Severity of Spinal Cord Injury Influences Diffusion Tensor Imaging of the Brain

Background: The purpose of this study was to determine whether DTI changes in the brain induced by a thoracic spinal cord injury are sensitive to varying severity of spinal contusion in rats. Methods: A control, mild, moderate, or severe contusion injury was administered over the eighth thoracic vertebral level in 32 Sprague-Dawley rats. At 11 weeks postinjury, ex vivo DTI of the brain was performed on a 9.4T Bruker scanner using a pulsed gradient spin-echo sequence. Results: Mean water diffusion in the internal capsule regions of the brain and pyramid locations of the brainstem were correlated with motor function (r2 = 0.55). Additionally, there were significant differences between injury severity groups for mean diffusivity and fractional anisotropy at regions associated with the corticospinal tract (P = 0.05). Conclusion: These results indicate that DTI is sensitive to changes in brain tissue as a consequence of thoracic SCI

Clinical Correlates of High Cervical Fractional Anisotropy in Acute Cervical Spinal Cord Injury

Objective: Fractional anisotropy (FA) of the high cervical cord (C1-C2), rostral to the injury site, correlates with upper limb function in patients with chronic cervical spinal cord injury (SCI). In acute cervical SCI, this relationship has not been investigated. The objective of this study was to identify functional correlates of FA of the high cervical cord in a series of patients with acute cervical SCI. Methods: Traumatic cervical SCI patients who underwent presurgical cervical spine diffusion tensor imaging at our institution were reviewed for this study. FA of the whole cord as well as the lateralcorticospinal tracts (CSTs) was calculated on axial images from C1-C2. Upper limb motor (C5-T1) and sensory (C2-T1) function scores were extracted from the admission American Spinal Injury Association (ASIA) examinations. Correlation analysis for FA with ASIA examinations was performed using a Pearson correlation. Results: Twelve subjects (9 men, 3 women; mean age 54.7 ± 4.0 years) underwent cervical spine diffusion tensor imaging at a mean duration of 3.6 ± 0.9 days postinjury. No patient had cord compression or intramedullary T2-weighted hyperintensities within the C1-C2 segments. FA correlated with upper limb motor score (whole cord: r = 0.59, P = .04; CST: 0.67, P = .01) and the ASIA grade (whole cord: r = 0.61, P = .03; CST: r = 0.71, P = .009). No correlation was found between FA and sensory scores. Conclusions: FA of the whole cervical cord as well as the CST, rostral to the injury site, is associated with preserved upper limb motor function as well as superior ASIA grades after acute cervical SCI. FA of the high cervical cord is a potential biomarker of neural injury after acute cervical SCI

Diffusion Tensor Imaging Correlates with Short-Term Myelopathy Outcome in Patients with Cervical Spondylotic Myelopathy

Objective To determine if spinal cord diffusion tensor imaging indexes correlate with short-term clinical outcome in patients undergoing elective cervical spine surgery for cervical spondylotic myelopathy (CSM). Methods A prospective consecutive cohort study was performed in patients undergoing elective cervical spine surgery for CSM. After obtaining informed consent, patients with CSM underwent preoperative T2-weighted magnetic resonance imaging and diffusion tensor imaging of the cervical spine. Fractional anisotropy (FA) values at the level of maximum cord compression and at the noncompressed C1-2 level were calculated on axial images. We recorded the modified Japanese Orthopaedic Association (mJOA) scale, Neck Disability Index, and Short Form-36 physical functioning subscale scores for all patients preoperatively and 3 months postoperatively. Statistical analysis was performed to identify correlations between FA and clinical outcome scores. Results The study included 27 patients (mean age 54.5 years ± 1.9, 12 men). The mean postoperative changes in mJOA scale, Neck Disability Index, and Short Form-36 physical functioning subscale scores were 0.9 ± 0.3, −6.0 ± 1.9, and 3.4 ± 1.9. The mean FA at the level of maximum compression was significantly lower than the mean FA at the C1-2 level (0.5 vs. 0.55, P = 0.01). FA was significantly correlated with change in mJOA scale score (Pearson r = −0.42, P = 0.02). FA was significantly correlated with the preoperative mJOA scale score (Pearson r = 0.65, P \u3c 0.001). Conclusions Preoperative FA at the level of maximum cord compression significantly correlates with the 3-month change in mJOA scale score among patients with CSM. FA was also significantly associated with preoperative mJOA scale score and is a potential biomarker for spinal cord dysfunction in CSM

Diffusion Tensor Imaging in a Large Longitudinal Series of Patients With Cervical Spondylotic Myelopathy Correlated With Long-Term Functional Outcome

