Equipment operation & quality control

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The advantages of large format spot film cameras, such as 100 mm and 105 mm, over smaller format cameras, such as 70 mm and 90 mm, include

improved image quality

Spot film cameras have replaced

conventional spot film cassettes

A significant advantage of spot film cameras is

the big reduction in patient dose that their use permits

However, as the film format increases (from 70 mm to 100 mm), so do

image quality, patient dose, and heat production

Patient dose, however

is so much smaller than the dose with conventional spot film cassettes that it is almost insignificant given the small improvement in image quality afforded by cassette spot films.

A star pattern is used to measure

focal spot resolution

What is essential to high-quality mammographic examinations?

1. Small focal spot x-ray tube
2. High radiographic contrast
3. Use of a compression device

Which of the following is (are) tested as part of a quality assurance (QA) program?

1. Beam alignment
2. Reproducibility
3. Linearity

Reproducibility

means that repeated exposures at a given technique must provide consistent intensity

Linearity

means that a given mAs, using different mA stations with appropriate exposure time adjustments, will provide consistent intensity.

The brightness level of the fluoroscopic image is dependent on

1. milliamperage.
2. kilovoltage.
3. patient thickness.

Focal spot blur is greatest

toward the cathode end of the x-ray beam

Focal spot blur, or geometric blur, is caused by

photons emerging from a large focal spot.

Because the projected focal spot is greatest at the cathode end of the x-ray tube,

geometric blur is also greatest at the corresponding part (cathode end) of the radiograph

The projected focal spot size becomes progressively smaller toward the

anode end of the x-ray tube

TV camera tubes used in image intensification, such as the Plumbicon and Vidicon, function to

transfer the output phosphor image to the TV monitor

Image intensification is a process that

converts the dim fluoroscopic image into a much brighter image, much like normal daylight

As x-ray photons emerge from the patient and enter the image intensifier, they

first encounter the input phosphor, which is generally composed of cesium iodide phosphors.

At the input phosphor, x-ray photons are converted to

light photons, which in turn strike the photocathode.

The photocathode

is a photoemissive metal (usually antimony and cesium compounds); when struck by light, it emits electrons in proportion to the intensity of the light striking it

The electrons are then directed to the

output phosphor via the electrostatic focusing lenses, speeded up in the neck of the tube by the accelerating anode, and directed to the output phosphor for further amplification.

From the output phosphor, the image is

taken by the TV camera, most often a Plumbicon or Vidicon tube, and transferred to the TV monitor

A cine camera

is required to record images on 16- or 35-mm film.

Which of the following waveforms has the lowest percentage voltage ripple?

High-frequency

high-frequency current

is almost constant potential, having less than 1% voltage ripple.

Double-focus x-ray tubes have two

1. focal spots.
2. filaments.

These focal spots are actually two available paths on the

focal track

The effective energy of the x-ray beam is increased by increasing the

1. added filtration.
2. kilovoltage.

To maintain image clarity, the path of electron flow from photocathode to output phosphor is controlled by

electrostatic lenses

The autotransformer

controls/selects the amount of voltage sent to the primary winding of the high-voltage transformer and operates on the principle of self-induction.

The instrument that is frequently used in quality control programs to measure varying degrees of x-ray exposure is the

densitometer

densities may be measured and given a numeric value with a device called a

densitometer

sensitometer

device used in quality control programs; it is used to give a precise exposure to a film emulsion

An aluminum step wedge (penetrometer) may be used to

show the effect of kVp on contrast

Several types of exposure timers may be found on x-ray equipment. Which of the following types of timers functions to accurately duplicate radiographic densities?

Phototimer

synchronous timer

an older type of x-ray timer that does not permit very precise, short exposures

impulse timer

permits a shorter, more precise exposure,

electronic timer

may be used for exposures as short as 0.001 second

The important advantage of the phototimer

it can accurately duplicate radiographic densities. It is therefore very useful for providing accurate comparison in follow-up examinations, and for decreasing patient dose by decreasing the number of "retakes" required because of improper exposure.

