Group 4 - CT Scanner

SCIENTIFIC REPORT
COMPUTED TOMOGRAPHY
SCANNING SYSTEMS
MAJOR: BIOMEDICAL ENGINEERING

LAB 1A- BIOMEDICAL INSTRUMENTATIONS
Teacher: Dr. Nguyen Thanh Qua

TA: Nguyen Hoang Phuc
Group 4:
Tran Phuong Anh-BEBEIU21002
Thai Nguyen Hao-BEBEIU21145
Le Nguyen Khai Hoan-BEBEIU21146
CONTENTS
CHAPTER 1: INTRODUCTION.......................................................................... 3
1.1. CT Scan............................................................................................................ 3
1.2. History and Revolution.....................................................................................3
1.2.1. Data-Acquisition Geometries..................................................................4
1.2.2.Comparisons of CT Scan Generations..................................................... 5
CHAPTER 2: WORKING PRINCIPLE................................................................... 6
2.1. Block Diagram of CT Scan...............................................................................6
2.2. Components...................................................................................................... 7
2.3. Working operation of CT Scan.......................................................................10
2.4. Data - Acquisition System.............................................................................. 10
2.5. Computer System............................................................................................11
2.6. Reconstruction of CT Image...........................................................................13
2.6.1. CT Imaging..........................................................................................13
2.6.2. Image Display......................................................................................14
2.7. CT Scanning Methods.................................................................................... 16
2.7.1. Conventional CT Scanner....................................................................16
2.7.2. Cone- beam CT Scanner......................................................................17
2.7.3. Spiral CT Scanner................................................................................18
2.7.4. Multislice CT Scanner......................................................................... 18
CHAPTER 3: CLINICAL APPLICATION......................................................20
3.1. Main Purposes of CT Scan............................................................................. 20
3.2. Medical treatments .........................................................................................20
3.3. The risks of CT Scanning……....................................................................... 21
3.4. How long does computed tomography take?……..........................................22
3.5. Preparation for computed tomography……................................................... 22
CHAPTER 4: DEVELOPMENT......................................................................... 24
FURTHER INFORMATION....................................................................................26
REFERENCE........................................................................................................... 29
2
INTERNATIONAL UNIVERSITY
BIOMEDICAL ENGINEERING DEPARTMENT
CHAPTER 1: INTRODUCTION
1.1. Computed Tomography Scan (CT Scan)

The process of taking a series of detailed images of an area of the body using a
computer connected to an X-ray device. Images are taken from different angles and
used to create a three-dimensional (3D) view of tissues and organs. Dyes can be
injected into veins or swallowed to make tissues and organs look clearer. Computed
tomography can be used to diagnose a disease, plan treatment, or see how well a
treatment is working. Also known as CAT scan, computer-aided axial tomography,
computed tomography, or CT scan.
When someone is damaged, becomes ill, or is seriously injured, the first thing
that springs to mind is how to get better. And it is during moments like these that a
doctor might be of assistance. They must search for the reasons for your discomfort to
comprehend what is causing it. These are the periods when doctors will use a variety
of tests to determine what is hurting your health. These tests include blood tests, X-
rays, MRIs, and CT scans, among others. Doctors undertake a variety of diagnostic
imaging examinations, the most popular and widely used of which is the CT scan.
The radiologist will have a highly detailed picture of the structures that make
up your body because to all of these varied slices and 3D reconstructions. This should
aid them in making a diagnosis (figuring out what's causing your current symptoms)
so that the appropriate therapy can be started as soon as feasible.
Instead of taking a sequence of photos of discrete slices of the body like the
original CT machines did, modern CT machines capture continuous pictures in a
helical (or spiral) form. Helical CT (also known as spiral CT) has significant
advantages over prior CT techniques: it is faster, creates higher-quality 3-D images of
inside organs, and can identify minor abnormalities more effectively.
1.2. History and Revolution
The CT was invented in 1972 by Godfrey Hounsfield, a British engineer at EMI
Laboratories in the United Kingdom, and Allan MacLeod, a South African-born
physicist at Tufts University in Massachusetts. Hounsfield and Hounsch were later
awarded the Nobel Peace Prize for their contributions to medicine and science. The
first clinical CT scanner was installed between 1974 and 1976. The original system
was intended solely for head imaging, but in 1976 a "whole body" system with a
larger patient opening became available. CT became popular around 1980. Currently,
there are about 6,000 CT scanners installed in the United States, and about 30,000 are
installed all over the world. The first CT scanner developed by Hounsfield in EMI's
lab took hours to collect raw data for a single scan or "slice" and days to reconstruct
one image from that raw data. It took. The latest multi-slice CT system can take up to
4 data slices in about 350 ms and reconstruct a 512 x 512 matrix image from millions
of data points in less than a second. The latest multi-slice CT system can scan the
entire breast (48 mm slice) in 5-10 seconds. CT has made great strides in speed,
patient comfort, and resolution over its 25-year history. The faster the CT scan time,
the faster you can scan more anatomical structures. Faster scans help eliminate patient
movement artefacts such as breathing and peristalsis. CT scans are faster and more
patient-friendly than ever before. A tremendous amount of research and development
has been done to provide excellent image quality for diagnostic reliability at the
lowest possible X-ray dose.
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1.2.1. Data-Acquisition Geometries

Based on the scanning configuration, scanning motions, and detector
arrangement, projection data can be obtained in one of several different geometries
detailed below. The evolution of these geometries is described in terms of
"generations," which mirrors the historical progression. Current CT scanners employ
third-, fourth-, or fifth-generation geometries, each with its own set of advantages and
disadvantages.
Figure 2. Schematic drawing of a typical CT scanner installation, consisting of (1) control

console, (2) gantry stand, (3) patient table, (4) head holder, and (5) laser imager.
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1.2.2. Comparisons of CT Scan Generations

