Computed Computed Tomography Tomography

RAD309RAD309

Dr. Eng. Sarah Hagi Dr. Eng. Sarah Hagi MSc (USA) PhD (UK)MSc (USA) PhD (UK)

Course Dr. Mawya Khafaji Book Practical TLD’s Grading:

Continuous Assessment (40%) Midterm, Quizzes, HM, Practical

Final Exams (60%) Written (40%) Practical (20%)

Course OutlineTopic Instructor

History, evolution of technology , process overview S.Hagi

Computer Technology and the use of Computers in Radiography Physical Principles and instrumentation of CT S.Hagi

Principles of CT, Characteristics of X-radiation, CT beam attenuation, and linear attenuation coefficients S.Hagi

Data Analysis S.Hagi

CT generations and Spiral CT S.Hagi

Components of CT Scanner, Gantry assembly (patient aperture, rotating frame,xray tube, collimator, and detectors), patient table, operator console, CT computer and workstations S.Hagi

Tissue Characteristics and Hounsfield attenuation numbers application M.Khafaji

Data acquisition and manipulation, image reconstruction algorithms, such as filtered back projection and transform M.Khafaji

Image Quality and operating console parameters M.Khafaji

Dose, technical parameters for dose measurement/possible reduction methods M.Khafaji

Quality Assurance of computed tomography M.Khafaji

WEEK Begining Date Lectures Instructor

1 March 7th Lect1&2 S.Hagi

2 March14th Lect3&4 S.Hagi

3 March21st Lect5&6 S.Hagi

4 March28th Lect7&8 S.Hagi

5 April 4th Lect9&10 S.Hagi

6 April 11th revision S.Hagi

7 April 18th Midterm S.Hagi

8 April 25th Break  

9 May 2nd Lect11&12 M.Khafaji

10 May 9th Lect13&14 M.Khafaji

11 May16th Lect15&16 M.Khafaji

12 May23rd lect17&18 M.Khafaji

13 May30th Lect19&20 M.Khafaji

14 June6th revision M.Khafaji

15 June13th revision M.Khafaji

16 June20th Final M.Khafaji

1. Visit to different hospitals to see components of available generations of CT in the field of Medical Imaging2. Group discussion-Physical principles and instrumentation involved in CT3. Group discussion-characteristics of x radiation, CT beam attenuation, linear

attenuation coefficient4. Tissue characteristics and Hounsfield attenuation numbers application,

demonstrated on display console-to show hounsfield numbers of different tissue5. Data acquisition and manipulation, image reconstruction algorithms, such as

filtered back projection and transform6. Group discussion on problem based learning of data acquisition and manipulation,

image reconstruction algothirms7. Demonstration of components including functions, CT scanner, Gantry assembly,

patient table, operator console, CT computer and workstation8. Demonstration -Operation of Scan console, to enter patient data, selection of scan

parameters 9. Demonstration -Operation of Display console manipulate scan data and post

processing such as Multiplanar reformatting....

Computed Tomography RAD309 PracticalSecond Semester, Third Year Conducted by Clinical Instructor

Introduction

A method of examining body organs by scanning them with X rays and using a computer to construct a series of cross-sectional scans along a single axis

Acquiring and reconstructing, thin cross section on the basis of measurement of attenuation

Tomography Since 1900s Several researchers were interested in a specific layer or section to represent a single slice of the body on radiographic film Tomo- section in Greek Transverse section were developed by Watson (transverse= cross

section) But with not enough details, clarity, not fully utilized as a clinical tool

Conventional Tomography Provides 2D view of a 3D distribution of an object (x,y,z) with

superimposition of all structures Disadvantages: depth information is lost overlapping structures may interfere with diagnosis, and small

differences in contrast is lost No quantitative

MethodThe idea is based on simple principles of projective

geometry: x ray source on one side of the object and the film on the

other (diagonal) Source and detector move at constant rate opposite

directions Source and detector distance, rate of motion, adjusted

such that objects in the imaging plane project to the same relative location on the film.

