advanced diagnostic aids

ADVANCED DIAGNOSTIC TECHNIQUES

(CT,MRI,ULTRASONOGRAPHY,BONE SCINTIGRAPHY)

Nov 1895

MAGNIFICATION, DISTORTION, OVERLAPPING, SUPERIMPOSITION, MISREPRESENTATIONS OF STRUCTURES

COMPUTED TOMOGRAPHY

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

INTRODUCTION

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

• G.N. Hounsfield developed first clinically useful CT head scanner

• First clinically useful CT head scanner was installed at Atkinson-Morley Hospital (England)

• First paper on CT presented to British Institute of Radiology by Hounsfield and Dr. Ambrose

• Dr. Ledley introduced the whole body CT scanner (ACTA scanner)

• G.N. Hounsfield shared the Nobel Prize with Allan MacLeod Cormack

IMPORTANT EVENTS

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.

DEFINITION

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.

CT SCAN

Think like looking into a loaf of bread by cutting it into thin slices and then viewing the slices individually

CROSS-SECTIONAL SLICES

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.

BASIC PRINCIPLE

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

COMPARISON OF CT WITH CONVENTIONAL RADIOGRAPHY

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.

GENERATION CONFIGURATION

DETECTOR BEAM MIN SCAN TIME

FIRST TRANSLATE -ROTATE

1-2 PENCIL THIN

2.5MIN

SECOND TRANSLATE -ROTATE

3-52 NARROW FAN

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

GENERATIONS OF CT

1.X-ray tube & collimator

2.Detector assembly

3.Tube controller

4.High freq. generator

5.Onboard computer

6.Stationary computer

CT GANTRY

CT GANTRY INTERNAL COMPONENTS

ADVANTAGES OF CT

COMPUTED TOMOGRAPHY

Cost Medical radiologist / Oral radiologist Dose Needs of dentist – Anatomy, Diagnosis, Rx plan Availability

how CT works…

Godfrey Hounsfield

Nobel prize in Medicine, 1979

Allan Cormack

x-ray source

detectors

acquisition

reconstruction

Voxels (Volume elements)

