Department of Radiology, University of California, San Diego, California.
Research Service, Veterans Affairs San Diego Healthcare System, San Diego, California.
Semin Musculoskelet Radiol. 2020 Aug;24(4):386-401. doi: 10.1055/s-0040-1710355. Epub 2020 Sep 29.
Bone is a composite material consisting of mineral, organic matrix, and water. Water in bone can be categorized as bound water (BW), which is bound to bone mineral and organic matrix, or as pore water (PW), which resides in Haversian canals as well as in lacunae and canaliculi. Bone is generally classified into two types: cortical bone and trabecular bone. Cortical bone is much denser than trabecular bone that is surrounded by marrow and fat. Magnetic resonance (MR) imaging has been increasingly used for noninvasive assessment of both cortical bone and trabecular bone. Bone typically appears as a signal void with conventional MR sequences because of its short T2*. Ultrashort echo time (UTE) sequences with echo times 100 to 1,000 times shorter than those of conventional sequences allow direct imaging of BW and PW in bone. This article summarizes several quantitative MR techniques recently developed for bone evaluation. Specifically, we discuss the use of UTE and adiabatic inversion recovery prepared UTE sequences to quantify BW and PW, UTE magnetization transfer sequences to quantify collagen backbone protons, UTE quantitative susceptibility mapping sequences to assess bone mineral, and conventional sequences for high-resolution imaging of PW as well as the evaluation of trabecular bone architecture.
骨是一种由矿物质、有机基质和水组成的复合材料。骨中的水可以分为结合水（BW）和孔（PW）。结合水与骨矿物质和有机基质结合，而孔水则存在于哈夫氏管以及骨陷窝和骨小管中。骨通常分为皮质骨和松质骨。皮质骨比松质骨致密，松质骨被骨髓和脂肪包围。磁共振（MR）成像已越来越多地用于皮质骨和松质骨的无创评估。由于其 T2*短，常规 MR 序列中骨通常表现为信号缺失。回波时间比常规序列短 100 到 1000 倍的超短回波时间（UTE）序列允许直接对 BW 和 PW 进行成像。本文总结了最近开发的几种用于骨评估的定量 MR 技术。具体而言，我们讨论了使用 UTE 和绝热反转恢复准备的 UTE 序列来定量 BW 和 PW、UTE 磁化传递序列来定量胶原主链质子、UTE 定量磁化率映射序列来评估骨矿物质以及常规序列来进行高分辨率 PW 成像以及评估松质骨结构。
