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