MRI provides high quality soft tissue imaging and is useful for evaluating many conditions of the head and neck region. It can identify soft tissue lesions, assess intracranial pathology, stage tumors, evaluate salivary glands and lymph nodes, and precisely image the TMJ for disorders like internal derangement. Dynamic contrast-enhanced MRI is particularly helpful for distinguishing normal and malignant tissues, differentiating tumor types, and assessing vascularity and recurrence risk.
11. Designed by Godfrey N.
Hounsfield to overcome the
visual representation
challenges in radiography
and conventional
tomography by collimating
the X-ray beam and
transmitting it only through
small cross-sections of the
body
12. In 1979, G.N. Hounsfield shared the Nobel Prize in
Physiology & Medicine with Allan MacLeod Cormack,
Physics Professor who developed solutions to
mathematical problems involved in CT
G.N.HOUNSFIELD ALLAN M. CORMACK
13. 1969
• G.N. Hounsfield developed first clinically useful CT head scanner
1971
• First clinically useful CT head scanner was installed at Atkinson-
Morley Hospital (England)
1972
• First paper on CT presented to British Institute of Radiology by
Hounsfield and Dr. Ambrose
1974
• Dr. Ledley introduced the whole body CT scanner (ACTA scanner)
1979
• G.N. Hounsfield shared the Nobel Prize with Allan MacLeod
Cormack
14. Computer tomography (CT), originally known as computed
axial tomography (CAT or CT scan) and body section
rontenography.
It is a medical imaging method employing tomography where
digital geometry processing is used to generate a three-
dimensional image of the internals of an object from a large
series of two-dimensional X-ray images taken around a single
axis of rotation.
The word "tomography" is derived from the Greek words
tomos (slice) and graphein (to write). CT produces a volume
of data which can be manipulated, through a process known
as windowing, in order to demonstrate various structures
based on their ability to block the X-ray beam.
15. Computed tomography (CT) scan machines uses X-
rays, a powerful form of electromagnetic energy.
CT combines X radiation and radiation detectors
coupled with a computer to create cross sectional image
of any part of the body.
17. The internal structure
of an object can be
reconstructed from
multiple projections of
the object.
CT scanning is a
systematic collection
and representation of
projection data.
18. Conventional radiography
suffers from the collapsing
of 3D structures onto a 2D
image
CT gives accurate
diagnostic information
about the distribution of
structures inside the body
19. A conventional X-ray image is basically a shadow.
Shadows give you an incomplete picture of an
object's shape
This is the basic idea of computer aided tomography. In a CT
scan machine, the X-ray beam moves all around the patient,
scanning from hundreds of different angles.
20. GENERATION CONFIGURATI
ON
DETECTOR BEAM MIN SCAN
TIME
FIRST TRANSLATE -
ROTATE
1-2 PENCIL
THIN
2.5MIN
SECOND TRANSLATE -
ROTATE
3-52 NARROW
FAN
10SEC
THIRD
ROTATE-
ROTATE
256-1000 WIDE FAN 0.5SEC
FOURTH ROTATE-
FIXED
600-4800 WIDE FAN 1SEC
FIFTH ELECTRON
BEAM
1284 WIDE FAN
ELECTRON
BEAM
33NS
GENERATIONS OF CT
100. LESS EXPENSIVE
1/4-1/5 COST OF CT
MINIMAL SPACE REQUIREMENT
HIGH QUALITY AND THIN SLICE
IMAGES
CONE SHAPED BEAM - SINGLE
ROTATIONAL SCAN
RAPID SCAN TIME
160-599 BASIS IMAGES
REDUCTION IN IMAGE
UNSHARPNESS
ACCURACY-ISOTROPIC VOXEL,
RESOLUTION- SUBMILLIMETER
VOLUME CONSTRUCTION – 3D
DISPLAY MODES UNIQUE TO
MAXILLOFACIAL IMAGING
INTERACTIVE ANALYSIS
DOSE REDUCTION – PULSED, FOV
TUBE EFFICIENCY INCREASED
101. Disadvantages
◦ Noise from radiation scatter
◦ Streak artifacts from metal restorations
◦ Image degradation from patient movement
◦ Cost
◦ Training
◦ Soft tissue contrast
104. Indications
◦ Evaluation of the jaw bones
Implant placement and evaluation
TMJ
Pathology
Bony
Periodontal assessment
Endodontic assessment
Assessment of the IAN prior to extraction of impactions
Orthodontic evaluation
◦ Airway assessment
◦ Need for 3D reconstructions
141. Direct trauma. Fracture of the posterior
wall of the right maxillary sinus (thin
arrows) and juxtaparietal soft tissue
emphysema (thick arrows). Slight blood
effusion in sinus.
144. Bilateral circular calcifications in the region
of the carotid sheath at the level of C3/C4
consistent with MAC (medial arterial
calcinosis) seen in diabetic patients
especially with end-stage renal disease
(ESRD).
145.
146. The story of MRI is one of the long courtship between physics & medicine. In
1952, Dr. Bloch from Stanford University & Dr. Purcell from Harvard
University were awarded the Nobel Prize for their work on what was then
known as Nuclear Magnetic Resonance (NMR). However the turning point
came after 20 yrs with the advent of computers in Medical imaging. By this
time, the word ‘nuclear’ is substituted & it is now known as “Magnetic
Resonance Imaging”.