BACKGROUND Fractional anisotropy (FA) of the high cervical cord correlates with upper limb function in acute cervical cord injury. We investigated the correlation between preoperative FA at the level of maximal compression and functional recovery in a group of patients after decompressive surgery for cervical spondylotic myelopathy (CSM). OBJECTIVE To determine the usefulness of FA as a biomarker for severity of CSM and as a prognostic biomarker for improvement after surgery. METHODS Patients received diffusion tensor imaging (DTI) scans preoperatively. FA values of the whole cord cross-section at the level of maximal compression and upper cervical cord (C1-2) were calculated. Functional status was measured using the modified Japanese Orthopedic Association (mJOA) scale preoperatively and at follow-up up to 2 yr. Regression analysis between FA and mJOA was performed. DTI at C4-7 was obtained in controls. RESULTS Forty-four CSM patients enrolled prior to decompression were compared with 24 controls. FA at the level of maximal compression correlated positively with preoperative mJOA score. Preoperative FA correlated inversely with recovery throughout the postoperative period. This was statistically significant at 12 mo postoperation and nearly so at 6 and 24 mo. Patients with preoperative FA0.55. CONCLUSION In the largest longitudinal study of this kind, FA promises a valid biomarker for severity of CSM and postoperative improvement. FA is an objective measure of function and could provide a basis for prognosis. FA is particularly useful if preoperative values are less than 0.55

Diffusion Tensor Imaging of the Spinal Cord: Insights From Animal and Human Studies

Diffusion tensor imaging (DTI) provides a measure of the directional diffusion of water molecules in tissues. The measurement of DTI indexes within the spinal cord provides a quantitative assessment of neural damage in various spinal cord pathologies. DTI studies in animal models of spinal cord injury indicate that DTI is a reliable imaging technique with important histological and functional correlates. These studies demonstrate that DTI is a noninvasive marker of microstructural change within the spinal cord. In human studies, spinal cord DTI shows definite changes in subjects with acute and chronic spinal cord injury, as well as cervical spondylotic myelopathy. Interestingly, changes in DTI indexes are visualized in regions of the cord, which appear normal on conventional magnetic resonance imaging and are remote from the site of cord compression. Spinal cord DTI provides data that can help us understand underlying microstructural changes within the cord and assist in prognostication and planning of therapies. In this article, we review the use of DTI to investigate spinal cord pathology in animals and humans and describe advances in this technique that establish DTI as a promising biomarker for spinal cord disorders

Alterations in Cortical Sensorimotor Connectivity following Complete Cervical Spinal Cord Injury: A Prospective Resting-State fMRI Study

Functional magnetic resonance imaging (fMRI) studies have demonstrated alterations during task-induced brain activation in spinal cord injury (SCI) patients. The interruption to structural integrity of the spinal cord and the resultant disrupted flow of bidirectional communication between the brain and the spinal cord might contribute to the observed dynamic reorganization (neural plasticity). However, the effect of SCI on brain resting-state connectivity patterns remains unclear. We undertook a prospective resting-state fMRI (rs-fMRI) study to explore changes to cortical activation patterns following SCI. With institutional review board approval, rs-fMRI data was obtained in eleven patients with complete cervical SCI (\u3e2 years post injury) and nine age-matched controls. The data was processed using the Analysis of Functional Neuroimages software. Region of interest (ROI) based analysis was performed to study changes in the sensorimotor network using pre- and post-central gyri as seed regions. Two-sampled t-test was carried out to check for significant differences between the two groups. SCI patients showed decreased functional connectivity in motor and sensory cortical regions when compared to controls. The decrease was noted in ipsilateral, contralateral, and interhemispheric regions for left and right precentral ROIs. Additionally, the left postcentral ROI demonstrated increased connectivity with the thalamus bilaterally in SCI patients. Our results suggest that cortical activation patterns in the sensorimotor network undergo dynamic reorganization following SCI. The presence of these changes in chronic spinal cord injury patients is suggestive of the inherent neural plasticity within the central nervous system

Essays in sustainable operations

In the first chapter, we study the impact of Environmentally Preferable Purchasing (EPP) and municipal supply uncertainty as a driver of recycled content in practice and explore the impact of recycled content claims made as an annual average vs. batch specific claims. We formulate a two stage stochastic dynamic program, consisting of a design stage, where a recycled content claim is declared, and a procurement stage where the manufacturer has recourse to self-collection to meet the commitment. Our goal is to compare manufacturer profits and recycled content levels under batch specific and time averaged claims and explore the effect of EPP and supply-side intervention i.e. moving from single stream to dual-stream collection of recyclables. Our main contributions are as follows: (a) We establish conditions under which batch specific claims are larger than time averaged claims; (b) we find that variability of supply in the municipal stream of recyclables increases (decreases) the recycled content claim if the collection cost is high (low), (c) we find that simultaneously increasing recovery of recyclables through dual-stream collection and/or container deposit legislation and creating demand side incentives for recycled content can create win-win conditions; and (d) show that EPP increases (decreases) the recycled content claim if the collection cost is sufficiently low (high). Based on analytical results, we show that demand side policies like EPP should be tailored to local supply limitations to achieve Pareto-improving outcomes for manufacturers and the environment. Our model is calibrated to data from the fiberglass insulation industry and a glass recycling study conducted in the State of Ohio. In the second chapter, we consider the case of a manufacturer investing production capacity in presence of R&D updates on development of an energy efficient technology. This problem is relevant to the development of clean energy technologies like direct drive wind turbines and energy efficient lighting, where R&D progress is tracked over a Technology Roadmap. We build a stylized model of a manufacturer adding assembly capacity based on realized R&D progress and calibrate it to data for the wind turbine industry. We provide option value estimates for the R&D projects along with the timing of capacity addition. In the third chapter, we consider the problem of a customer that contracts with a Product Recovery Facility (PRF) to dispose of its used electronic equipment in the most environmentally friendly manner i.e, by reuse and refurbishment or disassembly and recycling. Typical disposition contracts in the IT Asset disposition industry involve a fixed upfront payment by the customer to the PRF and a rebate for each unit resold that is credited back to the customer. We optimize the optimum transfer payment and rebate fraction, under uncertainty in condition of incoming units, while accounting for the PRFs bankruptcy risk. We find that as customers become increasingly environmentally conscious they choose a lower rebate fractions and decrease the upfront fee paid to the PRF. Moreover, as uncertainty in incoming condition and refurbishing cost increases customers again choose a lower rebate fraction. Overall, our model agrees with existing best practice in the industry i.e., customers who refresh\u27\u27 their IT Assets frequently keep a greater fraction of the resale value. We calibrate our model to a real dataset consisting of end-of-life laptops processed at a PRF

