Basic Principles of Digital 1

For digital imaging this pixel size becomes a limiting factor for the ________________ ________ of the image quality of the computer system and monitor screens can also be limiting for viewing __________

For digital imaging this pixel size becomes a limiting factor for the spatial resolution of the image quality of the computer system and monitor screens can also be limiting for viewing resolution

what is the equation for spatial frequency?

SF= 1/2 P (must be in mm)

what is the difference between spatial frequency and spatial resolution?

Spatial Frequency: -the unit of measure for spatial frequency is line pairs per millimeter resolved in the imaging system Spatial Resolution: -geometric factor, the accuracy of structural lines -higher spatial frequency then results in improved spatial resolution

The numerical value assigned to each pixel is determined first by ______ of the beam. Each pixel also has a ____ ______, or a number of bits that determines the amount of precision in digitizing the analog signal (through ADC) and therefore controls the exact amount of _____ _____ possible

The numerical value assigned to each pixel is determined first by attenuation of the beam. Each pixel also has a bit depth, or a number of bits that determines the amount of precision in digitizing the analog signal (through ADC) and therefore controls the exact amount of pixel brightness possible

define ADC

analog to digital conversion

operation code for digital based on _______ code

binary bi= two (on or off; yes or no)

define bit

binary digit -one single unit of data

_____ to pixels to ________

bits to pixels to matrix

what might pixel size be known as in digital?

brightness level (limiting factor of spatial resolution)

define matrix

columns and rows of pixels -2 dimensional array of numbers -ex. 512 x 512 = 262,144 pixels or two dimensional data points

digital image quality increases with a ___________ ______ that has ______ _____

digital image quality increases with a larger matrix that has smaller pixels

Does Field of View affect digital? how about CR?

does not affect digital bc detector elements are fixed does affect CR because you can change image receptors

density resolution can be thought of as

dynamic range and grayscale

define pixel size

each pixel contains a discrete value (number) represents brightness level

rows x columns are known as voxel true or false

false

small objects have lower spatial resolution to accurately image small objects

false

-larger bit depth allows a ____ number of shades of gray to be displayed -A system that can display a greater number of shades of gray (due to bit depth), has ______ _____ _____

greater higher contrast resolution

greater bit depth = greater ______ = greater ________

greater bit depth = greater contrast resolution = greater number of possible shades of gray that a pixel can have

as matrix size increases for the same FOV, image quality __________

improves

greater bit depth means

increased bit depth = increased contrast resolution = increased greater # of possible shades of gray

as spatial frequency number increases, the ability to resolve smaller detail _______

increases

_________ the matrix size for the same image allows smaller pixels and smaller detail can be resolved this equals _________ resolution of details

increasing the matrix size for the same image allows smaller pixels and smaller detail can be resolved this equals sharper resolution of details

pixel size is ______ related to spatial resolution

inversely

larger matrix= ________=__________

larger matrix= smaller pixels= improved sharpness

matrix size is dependent on the _______ _________ and the _______ ___________ _____

matrix size is dependent on the sampling frequency and the image receptor size

pixel size is dependent on the __________ __________, which is expressed in ______/____

pixel size is dependent on the sampling frequency, which is expressed in pixels/ mm

what are the two steps of digital image processing?

sampling and quantization

pixel size depends on

sampling frequency

which has higher spatial frequency small or large objects?

small objects have higher spatial frequency and large objects have lower spatial frequency -more difficult to accurately image small anatomic objects (high spatial frequency)

The ______ FOV will consist of more pixels in a given display then a ____ FOV

smaller larger

which is the greatest value? 1. kilo 2. mega 3. giga 4. tera

tera

what controls the actual relationship between a pixel numerical value and its displayed brightness at the time of viewing

the adjustments of the window controls prior to the image viewing

if the smaller the FOV the more pixels in a given display true or false

true

the size of a monitor has no effect on resolution true or false

true

Define Field of view (FOV)

-"how much of the patient" is imaged in matrix, AND displayed on the monitor -matrix size and FOV are independent -FOV may change w/o changing matrix size -size of a pixel is related to size of matrix and FOV -As matrix increases and FOV remains the same, pixel size must decrease to fit into matrix

-Digital images are recorded as a _____ or ______ ___ ______ each pixel is recorded as a single numerical value that corresponds to a single _______ level on a monitor

-Digital images are recorded as a matrix (rows and columns) or array of pixels each pixel is recorded as a single numerical value that corresponds to a single brightness level on a monitor

If matrix size increases, FOV?, pixel size?, and spatial resolution?

