Specialized Radiographic Technique Question And Answers

Specialized Radiographic Technique

Question 1. Write short note on xeroradiography.
Answer. This is a relatively new method of recording image and in this technique the usual silver halide films are not used. No chemical developer, fier and no darkroom is required.

Xeroradiographic Unit has Following Parts

• Conditioning unit.
• Processor or developing unit.
• Cassette-protecting selenium plate.
• Xerox opaque paper.
• Charged toner particles.

Read And Learn More: Oral Radiology Question And Answers

There are two systems in Xeroradiography

• The Medical 125 system
• The Dental 110 system

The Medical 125 system

• This method in based on electrostatic process similar to that used for xeroxing.
• Image is fist recorded on a plate which is made up of aluminum and is coated with a layer of selenium.
• Before put to use, selenium particles are given a uniform electrostatic charge and are stored in a unit called as conditioner.
• After charging the plate is ready for use, it is placed in light tight and air-tight cassettes.
• When X-rays are put on the film or the film is exposed it causes selective discharge of the selenium particles depending upon the amount of radiation used and the relative density of the object.
• Pattern of electric discharge on the plate is referred as latent image.
• Latent image is then converted into visible image by a process called development in a unit called processor.
• In the processor, the plate is exposed to charged powder particles called as toner.
• Unique feature of xeroradiographic technique is to have both positive and negative replica.
• When positive current is applied to the processor negative toner particles are attracted and vice versa.
• When the development is complete, the visible image is transferred to paper in a machine referred to as a developer.

Dental Xeroradiograph system

• The dental xeroradiograph system has a different physical design.
• The image receptor plates are the size no. l and 2 films and fi into the patient’s mouth.
• The image receptors are charged and processed into a final permanent image in a single piece of equipment.
• To make an image, the photoreceptor is charged at the output station. It is then put intraorally, exposed, and returned to the input station.
• The plate passes over a toner station, where charged toner particles suspended in a liquid, vehicle are deposited on the plate to develop the image.
• Next the plate is dried to remove the liquid vehicle. The image is recovered from the plate by using a clear adhesive transfer station.
• The adhesive tape is brought into contact with the plate and pulls of all the toner particles.
• The image is protected by applying the adhesive with the image to a translucent backing strip.

Xeroradiography Advantages

• Reduction in exposure time.
• Wide latitude of exposure.
• Ease in manipulation.
• Exam of viewing.
• High contrast.
• Good detail, as this method gives excellent definition of thin, fie structures due to edge enhancement.
• Height of alveolar crest better seen.
• Caries seen more readily.
• Useful in endodontics.
• Detection of cancer.
• Imaging biomaterials.

Xeroradiography Disadvantages

• Electrically charged plate causes discomfort to some patients.
• Edge enhancement artifacts.
• Processors are expensive.
• Slower speed.
• Temporary image retention.

Indications in head and Neck Region

• Periodontal and periapical assessment to show good bony details.
• Cephalometric radiography to show the required hard and sof tissue landmarks on one fim.
• Sialography to show fie duct structure.
• Assessment of soft tissue shadows in pharynx and larynx.

Question 2. Enumerate various specialized radiographic techniques and write in detail about sialography.
Answer. Enumeration of various specialized radiographic techniques

• Scanography
• Nuclear medicine
• Diagnostic ultrasound
• Arthrography
• Arthroscopy
• Xeroradiography
• Sialography
• Radiographic image storage via LASER optical technology.

Sialography

• Sialography is the specialized radiographic procedure used for detection and monitoring the salivary gland disease.
• This technique is used to examine the ductal and acinar systems of the major salivary glands. The glands are cannulated and filed with a radiopaque-contrast agent to make them visible on the radiographs. The procedure reveals the location and integrity of the salivary glands, and indicates the presence of diseases that change the internal architecture.

