Biomedical subjects

Frits Mastik

Publications and source records attributed to Frits Mastik.

At least 19 recordsLinked to original sources

PubMed2007

Local elasticity imaging of vulnerable atherosclerotic coronary plaques.

The material composition and morphology of vulnerable atherosclerotic plaque components are considered to be more important determinants of acute coronary syndromes than the degree of stenosis. Rupture of a plaque causes thrombogenic material to contact the blood, resulting in a thrombus. Rupture-prone plaques contain an inflamed thin fibrous cap covering a large soft lipid pool. Mechanically, rupture occurs when plaques cannot withstand the internal stresses induced by the pulsating blood. These stresses concentrate within/around the cap/edge, since the lipid pool cannot bear much stress. During plaque development these stresses further increase when caps become thinner, lipid pools become larger, or the difference in stiffness (modulus) between the cap and the lipid pool increases. Intravascular ultrasound (IVUS) strain elastography/palpography and IVUS modulus elastography are imaging techniques that assess local plaque elasticity (strain and modulus) based on the principle that tissue deformation (strain) by a mechanical stress is a function of its elastic properties (modulus). Combined use of these techniques provides clinicians an all-in-one modality for detecting plaques, assessing their rupture proneness and imaging their elastic material composition. This chapter describes the terminology and pathophysiology of vulnerable plaques and discusses the techniques behind, the methods for and the validations of the elasticity imaging techniques.

Algorithms↗

PubMed2006

Intravascular palpography for vulnerable plaque assessment.

Palpography assesses the local mechanical properties of tissue using the deformation caused by the intraluminal pressure. 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 88% sensitivity and 89% specificity for identifying these plaques. In vivo, the technique is validated in an atherosclerotic Yucatan minipig animal model. This study also revealed higher strain values in fatty than in fibrous plaques (p < 0.001). The presence of a high-strain region at the lumen-plaque interface has a high predictive value to identify macrophages. Patient studies revealed high strain values (1% to 2%) in noncalcified plaques. Calcified material showed low strain values (0% to 0.2%). With the development of three-dimensional palpography, identification of weak spots over the full length of a coronary artery becomes available. Patients with myocardial infarction or unstable angina have more high-strain spots in their coronary arteries than patients with stable angina. In conclusion, intravascular palpography is a unique tool to assess lesion composition and vulnerability. Three-dimensional palpography provides a technique that may develop into a clinically available tool for decision making to treat hemodynamically nonsignificant lesions by identifying vulnerable plaques. The clinical utility of this technique is yet to be determined, and more investigation is needed.

Animals↗

PubMed2006

Noninvasive detection of subclinical coronary atherosclerosis coupled with assessment of changes in plaque characteristics using novel invasive imaging modalities: the Integrated Biomarker and Imaging Study (IBIS).

OBJECTIVES: Our purpose was to assess noninvasive imaging in detection of subclinical atherosclerosis and to examine novel invasive modalities to describe prevalence and temporal changes in putative characteristics of "high-risk" plaques. BACKGROUND: Conventional coronary imaging cannot identify "high-risk" lesions. METHODS: Conventional (quantitative angiography and intravascular ultrasound [IVUS]) and novel imaging (IVUS-based palpography and gray scale echogenicity) were performed at baseline and 6 months later in 67 patients with diverse clinical presentations. Different imaging techniques were compared within a common segment defined by multislice computed tomography (MSCT). RESULTS: Compared with IVUS, the sensitivity, specificity, and positive and negative predictive value of MSCT for detecting significant plaque was 86%, 69%, 90%, and 61%, respectively. In coronary arteries with <50% stenosis, there were no temporal changes in luminal and plaque dimensions measured by quantitative coronary angiography or IVUS; however, a significant reduction in abnormal strain pattern was detected on palpography (density high strain spots/cm: 1.6 +/- 1.5 vs. 1.2 +/- 1.4, p = 0.0123. These changes were mainly related to significant changes in patients who presented with ST-segment elevation myocardial infarction. The assessment of plaque echogenicity showed no temporal changes. There were no correlations between circulating biomarkers and quantifiable imaging parameters. CONCLUSIONS: Mild angiographic disease is associated with large atherosclerotic plaques on MSCT. Conventional invasive coronary imaging reveals static luminal and plaque dimensions on standard medical therapy with plaque hypoechogenicity remaining unchanged over the 6-month period. By contrast, palpography measurements of strain correlate with clinical presentation and significantly decrease on standard medical therapy. Novel imaging modalities, such as palpography, might provide insights into plaque biology and might eventually serve as intermediate end points in interventional trials.

Coronary Angiography↗

PubMed2006

Young's modulus reconstruction of vulnerable atherosclerotic plaque components using deformable curves.

