good papers

2. INTRODUCTION
Designed by Godfrey N. Hounsfield
to overcome the visual representation
challenges in radiography and
conventional tomography by
collimating the X-ray beam and
transmitting it only through small
cross-sections of the body

3. G.N.HOUNSFIELD ALLAN M. CORMACK
In 1979, G.N. Hounsfield shared the Nobel Prize in Physiology &
Medicine with Allan MacLeod Cormack, Physics Professor who
developed solutions to mathematical problems involved in CT.

4. Important events
YEAR EVENTS
1969 G.N. Hounsfield developed first clinically useful
CT head scanner
1971 First clinically useful CT head scanner was
installed at Atkinson-Morley Hospital (England)
1972 First paper on CT presented to British Institute
of Radiology by Hounsfield and Dr. Ambrose
1974 Dr. Ledley introduced the whole body CT
scanner (ACTA scanner)
1979 G.N. Hounsfield shared the Nobel Prize with
Allan MacLeod Cormack

5. C.T. scan
• Computed tomography (CT) scan
machines uses X-rays, a powerful form
of electromagnetic energy.
• CT combines X radiation and radiation
detectors coupled with a computer to
create cross sectional image of any part
of the body.

6. Cross-sectional slices
Think like looking into a loaf of bread by cutting it into
thin slices and then viewing the slices individually.

7. BASIC PRINCIPLE
• The internal structure of an
object can be reconstructed
from multiple projections of the
object.
• CT scanning is a systematic
collection and representation of
projection data.

8. Comparison of CT with Conventional Radiography
• Conventional radiography
suffers from the collapsing of
3D structures onto a 2D
image
• CT gives accurate diagnostic
information about the
distribution of structures
inside the body

9. Comparison of CT with Conventional Radiography
A conventional X-ray image is basically a shadow.
Shadows give you an incomplete picture of an object's shape.
This is the basic idea of computer aided tomography. In a CT scan machine, the X-
ray beam moves all around the patient, scanning from hundreds of different angles.

10. Comparison of CT with Conventional Radiography

11. Comparison of CT with Conventional Radiography
Radiographic procedure is qualitative and not quantitative

12. Comparison of CT with Conventional Tomography
Limitations of Conventional
tomography:
1. Image blurring persists
2. Degradation of contrast
due to scatter radiation
3. Problems with
Film/screen combination

13. Comparison of CT with Conventional Radiography and Tomography
Although spatial resolution is lower in CT, it has
extremely good low contrast resolution, enabling
the detection of very small changes in tissue type
LINEAR
ATTENUATION
COEFFICIENT
MATTER
(µ)
FAT 0.194
WATER 0.222
CSF 0.227
PLASMA 0.230
RED BLOOD CELLS 0.247

14. GENERATIONS
• Data gathering techniques have
developed in stages termed
Generations.
• Scan time reduction is the predominant
reason for introducing new
configurations

15. FIRST GENERATION
• Narrow pencil beam
• Single detector per slice
• Translate –Rotate movements
of Tube- detector combination
• Scan time-5min
• Designed only for evaluation
of brain

16. I gen. CT
•The axis of rotation passed through the centre of the
patient’s head
•The total number of transmission measurements =
No. of linear measurements X No. of rotatory steps
= 160 X 180 = 28,800
Matrix size: 80 x 80
Scan time: 5min
Grey levels: 8
Over night image reconstruction

17. I Generation CT Scanner
• Head kept enclosed in a
water bath
• Two side-by-side detectors
• A reference detector

18. SECOND GENERATION
• Narrow fan beam
(30-100)
• Linear detector array(30)
• Translate-Rotate movements of
Tube-Detector combination
• Fewer linear movements are
needed as there are more detectors
to gather the data.
• Between linear movements, the
gantry rotated 30o
• Only 6 times the linear movements
got repeated
• Scan time~20secs

19. THIRD GENERATION
• Rotate(tube)-Rotate(detectors)
Translatory motion is
completely eliminated
• Pulsed wide fan beam(500-550)
• Arc of detectors(600-900)
• Detectors are perfectly aligned
with the X-Ray tube
• Both Xenon and scintillation
crystal detectors can be used
• Scan time< 5secs

20. III gen. CT scanners

21. FOURTH GENERATION
• Continuous wide fan beam(500-550)
• Ring of detectors(> 2000)
• Rotate(tube)-Fixed(detector)
• X-ray tube rotates in a circle inside the
detector ring
• When the tube is at predescribed
angles, the exposed detectors are
read.
• Scan time< 2 secs

22. III Vs IV gen. CT scanners

23. CT Data Acquisition Components

24. DATA ACQUISITION
The scanning process begins with
data acquisition.
Data Acquisition refers to a method
by which the patient is systematically
scanned by the X ray tube and
detectors to collect enough
information for image reconstruction.
A basic data acquisition scheme
consists of
• X ray tube
• Filters
• Collimators
• Detectors