Generation Source Source Detector Detector Source- Advantages Disadvantages
Collimation Collimation Detector
Movement
1st Single- Pencil Single None Move Scattered Slow
ray tube beam linearly energy is
and rotate undetected
in unison
2nd Single- Fan beam, Multiple Collimated Move Faster than Lower
ray tube not enough to source linearly 1st efficiency
to cover direction and rotate and larger
FOV in unison noise because
of the
collimators in
detectors
3rd Single- Fan beam, Many Collimated Rotate in Faster than More
ray tube enough to to source synchrony 2nd , expensive
cover FOV direction continuous than 2nd, low
rotation efficiency
using slip
ring
4th Single- Fan beam Stationary Cannot Detectors Higher High

ray tube covers fan ring of collimate are fixed, efficiency scattering
beam detectors detectors source than 3rd since
rotates detectors are
not
collimated
5th ( EBCT) Many Fan beam Stationary Cannot No Extremely High cost,
Tungsten ring of collimate moving fast, difficult to
anodes in detectors detectors parts capable of calibrate
a single stop action
large tube imaging of
beating
heart
Overview
Figure 1. Four Generations of CT Scanners illustrating the parallel- and fan-beam

geometries
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CHAPTER 2: WORKING PRINCIPLE

2.1. Block Diagram of CT Scan
A)
B)
Figure 4. Two basic block diagrams of CT Scan
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2.2. Components
X-Ray System
X-Ray is a photographic or digital image of the internal composition of
something, especially a part of the body, produced by X-rays being passed through it
and being absorbed to different degrees by different materials. X-ray is a high-energy
radiation with waves shorter than those of visible light. X-ray is used in low doses to
make images that help to diagnose diseases and in high doses to treat cancer.
The x-ray system consists of the x-ray source, detectors, and a data-acquisition
system.
X-Ray Source
The source of radiation for all CT scanners is bremsstrahlung x-ray tubes. X-rays
are produced by accelerating a beam of electrons onto a target anode in these tubes,
which are common in diagnostic imaging. The focus spot is the area of the anode
from which x-rays are emitted and projected along the beam direction. The most
common focal spot sizes are 0.5 x 1.5 mm and 1.0 x 2.5 mm for most systems. The
width of the fan beam is controlled by a collimator assembly, which adjusts the width
of the imaged slice between 1.0 and 10 mm.
These tubes typically require 120 kV at 200 to 500 mA to produce x-rays with an
energy spectrum spanning from 30 to 120 keV. High-frequency generators, which
typically operate between 5 and 50 kHz, are used in all modern systems. Some spiral
systems have a stationary gantry generator that requires high-voltage (120-kV) slip
rings, while others have a revolving generator that requires lower-voltage (480-V) slip
rings. Because the production of x-rays in bremsstrahlung tubes is inefficient, the
majority of the power given to the tubes is used to heat the anode. The tube is cooled
by a heat exchanger on the spinning gantry. Spiral scanning, in particular, puts a strain
on the x-ray tube's heat-storage capacity and cooling pace.
The x-ray beam's intensity is reduced as it goes through the patient due to
absorption and dispersion. The degree of attenuation is determined by the x-rays'
energy spectrum as well as the patient tissues' average atomic number and mass
density. The transmitted intensity is calculated as follows:
where Io and II are the incident and transmitted beam intensities, respectively; L is the length
of the x-ray path; and µ(x) is the x-ray linear attenuation coeffificient, which varies with
tissue type and hence is a function of the distance x through the patient.
The integral of the attenuation coeffificient is therefore given by
The reconstruction algorithm requires measurements of this integral along many paths in the
fan beam at each of many angles about the isocenter. The value of L is known, and Io is
determined by a system calibration. Hence values of the integral along each path can be
determined from measurements of It.
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X-Ray Detectors
X-ray detectors used in CT systems :
 Have a high overall effificiency to minimize the patient radiation dose, have a
large dynamic range.
 Be very stable with time.
 Be insensitive to temperature variations within the gantry.
Three important factors contributing to the detector effificiency are geometric
effificiency, quantum (also called capture) effificiency, and conversion effificiency.
The area of the radiation-sensitive detectors as a percentage of the total exposed area
is referred to as geometric efficacy. This value will be degraded by thin septa between
detector components to remove stray radiation or other insensitive regions. The
fraction of incident x-rays on the detector that are absorbed and contribute to the
measured signal is referred to as quantum efficacy. The capacity to accurately convert
an absorbed x-ray signal into an electrical signal is referred to as conversion efficacy
(but is not the same as the energy conversion effificiency). The product of the three is
overall efficacy, which typically ranges between 0.45 and 0.85. If picture quality is to
be maintained, a value of less than 1 implies a nonideal detection system, which
necessitates an increase in patient radiation dose. The term "dose efficacy" is
occasionally used to refer to total efficacy. Modern commercial systems use one of
two detector types: solid-state or gas ionization detectors.
Solid-State Crystal Detectors.
Solid-state detectors are made up of a series of
photodiodes and scintillating crystals. Although early
scanners used bismuth germanate crystals with
photomultiplier tubes, the scintillators are usually
cadmium tungstate (CdWO4) or a ceramic substance
comprised of rare earth oxides. Solid-state detectors
offer high quantum and conversion efficiencies, as
well as a wide dynamic range.
Xenon Gas Detectors.
Gas ionization detectors are made up of a series
of chambers filled with compressed gas (usually
xenon at up to 30 atm pressure). To gather ions
created by the radiation, a high voltage is applied to
tungsten septa between chambers. Although these
detectors have high stability and a wide dynamic
range, they have poorer quantum efficiency than
solid-state detectors.
Working operations of detectors
 Xenon Gas Detector
Pressurized xenon gas → Ionisation → Electrical signal
 Solid-State Crystal Detector
Ceramic or crystal scintillator → Photon capture → Light → Photon-diode →
Electrical signal
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Scintillattion Crystals
Materials that produce light (scintillate) when x-ray interact. It is similar to
intensifying screen. Number of light photons produced energy of incident xray beam.
Light photons need to be converted to electrical signal.
X-ray Generator
An X-ray generator is a device that produces X-rays.
Together with an X-ray detector, it is commonly used in a
variety of applications including medicine, X-ray fluorescence,
electronic assembly inspection, and measurement of material
thickness in manufacturing operations. In medical applications,
X-ray generators are used by radiographers to acquire x-ray
images of the internal structures (e.g., bones) of living
organisms, and also in sterilization.
The X-ray generator produces X-rays when an electrical
current is applied to it. The X-ray generator is a device that acts as the primary control
mechanism for the entire fluoroscope. It is through the X-ray generator that current is
allowed to flow into the X-ray tube.
X-Ray Tube
An X-ray tube is a vacuum tube that converts electrical
input power into X-rays. X-ray tubes should be focal spots 0.6
mm small, 1.0 mm or similar large. The X-ray tube should have
high-speed rotor circuitry. An x-ray tube functions as a specific
energy converter, receiving electrical energy and converting it
into two other forms of energy: x-radiation (1%) and heat (99%).
Because heat is an undesirable byproduct of this conversion
process, x-radiation is created by extracting energy from
electrons and converting it to photons.
=> In the x-ray tube, this very specific energy conversion
takes place.
X-Ray Beam
The x-ray beam is polyenergetic (has many energies) and
the x-ray emission spectrum contains a wide range of energies.
The lowest energies are always around 15 to 20 keV, while the
highest energies are always the kVp set on the control panel.
Collimator
A collimator is a device which narrows a beam of particles or
waves. Collimator is a device for producing a beam of parallel
rays (as of light) or for forming an infinitely distant virtual image that can be viewed
without parallax. Collimator is a device for changing the diverging light or other
radiation from a point source into a parallel beam.This collimation of the light is
required to make specialized measurements in spectroscopy and in geometric and
physical optics.
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Attenuation
Attenuation is the reduction of the intensity of an x-ray beam as it traverses
matter. The reduction may be caused by absorption or by deflection (scatter) of
photons from the beam and can be affected by different factors such as beam energy
and atomic number of the absorber.
Main purposes of X-Ray
X-rays can be used to examine most areas of the body. They're mainly used to
look at the bones and joints, although they're sometimes used to detect problems
affecting soft tissue, such as internal organs. Problems that may be detected during an
X-ray include: bone fractures and breaks.
The most familiar use of x-rays is checking for fractures (broken bones), but x-
rays are also used in other ways. For example, chest x-rays can spot pneumonia.
Mammograms use x-rays to look for breast cancer.
Bone x-ray uses a very small dose of ionizing radiation to produce pictures of
any bone in the body. It is commonly used to diagnose fractured bones or joint
dislocation. Bone x-rays are the fastest and easiest way for your doctor to view and
assess bone fractures, injuries and joint abnormalities.
2.3. Working operation of CT Scan
A CT Scanner looks like a big, square doughnut.
Inside the covers of the CT Scanner is a rotating
frame which has an x-ray tube mounted on one side
and the detector mounted on the opposite side. A fan
beam of x-ray is created as the rotating frame spins
the x-ray tube and detectors around the patient. As the
x-ray tube and detector make this 360° rotation, the
detectors takes numerous snapshots. Typically, in one
360° lap, about 1,000 profiles are sampled. Profiles
are then superimposed to generate a 3D images.
A moving scanning system, including an X-ray
source, collimators and detectors, rotates around a
part of the patient’s body, taking many readings of X-
ray transmissions across the analysed part (e.g. the
head). These readings are then sent along with the
output of a reference detector to a large memory disk
and to a computer, which through a suitable software
program reconstructs a cross-section of the analysed
part. The processing done by the computer is
essentially a 2-D (image) reconstruction from a 1-D
projection.
2.4. Data-Acquisition System
The transmitted fraction It/Io through an obese patient can be less than 10–4. The
data-acquisition system (DAS) is responsible for correctly measuring it over a
dynamic range of more than 104, encoding the results into digital values, and
transmitting the values to the system computer for reconstruction. Precision
preamplifiers, current-to-voltage converters, analog integrators, multiplexers, and
analog-to-digital converters are all used by some manufacturers. Some manufacturers,
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on the other hand, use the preamplifier to control a synchronous voltage-to-frequency

converter (SVFC), which eliminates the need for integrators, multiplexers, and
analog-to-digital converters. Depending on the manufacturer, the logarithmic
conversion is done with an analog logarithmic amplifier or a digital lookup table.
For some scanners, sustained data transfer rates
to the computer can reach 10 Mbytes/s. For systems
with a fixed detector array, this can be performed with
a direct connection. Third-generation slip-ring
systems, on the other hand, must employ more
advanced approaches. Optical transmitters on the
revolving gantry are used by at least one manufacturer
to send data to fixed optical receivers.
Figure 3: Data acquisition geometries used in

industrial x-ray digital radiography and computed
tomography imaging. (a) Discrete-beam
translate/rotate scanner configuration using a
single detector. (b) Well-collimated fanbeam
configuration using a linear detector array. This
geometry is the most common for industrial and
medical xray imaging. (c) Cone-beam
configuration using a area-array detector. These
geometries are also employed for neutron imaging,
while for protons (a) is the typical imaging
geometry.
2.5. Computer System

