Tags & Description
Digital Image
▪ A two-dimensional (2D) function ▪ f(x,y) ▪ Where x & y = plane coordinates ▪ f= amplitude (brightness level)
pixel
Each element of the 2d array is a ____
VOXEL (volume element)
If the digital image f(x,y,z) is 3-D, then the picture element is called a
4-D
As f(x,y,z) is collected through time t, the collection becomes a __ image set
Time
The fourth dimension is
f
used when mathematics is presented
p
picture or image is being emphasized
MATRIX
▪ A rectangular arrangement of numbers into rows & columns ▪ Each number in a matrix is referred to as a matrix element or entry
Dimensions
The ____ of a matrix give the number of rows and columns of the matrix in this order.
2x3
Matrix A has 2 rows and 3 columns, it is called a ___ matrix.
DIGITIZED
if the image is obtained through a digitizer
DIGITAL IMAGES
if it is generated digitally
8-bit
0-255
9-bit
0-511
10-bit
0-1023
11-bit
0-2045
12-bit
0-4095
Gray Levels
Represent physical, chemical, & physiological properties of the state of anatomical structures or physiological processes when the image was captured
DIGITIZER
Represents the optical density of the small square area of the film
COMPUTED TOMOGRAPHY
Represents the relative linear attenuation coefficient of the tissue
1000
Hounsfield unit of Bone:
0
Hounsfield unit of Water:
-1000
Hounsfield unit of Air:
MRI
▪ Corresponds to the MR signal response of the tissue
Ultrasound
▪ Echo signal of the utz beam when it penetrates the tissues
Image Size
▪ 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
SPATIAL RESOLUTION, DENSITY RESOLUTION, SIGNAL-TO-NOISE RATIO
Quality of a digital image, is measured by three parameters:
SPATIAL RESOLUTION and DENSITY RESOLUTION
related to the number of pixels and the range of pixel values used to represent the object of interest in the image
N
related to spatial resolution
k
– density resolution
signal-to-noise ratio
A high --___ ___ 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
IMAGE FILE FORMAT
▪ Provide a standardized way to store the information describing an image in a computer file
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 (4):
FILE FORMAT
▪ 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.
Analyze Nifti Minc Dicom
4 MAJOR FILE FORMATS USED IN MEDICAL IMAGING:
MEDICAL IMAGE
▪ Representation of the internal structure or function of an anatomic region in the form of an array of picture elements called pixels or voxels.
Imaging Modality Acquisition Protocol Reconstruction Post-processing
NUMERICAL VALUE OF A PIXEL DEPENDS ON:
PIXEL DEPTH
Number of bits used to encode the information of each pixel
bytes
Every image is stored in a file & kept in the memory of a computer as group of ____ (group of 8 bits)
color depth
The amount of unformation per pixel is ___ ___
PHOTOMETRIC INTERPRETATION
• Specifies how the pixel data should be interpreted for the correct image display as a monochrome or color image
Monochrome images
have one sample per pixel & no color information is stored in the image.
X-ray, CT, MRI
3 kinds of gray scale photometric interpretation
Nuclear Medicine, PET, SPECT
color map or color palette/LUT
color map
Each pixel of the image is associated with a color in a predefined
metadata
▪ Information that describes the image ▪ Stored at the beginning of the file as a header & contains at least the image matrix dimensions, spatial resolutions, pixel depth, & photometric interpretation ▪ Thanks to ____, a software application is able to recognize & correctly open an image in a supported file format
PIXEL DATA
▪ Numerical values of the pixels are stored
DICOM Analyze, Nifti and Minc
2 CATEGORIES FOR MEDICAL IMAGE FILE FORMATS:
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.
Medical image files are typically stored using one of the following two possible configurations.
Analyze
▪ 1980’s, Mayo Clinic in Rochester, MN, USA
.img
contains the voxel raw data
.hdr
header file, contains metadata
Neuroimaging Informatics Technology Initiative
NIFTI meaning
2000s
When was NIFTI created?
National Institute of Health
Who created NIFTI?
NIFTI
▪ With the intent to create a format for neuroimaging maintaining the advantages of the Analyze format ▪ Can be thought as revised Analyze format
A. Merging of the header & image information into one file “.nii” B. Possibility of extending the header information
NIFTI is almost identical to the Analyze format, but offers a few improvements:
1992
When was MINC created?
Montreal Neurological Institute (MNI)
Who created MINC?
MINC
▪ To provide a flexible data format for medical imaging ▪ Based on the Network Common Data Format (NetCDF) Minc 1 to Hierarchical Data Format version 5 (HDF5) Minc 2
1990s
When was DICOM created?
ACR (American College of Radiology) and NEMA (National Electric Manufacturers Association)
Who created DICOM
DICOM
▪ Backbone of every medical imaging department ▪ Pixel data cannot be separated from the description of the medical procedure which led to the formation in the image itself
meaningless
an image that is separate from its metadata becomes ____ as medical image
header
The DICOM _____ contains the most complete description of the entire procedure
.img and .hdr
Analyze extension
.nii
Nifti extension
.mnc
MINC extension
.dcm
DICOM extension
Analyze Header
Fixed-length: 348 byte binary format
Nifti Header
Fixed Length: 352 byte binary format
Minc Header
Extensible binary format
DICOM Header
Variable length binary format