16 Fluoroscopy pt 2

Digital fluoroscopy

Uses an analog-to-digital converter (ADC); ADC placed between TV camera and monitor; may use flat-panel detectors; some units operate at higher mA similar to radiographic mode; x-ray beam automatically pulsed to reduce heat loading on tube.

Analog-to-digital converter (ADC)

Placed between TV camera and display monitor; converts analog signal from camera into digital signal for processing.

Flat-panel detector (FPD)

More recent advancement; replaces image intensifier; considered the primary barrier; lighter weight; flexible positioning; FOV up to 43 cm × 43 cm; can rotate to match patient anatomy; more sensitive than image intensifiers; improved image quality.

Digital fluoroscopy standard of care

Digital flat-panel detector systems are the current standard, replacing traditional image intensifiers.

Advantages of flat-panel detectors

Reduce size/bulk/weight of fluoroscopy tower; easier manipulation; improved patient access; replace spot filming and recording devices; can operate in radiographic mode eliminating need for extra radiographs; images stored in PACS/MIMPS.

FPD technology (solid-state digital output)

Produces digital signal directly; no fiberoptic coupling; no “end of life” degradation; flat detector surface eliminates vignetting, pincushioning, distortion; improved contrast resolution.

FPD scintillator materials

Uses indirect design with scintillator layer: Cesium iodide (CsI) or Gadolinium oxysulfide (Gd2O2S).

FPD dose reduction

Flat-panel detectors provide significant radiation dose reduction compared to image intensifiers.

Automatic Exposure Rate Control (AERC)

Maintains image brightness by adjusting mA, kVp, filtration, and pulse width; provides quicker, more stable response in FPD systems.

RF system designs

Two designs: x-ray tube above patient OR x-ray tube below patient; both fully functional but scatter radiation patterns differ.

X-ray tube above patient

FPD located under tabletop; variable SID up to 72 inches; table tilt up to 90°; single detector used for both fluoroscopy and radiography; system often remotely operated.

X-ray tube below patient

Traditional design; facilitates table-side fluoroscopy; x-ray tube under patient and digital detector above; system may require additional digital detectors (table bucky, upright holder).

Scatter radiation distribution

Scatter most intense at waist level and above (upper trunk, neck, head); patient is primary source of operator exposure.

Scatter with x-ray tube below patient

Creates scatter area mainly at waist level and below.

Last image hold (LIH)

Displays last fluoroscopic image; visible lines indicate collimator plate position.

Virtual collimation

Allows operator to adjust collimation electronically without exposing the patient again.

Last frame hold / fluoro loop save

Saves a single frame or fluoro sequence; helps review without additional radiation.

Frame averaging

Reduces patient dose and image noise by averaging multiple frames.

AERC (fluoroscopy)

Automatically adjusts tube mA, kVp, filtration, pulse width to maintain constant exposure to detector.

Dose rate settings

Low, medium, high settings that adjust dose, often by set percentages (e.g., 50%).

Magnification with flat panel

Flat panel detectors improve image quality in magnification mode WITHOUT increasing patient dose (unlike image intensifiers).

Continuous fluoroscopy

Continuous x-ray exposure; increases patient dose.

Pulsed fluoroscopy

X-ray exposure occurs in pulses with gaps; decreases patient dose.

Pulsed fluoro optimization

Designed to provide good image quality at acceptable dose; uses high-frequency generator; controls pulse height (mA), pulse width, pulse interval, and pulse rate.

FPD operation (fluoroscopy)

Uses amorphous silicon photodetector layer; arranged in pixel array; operates using pulsed exposures; requires pixel binning during fast sequences.

Pixel binning

Combines detector elements (DELs) to speed frame rate during fluoroscopy at the cost of reduced spatial resolution.

Air kerma

Measures kinetic energy released in air; represents x-ray intensity at a point.

Cumulative air kerma

Reference dose measured in Gray (Gy); estimates patient skin dose during procedure; chamber intercepts entire beam for total calculation.

Kerma-area product (KAP/DAP)

Product of cumulative air kerma and x-ray beam area at patient entrance; measured in mGy·cm² or microgray; must be recorded along with fluoro time.

Display monitors

Flat-screen LCD monitors; black-and-white; high resolution (up to 5 megapixels); contain layered LCD structure with liquid crystal between polarizers.

Mobile C-arm units

Provide fluoroscopic imaging; used in OR and ED; C-shaped design holds tube and intensifier/detector; allows multiple viewing angles.

O-arm unit (closed design)

Provides static and dynamic imaging; supports 2D and 3D imaging; uses two FPDs in orthogonal orientation.

Radiation safety in fluoroscopy

Intermittent pulsing reduces exposure; use lowest pulsed mode and lowest dose setting; use time, distance, shielding; tabletop exposure must not exceed 10 R/min (≈88 mGy/min) with ABS/AERC; SSD ≥ 38 cm (15 in) for stationary units and ≥ 30 cm (12 in) for mobile units.

Shielding requirements

Lead aprons: 0.5 mm Pb; bucky slot cover: 0.25 mm Pb; protective curtain: 0.25 mm Pb placed between patient and operator.

Quality control program

Includes equipment performance inspection and testing; QC radiographer inspects equipment at least every 6 months; includes room condition inspection, cables, control booth structure, and wear/deterioration.