Fluoroscopy Lecture Notes

Fluoroscopy Study Notes

Chapter Overview

  • Instructor: Mrs. Beirdneau, M.A.Ed., R.T.(R)(MR)

  • Focus: Understanding fluoroscopic imaging exams, the technology involved, and safety protocols.

Objectives

  • Differentiate fluoroscopic examinations from static diagnostic radiographic examinations.

  • Describe the typical basic fluoroscopic imaging chain.

  • Explain the differences in operation between fluoroscopic and diagnostic x-ray tubes.

  • Explain the types of fluoroscopy equipment.

  • Describe the functions and operations of the following components:

    • Image Intensification Tube Input Screen

    • Photocathode

    • Electrostatic Focusing Lenses

    • Anode and Output Screen

  • State the formula for brightness gain.

  • Explain the basic function of automatic brightness control in fluoroscopy.

  • Discuss factors affecting fluoroscopic image quality:

    • Contrast

    • Resolution

    • Distortion

    • Quantum mottle

  • Explain digital fluoroscopic image acquisition.

  • Differentiate between multiple-detector and single-detector flat-panel systems.

  • Discuss methods for reducing radiation dose to:

    • Patients

    • Radiographers

    • Radiologists

Historical Development

  • Dynamic Examination: Evolved to allow active diagnosis, primarily within the radiologist's domain.

  • Fluoroscope: Invented by Thomas Edison in 1896. Components included:

    • X-ray tube

    • Hand-held fluoroscopic screen

  • Initial exposure risks observed included high radiation to eyes, neck, and hands.

  • Image Intensification: Developed in 1948 to improve imaging quality; replaced the original fluoroscopic approach with closed-circuit TV systems by 2005.

  • Shift to Digital Fluoroscopy: Enabled use of TFT matrices and post-processing capabilities.

Fluoroscopic Imaging Chain

  1. Specialized x-ray tube

  2. Image receptor

  3. Fluoroscopic screen

  4. Mirrors for viewing (now obsolete)

  5. Image intensification

  6. Video camera and monitor

Uses and Positioning

  • Functional Studies in Fluoroscopy:

    • Gastrointestinal (GI) tract studies

    • Angiograms

    • Line placements

    • Orthopedic surgeries

  • Positioning Considerations:

    • Radiographers must undergo training in patient positioning to avoid unnecessary radiation exposure.

    • Equipment should not be used to preview radiographic positions of patients.

Types of Equipment

  • C-arm Support: Portable systems for various settings.

  • Carriage Assembly: Integrated framework for structural support.

  • X-ray Tube Placement: Options include under-table or over-table systems for accurate image acquisition and dose optimization.

  • Image Receptor Positioning: Can adjust for accuracy and radiation savings.

Fluoroscopic X-Ray Tubes

  • mA Range: 0.5 – 5.0 mA depending on system configuration.

  • Minimum Source-to-Skin Distance (SOD): 15 inches for fixed fluoroscopy.

  • Operational Controls: Utilization of a foot switch and electronic collimation of the fluoroscopic field.

Image Intensification

  • Introduction Year: 1948

  • Purpose: Enhance visual acuity during imaging.

  • Photopic Vision Utilization: Primarily uses cone color receptors.

  • Lower fluoroscopic doses achieved with prolonged periods in a dark room after using special goggles.

Components of Image Intensification Tube

  1. Input Screen and Photocathode

  2. Electronic Lenses

  3. Magnification Tubes

  4. Anode and Output Screen

  5. Brightness Gain Calculation:

    • Defined as: Brightness Gain = Minification Gain x Flux Gain

Fluoroscopic Imaging Process

  • Initial Phase: X-rays emitted by an X-ray tube, exit the patient, and enter the glass envelop of the image intensifier.

  • Photoemission: Photocathode emits electrons that replicate the light image visible on the input phosphor.

  • Voltage Application: Accelerates electrons toward the anode (typically 25 to 35 kVp).

