SPECT/CT Pulmonary Perfusion Studies: Searching for aSolution During a Pandemic

ABSTRACT

Objectives: COVID-19 has created difficulties for everyone, especially in the medical field. Within Nuclear Medicine, lung ventilation and perfusion (VQ) studies used to rule out pulmonary embolism (PE) have become a challenge with COVID positive patients. SPECT/CT technology provides a potential deeper look into not only physiological butanatomical information. This could prove to be advantageous for patients that are unable to receive the ventilationportion of the study. As a student, 123I have the advantage of seeing multiple protocols for the VQ study at differentinstitutions. One hospital has started doing ventilation exams again. The patient must have tested negative forCOVID-19 from the time of admission to the time of exam to use the ventilation machine. If a patient has not had aCOVID test, the patient must do the ventilation through a single use bag. Absolutely no ventilation studies are doneon COVID positive patients. Two other institutions continue to do lung perfusion only studies on all patientsregardless of COVID status. Therefore, the purpose of this study is to review a SPECT/CT perfusion lung casestudy and evaluate the effectiveness in identifying the possibility of pulmonary embolism. Methods: An institution which is not performing ventilation is using SPECT/CT for lung perfusion only studies.These lung perfusion studies were observed and reviewed. The protocol utilized is as follows 5 mCi Tc99m MAA, followed by 8 standard spot views taken in a supine position anterior, posterior, oblique, and lateral views with 600kcounts in a 128 x 128 matrix. The SPECT/CT portion is completed immediately after the perfusion with 15 secondsper step and 60 steps total. CT parameters include mAs 3, kV 120, a slice thickness of 2.5mm, and a matrix512x512. Results: In one case, a 76-year-old female with history of asthma, DVT and shortness of breath was evaluatedusing SPECT/CT perfusion study to rule out PE. The patient received 5.5mCi of Tc99m MAA and subsequent planarimages were taken in the anterior, posterior, and 4 oblique views, followed by SPECT/CT. Images revealed bilateralsegmental perfusion defects which were concerning for pulmonary embolism. While other pathologies were identified on the CT images, the probability of PE could not be estimated from this study . CT information from thestudy was reviewed for abnormalities possibly related to COVID, but nothing was conclusive. The patient was negative for COVID prior to the exam. Conclusions: Continued research is required to decide if SPECT/CT can decrease the need for a ventilation in aVQ scan;however, this hybrid scanner provides an opportunity to perform an alternative perfusion only study with added anatomical information. Even in institutions that continue to perform ventilation exams, there are occasionswhere a SPECT/CT may prove to be beneficial. SPECT/CT adds anatomic information to a physiological study, itsuse in the determination of the probability of PE is still unknown. Another consideration would be the difference inradiation dose from a SPECT/CT lung perfusion study compared to planar VQ. An initial investigation is being doneby one of the institutions described in this abstract.