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UNIT 5
Medical Imaging
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CT Scan
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CT Scan
 Computed axial tomography (CAT or CT scanning) is a
medical imaging procedure that utilizes computerprocessed X-rays to produce tomographic images or 'slices'
of specific areas of the body.
 These cross-sectional images are used for diagnostic and
therapeutic purposes in various medical disciplines.
Unlike other medical imaging techniques, such as conventional
x-ray imaging (radiography), CT enables direct imaging and
differentiation of soft tissue structures, such as liver, lung
tissue, and fat.
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CT Scan
Due to the short scan times of 500 milliseconds to a few
seconds, CT can be used for all anatomic regions.
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CT Scan Machine
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CT Scan Principle
CT is based on the fundamental principle that the density of
the tissue passed by the X-ray beam can be measured from
the calculation of the attenuation coefficient.
 The CT process involves several steps:
Scanning
2. Reconstruction
3. Visualization
4. Data collection
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CT Scan Principle
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CT Scan Principle
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CT Scan Principle
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Advantages of CT Scan
Relatively inexpensive compared with MRI and PET
scanning
2. Accurate, 3-dimensional data including attenuation
information
3. Rapid acquisition of data and no need for patients to
remain for planning process
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Components in CT Scan
 4 BASIC STEPS OF CT SCANNING
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1.
X-Ray Production
2.
Data Acquisition
3.
Data Processing
4.
Image Display
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Components in CT Scan
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Components in CT Scan
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Types of CT Scan
 X-ray Computed Tomography:
 This is the conventional CT scanner that scans a
particular section of the subject at a time and sends it
across to a computer for further processing
 Spiral or Helical Computed Tomography:
 These provide accurate information on the internal
organs.
 In spiral CT, the X-ray beam is emitted on a continuous
basis and rotates around the subject, as the subject is
moved through.
 Micro Computed Tomography: In micro CT, the pixel size
of the images is in micrometer. It is used in cases involving
small animals, biomedical samples and other studies where
minute detailing is desired.
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Types of CT Scan
 Micro Computed Tomography:
 In micro CT, the pixel size of the images is in micrometer.
 It is used in cases involving small animals, biomedical
samples and other studies where minute detailing is
desired.
• Cone Beam Computed Tomography:
• The Cone Beam CT is a recent addition, where the X-ray
source is cone shaped and the resultant image is in 3-D.
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Types of CT Scan
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X- Ray
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X-RAY
•In 1895 Conrad Rontgen, a German physicist, discovered a
previously unknown type of radiation while experimenting
with gas-discharge tubes.
•X-radiation (composed of X-rays) is a form of electromagnetic
radiation.
• X-rays have a wavelength in the range of 0.01 to 10
nanometers,
•X-radiation is also called Rontgen radiation
•An X-ray generator is a device used to generate X-rays.
•The heart of an X-ray generator is the X-ray tube.
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X-RAY
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Electro Magnetic Spectrum
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Uses of X- Ray
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Uses of X-RAY
These devices are commonly used by radiographers to
acquire an x-ray image of the inside of an object (as in
medicine or non-destructive testing) but they are also used in
sterilization or fluorescence.
X-ray machines are used in health care for visualizing bone
structures and other dense tissues such as tumors.
Non-medicial applications include security and material
analysis.
The two main fields in which x-ray machines are used in
medicine are radiography and fluoroscopy.
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Uses of X-RAY
 Diagnostic still picture X-Ray
 Examine bones and internal organs
 Diagnostic continuous picture X-Ray(Fluoroscopy)
 Examine internal organs as they functioning
 Diagnostic motion picture X-Ray
Examine circulatory systems and its functioning
 Diagnostic still picture X-Ray Scans
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 CT scan
 Therapeutic X-Ray
 For treatment
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X-RAY in Radiography
 Some forms of radiography include:
 Orthopantomogram — a panoramic x-ray of the jaw
showing all the teeth
 Mammography — X-rays of breast tissue
 Tomography — X-ray imaging in sections
 Radiotherapy — the use of x-ray radiation to treat malignant
cancer cells, a non-imaging application
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X-RAY in Fluoroscopy
 Fluoroscopy is used in cases where real-time visualization is
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necessary (and is most commonly encountered in everyday
life at airport security).
