Phase-contrast MRI volume flow - a comparison of breath held and navigator based acquisitions

Abstract

Background: Magnetic Resonance Imaging (MRI) 2D phase-contrast flow measurement has been regarded as the gold standard in blood flow measurements and can be performed with free breathing or breath held techniques. We hypothesized that the accuracy of flow measurements obtained with segmented phase-contrast during breath holding, and in particular higher number of k-space segments, would be non-inferior compared to navigator phase-contrast. Volumes obtained from anatomic segmentation of cine MRI and Doppler echocardiography were used for additional reference. Methods: Forty patients, five women and 35 men, mean age 65years (range 53-80), were randomly selected and consented to the study. All underwent EKG-gated cardiac MRI including breath hold cine, navigator based free-breathing phase-contrast MRI and breath hold phase-contrast MRI using k-space segmentation factors 3 and 5, as well as transthoracic echocardiography within 2days. Results: In navigator based free-breathing phase-contrast flow, mean stroke volume and cardiac output were 79.7 ± 17.1ml and 5071 ± 1192ml/min, respectively. The duration of the acquisition was 50 ± 6s. With k-space segmentation factor 3, the corresponding values were 77.7ml ± 17.5ml and 4979 ± 1211ml/min (p = 0.15 vs navigator). The duration of the breath hold was 17 ± 2s. K-space segmentation factor 5 gave mean stroke volume 77.9 ± 16.4ml, cardiac output 5142 ± 1197ml/min (p = 0.33 vs navigator), and breath hold time 11 ± 1s. Anatomical segmentation of cine gave mean stroke volume and cardiac output 91.2 ± 20.8ml and 5963 ± 1452ml/min, respectively. Echocardiography was reliable in 20 of the 40 patients. The mean diameter of the left ventricular outflow tract was 20.7 ± 1.5mm, stroke volume 78.3ml ± 15.2ml and cardiac output 5164 ± 1249ml/min. Conclusions: In forty consecutive patients with coronary heart disease, breath holding and segmented k-space sampling techniques for phase-contrast flow produced stroke volumes and cardiac outputs similar to those obtained with free-breathing navigator based phase-contrast MRI, using less time. The values obtained agreed fairly well with Doppler echocardiography while there was a larger difference when compared with anatomical volume determinations using SSFP (steady state free precession) cine MRI.