Ch 7-2

What is set when the tube is in AEC mode

-In automatic exposure control (AEC) mode, the operator selects the x-ray voltage and the desired film density, and the generator circuits control the exposure time

How is the heel effect taken advantage of

-The heel effect can be taken advantage of by placing denser parts of the body at the cathode side and thinner parts at the anode side of the beam. In mammography, for example, the more intense cathode side is used to irradiate

What is the X-ray tube output directly proportional to

-The x-ray tube output is directly proportional to the x-ray tube current.

(80 x 1000 =80,000)

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Electrons passing through matter lose energy

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Note; The size of the focal spot is a factor in determining the rating of the X-ray tube

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Soft beams are produced at low peak voltages using less filtration.

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and current (mAs)

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current (mA), and is expressed in watts (1 W = 1

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dissipation by convection.

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exposure time, and number of exposures.

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increased actual focal spot size

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patient, when measured 1 m from the patient.

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rotation

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slit cameras.

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the denser chest wall region

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to heat.

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units)

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What is the size of the actual focal spot used in mammography

0.1-0.15 Magnification mammography http://o.quizlet.com/4Bg7sUuQwTIUA2a31xIshA.jpg

What is the size of the actual focal spot used in mammography with mag views

0.3 Mammography; magnification radiography http://o.quizlet.com/4Bg7sUuQwTIUA2a31xIshA.jpg

What is the size of the focal spot used in Flouro

0.6 Conventional radiography (small focal spot) http://o.quizlet.com/4Bg7sUuQwTIUA2a31xIshA.jpg

What is the size of the actual focal spot used in CR

0.6* Conventional radiography (small focal spot)

What is compton scatter

A Compton interaction is one in which only a portion of the energy is absorbed and a photon is produced with reduced energy. This photon leaves the site of the interaction in a direction different from that of the original photon http://o.quizlet.com/tC5R6Ah8E0.ULkS9RLwH7g.jpg

When are large focal spot sizes favored

A large focal spot is favored when a short exposure time is the priority

What are small focal spot sizes favored

A small focal spot is preferred when spatial resolution is a priority.

What is the typical currents that are used in radiology in an X-ray tube

A typical current for radiography is 100 to 1,000 mA

What is the 'actual focal spot'

Actual focal spot: The physical area of the focal track that is impacted. http://o.quizlet.com/4Bg7sUuQwTIUA2a31xIshA.jpg

What percent of electrical energy is converted into heat

Approximately 99% of the electrical energy supplied to an x-ray tube is converted

What does beam hardening refer to

Beam hardening refers to the preferential loss of lower-energy photons from a polychromatic beam with filtration.

What modality is there a risk of anode overheating

CT, flouro there is basically no risk. http://o.quizlet.com/wUKlfPE.ju1qlPfg.p4XHg.jpg

What is the typical kVp for CXR

Chest radiography is often performed at higher x-ray tube voltages of about 120 kVp.

primarily by:

Compton interactions http://o.quizlet.com/tC5R6Ah8E0.ULkS9RLwH7g.jpg

What interaction occurs in compton scatter

Compton scatter, incident photons interact with loosely bound valence (outer-shell) electrons. http://o.quizlet.com/tC5R6Ah8E0.ULkS9RLwH7g.jpg

What is the heel effect

Due to the geometry of the angled anode target, the radiation intensity is greater on the cathode side. http://o.quizlet.com/MRpA3A1wsZUKNsS1Hj6Eig.jpg

What are the sizes of 'effective focal spot' sizes

Effective focal spot sizes may be up to 50% larger than the nominal values listed

What is the 'effective focal spot'

Effective focal spot: The area of the focal spot that is projected out of the tube toward the object being radiographed http://o.quizlet.com/4Bg7sUuQwTIUA2a31xIshA.jpg

What is the federal requirement for leakage from an X-ray tube

Federal regulations require the leakage radiation at 1 m to be no more than 1 mGy/hour (100 mR/hour).