Rupture, with subsequent thrombosis, of thin-cap fibroatheromas (TCFAs) is a major cause of myocardial infarction. A TCFA has two main components: these are a large, soft lipid pool and a thin, stiff fibrous cap covering it. Quantification of their morphology and stiffness is essential for monitoring atherosclerosis and quantifying the effect of plaque-stabilizing pharmaceutical treatment. To accomplish this, we have developed a model-based Young's modulus reconstruction method. From a plaque strain elastogram, measured with an intravascular ultrasound catheter, it reconstructs a Young's modulus image of the plaque. To this end, a minimization algorithm automatically varies the morphology and stiffness parameters of a TCFA computer model, until the corresponding computer-simulated strain elastogram resembles the measured strain elastogram. The morphology parameters of the model are the control-points of two deformable Bézier curves; one curve delineates the distal border of the lipid pool region, the other the distal border of the cap region. These component regions are assumed to be homogeneous and their stiffness is characterized by a Young's modulus. Reconstructions from strain elastograms that were 1. simulated using a histology-derived computer TCFA, 2. measured from a physical phantom with a soft lipid pool, and 3. simulated with a computer TCFA, where the complexity of its plaque component borders was increased, demonstrated the superior reconstruction/delineation behavior of this method, compared with a previously developed circular reconstruction method that used only circles for border delineation. Consequently, this method may become a valuable tool for the quantification of both the morphology and stiffness of vulnerable atherosclerotic plaque components.

Algorithms↗

PubMed2006

Motion compensation for intravascular ultrasound palpography.

Rupture of vulnerable plaques in coronary arteries is the major cause of acute coronary syndromes. Most vulnerable plaques consist of a thin fibrous cap covering an atheromous core. These plaques can be identified using intravascular ultrasound (IVUS) palpography, which measures radial strain by cross-correlating RF signals at different intraluminal pressures. Multiple strain images (i.e., partial palpograms) are averaged per heart cycle to produce a more robust compounded palpogram. However, catheter motion due to cardiac activity causes misalignment of the RF signals and thus of the partial palpograms, resulting in less valid strain estimates. To compensate for in-plane catheter rotation and translation, we devised four methods based on block matching. The global rotation block matching (GRBM) and contour mapping (CMAP) methods measure catheter rotation, and local block matching (LBM) and catheter rotation and translation (CRT) estimate displacements of local tissue regions. These methods were applied to nine in vivo pullback acquisitions, made with a 20 MHz phased-array transducer. We found that all these methods significantly increase the number of valid strain estimates in the partial and compounded palpograms (P < 0.008). The best method, LBM, attained an average increase of 17% and 15%, respectively. Implementation of this method should improve the information coming from IVUS palpography, leading to better vulnerable plaque detection.

Algorithms↗

PubMed2006

Clinical imaging of the vulnerable plaque in the coronary arteries: new intracoronary diagnostic methods.

Rupture of a vulnerable plaque is the main cause of acute coronary syndromes and myocardial infarction. The features of rupture-prone atherosclerotic plaques have been previously described by pathologists. However, identification of vulnerable plaques in vivo is essential to study their natural history and to evaluate potential treatment modalities. Coronary angiography is the gold standard for the diagnosis of coronary artery disease, but it is unable to distinguish between stable and unstable plaques and to accurately predict future cardiac events. This current perspective describes the recently developed invasive imaging techniques to detect atherosclerotic vulnerable plaques in the coronary tree.

Angioscopy↗

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

Rationale and methods of the integrated biomarker and imaging study (IBIS): combining invasive and non-invasive imaging with biomarkers to detect subclinical atherosclerosis and assess coronary lesion biology.

Death or myocardial infarction, the most serious clinical consequences of atherosclerosis, often result from plaque rupture at non-flow limiting lesions. Current diagnostic imaging with coronary angiography only detects large plaques that already impinge on the lumen and cannot accurately identify those that have a propensity to cause unheralded events. Accurate evaluation of the composition or of the biomechanical characteristics of plaques with invasive or non-invasive methods, alone or in conjunction with assessment of circulating biomarkers, could help identify high-risk patients, thus providing the rationale for aggressive treatments in order to reduce future clinical events. The IBIS (Integrated Biomarker and Imaging Study) study is a prospective, single-center, non-randomized, observational study conducted in Rotterdam. The aim of the IBIS study is to evaluate both invasive (quantitative coronary angiography, intravascular ultrasound (IVUS) and palpography) and non-invasive (multislice spiral computed tomography) imaging techniques to characterize non-flow limiting coronary lesions. In addition, multiple classical and novel biomarkers will be measured and their levels correlated with the results of the different imaging techniques. A minimum of 85 patients up to a maximum of 120 patients will be included. This paper describes the study protocol and methodological solutions that have been devised for the purpose of comparisons among several imaging modalities. It outlines the analyses that will be performed to compare invasive and non-invasive imaging techniques in conjunction with multiple biomarkers to characterize non-flow limiting subclinical coronary lesions.

Adult↗

PubMed2005

Robustness of reconstructing the Young's modulus distribution of vulnerable atherosclerotic plaques using a parametric plaque model.

