Browsing by Subject "echocardiography"
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Item Open Access Automatic Volumetric Analysis of the Left Ventricle in 3D Apical Echocardiographs(2015) Wald, Andrew JamesApically-acquired 3D echocardiographs (echoes) are becoming a standard data component in the clinical evaluation of left ventricular (LV) function. Ejection fraction (EF) is one of the key quantitative biomarkers derived from echoes and used by echocardiographers to study a patient's heart function. In present clinical practice, EF is either grossly estimated by experienced observers, approximated using orthogonal 2D slices and Simpson's method, determined by manual segmentation of the LV lumen, or measured using semi-automatic proprietary software such as Philips QLab-3DQ. Each of these methods requires particular skill by the operator, and may be time-intensive, subject to variability, or both.
To address this, I have developed a novel, fully automatic method to LV segmentation in 3D echoes that offers EF calculation on clinical datasets at the push of a button. The solution is built on a pipeline that utilizes a number of image processing and feature detection methods specifically adopted to the 3D ultrasound modality. It is designed to be reasonably robust at handling dropout and missing features typical in clinical echocardiography. It is hypothesized that this method can displace the need for sonographer input, yet provide results statistically indistinguishable from those of experienced sonographers using QLab-3DQ, the current gold standard that is employed at Duke University Hospital.
A pre-clinical validation set, which was also used for iterative algorithm development, consisted of 70 cases previously seen at Duke. Of these, manual segmentations of 7 clinical cases were compared to the algorithm. The final algorithm predicts EF within ± 0.02 ratio units for 5 of them, and ± 0.09 units for the remaining 2 cases, within common clinical tolerance. Another 13 of the cases, often used for sonographer training and rated as having good image quality, were analyzed using QLab-3DQ, in which 11 cases showed concordance (± 0.10) with the algorithm. The remaining 50 cases retrospectively recruited at Duke and representative of everyday image quality showed 62% concordance (± 0.10) of QLab-3DQ with the algorithm. The fraction of concordant cases is highly dependent on image quality, and concordance improves greatly upon disqualification of poor quality images. Visual comparison of the QLab-3DQ segmentation to my algorithm overlaid on top of the original echoes also suggests that my method may be preferable or of high utility even in cases of EF discordance. This paper describes the algorithm and offers justifications for the adopted methods. The paper also discusses the design of a retrospective clinical trial now underway at Duke with 60 additional unseen cases intended only for independent validation.
Item Open Access Efficient Spatial Coherence Estimation for Improved Endocardial Border Visualization in Real-Time(2017) Hyun, DongwoonCoronary heart disease contributed to approximately one in four deaths in the United States in 2014, and is caused by a restriction of blood flow to myocardial tissue. Stress echocardiography is a clinical technique used to assess myocardial ischemia by observing changes (or lack thereof) in ventricular wall motion in response to cardiac stress. The American Society of Echocardiography (ASE) recommends that left ventricle functionality be quantified using a 16 or 17 segment model of the left ventricle (LV). To properly assess the function of the ventricle, clear endocardial border delineation is necessary.
However, an increasing prevalence of obesity has been linked to a rise in the number of unreadable ultrasound scans. Image degradation is attributed to tissue inhomogeneities and subcutaneous fat layers, giving rise to phase aberration errors and acoustical clutter from near-field reverberation. In the event that two or more segments are inadequately visualized, the ASE recommends the use of contrast agents. Though contrast agents are effective, they are invasive and increase the procedure time and costs.
Recent work has shown that clutter can be suppressed using a novel image reconstruction technique based on the second order statistics of ultrasound echoes called short-lag spatial coherence (SLSC). Unlike conventional B-mode imaging, which forms images of the echo magnitude, SLSC forms images of the spatial coherence of the echo. By suppressing clutter, a sufficient improvement in the visualization of the endocardial border could minimize the need for contrast agents and potentially reduce the level of expertise necessary to interpret images. Though promising in preliminary studies, SLSC has a high computational demand that limited previous studies to offline image reconstruction. The goal of this research was to implement spatial coherence imaging in real-time, and to assess its performance in echocardiography.
