Label-free imaging and classification of live P. falciparum enables high performance parasitemia quantification without fixation or staining
Fig 4
Wavelength and focus affect parasite contrast and classification efficiency.
a) Optical absorption spectrum of hemoglobin is plotted, with the visible portion of the spectrum highlighted in color. Vertical dashed lines indicate the wavelengths used for imaging on the UV scope (285, 365, and 565 nm), and on the commercial microscope (365, 405, and conventional visible spectrum LED). The hemoglobin (Hb) spectrum is suggestive that parasite identification should be influenced by absorption contrast (highest at peaks), while the shortest wavelengths enable the highest resolution (highest at short wavelengths). b) An array of images of the same ring-stage infected RBC generated by multi-dimensional image registration, enabling assessment of classifier performance as a function of wavelength and focal offset. The parasite becomes nearly impossible to observe in some of the focus slices at 565 nm (red box), illustrating the benefit of increased contrast and resolution.