Polarization sensitive optical coherence tomography - a review [Invited]

Abstract

Optical coherence tomography (OCT) is now a well-established modality for high-resolution cross-sectional and three-dimensional imaging of transparent and translucent samples and tissues. Conventional, intensity based OCT, however, does not provide a tissue-specific contrast, causing an ambiguity with image interpretation in several cases. Polarization sensitive (PS) OCT draws advantage from the fact that several materials and tissues can change the light's polarization state, adding an additional contrast channel and providing quantitative information. In this paper, we review basic and advanced methods of PS-OCT and demonstrate its use in selected biomedical applications.

Keywords: (110.5405) Polarimetric imaging; (170.4500) Optical coherence tomography.

Figures

Fig. 1

Vibrational ellipses (from left to right) for vertically linear polarized light (Ex=0), linear polarized light oriented at 45° with respect to the vertical and horizontal orientations (Ex=−Ey), and circularly polarized light (Ex=eiπ/2Ey). Reprinted from Ref [3].

Fig. 2

Electric fields components for various polarization states corresponding to the different Stokes parameters. Reprinted from Ref [3].

Fig. 3

Poincaré sphere representations of the effects of (a) diattenuation, (b) birefringence, and (c) the combined effect about a common optic axis A on a polarization state S. The “pulling” effect of diattenuation is evident from the trace (inner arc) of the transmitted polarization state as diattenuation increases (the normalized trace along the surface of the sphere is also shown). Birefringence is equivalent to a rotation in the Poincaré sphere. The combined effect has the appearance of a spiral. Reprinted from Ref [3].

Fig. 4

Birefringence calculation illustrating (a): the surface states, I1 and I2, in blue and the reflected states, I’1 and I’2, in green, (b, c) the planes P1 and P2 that span all possible rotation axes, and (d): the intersection of the planes resulting in determination of the optic axis. Reprinted from Ref [13].

Fig. 5

Sketch of basic PS-OCT system. BS, beam splitter; Det, detector; P, polarizer; PBS, polarizing beam splitter; QWP, quarter wave plate; RM, reference mirror; SLD, super luminescent diode.

Fig. 6

PS-OCT images recorded in a chicken myocardium in vitro. Image dimensions: horizontal: 14 mm, vertical: 5 mm (optical distance). (a) Intensity image (color bar: logarithmic intensity scale); (b) phase retardation image (color bar: 0 – 90°); (c) axis orientation image (color bar: −90° – + 90°). (Adapted from [43])

Fig. 7

PS-OCT B-scan of healthy human fovea. (a) Reflectivity (log scale), the white rectangle shows approximate areas of the zoom-ins (b)-(d); (b) retardation (color bar: 0°-90°); (c) optic axis orientation (color bar: 0°-180°); (d) DOPU (color bar: 0-1). ELM, external limiting membrane; IS/OS, boundary between inner and outer photoreceptor segments; ETPR, end tips of photoreceptors; RPE, retinal pigment epithelium. (Adapted from [33])

Fig. 8

Example of the interference fringes measured in the horizontal and vertically polarized channel. If the amplitude in the vertical channel is zero, the light must be horizontally polarized (Q-state in Stokes vector notation). If the interference fringes are of equal magnitude and are in phase, the polarization state is linear at 45 degrees (U-state in Stokes vector notation). If the interference fringes are of equal magnitude and are 90 degrees out of phase, the polarization state is circular (V-state in Stokes vector notation) .

Fig. 9

Schematic of the fiber-based PS-OCT system (p.c., polarization controller; p, polarizer; pm, polarization modulator; oc, optical circulator; RSOD, rapid scanning optical delay; fpb, fiber polarizing beamsplitter). Jin, Jout, and JS are the Jones matrix representations for the one-way optical path from the polarization modulator to the scanning handpiece, the one-way optical path back from the scanning handpiece to the detectors, and the round-trip path through some depth in the sample, respectively. Reprinted from [16].

Fig. 10

Cadaveric human coronary artery PS-OCT images with and without numerical non-common-path-PMD correction by a spectral binning method. The first row shows intensity, local retardation, DOPU without PMD correction (left to right). The second row shows intensity-local retardation composite, local retardation, DOPU with PMD correction (left to right.) The images were reprinted from [70].

Fig. 11

Retinal intensity OCT images taken by an optically buffered PS-OCT system without (a) and with (b) common-path-PMD correction. (c) and (d) are magnified images of (a) and (b), respectively. The comb-like artifacts in (a) and (c) were suppressed in (b) and (d). The figure was reprinted from [72].

Fig. 12

Examples of birefringence imaging of blebs. (a) and (b) are intensity OCT and (c) and (d) are birefringence cross-sections. In (e) and (f), the high birefringence pixels (red) are overlaid on intensity image. The numbers at the top left indicate the areal fraction of high birefringence regions in the conjunctiva (adapted from [85]).

Fig. 13

PS-OCT images recorded in the optic nerve head region of a healthy human eye. (a) Reflectivity B-scan; (b) retardation B-scan; (c) en-face RNFL retardation map. The white line indicates the position of the B-scans.

Fig. 14

Circumpapillar profiles of (a) RNFL retardation, (b) RNFL thickness, (c) RNFL birefringence. T, temporal; S, superior; N, nasal; I, inferior. Black line: mean value of 10 healthy eyes; red lines: mean value ± standard deviation. (Adapted from [110] by permission of the Association for Research in Vision and Ophthalmology)

Fig. 15

Wide field RNFL retardation maps obtained in human eyes. (a) Healthy eye; (b) glaucomatous eye. (Adapted from [111])

Fig. 16

Drusen segmentation by PS-OCT. (a) En face reflectivity projection image (pseudo SLO); (b1, b2) B-scans with segmentation lines: blue, inner limiting membrane; red, RPE; green, original position of RPE. (c) drusen map. (adapted from [117])

Fig. 17

Drusen imaging by PS-OCT (a) and intensity based OCT (b) in the same eye of a patient with AMD. Various forms of drusen can be differentiated in the PS-OCT image, where depolarizing tissue (red) has been segmented by its low DOPU value. Blue arrow: druse filled with depolarizing material; white arrowheads: small atrophic lesions; yellow arrow: drusenoid structure with complete loss of RPE. (Reproduced from [119] by permission of the Association for Research in Vision and Ophthalmology)

Fig. 18

Images of an eye with fibrotic neovascular AMD. (a) Color fundus photo; (b) fluorescein angiography; (c) PS-OCT mean retardation map; (d) PS-OCT reflectivity projection map; (e) PS-OCT median retardation map; (f) PS-OCT axis orientation map; (g) PS-OCT reflectivity B-scan; (h) same B-scan with segmented RPE (red); (i) PS-OCT axis orientation B-scan, fibrotic tissue generates column-like color pattern (color bar: −90 - + 90°); (j) PS-OCT retardation B-scan, fibrotic tissue is strongly birefringent (color bar: 0 – 90°). (Adapted from [126])

Fig. 19

Birefringence cross sectional B-scans extracted from a three dimensional data set acquired with Jones Matrix OCT in a patient with myopic choroidal neovascularization. A layered structure is visible in the sclera, as well as varying birefringence in the neovascular region. (Adapted from [128])

Fig. 20

Structural intensity (left) and polarization sensitive image (right) of a hamster cheek pouch cancer model. In the intensity image the features of the tumor tissue are visible, however, the PS image shows significant contrast between normal (left) and tumor tissue (right) based on the banding pattern. The normal cheek pouch tissue shows a much higher birefringence than the cancer tissue. (Adapted from [57])