F.A. Lupotti
Erasmus University Rotterdam
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Featured researches published by F.A. Lupotti.
internaltional ultrasonics symposium | 1998
A.F.W. van der Steen; E.I. Cespedes; C.L. de Korte; S.G. Carlier; Wenguang Li; Frits Mastik; C.T. Lancee; J. Borsbroom; F.A. Lupotti; Rob Krams; P. W. Serruys; N. Bom
In the development of intravascular ultrasound (IVUS), a serious emphasis has been given to the improvement of the image quality in terms of resolution. The image quality is indeed a very important issue, but there is lot more information hidden in the ultrasound signals than is currently exploited by commercially available IVUS equipment. Over the past few years, at the Thorax centre we have been exploring the possibilities of analysing sequences of radiofrequency (RF) traces. This could provide a significant extension of the functionality of the IVUS machines. It gives possibilities for local elasticity assessment, flow estimation and enhanced lumen detection. This paper is an up to date impression of where RF-data analysis has taken us.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control | 2000
F.A. Lupotti; E.I. Cespedes; A.F.W. van der Steen
In recent years, a new method to measure transverse blood flow based on the decorrelation of radio frequency (RF) signals has been introduced. In this paper, we investigated the decorrelation characteristics of transverse blood flow measurement using an intravascular ultrasound (IVUS) array catheter 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 was measured. The correlation coefficient method was used to present the results. The decorrelation patterns for RF and for RF-envelope signals were studied. The decorrelation patterns from the RF signals were in good agreement with those obtained from theoretical beam profiles. This agreement suggests that the decorrelation properties of an IVUS array catheter for measuring quantitative transverse blood flow can be assessed by measuring the ultrasound beam. A line of point scatterers, moved transversally across the acoustical beam (line spread function), can determine this decorrelation behaviour.
Ultrasound in Medicine and Biology | 2003
F.A. Lupotti; Frits Mastik; Stéphane G. Carlier; Chris L. de Korte; Willem J. van der Giessen; Patrick W. Serruys; Antonius F.W. van der Steen
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.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control | 2002
F.A. Lupotti; A.F.W. van der Steen; Frits Mastik; C.L. de Korte
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.
Ultrasound in Medicine and Biology | 2001
F.A. Lupotti; E.Ignacio Céspedes; Antonius F.W. van der Steen
A method to measure transverse blood flow, based on the correlation between consecutive radiofrequency (RF) signals, has been introduced. This method was validated for an intravascular (IVUS) rotating single element catheter. Currently, we are implementing the method for an IVUS array transducer catheter. The decorrelation characteristics during transverse blood flow using the IVUS array catheter were investigated using computer modeling. Before this, blood was simulated as a collection of randomly located point scatterers and, by moving this scattering medium transversely across the acoustical beam, blood flow was simulated. This paper presents a more realistic scattering media by simulating aggregates of red blood cells (RBCs) as strings of point scatterers. Three configurations of aggregates of RBCs were simulated. First, aggregates of RBCs were strings with different lengths and parallel to the catheter axis. Second, the strings were with a fixed length and angles of plus or minus 45 degrees with respect to the catheter axis. Third, the strings were with different lengths and random angles ranging from -45 degrees to + 45 degrees. The decorrelation characteristics for these configurations of aggregates of RBCs were investigated and compared with point scatterers. For the aggregates of RBCs parallel to the catheter axis, the decorrelation rate became slower when the aggregate length was increased. RBC aggregations with fixed and random lengths and angles resulted in a decorrelation rate that approaches the decorrelation pattern from point scatterers. Results suggests that the presence of aggregates of RBCs will probably not affect the measurements of transverse blood flow using a decorrelation-based method and an IVUS array catheter.
Ultrasonics | 2000
A.F.W. van der Steen; E.I. Cespedes; S.G. Carlier; Frits Mastik; F.A. Lupotti; J. Borsboom; Wenguang Li; P. W. Serruys; N. Bom
Coronary flow assessment can be useful for determining the hemodynamic severity of a stenosis and to evaluate the outcome of interventional therapy. We developed a method for measuring the transverse flow through the imaging plane of an intravascular ultrasound (IVUS) catheter. This possibility has raised great clinical interest since it permits simultaneous assessment of vessel geometry and function with the same device. Furthermore, it should give more accurate information than combination devices because lumen diameter and velocity are determined at the same location. Flow velocity is estimated based on decorrelation estimation from sequences of radiofrequency (RF) traces acquired at nearly the same position. Signal gating yields a local estimate of the velocity. Integrating the local velocity over the lumen gives the quantitative flow. This principle has been calibrated and tested through computer modeling, in vitro experiments using a flow phantom and in vivo experiments in a porcine animal model, and validated against a Doppler element containing guide wire (Flowire) in humans. Originally the method was developed and tested for a rotating single element device. Currently the method is being developed for an array system. The great advantage of an array over the single element approach would be that the transducer has no intrinsic motion. This intrinsic motion sets a minimal threshold in the detectable velocity components. Although the principle is the same, the method needs some adaptation through the inherent different beamforming of the transducer. In this paper various aspects of the development of IVUS flow are reviewed.
