MEDRADSC 2Y03 Lecture Notes - Lecture 12: Radiography, Latent Image, Digital Imaging
25 Oct 2019
School
Department
Course
Professor
Week 7 Lecture 1
October 23rd, 2018
Objectives
• Digital imaging
• WorkFlow
• Digital imaging receptors
• Computed radiography
• Matrix
Review
• CR – Computed Radiography
Fill in the Blanks
• When the x-ray beam exposes the PSP, the energy transfer results in excitation of the
electrons into a metastable state
o Some of the metastable electrons will return to their ground state immediately
and others will eventually go back to their ground state
o This is the latent image
CR reader Question
• During the stimulation step, a finely focused laser beam is directed at the PSP
o The diameter of the beam affects how much detail (spatial resolution)
• When the metastable electrons return to the ground state this results in the emission of
light
o Isotopically
• The final stage of the CR reader involves ensuring all metastable electrons have
transitioned to their ground state, this is done by flood the imaging plate with an
intense white light
• The last step in the CR reader ensures ghosting of the previous image doesn’t appear on
subsequent images
o What happens if it is not cleared correctly
Histograms
• By identifying the pertinent image data range through histrogram-matching algorithms
allows efficient and accurate digitization
• Important for maintaining the subtle contrast signal differences of the anatomic
structures
o Bitdepth gives it is number on the grey scale (personality)
Algorithms
• Specific to the type of detector
• Proprietary to manufacturer
• Require periodic measurement
Algorithms
• Are applied to determine the useful image data range of the x-ray exposure imprinted
on the detector
• Typically by using histogram analysis techniques to identify the minimum and maximum
signals
• A is the biggest spike because there is pure transmission
• B is soft tissue → attenuation, slightly less than A
• C is bone → more absorption (attenuation) → highest atomic number
• D is the area outside of collimation →
• Patient lies anode to cathode
Analog radiograph: Areal beam
• Composed of infinite number of points of relative blackening
• Each point represents one location in x-ray field
• Each point could have any quantity of blackening between Dmin (B+F) and Dmax
(highest possible OD on film)
• Each point’s blackening represents quantity of radiation transmitted through the path at
that location
Workflow for Film