Objects out of the plane, blurred

Tomography had been one of the pillars of radiologic diagnostics until the late 1970s

Goals of CT

To overcome superimposition of structures To improve contrast To measure small differences in tissue

contrast

CT came to solve the problems of tomography and conventional radiography, image reconstruction from projections

Solution

Transmitting a collimated beam through a cross section of the body

Detectors, measuring small differences in tissue contrast

Computer that allows data manipulation and reconstruction

The Birth of CTThe Birth of CT

1972 1972 Nobel Prize in 1979, Sir Godfrey Hounsfield Nobel Prize in 1979, Sir Godfrey Hounsfield

& Alan Cormack “ computer assisted & Alan Cormack “ computer assisted tomography”tomography”

Solved the problem of conventional Solved the problem of conventional

Image Reconstruction History

1917 Radon proved that it was possible to mathematically build an image from large number of its projections (different angles) Has been widely used in many fields

Images of the body can be reconstructed from a large number of projections from diff. locations

Theory When radiation passes through an objects, some of it is

absorbed, scattered attenuation (which we will discuss in details in another lecture)

Attenuation measurements is the basis of CT imaging Radiation passes through each section in a specific way

(depending on the tissue properties/characteristics) onto a detector that sends signal to a computer for processing

Computer produces clear, sharp image of internal structure of the object

This doesn’t happen spontaneously, there are algorithms mathematical computations to put the projections together and produce the image data

Cont. All trials to make use of image

reconstruction techniques in radiology were not successful

Technology barrier, computers In 1967 Hounsfield applied reconstruction

techniques to produce the first clinically useful scanner (used only for brain imaging)

Who is He?Who is He?

Production of X-RayProduction of X-Ray““fast-moving electrons slam into a metal fast-moving electrons slam into a metal

object, x-rays are produced”object, x-rays are produced” Roentgen experimented with electron Roentgen experimented with electron

beam in a vacuum tube surrounded beam in a vacuum tube surrounded by cardboardby cardboard

He noticed light/glowing spots on He noticed light/glowing spots on fluorescent screen fluorescent screen

Next, started to place objects b/w the Next, started to place objects b/w the screen and the tubescreen and the tube

Finally he placed his wife’s hand in Finally he placed his wife’s hand in front of the screenfront of the screen

Historical DevelopmentsHistorical Developments1895 Discovery of X-ray Wilhelm Roentgen1896-98 Discovery of natural

radioactivityHenri Becqurel and the Curie’s

1901 Nobel Prize (1st physics) Roentgen1917 Mathematical basis and

concepts of image reconstruction

Radon

1946 Discovery of NMR principles Flex Bloch and Edward Purcell

1972 Invention of CT Hounsfield and Cormack1973 Producing MR imaging Lauterber and P Mansfield

1979 Nobel Prize in Medicine Hounsfield and Cormack2003 Nobel in Physol.& Medicine Lauterber and Mansfield

Hounsfields Invention

Sir Godfrey N. Hounsfield, DSc, the father of computed tomography, died Sir Godfrey N. Hounsfield, DSc, the father of computed tomography, died on August 12, 2004 at the age of 84on August 12, 2004 at the age of 84

First CT

the "EMI-Scanner“ Limited to brain acquired the image data in about 4 minutes (scanning two adjacent

slices) images from these scans took 2.5 hours to be processed by

algebraic reconstruction techniques on a large computer scanner required use of a water-filled tank with a pre-shaped

rubber "head-cap" at the front, which enclosed the patient's head 160 parallel readings through 180 angles, each 1° apart, with each

scan taking a little over five minutes a single photomultiplier detector, and operated on the

Translate/Rotate principle

Basics of CTBasics of CT

Measurement of attenuationMeasurement of attenuation of a cross section of of a cross section of the bodythe body

