Applications of a 32-Channel Ultra-flexible Phased-Array Prototype Coil Design Optimized for Small Joint 3-Tesla MRI

Objective 
MRI of the hand and wrist region, containing small structures such as ligaments, peripheral nerves, and thin cartilage, is challenging, requiring both high spatial resolution and coverage, along with adequate signal-to-noise ratio (SNR) for image quality. This work aimed to evaluate whether a high-density, prototype flexible coil array could better visualize small anatomic structures without compromising SNR or field-of-view (FOV), compared to conventional hand and wrist coils. 

Approach 
A flexible, 32-channel phased-array prototype coil was developed for 3T hand and wrist MRI using novel, small dual-loop elements. A silicon oil phantom was used to analyze SNR and noise amplification arising from acceleration factors (R) of 2-5. Confirmation of the prototype's phantom performance was done in wrist MRI comparisons in two healthy volunteers and against two 16-channel commercially available coils for superior-inferior coverage and at different acceleration factors (R=1.5-4). Additional imaging in 6 patients was performed in the hand, wrist, elbow, brachial plexus, and foot for anecdotal, qualitative assessment of the coil's performance. 

Main Results 
Phantom testing demonstrated ~26% higher SNR and 19.2%-192.4% lower g-factors in the prototype compared to a 16-channel conventional coil. In comparisons against other coils, the prototype coil demonstrated larger superior-inferior coverage of 23.9 cm compared to 20.5 cm and 20.6 cm in conventional coils. Image quality was maintained at higher acceleration factors. Patient imaging successfully demonstrated visualization of small structures. 

Significance 
The 32-channel prototype coil's extended FOV, improved SNR, and flexible design enabled accelerated scans with high spatial resolution and broader anatomical coverage, offering technical improvements over conventional coil designs.