Power point presentation.

1. Radiology in Head and Neck
Presenter : Kanato T

2. INTRODUCTION
 Radiology is a continually evolving
medical specialty
 Since the discovery of x-rays.
 Resulting in the numerous imaging
modalities
 One should bear in mind that most
imaging techniques utilizing ionizing
radiation, including plain films,
computed tomography (CT) and nuclear
medicine
 Carry with them a lifetime risk of
developing cancer.

3. Radiological Investigations
Useful To The ENT Surgeon
 X-rays
 Ultrasound
 CT
 MRI
 PET Scans
 Barium Swallow
 Angiography
 Dacryocystography
 Sialography
 Orthopantomogram

4. X-ray photons
 What Is an X-Ray?
 An x-ray is a discrete bundle of
electromagnetic energy called a photon.
 similar to other forms of electromagnetic
energy such as light, infrared, ultraviolet,
radio waves, or gamma rays.
 Having no electrical charge, x-rays are
more penetrating than other types of
ionizing radiation (such as alpha or beta
particles) and are therefore useful for
imaging the human body.

5. Image Appearance
 Four basic densities:
1. Air is black or very dark.
2. fat is generally gray and darker than muscle
or blood
3. Bone and calcium appear almost white.
4. Items that contain metal (such as prosthetic
hips) and contrast agents also appear
white.
 The contrast agents are barium for
gastrointestinal studies and iodine for most
intravenously administered agents

6. Image clarity
Depends on kVp, mA, Time
(sec)
 If radiograph is too light
Increase kVp (increase the
penetrating power or energy
of the x-ray photons)
Increase mA (produce more
photons)
Or to increase time (produce
more x-ray photons)
 If a radiograph is too dark
(overexposed)
decrease kVp, mA, or time

7. Conventional Radiology
 Temporal Bone: Law’s View, Schullars view,
Stenver’s View, Transorbital View,
Submentovertical View.
 Nose and Paranasal Sinuses: Water’s View,
Caldwell View, Lateral View, Right and Left
Oblique Views, Lateral and Occlusal Views of
Nasal Bone.
 Neck: Lateral View and Anteroposterior
Views of Neck, Soft Tissue Lateral View
Nasopharynx, Submandibular Salivary Gland

8. Law’s View (Lateral view of
Mastoid)
 In 1913, Dr Frederik Law described lateral
view of mastoid bone.
 Sagittal plane of the skull is parallel to the flim
 X ray beam is projected 15 degree
cephalocaudal.

9. Structures seen:
 External auditory
canal (EAC)
(superimposed on
internal auditory
canal (IAC)),
 mastoid air cells,
 tegmen,
 lateral sinus plate
 temporomandibula
r joint.

10. Schullar’s view
 1906, Dr Arthur Schuller, an Austrian
neuroradiologist, described an oblique view
of mastoid bone.
 X-ray beam is projected 30° cephalocaudal
and prevents superimposition of two sides
of mastoid bones.
 Structures seen: EAC superimposed on
IAC, mastoid air cells, tegmen, lateral sinus
plate, condyle of mandible, sinodural angle
and atticoantral region (key areas for
cholesteatoma and its erosion).

12. SCHULLER S VIEW

13. Clinical applications:
 Extent of pneumatization, sclerotic
mastoid, destruction of intercellular
septa (mastoiditis),
 location of sinus plate (position of
sigmoid sinus) and
 tegmen (roof of middle ear and floor of
middle cranial fossa),
 cholesteatoma and
 longitudinal fracture of petrous
pyramid.

14. Stenver’s view:
 In 1917, Dr H. W. Stenver described Stenvers
view of temporal bone
 Long axis of the petrous bone lies parallel to
the film.

15. Structures seen
 Entire petrous pyramid,
 arcuate eminence,
 internal auditory meatus,
 labyrinth with its vestibule,
 Cochlea
 and mastoid antrum

16. Stenver’s view:

17. Towne’s view:
 In 1926, Dr E. B. Town of England described
Towns view.
 This is an anteroposterior view of skull with
30° tilt from above and in front.
 It shows both petrous pyramids, which can be
compared.

