PubMed Health⌕ Search

Biomedical subjects

Chris L de Korte

Publications and source records attributed to Chris L de Korte.

18 recordsLinked to original sources
PubMed2006

Improvement of heart function after balloon dilation of congenital valvar aortic stenosis: a pilot study with ultrasound tissue Doppler and strain rate imaging.

The aim was to investigate the effects of balloon dilation of congenital valvar aortic (Ao) stenosis on heart function with conventional and with new echocardiographic techniques. Nine patients, preballoon and 1 to 4 d postballoon dilation of Ao-valve, were included in the study. Assessment of heart function was made by using conventional echo/Doppler, tissue Doppler imaging (TDI) and strain rate imaging (SRI). Mean (and standard deviation) of posttreatment drop of aortic valve pressure gradient was 34.1 (sd 14.0) mmHg, p < 0.01. Conventional echo/Doppler end-diastolic left ventricular posterior wall (LVPW) thickness and interventricular septum (IVS) thickness did not change significantly. Mean change of LV fractional shortening (FS) was -5.2 (sd 3.2)%, p < 0.01. The observed changes of FS did not significantly correlate to the magnitude of pressure gradient changes. Changes of TDI and SRI parameters indicated that an increase in absolute value is observed in most cases, but correlation to pressure gradient change remains poor, with a few exceptions, both in LV free wall (LVFW) and IVS. Data from IVS are more consistent than of LVFW. It is concluded that the global functional parameter FS assessed by conventional echo/Doppler has diagnostic value for the assessment of (improved) heart function already shortly after intervention, when compared with the pretreatment value. Local parameters from the new echographic techniques show less significant short-term effects attributable to the intervention. Improvement of the precision of SRI measurements is needed. A larger study is indicated to fully investigate the expected potentials of TDI and SRI for the assessment of local improvement of heart function early after intervention, as well as for revealing eventual late effects on these functional parameters.

Adolescent↗
PubMed2005

Three-dimensional palpography of human coronary arteries. Ex vivo validation and in-patient evaluation.

BACKGROUND: Rupture of thin-cap fibroatheroma is a major cause of acute myocardial infarction and stroke. Identification of these plaques is one of the major challenges in cardiovascular medicine. At present, techniques with sufficient sensitivity and specificity to identify these unstable plaques are not clinically available. This paper describes a new technique to identify these plaques. METHODS AND RESULTS: Three-dimensional intravascular ultrasound palpography is a catheter-based technique that visualizes radial strain (deformation) of vascular tissue induced by physiological variations in intraluminal pressure. A three-dimensional palpogram of these cross sections can be constructed by performing a continuous pullback of the catheter. Phantom and animal experiments revealed feasibility and good reproducibility of three-dimensional palpography. Increased strain values were observed in areas with reduced cap thickness and increased macrophage accumulation. In patients (n = 2) three-dimensional palpography is feasible and identifies areas with high and low strain. CONCLUSION: Three-dimensional palpography allows scanning of coronary arteries in patients to identify and localize highly deformable regions.

Animals↗
PubMed2005

Modeling ultrasound contrast measurement of blood flow and perfusion in biological tissue.

The aim of this paper was to obtain a parametric description of ultrasound (US) contrast dilution curves obtained in piglet brain after a bolus injection of contrast agent (Sonovue). Several models for so-called dye-dilution curves were considered, and a choice for the gamma probability density function (pdf) was made. This function was chosen primarily because of the elegant mathematical opportunities to achieve a practical one-parameter curve fitting and to extend this model for incorporating recirculation. The model was fitted to US contrast data obtained in piglet brain. The software enables interactive insertion of curve landmarks and a single parameter (i.e., order of gamma pdf) iterative least squares fit was then made to the first bolus passage part of the curve. Sequential recirculation curve fits were calculated from this fit. A preliminary result for 24 experimental curves is a median value of 3 (range 3 to 5) for the order of the gamma function (kappa) and a median of 0.6/s (range 0.3 to 0.9) for the event rate (lambda). The theoretical background for obtaining the relative plasma flow and volume in tissue (i.e., "blood flow index", BFI, and "blood volume index", BVI, respectively) from the reconstructed first passage curve is given as well. The potential of assessment of the relative fraction of left-to-right shunting of the cardiac output in case of persistent ductus arteriosis is outlined. The requirements for an absolute measurement of tissue blood flow and tissue perfusion are discussed. The conclusion is that the gamma model can well be fitted to the experimental contrast curves; thus, yielding the parameters kappa and lambda. Assessment of BFI and BVI is feasible.

