CH 5 - Electricity, Magnetism, & Electromagnetism - Bushong

Gray in air are the measurement for x-ray:

Quantity, exposure, and intensity

The number of x-rays in the useful beam defines x-rays:

Quantity

Standard x-ray machines produce about micro-Gray/mAs at 70 kVp measured at _ SID

50; 100

X-ray quantity increases in direct proportion to increases in _.

mAs

If the distance from the source to the image (SID) is reduced by half, how is the x-ray intensity at the image affected?

Increased 4 times

if filter thickness is ___, then x-ray intensity is __

Increased; reduced

A 10% increase in kVp has effect on x-ray intensity than as a 10% increase in mAs

much greater

If the quantity (mAs) of electrons hitting the target are doubled, the x-ray quantity is:

Increased by a factor of two

If a technologist changed the technique from 70 kVp at 200 mAs to 70 kVp at 400 mAs, the x-ray intensity will?

Double

The inverse square law has the same effect on optical density and x-ray intensity

True

An increase of 15% in kVp is equivalent to increasing mAs _.

100%

If the intensity of a 70 kVp exposure at 20 mAs is 1.0 mGya, what would it be at 10 mAs?

0.5 mGy

If an exposure is 0.5 mGy at a SID of 40 inches, what would the exposure be at a SID of 60 inches?

0.22 mGy

X-ray intensity is proportional to _.

kVp2

The penetrability of an x-ray beam is called x-ray

quality

An x-ray beam that could pass through dense tissue would have high

Penetrability and quality

A low quality beam would also have low:

penetrability

The thickness of absorbing material necessary to reduce the x-ray intensity to half its original value is referred to as:

HVL

The HVL of an x-ray beam is a measurement of beam:

Quality

Image contrast is affected by:

beam quality and kVp

The HVL is lowered by a decrease in:

kVp and distance

X-ray beam quality is improved by _.

increasing filtration

The main purpose of added filtration is to reduce:

patient dose

Added filtration will beam quality and beam quantity.

Increase; decrease

A compensating filter is used to create intensity with a body part of __ thickness

Uniform; non-uniform

Milliamperage-second (mAs) directly affects?

Beam intensity, x-ray output, and beam quantity

The factors that directly affect x-ray quantity are:

mA and time (s)

X-ray quality is numerically represented by:

HVL

The factors that directly affect x-ray quality are:

kVp and beam filtration

The product of tube current and exposure time is equal to:

x-ray beam quantity

The relationship between mAs and exposure is:

directly proportional

If kVp is doubled, the amount of x-ray photons created approximately increases:

Fourfold

During the process of attenuation, x-ray photons in the beam:

Lose energy, reduce in number, and interact

The relationship between the intensity of radiation and distance is the:

inverse square law

When an x-ray photon passes through matter, it undergoes a process called

Attenuation

What is the maximum total filtration required for x-ray equipment producing 70 kV or greater?

2.5 mm aluminum equivalent

The two primary forms of x-ray interaction in the diagnostic range are:

Compton scattering and photoelectric absorption

An incident x-ray interacts with an atom without ionization during _.

Coherent scattering

What x-ray interaction involves the ejection of the k-shell electron?

Photoelectric absorption

An outer-shell electron is ejected and the atom is ionized during _.

Compton interactions

The scattered x-ray from a Compton interaction usually retains of the energy of the incident photons

Most

Compton scatter is directed at _ angle from the incident beam

Any

As kVp increases , the probability of photoelectric absorption __

Increases; decreases

In _, there is complete absorption of the incident x-ray photon

Photoelectric interaction

What occurs only at very high energies used in radiation therapy and nuclear medicine PET imaging?

Pair production

Only at energies above 10 MeV can _ take place.

Photodisintegration

When an x-ray photon with a slightly greater energy than the binding energy of the inner-shell electron interacts with that inner-shell electron, the following interaction results:

Photoelectric absorption

During the photoelectric interaction, as an electron transfers from an outer shell to a vacant inner shell, energy is released in the form of?

Characteristic photon

Unwanted radiographic image densities caused predominantly by scattered photons is called

Radiation fog

When the mass density of the absorber is , it results in Compton scatter.

Increased; increased

K-shell binding energy increase with increasing:

atomic number

What has the greatest mass density?

bone

Image fog in diagnostic imaging is caused by:

Compton scatter

What is the process called when x-ray photons interact with matter and change directions?

Scatter

Differential absorption in diagnostic imaging is caused by:

Photoelectric absorption

Because of differential absorption, about _% of the incident beam from the x-ray tube contributes to the finished image.

0.5

Differential absorption is dependent on:

kVp of the exposure, atomic number of the absorber, mass density of the absorber

Attenuation is caused by:

absorption and scattering

Barium is a good contrast agent because of its:

high atomic number

The use of contrast agents increases the amount of:

Differential absorption, photoelectric absorption, Compton scatter

A negative contrast agent is:

air

X-rays transmitted without interaction contribute to:

The radiographic image

Compton interactions, photoelectric absorption, and transmitted x-rays all contribute to:

Differential absorption

High kVp techniques reduce

patient dose

What interactions with matter results in a radiograph with higher contrast?

Photoelectric interactions

In an effort to decrease the mAs of an exposure, the 15% rule of kVp change may be considered. Changing the original kVp of 84 using the 15% rule will have what impact?

Greater Compton scattering interactions

At energies below 40 keV, the predominant x-ray interaction in soft tissue and bone is _.

Photoelectric absorption

If 5% of an incident beam is transmitted through a body part, then 95% of that beam was _.

Attenuated

The incidence of photoelectric effect increases with:

Increasing atomic number of the absorber

What is the relative probability that a 25 keV x-ray will undergo a photoelectric interaction in bone compared with soft tissue? Z (bone) =18.8, Z (soft tissue) = 7.4

6.5

In diagnostic radiology, radiographic image contrast is principally due to the predominance of:

Photoelectric interactions

The radiographic technique for a portable abdomen examination is 75 kVp at 50 mAs. The result is a patient exposure of 2.0 mGy. What will the exposure be if the mAs can be reduced to 20 mAs?

0.8 mGy

A small bowel follow-through technique calls for 110 kVp at 8 mAs, and results in an x-ray intensity of 0.25 mGy. What will be the intensity if the kVp is increased to 120 kVp and the mAs remains fixed?

0.3 mGy

A radiograph of the abdomen is taken using 75 kVp at 40 mAs at a distance of 40 inches. What mAs should be used to produce an acceptable radiograph if the distance is increased to 60 inches?

90 mAs

An x-ray exposure of 180 mR is recorded at a distance of 24 inches. If the same technical factors are used, what will the exposure be if the distance is increased to 48 inches?

45