19. Towne’s view
 Structures seen: Both side temporal
bones,
 arcuate eminence and superior
semicircular canal, mastoid antrum, IAC,
tympanic cavity, cochlea and EAC
 Clinical applications: Acoustic neuroma
and apical petrositis.

20. Transorbital view:
 This is an anteroposterior view of skull.
 Orbitomeatal line is at right angles to the
film.
 X-ray beam passes through the orbit.
 Structures seen: IAC, cochlea, labyrinth
and both
 petrous pyramids projected through the
orbits.
 Clinical applications: Acoustic neuroma
and petrous pyramid.

21. TRANSEORBITAL PROJECTION:

22. Submentovertical view:
 Vertex remains near the film and X-ray
beam is projected from the submental
area.

23. Structures seen:
 External auditory
cannal,
 Middle air cleft. ie.
mastoid cells, middle
ear & eustachian tube
 Internal auditory
canal
 sphenoid sinuses

24. nose and paranasal Sinuses
Water’s view (occipitomental view):
In 1914, Dr C. A. Waters and C. W. Waldron,
two British radiologists, introduced the Waters
view.
 Nose and chin touch the film and X-ray
beam is projected from occipital side.
 Open mouth view shows sphenoid sinus.
Petrous bones are projected below the
maxillary sinuses.
 Fractures of right and left nasal bones and
their lateral displacement can be seen.

26. Structures seen
 Maxillary (seen
best)
 Frontal and
sphenoid sinuses
 zygoma,
zygomatic arch
 Nasal bones,
frontal process of
maxilla, superior
orbital fissure
 and infratemporal
fossa.

27. Caldwell view (occipitofrontal
view):
 Eugene W. Caldwell, In 1903, described a
view of the paranasal sinuses that still bears
his name, “the Caldwell view”
 Nose and forehead touch the film and X-ray
beam is projected 15–20° caudally.
 Frontal and ethmoidal sinuses are seen well
in this view.

28. Structures seen
 Frontal, ethmoid and
maxillary sinuses,
 Frontal process of
zygoma, zygomatic
process of frontal
bone
 superior margins of
orbits, lamina
papyracea,
 superior orbital
fissures.

29. Lateral view
 Lateral side of the skull lies against
the flim and X ray beam is projected
perpendicular from other side.

30. Structures seen :
 Anterior and posterior extents of
sphenoid, frontal and maxillary
sinuses, sella turcica,
 Ethmoid sinuses, alveolar process,
condyle and neck of mandible.

31. Common radiologic abnormalities
 Air-fluid levels suggest an acute
process
 Opacification = secretions, polyps, etc.
 Thickened mucosa : Suggests chronic
inflammation

32. Lateral views of nasal bones:
 To see fracture line, depression or elevation of
the fractures segment.
 Lower part of nasal bones, which is thin,
fracture more frequently.
 Groove for ethmoidal nerve and vessels may
look like fracture line

33. Occlusal view of nasal bone:
 Film is held between
the teeth and X-ray
beam is projected
perpendicular to the
film.
 It shows fracture line
and lateral
displacement of the
nasal pyramid clearly.

34. Neck, Larynx and Pharynx
Lateral view of neck
 Structure seen: Outline of
base of tongue, vallecula,
 hyoid bone, epiglottis and
aryepiglottic folds,
arytenoids,
 false and true cords with
ventricle in between
them,
 thyroid and cricoid
cartilages, subglottic
space
 and trachea, prevertebral
soft tissues, cervical
spines
 and pretracheal soft
tissues and thyroid.

