Biomedical subjects

F Mastik

Publications and source records attributed to F Mastik.

At least 19 recordsLinked to original sources

PubMed2006

Remote non-invasive stereoscopic imaging of blood vessels: first in-vivo results of a new multispectral contrast enhancement technology.

We describe a contactless optical technique selectively enhancing superficial blood vessels below variously pigmented intact human skin by combining images in different spectral bands. Two CMOS-cameras, with apochromatic lenses and dual-band LED-arrays, simultaneously streamed Left (L) and Right (R) image data to a dual-processor PC. Both cameras captured color images within the visible range (VIS, 400-780 nm) and grey-scale images within the near infrared range (NIR, 910-920 nm) by sequentially switching between LED-array emission bands. Image-size-settings of 1280 x 1024 for VIS & 640 x 512 for NIR produced 12 cycles/s (1 cycle = 1 VIS L&R-pair + 1 NIR L&R-pair). Decreasing image-size-settings (640 x 512 for VIS and 320 x 256 for NIR) increased camera-speed to 25 cycles/s. Contrasts from below the tissue surface were algorithmically distinguished from surface shadows, reflections, etc. Thus blood vessels were selectively enhanced and back-projected into the stereoscopic VIS-color-image using either a 3D-display or conventional shutter glasses. As a first usability reconnaissance we applied this custom-built mobile stereoscopic camera for several clinical settings:* blood withdrawal;* vein inspection in dark skin;* vein detection through iodide;* varicose vein and nevi pigmentosum inspection. Our technique improves blood vessel visualization compared to the naked eye, and supports depth perception.

Blood Vessels↗

PubMed2005

Contactless multiple wavelength photoplethysmographic imaging: a first step toward "SpO2 camera" technology.

We describe a route toward contactless imaging of arterial oxygen saturation (SpO2) distribution within tissue, based upon detection of a two-dimensional matrix of spatially resolved optical plethysmographic signals at different wavelengths. As a first step toward SpO2-imaging we built a monochrome CMOS-camera with apochromatic lens and 3lambda-LED-ringlight (lambda1 = 660 nm, lambda2 = 810 nm, lambda3 = 940 nm; 100 LEDs lambda(-1)). We acquired movies at three wavelengths while simultaneously recording ECG and respiration for seven volunteers. We repeated this experiment for one volunteer at increased frame rate, additionally recording the pulse wave of a pulse oximeter. Movies were processed by dividing each image frame into discrete Regions of Interest (ROIs), averaging 10 x 10 raw pixels each. For each ROI, pulsatile variation over time was assigned to a matrix of ROI-pixel time traces with individual Fourier spectra. Photoplethysmograms correlated well with respiration reference traces at three wavelengths. Increased frame rates revealed weaker pulsations (main frequency components 0.95 and 1.9 Hz) superimposed upon respiration-correlated photoplethysmograms, which were heartbeat-related at three wavelengths. We acquired spatially resolved heartbeat-related photoplethysmograms at multiple wavelengths using a remote camera. This feasibility study shows potential for non-contact 2-D imaging reflection-mode pulse oximetry. Clinical devices, however, require further development.

Adult↗

PubMed2002

Effect of temperature increase and freezing on intravascular elastography.

Intravascular ultrasound (IVUS) elastography is a technique that assesses the local strain in the vessel wall and plaque. The strain is an important parameter for characterization of different plaque components. These regions are related to plaque vulnerability. IVUS elastography was validated in vitro using human coronary and femoral arteries. These experiments were performed on specimens that were stored frozen and measured at room temperature for practical issues. The aim of this study is to determine the influence of freezing and measuring the tissues at room temperature (23 degrees C instead of 37 degrees C) on the elastic properties. Four human coronary, one carotid and one femoral arteries were first measured at 23 degrees C and next at 37 degrees C. Additionally they were stored at -80 degrees C for up to 24 h and finally measured at 23 degrees C. Acquisitions at intraluminal pressures of 80 and 100 mmHg were performed using an EndoSonics 20 MHz Visions catheter. Elastograms were determined from the IVUS rf-data (sampled at 100 MHz in 12 bits) that were obtained from a digital interface. Qualitative and quantitative analysis of the elastograms obtained from fresh and frozen specimens measured at 23 degrees C reveals that storage of the specimen at -80 degrees C has no significant influence. In vitro experiments can be performed at room temperature after storage of the tissue at -80 degrees C without significant affection of the information with respect to measuring fresh ex vivo material at body temperature.

