane. Using vessel-mimicking phantoms, we demonstrate the feasibility of intravascular elastography experimentally. The elastograms are able to depict lesions of different elasticity independently of the echogenicity contrast, since the information provided by the elastograms is generally independent of that obtained from the conventional IVUS image. Thus, the elastogram can complement the characterization of lesions from the conventional IVUS image. Progress to in vitro and in vivo testing is expected in conjunction with ongoing improvements in the current instrumentation and processing.

Angioplasty, Balloon↗

PubMed1994

Ultrasonic spectroscopy of the porcine eye lens.

The purpose of the work is to measure and study the acoustic characteristics of the porcine eye lens and find correlations with chemical and optical parameters, obtained from literature. Ultrasonic spectroscopy was performed by using a scanning acoustic macroscope (frequency 20 MHz, resolution 150 microns). The transducer performed a two-dimensional scan over a central slice (1 mm thickness) of porcine lens (number of lenses = 10). A double transmission pulse-echo method was used to acquire the ultrasonic data from the lens. Two-dimensional images were reconstructed of the local ultrasound velocity and the frequency-dependent ultrasound attenuation. Axial and equatorial profiles of these parameters were calculated from the images. The acoustic parameters are not constant, but show a systematic dependence on the location within the lens. The profiles of the acoustic parameters are similar in shape to profiles of the protein and water contents of eye lens and to the profiles of the optical refractive index. A thorough quantitative correlation study is indicated, which should be based on detailed protein content data in porcine lenses.

Animals↗

PubMed1994

Acoustic velocity and attenuation of eye tissues at 20 MHz.

The ultrasound velocity and frequency-dependent attenuation of human and porcine eye tissues (cornea, lens, retina, choroid, sclera, vitreous body) were measured in the frequency range from 17 to 23 MHz. The results for the ultrasound velocity were compared to values taken from the literature and appeared to be in the same range. A comparison made between the acoustic parameters of human and porcine eyes showed that the porcine eye can serve as an animal model for the human eye. A mathematical operation is proposed to extrapolate the attenuation to the lower frequencies that are commonly used in clinical equipment. Finally, a first attempt was made to investigate the age dependence of the acoustic parameters of human tissues: some tissues showed a significant age effect.

Acoustics↗