DI Chap 30 - Digital Imaging Preprocessing

Preprocessing aka

acquisition processing

Preprocessing Definition

all corrections that are made to the ‘raw’ digital image data due to physical flaws in image acquisition that are inherent to the elements and circuitly of the particular image receptor system, or the physical elements and circuitry of the processing

Preprocessing purpose

image correction

Postprocessing Definition

All manipulation and adjustments of the digital image, whether by default settings in the processor or by an operator, made after corrections have been made for data acquisition

Postprocessing purpose

image refinement

Name the three pre-processing tasks

field uniformity, noise reduction for DEL Drop-Out, and image analysis

Flat-field Uniformity Corrections Purpose

evening out the overall signal or brightness across the entire area of the imaging field

Flat-field Uniformity Corrections Process

a low exposure is made to the IR without any objects in the x-ray beam. Pixel values are compared in the center and four corners. These values must be aligned within a narrow percentage range.

Electronic Response and Gain Offsets Purpose

correct for inherent flaws within the image receptor from electronics’ unavoidable variations in manufacturing which affects the uniformity of the detected field

DEL stands for

Detector Element

DEL definition

individual hardware cell in a DR image receptor, capable of producing a single electronic readout from the incoming photon energy

Variable Scintillator Thickness Purpose

correct for variable scintillator thickness in CR and indirect DR phosphor layers

Variable Scintillator Thickness Explaination

Thicker portions of phosphor layers will have slightly greater absorption efficiency, and will produce slightly more light output than other areas of the phosphor … creating a disruption in field uniformity

Light Guide Variations are only applicable in

CR

Light Guide Variations in CR Purpose

Correct for variations in the fiber-optic light guides used in the CR reader

Light Guide Variations in CR Process

detect and adjust amplification to the signal over specific spots on the IR, either by hardware or software.

Photodiode Job

absorb the electrons and generate electrical charges

Thin-Field Transistor (TFT) Job

isolates each pixel element and reacts like a switch which sends electrical charges to image processors

Closed Circuit means

data is transmitted

Open circuit means

data is stored

DEL Drop-out

flaws in the image receptor that results in missing information in the data sent into the computer for processing

Kernel

submatrix that is passed over the larger matrix of the image that executes some mathematical function

configure the ____ to an average of the pixels surrounding the malfunctioning component to fill in the ‘dead’ space

kernel

The action of filling in dead space with a kernel is called

interpolation

Steps of Image Analysis

Segmentation, Exposure Field Recognition, Histogram Formation, Histogram Analysis

Segmentation Definition

Used to ‘count’ the number of exposures on a single PSP plate so each exposed area can be treated separately by the reader

Segmentation is only used in which system

CR

If enough scatter reaches beyond collimated borders, _________ ________ occurs

segmentation errors

Exposure Field Recognition Definition

used to identify the pitch black background densities from ‘raw’ x-ray beam exposure outside of the anatomy

Exposure field recognition in flat panel systems looks for _______ _________ ___ ________ or differences in values of adjacent DELS along collimated borders

uniform termination of exposure

Histogram Formation

graphical representation of the collected exposure values extracted from the receptor

Histogram Formation Process

the raw data from the recognized collimated area produces a histogram from the minimum and maximum signals.

Histogram X-axis

receptor exposures

Histogram Y-axis

number of pixels in each shade of gray, sampling frequency

Smin is what color

white

Smax is what color

black

Histogram Analysis

When we select the procedure algorithm, the type of histogram analysis is assigned based on the shape the acquired histogram is expected to have

Priori Type 1

most common type of histogram

Priori Type 1

body parts taht do not cover the entire area of the IR/collimation

Priori Type 1

Raw radiation in the form of a tail or spike needs to be identified and eliminated before processing

Priori Type 2

Simplest type of histogram

Priori Type 2

Entire anatomy covers the collimated area so there is no tail/spike of raw radiation

Priori Type 3

Used with a significant attenuating object like prosthetics or barium

Priori Type 3

excludes the outlier area from the minimal signal which represents the highly attenuating object

Neural Histogram

constantly updating by using the most recent 50 histograms for the particular anatomy

Histogram Analysis Processing Errors

occurs when the type of histogram analysis used is mismatched to the shape of the actual histogram acquired or when a bizarre, unexpected shape is acquired

Histogram Analysis Processing Errors are ____________ errors not technique errors

mathematical

volume of interest definition

portion of an image histogram that contains data useful for digital processing and for calculating an accurate exposure indicator

Gray Scale Curve is

created by plotting the output ‘densities’ in the final processed image against the input exposure that they were generated from

Flatter Gray Scale Curves means

Lower Contrast

Steeper Gray Scale Curve means

Higher Contrast

Automatic Rescaling Definition

Software that allows images to have uniform density and contrast, regardless of the amount of exposure

Garbage In

Garbage Out