Department of Radiology, The Jikei University School of Medicine Hospital, 3-19-18 Nishishimbashi, Minato-ku, Tokyo, 105-8471, Japan.
Ann Nucl Med. 2012 Aug;26(7):603-7. doi: 10.1007/s12149-012-0615-2. Epub 2012 Jul 6.
Strontium-89 ((89)Sr) chloride has been used to treat metastases in bone. A method to visualize the distribution of (89)Sr chloride with a scintillation camera was developed in 1996. Studies using bremsstrahlung imaging have shown that (89)Sr accumulates in bone and that the bremsstrahlung generated from biological tissue surrounding bone does not exceed 30 keV. However, it was not clear how low-energy bremsstrahlung from bone can produce peak energy levels of around 75 keV. We speculate that a different (unidentified) factor is involved.
The energy spectrum of an (89)Sr source was acquired with a scintillation camera with or without a low-to-medium-energy general-purpose collimator. The energy window was set at 20-650 keV for 4 windows. A 50-mm thick acrylic block was placed between the scintillation camera and the (89)Sr source to exclude the effects of bremsstrahlung. The energy spectrum of (89)Sr covered with lead was acquired using the scintillation camera without a collimator.
With the collimator the energy spectrum curve was similar to that without the 50 mm of acrylic. The energy spectrum curve showed peaks at about 75, 170, and 520 keV. Without the collimator the energy spectrum showed a similar curve but no peak at 75 keV peak. The curve was similar to that obtained with the scintillation camera and the collimator; however, the curve obtained when the (89)Sr source had been placed in a lead container was similar to that obtained when the source was unshielded, and the collimator was not attached to the scintillation camera.
If bremsstrahlung of (89)Sr produces an image, a low-energy spectrum region should decrease when acrylic is placed between the (89)Sr source and the scintillation camera. However, similar curves were obtained both with the acrylic in place and without the acrylic. Therefore, we believe that the radiation detected by the scintillation camera was not bremsstrahlung due to the beta rays of (89)Sr. Most (89)Sr preparations are contaminated by (85)Sr, and most of the gamma ray energy of (85)Sr is 514 keV. The scintillation camera detected the characteristic X-ray energy of about 75 keV from the materials of the collimator (lead and others) through interaction with the gamma rays of (85)Sr.
锶-89((89)Sr)氯化物已被用于治疗骨转移。1996 年开发了一种用闪烁相机可视化(89)Sr 氯化物分布的方法。使用韧致辐射成像的研究表明，(89)Sr 在骨中积累，并且来自骨周围生物组织的韧致辐射不超过 30keV。然而，目前尚不清楚来自骨骼的低能韧致辐射如何产生约 75keV 的峰值能量。我们推测涉及到另一个（未识别的）因素。
使用闪烁相机获取(89)Sr 源的能谱，有或没有低-中能通用准直器。能谱窗口设置为 20-650keV 共 4 个窗口。在闪烁相机和(89)Sr 源之间放置 50mm 厚的亚克力块以排除韧致辐射的影响。使用没有准直器的闪烁相机获取覆盖铅的(89)Sr 源的能谱。
使用准直器时，能谱曲线与不使用 50mm 亚克力时相似。能谱曲线在约 75、170 和 520keV 处出现峰值。没有准直器时，能谱显示出类似的曲线，但没有 75keV 峰。该曲线与带有准直器的闪烁相机获得的曲线相似；然而，当将(89)Sr 源放置在铅容器中时获得的曲线与未屏蔽且未将准直器附接到闪烁相机时获得的曲线相似。
如果(89)Sr 的韧致辐射产生图像，则在(89)Sr 源和闪烁相机之间放置亚克力时，低能谱区应该减少。然而，在放置亚克力和不放置亚克力时都获得了相似的曲线。因此，我们认为闪烁相机检测到的辐射不是由于(89)Sr 的β射线产生的韧致辐射。大多数(89)Sr 制剂都受到(85)Sr 的污染，而(85)Sr 的大部分伽马射线能量为 514keV。闪烁相机通过与(85)Sr 的伽马射线相互作用，检测到来自准直器（铅等）材料的约 75keV 的特征 X 射线能量。
