Real-time ultrasound techniques to determine particle size distribution

A well system including a drill string having an inlet and extending from a surface location into a wellbore and defining an annulus between the drill string and the wellbore; a fluid circuit that circulates a treatment fluid, the fluid circuit extending from the inlet, through the drill string to a bottom of the wellbore, back to the surface location within the annulus, and back to the inlet; and one or more ultrasound devices arranged at-line, off-line, or in-line with fluid circuit to monitor the treatment fluid and track a real-time particle size distribution (PSD) of one or more particles suspended within the treatment fluid.