≈ 100 million voxels (200 Mb)400

slices512 x 512 x

density:0 - 4095

NORMAL ANATOMICAL LAND MARKS IN CT

1SINUS-CTAxial view1. Frontal Sinus

CT of Sinus Axial view

1. Ethmoid Sinus

2. Sphenoid Sinus

3. Carotid canal

Axial scan of facial bones

1. Ossicular chain (malleous/ incus)

2. Internal auditory meatus

CT of Sinus Axial view

1. Maxillary Sinus

2. Pterygoid plate

3. Nasopharynx

4. Nasal septum

5. Inferior turbinate2

CT of Sinus- Axial View

1. Maxillary Sinus

2. Hard Palate

3. Oropharynx

4. Masseter muscle

Axial scan of facial bones

1. Zygomatic arch

2. Mastoid air cells

Axial Scan of facial bones1. Mandible

Coronal view of sinus1. Fronto-nasal suture

Coronal view of sinus1.Ethmoid sinus2. Inferior turbinate

Coronal view of sinus1. Maxillary sinus

Coronal View of sinus1. Sphenoid sinus

2. Zygomatic frontal suture 3. Middle turbinate

4. Inferior turbinate 5. Maxillary ostea

Coronal Scan of sinus

Axial scan of orbit

1. Retrorbital fat

2. Medial rectus

3. Lens

4. Lateral rectus

5. Optic nerve

Axial scan of neck

1. Medial pterygoid muscle

2. Masseter muscle

3. Parotid gland

Axial scan of neck

1. Common carotid artery

2. Thyroid cartilage

3. Sternocleido- mastoid muscle

4. Internal jugular vein

Axial scan of neck1. Thyroid gland

INCISIVE CANAL & FORAMEN

MIDDLE SUTURE

HARD PALTE

GREATER & LESSER PALATINE CANAL

NASO PHARYNX

MAXILLARY SINUS

MAXILLARY TUBEROSITY

PTERYGOID PROCESS

MANDIBULAR NOTCH

STYLOID PROCESS

MAXILLA

MANDIBLE

MANDIBULAR

FORAMEN

MANDIBULAR CANAL

DENS AXIS

INFRA TEMPORAL FOSSA

LACRIMAL BONE

MAXILLARY SINUS

PTERYGOPALATINE FOSSA

INFRA ORBITAL CANAL

NASOLACRIMAL CANAL

E.A CANAL

CORONOID PROCESS

NASAL SEPTUM

SPHENOZYGOMATIC SUTURE

MIDDLE SUTURE OF

HARD PALATE

NASOPHARYNX

NASO LACRIMAL CANAL

ZYGOMA

SPHENOID BONE

CAROTID CANAL

SPHENOID SINUS

SEPTUM

FRONTAL BONE

FRONTAL SINUS

NASAL BONE

NASAL SEPTUM

NASO FRONTAL SUTURE

CRISTA GALLI

NASO LACRIMAL CANAL

┴ PLATE OF ETHMOID

CONCHA BULOSA

MAXILLA

MAXILLARY SINUS

MANDIBLE

ETHMOID SINUS

MIDDLE MEATUS

CRISTA GALLI

HARD PALATE

INFRA ORBITAL CANALINFERIOR

MEATUS

MIDDLE SUTURE OF

HARD PALATE

MANDIBULAR FORAMEN

┴PLATE OF ETHMOID

GREATER PALATINE

SUB MANDIBULAR SPACE

SUBMANDIBULAR GLAND

MANDIBULAR CANAL

TONGUE

ZYGOMATIC ARCH

INFERIOR ORBITAL CANAL

ETHMOID SINUSGREATER WING OF SPHENOID

SPJENOID SINUS

PTERYGOID FOSSA

HYOID BONE

SPHENOID SINUS SEPTUMFORAMEN

ROTUNDUMZYGOMATI

C ARCHLATERAL

PTERYGOID MEDIAL PTERYGOID

PLATEHAMULUS OF MPP

FORAMEN OVALE

GLENOID FOSSA

OROPHARYNX

PARAPHARYNGEAL SPACE

SPHENOID BONE

MANDIBULAR

CONDYLE

GENIALTUBERCLE OF MANDIBLE

ZYGOMATIC ARCH

MANDIBULAR FORAMEN

NewTom 3G by AFP MercuRay by Hitachi

3D Accuitomo by J. Morita

CONE-BEAM UNITS

Galileos by Sirona

I-CAT by ISI Iluma by IMTEC

cone-beam CT(CBCT)

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 UNSHARPNESSACCURACY-ISOTROPIC VOXEL, RESOLUTION- SUBMILLIMETERVOLUME CONSTRUCTION – 3DDISPLAY MODES UNIQUE TO MAXILLOFACIAL IMAGINGINTERACTIVE ANALYSISDOSE REDUCTION – PULSED, FOVTUBE EFFICIENCY INCREASED

C B C T

Disadvantages◦ Noise from radiation scatter◦ Streak artifacts from metal restorations◦ Image degradation from patient movement◦ Cost◦ Training◦ Soft tissue contrast

52 – 1025 microsieverts = 4 – 77 OPG Head CT – 1400-2100 microsieverts

NutellaKinder

…CBCT

MULTI-SPECIALTYPRACTICES

PERIODONTICS

ORTHODONTIC PEDODONTICS

IMPLANTS

ENDODONTICS

ORAL & MAXILLOFACIAL

SURGEONS

APPLICATIONS

C B C T 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

Implant Planning

SECUNDERBAD DENTAL IMAGING

Can we place implant ???

ORTHODONTICS

C B C T - ORTHO

PERIODONTICS As accurate as direct

measurements using a periodontal probe

ENDODONTICS

Visualization of canals

Periapical lesions.

Root fracture

Elucudation of internal and external resorption

Conventional TMJ radiograph

TMJ IMAGING

osteophytes ,condylar erosion, fracture,ankylosis,dislocation and growth abnormalities such as condylar hyperplasia.

Erosion Osteophyte Bifid condyle

Dentigerous cyst

PANORAMIC VIEW

Salivary calculi

CLEFT PALATE

ENT APPLICATIONS

radiculodental cyst on incomplete filling of distal vestibular canal of tooth 16, microperforation of sinus floorand facing mucosal thickening.

