1. A method of processing an ultrasound spectrum image, comprising the steps of: forming a spectrum image based on ultrasound data; dividing the spectrum image into a number of sections; calculating an average intensity of pixels in each of the sections; comparing the average intensities calculated for the sections to select a section having a smallest average intensity; analyzing a histogram of the section having the smallest average intensity to detect a maximum intensity in the histogram; determining the detected maximum intensity as a threshold for removing a noise from the spectrum image; and removing the noise from the spectrum image based on the determined threshold.