-FOV remains the same -pixel size decreases -spatial resolution increases

define bits

-a digital image is represented in imaging and computer system by numbers in the form of binary digits

Define spatial resolution

-ability of an imaging system to distinguish small adjacent details from each other

-all digital images (photographic, radiographic, or fluoroscopic) consist of a ______ of numbers (or _____ ___) stored in computer memory -Each pixel represents a cell __________ (or ____) assigned to that location.

-all digital images (photographic, radiographic, or fluoroscopic) consist of a matrix of numbers (or binary codes) stored in computer memory -Each pixel represents a cell brightness (or density) assigned to that location.

In CR what should you always remember when it comes to FOV

-always take your image on the smallest IR possible -for imaging small structures the spatial resolution, are clearer allowing for optimal diagnosis

define grayscale bit depth

-contrast -refers to the amount or depth of data available to create an image -how many shades of gray we choose to display is the bit depth

dynamic range

-density resolution -bit depth -determines number of density values -affects density and contrast of system -controlled by ADC 10 bit= 2^10 = 1024 shades of gray 12 bit= 2^12 = 4096 shades of gray ect.

define FOV

-field of view -overall dimension of image matrix -determined by size of detector

Pixel size is determined by:

-field of view (image receptor size) -matrix size

define LUT

-look up tables -procedural algorithm specific to the part -used when the histogram is automatically rescaled to optimize the anatomy

If FOV decreases, matrix size?, pixel size? and spatial resolution?

-matrix size remains the same -pixel size decreases -spatial resolution increases

If FOV increases, matrix size?, pixel size? and spatial resolution ?

-matrix size remains the same -pixel size increases -spatial resolution decreases

define grayscale bit depth

-number of bits per pixel or shades of gray possible per pixel

what determines the size of the computer file for a given image

-pixel size -matrix -gray scale bit depth

If matrix size decreases pixel size?, FOV? and spatial resolution?

-pixel size increases -FOV remains the same -spatial resolution decreases

what is image file size affected by?

-pixel size: each pixel contains a discrete value (number) represents brightness level -bit depth: number of bits per pixel -matrix: 2 dimensional array of numbers, columns (M) and rows (N) (matrix size is sometimes called FOV/ field of view)

what is the size of the digital image determined by?

-product of horizontal pixels x vertical pixels x number of bits (depth) assigned to the pixels (M x N x k bits)

define pixel

-represented by a series of bits -each pixel is represented by a numerical value -pixel value is related to the brightness (density) that we will see when the digital image is converted from an analog image for display and viewing

define sampling frequency

-sampled to find location and size of signal, quantified to determine average value of signal in sample -expressed in pixels/ mm

ADC consists of 2 distinct steps

-sampling -quantization

digital images represented in 2 domains based on how the image is acquired

-spatial domain: is location, where the pixel is according to the x and y coordinates -spatial frequency domain: described as the resolution and contrast based on the # of cycles per unit length (definition of frequency) *small structures produce high frequency and high contrast

define pixel bit depth

-the number of bits that have been made available in the digital system to represent each pixel in the image -use base 2 to calculate -4 bits = 16 different shades of gray

define digital data

-think digital clock -its exactly 6:11 AM -these are discrete values and specific -no decimals allowed

define analog data

-think of classroom clock -its about 10:41 AM

define spatial frequency

-used to describe spatial resolution and refers to number of details that can be clearly visualized in a set amount of space (distance) -line pairs per mm -directly related to pixel size

most digital systems use a ____, ____, or ____ bit ADC which determine the density values of the analog signal and so the grayscale of the system

12, 14, or 16 bit

how many pixels are needed to make up one line pair?

2 pixels = 1 detail

define voxel

3D pixel -MRI and CT offers 3 dimensions

How many bits equal a byte?

8

define byte

8 bits -the amount needed to store one alphanumeric character) -computer memory is often kilobytes (1024), megabytes (1,048,576), and gigabytes (1,073,741,824)

Electronic devices produce radiographic images from ______ _______, consisting of series of voltage fluctuations on continuous waveform. There must be converted to _______ language

Electronic devices produce radiographic images from analog signals, consisting of series of voltage fluctuations on continuous waveform. There must be converted to binary language

what is the equation for pixel size?

FOV/matrix (must be in mm)