Transcript Computers in Imaging - Radiation Safety Engineering, Inc.

Computers in Imaging
Robert Metzger, Ph.D.
Decimal Form (Base 10)
In general, a positional numbering system
encodes the numbers as: anbn + an-1bn-1 + . . . +
a2b2+ a1b1+ a0b0 (0 < ai < b, i = 0,1,2,...,n), where
the integer b > 1 is the radix (or base) of the
numbering system
The leftmost digit is called the most significant
digit, the rightmost the least significant digit
Whenever it is not clear which base is being used
either a subscript will be used to denote it or the
base will be written in parentheses
Decimal form (radix 10): 4210 = (4x101)+(2x100)
Binary Form (Base 2)
Powers of 2: 1, 2, 4, 8, 16, 32, 64, 128,
256, 512, 1024...
Binary form (radix 2): 1010102 =
(1x25)+(0x24)+ (1x23)+(0x22)+
1
0
(1x2 )+(0x2 ) = 3210 + 810 + 210 = 4210
Other radices used in computing Octal
(b=8) Hexadecimal (b=16; A=10, …
F=15)
4
Digital Representation of Data

Bits, Bytes and Words
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Smallest unit of storage capacity = 1 bit (binary digit:1 or 0)
Bits grouped into bytes: 8 bits = byte
Word = 16, 32 or 64 bits, depending on the computer system
addressing architecture
Computer storage capacity is measured in:
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kilobytes (kB) - 210 bytes = 1024 bytes  a thousand bytes
megabytes (MB) - 220 bytes = 1024 kilobytes  a million bytes
gigabytes (GB) - 230 bytes = 1024 megabytes  a billion bytes
terabytes (TB) - 240 bytes = 1024 gigabytes  a trillion bytes
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Digital Representation of Data

Digital Representation of Different Types of Data
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Alphanumeric text, integers, and non-integer data
Storage of Positive Integers
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In general, n bits have 2n possible permutations and can
represent integers from 0 to 2n-1 (the range usually denoted with
square brackets):
n bits represents 2n values with range [0, 2n-1]
8 bits represents 28 = 256 values with range [0, 255]
10 bits represents 210 = 1024 values with range [0, 1023]
12 bits represents 212 = 4096 values with range [0, 4095]
16 bits represents 216 = 65,536 values with range [0, 65535]
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Digital Representation of Data

Binary Representation of Signed Integers
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Floating Point Form
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For very large or very small numbers (e.g., 6.023 x 1023)
Similar to scientific notation: 0.111111112 x 2010011112
Binary Representation of Alphanumeric text
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Include the use of negative numbers
Reserve first bit for the sign (+/-): [-127,127] – one’s complement
Two’s complement: [-128, 127] – simplifies electronic circuitry
ASCII = American Standard Code for Information Interchange
ASCII code for representation of text, e.g., A = 01000001
Stored in one byte (128 characters)
Computer needs to keep track of the data type
Data Transfer

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Data are transferred between the various components of
the computer and with devices external to the computer
in binary format
A voltage of fixed value (e.g., +5V) is used to represent 1
Another voltage value (e.g., 0V) is used to represent 0
clock frequency = 1/t (usually given in MHz or GHz)
Changes between the voltage states occur through
synchronization signals from the computer’s clock 1 clock
cycle = the minimum time increment (t) at which a 1 → 0
or 0 → 1 transition can occur
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Serial vs. Parrellel
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Serial - pulses transmitted one after another over single wire
Parallel - All pulses transmitted simultaneously over several wires
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If N wires are used, parallel transmission is predominantly N times
faster than serial transmission
Bus: a bundle of wires used for parallel data transfers
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 66.
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Digital Data Transfer
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Each device connected to the bus is identified by an
address or a range of addresses
Only one device at a time can transmit data on the bus
In general only one device receives the transmitted data
The sending device transmits receiving address & data
The width of a bus refers to the number of wires used to
transmit data in parallel (e.g., 32 bits) A bus also contains
wires for ground, control signaling, etc.
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Analog and Digital
Representation of Data

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Analog: continuous waveform
where the amplitude
represents the numerical
signal magnitude
Advantages of digital:
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resistance to accumulated
errors
error correction possible with
the transmission of redundant
information
digital circuitry most often less
expensive than analog
Advantage of analog:

