Biomedical Engineering Reference
In-Depth Information
Fig. 4.5
(
a
) Whole blood samples are placed on a sensor chip with a cuvette to measure their
photon transmission, which enables measurement of the hemoglobin density of the blood samples
with <3 % error, as compared against a commercial hematology analyzer. (
b
) The plot shows that
WBCs can be automatically counted with <10 % error
compared to Coulter counter results. The large FOV is a key enabler to achieve
this, as it allows counting statistically significant numbers of WBCs with a single
holographic image despite their 1000
lower density in whole blood compared to
RBCs (Fig.
4.5
b). Furthermore, the subcellular spatial resolution in our lensfree
images can also permit three-part differential imaging of white blood cells [
12
].
This simple lensfree holographic microscopy platform can further be enhanced
by differential interference contrast (DIC) imaging techniques [
10
]. To achieve
that, cost-effective thin nonlinear crystals can be placed on the sensor to shear the
optical field transmitted by the sample into two orthogonal polarizations, which can
interfere through the use of a plastic polarizer, allowing us to record DIC-enhanced
holograms that can be processed as explained in Sect.
4.2
to reconstruct lensfree
DIC images [
9
,
10
]. Consequently, without adding significant cost or complexity
to the system, our lensfree imagers can also perform DIC microscopy, which can
especially be useful to image weakly scattering transparent objects with increased
natural contrast.
4.4
Lensfree Holographic Microscopy on a Cell Phone
The ubiquity of cell phones throughout the world is making them increasingly
attractive for use in point-of-care diagnostics. As of 2011, more than 80 % of the
world population lives in regions that are covered by GSM networks, and around 90
% of the entire world population is expected to own a cell phone by 2015 [
34
]. This
rapid growth in wireless communications has enabled cell phones to be equipped
with advanced functionalities at significantly lower manufacturing costs. Being
integrated with imaging, sensing, and communication interfaces that operate almost
everywhere in the world, cell phones can actually transform healthcare by facilitat-
ing, for example, diagnosis through telemedicine in low-resource settings. In this
respect, much research has been done to develop ubiquitous imaging and diagnosis
