L5 Flashcards
• Traditionally, radiographic images were formed in an
analog fashion
, containing fluorescent screens and film sensitive to the light
Produced by the screens, is exposed to radiation and then processed in
Chemical solutions.
A
Cassette
In an analog system such as film/screen radiography, x-
Ray energy is converted to ____, and the light waves are recorded just as they
Are.
light
In digital radiography, analog signals are converted into
numbers that are
Recorded
are formed through multiple samplings of the signal
Rather than the one single exposure of an analog image.
Digital images
A digital image begins as an
analog signal.
Through ____, the image becomes digitized and is sampled multiple times.
computer data
Processing
can be described with respect to several characteristics
Or fundamental parameters, including the matrix, pixels, voxels, and the bit dep
A digital image
• A digital image is made up of a two-dimensional array of numbers called a
Matrix
The matrix consists of ___&____that define pixels.
columns (M) and rows (N)
The dimensions of the image are described by
M (columns) and N (rows).
• When M=N, the image is_____ ; typically, diagnostic images are
square
rectangular.
The _____ (or FOV) is selected during imaging.
matrix size
require more processing time and storage space.
Larger images
also take longer to transmit to remote locations.
Larger images
is necessary to facilitate efficient storage and Transmission
Image compression
, or picture element, is the smallest element in a digital Image. If you have ever Magnified a digital picture to the point that you see the image as small squares of Color, you have seen pixels.
A pixel
A pixel represents the _______ element in an image.
• It has dimensions given along two axes in millimeters, dictating in-plane spatial
resolution.
smallest sampled 2D
• The pixels that make up the matrix are
generally square.
Each pixel contains a _____ number representing a
discrete
brightness level.
• In radiography and CT, the numbers relate to the ___&____
atomic number and
mass density of tissues.
In MRI, the numbers represent other tissue characteristics like _____&___
proton
density and relaxation times.
A typical digital chest x-ray might contain ___ columns of pixels and
_____rows of pixels for a total of __ million pixels.
2000
2500
5
• Each pixel contains a series of ____&____ defining the grayscale or shade
of that particular point on a digital x-ray image.
1s and 0s
• Each space available or a 1 or 0 is called a ___. A group of 8 bits is called
a ___
bit
byte.
• Each pixel is coded with ____ to show different shades, helping to
create the detailed digital image you see
numbers
• The pixel size can be calculated using the relationship:
Pixel size = FOV/matrix size
• For digital imaging modalities, the larger the ___, the smaller the
_____ (for the same FOV) and the better the ____
matrix size
pixel size
spatial resolution.
• The _____ is the number of bits per pixel.
An image that is described as having a bit depth of 8 will have ____ shades of gray.
bit depth
256 (28)
• The term field of view, or FOV, is synonymous with the
_____. In other words, it is the amount of body part or patient included in the image.
x-ray field.
The larger the FOV, the more area is
imaged.
• Changes in the FOV will not affect the size of the matrix; however, changes in
the matrix will affect ____. This is because as the matrix increases (e.g., from 512 × 512 to 1024 × 1024)
and the FOV remains the same size, the pixel size must decrease to fit into the
matrix
pixel size.
• The characteristics of a digital image can affect the appearance of the digital
image, particularly its ____&___
spatial resolution and its density resolution.
refers to the ability of an imaging modality to differentiate
two adjacent structures as being distinct from one another.
• Spatial resolution
refers to the ability of an imaging system to distinguish
between different levels of radiographic density or optical density (OD)
• Density resolution
has an effect on the detail or spatial resolution of the image.
• The larger the ____ (for the same FOV), the smaller pixel size, hence the
better the appearance of detail.
• The matrix size
matrix size
• Additionally, as the ___ decreases, without a change in matrix size, the size of
the pixel decreases as well, thus improving detail.
FOV
selects a larger matrix size when imaging larger body parts, such
as a chest, in order to show small details in the anatomy.
• The operator
has an effect on the number of shades of gray, hence the
density resolution of the image.
The bit depth
- In____ , the image is first divided into an array of small square regions
called
scanning
pixels.
- The second step, _____, simply involves measuring the brightness level
of each of the pixels using special devices such as a photomultiplier tube
(PMT).
sampling
The signal from the PMT is an _____ (voltage waveform)
that must be converted into a digital image for processing by a digital
computer.
analog signal
. The third step in digitizing an image is ____. This is a process
whereby the brightness levels obtained from sampling are assigned an
integer (zero, a negative, or a positive number) called a ____.
quantization
gray level
The
image is now made up of a range of gray levels. The total number of gray
levels is called the
gray scale.
plays an important role in the process
of converting an analog signal into digital data for input into a digital
computer. The ADC consists of several components that will divide up the
analog signal into equal parts.
• The Analog-Digital Converter (ADC
• Digital imaging modalities have ____ ADCs. The greater the bits, the
more accurately the signals from the detectors can be digitized for a faithful
reproduction of the original signal. This means that image quality is better
with higher bit ADCs compared to lower bit ADCs.
12- to 32-bit
Deals with the development of problem specific
approaches to enhance the raw medical data for the
purpose of selective visualization as well as further
analysis.
Basic Image Processing
Concentrates on the development of techniques to
supplement the usually qualitative and frequently
subjective assessment of medical image by human
experts.
Basic Image Analysis
Plays an important role in assessing any new hardware,
software, image acquisition techniques, image reconstruction
or post- processing algorithms.
Quality Evaluation
Statistics of medical imaging fills the gap and
provides a theoretical framework for statistical
investigation into medical imaging technologies.
Statistical Analysis and Entropy
in digital images is used form any
practical purpose, mainly in security fields and also
with gray scale images applications.
Color information
The system is said to be stable only when the output is bounded for
____. For a bounded input, if the output is unbounded in the
system then it is said to be ____.
bounded input
Unstable
A ___ system satisfies the BIBO means finite in amplitude.
Stable and Unstable Signal Processing
stable
BIBO stands for
Bounded input for Bounded Output
An ____ can be applied to an image to convert it
from one domain to another. Viewing an image in domains such as
frequency or hough space enables the identification of features
that may not be easily detected in the spatial domain.
image transformation
Common Image Transforms include:
• Hough Transform
• Radon Transform
• Discrete Cosine Transform
• Discrete Fourier Transform
• Wavelet Transform
A principal advantage of digital radiographic imaging over screen-film
radiographic imaging is the ability to _____ the image before and after
display - preprocessing and postprocessing, respectively.
manipulate
Pre and Post image processing alter image appearance, usually for the
purpose of improving
image contrast.
Preprocessing of digital images is largely
automatic.
is designed to produce artifact-free
digital images.
Preprocessing
describes the manipulation
of radiographic images to derive additional qualitative or
quantitative data.
Advanced post-processing
is a key element of information
technology platforms in a modern radiology department.
The adequate and repeatable performance of the image
display system
