PART I Flashcards
[year, person] proved it is possible to reconstruct or built up an image of 2D object from a large number of projections from different projections
1917
J. Radon
[year, terms] earlier terms of computer tomography
1920
“body section radiography”
“Stratigraphy” - stratum (layer), graphia (to describe)
[person,year]
redefined the technique and labeled it “tomography”
“Tomos” - section
1935
Grossman
Image of a section of the patient that is oriented parallel to the film
Conventional Tomogram
[person, year]
developed another technique (cross-sections) referred to as “Transverse Axial Tomography”
1937
Watson
[person, year] basic idea for today’s tomography, drawings of equipment to for sonograms and optical projection techniques to reconstruct
1940
Gabriel Frank
[person, year] practical application of projections in medicine, series of experiments on a phantom
[person, year]-studied nuc med
1960
William Oldendorf
David E. Kuhl & Roy Q. Edwards
[person, year] theory of image reconstruction; applied techniques in nuclear medicine
1963
Allan McLead Cormack
[person, year] development of first clinical CT scanner at Central Research Laboratories of EMI Ltd. In England
1967
Godfrey N. Hounsfield
[person, year] consultant of Atkinson-Morley’s Hospital - obtained reading from specimen of human brain with Hounsfield
1971
Dr. James Ambrose
[person, year] developed first whole body CT Scanner, Georgetown University
1974
Dr. Robert Ledly
[year, development] has the goals to carry out dynamic volumes scanning to accommodate imaging the dynamics of organ system with high temporal resolution
1975
Dynamic Spatial Reconstructor (DSR)
[year, person] [..] shared Nobel Prize in medicine and physiology [..]
1979 Hounsfield
with Allan McLead Cormack
[person, year] introduced External Beam CT (EBCT)
1980s
Dr. Douglas Boyd
Other uses for ct
- Study of internal log defects in sawmill
- Paleoanthropology
- Baggage inspection at airports
- Oil Exploration
- Fat Stock Breeding
- Animal Investigation
- Evaluate bowed stringed instruments
[components]
DESCRIBE Gantry
-ring/doughnut shaped
-tilted fwd and bwd (15-30 deg)
-laser light for positioning
-control panel on sides
Size of aperture
70-90cm
[components]
DESCRIBE Patient Table/ Couch
-table to top made of carbon fiber
-should be strong and rigid
-comfort and safety
Reasons for using carbon fiber in patient table
- Light weight
- Does not attenuate easily
[components]
DESCRIBE x-ray system (generator)
-uses three-phase flow for the efficient production of x-rays
-high freq. generators now utilized
-located inside gantry
-voltage ripple from high frequency generator is less than 1%
Fluctuation of current after it is rectified
Voltage ripple
[components]
DESCRIBE Slip ring
-wires in systemic manner
-x-ray tube rotate continuously
-use a brush like apparatus to provide continuous electrical power and electrical communication across a rotating surface
Component of tube enclosure of CT scan (x-ray tube)
Metal envelope
Consist of tungsten filaments positioned in a focusing cup
Cathode assembly
-made of barium metal compounds
-absorb gas molecules in a vacuum
Internal Getter
Components of the anode assembly
Disk
rotor stud
hub
rotor
bearing assembly
Small target angle of around 12 degrees
Anode
Small target effect on Image Formation
- Increase Spatial Resolution
- Anode Heel Effect
- if angulated too much, less surface area
-if smaller-more surface area
Reason for high rotational speed 3600 rpm to 10,000 rpm of anode
For heat dissipation-it will hit different parts of the focal spot
-uses ceramic insulators - so that envelope will not be affected
-uses thicker (5cm) and larger diameter (200mm) anode disk
Anode assembly
Types of anode disk
A. All Metal Disk Design
B. Brazed Graphite Anode Disk Design
C. Chemical Vapor Deposition (CVD) Graphite Anode Disk
[base body, focal track] All Metal Disk Design
Base body: Titanium, Zirconium and Molybdenum
Focal Track Layer: 10% rhenium & 90% tungsten
[adv, disadv] All Metal Disk Design
Adv: quick heat transfer
Disadv: weight/heavy
[base body, focal track] Brazed Graphite Anode Disk Design
Body base: graphite -10x more heat capacity than tungsten
Focal track layer: tungsten-rhenium
[adv] Brazed Graphite Anode Disk Design
High heat storage capacity
Faster anode cooling
[base body, focal track] Chemical Vapor Deposition (CVD) Graphite Anode Disk
Base body: graphite
Focal track layer: tungsten-rhenium
[adv.] Chemical Vapor Deposition (CVD) Graphite Anode Disk
Can accommodate large heat storage capacity
light weight disks
Help reduce radiation dose and improve image
Filtration
Purposes of filtration
A. Remove long wavelength x-ray
B. Shapes the energy distribution across the radiation beam by using shaped filter
-Restricts x-ray beam to specific area
-control slice thickness
Collimator
Collimators present in CT:
A. Prepatient collimator
B. Predetector collimator
Determining the radiation dose profile and patient radiation dose
Prepatient Collimator
Determine the sensitivity profile and improve image contrast
Predetector Collimator
Capture the radiation beam from the patient and convert it into electrical signals which are subsequently converted into binary coded information
CT Detector
Types of CT detector accdg to Materials
A. Xenon gas detector
B. Solid State Crystal (Scintillation Detectors)
[adv, disadv] Xenon gas detector
Adv: ability to remain stable under pressure, cheaper, easier to calibrate
Disadv: must be kept under pressure in an aluminum casing
[adv, compo] Solid State Crystal (Scintillation Detector)
Adv: sensitive to fluctuation in temperature and moisture
Composition: cadmium tungstate, bismuth germinate, cesium iodide, gadolinium or yttrium
Major Limitation of Radiography
- Superimposition of anatomical structures
- Radiography is qualitative rather than quantitative
Goals of CT
A. Eliminate/ minimize superimposition
B. Improve image contrast
C. Recording of very small differences in tissue contrast
