Systems and methods for grading signals from microemboli in blood flow monitored using a Doppler ultrasound system. Signals from microemboli in blood flow are graded by calculating a value related to a power for the signals from microemboli in blood flow and categorizing the signals into one of at least two grades based on the calculated value. Alternatively, signals can be categorized by assessing a power value for the microemboli in blood flow during a period of monitoring. In response to the power value being greater than or equal to a threshold value, the microemboli in blood flow are categorized based on the power value, and in response to the power value being less than the threshold value, a number of microemboli are counted during at least a portion of the period of monitoring and the microemboli are categorized based on the number.