SPECIALIZED IMAGING IN DENTISTRY

NEW CUTTING EDGE IMAGING MODALITIES IN DENTISTRY.

SPECIALISED IMAGING TECHNIQUES

Research and development has focused on manipulating and altering many basic radiographic techniques.

Recent advances in the field of science have provided a path to much innovative imaging techniques.

These imaging modalities can be grouped broadly according to the type of physical principles applied.

CONTRAST IMAGING

Sialography

Arthrography

RADIONUCLIDE IMAGING

Positron emission tomography

Single photon emission computed tomograph

AUCOSTIC IMAGING

Ultrasound

OPTICAl IMAGING

Optical coherence tomography

Stereoscopy

THERMAL IMAGING

Thermography

MAGNETIC RESONANACE IMAGING

COMPUTED TOMOGRAPHY

Contrast studies

—  These investigations use contrast media., radiopaque substances that have been developed to alter artificially the density of different parts of the patient, so altering subject contrast — the difference in the X-ray beam transmitted through different parts of the patient's tissues.

—  They include:-

—  Sialography — salivary glands

—  Arthrography — joints

contrast media

—  Barium sulphate suspensions for investigating the gastrointestinal tract

—   Iodine-based aqueous solutions used for all other investigations and divided into:

—  — Ionic monomers, including:

—  * iothalmate (e.g. Conray®)

—  * metrizoate (e.g. Isopaque®)

—  * diatrizoate (e.g. Urografin®)

—  — Ionic dimers, including:

—  * ioxaglate (e.g. Hexabrix®)

—  — Non-ionic monomers, including:

—  * iopamidol (e.g. Niopam®)

—  * iohexol (e.g. Omnipaque®)

—  * iopromide (e.g. Ultravist®)

—   Iodine-based oil solutions such as Lipiodol®(iodized poppy seed oil) used for lymphography and sialography.

—  Water-insoluble organic iodine compounds, e.g. Pantopaque®.

—   MRI contrast agents (e.g. gadolinium)

—  Oil based contrast media

Advantages:-

—  Densely radiopaque, thus show good contrast

—  High viscosity, thus slow excretion from the gland

Disadvantages:-

—  Extravasated contrast may remain in the soft tissues for many months, and may produce a foreign body reaction

—  High viscosity means considerable pressure needed to introduce the contrast, calculi may be forced down the main duct

Aqueous contrast media

Advantages:-

—  Low viscosity, thus easily introduced

—  Easily and rapidly removed from the gland

—  Easily absorbed and excreted if extravasated

Disadvantages:-

—  Less radiopaque, thus show reduced contrast

—  Excretion from the gland is very rapid unless used in a closed system

Harmful effects of contrast media

—  Ideally, contrast media should have no harmful effects at all.

—  small risk associated with their use, especially with the iodinebased aqueous solutions (the so-called general contrast media} when they are introduced into the blood stream, because a single dose of contrast medium contains more than 2000 times as much iodine as the body's total physiological content.

Complications

—  Mild:-

—  headache, nausea, warmth and/or pain, flushing, sneezing and constipation.

—  Moderate:-

—  vomiting, bronchospasm, urticaria and hypotension

—  Severe:-

—  cardiac arrhythmias, cardiac arrest, convulsions, anaphylactic shock and pulmonary oedema

—  Fatal

Sialography:-

—  Sialography can be defined as the radiographic demonstration of the major salivary glands by introducing a radiopaque contrast medium into their ductal system.(ERIC WHITE 4^TH EDITION).

—  It was first introduced by Barsony in 1930’s.

PROCEEDURE:-

—  The proceedure can be broadly divided into 3 phases:-

—  The preoperative phase

—  The filling phase

—  The emptying phase.

—  The type of radiographs used for sialography depend on the site and type of gland:-

Preoperative phase

—  Phase before introduction of contrast media.

—  It starts with taking a scout radiograph. Interpret the radiograph for :-

—  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.

