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Authors: Dr. Suraj Agarwal

HIGHLIGHTS OF DIGITAL IMAGING

The digital revolution has propelled our field into the most dynamic times of medicine, rivalling the introduction of antibiotic, and introduction of X-rays. From the simple intra-oral periapical X-rays, advanced imaging techniques like computed tomography, cone beam computed tomography, magnetic resonance imaging and ultrasound have also found place in modern dentistry. Changing from analogue to digital radiography has not only made the process simpler and faster but also made image storage, manipulation (brightness/contrast, image cropping, etc.) and retrieval easier. The three-dimensional imaging has made the complex cranio-facial structures more accessible for examination and early and accurate diagnosis of deep seated lesions. The role of Oral and Maxillofacial Radiology was limited until the encroachment of neoplasms into the aerodigestive tract. The discovery of computed tomography(CT) scan in the 1970’s by Hounsfield gave an impetus to the field of radiology to think in three dimensions. With its ubiquitous presence, today multidetector computerized scan with 64 ring detectors has become the norm of the day.The advent of magnetic resonance imaging (MRI) was a quantum jump in diagnostic imaging of body, including imaging of head and neck pathology. It has added value for detection of soft tissue extent, marrow involvement, and perineural spread. The excellent tissue characterization and multiplanar imaging capability of MRI results in more accurate diagnosis of neoplastic and benign processes. Spin echo imaging is still the mainstay of MRI, but now various new techniques hold promise for the future of head and neck imaging.A new initiative in the field of MRI scan is blood oxygen level-dependent MRI. It is a non-invasive functional imaging technique that can identify hypoxic cancers which are likely to respond to accelerated radiotherapeutic treatment with radiosensitizers.


The introduction of cone beam CT (CBCT) has changed the face of maxillofacial radiology. Larger field of view helps to encompass an array of diagnostic needs. Higher resolution with minimal radiation is the key for the popularity of CBCT. Today, CBCT is synonymous with dental radiology for assessment of tumors, cysts, implant imaging, assessment of root canals for endodontic treatment, and a host of other indications.Ultrasonography (USG) has been reserved for imaging of the abdomen. However, with recent advances in the transducer systems, scope of USG has been extended to head and neck region also. The use of positron emission tomography (PET) has been instrumental in staging, identifying tumor recurrence, and evaluation of the prognosis of therapy. PET is based on tumor metabolic activity and hence is more sensitive than CT or MRI alone. The combination of PET with CT has added to the advantages of radionuclide imaging in dentistry. However, the frequency of use of PET by the maxillofacial radiologist has been dismal. This could be due to lack of knowledge and awareness about the various aspects of PET.
 

SECTIONAL ANATOMY OF MAXILLOFACIAL COMPLEX ON COMPUTED TOMOGRAPHY: PICTORIAL ASSAY: PART 1

INTRODUCTION

Da Vinci was the originator of cross sectional anatomy. The most admirable and important work done by him in the field of anatomy was the collection of drawings of the things he observed.These drawings were made with extreme perfection. He made a total of 500 diagrams in his 60 notebooks. The word Tomography can be traced to the 1920’s.Greek words tomos = section/slice &graphy = picture/describing. 1962: adopted by the International Commission on Radiological Units & Measurements to describe all forms of body section radiography.Mathematical principle for Tomography was given in 1917. Developed by Dr. Godfrey Hounsfield, Born 1919 in Nottinghamshire, England, First patient scanned in 1972 (Demonstrated a suspected brain lesion). Dr. Allan Cormack, Born 1924 in Johannesburg, South Africa, Developed solutions for the mathematical problems in CT. Both were awarded the Nobel Prize in 1979 for their contributions. To identify anatomical structure on the sectional images, a complete understanding of the basic anatomic is important for which 3D understanding develops.V iewing sectional images depicts a volume of the body or what is commonly called a slice of the body. Thickness of sections, varies from several mm to 1 cm. To visualize all structures within a given region of body, sections are typically taken in sequence and locations are annotated on the scanogram or scout image. Traditional anatomy focuses on names and shapes of anatomical structures.Sectional anatomy emphasis on the physical relationship among structures. Axial (also know as the transverse plane) plane cuts the body horizontally, into superior (upper) and inferior (lower) portions. Coronal (also known as the frontal plane) plane cuts the body vertically, into anterior (front) and posterior (back) portions. Sagittal plane cuts the body vertically, into left and right portions.

Computed Tomography

Radiographic technique that blends the principle of thin layer radiography with computer synthesis.Digital & mathematical imaging technique that creates tomographic sections where the tomographic layer is not contaminated by blurred structures from adjacent anatomy.(Dental &Maxillofacial Radiology, 2nded, Freny). The use of X-ray based imaging method to produce 3D images, usually displayed in the form of image slices (ContemporaryDental&Maxillofacial Imaging, Oct 2008, Vol 52,Nno. 4).


CONCLUSION

CT image has become useful for the diagnosis of disease in the maxillofacial complex, including the salivary gland and TMJ. Thus athrough knowledge about Interpretation of various anatomical landmarks on CT is essential for Dental surgeons for the diagnosis of pathologies related to orofacial region in day to day practice.
 
TISSUE; CT No.
Air - 1000
Lung - 200
Fat - 100
Water 0
CSF + 15
Blood + 20
Gray Matter + 40
White Matter + 45
Muscle + 50
Medullary Bone + 300
Cortical Bone + 1000
 
References
  1. 1. Webb S. Historical experiments predating commercially available computed tomography. Br J Radiol. 1992;65:835–837.
  2. 2. Hounsfield GN. Historical notes on computerized axial tomography. J Can AssocRadiol. 1976;27:135–142.
  3. 3. Bull J. History of computed tomography. In: Newton TH, Potts DG, eds. Technical
  4. 4. Aspects of Computed Tomography. St. Louis, MO: C.V. Mosby Co.; 1981:3835– 3849.
  5. 5. Hounsfield GN. Computerized transverse axial scanning (tomography), part 1: description of system. Br J Radiol. 1973;46:1016–1022.
  6. 6. Introduction to Computed Tomography. General Electric Co.; 1976.
  7. 7. Ledley RS, Di Chiro G, Luessenhop AJ, Twigg HL. Computerized transaxial x-ray tomography of the human body. Science. 1974;186:207–221.
  8. 8. T.B.Moller, E.Reif. Pocket Atlas of Sectional Anatomy, Computed Tomography & Magnetic Resonance Imaging. Vol 1. Head & Neck, 3rd Edition.
  9. 9. Mahmood F. Mafee, GaldinoE.Valvassori. Imaging of Head & Neck. 2nd Edition.

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