What is the focal spot tract

Focal Track: The portion of the anode where the high-voltage electron stream will impact. When discussing a rotating anode this describes the circular path that will be impacted by the electron beam http://o.quizlet.com/4Bg7sUuQwTIUA2a31xIshA.jpg

What determines the focal spot size

Focal spot size is a result of the filament shape, focusing cup, and electric field cre-ated between the cathode and anode.

What are the range of 'actual focal spot' sizes

Focal spot sizes, as quoted by manufacturers of x-ray tubes, range from about 0.1 to 1.2 mm

How is tube loading measured if there is a X-ray tube voltage

For a constant x-ray tube voltage (V) and current (I), the energy deposited during an x-ray exposure is V x I x t joules, where t is the exposure time measured in seconds.

What is the typical kVp for small body parts

For small body parts, such as the extremities, x-ray tube voltages are generally 55 cto 65 kVp.

What is the difference if there is a single phase generator

For systems with single-phase power supplies and full-wave rectification, the quan-tity kVp (peak voltage) x mA x time is termed heat units. One heat unit = 0.74 J (1 J = 1.35 heat

What is the difference between soft and heard X-ray beams

Hard beams are produced at high peak voltages using heavy filtration.

How is heat transferred to the surrounding from the focal spot in an X-ray tube

Heat is transferred from the focal spot by RADIATION to the tube housing and CONDUCTION into the anode.

Diagram illustrating that the size of the 'actual focal spot' will determine the size of the 'effective focal spot'

Here are two anode with different size actual focal spots. The one on the left has a larger actual focal spot than the one on the right. Because of the angle of the anode the effective focal spot is also different for each anode. http://o.quizlet.com/QZxT4SBzmzquDYIK9WsuKw.jpg

What is the typical current used in flouroscopy

In fluoroscopy, tube currents are typically between 1 and 5 mA. (remember plain film is 100-1000 mA)

What is the line focus principle

Line-Focus Principle: Used to reduce the effective area of the focal spot

How fast do anodes typically rotate

Modern anodes are circular and rotated at high speeds (3,000 to 10,000 rpm) to spread heat loading over a large area.

What is the range of kVp that most X-ray imaging is performed at

Most radiographic and fluoroscopy imaging is performed at x-ray tube voltages be-tween 70 and 90 kVp

What percent of electrical energy is converted into X-rays

Only about 1 % of the electric energy supplied to the x-ray tube is converted to x-rays.

What is kVp

Peak kilovoltage (kVp) is the maximum voltage applied across an X-ray tube. It determines the kinetic energy of the electrons accelerated in the X-ray tube and the peak energy of the X-ray emission spectrum http://o.quizlet.com/kpWu3XrKNhQH2EzuYj9cbw.jpg

What is power

Power is the product of the voltage (kV) and

What is scatter radiation

Scattered radiation has been deviated in direction after leaving the tube. The intensity of scattered radiation is typically 0.1% of the intensity incident on a

What is stray radiation

Stray radiation is the sum of the leakage and scattered radiation

What is tube loading

The amount of heat energy deposited during an x-ray exposure is known as the tube loading.

How does the anode angle effect the effective focal spot size

The angle of the focal spot is one way to control the size of the effective focal spot. The larger the angle the larger the effective focal spot http://o.quizlet.com/0ZqRAy8B6S22z3H8EPWz0Q.jpg

What happens to the quantity and quality of the X-ray beam as fitration is added

The diagram below shows what happens when filtration is added to the beam. Notice that the quantity goes down, but the quality goes up. The peak is moving to the right. http://o.quizlet.com/ElBDzDuWMnskQqDtBNTmOA.jpg

What is blooming

The focal spot size enlarges as milliamperes increase owing to the repulsion of adjacent electrons. This effect is called blooming.