First, the existing spatial coherence estimation methodology was investigated, and three computationally efficient modifications were proposed: a reduced kernel, a downsampled receive aperture, and the use of an ensemble correlation coefficient. The proposed methods were implemented in simulation and in vivo studies. Reducing the kernel to a single sample improved computational throughput and improved axial resolution. Downsampling the receive aperture was found to have negligible effect on estimator variance, and improved computational throughput by an order of magnitude for a downsample factor of 4. The ensemble correlation estimator was found to have lower variance than the currently used average correlation estimator. Combining the three methods, the throughput was improved 105-fold in simulation with a downsample factor of 4 and 20-fold in vivo with a downsample factor of 2.
Spatial coherence estimation techniques were also expanded to 2D matrix array transducers. SLSC images generated with a 2D array yielded superior contrast-to-noise ratio (CNR) and texture signal-to-noise ratio (SNR) measurements over SLSC images made on a corresponding 1D array and over B-mode imaging. SLSC images generated with square subapertures were found to be superior to SLSC images generated with subapertures of equal surface area that spanned the whole array in one dimension. Subaperture beamforming was found to have little effect on SLSC imaging performance for subapertures up to 8x8 elements in size on a 64x64 element transducer. Additionally, the use of 8x8, 4x4, and 2x2 element subapertures provided an 8, 4, and 2 times improvement in channel SNR along with a 2640-, 328-, and 25-fold reduction in computation time, respectively.
The improved spatial coherence estimation methodology was implemented using a GPU-based software beamformer to develop a real-time SLSC imaging system suitable for echocardiography. The system went through several iterations, with the final form consisting of a stand-alone CUDA C++ library for GPU-based beamforming, and a second CUDA C++ library to interface a research ultrasound scanner with the first. The resulting system was capable of live spatial coherence imaging at more than 30 frames per second, a rate sufficient for echocardiography.
The system was then used in a clinical study to image 15 stress echocardiography patients with poor image quality. A fundamental and harmonic imaging study was conducted. The latter study, which had greater clinical significance, was an assessment of the visibility of 17 LV segments using conventional tissue harmonic imaging (THI) and harmonic spatial coherence imaging (HSCI). A cardiologist rated the visibility of each of 17 LV segments as 0=invisible, 1=poorly visualized, or 2=well visualized, where scores of 0 and 1 indicated a need for contrast agent. There was a clear superiority of HSCI over THI in a comparison of overall segment scores (p < 0.0001 by symmetry test unadjusted for clustering). When comparing the number of segments with clinically acceptable image quality per patient, HSCI again showed superiority over THI (p < 0.0001 by McNemar test adjusted for clustering). In one patient, HSCI improved visualization sufficiently to eliminate the need for contrast agents altogther. These results indicate that spatial coherence imaging may provide sufficient improvements in LV wall visualization in certain patients to proceed without contrast agents.
The research in spatial coherence estimation techniques also proved fruitful in other areas of ultrasound imaging, such as ultrasound molecular imaging (USMI). USMI is accomplished by detecting microbubble (MB) contrast agents that have bound to specific biomarkers, and can be used for the early detection of cancer. However, USMI in humans is challenging because of the signal degradation caused by the presence of heterogenous subcutaneous tissue. In a phantom and in vivo study, USMI performance was assessed using conventional contrast-enhanced ultrasound (CEUS) imaging and SLSC-CEUS. In a USMI-mimicking phantom, SLSC-CEUS was found to be more robust than DAS to additive thermal noise, with a 9 dB and 15 dB SNR improvement without and with -6 dB thermal noise, respectively. USMI performance was also measured in vivo using VEGFR2-targeted MBs in mice with subcutaneous human hepatocellular carcinoma tumors. SLSC-CEUS improved the SNR in each of 10 tumors by an average of 65%, corresponding to 4.3 dB SNR. These results indicate that the SLSC beamformer is well-suited for USMI applications because of its high sensitivity and robust properties.
These studies are a demonstration of the feasibility of real-time spatial coherence imaging using current technology, and an exposition of its utility in medical ultrasound imaging.
