8. Digital Medical Imaging Fundamentals Flashcards
A two-dimensional (2D) function
Digital Image
f(x,y); Where x & y =
plane coordinates
x
length
y
height
z
width
f
amplitude (brightness level)
Function f(x,y) where x and y are
spatial coordinates
is a 2D representation of a continuous image by a 2D array of discrete samples
Digital Image
Each element of a 2D array is a
pixel
If the digital image f(x,y,z) is 3-D, then the picture element is called a
VOXEL (volume element)
VOXEL
Volume Element
As f(x,y,z) is collected through time t, the collection becomes a
4-D image set
fourth dimension is
Time (t)
used when mathematics is presented
f
picture or image is being emphasized
p
w
Time (t)
Point Dimension
0D
Line Dimension
1D
Plane Dimension
2D
Solid Dimension
3D
A rectangular arrangement of numbers into rows & columns
Matrix
Each number in a matrix is referred to as a
matrix elementorentry
Thedimensionsof a matrix give the number of _____ of the matrixin this order
rows and columns
horizontal and the first number in matrix
rows
vertical and the second number in the matrix
columns
if the image is obtained through a digitizer
Digitized
if the image is generated digitally
Digital Image
The pixel (voxel) value (gray level) can range from: 8-bit
0-255
The pixel (voxel) value (gray level) can range from: 10-bit
0-1023
The pixel (voxel) value (gray level) can range from: 9-bit
0-511
The pixel (voxel) value (gray level) can range from: 11-bit
0-2045
The pixel (voxel) value (gray level) can range from: 12-bit
0-4095
Represent physical, chemical, & physiological properties of the state of anatomical structures or physiological processes when the image was captured
Gray Levels
0 represents
Black (Radiolucent)
255 or highest number represent
White (Radiopaque)
Represents the optical density of the small square area of the film
Digitizer
Represents the relative linear attenuation coefficient of the tissue
Computed Tomography (CT)
Hounsfield Units of Bone
1000
Hounsfield Units of Muscle
50
Hounsfield Units of Brain White
45
Hounsfield Units of Brain Gray
40
Hounsfield Units of Blood
20
Hounsfield Units of Water
0
Hounsfield Units of Fat
-100
Hounsfield Units of Lung
-200
Hounsfield Units of Air
-1000
Corresponds to the MR signal response of the tissue
Magnetic Resonance Imaging (MRI)
Uses echo signal to penetrates the tissues
Ultrasound (UTZ)
2D projection image is the
ordered pair (M,N) signals
Size of the image is the product of M x N bits where 2k represents the
gray level range
Sectional images of a 3D volume, most of the time
M=N
IMAGE DISPLAY
- Digital image can be printed on film or paper as hard copy or displayed on a CRT & LCD as a soft copy
- To display a soft copy digital medical image, the pixel values are first converted to analog-signals, to digital-to-analog conversion
- Current software display devices can display up to a 2K image on one screen
- Up to date, no commercially available system can handle a 4K image
Quality of a digital image, is measured by three parameters:
- Spatial Resolution
- Density Resolution
- Signal-to-Noise Ratio
related to the number of pixels and the range of pixel values used to represent the object of interest in the image
Density Resolution
In a square image,
N x N x k, where:
N - ____,
k - ____
N - related to spatial resolution,
k – density resolution
means that the image has strong signal with little noise, as a result, the image would please the eyes as seeing a good quality image
high signal-to-noise ratio
Provide a standardized way to store the information describing an image in a computer file
Image File Format
One or more images representing the projection of an anatomical volume onto an image plane
projection or planar imaging
A series of images representing thin slices through a volume
tomographic or multi-slice 2D imaging
A set of data from a volume
volume or 3D
Multiple acquisition of the same tomographic or volume image over time to produce a dynamic series of acquisitions
4D
MEDICAL IMAGE DATA SET CONSISTS:
- projection or planar imaging
- tomographic or multi-slice 2D imaging
- volume or 3D
- 4D
Describes how the image data are organized inside the image file and how the pixel data should be interpreted by a software for the correct loading and visualization
File Format
4 MAJOR FILE FORMATS USED IN
MEDICAL IMAGING:
- Analyze
- DICOM
- Minc
- Nifti
Nifti
Neuroimaging Informatics Technology Initiative
Representation of the internal structure or function of an anatomic region in the form of an array of picture elements called pixels or voxels
Medical Image
NUMERICAL VALUE OF A PIXEL DEPENDS ON (Factors that affect the pixel/image):
- Acquisition Protocol
- Imaging Modality
- Post-processing
- Reconstruction
Number of bits used to encode the information of each pixel
