Liu Ya tries to put on the 15-kilogram lead uniform before she goes into the surgery room . [Photo by Ran Wen/for China Daily]

Depending on the conditions of the patient and his/her blood vessels, the duration of each operation ranges from one to three hours. Since X-ray examination is performed continuously during the procedure, doctors need to wear protective lead clothing all the time.

During the surgery, the protected body parts will take in a radiation dose equivalent to two or three chest X-rays and the unprotected areas equivalent to about 100 chest X-rays.

Mao said there are around 400 interventional surgeries at the hospital each year conducted by three doctors.

Many long-term interventional surgeons have only 3,000 to 4,000 white blood cells, which is lower than the normal threshold of 4,000 to 10,000. That makes these doctors less resistant to viruses and infection than normal healthy people.

Liu and Mao always wear a dosimeter, which automatically records the amount of radiation they take in. They need to hand in the dosimeter to the CDC (Center of Disease Control) every three months to ensure it doesn't exceed the prescribed limits. They are required to have medical examinations organized by the CDC every two years. If their white blood cell count is found to be at an unsafe level, they will be forced to leave their post.