DIGITAL IMAGE PROCESSING-CT EXAM 2024/2025 questions and answers | verified
Limitations of film based imaging - Been around since 1895 Used in all radiology modalities.
Patient is exposed to predetermined amount of radiation that is needed to provide a diagnostic image. If
image is under/over penetrated the patient would have to be exposed again, increasing dose. Not ideal
way to perform radiation detection, image display and image archiving. Film-screen(x-Ray) can't show
differences in tissue contrast less than 10%(contrast resolution). Optical range and contrast for film are
fixed and limited(can't window/level them, have to retake). Stored in envelopes requires manual
handling for archiving and retrieval.
Major components of generic digital imaging system - Data acquisition, Image processing,
Display/storage/archivingImage communication
Data acquisition - 1st step- systematic method of collecting data from the patient, Attenuation
data collected for imaging modality, Ct- x-Ray tube and digital image detectors do this, Output signal is
an electrical signal(analog signal that varies continuously on time), Analog, signal must be converted into
a digital signal for, computer processing using an ADC converter
Image processing - Performed by digital computer , Takes input digital image, processes it to
produce output digital image(using binary number system), ADC sends digital data for digital image
processing by a digital computer, Accomplished by set of operations, techniques to the input image into
an output image, these operations can reduce noise, enhance sharpness, or change the contrast
Image display, storage, and communication - Output digital image must be converted into an
analog signal before it can be displayed on the monitor using a DAC, Can be archived on magnetic data
carriers and laser optical disks for retrospective viewing and manipulation, Can be communicated
electronically through computer networks to remote sites
Image formations and representation analog images - Analog images are continuous images,
Images formed when x-rays pass through patient and projected onto x-Ray film, Films processed in
chemical solutions to render visible. These images formed by photochemical process, Images can be
formed by photo electronic means, images may be represented as electrical(analog) signals that emerge
from photo electrical device
Image formation and representation digital images - Numerical representations or images of
objects, Formation of any digital image requires digital computer, Any information that enters the
computer must be converted into digital form(numbers). ADC converts continuous signals to discrete
, signals(digital data). Computer receives data and then does necessary processing. Result=digital and can
be displayed as digital image, Output=analog image
Digital image processing - In image processing it's necessary to convert an input image into an
output image, if both are analog this is referred to as analog processing, if both are discrete this is
referred to as digital processing, When an analog image must be converted into digital data for computer
input a digitizations system is required , CT is based on a reconstruction process whereby digital image,
changed into a visible physical image, process-"a series of actions or operations leading to a desired
result; thus, a series of actions or operations are performed upon an object to alter its form in a desired
manner".
Spatial location domains=CT - Used in radiography and CT, The digital image is a numerical image
arranged in such a manner thAt the location of each number in the image can be identified using the x-y
coordinate system, x=columns(horizontal), y=rows(vertical), The first pixel in the upper left hand corner
is always identified as 0,0
Spatial frequency domains - Used in MRI, frequency refers to the number of cycles per unit
length(the number of times the signal changes per unit length).
Image domains - Digital image processing can transform one image domain into another image
domain, An image in the spatial location can be transformed into a spatial frequency domain image, The
Fourier transform(FT) is used to perform this task, converts a function in the time domain to a function in
the frequency domain, the inverse FT is used to transform an image in the frequency domain back to the
spatial location domain for viewing by radiologist/technologist
Characteristics of the digital image - The structure of a digital image can be described with respect
to several characteristics or fundamental parameter. Matrix, Pixel, Voxel,Bit depth
Matrix - A two dimensional array of numbers that make up a digital image, consists of columns(m)
and rows(n) that define small square regions called picture elements(pixels), The matrix size is selected
by the technologist(FOV), In CT we use 512x512
Pixels(2D) - Make up the matrix, Generally square, Containsa number(characterized by the tissue
imaged) that represents the brightness level. In CT, the numbers are related to the atomic number and
mass density of the tissues, Pixel size can be calculated by: pixel size=FOV/matrix size The larger the
matrix size the smaller the pixel size and the better the spatial resolution
Limitations of film based imaging - Been around since 1895 Used in all radiology modalities.
