Bushong Chapter 8

Xray quantity

The number of xrays in the useful beam

X-ray quality

The penetrability of the beam

The intensity of the X-ray beam of an X-ray imaging system is measured in ___________ and is called the X-ray __________.

Milligray in air (mGya) ; quantity

Another term, _________ __________ is often used instead of X-ray intensity or X-ray quantity.

Radiation exposure

The mGya is a measure of the number of _______ ________ produced in air by a quantity of X-rays.

Ion pairs

__________ of air increases as the number of X-rays in the beam increases.

Ionization

X-ray quantity is proportional to ______.

mAs

mAs is a measure of the total number of ________ that travel from cathode to anode to produce X-rays.

Electrons

X-ray quantity is proportional to the ____ squared.

kVp

X-ray quantity varies rapidly with changes in _____.

kVp

The change in X-ray quantity is proportional to the ______ of the ratio of the kVp.

Square

Theoretically, doubling the X-ray intensity by kVp manipulation alone requires an increase of _____ in kVp.

40%

Note that by increasing kVp and reducing mAs so that image receptor exposure remains constant, the patient dose is ________ significantly. The disadvantage of such a technique adjustment is reduced image contrast when screen film is the image receptor.

Reduced

There is no change in contrast when using ________ image receptors.

digital

If you increase the mAs, (which is the biggest contributor), the X-Ray quantity is _________ _________

and the image receptor exposure is ___________.

increased proportionately ; increased

If you increase the filtration, the X-ray quantity is _______

and the image receptor exposure is ___________.

reduced ; reduced

Most general purpose radiographic tubes, when operated at approximately 70 kVp, produce X-ray intensities of approximately _____ mGya/mAs at 100 cm source to image receptor distance (SID).

50

X-Ray intensity varies inversely w/ the square of the ______ from the x-ray tube target. This relationship is known as the __________ __________ ________.

distance ; inverse square law

X-ray quantity is inversely proportional to the ________ of the distance from the source.

square

To maintain a constant exposure of the image receptor, an increase of _______ % in kVp should be accompanied by a reduction of one half in mAs.

15

When SID is increased, ______ must be increased by SID squared to maintain constant exposure to the image receptor.

mAs

X-ray imaging systems have metal _______, usually ____ to _____ mm of aluminum (AL), positioned in the useful beam, and the purpose of these filters is to reduce the number of ______ _______ ________.

filters ; 1 ; 5 ; low energy x-rays

Adding filtration to the useful x-ray beam ________ patient dose.

reduces

The disadvantage of x-ray beam filtration can be _______ _______ ________ when using screen film caused by x-ray beam hardening.

reduced image contrast

X-ray beam hardening _________ the number of high energy x-rays in the beam by removing the low-energy non-penetrating x-rays.

increases

X-Ray Quality = ______

kVp

_____________ refers to the ability of x-rays to penetrate deeper in tissue.

Penetrability

_________ energy x-rays are able to penetrate tissue more deeply than ________ energy x-rays.

High ; low

The penetrability of an x-ray beam is called the ________ __________.

x-ray quality

X-rays with high penetrability are termed _____ ______ _____.

high quality x-rays

X-rays with low penetrability are termed ______ ______ ____.

low quality x-rays

____________ is one description of the ability of an x-ray beam to pass through tissue.

Penetrability

Distance and mAs do not affect radiation __________ ; they do affect radiation __________.

quality ; quantity

_________ is the reduction in x-ray intensity that results from absorption and scattering.

Attenuation

In radiography, the quality of x-rays is measured by the _______.

HVL

HVL = ________.

Half Value Layer

The HVL is a ____________ of the useful x-ray beam

characteristic

A diagnostic x-ray beam usually has an HVL in the range of _____ to _____ mm AL or ____ to _____ cm of soft tissue.

3 ; 5 ; 3 ; 6

The _______ of an x-ray beam = the thickness of absorbing material necessary to reduce the x-ray intensity to half it's original intnsity.

HVL

The thickness of _________ that reduces the x-ray intensity to half of it's original value is the HVL.

filtration

_______ is the best method for specifying x-ray quality.

HVL

X-ray beam quality can be identified by kVp or filtration, but _______ is most appropriate.

HVL

As the _____ is increased, so is x-ray beam quality and therefore the HVL.

kVp

Increasing the ______ increases the quality of an x-ray beam.

kVp

An increase in kVp results in a shift of the x-ray emission spectrum toward the ______ energy side, indicating an ________ in the effective energy of the beam.

high ; increase

The primary purpose of adding _________ to an x-ray beam is to remove selectively low energy x-rays that have little chance of getting to the image receptor.

filtration

Increasing filtration ___________ the quality of an x-ray beam.

increases

Almost any material could serve as an x-ray filter, ______ is chosen because it is efficient in removing low-energy x-rays through the photoelectric effect and because it is readily available, inexpensive, and easily shaped.

Al (Aluminum)

Filtration of diagnostic x-ray beams has 2 components; _______ _______ and _______ ________.

Inherent filtration ; added filtration

The glass or metal enclosure of an x-ray tube filters the emitted x-ray beam; This type of filtration is called _______ ________.

Inherent Filtration

The part of the glass or metal enclosure through which x-rays are emitted is called the ________ and it is very thin.

window

The inherent filtration of a general x-ray purpose tube is approximately ________ mm AL equivalent.

.5

Special purpose tubes, such as those used in mammography, have very thin x-ray tube windows. They are sometimes made of _________ rather than glass and have an inherent filtration of approximately _____ mm AL.

beryllium (Z=4) ; .1

A thin sheet of aluminum positioned between the protective x-ray tube housing and the x-ray beam collimator is the usual form of _______ ________.

added filtration

The addition of a filter to an x-ray beam attenuates x-rays of all energies emitted, but it attenuates a greater number of ______ energy x-rays than _______ energy x-rays.

low ; high

The addition of a filter to an x-ray beam shifts the x-ray emission spectrum to the ________ energy side, resulting in an x-ray beam w/higher energy, greater penetrability, and better quality.

high

Because added filtration attenuates the x-ray beam, it affects x-ray ________.

quantity

The addition of filtration equal to the beam HVL reduces the beam quantity to half its pre-filtered value and results in a ________ x-ray beam quality.

higher

2 sources of added filtration

1mm or more sheets of aluminum permanently installed in the port of the x-ray tube housing, and the collimator contributes an additional 1mm AL equivalent of added filtration (resulting from the silver surface of the mirror in the collimator)

One of the most difficult tasks facing radiographers is producing an image with a _______ __________ when a body part is examined that varies greatly in thickness or tissue composition.

uniform intensity

A ________ __________ compensates for differences in subject radiopacity.

compensating filter

Compensating filters are almost always constructed of _____ but ______ materials can also be used.

Aluminum ; plastic

The _________ filter is principally used during radiographic procedures of a body part, such as the foot, that varies considerably in thickness.

wedge

A _________ __________ filter, or a trough filter, is sometimes used in chest radiography. The thin central region of the filter is positioned over the mediastinum, and the lateral thick portions shadow the lung fields.

bilateral wedge

A _________ __________ filter is is an adaption of the wedge filter and is used in some interventional radiography procedures, usually when long sections of the anatomy are imaged w/ the use of 2 or 3 seperate image receptors.

step wedge