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Specialized radiographic
techniques
Specialized Radiographic
Techniques
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•
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1- Tomography.
2- Stereoscopy.
3- Scanography.
4- computed tomography.
5- Cone Beam Computed Tomography.
6- Magnetic Resonance Imaging.
7- Nuclear Medicine.
8- Ultrasonography.
1- Tomography
• It is a technique by
which structures are
blurred below & above
a certain plane at
which image is sharp
(tomographic cut).
• This is done by filmtube assembly
connected by pivot and
moved opposite to
each other.
Tomography (cont.)
• Conventional film-based
tomography (body section
tomography) is applied
primarily to high contrast
anatomy such as TMJ and
dental implants.
The examination begins with
the x-ray tube and film
positioned on opposite sides of
the fulcrum, which is located
with in the body’s plane of
interest (focal plane). As the
exposure begins, the tube and
film move in opposite
directions simultaneously
through a mechanical linkage.
Blurring of image increases in
• The farther the structure lies
from focal plane , the greater the
distance between structure and
film.
• The long axis of blurred
structure perpendicular to the
direction of tube travel
• The greater of tomographic
angle or arc.
Tomography (cont.)
• There are 5 types of tomographic
movements:
• 1-Linear.
• 2-Circular.
• 3- trispiral.
• 4- Elliptical.
• 5- Hypocycloidal.
Tomography (cont.)

• Linear tomography can be done by 2 ways:
• 1- the x-ray tube and film move in opposite
directions a fixed fulcrum .
• 2- both x-ray tube and film move along
concentric arcs rather than straight line.
Drawbacks of linear tomography

• 1-The blurring pattern is irregular
and incomplete.
• 2-Horizontal streaks (false images
or parasite lines) , represent the
image of objects outside the focal
plane.
• 3- changing the angulations of
beam to focal plane leading to
Inconsistent magnification,
dimensional instability and non
uniform density.
• panoramic Machines which uses
arc shape tomogram cause
distorted image because
magnification in the vertical plane
is independent of that in horizontal
plane.
Linear Tomography (cont.)
• Multidirectional Tomographic
motion is necessary as
Tomographic layer has width
(thickness of the cut) is inversely
proportion to the Tomographic
angle.
• The greater the angle, the
thinner of the cut thickness.
• Wide angle tomography
(>10º)allow visualization of fine
structures (1mm) but suffer from
decreased image contrast.
• Narrow angle tomography (<10º)
→Zonography due to thick zone
of tissue (up to 25mm)
2- Stereoscopy

• Stereoscopy was introduced by J.Mackenzie Davidson in
1898.
• Stereoscopic imaging requires the exposure of two films ,
one for each eye as the tube was shifted to 10% of focal
film distance .
• Then they viewed with stereoscope that uses either mirrors
or prisms to coordinate the accommodation .
• It is used for evaluation of bony pockets in periodontal
diseases, TMJ, endodontic root configuration & dental
implants.
3- Scanography.
• Narrow collimated fan
shaped beam of radiation to
scan an area of interest the
same as panoramic
radiography.
• It demonstrate higher
contrast with perception of
greater detail.
• Higher contrast is due to
collimation of beam so
reduce scattering so
producing image with high
quality.
Scanography (cont.)
• Rotational Scanography the
beam of radiation rotates about
a fixed axis that is
predetermined based on the
area to be imaged so produce
2 or 4 scanograms.
• It is effective as intraoral
periapical films.
• Linear Scanography like
panoramic (straightened out).
• The scanora system capable
of both postero-anterior and
lateral linear scanning of
maxillofacial complex.
4- Computer tomography (CT) scan:
• It is a a radiographic
technique that blends the
concept of thin layer
radiography (tomography)
with computer synthesis
of the image.
• In 1972, Godfrey
Hounsfield , a researcher
working for EMI limited in
England developed a
prototype scanner based
on image reconstruction.
Computed Tomography
x-ray source

360° rotation

detectors
Computed Tomography
x-ray tube
Fan beam
collimator

detectors
Computed Tomography (CT)Cont.
• CT scanner consists of
x-ray tube and an array
of scintillation detectors
both move around
patient .
• 2nd type where
detectors forming a
continous ring round pt
and x-ray tube may
move in a circle within
the detector ring
(incremental scanner)
due to overlapping
layers.
Computed Tomography (CT)Cont.

