Basic Concepts of Other Imaging Modalities Dent 5101

Body-section Radiography A special radiographic technique that blurs out the shadows of superimposed structures Object of interest less blurred Does not improve the sharpness

Tube and Film Move in Opposite Direction

Tube and film move in opposite direction, and rotate about a fulcrum The level of the fulcrum is the focal plain

Blurring Determined by: Distance of the tube travel Distance from the focal plain Distance from the film Orientation of tube travel

Types of Tomographic Motions Linear Circular Elliptical Figure 8 Hypocycloidal Trispiral

Panoramic Radiography

Panoramic Radiography Obtained by rotating a narrow beam of radiation in the horizontal plane The film is rotated in the opposite direction while the object (jaws) is stationary

Focal Trough A 3-dimensional curved zone or image layer in which structures are reasonably well defined.

Types of Panoramic Machines Panorex – Two centers of rotation. Interruption of exposure in the midline Orthopantomogram – Three centers of rotation. Continuous image

Panorex Image

Orthopantpmograph

Image Intensification

Early Fluoroscopy Early fluoroscopy done by direct observation Screen was poorly illuminated - image perception inadequate

Image Intensification Image intensifier improved viewing of fluoroscopy

Intensifier Tube Four parts: Input phosphor and photocathode Electrostatic focusing lens Accelerating anode Output phosphor

Intensifier Tube (Cont.) Input phosphor: cesium iodide (CsI) or zinc-cadmium-sulfide. Photocathode: A photo-emissive metal. Electrostatic focusing lens: series of negatively charged electrodes—focuses the electron beam. Output phosphor: Provides thousand-fold more light photons.

Intensifier Tube Used in: Sialography Arthrography

Digital Imaging

Digital Imaging Conventional film-intensifying screen radiograph - analog image. Digital radiograph—film-less. Conventional films can be digitized, with a likelihood of loss of information.

Photostimulable Phosphor (PSP) Storage phosphor Indirect Digital Radiography Similar to the intensifying screen phosphors Difference - PSP traps a significant number of electrons in its phosphor, which is later read by a laser beam

Photostimulable Phosphor (PSP)

Charge-coupled Devices An amorphous silicon wafer containing an array of pixels (picture elements) Each pixel acts as a capacitor storing charge On radiation exposure, electric charge is deposited in the pixels proportional to the intensity of the beam The variation in charge deposition can be digitally converted to an image

Pixels Each square (pixel) has its own color (numerical value)

Pixel Array

CMOS Complimentary Metal Oxide Semiconductor Principle similar to CCD Simpler circuit design

CCD, CMOS

Resolution Ability to identify two different objects that are close to each other D-speed films: >10 line pair/mm Digital images:7-10 line pair/mm Eyes: 4-6 line pair/mm

Digital Subtraction Shows changes in an area over time Requires two films exposed with similar geometry

Digital Subtraction Two radiographs are obtained Identical position One superimposed over another Differences in two images identified digitally Allows identifying changes in hard tissue that occurred between the two examinations

Radiation Dose Full Mouth Series D Round 8 days E 4 days Digital Receptor Collimation Background equivalent D Round 8 days E 4 days Digital 2 days Rectangular 1 day

Image Processing/Reconstruction To improve diagnostic accuracy May improve the diagnosis of one disease, while obscure another Fraud

Digital Radiography: Advantages Instant images Consistent quality High signal/noise ratio Image Manipulation Lower radiation dose

Disadvantages Lower resolution Quality depends on monitor and printer Print quality often not optimal Higher initial cost Unwanted manipulation of images