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IMAGE INTERPRETATION · LUNG V/Q IMAGING

Ventilation Agents: Tc-99m DTPA Aerosol vs Xe-133

Lung scintigraphy — ventilation and perfusion images
Lung scintigraphy — ventilation and perfusion images

Public domain · Wikimedia Commons · source file

Question

Two ventilation agents are used for V/Q lung scanning: Xe-133 (xenon gas) and Tc-99m DTPA aerosol. Which of the following correctly compares these two agents?

  1. ATc-99m DTPA aerosol can be imaged in multiple projections; Xe-133 is limited to a single-detector projection due to its poor 81 keV photon energy
  2. BXe-133 provides better spatial resolution than Tc-99m aerosol
  3. CTc-99m DTPA aerosol requires a gas-handling exhaust system
  4. DXe-133 and Tc-99m aerosol are equivalent in all clinical situations
Show the answer and explanation

A. Tc-99m DTPA aerosol can be imaged in multiple projections; Xe-133 is limited to a single-detector projection due to its poor 81 keV photon energy

Xe-133 (81 keV gamma, 5.3-day half-life) and Tc-99m DTPA aerosol (140 keV) differ importantly: (1) Xe-133 is imaged at a SINGLE projection (usually posterior) because the patient must breathe the gas continuously and cannot be repositioned; it requires a gas-handling system with exhaust. (2) Tc-99m DTPA aerosol is inhaled as an aerosol and deposits in the lungs, after which the patient can be repositioned for multiple planar projections or SPECT — dramatically improving diagnostic quality. (3) Tc-99m aerosol has better photon energy (140 keV) for gamma camera imaging. However, in central airway disease (COPD), aerosol may clump in the central airways ('hot spots'), while Xe-133 distributes more uniformly.

More lung v/q imaging images

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← V/Q Scan vs CTPA for Pulmonary Embolism in PregnancyIntermediate-Probability V/Q Scan →

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