35. Clinical applications:
 Radio-opaque foreign bodies of larynx, pharynx and
upper esophagus
 Acute epiglottitis
 Retropharyngeal abscess:
 Position of tracheostomy tube and laryngeal stent
 Laryngeal stenosis
 Fractures of larynx and hyoid bone and their
displacement
 Compression of trachea by thyroid or
retropharyngeal masses
 Caries of cervical spine associated with
retropharyngeal abscess
 Osteophytes in cervical vertebrae and injuries of
spine.

36. Chronic Retropharyngeal abscess
 Secondary to TB
spine(Pott’s spine)
 Erosion of cervical
vertebra
 Treatment with
ATT

37. FB Cricopharynx with Acute
retropharyngeal abscess

38. Acute epiglottitis(Thumb sign)

39. Anteroposterior view of neck:
 It helps in differentiating between a
foreign body of larynx and esophagus
(lateral view is also needed).
 It shows compression or displacement
of trachea by lateral neck masses
such as thyroid swellings.

40.  Round radio
opaque object
(Coin) in
Esophagus
 Because the
esophagus is an
AP compressed
tubular structure.

41. Croup (acute laryngotracheobronchitis)
Steeple Sign

42. Soft tissue lateral view nasopharynx:
 For soft tissue masses in the nasopharynx,
soft palate, roof and posterior wall of
nasopharynx.
 Clinical applications:
 Adenoids
 Angiofibroma
 Antrochoanal polyp
 Foreign body nose and tumor.
 Choanal atresia

43. Enlarged Adenoids

44. Submandibular salivary gland:
 Radio-opaque calculus can be seen.

45. Barium Swallow
 procedure used to examine upper
gastrointestinal tract,which include the
pharynx, esophagus, cardia of stomach.
 The contrast used is barium sulfate.
 TYPES OF CONTRAST STUDY
(i) SINGLE CONTRAST STUDY
(ii) DOUBLE CONTRAST STUDY

46. CONTRAINDICATION
 Suspected esophageal perforation.
 Tracheo-esophageal fistula
 If strong clincal suspicion of aspiration
or TEF,then omnipaque swallow
(iohexol) advised.
XRAY VIEW
 SOFT TISSUE NECK,CHEST – AP &
LAT

47. NORMAL-AP /LAT VIEW - SCOUT

48. AP/LAT VIEW WITH BARIUM

49.  EFT: Lateral view: Epiglottis (red arrow). Post cricoid
impression (yellow arrows).
 Cricopharyngeous impression (white arrow).RIGHT:
AP-view: Small lateral pharyngeal pouches (arrows)

50. CA ESOPHAGUS
 The stenotic segment is long giving a “rat-
tail” appearance
Barium swallow shows mild dilatation of the
esophagus with irregular stenotic lesion in
the lower end of the esophagus “moth
eaten appearance

51. ACHALASIA CARDIA
Bird beak appearance

52. Sialography
 Radiologic examination of the salivary
glands
 The submandibular and parotid glands
are investigated by this method
 The sublingual gland is usually not
evaluated this way because of
difficulty in cannulation

53. Procedure
 Obtain preliminary radiographs
Any condition that is visibe w/o contrast
Optimum technique obtained
 2-3 min before procedure give lemon
 Contrast media (iohexol) injected into
main duct
 After procedure suck on lemon to clear
contrast
 10 min after procedure take radiograph

54. Parotid Radiographs Set-Up

57. ORTHOPANTOMOGRAPHY
(tomography of the mandible)
 A pantomograph is a
panoramic radiograph
machine.
 It permits
visualization of entire
maxillary and
mandibular dentition,
 alveolar arches and
contiguous structures
on a single extraoral
film

58. ULTRASOUND
 Ultrasound is sound within a frequency above
the upper limit of normal hearing.
 Ultrasound images are formed from reflected
sound waves.
 Sound waves are generated in short bursts by
the transducer (or probe)
 and the sound energy that is reflected back is
collected at the point of origin (the transducer)