Indications of sialography

• For detection of calculus or calculi or foreign bodies, whether these are radiopaque or radiolucent.
• For determination of the extent of destruction of the gland secondary to obstructing calculi or foreign bodies. This will aid in deciding whether a total excision of the gland or a simple lithotomy should be performed.
• For detection and portrayal of fitulae, diverticula or strictures.
• For determination and diagnosis of recurrent swellings and inflmmatory processes.
• For demonstration of a tumor and the determination of its location, size and origin, whether the radiograph suggests a benign or a malignant lesion.
• In selection of a site for biopsy.
• Outline of the plane of the facial nerve as a guide in planning a biopsy or dissection.
• For detection of residual stone or stones, residual tumor, fitula or stenosis; or retention cysts following simple lithotomy or other surgical procedures.
• Sialography has also been recognized as a therapeutic procedure because:
  • The dilatation of the ductal system produced during the study may aid in the drainage of the ductal debris.
  • The therapeutic effct produced by the iodinated contrast media when injected into the ductal system has also been seen.

Contraindications of sialography

• In patient with a known sensitivity to iodine compounds and patients who have experienced severe asthmatic attcks or anaphylaxis following use of iodine compounds in a prior radiologic examination, should not be considered subjects for this technique. A history of nausea and vomiting following the intravenous injection of contrast media is not considered a contraindication.
• Use of sialography during a period of acute inflmmation of the salivary system is contraindicated. During this period, the ductal epithelium may be disrupted, and escape of the contrast medium from the ductal system into the parenchyma can produce severe foreign body reaction, accompanied by severe pain. This is especially true when the oily contrast medium is used. Foreign body reaction following the use of water soluble media has not been reported.
• Administration and retention of the iodinated contrast material may interfere with subsequent thyroid function tests, such function studies if required, should be done prior the sialography procedure.

Procedure of sialography

Armamentaria required for carrying out sialography:

• Polyethylene tubing with a special blunt end metallic tip with
  • Side hole for parotid gland
  • End terminal hole for submandibular gland
• 5 or l0 cc syringe.
• Lacrimal dilators.
• Contrast media.
• Sialagogue-like 5 lemon slices or lemon extract or chewing gum.
  • Locate the parotid orifice at the base of the papilla in the buccal mucosa adjacent to the fist or second molar.
  • Area over the mucosa where the duct orifice is expected to be located should be dried with a sponge.
  • If gland consists of some degree of function, a drop of saliva can be expressed by applying gentle pressure to the skin over main parotid area, thus identifying the location of the orifie.
  • Submandibular excretory duct orifice is situated over the summit of the small papilla at the side of the lingual frenum, but care should be taken to diffrentiate it from the sublingual gland orifies in the same region.
  • Explore the duct with lacrimal probe, after the appropriate orifie is identifid.
    • In case of the submandibular gland, the probe should pass through the length of the flor of the mouth to the level of the posterior border of the mylohyoid muscle, a penetration of about 5 cm.
    • Because of the tortuous course of the parotid duct, the cheek has to be turned outward before it is inserted into the duct. The aversion of the cheek will help reduce the possibility of penetrating the duct at one of the sharp angles in its course.
    • In both the parotid and submandibular ducts, the probe should slide easily back and forth and also rotate freely without dragging.
• When the duct orifie has been adequately sized and enlarged, the sialographic cannula is inserted into the duct so that the tissue stop presses fimly into the orifie to prevent dye reflx.
• After inserting the cannula, the radiopaque dye is slowly introduced into the duct. The amount of dye to be injected into the gland for adequate filing varies from patient to patient and depends on the condition of the gland.
• The amount used is best determined by fluoroscopic observation; the patient should be instructed to inform the operator when the gland area feels tight or full.
• Appropriate volumes of dye required vary from 0.76 to 1.00 mL for the parotid glands, and 0.0 to 0.75 mL for submandibular glands. The cardinal rule is that the injection should be stopped when the gland is full, if the dye is extravasated, or when the patient experiences mild discomfort.

