computers in imaging

Computers in Imaging

Robert Metzger, Ph.D.

Decimal Form (Base 10)

In general, a In general, a positional numbering systempositional numbering system encodes the numbers as: encodes the numbers as: aannbbnn + a + an-1n-1bb

n-1n-1 + . . . + + . . . + aa22bb

22+ a+ a11bb11+ a+ a00bb

00 (0 (0 << a aii < b, i = 0,1,2,...,n), where the < b, i = 0,1,2,...,n), where the integer b > 1 is the radix (or base) of the integer b > 1 is the radix (or base) of the numbering system numbering system The leftmost digit is called the The leftmost digit is called the most significant most significant digitdigit, the rightmost the , the rightmost the least significant digit least significant digit Whenever it is not clear which base is being used Whenever it is not clear which base is being used either a subscript will be used to denote it or the either a subscript will be used to denote it or the base will be written in parentheses base will be written in parentheses

Decimal form (radix 10): 42Decimal form (radix 10): 421010 = (4x10 = (4x1011)+(2x10)+(2x1000) )

Binary Form (Base 2)

Powers of 2: 1, 2, 4, 8, 16, 32, 64, 128, Powers of 2: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024... 256, 512, 1024...

Binary form (radix 2): 101010Binary form (radix 2): 10101022 = = (1x2(1x255)+(0x2)+(0x244)+ (1x2)+ (1x233)+(0x2)+(0x222)+ )+ (1x2(1x211)+(0x2)+(0x200) = 32) = 3210 10 + 8+ 810 10 + 2+ 21010 = 42 = 421010

Other radices used in computing Octal Other radices used in computing Octal (b=8) Hexadecimal (b=16; A=10, … (b=8) Hexadecimal (b=16; A=10, … F=15) F=15)

Digital Representation of Data

44

Bits, Bytes and Words Bits, Bytes and Words Smallest unit of storage capacity = 1 bit (Smallest unit of storage capacity = 1 bit (bbinary diginary digitit:1 or 0) :1 or 0) Bits grouped into bytes: 8 bits = byte Bits grouped into bytes: 8 bits = byte Word = 16, 32 or 64 bits, depending on the computer system Word = 16, 32 or 64 bits, depending on the computer system

addressing architecture addressing architecture

Computer storage capacity is measured in: Computer storage capacity is measured in: kilobytes (kB) - 2kilobytes (kB) - 21010 bytes = 1024 bytes bytes = 1024 bytes a thousand bytes a thousand bytes megabytes (MB) - 2megabytes (MB) - 22020 bytes = 1024 kilobytes bytes = 1024 kilobytes a million bytes a million bytes gigabytes (GB) - 2gigabytes (GB) - 23030 bytes = 1024 megabytes bytes = 1024 megabytes a billion bytes a billion bytes terabytes (TB) - 2terabytes (TB) - 24040 bytes = 1024 gigabytes bytes = 1024 gigabytes a trillion bytes a trillion bytes


55

Digital Representation of Different Types of Data Digital Representation of Different Types of Data Alphanumeric text, integers, and non-integer data Alphanumeric text, integers, and non-integer data

Storage of Positive Integers Storage of Positive Integers In general, n bits have 2In general, n bits have 2nn possible permutations and can possible permutations and can

represent integers from 0 to 2represent integers from 0 to 2nn-1 (the range usually denoted with -1 (the range usually denoted with square brackets): square brackets):

n bits represents 2n bits represents 2nn values with range [0, 2 values with range [0, 2nn-1] -1] 8 bits represents 28 bits represents 288 = 256 values with range [0, 255] = 256 values with range [0, 255] 10 bits represents 210 bits represents 21010 = 1024 values with range [0, 1023] = 1024 values with range [0, 1023] 12 bits represents 212 bits represents 21212 = 4096 values with range [0, 4095] = 4096 values with range [0, 4095] 16 bits represents 216 bits represents 21616 = 65,536 values with range [0, 65535] = 65,536 values with range [0, 65535]


66

Binary Representation of Signed Integers Binary Representation of Signed Integers Include the use of negative numbers Include the use of negative numbers Reserve first bit for the sign (+/-): [-127,127] – one’s complement Reserve first bit for the sign (+/-): [-127,127] – one’s complement Two’s complement: [-128, 127] – simplifies electronic circuitry Two’s complement: [-128, 127] – simplifies electronic circuitry

Floating Point Form Floating Point Form For very large or very small numbers (e.g., 6.023 x 10For very large or very small numbers (e.g., 6.023 x 102323) ) Similar to scientific notation: 0.11111111Similar to scientific notation: 0.1111111122 x 2 x 20100111101001111