25. CT Gantry

26. CT gantry internal components
1.X-ray tube & collimator
2.Detector assembly
3.Tube controller
4.High freq. generator
5.Onboard computer
6.Stationary computer

27. CT gantry internal components

28. CT Patient Couch

29. CT

30. X-RAY TUBE
• Rotating anode type
• More heat loading
and heat dissipation
capabilities
• Small focal spot size
(0.6mm) to improve
spatial resolution

31. FILTERS
Compensation filter is being used
• To absorb low energy x rays
• To reduce patient dose
• To provide a more uniform beam

32. COLLIMATORS
• To decrease scatter
radiation
• To reduce patient dose
• To improve image quality
• Collimator width determines
the slice thickness

33. DETECTORS
• The detectors gather information by measuring the x-
ray transmission through the patient.
• Two types:
Scintillation crystal detector
(Cadmium tungstate+ Si Photodiode)
Can be used in third and fourth generation scanners
Xenon gas ionisation chamber
Can be used in third generation scanners only

34. Scintillation crystal detector used in I & II gen. CT scanners

35. Scintillation crystal detector used in III and IV gen. CT scanners

36. Detector Cross-talk
• Detector cross talk occurs when
a photon strikes a detector, is
partially absorbed and then
enters the adjacent detector and
is detected again.
• Crosstalk produces two weak
and signals coming from two
different detectors.
• Crosstalk is bad because it
decreases resolution.
• Crosstalk is minimized by using
a crystal that is highly efficient in
absorbing X-rays (high stopping
power).

37. Xenon gas ionization chamber

38. Gas filled detector’s efficiency
Gas filled detectors are less efficient than solid state detectors.
The problem can be partially overcome by the following 3 ways.
• By using Xenon (z=54), the heaviest of the inert gases
• By compressing the Xenon 8 to 11 atmospheres to increase its density
• By using a long chamber to increase the number of atoms along the
path of the beam.

39. Why are Xenon gas detectors not used
in IV generation CT scanners?
• Typical size of a chamber is
1-2 mm wide, 10mm high
and 8-10cm deep
• These 10mm long side
plates are the reason why
Xenon detectors are not in
IV generation CT scanners.

40. Disadvantage of Xenon gas detector
Efficiency - 50 to 60%
This low efficiency is caused by two factors.
• Low density of the absorbing material
• Absorption of X-rays by the front window, which
is needed to contain the high pressure gas

41. OTHER SCAN
CONFIGURATIONS
Interest in faster scan times evolves from a desire
to image moving structures such as the wall of the
heart and contrast material in blood vessel and heart
chambers and to overcome motion artifacts due to
cardiac rhythm and patient breathing .
• Dynamic Spatial Reconstructor(DSR)
• Electron beam computed tomography

42. DYNAMIC SPATIAL RECONSTRUCTOR
• 28 X-ray tubes
• X-ray tubes are aligned with 28
light amplifiers and TV cameras
that are placed behind a single
curved fluorescent screen
• The gantry rotates about the
patient at a rate of 50 RPM
• Data for an image acquired in
about 16 ms.
• Reconstruct 250 C.S. images
from each scan data

43. DSR

44. DSR

45. Disadvantages of DSR
• High Cost
• Mechanical motion is not eliminated

46. Electron Beam Computed
Tomography
• Electron gun
• Large Arcs of tungsten targets
• Detector ring
• 17 slices per second

49. • What is the radiation dose with EBT?
• An advantage of the EBT scanner over
conventional scanners is instead of exposing
the entire circumference of the body to the X-
ray beam, the EBT X-ray beam enters from
the back. Thus, anterior structures such as
the breast and thyroid are subjected to a
lesser dose of radiation (17% of the entrance
skin dose). EBT scanning is usually 1/5th to
1/10th the radiation exposure as Spiral CT
scanning.

