CT scan and MRI are the techniques for body imaging. Computed Tomography or Computerized Axial Tomography is commonly referred to as a CT scan. C- computed (Use of computer) and T- tomography (Greek word “Tomos” means “slice” and “Grapho” means “ To write” The first commercial CT scanner was invented by Sir Godfrey Hounsfield in United Kingdom. It is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images of the inside of the body. It shows detailed images of any part of the body including the bones, muscles, fat, organs and blood vessels. CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage. Computed Tomography or Computerized Axial Tomography is commonly referred to as a CT scan. C- computed (Use of computer) and T- tomography (Greek word “Tomos” means “slice” and “Grapho” means “ To write” The first commercial CT scanner was invented by Sir Godfrey Hounsfield in United Kingdom. It is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images of the inside of the body. It shows detailed images of any part of the body including the bones, muscles, fat, organs and blood vessels. CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage. Computed Tomography or Computerized Axial Tomography is commonly referred to as a CT scan. C- computed (Use of computer) and T- tomography (Greek word “Tomos” means “slice” and “Grapho” means “ To write” The first commercial CT scanner was invented by Sir Godfrey Hounsfield in United Kingdom. It is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images of the inside of the body. It shows detailed images of any part of the body including the bones, muscles, fat, organs and blood vessels. CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage. MRI stands for Magentic Resonance Imaging which is a non-invasive medical imaging test that produces detailed images of almost every internal structure in the human body, including the organs, bones, muscles and blood vessels. MRI scanners create images of the body using a large magnet and radio waves. No ionizing radiation is produced during an MRI exam, unlike X-rays. These images give your physician important information in diagnosing your medical condition and planning a course of treatment. Raymond Damadian, the inventor of the first magnetic resonance scanning machine performed the first full-body scan of a human being in 1977. The Nobel Prize was awarded to the American chemist, Paul Lauterbur, and the British physicist, Peter Mansfield, for developing a method to represent the information gathered by a scanner as an image. This is fundamental for the way the technology is used today.

1. ASSIGNMENT ON CT SCAN AND
MRI
-SANDHYA DHYANI
(PhD Scholar, Dept. of Human
Nutrition)
G.B.P.U.A.T. Pantnagar

2. CT SCAN
 Computed Tomography or Computerized Axial Tomography is commonly referred to as a
CT scan.
 C- computed (Use of computer) and T- tomography (Greek word “Tomos” means “slice”
and “Grapho” means “ To write”
 The first commercial CT scanner was invented by Sir Godfrey Hounsfield in United
Kingdom.
 It is a diagnostic imaging procedure that uses a combination of X-rays and computer
technology to produce images of the inside of the body. It shows detailed images of any part
of the body including the bones, muscles, fat, organs and blood vessels.
 CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check
for other internal injuries or damage.

3. Parts of CT scanner
Scanner
system
Operating
console
Data
acquisition
system

4. Gantry
 The Gantry assembly is the largest part of the CT scanner.
 It is a mounted framework that surrounds the patient in a vertical plane.
 The diameter of gantry aperture is about 50-85 cm.
 It can rotate 360 degrees around its axis.
 It contains:
1. X-ray tube
2. Collimator
3. Detector
4. Filter
5. Patient couch

5. Scanner system:
 X-ray tube: It is located at the heart of gantry.
 It has high frequency generator and rotating anode which is responsible for generating X-
ray beams or radiation source for CT.
 Tungsten, which has an atomic number of 74, is usually used for the anode target material,
which produces a higher intensity x-ray beam because the intensity of x-ray production is
approximately proportional to the atomic number of the target material.
 The Earlier borosilicate was used as glass envelop but nowadays the metal ceramic x-ray
tubes are used.
 Generator: High voltage generators are used in CT located within the gantry. These
generators produce high voltage (120-140 kV) and transmit it to the X-ray tube. CT
generators produce enough voltage to increase the intensity of the beams which will
increase their penetration ability of X-ray beams.

6.  Detector: It detects the X-rays passing through the patient’s body. It measures the intensity of
transmitted X-ray radiation along a beam that is projected from the source to detector element.
 There are basically two types of detectors used i.e. GAS IONIZATION DETECTOR (converts
X-ray energy directly into electrical signals) and SCINTILLATION DETECTOR (converts X-
ray energy into light).
 Gas ionization detectors are also called as Xenon Gas Detectors:
 It use pressurized xenon gas to fill the hollow chamber to produce detectors that
absorb 60-87% of the photons that reach them. Xenon gas is used because it remain
stable under pressure and is significantly less expensive. A Xenon Detector Channel
consists of three tungsten plates. The xenon gas is ionized when a photon enters the
channel. These ions are accelerated and amplified by the electric field between the
three plates. This collection charge produces an electric current, which is then
processed as raw data. The downside of xenon gas is that it must be kept under
pressure. The major factors hampering detector efficiency are the loss of x-ray
photons.