59. Transducer(probe)
 Piezoelectric material is used to
produce sound wave
 Usually lead zirconate titanate
 The higher the frequency of the probe
the lesser the depth of penetration but
gives better spatial resolution.
 In neck most of the structures of interest
are superficial and required a higher
frequency probe of greater than 7.5
MHz

60. Advantages
 no known harmful effects and no
contraindications.
 High-resolution ultrasound is quick and
accurate;
 Further, it is relatively inexpensive
compared to CT or MRI.
 In addition to using echoes to generate
images, we can analyze the returning
echo frequencies. This Doppler analysis
allows identification of moving blood as
well as its direction and magnitude

61. Ultrasound appearance of
common abnormalities.
Lymph Nodes
 Normal lymphnode may be visualized by usg
in healthy subject, they are often not seen
due to their small size and similar echo-
texture with surrounding structure.
 When apparent, lymph nodes are reactive,
inflammatory or neoplastic.
 Retropharyngeal lymph nodes cannot be
seen with ultrasound.

62.  Reactive lymph node.
(a) An oval-shaped,
low-reflective lymph
node with an
echogenic hilum
(arrow)
 (b) Florid colour
Doppler flow to the
central hilum
consistent with a
benign reactive
lymph node

63.  Squamous cell
carcinoma lymph
node metastasis.
 An enlarged low
reflective mass with
an irregular border
(long arrow)
 carotid artery (short
arrow)

64. Thyroid
 For ultrasound imaging thyroid disorder may be
considered into two groups
 Nodular
 Diffuse
 Major role of usg in the assessment of disease
1. Detection of focal masses
2. Differentiation of multinodular goiter/hyperplasia
from other nodular disease
3. To document the extent of a known thyroid
malignancy;
4. Follow up to look for residual, recurrent or
metastatic carcinoma;
5. Guidance for FNAC or fine needle aspiration for
biopsy.

65. Salivary gland disease
 Both the parotid and submandibular glands
are superficial and well sited for ultrasound
examination
 Ultrasound accurately differentiates salivary
gland tumors from other lesions outside gland
 Calculi larger than 2mm are detected by usg
 And useful in defining location of calculi in
relation to the gland parenchyma
 It detects the presence and extends of any
abscess formation.

66.  Doppler ultrasound measures blood
flow of vessels.
 In Color Doppler flowing blood
appears either red or blue,
 which depends upon the blood
direction, towards or away from the
transducer.
 „Power Doppler: It can demonstrate
tissue perfusion.

67. Applications of Ultrasound
 Differentiating cystic from solid masses
 „Metastatic lymph nodes
 „Tumor invasion of carotid vessels and internal jugular
vein.
 „Tumors of parotid and submandibular salivary glands
 „Salivary duct stones even less than 2 mm
 „Detection and drainage of salivary gland abscess
under US guidance
 „Masses of thyroid and parathyroid glands and US
guided fine needle biopsy
 „Neck lymphoma.

68. Computed tomography
 In 1972 Godfrey Hounsfield of Great
Britain invent CT.
 Computed tomography (CT) is
accomplished by passing a rotating fan
beam of x-rays through the patient and
measuring the transmission at thousands
of points.
 The data are handled by a computer that
calculates exactly what the x-ray
absorption was at any given spot in the
patient.
 Compared with plain x-rays, CT uses
about 10 to 100 times more radiation

70. Computed tomography imaging
 Imaging can be obtained in several
planes.
 In most cases the axial (transaxial)
plane, usually parallel to the
orbitomeatal or infraorbitomeatal plane,
is used with the patient lying Supine
 In addition, direct coronal imaging and
even direct sagittal imaging can be
performed.
 In fact images can be reformatted in any
plane or any angle

71. Different views of CT pns
 Coronal image
Axial image
Sagittal image

72. Computed tomography
 Conventional CT scanners have traditionally
operated in a step-and-shoot mode, defined
by data acquisition and patient positioning
phases
 Helical CT is characterized by continuous
patient transport through the gantry while a
series of x-ray tube rotations simultaneously
acquires volumetric data.
 The evolution of multidetector CT scanners
(MDCTs) has resulted from the combination of
helical scanning with multislice data
acquisition.

