Papers by Sigmund Frigstad
IEEE Ultrasonics Symposium, 2004, 2004
Ultrasound tissue Doppler imaging (TDI) can be used to measure velocities of moving cardiac tissu... more Ultrasound tissue Doppler imaging (TDI) can be used to measure velocities of moving cardiac tissue during the cardiac cycle. Aortic valve closure (AVC) can be seen as a notch occurring after ejection, but before early relaxation in velocity/time curves from apical TDI images of the base of the left ventricle. The timing of AVC may be determined by manually looking for this event. An automated algorithm first detecting the timing of early relaxation and mitral valve opening, is however also able to determine the timing of AVC by searching in both space and time. The automated algorithm was tested on the apical four-chamber, two-chamber and long axis views of 16 healthy subjects. In 88% of the cine-loops the algorithm estimated the timing of AVC within 20 msec off the start of the second heart sound as visible in simultaneously recorded calibrated phonocardiograms. Automated detection of AVC might save manual effort, and provide a marker separating ejection and diastole for further automated analysis.
Cardiovascular ultrasound, 2005
Real-time myocardial contrast echocardiography (MCE) is a novel method for assessing myocardial p... more Real-time myocardial contrast echocardiography (MCE) is a novel method for assessing myocardial perfusion. The aim of this study was to evaluate the feasibility of a very low-power real-time MCE for quantification of regional resting myocardial blood flow (MBF) velocity in normal human myocardium. Twenty study subjects with normal left ventricular (LV) wall motion and normal coronary arteries, underwent low-power real-time MCE based on color-coded pulse inversion Doppler. Standard apical LV views were acquired during constant IV. infusion of SonoVue. Following transient microbubble destruction, the contrast replenishment rate (beta), reflecting MBF velocity, was derived by plotting signal intensity vs. time and fitting data to the exponential function; y (t) =A (1-e(-beta(t-t0))) + C. Quantification was feasible in 82%, 49% and 63% of four-chamber, two-chamber and apical long-axis view segments, respectively. The LAD (left anterior descending artery) and RCA (right coronary artery) ...
Ultrasonics, 2002
The challenge in ultrasound contrast imaging is a better discrimination between the perfused tiss... more The challenge in ultrasound contrast imaging is a better discrimination between the perfused tissue and the contrast bubbles, which is usually expressed by contrast to tissue ratio (CTR). Imaging based on the second harmonic frequency showed a higher CTR than imaging at the fundamental frequency. However, because of nonlinear propagation of ultrasound waves, harmonic frequencies are generated. These harmonic frequencies will be linearly reflected by the tissue and therefore limit the CTR at the second harmonic frequency. In order to reduce the scattering of tissue at harmonic frequencies and by that increase the CTR, nonlinear distortion has to be reduced. We demonstrate in this study that the CTR increases with the harmonic number. The increase is substantial when transmitting at lower frequencies. To take advantage of the higher harmonics (third, fourth, fifth and the ultraharmonics and termed here super harmonics), we have developed a new phased array transducer with a wide frequ...
Lecture Notes in Computer Science, 2010
In this work, we address the problem of automated measurement of the interventricular septum thic... more In this work, we address the problem of automated measurement of the interventricular septum thickness, one of the key parameters in cardiology, from B-mode echocardiograms. The problem is challenging due to high levels of noise, multi modal intensity, weak contrast due to near field haze, and non rigid motion of the septum across frames. We introduce a complete system for automated measurement of septum thickness from B-mode echocardiograms incorporating three main components: a 1D curve evolution algorithm using region statistics for segmenting the septum, a motion clustering method to locate the mitral valve, and a robust method to calculate the septum width from these inputs in accordance with medical standards. Our method effectively handles the challenges of such measurements and runs in near real time. Results on 57 patient recordings showed excellent agreement of the automated measurements with expert manual measurements.