How does distance effect the heel effect

The further away the more pronounced the heel effect. http://o.quizlet.com/R4gAaAxF5omNQWkrxHsrQg.jpg

How is an X-ray tube rated

The rating of an x-ray tube is based on maximum allowable kilowatts (kW) at an

What is the cause of the heel effect

The reason that the Heel Effect occurs is illustrated here. The letters represent interactions with electrons from the cathode and the lines coming from the interactions are x-rays. More x-rays will be able to get out of the anode on the right side (the angle side) than on the left side because of all the material the x-rays must pass through to get out of the anode. http://o.quizlet.com/toR2Swz8E4rgbPGCi-q5tw.jpg

Why are filters used

The x-ray beam emerging from the x-ray tube may contain a high number of low-energy photons. Low-energy photons have a negligible chance of getting through the patient,

What happens to the AVERAGE X-ray energy

The x-ray beam output is decreased with increased filtration but the average x-ray energy is increased.

How is the heel effect decreased

To reduce the heel effect, the anode angle should be increased, source-to-image detector distance increased, and field size decreased.

What are the typical anode angle sizes

Typical anode angles range from about 7 to 20 degrees http://o.quizlet.com/0ZqRAy8B6S22z3H8EPWz0Q.jpg

How long is exposure time in plain film

Typical tube current exposure times in radiography are 10s of mAs.

Filtration with characteristics X-rays included (more accurate)

X-ray emission spectra from a tungsten target produced at 100 kV. Curve 1 is the the-oretical spectrum without any filtration. Curve 2 is the typical spectrum with the inherent filtra-tion of the x-ray tube and added filtration. Curve 3 shows the effect of additional filtration. http://o.quizlet.com/Kz3vNSsajI2jdv9QJFcgYg.jpg

What factors will determine the tube loading that may occur

X-ray tube loading depends on the tube voltage (kVp), voltage waveform, tube current,

What prevents unwanted X-rays from leaving the X-ray tube in the incorrect location

X-ray tubes are surrounded by lead to absorb unwanted radiation. http://o.quizlet.com/Ks04ISuLhwsXC-nFRIcTnQ.jpg

What are X-ray tubes typically immersed in to help with heat disipation

X-ray tubes are usually immersed in oil for electrical insulation and for aiding heat

What is an example of how an X-ray tube is rated

a tube with a rating of 80 kW (80,000 W) tolerates a maximum ex-posure of 80 kVp and 1,000 mA at 0.1 second

What type of filter is added to plain film radiography

aluminum

What are typical X-ray tube ratings

between 5 and 100 kW

What is the line focus principle

by using a small anode angle you can change the size of the effective focal spot (make it smaller for better resolution) without increasing the heat and damaging the anode.

What is keV

has to do with the photons (X-rays)

;The following data were obtained with a fluoroscopic x-ray tube operated at 80 kVp. The exposure levels were measured 50 cm above the table top with aluminum absorbers positioned on the surface. Estimate the HVL by graphing the data.

http://o.quizlet.com/1G60QlH0L6uqpk098fQ02Q.jpg

;The High Frequency power generators have the least amount of voltage ripple. The circuit is more complicated than the other circuits. Voltage ripple of 3-4%.

http://o.quizlet.com/2UIWuxJrYP2fz8j29BCyOw.jpg

1.2 Conventional radiography (large focal spot)

http://o.quizlet.com/4Bg7sUuQwTIUA2a31xIshA.jpg

thereby contributing to patient dose but adding nothing to the imag

http://o.quizlet.com/4IVZ7TiLj8MooB8sr640tg.jpg

;The above diagram shows that with single phase power there are times when the x-rays are not powerful enough for diagnostic purposes. These are when the current dips to zero, the brown sections, and no photon (x-rays) are produced. Therefore, single phase power does not produce consistently good x-rays

http://o.quizlet.com/5iiPKVRBwrkXvqB5siE0ZQ.jpg

;The housing controls leakage and scatter radiation, isolates the high voltages, and provides a means to cool the tube.

http://o.quizlet.com/B-4xEIh3Adyz1bk6DepcIQ.jpg

Note the angle is from the vertical directions.

http://o.quizlet.com/CwB8AI90k1auSM5Dmjh6CA.jpg

Beam hardening results in a change in x-ray spectrum shape but not in maximum photon energy.

http://o.quizlet.com/F7JWowEx5O7zEGmqfbkujg.jpg

Image shows a pinhole collimator measuring a focal spot size.

