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Clinical magnification error in lateral spinal digital radiographs
Bheeshma Ravi1, Raja Rampersaud
1Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
Study Design:
Observational.
Objective:
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.
Summary Of Background Data:
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.
Methods:
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.
Results:
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.
Conclusion:
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.
Insights
Magnification error in spinal digital radiographs varies and increases with body mass index (BMI). This error impacts clinical decisions, necessitating adjustments for accurate measurements, especially when using computed tomography (CT) or magnetic resonance imaging (MRI).
Area of Science:
- Radiology
- Medical Imaging
- Spinal Diagnostics
Background:
- Magnification error in plain radiographs is typically estimated between 15% and 30%.
- The variability of magnification error in digital spinal radiographs remains unassessed.
- Accurate spinal measurements are crucial for diagnosis and treatment planning.
Purpose of the Study:
- To determine the range of clinical magnification error in lateral spinal digital radiographs.
- To evaluate the impact of body mass index (BMI) on this magnification error.
- To compare digital radiograph measurements with computed tomography (CT) and magnetic resonance imaging (MRI) for accuracy.
Main Methods:
- Observational study analyzing 250 patients with digital radiographs and CT/MRI.
- Digital imaging software used to measure anteroposterior vertebral body dimensions at C2, C5, L1, and L4.
- Magnification values calculated by comparing digital radiograph measurements to CT/MRI; patient BMI obtained via chart review.
Main Results:
- Mean magnification observed at the cervical spine (1.22) and lumbar spine (1.31), with ranges up to 1.57 and 1.63 respectively.
- Significant positive correlation found between patient BMI and magnification error at both cervical and lumbar spine levels.
- Obese patients exhibited significantly higher magnification errors compared to nonobese patients at both spinal levels.
Conclusions:
- Linear measurements from spinal digital radiographs are prone to significant magnification errors.
- This magnification error is directly correlated with a patient's body mass index (BMI).
- Clinical decisions based on uncorrected radiograph measurements are invalid; CT/MRI data can help correct for this error.
