A method for imaging particles using a particle analysis system configured for combined viscosity and geometric hydrofocusing, the particles comprising cells included within a biological fluid sample, the method comprising: injecting a sheath fluid along a flowpath of a flowcell (22, 33, 420) of the particle analyzer, the sheath fluid having a viscosity that is greater than a viscosity of the biological fluid sample; injecting the biological fluid sample from a sample fluid injection tube (29, 412, 400d) at a flow rate into the flowing sheath fluid within the flowcell (22, 33, 420) so as to provide a sample fluid stream (32, 428) having a first thickness adjacent the injection tube (21, 312, 400d), the flowpath of the flowcell (22, 33, 420) having a decrease in flowpath size (21, 419) such that thickness of the sample fluid stream (32, 428) decreases from the initial thickness to a second thickness adjacent an image capture site; imaging a first plurality of the particles from the biological fluid sample at the image capture site of the flowcell (22, 33, 420); wherein the decrease in flowpath size is defined by a proximal flowpath portion having a proximal thickness, and distal flowpath portion having a distal thickness less than the proximal thickness, the ratio of the proximal thickness to the distal thickness is in the range 10 to 200, wherein a downstream end of the sample fluid injection tube (29, 412, 400d) is positioned distal to the proximal flowpath portion, wherein the viscosity difference between the sheath fluid and biological fluid sample, in combination with the decrease in flowpath size and the flow rate of the sample, is effective to deliver cells in the biological fluid sample from the sample fluid injection tube (29, 412, 400d) to the image capture site in four seconds or less, while a viscosity agent in the sheath fluid retains viability of cells leaving structure and content of the cells intact when the cells extend from the sample fluid stream (32, 428) into the flowing sheath fluid as the cells travel from the sample fluid injection tube (29, 412, 400d) to the image capture site. injecting a sheath fluid along a flowpath of a flowcell (22, 33, 420) of the particle analyzer, the sheath fluid having a viscosity that is greater than a viscosity of the biological fluid sample; injecting the biological fluid sample from a sample fluid injection tube (29, 412, 400d) at a flow rate into the flowing sheath fluid within the flowcell (22, 33, 420) so as to provide a sample fluid stream (32, 428) having a first thickness adjacent the injection tube (21, 312, 400d), the flowpath of the flowcell (22, 33, 420) having a decrease in flowpath size (21, 419) such that thickness of the sample fluid stream (32, 428) decreases from the initial thickness to a second thickness adjacent an image capture site; imaging a first plurality of the particles from the biological fluid sample at the image capture site of the flowcell (22, 33, 420); wherein the decrease in flowpath size is defined by a proximal flowpath portion having a proximal thickness, and distal flowpath portion having a distal thickness less than the proximal thickness, the ratio of the proximal thickness to the distal thickness is in the range 10 to 200, wherein a downstream end of the sample fluid injection tube (29, 412, 400d) is positioned distal to the proximal flowpath portion, wherein the viscosity difference between the sheath fluid and biological fluid sample, in combination with the decrease in flowpath size and the flow rate of the sample, is effective to deliver cells in the biological fluid sample from the sample fluid injection tube (29, 412, 400d) to the image capture site in four seconds or less, while a viscosity agent in the sheath fluid retains viability of cells leaving structure and content of the cells intact when the cells extend from the sample fluid stream (32, 428) into the flowing sheath fluid as the cells travel from the sample fluid injection tube (29, 412, 400d) to the image capture site.