2 2

Binary Representation of Alphanumeric text Binary Representation of Alphanumeric text ASCII = American Standard Code for Information Interchange ASCII = American Standard Code for Information Interchange ASCII code for representation of text, e.g., A = 01000001 ASCII code for representation of text, e.g., A = 01000001 Stored in one byte (128 characters) Stored in one byte (128 characters)

Computer needs to keep track of the data typeComputer needs to keep track of the data type

Data Transfer Data are transferred between the various components of Data are transferred between the various components of

the computer and with devices external to the computer the computer and with devices external to the computer in binary format in binary format

A voltage of fixed value (e.g., +5V) is used to represent 1 A voltage of fixed value (e.g., +5V) is used to represent 1 Another voltage value (e.g., 0V) is used to represent 0 Another voltage value (e.g., 0V) is used to represent 0 clock frequency = 1/clock frequency = 1/ (usually given in MHz or GHz) (usually given in MHz or GHz)

Changes between the voltage states occur through Changes between the voltage states occur through synchronization signals from the computer’s clock 1 clock synchronization signals from the computer’s clock 1 clock cycle = the minimum time increment (cycle = the minimum time increment () at which a 1 → 0 ) at which a 1 → 0 or 0 → 1 transition can occur or 0 → 1 transition can occur

Serial vs. Parrellel

88

Serial - pulses transmitted one after another over single wire Serial - pulses transmitted one after another over single wire Parallel - All pulses transmitted simultaneously over several wires Parallel - All pulses transmitted simultaneously over several wires

If N wires are used, parallel transmission is predominantly N times faster If N wires are used, parallel transmission is predominantly N times faster than serial transmission than serial transmission

Bus: a bundle of wires used for parallel data transfersBus: a bundle of wires used for parallel data transfers

Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 66.Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 66.

Digital Data Transfer

99

Each device connected to the bus is identified by an Each device connected to the bus is identified by an address or a range of addresses address or a range of addresses

Only one device at a time can transmit data on the bus Only one device at a time can transmit data on the bus In general only one device receives the transmitted data In general only one device receives the transmitted data The sending device transmits receiving address & data The sending device transmits receiving address & data

The width of a bus refers to the number of wires used to 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 transmit data in parallel (e.g., 32 bits) A bus also contains wires for ground, control signaling, etc.wires for ground, control signaling, etc.

1010

Analog and Digital Analog and Digital Representation of DataRepresentation of Data

Analog: continuous waveform Analog: continuous waveform where the amplitude where the amplitude represents the numerical represents the numerical signal magnitude signal magnitude

Advantages of digital: Advantages of digital: resistance to accumulated resistance to accumulated

errors errors error correction possible with error correction possible with

the transmission of redundant the transmission of redundant information information

digital circuitry most often less digital circuitry most often less expensive than analog expensive than analog

Advantage of analog: Advantage of analog: Often transmitted quickerOften transmitted quicker

Bushberg, et al., The Essential Physics of Medical Imaging, Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 67.2nd ed., p. 67.

1111

Conversion of Analog Data to Digital FormConversion of Analog Data to Digital Form

The electronic measuring devices of medical scanners (e.g., The electronic measuring devices of medical scanners (e.g., transducers and detectors) produce analog signals transducers and detectors) produce analog signals

Analog to digital conversion (analog to digital converter – ADC) Analog to digital conversion (analog to digital converter – ADC) ADCs characterized by ADCs characterized by

sampling rate or frequency (e.g., samples/sec – 1 MHz) sampling rate or frequency (e.g., samples/sec – 1 MHz) number of bits output per sample (e.g., 12 bits/sample = 12-bit ADC)number of bits output per sample (e.g., 12 bits/sample = 12-bit ADC)


1212

Sampling and quantization (digitization): loss of data (necessary Sampling and quantization (digitization): loss of data (necessary evil) Minimum sampling frequency (Nyquist limit) to accurately evil) Minimum sampling frequency (Nyquist limit) to accurately represent signal Quantization error minimized through use of large represent signal Quantization error minimized through use of large number of bits/sample number of bits/sample


ADC Potential Loss of DataADC Potential Loss of Data

Back to the Future1313

““I think there is a world market for I think there is a world market for maybe five computers.” maybe five computers.”

- Thomas Watson, chairman of IBM, 1943- Thomas Watson, chairman of IBM, 1943

Components & Function of a Digital Computer

1414

Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., pp. 70 and 78.Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., pp. 70 and 78.

