Radiology Chapter 15 mAs Flashcards

Questions and Answers

Milliamperage measures the flow ________ of electrical current through a circuit.

quantity

The ________ control on the x-ray machine console is actually a selector which taps off a different resistor in the filament circuit.

The set mA is applied to the filament in the x-ray tube cathode each time the ________ switch is depressed.

rotor

Higher mA causes greater friction and temperature of the filament, so more electrons are emitted through the process of ________________.

thermionic emission Signup and view all the answers

Liberated electrons form a charge or electron around the filament which is maintained at equilibrium as long as the rotor button is held down.

space, cloud Signup and view all the answers

Ultimately, the intensity rate of the ________ beam is directly controlled by the mA station set at the console.

x-ray Signup and view all the answers

The exposure time is abbreviated ________.

s - for seconds Signup and view all the answers

The radiographic term mAs derives from multiplying the x .

mA x s Signup and view all the answers

The term mAs refers to the ________ amount of electricity used during a radiographic exposure.

total Signup and view all the answers

Primarily because it doesn't affect other factors, the mAs is considered the primary ________ over x-ray exposure.

control Signup and view all the answers

Doubling the mA makes a graph of the x-ray beam spectrum twice as ________.

dark Signup and view all the answers

For a particular amount of exposure, mA and exposure time are ________ proportional to each other.

inversely Signup and view all the answers

When the mA stations are listed in multiples of 100, to mentally find the mAs before multiplying you can move the decimal place in the exposure time to the two places and the decimal place in the mA to the two places.

right, left Signup and view all the answers

The x-ray beam is a shower of x-rays which have a ________ distribution just like the drops in a rain shower.

random Signup and view all the answers

When exposure is very light and there are few photons striking the image receptor, one can see the ________ distribution of the exposure across the image.

uneven Signup and view all the answers

The grainy or 'blotchy' appearance caused by insufficient exposure is called .

quantum mottle Signup and view all the answers

The best way to keep the SNR for the image high is to subdue quantum mottle by 'overwhelming it' with ________, so it makes a lesser percentage contribution to the overall image.

good exposure Signup and view all the answers

Anything which results in an insufficient amount of exposure at the image receptor plate can lead to mottle, including ________ kVp.

inadequate Signup and view all the answers

Because pixel values are amplified by digital imaging systems, only ________ underexposure can result in the appearance of quantum mottle.

slight Signup and view all the answers

For all electronic display systems such as LCDs and CRTs, electronic ________ constitutes additional noise in the image.

mottle Signup and view all the answers

For digital images, the only means for the radiographer to become aware of overexposure due to the use of excessive mAs is to monitor the exposure ________ readout.

indicator Signup and view all the answers

Since subject contrast is determined by the percentage contribution from each type of interaction to the total information reaching the IR, changes in ________ do not have any direct bearing upon contrast in the final image.

mAs Signup and view all the answers

The mAs can have no relation whatever to any of the recognizability functions in the image, because they are all ________ factors, whereas the mAs is an electrical factor.

geometrical Signup and view all the answers

Although exposure time is not the direct cause of , the longer the exposure time, the greater chance there is for to occur.

motion, motion Signup and view all the answers

Since some types of motion cannot be controlled, exposure time is generally considered to be a ________ factor for motion blur during radiographic exposures.

contributing Signup and view all the answers

It is generally assumed that the shorter the exposure time, the ________ radiographic images are likely to be.

sharper Signup and view all the answers

What is mA (milliamperage)?

The flow rate of electrons along a wire, per second ----> # of x-rays created Signup and view all the answers

What is amperage?

current Signup and view all the answers

What does the rotor switch do?

Negative electrons (e-) are boiled off at the filament. The filament circuit is engaged whenever the rotor switch is depressed. Signup and view all the answers

What is exposure time? (abbreviated 's')

The # of seconds during which exposure is occurring. Signup and view all the answers

What is thermionic emission?

High-amperage current flows through the thin filament, causing friction and the ejection of electrons. Signup and view all the answers

What is the electron cloud / space charge?

Certain # of electrons that hang out until the others are sent across (the rotor is pressed down and held) ultimately determines the intensity of the x-ray beam. Signup and view all the answers

What is mAs considered to be?

The primary control for the amount of x-ray exposure. Signup and view all the answers

________ the mAs, mA or time raises the x-ray spectrum curve twice as high at every point.

Doubling Signup and view all the answers

________ radiographs show a doubling in density for each doubling of the mAs.

Conventional film Signup and view all the answers

A disadvantage of is the lack of immediate feedback when doubling the mAs.

digital radiography Signup and view all the answers

Sufficient exposure ensures a high ________________ ratio.

signal-to-noise (SNR) Signup and view all the answers

Anything which results in an insufficient exposure at the image receptor can lead to mottle, including: 1. 2. 3..

