The spectral quality of magnetic resonance spectroscopic imaging (MRSI) can be affected by strong magnetic field inhomogeneities, posing a challenge for 3D-MRSI’s widespread clinical use with standard scanner-equipped 2nd-order shim coils. To overcome this, we designed an empirical unified shim–RF head coil (32-ch RF receive and 51-ch shim) for 3D-MRSI improvement. We compared its shimming performance and 3D-MRSI brain coverages against the standard scanner shim (2nd-order spherical harmonic (SH) shim coils) and integrated parallel reception, excitation, and shimming (iPRES) 32-ch AC/DC head coil. We also simulated a theoretical 3rd-, 4th-, and 5th-order SH shim as a benchmark to assess the UNIfied shim–RF coil (UNIC) improvements. In this preliminary study, the whole-brain coverage was simulated by using B0field maps of twenty-four healthy human subjects (n= 24). Our results demonstrated that UNIC substantially improves brain field homogeneity, reducing whole-brain frequency standard deviations by 27% compared to the standard 2nd-order scanner shim and 17% compared to the iPRES shim. Moreover, UNIC enhances whole-brain coverage of 3D-MRSI by up to 34% compared to the standard 2nd-order scanner shim and up to 13% compared to the iPRES shim. UNIC markedly increases coverage in the prefrontal cortex by 147% and 47% and in the medial temporal lobe and temporal pole by 29% and 13%, respectively, at voxel resolutions of 1.4 cc and 0.09 cc for 3D-MRSI. Furthermore, UNIC effectively reduces variations in shim quality and brain coverage among different subjects compared to scanner shim and iPRES shim. Anticipated advancements in higher-order shimming (beyond 6th order) are expected via optimized designs using dimensionality reduction methods.
磁共振波谱成像(MRSI)的谱图质量易受强磁场不均匀性影响，这为标准扫描仪配备的二阶匀场线圈在三维MRSI中的广泛应用带来挑战。为此，我们设计了一种经验性统一的匀场-射频头线圈（32通道射频接收与51通道匀场）以优化三维MRSI性能。本研究将其匀场效能及三维MRSI脑区覆盖范围与标准扫描仪匀场系统（二阶球谐函数匀场线圈）、集成并行接收-激励-匀场32通道交直流头线圈进行对比，并模拟三阶、四阶及五阶球谐函数匀场作为基准，评估统一匀场-射频线圈的性能提升。在此初步研究中，通过24名健康受试者的B0场图数据模拟全脑覆盖情况。结果显示：相较于标准二阶扫描仪匀场系统，UNIC使全脑频率标准差降低27%；相较于iPRES匀场系统降低17%。在三维MRSI应用中，UNIC将全脑覆盖范围较标准二阶扫描仪匀场系统提升达34%，较iPRES匀场系统提升达13%。在体素分辨率分别为1.4立方厘米和0.09立方厘米条件下，UNIC使前额叶皮层覆盖分别提升147%和47%，内侧颞叶与颞极区域覆盖分别提升29%和13%。此外，相较于扫描仪匀场与iPRES匀场系统，UNIC能有效降低不同受试者间匀场质量及脑区覆盖的差异性。通过采用降维方法进行优化设计，预计未来可实现超越六阶的高阶匀场技术突破。
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