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Deep Learning Approach for Dynamic Sampling for
Multichannel Mass Spectrometry Imaging
David Helminiak, Member, IEEE, Hang Hu, Julia Laskin, and Dong Hye Ye, Member, IEEE
Abstract—Mass Spectrometry Imaging (MSI), using traditional
rectilinear scanning, takes hours to days for high spatial resolution
acquisitions. Given that most pixels within a sample's field of view
are often neither relevant to underlying biological structures nor
chemically informative, MSI presents as a prime candidate for
integration with sparse and dynamic sampling algorithms. During
a scan, stochastic models determine which locations
probabilistically contain information critical to the generation of
low-error reconstructions. Decreasing the number of required
physical measurements thereby minimizes overall acquisition
times. A Deep Learning Approach for Dynamic Sampling
(DLADS), utilizing a Convolutional Neural Network (CNN) and
encapsulating molecular mass intensity distributions within a
third dimension, demonstrates a simulated 70% throughput
improvement for Nanospray Desorption Electrospray Ionization
(nano-DESI) MSI tissues. Evaluations are conducted between
DLADS and a Supervised Learning Approach for Dynamic
Sampling, with Least-Squares regression (SLADS-LS) and a
Multi-Layer Perceptron (MLP) network (SLADS-Net). When
compared with SLADS-LS, limited to a single m/z channel, as well
as multichannel SLADS-LS and SLADS-Net, DLADS respectively
improves regression performance by 36.7%, 7.0%, and 6.2%,
resulting in gains to reconstruction quality of 6.0%, 2.1%, and
3.4% for acquisition of targeted m/z.
Index Terms— Compressed Sensing, Deep Learning, Machine
Learning, Mass Spectroscopy Imaging, Sparse Sampling
I. INTRODUCTION
ECTILINEAR or raster scanning typically conducts
measurements with statically defined top-down/left-
right movements and remains the most common
imaging pattern for spectroscopy and microscopy,
including Mass Spectrometry Imaging (MSI). MSI measures
molecular distributions at high spatial resolutions and chemical
specificity. However, raster scanning obtains all of the
information within an equipment's Field Of View (FOV),
regardless of that information's relevance to research
objectives. Whether determining the distribution of a targeted
set of molecules or isolating measurements inside the
encapsulated tissue area, avoiding the acquisition of non-
relevant voxels offers potential for significant throughput gains,
even when paired with only basic reconstruction techniques.
Nanospray Desorption Electrospray Ionization (nano-DESI)
[1] serves as an example MSI technology, where such
approaches may be applied, since it can take hours to days for
even a small tissue section to be imaged at high spatial
resolutions. Operationally, nano-DESI MSI moves a sample
This project was funded by award UG3HL145593 from the National Institute
of Health (NIH) Common Fund, through the Office of Strategic Coordination,
as part of the Human BioMolecular Atlas Program's (HuBMAP)
Transformative Technology Development division [22].
Code available at github.com/Yatagarasu50469/SLADS version 0.9.2.
under a dynamic liquid bridge, extracting molecules from its
surface and subsequently analyzing these in a mass
spectrometer. This process yields the spatial distribution of
mass spectra for the sample, quantifying intensities for varying
mass-to-charge (m/z) channels. Contrary to other popular MSI
technologies, particularly Matrix-Assisted Laser Desorption
Ionization (MALDI), nano-DESI requires minimal sample
preparation and can be conducted outside of a vacuum.
However, existing experimental nano-DESI platforms have a
line-bounded geometry constraint, performing independent sets
of measurements along singular rows. While the movement
restriction potentially makes nano-DESI the worst-case MSI
technology for dynamic sparse sampling, the throughput can
still be notably improved through the integration of DLADS.
A. Background
Static scanning patterns using predetermined locations can be
generated for well-defined and consistent structures [2],
alternatively being produced uniformly, randomly, or through
stochastic models [3], [4], [5]. A method growing in popularity,
within Magnetic Resonance Imaging (MRI) and Computed
Tomography (CT), performs random sampling and then relies
on deep learning for in-painting. Although a promising prospect
for improving imaging throughput, there still exist practical and
regulatory requirements for improved result explainability.
An alternative class of algorithms perform dynamic sampling
[6], [7], through the merger of stochastic models and
compressed sensing, where measurement locations are
progressively determined based on data actively being
obtained. A particularly successful implementation is the
Supervised Learning Approach to Dynamic Sampling
(SLADS), first made available in 2017 by Godaliyadda [8].
Thereafter, Scarborough et al. [9] applied SLADS to produce a
20-fold reduction in applied radiation dosage for dynamic X-
Ray crystalline protein acquisition, with only a ~0.1% absolute
difference compared to a full scan. SLADS, or SLADS-LS,
uses a least-squares regression model to produce an Estimated
Reduction in Distortion (ERD), indicating the amount of
entropy that can be removed from a reconstruction for as-of-yet
unmeasured locations, derived from extracted statistical
features. SLADS was generally evaluated by Zhang et al. in
2018, reducing the number of required measurements for
acceptable reconstructions in confocal Raman microscopy [10]
D. Helminiak and D. Ye are with the Department of Electrical and Computer
Engineering, Marquette University, Milwaukee, WI, 53233 USA (e-mail:
david.helminiak@marquette.edu and donghye.ye@marquette.edu).
H. Hu and J. Laskin are with the Chemistry Department, Purdue University,
West Lafayette, IN, 47907 USA (e-mail: hu518@purdue.edu and
jlaskin@purdue.edu).