An image flow cytometer for observing microparticulate samples includes a flow system directing a carrier fluid including the samples through a sensing area in a hydrodynamically planar flow. The flow system includes an elongated flow chamber having opposed first and second apertures and the sensing area downstream of the apertures, and receiving the carrier fluid upstream of the first and second apertures. A sheath- fluid channel includes two branches configured to carry the sheath fluid from opposite directions into the flow chamber through the first aperture, and likewise third and fourth branches through the second aperture. An irradiation spot smaller than the flow thickness is scanned across the sensing area across the flow direction. A detection optical system detects a time -varying light intensity of resultant light from the flow chamber. A processor detects two or more of the microparticulate samples according to the detected intensity.
