DEN 130 1 H - Dental Radiology- 25

Panoramic Imaging Notes

Chapter Overview

  • Subject: Panoramic Imaging

  • Chapter Number: 22

Learning Objectives

  • Definition of Key Terms:

    • Understand key terms associated with panoramic imaging.

  • Purpose and Uses:

    • Describe the uses of panoramic imaging, including diagnostic utility.

  • Fundamentals:

    • Explain the basic concepts that underlie panoramic imaging.

  • Equipment:

    • Identify types of equipment utilized in panoramic imaging.

  • Procedures:

    • Describe patient preparation, equipment preparation, and positioning procedures essential before exposing a panoramic projection.

  • Diagnostics:

    • Describe what constitutes a diagnostic panoramic image.

  • Error Identification:

    • Identify common patient preparation and positioning errors in panoramic imaging and discuss their causes and corrections.

  • Advantages and Disadvantages:

    • Discuss pros and cons of panoramic imaging.

Introduction to Panoramic Imaging

  • Purpose:

    • Present the fundamental concepts of panoramic imaging.

    • Describe necessary procedures for patient and equipment preparation.

Basic Concepts of Panoramic Imaging

  • Image Characteristics:

    • Panoramic images illustrate a wide view of both upper and lower jaws.

    • This imaging technique is used to examine the upper and lower jaws captured in a single projection; categorized as an extraoral technique.

Specific Uses of Panoramic Imaging

  • Evaluation of:

    • Dentition and Supporting Structures: Assess the formation and condition of teeth and supporting elements.

    • Impacted Teeth: Identify teeth that have not erupted properly or are obstructed.

    • Eruption Patterns: Observe developmental patterns within the dental framework.

    • Pathology: Detect diseases, lesions, or conditions affecting the jawbones.

    • Extent of Large Lesions: Examine the size and spread of significant abnormalities.

    • Trauma Evaluation: Analyze the effects of injuries to the jaw area.

  • Limitations:

    • Panoramic images typically lack the sharpness and definition compared to intraoral projections.

Fundamentals: Mechanics of Panoramic Imaging

  • Imaging Process:

    • The receptor and x-ray tubehead rotate around the patient, coordinating movements in opposite directions.

    • The patient can adopt either a standing or sitting position during imaging.

Tomography in Panoramic Imaging

  • Tomography Explained:

    • An imaging technique where only a specific layer or section of the body is visualized while structures in other planes become blurred.

Rotation Center

  • Definition:

    • The pivotal point or axis around which the cassette carrier and x-ray tubehead rotate.

    • Modern panoramic x-ray systems utilize a continuously moving center of rotation, rather than fixed locations, enhancing imaging efficiency.

Focal Trough

  • Definition:

    • A three-dimensional curved zone where structures are depicted clearly on the panoramic image.

    • Guides the positioning of dental arches for optimal image quality.

Resultant Image Types

  • Real Image:

    • Produced when structures are correctly positioned between receptor and moving rotation center.

  • Double Image:

    • Occurs when an anatomical structure located behind the rotation center is penetrated by the x-ray beam twice.

  • Ghost Image:

    • Results from objects located outside the focal plane being passed close to the x-ray source, yielding an indistinct and larger image on the opposite side of the receptor.

Equipment Used in Panoramic Imaging
Panoramic X-ray Units

  • Components:

    • All units feature similar components:

    • X-ray tubehead

    • Head positioner

    • Exposure controls

X-ray Tubehead Characteristics

  • Collimator:

    • Unlike intraoral versions, panoramic x-ray units employ a lead plate with an opening in a narrow vertical slit that focuses the x-ray beam.

Image Receptors

  • Types of image receptors:

    • Direct Digital Sensor

    • PSP Plate

    • Film:

    • Specifically, screen film is used, sensitive to light emitted by intensifying screens and positioned between two screens in a light-tight cassette.

Intensifying Screens

  • Calcium Tungstate:

    • Emits blue light.

  • Rare Earth:

    • Emits green light and requires lower radiation exposure compared to calcium tungstate.

Cassette Specifications

  • Function:

    • Holds the extraoral film and intensifying screens.

    • Must be light-tight, may be rigid or flexible, and labeled to indicate the orientation of the finished image.

Step-by-Step Procedures

  • Equipment Preparation

    • Steps to prepare equipment for panoramic imaging:

    1. Prepare Receptor:

      • Load the film in the cassette using safelight conditions in a darkroom.

      • Securely close after placing extraoral film and two intensifying screens inside.

      • Load cassette into panoramic unit's cassette carrier.

    2. Prepare Bite-Block:

      • Cover with plastic to maintain sterility. If no covering, sterilize between uses.