     Filling phase

—  the relevant duct orifice needs to be found, probed and dilated and then cannulated.

—  A multiple spot sialograms assures better opportunities for the study of the total duct system.

—  The three main techniques available for introducing the contrast medium into the ductal system:-

—  Simple injection technique:-

—  Hydrostatic technique

—  Continuous infusion pressure monitored technique

Simple injection technique

—  Contrast medium is introduced using gentle hand pressure until the patient experiences tightness or discomfort in the gland.

—  0.7 ml for the parotid gland, 0.5 ml for the submandibular gland

—  Advantages

—  Simple

—  Inexpensive.

—  Disadvantages

—  The arbitrary pressure which is applied may cause damage to the gland

—  Reliance on patient's responses may lead to underfilling or overfilling of the gland.

         Hydrostatic technique

—  Aqueous contrast media is allowed to flow freely into the gland under the force of gravity until the patient experiences discomfort

Advantages

—  The controlled introduction of contrast medium is less likely to cause damage or give an artefactual picture

—  Simple

—  Inexpensive.

Disadvantages

—  Reliant on the patient's responses

—  Patients have to lie down during the procedure, so they need to be positioned in advance for the filling-phase radiographs.

Continuous infusion pressure monitored technique

—  Using aqueous contrast medium, a constant flow rate is adopted and the ductal pressure monitored throughout the procedure.

Advantages

—  The controlled introduction of contrast media at known pressures is not likely to cause damage

—  Does not cause overfilling of the gland

—  Does not rely on the patient's responses.

Disadvantages

—  Complex equipment is required

—  Time consuming.

Parenchymal Opacification stage:

—  This is the final stage of filling phase

—  Injection of contrast material under fluoroscopic control is carried to the stage where filling of the acini can be recognized. At this stage the syringe is disconnected and the stop-cock is closed to prevent spillage of the contrast material through the catheter.

Emptying 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.

indications

—  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

Sialographic interpretation

—  Normal sialographic appearances of the parotid gland

—  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

submandibular 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

FILLING PHASE:-

—  Better opportunities for the study ofthe total duct system. If an ordinary branching of the duct system is absent, one must consider the following possibilities:

—  (a) complete obstruction of the main duct by an impacted stone or cicatricial obstruction;

—  (b) invasion of the main duct by neoplasm.

—  (c) improper catheter positioning with the catheter tip beyond the wall of the main duct

Parenchymal Opacification Phase :-

—  useful in the diagnosis of 2 major clinical conditions:

—  (a) subacute autoimmune sialosis:-

—   In this condition there is diffuse parenchymal edema with consequent elevation of the pressure in the acini.

—  Acinar filling may be impossible by the retrograde sialographic technique.

—  Further con firmation of this situation is possible by re-injecting the duct with aqueous contrast material such as meglumine diatrizoate. If nonfilling of the acini continues, diffuse parenchymal edema is very likely.

—  (b)peripheral intraglandular space occupying lesion:-

—   Lesions of this type can be easily missed by duct system opacification only. Faint diffuse and uniform opacification of the parenchyma is felt more desirable than a distorted overdistended gland.

Post evacuation phase:-

—  If a portion of the injected contrast material remains in the gland beyond 24 hours, this is distinctly abnormal.

—  This  may be secondary to:-

—   Faulty technique with traumatization

—   Disease such as invasive neoplasm or inflammatory processes.

—  Complete evacuation may be delayed by the presence of stricture of the duct system.

—   The contrast material may also remain within the duct and acini due to absence ofsecretion of the salivary gland.

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.

Sialographic appearances of sialadenitis include:

—  Dots or blobs of contrast medium within the gland, an appearance known as sialectasis caused by the inflammation of the glandular tissue producing saccular dilatation of the acini

Sialographic appearances in Sjogren 's syndrome include:

—  Widespread dots or blobs of contrast medium within the gland, an appearance known as punctate sialectasis or snowstorm This is caused by a weakening of the epithelium lining the intercalated ducts, allowing the escape of the contrast medium out of the ducts

—  Considerable retention of the contrast medium during the emptying phase

—  The main duct is usually normal.

