RADIOLOGY INTERPRETATION

655

Panoramic Radiography

Robert A. Cederberg, MA, DDSProfessor, Dept. of Restorative Dentistry & Biomaterials

University of Texas HSC at Houston Dental Branch

PANORAMIC RADIOGRAPHYPANTOMOGRAPHY

Linear Tomography

Panoramic Radiography Radiographic technique for

producing a single image of both maxillary and mandibular arches and their supporting structures.

Drs. Paatero and Numata were the first to describe the principles of panoramic radiography.

Historical DevelopmentPanoramic radiographs can be made

using two different methods:

1. Use of an intraoral source of radiation

2. Use of an extraoral source of radiation

a. Film placement is intraoral

b. Film placement is extraoral

Panoramic RadiographyIntraoral Source of Radiation

Status-X, Siemens Co., Erlangen, Germany

Development of Extraoral Source of Radiation

Dr. Numata was the first to propose this method in 1933. He placed a curved film in the mouth lingual to the teeth and used a slit beam of radiation which rotated around the patient’s jaw to expose the film. The patient was stationary.

ParabolographyDr. Paatero

Parabologram of maxillary teeth

Dr. Paatero in 1946 demonstrated a similar method using a rotating chair.

Pantomography(Linear Tomography) Dr. Blackman collaborated with Dr.

Paatero using a pantomographic technique.

Watson & Sons, Ltd. in collaboration with Dr. Blackman developed the first commercial model of the pantomograph known as the Rotograph.

Rotary Radiography

RotographWatson & Sons, Ltd., Wembley, England

Development of Orthopantomographic Technique

Limitations of Rotary panoramic technique: rotation of patient and film in circular paths (jaws are not circular but elliptical), overlapping of teeth posteriorly and streak artifacts.

Orthopantomograph uses 3 rotation centers producing an elliptical path of rotation. Paatero – first prototype 1958.

Orthopantomograph

Panoramic Radiography Advantages:

Broad anatomic coverage Relatively low patient radiation dose Convenience and speed of the exam Easily tolerated by patients - Ex:

patients who are unable to open their mouths

Easy to explain treatment plans

Panoramic RadiographyDisadvantages:

Does not resolve fine detail, consequently additional images (PA, BW) required

Magnification Distortion and overlapping of teeth Objects located outside the image

layer are distorted, obscured or not seen

Principles of Rotational Panoramic Radiography

Panoramic radiograph is unique in the foci of projection

Focus of projection is not the same in the vertical and the horizontal planeHorizontal plane - center of rotationVertical plane - x-ray source

Central projection:

Principles of Rotational Panoramic Radiography

X-ray source placed intraorally and curved film is placed extraorally, still a central projection, although magnified equally hor. & vert.

Principles of Rotational Panoramic Radiography

If you replace the stationary intraoral x-ray source with an extraoral

rotating slit beam x-ray source, magnification will be equal in the rotation or horizontal plane but different in the x-ray source or vertical plane.

Principles of Rotational Panoramic Radiography

Principles of Rotational Panoramic Radiography

The combination of a rotating beam and a moving film changes the horizontal dimension of the recorded image, but the projection of the object remains the same, so that the proportions are restored in the resultant image.

Principles of Rotational Panoramic Radiography

Panoramic Cassettes

Screens

Panorex

Panelipse

Focal Trough The three-dimensional curved zone or

Image Layer in which structures are well defined.

Focal trough size affected by arc path, velocity of the film and x-ray tube, beam alignment, and collimator width.

Influence of Patient Positioning on Image Magnification

As the position of the object is moved within the focal trough the size and shape of the resultant image change.

Influence of Patient Positioning on Image Magnification

Correct Position

Forward Position

Backward Position

Correct Patient Positioning and Head Alignment Occlusal plane 20 to 30 degrees

below horizontal Tragus to outer canthus is parallel to

the floor Back and spine erect and neck

extended Groove of bite block is positioned

inter-incisally and midline is centered Tongue placed in roof of the mouth

Correct Patient Position and Head Alignment

Improper Patient Positioning

Too Far Forward

Improper Patient Positioning

Positioned Too Far Back

Improper Patient Positioning

Chin Too Far Up

Improper Patient Positioning

Chin Tilted Down

Improper Patient Positioning

Patient placed in slumped position

Slumped Correct

Improper Patient Positioning

Rotated Position

Ghost Images

Superimposition of structures from the contralateral side to the side being viewed

Ghost Images

Improper Patient Positioning and Patient Preparation

Improper Patient Positioning and Patient Preparation

Improper Patient Positioning and Patient Preparation

Improper Film and/orCassette Handling

Improper Film and/orCassette Handling

Improper Exposure Techniques

hard palate

pterygomaxillary fissure

hyoid bone

tongue shadow

infraorbital canal

infraorbital rimmaxillary sinus

Soft Palate & Uvula Floor of Nasopharynx

Inferior Alveolar Canal Cornoid Notch

Articular Tubercle Angle of the Mandible

condylecoronoid process

nasal septumlateral wall of nasal fossa

zygoma zygomatic arch

Panoramic Radiographic Anatomy – Hard Tissues

Panoramic Radiographic Anatomy – Soft Tissues