Patient is exposed to predetermined amount of radiation that is needed to provide a diagnostic image. If
image is under/over penetrated the patient would have to be exposed again, increasing dose. Not ideal
way to perform radiation detection, image display and image archiving. Film-screen(x-Ray) can't show
differences in tissue contrast less than 10%(contrast resolution). Optical range and contrast for film are
fixed and limited(can't window/level them, have to retake). Stored in envelopes requires manual
handling for archiving and retrieval.
Major components of generic digital imaging system - Data acquisition, Image processing,
Display/storage/archivingImage communication
Data acquisition - 1st step- systematic method of collecting data from the patient, Attenuation
data collected for imaging modality, Ct- x-Ray tube and digital image detectors do this, Output signal is
an electrical signal(analog signal that varies continuously on time), Analog, signal must be converted into
a digital signal for, computer processing using an ADC converter
Image processing - Performed by digital computer , Takes input digital image, processes it to
produce output digital image(using binary number system), ADC sends digital data for digital image
processing by a digital computer, Accomplished by set of operations, techniques to the input image into
an output image, these operations can reduce noise, enhance sharpness, or change the contrast
Image display, storage, and communication - Output digital image must be converted into an
analog signal before it can be displayed on the monitor using a DAC, Can be archived on magnetic data
carriers and laser optical disks for retrospective viewing and manipulation, Can be communicated
electronically through computer networks to remote sites
Image formations and representation analog images - Analog images are continuous images,
Images formed when x-rays pass through patient and projected onto x-Ray film, Films processed in
chemical solutions to render visible. These images formed by photochemical process, Images can be
formed by photo electronic means, images may be represented as electrical(analog) signals that emerge
from photo electrical device
Image formation and representation digital images - Numerical representations or images of
objects, Formation of any digital image requires digital computer, Any information that enters the
computer must be converted into digital form(numbers). ADC converts continuous signals to discrete
, signals(digital data). Computer receives data and then does necessary processing. Result=digital and can
be displayed as digital image, Output=analog image
Digital image processing - In image processing it's necessary to convert an input image into an
output image, if both are analog this is referred to as analog processing, if both are discrete this is
referred to as digital processing, When an analog image must be converted into digital data for computer
input a digitizations system is required , CT is based on a reconstruction process whereby digital image,
changed into a visible physical image, process-"a series of actions or operations leading to a desired
result; thus, a series of actions or operations are performed upon an object to alter its form in a desired
manner".
Spatial location domains=CT - Used in radiography and CT, The digital image is a numerical image
arranged in such a manner thAt the location of each number in the image can be identified using the x-y
coordinate system, x=columns(horizontal), y=rows(vertical), The first pixel in the upper left hand corner
is always identified as 0,0
Spatial frequency domains - Used in MRI, frequency refers to the number of cycles per unit
length(the number of times the signal changes per unit length).
Image domains - Digital image processing can transform one image domain into another image
domain, An image in the spatial location can be transformed into a spatial frequency domain image, The
Fourier transform(FT) is used to perform this task, converts a function in the time domain to a function in
the frequency domain, the inverse FT is used to transform an image in the frequency domain back to the
spatial location domain for viewing by radiologist/technologist
Characteristics of the digital image - The structure of a digital image can be described with respect
to several characteristics or fundamental parameter. Matrix, Pixel, Voxel,Bit depth
Matrix - A two dimensional array of numbers that make up a digital image, consists of columns(m)
and rows(n) that define small square regions called picture elements(pixels), The matrix size is selected
by the technologist(FOV), In CT we use 512x512
Pixels(2D) - Make up the matrix, Generally square, Containsa number(characterized by the tissue
imaged) that represents the brightness level. In CT, the numbers are related to the atomic number and
mass density of the tissues, Pixel size can be calculated by: pixel size=FOV/matrix size The larger the
matrix size the smaller the pixel size and the better the spatial resolution