As the CR laser scanner recognizes various tissue densities, it constructs a graphic representation of pixel value distribultion called a

histogram

histogram

a graphic representation showing the distribution of pixel values.

the radiographer has selected a processing algorithm by

selecting the anatomical part and particular projection on the computer

The CR unit matches that information with a particular

Lookup Table (LUT)—a characteristic curve that best matches the anatomical part being imaged

histogram analysis and use of the appropriate LUT together function to

produce predictable image quality in CR.

Histogram appearance can be affected by

Degree of accuracy in positioning and centering

Change is affected in

average exposure level and exposure's latitude; these changes will be reflected in the images informational numbers ("S number," "Exposure Index," etc).

Other factors affecting histogram appearance and, therefore, these informational numbers, include

selection of the correct processing algorithm (eg, chest vs femur vs cervical spine), changes in scatter, SID, OID, and collimation. In short, anything that affects scatter and/or dose

Three-phase current is obtained from

three individual alternating currents superimposed on, but out of step with, one another by 120°

All of the following statements regarding three-phase current are true

1. Three-phase equipment produces more x-rays per mAs.
2. Three-phase produces higher-average-energy x-rays than single-phase.
3. The three-phase waveform has less ripple than the single-phase.

A focal spot size of 0.3 mm or smaller is essential for which of the following procedures?

Magnification radiography

A fractional focal spot of 0.3 mm or smaller is essential for

reproducing fine detail without focal spot blurring in magnification radiography

As the object image is magnified, so will be

the associated blur unless the fractional focal spot is used

The image intensifier's input phosphor differs from the output phosphor in that the input phosphor

is much larger than the output phosphor

The image intensifier's input phosphor is

six to nine times larger than the output phosphor. It receives the remnant radiation emerging from the patient and converts it into a fluorescent light image.

Very close to the input phosphor, separated only by a thin transparent layer, is the

photocathode

the fluorescent light image strikes the

photocathode and is converted to an electron image, which is focused by the electrostatic lenses to the small output phosphor

bar pattern

used to evaluate screen resolution

star pattern

used to evaluate the focal spot

Wisconsin cassette

can be used to evaluate kVp calibration.

To eject a K shell electron from a tungsten atom, the incoming electron must have an energy of at least

70 keV

Characteristic radiation makes up

only about 15% of the primary beam.

The biggest advantage of coupling the image intensifier to the TV camera or CCD via a lens coupling device is its

ability to accommodate cine and/or spot films

The image intensifier can be coupled to the TV camera via

a fiber optic bundle or via a lens coupling device

The fiber optic connection offers

less fragility, more compactness, and ease of manuverability

The big advantage of the objective lens is

that it allows the use of auxiliary imaging devices such as a cine camera or spot film camera

Which of the following x-ray circuit devices operate(s) on the principle of mutual induction?

1. High-voltage transformer
2. Filament transformer

mutual induction

two coils are in close proximity, and a current is supplied to one of the coils. As the magnetic field associated with every electric current expands and "grows up" around the first coil, it interacts with and "cuts" the turns of the second coil. This interaction, motion between magnetic field and coil (conductor), induces an emf in the second coil. This is mutual induction, the production of a current in a neighboring circuit.

Transformers such as the high-voltage transformer and the filament (step-down) transformer operate on

mutual induction

The autotransformer operates on the principle of

self-induction

Both the transformer and the autotransformer require the use of

alternating current

The line focus principle refers to the fact that

the actual focal spot is larger than the effective focal spot

The effective focal spot is the

foreshortened size of the focus as it is projected down toward the image receptor

The quoted focal spot size is the

effective focal spot size

What are the advantages of photospot camera imaging over cassette spot imaging during fluoroscopy?

1. Lower patient dose
2. Less interruption of the fluoroscopic examination

Photospot camera film comes in

90- and 105-mm sizes.

Comparing these two sizes,

the larger size provides better resolution but more patient dose

when compared to cassette-loaded spot films, photospot camera film produces

less resolution than cassette-loaded film, but requires half the exposure

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