Main Memory1515

Random access memory Random access memory (RAM): volatile (RAM): volatile

Buffer between CPU and mass Buffer between CPU and mass storage devices storage devices

Memory addresses where data Memory addresses where data and instructions reside and instructions reside

Also read-only memory Also read-only memory (ROM): static (ROM): static

DRAM: dynamic RAM DRAM: dynamic RAM SRAM: static RAM (cache) SRAM: static RAM (cache) VRAM: video RAM (display VRAM: video RAM (display

card) card) All RAM volatile!All RAM volatile!

Bushberg, et al., The Essential Physics of Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 71.Medical Imaging, 2nd ed., p. 71.

Central Processing Unit (CPU)

1616

CPU executes a sequence of instructions: program CPU executes a sequence of instructions: program A CPU contained on a single chip: microprocessor A CPU contained on a single chip: microprocessor A number of data storage locations: storage registers A number of data storage locations: storage registers

Data Data Memory addresses Memory addresses

Arithmetic Logic Unit (ALU) Arithmetic Logic Unit (ALU) Logic operations and data transfer signaled via clock Logic operations and data transfer signaled via clock CPU speed measured in instructions or operations per CPU speed measured in instructions or operations per

second (e.g., MIPS or GFLOPS) and determined by: second (e.g., MIPS or GFLOPS) and determined by: CPU clock rate (e.g., MHz or GHz) CPU clock rate (e.g., MHz or GHz) Architecture (bits per instruction, e.g., 32-bit vs. 64-bit and Architecture (bits per instruction, e.g., 32-bit vs. 64-bit and

parallel processing capabilities) parallel processing capabilities)

Central Processing Unit (CPU)

1717

CPU program execution CPU program execution A program is a sequence of A program is a sequence of

instructions for CPU execution instructions for CPU execution Instruction cycle - CPU fetches Instruction cycle - CPU fetches

the instructions from memory and the instructions from memory and executes them sequentially executes them sequentially

An instruction may cause the CPU An instruction may cause the CPU to perform one of the following: to perform one of the following:

Mathematical operation Mathematical operation Transfer data Transfer data Compare Compare Jump to an instruction other than Jump to an instruction other than

the next in the sequence the next in the sequence Each instruction consists of two Each instruction consists of two

parts: an opcode specifying the parts: an opcode specifying the operation to be performed and an operation to be performed and an addressaddress

Input-Output (I/O) Bus and Expansion Slots

1818

Bus described under serial vs. parallel data transfer Bus described under serial vs. parallel data transfer Most I/O buses are provided with expansion slots to Most I/O buses are provided with expansion slots to

accommodate printed circuit (PC) cards with multiple accommodate printed circuit (PC) cards with multiple functions, e.g.: functions, e.g.: Modem card Modem card → modem and v→ modem and video display card ideo display card → video monitor→ video monitor

Makes it possible to customize general-purpose Makes it possible to customize general-purpose computers for specific applications (e.g., MRI scanner) computers for specific applications (e.g., MRI scanner) and to add additional functions and capabilities (e.g., and to add additional functions and capabilities (e.g., ADC) ADC)

I/O Ports: serial, parallel, USB (Universal Serial Bus) and I/O Ports: serial, parallel, USB (Universal Serial Bus) and SCSI (Small Computer System Interface)SCSI (Small Computer System Interface)

Mass Storage Devices1919

Permit the non-volatile storage of programs and data Permit the non-volatile storage of programs and data Various formats based on: Various formats based on:

Access time (e.g., msec or minutes): random or sequential Access time (e.g., msec or minutes): random or sequential Data transfer rate (e.g., kbps, Mbps or Gbps) Data transfer rate (e.g., kbps, Mbps or Gbps) Cost Cost Portability Portability Permanence (CD-R vs. CD-RW) Permanence (CD-R vs. CD-RW)

All consist of: All consist of: Mechanical drive Mechanical drive Storage medium Storage medium Controller Controller

Hierarchical: trade-off speed vs. cost per MB Hierarchical: trade-off speed vs. cost per MB

Mass Storage Devices 2020


Display Interface and Keyboard/Pointing Devices

2121

Display computer information in visual form Display computer information in visual form Usually displayed on a video monitor or printed Usually displayed on a video monitor or printed

Cathode ray tube (CRT) Cathode ray tube (CRT) Flat-panel display (TFT = thin-film transistors) Flat-panel display (TFT = thin-film transistors)

Video display controller/card Video display controller/card Receive digital data from computer memory Receive digital data from computer memory Store locally on card with VRAM (video RAM) Store locally on card with VRAM (video RAM) Registers to manipulate the original image or text data Registers to manipulate the original image or text data DACs to convert into on-screen video image DACs to convert into on-screen video image

