有趣的是，一次胸透所受的放射线剂量等同于坐4小时的飞机所受的辐射量，那么从美国飞回中国来回一趟共在飞机上约26小时，这量相当于接受胸透6。5次，是不是孕妇和小婴儿就最好不要坐飞机了？
http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray
Measuring radiation dosage
The scientific unit of measurement for radiation dose, commonly referred to as effective dose, is the millisievert (mSv). Other radiation dose measurement units include rad, rem, Roentgen, Sievert, and Gray.
Because different tissues and organs have varying sensitivity to radiation exposure, the actual radiation risk to different parts of the body from an x-ray procedure varies. The term effective dose is used when referring to the radiation risk averaged over the entire body.
The effective dose accounts for the relative sensitivities of the different tissues exposed. More importantly, it allows for quantification of risk and comparison to more familiar sources of exposure that range from natural background radiation to radiographic medical procedures.
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Naturally-occurring "background" radiation exposure
We are exposed to radiation from natural sources all the time. The average person in the U.S. receives an effective dose of about 3 mSv per year from naturally occurring radioactive materials and cosmic radiation from outer space. These natural "background" doses vary throughout the country.
People living in the plateaus of Colorado or New Mexico receive about 1.5 mSv more per year than those living near sea level. The added dose from cosmic rays during a coast-to-coast round trip flight in a commercial airplane is about 0.03 mSv. Altitude plays a big role, but the largest source of background radiation comes from radon gas in our homes (about 2 mSv per year). Like other sources of background radiation, exposure to radon varies widely from one part of the country to another.
To explain it in simple terms, we can compare the radiation exposure from one chest x-ray as equivalent to the amount of radiation exposure one experiences from our natural surroundings in 10 days.
Following are comparisons of effective radiation dose with background radiation exposure for several radiological procedures described within this website:
For this procedure: * Your approximate effective radiation dose is: Comparable to natural background radiation for: ** Additional lifetime risk of fatal cancer from examination:
ABDOMINAL REGION:
Computed Tomography (CT)-Abdomen and Pelvis 15 mSv 5 years Low
Computed Tomography (CT)-Abdomen and Pelvis, repeated with and without contrast material 30 mSv 10 years Moderate
Computed Tomography (CT)-Colonography 10 mSv 3 years Low
Intravenous Pyelogram (IVP) 3 mSv 1 year Low
Radiography (X-ray)-Lower GI Tract 8 mSv 3 years Low
Radiography (X-ray)-Upper GI Tract 6 mSv 2 years Low
BONE:
Radiography (X-ray)-Spine 1.5 mSv 6 months Very Low
Radiography (X-ray)-Extremity 0.001 mSv 3 hours Negligible
CENTRAL NERVOUS SYSTEM:
Computed Tomography (CT)-Head 2 mSv 8 months Very Low
Computed Tomography (CT)-Head, repeated with and without contrast material 4 mSv 16 months Low
Computed Tomography (CT)-Spine 6 mSv 2 years Low
CHEST:
Computed Tomography (CT)-Chest 7 mSv 2 years Low
Computed Tomography (CT)-Chest Low Dose 1.5 mSv 6 months Very Low
Radiography-Chest 0.1 mSv 10 days Minimal
DENTAL:
Intraoral X-ray 0.005 mSv 1 day Negligible
HEART:
Coronary Computed Tomography Angiography (CTA) 16 mSv 5 years Low
Cardiac CT for Calcium Scoring 3 mSv 1 year Low
MEN'S IMAGING:
Bone Densitometry (DEXA) 0.001 mSv 3 hours Negligible
WOMEN'S IMAGING:
Bone Densitometry (DEXA) 0.001 mSv 3 hours Negligible
Mammography 0.4 mSv 7 weeks Very Low
Note for pediatric patients: Pediatric patients vary in size. Doses given to pediatric patients will vary significantly from those given to adults.* The effective doses are typical values for an average-sized adult. The actual dose can vary substantially, depending on a person's size as well as on differences in imaging practices.** Legend: Risk Level Approximate additional risk of fatal cancer for an adult from examination:
Negligible: less than 1 in 1,000,000
Minimal: 1 in 1,000,000 to 1 in 100,000
Very Low: 1 in 100,000 to 1 in 10,000
Low: 1 in 10,000 to 1 in 1000
Moderate: 1 in 1000 to 1 in 500
Note: These risk levels represent very small additions to the 1 in 5 chance we all have of dying from cancer.