MRI is another recently developed imaging modality that totally replaces
conventional X-ray generating equipment and film .It is a test that uses a
magnetic field and pulses of radio wave energy to make pictures of organs and
structures inside the body . Essentially it involves the behaviour of proton in a
magnetic field. The simplest atom is hydrogen, consisting of one proton in the
nucleus and one orbiting electron and it is the hydrogen protons that are used to
create the MRI image
147. 1.Identifying and localizing orofacial soft tissue lesions; and assessment
of intracranial lesions involving particularly the posterior cranial fossa, the
pituitary and the spinal cord,
2. The pharynx, larynx, sinuses, orbits, and tumour staging. Two studies
have shown MRI to be more
sensitive than bone scan for the detection of vertebral bone
metastases.49,50
3. To evaluate the site, size and extent of all soft tissue tumours including
nodal involvement, involving
all areas in particular the tongue and floor of mouth.
4 .The salivary glands - providing images of salivary gland parenchyma
In particular, dynamic MR imaging may predict whether head and neck
lesions including those affecting salivary glands are malignant, it can help
limit differential diagnosis, and has the potential of predicting
vascularity and recurrence
148. 5.Dynamic contrast-enhanced MR images are useful for diagnosing
lymph node metastases. 39
6.Metastatic lymph nodes with heterogeneous contrast enhancement
demonstrate a longer time to peak, a lower peak enhancement, a
lower maximum slope, and a slower washout slope than normal
lymph nodes with homogeneous enhancement. 41 ,42
7.Dynamic contrast-enhanced MR images can also be used to
distinguish between normal and malignant tissue and to differentiate
a malignant lymphoma from other lymph node enlargements
becausemetastatic lymph nodes associated with squamous cell
carcinoma had greater and faster peak enhancement than malignant
lymphoma .43
8.In TMJ - Precise localization of the disk is very important in the
diagnosis of TMJ internal derangement and can easily be achieved
with MR imaging. 44, 45,46
and a normal disk position has been depicted in 16%–23% of
symptomatic patients .47,48
149. 9.Investigation of the TMJ to show both the bony and soft tissue
components of the jointincluding the disc position MRI may be
indicated: When diagnosis of internal derangement is in doubt.
10.As a preoperative assessment before disc surgery implant
assessment.
11.Cyst and tumors of orofacial region -MR imaging of lesions such
as tumors and cysts, fat suppression T2-weighted and enhanced T1-
weighted images are commonly applied.
The tumor shows mild to moderate hyperintensity signals on fat
suppression T2-weighted images, and the cyst shows hyperintensity
on T2-weighted images. Therefore, one can differentiate between
these two diseases. Recently, it was shown that the findings and
parameters of dynamic contrast-enhanced MR images could be used
as diagnostic tools for tumors in the oral and maxillofacial regions
150. The time constant that describes the rate at which net magnetization
returns to equilibrium by this transfer of energy is called the Tl
relaxation time or spin-lattice relaxation time.
The time constant that describes the rate of loss of transverse
magnetization is called the T2 relaxation time or transverse(s pin-
spin) relaxation time.
In general, T1-weighted images are used to show normal anatomy,
whileT2-weighted images are useful for detection of infection,
haemorrhage and tumours.
151. Due to the different information available from T1- and T2-
weighted images in neoplastic tissue, both sequences should be
obtained when investigating pathology
A tissue with a long T2 produces a high-intensity signal and is
bright in the image. One with a short T2 produces a low-intensity
signal and is dark in the image.
To reduce the effect of fatty tissue such as cancellous bone making
interpretation difficult, the technique of fat saturation may be used.
This technique utilises the small difference (3.5 parts per million
(p.p.m.)) in resonant frequency between protons in water
molecules, and those in lipid molecules, to suppress the signal
from fat.
152. THE COMPONENTS OF THE MRI SYSTEM
INCLUDE
The magnet which is a key element (usually with magnetic
field strength of 0.3, 0.5, 1.0, 1.5 & 3 Tesla)
of the MRI system. It is integrated to the system which
also includes Radiofrequency & the Gradient system.
1. Power supplies
2. Computer system
3. Documentation system cooling system
4. Monitoring camera
153.
154.
155.
156. Camera can be placed to monitor a patient inside the
Magnet Bore. Magnet room has to be shielded by a
Faraday’s cage to prevent interferences between
outside frequency waves & those used with the MR
equipment
166. Body of corpus callosum Thalamus
Splenium of
Corpus
callosumGenu of corpus
callosum
Pons
Superior
Colliculus
Inferior
Colliculus
NasalNasal Septuml
Medulla
167. Cingulate Gyrus
Genu of corpus
callosum
Ethmoid
air cells
Oral cavity
Splenium of
Corpus
callosum
Fourth Ventricle
175. Frontal Lobe
Anterior Limb
Internal Capsule
Lentiform Nucleus
Posterior Limb
Internal Capsule
Splenium of
Corpus
Callosum
Genu of
Corpus Callosum
Head of the
Caudate Nucleus
Thalamus
Lateral Ventricle
219. Lateral pterygoid:
upper head
lower head
Line of action of lateral pterygoids is from
anterior to posterior in horizontal plane.
