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Open Access Publications from the University of California

Scholarly Works (19 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2017)

Coronary Artery Diseases (CAD) are believed to be the most common form of heart diseases and the leading cause of deaths of both men and women in the United States. The diagnosis of CAD is largely dependent on various medical imaging procedures and the experience of the radiologists and cardiologists to form a diagnosis based upon those

images. In case of using Coronary Computed Tomography Angiography (CCTA) to assess coronary vessel stenosis, the geometry of the vessels and the cardiac rhythm can alter the image produced during the scan.

There is a need to study the effects of these artifacts on the image, as it could largely impact the decision of calling a vessel stenosis. These artifacts cause an increasing number of false positive diagnosis, thereby leading several patients without lesions or stenosis to catheterization. The small motion causes changes in the signal intensity in those lesions, leading to incorrect diagnosis. Hence, based on the results of the previous computer simulation research done on the effects of coronary geometry and motion on the CT images, a similar study is aimed on the physical phantom and some real patient data set. We aim to characterize motion in the coronary arteries and make inferences about suggestive CT procedures or post processing required after a CCTA. A part of this study involved doing real time CT scans on phantom and using pre-recorded CT data. The outcome of the research is the various trends in motion and the effect of that motion on the intensity of the resulting images.

  • 1 supplemental PDF
  • 2 supplemental ZIPs
Cover page: Effect of small linear motion on the accuracy of estimating coronary vessel stenosis in Cardiac Computed Tomography
  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2022)

Assessment of regional cardiac function has implications in the diagnosis and management of cardiac diseases such as myocardial ischemia, heart failure, dyssynchrony, and cardiotoxicity. Over the past 30 years, significant effort has been focused on developing methods for measuring regional cardiac function; however, there remains an urgent unmet clinical need for a method that is easily available, accurate, reproducible, and operator independent. Modern four-dimensional computed tomography (4DCT) imaging systems can acquire full heart volume, 1 x 1 x 1 mm^3 voxel cardiac images spanning the entire cardiac cycle from a single table position and within a single heartbeat; no other non-invasive cardiac imaging modality comes close to this capability. The images have very high spatial resolution and are now routinely acquired with ultra-low exposure to ionizing radiation. In this proposal, we aim to leverage the advancements in 4DCT technology and develop methods that yield accurate and reproducible high-resolution estimates of regional cardiac function. First, we develop anthropomorphically accurate phantoms of the human left ventricle (LV) and use these phantoms as ground-truth in the development and optimization of methods for the assessment of regional LV strains with high spatial resolution. Second, we use the developed phantoms to understand and improve the temporal resolution of 4DCT; the accurate and reproducible estimation of the timing of LV mechanics has been shown to be a very important feature in predicting patient response to cardiac resynchronization therapy (CRT). Third, we apply the developed methods to cohorts of routinely acquired clinical 4DCT scans and investigate the potential effect of the developed 4DCT methods in the diagnosis and management of cardiac diseases, using CRT as an example. In conclusion, this dissertation has broadened our understanding of the spatio-temporal resolution of 4DCT and potentially fulfils the unmet clinical need for a highly accurate and reproducible method to estimate regional cardiac function.

    Cover page: Spatio-temporal resolution of regional cardiac function assessment with four-dimensional computed tomography
    • Thesis
    • Peer Reviewed
    UC San Diego Electronic Theses and Dissertations (2021)

    The increased complexity of percutaneous procedures continues to demand new imaging techniques to assist these interventions and improve clinical planning and outcomes. Recent developments in 4D X-ray computed tomography (4DCT) technology, including dose reduction protocols, iterative reconstruction methods, and wide-range detectors, allow for full 3D volumes to be acquired across the entire cardiac cycle within a single heartbeat with very low radiation dose. In addition, with the use of a contrast bolus, 4DCT provides highly reproducible and high-resolution metrics of left ventricular (LV) endocardial function. This dissertation thoroughly investigates the development and application of novel methods for evaluating both global and regional LV function using 4DCT data. These novel methods present highly translational research which can be implemented immediately on many existing CT scanners as well as on existing datasets, retrospectively. First, we evaluate the accuracy and reproducibility of previously developed and validated metrics, like CT SQUEEZ, and newly proposed algorithms for measuring LV rotation, torsion, longitudinal strain, and circumferential strain through phantom experiments and cross-modality comparison studies. Then, we demonstrate the feasibility of these methods in patients with various cardiovascular disease states, such as mitral regurgitation (MR) and heart failure. In transcatheter mitral valve (TMVI) patients we show that analysis of 4DCT-derived metrics of LV function can provide a more precise understanding of the effect of MR and TMVI on regional LV function and remodeling than current imaging methods. In heart failure patients, we demonstrate that 4DCT-derived metrics of LV shape, global and regional LV function, and dyssynchrony have the potential to predict response to cardiac resynchronization therapy (CRT) through the development of the lead placement score (LPS). Overall, these results demonstrate that 4DCT imaging, combined with the novel methods we have developed, is a remarkably promising candidate for transforming clinical cardiac imaging, especially for patients undergoing transcatheter-based procedures.