Journal Article↗

PubMed2002

Morphological and mechanical information of coronary arteries obtained with intravascular elastography; feasibility study in vivo.

AIMS: Plaque composition is a major determinant of coronary related clinical syndromes. In vitro experiments on human coronary and femoral arteries have demonstrated that different plaque types were detectable with intravascular ultrasound elastography. The aim of this study was to investigate the feasibility of applying intravascular elastography during interventional catheterization procedures. METHODS AND RESULTS: Data were acquired in patients (n=12) during PTCA procedures with an EndoSonics InVision echoapparatus equipped with radiofrequency output. The systemic pressure was used to strain the tissue, and the strain was determined using cross-correlation analysis of sequential frames. A likelihood function was determined to obtain the frames with minimal motion of the catheter in the lumen, since motion of the catheter prevents reliable strain estimation. Minimal motion was observed near end-diastole. Reproducible strain estimates were obtained within one pressure cycle and over several pressure cycles. Validation of the results was limited to the information provided by the echogram. Strain in calcified material (0.20%+/-0.07) was lower (P<0.001) than in non-calcified tissue (0.51%+/-0.20). CONCLUSION: In vivo intravascular elastography is feasible. Significantly higher strain values were found in non-calcified plaques than in calcified plaques.

Adult↗

PubMed2001

Advancing intravascular ultrasonic palpation toward clinical applications.

This paper describes the first reported attempt to develop a real-time intravascular ultrasonic palpation system. We also report on our first experience in the catherization laboratory with this new elastographic imaging technique. The prototype system was based on commercially available intravascular ultrasound (US) scanner that was equipped with a 20-MHz array catheter. Digital beam-formed radiofrequency (RF) echo data (i.e., 12 bits, 100 Hz) was captured at full frame rate from the scanner and transferred to personal computer (PC) memory using a fast data-acquisition system. Composite palpograms were created by applying a one-dimensional (1-D) echo tracking technique in combination with global motion compensation and multiframe averaging to several pairs of RF echo frames that were obtained in the diastolic phase of the cardiac cycle. The quality of palpograms was assessed by conducting experiments on vessel phantoms and on patients. The results demonstrated that robust and consistent palpograms could be generated in almost real-time using the proposed system. Good correlation was observed between low strain values and regions of calcification as identified from the intravascular US (IVUS) sonograms. Although the clinical results are clearly preliminary, it was concluded that the prototype system performed sufficiently well to warrant further and more in-depth clinical investigation.

Calcium↗

PubMed2000

Flow estimation using an intravascular imaging catheter.

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.

Animals↗

PubMed2000

Optical imaging of contrast agent microbubbles in an ultrasound field with a 100-MHz camera.

Ultrasound (US) contrast agents, used in the field of medical diagnosis, contain small microbubbles of a mean diameter of about 3 microm. The acoustic behavior of these bubbles in US field has been subject to many investigations. In this study, we propose a method to visualize the behavior of the bubbles in a 0.5-MHz US field under a microscope with a frame rate of 4 MHz. For low acoustic pressures (peak negative pressure of 0.12 MPa), the radius-time curve as measured from the optical images is in agreement with the theory. For higher acoustic pressures (peak negative pressure of 0.6 MPa), the recorded radius is significantly larger than predicted by theory and sudden change in the bubbles shapes has been noticed. The proposed method enables the study and characterization of individual bubbles and their encapsulation. It is expected that this will open new areas for quality control, US contrast imaging and US-guided drug delivery.

Contrast Media↗

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↗

PubMed1999

Echo decorrelation estimated from signal powers.

Volume flow can be estimated from the decorrelation of radiofrequency (RF) intravascular ultrasound signals. The method is based on a rather time-consuming process that measures the decorrelation slope from a time signal sequence. To improve the speed of flow processing, a more efficient way of estimating the flow velocity from the ratio between the power of the temporal averaged signal and the mean signal power is described in this paper. The relationship between the signal power-ratio index and the decorrelation slope was analyzed and tested using computer-simulated data. Volumetric flow data obtained with the power-ratio method were compared to those derived from the decorrelation slope in five patients. Results of the comparison studies indicate that no significant differences in flow measurements were found between the two methods, but the power-ratio method is able to improve the processing speed significantly.