Xeroradiography Radiographic Projections

• Filming procedure should be carried out with the patient in the supine position. Oftn several fims are obtained during the injection in order to monitor the filing phase and degree of filing.
• The lateral oblique projection or mandibular occlusal view is used to delineate the submandibular gland.
• In the lateral oblique view, the duct pattrn is not distorted, while a sialolith is well demarcated on the occlusal view. The AP view of both glands demonstrates the medial and lateral gland structures.
• In case of the parotid gland, the patient should be asked to keep the mouth open. The panoramic projection may also be taken, which is helpful in studying erosion of bone or destruction of the mandible, in case of salivary tumors.
• The evacuation (fat soluble medium) or the parenchymal phase (water-soluble medium)
  • After the fial sialographic views have been made, the cannula should be removed from the duct orifie. The patient is instructed to chew gum or the lemon slice and then asked to rinse. This is done to stimulate the gland and cause excretion of the dye.
  • Lateral jaw, lateral oblique or anteroposterior view radiographs should be made 5 minutes aftr removal of the cannula. They provide the information about the excretory function of the gland.
  • Normal salivary gland will excrete l00% of the contrast dye within 5 minutes aftr removal of the cannula.

Additional Views Required to be taken to study special Features

• Reverse basilar view to demonstrate the deep portion of the parotid.
• Afim made with the cheek in the blow-out position in the anteroposterior view to demonstrate the superfiial portion of the course of the Stensen duct of the parotid gland.
• Occlusal view for demonstration ofthe distal submandibular gland’s Wharton duct.
• Filming ofthe filing phase withthe mouthopenwill reduce superimposition of the mandible on the parotid gland.
• Stereoscopic studies are invaluable for the study of tube spatial relationships of the gland and the duct.
• Subtraction views are of great value in the delineation of the finer ducts and of the sublingual ductal system.
• Plesioradiography is a technique in which a small X-ray tube is placed in contact with the facial soft tissues contralateral to the gland being examined in an attempt to eliminate the obscuring overlying bony structures.

Question 3. Write short note on sialography.
Answer.

Sialography

It is a radiographic procedure that is useful diagnostic adjunct for the detection and monitoring of salivary gland disease.

The glands are cannulated and filed with a radiopaque contrast to make them visible on the radiograph.

Sialography Indications

• Detection of calculi or foreign bodies.
• Determination of the extent of destruction of gland secondary to obstructing calculi or foreign bodies.
• Determination and diagnosis of recurrent swelling and inflammatory processes.
• Demonstration of tumor and determinations of its location, size and origin.
• Selection of a site for biopsy.
• Detection of residual stones, residual tumors, fitula or stenosis or retention cysts following surgical procedure.

Sialography Contraindications

• Patient who is sensitive to iodine or experienced severe asthmatic attcks or anaphylaxis following use of iodine.
• During a period of acute inflmmation.
• In case of congenital aplasia and atresia.
• Iodinated contrast media may interfere with subsequent thyroid function tests, such function tests if required, should be done prior the sialography procedure.

Sialography Procedure

• A radiographic media is forced through orifice of duct into the gland.
• Keeping the radiopaque media in place a radiograph is taken.
• For submandibular sialograph and sublingual sialograph, a modified lateral oblique radiograph is the best projection and for parotid a modified posteroanterior view of injected side is best.
• Modified PA view for parotid is taken by having the patient puff his cheeks out forcing parotid gland away from the lateral border of mandible and then taking a PA exposure.

Question 4. Write short note on contrast agent.
Answer. Contrast agent in sialography is the compounds with high concentration of iodine.

Characteristics of an ideal sialographic contrast Media

An ideal sialographic contrast media should have the following characteristics:

• Physiological properties similar to that of saliva.
• Miscibility with saliva.
• Absence of local or systemic toxicity
• Pharmacological inertness.
• Satisfactory opacifiation.
• Low surface tension and low viscosity to allow filing of fie components of the ductal system.
• Easy elimination, but should be durable for suffient time so as to permit time for satisfactory radiographs.
• Residual contrast media should be absorbed by the salivary gland and detoxifid by the liver or excreted by the kidney.