Some medical applications of fluoroscopy include:
Angiography — used to examine blood vessels in real time
Barium enema — a procedure used to examine problems of
the colon and lower gastrointestinal area
Barium swallow — similar to a barium enema, but used to
examine the upper gastroinstestional area
biopsy — the removal of tissue for examination
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X- Ray Tube
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X-RAY Generation
 Like any vacuum tube, the X-ray tube contains a cathode,
which directs a stream of electrons into a vacuum, and an
anode, which collects the electrons.
 The anode in an X-ray tube is made of tungsten,
molybdenum, or copper.
 The electrons are then focused and accelerated by an
electrical field towards an angled anode target.
 The point where the electron beam strikes the target is
called the focal spot.
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X-RAY Generation
 When electrons collide with the anode, about 1% of the
resulting energy is emitted as X-rays, with the remaining
99% released as heat.
 A cooling system is necessary to cool the anode; many X-ray
generators use water or oil re-circulating systems
 The intensity of X rays depends on the current through the
tube.
 This current can be varied by varying the heater current.
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X-RAY Generation
•The wavelength of the X rays depends on the target material
and the velocity of the electrons hitting the target.
 It can be varied by varying the target voltage of the tube.
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X ray tube
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Generation of X- ray from X ray tube
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Block Diagram
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X-RAY Generation
•The intensity of X rays depends on the current through the
tube.
•This current can be varied by varying the heater current.
•The wavelength of the X rays depends on the target material
and the velocity of the electrons hitting the target.
 It can be varied by varying the target voltage of the tube.
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Simple Block Diagram
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Block Diagram
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Collimators
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Collimators
A collimator is a device that narrows a beam of particles or
waves.
In optics, a collimator may consist of a curved mirror or lens
with some type of light source and/or an image at its focus.
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Collimators in X-rays
In X-ray, and gamma ray optics, a collimator is a device that
filters a stream of rays so that only those traveling parallel to
a specified direction are allowed through.
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Collimators in X-rays
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Collimators
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Collimators in X-rays
This may be a sheet of lead or other material opaque to the
incoming radiation with many tiny holes bored through it.
Only rays that are travelling nearly parallel to the holes will
pass through them—any others will be absorbed by hitting
the plate surface or the side of a hole.
It allows the radiographer to control the exposure of
radiation to expose a film.
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Gantry detectors
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Gantry detectors
The gantry is the 'donut' shaped part of the CT scanner that
houses the components necessary to produce and detect xrays to create a CT image.
The x-ray tube and detectors are positioned opposite each
other and rotate around the gantry aperture.
This gantry can rotate 360 degrees around its axis.
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Gantry detectors
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Gantry detectors
1. gantry aperture (720mm diameter)
2. microphone
3. sagittal laser alignment light
4. patient guide lights
5. x-ray exposure indicator light
6. emergency stop buttons
7. gantry control panels
8. external laser alignment lights
9. patient couch
10. ECG gating monitor
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Gantry detectors
CT scanner with cover removed to show internal components.
T: X-ray tube
D: X-ray detectors
X: X-ray beam
R: Gantry rotation
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X-Ray Detectors
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X-Ray detectors
 The two most common types of X-ray detector used are the
scintillation and the gas-filled detectors.
 Scintillation detectors work by converting x-rays to optical
photons in special materials and then detecting the light
with a photomultiplier tube or a photodiode.
 The X-ray photon collides with a phosphor screen, or
scintillator and produces photons in the blue region of the
visible spectrum.
 These are subsequently converted to voltage pulses by
means of a photomultiplier tube attached directly behind
the scintillator.
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X-Ray detectors
 A gas filled detector consists of a rectangular gas cell with
thin entrance and exit windows.