Item Open Access Implementing a Continuous Quality Improvement Program in a High-Volume Clinical Echocardiography Laboratory: Improving Care for Patients With Aortic Stenosis.(Circ Cardiovasc Imaging, 2016-03) Samad, Zainab; Minter, Stephanie; Armour, Alicia; Tinnemore, Amanda; Sivak, Joseph A; Sedberry, Brenda; Strub, Karen; Horan, Seanna M; Harrison, J Kevin; Kisslo, Joseph; Douglas, Pamela S; Velazquez, Eric JBACKGROUND: The management of aortic stenosis rests on accurate echocardiographic diagnosis. Hence, it was chosen as a test case to examine the utility of continuous quality improvement (CQI) approaches to increase echocardiographic data accuracy and reliability. A novel, multistep CQI program was designed and prospectively used to investigate whether it could minimize the difference in aortic valve mean gradients reported by echocardiography when compared with cardiac catheterization. METHODS AND RESULTS: The Duke Echo Laboratory compiled a multidisciplinary CQI team including 4 senior sonographers and MD faculty to develop a mapped CQI process that incorporated Intersocietal Accreditation Commission standards. Quarterly, the CQI team reviewed all moderate- or greater-severity aortic stenosis echocardiography studies with concomitant catheterization data, and deidentified individual and group results were shared at meetings attended by cardiologists and sonographers. After review of 2011 data, the CQI team proposed specific amendments implemented over 2012: the use of nontraditional imaging and Doppler windows as well as evaluation of aortic gradients by a second sonographer. The primary outcome measure was agreement between catheterization- and echocardiography-derived mean gradients calculated by using the coverage probability index with a prespecified acceptable echocardiography-catheterization difference of <10 mm Hg in mean gradient. Between January 2011 and January 2014, 2093 echocardiograms reported moderate or greater aortic stenosis. Among cases with available catheterization data pre- and post-CQI, the coverage probability index increased from 54% to 70% (P=0.03; 98 cases, year 2011; 70 cases, year 2013). The proportion of patients referred for invasive valve hemodynamics decreased from 47% pre-CQI to 19% post-CQI (P<0.001). CONCLUSIONS: A laboratory practice pattern that was amenable to reform was identified, and a multistep modification was designed and implemented that produced clinically valuable performance improvements. The new protocol improved aortic stenosis mean gradient agreement between echocardiography and catheterization and was associated with a measurable decrease in referrals of patients for invasive studies.Item Open Access Improved Endocardial Border Definition with Short-Lag Spatial Coherence (SLSC) Imaging(2012) Lediju Bell, Muyinatu A.Clutter is a problematic noise artifact in a variety of ultrasound applications. Clinical tasks complicated by the presence of clutter include detecting cancerous lesions in abdominal organs (e.g. livers, bladders) and visualizing endocardial borders to assess cardiovascular health. In this dissertation, an analytical expression for contrast loss due to clutter is derived, clutter is quantified in abdominal images, and sources of abdominal clutter are identified. Novel clutter reduction methods are also presented and tested in abdominal and cardiac images.
One of the novel clutter reduction methods is Short-Lag Spatial Coherence (SLSC) imaging. Instead of applying a conventional delay-and-sum beamformer to measure the amplitude of received echoes and form B-mode images, the spatial coherence of received echoes are measured to form SLSC images. The world's first SLSC images of simulated, phantom, and in vivo data are presented herein. They demonstrate reduced clutter and improved contrast, contrast-to-noise, and signal-to-noise ratios compared to conventional B-mode images. In addition, the resolution characteristics of SLSC images are quantified and compared to resolution in B-mode images.
A clinical study with 14 volunteers was conducted to demonstrate that SLSC imaging offers 19-33% improvement in the visualization of endocardial borders when the quality of B-mode images formed from the same echo data was poor. There were no statistically significant improvements in endocardial border visualization with SLSC imaging when the quality of matched B-mode images was medium to good.
