Optimizing the ventilation-perfusion lung scan for image quality and radiation exposure.
Our purpose was to compare the performance of an initial ventilation-perfusion (V/Q) scan protocol with that of a data-driven modified protocol to improve diagnostic quality without increasing radiation dose to the patient.


METHODS
The initial V/Q scan protocol consisted of a ventilation scan after inhalation of (99m)Tc-diethylenetriaminepentaacetic acid (DTPA) aerosol for 5 min followed by a (99m)Tc-macroaggregated albumin perfusion scan. Interim analysis after 34 scans under an initial protocol included calculations of ventilation efficiency, perfusion efficiency, and perfusion-to-ventilation counting rate ratio (Q:V). Ventilation efficiency was defined as ventilation counting rate divided by ventilation dose, perfusion efficiency as perfusion counting rate divided by perfusion dose, and Q:V as perfusion counting rate divided by ventilation counting rate. From these data, the protocol was modified to improve the Q:V ratio and was applied to 60 patients. Results from the 94 scans were tabulated, and a comparison of ventilation efficiency, perfusion efficiency, and Q:V between the 2 protocols was statistically analyzed.


RESULTS
The initial protocol returned a mean ventilation efficiency of 7.8% (SD, 4.6%; range, 1.4%-19%), mean perfusion efficiency of 100% (SD, 31%; range, 39%-160%), and mean Q:V of 2.4 (SD, 1.9; range, 0.51-9.0). All 3 parameters displayed a wide range. Fifty-four percent of these cases demonstrated an unacceptable Q:V (≤2) indicating that the perfusion dose did not overwhelm the ventilation dose. To improve Q:V, options included decreasing ventilation dose, increasing perfusion dose, or performing the ventilation scan with a much higher dose after the perfusion scan. To minimize radiation, the protocol was modified to decrease the ventilation from 5 min to 2.5 min. The modified protocol yielded a mean ventilation efficiency of 5.1% (SD, 1.8; range, 2.0-11), mean perfusion efficiency of 120% (SD, 27%; range, 65%-170%), and mean Q:V of 3.6 (SD, 1.7; range, 1.2-12). Differences between protocols were statistically significant for ventilation efficiency, perfusion efficiency, and Q:V (P < 0.02). Less than 8% of cases under the modified protocol exhibited an unacceptable Q:V.


CONCLUSIONS
The initial V/Q scan protocol was successfully modified to improve image quality with less radiation. By decreasing the ventilation time by half, the percentage of studies with an unacceptable Q:V decreased from 54% to 8%. This analysis may help others to optimize their V/Q protocols.
Department of Medical Imaging, University of Arizona, Tucson, Arizona.
Seung
S
Hur
Adam
A
Bauer
Natalie
N
McMillan
Elizabeth A
EA
Krupinski
Phillip H
PH
Kuo
D004781:Environmental Exposure / Q000009:adverse effects*; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000502:physiology*; D004369:Pentetic Acid / Q000009:adverse effects; D055420:Perfusion Imaging / Q000009:adverse effects* / Q000379:methods*; D011786:Quality Control; D011829:Radiation Dosage; D013997:Time Factors; D014692:Ventilation-Perfusion Ratio
D004369:Pentetic Acid
embolism; protocol optimization; ventilation perfusion (V/Q)