Physics: CT

Multiple scan average dose
Computer tomography dose index (CDTI)
dose lenght product (DLP)

CTDI 199
CTDI w
CTDI vol

beam energy
tube current time product
pitch
collimation
patient size
dose reduction options

reducing the milliampere-second value
increasing the pitch
reducing the beam energy

small increments of couch movement

spatial resolution

z-axis

roentgens

with an ionizing chamber and an electrometer

the ability of an X-ray to ionize air

yes

no

radiation dose

describes the amount of energy absorbed per unit mass at a specific point

gray or rads

100 rad = 1 grey

it does not describe where
that radiation dose is absorbed or reflect the rela-
tive radiosensitivity or risk of detriment to those
tissues being irradiated

The effective dose is the sum of weighted equivalent doses in all the organs and tissues of the body.

Effective dose = sum of [organ doses x tissue weighting factor]

Tissue weighting factors represent relative sensitivity of organs for developing cancer.

The effective dose is the sum of weighted equivalent doses in all the organs and tissues of the body.

Effective dose = sum of [organ doses x tissue weighting factor]

Tissue weighting factors represent relative sensitivity of organs for developing cancer.

onizing radiation is radiation that has enough energy to remove electrons from atoms or molecules (groups of atoms) when it passes through or collides with some material. The loss of an electron with its negative charge causes the atom (or molecule) to become positively charged. The loss (or gain) of an electron is called ionization and a charged atom (or molecule) is called an ion.

onizing radiation is radiation that has enough energy to remove electrons from atoms or molecules (groups of atoms) when it passes through or collides with some material. The loss of an electron with its negative charge causes the atom (or molecule) to become positively charged. The loss (or gain) of an electron is called ionization and a charged atom (or molecule) is called an ion.

Forms of ionizing radiation include:

Gamma rays
X rays
Alpha particles
Beta particles
Neutrons.

Forms of ionizing radiation include:

Gamma rays
X rays
Alpha particles
Beta particles
Neutrons.

rays refer to a kind of electromagnetic radiation generated when a strong electron beam bombards metal inside a glass tube. The frequency of this radiation is very high - 0.3 to 30 Ehz (exahertz or million gigahertz). By comparison FM radio stations transmit at frequencies around 100 MHz (megahertz) or 0.1 Ghz (gigahertz).

rays refer to a kind of electromagnetic radiation generated when a strong electron beam bombards metal inside a glass tube. The frequency of this radiation is very high - 0.3 to 30 Ehz (exahertz or million gigahertz). By comparison FM radio stations transmit at frequencies around 100 MHz (megahertz) or 0.1 Ghz (gigahertz).

Radioactivity or the strength of radioactive source is measured in units of becquerel (Bq).

1 Bq = 1 event of radiation emission per second.

One becquerel is an extremely small amount of radioactivity. Commonly used multiples of the Bq unit are kBq (kilobecquerel), MBq (megabecquerel), and GBq (gigabecquerel).

1 kBq = 1000 Bq, 1 MBq = 1000 kBq, 1 GBq = 1000 MBq.

an old and still popular unit of measuring radioactivity is the curie (Ci).

1 Ci = 37 GBq = 37000 MBq.

One curie is a large amount of radioactivity. Commonly used subunits are mCi (millicurie), µCi (microcurie), nCi (nanocurie), and pCi (picocurie).

1 Ci = 1000 mCi; 1 mCi = 1000 µCi; 1 µCi = 1000 nCi; 1 nCi = 1000 pCi.

1 Bq = 27 pCi.

Becquerel (Bq) or Curie (Ci) is a measure of the rate (not energy) of radiation emission from a source.

X-ray and gamma-ray exposure is often expressed in units of roentgen (R). The roentgen (R) unit refers to the amount of ionization present in the air. One roentgen of gamma- or x-ray exposure produces approximately 1 rad (0.01 gray) tissue dose

One roentgen of gamma- or x-ray exposure produces approximately 1 rad (0.01 gray)

1 roentgen = 1 rad = 0.01 gray

Another unit of measuring gamma ray intensity in the air is "air dose or absorbed dose rate in the air" in grays per hour (Gy/h) units. This unit is used to express gamma ray intensity in the air from radioactive materials in the earth and in the atmosphere

When ionizing radiation interacts with the human body, it gives its energy to the body tissues. The amount of energy absorbed per unit weight of the organ or tissue is called absorbed dose and is expressed in units of gray (Gy)

One gray dose is equivalent to one joule radiation energy absorbed per kilogram of organ or tissue weig

The gray is bigger. One gray is equivalent to 100 rads.