50. DSR
• The Dynamic Spatial Reconstructor
•
The seminal scanner for dynamic volumetric imaging is the x-ray CT scanner known as the Dynamic Spatial Reconstructor (DSR)
designed and installed at the Mayo Clinic.[1, 2] The DSR has the ability to obtain up to 240 contiguous 0.9mm thick sections in a
short a time period as 1/60 second and to repeat this acquisition rate 60 times per second. In practice, the data rate is somewhat
reduced from these numbers. The DSR consists of a gantry weighing approximately 17 US tons with a length of 20.5 feet and a
diameter of 15 feet. 14 x-ray guns reside in a hemicylindrical configuration and aim at a juxtaposed hemicylindrical fluorescent
screen. The images produced on the fluorescent screen by the firing of the x-ray guns are recorded by a bank of 14 television
cameras which, until recently, were image isocons which sent analogue signals to be recorded on a bank of 8 video disc
recorders. Since american television is comprised of 240 usable lines, and video rates are 60 per second, it is possible to
reconstruct a cross sectional image of the body by digitizing each of the 240 television line for each of the 14 cameras and
produce 240 cross sections representing 1/60 second resolution. Each stop action stack of slices in actuality represents
approximately 0.1second which is the time in which all 14 x-ray guns are sequentially pulsed on. Because there were only 8 video
disc recorders, every two television line were averaged to reduce the lines per camera to 120, and the data from two cameras
were recorded interlaced on a single video channel. In addition, as the images are produced the gantry rotates at 15 rotations per
minute. Thus, in 1/60 second, the gantry moves a degree and a half such that if the organ system of interest moves slow enough
to allow for 2/60 second of scanning, it is possible to generate 28 angles of view to use in the reconstruction process. Up to a
point, the more angles of view used in the reconstruction process, the better the images. Typically, at least 4/60 seconds of
scanning are used to generate a good quality reconstruction. This can not only be accomplished by utilizing contiguous 1/60
second data sets, but it is possible to retrospectively gate the data together by selecting the same time point from within several
physiologic cycles such as the cardiac or respiratory cycle. Physiologic signals are recorded in with the video signals to allow for
this retrospective gating process. The designers of the DSR, to achieve the ability to obtain dynamic, volumetric image data sets
made compromises in the image resolution such that grey scale resolution was sacrificed. To improve the image quality, the
video imaging chains have been converted from image isocon cameras to charged coupled device (CCD) cameras. [76] Much
larger lenses were ground by Old-Delf and tapered fiberoptics were pulled to take the images from the lens to a microchannel
plate intensifier which then transmits the image to the CCD chips. The process of pulling the tapered fiberoptics introduces some
twisting of the fiberoptics and therefor custom warping algorithms had to be developed for each camera. The images are digitized
on each, camera, the images are unwarped, and the data is sent now to digital tape running at video rates. Although the DSR has
remained a one of a kind system and represents a true tour de force, much of the current image manipulation and display
associated with the massive data sets generated have served as the vanguard for data handling of images coming off of the
currently commercially available scanners.

51. Dynamic Spatial
Reconstructor
• The Dynamic Spatial Reconstructor (DSR) is a high-
temporal resolution, three-dimensional (3-D) X-ray
scanning device based on computed tomography
(CT) principles. It was designed for investigation of
some problems inherent in current diagnostic imaging
techniques, and to allow quantitative studies of
cardiovascular structure and function. One of the
research protocols in which DSR is currently used
involves studying selected pediatric patients with
complex congenital heart disease. Initial results show
that 3-D dynamic images can be obtained from these
patients with minimal invasiveness and that these
images may provide useful diagnostic information.

52. Dynamic Spatial Reconstructor
• Dynamic Spatial Reconstructor
• The first three-dimensional volume scanning (simultaneous acquisition
of multiple contiguous slices) CT scanner with high temporal resolution
(scan repetition rate of up to 60 times/sec), called the dynamic spatial
reconstructor (DSR), was presented in 1980 [8].
• This machine allowed to examine the renovascular anatomy, detecting
arterioles as small as 1 mm in diameter [9] and providing detailed
dilution curves that showed the transit of contrast in the four zones of
the renal cortex (superficial, middle, inner and juxtamedullary) and in
two different areas (outer and inner) of the renal medulla. These dilution
curves allowed a precise calculation of intrarenal RBF. Despite the
great potential of the DSR, it was not extensively used because of its
limited availability, and its high operating and maintenance costs.
However, further studies on intrarenal hemodynamics were made
possible when Imatron, a California company, marketed the first
commercially available EBCT, which is described in the next section.

53. Dynamic scanning
• the acquisition of the same physical image or set of images in rapid succession
such that time dependent changes (e.g. contrast enhancement, motion) can be
studied. The term was originally used and most often refers to
computed tomography CT scanning. Very rapid dynamic CT acquisitions have
been accomplished by cine CT, which has scan times as short as 50 msec.
Recently, the development of slip ring technology has resulted in sub-second
scan times on conventional X-ray tube based CT scanners. With these faster
scan times, many dynamic processes can be monitored. Ultimately, the number
of images that can be obtained during a dynamic image study is limited by the
heat loading of the X-ray tube.
• There are a variety of applications for dynamic CT scanning. These include dual-
phase abdominal studies after contrast administration, cardiac imaging studies,
studies of perfusion using iodinated contrast media, and measurement of
cerebral blood flow using administered xenon as a diffusible agent (see
xenon CT scanning and perfusion measurements). Sometimes, the term
dynamic scanning is used for rapid scanning of a volume even if only a single
time point is sampled. This is in some respects a misuse of the term since the
images do not portray dynamic events. It derives from the increased scanning
rates made available by the advent of dynamic scanning (see
incremented dynamic scanning).

