Lord M L, McNeill F E, Gräfe J L, Noseworthy M D, Chettle D R
Department of Medical Physics and Radiation Science, McMaster University, Main St. W., Hamilton, Canada L8S 4L8.
Department of Physics, Ryerson University, Victoria St., Toronto, Canada M5B 2K3.
Appl Radiat Isot. 2016 Jun;112:103-9. doi: 10.1016/j.apradiso.2016.03.021. Epub 2016 Mar 21.
Gadolinium (Gd) based contrast agents have been commonly used over the past three decades to improve contrast in magnetic resonance imaging. These complexes, originally thought to be stable and clear from the body shortly after administration, have been shown to dissociate to a small extent and deposit in organs such as bone. A safe and non-invasive method for measuring Gd in bone is necessary for further exploring Gd retention in the body following the administration of a contrast agent. A feasibility study using a K x-ray fluorescence (K-XRF) system to measure Gd in human tibias was investigated. Bone phantoms mimicking human tibia were created with Gd concentrations ranging from 0 to 120ppm. The minimum detection limit (MDL) was calculated from 20-hour and 7-hour phantom measurements with a source activity of 0.11GBq. All MDL values were scaled to a more realistic measurement time of 30-minutes with a stronger source. Scaling arguments were based on activity ratio, measurement time, and system dead time. The MDL for a 1GBq source was estimated to be 3.60-3.64ppm, for an average range of tissue thicknesses overlaying a human tibia. For a stronger source of 5GBq and a four detector cloverleaf system, the MDL was estimated to be 1.49-1.52ppm. Determined and predicted MDLs are within the range of previous in-vitro Gd measurement data. The K-XRF system shows promising results for detecting Gd in bone and should be seriously considered for in-vivo measurements.
在过去三十年中，钆（Gd）基造影剂已被广泛用于改善磁共振成像中的对比度。这些复合物最初被认为是稳定的，并且在给药后不久就能从体内清除，但现已证明它们会在一定程度上解离并沉积在骨骼等器官中。为了进一步探索造影剂给药后钆在体内的滞留情况，需要一种安全且非侵入性的方法来测量骨骼中的钆。本研究对使用K射线荧光（K-XRF）系统测量人体胫骨中钆的可行性进行了调查。制作了钆浓度范围为0至120ppm的模拟人体胫骨的骨模体。通过对源活度为0.11GBq的骨模体进行20小时和7小时的测量来计算最低检测限（MDL）。所有MDL值均按比例换算到源更强、测量时间更实际的30分钟。比例换算依据活度比、测量时间和系统死时间。对于覆盖人体胫骨的平均组织厚度范围，1GBq源的MDL估计为3.60 - 3.64ppm。对于5GBq的更强源和四探测器苜蓿叶形系统，MDL估计为1.49 - 1.52ppm。测定的和预测的MDL值在先前体外钆测量数据的范围内。K-XRF系统在检测骨骼中的钆方面显示出有前景的结果，应认真考虑将其用于体内测量。
