Electronic Radiology Laboratory, Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Boulevard, Campus Box 8131, St. Louis, MO 63110, USA.
Osteoporos Int. 2012 Jul;23(7):1977-85. doi: 10.1007/s00198-011-1851-3. Epub 2011 Dec 7.
Few studies exist for bone densitometry of the whole foot. A phantom study demonstrated the sources of error and necessary controls for accurate quantitative computed tomography of the foot. A loss in bone mineral density (BMD) in the small foot bones may be an early indicator of diabetic foot complications.
Volumetric quantitative computed tomography (vQCT) facilitates the assessment of pedal bone osteopenia, which, in the presence of peripheral neuropathy, may well be an early sign of diabetic foot deformity. To date, sources and magnitudes of error in foot vQCT measurements have not been reported.
Foot phantoms were scanned using a 64-slice CT scanner. Energy (in kilovoltage peak), table height, phantom size and orientation, location of "bone" inserts, insert material, location of calibration phantom, and reconstruction kernel were systematically varied during scan acquisition.
Energy (in kilovoltage peak) and distance from the isocenter (table height) resulted in relative attenuation changes from -5% to 22% and -5% to 0%, respectively, and average BMD changes from -0.9% to 0.0% and -1.1% to 0.3%, respectively, compared to a baseline 120-kVp scan performed at the isocenter. BMD compared to manufacturer-specified values ranged, on average, from -2.2% to 0.9%. Phantom size and location of bone-equivalent material inserts resulted in relative attenuation changes of -1.2% to 1.4% compared to the medium-sized phantom.
This study demonstrated that variations in kilovoltage peak and table height can be controlled using a calibration phantom scanned at the same energy and height as a foot phantom; however, error due to soft tissue thickness and location of bones within a foot cannot be controlled using a calibration phantom alone.
针对整个足部的骨密度测定，目前仅有少量研究。一项体模研究展示了足部定量 CT 扫描的误差来源和必要的控制方法，以确保结果的准确性。足部小骨骨密度的降低可能是糖尿病足并发症的早期指标。
容积定量 CT（vQCT）有助于评估足骨骨质疏松症，在外周神经病变的情况下，这可能是糖尿病足畸形的早期迹象。迄今为止，尚未报道足部 vQCT 测量的误差来源和幅度。
使用 64 层 CT 扫描仪对足模进行扫描。在扫描采集过程中，系统地改变了能量（千伏峰值）、检查床高度、体模大小和方向、“骨”插件的位置、插件材料、校准体模的位置以及重建核。
与在等中心进行的 120kVp 基线扫描相比，能量（千伏峰值）和距等中心的距离（检查床高度）分别导致相对衰减变化为-5%至 22%和-5%至 0%，平均骨密度变化为-0.9%至 0.0%和-1.1%至 0.3%。与制造商规定值相比，骨密度平均偏差范围为-2.2%至 0.9%。体模大小和骨等效材料插件的位置导致与中号体模相比，相对衰减变化为-1.2%至 1.4%。
本研究表明，使用与足部体模在相同能量和高度下扫描的校准体模可以控制千伏峰值和检查床高度的变化；但是，仅使用校准体模无法控制由于软组织厚度和足部骨骼位置引起的误差。
