Full-pupil versus divided-pupil confocal line-scanners for reflectance imaging of human skin in vivo

A full-pupil confocal line-scanning microscope is under development for imaging human skin in vivo in

reflectance. The new design potentially offers an alternative to current point- and line-scanners that may

simplify the optics, electronics and mechanics, and lead to simpler and smaller confocal microscopes. With

a combination of a cylindrical lens and an objective lens, the line-scanner creates a focused line of laser

light in the object plane within tissue. An oscillating galvanometric mirror scans the focused line

transverse to its axis. The backscattered light from the tissue is de-scanned and focused onto a linear

CMOS detector array. Preliminary measurements of the axial line-spread function, with a 30x, 0.9-NA

water immersion objective lens and illumination wavelength of 633 nm, determined the optical sectioning

to be 10 μm. The new design is simple, requiring only eight optical components. However, the

disadvantage is non-confocality in one dimension that results in 20% weaker sectioning than with a pointscanner,

and reduced contrast in scattering tissue. The images of standard reflective targets such as a

mirror and grating as well as dermis-like scattering target such as paper offer a preliminary glimpse into the

performance of the line-scanner. A similar alternative design is the divided-pupil (theta) line-scanner,

which provides 50% weaker sectioning than with a point scanner, but better contrast and less speckle due to

the theta configuration. Such line scanners may prove useful for routine imaging of humans in clinical

settings.