Bucco-sinus communication after tooth extraction.The gaseous fistula is clearly visible (arrows).

Direct trauma. Fracture of the posterior wall of the right maxillary sinus (thin arrows) and juxtaparietal soft tissueemphysema (thick arrows). Slight blood effusion in sinus.

Nasal bone fracture and displacement fracture of nasal septum.

Air way study

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).

MAGNETIC RESONANCE IMAGING

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

INTRODUCTION

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 moresensitive than bone scan for the detection of vertebral bone metastases.49,503. To evaluate the site, size and extent of all soft tissue tumours including nodal involvement, involvingall areas in particular the tongue and floor of mouth.4 .The salivary glands - providing images of salivary gland parenchymaIn 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 predictingvascularity and recurrence

indications for MRI in the head and Neck

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, 45,46and a normal disk position has been depicted in 16%–23% of symptomatic patients .47,48

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

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.

T1 & t2 WEIGHTED IMAGES

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.

T1 & T2 WEIGHTED IMAGES

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

COMPONENTS OF MRI

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

Grey Matter

White Matter

Occipital Lobe

Cerebellum

Grey Matter

Frontal Lobe

Lateral Sulcus

Parietal Lobe

Temporal Lobe

Gyri of cerebral cortex

Sulci of cerebral Cortex

Cerebellum

Frontal LobeTemporalLobe

Frontal Lobe

Temporal Lobe

Parietal Lobe

OccipitalLobe

Cerebellum

Frontal Lobe

EyeBall

Parietal Lobe

Occipital Lobe

Transverse Sinus

CerebellarHemisphere

Optic Nerve

Maxillary Sinus

Precentral Sulcus

Lateral Ventricle

Occipital Lobe

Caudate Nucleus

Tongue

Corpus callosum

Thalamus

TentoriumCerebelli

Thalamus

Splenium of Corpus callosum

Ethmoid air Cells

Inferior nasalConcha

Mesencephalon

Fourth Ventricle

Genu of CorpusCallosum

Hypophysis

Body of corpus callosum Thalamus

Splenium of Corpus callosumGenu of corpus

callosum

SuperiorColliculus

Inferior Colliculus

NasalNasal Septuml

Medulla

Cingulate Gyrus

Genu of corpuscallosum

Ethmoid air cells

Oral cavity

Splenium of Corpus callosum

Fourth Ventricle

FrontalLobe

MaxillarySinus

Parietal Lobe

Occipital Lobe

Corpus CallosumThalamus

Cerebellum

Frontal Lobe

TemporalLobe

Parietal Lobe

Lateral Ventricle

Occipital Lobe

Cerebellum

Parietal Lobe

Occipital Lobe

Cerebellum

Frontal Lobe

Temporal Lobe

Frontal Lobe

Lateral Sulcus

Superior TemporalGyrus

Inferior TemporalGyrus

Parietal Lobe

Middle Temporal Gyrus

External Auditory Meatus

Eye Ball

Cerebral Peduncle

Temporal HornLateral Ventricle

Occipital Lobe

Lateral Sulcus(Sylvian)

