Procedure
|
Radiation dose (millisievert) 1, 2
|
Comparable exposure from natural sources, such as radon
|
Should you get it?
|
Minimal dose: Less than 0.1 millivert
|
X-ray of teeth (bitewing)
|
0.005
|
less than 1 day
|
Most people need one only every 24 to 36 months.
|
X-ray of teeth (full mouth)
|
0.010
|
about 1 day
|
Many people can go a decade between exams.
|
Cone-beam CT of jaw and teeth
|
0.06
|
7 days
|
Rarely needed for most orthodontic procedures.
|
Low dose: 0.1 to 1 millivert
|
X-ray of chest (two views)
|
0.1
|
12 days
|
Presurgery X-rays needed only for people with a history of lung or heart disease
(or those at risk) or before chest surgery.
|
Mammogram
|
0.4
|
7 weeks
|
Needed every two years for women ages 50 to 74.
|
Medium dose: 1 to 10 milliverts
|
X-ray of spine
|
1.5
|
6 months
|
Rarely needed in first month back pain.
|
CT of head
|
2
|
8 months
|
Not needed for most head injuries. CTs usually aren’t needed for a concussion.
|
CT of spine
|
6
|
2 years
|
Rarely needed in first month of back pain.
|
High dose: 10 milliverts and over
|
CT colonoscopy
|
10
|
3 years
|
Not as accurate as standard colonoscopy.
|
CT of abdomen and pelvis
|
10
|
3 years
|
For possible appendicitis or kidney stone, ask whether ultrasound can be used.
|
CT angiography (of the heart)
|
12
|
4 years
|
1 in every 1,300 60-year-olds may get cancer as a result, so it probably shouldn’t be used for screening.
|
CT of abdomen and pelvis repeated with and without contrast
|
20
|
7 years
|
“Double scans” are rarely necessary; fewer than 5 percent of patients should receive one.
|
PET with CT
|
25
|
8 years
|
It exposes patients to very high radiation doses, so make sure that it is really necessary.
|