Algorithms↗
PubMed2005

Intravascular Ultrasound Elastography: A Clinician's Tool for Assessing Vulnerability and Material Composition of Plaques.

The material composition and morphology of the atherosclerotic plaque components are considered to be more important determinants of acute coronary ischemic syndromes than the degree of stenosis. When a vulnerable plaque ruptures it causes an acute thrombotic reaction. Rupture prone plaques contain a large lipid pool covered by a thin fibrous cap. The stress in these caps increases with decreasing thickness. Additionally, the cap may be weakened by macrophage infiltration. IntraVascular UltraSound (IVUS) elastography might be an ideal technique to assess the presence of lipid pools and to identify high stress regions. Elastography is a technique that assesses the local elasticity (strain and modulus) of tissue. It is based on the principle that the deformation of tissue by a mechanical excitation is a function of its material properties. The deformation of the tissue is determined using ultrasound. For intravascular purposes, the intraluminal pressure is used as the excitation force. The radial strain in the tissue is obtained by cross-correlation techniques on the radio frequency signals. The strain is color-coded and plotted as a complimentary image to the IVUS echogram. IVUS elastography, and IVUS palpography (which uses the same principle but is faster and more robust), have been extensively validated using simulations and by performing experiments in vitro and in vivo with diseased arteries from animals and humans. Strain was shown to be significantly different in various plaque types (absent, fatty, fibrous or calcified). A high strain region with adjacent low strain at the lumen vessel-wall boundary has 88% sensitivity and 89% specificity for detecting vulnerable plaques. High strain regions at the lumen plaque-surface have 92% sensitivity and 92% specificity for identifying macrophages. Furthermore, the incidence of vulnerable-plaque-specific strain patterns in humans has been related to clinical presentation (stable angina, unstable angina or acute myocardial infarction) and the level of C-reactive protein. In conclusion, the results obtained with IVUS (strain and modulus) elastography/palpography, show the potential of the technique to become a unique tool for clinicians to assess the vulnerability and material composition of plaques.

Animals↗
PubMed2004

Incidence of high-strain patterns in human coronary arteries: assessment with three-dimensional intravascular palpography and correlation with clinical presentation.

BACKGROUND: Rupture of thin-cap fibroatheromatous plaques is a major cause of acute myocardial infarction (AMI). Such plaques can be identified in vitro by 3D intravascular palpography with high sensitivity and specificity. We used this technique in patients undergoing percutaneous intervention to assess the incidence of mechanically deformable regions. We further explored the relation of such regions to clinical presentation and to C-reactive protein levels. METHOD AND RESULTS: Three-dimensional palpograms were derived from continuous intravascular ultrasound pullbacks. Patients (n=55) were classified by clinical presentation as having stable angina, unstable angina, or AMI. In every patient, 1 coronary artery was scanned (culprit vessel in stable and unstable angina, nonculprit vessel in AMI), and the number of deformable plaques assessed. Stable angina patients had significantly fewer deformable plaques per vessel (0.6+/-0.6) than did unstable angina patients (P=0.0019) (1.6+/-0.7) or AMI patients (P<0.0001) (2.0+/-0.7). Levels of C-reactive protein were positively correlated with the number of mechanically deformable plaques (R2=0.65, P<0.0001). CONCLUSIONS: Three-dimensional intravascular palpography detects strain patterns in human coronary arteries that represent the level of deformation in plaques. The number of highly deformable plaques is correlated with both clinical presentation and levels of C-reactive protein. Further studies will assess the potential role of the technique to identify patients at risk of future clinical events

Aged↗
PubMed2004

Finite element modeling and intravascular ultrasound elastography of vulnerable plaques: parameter variation.

