Quantitative metrics for assessment of chemical image quality and spatial resolution

Abstract

ChemIC and cRPF, respectively, were developed and successfully applied for the objective description of chemical image quality and spatial resolution of chemical images collected from model surfaces using a laser ablation/liquid vortex capture mass spectrometry imaging system. Published in 2016. This article is a U.S. Government work and is in the public domain in the USA.

Polymeric spatial resolution test patterns for mass spectrometry imaging using nano‐thermal analysis with atomic force microscopy

“…(e), (f), (k), (l), (q), and (r)) were used for the calculation of the individual cRPF values. The number of lines statistically analyzed simultaneously corresponded to the feature size(s) investigated so as not to bias the calculations towards higher spatial resolutions and to report spatial resolutions as accurately as possible . For this reason, all possible consecutive two‐ and three‐line‐wide bands (corresponding to total band widths of 660 nm and 990 nm, respectively) were used to evaluate patterns with 700 nm and 1000 nm diameters, respectively.…”

“…The presence or absence of overlap between adjacent standard deviation values indicates if a feature was resolved or not (red arrows in Figs. (d) and (p) indicate areas in which adjacent standard deviation values did in fact overlap), respectively, by definition of cRPF . (Signal intensity asymmetry, i.e.…”

“…Complicating the issue is the fact that the nature of the sampling process (e.g., laser ablation, liquid extraction, thermal desorption) and intertwined (e.g., matrix-assisted laser desorption/ionization (MALDI)) or separate ionization processes (e.g., electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI)) may necessitate a specific reference standard appropriate for each particular type of MSI system. Some typical resolution standards that have been reported in the literature include stamped ink patterns, [10][11][12] ink jet patterns printed using 'ink' containing a suitable test compound, [13][14][15][16] analyte surfaces covered by masking grids, [5,17] patterns in photoresist materials [18,19] and microfabricated surface wells and patterns filled, covered or functionalized with organic or biological molecules. [3][4][5] One MSI approach that we are advancing is based on an ambient environment nanoscale thermal desorption, or a thermolysis, sampling process using nano-thermal analysis (TA) probes controlled with an atomic force microscope.…”

“…The mass spectra spatial resolution was evaluated in a non-biased, quantitative fashion using the recently developed metric "corrected resolving power factor" (cRPF). [19] The best imaging resolution for the given PMMA thin film, achieved with the heated interface, was estimated to be 1.4 μm based on the ability to statistically distinguish 0.7-μm-wide lines separated by 0.7-μm-wide spacings.…”

“…The general utility of these test patterns is demonstrated by their use in evaluating the changing mass spectral image quality achieved as a function of the ionization interface temperature on our current nano‐TA AFM/MS system. The mass spectra spatial resolution was evaluated in a non‐biased, quantitative fashion using the recently developed metric "corrected resolving power factor" ( cRPF) . The best imaging resolution for the given PMMA thin film, achieved with the heated interface, was estimated to be 1.4 μm based on the ability to statistically distinguish 0.7‐μm‐wide lines separated by 0.7‐μm‐wide spacings.…”