Resolution-enhanced intensity diffraction
tomography in high numerical aperture label-free
microscopy
JIAJI LI,
1,2
ALEX MATLOCK,
3
YUNZHE LI,
3
QIAN CHEN,
1
LEI TIAN,
3,4
AND CHAO ZUO
1,2,
*
1
School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
2
Smart Computational Imaging Laboratory (SCILab), Nanjing University of Science and Technology, Nanjing 210094, China
3
Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215, USA
4
e-mail: leitian@bu.edu
*Corresponding author: zuochao@njust.edu.cn
Received 31 July 2020; revised 25 September 2020; accepted 30 September 2020; posted 2 October 2020 (Doc. ID 403873);
published 12 November 2020
We propose label-free and motion-free resolution-enhanced intensity diffraction tomography (reIDT) recovering
the 3D complex refractive index distribution of an object. By combining an annular illumi nation strategy with a
high numerical aperture (NA) condenser, we achieve near-diffraction-limited lateral resolution of 346 nm and
axial resolution of 1.2 μm over 130 μm × 130 μm × 8 μm volume. Our annular pattern matches the system’s
maximum NA to reduce the data requirement to 48 intensity frames. The reIDT system is directly built on
a standard commercial microscope with a simple LED array source and condenser lens adds-on, and promises
broad applications for natural biological imaging with minimal hardware modifications. To test the capabilities of
our technique, we present the 3D complex refractive index reconstructions on an absorptive USAF resolution
target and Henrietta Lacks (HeLa) and HT29 human cancer cells. Our work provides an important step in in-
tensity-based diffraction tomography toward high-resolution imaging applications.
© 2020 Chinese Laser Press
https://doi.org/10.1364/PRJ.403873
1. INTRODUCTION
The refractive index (RI) of biological cells and tissues plays a
crucial role in biomedical imaging as it captures the physiologi-
cal characteristics and morphological features of a sample [1–3].
Imaging 3D biological samples with high resolution, however,
remains a challenging task. Fluorescence-based 3D imaging
methods, such as confocal microscopy [4] and multiphoton
microscopy [5], already provide excellent optical sectioning
and enable super-resolution 3D volume imaging of nanoscale
subcellular structures. Unfortunately, the exogenous labels
(e.g., dyes and fluorophores) in these techniques can be photo-
toxic and cause photobleaching due to the absorption of the
excitation light [6] and can artificially alter the sample’s behav-
ior and cellular structure [7]. Here, we introduce a resolution-
enhanced intensity diffraction tomographic (reIDT) technique
based on a conventional bright-field microscope and a high-
density LED array illumination unit with sparse annular illu-
mination. The imaging method is label-free, motion-free, fast,
and enables the high-resolution quantitative recovery of 3D in-
trinsic structural features at the single cell level.
Quantitative phase imaging (QPI) [3] is an often-used tech-
nique to recover biological cells with high contrast in their
natural states. QPI reconstructs a quantitative image of the
sample-induced two-dimensional (2D) optical path thicknesses
or phase delay based on interferometry [8–11] and noninter-
ferometry [12–18] methods. However, these phase maps evalu-
ate the sample’s total optical delay along the integrated direction
over a thin layer and provide limited volumetric information
about the object’s internal structure. To capture this informa-
tion and evaluate thicker specimens, tomographic methods
recovering 3D information are required. Recently developed
3D RI tomography techniques enable the reconstruction of
the sample’s 3D RI distribution to visualize intracellular struc-
tures, and the related 3D imaging techniques can be largely
categorized into two classes, interferometry-based and inten-
sity-only methods.
Optical diffraction tomography (ODT) is the most widely
used interferometry-based 3D QPI technique [19,20].
Standard implementations of ODT use either a rotating sample
[21] or a scanning laser beam [22–24] to capture the angle-
specific scattering arising from the sample. A 2D complex scat-
tered field containing the object’s phase and amplitude infor-
mation is directly recorded as digital interferograms under
various illumination angles, and a tomographic reconstruction
algorithm is applied to recover the sample’s 3D RI distribution.
The interferograms are captured using either an off-axis
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Vol. 8, No. 12 / December 2020 / Photonics Research
Research Article
2327-9125/20/121818-09 Journal © 2020 Chinese Laser Press