73. Computed tomography
 In general, the basic four densities on
CT images are the same as those in
plain x-rays:
 air is black,
 fat is dark gray,
 soft tissue is light gray,
 bone or calcium and contrast agents
are white

74. CT image display
 Hounsfield unit: value of CT number
 Defined by the relationship between the
linear attenuation value of the material
being scanned and that of water.
 Gas = -1000 HU
 Water = 0 (zero) HU
 Bone = +1000 HU
 Fat = - 80 to -100 HU

75. CT image display
 The window level is simply the midpoint of the
densities chosen for display
 For imaging of the soft tissues of the head and
neck, a window level of approximately 40 to 70
HU is usually chosen, at a midpoint
approximately equal to the density of muscle
 For imaging bony structures such as paranasal
sinuses and temporal bone, window levels from
0 to +400 HU and a very wide window width of
2000 to 4000 HU may be chosen

76. The terminology commonly used to describe
the above mentioned windows includes soft
tissue windows (window width of 250 to 400
HU) and bone windows (2000 to 4000 HU).
 Soft tissue window CT
image
 Bone window CT
image

77. Contrast CT:
 Intravenous
contrast agents
allow identification
of rim
enhancement in
pathological lymph
nodes and
 increase the
definition of
primary tumors.

78. Spiral CT
 Helical or spiral CT scans a volume of
tissue and
 provides better quality images than
the conventional CT.
 It covers more than 300 cm tissue
during a single breathhold of 30
seconds

79. multidetector CT scanners
(MDCTs)
 MDCT can reduce scan time, permit
imaging with thinner collimation, or
both
 Multidetector CT offers the additional
advantages of decreased contrast
load, reduced respiratory and cardiac
motion artifacts, and enhanced
multiplanar reconstruction capabilities.

80. CT angiography:
 With intravenous bolus administration
of iodinated contrast material.
 permitted successful imaging of entire
vascular distributions
 CT angiography has become an
important tool for assessment of the
abdominal and iliac arteries and their
branches, the thoracic aorta, the
pulmonary arteries, and the extra- and
intracranial carotid circulation.

81. Processing of volumetric data:
 The volumetric data can be processed
to produce
 Multiplanar images: Sagittal and
coronal
 Three-dimensional (3D) images
 Virtual endoscopy: Such as
laryngoscopy, bronchoscopy and
sinuscopy

82. 3-D image reformatting
 To evaluate bony
Structure
 Like fracture,
tumour,
exostosis,
destructive
lesions etc.
 Helps immensely
in planning
reconstruction
operation

83. 3-D reconstruction of
ct-angiography
 3- D
reconstruction of
cervical vessels
from CT
volumetric data
set obtained after
administration of
contrast material
 Gives better result
than MR
angiography

84. Optimal slice thickness
 3 mm or 5mm = Neck structure
 2 mm = facial bone, sinunasal cavities
and orbit, laryngohypopharyngeal
region
 0.8 – 1 mm = Temporal bone

85. Applications of CT,
 Extension of mucosal tumors of suprahyoid neck and metastatic
neck lymph nodes (ring enhancement)
 „Postoperative neck
 „Salivary gland tumors and metastatic neck lymph nodes
 „Computed tomography sialography
 Cervical lymphadenopathy
 „Trauma, inflammation and cancer of larynx and laryngopharynx
with metastatic neck nodes
 „Large or fixed thyroid tumors invading and compressing larynx,
laryngopharynx, trachea and mediastinum
 „Paranasal sinuses prior to endoscopic sinus surgery, severe
nasal polyposis, tumors
 „Facial trauma
 „Temporal bone and skull base tumors, semicircular canal fistulas,
cochlear implants.