Inferior Colliculus

Putamen

Globus Pallidus

Third Ventricle

Thalamus

Frontal HornLateral Ventricle

Anterior LimbInternal Capsule

Posterior LimbInternal Capsule

Thalamus

Head of theCaudate Nucleus

Frontal Lobe

Anterior LimbInternal Capsule

Lentiform Nucleus

Posterior LimbInternal Capsule

Splenium of Corpus Callosum

Genu ofCorpus Callosum

Head of the Caudate Nucleus

Thalamus

Lateral Ventricle

Longitudinal Fissure

Caudate NucleusFrontal HornLateral Ventricle

Occipital HornLateral Ventricle

Lateral VentricleCorpus Callosum

Cingulate GyrusCorona Radiata

SulciFalx cerebri

Calvarium

Superior Sagittal Sinus

Straight Sinus

Transverse Sinus

Straight Sinus

Cerebellum

Superior SagittalSinus

Cerebellum

Occipital Lobe

LongitudinalFissure

Sigmoid Sinus

Straight Sinus

Vermis of Cerebellum

Straight Sinus

Cerebellum

Lateral Ventricle,Occipital Horn

Arachnoid Villi

Great CerebralVein

TentoriumCerebelli

Falx Cerebri

Lateral Ventricle

Vermis ofCerebellum

Cerebellum

Splenium ofCorpus callosum

Posterior CerebralArterySuperior CerebellarArtery

Foramen Magnum

Lateral Ventricle

Internal CerebralVein

Tentorium Cerebelli

Fourth Ventricle

Cingulate Gyrus

Choroid Plexus

Superior Colliculus

Cerebral Aqueduct

Corpus Callosum

Thalamus

Pineal Gland

Vertebral Artery

Insula

Lateral Sulcus

Cerebral Peduncle

Crus of Fornix

Middle CerebellarPeduncle

Caudate Nucleus

Third Ventricle

Hippocampus

Corpus Callosum

Thalamus

CerebralPeduncle

Parahippocampalgyrus

Lateral Ventricle

Uncus Of Temporal Lobe

Lateral Ventricle,Temporal Horn

Body of Fornix

Third Ventricle

Hippocampus

Internal Capsule

Insula

Optic Tract

Caudate Nucleus

Lentiform Nucleus

Hypothalamus

Amygdala

Parotid Gland

Internal Capsule

Optic Nerve

Nasal part of Pharynx

Cingulate Gyrus

Caudate Nucleus

Lentiform Nucleus

Internal Carotid Artery

LongitudinalFissure

Lateral Sulcus

Parotid Gland

Superior SagittalSinus

Genu of CorpusCallosum

Temporal Lobe

Ethmoid Sinus

Nasal Septum

Nasal Cavity

Tongue

Frontal Lobe

Nasal Turbinate

Masseter Muscle

Rectus Medialis

Rectus Lateralis

Inferior Turbinate

Frontal Lobe

Rectus Superior

Rectus Inferior

Maxillary Sinus

Grey Matter

White Matter

Eye Ball

Maxillary Sinus

Tongue

Nasal Septum

Eye Ball

Frontal Lobe

Oral Cavity

Nasal Turbinate

Medulla Oblongata

ExternalAuditoryMeatus

Auricle

Maxillary Sinus

Trigeminal Nerve

Fourth Ventricle

Cerebellum

Rhombencephalon(Hindbrain)

Inferior CerebellarPeduncle

Temporal Lobe

Fourth Ventricle

Maxillary Sinus

Middle CerebellarPeduncle

Temporal Lobe

Fourth Ventricle

Ethmoid sinus

CerebellarHemisphere

Pituitary Gland

Cerebral aqueduct

Eye Ball

Optic Nerve

Optic Chiasm

Cerebellum

Temporal lobe

Lateral Rectusmuscle

Nasal Septum

Cerebral Peduncle

Inferior colliculus

Eye Ball

Cerebellum

Eye Ball

Third Ventricle

Cerebral Peduncle

Cerebellum

Hypothalamus

Inferior Colliculus

Third Ventricle

Superior colliculus

Cerebellum

Lateral Sulcus(Sylvian)

Lateral Ventricle

Head of Caudate Nucleus

Posterior Limb,Internal Capsule

Genu,Corpus Callosum

Anterior Limb,Internal Capsule

Thalamus

Lateral Ventricle

Choroid Plexus

Lateral Ventricle

Anterior Limb,Internal Capsule

Thalamus

Third Ventricle

Lateral Ventricle

Longitudinal Fissure

Genu of corpuscallosum

Internal capsule

Falx cerebri

Lateral ventricle,Frontal horn

Lateral Ventricle,Occipital horn

Cingulate gyrus

Corona radiata

Calvarium

Falx cerebri

Grey Matter

White MatterFalx cerebri

SulcusGyri

masseter

Three layers:

Superficial, middle and deep with slightly different fiber orientations; important in recruitment for chewing

zygomatic

temporalis

buccinatorPosterior belly of digastric

Stylomandibular ligament

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

Mental foramen for V3 sensory branch

Coronoid process of mandible

Mandibular notch

condyle

Mandibular fossa

Articular emminence

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

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”

MRI series 1 of 6 – coronal section, anterior to posterior

Temporalis m.