Manufacturers employ a variety of computer systems to manage system
hardware, acquire projection data, reconstruct, display, and alter tomographic images.
Figure 62.11 shows a typical system with 12 independent processors connected via a
40-Mbyte/s multibus. To produce an image on a 1024 x 1024 pixel display, multiple
custom array processors are needed to provide a total computing speed of 200
MFLOPS (million floating-point operations per second) and a reconstruction time of
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around 5 s. To coordinate tasks, a simplified UNIX operating system is employed to

create a multitasking, multiuser environment.
Figure 5. The computer system controls the gantry motions, acquires the x-ray
transmission measurements, and reconstructs the fifinal image. The system shown here
uses 12 68000-family CPUs.
Figure 6. Summary of the CT Dose Index (CTDI) Values at Two Positions (Center
of the Patient and Near the Skin) as Specifified by Four CT Manufacturers for Standard
Head and Body Scans.
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2.6. Reconstruction of CT Image

Image reconstruction is a set of rules or directions for getting a specific output
from a specific input. The distinguishing feature of an algorithm is that all vagueness
must be eliminated, the rules must describe operations that are so simple and well
defined, they can be executed by a machine. Furthermore, an algorithm must always
terminate after infinite number of steps.
2.6.1. CT Imaging
Goal of x-ray CT is to reconstruct an image whose signal itensity at every point
in region imaged is proportional to µ (x, y, z), where is linear attenuation coefficient
for x-rays. In practice, µ is a function of x-ray energy as well as position and this
produces a number of complications that we will not investigate here. X-ray CT is
now a mature (though still rapidly developing) technology and a vital component of
hospital diagnosis.
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2.6.2. Image Display
Figure 7. General Principles of Image Reconstruction
Pixel - voxel
+ Pixel - picture element
+ Voxel - volume element
µ to CT number
+ Originally measured was the distribution of µ
+ µ values are scaled to that of water to give the CT number
CT number = ( ( µ tissue - µ water) / ( µ water ) ) x 1000
+ We can change the appearance of the image by varying the window width (WW)
and window level (WL).
+ This spreads a small range of CT numbers over a large range of grayscale values.
+ This makes it easy to detect very small changes in CT number.
Figure 8. Typical CT values
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CT Number Window
+ CT images can be displaced with user definable brightness and contrast.
+ Display is defined using window level (WL) and window width (WW).
- WL is CT number of mid -grey
- WL is number of HU from black → white
+ Choice of WW and Wl dictated by clinical need.
Figure 9. Computed grayscale and CT Numbers

Windowing
+ The picture contrast is easily changed with two control mechanisms: the window
width and window level.
+ Usual CRT can display 256 gray levels.
+ 2000 CT numbers.
+ Select the CT number of the tissue of interest, then range of ±128 shades.
Imaging manipulation
Do not produce any additional information. The information content in the
processed image is always less than or equal to that in the original image.
Image Quality in CT
+ The average linear attenuation coefficient, µ, between
tube an detectors.
+ Attenuation coefficient reflects the degree to which the
x-ray intensity is reduced by a material.
Projections
+ 2D views - ‘projections’ at ngles all the way round the patient.
- Sample at each detector to generate a projection.
- Rotate tube and detectors a small amount and repeat the measurements.
Back Projection
+ Reverse the process of measuremner of projection
data to reconstruct an image.
+ Each projection is ‘smeared’ back across the
reconstructed image.
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Filtered Back Projection

+ Back projection produces blurred trans-axial images.
+ Projection data needs to be filtered before reconstruction.
+ Different filters can be applied for different diagnostic
purposes.
＊ Smoother filters for viewing soft tissue
＊ Sharp filters for high resolution imaging
+ Back projection process as before.
Type of Data
Equipment Configuration
Three major systems:
1. Imaging systems ------- located in scanner room.
2. Computer system------- located in the computer room.
3. Image display, recording------ located in the operation room.
2.7. CT Scanning Methods

2.7.1. Conventional CT Scanner
Computed tomography, more commonly known as a CT or
CAT scan, is a diagnostic medical imaging test. Like traditional
x-rays, it produces multiple images or pictures of the inside of
the body. A CT scan generates images that can be reformatted in
multiple planes. It can even generate three-dimensional images.
Conventional X-ray
For conventional radiography, an x-ray beam is generated
and passed through a patient to a piece of film or a radiation
detector, producing an image. Different soft tissues attenuate x-
ray photons differently, depending on tissue density; the denser
the tissue, the whiter (more radiopaque) the image.
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2.7.2. Cone - beam CT scanner

Cone beam CT (CBCT) is a variant type of computed tomography (CT), and is
used particularly in dental and extremity imaging but has recently found new
application in dedicated breast imaging 4,5. It differs from conventional CT in that it
uses a cone-shaped x-ray beam and two dimensional detectors instead of a fan-shaped
x-ray beam and one dimensional detectors.
Cone beam computed tomography (or CBCT, also referred to as C-arm CT,
cone- beam volume CT, flat panel CT or Digital Volume Tomography (DVT))
+ The recent technology initially developed
for angiography in 1982.
+ It is a digital analog of film tomography in
a more exact way than is traditional CT.
+ It uses a divergent or “cone” shape source
of ionizing radiation (conical or pyramidal) and a
2D area detector fixed on a rotating complex scan
around the area of interest.
 Main purpose
Cone beam CT is used to evaluate diseases
of the jaw, dentition, bony structures of the face, nasal cavity, and sinuses by
providing detailed images of the bone. CBCT is useful as a primary and supplemental
form of imaging. It is an excellent adjunct to DSA and fluoroscopy for soft tissue and
vascular visibility during complex procedures. The use of CBCT before fluoroscopy
potentially reduces patient radiation exposure. Dental cone beam computed
tomography (CT) is a special type of x-ray equipment used when regular dental or
facial x-rays are not sufficient. Your doctor may use this technology to produce three
dimensional (3-D) images of your teeth, soft tissues, nerve pathways and bone in a
single scan.
 Application
 Research
 General dentistry
 Endodontics
 Oral & Maxillofacial Surgery
 Orthodontics & Pedodontics
 Periodontics
 TMJ Imaging
 Dental Implants
 ENT Applications
 Cone-beam reconstruction
 Cone beam reconstruction uses a 2-
dimensional approach for obtaining projection
data.
 Instead of utilizing a single row of detectors,
as fan beam methods do, a cone beam system uses
a standard charge-coupled device camera, focused
on a scintillator material.
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 Projections from different angles are

