Hệ thống PACS và mạng máy tính, hệ thống lưu trữ dữ liệu trong bệnh viện y tế

Stewart, PhD, DABMPOutline ¬ Storage and Transfer of Data in Computers ¬ Analog Data and Conversion between Analog and Digital Forms ¬ Components and Operations of Computers ¬ Performanc

Computer Networks, PACS and

Brent K Stewart, PhD, DABMP Professor, Radiology and Medical Education

Director, Diagnostic Physics

a copy of this lecture may be found at:

http://courses.washington.edu/radxphys/PhysicsCourse04-05.html

Brent K Stewart, PhD, DABMP

Outline

¬ Storage and Transfer of Data in Computers

¬ Analog Data and Conversion between Analog and Digital Forms

¬ Components and Operations of Computers

¬ Performance of Computer Systems

Brent K Stewart, PhD, DABMP

Decimal Form (Base 10)

¬ In general, a positional numbering system encodes the

numbers as: a n b n + a n-1 b n-1 + + a 2 b 2 + a 1 b 1 + a 0 b 0 (0 <

a i < 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)

Brent K Stewart, PhD, DABMP

Conversion between Decimal and Binary Forms

¬ Conversions between decimal

and binary forms: keep

dividing by powers of the target

radix until you are left with a

remainder < b

Bushberg, et al., The Essential Physics of Medical Imaging,

2nd ed., pp 62-63.

Digital Representation of Data (1)

¬ Bits, Bytes and Words

¬ 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:

¬ 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

Brent K Stewart, PhD, DABMP

Digital Representation of Data (2)

¬ Digital Representation of Different Types of Data

¬ Alphanumeric text, integers, and non-integer data

¬ Storage of Positive Integers

¬ 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]

Digital Representation of Data

¬ Binary Representation of Signed Integers

¬ 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

¬ Floating Point Form

¬ 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

¬ 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

Brent K Stewart, PhD, DABMP

Transfers of Data in Digital Form

¬ 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

¬ Changes between the voltage states occur through

synchronization signals from the computer’s clock

¬ 1 clock cycle = the minimum time increment (τ) at which

a 1 0 or 0 1 transition can occur

¬ clock frequency = 1/τ (usually given in MHz or GHz)

Serial vs Parallel Transfer of Data

¬ Serial - pulses transmitted one after another over single wire

¬ Parallel - All pulses transmitted simultaneously over several wires

faster than serial transmission

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

Brent K Stewart, PhD, DABMP

Transfers of Data in Digital Form

¬ 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

Analog and Digital Representation of Data

¬ Analog: continuous waveform

where the amplitude

represents the numerical

signal magnitude

¬ Advantages of digital:

errors

the transmission of redundant information

expensive than analog

¬ Advantage of analog:

Bushberg, et al., The Essential Physics of Medical Imaging,

2nd ed., p 67.

Brent K Stewart, PhD, DABMP

Conversion of Analog Data to Digital Form

¬ 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

Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p 69.

ADC Potential Loss of Data

¬ Sampling and quantization (digitization): loss of data (necessary

Brent K Stewart, PhD, DABMP

Back to the Future

“I think there is a world market for

maybe five computers.”

Components & Function of a Digital Computer

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

Brent K Stewart, PhD, DABMP

¬ 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.

Central Processing Unit (CPU)

¬ CPU executes a sequence of instructions: program

¬ A CPU contained on a single chip: microprocessor

¬ A number of data storage locations: storage registers

¬ 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:

¬ CPU clock rate (e.g., MHz or GHz)

¬ Architecture (bits per instruction, e.g., 32-bit vs 64-bit and

parallel processing capabilities)

Brent K Stewart, PhD, DABMP

Central Processing Unit (CPU)

¬ 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:

the next in the sequence

¬ Each instruction consists of two

parts: an opcode specifying the

operation to be performed and an

address

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

¬ 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.:

¬ 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)

Brent K Stewart, PhD, DABMP

Mass Storage Devices

¬ Permit the non-volatile storage of programs and data

¬ Various formats based on:

¬ Access time (e.g., msec or minutes): random or sequential

¬ Data transfer rate (e.g., kbps, Mbps or Gbps)

Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p 76.