54. Dynamic Spatial
Reconstructor
• The Dynamic Spatial Reconstructor (DSR) is an experimental
apparatus that deserves
• mention, being the only method besides RT3D ultrasound
capable of real time 3D cardiac
• imaging. It was constructed for research (and recently
decommissioned) at the Mayo Clinic
• and was too expensive for general clinical use. The DSR
incorporated aspects of fluoroscopy
• and CT, using multiple X-ray sources and fluoroscopic screens
to gathered 3D data in real-time
• (Robb 1983). During its many years of operation, the DSR
gathered unique and valuable data
• for research in cardiac dynamics and for validation of other
methods of measurement.

55. • Cardiovascular Computed Tomography (CVCT)
• Also called as ultrafast CT / Electron beam CT (EBCT)
• Motion of the parts of the machine is completely eliminated
• Electron gun (320cm long, 130keV)
• Focusing and deflecting coils
• Four 180cm diameter tungsten target arcs
• 2 Rings of detectors
• Electron beam scans the large target, X-rays are produced and
collimated into a 2cm wide fan beam by a set of circular collimators
• The X-ray beam passes through the patient and is detected by an array
of luminescent crystals
• Both the tungsten targets and the detector array cover an arc of 2100
• One scan can be obtained in 50Mts
• Without moving the patient, 8 contiguous tomographic images can be
obtained.

56. Electron Beam Computerized
Tomography (EBCT)
• This instrument represents a novel concept in the use of x-ray to obtain fast tomographic
scanning. In contrast to the DSR and conventional CT, EBCT has no mechanical parts (x-
ray tubes and/or TV cameras) moving around the patients, resulting in lower heat
production and enabling fast scanning. An electron beam, originating from an electron gun
located behind the patient is magnetically deflected sequentially onto four tungsten target
rings, producing eight fan beams (two from each target ring) of x-ray radiation that pass
through the patient. Eight almost simultaneous renal tomographic sections can thereby be
obtained, that are thicker (8 mm) than those produced by the DSR. Alternatively,
consecutive 1.5, 3, or 6 mm thick tomographic slices can be obtained by using a single
target ring and moving the patient table at pre-determined increments. Although its
temporal resolution is lower than that offered by the DSR (50 or 100 msec/image), it is
nonetheless sufficient to obtain adequate evaluation of renal function. Furthermore,
because of the slightly longer scan duration and lower image noise compared to the DSR,
its spatial resolution is superior [10].
• Jaschke, et al. [11, 12] were the first to demonstrate the potential of the EBCT in measuring
RBF, and establish the basic principles for that calculation which correlated highly with
measurements obtained with radioactive microspheres. Subsequent validation studies
demonstrated the accuracy of EBCT-derived measurements of renal, cortical and medullary
(compared to their in vitro) volumes [13] and perfusion (compared to electromagnetic
flowmetry) within a wide range of RBF values [14], as well as changes in blood flow
distribution

57. • The Imatron Electron Beam Tomography (EBT) Scanner
• Imatron's Electron Beam Tomography (EBT) scanner combines
advanced science and technology to create an innovative diagnostic
imaging system. Dramatically different from conventional (mechanical)
CT scanners, Imatron's patented electron beam technology and unique
design offer diagnosticians scan times as fast as 50 and 100
milliseconds. In addition to routine cross sectional imaging of all body
organs, EBT is able to evaluate physiology and blood flow and to
perform any other examination where speed is essential.
Utilizing proprietary EBT technology, a powerful electron beam is
generated and then focused onto one of four tungsten target rings
positioned beneath the patient. Each 210 degree sweep of the electron
beam produces a continuous 30 degree fan beam of x-rays that pass
through the patient to a stationary array of detectors which generates
cross-sectional images.

58. • Engineering
• Imatron's engineering department is an accomplished group of
scientists and engineers working to create the world's most advanced
computed tomography (CT) scanner. Together, they harness and
shape a powerful (650 mA at 130 kV) electron beam, then guide it
through a high-vacuum chamber and around multiple tungsten-coated
target rings.
These patented image acquisition techniques are at the heart of the
Electron Beam Tomography (EBT) scanner, creating a scanner so fast
that it can capture stop-action images of the human heart.
The vast amounts of data captured in a single breath-hold are
transferred at speeds of 200 Mbs to 1 Gbs over a DICOM network to
our near real-time reconstruction systems. Sophisticated programming
techniques enable us to create 2D and 3D images, including virtual
angiograms (fly-throughs of the arteries of the heart) and virtual
colonoscopies (fly-throughs of the colon).