Item Open Access Prevalence and Outcomes of Left-Sided Valvular Heart Disease Associated With Chronic Kidney Disease.(J Am Heart Assoc, 2017-10-11) Samad, Zainab; Sivak, Joseph A; Phelan, Matthew; Schulte, Phillip J; Patel, Uptal; Velazquez, Eric JBACKGROUND: Chronic kidney disease (CKD) is an adverse prognostic marker for valve intervention patients; however, the prevalence and related outcomes of valvular heart disease in CKD patients is unknown. METHODS AND RESULTS: Included patients underwent echocardiography (1999-2013), had serum creatinine values within 6 months before index echocardiogram, and had no history of valve surgery. CKD was defined as diagnosis based on the International Classification of Diseases, Ninth Revision or an estimated glomerular filtration rate <60 mL/min per 1.73 m2. Qualitative assessment determined left heart stenotic and regurgitant valve lesions. Cox models assessed CKD and aortic stenosis (AS) interaction for subsequent mortality; analyses were repeated for mitral regurgitation (MR). Among 78 059 patients, 23 727 (30%) had CKD; of these, 1326 were on hemodialysis. CKD patients were older; female; had a higher prevalence of hypertension, hyperlipidemia, diabetes, history of coronary artery bypass grafting/percutaneous coronary intervention, atrial fibrillation, and heart failure ≥mild AS; and ≥mild MR (all P<0.001). Five-year survival estimates of mild, moderate, and severe AS for CKD patients were 40%, 34%, and 42%, respectively, and 69%, 54%, and 67% for non-CKD patients. Five-year survival estimates of mild, moderate, and severe MR for CKD patients were 51%, 38%, and 37%, respectively, and 75%, 66%, and 65% for non-CKD patients. Significant interaction occurred among CKD, AS/MR severity, and mortality in adjusted analyses; the CKD hazard ratio increased from 1.8 (non-AS patients) to 2.0 (severe AS) and from 1.7 (non-MR patients) to 2.6 (severe MR). CONCLUSIONS: Prevalence of at least mild AS and MR is substantially higher and is associated with significantly lower survival among patients with versus without CKD. There is significant interaction among CKD, AS/MR severity, and mortality, with increasingly worse outcomes for CKD patients with increasing AS/MR severity.Item Open Access Provocative biomarker stress test: stress-delta N-terminal pro-B type natriuretic peptide.(Open Heart, 2018-01) Limkakeng, Alexander T; Leahy, J Clancy; Griffin, S Michelle; Lokhnygina, Yuliya; Jaffa, Elias; Christenson, Robert H; Newby, L KristinObjective:Stress testing is commonly performed in emergency department (ED) patients with suspected acute coronary syndrome (ACS). We hypothesised that changes in N-terminal pro-B type natriuretic peptide (NT-proBNP) concentrations from baseline to post-stress testing (stress-delta values) differentiate patients with ischaemic stress tests from controls. Methods:We prospectively enrolled 320 adult patients with suspected ACS in an ED-based observation unit who were undergoing exercise stress echocardiography. We measured plasma NT-proBNP concentrations at baseline and at 2 and 4 hours post-stress and compared stress-delta NT-proBNP between patients with abnormal stress tests versus controls using non-parametric statistics (Wilcoxon test) due to skew. We calculated the diagnostic test characteristics of stress-delta NT-proBNP for myocardial ischaemia on imaging. Results:Among 320 participants, the median age was 51 (IQR 44-59) years, 147 (45.9%) were men, and 122 (38.1%) were African-American. Twenty-six (8.1%) had myocardial ischaemia. Static and stress-deltas NT-proBNP differed at all time points between groups. The median stress-deltas at 2 hours were 10.4 (IQR 6.0-51.7) ng/L vs 1.7 (IQR -0.4 to 8.7) ng/L, and at 4 hours were 14.8 (IQR 5.0-22.3) ng/L vs 1.0 (-2.0 to 10.3) ng/L for patients with ischaemia versus those without. Areas under the receiver operating curves were 0.716 and 0.719 for 2-hour and 4-hour stress-deltas, respectively. After adjusting for baseline NT-proBNP levels, the 4-hour stress-delta NT-proBNP remained significantly different between the groups (p=0.009). Conclusion:Among patients with ischaemic stress tests, static and 4-hour stress-delta NT-proBNP values were significantly higher. Further study is needed to determine if stress-delta NT-proBNP is a useful adjunct to stress testing.Item Open Access The Prevalence of Rheumatic Heart Disease in Western Kenya: An Echocardiographic Study(2012) Holland, Thomas LawrenceBackground:
Despite its declining incidence in resource-rich nations, rheumatic heart disease (RHD) remains a leading cause of morbidity and mortality in the developing world. Recent studies have demonstrated its high prevalence in Aboriginal populations in northern Australia, in Fiji, Tonga, and even parts of Africa including Nigeria and Mozambique, but little is known about its prevalence in Kenya. This epidemiologic data is needed to help inform prevention efforts.
