Mittl R L, Gomori J M, Schnall M D, Holland G A, Grossman R I, Atlas S W
Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104.
AJNR Am J Neuroradiol. 1993 Jul-Aug;14(4):881-91.
Recent papers have hypothesized that diamagnetic effects of clotting and conformational changes in aging red blood cells immobilize the hemoglobin protein and thus are responsible for the marked hypointensity of acute hematomas on T2-weighted spin-echo MR images. To test that hypothesis, the authors evaluated 24 hemorrhagic components of intracranial hemorrhagic lesions using accepted criteria based on spin-echo images as the definitions of the stage of the hemorrhage.
As a measure of the effects of macromolecular (hemoglobin protein) immobility, magnetization transfer contrast was elicited using a pulsed saturation magnetization transfer experiment. The apparent magnetization transfer contrast (AMTC) was determined by comparing the signal intensities of saturated with unsaturated images and quantified for acute isolated hemorrhages, acute nonisolated hemorrhagic lesions, and subacute-to-chronic hemorrhages.
The AMTC of isolated acute hemorrhage was significantly less than that of normal, white matter and gray matter, indicating the lack of significant magnetization transfer and therefore the lack of effects of restriction of hemoglobin mobility on the signal intensity of acute hemorrhage. Acutely hemorrhagic tissue (nonisolated acute hemorrhage) has significantly more AMTC than isolated acute hemorrhage, but still not exceeding that of brain parenchyma.
This in vivo data concurs with in vitro data and reinforces the concept that the marked hypointensity of acute hematomas is mainly a magnetic susceptibility effect.
近期有论文提出假说，认为凝血的抗磁效应以及衰老红细胞的构象变化会使血红蛋白蛋白固定，从而导致急性血肿在T2加权自旋回波磁共振图像上呈现明显低信号。为验证该假说，作者使用基于自旋回波图像的公认标准来定义出血阶段，对24例颅内出血性病变的出血成分进行了评估。
作为大分子（血红蛋白蛋白）固定效应的一种测量方法，通过脉冲饱和磁化传递实验来引发磁化传递对比。表观磁化传递对比（AMTC）通过比较饱和图像与不饱和图像的信号强度来确定，并针对急性孤立性出血、急性非孤立性出血性病变以及亚急性至慢性出血进行量化。
孤立性急性出血的AMTC显著低于正常白质和灰质，表明缺乏显著的磁化传递，因此血红蛋白流动性受限对急性出血信号强度没有影响。急性出血组织（非孤立性急性出血）的AMTC明显高于孤立性急性出血，但仍未超过脑实质。
该体内数据与体外数据一致，强化了急性血肿明显低信号主要是磁化率效应这一概念。