Often transmitted quicker
Bushberg, et al., The Essential Physics of Medical Imaging,
2nd ed., p. 67.
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Conversion of Analog Data to Digital Form
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The electronic measuring devices of medical scanners (e.g.,
transducers and detectors) produce analog signals
Analog to digital conversion (analog to digital converter – ADC)
ADCs characterized by
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sampling rate or frequency (e.g., samples/sec – 1 MHz)
number of bits output per sample (e.g., 12 bits/sample = 12-bit ADC)
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 69.
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ADC Potential Loss of Data

Sampling and quantization (digitization): loss of data (necessary
evil) Minimum sampling frequency (Nyquist limit) to accurately
represent signal Quantization error minimized through use of large
number of bits/sample
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 69.
Back to the Future
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“I think there is a world market for
maybe five computers.”
- Thomas Watson, chairman of IBM, 1943
Components & Function
of a Digital Computer
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., pp. 70 and 78.
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Main Memory
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Random access memory
(RAM): volatile
Buffer between CPU and mass
storage devices
Memory addresses where data
and instructions reside
Also read-only memory (ROM):
static
DRAM: dynamic RAM
SRAM: static RAM (cache)
VRAM: video RAM (display
card)
All RAM volatile!
Bushberg, et al., The Essential Physics of
Medical Imaging, 2nd ed., p. 71.
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Central Processing Unit
(CPU)
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CPU executes a sequence of instructions: program
A CPU contained on a single chip: microprocessor
A number of data storage locations: storage registers
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Data
Memory addresses
Arithmetic Logic Unit (ALU)
Logic operations and data transfer signaled via clock
CPU speed measured in instructions or operations per
second (e.g., MIPS or GFLOPS) and determined by:
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CPU clock rate (e.g., MHz or GHz)
Architecture (bits per instruction, e.g., 32-bit vs. 64-bit and
parallel processing capabilities)
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Central Processing Unit
(CPU)

