Equip/Image - Digital Imaging (Unit 2-2)

Digital Imaging

Replaces traditional film with a reusable detector.

What are the two types of Digital Imaging?

• Computed Radiography (CR)

• Digital Radiography (DR)

Computed Radiography (CR)

Uses a photostimulable storage phosphor imaging plate (PSP or IP), inside a cassette.

Digital Radiography (DR)

Uses a detector built-in to bucky or an independent device that acquires the image and sends it directly to a display monitor.

______________________ are the primary reason for transformation to true digital radiography using flat-panel technology.

Reimbursement Incentives

Digital Image

An image that has been converted into numerical values for processing.

Electronic devices that produce digital radiographic images produce ________________________.

Analog signals first

Analog-to-Digital Conversion (ADC)

Process where analog signals must be converted to a binary language.

ADC Steps

1. Sampling

2. Quantification

Sampling ADC Step

Analog voltage values are measured at a chosen sampling frequency on the analog waveform.

Quantification

Each sampled piece of analog data is computed and assigned a discrete analog value which is then converted to a binary digit (1 or 0).

Bit

A single unit of data.

Byte

Made up of 8 bits (binary code).

Pixel

The individual matrix boxes (aka picture element) located according to its electronic address (position in the matrix).

Matrix

A series of boxes laid out in rows and columns that gives form to the image.

Z (Voxel or Volume Element)

Represents the pixel’s shade value.

Number of shades of gray is determined by the ________________.

Bit depth

How many shades of gray does a bit depth of 16 have?

65,000 different shades of gray

As pixel size _______________, resolution _______________. It is ______________ related.

• Increases

• Decreases

• Inversely

Fewer and larger pixels = __________________ = ____________ distinct details.

• Poor resolution

• Lack of

More and smaller pixels = ____________________ = _______________ distinct details.

• Good resolution

• Visualization of

Resolution

How small features in the image can be distinguised from each other.

Pixel Pitch

Distance between the center of one pixel to the center of one pixel to the center of adjancent pixel.

FOV (Field of View)

The size of the aea captured in the image, determined by the detector dimensions (detecotr FOV) and any collimation applied (collimation FOV).

If detector FOV (size) remains the same, then as matrix size ____________, the pixels must ________________ to fit in the detector, creating a _________ image.

• Increases

• Get smaller

• Sharper

As Detector FOV decreases, and matrix size stays the same, the size of each pixel _____________ and spatial resolution _____________.

• Decreases

• Increases

Point Processing

Performed between the receipt of the input image from the IR and the output image that is viewed on the monitor.

One common point processing operation is called _________________.

Grayscale Processing

Histogram

Graph analysis that shows the range of exposures in an image and helps identify the values of interest.

VOI (Values of Interest)

Areas important for the anatomy being imaged.

Rescaling

Adjusts the bright/dark to optimal levels.

Comparison to Look Up Table (LUT)

Apply a predetermined scale of contrast to the digital exposure data set. Adjusts the contrast to optimal levels.

Chest LUT

Enhances contrast for lungs and ribs

Hand LUT

Enchances contrast for fine bone detail and soft tissue.

Windowing

Operation that changes the contrast and brightness of the image on the monitor.

Window Width (WW)

Controls shades of gray

Window Level (WL)

Controls the brightness of the image.

Which of the following analyzes data to identify the values of interest (VOI)?

• Point spead function

• Exposure value index

• Line spread function

• Histogram

Histogram

Which of the following controls image brightness?

• Window level

• Window width

• Histogram

• Exposure Index

Window Level

Post-Processing

After the computer has processed the image, further steps can be done to enhance the image.

Spatial Frequency Filtering

Step in the image processing that canbe used to sharpen, smooth, reduce noise, pull elements of interest from the image.

High-Pass Filtering

(aka Edge Enhancement) Removes low-spatial frequencies and produces a sharper output image, greater contrast.

Digital image quality can be described in terms of:

• Spatial Resolution

• Noise

• Detective Quantum Efficiency

• Artifacts

Spatial Resolution

Determined by pixel size and influenced by detecotr matrix size.

When matrix size is ___________, spatial resolution _____________.

• Increases

• Increases

Density Resolution

Number of shades of gray that can be displayed.

Contrast Resolution

Ability to distinguish between tissues based on small differences.

