  Optical diffraction tomography (ODT), initially described in the seminal
paper of Emil Wolf [Opt. Comm., 1(4), 153-156 (1969)], has received renewed
attention recently. The vast majority of ODT experiments reported to date have
been 3D images of single cells or beads demonstrating excellent image quality
and sectioning capability. The sample thickness in these experiments is 10 to
20 microns and the optical thickness is generally well below 2{\pi}. In this
paper, we explore ODT when the sample consists of multiple layers of cells. We
assess experimentally the impact of sample thickness for the different ODT
reconstruction algorithms and we describe a strategy that allows us to image,
for the first time, multi-cell clusters.
