Images in cardiovascular medicine: in vivo imaging of the adult Drosophila melanogaster heart with real-time optical coherence tomography.
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Abdomen↗
Biomedical subjects
Michael A Choma
Publications and source records attributed to Michael A Choma.
Drosophila as a model for the identification of genes causing adult human heart disease.
Drosophila melanogaster genetics provides the advantage of molecularly defined P-element insertions and deletions that span the entire genome. Although Drosophila has been extensively used as a model system to study heart development, it has not been used to dissect the genetics of adult human heart disease because of an inability to phenotype the adult fly heart in vivo. Here we report the development of a strategy to measure cardiac function in awake adult Drosophila that opens the field of Drosophila genetics to the study of human dilated cardiomyopathies. Through the application of optical coherence tomography, we accurately distinguish between normal and abnormal cardiac function based on measurements of internal cardiac chamber dimensions in vivo. Normal Drosophila have a fractional shortening of 87 +/- 4%, whereas cardiomyopathic flies that contain a mutation in troponin I or tropomyosin show severe impairment of systolic function. To determine whether the fly can be used as a model system to recapitulate human dilated cardiomyopathy, we generated transgenic Drosophila with inducible cardiac expression of a mutant of human delta-sarcoglycan (deltasg(S151A)), which has previously been associated with familial dilated cardiomyopathy. Compared to transgenic flies overexpressing wild-type deltasg, or the standard laboratory strain w(1118), Drosophila expressing deltasg(S151A) developed marked impairment of systolic function and significantly enlarged cardiac chambers. These data illustrate the utility of Drosophila as a model system to study dilated cardiomyopathy and the applicability of the vast genetic resources available in Drosophila to systematically study the genetic mechanisms responsible for human cardiac disease.
Animals↗
Spectral-domain phase microscopy.
Broadband interferometry is an attractive technique for the detection of cellular motions because it provides depth-resolved phase information via coherence gating. We present a phase-sensitive technique called spectral-domain phase microscopy (SDPM). SDPM is a functional extension of spectral-domain optical coherence tomography that allows for the detection of nanometer-scale motions in living cells. The sensitivity of the technique is demonstrated, and its calibration is verified. A shot-noise limit to the displacement sensitivity of this technique is derived. Measurement of cellular dynamics was performed on spontaneously beating cardiomyocytes isolated from chick embryos.
Animals↗
Spectral triangulation molecular contrast optical coherence tomography with indocyanine green as the contrast agent.
We report a new molecular contrast optical coherence tomography (MCOCT) implementation that profiles the contrast agent distribution in a sample by measuring the agent's spectral differential absorption. The method, spectra triangulation MCOCT, can effectively suppress contributions from spectrally dependent scatterings from the sample without a priori knowledge of the scattering properties. We demonstrate molecular imaging with this new MCOCT modality by mapping the distribution of indocyanine green, a FDA-approved infrared red dye, within a stage 54 Xenopus laevis.
Animals↗
Protein-based molecular contrast optical coherence tomography with phytochrome as the contrast agent.
We report the use of phytochrome A (phyA), a plant protein that can reversibly switch between two states with different absorption maxima (at 660 and 730 nm), as a contrast agent for molecular contrast optical coherence tomography (MCOCT). Our MCOCT scheme builds up a difference image revealing the distribution of phyA within a target sample from pairs of consecutive OCT A-scans acquired at a probe wavelength of 750 nm, both with and without additional illumination of the target sample with 660-nm light. We demonstrate molecular imaging with this new MCOCT modality in a target sample containing a mixture of 0.2% Intralipid and 83 microM of phyA.
Contrast Media↗
Images in cardiovascular medicine. Approaching cardiac development in three dimensions by magnetic resonance microscopy.
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Animals↗
Instantaneous quadrature low-coherence interferometry with 3 x 3 fiber-optic couplers.
We describe fiber-based quadrature low-coherence interferometers that exploit the inherent phase shifts of 3 x 3 and higher-order fiber-optic couplers. We present a framework based on conservation of energy to account for the interferometric shifts in 3 x 3 interferometers, and we demonstrate that the resulting interferometers provide the entire complex interferometric signal instantaneously in homodyne and heterodyne systems. In heterodyne detection we demonstrate the capability for extraction of the magnitude and sign of Doppler shifts from the complex data. In homodyne detection we show the detection of subwavelength sample motion. N x N (N > 2) low-coherence interferometer topologies will be useful in Doppler optical coherence tomography (OCT), optical coherence microscopy, Fourier-domain OCT, optical frequency domain reflectometry, and phase-referenced interferometry.
Equipment Design↗
Molecular contrast in optical coherence tomography by use of a pump-probe technique.
We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. A pump-probe technique is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample-arm light acting as probe light. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented.
Contrast Media↗
Improved preparation of chick embryonic samples for magnetic resonance microscopy.
