Atlas S W, Braffman B H, LoBrutto R, Elder D E, Herlyn D
Department of Radiology, University of Pennsylvania, Philadelphia 19104.
J Comput Assist Tomogr. 1990 Jul-Aug;14(4):547-54. doi: 10.1097/00004728-199007000-00009.
The etiology of the paramagnetic relaxation enhancement seen in malignant melanoma on proton magnetic resonance (MR) images has been the subject of many recent investigations and has been ascribed to iron from associated hemorrhage or chelated metal ions, rather than directly due to melanin. The purpose of this study was to correlate proton relaxation times on MR images in malignant melanomas with histopathologic features (i.e., degree of pigmentation, iron deposition, and necrosis), water content, and electron paramagnetic resonance (EPR) spectra to elucidate the etiology of the relaxation behavior demonstrated by these neoplasms. Cultured cells derived from human malignant melanoma metastases were implanted subcutaneously into nude mice. Twelve separate lesions were evaluated in 10 mice. Magnetic resonance imaging was performed in vivo at 1.9 T using spin echo and inversion recovery acquisitions for the purposes of calculating T1, T2, and proton density [N(H)]. Histopathologic examination was performed on specimens resected immediately after imaging, using hematoxylin/eosin, Prussian blue, and Fontana stains to assess tumor necrosis, and iron and melanin content. Dry/wet weight ratios and EPR spectra were also obtained on resected specimens. Our results indicate that T1 shortening correlates with increasing melanin content and not with increasing iron deposition, EPR-active metallic cations, necrosis, or water content. In fact, a presumably unrelated statistical correlation was found between increased iron and T1 prolongation. The T2 relaxation times did not correlate with the presence of any single factor other than proton density. Although the unique relaxation behavior of nonhemorrhagic malignant melanoma in vivo cannot be traced to a single cause, our data suggest that, contrary to previous investigations, it is strongly influenced by the presence of melanin rather than iron or other naturally occurring paramagnetic ions.
质子磁共振（MR）图像上恶性黑色素瘤中所见的顺磁弛豫增强的病因一直是近期许多研究的主题，并且已归因于相关出血中的铁或螯合金属离子，而非直接归因于黑色素。本研究的目的是将恶性黑色素瘤的MR图像上的质子弛豫时间与组织病理学特征（即色素沉着程度、铁沉积和坏死）、含水量和电子顺磁共振（EPR）光谱相关联，以阐明这些肿瘤所表现出的弛豫行为的病因。将源自人恶性黑色素瘤转移灶的培养细胞皮下植入裸鼠体内。在10只小鼠中评估了12个独立的病灶。使用自旋回波和反转恢复采集序列在1.9 T场强下进行体内磁共振成像，以计算T1、T2和质子密度[N(H)]。在成像后立即切除的标本上进行组织病理学检查，使用苏木精/伊红、普鲁士蓝和丰塔纳染色来评估肿瘤坏死以及铁和黑色素含量。还对切除的标本获得了干/湿重比和EPR光谱。我们的结果表明，T1缩短与黑色素含量增加相关，而与铁沉积增加、具有EPR活性的金属阳离子、坏死或含水量无关。事实上，发现铁增加与T1延长之间存在一种可能无关的统计相关性。除质子密度外，T2弛豫时间与任何单一因素均无相关性。尽管体内非出血性恶性黑色素瘤独特的弛豫行为无法追溯到单一原因，但我们的数据表明，与先前的研究相反，它受黑色素的存在强烈影响，而非铁或其他天然存在的顺磁离子。