Arthrography

—  Radiographic examination of soft tissue structures of joints after injection of contrast media.

—  Internal derangements of the temporomandibular joint (TMJ ID) are common problems causing jaw dysfunction and persistent pain in the jaw, head, and neck.

—  Useful in diagnosing abnormalities of articular disk

—  Small, oval fibrocartilage located between mandibular condyle  and mandibular fossa.

Technique

—  Non-ionic aqueous contrast medium (e.g. iopamidol-Niopam® 370) is injected carefully into the lower joint space, using fluoroscopy to aid the accurate positioning of the needle.

—  2. The primary record is obtained ideally using video-recorded fluorography or cinefluorography which allows imaging of the joint components as they move. Only the lateral aspects of the joints are seen.

—  3. Thin-section, multidirectional (e.g. hypocycloidal) tomography of the joint can also be performed if required, to provide information on the medial and lateral aspects of the joint. Typically, five or six slices, 2-3 mm apart, are used with the patient's mouth open and closed.

—  4. If further information is required, the contrast medium can be introduced into the upper joint space and the investigation repeated.

Diagnostic information

—  Dynamic information on the position of the joint components and disc as they move in relation to one another.

—  Static images of the joint components with the mouth closed and with the mouth open. Any anterior or anteromedial displacement of the disc can be observed.

—  The integrity of the disc, i.e. the presence of any perforations.

Main indications

—  Longstanding TMJ pain dysfunction unresponsive to simple treatments

—  Persistent history of locking

—  Limited opening of unknown aetiology.

—  Ankylosis

—  Arthritis

Main contraindications

—  Acute joint infection

—  Allergy to iodine or the contrast medium.

Radioisotope imaging

—  Radioisotope imaging relies upon altering the patient by making the tissues radioactive and the patient becoming the source of ionizing radiation.

—  This is done by injecting certain radioactive compounds into the patient that have an affinity for particular tissues — so-called target tissues.

—   The radioactive compounds become concentrated in the target tissue and their radiation emissions are then detected and imaged, usually using a stationary gamma camera.

—  This investigation allows the function and/or the structure of the target tissue

—  radiactivity

—  The spontaneous emission of radiation from atomic nuclei. The radiation can consist of alpha, beta, and gamma radiation

—  Isotopes with unstable nuclei which undergo radioactive disintegration. This disintegration is often accompanied by the emission of radioactive particles or radiation.

—  The important emissions include:

—  Alpha particles

—  Beta- (electron) and beta+ (positron) particles

—  Gamma radiation.

Radioisotopes used in conventional nuclear medicine

—  Technetium (99mTc) — salivary glands, thyroid, bone, blood, liver, lung and heart

—  gallium (67Ga) — tumours and inflammation

—  Iodine (123I) — thyroid

—  Krypton (81K) — lung.

—  99mTc is the most commonly used radioisotope. Its main properties include:

—  Single 141 keV gamma emissions which are ideal for imaging purposes

—  A short half-life of 6 hours which ensures a minimal radiation dose

—  It is readily attached to a variety of different substances that are concentrated in different organs, e.g.:

—  — Tc + MPD (methylene diphosphonate) in bone

—  — Tc + red blood cells in blood

—  — Tc + sulphur colloid in the liver and spleen

—  It can be used on its own in its ionic form (pertechnetate 99mTcO4), since this is taken up selectively by the thyroid and salivary glands

—  It is easily produced, as and when required, on site.

Main indications for conventional isotope imaging in the head and neck

—  Tumour staging — the assessment of the sites and extent of bone metastases

—  Investigation of salivary gland function, particularly in Sjogren's syndrome

—  Evaluation of bone grafts

—  Assessment of continued growth in condylar hyperplasia

—  Investigation of the thyroid

—  Brain scans and assessment of a breakdown of the blood-brain barrier.

