Ultra-high field upper extremity peripheral nerve and non-contrast enhanced vascular imaging

Abstract

ObjectiveThe purpose of this study was to explore the efficacy of Ultra-high field [UHF] 7 Tesla [T] MRI as compared to 3T MRI in non-contrast enhanced [nCE] imaging of structural anatomy in the elbow, forearm, and hand [upper extremity].Materials and methodA wide range of sequences including T1 weighted [T1] volumetric interpolate breath-hold exam [VIBE], T2 weighted [T2] double-echo steady state [DESS], susceptibility weighted imaging [SWI], time-of-flight [TOF], diffusion tensor imaging [DTI], and diffusion spectrum imaging [DSI] were optimized and incorporated with a radiofrequency [RF] coil system composed of a transverse electromagnetic [TEM] transmit coil combined with an 8-channel receive-only array for 7T upper extremity [UE] imaging. In addition, Siemens optimized protocol/sequences were used on a 3T scanner and the resulting images from T1 VIBE and T2 DESS were compared to that obtained at 7T qualitatively and quantitatively [SWI was only qualitatively compared]. DSI studio was utilized to identify nerves based on analysis of diffusion weighted derived fractional anisotropy images. Images of forearm vasculature were extracted using a paint grow manual segmentation method based on MIPAV [Medical Image Processing, Analysis, and Visualization].ResultsHigh resolution and high quality signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]—images of the hand, forearm, and elbow were acquired with nearly homogeneous 7T excitation. Measured [performed on the T1 VIBE and T2 DESS sequences] SNR and CNR values were almost doubled at 7T vs. 3T. Cartilage, synovial fluid and tendon structures could be seen with higher clarity in the 7T T1 and T2 weighted images. SWI allowed high resolution and better quality imaging of large and medium sized arteries and veins, capillary networks and arteriovenous anastomoses at 7T when compared to 3T. 7T diffusion weighted sequence [not performed at 3T] demonstrates that the forearm nerves are clearly delineated by fiber tractography. The proper digital palmar arteries and superficial palmar arch could also be clearly visualized using TOF nCE 7T MRI.ConclusionUltra-high resolution neurovascular imaging in upper extremities is possible at 7T without use of renal toxic intravenous contrast. 7T MRI can provide superior peripheral nerve [based on fiber anisotropy and diffusion coefficient parameters derived from diffusion tensor/spectrum imaging] and vascular [nCE MRA and vessel segmentation] imaging.

Prospective respiratory triggering improves high‐resolution brachial plexus MRI quality

“…Diffusion‐weighted neurography has been previously described as a technique for brachial plexus MRI evaluation . Diffusion imaging, however, conventionally employs echo‐planar techniques that are inherently susceptible to motion artifact . In a study comparing RT and breath holding for diffusion‐weighted MRI of liver lesions, Kandpal et al reported greater image quality and SNR with prospective RT .…”

“…22 Diffusion imaging, however, conventionally employs echo-planar techniques that are inherently susceptible to motion artifact. 16,23,24 In a study comparing RT and breath holding for diffusion-weighted MRI of liver lesions, Kandpal et al reported greater image quality and SNR with prospective RT. 25 We speculate that an RT approach may similarly reduce motion artifact for brachial plexus DTI sequences.…”

Recent Advances of Bioresponsive Nano-Sized Contrast Agents for Ultra-High-Field Magnetic Resonance Imaging

“…For instance, Gong et al performed an attempt on contrast enhanced MRI with low dose of contrast agent through deep learning of AI (Figure 11). By employing the non-contrast MRI and low-contrast MRI as inputs for deep learning, simulated model/algorithm will be predicted based on the obtained signal difference between non-contrast MRI and low-contrast MRI (Raval et al, 2017). Subsequently, this algorithm will be used to synthesize a full does contrast enhanced MRI to verify the formerly set-up full dose MRI.…”

“…As the fabrications of nanoparticle contrast agents focus on optimizing a variety of parameters, with the emerging of AI, the algorithm based on the deep learning will complete all these tasks prior to perform the final optimized experiments for verification, which will save substantial time, efforts and achieve the high resolution MRI (Moser et al, 2017;Raval et al, 2017). Furthermore, for future MRI, it is suggested to employ the convolutional neural networks in AI deep learning to get the multimodal imaging information with high resolution (Figure 14), where the conventional MRI can only achieve single information with the applied high magnetic field (over 7 T) (Donatelli et al, 2018;Henning, 2018;Turing, 2019).…”

Feasibility of Diffusion Tensor and Morphologic Imaging of Peripheral Nerves at Ultra-High Field Strength

“…Technical advances and particularly the availability of higher field strength have significantly improved visualization of peripheral nerves. Recently, morphologic peripheral nerve imaging has been performed at 7 T, 4 – 7 which substantially enhances the signal-to-noise ratio (SNR) and therefore the achievable spatial resolution, thus improving anatomical depiction of peripheral nerves. In contrast to morphologic sequences, most human peripheral nerve DTI has been implemented at lower field strength, with the exception of one recent attempt at 7 T in 3 healthy participants.…”