Transcript Chapter 23 Computer basics

Computer History
• Earliest computer was the abacus
• abacus invented around 3,000 B.C.
• other calculating machines developed in 1600’s
• digital computer started in 1960’s due to:
1. Baron Jean Fourier – math formulas
2. solid state electronics – 1940’s
3. microchip technology – 1960’s
Computers
Computer Operations
Alphanumeric Operations – Computers processes
alphanumeric operations (words, numbers, math
problems etc.).
This involves arithmetic and logical operations.
1. arithmetic operations – addition, subtraction,
i
multiplication, division
2. logical operations – compare and state
outcomes (this includes equations, word
processing, typing and editing)
Analog VS Digital Computers
Analog computers – Handle data comprised of
continuously varying voltages
Digital computers – Handle data comprised of
definite quantities of current (current “on” vs.
current “off”)
Binary Language
• “1” = current on, “0” = current off
• bit – binary digit
• byte – eight bits (a word)
computer memory is rated in bytes
• 10 megabyte hard drive holds 10,000,000 bytes
(80,000,000 bits)
• 10 gigabyte disk holds 10,000,000,000 bytes
(80,000,000,000 bits)
Computers in radiology hold large amounts
of information – usually require gigabyte
storage devices
Programs and Data
Programs – Software instructions for:
1) calculations
2) calling up programs
3) booting up computer
4) steps to be followed in computer operations
Data – Collected facts
Software – “Untouchables” – computer
instructions
Hardware – Items that can be touched
Central Processing Unit
• Directs information to and from various
components
- Contains an ALU (arithmetic logic unit)
• Bus – Parallel or series conductors that connect
the CPU to various components
- Accepts inputs from any point along
conductor
- Bus speed determines speed of computer
• Parallel conductors – Permits simultaneous
transmission of information (expensive)
•Series conductors – Only permits sequential
transmission of information (less expensive)
Memory
Primary Memory
•ROM (read only memory) – Permanent
memory (usually operating instructions)
• RAM (random access memory) – Temporary
memory (disappears when computer is turned
off)
- Temporary storage for operating &
programming instructions
Secondary Memory
Memory for storing images or operating
instructions on three kinds of media:
•Floppies
•CD-ROM disks
• Hard drives
•These are not erased when computer is turned off
Peripherals
Devices that permit input and/or out of
information to and from the CPU
These include:
1) Memory storage devices
- magnetic tapes – store information sequentially
using
- hard drives
- floppies
- optical laser disks
2) Input Devices:
- keyboard
- cursor
- mouse
3) Output Devices
- CRT
- printers
4) Array Processors – Specialized computer that
quickly performs math computations
Digital Image Processing
•Digital image – Composed of numbers
•All digital images require a detector such as
- ionizing radiation (digital rad., CT)
- ultrasound waves
- radiofrequency waves (MRI)
Digital images displayed on an image matrix:
- matrix – rows and columns of pixels that form
the image
- pixels – picture elements with length/width
- voxel – picture elements that include
length/width/depth (3D)
- pixel size determines the resolution of the image
current CRT resolution capabilities = 1-2 lp/mm
- a larger image matrix provides better resolution
(because of smaller pixels)
DICOM (digital imaging & communication in
medicine standard) – An imaging standard
that ensures all equipment manufacturers are
speaking the same computer language
Fourier Transformation
A mathematical method of converting raw
data into computerized medical images.
- adds together numerous sets of data from
detectors
Data Characteristics Affecting Image Quality
The quality of data acquired by the image
receptor (detectors) is measured by
frequency, contrast and noise.
• Frequency – The raw data to which fourier
transformation is applied
- frequency is a measure of the contrast in the
image
- high contrast = high frequency & vice versa
• Contrast – Difference between shades of gray
- Caused by a difference between data values
- Direct relationship b/w subject contrast &
data contrast
• Noise – Random background information that
does not contribute to image quality
- “White noise” – snow
- Measured by signal-to-noise ratio
- A high signal-to-noise ratio indicates little
noise in the image
Image Display Qualities
• The photon beam exiting the patient carries
information representing approximately 1,000
shades of gray
• The human eye can only detect 32 shades of
gray
• Window level – Controls the image density
- There is a direct relationship between image
level and density
- When window level increases, the image
density increases
• Window width – Controls image contrast
- There is an inverse relationship between
window width and image contrast
- When the window width is increased,
contrast is reduced
Resolution of Digital Images
• Controlled by matrix size
- There is a direct relationship between matrix
size and image resolution
- As matrix size increases (pixel size decreases),
resolution increases
- The primary determinant of resolution is
the pixel size
• Bandwidth (frequency response of the incoming
signal) also affects resolution
- Bandwidth of commercial TV is 4 MHz
- Bandwidth in digital images is 20 MHz
• Raster pattern also affects resolution
- 525 line systems have a 1 – 2 lp/mm resolution
- 1, 050 (1,000 line) systems have a 5-7 lp/mm
resolution
Filtering
The process of enhancing or suppressing selected
image frequencies to extract more diagnostic
information
• Low-pass filtering – amplifies or deletes all
but the low frequencies
- Used to decrease image contrast and
remove high frequency image noise
• High-pass filtering – amplifies or deletes all
but the high frequencies
- Used to increase image contrast
- Also called “edge enhancement” – enhances
the edges of structures
- Primarily used in digital vascular imaging
Picture Archiving and Communication Systems
(PACS)
A computer system involved in the acquisition,
storage and transmission of digital images.
- Includes digital images of CT, MRI, ultrasound,
mammography, CR and digital radiography
Advantages
• Eliminates space for storage
• Misfiling less likely
• Less acquisition time
• Eliminates film costs
Disadvantage
• Initial cost
• Memory storage
• Can require up to 3.2 terabytes (3.2 X 1012)
of computer memory per year.