1350661 - Feasibility of Strain Encoded MRI (SENC) on a commercial 0.55T system

Background: Low field CMR has gained recent attention as low field systems can provide access to a wider patient population due to larger bore size, reduced cost, and ease of installation [1, 2]. Quantification of myocardial strain is also gaining acceptance as a means to early detection of cardiac dysfunction, prior to overt functional or structural changes becoming evident [3].  Strain Encoded MRI (SENC) is a reproducible method of directly measuring longitudinal and circumferential strain [4]. In this study we investigate the feasibility of using SENC to measure global systolic strain on a commercially available 0.55T MRI system with limited gradient performance.

Methods: A prototype SENC sequence was implemented using a segmented k-space, spoiled gradient echo readout on a 0.55T system with 80 cm patient bore and maximum gradient amplitude 26mT/m and slew rate 45mT/m/ms (MAGNETOM Free.Max, Siemens Healthcare, Erlangen, Germany). The sequence was validated using a dynamic phantom that provides mechanical deformation of a gel block. Two settings were used to generate peak strains of approximately -20% and -30%. SENC results were compared to direct measurement of phantom deformation in cine images. Healthy volunteers were scanned using a 6-channel flexible body array and 6 spine coil elements. An MRI compatible patient monitor (IRadimed, Winter Springs, FL, USA) was used for ECG triggering. Scan parameters were as follows: TE/TR 2.8ms/6.9ms, temporal resolution 27.5ms, FOV 380mm x 240mm, acquisition window 600ms, matrix 96x60, slice thickness 15mm, flip angle 10 deg, BW 200Hz/pixel, segments 4, acceleration rate 2, breath-hold duration 8 heartbeats. Images were analyzed using MyoStrain (v5.4, MyoCardial Solutions, Morrisville, NC, USA) to measure the global longitudinal (GLS) and circumferential strain (GCS) in right (RV) and left ventricles (LV).
 


Results: Strain values measured at phantom settings using cine vs. SENC were -20.4% vs -21.8%, and -28.4% vs -27.2%, respectively. Six healthy volunteers (5 male, 1 female, age 46.3 +/- 13.5 years) were scanned. Pixel amplitude is proportional to strain in the high-tuning frames shown in Figure 1, quantification in a volunteer is shown in Figure 3. Mean global strain values across volunteers (Figure 2) were (mean +/- SD): GLS LV, -18.4% +/- 0.7%; GCS LV, -20.2% +/- 0.9%; GLS RV, -19.1% +/- 1.0%; GCS RV, -18.0% +/- 1.7%.

Conclusion: This study demonstrates the feasibility of measuring global LV and RV strain with SENC on a commercially available 0.55T scanner. Deformation phantom results indicated good agreement with direct measurement, and global strain values in volunteers fell within the expected normal range for healthy hearts. These results support the feasibility of SENC-based strain measurement at low field, despite the reduced signal and gradient performance of this scanner. Further studies are warranted in patients with abnormal strain.