Biomedical subjects

Marek Belohlavek

Publications and source records attributed to Marek Belohlavek.

At least 37 records · Page 2Linked to original sources

PubMed2004

Strain rate and strain: a step-by-step approach to image and data acquisition.

The advent of strain and strain rate imaging in clinical echocardiography prompted an examination of proper techniques for image acquisition and analysis. For this promising and relatively new method of assessing myocardial performance to be successful in diagnostic echocardiography, close adherence to a standardized method is imperative. This article provides the echocardiographer with a step-by-step approach.

Algorithms↗

PubMed2004

Both systolic and diastolic dysfunction characterize nonischemic inhibition of myocardial energy metabolism: an experimental strain rate echocardiographic study.

BACKGROUND: Ischemia is primarily a metabolic event. However, regional functional changes can be affected by structural alterations. We developed an experimental model of sole myocardial energy metabolism inhibition and characterized the resulting regional dysfunction. METHODS: In 12 pigs, we regionally inhibited creatine kinase (CK) and, consequently, myocyte high-energy phosphate transfer by intracoronary administration of iodoacetamide. Myocardial biopsies for CK activity and structural analyses and strain rate (SR) echocardiography scans were obtained at baseline and 60 minutes after iodoacetamide administration. Plasma levels of the CK isoenzyme MB and troponin I were assessed to determine possible myocardial damage. RESULTS: CK activity in the iodoacetamide-perfused myocardium decreased to 0.5% of the original value and was accompanied by a reduction in peak systolic SR ( P < .0001), end-systolic strain ( P < .0001), and peak SRs of myocardial early and late filling waves ( P < .0001). Microscopy showed contracture without sarcomere disruption. Plasma levels of CK isoenzyme MB and troponin I did not change. CONCLUSIONS: Regional inhibition of myocyte energetics leads to both systolic and diastolic dysfunction by SR echocardiography, but the presence of a residual phosphotransfer protects microstructural integrity.

Animals↗

PubMed2004

Spectral normalization for ultrasonic contrast microbubble detection.

Ultrasonic contrast agents consisting of microbubbles are used to assess tissue perfusion. The microbubbles are highly reflective and nonlinear and thus produce harmonics that are stronger than those from tissues. However, the magnitude of harmonic signals resulting from a region with microbubbles also depends on the acoustic pressure of incident ultrasound and the attenuation of intervening tissues in the ultrasound path. Therefore, the harmonic magnitude, as used in traditional harmonic imaging, may not be a reliable indicator of the presence or absence of microbubbles, and hence, tissue perfusion. To compensate for these effects, we present two parameters defined as the ratio of the harmonic to the fundamental component (HFR) and the ratio of the harmonic to squared fundamental (HSFR). A simplified model is used to illustrate the usefulness of these two parameters. Experiments show that both parameters improve detection of microbubbles and that HSFR performs better than HFR.

Contrast Media↗

PubMed2003

Myocardial contractility by strain echocardiography: comparison with physiological measurements in an in vitro model.

Strain echocardiography (SE) provides the rate and extent of myocardial segment shortening and lengthening. Thus we hypothesized that SE will noninvasively provide estimates of shortening velocity (SV) and length change (delta L). We compared SE-derived strain rate (SR) and strain (epsilon) to force/length transducer-derived SV and percent delta L in isolated muscle strips at multiple load levels and under varying conditions. Electrically stimulated contractions in left ventricular muscle strips (n = 20) were simultaneously recorded with a force/length transducer (to measure SV and percent delta L) and an ultrasound transducer (to measure SR and epsilon). Measurements were made at baseline, after inotropic stimulation, and during hypoxia at multiple load clamp levels (simulating multiple levels of afterload). Despite a difference in absolute numbers, there was a close correlation between SR and SV at baseline (R2 = 0.95), with dobutamine treatment (R2 = 0.99), and during hypoxia (R2 = 0.99). SR was load dependent at baseline (r = 0.98), with dobutamine treatment (r = 0.99), and during hypoxia (r = 0.92). Similarly, there was a close correlation between epsilon and delta L at baseline (R2 = 0.99), with dobutamine treatment (R2 = 0.96), and during hypoxia (R2 = 0.87). Percent epsilon was load dependent at baseline (r = 0.98), with dobutamine treatment (r = 0.98), and during hypoxia (r = 0.94). Bland-Altman analysis revealed a systematic overestimation of SV by SE-derived SR at baseline and with dobutamine treatment. There was no bias with SR measurements during hypoxia or with epsilon measurements. SE closely tracks standard physiological parameters of regional contractile function, such as SV and delta L, under conditions of varying afterload.

