Perfusion SPECT/CT to diagnose pulmonary embolism during COVID-19 pandemic.

The global pandemic of novel coronavirus disease 2019 (COVID-19) has affected the way we practice nuclear medicine [1]. The virus can spread from person to person very quickly through respiratory droplets, which is the major reason causing the global pandemic. Thus, it is very important for nuclear medicine service to take prudent measures when dealing with aerosol-generating procedures, such as request for ventilation/perfusion (V/Q) scan to diagnose pulmonary embolism (PE). The patients referred to nuclear medicine service for PE diagnosis usually had symptoms of dyspnea on exertion and elevated D-dimer levels, which were commonly seen in both PE and COVID-19 infection [2]. Meanwhile, there are increased evidence of association of PE in patients with COVID-19 infection, and failure to diagnose PE will worsen the prognosis [3, 4].

In routine V/Q procedures, ventilation studies may be accompanied by airborne radioaerosol contamination, with subsequent small degree of contamination to both the nuclear medicine personnel and imaging room surface [5-7]. In addition, the patients’ symptom of cough and shortness of breath frequently get temporarily worse after radioaerosol inhalation, which increased the potential risk of COVID-19 infection. To protect nuclear medicine personnel from potential respiratory viral infection, and provide the most clinical meaningful results for better patient care, we decide to abolish ventilation and adopt perfusion single photon emission computed tomography/computed tomography (Q-SPECT/CT) technique for PE diagnosis during the COVID-19 pandemic [1]. The practice algorithm is illustrated in Fig. 1.

Fig. 1

Diagnostic algorithm for nuclear medicine evaluation of PE during COVID-19 pandemic

For better patient care, it is important for nuclear medicine physician to understand referring physician’s concern and assess the patient’s pretest probability for COVID-19 and PE. Usually, the patients are symptomatic, with contraindications for CT pulmonary angiography (CTPA) or nondiagnostic on CTPA. It is a good practice to obtain planar perfusion images first due to the wide acceptance among technologists and physicians. In some cases, due to patient’s clinical status, only portable, bedside planar perfusion images can be obtained. However, normal planar perfusion images can safely rule out PE. When planar perfusion images showed abnormality, further Q-SPECT/CT should be obtained. The PE diagnosis on Q-SPECT/CT images can be made using the previously published “MSKCC Q-SPECT/CT criteria” [8, 9], whereas PE is indicated by at least one wedge-shaped peripheral defect estimated as ≥ 50% of a pulmonary segment without corresponding CT image abnormality and clearly seen in all three orthogonal planes. Based on the available CT lung images, additional interpretation should be made on the probability/suspicion for COVID-19 pneumonia [10] and other CT image abnormalities such as presence of lung tumor and pleural effusions. This practice can make most of Q SPECT/CT test, hit two birds with one stone: to diagnose PE and identify if there are suspicious CT findings of COVID-19 pneumonia. We think this is a safe and effective approach that will benefit nuclear medicine practice and patient management during the COVID-19 pandemic. To be cautious, even though we did not perform the ventilation study, given the high pretest probability of COVID-19 infection in patients referred for PE diagnosis, we still recommend that health care personnel in the room should wear an N95 mask, eye protection, gloves, and a gown based on the guidance from the US Centers for Disease Control and Prevention [11].