Reducing PNS with minimal performance penalties via simple pulse sequence modifications on a high-performance compact 3T scanner

Abstract

One of the major concerns associated with high-performance gradients is peripheral nerve stimulation (PNS) of the subject during MRI exams. Since the installation, more than 680 volunteer subjects (patients and controls) have been scanned on a compact 3 T MRI system with high-performance gradients, capable of 80 mT m−1 gradient amplitude and 700 T m−1 s−1 slew rate simultaneously. Despite PNS concerns associated with the high-performance gradients, due to the smaller physical dimensions of the gradient coils, minimal or no PNS sensation was reported with most pulse sequences. The exception was PNS reported by only five of 252 subjects (about 2%) scanned with a specific 3D fast spin echo pulse sequence (3DFLAIR). Rather than derating the entire system performance across all pulse sequences and all gradient lobes, we addressed reported PNS effect with a simple and specific modification to the targeted lobes of the problematic pulse sequence. in addition, the PNS convolutional model was adapted to predict sequence-specific PNS threshold level and its reduction after derating. The effectiveness of the targeted pulse sequence modification was demonstrated by successfully re-scanning four of the subjects who previously reported PNS sensations without further reported PNS. The pulse sequence modification did not result in noticeable degradation of image quality or substantial increase in scan time. The results demonstrated that PNS was rarely reported on the compact 3 T, and when it was, utilizing a specific modification of the gradient waveform causing PNS was an effective strategy, rather than derating the performance of the entire gradient system.

Improved Brain MR Imaging from a Compact, Lightweight 3T Scanner with High‐Performance Gradients

“…The patients tolerated imaging well on both the C3T and WB3T scanners. There were no reports of imaging related PNS on either scanner, consistent with previously reported results 4,8 …”

“…There were no reports of imaging related PNS on either scanner, consistent with previously reported results. 4,8 Overall, we report an inter-reader agreement of 80%; detailed agreements broken down by sequence and parameters are reported in Table 2. Sequence and parameter-specific agreement ranged from 40% (SNR in T2 FSE) to 96% (both overall quality in DWI and susceptibility artifact in T1 MP-RAGE).…”

“…4 As such, PNS is rarely observed on the C3T, and can also be easily managed with simple sequence modifications if it does become manifest. 8 The resulting 37 cm patient bore can accommodate a variety of existing head coils ranging from 8 to 32 channels, including compatibility with new adaptive image receive coil arrays. 9 The scanner weighs only 2000 kg and can fit in a freight elevator for delivery/installation.…”

“…Even with these high‐performance gradient specifications, peripheral nerve stimulation (PNS) with the C3T has a higher threshold compared to whole‐body gradient coils due to the smaller radius of the gradient coil 4 . As such, PNS is rarely observed on the C3T, and can also be easily managed with simple sequence modifications if it does become manifest 8 . The resulting 37 cm patient bore can accommodate a variety of existing head coils ranging from 8 to 32 channels, including compatibility with new adaptive image receive coil arrays 9 .…”

Systematic Dimensional Analysis of the Scaling Relationship for Gradient and Shim Coil Design Parameters

“…The quadratic dependence of inductance on gradient efficiency illustrates a fundamental tradeoff between maximum gradient amplitude and slew rate. 1,4 Note that Equation (9) can still be obtained from Equation (7), but only with a particular choice…”