BACKGROUND AND GOAL: More than 60% of all myocardial infarction is caused by rupture of a vulnerable plaque. A vulnerable plaque can be described as a large, soft lipid pool covered by a thin fibrous cap. Plaque material composition, geometry, and inflammation caused by infiltration of macrophages are considered as major determinants for plaque rupture. For diagnostic purposes, these determinants may be obtained from elastograms (i.e. radial strain images), which are derived from intravascular ultrasound (IVUS) measurements. IVUS elastograms, however, cannot be interpreted directly as tissue component images, because radial strain depends upon plaque geometry, plaque material properties, and used catheter position. To understand and quantify the influence of these parameters upon measured IVUS elastograms, they were varied in a finite element model (FEM) that simulates IVUS elastograms of vulnerable plaques. MATERIALS AND METHODS: IVUS elastography measurements were performed on a vessel mimicking phantom, with a soft plaque embedded in a hard wall, and an atherosclerotic human coronary artery containing a vulnerable plaque. Next, FEMs were created to simulate IVUS elastograms of the same objects. In these FEMs the following parameters were varied: Young's modulus (E), Poisson's ratio (nu) in range 0.49-0.4999, catheter position (translation of 0.8 mm), and cap thickness (t) in range 50-350 microm. Hereby the resulting peak radial strain (PRS) was determined and visualized. RESULTS: Measured static E for phantom was 4.2 kPa for plaque and 16.8 kPa for wall. Variation of E-wall in range 8.4-33.2 kPa and/or E-plaque in range 2.1-8.4 kPa using the phantom FEM, gave a PRS variation of 1.6%, i.e. from 1.7% up to almost 3.3%; for variation in nu this was only 0.07%, i.e. from 2.37% up to 2.44%. Variation of E-lipid in range 6.25-400 kPa and E-cap in range 700-2300 kPa using the artery FEM, gave a PRS variation of 3.1%, i.e. from 0.6% up to 3.7%. The PRS was higher for lower E-lipid and E-cap; it was located at a shoulder of the lipid pool. Variation of nu gave only a variation of 0.17%. Variation of t and E-cap resulted in a PRS variation of 1.4%, i.e. from 0.3% up to 1.7%; thinner and weaker caps gave higher PRS. Catheter position variation changed radial strain value. CONCLUSIONS: Measured IVUS elastograms of vulnerable plaques depend highly upon the Young's modulus of lipid and cap, but not upon the Poisson's ratio. Different catheter positions result in different IVUS elastograms, but the diagnostically important high strain regions at the lipid shoulders are often still detectable. PRS increases when cap weakens or cap thickness decreases.

Arteriosclerosis↗
PubMed2004

A finite element model for performing intravascular ultrasound elastography of human atherosclerotic coronary arteries.

Intravascular ultrasound (US) elastography measures in an artery the arterial radial strain and displays it in an elastogram. An elastogram adds diagnostic information, such as the proneness of a plaque to rupture and its material composition. However, radial strain depends upon the material properties of an artery, including geometry and used catheter position. Therefore, there is not always a one-to-one correspondence between radial strain and rupture-proneness or material composition. Both the dependence and the correspondence can be quantified after a proper finite element model (FEM) is available. Therefore, this paper proposes a FEM and shows that it can model the arterial strain behavior. Its modelling capability was evaluated by comparing simulated with measured elastograms. Measured elastograms were processed from radiofrequency (RF) data obtained in vitro from six objects: a vessel-mimicking phantom and five excised human atherosclerotic coronary arteries. A FEM was created for each object and used to simulate an elastogram; the material properties and geometry of the FEM were obtained from the histology of the object. Comparison was performed upon high strain regions (HStR), because these regions have proven to contain plaques that show the hallmarks of vulnerable plaques. Eight HStR were automatically identified from the five arteries. Statistical tests showed that there was no significant difference between simulated and corresponding measured elastograms in location, surface area or mean strain value of a HStR. The results demonstrate that the FEM can simulate elastograms measured from arteries. As such, the FEM may help in quantifying strain-dependencies and assist in tissue characterization by reconstructing a Young's modulus image from a measured elastogram.

Coronary Artery Disease↗
PubMed2004

Fully automatic luminal contour segmentation in intracoronary ultrasound imaging--a statistical approach.