Blood Flow Velocity↗

PubMed1998

Blood flow assessment with intravascular ultrasound catheters: the ideal tool for simultaneous assessment of the coronary haemodynamics and vessel wall?

We present the potentials of a novel method of intracoronary flow visualization and quantification that is based on conventional intravascular ultrasound (IVUS) imaging catheters. The quantification of flow is obtained from analysis of the rate of decorrelation of digitized radiofrequency ultrasound echo signals. Flow information is superimposed on the IVUS image using a colour scale. Integration of the blood velocity components normal to the scan plane permits calculation of the volume flow. Validation using IVUS and electromagnetic (EM) flowmeter recordings were obtained in vivo from instrumented pigs. IVUS flow (IVUS(f)) compared favourably to EM flow (EM(f)): IVUS(f)=1.0 EM(f)+5.72 cc/min, r2=0.98. Clinical results for the first five patients investigated are reported. A Doppler wire was used to measure the flow in four coronary arteries and one renal artery in baseline and hyperaemia conditions. IVUS flow and derived coronary flow reserve (CFR) demonstrated a very good agreement with the data derived from the combination of quantitative angiography and velocity when measured with the Doppler wire (DOP(f)): IVUS(f)=1.01 DOP(f)-20 cc/min, r2=0.90 and IVUS(cfr)=1.03 DOP(cfr)-0.03, r2=0.93. This demonstrates that simultaneous morphological and physiological assessment of coronary or peripheral arteries with one IVUS catheter is feasible. This method should be very useful for the evaluation of intermediate coronary stenoses or the results of revascularization procedures.

Angina Pectoris↗

PubMed1997

Influence of data processing on cyclic variation of integrated backscatter and wall thickness in stunned porcine myocardium.

This study was performed to investigate the relationship between the cyclic variation of integrated backscatter and myocardial wall thickening in stunned myocardium. Different definitions of cyclic variation were evaluated to be able to compare with other studies. Ultrasound data were acquired from 10 open-chested Yorkshire pigs (25-33 kg) at baseline, during regional ischemia and during 30 min of stunning, using a broadband ultrasound transducer (3-7 MHz) sutured directly upon the left ventricular myocardial wall. Cyclic variation of integrated backscatter and myocardial wall thickening were calculated using three definitions obtained from the literature. Independent of the definition, cyclic variation of wall thickness and integrated backscatter were blunted during acute ischemia and returned transiently to or above baseline during the first minute of reperfusion, followed by a gradual decrease to a level under baseline during stunning. An early return of the cyclic variation of the integrated backscatter was not observed in pigs, independent of the data processing used. The relationship between integrated backscatter and wall thickness was maintained.

Animals↗

PubMed1996

The relationship between myocardial integrated backscatter, perfusion pressure and wall thickness during isovolumic contraction: an isolated pig heart study.

To investigate the independent effect of myocardial wall thickness and myocardial perfusion pressure on integrated backscatter, experiments were designed in which integrated backscatter of normally perfused myocardial tissue was measured while changes in wall thickness during the cardiac cycle were reduced to a minimum. In nine blood-perfused isolated pig hearts, perfusion pressure was uncoupled from left ventricular pressure generation (Langendorff method) and isovolumic contraction and relaxation were realized by inserting a noncompressible water-filled balloon into the left ventricle. In a first experiment, at constant perfusion pressure (85 mmHg), the integrated backscatter (3-7 MHz), the myocardial wall thickness and the left ventricular pressure were determined simultaneously at various balloon volumes (5-25 mL). A quasistatic increase of balloon volume by 50% resulted in an average decrease of wall thickness of 6.5% (p < 0.01) and a mean increase in the integrated backscatter level of 1.1 dB (p < 0.01). Integrated backscatter levels increased statistically significant by 0.14 +/- 0.014 dB per percent decrease of wall thickness. Measurements of percentage end-systolic myocardial wall thickening ranged from -10% to +10%, mean 0.15 +/- 4.5% (NS from zero); whereas cyclic variation of integrated backscatter ranged from -3.9 to +3.9 dB, mean 0.19 +/- 1.5 dB (NS from zero). In a second experiment, at a constant midrange balloon volume, the same parameters were determined simultaneously at various perfusion pressures (20-120 mmHg). An increase in perfusion pressure by 50% resulted in a small but statistically significant increase of 1.5% in myocardial wall thickness, which could be explained by an increase of intravascular volume. The integrated backscatter levels did not change statistically significantly. Measurements of percentage end-systolic myocardial wall thickening ranged from -8.9 to +7.8%, mean 0.13 +/- 4.0% (NS from zero); whereas cyclic variation of integrated backscatter ranged from -1.8 to +4.2 dB, mean 0.37 +/- 1.3 dB (NS from zero). The magnitude of cyclic variation of integrated backscatter of myocardial tissue in a contractile state is reduced if myocardial muscle is prevented from normal thickening. In addition, changes in intravascular volume during the cardiac cycle have a negligible influence on the absolute backscatter level or its cyclic variation. We conclude, if only wall thickness and perfusion pressure are involved, that integrated backscatter is mainly determined by myocardial wall thickness.