      Cover page: Comprehensive analysis of left ventricular cardiac function using 4DCT data
      • Thesis
      • Peer Reviewed
      UC San Diego Electronic Theses and Dissertations (2020)

      Cardiovascular Diseases (CVD) are fatal heart diseases that can cause death regardless of gender, age, race and ethnicity. The statistics shows that one person dies every 37 seconds in the United States from CVD. The heart attack, also known as myocardial infarction, is caused by a deficiency in myocardial perfusion or blood flow to cardiac muscle tissue.

      In general, patients with suspicious heart disease symptoms undergo echocardiography first due to low cost, safety, and nonionizing radiation. However, echocardiography is limited by operator dependency, less field of view, technical artifact and low image quality. Cardiovascular Magnetic Resonance Imaging (CMR) is a non-invasive imaging modality which produces high quality images and perform safely. However, CMR requires a relatively long image acquisition time compared to Cardiac Computed Tomography (CCT). CCT provides high spatial and temporal resolution within relatively short time period. Retrospect data have proposed that the CCT provides accurately in left ventricle (LV) functional analysis, and characterizing the LV myocardium, which is complementary to echocardiography and CMR.

      The mean difference in end-systolic radial strain between manual segmentation and CNN segmentation was 12.42%. The mean global circumferential strain differences in endocardium and epicardium were 0.34% and 0.04%, respectively. The mean global longitudinal strain difference in endocardium and epicardium were 0.06% and 0.07%, respectively.

      The results summarize that the automated myocardium segmentation using CNN performs well in observing LV myocardial function. This could potentially assist finding the regional and global myocardial dysfunction and evaluating the myocardium diseases.

      • 1 supplemental PDF
      • 1 supplemental ZIP
      Cover page: Validation of Functional Analysis in the Left Ventricular Myocardium using Convolutional Neural Networks (CNN)
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2017)

      Purpose

      Coronary x-ray computed tomography angiography (CCTA) is used to non-invasively assess coronary artery geometry and has, combined with computational modeling, demonstrated the potential to identify physiologically significant lesions. These measurements require robust and accurate coronary imaging and delineation of vessels despite the presence of small motion. This simulation study characterizes the impact of small, uncorrected vessel drifts during data acquisition on the assessment of vessel intensity, diameter, and shape.

      Methods

      We developed a digital phantom and simulated projection data for a clinical scanner geometry for a range of vessel drifts that can occur during relative vessel stasis (0 to 2 mm per 360° gantry rotation) for vessels between 0.2 and 3.0 mm in diameter (covering 0% through 93% stenosis of a 3 mm vessel). In addition to the impact of vessel drift, we evaluated the performance of half-scan acquisitions (relative to full-scans) over a range of gantry positions. The performance of FDK reconstructions was compared to an iterative technique and potential improvement in sampling from focal spot deflection and quarter detector offset was compared.

      Results

      At rest, vessel intensity and diameter were accurately obtained in vessels greater than 1.5 mm with all vessels appearing circular in shape (major-to-minor axis ratio ~1). Vessels between 1.5 and 0.2 mm in diameter demonstrated a rapid decrease in signal intensity with full width half maximum (FWHM) vessel diameters remaining above 0.75 mm as true vessel diameter decreased. Uncorrected vessel motion resulted in decreased vessel intensity, increased vessel diameter, and distortion of vessel shape. The extent of these changes depended on both the position of the gantry as well as the reconstruction approach (half- vs. full-scan). FDK reconstruction results depended on choice of filter with Ram-Lak results yielding comparable performance to an unconstrained iterative reconstruction. Focal spot deflection and quarter detector offset did not result in large changes in performance, likely due to the high sampling density near the isocenter.