86. Magnetic resonance imaging
Principle
 The protons in the nuclei of hydrogen behave
like small spinning bar magnets and align with
a strong external magnetic field.
 A radio frequency pulse knocks protons out of
alignment, which release small amount of
energy while gradually returning to their original
position.
 This energy is detected by sensitive coils,
which are placed around patient.
 Hydrogen atoms are abundantly present in
body water and MRI can differentiate the water
content of various tissues

88. Imaging protocols
 The rate of energy loss is designated as the
longitudinal (T1) and transverse (T2)
relaxation times.
 T1 represents the restoration of the
longitudinal magnetization along the axis of
the main magnetic field
 T2 represents the decay time of the
magnetization in the transverse plane.
 Substances (e.g.,fluid) that have a long T1
will appear dark on T1-weighted images,
whereas those with short T1 (fat) will
display high signal intensity.

89. Imaging protocols
 On T2-weighted images, a long T2
substance (fluid) will appear bright.
 The commonly used pulse sequences
are T1-weighted (T1W), T2-weighted
(T2W), gadolinium-enhanced T1W, spin
(proton) density, fat-suppressed and
gradient echo imaging.

90.  T1W: Because of high soft tissue
discrimination, T1W images show
exquisite anatomical details.
 „T2W: The pathological lesions increase
T2 de-phase times, which produce
higher signal than surrounding normal
tissue in T2W images.
 The combination of T1W and T2W
images is good for characterizing fluid
containing structures, solid components
and hemorrhage.

91. MRI head sagittal section T1-
weighted
MRI head axial section T2-
weighted

92. Gadolinium-enhanced T1W:
 Intravenous gadolinium (used in T1W)
reduces T1 relaxation time and
enhances lesions, which appear as
high signal intensity areas
 Improved delineation of tumor margins
relative to the lower signal of muscle,
bone, vessel and globe.
 Gadolinium enhancement is optimally
used with specific fat suppression
techniques.

93. Short-tau inversion recovery:
 The STIR sequence suppresses high
signal intensity from fat (that turn fat
black) and fluid containing structures
remain high signal intensity.
 In STIR, decreased signal-to-noise ratio
degrades the image.
Magnetic resonance angiography:
 It uses specific sequences
 and demonstrates flowing blood.

94. Different characteristics
 (To quickly identify a
T1WI: fat is white,
CSF and vitreous are
black, and nasal
mucosa is low signal.)
 (To quickly identify a
T2WI: CSF, vitreous,
and nasal mucosa are
white. Fat is low to
intermediate in signal.)

95. Different characteristics
 To quickly identify a
gadolinium-enhanced
T1WI: nasal mucosa is
white, fat is white, and
CSF and vitreous are
black
 To quickly identify a
STIR image(fat
suppresion): fat is
almost completely
black; CSF, vitreous,
and mucosa are white

96. ADVANTAGES
 Superior soft tissue contrast resolution
than CT
 No radiation exposure
 Less image quality gets hampered by
the presence of dental fillings

97. DISADVANTAGES
 Long image acquisition time
 More chance of motion artifacts
 Difficult to stage both primary tumour and
neck nodal disease
 Higher cost and less availability
 Absolute contraindications to MRI include
patients with cardiac pacemakers,
cochlear implants, and ferromagnetic
intracranial aneurysm clips.
 Those patients at risk for metallic orbital
foreign bodies should be screened with
plain films or CT before MRI.

