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

i

Computer Operations

Alphanumeric Operations – Computers processes

alphanumeric operations (words, numbers, math

problems etc.).

This involves arithmetic and logical operations.

1. arithmetic operations – addition, subtraction,

multiplication, division

2. logical operations – compare and state

outcomes (this includes equations, word

processing, typing and editing)

Computers

Analog VS Digital Computers

Analog computers – Handle data comprised ofcontinuously varying voltages

Digital computers – Handle data comprised ofdefinite 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 amountsof information – usually require gigabytestorage devices

Programs and Data

Programs – Software instructions for:1) calculations2) calling up programs3) booting up computer4) 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 inmedicine standard) – An imaging standardthat ensures all equipment manufacturers arespeaking the same computer language

Fourier Transformation

A mathematical method of converting rawdata into computerized medical images.- adds together numerous sets of data from detectors

Data Characteristics Affecting Image Quality

The quality of data acquired by the imagereceptor (detectors) is measured byfrequency, 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 selectedimage frequencies to extract more diagnosticinformation

• 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.