Animals↗

PubMed2003

Automated quantitative analysis of the shift of frequency spectra generated by attenuated signals from contrast microbubbles.

The ultrasound-induced harmonic microbubble response spectrum is known to shift to lower frequencies with increasing tissue attenuation. We hypothesized that this shift could be reproducibly detected in received broadband radiofrequency spectra. We used an automatic Gaussian curve-fitting technique to measure the mean harmonic response generated by three different contrast agents at six incremental levels of attenuation. Analytical curve fitting identified a consistent, reproducible, and statistically significant shift in mean harmonic frequency with increasing attenuation. The presented method could be a step toward attenuation estimation by contrast harmonic imaging; optimization of harmonic signal reception by ultrasound systems; and, ultimately, automatic detection of contrast agents in tissue.

Acoustics↗

PubMed2003

Single-plane and biplane echocardiography: use of targeted scan planes improves the estimates of left ventricular volume and shape for analysis of postinfarction remodeling.

OBJECTIVE: Acute myocardial infarction and subsequent left ventricular (LV) remodeling induce complex geometric changes quantifiable by 3-dimensional (3D) echocardiography. Our objective was to determine accurate 2-dimensional echocardiographic techniques for analysis of diastolic and systolic LV volume and shape in remodeled hearts. METHODS: We obtained 3D apical scans from 16 patients at the acute stage, and at 1 and 6 months after acute myocardial infarction. LV volumes were calculated by 7 methods: (1) Teichholz; (2) Teichholz including the infarcted area; (3) single-plane area-length (AL) using a 2-chamber (2CH) view; (4) single-plane AL using a 4-chamber (4CH) view; (5) single-plane AL using a view including the infarcted area; (6) biplane AL using 2CH and 4CH views; and (7) biplane AL using a view including the infarction region and corresponding orthogonal view (method ALBMIO). LV shape was assessed by 5 methods: (1) a 2CH view; (2) a 4CH view; (3) a single-plane view including the infarcted area; (4) biplane (2CH and 4CH) views; and (5) biplane views including the infarction region and corresponding orthogonal view (method BMIO). RESULTS: For end-diastolic and end-systolic LV volume assessments, all 7 methods correlated with the 3D reference, but method ALBMIO performed best (end-diastolic: r = 0.931, bias = 17.4 mL; end-systolic: r = 0.946, bias = 11.2 mL). For LV shape assessments, method BMIO showed the smallest difference from the 3D reference. CONCLUSIONS: With 2-dimensional echocardiographic techniques, quantitative analysis of LV volume and shape is most accurate when a component scan plane is targeted through the infarcted myocardial region.

Aged↗

PubMed2003

Clinical applications of strain rate imaging.

Myocardial strain (epsilon) is a dimensionless index of change in myocardial length in response to an applied force. epsilon Rate (SR) is the rate of change of length and is usually obtained as the time derivative of the epsilon signal. In echocardiography, SR is calculated as the difference between 2 velocities normalized to the distance between the 2 velocities. SR imaging (SRI) has a theoretic advantage over Doppler tissue imaging in that SRI is relatively immune to cardiac translational motion and tethering. Therefore, SRI may be superior to Doppler tissue imaging in quantitative assessment of regional myocardial function and may find clinical application in the interrogation of coronary artery disease. The high frame rates of SRI have also renewed interest in timings of global and regional mechanical events, and their potential clinical applications. The high temporal resolution allows SRI to depict regional systolic and diastolic asynchrony. Ongoing clinical trials will determine the sensitivity, specificity, and accuracy of SRI parameters for a variety of clinical conditions. Potential clinical applications include investigation of ischemia (at rest and with stress), myocardial viability, and altered global and regional systolic and diastolic function in cardiomyopathies. Suboptimal signal quality remains a major limitation of strain imaging, and advances in data acquisition and postprocessing capabilities will help determine its future incorporation into standard regional myocardial assessment.

