The invention relates to an on-line
dose modulation method of an X-
ray CT (
Computed Tomography)
machine, which comprises the following steps: scanning
plain film data, extracting Z-direction attenuation information of a
human body, and calculating the attenuation area of the
human body in each
cut film along the Z direction; according to the attenuation area, calculating the average X-
ray dose in each
cut film to form a
dose distribution curve along the Z direction, and supplying to a user as an initial recommended value, so that the user can adjust the
dose distribution in the Z direction as required; scanning a patient, and simultaneously carrying out on-line
estimation on the attenuation value of the rotation direction of the patient to obtain an attenuation estimated value; combining the
dose distribution in the Z direction with the attenuation estimated value of the
human body in the rotation direction to calculate a
bulb tube mA value; transmitting the mA value to a high-
pressure system, and carrying out high-frequency
dose adjustment; and finishing the on-line dose modulation process if the scanning is completed. The invention reduces the overexposure and underexposure possibly caused by assuming sine laws. Besides, the invention does not assume that what passes through the central passage is the maximum attenuation, so that the dose modulation is better matched with the shape of the actual object.