Cardiac Magnetic Resonance for the Evaluation of Suspected Cardiac Thrombus: Conventional and Emerging Techniques

Cardiac Magnetic Resonance or CMR is important in the evaluation for potential thrombus because CMR can provide a definitive diagnosis of the etiology of a cardiac mass. CMR has advantages over other modalities such as echocardiography as CMR can provide multi-sequenced detailed characterization of soft tissue masses where echo offers primarily visualization and size measurements. Prior to the MRI, the patients are screened for metal or implanted devices that may be contraindicated.

If gadolinium is to be given, they are screened for allergies and renal function to ensure adequate safety. Cardiac MRI imaging faces several challenges. For optimal imaging, patients need to hold their breath.

Sometimes patients with shortness of breath have difficulty accomplishing this task. The EKG is also used for imaging and patients with cardiac arrhythmias may disrupt the gating. Parameters need to be adjusted to accomplish this goal.

Demonstrating the cardiac MRI exam with me will be Deb Brannon, our lead MRI technologist, and Chad Woodhouse, a cardiac MRI technologist. Before beginning the acquisition, provide the patient with headphones connected to the technologist's microphone so that commands can be efficiently communicated and place electrocardiogram leads in the optimal positions on the left chest. After confirming adequate EKG signal, the patient's position is confirmed on the scan table and an appropriately sized surface coil for maximizing signal-to-noise ratio is placed over the heart.

Inform the patient to breathe when instructed during the imaging by holding breath at the end of expiration. Imaging reproducibility is higher with this type of breath hold compared to inspiratory breath holds. When the patient is ready, obtain the scout images, the bright blood balanced cine steady-state free precision axial stack with full heart coverage.

Then obtain approximate two and four chamber sequences which will help with further scan prescriptions. For tissue characterization, obtain the black blood triple inversion recovery sequence. Obtain native T1 mapping scans.

To perform the first pass arterial perfusion module, deliver 0.05 to 0.1 millimoles per kilograms of contrast agent at a three to four milliliter per second administration rate. Then obtain dynamic first pass perfusion images along the axial plane or plane that best highlights the mass in question until the contrast passes through the left ventricle myocardium imaged during contrast injection. 10 minutes after the gadolinium injection, run the T1 scout sequence which will help define the scan time to inversion which will be approximately 200 to 450 milliseconds at 1.5 Tesla and 300 to 500 milliseconds at 3 Tesla.

Then obtain six to eight millimeter phase sensitive inversion recovery slices with the inversion time set. It is important to note that the proper inversion time setting will increase with each minute beyond the contrast injection. It is also recommended to acquire a high TI image around 600 milliseconds as thrombus should have an old black appearance at this setting while myocardium and tumors may have intermediate signal.

Evaluate the mass on cine bSSFP images. Axial plane is often helpful in imaging cardiac masses. For cardiac thrombus evaluation, the thrombus can demonstrate increased T2 weighted signal intensity in the subacute time period as this lateral right atrial mass demonstrates or low T2 weighted signal intensity in the chronic time period as shown in this right atrial mass in a different patient.

In cardiac thrombus evaluation, the mass in question is carefully analyzed for any internal perfusion that would suggest against thrombus and signify the presence of a vascular tumor. Evaluate for late gadolinium enhancement imaging within the suspected mass. No solid regions of internal late gadolinium enhancement are expected within a thrombus.

Here convention and emerging CMR sequences that are commonly used to evaluate for cardiac thrombus are shown. Cardiac thrombus is presented on the important CMR sequences. Highlighted by arrows, there is a mass in the right ventricle.

This mass has low signal on bSSFP and T2 weighted images and lacks internal arterial perfusion. A corresponding CT image shows hypodensity within the mass. Delayed post contrast imaging shows no internal late gadolinium enhancement.

The native T1 map shows mildly elevated T1 relaxation time. These findings are consistent with cardiac thrombus. In contrast to cardiac thrombus, a patient with hepatocellular carcinoma metastatic to the right atrium is also presented.

The mass at the right cavoatrial junction has low signal on bSSFP and intermediate signal on T2 weighted images. There is decreased native T1 relaxation time within the mass and mild internal enhancement is visible on the MRA image. These findings are consistent with intracardiac metastasis.

It's important to acquire high quality images, to repeat images if there is degradation due to patient motion, and to adjust scan parameters to make breath hold times manageable. Cardiac MR often gives a definitive diagnosis of cardiac thrombus adding to echo results by providing excellent soft tissue characterization with a perfusion and enhancement evaluation.