Usually computer equipped with keyboard, mouse, Usually computer equipped with keyboard, mouse, trackball or joystick (could be head-less though)trackball or joystick (could be head-less though)

Acquisition and Communications Interface

2222

Acquisition interface = ADC card(s), though more Acquisition interface = ADC card(s), though more efficient for the modality electronics to perform ADC efficient for the modality electronics to perform ADC

Computers also communications devices (PACS) Computers also communications devices (PACS) Modem = modulator/de-modulator (DAC - encoded Modem = modulator/de-modulator (DAC - encoded

signal on wire - ADC) signal on wire - ADC) Network interface card (NIC), e.g., Ethernet Network interface card (NIC), e.g., Ethernet Needs unique address on the network Needs unique address on the network

Phone number of modem pool, e.g., 206-685-5599 Phone number of modem pool, e.g., 206-685-5599 Internet Protocol (IP) address, e.g., 128.95.120.1Internet Protocol (IP) address, e.g., 128.95.120.1

Array Processor

2323

In the past when general-purpose CPU speeds were In the past when general-purpose CPU speeds were slow, custom-designed hardware (array processors) to slow, custom-designed hardware (array processors) to perform compute-intense mathematical operations (e.g., perform compute-intense mathematical operations (e.g., floating point computation) were manufactured Achieved floating point computation) were manufactured Achieved speed through specially designed circuits to make use of speed through specially designed circuits to make use of parallel processing and pipelining operation parallel processing and pipelining operation

Attaches to the computer bus for fast I/O operationAttaches to the computer bus for fast I/O operation Not needed as much these days with very fast general-Not needed as much these days with very fast general-

purpose microprocessors with parallel processing purpose microprocessors with parallel processing capabilities inherent in some operating systemscapabilities inherent in some operating systems

Performance of Computer Systems

2424

Review Review Clock speed of the CPU, e.g., 3.4GHz Pentium 4 Clock speed of the CPU, e.g., 3.4GHz Pentium 4 Width and clock speed of the I/O between Width and clock speed of the I/O between Memory hierarchy, dimensions and elements Memory hierarchy, dimensions and elements Access and transfer times of mass storage devices Access and transfer times of mass storage devices MIPS, MFLOPS and benchmark testingMIPS, MFLOPS and benchmark testing CPU architecture, e.g.. number of bits/instruction and CPU architecture, e.g.. number of bits/instruction and

parallelismparallelism

Computer Languages2525

Machine Language Machine Language Binary instructions to be executed by CPU requiring detailed Binary instructions to be executed by CPU requiring detailed

knowledge of the particular computer knowledge of the particular computer 0110101010101001001010101010001011110011110110101...) 0110101010101001001010101010001011110011110110101...)

High-Level Languages High-Level Languages Program writing without detailed knowledge of the machine Program writing without detailed knowledge of the machine This program is translated into machine language via a compiler This program is translated into machine language via a compiler Include FORTRAN, Basic, Pascal, C, Java Include FORTRAN, Basic, Pascal, C, Java Requires an Requires an compilercompiler or or interpreterinterpreter program to translate to program to translate to

binary binary

Heirarchy of Software2626

Applications Software - programs to perform specific functions Applications Software - programs to perform specific functions desired by the user desired by the user May be written in either high-level or machine language May be written in either high-level or machine language Generally an executable program run by the OS Generally an executable program run by the OS Hopefully user-friendly, flexible and intuitive to use Hopefully user-friendly, flexible and intuitive to use

Operating System (OS) - the program that, after being initially Operating System (OS) - the program that, after being initially loaded into the computer by a boot program, manages all the other loaded into the computer by a boot program, manages all the other programs in a computer programs in a computer On instruction to run a program, the OS copies it from mass storage to 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 memory, initiates execution of the first instruction by the CPU, transfers control to the program and regains control on completion of the task control to the program and regains control on completion of the task

Handles complex I/O tasks and sharing of resources Handles complex I/O tasks and sharing of resources Examples: Windows, Mac OS, Linux, UNIXExamples: Windows, Mac OS, Linux, UNIX

Computer Security2727

Goals Goals Deny unauthorized persons access to data Deny unauthorized persons access to data Protect programs and data from accidental or deliberate loss Protect programs and data from accidental or deliberate loss

Data Backup Data Backup Practicing “Safe Computing” Practicing “Safe Computing”

Malicious programs exist, such as viruses, worms, Trojans, time bombs, Malicious programs exist, such as viruses, worms, Trojans, time bombs, and password grabbers and password grabbers

Types of viruses: executable file, boot sector and macro infectors Types of viruses: executable file, boot sector and macro infectors Deny unauthorized users access to your system Deny unauthorized users access to your system

Good password selection (8-14 characters, not in the dictionary of any Good password selection (8-14 characters, not in the dictionary of any known language, mix of upper/lower case and numbers, and should known language, mix of upper/lower case and numbers, and should contain at least one non-alphanumeric character, e.g., !, @, #, %, etc.) contain at least one non-alphanumeric character, e.g., !, @, #, %, etc.)

