Validation of highly accelerated real-time cardiac cine MRI with radial k-space sampling and compressed sensing in patients at 1.5T and 3T

Abstract

Purpose: To validate an optimal 12-fold accelerated real-time cine MRI pulse sequence with radial k-space sampling and compressed sensing (CS) in patients at 1.5T and 3T.

Methods: We used two strategies to reduce image artifacts arising from gradient delays and eddy currents in radial k-space sampling with balanced steady-state free precession readout. We validated this pulse sequence against a standard breath-hold cine sequence in two patient cohorts: a myocardial infarction (n = 16) group at 1.5T and chronic kidney disease group (n = 18) at 3T. Two readers independently performed visual analysis of 68 cine sets in four categories (myocardial definition, temporal fidelity, artifact, noise) on a 5-point Likert scale (1 = nondiagnostic, 2 = poor, 3 = adequate or moderate, 4 = good, 5 = excellent). Another reader calculated left ventricular (LV) functional parameters, including ejection fraction.

Results: Compared with standard cine, real-time cine produced nonsignificantly different visually assessed scores, except for the following categories: 1) temporal fidelity scores were significantly lower (P = 0.013) for real-time cine at both field strengths, 2) artifacts scores were significantly higher (P = 0.013) for real-time cine at both field strengths, and 3) noise scores were significantly (P = 0.013) higher for real-time cine at 1.5T. Standard and real-time cine pulse sequences produced LV functional parameters that were in good agreement (e.g., absolute mean difference in ejection fraction <4%).

Conclusion: This study demonstrates that an optimal 12-fold, accelerated, real-time cine MRI pulse sequence using radial k-space sampling and CS produces good to excellent visual scores and relatively accurate LV functional parameters in patients at 1.5T and 3T. Magn Reson Med 79:2745-2751, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Keywords: Cartesian k-space; cardiac function; compressed sensing; radial k-space; real-time cine MRI; tiny golden angles.

Figure 1

(a) Pulse sequence diagram showing our sampling strategy. The first heartbeat was used to play pre-scan, dummy scans (green arrows) to approach steady state of magnetization. This is standard for all cine MRI with b-SSFP. Real-time, radial data were acquired in the subsequent 1.75 heartbeats using the TGA sequence (black arrows). Immediately after current data scan and before start of pre-scan, dummy scans for the following imaging plane, 48 rays of calibration data (red arrows; a pair of rays with opposite polarities per direction; 7.5° angular steps) were acquired in lieu of post-scan dummy scans (green arrows).

Figure 2

Representative multi-slice cine images of a patient with MI acquired at 1.5T. Real-time cine with radial CS produced results that approximate those produced by standard cine MRI. For the corresponding movie files, see Supporting Information (Video S1.avi for standard cine, Video S2.avi for real-time with radial CS).

Figure 3

Representative multi-slice cine images of a patient with CKD acquired at 3T. Real-time cine with radial CS produced results that approximate those produced by standard cine MRI. For the corresponding movie files, see Supporting Information (Video S3.avi for standard cine, Video S4.avi for real-time with radial CS).

Figure 4

The Bland-Altman plots showing agreement in LVEF between standard cine (reference) and real-time cine MRI pulse sequences: standard vs. real-time with radial CS at 1.5T (1^st column), and standard vs. real-time with radial CS at 3T (second column). The mean difference in LVEF was −3.0 and −1.6% for 1.5T and 3T, respectively, which correspond to −5.3 and −2.6% error relative to mean LVEF values 57.9 and 63.2 % at 1.5T and 3T, respectively.