<ol> <li>insufficient mAs setting 2. inadequate kVp setting to penetrate the body part 3. rectifier failure</li> </ol> Signup and view all the answers

________ systems amplify the input from each pixel, making them highly sensitive to image noise such as mottle.

Computer-based Signup and view all the answers

Result: Only slight underexposure can result in visible mottle for ________ systems.

digital imaging Signup and view all the answers

For all electronic display systems such as LCDs and CRTs, ________ constitutes additional noise in the image.

electronic mottle Signup and view all the answers

Overexposure is only detectable in digital systems by monitoring the ________.

exposure indicator read-out Signup and view all the answers

What end of the spectrum (exposure index values) does quantum mottle appear on? High or low end?

Quantum mottle results from too little exposure so therefore it is on the lower end of exposure index values. Signup and view all the answers

What is dose creep?

Techs overexposing on purpose: overexposure = no repeat, underexposure = repeat. Signup and view all the answers

_ is determined by these percentage contributions from the different interactions, so mAs does not affect .

Subject contrast, subject contrast Signup and view all the answers

The set mAs is an _________, not a geometrical one. It therefore has no bearing upon the recognizability functions in the image: sharpness, magnification or distortion.

electrical factor Signup and view all the answers

The set mAs does not directly affect: 1. level at the IR 2. brightness of the image 3. mottle, and thereby noise level and SNR.

<ol> <li>exposure 2. resulting 3. quantum</li> </ol> Signup and view all the answers

The greatest enemy to sharpness of recorded detail in the image is ________.

motion Signup and view all the answers

Exposure time is not a _________ cause of motion - it is the patient who moves.

direct Signup and view all the answers

The _________ the exposure times, the sharper the images are likely to be.

shorter Signup and view all the answers

Define thermionic emission, space charge, and dual filament.

Thermionic emission - high-amperage current flows through the thin filament, causing friction and the ejection of electrons. Space charge - liberated electrons form a space charge or electron cloud around the filament, which is maintained at equilibrium as long as the rotor button is held down. Dual filament - produces more x-rays which gives more variety in exposures. Signup and view all the answers

List image qualities which are not directly affected by mAs.

It does not change minimum, average, or peak energies in the beam. It does not affect subject contrast. Signup and view all the answers

Explain quantum mottle and how to correct it.

Quantum mottle is a result of underexposure. To prevent quantum mottle, the radiographer just needs to use the right technique or if they get an image with quantum mottle, increase the kVp. Signup and view all the answers

Explain the relationship between exposure time and motion unsharpness.

Exposure time is not a direct cause of motion; it’s the patient that moves. Long exposure times are considered a contributing factor for motion because internal motion cannot be controlled; shorter exposure time means less chance of capturing internal movement. The shorter the exposure time, the sharper the image. Signup and view all the answers

Study Notes

Milliampere-seconds (mAs) Overview

Milliamperage (mA) measures the quantity of electrical current through a circuit, impacting x-ray production.
The mA control on an x-ray console selects different resistors in the filament circuit, influencing electron emission.
Each time the rotor switch is pressed, the set mA is applied to the x-ray tube cathode, initiating a process for creating x-rays.

Thermionic Emission and Electron Dynamics

Higher mA levels generate increased friction and temperature in the filament, resulting in thermionic emission and more electron ejection.
Liberated electrons form a space charge or "cloud" around the filament, stabilizing while the rotor is engaged, crucial for defining x-ray beam intensity.
The x-ray beam's intensity rate directly corresponds with the mA settings, with mAs represented as mA multiplied by exposure time (in seconds).

mAs and Exposure Relationships

mAs indicates the total amount of electricity used during a radiographic exposure and is considered the primary control affecting x-ray exposure.
Doubling the mA results in a graph of the x-ray beam spectrum being twice as dark, showing a direct correlation between mA and exposure level.
Adjustments to mA and exposure time are inversely proportional; as one increases, the other decreases to maintain consistent exposure.

Image Quality and Exposure Effects

Shorter exposure times generally yield sharper radiographic images, as longer times increase the likelihood of motion blur.
Quantum mottle results from insufficient exposure, appearing as graininess in images, and is mitigated by ensuring good exposure.
Digital imaging systems are sensitive to noise and only slight underexposure can lead to the visibility of quantum mottle.

Additional Considerations

Various factors such as inadequate kVp settings or rectifier failures can result in insufficient exposure, leading to image mottle.
Digital systems do not provide immediate feedback for overexposure, necessitating monitoring of exposure indicator readouts.
Subject contrast is unaffected by mAs changes; it stems from differential interactions contributing to total image information.

Technical Definitions and Clarifications

Motion, rather than exposure time, is the key factor affecting unsharpness in images, emphasizing the importance of managing motion during exposure.
The electron cloud created by thermionic emission and the dual filament setup enhance x-ray production, offering a variety of exposures.
mAs is not an influencing factor for specific image recognizability functions like sharpness, magnification, or distortion since it is an electrical factor.

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Description

Test your knowledge of milliampere-seconds (mAs) with this set of flashcards focused on Chapter 15. Each card will help reinforce important concepts related to the flow of electrical current in radiology. Perfect for students preparing for exams in this field.