A scanner probe is placed on your skin and very high frequency sound waves that are inaudible to the human ear are passed into your body. As the sound waves pass over objects in fluid, they produce a pattern of echoes . These echoes are converted into electrical signals, which are processed and displayed on a screen as a two-dimensional image.
Doppler and Nuchal scans are both painless and non-invasive special ultrasound scans that are used to detect specific problems . Both types of scan are relatively new and they are available only at certain hospitals.