Blood Flow Velocity↗

PubMed2002

Higher myocardial strain rates during isovolumic relaxation phase than during ejection characterize acutely ischemic myocardium.

OBJECTIVES: The aim of this study was to define an index that can differentiate normal from ischemic myocardial segments that exhibit postsystolic shortening (PSS). BACKGROUND: Identification of ischemia based on the reduction of regional systolic function is sometimes challenging because other factors such as normal nonuniformity in contraction between segments, tethering effect, pharmacologic agents, or alterations in loading conditions can also cause reduction in regional systolic deformation. The PSS (contraction after the end of systole) is a sensitive marker of ischemia; however, inconsistent patterns have also been observed in presumed normal myocardium. METHODS: Twenty-eight open-chest pigs underwent echocardiographic study before and during acute myocardial ischemia induced by coronary artery occlusion. Ultrasound-derived myocardial longitudinal strain rates were calculated during systole (S(SR)), isovolumic relaxation (IVR(SR)), and rapid filling (E(SR)) phases in both ischemic and normal myocardium. Systolic strain (epsilon(sys)) and postsystolic strain (epsilon(ps)) were calculated by integrating systolic and postsystolic strain rates, respectively. RESULTS: During ischemia, S(SR), E(SR), and epsilon(sys) in ischemic segments were significantly lower (in magnitude) than in nonischemic segments or at baseline. However, some overlap occurred between ischemic and normal values for all three parameters. At baseline, 18 of 28 animals had negative IVR(SR) (i.e., PSS) in at least one segment. During coronary artery occlusion, IVR(SR) became negative and larger in magnitude than S(SR) in all ischemic segments. The IVR(SR)/S(SR) and epsilon(ps) best differentiated ischemic from nonischemic segments. CONCLUSIONS: In the presence of reduced regional systolic deformation, a higher rate of PSS than systolic shortening identifies acutely ischemic myocardium.

Animals↗

PubMed2002

Time to onset of regional relaxation: feasibility, variability and utility of a novel index of regional myocardial function by strain rate imaging.

OBJECTIVES: Time to onset of regional relaxation (T(R)) has been proposed as a novel index of regional myocardial function. This study sought to prospectively establish the feasibility and variability of T(R) in healthy volunteers (CONTROL) and to examine its utility in patients with inducible ischemia (PATIENT). BACKGROUND: Strain rate imaging (SRI) depicts myocardial deformation and enables quantitation of regional myocardial function with high temporal and spatial resolution. Thus, regional mechanical events can be accurately timed with SRI. The time point of regional transition from contraction to relaxation is altered in pathologic states. METHODS: Resting mean segmental T(R) was determined in 60 subjects: 20 in the CONTROL group and 40 in the PATIENT group. T(R) was also measured at peak dobutamine stress in the PATIENT group. An automated image analysis program determined the time point of transition from regional contraction to relaxation activity, and calculated T(R), defined as the time, in milliseconds, from the electrocardiogram R-wave to this transition point. RESULTS: Automated T(R) measurements were feasible in more than 90% of the segments in CONTROL and PATIENT groups. Mean T(R) was 353 +/- 24 ms and was shorter in the mid segments compared to apical and basal segments. Intra- and interobserver variability were low (6% and 9%, respectively). In the PATIENT group, the percent decrease in T(R) during dobutamine stress was significantly higher in normal compared to ischemic segments (30% vs. 19%, respectively, p = 0.01). A percent change >20% in T(R) identified patients with an ischemic response during dobutamine infusion (sensitivity 92%, specificity 75%). CONCLUSIONS: T(R), a novel quantitative index of regional myocardial function, can be determined with low variability and satisfactory feasibility in routine clinical settings. Percent change in T(R) identifies ischemic segments during dobutamine stress echocardiography (DSE) and may allow quantitative assessment of DSE.