CPU program execution
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A program is a sequence of
instructions for CPU execution
Instruction cycle - CPU fetches
the instructions from memory and
executes them sequentially
An instruction may cause the CPU
to perform one of the following:
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Mathematical operation
Transfer data
Compare
Jump to an instruction other than
the next in the sequence
Each instruction consists of two
parts: an opcode specifying the
operation to be performed and an
address
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Input-Output (I/O) Bus
and Expansion Slots
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Bus described under serial vs. parallel data transfer
Most I/O buses are provided with expansion slots to
accommodate printed circuit (PC) cards with multiple
functions, e.g.:
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Modem card → modem and video display card → video monitor
Makes it possible to customize general-purpose
computers for specific applications (e.g., MRI scanner)
and to add additional functions and capabilities (e.g.,
ADC)
I/O Ports: serial, parallel, USB (Universal Serial Bus) and
SCSI (Small Computer System Interface)
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Mass Storage Devices
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Permit the non-volatile storage of programs and data
Various formats based on:
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All consist of:
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Access time (e.g., msec or minutes): random or sequential
Data transfer rate (e.g., kbps, Mbps or Gbps)
Cost
Portability
Permanence (CD-R vs. CD-RW)
Mechanical drive
Storage medium
Controller
Hierarchical: trade-off speed vs. cost per MB
Mass Storage Devices
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 76.
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Display Interface and
Keyboard/Pointing
Devices
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Display computer information in visual form
Usually displayed on a video monitor or printed
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Video display controller/card
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Cathode ray tube (CRT)
Flat-panel display (TFT = thin-film transistors)
Receive digital data from computer memory
Store locally on card with VRAM (video RAM)
Registers to manipulate the original image or text data
DACs to convert into on-screen video image
Usually computer equipped with keyboard, mouse,
trackball or joystick (could be head-less though)
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Acquisition and
Communications
Interface
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Acquisition interface = ADC card(s), though more
efficient for the modality electronics to perform ADC
Computers also communications devices (PACS)
Modem = modulator/de-modulator (DAC - encoded
signal on wire - ADC)
Network interface card (NIC), e.g., Ethernet
Needs unique address on the network
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Phone number of modem pool, e.g., 206-685-5599
Internet Protocol (IP) address, e.g., 128.95.120.1
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Array Processor
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In the past when general-purpose CPU speeds were
slow, custom-designed hardware (array processors) to
perform compute-intense mathematical operations (e.g.,
floating point computation) were manufactured Achieved
speed through specially designed circuits to make use of
parallel processing and pipelining operation
Attaches to the computer bus for fast I/O operation
Not needed as much these days with very fast generalpurpose microprocessors with parallel processing
capabilities inherent in some operating systems
Performance of
Computer Systems
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Review
Clock speed of the CPU, e.g., 3.4GHz Pentium 4
Width and clock speed of the I/O between
Memory hierarchy, dimensions and elements
Access and transfer times of mass storage devices
MIPS, MFLOPS and benchmark testing
CPU architecture, e.g.. number of bits/instruction and
parallelism
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Computer Languages
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Machine Language
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Binary instructions to be executed by CPU requiring detailed
knowledge of the particular computer
0110101010101001001010101010001011110011110110101...)
High-Level Languages
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Program writing without detailed knowledge of the machine
This program is translated into machine language via a compiler
Include FORTRAN, Basic, Pascal, C, Java
Requires an compiler or interpreter program to translate to binary
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Heirarchy of Software
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Applications Software - programs to perform specific functions
desired by the user
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May be written in either high-level or machine language
Generally an executable program run by the OS
Hopefully user-friendly, flexible and intuitive to use
Operating System (OS) - the program that, after being initially
loaded into the computer by a boot program, manages all the other
programs in a computer
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On instruction to run a program, the OS copies it from mass storage to
memory, initiates execution of the first instruction by the CPU, transfers
control to the program and regains control on completion of the task
Handles complex I/O tasks and sharing of resources
Examples: Windows, Mac OS, Linux, UNIX
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Computer Security
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Goals
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Data Backup
Practicing “Safe Computing”
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Malicious programs exist, such as viruses, worms, Trojans, time bombs,
and password grabbers
Types of viruses: executable file, boot sector and macro infectors
Deny unauthorized users access to your system
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Deny unauthorized persons access to data
Protect programs and data from accidental or deliberate loss
Good password selection (8-14 characters, not in the dictionary of any
known language, mix of upper/lower case and numbers, and should
contain at least one non-alphanumeric character, e.g., !, @, #, %, etc.)
Firewall software/hardware, e.g., Zone Alarm or Black Ice
Grant each user only sufficient privileges required to accomplish
required tasks
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Back to the Future
“Computers in the future may weigh
 no more than 1.5 tons.”
 - Popular Mechanics, forecasting the
relentless march of science, 1949.
Digital Storage of
Images
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Usually stored as a 2D array of data, I(x,y): I(1,1), I(2,1), … I(n,m-1), I(n,m)
Typical matrices – CT: 512x512x12bits/pixel; DR: 2048x2560x10 bits/pixel
Total number of bytes/image = pixels/image ∙ bits/pixel‡ ∙ (1 byte/8 bits)
‡
aligned along byte boundaries, e.g., 12 bits/pixel  16 bits/pixel
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 71.
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Effect of Resolution and
Bits per Pixel
10242, 642, 322, 162 matrices
Bushberg, et al., The Essential Physics of Medical
Imaging, 2nd ed., p. 82.
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8, 3, 2, 1 bits/pixel
Bushberg, et al., The Essential Physics of Medical
Imaging, 2nd ed., p. 84.
Image Processing
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Addition or subtraction, e.g., digital subtraction angiography (DSA)
Spatial filtering
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Reconstruction from projections
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Smoothing (removing quantum mottle – noise)
Edge enhancement, e.g., computed radiography (CR)
Back-projection, e.g., computed tomography (CT), single photon and
positron emission tomography (SPECT and PET)
Fast Fourier Transform, e.g., magnetic resonance imaging (MRI)
Calculation of physiological performance indices, e.g., nuclear
medicine
Generation and manipulation of volumetric data sets
Image co-registration (“fusion”), e.g., CT and PET
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Back to the Future
“I have traveled the length and breadth
of this country and talked with the best
people, and I can assure you that data
processing is a fad that won't last out
the year.”
 - The editor in charge of business books
for Prentice Hall, 1957.
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Computer-Aided
Detection
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Also known as computer-aided diagnosis
Computer program that uses specific image processing
algorithms and decision threshold parameters to detect
features in an image likely to be of clinical significance in
images
Assist as a secondary reader to call attention to objects
that might have been overlooked
For example in mammography:
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Masses
Microcalcification clusters
Architectural distortions
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Image Display
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Conversion of a digital image matrix in the display card memory
(VRAM) into an analog video signal using a digital to analog
converter (DAC) Matrix digital values are scanned in raster fashion
as a function of time which through the DAC provides a time-varying
analog signal
The time-varying analog video signal is input to a video monitor
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., pp. 86 and 90.
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Gray-scale and Color
Cathode Ray Tube
Monitors
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Gray-scale monitors provide
better range of brightness and
dynamic range than COTS
color monitors
CRT elements and function
Intensity of light is proportional
to the electric current in the
beam, which is determined by
the analog voltage signal
applied from the video card
A color CRT uses three
independent electron guns
with tightly clustered red, green
and blue phosphor regions
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Flat Panel Monitors
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Most flat-panel monitors use
liquid crystal display (LCD)
technology
When voltage is applied to the
liquid crystal material it rotates
incident polarized light
This rotated light then passes
through another polarizer (90º
to the first) so that the input
voltage modulates the intensity
of fluorescent tube backlight
Active matrix LCDs are also
called thin-film transistor (TFT)
displays
Bushberg, et al., The Essential Physics of Medical
Imaging, 2nd ed., p. 89.
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Contrast Enhancement