Firewall software/hardware, e.g., Zone Alarm or Black Ice Firewall software/hardware, e.g., Zone Alarm or Black Ice Grant each user only sufficient privileges required to accomplish Grant each user only sufficient privileges required to accomplish

required tasksrequired tasks


““Computers in the future may weigh Computers in the future may weigh no more than 1.5 tons.” no more than 1.5 tons.”

- Popular Mechanics, forecasting the - Popular Mechanics, forecasting the relentless march of science, 1949.relentless march of science, 1949.

Digital Storage of Images2929

Usually stored as a 2D array of data, I(x,y): I(1,1), I(2,1), … I(n,m-1), I(n,m) 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 Typical matrices – CT: 512x512x12bits/pixel; DR: 2048x2560x10 bits/pixel Total number of bytes/image = pixels/image ∙ bits/pixelTotal number of bytes/image = pixels/image ∙ bits/pixel‡‡ ∙ (1 byte/8 bits) ∙ (1 byte/8 bits) ‡‡ aligned along byte boundaries, e.g., 12 bits/pixel aligned along byte boundaries, e.g., 12 bits/pixel 16 bits/pixel 16 bits/pixel


Effect of Resolution and Bits per Pixel

3030

Bushberg, et al., The Essential Physics of Medical Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 82.Imaging, 2nd ed., p. 82.


1024102422, 64, 6422, 32, 3222, 16, 1622 matrices matrices 8, 3, 2, 1 bits/pixel8, 3, 2, 1 bits/pixel

Image Processing 3131

Addition or subtraction, e.g., digital subtraction angiography (DSA) Addition or subtraction, e.g., digital subtraction angiography (DSA) Spatial filtering Spatial filtering

Smoothing (removing quantum mottle – noise) Smoothing (removing quantum mottle – noise) Edge enhancement, e.g., computed radiography (CR) Edge enhancement, e.g., computed radiography (CR)

Reconstruction from projections Reconstruction from projections Back-projection, e.g., computed tomography (CT), single photon and Back-projection, e.g., computed tomography (CT), single photon and

positron emission tomography (SPECT and PET) positron emission tomography (SPECT and PET) Fast Fourier Transform, e.g., magnetic resonance imaging (MRI) Fast Fourier Transform, e.g., magnetic resonance imaging (MRI)

Calculation of physiological performance indices, e.g., nuclear Calculation of physiological performance indices, e.g., nuclear medicine medicine

Generation and manipulation of volumetric data sets Generation and manipulation of volumetric data sets Image co-registration (“fusion”), e.g., CT and PETImage co-registration (“fusion”), e.g., CT and PET


““I have traveled the length and breadth I have traveled the length and breadth of this country and talked with the best of this country and talked with the best people, and I can assure you that data people, and I can assure you that data processing is a fad that won't last out processing is a fad that won't last out

the year.” the year.” - The editor in charge of business books - The editor in charge of business books

for Prentice Hall, 1957.for Prentice Hall, 1957.

Computer-Aided Detection3333

Also known as computer-aided diagnosis Also known as computer-aided diagnosis Computer program that uses specific image processing Computer program that uses specific image processing

algorithms and decision threshold parameters to detect algorithms and decision threshold parameters to detect features in an image likely to be of clinical significance in features in an image likely to be of clinical significance in images images

Assist as a secondary reader to call attention to objects Assist as a secondary reader to call attention to objects that might have been overlooked that might have been overlooked

For example in mammography: For example in mammography: Masses Masses Microcalcification clusters Microcalcification clusters Architectural distortionsArchitectural distortions

Image Display 3434

Conversion of a digital image matrix in the display card memory Conversion of a digital image matrix in the display card memory (VRAM) into an analog video signal using a digital to analog (VRAM) into an analog video signal using a digital to analog converter (DAC) Matrix digital values are scanned in raster fashion converter (DAC) Matrix digital values are scanned in raster fashion as a function of time which through the DAC provides a time-varying as a function of time which through the DAC provides a time-varying analog signal analog signal

The time-varying analog video signal is input to a video monitorThe 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.Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., pp. 86 and 90.

