Chapter 8: X-Ray Emission Flashcards

A set of 125 practice flashcards covering X-ray quantity, quality, filtration, and the laws governing beam intensity.

What two characteristics characterize the x-ray beam?

Quantity and quality.

How is x-ray quantity defined in the lecture notes?

The number of x-rays in the beam.

How is x-ray quality defined in the lecture notes?

The penetrability of the beam.

What is another term used to describe x-ray intensity?

Radiation exposure.

What is the unit of measurement for x-ray intensity in air?

$mGya$ (Milligray in air).

What was the former measurement unit for milligray in air ($mGya$)?

Milliroentgen ($mR$).

What does $mGya$ specifically measure in the air?

The number of ion pairs produced in the air by x-rays.

How does ionization of air change as the number of x-rays increases?

Ionization of air increases as the number of x-rays in the beam increases.

Are the number of x-rays and ionization of air strictly proportional?

No, they are directly related but not strictly proportional because ionization may vary depending on x-ray energy.

List one way radiation exposure rate can be expressed using $mGya$.

$mGya/s$ (mGya per second).

List the expression for radiation exposure rate relative to tube current and time.

$mGya/mAs$ (mGya per milliampere-second).

What is the typical x-ray quantity produced by a general-purpose tube at $70\,kVp$ and $100\text{-cm}$ SID?

About $50\,\mu Gya/mAs$ ($5\,mR/mAs$).

What are the four factors that affect x-ray quantity?

mAs, kVp, Distance, and Filtration.

What is the relationship between mAs and x-ray quantity?

Directly proportional.

If mAs is doubled, what happens to the number of electrons striking the tube target?

The number of electrons is doubled.

If mAs is doubled, what happens to the number of x-rays emitted?

The number of x-rays emitted is doubled.

What is the formula representing the relationship between x-ray intensity ($I$) and mAs?

$$\frac{I_1}{I_2} = \frac{mAs_1}{mAs_2}$$

What is the relationship between kVp and x-ray quantity?

X-ray quantity is proportional to the square of kVp.

If kVp were doubled, by what factor would x-ray intensity increase?

A factor of $4$.

What is the formula for the relationship between x-ray intensity ($I$) and kVp?

$$\frac{I_1}{I_2} = (\frac{kVp_1}{kVp_2})^2$$

According to clinical practice, how is mAs adjusted for a $15\%$ increase in kVp to maintain exposure?

The mAs should be halved.

What is the compensation for a decrease in kVp according to the $15\%$ rule?

Double the mAs.

Why is increasing kVp and lowering mAs beneficial for the patient?

It reduces the patient dose while keeping image exposure constant.

What is the effect of increasing kVp and lowering mAs on screen-film image contrast?

It can decrease image contrast.

Do digital receptors show significant contrast change with the $15\%$ kVp rule?

No, digital receptors show little change in contrast.

What is the relationship between distance and x-ray quantity?

Inversely proportional to the square of the distance from the source.

What law describes the decrease of x-ray intensity as distance increases?

The inverse square law.

What is the formula for the Inverse Square Law?

$$\frac{I_1}{I_2} = (\frac{d_2}{d_1})^2$$

If distance (SID) is doubled, what happens to the x-ray intensity?

Intensity drops to one-fourth ($1/4$) of its original value.

What adjustment to mAs is needed if SID is increased to maintain constant receptor exposure?

mAs must be increased by the square of the distance ($SID^2$).

What is the name of the law used to compensate for a change in SID by changing mAs?

The square law (or direct square law).

What is the formula for the square law relative to mAs and SID?

$$\frac{mAs_1}{mAs_2} = \frac{SID_1^2}{SID_2^2}$$

What is the alternative way to express the square law formula using 'Old' and 'New' values?

$$\frac{\text{Old } mAs}{\text{New } mAs} = \frac{\text{Old distance squared}}{\text{New distance squared}}$$

How does filtration affect x-ray quantity?

It is inversely proportional; as filtration increases, x-ray quantity decreases.

Why does patient dose decrease when filtration is added?

Filtration removes low-energy x-rays from the useful beam.

What is beam hardening?

Removing low-energy (soft) x-rays, leaving a higher proportion of high-energy (hard) x-rays.

What is x-ray penetrability?

The ability of x-rays to penetrate deeper in tissue.

What determines high-quality x-rays?

High penetrability.

What is the relationship between x-ray beam energy and penetrability?

As energy increases, penetrability increases.

Which factors do NOT affect radiation quality?

Distance and mAs.

What is the best method for specifying x-ray quality?

Half-Value Layer (HVL).

Define Half-Value Layer (HVL).

The thickness of material needed to reduce the x-ray intensity by half ($50\%$).

What is the typical HVL range for a diagnostic x-ray beam in millimeters of aluminum?

$3$ to $5\,mm\,Al$.

What is the typical HVL range for a diagnostic x-ray beam in centimeters of soft tissue?

$3$ to $6\,cm$ of soft tissue.

What is the definition of attenuation?