Although there are 10-bit DACs, the human visual
system (HVS) can only distinguish 26-28 shades of gray
Thus for a 12-bit CT image, only 256 shades of gray are
visualized at any one time of the 4096 levels stored Also,
radiographic contrast may vary between objects, so
there is a need to interactively alter image contrast
Altering the contrast so that it is more optimal involves
the operation of a translation table (or look-up table –
LUT) sitting between VRAM and the DAC, allowing
displayed image contrast enhancement
Video and Level
Controls

Modification of the translation table causes changes in the displayed
image brightness and contrast and is usually done through window
(contrast) and level (brightness) controls (e.g., under mouse control)

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In the example (below), the window is kept constant as the level is
increased, causing the image to become darker and darker
The narrower the window, the greater the displayed image contrast
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 92.
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False Color Displays and
Hardcopy Devices
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The amplitude of the signals
generated in the production of
radiographic images do not
have inherent color information
When color is used to display
some aspect of the received
signal then the resulting
images are called false-color
or pseudo-color images
Example: Doppler US and NM
Multiple LUTs and DACs
Hardcopy Devices - permit the
recording of digital images on
photographic film or paper,
e.g., laser imager
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Bushberg, et al., The Essential Physics of Medical
Imaging, 2nd ed., p. 92.
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PACS and Teleradiology
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Picture Archiving and Communications Systems
Teleradiology
Standards
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Networks for Image and Data Transfer
Acquisition of Digital Images
Storage of Images
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ACR Standards for Teleradiology
Digital Imaging and Communications in Medicine (DICOM)
Data Compression
Display of images for Interpretation and Consultation
ACR Standards for
Teleradiology

Teleradiology (transmission of images for viewing at sites
remote from where they are acquired) and reporting
back ACR published the first ACR Std for Teleradiology
in 1994 with subsequent revisions in 1996, 1998 and
2002:
http://www.acr.org/departments/stand_accred/standards/pdf/teleradiology.pdfThe
ACR Standard for Teleradiology document outlines the
qualifications of personnel involved, equipment
guidelines, licensing, credentialing, and liability,
communication, quality control for teleradiology, quality
improvement and has a listing of up to date references
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DICOM (Digital Imaging
in Communications and
Medicine

Most important functions
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unambiguous definition of terms used
define models of image communication
agreed upon by those who adopt the standard
Has become the predominant standard for the
communication of medical images
Takes into account existing standards for networks
By necessity, written in dry language with a minimum of
explanatory information (thousands of pages)
Web resource: http://medical.nema.org/
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Local Area Network
(LAN)
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Topology: star, ring and bus
Protocol: Internet and Ethernet use TCP/IP = Transport
Control Protocol/Internet Protocol
Media: wire, fiber-optic and air
Ethernet
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Shared bandwidth
Switched – full duplex
10, 100, 1000 and 10,000 Mbps/sec
ATM/SONET
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Asynchronous Transfer Mode
Synchronous Optical Network
155, 622 and 2,500 Mbps
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Wide Area Network
(WAN)
Internet = LANs mesh connected with WANs all using TCP/IP
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Acquisition of Digital
Images
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Film digitization and frame grabbers (old)
DICOM modalities
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Computed Tomography (CT)
Magnetic Resonance Imaging (MRI)
Nuclear Medicine (including SPECT and PET)
Ultrasound (US)
Computed Radiography (CR)
Digital Radiography (DR)
Digital Fluoroscopy (DF)
Mammography (one digital, but mostly film)
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Storage of Images

