Multiphoton laser scanning microscopy (MPLSM) was conducted using a Ti:Sapphire excitation laser controlled through a BX61WI upright microscope (Olympus, Shinjuku, Tokyo), with beam scanning and image acquisition controlled by an Olympus Fluoview FV300 scanning system. For all imaging, the excitation light was circularly polarized with 100 fs pulses at 80 MHz, where circular polarization at the sample was achieved by passing the excitation light through a Berek compensator (Model 5540, New Focus, Irvine, CA) before entering the scan box. The light was focused through an Olympus UMPLFL20XW water immersion lens (, 0.95 N.A.), which was also used to collect the backward propagating SHG and fluorescent signal. Backscattered signals were separated from the excitation beam using a 670 nm short-pass dichroic mirror. The backscattered collagen SHG signal was generated with an excitation wavelength of 810 nm, and the emission was filtered by a 405 nm band-pass filter (HQ405/30m-2P, Chroma, Rockingham, VT). The backward-scattered fluorescence signal, used to image tdTomato-labelled tumor cells, was excited using 740 nm light and the emission signal was filtered using a 580 nm band-pass (HQ580/180m-2P, Chroma) and a 700 nm short-pass filter (E700SP-2P, Chroma). Only SHG was captured in the forward-scattered direction, using an Olympus 0.9 N.A. optical condenser, reflected by a 565 nm long-pass dichroic mirror (565 DCSX, Chroma), and filtered by a 405 nm band-pass filter (HQ405/30m-2P, Chroma). All signals were captured by Hamamatsu HC125-02 photomultiplier tubes.