 Inside the detector, an electric field of about 100 V/cm is
applied across two parallel plates.
 Some of the x-rays in the beam interact with the chamber
gas to produce fast photoelectrons,
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Solid State X-ray Detectors
X-ray interacts in material to produce photoelectrons which are
collected by applying a drift field
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Ultra Sound Imaging
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Ultrasound
 Ultrasound is a mechanical disturbance that moves as a
pressure wave through a medium.
 Ultrasound is high frequency mechanical vibrations or
pressure waves above a frequency the human ear can
hear.
1.
2.
3.
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Infra sound Below 20Hz
Audible 20Hz and 20 000Hz.
Ultrasound Above 20 000Hz
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Ultrasound
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Ultrasound
 The velocity of propagation of US and the attenuation are the
2 most important parameters.
 Ultrasonic imaging equipment is designed on the premise that
the ultrasonic energy propagates through tissue in a straight
line and that the ultrasonic beam is very narrow.
 When the medium is a patient, the wavelike disturbance is the
basis for use of ultrasound as a diagnostic tool.
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Ultrasound in medical field
Ultrasound uses a pulse-echo technique of imaging the body.
Pulses transmitted into patient and give rise to echoes when
they encounter interfaces/reflectors.
These interfaces/reflectors are caused by variations in the
"acoustic impedance" between different tissues.
Echo signals are amplified electronically and displayed on a
monitor using shades of grey (from black to white),
The transducer is the component of the ultrasound imaging
equipment that is placed in direct contact with the patient's
body.
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Ultrasound in medical field
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Properties of an ultrasound wave
 Attenuation is the rate at which intensity wave diminishes with
the depth it covers or its penetration.
 3 Types:
1. Scattering
2. Absorption
3. Reflection.
 When an ultrasound wave passes through tissues
 Attenuation: Reduction in amplitude and intensity of wave
 Refraction: Change in direction & velocity of wave
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Properties of an ultrasound wave
 Frequency of wave - Higher the frequency, higher the
attenuation and less penetration of the wave
 Type of tissue the wave is traveling
 Depth the wave travels - more distance wave has to travel the
more energy is lost.
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Properties of an ultrasound wave
Like other forms of sonic energy, ultrasound exists as a
sequence of alternate compressions and rarefactions of a
suitable medium (air, water, bone, tissues etc) and is propagated
through that medium at some velocity.
Whenever a beam of ultrasound passes from one medium to
another, a portion of the sonic energy is reflected and the
remainder is refracted
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Properties of an ultrasound wave
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Properties of an ultrasound wave
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Properties of an ultrasound wave
The amount of energy reflected depends on the difference in
density between the two media and the angle at which the
transmitted beam strikes the medium.
 The greater the difference in media, the greater will be the
amount reflected.
 At interfaces of extreme difference in media, such as between tissues
and bone or tissues and a gas, almost all the energy will be
reflected and practically none will continue through the second
medium.
 For this reason, the propagation path for ultrasound into or
through the body must not include bone or any gaseous
medium, such as air.
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Properties of an ultrasound wave
 In applying ultrasound to the body, an airless contact is usually
produced through use of a gel or a water bag between the
transducer and the skin.
The combined effect of scattering and absorption is called
attenuation.
Ultrasonic attenuation is the decay rate of the wave as it
propagates through material.
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Characteristics of an ultrasound wave
Wave parameters
PERIOD: time taken for one particle in the medium through which
the wave travel, to make one complete oscillation (cycle)about its rest
position, in response to the wave
FREQUENCY: the number of oscillations per second of the particle in
the medium responding to the wave passing through it
WAVELENGTH: the distance between 2 consecutive, identical
positions in the pressure wave
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Characteristics of an ultrasound wave
Wave parameters
VELOCITY: the speed of propagation of a sound wave, determined by
a combination af the density and compressibility of the medium
through which it is propagating
PHASE:the stage at which a wave is within a cycle
AMPLITUDE:a measure of the degree of change within a medium,
caused by the passage of a sound wave and relates to the severity of the
disturbance
POWER: rate of flow of energy through a given are
INTENSITY: the power per unit area
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VELOCITY
 The velocity of an ultrasound wave through a medium varies with the
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physical properties of the medium.
