Prospective Heart Tracking for Respiratory Motion Compensation in Whole-heart Magnetic Resonance Angiography
Journal of Cardiovascular Magnetic Resonance volume 18, Article number: P12 (2016)
Electrocardiogram and respiratory navigator (NAV)-gated 3D whole-heart magnetic resonance angiography (MRA) acquired with an intravascular gadolinium-based contrast agent and a non-selective inversion recovery (IR) pulse to null the myocardial signal generates a high-resolution anatomic dataset allowing for a comprehensive evaluation of intra-cardiac, coronary, and vascular abnormalities . In this technique, an additional IR pulse is also included to selectively restore the signal in the liver, and thus allow NAV tracking of the diaphragm (liver-lung interface). This selective IR pulse, however, excites the blood flowing from veins into the heart creating a bright inflow artifact that hinders image interpretation . Therefore, we sought to develop a prospective respiratory-gating technique (Heart-NAV) that tracks the heart rather than the diaphragm position and eliminates the inflow artifact without compromising image quality.
Schematics of the proposed Heart-NAV technique for non-contrast and contrast-enhanced MRA sequences are shown in Fig. 1A&1B. One of the startup pulses for MRA sequence is used to collect the centerline of k-space, and its 1-dimensional reconstruction is fed into the conventional-NAV signal analysis process to prospectively gate and track respiratory-induced heart displacement. To assess the efficacy of Heart-NAV in the correction of respiratory motion, 10 volunteers (7 females; age 31 ± 6 years) underwent MRA acquisitions with conventional-NAV and Heart-NAV. For both acquisitions, imaging parameters were FOV ~386 × 230 × 120 mm3, spatial resolution 1.5 mm3; α/TE/TR 90°/2.4/4.7 ms, bandwidth 0.54 kHz, SENSE factor of 2, acceptance window of 5 mm, and a 32-element phased-array coil. To compare their image quality, sharpness of the coronary arteries was subjectively graded by 2 clinicians and objectively measured (Soap Bubble tool). Subjective and objective measures were compared using a signed-rank test and paired student t-test, respectively. To evaluate the effect on image inflow artifact, 6 patients (4 males; ages 0.3-6 years) each underwent contrast-enhanced (0.03 mmol/kg of gadofosveset trisodium) IR MRA acquisitions with a conventional-NAV and with Heart-NAV.
All acquisitions were successfully completed. Images from 2 healthy subjects with the non-contrast MRA sequences are shown in Fig. 1C. The vessel sharpness and image quality were equivalent for conventional-NAV and Heart-NAV acquisitions but the imaging time of Heart-NAV was 10% shorter (Table 1). Fig. 1D displays images with contrast-enhanced MRA acquisitions from 2 patients. Inflow artifact was present with the conventional-NAV but not with Heart-NAV.
Compared to a conventional-NAV, Heart-NAV achieved similar image quality for non-contrast whole-heart MRA, and eliminated inflow artifact in contrast-enhanced whole-heart MRA.
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Moghari, M.H., Geva, T. & Powell, A.J. Prospective Heart Tracking for Respiratory Motion Compensation in Whole-heart Magnetic Resonance Angiography. J Cardiovasc Magn Reson 18 (Suppl 1), P12 (2016). https://doi.org/10.1186/1532-429X-18-S1-P12