- Poster presentation
- Open Access
Effective saturation pulse for the whole heart at 3 T
© McGorty and Kim; licensee BioMed Central Ltd. 2009
- Published: 28 January 2009
- Right Ventricle
- Saturation Pulse
- Residual Magnetization
- Effective Saturation
- Proton Density Weighted Image
Cardiac MRI at 3 T is a promising modality to increase the contrast-to-noise ratio (CNR) in first-pass cardiac perfusion imaging. This CNR boost can improve the accuracy of perfusion estimation from dynamic contrast-enhanced images. However, radio-frequency (RF) field (B1) variations and dielectric effects are comparatively higher at 3 T than at 1.5 T. These challenging factors make it difficult to perform accurate T1-weighting using a conventional rectangular saturation pulse. Previous studies have shown improved saturation of magnetization at 3 T using adiabatic B1-insensitive rotation (BIR-4) , rectangular RF pulse train , and specific absorption rate (SAR) constrained rectangular RF pulse train . Unfortunately, these pulses did not achieve effective saturation of magnetization, which we shall define as residual magnetization after saturation < 5% of equilibrium magnetization (M0), within the whole heart, while remaining within clinically acceptable SAR limits. The purpose of this study was to develop an adiabatic-rectangular pulse train at 3 T that can achieve both of the aforementioned objectives.
The residual longitudinal magnetization left behind by the saturation pulse can be measured by performing a saturation-no-recovery experiment using a TurboFLASH pulse sequence with centric k-space reordering, as previously described . Normalization of the saturation image by the proton density weighted (PDW) image corrects for surface coil inhomogeneities and M0. Relevant imaging parameters include: field of view = 320–400 × 255–324 mm, acquisition matrix = 64 × 52, slice thickness = 8 mm, TE/TR = 1.1/2.3 ms, TD = 3 ms, image acquisition time = 78 ms, flip angle = 10°, parallel imaging acceleration factor = 1.5, and bandwidth = 1002 Hz/pixel. PDW image was acquired using 3° flip angle and without the saturation pulse. The RF and receiver scales were kept constant between the different acquisitions per subject.
Nine volunteers (5 males; 4 females) were imaged in 3 short-axis (apical, mid-ventricular, basal) views of the left ventricle (LV), 4-chamber view, and 2-chamber view of each ventricle.
The LV and right ventricle (RV) were segmented manually. For each subject, the mean normalized signal within the whole heart was computed by averaging the normalized intensities from all five regions of interests (i.e. 3 short-axis and 2 long-axis views). Reported data represent the mean and standard deviation over subjects (n = 9). Student t-test was performed to compare the residual magnetization values between the two RF pulses.
This study demonstrates that the new adiabatic-rectangular pulse train can effectively saturate the magnetization within the whole heart at 3 T, while remaining within clinically acceptable SAR limits. This saturation pulse can be used to acquire multiple slices (>5) with our typical clinical first-pass perfusion protocols. Effective saturation of magnetization is likely to produce more accurate estimation of cardiac perfusion.