98. Applications of MRI
 Tumors of nasopharynx, oropharynx, oral cavity
and tongue
 „Extracapsular spread of tumor from nodes
 „Perineural spread and extension beyond gland
of salivary gland tumors
 „Tumors of nose and paranasal sinuses:
Distinguish between tumor and obstructed sinus
secretions (hydrated fluid,viscous, desiccated);
 Perineural spread to anterior cranial fossa, orbit,
parapharyngeal space and pterygopalatine
fossa and cribriform plate extension
 „Lesions of IAC, facial nerve canal, and jugular
foramen; acoustic schwannoma
 „Skull base tumors

99. Radionuclide imaging
 Intravenously administered
radiopharmaceuticals
 such as technetium-99m (99mTc)-
pertechnetate concentrate selectively in
certain tissues and emit gamma
radiation detected by a gamma camera.
 It provides two-dimensional display of
physiological and functional changes in
tissue

100. Technetium-99m (99mTc)-
pertechnetate scan:
 In salivary gland imaging 99mTc pertechnetate
imaging may be useful for assessing salivary
gland function in autoimmune and
inflammatory disease of the salivary glands.
 If obstructed, the degree of obstruction as well
as the follow-up of obstruction after treatment
can be assessed.
 In evaluating neoplasms of the salivary glands
the findings of the 99mTcpertechnetate scan
are almost pathognomonic of Warthin's tumor
and oncocytoma.

101. Thyroid imaging
 Most nuclear medicine imaging uses
various isotopes of iodine (131I and
123I), Technitium-99m pertechnetate
to determine thyroid function, identify
hot or cold nodules, or access extent
of thyroid masses and tumors.
 1- 4 % of hot nodules – malignant
 Upto 25 % of cold nodule – malignant

102. Positron emission tomography
 The positron emission tomography provide a
means of identifying pathology based on
altered tissue metabolism.
 Imagining technique relies on a radioactive
molecule(radiotracer) that decay with positron
emission.
 The radiotracer is given intravenously to the
patient and is taken into cells.
 Malignant cell trap more radiotracer compare
to non malignant cells.
 The local radiotracer concentration can be
measured.

104.  PET image lack anatomical details, which
can be overcome by combining with CT/MR
using software technique
 Depending on the radiotracer used different
aspects of tissue metabolism can be
measured.
 An analogue of glucose, 2-[18F] fluoro-2-
deoxy-D-glucose (FDG) which reflects
glucose metabolism is commonly use.

105. Positron Emission Tomography
 Used for staging and evaluation of
recurrence for primary head and neck
tumors, detecting distant lymph node,
soft-tissue and skeletal metastases
 More accurate than CT or MRI in
detecting residual or recurrent nodes
 Highly reliable after 3 – 4 months of
end of treatment.

106. Indications of FDG with integrated PET/CT
 SCC patients with
 equivocal nodal disease following
conventional assessment;
-suspicion of recurrent/residual disease.
 Patients with occult primary tumors.
 Post-treatment papillary and follicular
thyroid cancer patients with elevated
thyroglobulin and negative 131-I scan.
 Patients with clinical suspicion of more
disease than conventional assessment
demonstrates.
 Patients where resectability is in doubt.

107. Effect of radiation
 The effects of radiation are usually classified
into two categories, depending on the intensity
of the radiation and the time period of
exposure.
 These electrons may damage DNA molecules
directly or produce free radicals that can
chemically damage genetic material; either
effect may result in cell death or mutation
 These categories are referred to as
1. stochastic effects
2. deterministic effects

108. Stochastic effects
 The severity of stochastic effects is
independent of the absorbed dose.
 Under certain exposure conditions, the
effects may or may not occur.
 There is no threshold and the probability of
having the effects is proportional to the dose
absorbed.
 Example: radiation induced cancer, genetic
effect

109. Deterministic effects
 severity of certain effects on human beings
will increase with increasing doses.
 There exists a certain level, the "threshold",
below which the effect will be absent.
 This kind of effects is called "deterministic
effects“
 Example: cataract, erythema, infertility etc.

110. References
 Adam Grainger & Allison's Diagnostic
Radiology 5th ed
 Basic Radiology LANGE clinical science.
 Scott-Brown’s Otorhinolaryngology, Head
and Neck Surgery 7th edition.
 Surgery of ear Glasscock Shambaugh 6th
edition.
 Mohan Bansal Disease of Ear, Nose and
Throat.
 Head and Neck Imaging, Peter M. Som
 Internet