Gray-scale and Color Cathode Ray Tube

Monitors

3535

Gray-scale monitors provide Gray-scale monitors provide better range of brightness and better range of brightness and dynamic range than COTS dynamic range than COTS color monitors color monitors

CRT elements and function CRT elements and function Intensity of light is proportional Intensity of light is proportional

to the electric current in the to the electric current in the beam, which is determined by beam, which is determined by the analog voltage signal the analog voltage signal applied from the video card applied from the video card

A color CRT uses three A color CRT uses three independent electron guns with independent electron guns with tightly clustered red, green and tightly clustered red, green and blue phosphor regionsblue phosphor regions

Flat Panel Monitors3636

Most flat-panel monitors use Most flat-panel monitors use liquid crystal display (LCD) liquid crystal display (LCD) technology technology

When voltage is applied to the When voltage is applied to the liquid crystal material it rotates liquid crystal material it rotates incident polarized light incident polarized light

This rotated light then passes This rotated light then passes through another polarizer (90through another polarizer (90ºº to the first) so that the input to the first) so that the input voltage modulates the intensity voltage modulates the intensity of fluorescent tube backlight of fluorescent tube backlight

Active matrix LCDs are also Active matrix LCDs are also called thin-film transistor (TFT) called thin-film transistor (TFT) displaysdisplays


Contrast Enhancement3737

Although there are 10-bit DACs, the human visual Although there are 10-bit DACs, the human visual system (HVS) can only distinguish 2system (HVS) can only distinguish 266-2-288 shades of gray shades of gray Thus for a 12-bit CT image, only 256 shades of gray are Thus for a 12-bit CT image, only 256 shades of gray are visualized at any one time of the 4096 levels stored Also, visualized at any one time of the 4096 levels stored Also, radiographic contrast may vary between objects, so radiographic contrast may vary between objects, so there is a need to interactively alter image contrast there is a need to interactively alter image contrast Altering the contrast so that it is more optimal involves Altering the contrast so that it is more optimal involves the operation of a translation table (or look-up table – the operation of a translation table (or look-up table – LUT) sitting between VRAM and the DAC, allowing LUT) sitting between VRAM and the DAC, allowing displayed image contrast enhancementdisplayed image contrast enhancement

Video and Level Controls3838

Modification of the translation table causes changes in the displayed Modification of the translation table causes changes in the displayed image brightness and contrast and is usually done through window image brightness and contrast and is usually done through window (contrast) and level (brightness) controls (e.g., under mouse control) (contrast) and level (brightness) controls (e.g., under mouse control) In the example (below), the window is kept constant as the level is In the example (below), the window is kept constant as the level is

increased, causing the image to become darker and darker increased, causing the image to become darker and darker The narrower the window, the greater the displayed image contrastThe narrower the window, the greater the displayed image contrast


False Color Displays and Hardcopy Devices

3939

The amplitude of the signals The amplitude of the signals generated in the production of generated in the production of radiographic images do not radiographic images do not have inherent color information have inherent color information

When color is used to display When color is used to display some aspect of the received some aspect of the received signal then the resulting signal then the resulting images are called false-color images are called false-color or pseudo-color images or pseudo-color images

Example: Doppler US and NM Example: Doppler US and NM Multiple LUTs and DACs Multiple LUTs and DACs Hardcopy Devices - permit the Hardcopy Devices - permit the

recording of digital images on recording of digital images on photographic film or paper, photographic film or paper, e.g., laser imagere.g., laser imager Bushberg, et al., The Essential Physics of Medical Bushberg, et al., The Essential Physics of Medical

Imaging, 2nd ed., p. 92.Imaging, 2nd ed., p. 92.

PACS and Teleradiology4040

Picture Archiving and Communications Systems Picture Archiving and Communications Systems Teleradiology Teleradiology Standards Standards

ACR Standards for Teleradiology ACR Standards for Teleradiology Digital Imaging and Communications in Medicine (DICOM) Digital Imaging and Communications in Medicine (DICOM)

Networks for Image and Data Transfer Networks for Image and Data Transfer Acquisition of Digital Images Acquisition of Digital Images Storage of Images Storage of Images

Data Compression Data Compression

Display of images for Interpretation and ConsultationDisplay of images for Interpretation and Consultation

ACR Standards for Teleradiology

4141

Teleradiology (transmission of images for viewing at Teleradiology (transmission of images for viewing at sites remote from where they are acquired) and reporting sites remote from where they are acquired) and reporting back ACR published the first ACR Std for Teleradiology back ACR published the first ACR Std for Teleradiology in 1994 with subsequent revisions in 1996, 1998 and in 1994 with subsequent revisions in 1996, 1998 and 2002: 2002: http://www.acr.org/departments/stand_accred/standards/pdf/teleradiology.

