World Journal of Cardiology
There are a wide variety of masses that can grow in the heart or the pericardial sac, from simple pericardial cysts and thrombus to malignant tumors and anatomic variants. This can present a significant diagnostic challenge and lead to missed diseases when analyzing heart images. There are multiple ways to image the heart:
The cardiac magnetic resonance imaging (cardiac MRI) has excellent resolution, does not emit radiation, and allows clear evaluation of morphology, tissue, and function of the heart. Fluorodeoxyglucose positron emission tomography (FDG PET) is another excellent choice. FDG is a radioactive sugar that emits signals, and PET captures those radiations. Because cancer loves sugar (it needs to eat more as it grows so fast), it takes up FDG much more than healthy cells. FDG PET has become a key modality in approaching cardiac masses as well, specifically in staging cancers, pinpointing its location, and therefore radiation therapy planning. Recently, there has been a development integrating the PET and MRI together. This paper reviews clinical scenarios where FDG PET-MRI combination imaging comes in as an asset.
The FDG uptake is able to distinguish between benign and malignant tumors. Even with an appearance of normal anatomical variants, variable uptake of FDG needs to prompt cardiac MR, which is useful in elucidating the diagnosis.
The biggest obstacle here with PET is the respiratory motion artifact. In PET-MRI, there are multiple ways to correct for this movement, such as self-navigation, and with this tool the combination imaging can reveal abnormal focus of hypermetabolism in or near the heart.
Tumor thrombus is the tumor extending into the vein. This is hard to distinguish with actual clots in the vein, as cancers cause the body to be in a hypercoagulable state. Combining the level of uptake of FDG and high resolutions of MRI, the PET-MRI can distinguish between tumor and large thrombus.
Cardiac MRI can identify primary tumors by evaluating anatomy, function, and tissue type. It can also detect distant metastases as well. Presently, a whole body diffusion weighted imaging is used. PET on the other hand is useful for actual M staging of different cancers. A whole body DW imaging with PET scan would allow for an effective detection of metastases.
Cardiac MR is highly effective in assessing tumor extension, because MRI provides sensitive contrast of soft tissues. However, PET is not suitable for systemic evaluation of cardiac tumors. Nevertheless, there is generally a correlation between FDG accumulation in tumors and the degree of malignancy. Combined PET-MRI, therefore, can accurately detect tumors at the T-stage and assess local invasion.
Combining PET and MRI in a single imaging session shows great promise in the diagnostic art. This may be the next step to approach a mass that is incidentally found in the heart.
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