Effects of physiologic waveform variability in triggered MR imaging: Theoretical analysis

Department of Medical Biophysics, University of Western Ontario, Canada.
Journal of Magnetic Resonance Imaging (Impact Factor: 3.21). 11/1994; 4(6):853-67. DOI: 10.1002/jmri.1880040618
Source: PubMed


One of the assumptions inherent in most forms of triggered magnetic resonance (MR) imaging is that the pulsatile waveform (be it cardiac, respiratory, or some other) is purely periodic. In reality, the periodicity condition is rarely met. Physiologic waveform variability may lead to image artifacts and errors in velocity or volume flow rate estimates. The authors analyze the effects of physiologic waveform variability in triggered MR imaging. They propose that this variability be treated as a modulation of the underlying motion waveform. This report concentrates on amplitude modulation of the velocity waveform, which results in amplitude and phase modulation of the transverse magnetization. Established Fourier and modulation theory and the recently described principles of (k,t)-space were used to derive the appearance of physiologic waveform variability artifacts in triggered MR images and to predict errors in time-averaged and instantaneous velocity estimates that may result from such motion effects, including effects such as ghost overlap. Simulations and experimental results are provided to confirm the theory.

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    • "We believe that if the duration of the main bolus were greater than venous enhancement time, arteriovenous circulation time would be the main parameter. Although some reports have suggested possibly insufficient coverage of K-space during a rapid short bolus injection (17, 22-24), we assumed that the standard dose of 0.1 mmol / kg during an injection lasting 3 - 5 seconds would more than cover the total length of arteriovenous circulation and image acquisition time. All second arterial-phase images and some 50-second delayed venous-phase images in our study revealed that arteries were still strongly enhanced, thus demonstrating that the extent by which arterial bolus length exceeded arteriovenous circulation time was sufficiently great. "
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    Full-text · Article · Sep 2000 · Korean Journal of Radiology
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    • "Variability is especially important in ungated procedures such as magnetic resonance angiography (MRA) (Nishimura 1990, Dumoulin 1989) and cardiac-gated cine MRI flow measurements (Pelc et al 1991). In these investigations, data collection may occur over hundreds of cardiac intervals, and cycle-to-cycle variations can lead to artefacts in the final data (Hangiandreou et al 1993, Hofman et al 1993, Lauzon et al 1994, Rogers and Shapiro 1993). We are interested in experimental investigations and numerical simulations of blood flow through the carotid bifurcation. "
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    ABSTRACT: Knowledge of human blood-flow waveforms is required for in vitro investigations and numerical modelling. Parameters of interest include: velocity and flow waveform shapes, inter- and intra-subject variability and frequency content. We characterized the blood-velocity waveforms in the left and right common carotid arteries (CCAs) of 17 normal volunteers (24 to 34 years), analysing 3560 cardiac cycles in total. Instantaneous peak-velocity (Vpeak) measurements were obtained using pulsed-Doppler ultrasound with simultaneous collection of ECG data. An archetypal Vpeak waveform was created using velocity and timing parameters at waveform feature points. We report the following timing (post-R-wave) and peak-velocity parameters: cardiac interbeat interval (T(RR)) = 0.917 s (intra-subject standard deviation = +/- 0.045 s); cycle-averaged peak-velocity (V(CYC)) = 38.8 cm s(-1) (+/-1.5 cm s(-1)); maximum systolic Vpeak = 108.2 cm s(-1) (+/-3.8 cm s(-1)) at 0.152 s (+/-0.008 s); dicrotic notch Vpeak = 19.4 cm s(-1) (+/-2.9 cm s(-1)) at 0.398 s (+/-0.007 s). Frequency components below 12 Hz constituted 95% of the amplitude spectrum. Flow waveforms were computed from Vpeak by analytical solution of Womersley flow conditions (derived mean flow = 6.0 ml s(-1)). We propose that realistic, pseudo-random flow waveform sequences can be generated for experimental studies by varying, from cycle to cycle, only T(RR) and V(CYC) of a single archetypal waveform.
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