Chapter 1: What Is Digital Imaging?

What is Digital Imaging?

Digital Imaging is the transforming of energy: (from light photon, sonic, magnetic, x-ray, or gamma radiation sources) to electrical signals that are measured and assigned discrete binary values.

Binary data is processed into image information which may be enhanced, printed, displayed on a monitor, and stored as a computer file.

Digital Modalitites

Every imaging modality may be digital. Some are only digital.

From an equipment standpoint, the major differencebetween the modalities is the type of energy used,how the energy is changed as is traverses the body, and how the remnant energy is measured as it leaves the body.

Computed Tomography (CT)

X-radiation passes through,and is attenuated by the atomiccomposition of cells and tissues.

Is only digital

Cardiovascular Interventional Technology (CVI) digital application started in the 1980s

X-radiation passes through,and is attenuated by the atomiccomposition of cells and tissues.

Magnetic Resonance Imaging (MRI)

Is only digital

Hydrogen atoms excited by radio frequencies (RF)create magneticvectors that sweepan antenna.

Nuclear Medicine Technology

An isotope is injected, ingested or inhaled. After being metabolized, concentrations of the isotope are collected by thenuclear medicine camera.

Diagnostic Medical Sonographyand Vascular Technology

Sound waves pass into, andare reflected off of interfacesof tissues and organs.

Digital Radiography (DR)

X-radiation passes through,and is attenuated by the atomiccomposition of cells and tissues.

Digital applications were available in the early 1980s, but the difficulties of displaying radiographic quality images (in terms of spatial resolution) made it unpopular. In the year 2000 it was beginning to be accepted.

Digital Mammography

X-radiation passes through, and is attenuated by the atomiccomposition of cells and tissues. Like digital radiography, highly dependant on excellent spatial resolution.

Digital Fluoroscopy (DF)

R/F Digital C-Arm

Question: How is an analog radiographic image made?

• Begin with photons coming off the anode.

• Outline the process, step by step.

• Use the appropriate terminology.

Incident, Attenuation, Remnant radiation, Latent, Manifest

Answer: How does a radiographic image get on a film?• Incident beam leaves anode.• Attenuation in body.• Remnant radiation exits in pattern of anatomy.• Photons interact with silver halide crystals.• Latent image is formed.• Manifest image on development.

Question: What does a graphic representation of density building on a film look like, and what is it

called?

D log E (or)H & D Curve (or)Hurter & Driffield Curve (or) Characteristic Curve (or)Sensitometric Curve

Producing a digital radiograph is the same as for analog film, up to the point of the photons interacting with the film.

Digital imaging samples the remnant radiation with (some kind of) a detector,

not film.

Analog : The continuous build up of density on a radiographic film

is an analog process.

For Example:Analog Time

• The passage of time as recorded on a watch with a continuous-sweep secondhand is an example of an analog measurement of time.

Digital Time

• The passage of time as recorded on a digital clock, in discrete values, is an example of a digital process

Analog is continuous.

Digital is discrete.

Computer circuitry is made up of a series of switches that store data in one of two elementary-discrete- states: on, or off.

= 0

= 1

Open

Closed

0 and 1 are the only two numbers used in the binary (two numbers)numbering system

0 and 1 are binary digitsor bits

Digital computersstore data as binarydigits.

Pascal’s calculator - 1642

A series of gears, turned by hand, rotated a wheel with numbersthat showed in a window. When the number in the ones columnreached nine, it turned the wheel in the tens column to 1, andthe ones column returned to zero. Pascal invented his device to relieve the fatigue of spiritassociated with the work of doing arithmetic.

A mechanical device, not programmable

Jacquard’s Loom - 1804

Instructions for weavingpatterns into cloth were fedinto Jacquard’s machine by this early version of punched cards that were made of wood.

The red arrows show thecards entering and leaving the machine.

A mechanical device, that was programmable

Babbage’s Difference Engine - 1822

A crank was turned to perform a mechanical progression of numbered gears in columns that, like Pascal’s calculator,represented increasing powers of ten.

Hollerith’s tabulator

Like Pacal’s calculator, and Babbage’s difference engine numbers were carried over from one column to the next. The great advantage of this device was the use of electric motors to drive mechanical parts, and punched cards to input data.

In 1880 it took 9 years to tally the results of the US census. Herman Hollerith built an electromechanical calculator that used punched cards to input data on the population (age, gender, numbers in family, etc), and reduced the time to do it in half, on a greater population, with a more detailed analysis.

George Boole

1815-1864

Mark I - 1944

The gears of its predecessors were replaced by mechanicalswitches. Electric motors, were used to drive the mechanicsthat opened and closed the switches, and punched cards wereused to input data.

An electromechanical device, that wasprogrammable.