They PROTRACT or pull the mandible
forward.
INFRATEMPOR-
AL FOSSA
borders:
Lateral: ramus
of mandible
Medial: lateral
pterygoid plate
Roof: greater
wing of
sphenoid, adj.
maxilla &
palatine bones
Inferior:
continuous
with deep
cervical fascia
220. Mental foramen for
V3 sensory branch
Coronoid
process of
mandible
Mandibular
notch
neck
condyle
Mandibular fossa
Articular
emminence
221. lingula
Mandibular
foramen for
inferior alveolar
branch of V3,
vv.
Injections to
numb the lower
teeth also
numb chin and
lower lip but
not uppers
Mylohyoid
line for m.
attachment
Mylohyoid
groove for V3
branch to
mylohyoid
222. Tensor veli
palatini Medial pterygoid
Lateral
pterygoid upper
head – to
articular disc
Lateral pterygoid
lower head to neck of
mandibular condyle
Sphenoid/Muscular origins
“Pterygoid” means “talon-like”
223. MRI series 1 of 6 – coronal section, anterior to posterior
Temporalis m.
Masseter m.
224. MRI series 2 of 6
Lateral
pterygoid
Upper head:
to
articular
disc
Lower head:
to neck of
mandibula
r condyle
230. Sialography can be defined as the radiographic
demonstration of the major salivary glands by introducing
a radiopaque contrast medium into their ductal system.
231. The procedure is divided into three phases.
The preoperative phase
The filling phase
The emptying phase.
232. This involves taking preoperative (scout) radiographs,if not
already taken, before the introduction of thecontrast medium,
for the following reasons:
To note the position and/or presence of any radiopaque
obstruction
To assess the position of shadows cast by normal
anatomical structures that may overlie the gland, such as the
hyoid bone
To assess the exposure factors.
233. Having obtained the scout films, the relevant duct orifice
needs to be found, probed and dilated and
thencannulated, The contrast medium can then be
introduced.
Three main techniques are available for
introducing the contrast medium, as described later.
When this is complete, the filling phase radiographs are
taken, ideally at least two different views at right
angles to one another.
234. The cannula is removed and the patient allowed to rinse
out.
The use of lemon juice at this stage to aid excretion of
the contrast medium is often advocated but is seldom
necessary.
After 1 and 5 minutes, the emptying phase radiographs
are taken, usually oblique laterals. These films can be
used as a crude assessment of function
235. The main clinical indications for sialography include:
To determine the presence and/or position of calculi or
other blockages, whatever their radiodensity
To assess the extent of ductal and glandular destruction
secondary to an obstruction
To determine the extent of glandular breakdown and as a
crude assessment of function in cases of dry mouth
To determine the location, size, nature and origin of a
swelling or mass. This indication is somewhat
controversial as other investigations often prove more
useful.
236. Allergy to compounds containing iodine
Periods of acute infection/inflammation, when there is
discharge of pus from the duct opening ( acute
sialadenitis.)
When clinical examination or routine radiographs have
shown a calculus close to the duct opening, as injection of
the contrast medium may push the calculus back down the
main duct where it may be inaccessible.
If thyroid function tests are to be performed and if iodine
interferes with them,they should be completed first.
238. Essential requirements include:
A systematic approach
A detailed knowledge of the radiographic appearances
of normal salivary glands
A detailed knowledge of the pathological conditions
affecting the salivary glands.
239.
240. These include:
The main duct is of even diameter (1-2 mm wide) and
should be filled completely and uniformly.
The duct structure within the gland branches regularly
and tapers gradually towards the periphery of the gland,
the so-called tree in winter appearance
241. These include:
The main duct is of even diameter (3-4 mm wide)
and should be filled completely and uniformly.
This gland is smaller than the parotid, but the overall
appearance is similar with the branching duct
structure tapering gradually towards the periphery —
the so-called bush in winter appearance
242. Main pathological changes can be divided into
Ductal changes associated with:
Calculi
Sialodochitis (ductal inflammation/infection)
Glandular changes associated with:
Sialadenitis (glandular inflammation/infection)
Sjogren's syndrome
Intrinsic tumours.
243. Sialographic appearances of calculi include:
Filling defect(s) in the main duct
Ductal dilatation proximal to the calculus
The emptying film usually shows contrast medium
retained behind the stone
244. Sialographic appearances of sialodochitis include:
Segmented sacculation or dilatation and stricture of
the main duct, the so-called
sausage link appearance
Associated calculi or ductal stenosis.
245.
246. • Dots or blobs of contrast medium within the
gland, an appearance known as sialectasis
247. Widespread dots or blobs of contrast medium within
the gland, an appearance known as punctate sialectasis
or snowstorm
Four stages of sialectasis have been
described: punctate, globular, cavitary, and destructive.
