Browsing by Subject "Ultrasound"
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Item Assessing the qualitative validity of a non-invasive ultrasound technique for estimating muscle glycogen change(2016-08) Allen, Jakob Richard; Coyle, Edward F., 1952-; Tanaka, HirofumiIntramuscular glycogen is a primary fuel source for intense exercise of any substantial duration, and the use of an invasive muscle biopsy is still the gold-standard of measurement. The purpose of this study is to assess the qualitative validity of a proprietary algorithm (MuscleSound®) for determination of intramuscular glycogen concentration against the body of literature on muscle glycogen depletion from exercise and subsequent recovery. To test whether this new technology appears valid, 12 healthy recreational students (n=1 female) (25.5 ± 1.25y, 74.03 ± 2.58kg, 174 ± 4.48cm) were recruited from the University of Texas at Austin campus for participation in this study. Subjects performed six bouts of six-minute efforts on a stationary cycle ergometer at 84% of their VO2peak; an exercise protocol designed to elicit substantial muscle glycogen depletion. Care was taken to maintain body hydration status to further elucidate whether the device was truly measuring glycogen or a proxy such as intramuscular water. Each interval was followed by a six-minute rest period, during which time ultrasound images were taken of the vastus lateralis (VL), rectus femoris (RF) and gastrocnemius/soleus (GS) muscles. Images were processed using the MuscleSound® (MS) algorithm which assigns a MS score (0-100) based on the opacity of the image. Following the exercise protocol, subjects remained in the laboratory for a six-hour recovery phase, wherein images were taken at the same three sites at two-hour intervals. A high carbohydrate (CHO) and protein (PRO) beverage was consumed immediately following exercise, and after two and four hours in order to assess the MS algorithm’s ability to capture the qualitative pattern of glycogen resynthesis established in the literature. It was hypothesized that the VL and RF muscles would decrease in a curvilinear fashion during the intervals to a greater extent than the GS and that during the recovery phase these muscles would show an increase in MS units every two hours for six hours. In support of our hypothesis, we found that during exercise, MS values decreased in a curvilinear pattern in the VL with significantly lower values after bouts 3 through 6 versus baseline. The RF showed a similar pattern with bouts 4 through 6 being significantly lower than baseline, while the GS remained constant throughout. After 120 minutes of recovery the MS values of the VL and RF had returned to baseline levels. It is established in the literature that a nearly depleted muscle should take approximately 24 hours to return to capacity (36); therefore it is unclear whether the MS technology is truly capturing muscle glycogen in its images. While an effective qualitative tool, more work should be done to determine if MS is a valid quantitative measurement of muscle glycogen.Item The assessment of autism risk and severity using prenatal ultrasound measures of the cerebellum(2012-05) Brinster, Meredith Irene; Allen, Greg, doctor of clinical psychology; Stark, KevinThe purpose of the current study is to contribute to the understanding of prenatal cerebellar pathology in autism. Reduction of Purkinje neurons is well reported in the cerebella of individual’s with autism. While there is evidence to suggest that this abnormality may be evident as early as prenatal development, no study to date has examined in the anataomical prenatal development of the cerebella in children later diagnosed with autism. The primary prediction being made is that a reduction of Purkinje neurons during prenatal development will present as reduced cerebellar size in the reports from mother’s prenatal ultrasound records. It is hypothesized that this reduction will be greater in children with an autism diagnosis compared to the records of children without an autism diagnosis. The secondary prediction will attempt to further support the link between aberrant cerebellar development and increased stereotyped behavior and repetitive interests. A retrospective analysis of prenatal ultrasound records and autism diagnostic information will test these hypotheses, predicting that records from children who have been diagnosed with an autism spectrum disorder will show reductions in transverse cerebellar diameter measurements when compared to TD peers, and that greater reductions will correlate with increased stereotypical and repetitive behaviors as measured by a standard diagnostic tool.Item Clinical