Browsing by Subject "Magnetic Resonance Spectroscopy"
Now showing 1 - 10 of 10
- Results Per Page
- Sort Options
Item Association of African Ancestry with Left Ventricular Hypertrophy Assessed by Electrocardiographic Voltage and Cardiac Magnetic Resonance: The Dallas Heart Study(2018-01-23) Alame, Aya J.; Garg, Sonia; Kozlitina, Julia; Ayers, Colby; Drazner, Mark H.INTRODUCTION: Left ventricular hypertrophy (LVH) is more common in blacks than whites, despite adjusting for differences in blood pressure. Whether environmental or genetic factors lead to this increased prevalence of LVH in blacks is unknown. If genetic factors are involved, we hypothesized that the proportion of African ancestry among self-reported blacks would be associated with an increased risk of LVH in this ethnic group. METHODS: Participants from the Dallas Heart Study underwent genotyping, an electrocardiogram (ECG), and Cardiac Magnetic Resonance (CMR) imaging. Ancestral admixture proportions were estimated using genetic markers (Illumina Exome Chip) and ADMIXTURE software assuming 3 ancestral populations. In this analysis, we included participants that self-identified as black or white (n=2077). First, we tested the association of genetically inferred African ancestry (AFR) and self-reported black race, separately, using multivariable linear regression models, with three LVH phenotypes: 12-lead ECG voltage, LV concentricity0.67 (LV mass/volume0.67, a marker of concentric LVH), and LV Wall Thickness (LVWT). Next, we entered both AFR and black race into the same models to determine if the association of black race with LVH would be accounted for by AFR. Finally, we tested the association of AFR with LVH phenotypes among self-reported blacks. RESULTS: The study cohort consisted of 1,251 black and 826 white participants. Black race and AFR were individually associated with ECG voltage, LV concentricity0.67, and LVWT (Table 1). When AFR and black race were entered together into multivariable models, AFR, but not black race, was significantly associated with the LVH phenotypes (Table 1). Among self-reported blacks, AFR remained significantly associated with these LVH phenotypes (Table 1). CONCLUSIONS: The association of black race with LVH phenotypes can be captured more robustly with a genetic estimate of African ancestry. Further, within blacks, the proportion of AFR was associated with LVH phenotypes. These data support a genetic basis, related to African ancestry, for the increased prevalence of LVH in blacks.Item The emerging role of magnetic resonance imaging in clinical medicine(1985-07-11) Peshock, Ronald M.Item Fiber Orientation Modeling: a Method to Improve Quantitation of Intramyocellular Lipids in Human Subjects at 7 Tesla(2011-10-03) Khuu, Anthony N.; Malloy, Craig R.BACKGROUND: Increased intramyocellular lipid (IMCL) content in skeletal muscle has been suggested to be a biomarker for insulin resistance. As a noninvasive method of estimating IMCL, 1H MR spectroscopy of muscle fat has been a popular method for measuring the concentration of IMCLs, a goal highly desirable for research in the pathogenesis of type 2 diabetes. Extramyocellular lipids (EMCL) are often considered to be deposited along strands that are parallel to Bo (the applied field) whereas IMCL are assumed to be spherical droplets in the muscle cells’ cytoplasm. Resolution between IMCL and EMCL signals mainly results from the angle-dependant bulk susceptibility of the 2 geometric structures. However, IMCL signal is usually contaminated by a broad and asymmetrical EMCL . Conventional fitting methods usually assume that both the IMCL and EMCL signals to be symmetrical, represented by a single Lorentzian, Gaussian or Voigt (hybrid lineshape between Gaussian and Lorentzian) lineshapes. However, significant asymmetry in the resonance assigned to the methylene protons (-CH2-)n in extramyocellular lipids (EMCL) interfered with fitting the spectra. In this work, we explore another approach, named Fiber Orientation Modeling (FOM) by using the bulk susceptibility effect theory to accurately assess the lineshape of EMCL. METHODS: The distribution of EMCL strand orientation at any angle from 0 degrees to 90 degrees relative to Bo was described by a Gaussian function, centered at a specific angle and a width representing a dispersion of EMCL strands. The chemical shift OMEGA from each strand was translated by the well-known orientation dependence interaction OMEGA = 3cos2THETA-1, where THETA is the angle between EMCL and the applied field. As the result, the location and amplitude of individual curves representing each strand could be derived. Depend on the aforementioned Gaussian distribution, the combination of these individual curves generated a unique EMCL shape. In this work, spectral simulations were generated using muscle fiber orientation reported previously. The phantom experiment with a fat cylinder (representing EMCL) submerged in Intralipid(TM) solution (representing IMCL) was also performed to determine the maximal shift at 0 degrees and 90 degrees. Under IRB approval, single voxel and chemical shift images were acquired from soleus and gastrocnemius muscle of healthy human subjects at 7T (Phillips Medical system, Cleveland, Ohio). All the spectra were fitted with the hybrid Voigt lineshape and the experimental lineshape. RESULTS: In simulated spectra with dominant angle of 00 to the applied field and little dispersion, fitting with the Voigt lineshape accurately determined IMCL/EMCL ratio over a range of different linewidths. Increasing dispersion and central angle caused overestimation of IMCL/EMCL ratios, up to three-fold when fitted with the Voigt lineshape. The error was substantially reduced using our method. The improvement is also observed in phantom spectra and human spectra. Estimates of [IMCL]/[EMCL] were significantly improved by including variations in fiber orientation in the lineshape analysis (fiber orientation modeling, FOM). Calculated soleus [IMCL] using FOM, 4.43 ± 2.32 mmol/kg wet weight, was lower compared to most previous reports in soleus. The average orientation of EMCL was calculated to be 35 degrees relative to Bo with a dispersion width of 24 degrees CONCLUSION: Since prominent asymmetrical EMCL signal tends to contaminate into IMCL region, this interaction results in the amplitude-dependence of IMCL signal on the average orientation and dispersion of EMCL. As the result, the use of symmetrical lineshape tends to overestimate the IMCL signal if all strands of EMCL are not parallel to Bo and one another. By accounting for the angular dispersion& orientation, the fit would improve both the residual and the IMCL estimate.Item [News](1981-08-07) Rutherford, SusanItem Non-Q-wave myocardial infarction(1986-06-05) Nixon, J. V.Item Principles of clinical nuclear magnetic resonance imaging and spectroscopy(1985-05-02) Malloy, Craig R.Item [Southwestern News](2002-09-19) Morrison, SusanItem [Southwestern News](2000-05-25) Baxter, MindyItem [UT News](1987-07-29) Rutherford, SusanItem [UT Southwestern Medical Center News](2009-09-17) Shear, Kristen Holland