This document provides an overview of specialized radiographic techniques used in dentistry, including computed tomography (CT), cone beam computed tomography, magnetic resonance imaging (MRI), nuclear medicine imaging, and ultrasonography. It describes the basic principles and applications of each technique, highlighting their benefits and limitations. The key points are that CT provides cross-sectional images to evaluate pathology while reducing superimposition, CBCT allows faster 3D imaging at lower radiation dose than traditional CT, MRI uses magnetic fields to image soft tissues without ionizing radiation, nuclear medicine involves injecting radiotracers to examine tissue function, and ultrasound uses sound waves to image structures in real-time without radiation.

1. Specialized radiographic
techniques
By
Dr. Hassan M. Abouelkheir
BDS, MSc, PhD

2. Objectives
By the end of this lecture students will
be able to:
1- Recognize specialized radiographic
techniques that help them in diagnosis and
treatment plane.
2- They will be able to choose the right
technique needed for patient evaluation.
3- They will be familiar with modern technology
in diagnostic imaging that will be available in
hospitals.

3. Specialized Radiographic
Techniques
1.Computed Tomography (CT).
2.Cone Beam Computed Tomography.
3. Magnetic Resonance Imaging.
4. Nuclear Medicine.
5. Ultrasonography.

4. 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.

5. Computed Tomography
x-ray source
360° rotation
detectors

6. Computed Tomography
x-ray tube
Fan beam
collimator
detectors

7. Computed Tomography (CT)Cont.
• 1st type 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.

8. 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%.

9. 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.

11. 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 (1.5mm6mm) so reduce the time
of scanning from original
30 min to 1-2 sec per
slice

12. 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 .

13. Computed tomography (cont.)
• Each voxel has a CT number or
Hounsfield unite between -1000
(air) to +1000 (dense bone) and
Zero (water).
• 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.

14. 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.

16. Indications in Dentistry
1. 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)

17. 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.

18. 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.
Artifacts:
1- partial volume artifact at the junction of soft and hard
tissue .
2- Beam –Hardening artifact .
3- Metal artifact.

19. 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..

20. 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

21. Cone Beam CT
tubehead
flat-panel detector

23. 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 into 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

24. 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

25. 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.

27. 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.

28. • 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.

29. 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

30. Magnetic Resonance
radiofrequency
coils
sliding table
Magnet

31. • If we apply Radiofrequency (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.

34. • 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)

35. 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.

36. 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.
radiopharmaceuticals
Tc+MPD →bone scan.
• - Tc+ RBCS → blood.
99m
99m

37. Scintigraphy
(Radionuclide Scan)
1. Radioactive
pharmaceutical agent
2. Tissue specificity
3. Gamma rays emitted
4. Gamma camera

39. • 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.

40. • 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.

41. 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.

42. 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.

43. Ultrasound
1. High-frequency ultrasonic vibrations
2. Echoes at tissue density differences
3. Varying echo intensities
image
NO IONIZING RADIATION

44. Ultrasound
echoes

45. • 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)

46. 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.

47. • 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.

48. Indications:
• 1- swelling in the
neck.
• 2- salivary gland &
duct calculi.
• 3- ass. Of
ventricular system in
babies.
• 4- Obstetrics and
Gynecology .

49. 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.