Noise

Result of undesirable signals, random background information that is detected, but does not contribute to image quality.

High SNR = ______ Noise = _________ Image Contrast

• Low

• Increased

Low SNR = ________ Noise = _________ Image Contrast

• High

• Decreased

Quantum Mottle

Type of noise that results from an insufficient quantity fo photons from improper exposure factors.

DQE

% of incoming x-ray photons that are detected and absorbed by the IR for transformation to the x-ray image.

Exposure Indicator (EI)

Reflects the amount of x-ray exposure to IR and is the best tool for image quality control.

Exposure Indicator Target (Elt)

Optimum exposure and acceptable noise levels.

S#

Range 150-250

• Higher = underexposed

• Lower = overexposed

EI#

Range 1500-1800

• Higher = overexposed

• Lower - underexposed

Deviation Index (DI)

% deviation from target. Value of 2 or more will need to evaluate for repeat.

Which of the following are true about an LUT? (select all that apply)

• The LUT applies a predetermined scale of contrast to the digital data set.

• The LUT determines the exposure index.

• Proper LUT will provide proper grayscale based solely on kVp and mAs values.

• LUT can’t fix exposure values outside the normal range.

• The LUT applies a predetermined scale of contrast to the digital data set.

• LUT can’t fix exposure values outside the normal range.

True or False. The radiographer can improve quantum noise by adjusting exposure factors to decrease SNR.

False

Photostimulable Phosphor Imaging Plate

Rigid sheet designed to record and enhance transmission of the image from a beam of ionizing radation.

Phosphor Layer

Holds the photostimulable phosphor that traps electrons during exposure.

Support Layer

Made of polyester provides the base.

Conductor Layer

Grounds the IP to eliminate static and absorb light to increase sharpness.

Light-Shielding Layer

Prevents light from erasing data on the IP or leaking through the backing, decreasing the spatial resolution.

Protective Layer

Insulates the imaging plate from handling trauma.

What is the most common phosphor used with CR?

Europium-doped barium fluorohalide.

Latent image will lose _____ of its energy in ___ hours if not processed.

• 25%

• 8

Image Reader Device (IRD)

Raster Pattern

Ghosting Artifact

When a plate is grossly overexposed it may not erase completely.

Photodector

Convert the visible light into an electronic signal whose output is in analog form.

Pixel Pitch

Physical distance between pixels measured from center to center; principal factor that determines spatial resolution of the image.

Sampling Frequency

Related to how the laser scans the plate.

The _______ signal sampled, the ______ info obtained, the _________ the pixels can be.

• More

• More

• Smaller

Sampling frequency is expressed as _______.

Pixels/mm

The ___________ the pixel pitch, the _________ the spatial resolution.

• Smaller

• Higher

Quanitification

Process that will measure the value of each sample to determine the brightness levels or grayscale for the pixels.

Higher analog sampling rate provide ________ accuracy and a ______ representation of the analog values.

• Greater

• Truer

Spatial Resolution in CR improves with:

• Increased sampling frequency

• Smaller pixel pitch

• Smaller pixel size

• Larger image matrix

As CR plate size increases, spatial resolution ______________.

True or False. The Moire effect occurs if the laser scan frequency and the grid frequency are similar but oriented in different directions.

Pre-Processing

Initial image processing where the raw image data are prepared according to the algorithms of the manufacturer.

Exposure Field Recognition

Identifies the collimated borders of the exposed field and eliminates signals from outside this area.

Histogram Analysis

Computer analyzes the histogram using processing algorithms and compares it with a preestablished histogram that has the appropriate contrast values for the anatomic part being imaged.

Grayscale Analysis

Transforming input data values to output values that will be displayed on a monitor.

Histogram Anaylsis Error

When an image does not fit the parameters that were used for the reference histogram.

Edge Enhancement

Radiologists use this feature to better visualize subtle bony cortical changes, micro-calcifications, and trabecular patterns within bone.

Image Stitching

Stitch together multiple images.

Dynamic Range

Number of gray shades that an imaging system can reproduce; aka latitude.

A 10×12 CR image plate with a matrix size of 2,625 × 3,225 would have ___________ resolution than a 10×12 CR image plate with a matrix size of 1,313 × 1,613.

Which IP later eliminates static and absorbs light to increase sharpness?