# Ten Years of Gabor-Domain Optical Coherence Microscopy
## 3 Gabor-Domain Optical Coherence Microscopy
After acquiring the desired number of zones (three in this case), the in-focus portions are extracted and fused in a high-definition volumetric image, which achieves cellular resolution throughout the volume. An en face view of the dermoepidermal junction (corresponding to the dashed teal line in the 3D view), with basal cells clearly visible (white arrows), is shown. Parallel processing of the acquired data on graphics processing units (GPUs) achieves near real-time visualization of the volumetric images [28]. The 2015 and 2018 implementations of GDOCM are shown in Figure 5. A standalone cart houses the entire GDOCM system. While the first prototype shown in Figure 5a included several elements mounted on a breadboard assembly, the instrument shown in Figure 5b was entirely re-engineered with precision mechanics for robust and reliable operation, and incorporates a custom software for semiautomated image acquisition, and 3D image visualization and analysis. The microscope can be operated either as a handheld or with an articulated arm (see Figure 6, for an example of contact mode with a mechanical arm). The use of a mechanical arm is desired to minimize motion artifacts introduced by operator hand tremor. A comparison of the imaging performance of confocal microscopy, spectral domain optical coherence tomography, optical coherence microscopy, full-field optical coherence tomography, and Gabor-domain optical coherence microscopy is reported in Table 1. The performance of the various imaging modalities relates to the chart in Figure 1, with SD-OCT suffering from limited transverse resolution while offering excellent imaging depth of several millimeters, while confocal microscopy, OCM, and FF-OCT achieve subcellular resolution over a limited imaging depth. GDOCM balances these  
Figure 5: (a) GDOCM system in use at the University of Rochester Department of Dermatology in its first in vivo study in the fall of 2015; (b) 2018 version of GDOCM (LighTopTech Corp. GDOCM 4D\({}^{\text{m}}\)). Figure 6: Handheld GDOCM microscope. A mechanical arm can be used to reduce operator hand tremor. parameters to achieve cellular resolution over an imaging depth of 2 mm. SD-OCT, OCM, and GDOCM, being spectral domain OCT systems, have a cross-sectional image orientation, while CM and FF-OCT (time domain OCT) have an en face image orientation. A main limitation of confocal microscopy, unlike OCT, is that the sectioning in depth is set by the NA of the objective lens. Contact operation is typically required with clinical confocal microscopes, however contactless implementations have been proposed. Higher sectioning is obtained with higher NA, yet this occurs at the expense of DOF. Because axial sectioning in OCT is independent of the NA, since it is set by the spectral bandwidth, both higher axial sectioning and larger DOF are possible with OCT. Furthermore, it may be difficult to assess the depth of imaging with confocal, as only en face planes are acquired. SD-OCT acquires depth scans, from which the volume is assembled, and the depth of any en face plane is directly acquired from the depth scan. While the methods that offer higher transverse resolution typically have limited FOV, mosaicking is often used to provide wide FOV imaging, naturally at the expense of acquisition time.