B超/彩超无放射性(安全),看到的图像是实时的(即刻看到).

Ultrasound image of a fetus in the womb, viewed at 12 weeks of pregnancy (bidimensional-scan)

FDA 的信息:

Medical Imaging > Ultrasound Imaging - Food and Drug Administration

彩超是Color Doppler ultrasound: 顾名思义,影像是彩色的.

Doppler Ultrasound of an Artery

Courtesy of Intermountain Medical Imaging, Boise, Idaho.

Figure 1 shows a color Doppler ultrasound picture of blood flowing through a normal artery (red) and vein (blue). Figure 2 shows an ultrasound picture of an artery narrowed by the buildup of calcium and fat (cholesterol) in the inner lining of the artery, called plaque, which leads to "hardening of the arteries" (atherosclerosis).