Adult↗

PubMed2002

Strain rate imaging for assessment of regional myocardial function: results from a clinical model of septal ablation.

BACKGROUND: Regional myocardial function assessment is essential in the management of coronary artery disease (CAD). Tissue Doppler imaging (TDI) by depicting local myocardial motion can potentially quantify regional myocardial function. Strain rate imaging (SRI) that depicts regional deformation is less susceptible to cardiac translation and tethering and may be superior to TDI for regional function analysis. We examined regional myocardial function using TDI and SRI in a unique clinical model of a small, discrete myocardial infarction. METHODS AND RESULTS: Ten patients with severely symptomatic septal hypertrophy underwent basal septal ablation via intracoronary alcohol injection and had TDI and SRI pre- and postablation. Invasive hemodynamics showed no appreciable change in global function. Peak systolic strain rate was significantly lower postablation versus preablation (-0.5 versus -1.2 s(-1), P<0.001) and when comparing infarct and noninfarct areas (-0.5 versus -1.5 s(-1), P<0.001). In contrast, peak systolic tissue velocities were similar pre- and postablation (3.9 versus 2.9 cm/s, P=0.16) and between infarct and noninfarct areas (2.9 versus 2.2 cm/s, P=0.13). SRI analysis demonstrated reduced systolic function in the peri-infarct zone and preserved systolic function in the remote nonischemic zone. CONCLUSION: In the clinical setting of a small, discrete infarct unaccompanied by changes in global function, SRI accurately depicted changes in regional function. These data suggest that SRI may be the optimal method for objective, quantitative assessment of regional myocardial dysfunction.

Cardiac Catheterization↗

PubMed2002

Rapid quantitative assessment of myocardial perfusion: spectral analysis of myocardial contrast echocardiographic images.

We described a novel rapid spectral analysis technique performed on raw digital in-phase quadrature (IQ) data that quantitatively differentiated perfused from nonperfused myocardium based on the simultaneous comparison of local fundamental and harmonic frequency band intensity levels. In open-chest pigs after ligation of the left anterior descending coronary artery (LAD) and continuous venous contrast infusion, the fundamental-to-harmonic intensity ratio (FHIR) for samples placed within the left ventricular (LV) cavity (10.8 +/- 1.7 dB) and perfused myocardium (13.7 +/- 1.6 dB) were significantly (P <.001) lower than for nonperfused myocardium (27.1 +/- 2.9 dB). In attenuated images, the FHIR for the LV cavity and perfused myocardium were also significantly (P <.05) lower than for the nonperfused myocardium (21.4 +/- 3.0 dB, 34.4 +/- 3.2 dB, and 40.2 +/- 4.4 dB, respectively). Spectral properties of contrast microbubbles, as characterized by the FHIR, allow for rapid quantitative assessment of myocardial perfusion from data contained in a single-image frame, without requiring background image subtraction and image averaging.

Acute Disease↗

PubMed2002

Radio frequency dual-spectra analysis of regional myocardial perfusion: Comparison with harmonic densitometric method.

Our objective was to compare harmonic-to-fundamental frequency ratio peak (HFRp) analysis with conventional harmonic gray-scale densitometric analysis on the basis of ability to eliminate heterogeneity in ultrasound signals. Broadband radio frequency and harmonic data were obtained by using intermittent short-axis scans in 10 open-chest pigs before and during infusion of contrast microbubbles. HFRp and gray-scale intensity values were measured in 6 segments of left ventricular myocardium. In baseline images, the influence of anisotropy on HFRp values was significantly less than that in gray-scale intensities. In perfusion assessment with subtraction, contrast heterogeneity in HFRp values was significantly smaller than that in gray-scale intensities. The increase in HFRp values after subtraction was significantly greater than that in gray-scale intensities in lateral (P <.001), posterior (P <.0001), and inferior (P <.01) myocardium. HFRp analysis can compensate for baseline myocardial anisotropy and regional contrast heterogeneity. With background subtraction, HFRp analysis allows better quantification of myocardial perfusion.