59. Radiation dose from EBT scans
compared to other sources of
radiation
50 to 70 mrem 0.5 to 0.70 mSv
• EBT Coronary Calcium 80 to 120 mrem 0.8 to 1.2 mSv
Scan
Non-invasive Coronary 100 to 150 mrem 0.75 to 1.5 mSv
Angiogram 100 to 300 mrem 0.75 to 3.0 mSv
EBT Low-dose Lung 300 mrem 3.0 mSv
Scan
EBT Abdominal/Pelvis 2 mrem 0.02 mSv
Scan 8 to 10 mrem 0.08 to 0.1 mSv
Background Sunshine
Radiation in 1 year 48 mrem 0.48 mSv
Cross country airplane 300 mrem 3.0 mSv
trip
Standard Chest X-ray 500 to 1000 mrem 6.0 to 10.0 mSv
Standard Abdominal X- 600 mrem 6.0 mSv
ray 600 to 1000 mrem 6.0 to 10.0 mSv
Standard Spine X-ray
series
Standard Coronary
Angiogram Mrem and mSv exposure varies with body size.
Standard Lower G.I. X-ray
Recommended safety limits for radiation
series
Spiral CT Whole body exposure is less than 5,000 mrem per year.
scan

60. Electron Beam CT
• The latest foray of technology in CT is the electron
beam CT (EBCT) scanner. In EBCT an electron
beam is electro-magnetically steered towards an
array of tungsten X-ray anodes that are positioned
circularly around the patient. The anode that was hit
emits X-rays that are collimated and detected as in
conventional CT. The use of an electron beam allows
for very quick scanning because there are no moving
parts. An entire scan can be completed in 50 to 100
milliseconds. This quick scan time makes this the
only CT method which can scan the beating heart. At
the present time, these machines are installed in only
a few sites world-wide.

61. Ultrafast / Electron Beam CT
Scan
• What is an ultrafast/electron beam CT (computed tomography) scan?
• In conventional x-rays, a beam of energy is aimed at the body part being
studied. A plate behind the body part captures the variations of the energy beam
after it passes through skin, bone, muscle, and other tissue. While much
information can be obtained from a regular x-ray, specific detail about internal
organs and other structures is not available. With computed tomography (also
called CT or CAT scan), the x-ray beam moves in a circle around the body. This
allows many different views of the same organ or structure, and provides much
greater detail. The x-ray information is sent to a computer which interprets the x-
ray data and displays it in two-dimensional form on a monitor. A new technology
called ultrafast CT (also known as electron-beam tomography, or EBT) is now
used, in some cases, to diagnose heart disease. Ultrafast CT can take multiple
images of the heart within the time of a single heartbeat, thus, providing more
detail about the heart's function and structures, and also greatly decreasing the
amount of time required for a study.
• A three-dimensional (3D) version of ultrafast CT may be used to assess the
pulmonary arteries and veins in the lungs.
• Ultrafast CT scan may also be used to evaluate selected heart defects after
birth.

62. Electron beam computed
tomography (CT)
• Exam Overview
• Electron beam computed tomography (CT) scanning
is a new test that can be used to detect calcium
buildup in the lining of arteries.
• Electron beam CT scanning is much faster than
standard CT scanning. Electron beam CT scanning
can produce an image in a fraction of a second and
can take an accurate picture of an artery even while
the heart is beating. Standard CT scanning is not fast
enough to take pictures of a pumping heart. In
standard CT, several pictures, or "slices," of the heart
are taken from different angles. These pictures are
then analyzed using a computer to create a three-
dimensional view of the heart.

63. EBCT
• Why Is It Done?
• This test is used to identify calcium
buildup in heart arteries, which can be a
risk factor for coronary artery disease
(CAD). It may be used as a screening
tool to detect hardening of the arteries
in people who are at high risk of
developing atherosclerosis.

64. EBCT
• Results
• Fat and calcium buildup may be seen in the arteries during an
electron beam CT scan. Aggressive treatment for
atherosclerosis may be appropriate.
• If electron beam CT scanning does not show the presence of
calcium buildup in the arteries, then the chances of having CAD
are low. 1 Most people who have a negative angiography test
result also have a negative electron beam CT scan test result. 1
• A high calcium score on an electron beam CT scan indicates a
greater risk of having cardiovascular problems within the next 2
to 5 years, especially when a person also has multiple risk
factors for developing coronary artery disease. 1 However, the
scan does have a fairly high rate of false-positive results.

65. Electron Beam CT
• Advanced Body Scan of Newport is a physician
owned facility that opened in June 2001 with a
mission to provide the community with cutting edge
diagnostic and screening medical imaging
procedures. Electron Beam Tomography (EBT) is an
innovative outgrowth of Computed Tomography (CT)
technology specifically developed to acquire images
fast enough to freeze the beating heart. This
'Ultrafast' cat scanner is open and non-
claustrophobic, and the X-ray radiation used to
acquire the body images is only about 20% of what
you would receive from a conventional CT scanner.
The full body EBT scan delivers not much more
radiation than your total annual radiation exposure

66. Electron Beam CT
• When you visit us at Advanced Body Scan of Newport, you can
be assured that you will be made to feel welcome and nurtured
from your initial greeting to your final medical consultation. You
stay fully clothed for the exam which takes only a few minutes to
complete. No shots or needles are involved. You simply lie
down on your back, hold your breath for a few seconds while the
images are taken, and within minutes, you can see the results
yourself on the screen.
• Advanced Body Scan of Newport offers discount scan packages
to corporate customers. Our sales staff will be happy to answer
any questions and customize any multiple scan package to
meet your needs.
• Only GE-Imatron™ Electron Beam CT Scanners have FDA
approval for Coronary Artery Calcium Scoring and CT Coronary
Angiography.

