Fluoroscopy – Core Exam Notes

Historical Background

  • Early fluoroscopes: x-ray tube → patient → fluorescent screen; images viewed in dark rooms or with red goggles (Trendelenburg, 1916).
  • Thomas Edison introduced calcium-tungstate screens; modern screens use cesium iodide (input) & silver-activated zinc-sulfide (output).
  • Shoe-fitting fluoroscopes (≈ 1920–1960) delivered 12–107\ \text{R/min} to customers; harmful effects (cancer, skin burns, cataracts) drove current radiation-safety standards.

Roles in a Fluoro Exam

  • Radiographer: equipment set-up, patient screening/consent/history, assist radiologist, post-exam clean-up & monitoring.
  • Radiologist: primary operator & interpreter of dynamic studies (e.g., barium swallow, UGI, BE, MBS, vascular exams).

Equipment Types

  • Fixed rooms, portable C-arms, Medtronic O-arm; x-ray tube & image receptor mounted on C-shaped gantry.
  • Carriage (over-table arm) carries image intensifier, spot-film selector, power & drive controls.
  • Fluoro tubes built for long exposure at low current 0.5–5.0\ \text{mA}.

Image Intensifier (II) – 4 Core Parts

  1. Vacuum/ glass envelope.
  2. Input phosphor (cesium iodide) + photocathode → converts x-rays to electrons.
  3. Electrostatic lenses → accelerate & focus electron stream to anode.
  4. Output phosphor (silver-activated zinc-sulfide) → electrons → visible light.

Image-Chain Workflow

\text{x-rays} \rightarrow \text{Input Phosphor} \rightarrow \text{Light} \rightarrow \text{Photocathode} \rightarrow \text{Electrons} \rightarrow \text{Electrostatic Lenses} \rightarrow \text{Output Phosphor} \rightarrow \text{Light} \rightarrow \text{Display / Storage}

  • Coupling to display: fiber-optics or lens system → vidicon / CCD / flat-panel detector.
  • Flux gain formula: \text{Flux Gain}=\dfrac{#\ \text{output light photons}}{#\ \text{input x-ray photons}}

Operational Features

  • Automatic Brightness Stabilization (ABS) adjusts kVp & mA in real-time (analogous to AEC).
  • Magnification mode ↑ spatial & contrast resolution but ↑ patient dose.

Image Quality Factors

  • Quantum mottle (grain) → raise mA to reduce.
  • Contrast: tissue differences + monitor quality.
  • Resolution: line pairs/mm; small pixel, large matrix ↑ detail.
  • Distortion: vignetting (edge dim), veiling glare (back-scattered light); curved input screen minimizes.

Dose & Distance Limits

  • Entrance skin exposure (ESE) measured at patient surface nearest tube.
    • Tabletop rate ≤ 10\ \text{R/min} (typ. 1–3\ \text{R/min}).
  • Source-to-skin distance: ≥ 15'' (stationary) / ≥ 12'' (mobile).
  • Audible 5-min timer mandatory; must be reset to continue exposure.
  • Bringing image receptor closer to patient ↓ dose (inverse square effect).

Personnel Protection

  • Minimum lead equivalencies: aprons 0.5\ \text{mm}, thyroid/ glasses/ curtain/ gloves 0.25\ \text{mm}.
  • Dosimetry: TLD, film badge, OSL; apply time, distance, shielding principles.

Key Takeaways

  • Fluoro provides real-time imaging of dynamic processes; modern systems use image intensifiers or flat panels with ABS and digital capture.
  • Patient dose management relies on low mA, proper SSD, receptor proximity, and timers.
  • Operator safety requires consistent lead shielding and awareness of scatter originating from the patient.