Purpose

We aimed at examining both the incidence and extent of diferent lung perfusion abnormalities as well as the relationship between them on Tc-99m macroaggregated albumin (MAA) perfusion-only SPECT/CT scans in COVID-19 patients.

Study participants

Q-SPECT/CT images of 91 participants (71.4 ± 13.9 years; range: 29–98 years, median age: 74 years) with positive diagnosis of SARS-CoV-2 virus infection and clinical symptoms suspicious of PE were evaluated in this single-center, retrospective study. The examinations were performed between 19/11/2020 and 07/01/2021. Forty-five (49.5%) of the patients studied were female and 46 (50.5%) were male. Reviewing the patient history, 6 (6.6%) of the selected individuals had a history of COPD and 3 (3.3%) of them had emphysema. Asthma has been reported in 11 (12.1%) of the included patients. Only 5 (5.5%) patients had a history of smoking. Due to the low number of cases in each group, subgroup analyzes were not performed. The indications of the examination included clinical deteriorations and symptoms characteristic for PE. Inclusion criteria were as follows: available Q-SPECT/CT images, confirmed diagnosis of COVID-19 maximum 2 weeks prior to the examination or clinically suspected COVID-19, which was laboratory confirmed by positive real-time polymerase chain reaction (RT-PCR) test within a week after the Q-SPECT/CT examination.

Acquisition protocol

Five minutes after the intravenous injection of 200 MBq (5.4 mCi) of Tc-99m MAA (Macro-Albumon, Medi-radiopharma Ltd., Érd Hungary) in supine position, acquisition started applying AnyScan® SPECT/CT/PET (Mediso Ltd., Budapest, Hungary) system. Low-dose CT scans of the chest were recorded during free-breathing at 120 kV, 50–150 mAs without intravenous contrast administration, while SPECT image parameters of the same region were the following: 64 views, 30 s/step and 128 matrix size. Q-SPECT images were reconstructed utilizing ordered subset expectation maximization reconstruction, then fused with the corresponding CT image slices. The examinations were performed according to the protocol prepared by the infection control department of the hospital.

Image interpretation and image processing

Selected Q-SPECT/CT scans were presented randomly and retrospectively reviewed by two nuclear medicine physicians with 6 and more than 20 years of experience. In case of discordance between readers, a simultaneous reading to reach consensus was achieved. Neither the clinical status of the patients nor the previous interpretation of the examinations was revealed to the evaluators. SPECT, CT and fused images were interpreted simultaneously using InterView™ FUSION software (version: 3.08.009.0000; Mediso Ltd., Budapest, Hungary).

The presence and the extent of the following CT morphological abnormalities, presumably caused by COVID-19, were evaluated: ground glass opacities (GGOs), consolidations, and mixed lesions. No distinction was made between the aforementioned lesions during the assessment.

The presence and extent of the following perfusion abnormalities (denominated after the terms applied in V/Q scintigraphy) were evaluated on fused SPECT/CT scans:

• Mismatch (MM) lesions: activity defects on SPECT images identical to apparently healthy pulmonary parenchyma on CT images (Fig. 1.).
• Matched (MA) lesions: activity defects with corresponding parenchymal lesions on CT scans (Fig. 2.).
• Reverse mismatch (RM) lesions: pulmonary parenchymal lesions with preserved or increased perfusion (Fig. 3.)

Fig. 1 Axial low-dose CT (a), fused Q-SPECT/CT (b), and SPECT images (c) of a COVID-19 patient with dyspnea. A representative figure of bilateral segmental and subsegmental perfusion defects (demonstrated with white arrows) without any ventilation abnormalities. No pulmonary opacities could be depicted in this case (total CT score was 0). CT computed tomography, Q-SPECT/CT perfusion single-photon emission computed tomography/computed tomography, COVID-19 coronavirus disease 2019

Fig. 2 Axial low-dose CT (a), fused Q-SPECT/CT (b), and SPECT images of a COVID-19 patient. Extensive areas with decreased perfusion are detected in both lungs corresponding to ground-glass opacities and consolidations (as demonstrated white arrows). Bilateral, pleural effusion with no tracer accumulation could also be visualized in dorsal lung territories. Preserved pulmonary parenchyma shows normal tracer-distribution. CT computed tomography, Q-SPECT/CT perfusion single-photon emission computed tomography/computed tomography, COVID-19 coronavirus disease 2019

Fig. 3 Axial low-dose CT (a), fused Q-SPECT/CT (b), and SPECT scans (c) of a COVID-19 patient. Fused SPECT/CT scan reveals remarkably extensive hyperperfused opacities in both lungs (shown with white arrows) compared to the relatively preserved lung areas. CT computed tomography, Q-SPECT/CT perfusion single-photon emission computed tomography/computed tomography, COVID-19 coronavirus disease 2019

Conclusions

In our Q-only SPECT/CT study heterogeneous perfusion abnormalities were found in most of the COVID-19 patients: parenchymal lesions were present with normal, decreased or increased perfusion and perfusion defects were frequently observed in healthy lung areas. These observed phenomena may be explained by the failure of the hypoxic pulmonary vasoconstriction mechanism and the presence of pulmonary thrombosis and embolism. Because our results are consistent with previous dual-energy CT and subtraction CT angiography studies, we hypothesize that Q-only SPECT/CT may be an useful tool in the evaluation of COVID-19 patients in whom CT contrast agent is contraindicated.

Full article on Annals of Nuclear Medicine