FastPtx: a versatile toolbox for rapid, joint design of pTx RF and gradient pulses using Pytorch’s autodifferentiation

IF 2 4区 医学 Q3 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING
Dario Bosch, Klaus Scheffler
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引用次数: 0

Abstract

Objective

With modern optimization methods, free optimization of parallel transmit pulses together with their gradient waveforms can be performed on-line within a short time. A toolbox which uses PyTorch’s autodifferentiation for simultaneous optimization of RF and gradient waveforms is presented and its performance is evaluated.

Methods

MR measurements were performed on a 9.4T MRI scanner using a 3D saturated single-shot turboFlash sequence for \(B_1^+\) mapping. RF pulse simulation and optimization were done using a Python toolbox and a dedicated server. An RF- and Gradient pulse design toolbox was developed, including a cost function to balance different metrics and respect hardware and regulatory limits. Pulse performance was evaluated in GRE and MPRAGE imaging. Pulses for non-selective and for slab-selective excitation were designed.

Results

Universal pulses for non-selective excitation reduced the flip angle error to an NRMSE of (12.3±1.7)% relative to the targeted flip angle in simulations, compared to (42.0±1.4)% in CP mode. The tailored pulses performed best, resulting in a narrow flip angle distribution with NRMSE of (8.2±1.0)%. The tailored pulses could be created in only 66 s, making it feasible to design them during an experiment. A 90° pulse was designed as preparation pulse for a satTFL sequence and achieved a NRMSE of 7.1%. We showed that both MPRAGE and GRE imaging benefited from the pTx pulses created with our toolbox.

Conclusion

The pTx pulse design toolbox can freely optimize gradient and pTx RF waveforms in a short time. This allows for tailoring high-quality pulses in just over a minute.

Abstract Image

FastPtx:使用 Pytorch 自分化技术快速联合设计 pTx 射频和梯度脉冲的多功能工具箱
目的利用现代优化方法,可在短时间内在线自由优化并行发射脉冲及其梯度波形。方法在一台9.4T核磁共振扫描仪上使用三维饱和单发涡轮闪烁序列进行MR测量,以进行\(B_1^+\)映射。射频脉冲模拟和优化是使用 Python 工具箱和专用服务器完成的。我们开发了一个射频和梯度脉冲设计工具箱,其中包括一个成本函数,用于平衡不同的指标并遵守硬件和法规限制。在 GRE 和 MPRAGE 成像中对脉冲性能进行了评估。结果用于非选择性激励的通用脉冲在模拟中将翻转角误差降低到相对于目标翻转角的 NRMSE (12.3±1.7)% ,而在 CP 模式中为 (42.0±1.4)%。量身定制的脉冲表现最佳,产生了窄翻转角分布,NRMSE 为 (8.2±1.0)%。定制脉冲仅需 66 秒即可创建,因此在实验过程中设计这些脉冲是可行的。我们设计了一个 90° 脉冲作为 satTFL 序列的准备脉冲,其 NRMSE 为 7.1%。结论pTx 脉冲设计工具箱可在短时间内自由优化梯度和 pTx 射频波形。这样就能在一分钟内定制出高质量的脉冲。
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来源期刊
CiteScore
4.60
自引率
0.00%
发文量
58
审稿时长
>12 weeks
期刊介绍: MAGMA is a multidisciplinary international journal devoted to the publication of articles on all aspects of magnetic resonance techniques and their applications in medicine and biology. MAGMA currently publishes research papers, reviews, letters to the editor, and commentaries, six times a year. The subject areas covered by MAGMA include: advances in materials, hardware and software in magnetic resonance technology, new developments and results in research and practical applications of magnetic resonance imaging and spectroscopy related to biology and medicine, study of animal models and intact cells using magnetic resonance, reports of clinical trials on humans and clinical validation of magnetic resonance protocols.
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