• A new CT scanners
have aqcuire image
data in spiral or helical
fashion.
• It reduces
multiplanner image
reconstruction time to
12 seconds versus 5
minutes .
• It reduce radiation
dose to 75%.
CT Equipment and Image Formation:
• It consists of:
• 1- Donut shaped
scanning gantry: which
contains x-ray source,
detectors and electronic
measuring devices.
• 2- Motorized table used
to position patient within
gantry.
• 3- x-ray power supplies
and controls.
• 4- viewing devices such
as video monitors.
Computer tomography (cont.)
• . X-ray tube and detectors
(scintillation crystals or
xenon gas) are arranged
in either a rotating arc
opposite the x-ray
generator or in a
360°aray around patient’s
body so rotate once per
slice (1.5mm-6mm) so
reduce the time of
scanning from original 30
min to 1-2 sec per slice
Computer tomography (cont.)
• The x-ray beam attenuation data
are collected in a grid pattern
called a matrix .
• Each square in the matrix is
made up of a pixel which
represents the x-ray attenuation
of small finite volume of tissue
(Voxel) or volume element.
• Typical matrix sizes in CT are
256*256 or 512*512 pixels.
• Each pixel is assigned CT
number representing the density
after x-ray attenuation .
Computed tomography (cont.)
• Each voxel has a CT number or
Hounsfield unite between -1000 (air)
to +1000 (dense bone).
• Head CT scanning slices are usually
made with 3mm slices while 3D
reformatting 1-1.5mm.
• The image can be reconstructed or
manipulated for 3D construction
without further exposure to pt.
• 3D reformatting requires each
original voxel shaped as rectangular
parallel piped or solid as
dimensionally altered into multiple
cuboidal voxels (cuberills)
→ Interpolation process.
Computer tomography (cont.)
• At the video monitor one
can select a window width
or the range of CT
numbers that represented
by pure white to pure
black.
• Window level or CT
number that represent the
middle of grey level scale
to differentiate between
soft and hard tissue.
Indications in Dentistry
• Evaluation & extent
of any suspected
pathology in the
head & neck,
including tumors,
cysts and infection.
• 2- Determination of
the location and
displacement of
facial fractures in
RTA pt (Road traffic
accident)
Indications in Dentistry (cont.)
• 3- 3D construction for
plastic or maxillofacial
surgeons for planning
reconstruction after facial
trauma.
• 4- radiographic presurgical evaluation of
the size and width of the
jaw before osseo integrated dental
implants insertion.
Advantages of CT Scan
1-Overcome the superimposition of structure.
2- image acquisition in cross-sectional or other
planes.
3- Soft tissue imaging.
4- adjustment of radiographic contrast.
Disadvantages:
1- high cost.
2- high pt’s dose.
3- metallic filling produce star artifacts.
5- Cone Beam Computed Tomography.
• The imaging source-detector and
the method of data acquisition
distinguish cone beam
tomography from traditional CT
imaging. Traditional CT uses a
high-output rotating anode X-ray
tube, while cone beam
tomography utilizes a low-power,
medical fluoroscopy tube that
provides continuous imaging
throughout the scan.
• Traditional computerized
tomography records data with a
fan-shaped X-ray beam into
image detectors arranged in an
arc around the patient, producing
a single slice image per scan..
Cone Beam CT
1.
Cone-shaped x-ray beam
2. 360-degree rotation around head
3.

Scan time around 20 seconds

4.

2D or 3D images

5.

Patient exposure = ½ AFM
Cone Beam CT

tubehead
flat-panel detector
Cone Beam Computed Tomography (cont)

• Each slice must overlap
slightly in order to properly
reconstruct the images. The
advanced cone beam
technology uses a coneshaped X-ray beam that
transmits onto a solid-state
area sensor for image
capture, producing the
complete volume image in a
single rotation. The sensor
contains an image intensifier
and a CCD camera, or an
amorphous silicon flat panel
detector
Cone Beam Computed Tomography (cont)

• The single-turn motion image-capture used in cone beam
tomography is quicker than traditional spiral motion, and can
be accomplished at a lower radiation dose as a result of no
overlap of slices. This type of imaging exposes a patient to
less radiation than traditional CT scanners.
• The next generation of CBCT is “Ultra Cone Beam CT
Scanners.”
• Ultra CBCT imaging provides important information about the
three-dimensional structure of blood vessels, nerves, soft
tissue, and bone
Cone Beam Computed Tomography (cont)