photoacoustic imaging for detection and characterization of metal implants(2011-08) Su, Jimmy Li-Shin; Emelianov, Stanislav Y.; Dunn, Andrew; Karpiouk, Andrei; Smalling, Richard; Sokolov, KonstantinAccurate insertion and monitoring of metal implants in-vivo is essential for clinical diagnosis and therapy of various diseases. Clinical studies and examples have demonstrated that the misplacement errors of these metal devices can have dramatic consequences. This thesis focuses on three main metal devices that are in widespread use today: needles, coronary stents and brachytherapy seeds. Each application requires proper image-guidance for correct usage. For needles, image guidance is required to ensure correct local injection delivery or needle aspiration biopsy. Fine needle aspiration biopsies are performed in order to avoid major surgical excisions when obtaining tissue biopsy procedures. However, because of the small biopsy sample, the risk is that the sample is collected outside of the tumorigenic region, resulting in a false negative result. Implantation of stents requires that confirmation that proper stent apposition has been achieved due to balloon inflation. Furthermore, it is important to guide the stent to shield the vulnerable region of an atherosclerotic plaque. With prostate brachytherapy seeds, the ability to monitor seed placement is crucial because needle deflections or tissue deformation can result in seed misplacement errors, decreasing the efficacy of the pre-established treatment plan. For the described applications and other possible clinical practices involving the use of metallic implants, an imaging technology that can accurately depict the location of the metal objects, relative to their respective backgrounds, in real-time, is necessary to improve the safety and the efficacy of these procedures. Currently, ultrasound is used because of its real-time capabilities, non-ionizing radiation, and soft tissue contrast. However, due to high acoustic scattering from tissue, the contrast of metal implants can be low. Photoacoustic imaging can be used as an alternative, or complementary, imaging method to ultrasound for imaging metal. This thesis focuses on the benefits and the pitfalls of using photoacoustic imaging for detecting three different metal implants, each having unique requirements. Overall, the goal of this work is to develop a framework for clinical applications using combined ultrasound and photoacoustic imaging to help guide, detect and follow-up on clinical metal implants introduced in-vivo.Item Defect analysis using resonant ultrasound spectroscopy(2009-05-15) Flynn, Kevin JosephThis thesis demonstrates the practicability of using Resonant Ultrasound Spectroscopy (RUS) in combination with Finite Element Analysis (FEA) to determine the size and location of a defect in a material of known geometry and physical constants. Defects were analyzed by comparing the actual change in frequency spectrum measured by RUS to the change in frequency spectrum calculated using FEA. FEA provides a means of determining acceptance/rejection criteria for Non-Destructive Testing (NDT). If FEA models of the object are analyzed with defects in probable locations; the resulting resonant frequency spectra will match the frequency spectra of actual objects with similar defects. By analyzing many FEA-generated frequency spectra, it is possible to identify patterns in behavior of the resonant frequencies of particular modes based on the nature of the defect (location, size, depth, etc.). Therefore, based on the analysis of sufficient FEA models, it should be possible to determine nature of defects in a particular object from the measured resonant frequency. Experiments were conducted on various materials and geometries comparing resonant frequency spectra measured using RUS to frequency spectra calculated using FEA. Measured frequency spectra matched calculated frequency spectra for steel specimens both before and after introduction of a thin cut. Location and depth of the cut were successfully identified based on comparison of measured to calculated resonant frequencies. However, analysis of steel specimens with thin cracks, and of ceramic specimens with thin cracks, showed significant divergence between measured and calculated frequency spectra. Therefore, it was not possible to predict crack depth or location for these specimens. This thesis demonstrates that RUS in combination with FEA can be used as an NDT method for detection and analysis of cracks in various materials, and for various geometries, but with some limitations. Experimental results verify that cracks can be detected, and their depth and location determined with