Doppler US gating of cardiac MR imaging

Rationale and Objectives, Electrocardiographic (ECG) gating of cardiac magn etic resonance (MR) imaging has been problematic for many reasons. The purp ose of this study was to demonstrate the feasibility of using Doppler ultra sound (VS) gating, either directly off the moving cardiac wall or the systo lic upstroke of the arterial signal from the great vessels in neck, in alte rnative gating modes. Materials and Methods. A 2.5-MHz, range-gated Doppler US device was used wi th A-mode guidance for gating directly off left ventricular wall motion. A 4- or 8.1-MHz, continuous-wave (CW) Doppler US device was used for gating o ff the systolic upstroke from the great Vessels in the neck. The subject un dergoing imaging held the transducer against his chest for range-gated Dopp ler US and against his neck for 8.1-MHz CW Doppler US. The 4-MHz transducer was strapped to the subject's neck. Modified Doppler signals were fed back into the gating circuitry of the MR imager to achieve cardiac syn synchron y. Results. Cardiac gating was achieved by using both the range-gated techniqu e directly off the cardiac wall and the CW method off blood flow from the g reat vessels. Problems occurred with radiofrequency shielding during the ra nge-gated method; however, these problems were almost completely removed by use of the CW Doppler probes. Conclusion. Doppler US gating of MR images is possible and potentially coul d overcome many shortcomings of ECG gating. Subsequent embodiments of the t echnique will require improved radiofrequency shielding in the range-gated technique.