• Three-dimensional
visualization
software can shade
images to
differentiate varying
densities of facial
structures.
Grayscale shading
provides the ability
to view the
relationships of
common internal
anatomy.
6- Magnetic Resonance Image (MRI):

• The simplest atom in the body is hydrogen atom
where it’s nucleus contains one proton and one
neutron. Each proton has it’s own magnetic field
with N &S poles inherent magnetism is called
magnetic moment the net result of this random
magnetism is zero.
• If external magnetic field
is applied so protons will
align themselves like
compass needle so
dipoles aligns with
direction of external
magnetic field.
• Each nucleus acts as
small gyroscope as it
wobbles in tinny circle
called precession and it’s
fastness called precession
frequency as it is known
as Larmor frequency .
• Determination of Larmor
frequency of precession is
called resonance
frequency of vibration.
Magnetic Resonance

Able to image soft tissue without
contrast agents
1. Magnetic field aligns atoms (Hydrogen)
2.
Radiowaves alter alignment
3.

Atoms realign, releasing energy

4.

Computer produces image
NO IONIZING RADIATION
Magnetic Resonance
radiofrequency
coils
sliding table

Magnet
• If we apply Radio-frequency
(RF) equal to Larmor
frequency the nuclei flip
changing their direction and
aligned opposite to the
external magnetic field.
when this RF energy is
removed the nuclei return
back to their previous
orientation.
• This way of returning to
normal is called relaxation
and required time is called
relaxation time.
• During relaxation RF
signals is emitted. This is
called free induction decay
(FID) from which the MR
image is formed . Then
mathematical calculation is
applied on FID to produce
details of the sample.
• We apply 90°pulse or 180°pulse
RF.
• MRI depends on 3 factors:
• 1- Spin Density (SD): the quantity
proportional to the number of
nuclei in tissue precessing at
Larmor frequency and contributing
to MR signal.
!
• 2- T1: the time required for
interaction between nuclear spin
and the tissue lattice to return to
normal following RF excitation
(spin-lattice relaxation time).
!
• 3- T2: the time required for
interaction between nuclear spins
and adjacent nuclear spin (spinspin) to return to normal following
RF excitation (0.5-1-5 Tesla)
• Indications:
• Investigations of intra cranial tumors and lesions.
• TMJ dysfunction for detection of internal disc
derangement.

• Advantages:
• 1- No ionizing radiation .
• 2- Image manipulation & high resolution.
• 3- Super differentiation between hard & soft
tissues.

• Disadvantages:
• 1-Bone cortex doesn’t give MR signals , only bone
marrow.
• 2- long scanning time.
• 3- contra indicated in pt having metallic implants.
• 4- expensive.
7- Radioisotope image:

• Radionuclide imaging relies upon
altering the pt by making the
tissues radioactive and pt
becoming the source of ionizing
radiation.
• Radioactive isotopes (radio
nuclides) are used to visualize
specific tissues from diagnostic
images produced by Gamma
camera or rectilinear scintillation
detectors.
• Radionuclides are conjugated
with chemical material to be
injected I.V. to accumulate in
certain tissues (target tissue) so
after preparation it is called
radiopharmaceuticals. e.g. 99mTc
+MPD →bone scan.
• - 99mTc+ RBCS → blood.
Scintigraphy
(Radionuclide Scan)

1.

!

Radioactive
pharmaceutical agent
2. Tissue specificity

3. Gamma rays emitted
4. Gamma camera
• Technetium 99m is commonly
used in salivary gland and bone
scanning.
• It has 6.03hs half life, emit 140.5
Kev Gamma photons
• The detected radiation is
computer processed to eliminate
unwanted background noise and
reconstruction of image for both
anatomical and functional
aspects.
• Abnormality can be detected by
local increase (hot spot) or
decrease (cold spot) in
concentration of radionuclide.
• Single photon emission computed
tomography (SPECT) which
rotate 360°,multiple detectors
allows acquistion of data from a
number of contiguous transaxial
slices.
• Positron emission computed tomography (PET)
100 time sensitive than Gamma camera.
• Pt is injected with positron-emitting radionulides
generated in cyclotronwhich emit of two 551 Kev
photons at 180°to each others.