7.  Scintillation detectors are also called as solid state crystal
 They use a crystal that fluoresces when struck by an x-ray photon. The
photodiode is attached to the crystal and transforms the light energy into
electrical energy. Individual detector elements are affixed to a circuit
board.
 Solid state crystal detectors are made from a variety of materials, like
cadmium tungstate, cesium iodide etc.
 Solid state detectors have higher absorption because these solids have
high atomic numbers and high density in comparison to gases.
 They absorb close to 100% of all photons that reach them.

8.  Collimators:
 Collimation restricts the x-ray beam to a specific area, which helps reduce scatter radiation. It controls the slice
thickness by narrowing or widening the x-ray beam.
 Scatter radiation can reduce image quality and increase the patient’s radiation dose. By reducing the scatter
radiation, you can get better contrast resolution and decrease patient dose, or the amount of x-ray beam before it
passes through the patient.
 These are present between the X-ray source and the patient (i.e Tube or pre-patient collimators) and between the
patient and the detectors (i.e. Post-patient collimators)

9.  Filters:
 In order to shape the x-ray beam, compensating
filters are used. These reduce the radiation dose
to the patient.
 Radiation emitted by a CT x-ray tube is
polychromatic x-ray photons. By filtering the x-
ray beam, the range of x-ray energies that reach
the patients are reduced.
 The filtering removes the long wavelength or
“soft rays,” which are readily absorbed by the
patient and don’t contribute to the CT image.
 These are used to filter some rays from entering
the patient’s body that may be harmful.

10. Operating Console
 It is the point from which the technologist controls the
scanner.
 A typical console is equipped with a keyboard for entering
patient data and a graphic monitor for viewing the images.
 Other input devices, such as a touch display screen and a
computer mouse, may also be used.
 The operator’s console allows the technologist to control
and monitor numerous scan parameters.
 Radiographic technique factors such as slice thickness
etc. are some of the scan parameters that are selected at
the operator’s console.

11. Data Acquisition System
 The detector is responsible for capturing the X-rays produced by
the CT tube and converting them into an electrical signal.
 The detector produces electrical signals, and the Data Acquisition
System (DAS) captures them.
 The DAS converts these signals into images by using complex
algorithms to process the data.
 The images show the body’s structure and composition. A
computer screen displays out the images produced by the DAS.
 Detectors may be arranged in a ring or helical configuration around
the patient. This allows for simultaneous acquisition of multiple
body views, and fast data acquisition.

12. Principle of CT scan
 CT scans are created using a series of x-rays, which are a form of radiation. The scanner emits x-rays towards the
patient from a variety of angles – and the detectors measure the difference between the x-rays that are absorbed by
the body, and x-rays that are transmitted through the body. This is called attenuation.
 The amount of attenuation is determined by the density of the imaged tissue, and they are individually assigned
a Hounsfield Unit or CT Number.
 High density tissue (such as bone) absorbs the radiation to a greater degree, and a reduced amount is detected by
the detector on the opposite side of the body.
 Low density tissue (such as the lungs), absorbs the radiation to a lesser degree, and there is a greater signal detected
by the detector.
 Conventional x-rays provide the radiographer with a two-dimensional image, and require the patient to be moved
manually to image the same region from a different angle. In contrast, because of the advanced mathematical
algorithms involved with CT, the 3-D planes of the human body can be imaged and displayed on a monitor as
stacked images, detailing the entirety of the field of interest.
 This is accomplished by acquiring projections from different angles and through a process known as reconstruction.

13. Working of CT Scan
• Inside the scanner system of CT scan there is a gantry which has an X-ray tube
mounted on one side and the detector mounted on the opposite side.
• As the X-ray tube and detector make this 360 degree rotation during the detector
takes numerous snapshots.
• Typically in 360 degree lap about 1000 images are sampled.
• These sliced images are then superimposed to generate a 3-D image.

14.  Contrast Imaging
 Depending on the structure being imaged, CT scans can be used with and/or
without contrast. The introduction of an intravenous radiofluorescent contrast into the
bloodstream can be used for a variety of diagnostic purposes, for example:
1. Used to visualise the cardiovascular system (e.g. investigating for atherosclerotic diseases
etc).
2. Used to identify whether a tumour is malignant.
 Contrast dyes contain barium or iodine and can be given in a number of ways, including
orally and intravenously (in your vein).
 These dyes increase the contrast level and resolution of the final images produced with the
CT scan for a more exact diagnosis.

15. The Image
 The density of the body tissue determines the degree to which the x-rays are attenuated. In
turn, this affects the brightness and contrast of the imaged tissues.
 Those tissues with high attenuation coefficients (strong absorption) show up white, and
those which absorb with low attenuation coefficients (weak absorption) show up black.
 This is quantified by the Hounsfield Scale of radiodensity.
 Tissues with a high Hounsfield score have a high attenuation coefficient, and so appear white:

16. CT scan Vs X-Rays
CT SCAN X-RAYS
• Combined multiple X-ray projections
taken from different angles to produce
more detailed cross-sectional image of
areas inside the body.
• It gives precise 3-D views of various
parts of the body.
• It is often used for diagnosing
problems in soft tissues and organs.
• Reduced overlapping of internal
structures.
• It uses radiations to produces images
of a person’s structure by sending X-
ray beams through the body which are
absorbed in different amounts
depending upon the density of the
material.
• It gives 2-D images of various body
parts.
• It is used to detect bones etc.
• It creates overlapping of internal
structures

17.  In standard 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, a lot
of detail about internal organs and other structures is not
available.
 In CT, 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 that interprets
the X-ray data and displays it in two-dimensional form
on a monitor. Newer technology and computer software
makes three-dimensional images possible.