On + Off = Off

Off + Off = Off

On + On = On

AND Gate

On + Off = On

Off + Off = Off

OR Gate

On + On = On

On = Off

Off = On

NOT Gate

0+0

0 0

Operation of a Half Adder

= 0

1+0

0 1

Operation of a Half Adder

= 1

0+1

0 1

Operation of a Half Adder

= 1

1+1

1 0

Operation of a Half Adder

= 2

Three Things a Computer Does

1. Arithmetic functions

2. Comparison functions

3. Memory

Accomplished with accuracy and speed

ENIAC - 1946

The first fully electronic calculator used 18,000 vacuum tubesthat replaced the switches of Mark I. The input of data wasaccomplished by turning knobs, reconfiguring telephonepatch cords, and punched cards.

UNIVAC I - 1951

The first commercial computer sold in the United States.UNIVAC was build by the inventors of ENIAC, J PresperEckert, and John Machly.

“Computers of the future may weigh nomore than 1.5 tons.”

Popular Science, 1949

Cathode Anode

Grid

Vacuum tube: When the grid is positively charged electrons are drawn from the cathode to the anode, creating a closed circuit (1).

When the grid is negatively charged electronsare repelled, and circuit is open (0).

Transistors: Similar in principle to theoperation of a vacuum tube. The solidstate semi-conducting material allowed this switching device to use less energyand produce less heat in a smaller component.

Vacuum Tubes and Transistors

Vacuum tube, Transistor, and IC

Within an integrated circuit (IC)are millions, billions, or trillionsof AND, OR, and NOT gatesembedded in the layers of theminiaturized circuits of the semi-conductor material.

Silicon wafers are manufacturedin clean rooms to prevent thesmallest contaminate from beingintroduced.

Integrated Circuits

Generations of Electronic Computing

1st - 1951- 57 Vacuum tubes

2nd - 1958 - 63 Transistors

3rd - 1964 - 69 Integrated circuits

4th - 1970 - 90 Very large scale integration (VLSI) leading to the microprocessor (computer in single chip).

5th - 1999 - Age of connectivity

Binary numbering

1248163264128256512

20

21

22

23

24

= 140 0 0 0 0 0 0 1 1 1 0= 421 0 1 0 1 0

1 1 1 1 1 1 1

= 127

Binary numbering

1248163264128256512

84

1128

0 1 0 1 0 0

Binary numbering

1248163264128256512

400

1512

1 0 0 1 0 0384

0 0

Picture Elements (PIXELS)

An image displayed on a monitor is comprisedof individual dots calledpixels.

One bit of computer memory (on or off)is all it takes to light up a pixel, or not.

One Pixel

Picture Elements (PIXELS)

The sum of the pixelsin an image displayforms a matrix

MRI: Mid-sagittalplane, brain scan.

Scale of contrast 21

Only one bit of datais needed to controleach pixel: on or off.

21 Scale of Contrast

Question: How can a simple on/off switch be used to store

complex information that contains many shades of gray?

Answer: Many switches are used in combination.

On/off switches are arranged in groups of eight in the computer’s circuitry

CC

Eight bits = one byte

Consider the expanded gray scale of two switches in combination. (Chapter 2 has a complete explanation of the binary numbering system.)

OFF OFF ONONOFFONOFF ON

Black Dark gray Light gray White

In addition to turning the electron been on and off, a second switch stores values that control the quantity of electrons in the beam,

creating a gray scale.

With enough bytes of memory, any number can be represented by

combinations of binary digits

off onon

16 8 4 2 1

1 0 1 = 5

1 1 1 = 7

250

The number 47 defines theshade of gray for the pixelin column 250, row 210.

Printout of the datain the matrix of aCT image

Column 250

Row 210

Values of digits stored in bytes of computer memory directly correspond to the illumination of pixels.

In this case, the pixel in column 250, row 210.

A representation of a CT section as image data,analogous to a paint-by-numbers drawing

Question: If one bit of data is enough to turn a pixel off or on, what can a byte of data do for a

single pixel?

Answer: A byte of image data stores values for 256 shades of gray.

(Chapter 2 has a complete explanation of the binary numbering system.)

How many KB of computer memory is required for a monitor with a 512 x 512 matrix displaying a gray scale of 2?

512 x 512 = 262,144 bits

262,144 / 8 bits per byte = 32,768 bytes

32,768 bytes / 1024 bytes in a kilobyte = 32KB

Answer = 32KB

How many bytes of computer memory is required for a for a monitor with a 512 x 512 matrix, displaying 256 shades of gray (2 )? 8

512 x 512 = 262,144 bits

262,144(8bits)/8 bits per bytes = 262,144 bytes

262,144 bytes/1024 bytes in a kilobyte =262KB

Answer = 262KB Conclusion: Images are memory hogs.