The absorbed dose is the average energy absorbed per unit mass.

The tissue absorbed energy in a small mass volume:
D = (dW/dm) [ Gy ]
D = absorbed dose in Gray (Gy); dW = in the tissue energy absorbed; DM = small volume of the mass.

The SI unit of absorbed dose is the joule per kilogram and its special name is the gray (Gy). In units often used by federal and state agencies, absorbed dose is given in rad; 1 rad = 0.01 Gy.

Absorbed dose is a feature that should increase dose awareness and help users in dose optimization. Absorbed dose in CT is quoted using the CTDI (computed tomography dose index)

CTDIvol (volume-averaged CT dose index) and the dose-length product (DLP) give an indication of the average absorbed dose and relative radiation risk to a standard patient. The user is being warned to scan parameter settings that may lead to high doses, and can adjust the protocol if appropriate. It should be noted that CTDIvol and DLP do not take patient size into account, and will give overestimates and underestimates for large and small patients, respectively.

Henri Becquerel demonstrated beta particles in 1900. Identical with electrons is there negative charge at -1. Their mass is 549 millionths of one AMU, 1/2000 of the mass of a proton or neutron. Beta particles consist of high energetic electrons emitted by radioactive nuclei or neutrons. By the process of beta decay, one of the neutrons in the nucleus is transformed into a proton and a new atom is formed which has one less neutron but one more proton in the core. Beta decay is accompanied by the emission of a positron (the antiparticle of the electron), a positive charged antineutrino. Beta particles have a greater range of penetration than alpha particles but less than gamma rays or x-rays. The name beta was coined by Rutherford in 1897. The traveling speed of beta particles depends on their energy. Because of their small mass and charge beta particles travel deep into tissues and cause cellular damage and possible cancer.

See also Radiation Shielding.

(kg) The base SI unit of mass of the metric system.
Definition: 1 kilogram is defined as the mass of the standard kilogram, a platinum-iridium bar in the custody of the International Bureau of Weights and Measures (BIPM) near Paris, France.
A traditional unit of mass or weight is also the pound (in general use, e.g. in the United States and Great Britain), with the symbol lb (derived from the Latin word libra).

1 kg = 2.204627 pound (lb. av., lbs.)
1 pound (lb. av., lbs.) = 0.453 kg.

Smaller units are, e.g.
1 000 gram (g) = 1 kg
1 000 milligram (mg) = 1 g
1 000 microgram (µg) = 1 mg

Binding energy is equal to the amount of energy which is used to free electrons or disintegrate nuclides from their atomic bond.
The electron binding energy of a hydrogen atom is with 13.6 eV very low. The nuclear binding energy of an alpha-particle, energy equivalent of the sum of the individual masses of nuclides minus the mass of the whole nucleus, is 28.3 MeV.

See also Alpha Decay, Beta Decay and Gamma Quantum.

Breast imaging methods include mammography (mammogram), ultrasound, breast MRI, positron emission tomography, xeromammography, diaphanography and thermography.
Mammography is widely used as a screening method and diagnostic tool for breast cancer detection or evaluation of breast disease. Digital mammography takes multiple thin digital image 'slices' through the breast, which provides higher potential to see a small mass within dense tissue. The mammography quality standards act guarantees a high image quality.
Breast ultrasound (also called ultrasonography) should only be used as an additional imaging modality to evaluate specific breast abnormalities, especially to differentiate cystic from solid masses. Ultrasound is also used to guide needle breast biopsies.
Magnetic resonance imaging (MRI) is useful for breast MRI screening in cases of high cancer risk. In addition, multifocal breast cancer can be missed by standard practice mammography and can be early detected with breast MRI.