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Image analysis Image analysis, Exams of Radiography

Massachusetts Institute of Technology (MIT)Radiography

Image analysis Image analysis Image analysis Image analysis

Typology: Exams

2023/2024

Available from 06/23/2024

DrShirley
DrShirley 🇺🇸

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4.6K documents

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Image analysis
Image analysis -
Analyzing the image includes the traditional image quality factors of density, contrast,
recorded detail, and distortion
radiographic quality -
refers to the fidelity with which the anatomic structure being examined is displayed on the
radiograph.
high-quality radiography -
A radiograph that faithfully reproduces structure and tissues
Spatial resolution -
-the ability to image small objects that have high subject contrast, such as bone-soft tissue
interface, a breast microcalcification, or a calcified lung nodule
*** -
spatial resolution improves as screen blur decreases, motion blur decreases, and geometric
blur decreases
Contrast resolution -
-Ability to distinguish anatomic structures having similar subject contrast
-It is always desired to have maximum spatial and contrast resolution.
-The terms 'detail' or 'recorded detail' are sometimes substituted for the
term 'resolution'.
Artifacts -
- An artifact is any irregularity on an image
-Artifacts are undesirable optical densities and must be prevented
Noise -
-the random fluctuation in the optical density of the image
-the lower the noise, the better the radiographic image because it improves contrast resolution
Noise Components -
Film Graininess
Structure mottle
Quantum mottle
pf3
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pf5

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Image analysis

Image analysis - Analyzing the image includes the traditional image quality factors of density, contrast, recorded detail, and distortion radiographic quality - refers to the fidelity with which the anatomic structure being examined is displayed on the radiograph. high-quality radiography - A radiograph that faithfully reproduces structure and tissues Spatial resolution - -the ability to image small objects that have high subject contrast, such as bone-soft tissue interface, a breast microcalcification, or a calcified lung nodule *** - spatial resolution improves as screen blur decreases, motion blur decreases, and geometric blur decreases Contrast resolution - -Ability to distinguish anatomic structures having similar subject contrast -It is always desired to have maximum spatial and contrast resolution. -The terms 'detail' or 'recorded detail' are sometimes substituted for the term 'resolution'. Artifacts -

  • An artifact is any irregularity on an image -Artifacts are undesirable optical densities and must be prevented Noise - -the random fluctuation in the optical density of the image -the lower the noise, the better the radiographic image because it improves contrast resolution Noise Components - Film Graininess Structure mottle Quantum mottle

Film Graininess - -the distribution in size and space of the silver halide grains in the film emulsion -Inherent in IR-technologist has no control Structure mottle - -Refers to phosphor of the radiographic intensifying screen -Inherent in IR (image receptor)-technologist has no control Quantum mottle - -Refers to the random nature by which x-rays interact with the IR -Is under the control of the radiographer and is the principal contributor to radiographic noise -The use of high mAs, low kVp settings and slower IR's reduces quantum mottle Speed of the IR - -Not apparent on the radiographic image -Influences resolution and noise -Any variation in one of the three characteristics alters the other two (speed, resolution, and noise) Fast image receptors - have high noise and low spatial resolution and contrast resolution *** - High spatial resolution and contrast resolution require low noise and slow image receptors *** - Low noise accompanies slow image receptors with high spatial resolution and contrast resolution Technique Formation - ... To achieve high quality radiographs three interrelated categories of radiographic quality are required - -Film Factors -Geometric Factors -Subject Factors

-Asthenic patient (small, frail, sometimes emaciated and often elderly) Body Thickness - -The thicker the patient the more x-radiation is required to penetrate the patient and expose the IR. *Radiographers should always use calipers to measure body thickness or the part being examined. *Patient thickness should not be guessed Body Composition - The anatomical part may have the same thickness but require a totally different radiographic technique depending on the tissues involved Pathology - -Some pathology is destructive, causing the tissue to be radiolucent -Some pathology can constructively increase mass density causing the tissue to be radiopaque Image quality factors - -Image quality factors are considered the "language" of radiography -Image quality factors refers to the characteristics of the radiographic image and includes optical density, contrast, image detail and distortion four types of technique charts - -Variable kVp charts -Fixed kVp chart -High voltage kVp chart -Automatic exposure charts Variable kVp charts - Uses fixed mAs value and a kVp that varies according to the thickness of the anatomical part being examined Fixed kVp chart - -Used most often -(kVp selected is the optimum required for penetration of the anatomical part High voltage kVp chart - -Used when the kVp selected is greater than 100 kVp -Example: overhead radiographs for procedures in which barium is used

Automatic exposure charts - -Automatic exposure control systems are not completely automatic -Chart is needed for selection of the peak kVp, optical density, collimation and radiation dose-image quality ratio Calibration considerations: - -Total filtration - 2.5 mm Al is the prescribed standard -The type of grid to be used Steps for setting-up a fixed kVp chart -

  1. separate the anatomical thickness into three groups - small, medium, and large
  2. make a test exposure using a medium-sized phantom beginning with 80 kVp and a range of mAs increments of 40, 60, 80 until the proper optical density is achieved
  3. when the OD has been selected, the chart can be calculated with mAs values for every 2-cm thickness. *** - For large parts, expand the mAs by 30%. For swollen parts as a result of trauma, a 50% increase may be required. Advantages of Using Optimum kVp - -kVp is the primary control of the x-ray beam quality therefore beam penetrability -kVp controls radiographic contrast -kVp has more effect than any other factor on IR exposure because it affects beam quality and to a lesser degree beam quantity. -Most importantly, kVp controls the scale of contrast on the finished radiograph