Methods:
Transthoracic echocardiograms were performed on 526 randomly selected hospitalized patients, ages 5-35, on the surgical wards. These patients did not have known rheumatic heart disease. Data were collected on socioeconomic status, living conditions, and medical comorbidities. The primary outcome was the prevalence of echocardiographically confirmed rheumatic heart disease.
Results:
A total of 526 patients were enrolled. 9 had echocardiographic evidence of rheumatic heart disease (1.7%, 95% CI 0.6-2.8). Patients with rheumatic heart disease were more likely to be female. An association between RHD and crowded living conditions or socioeconomic status was not demonstrated in this study.
Conclusions:
Screening with echocardiography in Western Kenya has the potential to identify subclinical rheumatic heart disease, which can inform secondary prevention efforts. Given low overall rates of rheumatic heart disease in the population in this study, efforts at primary prevention, i.e. identification and treatment of streptococcal pharyngitis and acute rheumatic fever, may yield greater population-level benefits.
Item Open Access Volumetric Acoustic Radiation Force Impulse Imaging Using Intracardiac Echocardiography(2020) Kim, Young-JoongIntracardiac echocardiography (ICE) based elastography methods have the potential to be useful for a number of clinical purposes including monitoring of ablation lesion formation and myocardial substrate characterization. However, 2-D field-of-view ICE catheters currently in use in the clinic have difficulties imaging face-on regions of myocardial tissue, requiring meticulous and time-consuming translational and rotational scanning of the array. This dissertation investigates the use of helicoid array transducers to perform ICE-based acoustic radiation force impulse (ARFI) imaging on multiple elevation planes at once, improving on current methods in terms of speed and ease-of-use.
The Siemens Acuson SC2000 ultrasound scanner was programmed with sequences to perform SWEI imaging on the Soundstar 8F linear array ICE catheter and to perform volumetric ARFI scans using the AcuNav V helicoid array catheter. These sequences were used respectively to characterize the stiffness contrast in ablated human atrial tissue and to characterize the performance of volumetric ARFI at detecting gaps in atrial tissue phantoms.
The first research chapter is a clinical study showing that shear wave elastography (SWE) using a traditional 2-D field-of-view ICE catheter can be used to distinguish between baseline and ablated left atrial (LA) tissue in patients undergoing radiofrequency ablation (RFA) for atrial fibrillation (AF). Shear wave velocities of baseline LA and right atrium (RA), low electrogram voltage areas of the LA, and ablated LA are reported. The second chapter investigates through simulation and experiments the volumetric B-mode imaging performance of helicoid array transducers. Experimental verification of pressure field simulations is done by the use of the Siemens Acuson AcuNav V, a 128-element helicoid array transducer. Guided by these results, a discussion of the design of helicoid array transducer imaging sequences is presented. The final chapter is about the use of the helicoid array transducer for volumetric ARFI imaging. Experiments in tissue phantoms of varying elasticities and inclusions demonstrate that it is possible to identify gaps as narrow as 1 mm when the contrast is similar to that of baseline and ablated human LA myocardium.
This work demonstrates the feasibility of using helicoid array transducers for volumetric elastography imaging of the heart and establishes a foundation for future clinical investigations using this technology.