Types of contrast Media

There are two types of contrast media available, i.e. water soluble and fat soluble

Water soluble Media

• These are principally iodinated benzene or pyridone derivatives.
• These compounds have a low viscosity, less surface tension and are more miscible with the salivary secretions.
• These physical characteristics permit filing of the fier ductal system under lower pressure and facilitate prompt drainage.
• Causes less pain or discomfort, with no granulomatous reaction, in the glands.
• Opacification of the water-based media is not as good as that of oil media.

Fat soluble Media (oil Based)

• There are two types of fat soluble contrast media, i.e. Iodized Oil and Water insoluble Organic Iodine Compounds.
• These compounds are more viscous have more surface tension and are less miscible with the salivary secretions.
• It requires a higher injection pressure than that of the water soluble media, to visualize fier ducts. Oil based media is poorly eliminated and causes ductal obstruction.
• Usually accompanied with pain and a lot of discomfort. Extravasation of the fat soluble media can produce severe foreign body reaction with focal necrosis of the parenchyma and stroma.
• The fat soluble contrast media on the whole produces a satisfactory degree of opacifiation. This is an excellent media, if the ductal systems under examination are intact.

Question 5. Write short note on sialography of parotid gland.
Answer. Following is the sialography procedure of salivary gland:

Armamentaria required for carrying out sialography in

Parotid gland:

• Polyethylene tubing with a special blunt end metallic tip with
  • Side hole for parotid gland
  • End terminal hole for submandibular gland
• 5 or l0 cc syringe.
• Lacrimal dilators.
• Contrast media.
• Sialagogue-like 5 lemon slices or lemon extract or chewing gum.

Sialography of parotid gland Procedure

• Parotid is the largest of all salivary glands and lie just below zygomatic arch in front and below the ear and on masseter muscle over the ramus of mandible. Duct from parotid gland i.e. Stensen’s duct run along outer surface of masseter to buccal mucous membrane opposite to upper second molar tooth.
• Locate the parotid orifie at the base of the papilla in the buccal mucosa adjacent to the fist or second molar.
• Area over the mucosa where the duct orifie is expected to be located should be dried with a sponge.
• If gland consists of some degree of function, a drop of saliva can be expressed by applying gentle pressure to the skin over main parotid area, thus identifying the location of the orifie.
• Explore the duct with lacrimal probe, aftr the appropriate orifie is identifid. Because of the tortuous course of the parotid duct, the cheek has to be turned outward before it is inserted into the duct. The aversion of the cheek will help reduce the possibility of penetrating the duct at one of the sharp angles in its course.
• In parotid ducts, the probe should slide easily back and forth and also rotate freely without dragging.
• When the duct orifie has been adequately sized and enlarged, the sialographic cannula is inserted into the duct so that the tissue stop presses fimly into the orifie to prevent dye reflx.
• Aftr inserting the cannula, the radiopaque dye is slowly introduced into the duct. The amount of dye to be injected into the gland for adequate filing varies from patient to patient and depends on the condition of the gland.
• The amount used is best determined by fluoroscopic observation; the patient should be instructed to inform the operator when the gland area feels tight or full.
• Each of the gland is examined turnwise and small amount of the contrasting medium should be injected.
• Appropriate volumes of dye required vary from 0.76 to 1.00 mL for the parotid glands. The cardinal rule is that the injection should be stopped when the gland is full, if the dye is extravasated, or when the patient experiences mild discomfort.

Sialography of parotid gland Radiographic Projections

• Filming procedure should be carried out with the patient in the supine position. Oftn several fims are obtained during the injection in order to monitor the filing phase and degree of filing. In case of the parotid gland, the patient should be asked to keep the mouth open. The panoramic projection may also be taken, which is helpful in studying erosion of bone or destruction of the mandible, in case of salivary tumors.
• In the later positioning, head is in exactly lateral position with angle ofmandible over shadowing each other. Central rays of X-rays are passed over the angle of mandible.
• In lateral oblique view, head is straight similar to lateral view. Only diffrence is that the central ray is projected below and behind the angle of jaw away from the fim, 250 towards the head.
• In frontal position i.e. AP view, median plane is kept at right angle to the fim. Head should be slightly raised and chin is lowered towards the chest. In such cases, view of main duct is clear as it crosses the mandible, but gland region is overexposed with intraglandular ducts which are largely obliterated.

