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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2012)

In this dissertation a novel method for rapid quantification of left ventricular (LV) twist was developed, validated, and clinically evaluated. LV twist is defined as the difference in rotation of the apex relative to the base of the heart. Alteration in LV twist has been shown the correlate with LV dysfunction. Rotation was measured using Fourier Analysis of STimulated echoes (FAST), an image acquisition and rapid processing method. FAST can be applied to cardiovascular magnetic resonance (CMR) images with myocardial tagging, which imparts a sinusoidal pattern on the myocardial tissue that deforms with the LV during contraction and relaxation. First, FAST estimates of LV twist were validated using intra- and inter-observer comparison, intra- and inter-scan comparison, and comparison to values derived from a `gold-standard' technique. Second, FAST was used in conjunction with a CMR imaging technique designed to lengthen the duration of myocardial tag detection to acquire diastolic twist information. Third, FAST was applied to an imaging technique developed to minimize chemical shift induced myocardial tagging pattern artifacts, which produces more accurate measurements of LV twist. Fourth, FAST was used in combination with two free-breathing techniques to determine the impact of free-breathing on FAST estimates of LV twist. Fifth, FAST was used to characterize differences in LV twist in patients with moderate and severe mitral regurgitation. LV twist measurements derived from FAST showed good agreement for the intra- and inter-observer study and the intra- and inter-scan study. Additionally, systolic LV twist values matched well with the `gold-standard'. When used in combination with the improved myocardial tag duration, FAST estimates of diastolic LV twist matched well with literature values. LV twist derived from the normal imaging technique compared with the artifact minimizing technique did not detect any significant differences, however this study was performed in healthy subjects, specific patient populations may provide different results. The free-breathing study detected a significant decrease peak LV twist due to free-breathing compared with breath-held imaging derived values. A significant decrease in peak LV twist was detected in patients with moderate and severe mitral regurgitation. Overall, the FAST method for quantitative LV twist measurement has been validated and shown to produce accurate measurements of twist with limited user interaction.

    Cover page: Quantification of Systolic and Diastolic Left Ventricular Twist Using Fourier Analysis of STimulated Echoes (FAST) Magnetic Resonance Imaging
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2014)

    Purpose

    To evaluate Off Resonance Insensitive Complementary SPAtial Modulation of Magnetization (ORI-CSPAMM) and Fourier Analysis of STimulated echoes (FAST) for the quantification of left ventricular (LV) systolic and diastolic function and compare it with the previously validated FAST+SPAMM technique.

    Materials and methods

    LV short-axis tagged images were acquired with ORI-CSPAMM and SPAMM in healthy volunteers (n = 13). The FAST method was used to automatically estimate LV systolic and diastolic twist parameters from rotation of the stimulated echo and stimulated anti-echo about the middle of k-space subsequent to ∼3 min of user interaction.

    Results

    There was no significant difference between measures obtained for FAST+ORI-CSPAMM and FAST+SPAMM for mean peak twist (12.9 ± 3.4° versus 11.9 ± 4.0°; P = 0.4), torsion (3.3 ± 0.9°/cm versus 2.9 ± 1.0°/cm, P = 0.3), circumferential-longitudinal shear angle (9.1 ± 3.0° versus 8.2 ± 3.4°, P = 0.3), twisting rate (79.6 ± 20.2°/s versus 68.2 ± 23.4°/s, P = 0.1), untwisting rate (-117.5 ± 31.4°/s versus -106.6 ± 32.4°/s, P = 0.3), normalized untwisting rate (-9.3 ± 2.0/s versus -9.9 ± 4.4/s, P = 0.7), and time of peak twist (281 ± 18 ms versus 293 ± 25 ms, P = 0.04). FAST+ORI-CSPAMM also provided measures of duration of untwisting (148 ± 21 ms) and the ratio of rapid untwisting to peak twist (0.9 ± 0.3). Bland-Altman analysis of FAST+ORI-CSPAMM and FAST+SPAMM twist data demonstrates excellent agreement with a bias of -0.1° and 95% confidence intervals of (-1.0°, 3.2°).

    Conclusion

    FAST+ORI-CSPAMM is a semi-automated method that provides a quick and quantitative assessment of LV systolic and diastolic twist and torsion. ORI-CSPAMM corrects off-resonance accrued during tagging preparation and readout and visibly removes chemical shift from the tagging pattern, which confers greater robustness to the derived quantitative measures.
      Cover page: Off‐resonance insensitive complementary SPAtial Modulation of Magnetization (ORI‐CSPAMM) for quantification of left ventricular twist
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2015)

      Purpose

      To develop and evaluate complementary radial tagging (CRT) for improved myocardial tagging contrast.

      Methods

      We sought to develop and evaluate CRT, which aims to preserve the radial tag contrast throughout the cardiac cycle. Similar to complementary spatial modulation of magnetization, CRT acquires two sets of images with a phase shift in the tag pattern. The combination of a ramped imaging flip angle and image subtraction enhances tag contrast throughout the cardiac cycle. The proposed CRT technique uses a small table shift away from the isocenter to improve the uniformity of the radial tag pattern. We provide a mathematical solution for the optimal table shift and validate the solution in using a retrospective analysis of images from 500 patients in the Cardiac Atlas Project database.

      Results

      CRT simulations, phantom experiments, and in vivo images all demonstrate the improved tag contrast of CRT compared to RT. The retrospective evaluation demonstrated that acceptable CRT images could be acquired in over 98% of the clinical exams.