Advantages:-

—  Target tissue function is investigated

—  All similar target tissues can be examined during one investigation, e.g. the whole skeleton can be imaged during one bone scan

—  Computer analysis and enhancement of results are available.

Disadvantages:-

—  Poor image resolution — often only minimal information is obtained on target tissue anatomy

—  The radiation dose to the whole body can be relatively high

—  Images are not usually disease-specific

—  Difficult to localize exact anatomical site of source of emissions

—  Some investigations take several hours

—  Facilities are not widely available.

recent developments in radioisotope
imaging techniques

—  PET

—  SPECT

—  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.

History:

—  The concept was introduced by David E. Kuhl and Roy Edwards in the late 1950.

—  Work by Gordon Brownell, Charles Burnham and their associates at the Massachusetts General Hospital beginning in the 1950s contributed significantly to the development of PET technology and included the first demonstration of annihilation radiation for medical imaging.

—  In the 1970s, Tatsuo Ido at the Brookhaven National Laboratory was the first to describe the synthesis of 18F-FDG, the most commonly used PET scanning isotope carrier.

—  The PET/CT scanner, attributed to Dr David Townsend and Dr Nutt

principle

—  some radioactive isotopes decay by the emission of a positively charged electron (positron) from the nucleus. This positron usually travels a very short distance (1-2 mm) before colliding with a free electron.

—   In the ensuing reaction, the mass of the two particles is annihilated with the emission of two (photons) gamma rays of high energy (511 keV) at almost exactly 180° to each other.

—  These emissions, known as annihilation radiation, can then be detected simultaneously (in coincidence) by opposite radiation detectors which are arranged in a ring around the patient.

—  The exact site of origin of each signal is recorded and a cross-sectional slice is displayed as a PET scan.

—  The major advantages of PET as a functional imaging technique are due to this unique detection method and the variety of new radioisotopes which can now be used clinically.

Radio- isotopes

—  As in conventional nuclear medicine, these radioisotopes can be used on their own or incorporated into diverse and biologically important compounds (e.g. glucose, amino acids, and ammonia) and then administered in trace amounts.

indications

—  PET can therefore be used to investigate disease at a molecular level, even in the absence of anatomical abnormalities apparent on CT or MRI

—  It is also possible to superimpose a PET scan on a CT scan, by a technique known as co-localization, to determine a lesion's exact anatomical position.

—   Clinically it has been used in the management of patients with epilesy, cerebrovascular and cardiovascular disease, dementia and malignant tumours.

ADVANTAGES:-

—  Shows the chemical functioning of organs and tissues in vivo.

DISADVANTAGES:-

—  Uses ionizing radiation

—  Expensive

—  Poor resolution , hence fused  with M.R.I and C.T.

—  Requires care with radio-nuclides

—  Application for clinical PET imaging:-

—  Grading of primary tumors.

—  Differentiate benign and malignant lesions.

—  Evaluation of response to Radiation theraphy.

—  Identifying the site of recurrent tumors.

—  Staging of head and neck cancers.

—  For localizing Epileptogenic  foci.

SPECT

—  Single photon emission computed tomography

—  (SPECT), where the photons (gamma rays) are emitted from the patient and detected by a gamma camera rotating around the patient and the distribution of radioactivity is displayed as a cross-sectional image or SPECT scan enabling the exact anatomical site of the source of the emissions to be determined.

Ultrasound

—  Sound:-Sound is a mechanical, longitudinal wave that travels in a straight line

—  sound requires Medium for its transmission.

—  Sound waves travel slowest in gases, at intermediate velocity in liquids and most rapidly in solids.

—  All body tissues except bone behave like liquids and therefore, they all transmit sound at about some velocity.

—   A velocity of  1540 m/sec is used as an average for body tissues

What is Ultrasound?

