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Trigger Delay (trigger + delay)
Selected AbstractsCorrection for heart rate variability during 3D whole heart MR coronary angiographyJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2008Stijntje D. Roes MD Abstract Purpose To evaluate the effect of a real-time adaptive trigger delay on image quality to correct for heart rate variability in 3D whole-heart coronary MR angiography (MRA). Materials and Methods Twelve healthy adults underwent 3D whole-heart coronary MRA with and without the use of an adaptive trigger delay. The moment of minimal coronary artery motion was visually determined on a high temporal resolution MRI. Throughout the scan performed without adaptive trigger delay, trigger delay was kept constant, whereas during the scan performed with adaptive trigger delay, trigger delay was continuously updated after each RR-interval using physiological modeling. Signal-to-noise, contrast-to-noise, vessel length, vessel sharpness, and subjective image quality were compared in a blinded manner. Results Vessel sharpness improved significantly for the middle segment of the right coronary artery (RCA) with the use of the adaptive trigger delay (52.3 ± 7.1% versus 48.9 ± 7.9%, P = 0.026). Subjective image quality was significantly better in the middle segments of the RCA and left anterior descending artery (LAD) when the scan was performed with adaptive trigger delay compared to constant trigger delay. Conclusion Our results demonstrate that the use of an adaptive trigger delay to correct for heart rate variability improves image quality mainly in the middle segments of the RCA and LAD. J. Magn. Reson. Imaging 2008;27:1046,1053. © 2008 Wiley-Liss, Inc. [source] Estimation of pulse wave velocity in main pulmonary artery with phase contrast MRI: Preliminary investigationJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2006Hsu-Hsia Peng MS Abstract Purpose To assess the feasibility and reproducibility of a noninvasive MRI method to measure pulse wave velocity (PWV) in the main pulmonary artery (MPA). Materials and Methods A total of 17 subjects without history of pulmonary diseases (38.2 ± 18.4 years) participated in this study. Series of MR velocity maps of the MPA were acquired at 2 cm above the pulmonary valves using a two-dimensional phase-contrast sequence. Effective temporal resolution was 11 msec after interleaving two dynamic series with different values of electrocardiograph (ECG) trigger delay. PWV was derived as the rate of MPA flow variations per unit change in MPA cross-sectional area, during early systole. Seven healthy subjects underwent three repetitive examinations to investigate intrascan and interscan reproducibility. Results Flow vs. area was highly linear in the MPA during early systole, with Pearson's coefficients ranging from 0.982 to 0.999, rendering derivation of PWV with little difficulty. Average value of PWV in MPA was 1.96 ± 0.27 m/second, in good agreement with literature values measured using invasive means. The percentage intra- and interscan differences were 5.46% and ,10.86%, respectively. Conclusion Phase-contrast MRI to noninvasively measure PWV in the MPA is feasible with good reproducibility. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Image-based coronary tracking and beat-to-beat motion compensation: Feasibility for improving coronary MR angiographyMAGNETIC RESONANCE IN MEDICINE, Issue 3 2008Maneesh Dewan Abstract A method to reduce the effect of motion variability in MRI of the coronary arteries is proposed. It involves acquiring real-time low-resolution images in specific orthogonal orientations, extracting coronary motion from these images, and then using this motion information to guide high-resolution MR image acquisition on a beat-to-beat basis. The present study establishes the feasibility and efficacy of the proposed approach using human motion data in an offline implementation, prior to future online implementation on an MRI scanner. To track the coronary arteries in low-resolution real-time MR images in an accurate manner, a tracking approach is presented and validated. The tracking algorithm was run on real-time images acquired at 15,20 frames per second in four-chamber, short-axis, and coronal views in five volunteers. The systolic and diastolic periods in the cardiac cycles, computed from the extracted motion information, had significant variability during the short time periods typical of cardiac MRI. It is also demonstrated through simulation analysis using human tracked coronary motion data that accounting for this cardiac variability by adaptively changing the trigger delay for acquisition on a beat-to-beat basis improves overall motion compensation and hence MR image quality evaluated in terms of SNR and CNR values. Magn Reson Med 