ABSTRACT
The preparation of pathology, either during surgery or after, is time consuming and labor intensive. In the setting of nonmelanoma skin cancers, frozen pathology that is prepared during Mohs surgery requires 20-45 minutes per excision, and two or more excisions are performed, such that the total preparation time lasts from two to several hours.1 In other settings, such as head-and-neck and breast cancer, patients are sent home after the initial surgery because results from fixed pathology are obtained only after 1 or 2 days. A technology that can image large areas of excised or biopsied tissue at high resolution with minimal tissue preparation could provide real-time diagnosis or margin detection. Currently, confocal microscopy and full-field optical coherence tomography are being developed for this purpose.2-11
Because confocal microscopy provides cellular resolution on minimally processed, freshly excised tissue, it has the potential to rapidly diagnose tumor margins at the bedside or in the surgical suite. However, conventional confocal microscopes can cover only small fields of view, typically 0.5 × 0.5 mm2, compared to the size (several mm2 or cm2 in extent) of the excised tissue. This size difference undermines the use of confocal microscopy on excised tissue in surgical settings. To overcome this barrier, a method called mosaicking has been developed, in which the small images are stitched together to form a large area view of the tissue while maintaining resolution and sectioning. Early mosaicking techniques involved the stitching of individual square confocal images into a pattern of rows and columns.12-16 Although early mosaicking techniques allowed a view of a large area of excised tissue, the stitching and smoothing of borders among individual images was time consuming. Mosaicking of 36 × 36 images to display 12 cm2 of excised tissue from Mohs surgery was demonstrated in 9 minutes.14,17,18 However, this time excluded the time to determine parameters of the stitching algorithm, time for minimal processing, and time for
mounting the tissue on the microscope. In a blinded examination of 45 fluorescence mosaics by two Mohs surgeons, basal cell carcinoma margins were detected with an overall sensitivity of 96.6% and a specificity of 89.2%.17,19 The results of this preclinical study demonstrated the promise of confocal mosaicking microscopy. Although 9 minutes is certainly faster than current conventional histopathology techniques, the routine implementation in surgical settings requires shorter times. To reach practical and routine use in any operating room setting, mosaicking must meet the surgeons’ need to examine tumor margins in large areas (∼cm2) within a few minutes. To this end, investigators developed a novel microscope called the confocal strip-mosaicking (CSM) microscope where long image strips are stitched together side by side to cover the entire tissue. The CSM technique produces a 1 cm2, seamless, smooth image in 90 seconds once the tissue is mounted on the microscope.