Som et al (1981) reported that the punctate and
globular forms may actually represent extravasation of
contrast media through damaged ducts
248. An area of underfilling within the gland, owing to
ductal compression by the tumour
Ductal displacement — the ducts adjacent to the
tumour are usually stretched around it, an appearance
known as ball in hand
249. Sialograph of a right parotid showing a large area of underfilling
in the lower lobe (arrowed) caused by an intrinsic tumourA Rotated
AP view showing the lateral bowing and displacement of the ducts
(arrowed) around the tumour.
B Rotated AP view of a normal parotid gland for comparison
250. Sialograph of a right parotid gland showing a large area of underfilling in the
lower lobe
(arrowed) caused by an intrinsic tumour (pleomorphic adenoma).
B Rotated AP view showing extensive ductal displacement, the appearance
described as ball in hand
251. Retention of contrast medium in the displaced ducts during
the emptying phase.
Several sialographic changes are characteristic of
malignant tumors. These are
destruction of ducts,
irregular borders,
encasement of major ducts, and
cystic cavities that fill with contrast media.
252. Conventional sialographic techniques can be supplemented and
expanded into minimally invasive
interventional procedures by using balloon catheters
and small Dormia baskets under fluoroscopic guidance.
The balloon catheter, as the name implies, can be inflated once
positioned within a duct to produce dilatation of ductal
strictures.The Dormia basket may be used to retrieve mobileductal
salivary stones . Both these procedures are now being used
successfully to relieve salivary glandobstruction without the need
for surgery
253. Several variations in technique have been introduced
over the years to improve the capability for
diagnosing various lesions.
xeroradiography(Ferguson et al, 1976),
the use of pneumography with tomography (Granone
and Julian,1968),
secretory sialography (Rubin and Blatt, 1955), and
CT sialography (Mancuso et al,1979).
254. The Meditech (Boston Scientific) Dormia basket — A closed for insertion
down the main duct and beyond the stone; B open ready to draw back over
the stone; C open with the stone inside and
D closed around the stone ready for withdrawal back along the duct,
(ii) Fluoroscopic sialograph showing the open Dormia basket in the left
submandibular duct. The stone has been captured and is inside the basket
(open arrows). Contrast media is evident in the dilated main duct within the
gland (solid arrow)
255. Sialography is currently best for studying the ductal
system. No other test supplies useful information about
ductal architecture and glandular patterns. On the other
hand, sialography has little to offer in the study of mass
lesions. The information obtained is severely restricted if
the mass is small or extrinsic to the gland.
256. Pharmaceuticals that are labeled
with radionuclides
Accumulate in organs of interest
Emit gamma radiation
Detection system sensitive to this
obtain images
257. Neutron rich isotopes can decay by
Negative beta
emission
Proton rich isotopes can decay by 2 modes
Electron capture
Positron emission
• The result of the decay modes is a better balance between the
forces acting on the nucleus.
258. A positron is a particle similar to electron except
that it has a positive electric charge.
p+ n + β + + ѵ + energy.
The behaviour of positron in the
tissue is very similar to β particles with
one important difference – once the
positron has been slowed down by
the atomic collision s , it is annihilated by the
interaction with an electron from a nearby atom.
The combined mass of the proton & electron is
converted into two annihilation photons – each
with energy 511 KeV .
The two photons are emitted at 180° to each
other – this property is exploited by PET.
E.g. Carbon-11 (11C) to Boron-11 (11B)
259. In most isomeric transitions, a nucleus will emit its excess energy
in the form of a gamma photon.
A gamma photon is a small unit of energy that travels with the
speed of light and has no mass; its most significant characteristic
is its energy.
The photon energies useful
for diagnostic procedures
are generally in the range
of 100 keV to 500 keV.
260. An alpha particle consists of two neutrons and two protons.
α particles interact strongly with matter – very short range of
1mm or less.
Within this range α particles strongly collide with atoms –
disrupting their chemistry – extremely damaging to the tissues.
α particles have a potential to deliver a lethal radiation dose to
small metastatic cell clusters, while mostly sparing the
surrounding tissues.
262. Components of a gamma camera
Collimator
Detector/ Scintillator
Photomultiplier
Collimator:
This is a device made of a highly absorbing material such as
lead, which selects gamma rays along a particular direction.
They serve to suppress scatter and select a ray orientation.
The simplest collimators contain parallel holes.
263.
264. Detector / Scintillator :
Made up of sodium iodide crystals.
It produces multi-photon flashes of light when an impinging
gamma ray, X-ray or charged particle interacts with the single
sodium iodide crystal of which it is comprised.
265. The scintillation counter not only detects the presence and
type of particle or radiation, but can also measure their
energy.
The passage of gamma rays through the scintillator material
excites electrons, which can subsequently de-excite, emitting
a photon.
266. This is an extremely sensitive photocell used to convert light
signals of a few hundred photons into a usable current pulse
267.
268.
269. PULSE ARITHMATIC (POSITION LOGIC) :
The light pulse illuminates diffrentially the array of photomultiplier
tubes.
Largest electric pulse – photomultiplier tube close to the
collimator hole ; smaller pulses in adjacent photomultiplier tube.
Microprocessor chip – ‘pulse arithmetic circuit’ – combines the
pulses from all photomultipliers according to certain equations.