Pixel Depth
Every image is stored in a file & kept in the memory of a computer as group of
bytes (group of 8 bits)
The amount of information per pixel is
color depth
1 bit of information per pixel
Monochrome
8 bits of information per pixel
Grey-scale
8 or 16 bits of information per pixel
Color (RGB)
24 or 32 bits of information per pixel
True Color (RGB)
If a 256 x 256 pixels image has a pixel depth of 12 or 16 bits, the computer will always store ___ bytes per pixel & then the pixel data will require 256 x 256 x 2 = 131,072 bytes of memory
two
More color= More ____= More ___
Information,
Bits
Specifies how the pixel data should be interpreted for the correct image display as a monochrome or color image
Photometric Interpretation
have one sample per pixel & no color information is stored in the image
Monochrome images
Gray scale photometric interpretation
X-ray, CT, MRI
color map or color palette/LUT
Nuclear Medicine, PET, SPECT
SPECT
Single-Photon Emission Computed Tomography
PET
Positron Emission Tomography
Each pixel of the image is associated with a ___ in a predefined color map
color
Information that describes the image
Metadata
Stored at the beginning of the file as a header & contains at least the image matrix dimensions, spatial resolutions, pixel depth, & photometric interpretation
Metadata
Thanks to ______, a software application is able to recognize & correctly open an image in a supported file format
Metadata
Numerical values of the pixels are stored
Pixel Data
Creation of Digital Image
a. Analog Image
b. Digital Sampling
c. Pixel Quantization
2 CATEGORIES FOR MEDICAL IMAGE FILE FORMATS:
- DICOM
2. Analyze, Nifti & Minc
Formats intended to standardize the images generated by diagnostic modalities
DICOM
Formats born with the aim to facilitate & strengthen post-processing analysis
Analyze, Nifti & Minc
Medical image files are typically stored using one of the following two possible configurations.
- One in which a single file contains both the metadata and image data, with the metadata stored at the beginning of the file
- The second configuration stores the metadata in one file and the image data in a second one
Analyze was developed in
1980’s in Mayo Clinic in Rochester, MN, USA
Consists of two binary files, image file with extension
Analyze
Analyze file extensions
.img,
.hdr
contains the voxel raw data
.img
header file, contains metadata
.hdr
Nifti was developed in
2000s in National Institute of Health
With the intent to create a format for neuroimaging maintaining the advantages of the Analyze format
Nifti
Can be thought as revised Analyze format
Nifti
Nifti is almost identical to the Analyze format, but offers a few improvements:
a. Merging of the header & image information into one file “.nii”
b. Possibility of extending the header information
Nifti file extension
.nii
Minc was developed in
1992 in Montreal Neurological Institute (MNI)
MNI
Montreal Neurological Institute
To provide a flexible data format for medical imaging
Minc
Based on the Network Common Data Format (NetCDF) Minc 1 to Hierarchical Data Format version 5 (HDF5) Minc 2
Minc
DICOM was developed in
1990s by ACR and NEMA
ACR
American College of Radiology
NEMA
National Electrical Manufacturers Association
Backbone of every medical imaging department
DICOM
Pixel data cannot be separated from the description of the medical procedure which led to the formation in the image itself
DICOM
The standard stressed the concept that “an image that is separate from its metadata becomes _______ as medical image”
meaningless
______ are merged in a unique file, and the ______ contains the most complete description of the entire procedure
Metadata & pixel data,
DICOM header
Minc file extension
.mnc
DICOM file extension
.dcm
has a mechanism to extend the header
Nifti
is simply data about data. It means it is a description and context of the data. It helps to organize, find and understand data.
Metadata
Those are some typical metadata elements:
- Title and description
- Tags and categories
- Who created and when
- Who last modified and when
- Who can access or update
A few real world examples of metadata:
Photo, Book, Email, Word Document, Web Page,
Blog Post, Spreadsheet, Rational Database, Computer Files, Paper Files
In radiology refers to the ability of
an imaging system to differentiate
between two near-by objects
Spatial Resolution
In digital imaging, it depends on the size
of the pixel used.
Spatial Resolution
A ___ pixel size will be unable to
resolve two near-by structures as
compared to a ___ pixel size.
large,
small
LUT
look-up table
MINC
Medical Imaging Network Common Data Format
NetCDF
Network Common Data Format
HDF5
Hierarchical Data Format version 5
convert hard-copy x-ray, CT, ultrasound, MRI and dosefilmsto digital images
film digitizers
