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Sensitometry

Chapter 9 Fosbinder

QuestionAnswer
What is sensitometry? The study of the relationship between from the amount of intensity from tube and amount of density on the film
What 3 things can sensitometry measure? 1. Speed 2. Exposure Latitude 3. Contrast
What will always be on the film? Chemical Fog
Equipment is needed for sensitometry? (2) Penetrometer or Sensitometer Densitometer
What is a penetrometer? (Step wedge) Piece of aluminum with varying densities in the shape of a step wedge. Step 1- black (X-rays pass through, thinest step) Step 11- white
What is a Sensitometer? A device that is designed to expose a reproducible, uniform, optical step wedge onto a film.
Which is more effective, a penetrometer or Sensitometer? Sensitometer
What is a densitometer? A device used to numerically measure the amount of blackness on the film after processing.
What is the light transmit formula? The amount of light that is actually transmitted through the film. it x 100 io ***only have to recognize formula***
What Optical Density? The numerical calculation of transmitted light through a film to incident light originally striking the film. Log10 (io) (it) OD ranges 0-4 0 = white part of the image 4 = black part of an image **only have to recognize formula **
What is the relationship between optical density and light transmittance? Increased optical density (more black) = decreased light transmittance Decreased optical density (more white) = increased light transmittance OD increases by .3 and decreases light by 1/2 OD decreased by .3 and increases light by double
What is a sensitometric curve? A graph demonstrating how a film respond to a series's of increasing exposures.
5 Parts of the sensitometric curve? 1. Toe 2. Threshold 3. Straight-line region/ slope/ gamma 4. Average gradient 5. Shoulder
What is the toe of the curve? Bottom of curve, low density/underexposed, never at zero because of base + fog
What is base + fog? Film has a tint added to the base, fog is present due to processing chemicals. Acceptable range of B+F is between 0.1-0.2 optical density
Where do you find base + fog on a film? On any blank unexposed part of the film.
What is the threshold of the curve? Area where the curve begins to turn upward.
What is the straight line region (slop/gamma)? Area of the diagnostic and useful ranges in density. Found between the threshold and the shoulder.
What is the optical density range on a graph? 0-4
What is the useful range of optical density on a graph? 0.25-2.5
What is the diagnostic range of optical density on a graph? 0.5-2.0
What is the shoulder of the curve? The point on the curve where the maximum density have be produced. Most amount of black. (Dmax)
What is average gradient? A line drawn on the slope representing the densities found within the image. Normal average gradient diagnostic range = 0.25-2.0 about the B+F measurement
What is solarization? The point on the curve beyond where the maximum density had been produced (Dmax)
What are the 3 film characteristics determined by the curve? 1. Film Speed 2. Film Contrast 3. Exposure Latitude
What is film speed? The films sensitivity to radiation, and indicated the amount of optical density produced for a given radiation exposure.
What is a speed point? The point on hype sensitometric curve that corresponds to the optical density of 1.0 + B + F
What is the speed exposure point? The point in the x-axis that corresponds to the speed point on the y-axis which indicated the intensity of the exposure needed to produce a density of 1.0 + B + F regardless of the shape of the curve.
What is film contrast controlled by? The design and manufacturing of the film components and effects of processing.
If the graph has a high contrast, what will the slope look like? More vertical.
If the graph has a more horizontal slope what type of contrast will the film have? Low
How do you find the slop of a curve? Rise Or Y2-Y1 Run X2-X1 High number = steep slope = high contrast Low number = long slope = low contrast
What is exposure latitude? Refers to the range of exposures that produces optical density within the straight line region of the curve Horizontal slope = wide latitude = low contrast, lots of grays Vertical slope = narrow latitude = high contrast! more black and white
What is optimal density? It is achieved when radiographic densities are produced that lie within the straight-line region of the curve thus maximizing the amount of information visible.
Created by: Aborys88