European Journal of Echocardiography, 2003
High dose dipyridamole-atropine stress echocardiography (DASE) with left ventricular (LV) opacifi... more High dose dipyridamole-atropine stress echocardiography (DASE) with left ventricular (LV) opacification using ultrasound contrast agents has not been systematically validated against an angiographic gold standard. Hypothesis: LV opacification improves the diagnostic value and interobserver agreement of DASE. Methods: Forty-one patients (age 60.8 ± 9.1 years; 34 men (82.9%)) referred for coronary artery disease (CAD) evaluation underwent DASE and coronary angiography. Noncontrast and contrast loops were digitized in sequence using second harmonic imaging in standard views at baseline and peak stress during DASE (up to 0.84 mg/kg of dipyridamole and 2.0 mg of atropine). LV opacification was obtained using successive IV bolus injections (0.1 to 0.3 cc) of perflutren. The contrast and noncontrast DASE images were independently reviewed in random order on different days by 2 experienced echocardiographers blinded to the clinical and angiographic data. The LV was divided into 16 segments as suggested by the American Society of Echocardiography. An endocardial delineation score (EDS) was attributed to each LV segment: 0 = not visible; 1 = poorly visible; and 2 = clearly visible. Coronary angiograms were performed by experienced interventional cardiologists blinded to the results of DASE. CAD diameter stenosis ≥ 70% was considered significant. Results: Mean time between DASE and angiography was 8.9 ± 8.3 days. Significant CAD was present in 21 patients (51.2%). The proportion of LV segments with an EDS of 2 was higher in contrast images at baseline (contrast: 69.6% (1256/1804) vs noncontrast: 62.7% (1128/1798); p < 0.0001) and at peak stress (contrast: 73.7% (1331/1804) vs noncontrast: 62.4% (1126/1804); p < 0.0001). Sensitivity for significant CAD detection rose from 66.7% for noncontrast to 85.7% for contrast DASE (p = 0.040). Specificity was not significantly influenced by contrast use (55.0% for noncontrast vs 57.5% for contrast DASE). Interobserver agreement for DASE results increased from 70.7% (kappa = 0.41) for noncontrast to 82.9% (kappa = 0.63) for contrast imaging. Conclusion: LV opacification during DASE improves endocardial delineation at baseline and peak stress, increases sensitivity for detection of significant CAD and results in higher interobserver agreement.
IEEE Ultrasonics Symposium, 2004, 2004
Extraction of the endocardial boundary of the left ventricle is a key challenge in cardiac ultras... more Extraction of the endocardial boundary of the left ventricle is a key challenge in cardiac ultrasound imaging. The cardiac anatomy may be difficult to determine automatically without incorporating knowledge of both wall shape and intensity signature into the detection algorithm. The aim of this study is to establish a framework for knowledge based extraction of the left ventricular endocardial boundary.
Ultrasound in Medicine & Biology, 2002
For ultrasound contrast agents (UCA), nonlinear imaging now has become fundamental. All of the cu... more For ultrasound contrast agents (UCA), nonlinear imaging now has become fundamental. All of the current contrast-imaging methods are dominantly based on the nonlinear response of UCA bubbles. The discrimination between the perfused tissue and the UCA is the challenge in the field of UCA-imaging. This differentiation is usually associated or expressed by the ratio of the scattered power from the contrast agent to the scattered power from the tissue and is termed &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;contrast-to-tissue ratio&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; (CTR). Second harmonic imaging showed a better discrimination between tissue and UCA than fundamental imaging because of a higher CTR. We demonstrate, in this study, that the CTR increases as a function of the order of the harmonic frequency. Currently, due to the limited bandwidth of the transducers, only the second harmonic is selectively imaged, resulting in images with a superior quality to fundamental images, but still degraded and not optimal because of the harmonic generation in the underlying tissue (due to nonlinear propagation) and hence giving a limited CTR. To increase the CTR and to take advantage of the higher harmonics (third, fourth, fifth and the ultraharmonics and termed here super harmonics), we have developed a new phased array transducer. The array transducer contains two different types of elements arranged in an interleaved pattern (odd and even elements). The total number of elements is 96. The elements can operate separately and at a distinct frequency, enabling separate transmission and reception modes. The odd elements (48) operate at typically 2.8 MHz center frequency and 80% bandwidth. The even elements (48) have a center frequency of 900 kHz with a bandwidth of 50%. In vitro measurements using the dual frequency probe show an increase of 40 dB in the CTR for super harmonic components over the conventional second harmonic system. The increase in CTR is in agreement with the calculations using existing models for the response of encapsulated bubbles and known theory of nonlinear propagation. Animal experiments have demonstrated the feasibility of this approach using commercially available UCA and showed a similar increase of the CTR.
Ultrasound in Medicine & Biology, 2006
Ultrasound color tissue Doppler imaging (TDI) can be used to estimate velocities of moving left v... more Ultrasound color tissue Doppler imaging (TDI) can be used to estimate velocities of moving left ventricular cardiac tissue. Aortic valve closure (AVC) can be observed as a notch in apical TDI velocity/time curves occurring after ejection, but before early relaxation. This work sought to evaluate automatic and automated algorithms using TDI for timing AVC. Mitral valve position and the time point of early relaxation were extracted and used to accomplish the task. To test the algorithms, phonocardiogram of the second heart sound was recorded simultaneously with TDI and used as a reference method. The algorithms were tested on apical views of 16 healthy subjects. In 98% of the cardiac cycles, the automatic algorithm estimated the time point of AVC within 25 ms of the reference. Automatic detection of AVC might save manual effort and provide a marker separating ejection and diastole for further automated analysis.