Alpha particles produce greater harm than do beta particles, gamma rays and x rays for a given absorbed dose.

no

To account for this difference, radiation dose is expressed in a different quantity called equivalent dose (NOT effective dose which is also Sv) in units of sievert (Sv). Dose equivalent is proportional to the absorbed dose (D), the quality factor (Q...the type of radiation), and other modifying factors (N) of the specific type of radiation. Most radiations encountered in diagnostic procedures (x-ray, gamma, and beta) have quality and modifying factor values of 1. Therefore, the dose equivalent is numerically equal to the absorbed dose. Some radiation types consisting of large (relative to electrons) particles have quality factor values greater than 1. For example, alpha particles have a quality factor value of approximately 20.

To account for this difference, radiation dose is expressed in a different quantity called equivalent dose (NOT effective dose which is also Sv) in units of sievert (Sv). Dose equivalent is proportional to the absorbed dose (D), the quality factor (Q...the type of radiation), and other modifying factors (N) of the specific type of radiation. Most radiations encountered in diagnostic procedures (x-ray, gamma, and beta) have quality and modifying factor values of 1. Therefore, the dose equivalent is numerically equal to the absorbed dose. Some radiation types consisting of large (relative to electrons) particles have quality factor values greater than 1. For example, alpha particles have a quality factor value of approximately 20.

Dose equivalent is often referred to simply as "dose" in every day use of radiation terminology. The conventional unit of "dose equivalent" or "dose" was rem.

1 Sv = 100 rem

Dose in rem = Dose in rad x Quality factor of radiation and modifying factor

Dose equivalent (H) is the quantity commonly used to express the biological impact of radiation on persons receiving occupational or environmental exposures. Personnel exposure in a clinical facility is often determined and recorded as a dose equivalent.



Dose equivalent is proportional to the absorbed dose (D), the quality factor (Q), and other modifying factors (N) of the specific type of radiation. Most radiations encountered in diagnostic procedures (x-ray, gamma, and beta) have quality and modifying factor values of 1. Therefore, the dose equivalent is numerically equal to the absorbed dose. Some radiation types consisting of large (relative to electrons) particles have quality factor values greater than 1. For example, alpha particles have a quality factor value of approximately 20.



The conventional unit for dose equivalent is the rem, and the Sl unit is the sievert (Sv). When the quality factor is 1, the different relationships between dose equivalent (H) and absorbed dose (D) are

H(rem) = D(rad)

H(Sv) = D(Gy).

the quality factor (Q), and other modifying factors (N) of the specific type of radiation. Most radiations encountered in diagnostic procedures (x-ray, gamma, and beta) have quality and modifying factor values of 1. Therefore, the dose equivalent is numerically equal to the absorbed dose. Some radiation types consisting of large (relative to electrons) particles have quality factor values greater than 1

1rem = 10mSv (remember 1 Sv = 100 rem)

1 R (roentgen) exposure is approximately equivalent to 1 rad and 1 rad is equal to 1 rem and this is equal to 10 mSv tissue dose (assuming the quality factor and modifying factors are 1)

yes...The recommended TLV is average annual dose of 0.05 Sv (50 mSv).

10 Sv - Risk of death within days or weeks

Risk of cancer later in life (5 in 100)

Risk of cancer later in life (5 in 1000)

The Threshold Limit Values (TLVs)

50 mSv - TLV for annual dose for radiation workers in any one year

20 mSv - TLV for annual average dose, averaged over five year

1 mSv - Recommended annual dose limit for general public

Ci, roentgen, rad and rem

When a radioactive material is gets in the body by inhalation or ingestion, the radiation dose constantly accumulates in an organ or a tissue

The total dose accumulated during the 50 years following the intake is called the committed dose

The effective dose is the sum of weighted equivalent doses in all the organs and tissues of the body.

Effective dose = sum of [organ doses x tissue weighting factor]

Sv

the parameters set and the attenuation by the scout film. Although the CDTI (and DLP) reading is in mGy it is not actually mGy it is just an estimate of mGy using a programmed best guess) in other words the CT does not fator things like percent body fat and bone density (with different conversion factors) it is simply an average that the company made up. The only parameter that is specific to a patient is the attenuation that is created by the scout film.