Goodwin P N
Department of Radiology, Albert Einstein College of Medicine, Bronx, NY 10461.
Semin Nucl Med. 1987 Oct;17(4):293-304. doi: 10.1016/s0001-2998(87)80022-3.
Radiographic methods of determining bone density have been available for many years, but recently most of the efforts in this field have focused on the development of instruments which would accurately and automatically measure bone density by absorption, or by the use of x-ray computed tomography (CT). Single energy absorptiometers using I-125 have been available for some years, and have been used primarily for measurements on the radius, although recently equipment for measuring the os calcis has become available. Accuracy of single energy measurements is about 3% to 5%; precision, which has been poor because of the difficulty of exact repositioning, has recently been improved by automatic methods so that it now approaches 1% or better. Dual energy sources offer the advantages of greater accuracy and the ability to measure the spine and other large bones. A number of dual energy scanners are now on the market, mostly using gadolinium-153 as a source. Dual energy scanning is capable of an accuracy of a few percent, but the precision when scanning patients can vary widely, due to the difficulty of comparing exactly the same areas; 2 to 4% would appear to be typical. Quantitative computed tomography (QCT) can be used to directly measure the trabecular bone within the vertebral body. The accuracy of single-energy QCT is affected by the amount of marrow fat present, which can lead to underestimations of 10% or more. An increase in marrow fat would cause an apparent decrease in bone mineral. However, the precision can be quite good, 1% or 2% on phantoms, and nearly as good on patients when four vertebrae are averaged. Dual energy scanning can correct for the presence of fat, but is less precise, and not available on all CT units. QCT of the femoral neck has recently been attempted, but presents difficulties that make it unlikely to become widely accepted. Recently there has been much interest in using gamma cameras for dual energy bone density measurements. Although this can present some difficulties, several groups reportedly have overcome them, and this technique may have more widespread application in the future.
测定骨密度的放射学方法已经存在多年，但最近该领域的大部分工作都集中在开发能够通过吸收或使用X射线计算机断层扫描（CT）准确自动测量骨密度的仪器上。使用碘-125的单能吸收仪已经问世数年，主要用于测量桡骨，不过最近也有了测量跟骨的设备。单能测量的准确度约为3%至5%；由于难以精确重新定位，其精密度一直较差，但最近通过自动方法得到了改善，现在已接近1%或更高。双能源具有更高的准确度以及能够测量脊柱和其他大骨骼的优势。现在市场上有多种双能扫描仪，大多使用钆-153作为源。双能扫描的准确度可达百分之几，但扫描患者时的精密度会因难以精确比较相同区域而有很大差异；2%至4%似乎是典型值。定量计算机断层扫描（QCT）可用于直接测量椎体内部的小梁骨。单能QCT的准确度受骨髓脂肪量的影响，这可能导致低估10%或更多。骨髓脂肪增加会导致骨矿物质明显减少。然而，精密度可以相当好，在体模上为1%或2%，对患者进行四个椎体平均测量时也几乎一样好。双能扫描可以校正脂肪的存在，但精密度较低，并非所有CT设备都具备。最近有人尝试对股骨颈进行QCT测量，但存在一些困难，不太可能被广泛接受。最近，人们对使用伽马相机进行双能骨密度测量产生了浓厚兴趣。尽管这可能会带来一些困难，但据报道有几个研究小组已经克服了这些困难，这项技术未来可能会有更广泛的应用。
