  Intravascular polarimetry with catheter-based polarization-sensitive optical
coherence tomography (PS-OCT) complements the high-resolution structural
tomograms of OCT with morphological contrast available through polarimetry. Its
clinical translation has been complicated by the need for modification of
conventional OCT hardware to enable polarimetric measurements. Here, we present
a signal processing method to reconstruct polarization properties of tissue
from measurements with a single input polarization state, bypassing the need
for modulation or multiplexing of input states. Our method relies on a
polarization symmetry intrinsic to round-trip measurements and uses the
residual spectral variation of the polarization states incident on the tissue
to avoid measurement ambiguities. We demonstrate depth-resolved birefringence
and optic axis orientation maps reconstructed from in-vivo data of human
coronary arteries. We validate our method through comparison with conventional
dual-input state measurements and find a mean cumulative retardance error of
13.2deg without observable bias. The 95% limit of agreement between
depth-resolved birefringence is 2.80 x 10^(-4), which is less than the
agreement between two repeat pullbacks of conventional PS-OCT (3.14 x 10^(-4)),
indicating that the two methods can be used interchangeably. The hardware
simplification arising from using a single input state may be decisive in
realizing the potential of polarimetric measurements for assessing coronary
atherosclerosis in clinical practice.
