1. Historical Perspective
Computed Tomography
Historical Perspective

2. Meaning Tomography – from the Greek word tomos meaning section
Early images lacked enough detail and clarity to be useful
CT had to wait until the discovery of higher order mathematics and computers
CT now overcomes limitations by using image computer reconstruction from projections to produce sharp, clear cross-sectional images

3. Conventional Tomography
Radiograph obtained with a moving x-ray tube
Results in an image with superimposed tissues (CT does not)
Tissues are blurred above and below the focal plane – no improvement in spatial resolution

4. Image Reconstruction from Projections
1917 – Radon proved that a 2d or 3d model could be produced by collecting a large number of projections from different projections
This method is used in a variety of applications including astronomy and electron microscopy
Cormack developed reconstruction by back projection in the 1950’s and 1960’s

5. Projections
In CT radiation passed through each cross-section in a specific way and is projected onto a detector that sends signals to a computer for processing. After processing a clear, sharp, digital image is produced.

6. Technical Definition
Herman (1980) – Image reconstruction from projections is the process of producing an image of a two dimensional distribution from estimates of its line integrals long a finite number of lines of known locations.

7. Image Reconstruction in Medicine
Hounsfield (1967) – applied reconstruction techniques to produce the worlds first useful CT scanner for imaging the brain.
Hounsfield’s studies resulted in emission CT (nuclear medicine) and transmission CT (computed tomography).
Hounsfields first machine used a gamma source
Output too low
Source too large
Image reconstruction is also used in Ultrasound and MRI

8. Evolution of Terms
Hounsfield first coined the term computerized transverse axial scanning.
Other terms include: Computerized transverse axial tomography, computerized transverse axial tomography, computer-assisted tomography, computerized axial tomography, computerized transaxial transmission reconstructive tomography.

9. Terms
The term Computed Tomography was established by the Radiological Society of North America in their major journal Radiology
Additionally the American Journal of Roentgenology accepted this term.
The term Computed Tomography is considered the correct term

10. Process Data acquisition Image reconstruction
Image display, manipulation, storage, recording, and communication

11. Data Acquisition
Data acquisition – refers to the collection of x-ray transmission measurements from the patient
Patient -> detector = transmission values/attenuation values
Initial scanners took an inordinate amount of time to complete one slice

12. Image Reconstruction Transmission measurements are sent to a computer
The computer uses mathematical techniques to reconstruct the CT image in a finite number of steps called reconstruction algorithms
Hounsfield developed an algorithm called the algebraic reconstruction technique

13. Image Reconstruction
A variety of computers are integral to the reconstruction process
Computer equipment includes array processor, minicomputer, and microprocessors

14. Image Display, Manipulation, Storage, Recording, and Communications
After reconstruction the images can be displayed, recorded, and analyzed
Typically images are displayed on a cathode ray tube.
Monitors allow a variety of individuals to view and manipulate the images

15. Manipulation
Many computer packages allow images to be manipulated after the scan is complete (post-processing)
Images can be reconstructed in a variety of planes, can be colored, and 3d models may be created.

16. Storage
Images can be recorded and stored on a variety of archive media
Archive media include radiographic film, mag tapes, optical disks, and cd-rom

17. Communications
CT scanners can be connected to a wide array of devices:
Laser printers, diagnostic workstations, display monitors, and computers outside the hospital.
Many different types of CT systems and equipment can communicate through a standard protocol called Digital Imaging and Communication in Medicine(dicom)

18. Brief History of CT 1895 – Roentgen discovers x-rays
1917 – Radon develops reconstruction mathematics
1963 – Cormack formulates x-ray absorption in tissue
1972 – Hounsfield demonstrates CT
1974 – Convolution and back projection

19. Brief History of CT 1975 – First whole body CT
1976 – Somatom scanner operating on fan beam principle, 5s scan with instant image reconstruction
1978 – Topogram
1979 – Hounsfield and Cormack Nobel Prize
1981 – 512 squared matrix
1983 – High frequency generators & EBCT

20. Brief history of CT
1984 – Opti 155 CT tube with 1.75 MHU, 70cm gantry opening, +/- 25 degree tilt
1986 – Osteo CT (BMD), xenon CT (measures cerebral blood flow)
1987 – Continuous rotation flying focal spot CT tube
1989 – Spiral CT
1991 – Multislice CT introduced

21. Brief history of CT 1991 – intuitive mouse-driven Windows interface
1992 – Integrated CT angiography
1994 – Routine sub second spiral CT
1996 – Spiral “4” everything; neuro and high-resolution spiral
1997 – multi detector arrays; volume scans

22. Nobel Laureate Godfrey Hounsfield
Associated Press Monday, August 23, 2004; Page B05
Godfrey Hounsfield, 84, who developed the first practical CAT scan machine and shared a Nobel Prize in 1979 for inventing CAT scan technology, died Aug. 12 at a hospital in Kingston upon Thames, England. The cause of death was not reported.

23. Nobel Laureate Godfrey Hounsfield
The Nobel committee described Mr. Hounsfield, who worked at EMI laboratories' medical research division, as "the central figure in computer-assisted tomography." The device uses X-rays to scan from different angles and a computer to assemble the images into a cross section.

24. EMI Electric and Musical Industries
Not only did EMI employ Hounsfield and market the first UK “CAT” Scanner, they also signed contracts with

25. The Beatles

26. Pink Floyd

27. Queen

28. Emission vs. Transmission
Emission CT involves nuclear medicine and Gamma-ray emission from the patient
Computed Tomography utilizes x-ray transmission through a patient

29. Limitations of CT Spatial resolution Relatively high patient dose
Z-axis reformation
Distinct artifacts

30. Advantages of CT Better contrast resolution
No superimposition of tissues
Less scatter radiation
3D imaging
Bone mineral assay