Animals↗

PubMed1993

Ultrasound myocardial integrated backscatter signal processing: frequency domain versus time domain.

In the literature, different forms of measuring the ultrasound power returned by myocardial tissue are reported. Frequency domain methods will give the maximum frequency information, whereas time domain methods are limited in bandwidth, but more practical to realize. It was the purpose of this study to compare the various methods of signal processing. High frequency ultrasound signals from a pig's myocardium, digitally recorded during normal contractile performance, were analyzed by six different methods of signal processing to obtain estimates of backscatter power. The myocardial tissue characterization parameters studied were the integrated power as well as its cyclic variation during the cardiac cycle. A total number of 8109 ultrasound traces obtained in 16 pigs were processed. The study included three signal processing methods in the frequency domain: frequency compensated integrated backscatter calculated over both a large (4 MHz, method 1) as well as a small frequency bandwidth (2 MHz, method 2) and uncompensated integrated backscatter (method 3), and three methods in the time domain: high frequency signal squared and integrated (method 4), mean rectified signal level (method 5) and mean signal level after logarithmic compression and envelope detection (method 6). The random measurement variation (including beat-to-beat variation) was analyzed as well as the paired differences of the backscatter parameters obtained by the respective methods as compared with the only theoretically correct method in the time domain (method 4). The magnitudes of the random measurement variation expressed as a standard deviation (SD) were comparable (range 0.93-1.2 dB) except for method 6 (0.61 dB), where the measurement variation is decreased by the logarithmic compression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

The relative contributions of myocardial wall thickness and ischemia to ultrasonic myocardial integrated backscatter during experimental ischemia.

The purpose of this study was to assess the empirical relationship between myocardial integrated backscatter (IB) and myocardial wall thickness (WT) in normal myocardium. A second object was to estimate the additional contribution to acute ischemic integrated backscatter levels given this relationship. Myocardial IB measurements and simultaneous myocardial WT measurements were made in 16 open-chested pigs with intact coronary circulation (normal myocardium) and 10 min after the flow in the left anterior descending coronary artery had been reduced to 20% of its baseline value (ischemic myocardium). Measurements were made 50 times during one cardiac cycle and averaged over 10 cardiac cycles. IB and WT measurements were normalized with respect to the nonischemic end-diastolic values. The relationship between IB and WT in normal myocardium was estimated in every individual pig by simple linear regression. Estimates of IB during ischemia were calculated on the basis of this relationship and the ischemic WT measurements. Differences of the estimator and the actual measurement made during ischemia depict the actual contribution of the state of acute ischemia, without the influence of WT. The slope of the relationship between IB and WT during normal myocardial contraction ranged from -0.16 to 0.03 dB/% (mean = -0.036 dB/%, SD = 0.06 dB/%). The additional contribution of ischemia ranged from -3.84 to 5.56 dB (mean = 0.31 dB, SD = 2.72 dB). It was concluded that the average contribution of ischemia to IB measurements is insignificant if the IB dependency on WT is removed from the data and that the higher level of ischemic IB measurements can be explained by the decrease in wall thickness during ischemia and not by the ischemia itself.

Animals↗

PubMed1991

Influence of attenuation on measurements of ultrasonic myocardial integrated backscatter during cardiac cycle (an in vitro study).

