CT scans and X-rays---Tests by the radiation dose.

Lilac2003 · 2016-06-09 07:06:04Z

CT scans and X-rays---Tests by the radiation dose.简介

来源: Lilac2003 于 2016-06-09 07:06:04 [档案] [博客] [旧帖] [给我悄悄话] 本文已被阅读：次 (13078 bytes)

Where the rays are—and aren’t

The colored dots on each test below indicate its radiation dose.

Ultrasound

High-frequency sound waves sent through the body create echoes as they bounce off organs and tissues. Echoes are then turned into real-time images called sonograms. Produces fairly good images of soft-tissue disease, but they’re not very detailed, especially in obese patients. Radiation exposure: none.

MRI

Magnetic resonance imaging uses magnets and radio waves to create detailed images that can help spot cancers and soft-tissue problems. Patients are enclosed in the machine for 45 minutes to 2 hours before the image is captured. Radiation exposure: none.

Mammogram

Uses low-dose X-rays to spot masses and mineral deposits that could indicate breast cancer. Radiation exposure: low.

X-ray

The standard scan emits a broad beam that passes through the body before landing on film, casting shadowlike images. Fluoroscopy produces a continuous image, or X-ray movie. X-ray is excellent for bones. Radiation exposure: minimal to medium.

CT

Computed tomography uses a pencil-thin X-ray beam to create a series of images from multiple angles, which are then transferred to a computer, creating a 3D image that can be enlarged and rotated onscreen. Excellent for looking at soft tissue. Radiation exposure: minimal to high.

PET

Positron emission tomography requires the patient to ingest a radioactive tracer, usually thru injection, that lands in cells, especially cancer cells. Some machines that are used combine PET and CT scans. Radiation exposure: medium to high.

Tests by the radiation dose

Just one CT scan of the abdomen and pelvis equals about 10 millisieverts, more radiation than most residents of Fukushima, Japan, absorbed after the Fukushima Daiichi nuclear power plant accident in 2011.

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.

1. 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. 2. For every 2,000 people exposed to 10 millisieverts of radiation from a ct scan, one will develop cancer, according to the Food and Drug Administration.

http://www.consumerreports.org/cro/magazine/2015/01/the-surprising-dangers-of-ct-sans-and-x-rays/index.htm

Editor's Note:

This article also appeared in the March 2015 issue of Consumer Reports magazine.