Podium Presentation in Room 4 on Wednesday at 9:00 (Chair: Peggi Angel / Anna Krieger)
Authors: Sankha S. Basu (1), Michael S. Regan (2), Elizabeth C. Randall (3), Walid M. Abdelmoula (2), Amanda R. Clark (2), Begoña Gimenez-Cassina Lopez (2), Dale S. Cornett (4), Andreas Haase (5), Sandro Santagata (1,6), and Nathalie Y.R. Agar (2,3,7)
Introduction: The frozen section procedure (FSP) is a century-old technique used by surgeons and pathologists for intraoperative tissue analysis. The procedure involves tissue excision, specimen transport, cryo-sectioning, and histopathological assessment. Although the FSP remains the standard method for intraoperative tissue assessment due to its fast turnaround time, it is largely limited to hematoxylin and eosin (H&E) staining only. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) has emerged as a promising analytical technique capable of providing spatially-resolved biochemical characterization of tissue specimens. However, extensive pre-analytical steps, combined with long acquisition times have limited its clinical translation. Here, we present a rapid MALDI MSI method for tissue assessment, providing a method which can be utilized in the frozen section room.
Methods: To improve MALDI MSI turnaround time, we shortened or eliminated the three most time-consuming steps, namely, matrix application, acquisition set-up, and data acquisition. We effectively eliminated matrix application time by mounting tissue sections on indium tin oxide (ITO) slides with pre-coated matrix. Next, we used a templated ITO slide with a pre-selected region for analysis, eliminating the need for high resolution scanning, image registration, and region of interest selection. Finally, to reduce data acquisition time, we used a high frequency laser and optimized the firing pattern to provide the highest quality ion images. The optimized method was applied to tissue specimens and compared with conventional MALDI MSI approaches. Finally, we used high dimensional data visualization and automated multi-modal integration to align MSI and H&E stained images.
Results: After optimization, we were able to image tissue specimens with a total preparation and run time of less than five minutes, with data quality comparable to conventional MALDI MSI methods. We then applied this “streamlined” method to cryo-sectioned brains from healthy mice which highlighted the major landmarks of the mouse brain. We also used the technique in a patient derived xenograft (PDX) model of glioblastoma, as well as surgically resected human breast and brain specimens, each demonstrating unique metabolomic signatures. We then used t-distributed stochastic neighbor embedding (t-SNE) algorithm to reduce the high dimensional data, which was then spatially projected onto the tissue specimens to reveal molecularly defined structures not apparent histologically, thereby enhancing the diagnostic power of the frozen section procedure.
Conclusions: We present a MALDI MSI method that can be completed in under five minutes including preparation and run time. This can serve as a complementary tool to histopathology during the frozen section procedure to help surgeons and pathologists provide improved diagnostic capabilities.
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