Data Storage Technologies (redundancy and backup)
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Hierarchical Storage Management (HSM) systems
RAID: redundant array of inexpensive disks
Magneto-optic disk (MOD/EOD)
WORM optical disks
Digital Linear Tape (DLT) and other tape formats, e.g., D2, D3 ...
Data Compression

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Lossless (compression ratio < 4:1)
Lossy (compression ratio > 4:1)
10 Mbytes
4 Mbytes
2.5:1
4 Mbytes
10 Mbytes
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Display of Images for Interpretation
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Large format raster-scanned CRT and LCD (flat panel)
CRT/LCD more or less equivalent to film
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Lesser spatial resolution, greater contrast resolution (LUT)
Pixel Resolution: 1024 x 1280 (C), 1200 x 1600 (B),
1728 x 2304 (A)
Luminance: 240-280 cd/m2 vs. 1713 cd/m2 (light box)
Dynamic Range: bit depth (16-bit per pixel frame buffer)
Veiling Glare: stray ambient light reduces contrast
ROC Studies: OK for primary diagnosis
Flat panel monitors available.

1536 x 2048 pixels and 700 cd/m2
Standard Image Matrices
STANDARD IMAGE MATRICES
• NUCLEAR MEDICINE IMAGES
– 128 x 128 MATRIX
– 256 LEVELS PER PIXEL
• MRI IMAGES
– 256 x 256 MATRIX
– 4096 LEVELS PER PIXEL
• CT IMAGES
– 512 x 512 MATRIX
– 4096 LEVELS PER PIXEL
STANDARDImage
IMAGE Matrices
MATRICES
Standard
• ULTRASOUND
– 512 x 512 MATRIX
– 256 LEVELS PER PIXEL
• ANGIO & CATH IMAGES
– 1029 x 1029 MATRIX
– 4096 LEVELS PER PIXEL
• CR & DR IMAGES
– 2000 x 2000 MATRIX
– 4096 LEVELS PER IMAGE
IMAGE MODALITY
IMAGE SIZE (MB)
CT
0.5
MRI
0.125
CHEST
10.0
CR RAD
8.6 - 10.2
GI FLUORO
0.25
ANGIO --DSA & FLUORO
0.5 - 2.0
NUCLEAR MED
0.033
ULTRASOUND
0.25 (0.75 COLOR)
modality #units
#images/ #pat / yr
pat
/ unit
#GB /
year
% of all
GB data
CT
6
80
7,250
1,740
13.5 %
MRI
3
80
2,900
87
0.7 %
CHEST
4
2
14,000
1,120
8.7 %
BONE
15
6
5,800
5,220
40.4 %
8
45
2,500
1,256
9.7 %
GI
modality #units
#images/ #pat / yr
pat
/ unit
#GB /
year
% of all
GB data
ANGIO
4
700
1,500
1,800
13.9 %
IVP
2
8
1,200
192
1.5 %
RAD P
13
1
5,800
754
5.8 %
C-ARM
30
8
1,750
105
0.8 %
US
25
40
2,500
625
4.8 %
NUC
MED
6
2,250
18
0.1 %
20 - 50
OPTICAL DISK DATA
OPTICAL DISK DATA STORAGE
STORAGE
1 0
1 1
0 0
1
OPTICAL DISK HAS SURFACE
BURN HOLES WITH LASER
TO STORAGE A BINARY “1” &
NO HOLE IS A BINARY “0”
MAGNETIC
DATA
MAGNETIC DATA STORAGE
STORAGE
0
1
A COIL OF WIRE HAS A CURRENT
PASS THROUGH IT CAUSING A
MAGNETIC FIELD WHICH ALIGNS
FERROMAGNETIC PARTICLE IN
TAPE & BECOMES MAGNETIC
WHAT ABOUT DIGITAL
MAMMO?
TYPICAL IMAGE SIZE