System uses the data to reconstruct a digital System uses the data to reconstruct a digital image of the cross sectionimage of the cross section Each pixel in the image represents mean attenuation of a Each pixel in the image represents mean attenuation of a

voxel (boxlike element)voxel (boxlike element)

Attenuation measurements: quantifies the fraction Attenuation measurements: quantifies the fraction of radiation removed in passing through a given of radiation removed in passing through a given mount of material of thickness xmount of material of thickness x

Cont

Different names in the past 30 years: Computerized transverse axial scanning

(tomography) Computer assisted tomography Computerized axial tomography (CAT) But the final name is CT

CT Process Overview

The formation of CT image by CT scanner three steps: data acquisition, image reconstruction, and image display, manipulation, storage, and recording.

Data Acquisition Collection of x ray transmission measurements

After passing through patient they fall onto detectors Detector measures the attenuation value

Reconstruct an image, enough data needed (transmission measurements)

Data collection scheme: Example tube & detector move in a straight line (translate) across

body part (from left to right); after collecting number of transmission measurements they rotate 1 degree and start again bt from right to left

Translate-rotate-stop-rotate (repeated 180 times) 180°

More efficient scanning schemes were developed

Image Reconstruction

After enough transmission measurements (detector) Sent to the computer for processing Computer (uses mathematical techniques to reconstruct the

CT image) Reconstruction algorithms (example: algebraic reconstruction

technique) Need: minicomputer and microprocessors for performing the

function/ or array processors for calculations.

Image Display/Manipulation/Storage/Recording

After image reconstruction Image displayed on CRT (cathode ray tube), best for a gray

scale image These monitors are on the console allowing the technologist

(operator console) and radiologist (doctors console) Manipulation: transverse axial images can be reformatted

into coronal , sagital, and paraxial sections./ and three dimensional processing

Storage: magnetic tapes and magnetic disks and optical storage.

How CT Scanners Work

Turn on power of scanner Perform a quick test to make sure scanner

is working properly Place the patient in the scanner opening/

setup depending on exam Technical factors are setup by the

technologist at the console

What happens when x-ray passes through the patient?

Attenuated and measured by the detector X ray tube and detectors are hidden inside the gantry of

scanner and rotate around patient during scanning Detector converts x ray photons into electrical signals

(analog), which must be converted into digital (numerical) for input on computer

Computer makes the image reconstruction process Reconstructing an image is in numerical form and must be

converted into electrical signal so it can be displayed on a television monitor for viewing

Image can be stored on magnetic tapes or optical disks and recorded on x-ray film

Computers

A computer performs wide range of tasks Image reconstruction to storage, recording, digital

transmission to remote locations Use in radiology, one of the reasons is film-less

hospitals Advantage of computers: can process, store,

retrieve, and communicate information quickly and accurately

What is a Computer System

A machine for solving problems High-speed electronic computational machine that

accepts information in the form of data and instructions (though an input) and process the information by performing arithmetic and logic operations using a program stored in its memory

Results of the process can be displayed/stored/recorded/transmitted

Three Components Hardware: physical component of the

machine, input devices, output devices, processing hardware

Software: instructions to solve the problem User/operator : design hardware/software

and operate the machine

Software The hardware receives instruction from the

software ( instruction = written step by step how to solve the problem/programs)

Three types: Systems software- start up, coordinate the activities Applications software- programs we run or use on the

computer Software development tool- programming languages

History of Computers 1642 the abacus, counting machine 1694, calculating machine (multiplication and

division) 1890 – punch card machine Rapid development till Howard Aiken’s MARK1 (large

electromechanical calculator) 1951, UNIVAC – universal automatic computer (first

commercially available) Today's computers are fifth generations Generation – a period of significant technical

developments in hardware and software

Computer Generations

1st: 1951-1958, large, slow, heat during operation, housed in an air-conditioned room

2nd: 1959-1963, solid-state devices (transistors and magnetic cores) for internal memory, less heat, smaller, less power for operation