In this paper, a fully automatic method for luminal contour segmentation in intracoronary ultrasound imaging is introduced. Its principle is based on a contour with a priori properties that evolves according to the statistics of the ultrasound texture brightness, which is generally Rayleigh distributed. The main interest of the technique is its fully automatic character. This is insured by an initial contour that is not set by the user, like in classical snake-based algorithms, but estimated and, thus, adapted to each image. Its estimation combines two pieces of information extracted from the a posteriori probability function of the contour position: the function maximum location (or maximum a posteriori estimator) and the first zero-crossing of its derivative. Then, starting from the initial contour, a region of interest is automatically selected and the process iterated until the contour evolution can be ignored. In vivo coronary images from 15 patients, acquired with the 20-MHz central frequency Jomed Invision ultrasound scanner, were segmented with the developed method. Automatic contours were compared to those manually drawn by two physicians in terms of mean absolute difference. The results demonstrate that the error between automatic contours and the average of manual ones is of small amplitude, and only very slightly higher (0.099 +/- 0.032 mm) than the interexpert error (0.097 +/- 0.027 mm).

Algorithms↗
PubMed2003

From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies: Part II.

Atherosclerotic cardiovascular disease results in >19 million deaths annually, and coronary heart disease accounts for the majority of this toll. Despite major advances in treatment of coronary heart disease patients, a large number of victims of the disease who are apparently healthy die suddenly without prior symptoms. Available screening and diagnostic methods are insufficient to identify the victims before the event occurs. The recognition of the role of the vulnerable plaque has opened new avenues of opportunity in the field of cardiovascular medicine. This consensus document concludes the following. (1) Rupture-prone plaques are not the only vulnerable plaques. All types of atherosclerotic plaques with high likelihood of thrombotic complications and rapid progression should be considered as vulnerable plaques. We propose a classification for clinical as well as pathological evaluation of vulnerable plaques. (2) Vulnerable plaques are not the only culprit factors for the development of acute coronary syndromes, myocardial infarction, and sudden cardiac death. Vulnerable blood (prone to thrombosis) and vulnerable myocardium (prone to fatal arrhythmia) play an important role in the outcome. Therefore, the term "vulnerable patient" may be more appropriate and is proposed now for the identification of subjects with high likelihood of developing cardiac events in the near future. (3) A quantitative method for cumulative risk assessment of vulnerable patients needs to be developed that may include variables based on plaque, blood, and myocardial vulnerability. In Part I of this consensus document, we cover the new definition of vulnerable plaque and its relationship with vulnerable patients. Part II of this consensus document will focus on vulnerable blood and vulnerable myocardium and provide an outline of overall risk assessment of vulnerable patients. Parts I and II are meant to provide a general consensus and overviews the new field of vulnerable patient. Recently developed assays (eg, C-reactive protein), imaging techniques (eg, CT and MRI), noninvasive electrophysiological tests (for vulnerable myocardium), and emerging catheters (to localize and characterize vulnerable plaque) in combination with future genomic and proteomic techniques will guide us in the search for vulnerable patients. It will also lead to the development and deployment of new therapies and ultimately to reduce the incidence of acute coronary syndromes and sudden cardiac death. We encourage healthcare policy makers to promote translational research for screening and treatment of vulnerable patients.

Animals↗
PubMed2003

From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies: Part I.