—  Ultrasound is a mechanical, longitudinal wave with a frequency exceeding the upper limit of human hearing, which is 20,000 Hz or 20 kHz.

—  Diagnostic Medical Ultrasound is the use of high frequency sound to aid in the diagnosis and treatment of patients.

—  Frequency ranges used in medical ultrasound imaging are 2 - 15 MHz

—  History of Ultrasound

—  Piezoelectricity discovered by the Curies in 1880 using natural quartz.

—  SONAR was first used in 1940’s war-time

—  Diagnostic Medical applications in use since late 1950’s

—  Ultrasonic energy was first applied to the human body for medical purposes by Dr. George Ludwig at the Naval Medical Research Institute, Bethesda, Maryland in the late 1940.

—  English born and educated John Wild (1914–2009) first used ultrasound to assess the thickness of bowel tissue as early as 1949: for his early work he has been described as the "father of medical ultrasound"

—  In 1962, after about two years of work, Joseph Holmes, William Wright, and Ralph Meyerdirk developed the first compound contact B-mode scanner.

—  The first demonstration of color Doppler was by Geoff Stevenson, who was involved in the early developments and medical use of Doppler shifted ultrasonic energy

ULTRASOUND – How is it produced?

Produced by passing an electrical current through a piezoelectrical crystal

Piezoelectric material

—  The property of certain crystals that causes them to produce voltage when a mechanical pressure is applied to them such as sound vibrations.

—  AC applied to a piezoelectric crystal causes it to expand and contract – generating ultrasound, and vice versa

—  Naturally occurring  - quartz

—  Synthetic - Lead zirconate titanate (PZT)

Electronic Arrays

—  Groups of piezoelectric material working singly or in groups

Transducer Construction

Transducer Types

Mechanical

—  – Oscillating

—  – Rotating

Electronic

—  – Linear Arrays

—  – Curved Arrays

—  – Phased Arrays

US Transducer Operation

—  alternating voltage (AC) applied to piezoelectric element

—  Causes

—  alternating dimensional changes

—  alternating pressure changes

—  pressure propagates as sound wave

Ultrasound Production

—  Transducer contains piezoelectric elements/crystals which produce the ultrasound pulses (transmit 1% of the time)

—  These elements convert electrical energy into a mechanical ultrasound wave

The Returning Echo

—  Reflected echoes return to the scanhead where the piezoelectric elements convert the ultrasound wave back into an electrical signal

—  The electrical signal is then processed by the ultrasound system

Piezoelectric  Crystals

—  The thickness of the crystal determines the frequency of the scanhead

—  Frequency vs. Resolution

Frequency is defined as Number of complete cycles per unit of time

—  Man-made transducer frequency is predetermined by design

The frequency also affects the QUALITY of the ultrasound image

—  The HIGHER the frequency, the BETTER the resolution

—  The LOWER the frequency, the LESS the resolution

—  A 12 MHz transducer has very good resolution, but cannot penetrate very deep into the body

—  A 3 MHz transducer can penetrate deep into the body, but the resolution is not as good as the 12 MHz

Transducer Frequencies

—  • 2.5 MHz--------------- Deep abdomen, OB/Gyn

—  • 3.5MHz-----------------• General abdomen,

—  • 5.0 MHz------------------ Vascular, Breast

—  • 7.5 MHz------------- Breast, Thyroid, Superficial veins

—  • 10.0 MHz------------------ Superficial masses

Interactions of Ultrasound with Tissue

—  Reflection

—  Refraction

—  Transmission

—  Attenuation

Interactions of Ultrasound with Tissue

Reflection

—  The ultrasound reflects off tissue and returns to
the transducer, the amount of reflection depends on differences in acoustic impedance

—  The ultrasound image is formed from reflected echoes

Refraction

—  Interactions of Ultrasound with Tissue

Transmission

—  Some of the ultrasound waves continue deeper into
the body

—  These waves will reflect from deeper tissue structures

—  Interactions of Ultrasound with Tissue

Attenuation

—   Defined - the deeper the wave travels in the body, the weaker it becomes -3 processes: reflection, absorption, refraction