The evacuation (fat soluble medium) or the parenchymal phase (water-soluble medium)

• After the fial sialographic views have been made, the cannula should be removed from the duct orifie. The patient is instructed to chew gum or the lemon slice and then asked to rinse. This is done to stimulate the gland and cause excretion of the dye.
• Lateral jaw, lateral oblique or anteroposterior view radiographs should be made 5 minutes aftr removal ofthe cannula. They provide the information about the excretory function of the gland.
• Normal salivary gland will excrete l00% of the contrast dye within 5 minutes aftr removal of the cannula.

Question 6. Write short answer on advantages and disadvantages of CBCT.
or
Discuss about CBCT. Write its advantages, disadvantages, indications and contraindications in dentistry.
Answer. Full form of CBCT is cone beam computerized tomography

CBCT introduces most complex and accurate imaging with 3D visualization as compared to routinely used analog and digital radiographs.

Advantages of CBCT

• Cone-beam computed tomography provides superior alternative technology for numerous complex interpretative procedures currently used, for example, in paralleling technique (SLOB rule) for location of foreign bodies or unerupted or impacted teeth. CBCT provides much more detail, added advantage of reduced exposure dose. Three dimensional nature of data obtained permits simple and direct visualization of structures of the complex maxillofacial anatomy.
• CBCT imaging is synchronized for craniofacial area, mainly for assessing bone and the dental hard tissue. Data acquired is compatible with commercial maxillofacial imaging softare available in the market for implant planning, orthodontic analysis, etc.
• X-ray beam limitation or collimation of primary beam is used to reduce the size of the irradiated area thereby minimizing the radiation dose. Most CBCT units have the facility for the operator to select the FOV as per the region prescribed by the dental surgeon. Hence, a small FOV can be adjusted to scan small regions for specifi diagnostic tasks and medium or large FOV for scanning the entire craniofacial complex.
• Image accuracy: CBCT units have isotropic voxel resolutions that are equal in all 3-D representing a precise degree of X-ray absorption. Size of these voxels regulates the resolution of the image. This produces submillimeter resolutions which are superior to the highest grade
• multislice CT ranging from 0.4 mm to 0.125 mm. Because of this characteristic and subsequent secondary (axial, coronal and sagittal) and MPR images realize a level of spatial resolution that is exact for measurement in maxillofacial applications where meticulous precision in all measurements is important for example facial growth in orthodontics analysis, implant site assessment, etc.
• Rapid scan time: CBCT acquires all basis images in a single rotation, so scan time is less and subsequently motion artifacts due to subject movement are reduced. These scan times are analogous to conventional dental panoramic imaging and newer helical CT units.
• Dose reduction: There is up to 98% reduction in the effctive dose ofradiation when compared with medical CT systems which consequently reduces the effctive patient dose.
• Reduced image artifact: CBCT images provide superior quality images of the oral anatomy as the secondary reconstructions are tailored for especially viewing the teeth and jaws, resulting in a low level of metal artifact as compare to the streak artifacts in CT images.
• Interactive display modes applicable to maxillofacial imaging: CBCT provides exclusive images representing features in 3D that conventional and digital intraoral and extra-oral techniques cannot. CBCT units reconstruct the projection data to make available inter – relational images in threeorthogonal planes (axial, sagittl, and coronal). Cursor driven measurement algorithms deliver the clinician with an interactive capability for real-time dimensional assessment. Onscreen measurements offr distortion and magnifiation free dimensions.
• CBCT gives adequate information for dental procedures without the patient undergoing the claustrophobic CT procedure at a much reduced cost.

