Specialized Radiographic Techniques Notes

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Specialized Radiographic Techniques Important Notes

  • Xero radiography uses photoconductive selenium plates instead of film.
    • It produces images with high contrast, resolution, edge, enhancement, positive and negative display.
  • Computer tomography (Axial tomography or computerized axial transverse scanning)
    • CT scanner consists of a radiographic tube that emits a finely collimated fan-shaped X-ray beam that is directed to a series of scintillation detectors or ionization chambers.
    • The CT image is recorded and displayed as a matrix of individual blocks called voxels.
    • Each square of the image matrix is called a pixel.
    • For image display each pixel is assigned with a CT number representing density.
    • These numbers are also known as Hounsfield units, which may range from – 1000 to +1000
    • Each constitutes a different level of optical density.
    • To convert a two-dimensional CT image into a three-dimensional CT image, each rectangular solid voxel is dimensionally altered into multiple cuboidal voxels.
    • This process is called INTERPOLATION.
    • IT Creates sets of evenly shaped cuboidal voxels (Aubervilliers) that occupy the same volume as the original voxel.
    • Computed tomography is useful in evaluating structures in and adjacent to salivary glands.
    • It distinguishes both soft and hard tissues as well as minute differences in soft tissue densities.
    • It is useful in assessing acute inflammatory processes and abscesses as well as cysts, mucoceles, and neoplasias.
  • Salivary gland radiology:
    • Arcelin: Introduced sialography in 1913. Jacobvisi introduced the sialography technique.
    • Contrast agents used in sialography are
      • Water soluble – Eg: Pyridone, Singoaffin
      • Fat-soluble – Eg: Lipidiol, Ethiodol
    • Water-based contrast agents are used for chronic inflammatory lesions
    • Oil-based contrast agents are used in neoplasms.
    • Different projection after injection of contrast agent.
  • Nuclear medicine/ scintigraphy provides a functional study of salivary glands.
    • The isotope used in the technique is “99 Tc – per technetate”.
    • All major salivary glands can be studied at once by scintigraphy.
    • It is especially advantageous for conditions in which sialography is contraindicated as well as for patients whose ducts can not be cannulated.
  • Ultrasonography is a relatively inexpensive, widely available painless, easy-to-perform, and non-invasive technique.
    • The primary application of ultrasonography is for the differentiation of solids from cystic ones.
  • Radiographic techniques

Oral Radiology Specialized Radiographic Techniques Radiographic Techniques 1

Read And Learn More: Oral Radiology Question and Answers

Oral Radiology Specialized Radiographic Techniques Radiographic Techniques 2

Specialized Radiographic Techniques Short Answers

Question 1. Indications and contraindications of sialography.
Answer.

Indications:

  • Detection of calculus or foreign bodies
  • Determination of the extent of destruction of the gland secondary to obstructing calculi or foreign bodies
  • Detection of fistula, diverticula, or strictures
  • Determination and diagnosis of recurrent swellings and inflammatory processes
  • Demonstration of a tumor and the determination of its location, size, and origin
  • Selection of a site for biopsy
  • Outline of the plane of the facial nerve
  • Detection of residual stones
  • Sialography can be used for therapeutic procedures

Contradictions:

  • Patients with known sensitivity to iodine
  • During the presence of acute inflammation
  • It may interfere with subsequent thyroid function tests

Question 2. Technique for transcranial view of TMJ
Answer.

Transcranial projection:

Structure Seen:

  • Useful in detecting arthritis of the articular surfaces
  • To evaluate the joint’s bony relationship

Film Position:

  • The cassette is placed against the patient’s ear and centered over the TMJ of interest
  • It is placed parallel to the sagittal plane

Patient’s Position:

  • The sagittal plane must be vertical
  • The ala tragus line should be parallel to the floor
  • The view is taken with
    • Open mouth
    • Rest position
    • Closed mouth

Central Ray:

  • It differs according to the technique
    • Postauricular
      • Point of entry is 1/2 “behind and 2” above the auditory meatus
    • Grewcock approach
      • The path of entry is through point 2 above the auditory meatus
    • Gill’s approach
      • Point of entry is 1/2 “anterior and 2” above the auditory meatus
    • Angulation: +20º To +25º
    • Point Of Exit: TMJ of interest

Question 3. Indication of sub mento vertex view.
Answer.

Indication of sub mento vertex view

  • To demonstrate the base of the skull
  • To examine the position and orientation of the condyle and sphenoid sinus
  • To reveal the fracture in the zygomatic arch of the maxilla
  • To assess the medial and lateral pterygoid plates

Question 4. Radionuclide imaging.
Answer.

Method:

  • Radioactive substances should be injected intravenously into the patient
  • Rectilinear scanner or gamma scintillation camera records the gamma emission from the patient
  • The camera uses a scintillation crystal that can fluorescence on interaction with gamma rays emitting from the radioactive substances
  • The emitting light fluorescence is detected by a photomultiplier tube that magnifies and amplifies the signals many times to produce an image

Atom Used:

  • Iodine
  • Gallium
  • Selenium
  • Technetium

Specialized Radiographic Techniques

Question 5. Digital imaging.
Answer.

Digital imaging

  • The use of digital technology results in a 50 to 90% reduction in patient radiation exposure because of the greater sensitivity of the digital receptor

Digital Imaging Types:

  • Direct digital radiography
  • Indirect digital radiography

Digital imaging Uses:

  • It can be used to view the images where multiple images are required for analyzing
  • In endodontic practice, the root canal length, working length, and distance between obturating material and the root apex
  • In periodontics, to assess and measure the height of the alveolar bone
  • It can be used in a patient who is un cooperative for regular radiographic techniques
  • To evaluate the bony changes in the pathology of jaws
  • To detect early dental caries

Question 6. Sialography – indications
Answer.

Sialography – indications

  • Detection of calculus or foreign bodies
  • Determination of the extent of destruction of the gland secondary to obstructing calculi or foreign bodies
  • Detection of fistula, diverticula, or strictures
  • Determination and diagnosis of recurrent swellings and inflammatory processes
  • Demonstration of a tumor and the determination of its location, size, and origin
  • Selection of a site for biopsy
  • Outline of the plane of the facial nerve
  • Detection of residual stones
  • Sialography can be used for therapeutic procedures

Viva Voce

  • Transpharyngeal projection is used for viewing the lateral surface of the condylar head and neck
  • Reverse Towne’s projection is used for viewing the posterior aspect of both the condylar head and neck
  • Selenium plate is used in xeroradiography
  • Water’s view is used to view maxillary sinus

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