Absorptiometry, Photon↗

PubMed2002

Epicardial ultrasound guidance of coronary catheter placement in an experimental animal model.

We evaluated epicardial ultrasonography with a 10-MHz transducer for coronary catheter guidance in 18 normal pigs. A modified long-axis view of the aortic root was used to direct a coronary catheter into the root, and then with a short-axis view of the aortic root, the catheter tip was placed selectively into either the right or the left main coronary artery. Subsequently, with modified coronary views, an angioplasty infusion catheter was guided with precision to the exact location desired in the coronary artery. Position was confirmed by direct visualization and palpation of the epicardial vessels, and the procedure was completed within 5 to 15 minutes without complication. Epicardial ultrasonography is a suitable alternative to fluoroscopy for guidance of coronary catheter placement in an open-chest experimental model.

Animals↗

PubMed2002

Strain and strain rate echocardiography.

Strain and strain rate echocardiography is an emerging technique for assessing myocardial systolic and diastolic function. It is envisioned that this modality could change the quantitative assessment of regional wall motion and improve the accuracy and reproducibility of test readings. Myocardial strain and strain rate can detect inducible ischemia and at earlier stages than visual estimation of wall motion or wall thickening parameters. Changes in systolic strain rate and strain have potential to discriminate between different myocardial viability states. Measurement of diastolic rate of deformation can differentiate physiologic from pathologic hypertrophy, and restrictive from constrictive cardiomyopathy. This article reviews basic principles and current experimental and clinical applications of strain and strain rate echocardiography.

Animals↗

PubMed2002

Dual-spectra ultrasonography: an attenuation-compensating technique for myocardial perfusion analysis.

OBJECTIVE: To validate the harmonic-fundamental frequency ratio peak for user-independent differentiation of myocardial perfusion under clinically relevant levels of signal attenuation. METHODS: Radio frequency data were obtained by using apical long-axis scans in 11 open-chest pigs during continuous infusion of a contrast agent after left anterior descending artery occlusion. Silicone pads were interposed between the transducer and the heart to simulate levels of thoracic wall attenuation. Samples of image data from perfused and nonperfused regions were collected; values using harmonic-fundamental frequency ratio peak and conventional harmonic gray scale intensity techniques were calculated. RESULTS: At each attenuation level, the harmonic-fundamental frequency ratio peak value of perfused myocardium was higher than that of nonperfused myocardium (P < .0001). The variance of these values was smaller than that of the gray scale intensity values (P < .0001), with smaller overlap between harmonic-fundamental frequency ratio peak values differentiating perfused and nonperfused regions. In the receiver operating characteristic curves, this analysis had better diagnostic performance than gray scale analysis. In the optimal cutoff value, harmonic-fundamental frequency ratio peak analysis provided 87% sensitivity and 91% specificity; gray scale analysis had 80% sensitivity and 78% specificity. CONCLUSIONS: Harmonic-fundamental frequency ratio peak analysis differentiated perfused from nonperfused myocardium under clinically relevant attenuation conditions and provided higher sensitivity and specificity for perfusion determination in attenuated myocardium than did gray scale intensity analysis.

Animals↗

PubMed1999

Rapid Three-Dimensional Myocardial Contrast Echocardiography: Volumetric Quantitation of Nonperfused Myocardium After Intravenous Contrast Administration.