      Conclusion

      The CRT technique improves radial tag contrast throughout the cardiac cycle and should produce high quality tag patterns in nearly all patients.
        Cover page: Complementary radial tagging for improved myocardial tagging contrast
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2014)

        Purpose

        To assess the intra- and interscan reproducibility of LV twist using FAST. Assessing the reproducibility of the measurement of new MRI biomarkers is an important part of validation. Fourier Analysis of STimulated Echoes (FAST) is a new MRI tissue tagging method that has recently been shown to compare favorably with conventional estimates of left ventricular (LV) twist from cardiac tagged images, but with significantly reduced user interaction time.

        Materials and methods

        Healthy volunteers (N = 10) were scanned twice using FAST over 1 week. On day 1, two measurements of LV twist were collected for intrascan comparisons. Measurements for LV twist were again collected on day 8 for interscan assessment. LV short-axis tagged images were acquired on a 3 Tesla (T) scanner to ensure detectability of tags during early and mid-diastole. Peak LV twist is reported as mean ± SD. Reproducibility was assessed using the concordance correlation coefficient (CCC) and the repeatability coefficient (RC) (95% confidence interval [CI] range).

        Results

        Mean peak twist measurements were 13.4 ± 4.3° (day 1, scan 1), 13.6 ± 3.7° (day 1, scan 2), and 13.0 ± 2.7° (day 8). Bland-Altman analysis resulted in intra- and interscan bias and 95% CI of -0.6° [-1.0°, 1.6°] and 1.4° (-1.0°, 3.0°), respectively. The Bland-Altman RC for peak LV twist was 2.6° and 4.0° for intra- and interscan, respectively. The CCC was 0.9 and 0.6 for peak LV twist for intra- and interscan, respectively.

        Conclusion

        FAST is a semi-automated method that provides a quick and quantitative assessment of LV systolic and diastolic twist that demonstrates high intrascan and moderate interscan reproducibility in preliminary studies.
          Cover page: Intra‐ and interscan reproducibility using Fourier Analysis of STimulated Echoes (FAST) for the rapid and robust quantification of left ventricular twist
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2015)
            Cover page: The effect of free-breathing on left ventricular rotational mechanics in normal subjects and patients with duchenne muscular dystrophy
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2017)

            Purpose

            Cardiovascular magnetic resonance imaging exams can be performed during free-breathing. This may be especially important for boys with Duchenne muscular dystrophy (DMD) given their frequently limited breath-hold abilities. The impact of the respiratory compensation method on quantitative measurements of left ventricular (LV) rotational mechanics is incompletely understood. The purpose of this study was to evaluate differences in LV rotational mechanics acquired during breath-holding (BH), free-breathing with averaging (AVG), and free-breathing with respiratory bellows gating (BEL).

            Methods

            LV short-axis tagged images from healthy subjects (N = 16) and DMD patients (N = 5) were acquired with BH, AVG, and BEL. LV twist and circumferential-longitudinal shear (CL-shear) angle were measured using the Fourier Analysis of STimulated echoes (FAST) method.

            Results

            Peak LV twist estimates using BEL were significantly lower compared with BH in both healthy subjects (10.2 ± 3.6 ° versus 12.9 ± 2.3 °, P = 0.003) and patients with DMD (8.6 ± 3.6 ° versus 10.5 ± 3.6 °, P = 0.004). AVG results were in between BEL and BH. No significant differences in CL-shear were detected between BEL and BH.

            Conclusion

            Breath-holding directly affects estimates of peak LV twist, but not CL-shear. Using a free-breathing strategy for the evaluation of cardiac function is important for intrasubject longitudinal studies, intersubject comparisons, and multicenter trials for patients with DMD. Magn Reson Med 77:864-869, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
              Cover page: Effect of free‐breathing on left ventricular rotational mechanics in healthy subjects and patients with duchenne muscular dystrophy
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2015)
                Cover page: Quantitative left ventricular rotational mechanics in Duchenne and Becker muscular dystrophy patients
                • Article
                • Peer Reviewed
                UCLA Previously Published Works (2015)

                Purpose

                To evaluate the relationship between left ventricular (LV) twist, shear, and twist-per-volume and the severity of mitral regurgitation (MR). Primary MR is a valvular disorder that induces LV dysfunction. There exist several measures of LV rotational mechanics, but it remains unclear which measure of LV dysfunction best accords with the severity of MR. We hypothesized that LV systolic twist-per-volume slope would decrease with increasing severity of MR because of both decreases in rotational mechanics and increases in stroke volumes.

                Materials and methods

                Normal subjects (n = 54), moderate MR patients (n = 29), and severe MR patients (n = 54) were studied. Magnetic resonance imaging (MRI) was performed on a 1.5T scanner and grid-tagged LV images were collected at the LV base and LV apex. Measures of LV rotational mechanics were derived from tagged images using Fourier Analysis of STimulated echoes (FAST).

                Results

                Peak systolic twist-per-volume slope was significantly different for all pairwise comparisons (P < 0.0001) and compared to normal subjects (-0.14 ± 0.05°/mL) was decreased in moderate MR (-0.12 ± 0.04°/mL) and further decreased in severe MR (-0.07 ± 0.03°/mL).

                Conclusion

                Peak systolic twist-per-volume slope significantly decreased with increasing severity of MR and is therefore a suitable quantitative imaging biomarker for LV dysfunction in patients with MR.
                  Cover page: Left ventricular twist and shear in patients with primary mitral regurgitation
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