Advantages:
1- target tissue function.
2- computer analysis and enhancement.
Disadvantages:
1- poor resolution.
2- Expensive.
3-Time consuming.
4-Contraindicated in pregnancy.
Advances in radionuclide imaging:
• Single photon emission computed
tomography(SPECT):
• Cross sectional image or SPECT scan
enabling the exact anatomical site of
the source of emission to be
determined.
Positron emission Tomography(PET):

• Some isotopes decay by the emission
of positively charged electron
(Positron) from nucleus which interact
with high energy Gamma rays to
produce annihilation radiation that can
be detected by PET .
• It is used to investigate disease at
molecular level and cross sectional
slice is displayed even if there is no
anatomical abnormalities appeared on
CT or MRI scans.
8- Ultrasound:
• Ultrasonography is medical
imaging technique that uses
high frequency sound waves
and their echoes.
• Ultrasound machine transmits
high frequency (1-5 mega
Hertz) sound pulses into the
body using transducer probe.
• These waves hit boundaries
between tissues (fluid/
softtissue/ bone).
• Most of them are reflected
back to be received by the
same probe & relayed to
machine.
Ultrasound
1.

!

High-frequency ultrasonic vibrations
2. Echoes at tissue density differences
3. Varying echo intensities

image

NO IONIZING RADIATION
Ultrasound
echoes
• The machine
calculates the
distance from the
probe to tissue or
boundaries using
the speed of sound
in tissue (1,540m/s)
and time of each
echo’s return (in
millionths of second)
Transducer probe:
•

•

•

•
•

Makes the sound waves and receives
the echoes using principle called
piezoelectric (pressure electricity)
effect discovered by Pierre & Jacques
curie in 1880.
In probe there are one or more quartz
crystals called piezoelectric crystals
when electric current is applied , they
vibrate producing sound waves that
travel outside .
At the same time when echo returned
back to crystals causing vibration as a
result of that they emit electric
current .
Therefore they used for sending &
receiving sound waves.
Cpu transfer electric impulses into a n
image of topographic or cross sectional
picture that represent the depth of
tissue interfaces.
• Recently doppler effect
can be used to measure a
change of frequency of
sound reflected from a
moving source e.g.
arterial, venous blood
flow.
• 3D doppler allow:
• 1-early detection of
cancerous and benign
tumors.
• 2- masses in colon &
rectum.
• 3- breast lesions for
possible biopsy.
Indications:
• 1- swelling in the
neck.
• 2- salivary gland &
duct calculi.
• 3- ass. Of ventricular
system in babies.
• 4- Obstetrics and
Gynecology .
Disadvantages:
• 1- Restricted use in head & neck as
sound waves are absorbed by
bone.
• 2- Very operator dependant.
• 3- Image is very difficult to interpret
form inexperienced operator.
• 4- Real time image.
THANK YOU

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Specialised Techniques in Oral Radiology