Atherosclerotic cardiovascular disease results in >19 million deaths annually, and coronary heart disease accounts for the majority of this toll. Despite major advances in treatment of coronary heart disease patients, a large number of victims of the disease who are apparently healthy die suddenly without prior symptoms. Available screening and diagnostic methods are insufficient to identify the victims before the event occurs. The recognition of the role of the vulnerable plaque has opened new avenues of opportunity in the field of cardiovascular medicine. This consensus document concludes the following. (1) Rupture-prone plaques are not the only vulnerable plaques. All types of atherosclerotic plaques with high likelihood of thrombotic complications and rapid progression should be considered as vulnerable plaques. We propose a classification for clinical as well as pathological evaluation of vulnerable plaques. (2) Vulnerable plaques are not the only culprit factors for the development of acute coronary syndromes, myocardial infarction, and sudden cardiac death. Vulnerable blood (prone to thrombosis) and vulnerable myocardium (prone to fatal arrhythmia) play an important role in the outcome. Therefore, the term "vulnerable patient" may be more appropriate and is proposed now for the identification of subjects with high likelihood of developing cardiac events in the near future. (3) A quantitative method for cumulative risk assessment of vulnerable patients needs to be developed that may include variables based on plaque, blood, and myocardial vulnerability. In Part I of this consensus document, we cover the new definition of vulnerable plaque and its relationship with vulnerable patients. Part II of this consensus document focuses on vulnerable blood and vulnerable myocardium and provide an outline of overall risk assessment of vulnerable patients. Parts I and II are meant to provide a general consensus and overviews the new field of vulnerable patient. Recently developed assays (eg, C-reactive protein), imaging techniques (eg, CT and MRI), noninvasive electrophysiological tests (for vulnerable myocardium), and emerging catheters (to localize and characterize vulnerable plaque) in combination with future genomic and proteomic techniques will guide us in the search for vulnerable patients. It will also lead to the development and deployment of new therapies and ultimately to reduce the incidence of acute coronary syndromes and sudden cardiac death. We encourage healthcare policy makers to promote translational research for screening and treatment of vulnerable patients.

Acute Disease↗
PubMed2003

Intravascular palpography for high-risk vulnerable plaque assessment.

BACKGROUND: The composition of an atherosclerotic plaque is considered more important than the degree of stenosis. An unstable lesion may rupture and cause an acute thrombotic reaction. Most of these lesions contain a large lipid pool covered by an inflamed thin fibrous cap. The stress in the cap increases with decreasing cap thickness and increasing macrophage infiltration. Intravascular ultrasound (IVUS) palpography might be an ideal technique to assess the mechanical properties of high-risk plaques. TECHNIQUE: Palpography assesses the local mechanical properties of tissue using its deformation caused by the intraluminal pressure. IN VITRO VALIDATION: The technique was validated in vitro using diseased human coronary and femoral arteries. Especially between fibrous and fatty tissue, a highly significant difference in strain (p = 0.0012) was found. Additionally, the predictive value to identify the vulnerable plaque was investigated. A high-strain region at the lumen-vessel wall boundary has an 88% sensitivity and 89% specificity for identifying such plaques. IN VIVO VALIDATION: In vivo, the technique was validated in an atherosclerotic Yucatan minipig animal model. This study also revealed higher strain values in fatty than fibrous plaques (p < 0.001). The presence of a high-strain region at the lumenplaque interface has a high predictive value to identify macrophages. PATIENT STUDIES: Patient studies revealed high-strain values (1-2%) in thin-cap fibrous atheroma. Calcified material showed low strain values (0-0.2%). With the development of three-dimensional (3-D) palpography, identification of highstrain spots over the full length of a coronary artery becomes available. CONCLUSION: Intravascular palpography is a unique tool to assess lesion composition and vulnerability. The development of 3-D palpography provides a technique that may develop into a clinical tool to identify the high-risk plaque.

Animals↗
PubMed2003

Quantitative IVUS blood flow: validation in vitro, in animals and in patients.

In recent years, a new method to measure transverse blood flow based on the decorrelation of the radiofrequency (RF) signals of intravascular ultrasound (IVUS) rotating single-element scanners was introduced. We report here in vitro, animal and patient testing to evaluate the correlation-based method using an IVUS array catheter. A new correlation-based method to dynamically correct the correlation coefficients for noise is implemented. The decorrelation due to noise was estimated from the correlation coefficients from flowing blood obtained at increasing time lags. First, blood flow experiments were carried out with different catheters in a tissue-mimicking flow phantom with an inner diameter ranging from 3.0 to 5.0 mm. A calibrated electromagnetic flow meter (EMF, range: 0 to 250 cc/min) was used as a reference. Good linear relationships were found between the IVUS-derived flow and the calibrated EMF (all R(2)> 0.96). The catheter position within the flow phantom and the size of the ring-down were theoretically analyzed. These elements, and noise in the RF signals, have an important influence on the IVUS blood flow measurements reflected by the offset and the slope of the linear relationships. By placing the IVUS catheter outside the flow phantom, parabolic blood flow profiles were also measured. Second, IVUS blood flow measurements were performed in the carotid artery of two Yorkshire pigs, which showed linear relationships (all R(2)> 0.85) between the IVUS-derived flow and the calibrated EMF. Experimentally, the offset was lower than 3 mL/min and the slope was close to 1. Third, IVUS blood flow measurements were performed in coronary arteries in patients. Preliminary results for the coronary flow reserve (CFR = high flow/baseline flow) in patients using the decorrelation method of RF signals of an array IVUS scanner were comparable with CFR based on Doppler measurements.

