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• Computed Radiography (CR):

  • Uses photo stimulable phosphor, Storage phosphors to produce digital images using existing x-ray equipment
  • Uses processing data by radiographic means to produce digital images
  • Used in clinical practice
  • Photo stimulable phosphor is barium fluoro-halide crystals coated in the IMP
  • Uses a digital detector
  • Exposure latitude is wider, about 10-4 times wider than SF system
  • Main drawback is limited image detail (spatial resolution)
  • Detail about 3-5 line pairs/mm, while SF has 10-15 line pairs/mm
• V. The IP is exposed to bright light to erase it, and it can be used again
• Steps in the production of a Computerized Radiography (CR) Imaging System:

  I. The IP is exposed to x-rays, causing electrons in the phosphor to move to another energy level, creating a latent image

  II. The plate is taken to the CR reader/processor where it is scanned by a laser beam, causing trapped electrons to return to their original orbit and emit light

  III. Light is collected by a light guide and sent to a photomultiplier tube (PMT), which converts the electrical signal output to digital image data

  IV. A digital processor processes the data to produce a CR image viewable on a monitor
• Flat-Panel Digital Radiography:

  • Digital detector designed as a flat panel plate
  • Indirect conversion and direct digital radiography system
• Digital Mammography:

  • Radiography of the breast for soft tissue imaging
  • Used to detect breast cancer
  • Allows the use of digital image-processing tools for enhanced diagnostic interpretation
  • Uses computer-aided diagnosis (CAD) software to help enhance detection of micro-calcifications and malignant lesions
• Digital Fluoroscopy:

  • Improves contrast resolution compared to conventional methods
  • Uses digital image processing software
  • Utilizes gray-scale processing, temporal frame averaging, and edge enhancement
  • Produces dynamic images acquired in real-time
  • Used to study the motion of organ systems and hollow internal structures like the GIT and blood circulatory system
• Conventional Fluoroscopy:

  • Consists of x-ray tube, image intensifier, associated optics, and a television image display or CCD camera tube
• Digital Image Processing:

  • Involves processing images using computer-based systems
  • Data collected from the patient during imaging is converted into digital data for computer processing
  • Result is a digital image suitable for viewing by radiologists
• Image Formation & Representation:

  • Images can be conceptualized as subsets of objects, including visible and invisible light
  • Analog images are scanned using light sources and PMT to detect transmitted light
  • Digital radiography detectors output analog signals that are converted to discrete digital data for computer processing
• Image Domains:

  • Images in radiology can be represented in two domains: spatial location and spatial frequency
  • Digital radiography and image processing can transform images between these domains
  • Fourier transformation is used to convert images from the spatial location domain to the spatial frequency domain
• Classes of Digital Image Processing Operations:

  • Image Enhancement: enhances image characteristics like contours and shapes
  • Image Restoration: improves quality of distorted or degraded images
  • Image Analysis: allows measurements, statistics, segmentation, feature extraction, and object classification
  • Image Compression: reduces image size for faster transmission and storage reduction
• Image Compression:

  • Reduces image size to decrease transmission time and storage
  • Two forms: Lossy and Lossless
  • Lossless compression retains all image information when decompressed
  • Lossy compression results in some loss of image details when decompressed
  • Compression form: wavelet, preserves spatial and frequency information
• Image Synthesis:

  • Creates images from other image or non-image data
  • Used when desired image is physically impossible or impractical to acquire
  • Example: image reconstruction techniques for CT and MR images, 3D visualization techniques
• Characteristics of Digital Image:

  • Matrix: 2D array of numbers defining image size
  • Pixels: square elements in the matrix representing brightness level
  • Voxel: pixels in the image representing volume of tissue
  • Bit Depth: number of bits per pixel, determines gray levels
• Steps in Digitizing an Image:

  • Scanning: dividing image into pixels
  • Sampling: measuring brightness level of each pixel
  • Quantization: assigning brightness levels to pixels
• Digital Image Processing Operations:

