RTE 006: Chapter 13 Screen-Film Radiographic Technique

P2 Coverage •Exposure Factors ‒Kilovolt Peak ‒Milliamperes ‒Exposure Time ‒Distance •Imaging System Characteristics ‒Focal-Spot Size ‒Filtration ‒High-Voltage Generation •Patient Factors ‒Thickness ‒Composition ‒Pathology

common (SID) at 180 cm (72 in)

currently, 300 cm

The source-to-image distance (SID) from chest radiography is

common (SID) fixed at 100 cm (40 inches)

currently, 120

For most radiographic examinations, the source-to-image distance (SID) from the tabletop radiography is

Screen-film Radiographic Technique

The combination of settings selected on the control panel. Its purpose is to produce a high-quality image.

Exposure factors

The factors that influence and determine the quantity and quality of x-radiation to which the patient is exposed are called

Radiation Quantity

Refers to radiation intensity measured in mGya or mGya/mAs (mR or mR/mAs)

Radiation Quality

Refers to x-ray beam penetrability, best measured by the half-value layer (HVL) of the x-ray beam

kVp, mAs, Exposure time, SID (source-to-image receptor distance)

What are the primary exposure factors?

Kilovolt Peak (kVp)

Meaning of kVp

Focal-spot size, Distance, Filtration

What are the secondary factors of exposure factors?

kVp and mAs

The factors principally responsible for x-ray quality and quantity.

kVp

The primary control of x-ray beam quality (beam penetrability)

Controls radiographic contrast, Influences beam quantity, and Determines the average OD

Functions of kvp

mA/s (milliamperes / per second)

It determines the number of x-rays produced (radiation quantity) 1 A = 1 C/s = 6.3 x 1018 per second

Higher kVp:
-Higher beam quality
-Greater beam penetrability
-More scatter radiation
• Rationale: more Compton effect interaction
- Less differential absorption
-Result: reduced image contrast

What does high kVp do?

Higher mA:
-More electrons produced
-Higher x-ray quantity
-Higher patient dose
-No change in x-ray quality

What higher mA do?

1 A = 1 C/s (coulomb per second) = 6.3 x 10^18 electrons per second

Formula in getting 1 A (ampere)

Inversely proportional

The relationship between low exposure time and high mAs are

Kept as short as possible (ALARA)

Exposure time needs to be

To minimize the motion blur due to patient motion because it provides the required x-ray intensity

The purpose for keeping the exposure time short is to

Also the patient dose

With a constant exposure time, mA controls the x-ray quantity and therefore

mA

X-ray quality remains fixed with a change of what

mAs = mA x time

(don't forget to convert to seconds)

Formula of mAs

mA (second exposure) time (second exposure)
------------------------=
mA (first exposure) time (first exposure)

Other formula for getting the mAs value?

mA (first exposure) x time (first exposure)

mA (second exposure) x time (second exposure)

Distance

It determines the intensity of the x-ray beam at the image receptor.

Inverse Square Law

Distance affects exposure of the image receptor according to

600 mA

Inexpensive radiographic imaging systems designed for private physician's offices normally have a maximum capacity of

1500 mA

Interventional radiology imaging systems may have the capacity of

Motion Blur

Short exposure time reduces

mAs

What is the key factor on the control of OD (optical density) on the radiograph?

mAs value

It is a measure of the total number of electrons conducted through the x-ray tube for a particular exposure

mAs (milliampere per second)

One measure of electrostatic charge

Direct Square Law

It allows a radiologic technologist to calculate the required change in mAs after a change in SID to maintain constant OD.

To minimize the cardiac magnification

What is the purpose of Inverse Square Law?

(Note that both the original mAs value and the original SID are in the denominator rather than reversed, as in the inverse square law.)

Inverse Square Law Formula

Distance (SID)

What affects OD?

Distance

____________ has no effect on radiation quality

What are the uses of Large focal spot?

- It is used in general imaging
- Ensures that sufficient mAs can be used to image thick or dense body
parts.
- Provides for a shorter exposure time, which minimizes motion blur.
- Produce more x-rays compared with small focal spot

What are the uses of Small focal spot?

-It is used for fine-detail radiography, in which the quantity of x-rays is
relatively low.
-Always used for magnification radiography
- These are normally used during extremity radiography and in
examination of other thin body parts in which higher x-ray
quantity is not necessary.

The x-ray quantity or quality

Changing the focal spot for a given kVp/mAs setting does not change

(Note that both the original mAs value and the original SID are in the denominator rather than reversed, as in the inverse square law.)

Direct Square Law Formula

Small Focal Spot and Large Focal Spot

What are 2 focal spot?

Bi focal X-ray Tube

Another name for 2 Focal Spot

0.3 mm/1.0 mm focal spots

X-ray tubes used in interventional radiology procedures or magnification radiography may have, how many focal spot?

0.1 mm/0.3 mm focal spots

Mammography x-ray tubes have, how many focal spot?

Microfocus Tube

Are designed specifically for imaging very small microcalcifications at
relatively short SIDs?