The reduction in x-ray intensity that results from absorption and scattering.

What type of mathematical attenuation do x-rays undergo?

Exponential attenuation.

How does atomic number affect x-ray penetration?

X-rays are more penetrating in material of low atomic number than high atomic number.

What equipment is used to experimentally determine HVL?

An x-ray tube, a radiation detector, and varying thicknesses of aluminum filters.

What are the two factors that affect x-ray quality?

kVp and Filtration.

What is the relationship between kVp and x-ray quality?

Directly proportional.

How does increasing kVp affect the HVL?

Increasing kVp increases the HVL.

Why does a higher energy beam require a higher HVL?

A 'harder' beam requires a greater thickness of material to reduce its intensity by half.

What is the approximate HVL in $mm\,Al$ at $50\,kVp$?

$1.9\,mm\,Al$.

What is the approximate HVL in $mm\,Al$ at $100\,kVp$?

$3.7\,mm\,Al$.

What is the approximate HVL in $mm\,Al$ at $150\,kVp$?

$5.4\,mm\,Al$.

How does filtration affect x-ray quality?

Directly proportional; increasing filtration increases x-ray quality.

What effect does adding filtration have on the emission spectrum?

It shifts the emission spectrum to higher energies.

What is the standard total filtration required for an x-ray beam?

$2.5\,mm\,Al$.

Would an ideal x-ray beam be polyenergetic or monoenergetic?

Monoenergetic.

What is the primary material used for x-ray filters?

Aluminum ($Z=13$).

Why is aluminum the preferred filter material?

It is efficient, readily available, and low cost.

Name two types of specialized filtration.

Inherent filtration and added filtration.

What defines inherent filtration?

Filtration provided by the x-ray tube's glass or metal enclosure.

What is the typical value of inherent filtration in general-purpose tubes?

About $0.5\,mm\,Al$.

How does inherent filtration change with the age of the x-ray tube?

It increases as materials deposit on the tube window.

What is added filtration?

A thin sheet of aluminum placed between the tube and the collimator.

Where is the aluminum sheet for added filtration placed?

Between the x-ray tube and the collimator.

What provides added filtration besides aluminum sheets?

The silver surface of the collimator mirror.

How does added filtration affect x-ray quantity?

It reduces x-ray quantity.

What is the purpose of compensating filters?

To produce uniform image intensity when imaging body parts with varying thickness or density.

Are compensating filters designed for radiation protection?

No, they are used to maintain image quality by balancing radiopacity.

What type of compensating filter is used for the foot?

Wedge Filter.

What is another name for the Bilateral Wedge filter?

Trough Filter.

Where is a Trough Filter used in radiography?

In chest radiography to balance intensity between the mediastinum and lung fields.

What type of compensating filter is used in CT imaging?

Bow-Tie Filter.

What type of filter is used in interventional radiology for long anatomical sections?

Step-Wedge Filter.

In chest radiography, how does a wedge filter affect the thick part of the patient?

The thin part of the wedge is positioned over the more radiopaque (thicker/denser) area to allow more x-rays through.

In chest radiography, where is the thick part of the wedge filter placed?

Over the less radiopaque (darker/less dense) area to increase attenuation.

What happens to x-ray quality when mAs is increased?

There is no change in quality.

What happens to x-ray quantity when mAs is increased?

X-ray quantity is increased.

What happens to x-ray quality when kVp is increased?

X-ray quality is increased.

What happens to x-ray quantity when kVp is increased?

X-ray quantity is increased.

What happens to x-ray quality when distance is increased?

There is no change in quality.

What happens to x-ray quantity when distance is increased?

X-ray quantity is decreased.

What happens to x-ray quality when filtration is increased?

X-ray quality is increased.

What happens to x-ray quantity when filtration is increased?

X-ray quantity is decreased.

What is the unit abbreviation for milligray in air?

$mGya$.

What is the atomic number ($Z$) of Aluminum?

$13$.

Which filter shape matches the shape of the head or body in CT?

Bow-Tie Filter.

What does a $15\%$ increase in kVp equivalent to regarding film-screen exposure?

Doubling the mAs.

What does SID stand for in the context of the square law?

Source-to-Image Distance.

Does kVp affect contrast in digital receptors as much as in screen-film?

No, digital receptors show little change in contrast with kVp adjustments.

What is the relationship between beam hardening and image contrast on screen-film?

Beam hardening can reduce image contrast.

List one material other than aluminum used as a specialized x-ray filter.

Copper (or tin, gadolinium, holmium).

What is the typical inherent filtration for mammography tubes?

$0.1\,mm\,Al$.

Does the HVL increase or decrease when kVp increases?

The HVL increases.

What process is characterized by both absorption and scattering of x-rays?

Attenuation.

What is the result of increasing the energy of an x-ray beam on its penetrability?

Penetrability increases.

If you move further from the source, why does x-ray quantity decrease?

Because the x-rays spread out over a larger area according to the inverse square law.

Who is the author of the textbook mentioned in the notes?

Stewart Carlyle Bushong.