This leaves 3 voltage pulses , X Y Z which are proportional to the
horizontal or X , & vertical Y co – ordinates of the light flash in
the crystal & the photon energy of the original gamma ray (Z).
The size or the height of the Z pulse ∞ the gamma ray energy
absorbed (KeV).
270. PHOTOPEAK:
Comprising pulses produced by the complete photoelectric
absorption in the crystal of those gamma ray photons which
have come from within the patient without suffering compton
scattering.
PULSE HEIGHT ANALYZER (PHA):
Z pulses – enter a PHA which is set by the operator to reject
pulses , which are either lower or higher than the preset
values.
It lets through only those pulses which lay within the window of
+_ 10 % of the photopeak energy.
The pulses so selected – ‘Counts’.
The X Y Z pulses are next applied directly to a monitor for
visual interpretation as in older machines or in newer systems
via analogue – to – digital converters into a computer.
This enables dynamic & gated studies to be undertaken as
well as range of image processing.
271. MONITOR:
The X Y Z pulses steer the stream of electron beam in a
monitor tube .
If & only if the Z pulse has passed through the PHA does a
pinpoint of light appears momentarily on the screen.
Thousands of such dots , equally bright make up the image.
272. Pre-examination procedures:
Patient preparation:
A thorough explanation of the test should be provided to the
patient in advance by the technologist or physician (including
time taken for scan, and details of the procedure itself).
Pre-injection:
The nuclear medicine physician should take account of all
information that is available for optimal interpretation of bone
scintigraphy, especially:
Relevant history
Current symptoms, physical findings.
Results of previous radionulide imaging
Results of other imaging studies such as conventional
radiographs, CT, MRI
Relevant laboratory results
273. Radiopharmaceutical administration: The
radiopharmaceutical should be administered by the
intravenous route.
Post injection:
Unless contraindicated, patients should be well-hydrated and
instructed to drink one or more liters of water (4-8 glasses)
between the time of injection and the time of imaging as well
as during the 24 hours after administration.
All patients should be asked to void frequently during the
interval between injection and delayed imaging as well as
immediately prior to the scan.
274. Image acquisition:
Routine images are usually obtained between 2 and 5 hours
after injection.
Later (6-24 hour) delayed images are obtained which may
result in a higher target-to-background ratio and may permit
better evaluation.
Image Processing :
No particular processing procedure is needed for planar
images.
In case of SPECT and PET one should take into account the
different types of gamma camera and software available:
careful choice of imaging processing parameters should be
adopted in order to optimize the imaging quality.
275. Radionuclides Half-life Uses
Technetium-99m 6 hrs Skeleton and heart muscle
imaging, brain, thyroid, lungs
(perfusion and ventilation),
liver, spleen, kidney (structure
and filtration rate), gall bladder,
bone marrow, salivary and
lacrimal glands, heart blood
pool, infection
Xenon-133 5 days Used for pulmonary (lung)
ventilation studies.
Ytterbium-169 32 days Used for cerebrospinal fluid
studies in the brain.
Carbon-11
Nitrogen-13
Oxygen-15
Fluorine-18
They are positron emitters used
in PET for studying brain
physiology and pathology,
cardiology, detection of cancers
and the monitoring of progress
in their treatment.
Iodine-131 8 days Imaging of thyroid
Gallium-67 78 hrs Used for tumour imaging and
localization of inflammatory
lesions (infections).
Indium-111 2.8 days Used for brain studies, infection
and colon transit studies
276. Rubidium-82 65 hrs PET agent in myocardial
perfusion imaging
Thallium-201 73 hrs Used for diagnosis of coronary
artery disease other heart
conditions and for location of
low-grade lymphomas.
Routes of administration:
• Injected into a vein
• Swallowed
• Inhaled as gas.
277. Technetium (99mTc) : The most commonly used isotope for the
following reasons:
Gamma emission : Single 141 KeV gamma emissions which are
ideal for imaging purposes.
Short half - life : A short half life of 6 ½ hours that ensures a
minimal radiation dose.
Readily attached to different substances : It can be readily
attached to a variety of different substances that get concentrated
in different organs . Egs. 99m Tc + MPD ( Methylene
diphosponate ) in bone , 99m Tc + RBC in blood , 99mTc +
sulphur colloid in the liver and spleen.
Ionic form : It can be used on its own in its ionic form
(pertecnetate 99m Tc O+) , since the thyroid and salivary glands
take this up selectively.
Easily produced : as and when required.
278. Gallium (67Ga) : Used in tumor and at the site of
inflammation.
Iodine (20 I) : Used for thyroid examination.
Krypton (81 Kr) : Used in lung examination.
279. Radiopharmaceuticals :
• Substances which tend to localize in the tissue of interest is
tagged with gamma ray emitting radionuclide.
o Pyrophosphate and Methylene Disphosphonate (MDP) - bone
imaging.
o Sodium iodine - thyroid gland
o Xenon and/or krypton gas - pulmonary studies.
o Sulfur colloid - liver, spleen and bone marrow.
280. Detection : For external imaging of a radionuclide deposited
within the body the energy of gamma rays emitted should be
high enough to be detected.