3rd: 1963-1970, integrated circuit, silicon chips/use of magnetic disks for storage (several programs processed at the same time) , faster, smaller, more reliable

Generations

4th: 1971-1987, 1000’s of integrated circuits on chip

5th: 1987-date, gallium based circuitry instead of silicon, parallel processing, many processors are used to operate on data at the same time

These computer developments affected development in other technologies and medical imaging is a important example

Classification

Depending on their processing capabilities Supercomputers-large, high capacity,

processes data at extremely high speed Use: weather forecasting, oil exploration,

scientific modeling CRAY2, one of the fastest computers available today

Cont. Mainframe Computers- large, high speed

computation, large memories, terminals enable multiple users access to primary memory (use in banks, universities) Millions of Instructions Per Second multiple operating systems, and thereby operate not as a

single computer but as a number of virtual machines. In this role, a single mainframe can replace dozens or even hundreds of smaller servers.

Cont. Minicomputers- mid level computer built to

perform complex computations while dealing with high level of input and output for users connected via terminals (multi user computer) much smaller than mainframes (fill a room) minicomputers will be discussed more when we

talk about CT components

Cont. Microcomputers- small digital computers/

personal computers, built so all circuitry is placed in a single chip or multiple circuit boards (microprocessor, central processing unit CPU) Microprocessor is a digital integrated circuit that

processes data, controls work of microcomputer The processing capability is related to number of bits,

binary digits(0 and 1)used to represent data

Cont. 8-bit (28)processor = represents 256 numbers 16-bit (216) processor = 65,536 numbers can be represented 32-bit(232) 2 types of computers Digital and Analog

Digital operate on digital data (discrete units) and analog operate on continuous physical quantities

Digital computes are most common, they operate on digital data through arithmetic and logic operations, used in radiological applications, its important that we understand the nature of digital systems

Numbering Systems Decimal numbers system = based on ten 0,1,2,3,4,5,6,7,8,9 Any number written must be a sum of these

digits multiplied by 10x

Example 321 Unit/tens/hundreds/thousands/ten

thousands/hundreds thousands/million

Binary numbers system based on factors of 2 Only two values 0 and 1 1 2 4 8 16 32 64 128 Writing 7 and 10 in binary 0111 and 1010

Converting Decimal to Binary Example 133 , list 1 to 128

Binary to Decimal Example 01010110 , count 8 Put 0’s and 1’s under numbers then add

Other Numbers Since binary numbers can be long, octal

and hexadecimal systems Octal 8 digits 0 1 2 3 4 5 6 7 Hexadecimal 16 Example: convert binary to octal

010110100, group them 010, 110, 100 100=4; 110=6; 010=2 so

the octal number is 264

Why A binary digit, a bit, which is a single binary

number, 4 binary bits (0.5byte) 8 binary bits (1byte) 16 binary bits (2 bytes) 32 binary bits (4 bytes)

Binary numbers, grouped in 8 digits called bytes Byte is a location in the memory, memory

capacity is measured in bytes

Why When we enter information on computer,

the characters we use are converted into binary codes, two famous ones are ASCII and EBCDIC

Data Communications

Hardware: modem a device that converts digital data to analog signals and converts analog signals to digital data to be transmitted and received

Multiplexer allows many computers to share communication line

Network , more on communication

Computers in Radiology

1955, to calculate radiation dose distribution in cancer patients

Mathematical approaches in radiology Two categories: imaging and no imaging

Imaging

Information from the patient needs processing

Digital image processing techniques Digital images: digital radiography, digital

fluoroscopy, MRI, CT

Non-imaging Radiology information system (RIS), like patient

admission, billing, film library, word processing.. An electronic system for archiving, transmitting,

viewing, and manipulating images (Picture Archiving and Communication Systems

PACS) HIS (hospital information system) Mechanical view boxes are being replaced by

workstations workstation = powerful stand alone computer with

high graphic capability