obtained in one of two ways.
 The second method involves rotating the X-
ray source and camera around the object, as is
done in ordinary CT scanning and SPECT
imaging.
 Close-up to show the shadow image
 The method is referred to as cone-beam
reconstruction because the X-rays are emitted
from the source as a cone-shaped beam.
2.7.3. Spiral CT scanner
A procedure that uses a computer linked to an x-ray machine to make a series
of detailed pictures of areas inside the body. The x-ray machine scans the body in a
spiral path. This allows more images to be made in a shorter time than with older CT
methods.
Spiral CT is a type of computed tomography (CT) scan. It is being used more
and more in medical centers across the country to diagnose lung cancer. Spiral CT
uses a faster machine that spins continuously around the body. This allows it to more
quickly detect images and spot problems.
 Advance of spiral CT over conventional CT
 Slip ring device
 More efficient tube cooling
 Increased milliampere capability
 Smoother table movement
 Software adjustment for table movement
 Efficient detectors
Advantage
 Thin slice scanning of large range:
Nodular pathologic changes can be displayed clearly
 Lower usage of enhancement medium:
To acquire different phases images of viscera
 More easy to patient exam:
Reduce breath and motion artifacts
 Scanning speed is increased greatly
More easy to patient exam. Increase outpatient
Reduce motion artifacts. Lower dosage of enhancement medium
 Volume scanning
Reduce the missed diagnosis
Image post-processing making 3D visualization into reality
2.7.4. Multislice CT scanner

 MSCT scanners offer the following improvements
1. Imaging up to 4, 16, 32, 64 and more times the volume in a single rotation.
2. Rotation speed is 50-100% greater.
3. Minimum slice width is halved.
4. Improves x-ray utilization.
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 MSCT scanners can be divided into two categories

1. Fixed or symmetric matrix type: Have detector elements that are essentially of
equal length in the z-direction.
2. Adaptive or asymmetric type: Have detector elements that increase in length
with distance along the z-axis from the centre of the array.
Multislice or multidetector CT scanners are capable of acquiring several
tomographic slices in a single rotation of the x-ray tube and detector assembly.
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CHAPTER 3: CLINICAL APPLICATION
3.1. Main Purposes of CT Scan

