Abstract
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Introduction: COVID-19 pandemic has changed lung scan protocols in many nuclear medicine facilities throughout the world. We thought to evaluate the impact of this change in our institution.
Objectives: To evaluate the results of perfusion only lung scans and the frequency of necessary use of the ventilation part of the scans to diagnose acute pulmonary embolism (PE) during COVID 19 pandemic.
Methods: COVID 19 pandemic has resulted in a change of our lung scan protocol to perform perfusion only scans for the evaluation of acute pulmonary embolism. Ventilation images were acquired only if necessary to make the diagnosis of acute PE and only after the patient tests negative for COVID 19 to ensure the safety of using our xenon gas ventilation machine among patients. After obtaining IRB approval, we retrospectively reviewed our lung scans perfumed between March to December 2020; the period when our protocol to diagnose acute PE was changed to perfusion only. Data was collected regarding the patients’ demographics, clinical indications, results of the perfusion scans, and the number of ventilation scans needed to make a certain diagnosis of acute PE. Perfusion lung scans were performed according to the routine protocol of 8 static standard views around the lungs after injecting a Tc-99m MAA dose ranging between 85.1-225.7 MBq (2.3-6.1 mCi) according to the indication. The images were interpreted by two experienced nuclear medicine physicians as daily routine studies. Results of their interpretations were collected for this study.
Results: A total of 128 lung perfusion scans were performed at our institution, including 69 females and 59 male patients with average age of 59.7 yr (range 12-88 yrs). Perfusion scans were performed for 100 inpatients, 25 outpatients and 3 emergency room patients. The indications were shortness of breath in 46 patients, chest pain 6, tachycardia 10, deep vein thrombosis 5, pulmonary hypertension 13, hypoxia 10, chronic thromboembolic phenomena 16, respiratory failure 5, elevated D-dimer 5 and miscellaneous reasons in 12 patients. The scans were interpreted with certainty using the modified PIOPID criteria in 122 patients (95.3%). These results included low probability for acute PE in 110 patients (85.9%), normal in 6 patients (4.7%) and 6 high probability of acute PE (4.7%). Ventilation imaging using xenon-133 gas was performed per Nuclear Medicine physician request to confirm mismatched segmental perfusion defects in high probability results only in 4 patients after negative testing for COVID19. The other 2 high probability results were confirmed with the clinical presentation and additional radiologic imaging. Only 6 out of 128 patients (4.7%) were interpreted as indeterminate perfusion scans, two of which due to inability to differentiate old from new perfusion defects in patients with history of chronic thromboembolic disease. Thus, the true indeterminate results may be due to the lack of ventilation scan was encountered in only 4 out of 128 patients (3.1%). Conclusion: The ventilation part of lung scans is required only in a small number of patients for certain interpretation of the result. The Perfusion part of lung scans is sufficient for evaluation of acute PE with certainty in most patients.