PURPOSE High resolution multi-gradient echo (MGE) scanning is typically used for detection of molecularly targeted iron oxide particles. The images of individual echoes are often combined to generate a composite image with improved SNR from the early echoes and boosted contrast from later echoes. In 3D implementations prolonged scanning at high gradient duty cycles induces a B0 shift that predominantly affects image alignment in the slow phase encoding dimension of 3D MGE images. The effect corrupts the composite echo image and limits the image resolution that is realised. A real-time adaptive B0 stabilisation during respiration gated 3D MGE scanning is shown to reduce image misalignment and improve detection of molecularly targeted iron oxide particles in composite images of the mouse brain. METHODS An optional B0 measurement block consisting of a 16 μs hard pulse with FA 1°, an acquisition delay of 3.2 ms, followed by gradient spoiling in all three axes was added to a respiration gated 3D MGE scan. During the acquisition delay of each B0 measurement block the NMR signal was routed to a custom built B0 stabilisation unit which mixed the signal to an audio frequency nominally centred around 1000 Hz to enable an Arduino based single channel receiver to measure frequency shifts. The frequency shift was used to effect correction to the main magnetic field via the B0 coil. The efficacy of B0 stabilisation and respiration gating was validated in vivo and used to improve detection of molecularly targeted microparticles of iron oxide (MPIO) in a mouse model of acute neuroinflammation. RESULTS Without B0 stabilisation 3D MGE image data exhibit varying mixtures of translation, scaling and blurring, which compromise the fidelity of the composite image. The real-time adaptive B0 stabilisation minimises corruption of the composite image as the images from the different echoes are properly aligned. The improved detection of molecularly targeted MPIO easily compensates for the scan time penalty of 14% incurred by the B0 stabilisation method employed. Respiration gating of the B0 measurement and the MRI scan was required to preserve high resolution detail, especially towards the back of the brain. CONCLUSIONS High resolution imaging for the detection of molecularly targeted iron oxide particles in the mouse brain requires good stabilisation of the main B0 field, and can benefit from a respiration gated image acquisition strategy.

中文翻译：

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使用 B0 场稳定高分辨率 MRI 改进了对小鼠大脑中分子靶向氧化铁颗粒的检测。


目的 高分辨率多梯度回波 (MGE) 扫描通常用于检测分子靶向氧化铁颗粒。通常将各个回波的图像组合起来生成合成图像，该图像具有来自早期回波的改进的信噪比和来自后期回波的增强的对比度。在 3D 实现中，高梯度占空比下的长时间扫描会导致 B0 偏移，该偏移主要影响 3D MGE 图像的慢相位编码维度中的图像对准。该效应会破坏复合回波图像并限制所实现的图像分辨率。呼吸门控 3D MGE 扫描期间的实时自适应 B0 稳定可减少图像错位，并改善小鼠大脑复合图像中分子靶向氧化铁颗粒的检测。方法 将可选的 B0 测量模块添加到呼吸门控 3D MGE 扫描中，该测量模块由 FA 1° 的 16 μs 硬脉冲、3.2 ms 的采集延迟以及所有三个轴上的梯度破坏组成。在每个 B0 测量块的采集延迟期间，NMR 信号被路由到定制的 B0 稳定单元，该单元将信号混合到名义上以 1000 Hz 为中心的音频，以使基于 Arduino 的单通道接收器能够测量频移。频移用于通过 B0 线圈对主磁场进行校正。 B0 稳定和呼吸门控的功效在体内得到验证，并用于改善急性神经炎症小鼠模型中氧化铁分子靶向微粒 (MPIO) 的检测。结果 如果没有 B0 稳定，3D MGE 图像数据会表现出不同的平移、缩放和模糊混合，这会损害合成图像的保真度。 由于来自不同回波的图像正确对齐，实时自适应 B0 稳定功能可最大限度地减少合成图像的损坏。改进的分子靶向 MPIO 检测可以轻松补偿因采用 B0 稳定方法而导致的 14% 扫描时间损失。 B0 测量和 MRI 扫描的呼吸门控需要保留高分辨率细节，尤其是大脑后部的细节。结论 用于检测小鼠大脑中分子靶向氧化铁颗粒的高分辨率成像需要主 B0 场的良好稳定性，并且可以受益于呼吸门控图像采集策略。