Current acquisition methods for quantitative three-dimensional myocardial contrast echocardiography require long acquisition times and therefore require the invasive administration of deposit contrast agents administered intra-arterially or into the left atrium. This study addressed the feasibility of obtaining accurate and precise quantitative volumetric measurements of nonperfused myocardium after an intravenous bolus of echocardiographic contrast agent using a rapid three-dimensional myocardial contrast echocardiographic acquisition technique. An open-chest pig model of acute left anterior descending coronary artery (LAD) occlusion was used. After LAD ligature, an intravenous bolus of contrast agent was given and images were obtained over a 12-second period using a continuously rotating transducer placed at the apical position. There was no significant microbubble destruction during the rotational acquisition period as measured by differences in mean gray scale values of apical, mid, and basal myocardial regions between the first and last image frames of acquisition. Calculated volumes of nonperfused myocardium demonstrated significant agreement and correlation (mean difference +/- SD = -0.30 +/- 1.71 cm(3); r = 0.89; P < 0.01; y = 1.06x - 1.08) with anatomic specimens. When expressed as percent of total LV volume being nonperfused, the mean difference +/- SD was 2.1 +/- 3.6%, r = 0.94, P < 0.01, and y = 1.33x - 4.08. We conclude that accurate and precise measurements of nonperfused myocardium after an acute LAD coronary artery occlusion can be obtained after the intravenous bolus administration of a contrast material when a rapid 12-second acquisition with a continuously rotating transducer is used.

Journal Article↗

PubMed1998

Three-Dimensional Imaging Used for Virtual Dissection, Image Banking and Physical Replication of Anatomy and Physiology.

Historically, techniques of dissection have been used to aid in our understanding of human anatomy, physiology, and pathology. However, these techniques alter the structures and fine details being studied. New advances in computer technology, imaging equipment, data acquisition, processing, storage, and display now allow multidimensional imaging. Interactive computer programs can electronically display both static three-dimensional and higher-dimensional images that retain features such as motion, pressure, and temporal change. Multidimensional images can be reconstructed and manipulated using different holographic, stereolithographic, or interactive two-dimensional displays. We describe the unique potential of multidimensional reconstruction, virtual dissection, and replication of cardiovascular structures using ultrasound data. Ultrasound technology has the advantage of depicting both anatomy and physiology. The ability to perform virtual dissection and surgery in the living patient without disruption of anatomy or physiology provides the clinician with a powerful new tool for diagnosis, teaching, and therapeutics.

Journal Article↗

PubMed1998

Three-Dimensional Echocardiography: Precision and Accuracy of Left Ventricular Volume Measurement Using Rotational Geometry with Variable Numbers of Slice Resolution.

We developed a new, rapid (6 seconds) acquisition technique allowing collection of approximately six through nine apical rotational tomograms for three-dimensional (3-D) echocardiography. To justify an appropriate sampling density for precise and accurate measurement of chamber volumes in left ventricles with complicated shape, we designed a validation study in vitro using six canine heart specimens with irregular, asymmetric left ventricles with known volumes (28.5 to 104.3 ml; mean, 71.2 ml). The number of equally spaced slices were incrementally deleted from the original high resolution scans (48 slices) to 2 slices in 3-D reconstruction. We created subgroups of 48- and 36-, 24- and 16-, 12- and 8-, 6- and 4-, and 3- and 2-component slices to compare left ventricular (LV) volumes measured in 3-D images with different slice resolution with the reference standard measured in the specimen. The accuracy and precision of LV volume were relatively constant in the subgroup of 4- and 6- through 36- and 48-component slices. When the subgroup with 6- and 4-component slices was used, the correlation was r = 0.991, P < 0.0001, root-mean-square percent error of 5.0%, bias of 0.5 +/- 3.7 ml, and interobserver variability of 5.0%. With the reduction in component slices equal or less than three, the accuracy decreased significantly (root-mean-square percent error = 8.1% and bias = -2.0 +/- 5.7 ml) compared with higher slice resolutions. This study demonstrated that 3-D echocardiography using apical rotational techniques can accurately quantify LV volume in the canine heart specimens with irregular shapes with as few as 4-6 axial slices. The rapid 3-D acquisition technique is therefore anticipated to yield precise and accurate LV volumetry.

Journal Article↗