RESUMO
AIM: Implementation of the individual calculation of perfusion activity to ensure the guideline-compliant ratio of perfusion to ventilation (P/V-ratio) of ≥â3 in the diagnosis of acute pulmonary embolism (PE) using V/P-SPECT. MATERIAL AND METHODS: 50 consecutive V/P-SPECT examinations, in which a standard activity of 160âMBq was applied for perfusion imaging, are evaluated retrospectively. Based on this patient group an activity factor is determined, which provides a correlation between the applied perfusion activity and the expected perfusion counts of the gamma camera. Using the mean activity factor, the perfusion activity required for a P/V-ratio of four is calculated using the previously acquired ventilation count rate. This is applied prospectively to the 100 subsequent examinations. RESULTS: The mean perfusion activity factor is (54.56â± 10.13)âcps/MBq. The individually calculated perfusion activities range from 80âMBq toâ200âMBq with an average value of (146.9â±â35.3)âMBq and a median of 140âMBq. The individual activity calculation thus reduced the mean perfusion activity by 8.2â% and the median by 12.5â%. In addition, the individual calculation reduced the proportion of P/V ratios <â3 from 14â% to 0â% and the proportion of P/V ratios >â5 from 24â% to 19â%. CONCLUSION: The presented method for the individual calculation of perfusion activity offers a simple way to ensure a guideline-compliant P/V-ratio. Furthermore, unnecessarily high perfusion activity as a result of inadequate ventilation can be avoided.