Fauber Ch 4 Digital Imaging

The image receptor receives exit radiation and creates the ______________ or ___________________.

latent image or invisible image

Define latent image

the pattern of stored energy on the exposed film that cannot be seen. The latent energy remains invisible until processed by a computer for viewing on a display monitor.

What two types of digital imaging systems are being used today?

CR and DR

Digital images are composed of what type of data that can be easily manipulated by a computer?

numerical

Define Matrix

digital image displayed as a combination of rows and columns (array) if small usually square picture elements (pixels)

Define pixel

the smallest component of the matrix also known as picture elements

the size of a pixel is measured in________.

Microns

100 microns= ______ mm

.1

Digital image quality is improved with:

larger size matrix and smaller size pixels

FOV stands for

field of view

A greater number of small pixels __________ spacial resolution. (increases or decreases)

increases / improves

define pixel bit depth

number of bits that determines the precision with which exit radiation is recorded and controls the exact pixel brightness that can be displayed

if field of view (FOV) is decreased but matrix size remains the same, pixel size __________(increases or decreases)

decreases

if FOV remains the same but matrix size increases, pixel size___________ (increases or decreases)

decreases

If you decrease the size of a pixel it will (increase/decrease) spatial resolution

increase

increase matrix size for a given FOV will (increase/decrease) size of the pixel?

decrease

pixel size is _________related to FOV

directly

pixel size is ___________related to matrix size

inversely

Important relationship

Pixel Size, FOV, and Matrix Size

the pixel size is directly related to FOV size

pixel size is indirectly related to Matrix size

increasing FOV for the same matrix size will increase the size of the pixel and decrease spatial resolution

increasing the matrix size for the same FOV will decrease the pixel size and increase spacial resolution

The numerical value assigned to each pixel is determined by what?

The relative attenuation of X-rays passing through the corresponding volume of tissue

define bit depth

number of pits that determines the precision with which the exit radiation is recorded and controls the exact pixel brightness that can be displayed

Bit depth is determined by what

an analog-to-digital converter. which is an integral component of every digital imaging system

A larger bit depth allows a (greater / lesser) number of shades of gray to be displayed on a computer monitor

greater

Important Relationship:

pixel bit depth and contrast resolution

the greater the pixel depth (ie 16 bit), the more precise the digitization of the analog signal, and the greater number of shades of gray available for image display. Increasing the number of shades of gray available to display on a digital image improves contrast resolution

The greater number of pixels in an image matrix, the _________(smaller / larger) their size?

Smaller

Define pixel density

number of pixels per unit area

A greater number of pixels per unit area (pixel density) provides ____________(increased/ decreased) spatial resolution

increased

Define pixel pitch

The space from the middle of one pixel to the middle of the next pixel

IMPORTANT RELATIONSHIP:

Pixel Density and Pitch and Spatial Resolution

increasing pixel density and decreasing pixel pitch (same thing) increases spatial resolution

vise versa

define spatial frequency

the unit of line pairs per millimeter (lp/mm)

An imaging system that can resolve a greater number of line pairs per millimeter (lp/mm) has ___________ (increased / decreased) spatial resolution?

increased

The ability to resolve or demonstrate a specific spatial frequency is directly impacted by _____________.

the size of the pixel

IMPORTANT RELATIONSHIP:

Spatial Frequency and Spatial Resolution

the unit of measure for spatial frequency is lp/mm. increasing the number of line pairs per millimeter resolved in the imaging system (higher spatial frequency) increases spatial resolution

the unit of measure for spacial frequency is?

lp/mm (line pairs per millimeter)

What does MTF stand for

modulation transfer function

define modulation transfer function (MTF)

a measure if the imaging systems ability to display the contrast of anatomic objects varying in size

(the value will be between 0 and 1)

IMPORTANT RELATIONSHIP

Modulation Transfer Function (MTF) and Anatomic Detail

MFT is a measure of the image systems ability to accurately display small anatomic objects having high spatial frequency. An imaging system that has high MFT can display anatomic detail with improved visibility

what are the two types of digital IR's used in radiography?

Computed radiography (CR)

Direct radiography (DR)

define luminescence

the emission of light when stimulated by radiation

Define DQE (defective quantum efficiency)

a measurement of the efficiency of an image receptor in converting the Xray exposure to a quality radiographic image

An image receptor with a (LOWER/HIGHER) DQE requires less X-ray exposure to produce a quality radiographic image when compared to a detector with a (LOWER?HIGHER) DQE

higher

lower

Define signal-to-noise ratio.

is a method of describing the strength of the radiation exposure compared with the amount of noise apparent in a digital image

quantum noise results when there are too (FEW/MANY) photons captured by the IR to create the latent image

few

Contrast to Noise Ratio (CNR)

a method of describing the contrast resolution with the amount of noise apparent in a digital image

Digital images with higher CNR will (INCREASe/DECREASE) the visibility of anatomic tissues

increase

Histogram analysis

image processing technique commonly used to identify the edges of an image and assess the raw data prior to image display

VOI (values of interest)

histogram models which determine the range of the histogram data that should be included in the displayed image

automatic rescaling

process by which images are produced with uniform brightness and contrast, regardless of the amount of exposure (histogram analysis)

exposure indicator

Provides a numeric value indicating the level of radiation exposure to the digital IR

Fuji and Konica use what type of exposure indicator?

Sensitivity numbers

Define deviation index

Is a value that reflects the difference between the desired or target exposure to the IR

Define lookup table

Provide a method of altering the image to change the display of the digital image in various ways. Could be original pixel values to improve brightness and contrast of the image.

Define Electric masking (shuttering)

A post processing function that can remove regions of the digital image

Define Window level

(Or center) sets the midpoint of the range of brightness visible in the image.

Define grayscale

The number of different shades of gray that can be stored and displayed by a computer system i

Define contrast resolution (in relation to digital)

Another term associated with digital imaging and is used to describe the ability of the imaging system to distinguish between objects that exhibit similar densities because they attenuate the X-ray bean similarly

Define window width

A control that adjusts the Radiographic contrast

A (direct or inverse) relationship exists between window width and image contrast?

Inverse (wide window width lower contrast/small window width higher contrast)

Define subtraction

A technique that can remove superimposed structures so that the anatomical area of interest becomes more visible

Define contrast enhancement

A post processing technique that alters the pixel values to increase image contrast

define edge enhancement

(High pass filtering) post processing technique that improves visibility of small high contrast structures. However image noise may be slightly increased

Define inversion

(Black and white reversal) post processing technique that reversed the grayscale from the original radiograph

Define smoothing (low pass filtering)

A post processing technique that suppresses image noise (quantum noise) however spatial resolution is degraded

Define equalization

The process to even the brightness of the image.

What's the equation for pixel size

Pixel size= FOV / matrix size

Define quantization

The process of assigning a numerical value to represent a brightness value

True or false? A lower signal-to-noise ratio improves the quality of a digital image

FALSE

What process is employed to maintain consistent digital image brightness for overexposure and under exposure?

Automatic rescaling

What digital process alters image brightness and grayscale to improve the visibility of an atomic structures

Lookup tables

What is the communication standard for j formation sharing between PACS and imaging modalities

DICOM