Ultrasound in Medicine and Biology | 2002
F.A. Lupotti; Chris L. de Korte; Frits Mastik; Antonius F.W. van der Steen
In recent years, a new method to measure transverse blood flow based on the decorrelation of the radio-frequency (RF) signals, has been developed. Transverse blood flow estimation may be influenced by noise. In this paper, we investigated a new correlation-based method for noise correction. The decorrelation characteristics of transverse blood flow using an intravascular ultrasound (US) or IVUS array catheter were studied by means of computer modeling. Blood was simulated as a collection of randomly located point scatterers; moving this scattering medium transversely across the acoustical beam represented flow. Parabolic blood flow was simulated. Additive noise was added to the RF signals at a given signal-to-noise ratio (SNR). Next, a new method to dynamically estimate and suppress the decorrelation due to noise is presented. The decorrelation due to noise was estimated from the correlation coefficients from flowing blood obtained at increasing time lags. The correlation graphs are corrected for the decorrelation due to noise, leaving the decorrelation due to blood flow. The method shows promise to estimate and correct the correlation coefficients for noise.
Ultrasonics | 2002
F.A. Lupotti; E.Ignacio Céspedes; Frits Mastik; Antonius F.W. van der Steen
A method to measure transverse blood flow, based on correlation between consecutive radio frequency (RF) signals, has been developed. Currently, we are implementing the method for an intravascular (IVUS) array catheter. In this paper, the acoustical beam (line-spread function, LSF) was experimentally measured and compared with the simulated one. Next, the experimental LSF(E) was convolved with a matrix of white noise to produce RF(E) signals. Decorrelation pattern from the RF(E) signals was compared with the correspondent autoconvolution of the LSF(E) and a good agreement was found. We conclude that the transverse decorrelation pattern of the IVUS array catheter can be assessed from the properties of the acoustical beam.
computing in cardiology conference | 2001
F.A. Lupotti; Frits Mastik; S.G. Carlier; E.I. Cespedes; A.F.W. van der Steen
In recent years, a new method to measure transverse blood flow, based on the decorrelation of radiofrequency (RF) signals has been introduced. In this paper, we studied the decorrelation characteristics of transverse blood flow using an intravascular ultrasound (IVUS) array catheter by means of computer modeling. Blood was modeled first as randomly located point scatterers and then as aggregates moving across the ultrasound beam. The spread of flow and flow gradient were then simulated. IVUS flow measurements were used to study the influence of the ring-down size on flow measurements. Coronary flow reserve (CFR) was computed from this data and from a calibrated transonic flowmeter. The decorrelation pattern for point scatterers, aggregates and nonhomogeneous flow is in agreement with theoretical predictions from sound field calculations. Underestimation of flow occurs by ring-down obscuring but good agreement between IVUS and flowmeter CFR was found.
internaltional ultrasonics symposium | 1999
F.A. Lupotti; E.I. Cespedes; A.F.W. van der Steen
The decorrelation properties of the phased array transducer, as well as the influence of red blood cell aggregation on the decorrelation properties of flowing blood are studied using computer modeling. Blood was modeled as randomly located omnidirectional point scatterers moving across the ultrasound beam. To study the influence of aggregation, blood was modeled as single scatterers and as aggregates of various lengths. The aggregates were organized parallel to the catheter and at random angles. The decorrelation patterns, in the near and far field, are in agreement with theoretical predictions from sound field calculations. Thus, the decorrelation properties of an IVUS array catheter (in relation to transverse blood flow) can be assessed from the properties of the ultrasound beam. The decorrelation of the echo signal is influenced by the characteristics of the scattering medium. However, a complex model of flowing blood, which consists of moving aggregates of various length and orientation, shows a similar decorrelation pattern to that of moving point scatterers.