Disadvantages of CBCT

• Cost for equipment and imaging studies.
• Radiation dose is high as compared to conventional radiographs. For most CBCT systems, the kVp is fied, and the tube current (mA) and exposure time (s) can be varied depending on the desired image quality and patient size. In current dental CBCT practice, this is typically performed either manually or through the selection of preset exposure protocols.
• Relative sophistication of operation and requires skilled and experienced personnel for interpretation of the resultant data. Especially when using a smaller FOV, as it is easy to become confused when scrolling through the images, inadequate orientation with the anatomical structures can make points of reference such as normal dental landmarks or anomalous anatomy diffilt.
• Cone-beam technology centered on an image intensifir may create distortion of periphery of images.
• Prolonged time is needed for image manipulation and interpretation.
• Artifact is one of the foremost factors in corrupting CBCT image quality and is thus a vital part in diagnostic precision.

Indications of CBCT

• In implant planning and anatomical considerations
  • It is indicated for cross-sectional imaging before implant placement as an alternative to existing cross sectional techniques where radiation dose of CBCT is shown to be lower.
  • It is also indicated in planning the precise implant position.
• In sinus lift procedures.
• In planning the templates
• In maxillofacial surgery.

Contraindications of CBCT

• Soft tissue pathology
  • TMJ discs
  • Vascular structures
  • Lymphatic structures
  • Muscles
  • Salivary glands: They would require sialography
• Metal
  • Steel, gold and silver produce stronger artifacts than titanium or aluminum
  • Higher atomic number = more metal artifacts
• Non-displaced fractures in roots or bone
  • cannot visualize non-displaced fractures directly
  • Must look for secondary signs of fracture in the surrounding bone
• Caries
  • Cannot diagnose caries adjacent to metal restorations
• Bone loss adjacent to implants
  • Metal artifacts prevent evaluation of osseointegration
• Patient factors
  • Age
  • Radiosensitivity (e.g. Gorlin-Goltz Syndrome)
  • Pregnancy
  • History of heavy radiation exposure
• Screening
  • CBCT is not a screening tool
  • There should be a diagnostic reason for the scan
• Reconstructing 2D images from 3D data

One would not take a 3D image just to reconstruct a 2D panoramic/cephalogram, ifall you want is a 2D panoramic/ cephalogram.

Question 7. Write short note on advantages of computed tomography.
Answer. Following are the advantages of computed tomography:

• CT scanners produce very high-resolution images. There are two types of resolution i.e. geometric and contrast. Conventional diagnostic radiographic technique provides images with fewer than 30 variations of gray, whereas CT scanning technology generates images with more than 200 shades of gray. The increased CT scan grayscale shows subtle variations in tissue density that is not discernable with conventional radiology.
• Evaluation of jaws with CT needs very precise patient positioning. Without specialized machines, it is necessary to reorient the patient for each series of images to keep image plane perpendicular to the alveolar ridge. The reformattd CT examination, onthe other hand, permits the production of all possible cross-sections from a single data acquisition without moving the patient or reconfiuring the X-ray machine, Each of these pictures produced in this manner can be localized in a three dimensional space, so that there is never a doubt as to which position of alveolar ridge is included in image.
• Dimensional accuracy of three-dimensional rendered images has been established. Linear measurements of anatomic structures are accurate to within 0.19 mm (0.28%) and angular measures are correct within 0.380 mm (1.39%). The linear measures of anthropologic dimensions of the skull using three-dimensional CT compared favorably with measurements made from original two dimensional slice data and are generally accurate to within 1 mm. Hence, it gives accurate assessment of bone height, width, ridge inclination, bone quality, anatomic spatial relationship, without any superimposition.
• Special dental processing softare programs, which are capable of greater enhancement of CT scan, show threedimensional image and one-to-one correspondence in contrast to conventional tomograms. These programs were introduced in 1987 and provide panoramic and crosssectional views in addition to three-dimensional images of either maxilla or mandible. Measures can directly made from CT fims.
• Use of CT scan splint lined with barium sulfate and methyl methacrylate in tooth portion of template permit the implant team to evaluate proposed tooth position, abutment selection and implant placement before initiating the therapy, especially in maxillary anterior region.
• Position of critical structures can be accurately assessed with bettr contrast sensitivity than fim tomography and less time consuming for multiple slices.
• It is helpful for patient education and the motivation.