18. ADVANTAGES OF CT SCAN
 Quick, non-invasive and pain less technique
 Less costly than MRI
 Rapidly acquire precise images
 Eliminate superimposition of images
 It is less sensitive to patient’s movement
 It can be performed if patient is having any kind of implant unlike
MRI
 Provide clear and specific information
 Improving cancer diagnosis and treatment
 No radiation remains in patient’s body after a CT examination

19. Drawbacks of CT
 Exposure to ionization radiation that can potentially
be harmful, especially with younger patients and
children.
 Use of iodinated contrast material
 Time consuming as one patient can undergo
scanning at a time.

20. MRI
 MRI stands for Magentic Resonance Imaging which is a non-invasive medical imaging test
that produces detailed images of almost every internal structure in the human body, including
the organs, bones, muscles and blood vessels.
 MRI scanners create images of the body using a large magnet and radio waves.
 No ionizing radiation is produced during an MRI exam, unlike X-rays. These images give your
physician important information in diagnosing your medical condition and planning a course
of treatment.
 Raymond Damadian, the inventor of the first magnetic resonance scanning machine
performed the first full-body scan of a human being in 1977.
 The Nobel Prize was awarded to the American chemist, Paul Lauterbur, and the British
physicist, Peter Mansfield, for developing a method to represent the information gathered by
a scanner as an image. This is fundamental for the way the technology is used today.

21. Parts of MRI
 An MRI system consists of four major
components:
1. Magnet
2. Gradient coils
3. Radiofrequency (RF) coils
4. Computer systems

22.  Magnet:
1. The magnet is the most important and biggest part of the
MRI device.
2. It is this magnet that allows the MRI machine to produce
high quality images.
3. There is a horizontal tube that runs through the magnet and
is called a bore. The magnet is extremely powerful and its
strength is measured in either ‟teslaˮ or ‟gaussˮ (1 tesla =
10 000 gauss).
4. Most MRI magnets use a magnetic field of 0.5 to 2.0 tesla,
when the Earth’s magnetic field is only 0.5 gauss.
5. The magnetic field is produced by passing current through
multiple coils that are inside the magnet, resulting in a state
of superconductivity, which produces a lot of energy.

23.  Gradient Coils:
1. There are three different gradient coils that
are inside the MRI machine and are located
within the main magnet.
2. Each one of these produce three different
magnetic fields that are each less strong than
the main field.
3. The gradient coils create a variable field (x, y,
z) that can be increased or decreased to
allow specific and different parts of the body
to be scanned by altering and adjusting the
main magnetic field.

24.  Radio Frequency (RF) coils:
1. The basic function of the RF coils is to
transmit radio frequency waves into the
patient’s body.
2. There are different coils located inside the
MRI scanner to transmit waves into
different body parts.
3. If a certain area of the body is specified,
then all the RF coils usually
become focussed on the body part being
imaged to allow for a better scan

25.  Patient Table:
1. This component simply slides the patient into the
MRI machine.
2. The position at which the patient lies down on
the table is determined by the part of the body
that is being scanned.
3. Once the part of the body under examination is
in the exact
centre of the magnetic field, which is referred to
as the isocentre, the scanning process is
started.

26.  Computer System:
1. The antenna is a very sensitive device that easily
detects the RF signals emitted by
a patient’s body while undergoing examination and
feeds this information into
the computer system.
2. The computer system is a powerful system, whose
major function is to receive, record, and analyze the
images of the patient’s body that have been
scanned.
3. It interprets the data sent in by the antenna and then,
helps to produce an understandable image of the
body part being examined.

27. WORKING OF MRI
 The MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around the
patient and sends pulses of radio waves from a scanner. Some MRI machines look like narrow tunnels, while
others are more open.
 MRI exploits the presence of vast amount of hydrogen in a human body as the water content in human body is
said to be about 80%.
 At the centre of each hydrogen atom is even smaller particle called as proton.
 Protons are like tiny magnets and are very sensitive to magnetic fields and has magnetic spin.
 MRI utilizes this magnetic spin properties of protons of hydrogen to elicit images.
 The strong magnetic field created by the MRI scanner causes the atoms in your body to align in the same
direction.
 Radio waves are then sent from the MRI machine and move these atoms out of the original position. As the radio
waves are turned off, the atoms return to their original position and send back radio signals. These signals are
received by a computer and converted into an image of the part of the body being examined. This image appears
on a viewing monitor.

30. THANK YOU