Ravi Bheeshma, Rampersaud Raja
Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
Spine (Phila Pa 1976). 2008 May 1;33(10):E311-6. doi: 10.1097/BRS.0b013e31816f6c3f.
Observational.
The objectives of this study were to determine the range of clinical magnification error in lateral spinal digital radiographs, and to determine the effect of body mass index (BMI) on this error.
The magnification error in plain radiographs is often estimated at 15% to 30%. The variability of this error in digital spinal radiographs has not been assessed.
An analysis of 250 patients with digital radiographs and computed tomography (CT)/magnetic resonance images (MRIs) was performed. Digital imaging software was used to measure the anteroposterior vertebral body dimensions at C2, C5, L1, and L4. Magnification values were determined in comparison to CT/MRI. CT measurements were also compared with MRI. BMI for each patient was obtained by chart review.
The mean magnification at the cervical spine (C2 and C5 combined) was 1.22 +/- 0.01, with a range of 1.06 to 1.57 (n = 198, STDEV = 0.08); at the lumbar spine (L1 and L4 combined) it was 1.31 +/- 0.01, with a range of 1.09 to 1.63 (n = 300, STDEV = 0.08). The difference between the mean anteroposterior vertebral body dimensions as measured on CT and MRI was < 0.1 mm (n = 135, P < 0.2514, paired t test). There was a significant positive correlation between BMI and magnification at both the cervical and lumbar spines by linear regression (Cervical: n = 99; P = 0.0019; Lumbar: n = 150; P < 0.0001). There was a significant difference in magnification between nonobese and obese patients at both the cervical and lumbar levels. Cervical: 1.19 +/- 0.01 magnification for nonobese (n = 144), versus 1.26 +/- 0.01 for obese (n = 39) (P < 0.0001). Lumbar: 1.28 +/- 0.01 (n = 208), versus 1.38 +/- 0.01 (n = 78) (P < 0.0001), respectively.
Linear clinical measurements obtained on digital radiographs are subject to significant magnification errors at both the cervical and lumbar spines. This error correlates to the patient's BMI. Consequently, clinical decision-making that is based on linear measurements obtained from radiographs that do not account for this error is invalid. In a scenario where this measurement is crucial (e.g., dynamic radiographs), this error can be corrected by comparison to morphometric data from a CT/MRI.
观察性研究。
本研究的目的是确定脊柱侧位数字X线片的临床放大误差范围，并确定体重指数（BMI）对该误差的影响。
普通X线片的放大误差通常估计为15%至30%。数字脊柱X线片中该误差的变异性尚未得到评估。
对250例有数字X线片及计算机断层扫描（CT）/磁共振成像（MRI）的患者进行分析。使用数字成像软件测量C2、C5、L1和L4椎体的前后径。与CT/MRI比较确定放大值。还将CT测量值与MRI测量值进行比较。通过查阅病历获取每位患者的BMI。
颈椎（C2和C5合并）的平均放大倍数为1.22±0.01，范围为1.06至1.57（n = 198，标准差 = 0.08）；腰椎（L1和L4合并）为1.31±0.01，范围为1.09至1.63（n = 300，标准差 = 0.08）。CT和MRI测量的椎体前后径平均差值<0.1 mm（n = 135，P < 0.2514，配对t检验）。通过线性回归分析，BMI与颈椎和腰椎的放大倍数均呈显著正相关（颈椎：n = 99；P = 0.0019；腰椎：n = 150；P < 0.0001）。非肥胖和肥胖患者在颈椎和腰椎水平的放大倍数存在显著差异。颈椎：非肥胖患者放大倍数为1.19±0.01（n = 144），肥胖患者为1.26±0.01（n = 39）（P < 0.0001）。腰椎：分别为1.28±0.01（n = 208）和1.38±0.01（n = 78）（P < 0.0001）。
数字X线片上获得的线性临床测量在颈椎和腰椎均存在显著放大误差。该误差与患者的BMI相关。因此，基于未考虑此误差的X线片线性测量做出的临床决策是无效的。在这种测量至关重要的情况下（例如动态X线片），可通过与CT/MRI的形态学数据比较来校正此误差。
