We present 3-dimensional volume-rendered in vivo images of developing embryos of the
African clawed frog Xenopus laevis taken with our new en-face-scanning, focus-tracking
OCM system at 1300 nm wavelength. Compared to our older instrument which operates
at 850 nm, we measure a decrease in the attenuation coefficient by 33%, leading to a
substantial improvement in depth penetration. Both instruments have motion-sensitivity
capability. By evaluating the fast Fourier transform of the fringe signal, we can produce
simultaneously images displaying the fringe amplitude of the backscattered light and
images showing the random Brownian motion of the scatterers. We present time-lapse
movies of frog gastrulation, an early event during vertebrate embryonic development in
which cell movements result in the formation of three distinct layers that later give rise to
the major organ systems. We show that the motion-sensitive images reveal features of the
different tissue types that are not discernible in the fringe amplitude images. In particular,
we observe strong diffusive motion in the vegetal (bottom) part of the frog embryo which
we attribute to the Brownian motion of the yolk platelets in the endoderm.
We compare the dynamic range of OCT/OCM instruments configured with unbalanced interferometers, e.g., Michelson interferometers, with that of instruments utilizing balanced interferometers and balanced photodetection. We define the dynamic range (DR) as the ratio of the maximum fringe amplitude achieved with a highly reflecting surface to the root-mean-square (rms) noise. Balanced systems achieve a dynamic range 2.5 times higher than that of a Michelson interferometer, enabling an image acquisition speed roughly 6 times faster. This maximum improvement occurs at light source powers of a few milliwatts. At light source powers higher than 30 mW, the advantage in acquisition speed of balanced systems is reduced to a factor of 4. For video-rate imaging, the increased cost and complexity of a balanced system may be outweighed by the factor of 4 to 6 enhancement in image acquisition speed. We include in our analysis the "beat-noise" resulting from incoherent light backscattered from the sample, which reduces the advantage of balanced systems. We attempt to resolve confusion surrounding the origin and magnitude of "beat-noise", first described by L. Mandel in 1962. Beat-noise is present in both balanced and unbalanced OCT/OCM instruments.