      Conclusions

      Despite improvement in gantry speed and acquisition of coronary images during cardiac phases that have relatively stationary vessels, small coronary drifts (0-2 mm per 360° rotation) have been reported and if uncorrected, can present challenges to visual grading and computational modeling of stenoses because vessels will appear dimmer, larger, and more ellipsoidal in shape. The impact of a particular motion depends on the gantry position, the use of half vs. full-scan acquisitions, and the reconstruction technique.
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2021)

        Objectives

        The goal of this study was to assess the utility of a genetic risk score (GRS) in targeted coronary artery calcium (CAC) screening among young individuals.

        Background

        Early CAC screening and preventive therapy may reduce long-term risk of a coronary heart disease (CHD) event. However, identifying younger individuals at increased risk remains a challenge. GRS for CHD are age independent and can stratify individuals on various risk trajectories.

        Methods

        Using 142 variants associated with CHD events, we calculated a GRS in 1,927 individuals in the CARDIA (Coronary Artery Risk Development in Young Adults) cohort (aged 32 to 47 years) and 6,600 individuals in the MESA (Multi-Ethnic Study of Atherosclerosis) cohort (aged 44 to 87 years). We assessed GRS utility to predict CAC presence in the CARDIA cohort and stratify individuals of varying risk for CAC presence over the lifetime in both cohorts.

        Results

        The GRS predicted CAC presence in CARDIA males. It was not predictive in CARDIA females, which had a CAC prevalence of 6.4%. In combined analysis of the CARDIA and MESA cohorts, the GRS was predictive of CAC in both males and females and was used to derive an equation for the age at which CAC probability crossed a predetermined threshold. When assessed in combination with traditional risk factors, the GRS further stratified individuals. For individuals with an equal number of traditional risk factors, probability of CAC reached 25% approximately 10 years earlier for those in the highest GRS quintile compared to the lowest.

        Conclusions

        The GRS may be used to target high-risk younger individuals for early CAC screening.
          Cover page: Targeted Coronary Artery Calcium Screening in High-Risk Younger Individuals Using Consumer Genetic Screening Results
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2017)

          Background

          Measuring local RV function in adult congenital heart disease (ACHD) with echocardiography or MRI is challenging because of the complex geometry and existing pacing devices. Visual assessment of ventricular function via low-dose cardiac CT has been recently performed. This pilot study assessed whether low-dose 4D cine CT combined with automatic measurement of regional shortening could quantify right-ventricular function in ACHD patients.

          Methods

          Seven patients with Tetralogy of Fallot either contraindicated for MRI or assessed for coronary artery disease and seven non-congenital patients were imaged with ECG-gated cardiac CT utilizing a 320-detector row scanner. Right ventricular global function and regional shortening were quantified.

          Results

          Non-congenital patients were imaged with 2.9±2.1mSv and 395±359 HU blood-myocardium contrast. The ACHD patients were imaged with 2.1±1.3mSv and 726±296 HU contrast. Right ventricles of the ACHD patients had higher end-diastolic volume (297±107mL vs 123±34mL, p=0.001), lower ejection fraction (32.0±4.9% vs 45.0±6.0%, p=0.001), and higher dyskinetic fraction (10.9±3.7% vs 2.6±2.8%, p<0.001) relative to the non-congenital controls.

