Study guide - Digital Acquisition Pt. II

In which system is electronic mottle more common?

DR

What is the core cause of Aliasing?

Insufficient sampling of high-frequency signals

What are 5 causes of Aliasing?

1. Copy of a digital image (copying machine, camera)

2. Repeated zoom/magnification on a display monitor

3. Insufficient sampling rate in a CR reader

4. Placing a low-frequency radiographic grid over a high-frequency digital image

5. Superimposing grids or other "sampling" devices

How is the pixel size changed in CR?

1. In a soft matrix, the FOV and matrix size CAN change the pixel size

2. For a CR reader, the diameter of the laser beam can collimate the widths of the pixel size

3. On a display monitor, the "zoom" feature can make the visually apparent pixels of the light image larger

What are 4 ways to prevent grid aliasing?

1. Use a conventional grid with very high frequency

2. Use a special "hole" grid (expensive)

3. Use non-grid technique

4. Virtual grid software negates the need for grids in many cases

What is Pixel Pitch?

Distance measured from the center of a pixel to an adjacent pixel

What is pixel pitch approximately equal to?

Pixel size

What are the 4 types of matrices?

1. The hardware matrix of dels in a DR detector (AMA)

2. The light image matrix created by a CR reader that is sampling a PSP plate

3. The hardware matrix array of hardware pixels in a display monitor

4. The light matrix of the displayed image itself

What is Sampling Frequency?

The number of samples per line

In a CR reader, what is the only way to increase the sampling frequency?

To reduce the distance between them

Indirect-Conversion has increased efficiency, meaning it requires less ____ than Direct-Conversion DR

Dose

Why is the inherent sharpness of DR not changed by collimation?

The size of the dels are fixed and not subject to change

What is the Fill Factor?

The percentage of a del's square area that is devoted to the Semiconductor Detection Layer

What is the benefit of a higher fill factor?

1. Higher contrast resolution

2. Higher SNR

What is the current limitation on del size?

The inability to further miniaturize the TFT and capacitor

Since we can't shrink the TFT and capacitor, the smaller the del, the ____ the fill factor

Lower

What is the detriment of having a low fill factor?

The smaller percentage of detection surface area requires an increase in technique/dose

What is Zoom?

On a display monitor, the zoom feature can magnify or reduce the displayed image

How is Zoom/Magnification of the displayed image accomplished?

Magnifying each "soft" pixel of the light image

During zoom, the hardware pixels of the monitor do __ change, but the visually apparent pixels of the light image itself are getting ___

Not; Larger

What happens if there is excessive zoom/magnification?

The displayed image becomes pixelated because sharpness is lost

What is Sensitivity?

The ability to detect and measure small amounts of radiation

What is the relationship between sensitivity and exposure?

The more sensitive = the less exposure required to produce a diagnostic image

What is Contrast Resolution?

The ability to distinguish and display a range of different tissues based on subject contrast (blacks & whites)

What is the most common artifact in DR?

Quantum Mottle

What is could cause Del Dropout artifacts in DR?

Detector elements can suffer from various electronic faults

What is the most common CR artifact?

IR plate having scratches, dirt, or dust

What could cause a Ghost Image as a CR artifact?

Incomplete erasure of the last exposure

What would CR artifacts that appear consistently on different cassettes likely be due to?

CR Reader probelms

What could cause lime or column drop-out as a CR artifact?

Malfunction of the reader transport and scanning systems

What could cause pixel drop-out as a CR artifact?

Dust particles sticking to optical components in the CR reader

What is the Pixel Size formula?

PS = FOV/Matrix

What is the "soft" pixel size for a 305 mm image (FOV) displayed on a monitor screen with a 1024x1024 matrix?

PS = 305/1024 = 0.298 = 0.3 mm

At 70 kV, what is the CR phosphor plate DQE?

0.3 (30%) or less

At 70 kV, what is the Direct-Conversion DR Receptor DQE?

0.67 (67% heheheh)

At 70 kV, what is the Indirect-Conversion DR Receptor DQE?

0.77 (77%)

What is the maximum resolution of display monitors determined by?

The hardware pixel size for that brand of monitor

Materials for the front panel of IRs must be as ___ as possible while still providing structural protection

Radiolucent

What is the Nyquist Theorem?

The sampling frequency must be at least 2x the spatial frequency of the image being sample (aka, each pulse of the digital signal must be sampled)

In either type of DR system, once x-ray or light photons are absorbed in a del of the AMA, the conversion of this energy into electric charge is nearly ___%

100%

What is a Fixed Sampling system?

Achieves consistent sharpness by keeping the pixel size the same regardless of the IR size/FOV

What is a Fixed Matrix System?

The scan divides the image into the same number of pixels per row regardless of the IR size/FOV/collimation

Fixed Matrix Systems causes sampling frequency to ___ based on the size of the IR

Vary

In Fixed Matrix Systems, pixels must be ___ relative to the image

Smaller

In Fixed Matrix Systems, smaller IRs present ___ sharpness compared to larger IRs

Improved

What is the overall difference between Fixed Sampling systems and Fixed Matrix systems?

Fixed Sampling keeps the pixel size the same, Fixed Matrix keeps the number of pixels the same

Most modern CR systems are fixed ___ systems

Sampling

In a soft matrix, the pixel size can be ___

Variable

In a soft matrix, what can affect the pixel size?

FOV and Matrix Size

What causes the Moire Pattern?

Insufficient sampling of high-frequency signals

What does the Moire Effect look like?

False patterns of straight, diagonal, or curved lines

What is a Soft Matrix?

Can be physically changed (which can change pixel size/spatial resolution)

What is a Hard Matrix?

Size of the dels is fixed and not subject to change, there is the inherent spatial resolution is also unvariable

What are the 3 Efficiency Characteristics of phosphor plates?

1. Absorption efficiency

2. Conversion efficiency

3. Emission efficiency

What can help absorption efficiency?

High-atomic detection layers

What is Conversion efficiency a function of?

The particular chemical used for the phosphor

What helps with emission efficiency?

In a CR PSP plate, the reflective backing helps direct some light back toward the light guide of the reader

What is the Spatial Frequencyformula?

SF = 1/(2P)

What is P in the SF formula?

Del or pixel size

What is the spatial frequency for an imaging system with a del size of 0.1mm?

SF = 1/(2x0.1) = 5 LP/mm

What is the DQE formula?

DQE = (SNR_out)^2 / (SNR_in)^2

What 4 things is the inherent spatial resolution of hardware arrays unaffected by?

1. FOV

2. IR Size

3. Collimation

4. Zoom

What is the spatial resolution Soft Matrices affected by?

FOV and matrix size

What is Dynamic Range?

The range of pixel values made available for image formation

The ___ of the image displayed on a monitor is selected from the available Dynamic Range

Grayscale

True or False: The IR has inherent dynamic range, but the computer sets a default amount that can be adjusted by equalization

True

What is Image Detail?

The edge between 2 pixels with different values

What is the minimum number of pixels required with different values to make a detail?

2

The number of resolvable details is ___ the number of available pixels

1/2

What is Spatial Resolution?

The ability to distinguish and display small pixels to produce sharpness

How can the term Spatial Resolution be used?

Describes the displayed image itself

What is the measurement of spatial frequency?

Line-pairs per millimeter (LP/mm)

What does LP/mm measure?

Spatial frequency

What is a Line Pair?

2 adjacent pixels with different values (detail)