Image Production - Corectec

What is spatial resolution

A measure of how well an imaging system can display two closely spaced objects as separate

At least how much lp/mm must be discernable in a digital image for it to be considered diagnostic quality?

2.5 lp/mm

Digital can display what range of lp/mm?

2-5 lp/mm

Spatial resolution can be no better than what?

The size of the pixel

Pixel size is determined by what two things?

Matrix size and the size of the FOV

What is matrix size?

The number of columns and rows that are displayed on a monitor

The _____ (larger/smaller) the matrix size the better the spatial resolution

larger

Casts made of plaster require an increase in kVp of how much when wet? When dry?

When wet: 15 kVp

When dry: 10 kVp

Thicker fiberglass casts may require a kVp increase of how much?

5 kVp

For additive conditions, do what with the kVp?

Add 5 kVp

For destructive conditions, do what with the kVp?

Subtract 5 kVp

Do not use over how much kVp with iodinated contrast?

70 kVp

Use how much kVp with barium based contrast?

over 100 kVp

What is fill factor?

The fraction of each detector element that efficiently collects charges from energy deposited by x-rays

Typical fill factors range from what?

50%-80%

What is sampling frequency?

The number of times data is recorded as an imaging plate is being read

The _______ (faster/slower) the sampling frequency the smaller the pixel pitch and the better the spatial resolution?

Faster

What is the Modulation Transfer Function (MTF)?

A measure of how well an imaging system can transfer a signal

What is bit depth?

The number of shades of gray that can be used to define each pixel

The ______ (greater/lesser) the bit depth the greater the number of tones that can be represented

Look-up tables determine what?

The contrast in a digital image

A ______ (high/low) signal to noise ratio (SNR) produces better images

high

Quantum noise occurs when the IR is how much overexposed?

2x

Saturation occurs if the IR is overexposed by how much?

4x

Contrast in digital imaging is limited by what?

the range of exposures that may be captured by the IR and the number of bits per pixel that can be displayed by the monitor

kVp that is set too low will cause ____ (high/low) contrast

high

An increase in grid ratio will cause ______ (higher/lower) contrast

higher

What is the Moire effect? Why does it occur?

A wavy pattern that occurs in digital images

It occurs because the digital system is sampling at the same frequency as the grid frequency and the grid lines run in the same direction as the laser is reading in the imaging plate, causing the system to record the grid lines

What is aliasing caused by?

When the sampling frequency is less than 2 cycles per sample

What is a ghost image?

An image from the previous exposure if the imaging plate is not fully erased

What is banding artifact?

alternating light/dark strips caused by transport of the imaging plate through the CR reader in the slow scan direction

Anode heel effect is more pronounced at shorter or longer SIDs?

Shorter

When is a magnetic field induced?

Whenever there is a charge in motion

What kind of magnets have a strong attraction?

Ferromagnets

What kind of magnets have a weak attraction?

Paramagnets

Single phase generators with full rectification produce how many pulses/sec

120 pulses/sec

3 phase 6 pules generators produce how many pulses/sec

360 pulses/sec

3 phase 12 pulse produces how many pulses/sec

720 pulses/sec

Increasing total tube filtration reduces average effective dose by ____% and entrance dose by ___%

effective dose: 9%

Entrance dose: 16%

Most rotating anodes spin at ____rpm

High capacity anodes spin at ___rpm

Most anodes: 3400rpm

High capacity anodes: 10,000 rpm

What is an anode disk made of?

Rhenium alloyed tungsten

What is the formula for heat units?

kVp x mA x Time

How to calculate heat units for a 3 phase 6 pulse generator

kVp x mA x Time x 1.35

How to calculate heat units for a 3 phase 12 pulse generator

kVp x mA x Time x 1.41

How to calculate heat units for a high frequency generator

kVp x mA x Time x 1.45

With AEC, the shortest exposure time that a system can produce is what?

1 ms

A photostimulable phosphor plate (PSP) is used in what kind of radiography?

Computed radiography

What are the phosphors made of in a PSP pate?

a barium fluoride compound doped with europium

How is a latent image formed in computed radiography?

When x-rays interact with the electrons in the phosphors of the PSP it raises them to a higher level. About ½ of the electrons are trapped at this higher state, forming the latent image

How long can the latent image be stored for on a PSP plate?

24 hrs

Direct capture uses what element?

Amorphous selenium

Indirect capture uses what element?

Amorphous silicon

What is the input phosphor made of in an image intensifier? How does it work?

cesium iodide

It absorbs x-rays and emits light photons

What does the photocathode do in an image intensifier?

It absorbs the light photons and emits electrons

What is the output phosphor made out of in an image intensifier? How does it work?

Zinc cadmium sulfide

It converts the electron image into a visible light image

To avoid the Moire effect, stationary grids must be higher than ____lines/cm and must run ______ 

60; perpendicular

What is a histogram?

A graphical display of pixel values that make up the image

What are the three purposes of a histogram?

To determine values of interest

To determine the median number

To automatically rescale the values of interest

What is the median number used for?

Exposure indicator determination

What is edge enhancement?

Increases contrast along the edges of structures

Excessive edge enhancement causes what?

A halo artifact around the edges

What are look-up tables used for?

Used to enhance contrast in a digital image

A LUT with a slope steeper than 45 degrees will produce a digital image with _____(higher/lower) contrast

Higher

The steeper the slope of the LUT, the _____ (higher/lower) the contrast

higher

What is off-distance grid cutoff caused by?

The SID does not match the focal range of the grid

What is off-level grid cutoff caused by?

The grid and the CR are not perpendicular

Imaging plates should be cleaned only with what?

Anhydrous ethyl alcohol

What can water do to an imaging plate?

It can discolor the plates. causing artifacts

What is an erasure test used for?

To verify that there is no residual image left on the imaging plate

Fluoroscopic lead aprons and gloves should be tested at least how often?

Every year

Linearity tests should be performed how often?

Annually

A star pattern test determines what?

Focal spot size

Linearity tests states that adjacent mA stations must produce the same output within what percentage?

5%

Dirt in the light guide of a CR reader would appear as what?

White lines