Brent K Stewart, PhD, DABMP

Display Interface and Keyboard/Pointing Devices

¬ Display computer information in visual form

¬ Usually displayed on a video monitor or printed

¬ Cathode ray tube (CRT)

¬ Flat-panel display (TFT = thin-film transistors)

¬ Video display controller/card

¬ 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)

Acquisition and Communications Interface

¬ 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

¬ Phone number of modem pool, e.g., 206-685-5599

¬ Internet Protocol (IP) address, e.g., 128.95.120.1

Brent K Stewart, PhD, DABMP

Array Processor

¬ 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

general-purpose microprocessors with parallel processing

capabilities inherent in some operating systems

Brent K Stewart, PhD, DABMP

Performance of Computer Systems

¬ Review

¬ Many factors that affect the time required for a computer

to complete a task

¬ Clock speed of the CPU, e.g., 3.4GHz Pentium 4

¬ CPU architecture, e.g., number of bits/instruction and

parallelism

¬ 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

Computer Languages

¬ Machine Language

¬ Binary instructions to be executed by CPU requiring detailed

knowledge of the particular computer

¬ 0110101010101001001010101010001011110011110110101 )

¬ High-Level Languages

¬ 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

Brent K Stewart, PhD, DABMP

Raphex 2000 General Question

storage devices (answers may be used more than once).

goes off?

Raphex 2002 General Question

¬ G82 Concerning digital computers, all of the following

are true, except:

¬ A ROM stands for Random Order Memory.

¬ B A word is a set of consecutive bits treated as an entity, and

occupying one storage location in memory.

¬ C A byte contains 8 bits.

¬ D A modem is a device that converts a digital signal into a

frequency-coded signal for transmission over a telephone line.

Brent K Stewart, PhD, DABMP

Hierarchy of Software

¬ Applications Software - programs to perform specific functions

desired by the user

¬ 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

control to the program and regains control on completion of the task

Computer Security

¬ Goals

¬ Data Backup

¬ Practicing “Safe Computing”

and password grabbers

¬ Deny unauthorized users access to your system

known language, mix of upper/lower case and numbers, and should

contain at least one non-alphanumeric character, e.g., !, @, #, %, etc.)

¬ Grant each user only sufficient privileges required to accomplish

required tasks

Brent K Stewart, PhD, DABMP

Back to the Future

“Computers in the future may weigh

no more than 1.5 tons.”

relentless march of science, 1949.

Digital Storage of Images

represented by one value (e.g., digital value, gray level or Hounsfield unit)

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

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

Brent K Stewart, PhD, DABMP

Effect of Resolution and Bits per Pixel

Bushberg, et al., The Essential Physics of Medical

Imaging, 2nd ed., p 82.

Bushberg, et al., The Essential Physics of Medical

Imaging, 2nd ed., p 84.

Image Processing

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

¬ Spatial filtering

¬ Reconstruction from projections

positron emission tomography (SPECT and PET)

¬ 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

Brent K Stewart, PhD, DABMP

Raphex 2002 General Question

Raphex 2001 Diagnostic Question

¬ D98. Going from a 256 x 256 image to a 512 x 512

image, which of the following may be true?

Resolution Pixel noise Storage bytes

¬ A Decreases Decreases Increase x2

¬ B Increases Decreases Increase x2

¬ C Increases Increases Increase x4

¬ D Increases Increases Increase x2

Brent K Stewart, PhD, DABMP

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.”

for Prentice Hall, 1957.

Computer-Aided Detection

¬ 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:

¬ Masses

¬ Microcalcification clusters

¬ Architectural distortions

Brent K Stewart, PhD, DABMP

Image Display

¬ 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.

Gray-scale and Color Cathode Ray Tube Monitors

¬ 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

Bushberg, et al., The Essential Physics of Medical

Brent K Stewart, PhD, DABMP

Flat Panel Monitors

¬ 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.

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