pdfThe ACR Standard for Teleradiology document The ACR Standard for Teleradiology document outlines the qualifications of personnel involved, outlines the qualifications of personnel involved, equipment guidelines, licensing, credentialing, and equipment guidelines, licensing, credentialing, and liability, communication, quality control for teleradiology, liability, communication, quality control for teleradiology, quality improvement and has a listing of up to date quality improvement and has a listing of up to date referencesreferences

DICOM (Digital Imaging in Communications and

Medicine

4242

Most important functions Most important functions unambiguous definition of terms used unambiguous definition of terms used define models of image communication define models of image communication agreed upon by those who adopt the standard agreed upon by those who adopt the standard

Has become the predominant standard for the Has become the predominant standard for the communication of medical images communication of medical images

Takes into account existing standards for networks Takes into account existing standards for networks By necessity, written in dry language with a minimum of By necessity, written in dry language with a minimum of

explanatory information (thousands of pages) explanatory information (thousands of pages) Web resource: Web resource: http://medical.nema.org/

Local Area Network (LAN)4343

Topology: star, ring and bus Topology: star, ring and bus Protocol: Internet and Ethernet use TCP/IP = Transport Protocol: Internet and Ethernet use TCP/IP = Transport

Control Protocol/Internet Protocol Control Protocol/Internet Protocol Media: wire, fiber-optic and air Media: wire, fiber-optic and air Ethernet Ethernet

Shared bandwidth Shared bandwidth Switched – full duplex Switched – full duplex 10, 100, 1000 and 10,000 Mbps/sec 10, 100, 1000 and 10,000 Mbps/sec

ATM/SONET ATM/SONET Asynchronous Transfer Mode Asynchronous Transfer Mode Synchronous Optical Network Synchronous Optical Network 155, 622 and 2,500 Mbps155, 622 and 2,500 Mbps

Wide Area Network (WAN)4444

Internet = LANs mesh connected with WANs all using TCP/IP Internet = LANs mesh connected with WANs all using TCP/IP

Acquisition of Digital Images

4545

Film digitization and frame grabbers (old) Film digitization and frame grabbers (old) DICOM modalities DICOM modalities

Computed Tomography (CT) Computed Tomography (CT) Magnetic Resonance Imaging (MRI) Magnetic Resonance Imaging (MRI) Nuclear Medicine (including SPECT and PET) Nuclear Medicine (including SPECT and PET) Ultrasound (US) Ultrasound (US) Computed Radiography (CR) Computed Radiography (CR) Digital Radiography (DR) Digital Radiography (DR) Digital Fluoroscopy (DF) Digital Fluoroscopy (DF)

Mammography (one digital, but mostly film)Mammography (one digital, but mostly film)

Storage of Images4646

Data Storage Technologies (redundancy and backup) Data Storage Technologies (redundancy and backup) Hierarchical Storage Management (HSM) systems Hierarchical Storage Management (HSM) systems RAID: redundant array of inexpensive disks RAID: redundant array of inexpensive disks Magneto-optic disk (MOD/EOD) Magneto-optic disk (MOD/EOD) WORM optical disks WORM optical disks Digital Linear Tape (DLT) and other tape formats, e.g., D2, D3 ... Digital Linear Tape (DLT) and other tape formats, e.g., D2, D3 ...

Data Compression Data Compression Lossless (compression ratio < 4:1) Lossless (compression ratio < 4:1) Lossy (compression ratio > 4:1)Lossy (compression ratio > 4:1)

10 Mbytes 4 Mbytes

2.5:1

10 Mbytes4 Mbytes

Display of Images for InterpretationDisplay of Images for Interpretation

4747

Large format raster-scanned CRT and LCD (flat panel) Large format raster-scanned CRT and LCD (flat panel) CRT/LCD more or less equivalent to film CRT/LCD more or less equivalent to film

Lesser spatial resolution, greater contrast resolution (LUT) Lesser spatial resolution, greater contrast resolution (LUT) Pixel Resolution: 1024 x 1280 (C), 1200 x 1600 (B), Pixel Resolution: 1024 x 1280 (C), 1200 x 1600 (B),

1728 x 2304 (A) 1728 x 2304 (A) Luminance: 240-280 cd/mLuminance: 240-280 cd/m22 vs. 1713 cd/m vs. 1713 cd/m22 (light box) (light box) Dynamic Range: bit depth (16-bit per pixel frame buffer) Dynamic Range: bit depth (16-bit per pixel frame buffer) Veiling Glare: stray ambient light reduces contrast Veiling Glare: stray ambient light reduces contrast ROC Studies: OK for primary diagnosis ROC Studies: OK for primary diagnosis Flat panel monitors available. Flat panel monitors available.

