MR imaging of proton beam-induced oxygen depletion

IF 3.2 2区医学 Q1 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING

Medical physics Pub Date : 2025-01-28 DOI:10.1002/mp.17622

Juliane Schieferecke, Aswin Hoffmann, Jörg Pawelke

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引用次数: 0

Abstract

Background

Previous studies have shown that in-beam magnetic resonance imaging (MRI) can be used to visualize a proton beam during the irradiation of liquid-filled phantoms. The beam energy- and current-dependent local image contrast observed in water was identified to be predominantly caused by beam-induced buoyant convection and associated flow effects. Besides this flow dependency, the MR signal change was found to be characterized by a change in the $T_{1}$ relaxation time of water, hinting at a radiochemical contribution, which was hypothesized to lie in oxygen depletion-evoked $T_{1}$ relaxation time lengthening. The elucidation of the underlying contrast mechanism is required to enable the further assessment of the application potential of MRI-based proton beam visualization in tissue.

Purpose

The underlying radiochemical cause of the observed local beam-induced change in the $T_{1}$ relaxation time of water should be identified in beam visualization experiments testing the hypothesis of beam-induced oxygen depletion-evoked $T_{1}$ relaxation time lengthening.

Methods

Combined irradiation and imaging experiments were performed using static proton pencil beam irradiation, background-nulled inversion recovery (IR) MRI and a range of flow-restricted phantoms differing in initial oxygen concentration and homogeneity. The similarity of the irradiation-induced MRI contrast to the proton pencil beam dose distribution acquired on radiochromic film, the expected dose dependence and temporal stability, the TR dependence as well as the dependence on the initial oxygen concentration and the oxygen consumption rate were tested. Moreover, the feasibility of oxygen depletion-based beam visualization in tissue-mimicking phantoms was assessed. The levels of irradiation-induced oxygen depletion and $T_{1}$ relaxation time lengthening were estimated based on the measured temperatures and initial oxygen concentrations of the phantoms, the experimentally determined inversion times required for phantom background signal nulling and dosimetric measurements.

Results

The proton irradiation-induced contrast in background-nulled IR images of well oxygenated phantoms was found similar to the proton pencil beam dose distribution and showed the characteristics expected for oxygen depletion-induced MRI contrast. No beam-induced contrast was observed in the poorly oxygenated, inhomogeneous tissue-mimicking phantoms.

Conclusions

Proton beam-induced radiochemical oxygen depletion can be visualized using $T_{1}$ relaxation time contrast-based IR MRI and represents the first identified flow-independent contrast mechanism in MRI-based proton beam visualization in real-time. Beam detection in tissue, however, will be complicated by the increased $T_{1}$ relaxation time inhomogeneity and the lowered levels of initial oxygen concentration compared to in liquids at atmospheric equilibrium and requires further assessment.

Abstract Image

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质子束诱导氧耗竭的磁共振成像。

背景：先前的研究表明，束内磁共振成像（MRI）可以用来显示质子束在充满液体的幻影照射期间的图像。在水中观察到的光束能量和电流相关的局部图像对比度主要由光束诱导的浮力对流和相关的流动效应引起。除了这种流动依赖性外，MR信号的变化还表现为水的t1 ${\rm T}_{1}$弛豫时间的变化，暗示了放射线化学的贡献，假设这是由于缺氧引起的t1 ${\rm T}_{1}$弛豫时间延长。阐明潜在的对比机制是必要的，以便进一步评估基于mri的质子束可视化在组织中的应用潜力。目的：在离子束显像实验中，应明确离子束局部诱导水的t1 ${\rm T}_{1}$弛豫时间变化的潜在放射化学原因，以验证离子束诱导耗氧引起的t1 ${\rm T}_{1}$弛豫时间延长的假说。方法：采用静态质子铅笔束照射、背景反演恢复（IR） MRI和一系列不同初始氧浓度和均匀性的受限流影进行联合照射和成像实验。测试了辐照诱导的MRI对比与在放射致色膜上获得的质子铅笔束剂量分布的相似性，期望剂量依赖性和时间稳定性，TR依赖性以及对初始氧浓度和耗氧速率的依赖性。此外，还评估了在组织模拟幻影中基于缺氧的光束可视化的可行性。根据测量的温度和幻影的初始氧浓度、实验确定的幻影背景信号零化所需的反转时间和剂量学测量，估计了辐照引起的氧消耗水平和t1 ${\rm T}_{1}$弛豫时间延长。结果：在氧合良好的幻影的背景空化红外图像中，发现质子辐照诱导的对比度与质子铅笔束剂量分布相似，并显示出缺氧诱导的MRI对比度的特征。在缺氧、不均匀的模拟组织的幻影中没有观察到光束诱导的对比。结论：基于t1 ${\rm T}_{1}$弛豫时间对比的IR MRI可以实时显示质子束诱导的放射化学氧耗损，这是首次在基于MRI的质子束实时可视化中发现与流量无关的对比机制。然而，由于松弛时间不均匀性的增加和初始氧浓度与大气平衡下液体相比的降低，组织中的光束检测将变得复杂，需要进一步评估。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Medical physics 医学-核医学

CiteScore

6.80

自引率

15.80%

发文量

660

审稿时长

1.7 months

期刊介绍： Medical Physics publishes original, high impact physics, imaging science, and engineering research that advances patient diagnosis and therapy through contributions in 1) Basic science developments with high potential for clinical translation 2) Clinical applications of cutting edge engineering and physics innovations 3) Broadly applicable and innovative clinical physics developments Medical Physics is a journal of global scope and reach. By publishing in Medical Physics your research will reach an international, multidisciplinary audience including practicing medical physicists as well as physics- and engineering based translational scientists. We work closely with authors of promising articles to improve their quality.