Doctors order CT scans for a long list of reasons
 CT scans can detect bone and joint problems, like complex bone fractures and
tumors.
 If you have a condition like cancer, heart disease, emphysema, or liver masses,
CT scans can spot it or help doctors see any changes.
 They show internal injuries and bleeding, such as those caused by a car
accident.
 They can help locate a tumor, blood clot, excess fluid, or infection.
 Doctors use them to guide treatment plans and procedures, such as biopsies,
surgeries, and radiation therapy.
 Doctors can compare CT scans to find out if certain treatments are working.
For example, scans of a tumor over time can show whether it’s responding
to chemotherapy or radiation
3.2. Medical treatments
CT is used in cancer in many different ways:
+ To screen for cancer
+ To help diagnose the presence of a tumor
+ To provide information about the stage of a cancer
+ To detect recurrence of a tumor
CT can be effective in both colorectal cancer screening (including screening for
large polyps) and lung cancer screening.
Colorectal cancer
Both large colorectal polyps and colorectal tumors can be detected using CT
colonography (also known as virtual colonoscopy).
CT colonography uses the same 10 millisieverts of radiation that is used in
standard CT of the abdomen and pelvis (mSv).
CT colonography is less invasive and has a lower risk of complications than
traditional colonoscopy.
Noncolorectal abnormalities may be discovered because CT colonography can
produce images of organs and tissues outside the colon.
Lung Cancer
The only recommended screening test for lung cancer is low-dose computed
tomography (also called a low-dose CT scan, or LDCT). During an LDCT scan, you
lie on a table and an X-ray machine uses a low dose (amount) of radiation to make
detailed images of your lungs. The scan only takes a few minutes and is not painful.
Lung cancer screening is a procedure for detecting the presence of lung cancer in
people who are otherwise healthy but have a high risk of developing the disease. Lung
cancer screening is recommended for older adults who have smoked for a long time
but have no symptoms or signs of lung cancer.
To check for lung cancer, doctors use a low-dose computerized tomography
(LDCT) scan of the lungs. Lung cancer is more likely to be cured with treatment if it
is detected early.
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Talk to your doctor about the advantages and disadvantages of LDCT lung
cancer screening. Working together will assist you in determining whether or not
screening is appropriate for you.
3.3. The risks of CT scanning
Radiation exposure
CT, like most other tests and drugs recommended by your doctor, has hazards
that must be avoided. The highly trained professionals at the hospital or radiology
facility you are visiting will, however, minimize these dangers.
A CT scanner uses X-rays to produce the images that a radiologist needs to make
a diagnosis. X-rays, as is well known, are a sort of radiation that must be utilized with
caution by qualified professionals in order to minimize the risks. Modern CT scanners
can produce many images at a lower dose than a single X-ray test.
The risks of radiation exposure are detailed in the InsideRadiology article
"Radiation risk of medical imaging for adults and children," but in a nutshell, they are
as follows:
 A very small increase in the risk of developing cancer later in life. This low
risk is considered to be outweighed by the benefits provided by the scan.
 Risk to an unborn child if you are pregnant. This risk could take the form of a
very small increase in the risk of cancer or a malformation if you are exposed
to radiation during the first months of your pregnancy.
Making sure that every CT scanner in use is constantly maintained and
calibrated (checked and configured to assure accuracy) by specialized experts is one
way to reduce radiation hazards. State and federal laws also require this.
Radiographers are also educated to use the least amount of radiation feasible to
provide high-quality images that allow the radiologist to make an accurate diagnosis
of your problem.
Aside from employing specialized equipment, the radiographer will only scan
the body part(s) that are needed. They will also try to avoid scanning areas that are
highly vulnerable to radiation, which may necessitate the use of lead or bismuth
shields (a type of metallic substance).
Radiation is only present while the scan is being performed, and no radiation is
left in the environment or in your body afterward.
Contrast medium
When iodinated contrast is injected, there is a slight risk of an allergic reaction.
This is not a risk with swallowed contrast. It's impossible to foresee whether or not
you'll be allergic to iodinated contrast, and just because you've had it previously and
didn't have an allergic reaction doesn't guarantee you won't have one the next time. If
an allergic response occurs, the hospital or radiology practice personnel is well
qualified to handle it. Before getting the injection, make sure the radiographer or
nurse is aware of any additional allergies you may have. If you have allergies to other
foods or medications, you're more likely to develop an allergic reaction to iodinated
contrast.
21
People who are allergic to the iodinated contrast used in CT may have some of
the following symptoms:
 nausea and/or vomiting;
 a skin rash or hives;
 itching;
 sneezing or watering eyes;
 dizziness and/or headache;
 gagging or feeling of suffocation, or swelling of the inside of the throat or
mouth;
 change in blood pressure.
You should be able to eat and drink normally after the test and resume your
routine activities. If you experience any of these symptoms during or after your scan,
notify the radiographer or nurse right once. If you have these feelings after leaving the
hospital or radiology practice, go back there right away (if the department is open and
close by), or go to the nearest doctor's office or emergency room.
For more information on the dangers of contrast media, see Iodine-containing
contrast medium (ICCM).
3.4. How long does computed tomography take?
The length of time it takes to complete the scan depends on why you're having it
done.
+ CT scans that do not require an injection or much preparation are usually quite
quick, and may be completed within 5 minutes.
Preparation time for tests that require you to drink a contrast solution or receive
an injection is often much longer than the scan itself.
+ When an abdominal scan (of your stomach or tummy) requires a drink, it's common
to be asked to have it an hour before the appointment. This can be done either before
you arrive at the hospital or while you are waiting in the waiting room.
+ If you are asked to arrive early for your scan, the time before the scan is frequently
used to prepare you. This could include changing into a gown, discussing the need for
iodinated contrast injection or contrast to drink, inserting a cannula, and explaining
what to expect during the test.
=> Even when you have a scan that requires an injection, a drink, or other preparation,
the scan itself (that is, the time you are in the CT scanner machine) usually takes less
than 10 minutes.
3.5. Preparation for computed tomography
Before your appointment, you should receive instructions from the hospital or private
radiology practice where you will be having the CT scan. These instructions are crucial
because they may affect the test's accuracy or necessitate rescheduling if you are not properly
prepared for the CT scan.
The brain, sinuses, or facial bones, temporal bones (inner ear), spine, knee, or wrist, and bone
CTs are among the tests that do not require any preparation.
+ To see blood vessels and some organs, many types of CT require the injection of an
iodinated contrast material (see InsideRadiology: Iodine-containing contrast medium
(ICCM)).
22
+ Most hospital departments or radiology practices will require you to fast (not eat or drink)
before your appointment for these tests.
+ Fasting for 2–4 hours is common, and water may be consumed during this time to avoid
dehydration (losing too much water from your body).
+ It's critical that the need to fast does not make you ill, especially if you have other dietary
restrictions (e.g. diabetes).
+ If you have any concerns, please consult your doctor or the hospital or radiology practice
where the CT is being performed.
+ If your test requires an iodinated contrast injection, you will most likely be taken to a room
where a radiologist, radiographer, or nurse will discuss your options.
23
CHAPTER 4: DEVELOPMENT
Scanning radiation exposure