67. Electron Beam CT
• Heart Scan: Coronary Artery Calcium Score) the EBT Heart
Scan is a breakthrough in Early Detection and Cardiac Risk
Assessment. Coronary artery calcium is a marker for plaque in a
blood vessel. These calcium deposits form years before the first
symptoms of heart disease, such as chest pain or shortness of
breath, appear.
• Full Body Scan: The Body Scan includes the Heart Scan, the
Lung Scan, a CT scan of your Abdomen and Pelvis and a Bone
Scan, allowing us to detect liver tumors, gallstones, kidney
stones, kidney tumors, aneurysms and abnormalities of the
prostate or ovaries. Before you leave you will have had a
personal consultation with our health professional.
• Electron Beam CT Coronary Angiography (EBA):
Approved by the FDA in November 1999, the Electron Beam
CT scanner provides an opportunity to examine your
coronary arteries without the risks of conventional
angiography. Coronary angiography done on the Electron
Beam CT Scanner takes only about half an hour and is
reimbursed by insurance plans

68. Electron Beam CT
• Lung Scan: Lung Cancer strikes 150,000 Americans each year.
Despite treatment advances, five-year survival for lung cancer
patients remains only 14%. Only CT scans can find lung cancer
at an earlier and potentially more curable stage. All current or
former smokers or those exposed to carcinogens such as
asbestos could benefit from this test.
• 3D QCT Bone Scan: Bone density provides the critical
information you need to identify osteoporosis, a debilitating
disease that can lead to bone fractures. An essential exam for
all post-menopausal women, 3D QCT Bone Densitometry is
more accurate than conventional DEXA studies.
• Virtual Colonoscopy: Colorectal Cancer is the second leading
cause of cancer death. This test is a new technique for
visualizing colon polyps that could become cancerous. This
alternative to standard Colonoscopy does not require a hospital
or outpatient stay, or anaesthesia. Utilizing air and advanced
image rendering, a virtual voyage through your colon is
generated from the scan images.

69. CVCT
• Cardiovascular CT
•
• Integrating knowledge from Philips' leadership in cardiac imaging and monitoring
systems, Brilliance CT is uniquely designed to adapt to your patients and
overcome the many challenges that unpredictable heartbeat rhythms can
present. Philips-patented Rate Responsive™ image acquisition technology
adapts to your patients - rather than the other way around. The many intelligent
technologies built into the Brilliance CT configurations not only improve
departmental workflow, but the early detection of cardiac disease as well.
•
•
• Features and Benefits
• Redefining patient care through automatic adjustment to variations in patient
heart rate and rhythm during the scan and subsequent image reconstruction
• Least invasive, most reliable solution for assessment through accurate
determination of the most stable cardiac phase for each heart region
• Achieve temporal resolutions as low as 53ms to visualize coronary anatomy and
determine stenosis as well as plaque constituents.

70. Toshiba CVCT
• Expanding the Limits of Cardiovascular CT
Delivering 16 0.5mm isotropic slices with 400msec rotation
times, the Aquilion™ 16 CFX images the smallest vessels with
confidence in the widest range of patients.
• Temporal resolution as low as 400 msec for clear, detailed
cardiac evaluation
• Flexible scan speeds and SURECardio software ensure optimal
imaging for variable and high heart rates
• Industry’s longest couch supports whole-body CTA without
patient repositioning
• Ideal for use in cardiology, trauma, neurology and oncology
• A suite of applications, called SURETechnologies, specifically
designed to provide the highest productivity and best image
quality at the lowest possible dose

71. Cine ct
• Cine ct,
• a very fast computed tomography CT scanner which can
acquire images from a single or small number of image
locations in a small fraction of a second. The scanner, also
named millisecond CT, ultrafast CT or electron beam CT,
requires no mechanical motion to acquire the projection data.
Instead of rotating an X ray tube around the object, the cine CT
system sweeps an intense electron beam across a large,
stationary anode target which surrounds the patient. X-rays are
emitted from the point where the electrons strike the target. The
X-rays transmitted through the object are measured by a
stationary array of detectors. The time needed for collecting
data for a single slice is 50-100 ms, although a longer scan time
can be used to reduce image noise.