    3. Choose Exposure Settings:

      • Set exposure factors in line with manufacturer's recommendations, varying settings based on patient size.

    4. Adjust Machine Height:

      • Modulate the machine's height to fit patient’s size while aligning movable elements.

  • Patient Preparation:

    • Explain the procedure thoroughly to the patient.

    • Remove obstructive items from head and neck.

    • Use a lead apron without a thyroid collar for safety, preferably a double-sided design.

  • Patient Positioning:

    1. Instruct the patient to maintain a tall and straight posture.

    2. Ensure the bite-block is used correctly.

    3. Make the midsagittal plane perpendicular to the floor.

    4. Align the Frankfort plane parallel to the floor.

    5. Use light guidance to ensure the patient’s teeth align with the focal trough, focusing on canine alignment.

    6. Instruct to close lips around the block, swallow, and place the tongue against the roof of the mouth.

    7. Instruct the patient to remain still as the imaging process occurs.

Quality of Diagnostic Panoramic Images
Factors for Diagnostic Quality

  • Key attributes of a diagnostic panoramic image include:

    • Correct equipment preparation, patient preparation, and patient positioning.

    • Must exhibit accurate anatomy visualization, consistent density, and contrast.

    • Important features include:

    • Anterior teeth must be in clear focus and pulp chambers visible.

    • Anterior teeth proportions should be accurate (not too skinny or fat).

    • Posterior teeth should visually match in size on both sides.

    • Both condyles must be present in the image.

    • The palate must appear above the maxillary teeth apices.

    • Ramus width should be equal on both sides.

Density and Contrast Requirements

  • Diagnostic images should feature adequate exposure levels to ensure correct density and contrast, where proper conditions allow for clear identification of enamel-dentin junctions in molar areas.

Common Errors in Panoramic Imaging
Patient Preparation Errors

  • Ghost Images:

    • Artifacts caused when metallic objects are penetrated twice, appearing larger and indistinct on images.

    • Problem: Objects not removed lead to obscured diagnostic clarity.

    • Solution: Instruct patients to remove radiodense objects from the head and neck prior to imaging.

  • Lead Apron Artifact:

    • A cone-shaped radiopaque artifact occurs due to improper lead apron placement or the use of an apron with a thyroid collar.

    • Problem: This obscures important diagnostic details.

    • Solution: Use a lead apron without a thyroid collar for panoramic imaging.

Patient Positioning Errors

  1. Lips and Tongue Position:

    • If lips are not closed, or tongue is not on the palate, dark shadows obscure teeth details.

    • Solution: Ensure proper instruction to close lips and place tongue during the exposure.

  2. Chin Tipped Up:

    • Causes a “reverse smile line” to appear in the image.

    • Problem: Higher chin misalignment.

    • Solution: Ensure Frankfort plane is parallel with the floor.

  3. Chin Tipped Down:

    • Yields an “exaggerated smile line.”

    • Problem: Low chin positioning identified.

    • Solution: Again, Frankfort plane must be aligned parallel with the floor.

  4. Teeth Anterior to Focal Trough:

    • Results in “skinny” and out-of-focus anterior teeth.

    • Solution: Position the teeth end-to-end in the groove of the bite-block.

  5. Teeth Posterior to Focal Trough:

    • Produces “fat” and out-of-focus anterior teeth.

    • Solution: Similar alignment as the previous positioning error.

  6. Head Turned:

    • Causes unequal magnification of the ramus and posterior teeth, with the farthest side appearing larger.

    • Solution: Center the midsagittal plane with the floor while ensuring midline is aligned on the bite-block.

  7. Slumped Posture:

    • Improper posture can introduce a radiopacity of the cervical spine obstructing diagnostic usefulness.

    • Solution: Instruct to maintain an upright, straight-back posture during imaging.

Advantages of Panoramic Radiography

  • Field Size:

    • Ability to capture a broad view of anatomical structures.

  • Simplicity:

    • Procedure is less complex than other imaging methods.

  • Patient Cooperation:

    • Generally, patients find the technique non-intrusive and easier.

  • Minimal Exposure:

    • Radiographic exposure levels are comparatively lower.

Disadvantages of Panoramic Radiography

  • Image Quality:

    • Less sharpness compared to intraoral images.

  • Focal Trough Limitations:

    • Restrictions in focal trough can limit imaging quality.

  • Distortion:

    • Possible distortion in images due to positioning variability.

  • Equipment Cost:

    • Initial costs for panoramic x-ray units can be high.

Conclusion

  • The notes detail the comprehensive aspects of panoramic imaging including objectives, basic concepts, common errors, and the advantages and disadvantages of the technique. This will serve as a definitive guide for anyone studying panoramic radiography.