1136 Cardiovascular radiofrequency (B 1 ) field maps using HASTE
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BioMed Central
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Meeting abstract
1136 Cardiovascular radiofrequency (B1) field maps using HASTE Kelvin Chow*, Ian Paterson and Richard Thompson Address: University of Alberta, Edmonton, AB, Canada * Corresponding author
from 11th Annual SCMR Scientific Sessions Los Angeles, CA, USA. 1–3 February 2008 Published: 22 October 2008 Journal of Cardiovascular Magnetic Resonance 2008, 10(Suppl 1):A261
doi:10.1186/1532-429X-10-S1-A261
Abstracts of the 11th Annual SCMR Scientific Sessions - 2008
Meeting abstracts – A single PDF containing all abstracts in this Supplement is available here. http://www.biomedcentral.com/content/pdf/1532-429X-10-S1-info.pdfThis abstract is available from: http://jcmr-online.com/content/10/S1/A261 © 2008 Chow et al; licensee BioMed Central Ltd.
Introduction Quantitative cardiovascular magnetic resonance (CMR) imaging assumes spatially uniform excitation of spins. Heterogeneities in the radiofrequency (B1) field due to effects such as coil loading, conductivity, and dielectric resonance violate this assumption and may result in apparent changes in tissue properties. Previous CMR B1 mapping approaches have relied heavily on custom pulse sequences [1] and have not included the lungs.
All data was acquired on a Siemens Sonata 1.5 T MRI scanner. Typical HASTE scan parameters are: body coil reception, cardiac gating (diastolic imaging), black blood preparation, 360 × 250 mm FOV, 8–12 mm slice thickness, 192 × 70 matrix, 12–22 ms TE, 2.75 ms inter-echo spacing, ~4–5 seconds TR, and 10 repetitions (if free breathing). Each slice was acquired in ~10 seconds (breath-hold) or ~80 seconds (free breathing). Heart and lung tissue were manually segmented and averaged within regions of interest (~3.5 cm2).
Purpose To develop a robust B1 field mapping approach that is applicable to the heart and lungs.
Methods The double angle method for B1 field mapping [2] utilizes two images acquired with different flip angles: θ1 and commonly θ2 = 2θ1. Signal intensities from the two images are compared to solve for the true achieved θ1. We used a single shot fast spin echo (HASTE) pulse sequence with excitation flip angles of 60° and 120° for the double angle experiment (refocusing pulses not modified). This rapid acquisition alleviates the need for breath-holding as a means of eliminating respiratory motion in the chest. Representative heart coverage was achieved using short axis and four chamber view slice prescriptions. Images can be acquired during a single breath-hold or during free breathing. For free breathing, each image acquisitions was repeated 10 times and the position of the diaphragm and heart was used to select images of similar respiratory phase.
Results In Figure 1, a four chamber view shows a significantly varying B1 field across both lungs and the heart. Results are expressed as actual flip angles for prescribed 90° RF pulses. For this volunteer, flip angles in the left lung closely matched the prescribed flip angles, while the right lung flip angles were 10°–20° lower. In
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