Multi-resolution simultaneous 19F/1H 3D radial imaging for self-navigated respiratory motion-corrected and quantitative imaging
© Caruthers et al; licensee BioMed Central Ltd. 2010
Published: 21 January 2010
Fluorine MRI/MRS offers unique benefits in molecular imaging, including background-free, highly-specific detection of targeted 19F-imaging agents. However, in cardiovascular applications, physiological motion compromises the quantification of sparse 19F-agents and no sufficient motion information is contained in the 19F-signal. Therefore, truly-simultaneous 19F/1H-MRI with efficient 3D-sampling is developed. It allows individual post-processing of 1H and 19F-data for optimized temporal, spatial resolution and SNR, needed for self-navigated, 1H-based motion detection and sensitive 19F-agent quantification.
Using a clinical 3 T (Achieva, Philips Healthcare) with a dual-tuned 19F/1H spectrometer and surface coil (transmit/receive; 7 × 12 cm) , isotropic 3D-radial gradient echo imaging was performed (FOV = 140 mm, matrix = 963, TE/TR = 2.1/6.1 ms, flip angle α19F/α1H = 48°/12°, 15 averages, 14 min). Robust for sub-sampling, radial acquisition was employed choosing the angle between interleaves defined as the golden-section fraction providing optimal coverage of k-space independent of sub-sample size . Thus, the dynamic imaging frame rate can be chosen retrospectively to optimize temporal resolution and SNR. Furthermore, the balance between SNR and spatial resolution can be modified via k-space weighting (standard k2-weighting within a defined radius, uniform weighting outside). Anesthetized, hyper-cholesterolemic, atherosclerotic rabbits were imaged 3 h post-injection of αvβ3-targeted perfluoro-15-crown-5-ether nanoparticles. A respiration sensor was placed on the abdomen as external reference. For respiratory motion tracking, dynamic 1H images were reconstructed with a temporal resolution of 0.35 s (58 profiles/frame, 160× sub-sampling). The k-radius weighting factor was varied from 0.025-1.0 to ascertain a favorable compromise between SNR and resolution for detecting diaphragm motion. 3D translational motion information, extracted from 1H data via cross-correlation within a volume-of-interest, was used to correct 1H and 19F image datasets. The k-radius in weighted reconstruction of 19F-data was chosen independently to optimize the spatial resolution for a given concentration and SNR of the nanoparticle agent on the aorta.
Sub-sampled, 3D isotropic radial imaging with golden section profile interleaving allows flexible, self-navigated 3D respiratory motion compensation based on simultaneously-acquired 1H signal for multi-resolution 19F imaging and quantification.