High Energy : Energy should be somewhere within the range of
20 – 400 KeV.
More energetic emission : For organs lying deeper within the
body more energetic emissions are required.
Half – life : The physical half – life should only be few hours and
not much longer than the time necessary to obtain the data.
Easy availability : An ideal radionuclide should be readily
available , at reasonable cost and in a sufficiently high specific
gravity so that the administration of the required dose of the
radioactive substance does not produce a physiological , toxic
or pharmacological response.
281. Planar scintigraphy
SPECT
PET
Hybrid scanning techniques
Planar Scintigraphy :
• Planar imaging produces a 2D
image with no depth information
and structures at different depths
are superimposed.
•The result is loss of contrast in
the plane of interest.
From H. Graber, Lecture Note for
BMI1, F05
282. SPECT was developed as an enhancement of planar imaging.
It detects the emitted gamma photons (one at a time) in
multiple directions.
Uses one or more rotating cameras to obtain projection data
from multiple angles.
SPECT displays traces of radioactivity in only the selected
plane.
◦ Axial, coronal and sagittal.
Computer manipulation of the detector radiation is also
possible.
283. SPECT is a method of acquiring tomographic slices through a
patient .
Most gamma camera have SPECT capability.
In this technique either a single or multiple ( single , dual or triple
headed system ) gamma camera is rotated 360° about the
patient
Image acquisition takes about 30 -45 minutes.
The acquired data are processed by filtered back projection &
most recently iterative reconstruction algorithms to form a
number of contiguous axial slices similar to CT by X – ray.
The sensitivity of an SPECT system is ∞ to the number of
detectors.
Parallel hole , converging hole , slit / pin hole or focussed
collimators can be used to optimize spatial resolution , detection
efficiency & field of view size.
A gamma camera with a parallel hole collimator rotates slowly in
a circular orbit around a patient lying on a narrow cantilever
couch .
284. After every 6° camera halts for 20 – 30 seconds & acquires the
view of the patient .
60 views are taken from different directions .
These data can then be used to construct multiplanar images
of the study area.
SPECT studies can be presented either as a series of slices or
3 D displays.
By changing contrast & localization , SPECT imaging increases
sensitivity & specificity of disease detection.
Tomography enhances contrast & removes superimposed
activity.
SPECT images have been fused recently with CT images to
improve identifying of the location of the radionuclide.
287. SPECT bone scintigrams show increased uptake in the right mandible
(arrows) in the region of a sequestrum.
288. Positron emission tomography (PET) is a nuclear medicine
imaging technique which produces a three-dimensional image
or picture of functional processes in the body.
The system detects pairs of gamma rays emitted indirectly by a
positron-emitting radionuclide (tracer).
289. Positron Emission
In this, a proton in the nucleus is transformed into a neutron &
a positron.
Positron emission is favored in low atomic number elements.
290. The positron (e+) has the same mass as the electron but has a
positive charge of exactly the same magnitude as the negative
charge of an electron.
Positron Annihilation:
The positron has short life in solids & liquids.
Interactions with atomic
electrons
Rapidly loses kinetic energy
Reaches the thermal energy of
the electron
Combines with the electron
Undergoes annihilation
291. Their mass converts into energy in the form of gamma rays.
The energy released in annihilation is 1022 KeV.
To simultaneously conserve both momentum & energy,
annihilation produces 2 gamma rays with 511 keV of energy that
are emitted 180 degree to each other.
The detection of the two 511 keV gamma rays forms the
basis for imaging with PET.
292. Coincidence detection- simultaneous detection of the 2 gamma
rays on opposite sides of the body.(bismuth germanates )
If both gamma rays can subsequently be detected, the line
along which annihilation must have occurred can be defined.
293. By having a ring of detectors surrounding the patient, it is
possible to build a map of the distribution of the positron
emitting isotope in the body.
PET employs electronic collimation.
3 types of coincidence detection .
Sensitivity in PET
- Measures capability of system to detect ‘trues’ & reject
‘randoms’
294. Radionuclides used in PET scanning are typically isotopes with
short half lives:
◦ Carbon-11 (~20 min),
◦ Nitrogen-13 (~10 min),
◦ Oxygen-15 (~2 min), and
◦ Fluorine-18 (~110 min).
These radionuclides are incorporated either into compounds
normally used by the body such as glucose (or glucose
analogues), water or ammonia, or into molecules that bind to
receptors or other sites of drug action.
295. ADVANTAGES :
Sensitive method for imaging.
Can investigate disease at a molecular level even in the
absence of anatomical abnormalities.
It is possible to quantify the amount of tracer within a region of
interest in the patients body ; possible to monitor the amount
of tracer in mg/100ml of tissues.
296. DISADVANTAGES:
High cost of PET setup.
Requires more space , electricity & air conditioning than
conventional nuclear medicine.
Requires an on – site cyclotron due to the short half life of the
positron emitting .
CT data better identifies the invasion of the oral carcinomas
into the jaws than FDG PET.
Major image quality degradation is due to the metallic dental
implants therefore all removable artificial dentures & metal
parts to be removed during scanning.