Previous work demonstrated the power of three-dimensional (3D) magnetic resonance microscopy (MRM) to follow complicated morphologic development in the embryonic cardiovascular system. In this study we describe a new dual-contrast method for specimen preparation that combines perfusion fixation and immersion in fixative with macro- and small molecular gadolinium agents to provide enhanced definition of both the heart wall and chamber. MRM was performed at 9.4 T with image resolutions of 25, 31, and 50 microm isotropic voxels for three stages of chick embryos (day 4, day 5.5, and day 9), and compared to histological sections of the same embryos. The results show considerable improvement of image quality over previous efforts, with better signal-to-noise ratio (SNR) and contrast between the cardiac chamber and myocardial wall. Excellent correlation was shown between the MRM images and histological sections. Thus, 3D high-resolution MRM in combination with the dual-contrast technique is useful for acquiring quantitative 3D morphologic data regarding heart development.
Animals↗
Optical coherence tomography: a new high-resolution imaging technology to study cardiac development in chick embryos.
BACKGROUND: Optical coherence tomography (OCT) is a depth-resolved, noninvasive, non-destructive imaging modality, the use of which has yet to be fully realized in developmental biology. METHODS AND RESULTS: We visualized embryonic chick hearts at looping stages using an OCT system with a 22 micro m axial and 27 micro m lateral resolution and an acquisition rate of 4000 A-scans per second. Normal chick embryos from stages 14 to 22 and sham-operated and cardiac neural crest-ablated embryos from stages 15 and 18 were scanned by OCT. Three-dimensional data sets were acquired and processed to create volumetric reconstructions and short video clips. The OCT-scanned embryos (2 in each group) were photographed after histological sectioning in comparable planes to those visualized by OCT. The optical and histological results showing cardiovascular microstructures such as myocardium, the cardiac jelly, and endocardium are presented. CONCLUSIONS: OCT is a powerful imaging modality which can provide new insight in assessing and understanding normal and abnormal cardiac development in a variety of animal models.
Animals↗
Swept source optical coherence tomography using an all-fiber 1300-nm ring laser source.
The increased sensitivity of spectral domain optical coherence tomography (OCT) has driven the development of a new generation of technologies in OCT, including rapidly tunable, broad bandwidth swept laser sources and spectral domain OCT interferometer topologies. In this work, the operation of a turnkey 1300-nm swept laser source is demonstrated. This source has a fiber ring cavity with a semiconductor optical amplifier gain medium. Intracavity mode selection is achieved with an in-fiber tunable fiber Fabry-Perot filter. A novel optoelectronic technique that allows for even sampling of the swept source OCT signal in k space also is described. A differential swept source OCT system is presented, and images of in vivo human cornea and skin are presented. Lastly, the effects of analog-to-digital converter aliasing on image quality in swept source OCT are discussed.
Cornea↗
Heterodyne swept-source optical coherence tomography for complete complex conjugate ambiguity removal.
Fourier domain (FD) techniques have increasingly gained attention in optical coherence tomography (OCT). This is primarily due to their demonstrated sensitivity of two to three orders of magnitude over conventional time-domain techniques. FDOCT images are subject to two primary sources of artifacts. First, a complex conjugate ambiguity arises because the Fourier transform of the real-valued spectral interferometric signal is Hermitian symmetric. This ambiguity leads to artifactual superposition of reflectors at positive and negative pathlength differences between the sample and reference reflectors. Second, noninterferometric and sample autocorrelation terms appear at dc, obscuring reflectors at zero pathlength difference. We show that heterodyne detection in swept-source OCT (SSOCT) enables the resolution of complex conjugate ambiguity and the removal of noninterferometric and autocorrelation artifacts. We also show that complex conjugate ambiguity resolution via frequency shifting circumvents fall-off induced by finite source linewidth in SSOCT when samples are shifted to large pathlength differences. We describe an efficient heterodyne SSOCT design that enables compensation of power losses from frequency-shifting elements. Last, we demonstrate this technique, coupled with wavenumber triggering and electronic demodulation, for in vivo imaging of the human anterior eye segment.
Artifacts↗
Doppler flow imaging of cytoplasmic streaming using spectral domain phase microscopy.
Spectral domain phase microscopy (SDPM) is a function extension of spectral domain optical coherence tomography. SDPM achieves exquisite levels of phase stability by employing common-path interferometry. We discuss the theory and limitations of Doppler flow imaging using SDPM, demonstrate monitoring the thermal contraction of a glass sample with nanometer per second velocity sensitivity, and apply this technique to measurement of cytoplasmic streaming in an Amoeba proteus pseudopod. We observe reversal of cytoplasmic flow induced by extracellular CaCl2, and report results that suggest parabolic flow of cytoplasm in the A. proteus pseudopod.
Amoeba↗