reasonable accuracy. However, experimental results also indicate that there are limits to the applicability of such a method, the primary one being a lower limit to the size of crack ? especially thickness of the crack - for which this method can be applied.Item Effect of Temporal Acquisition Parameters on the Image Quality of Ultrasound Axial Strain Time-constant Elastograms(2011-08-02) Varghese, JoshuaRecent developments in ultrasound elastography have suggested the possibility of using elastographic methods to estimate the temporal mechanical properties of complex tissues. In this context, elastographic methods to image the axial strain time constant (TC) have been developed. The axial strain TC is a parameter that is related to the viscoelastic and poroelastic behavior of tissues. Estimation of this parameter can be done using curve fitting methods. However, the effect of temporal ultrasonic acquisition parameters, such as window of observation, acquisition rate, and input noise, on the image quality of the resultant TC elastograms has not been investigated yet. Elucidating such effects could be useful for diagnostic applications. This work explores the effects of varying windows of observation, acquisition rate, and input noise on the image quality (accuracy and signal-to-noise ratio (SNR)) of axial strain TC estimates and elastograms using a previously developed simulation model. By varying the amount of data collected as a percentage of the expected TC, the algorithms were able to compute a minimum threshold collection time for an accurate TC estimation as a percentage of the expected TC. The effect of acquisition parameters such as acquisition rate and input noise on the minimum threshold collection time was assessed. Experimental data, collected for previous experiments, were used as a proof of principle to corroborate the simulation findings. The results of this work suggest that there is a linear dependence of the total acquisition time necessary for accurate TC estimates on the true time constant value. The simulation results also indicate that it might be possible to make accurate estimates of the axial strain TC using small windows of observation (as small as 20% of the expected TC) with fast acquisition rates and high input SNR levels. Experimental results suggest that, in practice, a larger window of observation should be used to account for multiple noise sources typically not considered in simulations. This work also suggests that the minimum window of observation necessary for an accurate TC estimate is highly dependent on the acquisition frame rate and the input SNR level. Therefore, use of imaging systems with fast acquisition rates is recommended for studies aiming at measuring time-dependent phenomena in tissues.Item Intravascular photoacoustics as a theranostic platform for atherosclerosis(2014-08) Yeager, Douglas Edward; Emelianov, Stanislav Y.; Baker, Aaron; Sessler, Jonathan; Smalling, Richard; Sokolov, KonstantinThe persistence of high global mortality rates directly attributable to cardiovascular disease drives ongoing research into novel approaches for improved diagnosis and treatment of its primary underlying cause, atherosclerosis. Combined intravascular ultrasound and photoacoustic (IVUS/IVPA) imaging is one such modality, actively being developed as a tool for improved characterization of high-risk atherosclerotic plaques. The pathophysiology associated with progression and destabilization of atherosclerotic plaques leads to characteristic changes in arterial morphology and composition. IVUS/IVPA imaging seeks to expand upon the ability of clinically utilized intravascular ultrasound (IVUS) imaging to assess vessel anatomy by adding improved sensitivity to image the underlying cellular and molecular composition through intravascular photoacoustic (IVPA) imaging of either endogenous chromophores (e.g. lipid) or exogenously delivered contrast agents. This dissertation focuses on the expansion of IVUS/IVPA imaging using exogenous contrast agents to enable the detection and subsequent optically-triggered therapy of atherosclerotic plaques. The passive extravasation and aggregation of systemically injected plasmonic gold nanorods absorbing within the near infrared tissue optical window within plaques of atherosclerotic rabbit models is first demonstrated, along with the ability to localize the contrast agents using ex vivo IVUS/IVPA imaging. The motivation for nanoparticle labeling of atherosclerosis is then expanded from that of purely image contrast agents to vehicles for image-guided, dual-modality phototherapy. The integrated IVUS/IVPA imaging catheter is utilized for photothermal delivery with