Today, medical imaging technology has reduced the CT dose that patients
receive during the scanning procedure. The Objective of the manufacturer is to
produce a CT scanner to provide high-quality images at a lower radiation dose. A
target dose range for cardiac CT scanning may be considered at around 3 mSv or
below.
Improvements in Image resolution
Improvements in image resolution The detailed images of smaller anatomical
structures are reliant on the spatial resolution of the CT scanner used. The majority of
CT scanners have a spatial resolution of about 0.50. This could be further reduced by
developing improvements in detector and software. For example, Toshiba has been
developing a CT scanner with a spatial resolution of 0.25. However, at a 0.50
resolution, the radiologists can tell whether there is a stent in a vessel, but it is often a
blurry image. At a 0.25 resolution, the images can definitely confirm a stent. Also, the
latest model-based iterative reconstruction software can help improve spatial
resolution and contrast.
The detailed images of smaller anatomical structures are reliant on the spatial
resolution Of the CT scanner used. The majority Of CT scanners have a spatial
resolution Of 0.50. This could further reduced by developing improvements in
detector and software.
Miscellaneous
Other considerations regarding CT scanners are the sensitivity of the detectors in
capturing photons. A lower radiation dose can be used with more efficient detectors to
produce diagnostic-quality images.
Speed of CT scanning – Higher Slice CT Systems
The next generation of computed tomography scanners will be faster, fully
automated and easier to use. This technology platform will depend on the transition
from standard CT machines to more advanced systems which improve quantification
and quicker diagnosis. The overall emphasis is to assist medical imaging professionals
to limit the length of stay of the patient and thereby reduce cost and improve
efficiency.
These future CT scanners will be able to consistently deliver anatomical
information and contain the ability to characterise anatomical structures within a
single scan. In these cases, it is paramount for the patient to undergo evaluation
quickly to reduce the time spent in the emergency department and to facilitate a safe
discharge.
Spectral CT Imaging
Manufacturers manage to invent Future Scanning Photon counting CT. It
means that they use the Spectral imaging AI-operation AI reconstruction AI-
analysis.
Mobile and Portable CT Scanning
Throughout the years, the demand for a mobile CT scanner has increased
exponentially due to the influx of incidents where medics have failed to swiftly
provide care to stroke patients. These incidents paved the way to the study of utilizing
24
and funding mobile stroke units (MSUs) in 2003. More importantly, the presence of a
portable CT scanner in these MSUs ensured that the professionals could treat patients
quickly and accurately during emergencies. Basing its setup on the recommendations
of neurologists, the company incorporated a portable CT scanner in its hospital on
wheels to drastically cut down on the treatment time.
Figure 10. Modern MSU
25
FURTHER INFORMATION
 Comparison of spiral CT and conventional CT in 3D visualization of facial
trauma
Spiral computed tomography (SCT) differs from conventional CT (CCT) in that
regions of the body can be rapidly imaged via continuous scanning. This is
accompanied by simultaneous advancement of the patient, thus allowing volumetric
data acquisition of up to 60 cm in less than a minute. Thus motion is minimized and
slice misregistration is minimized when multiplanar and three dimensional
reconstructions are performed.
 Similarities and Differences Between the Three Main Types (X-ray - CT
Scan - MRI) of Diagnostic Imaging
X-rays, MRIs and CT scans have a few similarities. All three are a type of
imaging scan. You can have both x-rays and CT scans completed within minutes. All
three imaging tools can be used to help with the diagnosis of one or more medical
conditions. You need to remain still for all three tests according to the instructions
given by the technologist. However, they also have several major differences.
1. What Is the Difference Between an X-Ray and a CT Scan?
While the difference between CT scan and x-ray is minor, it’s also significant.
Doctors use x-rays to detect dislocations and fractures of bones as well as detect
cancers and pneumonia. However, CT scans are a type of advanced x-ray devices
doctors use for diagnosing internal organ injuries, using x-ray images of the structure
and a computer.
X-ray machines in some cases fail to diagnose problems with muscle damage,
soft tissues or other body organs, but with the CT scan, it’s entirely possible. x-ray
images are in 2D, while CT scan images are 3D. The CT scanning machine rotates on
an axis and takes various 2D images of an individual’s body from multiple angles.
Then, the computer will place all the cross-sectional images together on its screen,
resulting in a 3D image of the body’s inside, revealing the presence of injury or
disease to the doctor.
2. What Is the Difference Between a CT Scan and an MRI?
X-rays and CT scans both use a small dose of ionizing radiation to produce
images.
An MRI scan, however, doesn’t work this way. It uses powerful magnets and
radio waves to create the images instead of ionizing radiation. So, you are not exposed
to radiation when you have an MRI scan, unlike a CT scan or x-ray. The MRI applies
a magnetic field, lining up each of the protons in your body. The radio waves are
applied in short bursts to these protons, relaying a signal the MRI scanner picks up.
Then the computer processes this signal and creates a 3D image of the examined body
areas.
The diagnostic images of a CT scan are taken typically quicker than an MRI scan.
For instance, a CT scan, as with x-rays, often takes five minutes or less while MRIs
can take 30 minutes or more.
Doctors also use MRIs and CT scans for different reasons. A CT scan is very
helpful in diagnosing severe injuries of the chest, head, spine or abdomen, particularly
fractures. They’re also useful in pinpointing the location and size of tumors.
An MRI, however, often does a better job at diagnosing problems in the joints, soft
tissues, ligaments and tendons. Doctors will often order an MRI to scan the spine,
26
brain, breasts, muscles, abdomen and neck. They’re an excellent tool for evaluating
spinal ligaments.
3. What Is the Difference Between an MRI and an X-Ray?