Animals↗
PubMed2003

Intravascular elastography: from bench to bedside.

An unstable lesion may rupture and cause an acute thrombotic reaction. These lesions contain a large lipid pool covered by a thin fibrous cap. The stress in the cap increased with decreasing thickness and increasing macrophage infiltration. Intravascular ultrasound (IVUS) elastography might be an ideal technique to assess the presence of lipid pools and identify high stress regions. Elastography assesses the local mechanical properties of tissue using its deformation caused by the intraluminal pressure. The technique was validated in vitro using diseased human coronary and femoral arteries. These experiments demonstrated that the strain in the three plaque types is different (P < 0.001). Especially between fibrous and fatty tissue, a highly significant difference (P = 0.0012) was found. Additionally, the predictive value for identifying the vulnerable plaque was investigated. A high strain region at the lumen vessel wall boundary has 88% sensitivity and 89% specificity for identifying these plaques. In vivo, the technique is validated in an atherosclerotic Yucatan mini-pig animal model. This study also revealed higher strain values in fatty than fibrous plaques (P < 0.001). The presence of a high strain region at the lumen plaque interface has a high predictive value for identifying macrophages. Patient studies revealed high strain values (1-2%) in soft plaques. Calcified material shows low strain values (0-0.2%). With the development of three-dimensional elastography, identification of weak spots over the full length of a coronary artery becomes possible. In conclusion, intravascular elastography is a unique tool to assess lesion composition and vulnerability. The development of three-dimensional elastography provides a technique that may develop into a clinical available tool for identifying the rupture-prone plaque.

Animals↗
PubMed2002

Identification of atherosclerotic plaque components with intravascular ultrasound elastography in vivo: a Yucatan pig study.

BACKGROUND: Intravascular ultrasound elastography assesses the local strain of the atherosclerotic vessel wall. In the present study, the potential to identify different plaque components in vivo was investigated. METHODS AND RESULTS: Atherosclerotic external iliac and femoral arteries (n=24) of 6 Yucatan pigs were investigated. Before termination, elastographic data were acquired with a 20-MHz Visions catheter. Two frames acquired at end-diastole with a pressure differential of approximately 4 mm Hg were acquired to obtain the elastograms. Before dissection, x-ray was used to identify the arterial segments that had been investigated by ultrasound. Specimens were stained for collagen, fat, and macrophages. Plaques were classified as absent, early fibrous lesion, early fatty lesion, or advanced fibrous plaque. The average strains in the plaque-free arterial wall (0.21%) and the early (0.24%) and advanced fibrous plaques (0.22%) were similar. Higher average strain values were observed in fatty lesions (0.46%) compared with fibrous plaques (P=0.007). After correction for confounding by lipid content, no additional differences in average strain were found between plaques with and without macrophages (P=0.966). Receiver operating characteristic analysis revealed a sensitivity and a specificity of 100% and 80%, respectively, to identify fatty plaques. The presence of a high-strain spot (strain >1%) has 92% sensitivity and 92% specificity to identify macrophages. CONCLUSIONS: To the best of our knowledge, this is the first time that intravascular ultrasound elastography has been validated in vivo. Fatty plaques have an increased mean strain value. High-strain spots are associated with the presence of macrophages.

Animals↗
PubMed2002

Intravascular ultrasound elastography: an overview.

