Figure 2.

Representative images of MNP-laden murine melanoma tumors with differential degrees of overall and local cellularity. A-C. I. Simultaneously-acquired in vivo OCT (left) and MM-OCT (right) depth-resolved cross-sectional images of melanoma tumor tissue with high overall and local cellularity (A), low overall and local cellularity (B), or high overall and low local cellularity (C). MM signals are color-coded in green, which are overlaid on top of structural OCT images color-coded in red. II. The presence of intratumor MNPs (blue asterisks) confirmed with iron-oxide staining. III. High magnification photomicrographs of histological tumor sections stained with Picrosirius Red (PR). These enlarged images correspond to the areas indicated by the dashed black line boxes in the low magnification images (IV). C. The structures in a representative MT-stained slide section (V) strongly correlate with those detected by PR (III); the cytoplasm appears as (III) yellow or (V) pink. VI shows a representative masked image utilized for quantification of tissue cellularity, where the cytoplasm, non-cytoplasm, and MNP areas were coded in yellow, red, and blue, respectively. Histological images were all obtained under bright-field microscopy. Blue asterisks indicate MNPs. The dotted black lines delineate the tumor margin. One tumor was severely necrotic and a few of its histological sections were lost (B, II) as the tissue sections did not retain any structural integrity. As a result, they were shattered upon sectioning, or dissolved instantly when floated on the warm water bath, or weakly attached to the microscope slides, and hence were washed off easily.