60:604,615, 2008. © 2008 Wiley-Liss, Inc. [source] Navigator gating and volume tracking for double-triggered cardiac proton spectroscopy at 3 TeslaMAGNETIC RESONANCE IN MEDICINE, Issue 6 2004Michael Schär Abstract Respiratory motion compensation based on navigator echoes for double-triggered cardiac proton spectroscopy at 3.0T is presented. The navigators measure the displacement of the liver,lung interface during free breathing. This information allows for double triggering on a defined window within the respiratory cycle and on a defined trigger delay after the R-wave based on the ECG. Furthermore, it allows the excitation volume to be shifted by the determined respiratory displacement within the defined window in real-time (volume tracking). Static and motion phantom experiments were performed in this study, and it was demonstrated that volume tracking permits the suppression of signal from tissue next to the localized volume. However, triggering on a defined respiratory position is still necessary to achieve high spectral quality, because shimming and water suppression calibration are only optimal for a small window of the respiratory cycle. Single-volume spectra obtained in the myocardial septum of healthy subjects are presented. Magn Reson Med 51:1091,1095, 2004. © 2004 Wiley-Liss, Inc. [source] 3D nongadolinium-enhanced ECG-gated MRA of the distal lower extremities: Preliminary clinical experienceJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2008FRANZCR, Ruth P. Lim MBBS Abstract Purpose To report our initial experience implementing a noncontrast-enhanced electrocardiograph (ECG) gated fast spin echo magnetic resonance angiography (MRA) technique for assessment of the calf arteries. Materials and Methods Noncontrast MRA images of 36 clinical patients examined over a 6-month period were evaluated by two radiologists for length and degree of stenosis of arterial segments. Diagnostic confidence in the technique was also recorded. The reference standard was a consensus reading by both radiologists using the noncontrast technique combined with two gadolinium-enhanced techniques: bolus-chase and time-resolved imaging. Results For stenosis evaluation the noncontrast technique demonstrated accuracy 79.4% (1083/1364), sensitivity 85.4% (437/512), and specificity 75.8% (646/852). The sequence demonstrated high negative predictive value (92.3%, 646/700). The technique had serious artifacts leading to poor diagnostic confidence in 17 patients (47.2%). These included motion (n = 7) and artifacts specific to the sequence, including inaccurate trigger delays (n = 5), linear artifact (n = 7), and vessel blurring (n = 5). When only patients in whom there was satisfactory diagnostic confidence were considered, accuracy, sensitivity, and negative predictive value were 92.2% (661/717), 92.4% (158/171), and 97.5% (503/516), respectively. Conclusion Our results indicate that when technically successful, noncontrast-enhanced MRA using ECG-gated fast spin echo can provide accurate imaging of the calf and pedal arteries. However, further development and optimization are needed to improve the robustness of the technique. J. Magn. Reson. Imaging 2008;28:181,189. © 2008 Wiley-Liss, Inc. [source] Effects of cord motion on diffusion imaging of the spinal cordMAGNETIC RESONANCE IN MEDICINE, Issue 2 2006Hardave S. Kharbanda Abstract Measurement of diffusion and its dependence on direction has become an important tool for clinical and research studies of the brain. Diffusion imaging of the spinal cord may likewise prove useful as an indicator of tissue damage and axonal integrity; however, it is more challenging to perform diffusion imaging in the cord than in the brain. Here we report a study of the effects of motion on single-shot fast spin echo (FSE) diffusion tensor imaging (DTI) of the spinal cord. Diffusion imaging was performed at four different times in the cardiac cycle both without and with velocity compensation of the diffusion gradients. Uncompensated diffusion images demonstrated substantial signal loss artifacts in the cord that were strongly dependent on the delay after the pulse-oximeter trigger. Quantitative diffusion analysis was also strongly affected by this motion artifact. The use of flow-compensated gradients helped to restore normal signal in the cord, especially at particular trigger delays. Theoretical arguments suggest that improved spatial resolution may help eliminate this signal loss. Even with higher spatial resolution, motion-related signal attenuation may still occur in diffusion imaging of pathologies that alter the motion of the cord. However, this same cord motion may contain diagnostically valuable information when probed using appropriate diffusion imaging approaches. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] | ||||||||||