image production - Equipment Operation (Pt. 3)

What is an analog signal?

Data transmission that is continuously varying in proportion to the intensity of a given signal

What is a disadvantages of an analog signal?

Signal Distortion due to amplification, attenuation, or electronic noise

What is a Digital Signal

data transmission in which the signal varies in discrete steps and not in a continuous manner

What is the advantage of a digital signal?

Ability to manipulate the signal without loss of data

What are some image processing classes that give digital signal an advantage?

• Image Restoration
• Image Analysis
• Image Compression (File Size)
• Image synthesis (3D visualization)

What is an analog-to-digital conversion?

Device that converts a varying analog signal into a discrete digital signal to be processed/used by computers

What are the steps to ADC process?

• Scanning
• Sampling
• Digitization/quantization

What occurs during image Scanning?

Image matrix is divided into smaller portions; rows and columns of pixels

What occurs during Sampling?

The strength of the analog signal is measured and taken as a data point

What is aliasing in ADC?

Lack of samples taken will result in misrepresentation; Moire Effect

Each sample is assigned an integer correlating to a _____ of a specific pixel

Gray-Scale level; Amount of radiation received

What occurs during Digitization/Quantization?

Analog samples are converted into digital signal

What is the Path of a Digital Image?

• Acquisition
• Processing (Pre + Post)
• Image Display
• Image Analysis

What is Pre-processing?

Any process which occurs before data is stored in the memory

What occurs during pre-processing?

• Patient Selection
• Control Booth Exam Selection

What is processing?

involves converting or transforming raw data into useful output; manifest image

What happens during Processing?

• Data Recognition
• Pixel Arrangement
• Histogram analysis
• LUT Adjustment
• Rescaling

What happens during Data Recognition?

Determines what data is clinically useful

What happens during Pixel Arrangement?

Sampled image data is assigned specific pixel locations in the image matrix

What is a histogram used for?

Brightness Adjustment

What is a Histogram analysis?

• Determines values of interest (VOI)
• Compares it to a histogram reference stored in a computer for each body part

Histogram X-Axis =

Pixel Brightness value

Higher the Density, _____ the Histogram x-axis value

Higher

Historgram Y-Axis =

Frequency of Brightness value

What is the process of Histogram Creation?

• Defining values of interest
• Contour of anatomy outline
• Landmark Identification
• Graph construction

High kVp will result in a _____ Histogram indicating ______ contrast

Wide; High

Low kVp will result in a _____ Histogram indicating ______ contrast

Narrow; Low

Low mAs will result in a Histogram shifted toward the _____

Left (Lighter Shades)

What is a Look-up table (LUT)?

An algorithm that plots and manipulates pixel values to control contrast

A Steep LUT will _____ Contrast

Increase

A Decreasing LUT will ______ Contrast

Reverse/Invert (Negative Radiograph)

What is Rescaling?

A digital processing technique that
compares and aligns the histogram and LUT to modify an overexposed or underexposed image

Saturated images can be rescaled up to _____

200% from Ideal

Underexposed images can be rescaled as low as ________

60% from Ideal

What is Post-Processing?

The manipulation of image data after computer storage

What can be adjusted or done post-processing?

• Contrast & Brightness
• Enhancement
• Inversion (LUT)
• Energy Subtraction
• Magnification
• Annotation
• Stitching
• Statistical Analysis (measurements)
• Image orientation
• Filtering

What is the Window Level?

Adjustment of the midpoint of all brightness values

Lowering the Window Level/Center will _______ Brightness

Increase

What is the Window Width?

Adjustment of the range of pixel values (Gray Shades) available

Widening the Window Width will ________ Contrast

Decrease

What is the Contrast Enhancement Function?

Alters pixel values to increase image contrast

What is the Edge Enhancement function?

A post-processing technique that improves visibility of small, high-contrast structures

What is Pixel Shift?

A feature that reduces Image blur

What is the Energy Subtraction function?

Two images taken at different kVp are overlapped onto each other to remove certain structures (anatomical Noise)

What is the Statistical Analysis function?

Measurement software installed to allow for distance and volume measurements of specific structures and regions

What is Filtering?

processing function used to reduce different noise, thus increase contrast resolution

Filtering also known as _____

Masking or Convolution

What are types of filtering?

• Low Pass
• Band Pass
• High Pass

What is low pass filtering?

filtering out high frequencies to intentionally blur the image to reduce noise & displayed brightness

low pass filtering is commonly used in ______

Low Radiation areas - Nuc Med or Sonography

Low-pass filtering is also known as:

Smoothing

What is band-pass filtering?

either amplifies or deletes all but a selected range or band of frequencies

What is high pass filtering?

either amplifies the high spatial frequencies or deletes the low spatial frequencies to produce a sharper output image

High-pass filtering is a function used for

Edge Enhancement

What are displays used for?

Soft copy demonstration of digital images

What is Display interpolation?

Mapping of an image on one image matrix to another matrix of a different size

What is Monitor Resolution?

spatial resolution of monitor measured by amount of pixels in display

What is aspect ratio?

Ratio of the height and width of the image

What is the refresh rate?

Number of times monitor refreshes image display per second

What is temporal resolution?

ability to precisely position moving structures from instant to instant

Better temporal resolution has ____ frame rate

High

What is pixel pitch?

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

A smaller pixel pitch = ______ spatial resolution

Greater

What are the types of monitors?

• Primary
• Secondary

What is a Primary Monitor?

used for interpretation of diagnostic images of radiologist and physcians

What is the resolution for Primary monitors?

• Typical range: 2560 x 2048 (5 megapixels) to 4280 x 3520 (15 megapixels)
• Mammography Resolution: 6144 x 4096 (25 MP)

What is a secondary monitor?

Used for everyday tasks

What is the resolution for Secondary monitors?

• 1024 x 1280 (1.3 megapixels) to 1920 x 1080 (2 megapixels)

What are the advantages of the Primary Monitor

• Wider Viewing Angle (Cosine law)
• Luminance (Brightness)
• Uniformity
• Spatial Resolution
• Bit Depth

What can monitors be made of?

• Liquid Crystal Displays (LCD)
• Plasma Screen

What are the only advantages of a Plasma Screen?

• Brightness
• Viewing Angle

What are some advantages of LCD Displays?

• Less heat emission
• Better Spatial and Contrast
• Uses less electricity
• little amount of flicker

What is Angular Dependence in terms of Displays?

Cosine Law; The luminous intensity (brightness) and contrast of a monitor decrease as the viewing angle from the monitor increases