A flexible nested sodium and proton coil array with wideband matching for knee cartilage MRI at 3T

Abstract

Purpose We describe a 6×2 channel sodium/proton array for knee MRI at 3 Tesla. Multi-element coil arrays are desirable because of well-known signal-to-noise ratio advantages over volume and single-element coils. However, low coil-tissue coupling that is characteristic of coils operating at low frequency can make the potential gains from a phased array difficult to realize. Methods The issue of low coil-tissue coupling in the developed six channel sodium receive array was addressed by implementing 1) a mechanically flexible former to minimize coil-to-tissue distance and reduce the overall diameter of the array and 2) a wideband matching scheme that counteracts preamplifier noise degradation caused by coil coupling and a high quality factor. The sodium array was complemented with a nested proton array to enable standard MRI. Results The wideband matching scheme and tight-fitting mechanical design contributed to greater than 30% central SNR gain on the sodium module over a mono-nuclear sodium birdcage coil, while the performance of the proton module was sufficient for clinical imaging. Conclusion We expect the strategies presented in this work to be generally relevant in high density receive arrays, particularly in x-nuclei or small animal applications, or in those where the array is distant from the targeted tissue.

Subject‐loaded quadrifilar helical‐antenna RF coil with high B1+ field uniformity and large FOV for 3‐T MRI

“…The maximum efficiency in Fig. 3b is comparable with those reported for various coils and phantoms at 3 T, as well as 7 T in Refs 14,[35][36][37][38][39][40][41][42] In the next example, we further analyze the magnetic field B 1 uniformity of the system in Fig. 2.…”

X‐nuclei imaging: Current state, technical challenges, and future directions

“…By avoiding coil exchange between measurements, patient comfort is increased, and the total measurement time is reduced. Various 23 Na coil designs have been presented for head, breast, and knee applications. Solutions for synchronous acquisition of 23 Na and 1 H signal have been developed .…”

Size‐adaptable “Trellis” structure for tailored MRI coil arrays

“…The research community has further advanced flexible coil technology by demonstrating a variety of techniques. Nordmeyer‐Massner et al replaced conventional semirigid circuit board substrate with woven copper conductors mounted on stretchable fabric to image the knee over a range of flexion angles; Corea et al helped open the door for wearable coils by printing conductive ink onto thin, flexible plastic film; X. Yan et al proposed an imbalanced capacitor distribution such that magnetic and electric coupling cancel each other to form a self‐decoupled loop, which can provide robust SNR that is independent of coil spacing within an array; and some others have demonstrated a range of novel electromechanical structures and materials . Whereas these developments generally focused on substrate flexibility and/or reducing coupling, we saw an opportunity to create a new coil structure that provides encircling coverage of cylindrical objects over a range of diameters without coverage overlap or gaps.…”

“…Nordmeyer-Massner et al replaced conventional semirigid circuit board substrate with woven copper conductors mounted on stretchable fabric to image the knee over a range of flexion angles 10,11 ; Corea et al helped open the door for wearable coils by printing conductive ink onto thin, flexible plastic film 12 ; X. Yan et al proposed an imbalanced capacitor distribution such that magnetic and electric coupling cancel each other to form a self-decoupled loop, which can provide robust SNR that is independent of coil spacing within an array 13,14 ; and some others have demonstrated a range of novel electromechanical structures and materials. [15][16][17][18] Whereas these developments generally focused on substrate flexibility and/or reducing coupling, we saw an opportunity to create a new coil structure that provides encircling coverage of cylindrical objects over a range of diameters without coverage overlap or gaps. The main challenges in building such an adjustable array are to design a flexible substrate that minimizes the distance between the coil and object while simultaneously minimizing shifts in tuning and matching that arise from positioning changes, which can reduce SNR, attributed to nonoptimal noise matching 19 and coil coupling, which injects preamplifier noise into the multiple-channel receive coil.…”