Cryo-imaging is now described. The cryo-imaging system consists of a modified large section cryo-microtome (8250 large section cryostat, Vibratome, St. Louis, Missouri), XYZ robotic positioner carrying an imaging system that consists of a stereo microscope (SZX12, Olympus, Japan), GFP fluorescent filters (exciter: HQ470/40x, dichroic: Q495LP, emitter: HQ500LP, Chroma, Rockingham, Vermont), low light digital camera (Retiga Exi, QImaging., Canada), and color light source (XCite 120PC, EXFO, Canada). The cryo-imaging system is controlled by a control computer running Labview (National Instruments, Austin, Texas). The stereomicroscope used an objective of 0.11 NA and a zoom settings of 7 to . Once equilibrated to cutting temperature, blocks were fixed to the stage of the cryo-microtome using optimal cutting temperature compound. The specimen was then sectioned until the surface of the block face was flat. The bright-field lamp was turned on and the camera was positioned over and focused onto the region of the block-face surface containing the vessel. A white board was placed over the surface of the block face and was used to white-balance the camera. The white board was removed and the bright-field exposure time for the camera was determined. For color imaging, typical exposure times for the green channel were . The color lamp was turned off, the fluorescent light was turned on, and the fluorescent exposure time was determined. For fluorescent imaging, typical exposure times for the green channel were . The machine was then set to run such that a section was removed from the specimen, a bright-field followed by a fluorescence image of the block face was acquired, and the process was repeated until the whole specimen was imaged.