Assessment of atherosclerotic plaque composition is crucial for quantitative monitoring of atherosclerosis and for quantifying the effect of pharmaceutical plaque-stabilizing treatments during clinical trials. We assessed this composition by applying a geometrically constrained, iterative inverse solution method to reconstruct a modulus elastogram (i.e., Young's modulus image) from a plaque strain elastogram (i.e., radial strain image) that is measured using intravascular ultrasound strain elastography. This reconstruction method is especially suited for thin-cap fibroatheromas (TCFAs) (i.e., plaques with a thin fibrous cap overlaying a lipid pool). Because a strain elastogram of a plaque depends upon the plaque material composition, catheter position within the vessel and measurement noise, this paper investigates how robust the reconstruction is when these parameters are varied. To this end, a standard plaque was defined as the modulus elastogram that was reconstructed from an in vivo measured strain elastogram of a human coronary plaque. This standard plaque was used to computer-simulate different strain elastograms, by varying the 1. geometry and material properties of its plaque components, 2. catheter position and 3. level of added strain noise. Robustness was evaluated by quantifying the correctly reconstructed size, shape and Young's modulus of each plaque component region and minimal cap thickness. The simulations showed that TCFAs can be adequately reconstructed; the thinner and stiffer the cap or the softer and larger the lipid pool, the better is the reconstruction of these components and minimal cap thickness. Furthermore, reconstructions were 1. independent of catheter position and 2. independent of strain noise. As such, this method has potential to monitor robustly and quantitatively atherosclerosis in vivo.

Algorithms↗

PubMed2005

Assessment of vulnerable plaque composition by matching the deformation of a parametric plaque model to measured plaque deformation.

Intravascular ultrasound (IVUS) elastography visualizes local radial strain of arteries in so-called elastograms to detect rupture-prone plaques. However, due to the unknown arterial stress distribution these elastograms cannot be directly interpreted as a morphology and material composition image. To overcome this limitation we have developed a method that reconstructs a Young's modulus image from an elastogram. This method is especially suited for thin-cap fibroatheromas (TCFAs), i.e., plaques with a media region containing a lipid pool covered by a cap. Reconstruction is done by a minimization algorithm that matches the strain image output, calculated with a parametric finite element model (PFEM) representation of a TCFA, to an elastogram by iteratively updating the PFEM geometry and material parameters. These geometry parameters delineate the TCFA media, lipid pool and cap regions by circles. The material parameter for each region is a Young's modulus, EM, EL, and EC, respectively. The method was successfully tested on computer-simulated TCFAs (n = 2), one defined by circles, the other by tracing TCFA histology, and additionally on a physical phantom (n = 1) having a stiff wall (measured EM = 16.8 kPa) with an eccentric soft region (measured EL = 4.2 kPa). Finally, it was applied on human coronary plaques in vitro (n = 1) and in vivo (n = 1). The corresponding simulated and measured elastograms of these plaques showed radial strain values from 0% up to 2% at a pressure differential of 20, 20, 1, 20, and 1 mmHg respectively. The used/reconstructed Young's moduli [kPa] were for the circular plaque EL = 50/66, EM = 1500/1484, EC = 2000/2047, for the traced plaque EL = 25/1, EM = 1000/1148, EC = 1500/1491, for the phantom EL = 4.2/4 kPa, EM = 16.8/16, for the in vitro plaque EL = n.a./29, EM = n.a./647, EC = n.a./1784 kPa and for the in vivo plaque EL = n.a./2, EM = n.a./188, Ec = n.a./188 kPa.

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

Characterizing vulnerable plaque features with intravascular elastography.

BACKGROUND: In vivo detection of vulnerable plaques is presently limited by a lack of diagnostic tools. Intravascular ultrasound elastography is a new technique based on intravascular ultrasound and has the potential to differentiate between different plaques phenotypes. However, the predictive value of intravascular elastography to detect vulnerable plaques had not been studied. METHODS AND RESULTS: Postmortem coronary arteries were investigated with intravascular elastography and subsequently processed for histology. In histology, a vulnerable plaque was defined as a plaque consisting of a thin cap (<250 microm) with moderate to heavy macrophage infiltration and at least 40% of atheroma. In elastography, a vulnerable plaque was defined as a plaque with a high strain region at the surface with adjacent low strain regions. In 24 diseased coronary arteries, we studied 54 cross sections. In histology, 26 vulnerable plaques and 28 nonvulnerable plaques were found. Receiver operator characteristic analysis revealed a maximum predictive power for a strain value threshold of 1.26%. The area under the receiver operator characteristic curve was 0.85. The sensitivity was 88%, and the specificity was 89% to detect vulnerable plaques. Linear regression showed high correlation between the strain in caps and the amount of macrophages (P<0.006) and an inverse relation between the amount of smooth muscle cells and strain (P<0.0001). Plaques, which are declared vulnerable in elastography, have a thinner cap than nonvulnerable plaques (P<0.0001). CONCLUSIONS: Intravascular elastography has a high sensitivity and specificity to detect vulnerable plaques in vitro.

Collagen↗

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↗