In low-density media such as air and other gases, molecules may
move over relatively large distances before they influence
neighboring molecules.
In these media, the velocity of an ultrasound wave is relatively low.
In solids, molecules are constrained in their motion, and the velocity
of ultrasound is relatively high.
Liquids exhibit ultrasound velocities intermediate between those in
gases and solids.
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Characteristics of an ultrasound wave
One of the most significant characteristics of sound is its frequency.
The basic unit for specifying frequency is the hertz, which is one
vibration, or cycle, per second.
Pitch is a term commonly used as a synonym for frequency of sound.
Frequency higher than 20 000Hz (20kHz)
Frequencies in the range of 2 MHz (million cycles per second) to 20
MHz are used in diagnostic ultrasound.
The Ultrasound frequencies cannot be heard by a normal young
adult.
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Characteristics of an ultrasound wave
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Characteristics of Ultrasound
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Characteristics of Ultrasound
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Doppler effect
Doppler Effect is the shift in frequency and wavelength of
waves which results from a source moving with respect to
the medium, a receiver moving with respect to the medium,
or even a moving medium.
The perceived frequency (f ´) is related to the actual frequency (f0) and
the relative speeds of the source (vs), observer (vo), and the speed (v) of
waves in the medium by
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Pulse Echo system
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Characteristics of an ultrasound wave
The choice of using the plus (+) or minus (-) sign is made according to
the convention that if the source and observer are moving towards each
other the perceived frequency (f ´) is higher than the actual frequency (f0).
Likewise, if the source and observer are moving away from each other the
perceived frequency (f ´) is lower than the actual frequency (f0).
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Doppler effect
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Applications of Ultrasound
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Applications of Ultrasound: echocardiography
Echocardiography has become routinely used in the diagnosis,
management, and follow-up of patients with any suspected or known
heart diseases.
The pictures show the size and shape of your heart. They also show
how well your heart's chambers and valves are working.
It can provide a wealth of helpful information, including the size and
shape of the heart (internal chamber size quantification), pumping
capacity and the location and extent of any tissue damage.
Echocardiography can also help detect any cardiomyopathy,
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echoencephalography
Echoencephalography is the detailing of interfaces in the brain by
means of ultrasonic waves.[1
the use of ultrasound to examine and measure internal structures (as
the ventricles) of the skull and to diagnose abnormalities and disease
The reflected pulses from the skin, brain ventricle, skull, and other
head structures are recorded and amplified with a cathode-ray
oscilloscope, giving a measure of the distance between the probe and
the reflecting surfaces.
The method is rapid, painless, and harmless; it is a good screening test
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Ultrasound Transducer
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Ultrasound Transducer
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ULTRASOUND BEAMS from source of large
dimensions
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ULTRASOUND BEAMS from source of small
dimensions
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PRESENTATION MODES
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A-scans
A-scans can be used in order to measure distances.
A transducer emits an ultrasonic pulse and the time taken for the pulse
to bounce off an object and come back is graphed in order to
determine how far away the object is.
A-scans only give one-dimensional information and therefore are not
useful for imaging.
 In the A-mode presentation of ultrasound images, echoes returning
from the body are displayed as signals on an oscilloscope.
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A-scans
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A-scans
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A-scans
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B-scans
B-scans can be used to take an image of a cross-section through the
body.
The transducer is swept across the area and the time taken for pulses
to return is used to determine distances, which are plotted as a series
of dots on the image.
B-Scans will give two-dimensional information about the cross-
section.
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B-scans
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B-scans
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M-scans
in cardiac cycle
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Echo Cardiography (Heart)
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Echo Cardiograph
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Comparison
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Comparison
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Scanners
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Scanner
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Scanners
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