PET & PET / CT like any other imaging technique is not able
to identify micrometastasis ie; metastasis upto 2mm.
297. INDICATIONS:
Evaluation of the primary tumor – In HNSCC highly sensitive &
highly specific for detection of primary tumor & its extension to
adjacent anatomical structures.
Staging of the primary tumor ie; identification , assessment of
extension & functional characterization.
Lymph Node assessment – FDG PET can detect metastasis in
LN’s which are not enlarged.( smaller LN’s can contain
malignant cells & upto 40% of all LN metastasis are found in
LN’s smaller than 1 cm.)
Detection of metastasis & a second synchronus cancer.
Assessment of treatment response & early detection of recurrent
disease.
Used in knowing the metabolic activity of cancer during
treatment in a non – invasive way.
Used in the management of patients with epilepsy ,
cardiovascular disease & cerebrovascular disease.
299. PET scans are increasingly read alongside CT or magnetic
resonance imaging (MRI) scans, the combination ("co-
registration") giving both anatomic and metabolic information.
Clinically it has been used in the management of patients with
epilepsy, cerebrovascular disease and cardiovascular
disease, dementia and malignant tumors including
identification of recurrent head and neck cancers.
300.
301.
302. A bone scan or bone scintigraphy is a nuclear scanning test to
find certain abnormalities in bone which are triggering the
bone's attempts to heal.
Bone scintigraphy is an highly sensitive method for
demonstrating disease in bone, often providing earlier
diagnosis or demonstrating more lesions than are found by
conventional radiological methods.
Technique:
The patient is injected with a small amount
of radioactive material such as 600 MBq
of technetium-99m-MDP .
303. Methylene Diphosphonate (MDP) has affinity for calcium rich
hydroxyapatite crystals of bone.
The technetium (Tc) 99m-MDP undergoes ‘chemisorption’ and
gets bound to bone matrix.
In exposed bone, bone
remodelling (i.e. altered
metabolism).
The hydroxyapatite crystal is
most accessible to MDP
Increased radioactivity
304. Other determinants which lead to increased uptake are:
Increased blood flow
Increased capillary permeability
Loss of sympathetic tone resulting in capillary dilation
Any process that results in focally increased osteogenic activity
is visualized as an area of increased radioactivity called a 'hot
spot’.
305. Reduced radioactivity can result from:
Replacement of bone by destructive lesion (lytic lesion) - primary
or metastatic.
Disruption of normal blood flow consequent to radiation.
Reduced radioactivity is visualized as 'cold spot' or photopenic
bone lesion.
306. Much of the radiation is eliminated through urine -
radioactivity inside the patient is only for a short time.
Radiation absorbed dose is - 0.5 rad to bone and 0.1 rad to
whole body per 20 mCi.
Critical organ - the bladder; the radiation dose varies with
patient hydration and urine voiding frequency, it may be
around 0.13 rad/mCi.
307. The oncological indications are:
Primary tumors (e.g. Ewing’s sarcoma, osteosarcoma).
◦ Staging, evaluation of response to therapy and follow-up of
primary bone tumors
Secondary tumours (metastases)
Non neoplastic diseases such as:
Osteomyelitis
Avascular necrosis
Metabolic disorders (Paget, osteoporosis)
Assessment of continued growth in condylar hyperplasia
Arthropathies
Fibrous Dysplasia
Stress fractures, Shin splints, bone grafts
Loose or infected joint prosthesis
Low back pain
Reflex sympathetic syndrome
308. Symmetry of right and left sides of the skeleton and
homogeneity of tracer uptake within bone structures - normal
features.
Both increase and decrease of tracer uptake have to be
assessed; abnormalities can be either focal or diffuse.
Increased tracer activity - indicates increased osteoblastic
activity.
Compared to a previous study:
Increase in intensity of tracer uptake and in the
number of abnormalities
Progression of disease
309. Focal decrease in radioactivity:
◦ Benign conditions
◦ Attenuation
◦ Artefact
◦ Absence of bone e.g. surgical resection.
When compared to a previous study:
Decrease in intensity of tracer uptake and in number of
abnormalities
Improvement or may be secondary to focal therapy
(e.g. radiation therapy).
310.
311. Bone scintigram shows uptake in the right mandible Bone scintigram obtained approximately 17 months later
shows progression of the uptake
312.
313. It is traditionally used to evaluate salivary function, especially
in patients with dry mouth symptoms.
Technique:
An IV injection of a radionuclide.
Radionuclides used:
99m Technitium pertechnetate (99mTcO4) - 200 Mbq
Most commonly used
Gallium-67
Selenium-75
Iodine-131
314. It consists of dynamic or flow study followed by
static study.
It takes 30-60 minutes to perform.
Multiple images are taken during first 30-120
seconds that show the flow of blood.
◦ First into arterial & venous system
◦ Then into organ system
This will yield information about vascularity of the
area.
During next 30-45 minutes, sequential static
images are taken which demonstrate the anatomy
of major salivary gland & their ability to produce &
secrete saliva.
Stimulation of flow of saliva: finally patient is given
sialogogue such as lemon juice or 1% citric acid to
stimulate flow of saliva. Final series of static image
are taken to demonstrate the stimulated secretor
capabilities of gland.
