Effectiveness of ¹³N ammonia in aiding in the detection of cardiac sarcoidosis

Objectives: Prior to 2018, the institution where my research was performed used only ¹⁸F-FDG to detect cardiac sarcoidosis. With the addition of ¹³N ammonia, the cost of testing increased due to billing out two procedures, one for the ¹⁸F-FDG imaging and one for the ¹³N ammonia imaging. Therefore, the purpose of this study is to determine how often ¹³N ammonia is effective in helping diagnose patients with cardiac sarcoidosis. Background: ¹⁸F-FDG is used to detect cardiac sarcoidosis due to its ability to image inflammation. By quantifying the inflammation, ¹⁸F-FDG is useful for assessing treatment response and informing decisions on duration, intensity, or choice of therapy. When combined with ¹³N ammonia, perfusion defects due to cardiac sarcoidosis can be visualized. Perfusion defects are either caused by scarring or compression of the microvasculature due to the inflammation. In the instance of scarring, a perfusion defect is seen without any ¹⁸F-FDG uptake present. On the other hand, when the microvasculature is compressed, a perfusion defect is seen along with the uptake of ¹⁸F-FDG¹. Methods: A retrospective study was done on 59 scans. Each scan was examined and results were recorded based on positive findings for increased ¹⁸F-FDG uptake as well as positive findings for ¹³N ammonia perfusion defects. Statistical sensitivity tests were then performed to analyze the data. Results: It was found that 26 out of 59 scans had positive findings for ¹⁸F-FDG uptake. Of those 26 scans, eight (31%) had positive findings for ¹³N ammonia perfusion defects. Additionally, there were two scans that had ¹³N ammonia perfusion defects but no correlating ¹⁸F-FDG uptake. Conclusion: Overall, 31% of patients with noted ¹⁸F-FDG uptake had correlating ¹³N ammonia perfusion defects. This correlation helps in the staging and treatment planning of cardiac sarcoidosis. The two scans that showed ¹³N ammonia perfusion defects without correlating ¹⁸F-FDG uptake were due to scarring. However, without prior imaging it cannot be determined if the scarring was due to sarcoidosis. ¹³N ammonia is aiding in the diagnosis of cardiac sarcoidosis, and our physicians believe it is the standard of care for patients with sarcoidosis. Institutions should continue using ¹³N ammonia along with ¹⁸F-FDG for all patients with cardiac sarcoidosis.