—  Air (lung)> bone > muscle > soft tissue >blood > water

How does it works

—  Conventional X-ray-generating equipment is replaced by a very high frequency (3.5-10 MHz) pulsed ultrasound beam which is directed into the body from a transducer placed in contact with the skin

—  Luckily, the speed oF sound is almost the same for most body parts

—  Image formation

—  This image is a tomograph or sectional picture that represents a topographical map of the depth of tissue interfaces, just like a sonar picture of the seabed.

—  The thickness of the section is determined by the width of the ultrasound beam.

—  A more recent advance has been to utilize the Doppler effect — a change in the frequency of sound reflected from a moving source — to detect arterial and/or venous blood flow.

—   The computer then adds the appropriate colour, red or blue, to the vascular structures in the visual echo picture image, making differentiation between structures very straight forward.

—  The ultrasound wave must be able to travel through the tissue to return to the transducer. If it is absorbed by the tissue, no image will result.

—  Since air, bone and other calcified materials absorb nearly all the ultrasound beam, its diagnostic use is limited.

Modes of sonography

—  A-mode: A-mode is the simplest type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth. Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy.

—  B-mode: In B-mode ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen.

—  C-mode: A C-mode image is formed in a plane normal to a B-mode image. A gate that selects data from a specific depth from an A-mode line is used; then the transducer is moved in the 2D plane to sample the entire region at this fixed depth. When the transducer traverses the area in a spiral, an area of 100 cm2 can be scanned in around 10 seconds

Accomplishing this goal depends upon...

—  Resolving capability of the system

—  axial/lateral resolution

—  spatial resolution

—  contrast resolution

—  temporal resolution

Types of Resolution

—  Axial Resolution

—  specifies how close together two objects can be along the axis of the beam, yet still be detected as two separate objects

—  frequency (wavelength) affects axial resolution – frequency    resolution

—  Lateral Resolution

—  the ability to resolve two adjacent objects that are perpendicular to the beam axis as separate objects

—  beamwidth affects lateral resolution

—   

—  Spatial Resolution

—  also called Detail Resolution

—  the combination of AXIAL and LATERAL resolution - how closely two reflectors can be to one another while they can be identified as different reflectors

—  Temporal Resolution

—  the ability to accurately locate the position of moving structures at particular instants in  time

—  also known as frame rate

—  Contrast Resolution

—  the ability to resolve two adjacent objects of similar intensity/reflective properties as separate objects  - dependant on the dynamic range

Doppler mode:

—   This mode makes use of the Doppler effect in measuring and visualizing blood flow

—  Color doppler: Velocity information is presented as a color coded overlay on top of a B-mode image

—  Continuous doppler: Doppler information is sampled along a line through the body, and all velocities detected at each time point is presented (on a time line)

Applications in dentistry

—  Determination of the relationship of vascular structures and vascularity of masses with the addition of colour flow Doppler imaging

—  Ultrasound in dentistry is used for detection of fractures of the Maxillo facial region i.e Nasal bone fractures, Orbital rim fractures, Maxillary fractures,  Mandibular fractures, Zygomatic arch fractures.

—  Sonographically, benign lesions usually look well defined, homogeneous and hypoechoic, while Malignant lesions tend to be ill defined and hypoechoic with heterogeneous internal architecture

Lymph node examination

—  Salivary gland examination

—  Detection of salivary gland and duct calculi

—  Sonogram showing an illdefined, heterogeneous, hypoechoic lesion in the left parotid gland. Features are those of a malignant lesion

—  Transverse gray scale sonogram showing a welldefined, round, homogeneous, hypoechoic lesion in the left submandibular gland. These features suggest a benign salivary gland lesion

—  Ultra sound can also be used during FNAC (or) FNAB. Ultrasound ensures that the needle is placed with in the lesion and does not exit the lesion. And during biopsy of parotid gland there is chance of injuring the facial Nerve (or) seeding Neoplastic cells, under ultrasound guidance these can be avoided.