  • 2. Specialized Radiographic Techniques • • • • • • • • 1- Tomography. 2- Stereoscopy. 3- Scanography. 4- computed tomography. 5- Cone Beam Computed Tomography. 6- Magnetic Resonance Imaging. 7- Nuclear Medicine. 8- Ultrasonography.
  • 3. 1- Tomography • It is a technique by which structures are blurred below & above a certain plane at which image is sharp (tomographic cut). • This is done by filmtube assembly connected by pivot and moved opposite to each other.
  • 4. Tomography (cont.) • Conventional film-based tomography (body section tomography) is applied primarily to high contrast anatomy such as TMJ and dental implants. The examination begins with the x-ray tube and film positioned on opposite sides of the fulcrum, which is located with in the body’s plane of interest (focal plane). As the exposure begins, the tube and film move in opposite directions simultaneously through a mechanical linkage.
  • 5. Blurring of image increases in • The farther the structure lies from focal plane , the greater the distance between structure and film. • The long axis of blurred structure perpendicular to the direction of tube travel • The greater of tomographic angle or arc.
  • 6. Tomography (cont.) • There are 5 types of tomographic movements: • 1-Linear. • 2-Circular. • 3- trispiral. • 4- Elliptical. • 5- Hypocycloidal.
  • 7. Tomography (cont.) • Linear tomography can be done by 2 ways: • 1- the x-ray tube and film move in opposite directions a fixed fulcrum . • 2- both x-ray tube and film move along concentric arcs rather than straight line.
  • 8. Drawbacks of linear tomography • 1-The blurring pattern is irregular and incomplete. • 2-Horizontal streaks (false images or parasite lines) , represent the image of objects outside the focal plane. • 3- changing the angulations of beam to focal plane leading to Inconsistent magnification, dimensional instability and non uniform density. • panoramic Machines which uses arc shape tomogram cause distorted image because magnification in the vertical plane is independent of that in horizontal plane.
  • 9. Linear Tomography (cont.) • Multidirectional Tomographic motion is necessary as Tomographic layer has width (thickness of the cut) is inversely proportion to the Tomographic angle. • The greater the angle, the thinner of the cut thickness. • Wide angle tomography (>10º)allow visualization of fine structures (1mm) but suffer from decreased image contrast. • Narrow angle tomography (<10º) →Zonography due to thick zone of tissue (up to 25mm)
  • 10. 2- Stereoscopy • Stereoscopy was introduced by J.Mackenzie Davidson in 1898. • Stereoscopic imaging requires the exposure of two films , one for each eye as the tube was shifted to 10% of focal film distance . • Then they viewed with stereoscope that uses either mirrors or prisms to coordinate the accommodation . • It is used for evaluation of bony pockets in periodontal diseases, TMJ, endodontic root configuration & dental implants.
  • 11. 3- Scanography. • Narrow collimated fan shaped beam of radiation to scan an area of interest the same as panoramic radiography. • It demonstrate higher contrast with perception of greater detail. • Higher contrast is due to collimation of beam so reduce scattering so producing image with high quality.
  • 12. Scanography (cont.) • Rotational Scanography the beam of radiation rotates about a fixed axis that is predetermined based on the area to be imaged so produce 2 or 4 scanograms. • It is effective as intraoral periapical films. • Linear Scanography like panoramic (straightened out). • The scanora system capable of both postero-anterior and lateral linear scanning of maxillofacial complex.
  • 13. 4- Computer tomography (CT) scan: • It is a a radiographic technique that blends the concept of thin layer radiography (tomography) with computer synthesis of the image. • In 1972, Godfrey Hounsfield , a researcher working for EMI limited in England developed a prototype scanner based on image reconstruction.
  • 15. Computed Tomography x-ray tube Fan beam collimator detectors
  • 16. Computed Tomography (CT)Cont. • CT scanner consists of x-ray tube and an array of scintillation detectors both move around patient . • 2nd type where detectors forming a continous ring round pt and x-ray tube may move in a circle within the detector ring (incremental scanner) due to overlapping layers.
  • 17. Computed Tomography (CT)Cont. • A new CT scanners have aqcuire image data in spiral or helical fashion. • It reduces multiplanner image reconstruction time to 12 seconds versus 5 minutes . • It reduce radiation dose to 75%.
  • 18. CT Equipment and Image Formation: • It consists of: • 1- Donut shaped scanning gantry: which contains x-ray source, detectors and electronic measuring devices. • 2- Motorized table used to position patient within gantry. • 3- x-ray power supplies and controls. • 4- viewing devices such as video monitors.
  • 19.
  • 20. Computer tomography (cont.) • . X-ray tube and detectors (scintillation crystals or xenon gas) are arranged in either a rotating arc opposite the x-ray generator or in a 360°aray around patient’s body so rotate once per slice (1.5mm-6mm) so reduce the time of scanning from original 30 min to 1-2 sec per slice