72. Cine CT
• In some scanning modes, two detector rings allow the imaging of two
sections in a single scan of the X-ray target. Also, multiple target rings,
scanned sequentially, allow a volume to be imaged rapidly. The system
is very well suited to dynamic studies or studies where motion artefacts
might be a problem (e.g. cardiac applications), and for imaging of
uncooperative patients (e.g. children).
• Ideally, the X-ray target would completely surround the object, thereby
allowing the source of X-rays to rotate through 360. In the ideal system,
the detectors would also be on a complete ring. Mechanical constraints
do not allow this arrangement. As a result, the source and detectors are
not actually on the same plane, introducing complications to the
reconstruction process and the possibility of artefacts. Another
limitation in image quality results from the limit on the electron beam
current. Although the current is high (~ 1 000 mA), the very short
imaging time leads to a low mAs. Cine CT systems generally have
higher noise level and lower spatial resolution than conventional CT
systems, but are ideal when their high scanning speed is well suited to
the clinical application. Among the possible uses are cardiac imaging
with and without the use of contrast agents, lung imaging, and
paediatric studies.

73. Cine CT
• The cine CT system has no mechanical scanning motion. In this
system both the X-ray detector and the X-ray tube anode are
stationary. The anode, however, is a very large semicircular ring
that forms an arc around the patient scan circle, and is part of a
very large, non-conventional X-ray tube. The source of X-rays is
moved around the same path as a fourth generation CT scanner
by steering an electron beam around the X-ray anode. Because
the electron beam can be moved very rapidly, this scanner can
attain very rapid image acquisition rates. In the literature, this
system has been referred to variably as fifth generation and
sixth generation. It has also been described as a stationary-
stationary scanner. The terms millisecond CT, ultrafast CT and
electron beam CT have also been used, although the latter can
be confusing since the term suggests that the patient is exposed
to an electron beam.

74. CVCT

75. CVCT

76. Applications of CVCT
• CardioVascular CT is an effective, non-invasive
imaging technique for patients with congenital and
acquired heart disease. Various forms of aortic
disease - including aortic malpositions, dissections,
and coronary aneurysms - are well suited for
investigation by CV CT.
The ability of CV CT to acquire volumetric axial
images in a short breath-hold enables clinicians to
build accurate 3D anatomical models of the entire
heart and vascular structures. In addition, CV CT can
be used to screen pericardial lesions, and accurately
show the extent and location of intracardiac masses
and tumors adjacent to the heart.

77. Formation of CT images

78. CT Sinogram
The data acquired for one CT
slice can be displayed before
reconstruction. This type of
display is called a Sinogram.

79. What are we measuring?
The average linear attenuation
coefficient (µ), between tube
and detectors
Attenuation coefficient reflects
the degree to which the X-ray
intensity is reduced by a
material

80. PIXEL & VOXEL
• Cross sectional layer of
the body is represented
as an image matrix.
• Each square of the
image matrix is called
pixel(picture element)
and it represents tiny
block of tissue called
voxel (volume element)

81. Linear attenuation coefficient
• The linear attenuation coefficient (µ) of
each pixel is determined by :
1. Composition of the voxel
2. Thickness of the voxel µ
3. Quality of the radiation beam

83. Algorithms for image
reconstruction
• An algorithm is a mathematical method for
solving a problem
• The linear attenuation coefficients of all the
pixels in the image matrix should be
determined by solving thousands of
equations.
• All algorithms attempt to solve the equations
as rapidly as possible without compromising
accuracy.

84. IMAGE RECONSTRUCTION
Process of generating an image from the raw
data or set of unprocessed measurements
made by the imaging system.
Image reconstruction algorithms
• Back projection
• Iterative methods
• Analytic methods : 2D Fourier analysis
Filtered Back
Projection

85. Simple back projection method
• The image profiles look like steps. The height of the steps is
proportional to the amount of radiation that passed through the
block. The steps are then assigned to a gray scale density that
is proportional to their height. When the rays from the two
projections are super imposed, or back projected, they produce
a crude reproduction of the original object. In practice, many
more projections would be added to improve image quality.
• All points in the back projected image receive density
contributions from neighboring structures.
• The radio dense material severely attenuates the beam and
produces localized spikes in the image profiles. Back projection
of the rays from these spikes produces a star pattern. A great
number of projections will obscure the star pattern, but the back
ground density remains as noise to deteriorate the quality of the
CT image.

86. Simple back projection method

87. Iterative method
• Assumption (for eg. all points in the matrix
have same value)
• Comparison (with the measured values)
• Correction (to bring the two into agreement)
• Repetition (of the process until the assumed
and measured values are the same or within
acceptable limits)

88. Iterative method
Simultaneous reconstruction
• All projections for the entire matrix are calculated at the
beginning of the iteration, and all corrections are made
simultaneously for each iteration.
Ray by Ray correction
• One ray sum is calculated and corrected and these corrections
are incorporated into future ray sums, with the process being
repeated for every ray in each iteration.
Point – by – point correction
• The calculations and corrections are made for all rays passing
through one point, and these corrections are used in ensuring
calculations, again with the process being repeated for every
point.

89. Two – dimensional Fourier
analysis:
• Basis: Any function of time [f(t)] or
space [f(x)] can be represented by the
sum of various frequencies and
amplitudes of sine and cosine waves.

