Ma Ya-Jun, Fan Shujuan, Shao Hongda, Du Jiang, Szeverenyi Nikolaus M, Young Ian R, Bydder Graeme M
Department of Radiology, University of California, San Diego, San Diego, CA, USA.
Formerly Department of Electrical Engineering, Imperial College, London, UK.
Quant Imaging Med Surg. 2020 Jun;10(6):1334-1369. doi: 10.21037/qims-20-568.
The group of Multiplied, Added, Subtracted and/or fiTted Inversion Recovery (MASTIR) pulse sequences in which usually two or more inversion recovery (IR) images of different types are combined is described, and uses for this type of sequence are outlined. IR sequences of different types can be multiplied, added, subtracted, and/or fitted together to produce variants of the MASTIR sequence. The sequences provide a range of options for increasing image contrast, demonstrating specific tissues and fluids of interest, and suppressing unwanted signals. A formalism using the concept of pulse sequences as tissue property filters is used to explain the signal, contrast and weighting of the pulse sequences with both univariate and multivariate filter models. Subtraction of one magnitude reconstructed IR image from another with a shorter TI can produce very high T dependent positive contrast from small increases in T. The reverse subtracted IR sequence can provide high positive contrast enhancement with gadolinium chelates and iron deposition which decrease T. Additional contrast to that arising from increases in T can be produced by supplementing this with contrast arising from concurrent increases in ρ and T, as well as increases or decreases in diffusion using subtraction IR with echo subtraction and/or diffusion subtraction. Phase images may show 180º differences as a result of rotating into the transverse plane both positive and negative longitudinal magnetization. Phase images with contrast arising in this way, or other ways, can be multiplied by magnitude IR images to increase the contrast of the latter. Magnetization Transfer (MT) and susceptibility can be used with IR sequences to improve contrast. Selective images of white and brown adipose tissue lipid and water components can be produced using different TIs and in and out-of-phase TEs. Selective images of ultrashort and short T tissue components can be produced by nulling long T tissue components with an inversion pulse and subtraction of images with longer TEs from images with ultrashort TEs. The Double Echo Sliding IR (DESIRE) sequence provides images with a wide range of TIs from which it is possible to choose values of TI to achieve particular types of tissue and/or fluid contrast (e.g., for subtraction with different TIs, as described above, and for long T tissue signal nulling with UTE sequences). Unwanted tissue and fluid signals can be suppressed by addition and subtraction of phase-sensitive (ps) and magnitude reconstructed images. The sequence also offers options for synergistic use of the changes in blood and tissue ρ, T, T/T*, D* and perfusion that can be seen with fMRI of the brain. and illustrative examples of normal brain, cartilage, multiple sclerosis, Alzheimer's disease, and peripheral nerve imaged with different forms of the MASTIR sequence are included.
描述了乘法、加法、减法和/或拟合反转恢复（MASTIR）脉冲序列组，其中通常会组合两个或更多不同类型的反转恢复（IR）图像，并概述了此类序列的用途。不同类型的IR序列可以相乘、相加、相减和/或拟合在一起，以产生MASTIR序列的变体。这些序列提供了一系列选项，用于增加图像对比度、显示感兴趣的特定组织和液体以及抑制不需要的信号。使用脉冲序列作为组织特性滤波器的概念的形式主义，用单变量和多变量滤波器模型来解释脉冲序列的信号、对比度和加权。用较短TI的另一个幅度重建IR图像减去一个，可以从小的T增加中产生非常高的T依赖性正对比度。反向减法IR序列可以通过钆螯合物和铁沉积（它们会降低T）提供高正对比度增强。通过用ρ和T的同时增加以及使用回波减法和/或扩散减法的减法IR的扩散增加或减少所产生的对比度来补充这一点，可以产生除T增加之外的额外对比度。相位图像可能会显示180°的差异，这是由于正负纵向磁化都旋转到横向平面所致。以这种方式或其他方式产生对比度的相位图像可以乘以幅度IR图像以增加后者的对比度。磁化传递（MT）和磁化率可与IR序列一起使用以改善对比度。使用不同的TI以及同相和反相TE，可以生成白色和棕色脂肪组织脂质和水成分的选择性图像。通过用反转脉冲使长T组织成分归零，并从具有超短TE的图像中减去具有更长TE的图像，可以生成超短和短T组织成分的选择性图像。双回波滑动IR（DESIRE）序列提供具有广泛TI的图像，可以从中选择TI值以实现特定类型的组织和/或液体对比度（例如，如上所述用于不同TI的减法，以及用于用UTE序列使长T组织信号归零）。不需要的组织和液体信号可以通过相加和相减相位敏感（ps）和幅度重建图像来抑制。该序列还提供了协同利用大脑功能磁共振成像中可以看到的血液和组织ρ、T、T/T*、D*和灌注变化的选项。还包括用不同形式的MASTIR序列成像的正常大脑、软骨、多发性硬化症、阿尔茨海默病和周围神经的示例。