          Conclusions

          In this initial pilot study, right ventricular global and regional systolic function were measured using low-dose cine CT with SQUEEZ quantification in non-congenital patients as well as ACHD patients with Tetralogy of Fallot. Unique regional features of RV dyskinesia were identified in the ACHD patients which could yield a more precise quantification of RV function.
            Cover page: A novel method for evaluating regional RV function in the adult congenital heart with low-dose CT and SQUEEZ processing
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2019)
            We present an anthropomorphically accurate left ventricular (LV) phantom derived from human computed tomography (CT) data to serve as the ground truth for the optimization and the spatial resolution quantification of a CT-derived regional strain metric (SQUEEZ) for the detection of regional wall motion abnormalities. Displacements were applied to the mesh points of a clinically derived end-diastolic LV mesh to create analytical end-systolic poses with physiologically accurate endocardial strains. Normal function and regional dysfunction of four sizes [1, 2/3, 1/2, and 1/3 American Heart Association (AHA) segments as core diameter], each exhibiting hypokinesia (70% reduction in strain) and subtle hypokinesia (40% reduction in strain), were simulated. Regional shortening ( RSCT ) estimates were obtained by registering the end-diastolic mesh to each simulated end-systolic mesh condition using a nonrigid registration algorithm. Ground-truth models of normal function and of hypokinesia were used to identify the optimal parameters in the registration algorithm and to measure the accuracy of detecting regional dysfunction of varying sizes and severities. For normal LV function, RSCT values in all 16 AHA segments were accurate to within ±5% . For cases with regional dysfunction, the errors in RSCT around the dysfunctional region increased with decreasing size of dysfunctional tissue.
              Cover page: Anthropomorphic left ventricular mesh phantom: a framework to investigate the accuracy of SQUEEZ using Coherent Point Drift for the detection of regional wall motion abnormalities
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2019)

              Background

              Modern computed tomographic scanning can produce 4-dimensional images of the left atrial appendage (LAA). LAA function and morphology can then be measured, to plan interventions such as occlusion and to evaluate LAA flow for thrombogenic risk analysis. A current problem here is defining a reproducible boundary between the LAA and the left atrium.

              Methods

              This study used retrospectively gated 4-dimensional computed tomographic data from 25 implantation and coronary artery imaging patients. In each patient, the LAA ostium was defined at multiple time points during the RR interval. To examine the reproducibility of the definition of the LAA ostium, 3 observers analyzed all time frames in each patient 3 times. Five nonconsecutive time frames from each patient were then compared using intraclass correlation coefficients to quantify the precision of the method across patients. The correlation of LAA volumes for each time frame of each patient was determined across the different observers (interobserver) and within each observer's own data sets (intraobserver).

              Results

              The method was successful in 92% of patients. Two-way random-effect, absolute-agreement, single-measurement intraclass correlation coefficients for interobserver measurements were 0.984, 0.990, and 0.988, with intraobserver intraclass correlation coefficients of 0.989, 0.989, and 0.995. The intraclass correlation coefficient of all observations was 0.988.

              Conclusions

              Classification of the LAA ostium using a stepwise procedure identifying the coumadin ridge and 2 vascular landmarks in ECG-gated computed tomography provides a viable method of establishing a highly reproducible boundary between the atrium and LAA needed to obtain LAA metrics useful for procedure planning and measuring LAA function.
                Cover page: Vascular Landmark-Based Method for Highly Reproducible Measurement of Left Atrial Appendage Volume in Computed Tomography
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2018)

                Background

                CT SQUEEZ is a new automated technique to evaluate regional endocardial strain by tracking features on the endocardium from 4D cine CT data. The objective of this study was to measure the range of endocardial regional strain (RSCT) values obtained with CT SQUEEZ in the normal human left ventricle (LV) from standard clinical 4D coronary CTA exams.

                Methods

                RSCT was measured over the heart cycle in 25 humans with normal LV function using cine CT from three vendors. Mean and standard deviation of RSCT values were computed in 16 AHA LV segments to estimate the range of values expected in the normal LV.

                Results

                Curves describing RSCT vs. time were consistent between subjects. There was a slight gradient of decreasing minimum RSCT value (increased shortening) from the base to the apex of the heart. Mean RSCT values at end-systole were: base = -32% ± 1%, mid = -33% ± 1%, apex = -36% ± 1%. The standard deviation of the minimum systolic RSCT in each segment over all subjects was 5%. The average time to reach maximum shortening was 34% of the RR interval.

                Conclusions

                Regional strain (RSCT) can be rapidly obtained from standard gated coronary CCTA protocols using 4DCT SQUEEZ processing. We estimate that 95% of normal LV end-systolic RSCT values will fall between -23% and -43%; therefore, we hypothesize that an RSCT value higher than -23% will indicate a hypokinetic segment in the human heart.
                  Cover page: Regional myocardial strain measurements from 4DCT in patients with normal LV function.
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