As mentioned, x-rays expose you to ionizing radiation. MRI machines don’t emit
this radiation. x-rays take mere minutes while MRIs can take 30 minutes or longer —
up to a couple of hours — depending on what the doctor is looking for.
X-rays are limited to scanning for only a few body ailments. MRIs are more
versatile, and doctors use them for examining many medical conditions. For example,
x-rays are used more for examining broken bones, but they can also help detect
diseased tissue. MRIs are better for evaluating soft tissues such as tendon and
ligament injuries, brain tumors or spinal cord injuries.
 Defifining Terms
Absorption:
Some of the incident x-ray energy is absorbed in patient tissues and hence does not
contribute to the transmitted beam.
Anode: A tungsten bombarded by a beam of electrons to produce x-rays. In all but
one fififth-generation system, the anode rotates to distribute the resulting heat around
the perimeter. The anode heat storage capacity and maximum cooling rate often limit
the maximum scanning rates of CT systems.
Attenuation: The total decrease in the intensity of the primary x-ray beam as it passes
through the patient, resulting from both scatter and absorption processes. It is
characterized by the linear attenuation coeffificient.
Computed tomography (CT): A computerized method of producing x-ray
tomographic images. Previous names for the same thing include computerized
tomographic imaging, computerized axial tomography (CAT), computer-assisted
tomography (CAT), and reconstructive tomography (RT).
Control console: The control console is used by the CT operator to control the
scanning operations, image reconstruction, and image display.
Data-acquisition system (DAS): Interfaces the x-ray detectors to the system
computer and may consist of a preamplififier, integrator, multiplexer, logarithmic
amplififier, and analog-to-digital converter.
Detector array: An array of individual detector elements. The number of detector
elements varies between a few hundred and 4800, depending on the acquisition
geometry and manufacturer. Each detector element functions independently of the
others.
Fan beam: The x-ray beam is generated at the focal spot and so diverges as it passes
through the patient to the detector array. The thickness of the beam is generally
selectable between 1.0 and 10 mm and defifines the slice thickness.
Focal spot: The region of the anode where x-rays are generated.
Focused septa: Thin metal plates between detector elements which are aligned with
the focal spot so that the primary beam passes unattenuated to the detector elements,
while scattered x-rays which normally travel in an altered direction are blocked.
Gantry: The largest component of the CT installation, containing the x-ray tube,
collimators, detector array, DAS, other control electronics, and the mechanical
components required for the scanning motions.
Helical scanning: The scanning motions in which the x-ray tube rotates continuously
around the patient while the patient is continuously translated through the fan beam.
27
The focal spot therefore traces a helix around the patient. Projection data are obtained
which allow the reconstruction of multiple contiguous images. This operation is
sometimes called spiral, volume, or three-dimensional CT scanning.
Image plane: The plane through the patient that is imaged. In practice, this plane
(also called a slice) has a selectable thickness between 1.0 and 10 mm centered on the
image plane.
Pencil beam: A narrow, well-collimated beam of x-rays.
Projection data: The set of transmission measurements used to reconstruct the image.
Reconstruct: The mathematical operation of generating the tomographic image from
the projection data.
Scan time: The time required to acquire the projection data for one image, typically
1.0 s.
Scattered radiation: Radiation that is removed from the primary beam by a
scattering process. This radiation is not absorbed but continues along a path in an
altered direction.
Slice: See Image plane.
Tomography: A technique of imaging a cross-sectional slice.
Volume CT: See Helical scanning.
X-ray detector: A device that absorbs radiation and converts some or all of the
absorbed energy into a small electrical signal.
X-ray linear attenuation coeffificient µ: Expresses the relative rate of attenuation of
a radiation beam as it passes through a material. The value of µ depends on the
density and atomic number of the material and on the x-ray energy. The units of µ are
cm–1 .
X-ray source: The device that generates the x-ray beam. All CT scanners are
rotating-anode bremsstrahlung x-ray tubes except one-fififth generation system,
which uses a unique scanned electron beam and a strip anode.
X-ray transmission: The fraction of the x-ray beam intensity that is transmitted
through the patient without being scattered or absorbed. It is equal to It/Io, can be
determined by measuring the beam intensity both with (It ) and without (Io ) the
patient present, and is expressed as a fraction. As a rule of thumb, n2 independent
transmission measurements are required to reconstruct an image with an n × n sized
pixel matrix.
28
REFERENCE
1. https://medlineplus.gov/xrays.html
2. https://www.sciencedirect.com/science/article/abs/pii/0895611194900795
3. https://patient.info/doctor/computerised-tomography-ct-scans
4. https://pubmed.ncbi.nlm.nih.gov/7850736/
5. https://www.radiologyinfo.org/en/info/bodyct
6. https://www.medicinenet.com/x-ray/definition.htm
7. https://languages.oup.com/google-dictionary-en/
8. https://medlineplus.gov/xrays.html
9. https://www.radiologyinfo.org/en/info/bonerad
10. https://g.co/kgs/WjeU6S
11. https://www.nhlbi.nih.gov/health-topics/chest-x-ray
12. https://en.wikipedia.org/wiki/X-ray_generator
13. https://www.sciencedirect.com/topics/medicine-and-dentistry/x-ray-generator
14. https://www.slideshare.net/muffafa/2-components-of-xray-machine
15. https://www.slideshare.net/HuzaifaOxford/introduction-to-the-parts-of-x-ray-
machine
16. https://radiopaedia.org/articles/x-ray-tube-1
17. https://www.sciencedirect.com/topics/medicine-and-dentistry/x-ray-tube
18. https://radiologykey.com/the-x-ray-beam/
19. https://www.merriam-webster.com/dictionary/collimator
20. https://www.britannica.com/technology/collimator
21. https://pubs.rsna.org/doi/10.1148/radiographics.18.1.9460114
22. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/computed-
tomography-scan
23. https://hardingradiology.com/blogs/what-is-the-purpose-of-a-ct-scan/
24. https://www.imaginis.com/ct-scan/brief-history-of-ct?r
29