The purpose of this study was to investigate the dependence of ultrasonic integrated backscatter (IB) and attenuation in myocardium on wall thickness in a state of acute ischemia. Therefore, an in vitro experiment was set up in which attenuation, IB and wall thickness of a piece of freshly excised myocardium could be measured almost simultaneously. The myocardium was taken from 11 Yorkshire pigs (25-30 kg) that were killed less than 45 min before the experiment. The myocardium was placed in the far field of an ultrasound transducer (3.2-7.2 MHz) and then compressed by a stainless steel sphere. Data were processed off-line. Backscatter and attenuation were also measured as a function of frequency at 100% and 75% wall thickness, respectively. Both attenuation and IB varied during compression. Attenuation had an initial value of 2.19 +/- 0.76 dB/cm and a slope of 0.015 +/- 0.017 dB/cm% wall thickness. IB had an initial value of -76.9 +/- 2.7 dB and a slope of -0.12 +/- 0.07 dB/% wall thickness. After subtracting the influence of the attenuation from the IB the initial value of IB was -74.0 +/- 2.7 dB and the slope -0.08 +/- 0.07 dB/% wall thickness. Attenuation appeared to have a linear dependency on frequency. Backscatter appeared not to increase with increasing frequency without correction of the spectrum for the frequency dependent insonified volume.

Animals↗

PubMed1990

Ultrasonic myocardial integrated backscatter and myocardial wall thickness in animal experiments.

The purpose of this study was to distinguish between normal and ischemic myocardium using ultrasonic integrated backscatter (IB) measurements and to relate IB with myocardial wall thickness. IB was measured in 9 open-chested Yorkshire pigs (24-30 kg) before, after 30 minutes of partial occlusion of the proximal left anterior descending coronary artery (LADCA), and after 60 minutes of subsequent reperfusion. The ultrasound transducer (4 MHz) was sutured onto the epicardial surface perfused by the LADCA. IB measurements were made with a repetition rate of 50 times per heart rate simultaneously with a left ventricular pressure signal. Myocardial wall thickness was measured off-line. The measurements of integrated backscatter, left ventricular pressure and wall thickness were based on mean values of ten subsequent cardiac cycles. End-systolic IB measurements were 5.3 dB higher during occlusion as compared to the reference measurements (7.1 +/- 3.2 dB versus 1.8 +/- 2.6 dB; p = 0.002). No statistically significant differences were found in end-systolic IB measurements. End-systolic wall thickness was 5 mm smaller during occlusion as compared to the reference measurements (7.2 +/- 1.4 mm versus 12.2 +/- 1.2 mm; p less than 0.001). Simple linear regression analysis showed a statistically significant inverse relationship between IB measurements and wall thickness in 21 out of the 23 sequences in which wall thickness could be measured. End-systolic IB measurements are favourable to distinguish acute ischemic myocardium from normal myocardium. There is a distinct inverse relationship between IB and myocardial wall thickness.

Animals↗

PubMed1989

Intravascular echographic assessment of vessel wall characteristics: a correlation with histology.

In vivo application of intravascular high frequency ultrasonic imaging for peripheral and coronary artery disease is a promising technique for vascular surgeons, radiologists and cardiologists. This report demonstrates in vitro results obtained with a high frequency imaging catheter (40 MHz) in 70 human specimens including arteries with and without atherosclerosis, veins, coronary artery bypass grafts and vascular prosthetic material. Correlation between the ultrasonic images and the histologic characteristics of the corresponding vessel wall tissue and lumen geometry was established. In addition, the effect of intervention techniques i.e. balloon angioplasty, spark erosion and laser were studied with ultrasound and histology. It is anticipated that development of such a catheter imaging technique has potential for diagnostic imaging and for combination with therapeutic systems.

Angioplasty, Balloon↗

PubMed1989

Arterial wall characteristics determined by intravascular ultrasound imaging: an in vitro study.

The feasibility of assessing arterial wall configuration with an intravascular 40 MHz ultrasound imaging device was investigated in an in vitro study of 11 autopsy specimens of human arteries. The system consists of a single element transducer, rotated with a motor mounted on an 8F catheter tip. Cross sections obtained with ultrasound were matched with the corresponding histologic sections. The arterial specimens were histologically classified as of the muscular or elastic type. Muscular arteries interrogated with ultrasound presented with a hypoechoic media, coinciding with the smooth muscle cells. In contrast, the media of an elastic artery densely packed with elastin fibers was as echogenic as the intima and the adventitia. On the basis of the cross-sectional image, it was possible to determine the nature of the atherosclerotic plaque. The location and thickness of the lesion measured from the histologic sections correlated well with the data derived from the corresponding ultrasound images. This study indicates that characterization of the type of artery and detection of arterial wall disease are possible with use of an intravascular ultrasound imaging technique.

Adult↗