—  Ultra sound can provide the content of the lesion before any surgical procedure, both solid and cystic contents could be identified in ultrasound.

—  Ultrasound with aid of high resolution transducer, can demonstrate the internal Muscle structures.

—  Hyper echoic bands, which corresponds to the internal fascia are usually observed on US Image of normal Muscles. These bands diminish or disappear with inflammation; hence this is an important structural Index of Masseteric Infection.

—  In Ultrasound, color Doppler sonography has been developed to identify vasculatures and to enable evaluation of the blood flow, velocity and vessel resistance together with surrounding Morphology.

ADVANTAGES

—  Sound waves are NOT ionizing radiation

—  • There are no known harmful effects on any

—  tissues at the energies and doses currently

—  used in diagnostic ultrasound

—  • Images show good differentiation between

—  different soft tissues and are very sensitive for

—  detecting focal disease in the salivary glands

—  • Technique is widely available and inexpensive.

DISADVANTAGES

—  Ultrasound has limited use in the head and

—  neck region because sound waves are absorbed

—  by bone. Its use is therefore restricted to the

—  superficial structures

—  • Technique is operator dependent

—  • Images can be difficult to interpret for

—  inexperienced operators because image

—  resolution is often poor

—  • Real-time imaging means that the radiologist

—  must be present during the investigation.

—   

OPTICAL IMAGING

OPTICAL COHERENCE TOMOGRAPHY

—  Optical coherence tomography (OCT) is an evolving imaging modality that combines interferometry with low-coherence  broadband light to produce high-resolution tissue imaging.

—  History

—  In 1990 invivo ocular eye images were taken by using white-light interferometry principle.

—  Later developed by Naohiro Tanno in 1990 and by Huang et al in 1991 into optical coherence tomography.

—  The invivo images of retina were taken with OCT and published for the first time in the year 1993.

—  In 2006 James Ridigway etal, modified the OCT probe for taking images of oral cavity and pharynx.

EVOLUTION

—  OCT can be broadly classified as

—  Time domain OCT

—  Fourier /spectral domain OCT

—  Swept source OCT

Advantages of OCT

—  Live sub-surface images at near-microscopic resolution

—  Real time imaging.

—  No preparation of the sample or subject

—  No ionizing radiation

Disadvantages of OCT

—  The patient must remain static until the image is taken, slight motion can produce an artifract.

—   limited tissue imaging , only upto1 to 2 mm below the surface in biological tissue.

—  NORMAL  MICRO-ANATOMY

THERMAL IMAGING

—  Infrared thermography is the science of acquisition and analysis of thermal information by using non contact thermal imaging devices.

—  Thermography is a method of measurement of skin temperature distribution on the body over a given period of time.

history

—  1620 Sir Francis Bacon reported his conclusions on the existence of radiative heat, that is similar but distinct from visible light since it can be altered out by glass.

—  Herschel is often credited with the discovery of infrared radiation in 1800

Principle

—  Black body radiation:-

—  Proposed by Max plank.

—  when objects become very hot     they start to radiate.

—  This emitted energy is quantised.

—  Warm blooded animals , inorder to maintain temperature for active metabolism, are also considered as hot objects. They emit infra red radiation.

—  This information is generally displayed as a thermal image which tells the clinician the temperature of every spot over the area of interest at a certain instance in time.

—  Photoconductive photon detectors are semiconductive materials that momentarily increase the electron population in their conduction band on absorption of infrared photons.

—  The photoconductive semiconductors most commonly used for photon detection in the 8 ± 14 mm region are `three-metal alloys', such as mercury- cadmium-telluride (HgCdTe)

Applications

—  In Chronic orofacial pain patients:-

—  Gratt and his colleagues in 1996 developed a classification system using telethermographs for patients with chronic pain:-

—  Normal area temp – 0- 25 degrees celcius

—  hot when it is >0.35̊C, and cold when it is <0.35 ̊C.