Journal of the American Society of Echocardiography, 2006
Background: Real-time (RT) myocardial contrast echocardiography (MCE) is a novel method for asses... more Background: Real-time (RT) myocardial contrast echocardiography (MCE) is a novel method for assessment of regional myocardial perfusion. We sought to evaluate the feasibility and diagnostic accuracy of quantitative adenosine RT MCE in predicting significant coronary stenoses, with reference to quantitative coronary angiography.
Journal of the American Society of Echocardiography, 2006
contrast both potentially decrease operator dependency in interpretation of stress echocardiograp... more contrast both potentially decrease operator dependency in interpretation of stress echocardiography. The aim of this study was to evaluate whether contrast present during tissue velocity imaging (TVI) significantly affected measurements of velocity, â‘€, and SR. Secondly, we sought to evaluate whether increased scan line density improved feasibility of simultaneous TVI and contrast echocardiography.
Journal of the American Society of Echocardiography, 2002
To evaluate determinants of myocardial hypoperfusion using power Doppler harmonic imaging (PDHI) ... more To evaluate determinants of myocardial hypoperfusion using power Doppler harmonic imaging (PDHI) with myocardial contrast echocardiography (MCE) in clinical practice, a retrospective clinical study was performed comparing echocardiographic and angiographic data. Angiographic data of patients with a normal coronary angiogram (non-CAD) and symptomatic patients with low flow conditions caused by a stenosis of the left anterior descending coronary artery (LAD) or occlusion, or TIMI-II-flow in the LAD were compared with the PDHI data. In 32 patients, MCE was performed with a System Five Performance ultrasound system (GE Vingmed Ultrasound, Horten, Norway). Myocardial perfusion was semiquantitatively analyzed with the EchoPac 6.2b.134 software, bolus injection with Optison (0.35 mL with 5 mL saline flush), and continuous infusion with Levovist (400 mg/mL(-1); 3.5-5 mL/min(-1)) were performed (8 non-CAD patients, 8 CAD patients, respectively). After bolus injection, Doppler intensity (DI) kinetics showed a significant decrease of maximum DI wash-in rate (eg, apical septum [AS]: 4.9 +/- 3.3 vs 2.4 +/- 1.9 dB/s(-1)), of peak maximum DI (eg, AS: 25.3 +/- 6.3 vs 16.4 +/- 5.7 dB), and of DI determined 10 and 20 seconds after peak maximum DI (eg, AS: 22.1 +/- 4.9 vs 10.8 +/- 4.6 dB; AS: 20.4 +/- 5.3 vs 8.0 +/- 3.8 dB, respectively) using a trigger interval once every 3 cardiac cycles when normal perfused areas were compared with hypoperfused areas. During infusion coronary transit time (3.3 +/- 0.9 vs 7.0 +/- 3.6 seconds), maximum DI wash-in rate (eg, AS: 3.2 +/- 1.3 vs 1.3 +/- 0.8 dB/s(-1)) and DI-maximum plateau (eg, AS: 28.6 +/- 4.7 vs 18.3 +/- 6.4 dB) significantly decreased, respectively. Regional myocardial hypoperfusion at rest can be detected by using PDHI with MCE in clinical practice, according to a standardized methodologic protocol.
Journal of the American Society of Echocardiography, 2006
Objective: We sought to compare the feasibility, accuracy, and reproducibility of simultaneous tr... more Objective: We sought to compare the feasibility, accuracy, and reproducibility of simultaneous triplane echocardiography for measurements of left ventricular (LV) volumes and ejection fraction (EF) with reference to magnetic resonance imaging (MRI). Methods: Digital echocardiography recordings of apical LV views with and without intravenous contrast were collected from 53 consecutive patients with conventional 2-dimensional (2D) imaging and with simultaneous triplane imaging. MRI of multiple LV short-axis sections was performed with a 1.5-T scanner. Endocardial borders were manually traced, and LV volumes and EF from 2D biplane echocardiography and MRI were calculated by method of disks. On triplane data, a triangular mesh was constructed by 3-dimensional interpolation and volumes calculated by the divergence theorem. Results: Triplane image acquisition was less timeconsuming than 2D biplane. Precontrast feasibility
We evaluated the accuracy and reproducibility of contrast echocardiography versus tissue harmonic... more We evaluated the accuracy and reproducibility of contrast echocardiography versus tissue harmonic imaging for measurements of left ventricular (LV) volumes and ejection fraction (EF) compared to magnetic resonance imaging (MRI).
2000 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.00CH37121), 2000
Real-time modalities for ultrasound contrast imaging based on the pulse inversion (PI) principle ... more Real-time modalities for ultrasound contrast imaging based on the pulse inversion (PI) principle are proposed to be more sensitive than second harmonic (SH) imaging modalities. This is explained as a better separation of non-linear bubble response. By using two pulses, PI will also be sensitive to changes in the contrast agent due to bubble destruction and motion.
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Papers by Sigmund Frigstad