90. 2D FOURIER ANALYSIS

91. Filtered back projection
• The image is filtered or modified to counter balance
the effect of sudden density changes, which causes
blurring (star – pattern). Those frequencies
responsible fro blurring are eliminated to enhance
more desirable frequencies.
• The density of the projected rays is adjusted that is,
the inside margins of dense areas are enhanced
while the centers and immediately adjacent areas are
repressed. The net effect is an image more closely
resembling the original object.

92. FILTERED BACK PROJECTION

93. FILTERED BACK PROJECTION

94. Comparison of Mathematical methods
• In terms of speed, Analytical methods are
faster than iterative methods
• But with incomplete data, iterative methods
are faster than analytical methods. Analytical
methods does time – consuming
interpolations to fill in missing data, whereas
iterative methods simply average adjacent
points.

95. CT NUMBER & HOUNSFIELD UNIT
The computer calculates a relationship between the
linear attenuation coefficients of the pixel and water
which is given as CT number.
To image materials with µ higher than dense bone
CT number larger than 1000 should be available
CT numbers based on a magnification constant of
1000 are Hounsfield units

96. Relationship between CT numbers & Gray scale

97. WINDOWING
• Windowing is the process in which the gray level
can be manipulated using the CT numbers to provide
optimum demonstration of different structures seen
on the image.
• Window Width(WW) is the range of CT numbers for
the gray scale & WW control alters the image
contrast
• Window Level(WL) is the centre of the gray-scale
image & WL control alters the image density/CT
number of the tissue to be displayed

98. Graphic illustration of the effect of different
WW & WL settings on the CT image

99. Image Quality in CT
Image quality is the visibility of diagnostically
important structures in the CT image.
The factors that affect CT image quality are
• Quantum mottle (noise)
• Resolution : Spatial and contrast
• Patient exposure.
The factors are all interrelated

100. Quantum mottle (Noise)
• Quantum mottle is the statistical fluctuations
of X-photons absorbed by the detector
• The only way to decrease noise is to increase
the number of photons absorbed by the
detector.
• The way to increase the number of photons
absorbed is to increase x-ray dose to the
patient.
• Mottle becomes more visible as the accuracy
of the reconstruction improves.

101. RESOLUTION
i) Spatial resolution
• Spatial resolution is the ability of the CT
scanner to display separate images of
two objects placed close together.

102. ii) Contrast resolution
• Contrast resolution is the ability of the
CT scanner to display an image of a
relatively large (2 or 3mm) object that is
only slightly different in density from its
surroundings.

103. RADIATION DOSE
• Even distribution of radiation dose to
the tissues as exposures are from
almost all angles.
• No overlapping of scan fields takes
place.
• Exposure factors used are higher to
improve spatial and contrast resolutions
and to reduce noise.

104. Comparison of CT with Conventional Radiography

105. CT ARTIFACTS
Artifacts are distortions or errors in the
image that are unrelated to the object
scanned .
Most common artifacts in CT are
• Motion artifacts
• Streak artifacts
• Beam hardening artifacts
• Partial volume averaging artifacts
• Ring artifacts

106. EFFECTS OF ARTIFACTS
• DETERIORATE IMAGE QUALITY
• SUBJECT INFORMATION IS
LOST
• PATHOLOGICAL DETAILS ARE
LOST

107. MOTION ARTIFACTS
Cause : Patient movement
Appearance: Blurred / streaks / ghost images
Rectification:
• reduction in scan time
• Clear and concise instruction to the patient
• proper patient immobilization
• if needed,administration of
sedatives/antiperistaltic drugs

108. Motion artifact

109. STREAK ARTIFACTS
Cause: Presence and movements of
objects of very high density(contrast
media, metallic implants,surgical
clips)
Appearance: Streaks
REMEDY:-
•Remove the offending object
if possible. Use a smoothing
algorithm. e.g. Standard algorithm.

110. Streaking
Streaking occurs due to inconsistency in a
small group of readings
•Partial volume
•Photon starvation
•Metal artifacts
•Patient movement

111. DENTURES
PRODUCING
STREAK ARTIFACT
SURGICAL
CLIP IN HEART
PRODUCING
STREAK ARTIFACT

114. BEAM HARDENING
ARTIFACTS
Cause :
Polyenergetic X ray spectrum(25-120kV)
APPEARANCE:-
Wide dark streak
Rectification :
• Beam hardening correction algorithm

115. PARTIAL VOLUME
AVERAGING ARTIFACTS
• Cause: presence of tissues with highly
varying absorbtion properties in a voxel.
• Rectification : Usage of Thinner CT
slices

117. OUT OF FIELD ARTIFACT
CAUSE:-
Scan FOV not covering
the entire anatomy
APPEARANCE:-
Shading/streaks
REMEDY:-
Ensure that scan field of
view is larger than the
object to be scanned

118. RING ARTIFACTS
• CAUSE : Detector failure or miscalibration
of a detector
• APPEARANCE:-
Ring
• Rectification : regular quality assurance
checks

119. RING APPEARANCE