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SCIENTIFIC REPORT

MAJOR: BIOMEDICAL ENGINEERING

Teacher: Dr. Nguyen Thanh Qua

1.1. Computed Tomography Scan (CT Scan)

1.2.1. Data-Acquisition Geometries

Figure 2. Schematic drawing of a typical CT scanner installation, consisting of (1) control

1.2.2. Comparisons of CT Scan Generations

4th Single- Fan beam Stationary Cannot Detectors Higher High

Figure 1. Four Generations of CT Scanners illustrating the parallel- and fan-beam

CHAPTER 2: WORKING PRINCIPLE

Figure 4. Two basic block diagrams of CT Scan

on the other hand, use the preamplifier to control a synchronous voltage-to-frequency

Figure 3: Data acquisition geometries used in

2.5. Computer System

around 5 s. To coordinate tasks, a simplified UNIX operating system is employed to

2.6. Reconstruction of CT Image

2.6.2. Image Display

Figure 7. General Principles of Image Reconstruction

CT number = ( ( µ tissue - µ water) / ( µ water ) ) x 1000

Figure 8. Typical CT values

Figure 9. Computed grayscale and CT Numbers

Filtered Back Projection

2.7. CT Scanning Methods

2.7.2. Cone - beam CT scanner

 Projections from different angles are

2.7.4. Multislice CT scanner

 MSCT scanners can be divided into two categories

CHAPTER 3: CLINICAL APPLICATION

3.1. Main Purposes of CT Scan

Scanning radiation exposure

Figure 10. Modern MSU

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