simultaneous IVPA temperature monitoring using the high optical absorption of gold nanorod contrast agents to enable localized heating. Subsequently, the potential role for IVUS/IVPA-guided phototherapy is further expanded through the characterization and in vitro assessment of novel multifunctional theranostic nanoparticles comprised of a gold nanorod core with a degradable, photosensitizer-doped silica shell. Together, the results presented within this dissertation provide a framework for ongoing research into the expansion of IVUS/IVPA imaging as a platform for complimentary diagnosis and local treatment of atherosclerotic plaques using multifunctional theranostic nanoparticle contrast agents.Item Optically-triggered nanodroplets for enhanced ultrasound and photoacoustic imaging(2015-05) Hannah, Alexander Steward; Emelianov, Stanislav Y.Medical ultrasound imaging is ubiquitous in clinics due to its safety, low cost, portability, and imaging depth. The development of technologies to assist ultrasound in the diagnosis of diseases thus have a potentially broad clinical impact. More recently, photoacoustics has emerged as a complementary, high contrast modality for imaging optical absorption. Injectable dyes and nanoparticles locally amplify ultrasound and photoacoustic signal, helping to identify disease markers and track its progression. We have constructed a dual ultrasound and photoacoustic contrast agent that can be activated using an external optical trigger. In response to pulsed laser irradiation, the particle undergoes a liquid to gas phase change, or vaporization, which emits a strong acoustic wave and results in an echogenic microbubble, simultaneously enhancing contrast for both modalities. We designed and developed several iterations of particles, altering parameters to optimize biocompatibility, cost, and image contrast enhancement, and we then characterized key traits of the particles. Next, we imaged the contrast agents in phantom, ex vivo, and in vivo models to validate the image enhancement, developing image process algorithms to maximize image quality. These optically triggered contrast agents are a valuable tool for minimally invasive, highly specific, early identification of cancer.Item Photoacoustic imaging for temperature monitoring and photothermal therapy guidance(2015-08) Dumani Jarquin, Diego Sayed; Emelianov, Stanislav Y.; Aglyamov, Salavat; Cook, JasonCancer is among the leading causes of death in the United States and the world. Using combined ultrasound (US) and photoacoustic (PA) imaging can provide both anatomical and molecular information of cancerous cells for both diagnostic and therapeutic purposes. This thesis is focused on combining these two modalities, in conjunction with nanoparticles, to treat cancerous tumors and monitor the progress of the therapy. Specifically, the work evaluates the use of photoacoustic imaging as a temperature monitoring tool during photothermal therapy. In this study, the mathematical relationship between photoacoustic signal and temperature is presented and validated with a glass tube phantom using gold nanoparticles. Then in vitro and ex vivo studies were performed to validate the effect of photothermal therapy and the monitoring capability of photoacoustic imaging. The results show that photoacoustic imaging can be used to monitor temperature during photothermal therapy. Future directions include in vivo studies of image guided photothermal therapy and survival studies.Item Prenatal head circumference in autism spectrum disorder(2015-08) Brinster, Meredith Irene; Allen, Greg, doctor of clinical psychology; Landa, Rebecca; ; Keith, Tim; Cawthon, Stephanie; Levine, Ann; Ridgeway, JeffreyResearch has documented a phenomenon of early brain overgrowth in autism spectrum disorder (ASD). Although the most significant overgrowth seems to occur within the first few years of life, the exact timeline, clinical correlates, and relation to earlier brain development are not well understood. A growing body of research points to a prenatal origin, yet few studies have examined prenatal head circumference (HC) in children diagnosed with ASD. Previous investigations have been limited to comparing HC measurements at the second trimester, neglecting later points in gestation when critical regulatory and developmental processes may be going awry. In addition, these analyses may be influenced by biased normative data, as has been recently suggested by various research groups. Finally, the connection between prenatal HC and later developmental outcomes has yet to be explored. The current study sought to expand upon current literature by examining both second and third trimester prenatal HC