The composition and morphology of the atherosclerotic lesion are currently considered more important determinants of acute coronary ischemic syndromes than the degree of stenosis. When a lesion is unstable, it may rupture and cause an acute thrombotic reaction. A rupture prone plaque contains a large lipid pool covered by a thin fibrous cap. The stress in the cap increased with decreasing thickness. Additionally, it may be weakened by macrophage infiltration. Intravascular ultrasound elastography might be an ideal technique to assess the presence of lipid pools and identify high stress regions. Elastography is a technique to assess local mechanical properties of tissue. The underlying principle is that the deformation of tissue by a mechanical excitation is a function of its mechanical properties. The deformation of the tissue is determined using ultrasound. For intravascular purposes, the intraluminal pressure is used as the excitation force. The radial strain in the tissue is obtained by cross-correlation techniques on the radio frequency (rf) signal. The strain is colour-coded and plotted as a complimentary image to the IVUS echogram. Elastography was validated in vitro using diseased human coronary and femoral arteries. After the ultrasound experiments, the specimens were processed for routine histology to counterstain collagen, smooth-muscle cells, and macrophage activity. Regions were segmented in the elastograms based on their strain values. Next, the dominant plaque type (fibrous, fibro-fatty or fatty) was defined by observers blinded to the elastographic result. These experiments demonstrate that the strain in the three plaque types is different (Kruskall-Wallis p < 0.001). Especially between fibrous and fatty tissue, a highly significant difference (Wilcoxon p < 0.001) was found. In vivo, the technique is validated in an atherosclerotic Yucatan mini-pig animal model. High-resolution echo frames (30 frames per second) were acquired near end-diastole. In this phase of the pressure cycle, catheter motion was minimal. Frames with a pressure difference of approx. 5 mm Hg were taken to determine the elastograms. This in vivo validation study in Yucatan mini-pigs revealed higher strain values in fatty material (ANOVA p < 0.001). All cross-sections with a fatty plaque were identified with the elastogram by the presence of high strain values. Additionally, data are acquired in patients referred for Percutaneous Transluminal Coronary Angioplasty with the same set-up as tested in the animal study. Ultrasound data of soft, fibrous, calcified and stented plaques are acquired near end-diastole. The elastogram of soft plaques. as identified from the deformation during the pressure cycle, reveals strain values of 1% with increased strain up to 2% at the shoulders of the plaque. Calcified material, as identified from the echogram, shows low strain values of 0-0.2%. The elastogram of stented plaques reveals very low strain values, except for two regions: these are between the stent struts and at the shoulders of the plaque. In conclusion, intravascular elastography appears to be a unique tool to determine local mechanical properties in atherosclerotic lesions to identify fibrous and fatty tissue. Experiments have demonstrated the feasibility of this technique to be applied in vivo.

Animals↗
PubMed2002

Decorrelation-based blood flow velocity estimation: effect of spread of flow velocity, linear flow velocity gradients, and parabolic flow.

In recent years, a new method to measure transverse blood flow, based on the decorrelation of the radio frequency (RF) signals has been developed. In this paper, we investigated the influence of nonuniform flow on the velocity estimation. The decorrelation characteristics of transverse blood flow using an intravascular ultrasound (IVUS) array catheter are studied by means of computer modeling. Blood was simulated as a collection of randomly located point scatterers; moving this scattering medium transversally across the acoustical beam represented flow. First-order statistics were evaluated, and the signal-to-noise ratio from the signals were measured. The correlation coefficient method was used to present the results. Three velocity profiles were simulated: random spread of blood-flow velocity, linear blood-flow velocity gradient, and parabolic blood-flow. Radio frequency and envelope signals were used to calculate the decorrelation pattern. The results were compared to the mean decorrelation pattern for plug blood-flow. The RF signals decorrelation patterns were in good agreement with those obtained for plug blood flow. Envelope decorrelation patterns show a close agreement with the one for plug blood flow. For axial blood flow, there is a discrepancy between decorrelation patterns. The results presented here suggest that the decorrelation properties of an IVUS array catheter for measuring quantitative transverse blood flow probably will not be affected by different transverse blood-flow conditions.

Blood Flow Velocity↗
PubMed2002

Imaging of atherosclerosis. Elastography.

Intravascular ultrasound elastography is a method for measuring the local elastic properties of coronary atherosclerotic plaques using intravascular ultrasound (IVUS). Mechanical properties of the different tissues within a plaque are measured through strain. 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 and the focus will be on our approach to the application of intravascular elastography.

Coronary Artery Disease↗