Multi-resolution simultaneous 19F/1H 3D radial imaging for self-navigated respiratory motion-corrected and quantitative imaging
Journal of Cardiovascular Magnetic Resonance volume 12, Article number: O56 (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.
Isotropic 3D simultaneous 19F/1H images were acquired and successfully reconstructed using self-navigated respiratory motion correction (see Figure 1). For the required 0.35s temporal resolution, a k-radius of 0.10 provided optimal compromise between SNR and resolution for diaphragmatic motion detection. Motion-corrected 1H images clearly demonstrated improvement, especially near the diaphragm. Improvements in the lower resolution 19F images were also present (though less pronounced) and can be crucial for quantification accuracy.
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.
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Caruthers, S.D., Keupp, J., Rahmer, J. et al. Multi-resolution simultaneous 19F/1H 3D radial imaging for self-navigated respiratory motion-corrected and quantitative imaging. J Cardiovasc Magn Reson 12 (Suppl 1), O56 (2010). https://doi.org/10.1186/1532-429X-12-S1-O56