measurements in children with ASD, as well as the rate of growth between trimesters. Additionally, the current study explored the relation between prenatal HC growth and later symptom severity. Examining HC later in gestation contributes to a more complete understanding of how and when brain growth dysregulation occurs in the development of ASD. Analyses indicated an unanticipated finding of significantly smaller mean standardized HC for ASD participants as compared to normative growth charts. In addition, second and third trimester HC measurements suggested an accelerated rate of neural growth for children who later developed ASD.Item Statistical Analysis of a Three-dimensional Axial Strain and Axial-shear Strain Elastography Algorithm(2012-10-19) Li, MohanPathological phenomena often change the mechanical properties of the tissue. Therefore, estimation of tissue mechanical properties can be of clinical importance. Ultrasound elastography is a well-established strain estimation technique. Until recently, mainly 1D elastography algorithms have been developed. A few 2D algorithms have also been developed in the past. Both of these two types of technique ignore the tissue motion in the elevational direction, which could be a significant source of decorrelation in the RF data. In this thesis, a 3D elastography algorithm that estimates all the three components of tissue displacement is implemented and tested statistically. In this research, displacement fields of mechanical models are simulated. RF signals are then generated based on these displacement fields and used as the input of elastography algorithms. To evaluate the image quality of elastograms, absolute error, SNRe, CNRe and CNRasse are computed. The SNRe, CNRe and CNRasse values are investigated not only under different strain conditions, but also in different frame locations, which forms 3D strain filters. A statistical comparison between image qualities of the 3D technique and 2D technique is also provided. The results of this study show that the 3D elastography algorithm outperforms the 2D elastography algorithm in terms of image quality and robustness, especially under high strain conditions. This is because that the 3D algorithm estimates the elevational displacement, while the 2D technique only estimates the axial and lateral deformation. Since the elevational displacement could be an important source for the decorrelation in the RF data, the 3D technique is more effective and robust compared with the 2D technique.Item Ultrasound and photoacoustic imaging for cancer detection and therapy guidance(2011-08) Kim, Seungsoo; Emelianov, Stanislav Y.; Aglyamov, Salavat R.; Sokolov, Konstantin V.; Hamilton, Mark F.; Pearce, John A.Cancer has been one of main causes of human deaths for many years. Early detection of cancer is essential to provide definitive treatment. Among many cancer treatment methods, nanoparticle-mediated photothermal therapy is considered as one of the promising cancer treatment methods because of its non-invasiveness and cancer-specific therapy. Ultrasound and photoacoustic imaging can be utilized for both cancer detection and photothermal therapy guidance. Ultrasound elasticity imaging can detect cancer using tissue elastic properties. Once cancer is diagnosed, spectroscopic photoacoustic imaging can be used to monitor nanoparticle delivery before photothermal therapy. When nanoparticles are well accumulated at the tumor, ultrasound and photoacoustic-based thermal imaging can be utilized for estimating temperature distribution during photothermal therapy to guide therapeutic procedure. In this dissertation, ultrasound beamforming, elasticity imaging, and spectroscopic photoacoustic imaging methods were developed to improve cancer detection and therapy guidance. Firstly, a display pixel based synthetic aperture focusing method was developed to fundamentally improve ultrasound image qualities. Secondly, an autocorrelation based sub-pixel displacement estimation method was developed to enhance signal-to-noise ratio of elasticity images. The developed elasticity imaging method was utilized to clinically evaluate the feasibility of using ultrasound elasticity imaging for prostate cancer detection. Lastly, a minimum mean square error based spectral separation method was developed to robustly utilize spectroscopic photoacoustic imaging. The developed spectroscopic photoacoustic imaging method was utilized to demonstrate ultrasound and photoacoustic image-guided photothermal cancer therapy using in-vivo tumor-bearing mouse models. The results of these studies suggest that ultrasound and photoacoustic imaging can assist both cancer detection and therapy guidance.