  • Output Screen Functionality: Converts electron energy back into light, enhancing the image visibility, achieving about 4,000 to 6,000 times brightness gain.

Magnification Tubes

  • Increased voltage leads to higher electron acceleration, shifting the focal point away from the anode.

  • Dual and Multifield Intensifiers: Fabricated to enhance resolution and field of view, with sizes such as:

    • 23/15 cm (9”/6”)

    • Quad field configurations (14”/12”/9”/6”)

  • Increased resolution but correlated with increased patient dose.

Brightness Gain and Flux Gain

  • Definition of Brightness Gain:

    • Brightness Gain = Minification Gain x Flux Gain

    • Involves the concentration of electrons from the input to output phosphor.

  • Flux Gain Definition:

    • Represents the conversion efficiency of the output screen; a higher flux gain correlates to more light photons per electron.

    • Example: If 1 electron strikes the output screen, it can emit 50 light photons.

Maintaining Fluoroscopic Image Quality

  • Types of Systems:

    • Automatic Brightness Control (ABC)

    • Automatic Brightness Stabilization (ABS)

    • Automatic Dose Control (ADS)

    • Automatic Gain Control (AGS)

  • Feedback Loop Mechanism: Maintains optimal image brightness during operations by regulating exposure.

Image Quality Factors

  • Image Quality Components:

    • Contrast, Resolution, Distortion, Quantum Noise (mottle)

  • Contrast Management: Controlled via video signal amplitudes with digital systems employing post-processing techniques.

  • Resolution Limitations: Not as high as static radiography, typically under 3 lp/mm for CsI image intensifiers, varying with geometric factors.

  • Distortion Types:

    • Size distortion affected by geometric parameters like Object-to-Image Distance (OID).

    • Vignetting or pincushion effects minimized in advanced TFT technologies.

Quantum Mottle and its Remedies

  • Visual Effect: A blotchy, grainy appearance resulting from inadequate exposure.

    • Common solution: Increase mA or reduce distance to the input phosphor.

Video Viewing Systems in Fluoroscopy

  • Common Setups: Utilize a video camera linked to the output phosphor (often employing CCD technology) and display monitors.

  • Digital Systems: Implement flat-panel displays for enhanced quality and lower radiation exposure.

Flat Panel Fluoroscopy Benefits

  • Standard of Care for Angiographic Systems: Leverage solid-state technology without traditional image intensifiers.

  • Advantages: Higher resolution (>3 lp/mm), uniform resolution without peripheral fall-off and vignetting, and reduced dose during magnification.

Digital Fluoroscopy Variations

  • High-Power Generators: Operating in pulse progressive mode with adjustable interrogation and extinction times.

  • Resolution Trade-offs: Lower than conventional radiography due to patient safety concerns, balancing acquisition and effective display.

  • Post-processing Capabilities: Electronic storage and retrieval of images for later assessments.

Mobile Fluoroscopy

  • C-arm Units: Widely used for surgical applications and emergency departments, with operational similarities to stationary units.

Radiation Protection Protocols

Patient Protection

  • Exposure Rates: Maximum tabletop exposure limit of 10 R/min, typically ranges between 1-3 R/min.

  • Minimum Source-to-Skin Distance: Ensures safety (12 inches for mobile, 15 inches for stationary).

Radiographer and Radiologist Protection

  • Safety Measures: Utilize lead aprons (0.25 mm Pb equivalent), Bucky slot cover, and lead rubber drapes to minimize exposure.

  • Positioning: Maintain a safe distance and angles from the radiation source, preferably standing away at a 90-degree angle.

General Recommendations for Others

  • All personnel in the room are required to wear protective gear and be informed of safety measures before commencing fluoroscopy procedures.

Digital Flat Panel Fluoro System Designs

  • Two primary design models:

    • Tube Placement: Either below or above the patient, altering isodose curves significantly

  • Enhanced systems integrate flat-panel detectors providing dual functionality for both static and fluoroscopic imaging.