1500 x 1500 x 12 x 2 B = ~ 60 MB / IMAGE
4 image / pat x 100 pat / day x 290 days / year
~ 7000 GB / YEAR  ENTIRE SYSTEM
CAPACITY
HOW CAN FOLDER BE MADE WITH
MULTI-MODALITY IMAGES FOR
PATIENTS
LONG-TERM STORAGE & RETRIEVAL
DIFFERENT FROM REGULAR CLINICAL
IMAGES
TRANSMISSION OF IMAGE DATA
TRANSMISSION OF
IMAGE DATA
COAXIAL CABLE WITH SIGNAL
8 BITS in
0.000001 seconds
= 1 micro-second
8,000,000 BITS /sec
= 8 Mbaud
DATA TRANSMISSION TIMES
TYPE
SPEED
(Mbytes/sec)
TIME FOR
6 Mbytes
IMAGE
56 K
MODEM
.056
857 sec
ISDN
LINE
.128
375 sec
T1 LINE
1.540
31 sec
OPTICAL
FIBER &
COAXIAL
100.0
0.48 sec
GB LINE
1,000.0
0.05 sec
CR CASSETTE & PLATE
INSPECT FOR EXTERNAL
DAMAGE
INSPECT PLATE
CLEAN PLATE
BAR CODE ON
CASSETTE
SMOOTH OPEN / CLOSE
NO ARTIFACTS ON
PLATE
PLATE EDGES &
ALIGNMENT
FILM CHARACTERISTIC
CURVE
4
3.5
maximum density
FILM DENSITY [O.D.]
3
contrast ratio =
1000 µR / 20 µR
=50:1
2.5
2
1.5
1
low density
0.5
0
1
10
100
EXPOSURE [µR/frame]
1000
10000
DYNAMIC RANGE OF AN
IMAGING SYSTEM
FILM-SCREEN SYSTEMS
MAX DENSITY = 1000 R
= 50
MIN DENSITY = 20 R
DIGITAL SYSTEMS LIKE CR
MAX VALUE = 100,000 R
MIN VALUE = 10 R
= 10,000
SPATIAL RESOLUTION
# PIXELS / [ 2 x FoV (mm) ]
= 2500 PIXELS / [ 2 x 430 mm ]
= 2.9 LINE PAIRS PER mm
“FILM HAS ABOUT 6 - 8 LP / mm”
TYPE OF
PSP
CASSETTE
MATRIX
SIZE
PIXEL
SIZE
(mm)
SPATIAL
RESOLUTION
(LP/mm)
35 x 43 cm
GP-25
2048 x
2500
0.17
2.9
24 x 30 cm
GP-25
2048 x
2500
0.12
4.2
18 x 24 cm
GP-25
1792 x
2392
0.10
<5.0
18 x 24 cm
HR
1792 x
2392
0.10
~5.0
IMAGE RETRIEVAL
SPEEDS
DEPENDS UPON SYSTEM TRAFFIC
SHOULD BE EVALUATED DURING
ACCEPTANCE TESTING
TYPICAL SPEED FOR CR IMAGES FROM
RAID STORAGE ABOUT 5 -15 SECONDS
PER IMAGE
TYPICAL SPEED FOR CR IMAGES FROM
DLT LONG TERM STORAGE ABOUT 5 - 10
MINUTES --- IF TAPE ON-LINE
MAJOR SYSTEM PROBLEMS
FAILURE OF RAID DRIVES
CASSETTE DAMAGE FROM USE WITH MOBILE X-RAY
MONITOR INTENSITY DEGRADATION WITH AGE --- 1 - 2
YEAR REPLACEMENT
FAILURE OF CR ERASURE LIGHT SOURCES
CR READER MECHANICAL MISALIGNMENTS
NETWORK INTERRUPTS
LOST OR DUPLICATE IMAGE DUE TO TYPO’s
OPERATOR LACK OF FAMILIARITY ISSUES
INITIAL AEC & TECHNIQUE CHART SET-UP
E.I.# = 1000 x LOG10 [EXPOSURE in mR] + 2000
(Kodak)
INPUT TO CASSETTE TYPICALLY SET AT 1.0 mR for
AEC → 150 - 200 RELATIVE FILM-SCREEN SPEED
WE USE 0.8 - 0.85 mR
ADDED 1.0 mm Al FILTERS TO X-RAY TUBES
RAISE CLINICAL TECHNIQUE ABOUT +10 kVp
RESULTS: (1) CLINICAL NOISE & CONTRAST ABOUT
THE SAME, (2) PATIENT DOSES EQUALENT TO 250 300 FILM-SCREEN SPEEDS
66
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