1536 x 2048 pixels and 700 cd/m1536 x 2048 pixels and 700 cd/m22

Standard Image Matrices

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#pat /

yr / unit#images/

pat#GB / year

% of all GB data

CT 6 80 7,250 1,740

MRI 3 80 2,900 87

CHEST 4 2 14,000 1,120

BONE 15 6 5,800 5,220

GI 8 45 2,500 1,256

13.5 %

0.7 %

8.7 %

40.4 %

9.7 %

4 700 1,500 1,800

2 8 1,200 192

13 1 5,800 754

30 8 1,750 105

25 40 2,500 625

ANGIO

IVP

RAD P

C-ARM

US

NUC MED

6 20 - 50 2,250 18

13.9 %

1.5 %

5.8 %

0.8 %

4.8 %

0.1 %

modality #units#pat /

yr / unit#images/

pat#GB / year

% of all GB data

OPTICAL DISK DATA STORAGE

MAGNETIC DATA STORAGE

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 PATIENTSLONG-TERM STORAGE & RETRIEVAL DIFFERENT FROM REGULAR CLINICAL IMAGES

TRANSMISSION OF IMAGE DATA

DATA TRANSMISSION TIMES

TYPE SPEED (Mbytes/sec)

TIME FOR6 Mbytes IMAGE

56 K MODEM

.056

857 sec

T1 LINE

1.540

31 sec

GB LINE

1,000.0

0.05 sec

COAXIAL

OPTICALFIBER & 100.0 0.48 sec

ISDNLINE

.128 375 sec

CR CASSETTE & PLATE

INSPECT FOR EXTERNAL DAMAGEINSPECT PLATECLEAN PLATEBAR CODE ON CASSETTESMOOTH OPEN / CLOSENO ARTIFACTS ON PLATEPLATE EDGES & ALIGNMENT

0

0.5

1

1.5

2

2.5

3

3.5

4

1 10 100 1000 10000

EXPOSURE [µR/frame]

FIL

M D

EN

SIT

Y [

O.D

.] contrast ratio =1000 µR / 20 µR =50:1

low density

maximum density

FILM CHARACTERISTIC CURVE

FILM-SCREEN SYSTEMS

MAX DENSITY = 1000 R

MIN DENSITY = 20 R= 50

DIGITAL SYSTEMS LIKE CR

MAX VALUE = 100,000 R

MIN VALUE = 10 R= 10,000

DYNAMIC RANGE OF AN IMAGING SYSTEM

# PIXELS / [ 2 x FoV (mm) ]

= 2500 PIXELS / [ 2 x 430 mm ]

= 2.9 LINE PAIRS PER mm

“FILM HAS ABOUT 6 - 8 LP / mm”

SPATIAL RESOLUTION

TYPE OFPSP

CASSETTE

MATRIXSIZE

PIXELSIZE(mm)

SPATIALRESOLUTION

(LP/mm)

35 x 43 cmGP-25

24 x 30 cmGP-25

18 x 24 cmGP-25

18 x 24 cmHR

2048 x2500

2048 x2500

1792 x2392

1792 x2392

0.17

0.12

0.10

0.10

2.9

4.2

<5.0

~5.0

IMAGE RETRIEVAL SPEEDS

DEPENDS UPON SYSTEM TRAFFICSHOULD BE EVALUATED DURING ACCEPTANCE TESTINGTYPICAL SPEED FOR CR IMAGES FROM RAID STORAGE ABOUT 5 -15 SECONDS PER IMAGETYPICAL 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

6666

27 Step 27 Step PACS ShufflePACS Shuffle

PACSWeb Server

PACSArchive

PACSDatabase

HL7-DICOMBroker

MINDscape MIND

CRModality Worklist

Storage SCU

CTModality Worklist

Storage SCU

MRModality Worklist

Storage SCU

WebBrowser

IDXradRIS

HL7InterfaceEngine

RegistrationADT

2. ADT

2. ADT

4. Order

10. DICOM7. DICOM

8. SQL

6. SQL16. Report

17. SQL

9. SQL

19. Logon

20. Cookie

21. SelectReport

22. SQLQuery

23. SQLReturn

24. Report

25. SelectExam

26. CGIQuery

27.ExamSeries/Images

1. ADT

15. Report

18. SQL

2. ADT

4. Order

16. Report

7. DICOM

7. DICOM

5. DICOM

5. DICOM

5. DICOM

Talk VoiceRecognition

3. Order 14. Report

PACSWorkstation

13. Accession Number

11. SQL

12. DICOM

3. Order

computers in imaging

Documents