Advanced Imaging

7/28/2019 Advanced Imaging

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ULTRASONOGRAPHYThe human Ear can detact sound in thefrequency of 1500-20,000 cycles persecond (hertz). Sound waves travelling in

the frequency greater than 20 (kHz) aredesignated as ultrasound.

Medical and dental diagnostic imagingsound waves in the range of 1-20 mHzare used.


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WORKING PRINCIPLE

The equipment used for ultrasonograpbhy is made up oftwo principal components, namely the scanner and thetransducer. The scanner generates electrical impulsesand the transducer converts these electrical impulsesinto sonic waves.

The transducer is made of Zirconate Titanate crystal(piezo electric crystal). When electric impulses from thescanner are applied to the crystals due to realignment ofthe dipoles, the crystal changes its thickness therebyproducing sonic vibration. These sonic vibrations aredirected towards the target region in the body. The tissueinterface reflects the ultrasound to produce echoes. Thereflected echoes are picked up by the transducer andconverted back to electrical signals. These signals aredisplayed on the computer monitor as black, white and

gray images.


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INDICATIONS1. To assess the content and location of soft tissue tumor.

2. To assess vascularity of soft tissue masses.

3. to estimate the extent of fascial space infections.4. Evaluation of salivary gland tumors.

5. Temporomandibular joint imaging.

ADVANTAGES1. Widely available and inexpensive.

2. No known harmful effects of ultrasound.

3. Can be used effectively to differentiate between different softtissue masses.

LIMITATIONS1. No image produced when tissue absorb ultra

sonic waves.

2. not effective

air filled cavities bone and calcified str.


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CONVENTIONAL TOMOGRAPHYSince the introduction of CT, MRI, cone beam imaging, which have superiorcontrast resolution, film based. Tomography has been used less frequently.

When C. Tomography used in dentistry, it is applied primarily to high contrastanatomy such as TMJ and dental implant imaging.

Conventional Tomography uses an x-ray tube and radiographic film rigidlyconnected and capable of moving about a fixed axis.

The examination begins with the x-ray tube and film positioned on opposite

side of fulcrum, which is located within the body of focal plane.

As the exposure begins, the tube and film move in opposite direction.Simultaneously through a mechanical linkage. With this synchronousmovement of tube and film, the images of objects located within the focalplane (at the fulcrum) remain in fixed positions on the radiographic filmthroughout the length of tube and film travel and are clearly imaged. On the

other hand, the images of objects located outside the focal plane havecontinuously changing positions on the film; as a result, the images of theseobjects are blurred beyond recognition by motion unsharpness. The resultingzone of sharp image is called the tomographic layer. Blurring of overlyingstructures is greatest under the following circumstances:

Overlying structures lie far from the focal plane.

The focal plane lies far from the film.

The distance of tube travel is large.


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TYPES OF TOMOGRAPHICMOVEMENT

Linear, Circular, Trispiral, Elliptical,

Hypocycloidal and spiral.


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i) Tomography of sinus. Affords the followingadvantages:

It gives a more precise evaluation of sinuspathologies which are poorly visualizes onroutine radiogaphy.

When a pathology is strongly suspectedclinically, but plain films are negative.

Sphenoid and ethonoidal sinuses are moreclearly visualized.

ii) Tomography of facial bones, to study facial

fractures. Extent of orbital blow out fractures.iii) Tomography of the mandible.

iv) Tomography of the TMJ, especially when the pt. isunable to open his mouth or in conjunction witharthrography.

v) For dental implant patients.

TOMOGRAPHIC VIEWS ARE USED TO EXAMINE VARIOUS

FACIAL STRUCTURES:


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Advanced Imaging

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