  • Point Processing: basic framework mapping input to output pixel values
  • Gray-level mapping or gray-scale processing is a common point processing operation
  • Histogram: graph of pixels with same gray scale, altering it changes brightness and contrast
• Look-up Table (LUT):

  • Assigns numbers to input pixel values to change contrast and brightness of image
  • Determines output pixel values based on input values
• Windowing:

  • Technique to change image contrast and brightness
  • Window Width (WW) controls image contrast, Window Level (WL) controls brightness
  • Narrow WW provides higher image contrast, wide WW shows less contrast
• Image Subtraction and Temporal Averaging:

  • Point processing operations
  • Used in digital subtraction angiography
  • Image subtraction: post-contrast pixel values subtracted from pre-contrast to enhance diagnostic impression
  • Temporal averaging: averaging set of images to reduce image noise
• Local Processing Operations:

  • Output pixel value obtained from small area of pixels around input pixel
  • Spatial frequency filtering is a notable example
  • Spatial frequency processing can sharpen, smooth, blur images, reduce noise, and extract features of interest
• Spatial Location Filtering:

  • Convolution is a common example
  • Algorithm for convolution changes characteristics of the image
• X-ray are first converted into light using a phosphor such as

  cesium iodide .the emitted light from the phosphor falls

  upon a matrix array of electronic elements to create and

  store electrical charges in directly proportional to x-ray

  exposure.

  FLAT –PANEL DIGITAL RADIOGRAPHY: indirect
• Direct conversion digital radiography systems use

  detectors that convert x-ray directly into electronic

  signals. These signal are digitized and processed by a

  computer to produce an image.

  FLAT –PANEL DIGITAL RADIOGRAPHY: direct
• The second type of indirect conversion detector

  􀀀 Uses an array of charge –coupled devices (CCD) instead

  of an array of electronic elements. 􀀀 CCD are coupled to the scintillator phosphor ,cesium

  iodide.

  􀀀 X-ray fall upon the phosphor to produce light, which then

  falls upon the CCD array, which in turn covert the light into

  electrical signals that are the digitized and processed by a

  computer to produce image.

  􀀀 After all electrical charges are read-out, the flat panel

  digital detector can be erased and is ready to be use again.

  FLAT –PANEL DIGITAL RADIOGRAPHY: indirect
• Consist of x-ray tube 􀀀 Image intensifier (radiation detectors) 􀀀 Associated optics (snells law) 􀀀 A television image display or CCD camera tube

  Conventional Fluoroscopy
• electrical signal from the TV/CCD system is

  digitized by the ADC and sent to a computer for image

  processing.

  output signal
• is also image intensifier tube, it captures the

  x-ray attenuation data from the px.

  detector
• Digital fluoroscopy to angiography is referred to as

  Digital

  Subtraction Angiography (DSA)
• which images are subtracted in real

  time and energy subtraction . In which images are

  subtracted using different kilovoltages.

  temporal method
• Visible image, such as

  photographs, drawing, and

  painting
• Invisible image , such as:

  temperature, pressure ,elevated maps
• Optical image include

  holograms
• Images are Scanned from R to L light source (positioned in

  front of the image ) and (PMT positioned behind of the

  image ) to detect transmitted light.

  analog images
• The images obtained in radiology can be represented in to

  two domains, based on how they are acquired.

  The spatial location domain

  The spatial frequency domain.
• Small structures object ( of the px) produce high

  frequencies represents

  detail in the image
• large structure produce low frequencies represent

  contrast information of the image
• used to perform mathematical rigorous function .

  Fourier transformation
• converts the function in the time domain( say

  signal intensity versus time) to a function in

  frequency domain (say, signal intensity versus

  frequency).

  FT
• used to

  perform an image in the frequency domain back to

  the spatial location domain for viewing of the

  radiologist & technologist.

  inverse Fourier transformation (FT-1 )
• FIVE FUNDAMENTAL CLASSES OF OPERATIONS

  image enhancement

  image restoration

  image analysis

  image compression

  image synthesis