—  hot thermographs had the clinical diagnosis of:-

—   (1)sympathetically maintained pain, (2) peripheral nerve mediated pain, (3) TMJ arthropathy, or (4) maxillary sinusitis

—  Subjects classified with cold subareas on their thermographs were found to have the clinical diagnosis of:-

—   (1) peripheral nerve-mediated pain (2) sympathetically independent pain.

—  Subjects classified with normal telethermographs included patients with the clinicaldiagnosis of

—  (1) cracked tooth syndrome (2) trigeminal neuralgia (3) pretrigeminal neuralgia (4) psychogenic facial pain.

In TMJ disorders:-

—  Increased heat production on the side of tmd was observed when compared to normal counterpart.

—  For quantification of various thermal insults to pulp during various dental proceedures.

—  Quantification of the effects of post-surgical inflammation.

—  Quantification of the effects of analgesics, anti-inflammatory drugs, etc.

—  In the diagnosis of myofacial symptoms.

STEREOSCOPY

—  technique.]. MacKenzie Davidson . introduced it in 1898.

—  Before the advent of digital imaging 3d perception of a 2d image is very difficult. But stereograms made it possible. understanding normal anatomy is simplified with stereoscopic images.

principle

—  Stereoscopic imaging requires the exposure of two films, one for each eye, and thus delivers twice the amount of radiation to the patient. Between exposures the patient is maintained in position, the film is changed, and the tube is shifted from the right eye to the left eye position.

—  A slightly different or discrepant image will be formed.

—  after processing, the films commonly are viewed with a stereoscope that uses either mirrors or prisms to coordinate the accommodation and convergence of the viewer's eyes so that the brain can fuse the two image

applications

—  evaluation of bony pockets in patients with periodontal diseases.

—  morphology of the temporomandibular joint area.

—  determination of root configuration of teeth

—  assessmenot f the relationship of the mandibular canal to the roots ofunerupted mandibular third molar.

—  assessmenot f bone shape when placement of dental implants is considered.

—  disadvantages

—  Increased exposure to radiation

—  Depth perception cannot be appreciated by some people.

  

References

—  Dental Radiography: Principles and Techniques
by Joen I. Haring, Laura Jansen

—  Essentials of Dental Radiography and Radiology (4nd Edition)
by Eric Whaites

—  Oral Radiology: Principles and Interpretation
By Stuart C. White, DDS, PhD and Michael J. Pharoah, DDS

—  TEXT BOOK OF RADIOLOGY-  CHRISTENSEN.

—  TEXT BOOK OF ORAL RADIOLOGY; Freny karjodkar

—  THIEM’S ATLAS OF RADIOLOGY;

—  BRONSTEIN, D.L.; TOMASElTI, B.J.; and RYAN, D.E. (1981): Internal Derangements of the Temporomandibular Joint: Correlation of Arthrography with Surgical Findings, J Oral Surg 39:572-584.

—  Bone Scintigraphy as an Adjunct for the Diagnosis of Oral Diseases ; December 2002 ; Journal of Dental Education.

—  Ultrasound of salivary glands; ASUM ULTRASOUND BULLETIN; VOLUME 6 NUMBER 3 AUGUST 2003.

—  CURRENT STATUS OF SIALOGRAPHY* By HEUN Y. YUNE, M.D., and EUGENE C. KLATTE, M.D.; VOL. 115, No. 2, Seventy-second Annual Meeting of the American Roentgen Ray Society, Boston, Massachusetts, September 28- October 1, 1971.

—   Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science. 1991;254:1178.

—   Brezinski ME, Tearney GJ, Boppart SA, Swanson EA, Southern JF, Fujimoto JG. Optical biopsy with optical coherence tomography: feasibility for surgical diagnostics. J Surg Res. 1997;71:32-40.