315. Acute inflammation- diffusely increase tracer uptake & hot &
dense salivary gland image.
Sjogren’s syndrome- Decrease uptake in seen in decrease
function of salivary gland.
Chronic sialadenitis- In this, there are various degrees of
tissue damage & fibrosis, & findings depends upon the amount
of functional tissue remaining.
Atrophy of gland- There is usually decreased uptake (cold
spot) because of atrophic fibrosis of gland.
Salivary gland tumor- Radionuclide is taken by duct cell.
Therefore Warthins tumor that is characterized by proliferation
of striated duct cell & lymphocyte shows very high uptake of
99mTc.
Uptake of warthins tumor is 3-5 times more than normal
parotid tumor.
Benign tumors – decreased uptake/ clear cold lesion.
Malignant tumor – decreased uptake/ cold lesion.
316. Difference:
Benign tumors - sharp or regular contours
Malignant tumor - fuzzy or irregular.
Normal salivary glands show up as areas of increased
activity darkening on the digital image.
317.
318. Regions of interest on dynamic
scintigraphy. RP, right parotid; LP, left
parotid; RSm, right submandibular
gland; LSm, left submandibular gland;
B, background
319. Bilateral intraglandular lesions appears as
cold defects on scintigraphy (arrows).
(b) Dynamic images (1 min per frame)
following intravenous injection
of 99Tcm pertechnetate showed normal
uptake and response to secretion
stimulation in the upper poles of the
parotid glands (arrows). Neither
submandibular gland showed significant
uptake (arrowheads). Note physiological
uptake in thyroid gland
320. Dry mouth as a result of salivary gland diseases such as
Sjogren's syndrome.
To assess salivary gland function.
The lesions that are suspected of highly concentrating 99mTc.
E.g. Warthin's tumors & oncocytoma.
Developmental anomalies.
Obstructive disorders e.g. Sialolithiasis with or without
parenchymal damage.
Traumatic lesions and fistulae.
The need of post surgical information.
321. Provides an indication of salivary gland function.
The excretion fraction of both parotid & submandibular
glands can be quantified simultaneously.
Allows bilateral comparison & images of all four major
salivary glands at the same time.
Easy to perform.
Reproducible.
Well-tolerated by the patient.
It is of particular value in patients for whom cannulization is a
problem.
Computer analysis of results is possible.
Can be performed in cases of acute infection.
Co - localization of PET with CT or MRI scans.
322. Poor image resolution- Provides no indication of salivary
gland anatomy or ductal architecture.
Relatively high radiation dose to the whole body.
The final images are not disease - specific.
Although masses that excessively accumulate the
radionuclide can be identified, they are not as accurately
localized as on CT or MR image studies.
Masses that do not accumulate excessive radionuclide are
poorly seen, if they are even identified.
As a result, radionuclide sialograms are not routinely used to
study parotid & submandibular gland masses.
323. Analyse kidney function
Visualize cardiac blood low & function (Myocardial perfusion
scan)
Scan lungs for respiratory & blood flow problems.
Identify inflammation in the gall bladder.
Identify bleeding into the bowel.
Measure thyroid function to detect an overactive or
underactive thyroid.
Investigate abnormalities in the brain, such as seizures,
memory loss & abnormalities in blood flow.
Localize the lymph node before surgery in patients with
breast cancer or melanoma.
324. Metastasis : The assessment of the sites and extent of the
metastasis in tumor staging.
Salivary gland function : Assessment of salivary gland function
, particularly in Sjogren’s syndrome.
Graft assessment : Useful in bone graft assessment.
Growth pattern : Used in assessing continued growth in
condylar hyperplasia.
Thyroid examination : In the investigation of thyroid.
Brain : Brain scans and investigations of BBB.
325. Functional details of the target tissues are obtained.
Large anatomical areas can be imaged efficiently from a wide
variety of directions.
Examinations of total body skeleton can be done, as can
examinations of selected organs such as spleen, thyroid and
salivary glands.
It can display blood flow.
Computer analysis and enhancement of results are available.
326. Poor image resolution – often only minimal information is
obtained on target tissue anatomy.
Images are not usually disease specific i.e. they lack
diagnostic specificity.
Difficult to localize exact anatomical site of source of
emissions.
Dose received by the patient is high when compared to the
conventional radiography.
Investigation time might be prolonged.
Facilities are not widely available.
327. Nuclear medicine techniques are known for their sensitivity to
detect any change in function induced by a disease but not for
their specificity in determining the nature of the disease
process.
To overcome this problem – use of receptor binding technique
and antigen – antibody interaction.
The technique of using radiolabelled antibodies to image and
characterize the nature of the disease process in vivo – RIS.
Monoclonal antibodies (MAb’s) directed against tumor –
specific and tumor – associated antigens can be used for
selective tumor targetting.
MAb’s can be produced to bind to specific targets and can be
labelled with radionuclides that emit gamma rays.
Thus specific tumors can be visualized using gamma cameras.
328. “The best way to show that a stick is crooked is
not to argue about it or to spend time
denouncing it, but to lay a straight stick along
side it.” D L Moody