The COVID-19 Factor: Optimizing a less than optimal situation in Advanced Functional Lung Imaging

As a result of the recent potential threat of COVID-19 infecting Nuclear Medicine technologists, other patients and staff, the SNMMI [https://www.snmmi.org/NewsPublications/NewsDetail.aspx?ItemNumber=33543] and ACR [https://www.acr.org/Advocacy-and-Economics/ACR-Position-Statements/COVID19-Nuclear-Medicine-Ventilation-Scans] released statements recommending temporarily eliminating the Ventilation portion of the Ventilation-Perfusion (V/Q) scan.  These recommendations require departments to carefully contemplate what is best for patients who present with symptoms of a Pulmonary Embolism (PE). However, it is unknown how long the COVID-19 situation will linger.  It appears the community now has three options to consider as we move forward.

First, departments can eliminate the Ventilation portion of the study while taking safety into consideration.  While arguably safer, this option presents risks to the patient with higher indeterminate rates and a chance of serious diagnostic failure. [Mazurek Respiration 2015] The only scenario where this option is beneficial is when the images show no defects at all.

Mazurek published a Perfusion-Only (P-O) protocol in 2015, which has suddenly become the new normal for a lot of departments in 2020. However, this study clearly demonstrated how damaging the elimination of the Ventilation portion of a V/Q Scan can be, especially to the Specificity (the % of when a non-PE defect appears, and is correctly interpreted as such). This statistic, and also confidence in properly minimizing any aerosol contamination is why Departments did not switch to P-O.

While this option is prudent during this time, there is a trade-off between the obvious diagnostic limitations to and the safety benefits. Therefore, when the current COVID-19 threat subsides and proper point-of-care coronavirus testing occurs, we should return to the full ventilation and perfusion technique.

The fundamental reasoning for the P-O scanning protocol was in consideration of dose reduction for pregnant females.  However, the caveat is the majority of that population had little to no underlying co-morbidities, which could present as confusing non-PE imaging defects. But we must now consider the symptomatic COVID-19 population, which has the much greater possibility of presenting with underlying non-PE lung processes. This is a compelling reason to consider the second option; switching from Planar to SPECT (or preferably a SPECT/CT) platform, while still performing P-O studies.

Switching from Planar to SPECT or a SPECT/CT platform also takes safety into consideration, while providing a more accurate assessment for patients.  While this option may not be ideal, clinical data shows a 27% increase in Sensitivity (the % of when a true PE defect is present, it is interpreted as such), and an increase of 40% in Specificity when switching to SPECT/CT from a Planar acquisition. [Mazurek] The data shows that Sensitivity was consistently lower than Specificity in planar V/Q, which was consistently higher by a large margin when using SPECT/CT. However, if we are seeing defects and cannot definitively confirm that they are not PEs, where does that leave the referring physician? By irradiating patients on a consistent basis without concrete results, does a disservice to the technologist’s dedication, Nuclear Medicine and most importantly, the patient.

In fairness, all research is not performed on exactly the same patient population using the same equipment, processing, and interpreters. So absolutely comparing Mazurek ‘s study percentages, to other author’s published data, is not an exact science. Nevertheless, what he did observe quite clearly was that P-O SPECT/CT Specificity could not match that of a Planar V/Q value. Quite a stunning conclusion.

This option provides a way to optimize the P-O procedure and achieve more accurate results. By switching from a simple Planar format to a SPECT or SPECT/CT format, and performing true Advanced Functional Lung Imaging (AFLI), departments can substantially increase interpreted imaging accuracy.

The third option for the Nuclear Medicine community to consider is to continue to perform the standard V/Q procedure with SPECT/CT, while adhering to strict PPE guidance, contamination technique control, and careful apparatus disposal and room disinfection to eliminate or reduce cross contamination in the department.  This is the option many Nuclear Medicine departments have chosen.¹

We know from the data that the most accurate VQ analysis comes from a skillful Pre-Test Probability assessment followed by an optimal Ventilation and Perfusion matching acquisition technique. Consequently, this option is the ideal scenario, given the data shows that when a standard V/Q is performed using SPECT/CT acquisition, the Sensitivity improves by 21%. A fairly significant jump. The Specificity sees a modest increase of 6%, nearly reaching 100% [Mazurek], giving referring physicians a very reliable tool when managing their patients.

These three options are a lot to consider and should prompt very important conversations in the Nuclear Medicine community and with our referring physicians.  In the end, each department must do what is best for them and their patients.  Careful consideration must be taken when balancing all necessary precautions and the benefits of Advanced Functional Lung Imaging.

1. REF: BELNUC, Recommendations for performing V/Q scans in the context of COVID-19, Accessed June 2020

 

2020-US-PHARM-00053