Inherent filtration, Added filtration, and Compensating filters

Three types of filtration

Inherent filtration

It is made of glass or metal envelope.

approximately 0.5 mm Al equivalent

For general-purpose tubes, the value of inherent filtration is

1.0 mm Al equivalent

In light-localizing collimator, it provides an additional of

Added filtration

1-mm Al filter is inserted between the x-ray tube housing and the collimator

Compensating filters

Are shapes of aluminum mounted onto a transparent panel
that slides in grooves beneath the collimator.

These filters also balance the intensity of the x-ray beam so as to
deliver a more uniform exposure to the image receptor.

Single phase, Three phase, and High Frequency

Three basic types of high-voltage generators

the type of high-voltage generator that is used.

The radiation quantity and quality produced in the x-ray tube are influenced by

Half-wave rectification

Results in the same radiation quality as is produced by full-
wave rectification, but the radiation quantity is halved.
- Used in mobile and dental x-ray imaging systems

Full-wave rectification

Same as half-wave rectification except there is no dead time.
- X-rays are emitted continually as pulses.
- The required exposure time for full-wave rectification is only
half that for half-wave rectification.

Three-phase power 6p (pulse) /12p (pulse)

• Results in higher x-ray quantity and quality.

• more efficient than singlephase power.

• More x-rays are produced for a given mAs setting

• The average energy of those x-rays is higher.

• The x-radiation emitted is nearly constant rather than pulsed.

High-frequency generators

The voltage waveform is nearly constant, with less than 1% ripple.

• High-frequency generation results in even greater x-ray quantity and quality.

• Used increasingly with dedicated mammography systems, computed tomography (CT) systems, and mobile x-ray imaging systems.

(Anatomical) Thickness, (Body) Composition, and Pathology

First group of patient factors

Body habitus

The general size and shape of a patient is called

Sthenic

Meaning “strong, active”—patients are average patients.

Hyposthenic

Thin but healthy appearing; these patients require less radiographic technique.

Hypersthenic

Big in frame and usually overweight.

Asthenic

Small, frail, sometimes emaciated, and often elderly

the more x-radiation is required to penetrate the patient to expose the image receptor

The thicker the patient?

Sthenic, Hyposthenic, Hypersthenic, Asthenic

What are the four general states of body habitus?

Sthenic patients

Radiographic technique charts are based on

Calipers

Are available to the radiologic technologist for use to measure the thickness of the anatomy being imaged

This is due to the fact that the primary X-ray beam has not yet been attenuated by the tissue at this point, and also, that area is exposed by some of the scattered radiation from the body.

Why should we not guess the patient thickness?

They are image quality factors that consist of OD (optical density), contrast, detail, distortion

Second group of patient factors?

They are exposure technique factors that includes kVp, milliamperage, exposure time, SID, Grids, screens, focal-spot size, and filtration

Final group of patient factors?

The patient’s size, shape, and physical condition

What influences greatly the radiographic technique?

High subject contrast

The chest has

Low subject contrast

The abdomen has

Increased radiolucency or radiopacity

Pathology can appear with what?

Radiolucency or Radiopacity

Body tissues are often described by their degree of what?

Mass density

The radiologic technologist must estimate the __________ of the anatomical part and the range of ___________ involved. (Only one answer)

Low kVp and High mAs

Soft tissue requires ____ kVp and _____ mAs

Low kVp, thin

Extremity consists of soft tissue and bone, ___ kVp is used because the body part is ____

Low, high, intermediate

Lung tissue has very ___ mass density, the bony structures have ____ mass density, and the mediastinal structures have ____________ mass density.

It provides in an image with satisfactory contrast and low patient radiation dose

High kVp and low mAs can be used to good advantage as a result?

Type of pathology, size, and composition

The ______________, its ____, and its ___________ influence radiographic technique.

Destructive pathology

Causing the tissue to be more radiolucent.

Constructive pathology

Increasing mass density or composition, causing the tissue to be more radiopaque.

Patient examination request form and previous images.

(The radiologic technologist should also not hesitate to more information from the referring physician, the radiologist, or the patient regarding the suspected pathology.

In pathology, what do we need to help evaluate our patient before examination?

Increase

An increase in kVp will result in ________ x-ray quantity

Increase

An increase in mA will result in ________ x-ray quantity

Increase

An increase in exposure time will result in ________ x-ray quantity

Increase

An increase in mA/s will result in ________ x-ray quantity

Decrease

An increase in distance will result in ________ x-ray quantity

Decrease

An increase in voltage ripple will result in ________ x-ray quantity

Decrease

An increase in filtration will result in ________ x-ray quantity

Increase

An increase in kVp will result in ________ x-ray quality

No change

An increase in mA will result in ________ x-ray quality

No change

An increase in exposure time will result in ________ x-ray quality

No change

An increase in mA/s will result in ________ x-ray quality

No change

An increase in distance will result in ________ x-ray quality

Decrease

An increase in voltage ripple will result in ________ x-ray quality

Increase

An increase in filtration will result in ________ x-ray quality

manipulation

Secondary exposure factors require ____________ for particular examinations