Masseter m.

MRI series 2 of 6

Lateral pterygoid

Upper head: to articular disc

Lower head: to neck of mandibular condyle

MRI series 3 of 6

Medial pterygoid

MRI series 4 of 6

MRI series 5 of 6

MRI series 6 of 6

SIALOGRAHY

Sialography can be defined as the radiographic demonstration of the major salivary glands by introducing a radiopaque contrast medium into their ductal system.

DEFINITION

The procedure is divided into three phases. The preoperative phase The filling phase The emptying phase.

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.

PRE-OPERATIVE PHASE

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.

FILLING PHASE

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

EMPTYING PHASE

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.

CLINICAL INDICATIONS

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.

Contraindications

Simple injection technique

Hydrostatic technique

Continuous infusion pressure-monitored technique

SIALOGRAPHIC TECHNIQUES

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.

SIALOGRAPHIC INTERPRETATION

SYSTEMATIC APPROACH

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

NORMAL SIALOGRAPHIC APPEARANCES OF THE PAROTID GLAND

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

Normal sialographic appearances of the submandibular gland

Main pathological changes can be divided into

PATHOLOGICAL APPEARANCES

Ductal changes associated with:Calculi Sialodochitis (ductal inflammation/infection)

Glandular changes associated with: Sialadenitis (glandular inflammation/infection) Sjogren's syndromeIntrinsic tumours.

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

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.

SIALODOCHITIS

• Dots or blobs of contrast medium within the gland, an appearance known as sialectasis

SIALADENITIS

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

SJOGRENS SYNDROME

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

INTRINSIC TUMOURS

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

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

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.

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

INTERVENTIONAL SIALOGRAPHY

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).

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 andD 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)

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.

conclusion

Pharmaceuticals that are labeled with radionuclides

Accumulate in organs of interest

Emit gamma radiation

Detection system sensitive to this obtain images

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.

Positron Emission 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)

Gamma Emission

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.

Alpha Emission 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.

Gamma Imaging The Device

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.

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.

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.

Photomultiplier tube (PMT)

This is an extremely sensitive photocell used to convert light signals of a few hundred photons into a usable current pulse

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).

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.

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.

The Procedure

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

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.

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.

Various radioisotopes used in radionuclide imaging

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 daysUsed for cerebrospinal fluid studies in the brain.

Carbon-11 Nitrogen-13 Oxygen-15Fluorine-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

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.

Radioisotopes used in conventional nuclear medicine

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.

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.

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.

IDEAL PROPERTIES OF RADIONUCLIDES

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.

VARIOUS RADIONUCLIDE IMAGING PROCEDURES 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

Single Photon Emission Computed Tomography (SPECT)

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.

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 .

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.

SPECT acquisition protocols

MIBG : meta-iodo-benzylguanidine , HMPAO : 99Tcm-hexamethylpropyleneamine oxime , ECD :ethyl cysteinate dimer

SPECT bone scintigrams show increased uptake in the right mandible (arrows) in the region of a sequestrum.

Positron Emission Tomography (PET)

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).

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.

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

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.

Coincidence detection

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.

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’

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.

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.

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.

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.

Overview of the imaging modalities

Hybrid scanning techniques

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.

BONE SCINTIGRAPHY

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 .

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

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’.

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.

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.

Radiation Considerations

Clinical Indications

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

Interpretation:

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

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).

Bone scintigraphy in a patient with bisphosphonate-related ONJ

Bone scintigram shows uptake in the right mandible Bone scintigram obtained approximately 17 months later shows progression of the uptake

SALIVARY GLAND SCINTIGRAPHY

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

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.

Interpretation of salivary scintigraphy

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.

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.

Regions of interest on dynamic scintigraphy. RP, right parotid; LP, left parotid; RSm, right submandibular gland; LSm, left submandibular gland; B, background

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

Indications

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.

Advantages

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.

Disadvantages

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.

Other Indications of radionuclide imaging

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.

Indicatiions for isotope imaging in maxillofacial lesions

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.

Advantages of radionuclide imaging:

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.

Disadvantages:

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.

radioimmunoscintigraphy

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.

CONCLUSION“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

THANK YOUTHANK YOU

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