http://o.quizlet.com/IvRoYG31RjA7LiRX7Eob2w.jpg

Note: the current we are talking about is the current that is supplied to the cathode filament

http://o.quizlet.com/M9lDcu3fd56hb.x3kXOZtw.jpg

;In the diagram below the construction of a rotating anode is shown. The base is made of graphite for a solid base. The target (dual target for this example) is made of a tungsten-rhenium alloy. The parts holding the target are made of molybdenum.

http://o.quizlet.com/MR7Slko4c7M7KFVXl68Yvg.jpg

;left anode is a stationary anode because it does not move when an exposure occurs. The anode on the right is a rotating anode because the anode rotates during an exposure.

http://o.quizlet.com/S6fkidsxoTgOgJS9gd3oYg.jpg

;The housing controls leakage and scatter radiation

http://o.quizlet.com/ZJcznr8jTxQzbQsxx1pGxg.jpg

;When you use the Radiographic Tube Rating Charts for the X-Ray machine you want to make sure that the kVP setting and the time of the exposure intersect below the mA reading

http://o.quizlet.com/aKCrWvxQqUhvC5TBOZsYaw.jpg

exposure time of 0.1 second.

http://o.quizlet.com/cKTyIglNrOWYDNFFWZpH7A.jpg

Note that the effective focal spot is the apparent source of X-rays FROM the tube.

http://o.quizlet.com/dimwWmFpRnN3IWCmekRT7w.jpg

exposure time on the generator control panel.

http://o.quizlet.com/dmWPFIUbi6qFgNCVy4TZ-g.jpg

What are the different sizes of actual focal spots used in radiology

http://o.quizlet.com/o6kUsOI32ACKDxL5yDgQVQ.jpg

: the cathode side should penetrate the breast that is denser. So in this image I goes more inferior bc that is more breast to penetrate.

http://o.quizlet.com/vSUSTLBRfRdIH8VSwg-BVQ.jpg

J/second).

http://o.quizlet.com/vZgEhDLFIiOj3mFU1Y5OxA.jpg

;The energy radiated by solids, liquids, and gases in the form of electromagnetic waves as a result of their temperature. Also known as thermal radiation. This occurs when the electrons hit the anode target and heat up the anode. The x-ray radiation is given off which heats up the tube.

http://o.quizlet.com/wUKlfPE.ju1qlPfg.p4XHg.jpg

;The picture below shows what can happen to an anode when the anode stops turning. The anode actually melts.

http://o.quizlet.com/wxh7OUBSuuBZc0l-ez0Xlw.jpg

Blooming

increase in focal spot size with increased current

What are 3 techniques to prevent anode over heating

increased exposure time

What is the focal spot

it is the apparent source of X-rays from the tube http://o.quizlet.com/cHjrYyryGOq7Cp-pZd3pgQ.jpg

What happens if the focal spot size is too big

loses image sharpness

What type of filter is added to mammography

molybdenum

How is exposure time and current (mA) related

not that a small exposure time will compensate for a high current http://o.quizlet.com/MkznH6oQ9lggf19gOflhHg.jpg

How are focal spot sizes measured

pinhole cameras, star or bar test patterns, or

What does the shape of the cure look like if there is no filter inplace (number photons Vs photon energy)

removal of parts of the X ray spectrum using absorbing materials in the X-ray beam. The X-ray spectrum reaching the patient is filtered by attenuating material in its path. Filtering of the beam is used in order to modify the spectral or spatial distribution of X-rays, or both. http://o.quizlet.com/V7uXW42gPB8BFHnnl6G2gg.jpg

Single phase generator

results in longest exsposure time

What happens if the focal spot size is too small

the anode will get too hot

What is are the manual settings of an X-ray tube

x-ray tube voltage, x-ray tube current, and

Does filtration reduce the overall X-ray tube outpur

yes

If a larger patient is being imaged do u increased the kVp

yes

The larger the actual focal spot and the larger the angle of the anode makes a larger effective focal spot

yes