  • 21. Computer tomography (cont.) • The x-ray beam attenuation data are collected in a grid pattern called a matrix . • Each square in the matrix is made up of a pixel which represents the x-ray attenuation of small finite volume of tissue (Voxel) or volume element. • Typical matrix sizes in CT are 256*256 or 512*512 pixels. • Each pixel is assigned CT number representing the density after x-ray attenuation .
  • 22. Computed tomography (cont.) • Each voxel has a CT number or Hounsfield unite between -1000 (air) to +1000 (dense bone). • Head CT scanning slices are usually made with 3mm slices while 3D reformatting 1-1.5mm. • The image can be reconstructed or manipulated for 3D construction without further exposure to pt. • 3D reformatting requires each original voxel shaped as rectangular parallel piped or solid as dimensionally altered into multiple cuboidal voxels (cuberills) → Interpolation process.
  • 23. Computer tomography (cont.) • At the video monitor one can select a window width or the range of CT numbers that represented by pure white to pure black. • Window level or CT number that represent the middle of grey level scale to differentiate between soft and hard tissue.
  • 24.
  • 25. Indications in Dentistry • Evaluation & extent of any suspected pathology in the head & neck, including tumors, cysts and infection. • 2- Determination of the location and displacement of facial fractures in RTA pt (Road traffic accident)
  • 26. Indications in Dentistry (cont.) • 3- 3D construction for plastic or maxillofacial surgeons for planning reconstruction after facial trauma. • 4- radiographic presurgical evaluation of the size and width of the jaw before osseo integrated dental implants insertion.
  • 27. Advantages of CT Scan 1-Overcome the superimposition of structure. 2- image acquisition in cross-sectional or other planes. 3- Soft tissue imaging. 4- adjustment of radiographic contrast. Disadvantages: 1- high cost. 2- high pt’s dose. 3- metallic filling produce star artifacts.
  • 28. 5- Cone Beam Computed Tomography. • The imaging source-detector and the method of data acquisition distinguish cone beam tomography from traditional CT imaging. Traditional CT uses a high-output rotating anode X-ray tube, while cone beam tomography utilizes a low-power, medical fluoroscopy tube that provides continuous imaging throughout the scan. • Traditional computerized tomography records data with a fan-shaped X-ray beam into image detectors arranged in an arc around the patient, producing a single slice image per scan..
  • 29. Cone Beam CT 1. Cone-shaped x-ray beam 2. 360-degree rotation around head 3. Scan time around 20 seconds 4. 2D or 3D images 5. Patient exposure = ½ AFM
  • 31.
  • 32. Cone Beam Computed Tomography (cont) • Each slice must overlap slightly in order to properly reconstruct the images. The advanced cone beam technology uses a coneshaped X-ray beam that transmits onto a solid-state area sensor for image capture, producing the complete volume image in a single rotation. The sensor contains an image intensifier and a CCD camera, or an amorphous silicon flat panel detector
  • 33. Cone Beam Computed Tomography (cont) • The single-turn motion image-capture used in cone beam tomography is quicker than traditional spiral motion, and can be accomplished at a lower radiation dose as a result of no overlap of slices. This type of imaging exposes a patient to less radiation than traditional CT scanners. • The next generation of CBCT is “Ultra Cone Beam CT Scanners.” • Ultra CBCT imaging provides important information about the three-dimensional structure of blood vessels, nerves, soft tissue, and bone
  • 34. Cone Beam Computed Tomography (cont) • Three-dimensional visualization software can shade images to differentiate varying densities of facial structures. Grayscale shading provides the ability to view the relationships of common internal anatomy.
  • 35.
  • 36. 6- Magnetic Resonance Image (MRI): • The simplest atom in the body is hydrogen atom where it’s nucleus contains one proton and one neutron. Each proton has it’s own magnetic field with N &S poles inherent magnetism is called magnetic moment the net result of this random magnetism is zero.
  • 37. • If external magnetic field is applied so protons will align themselves like compass needle so dipoles aligns with direction of external magnetic field. • Each nucleus acts as small gyroscope as it wobbles in tinny circle called precession and it’s fastness called precession frequency as it is known as Larmor frequency . • Determination of Larmor frequency of precession is called resonance frequency of vibration.
  • 38. Magnetic Resonance Able to image soft tissue without contrast agents 1. Magnetic field aligns atoms (Hydrogen) 2. Radiowaves alter alignment 3. Atoms realign, releasing energy 4. Computer produces image NO IONIZING RADIATION
  • 40. • If we apply Radio-frequency (RF) equal to Larmor frequency the nuclei flip changing their direction and aligned opposite to the external magnetic field. when this RF energy is removed the nuclei return back to their previous orientation. • This way of returning to normal is called relaxation and required time is called relaxation time. • During relaxation RF signals is emitted. This is called free induction decay (FID) from which the MR image is formed . Then mathematical calculation is applied on FID to produce details of the sample.
  • 41.
  • 42.
