RESUMEN
OBJECTIVE. The objective of this study was to investigate the association of fractal-derived bone microstructural parameters with vertebral fracture status using in vivo digital tomosynthesis images of the spine. MATERIALS AND METHODS. Digital tomosynthesis images of the thoracic and lumbar spine from T1 to L5 were acquired from 36 patients with newly diagnosed multiple myeloma or monoclonal gammopathy of uncertain significance (age range, 39-85 years old). Scans were performed with patients in the supine position with reconstructed planes formed in the coronal direction. Bone mineral density (BMD) was recorded for 10 patients who had recently undergone dual x-ray absorptiometry. Vertebral fracture and lytic lesion status was determined by a radiologist from digital radiographs. Radiologist interpretation was reviewed to identify levels with a minimum number of fractures or lesions. For fractal analysis, the largest possible cuboid volume of interest within the cancellous bone was cropped from T7 and T11 images. Mean and SD of fractal variables between slices of fractal dimension (FD, a measure of self-similarity in the texture), mean lacunarity (λ, a measure of heterogeneity) and the slope of lacunarity versus box size relationship (Sλ, a measure of sensitivity of heterogeneity to size scale) were calculated using a box-counting method. A generalized estimating equation (GEE) platform was used to examine fractal variables as predictors of fracture status. RESULTS. Fracture status was not significantly associated with sex, race, age, stage of myeloma, presence of lesion in the spine, or BMD. In light of these results, no correction was made for these variables in further analyses of fractal variables. No interaction was found between vertebral level and any of the fractal variables (p = 0.12-0.77). Therefore, vertebral level was not considered further as an independent variable. Logistic regression analysis within GEE indicated that probability of fracture decreased with increasing mean FD (p = 0.02). In contrast, probability of fracture increased with increasing mean λ (p = 0.03). Although not to a statistically significant degree, probability of fracture increased with increasing mean Sλ (p = 0.08), SD of FD (p = 0.07), SD of λ (p = 0.07), and SD of Sλ (p = 0.06). CONCLUSION. We found FD and lacunarity calculated within the cancellous centrum of T7 and T11 vertebrae to be significantly associated with the presence of a vertebral fracture in this cohort. The decreased probability of fracture with increasing fractal dimension and increased probability of fracture with increasing lacunarity are consistent with the idea that cancellous bone with a better organized trabecular architecture is mechanically more competent. To our knowledge, this is the first in vivo evidence that fractal analysis of vertebral bone from tomosynthesis images may be useful in assessing vertebral fracture risk in patients with multiple myeloma.
RESUMEN
OBJECTIVE: The objective of our study was to analyze the use of screening cervical spine CT performed after trauma and establish the opportunity of potentially avoidable studies when evidence-based clinical criteria are applied before imaging. MATERIALS AND METHODS: All cervical spine CT examinations performed in the emergency department of a level 1 trauma center between January and December 2008 on adult patients with trauma were analyzed; 1589 studies were evaluated. Radiology reports and clinical data were reviewed for the presence of fracture or ligamentous injury and for the mode of injury. We also looked for documentation of clinical criteria used to perform the CT study. In particular, we looked for mention of posterior midline cervical tenderness, focal neurologic deficit, level of alertness, evidence of intoxication, and clinically apparent distracting injury. These five criteria were established by the National Emergency X-Radiography Utilization Study (NEXUS) to identify patients with a low probability of cervical spine injury who consequently needed no cervical spine imaging. RESULTS: Of the 1589 studies reviewed, 41 (2.6%) were positive for an acute cervical spine injury and 1524 (95.9%) were negative. The remaining 24 studies (1.5%) were indeterminate on the initial CT examination but subsequent imaging and clinical follow-up failed to show acute injury. Of the 1524 examinations with no acute injury, 364 (23.9%) had no documentation of any of the five NEXUS low-risk criteria. CONCLUSION: The strict application of the NEXUS low-risk criteria could potentially reduce the number of screening cervical spine CT examinations in the setting of trauma in more than 20% of cases, thereby avoiding a significant amount of unnecessary radiation and significant cost.