  • 43. • We apply 90°pulse or 180°pulse RF. • MRI depends on 3 factors: • 1- Spin Density (SD): the quantity proportional to the number of nuclei in tissue precessing at Larmor frequency and contributing to MR signal. ! • 2- T1: the time required for interaction between nuclear spin and the tissue lattice to return to normal following RF excitation (spin-lattice relaxation time). ! • 3- T2: the time required for interaction between nuclear spins and adjacent nuclear spin (spinspin) to return to normal following RF excitation (0.5-1-5 Tesla)
  • 44. • Indications: • Investigations of intra cranial tumors and lesions. • TMJ dysfunction for detection of internal disc derangement. • Advantages: • 1- No ionizing radiation . • 2- Image manipulation & high resolution. • 3- Super differentiation between hard & soft tissues. • Disadvantages: • 1-Bone cortex doesn’t give MR signals , only bone marrow. • 2- long scanning time. • 3- contra indicated in pt having metallic implants. • 4- expensive.
  • 45. 7- Radioisotope image:
 • Radionuclide imaging relies upon altering the pt by making the tissues radioactive and pt becoming the source of ionizing radiation. • Radioactive isotopes (radio nuclides) are used to visualize specific tissues from diagnostic images produced by Gamma camera or rectilinear scintillation detectors. • Radionuclides are conjugated with chemical material to be injected I.V. to accumulate in certain tissues (target tissue) so after preparation it is called radiopharmaceuticals. e.g. 99mTc +MPD →bone scan. • - 99mTc+ RBCS → blood.
  • 46. Scintigraphy (Radionuclide Scan) 1. ! Radioactive pharmaceutical agent 2. Tissue specificity 3. Gamma rays emitted 4. Gamma camera
  • 47.
  • 48. • Technetium 99m is commonly used in salivary gland and bone scanning. • It has 6.03hs half life, emit 140.5 Kev Gamma photons • The detected radiation is computer processed to eliminate unwanted background noise and reconstruction of image for both anatomical and functional aspects. • Abnormality can be detected by local increase (hot spot) or decrease (cold spot) in concentration of radionuclide. • Single photon emission computed tomography (SPECT) which rotate 360°,multiple detectors allows acquistion of data from a number of contiguous transaxial slices.
  • 49. • Positron emission computed tomography (PET) 100 time sensitive than Gamma camera. • Pt is injected with positron-emitting radionulides generated in cyclotronwhich emit of two 551 Kev photons at 180°to each others. Advantages: 1- target tissue function. 2- computer analysis and enhancement. Disadvantages: 1- poor resolution. 2- Expensive. 3-Time consuming. 4-Contraindicated in pregnancy.
  • 50. Advances in radionuclide imaging: • Single photon emission computed tomography(SPECT): • Cross sectional image or SPECT scan enabling the exact anatomical site of the source of emission to be determined. Positron emission Tomography(PET): • Some isotopes decay by the emission of positively charged electron (Positron) from nucleus which interact with high energy Gamma rays to produce annihilation radiation that can be detected by PET . • It is used to investigate disease at molecular level and cross sectional slice is displayed even if there is no anatomical abnormalities appeared on CT or MRI scans.
  • 51. 8- Ultrasound: • Ultrasonography is medical imaging technique that uses high frequency sound waves and their echoes. • Ultrasound machine transmits high frequency (1-5 mega Hertz) sound pulses into the body using transducer probe. • These waves hit boundaries between tissues (fluid/ softtissue/ bone). • Most of them are reflected back to be received by the same probe & relayed to machine.
  • 52. Ultrasound 1. ! High-frequency ultrasonic vibrations 2. Echoes at tissue density differences 3. Varying echo intensities image NO IONIZING RADIATION
  • 54. • The machine calculates the distance from the probe to tissue or boundaries using the speed of sound in tissue (1,540m/s) and time of each echo’s return (in millionths of second)
  • 55. Transducer probe: • • • • • Makes the sound waves and receives the echoes using principle called piezoelectric (pressure electricity) effect discovered by Pierre & Jacques curie in 1880. In probe there are one or more quartz crystals called piezoelectric crystals when electric current is applied , they vibrate producing sound waves that travel outside . At the same time when echo returned back to crystals causing vibration as a result of that they emit electric current . Therefore they used for sending & receiving sound waves. Cpu transfer electric impulses into a n image of topographic or cross sectional picture that represent the depth of tissue interfaces.
  • 56. • Recently doppler effect can be used to measure a change of frequency of sound reflected from a moving source e.g. arterial, venous blood flow. • 3D doppler allow: • 1-early detection of cancerous and benign tumors. • 2- masses in colon & rectum. • 3- breast lesions for possible biopsy.
  • 57. Indications: • 1- swelling in the neck. • 2- salivary gland & duct calculi. • 3- ass. Of ventricular system in babies. • 4- Obstetrics and Gynecology .
  • 58. Disadvantages: • 1- Restricted use in head & neck as sound waves are absorbed by bone. • 2- Very operator dependant. • 3- Image is very difficult to interpret form inexperienced operator. • 4- Real time image.