Association of magnetic resonance imaging signal changes and outcome prediction after surgery for cervical spondylotic myelopathy

OBJECT: Few studies have evaluated the prognostic significance of different types of T2-weighted MR imaging changes in patients with cervical spondylotic myelopathy (CSM). The object of this study was to determine whether the type of increased signal intensity (ISI) was an independent predictor of outcome following central corpectomy in patients with CSM or ossification of the posterior longitudinal ligament (OPLL). METHODS: Magnetic resonance images obtained in 197 patients who had undergone central corpectomy for CSM or OPLL were assessed for ISI within the cord on sagittal T2-weighted images and hypointensity on T1-weighted images. The T2-weighted changes were categorized as no change (Type 0), fuzzy (Type 1), or sharp (Type 2) based on the ISI characteristics. Outcomes were assessed as a change in Nurick grade of 1 grade or more from preoperatively to postoperatively, and cure as a follow-up Nurick grade of 0 or 1. Multilevel regression analysis was performed to identify predictors of change in Nurick grade ≥ 1 and cure. RESULTS: There were 30 patients (15.2%) with Type 0, 104 patients (52.8%) with Type 1, and 63 patients (32%) with Type 2 ISI on MR images. Age, duration of symptoms, and preoperative Nurick grade were similar among the groups. A preoperative Nurick grade of 4 or 5 (OR 0.23, p < 0.001) and presence of Type 2 ISI on T2-weighted images (OR 0.48, p = 0.04) negatively influenced the probability of cure after surgery. Hypointensity on T1-weighted images was only seen in patients who had Type 2 ISI changes. Among the 63 patients with Type 2 ISI, the presence of T1-weighted hypointensity (16 patients) was found to negatively impact cure (OR 0.1, p = 0.04). CONCLUSIONS: Increased signal intensity on preoperative T2-weighted MR images was seen in more than 80% of the cases. However, only Type 2 ISI on T2-weighted images had a prognostic significance of being associated with a decreased likelihood of cure in patients with C

Correlation between change in graft height and change in segmental angle following central corpectomy for cervical spondylotic myelopathy

Object: This study was undertaken to examine the correlation between change in graft height and change in angulation across grafted segments (segmental angle) in patients undergoing central corpectomy (CC) with autologous bone reconstruction for cervical spondylotic myelopathy (CSM). Methods: The authors performed a retrospective analysis of 70 cases in which patients with CSM underwent uninstrumented single- or multilevel CC and had evidence of osseous fusion of their grafts at follow-up. The segmental angles and heights of the grafted segments on preoperative, postoperative, and follow-up radiographs were compared. Results: The mean change in graft height (± standard deviation) was -7.3 ± 3.8 mm (mean duration of follow-up 19.7 ± 5.4 months, range 13-53 months). There was a mean kyphotic change in segmental angle of -7.3 ± 3.8° (p < 0.001). In patients who had a straight or kyphotic cervical spine (28 patients) or a straight or kyphotic segment (32 patients) preoperatively, there was a significant linear correlation between changes in graft height and changes in segmental angle (Pearson correlation, r = 0.40, p = 0.03; r = 0.40, p = 0.02, respectively). Such a correlation was not seen in the patients who had a lordotic cervical spine (42 patients) or a lordotic segment (38 patients) preoperatively (Pearson correlation, r = -0.04, p = 0.81; r = 0.08, p = 0.62, respectively). The change in segmental angle did not influence improvement in Nurick grade (p = 0.8). The degree of agreement between the 2 observers was almost perfect for measurement of graft height (postoperative intraclass correlation coefficient [ICC] = 0.94, follow-up ICC = 0.90) but was significantly lower for measurement of segmental angles (postoperative ICC = 0.71, follow-up ICC = 0.67). Conclusions: Among patients undergoing uninstrumented CC for CSM, there is a significant correlation between postoperative settling and kyphotic change across fused segments in those who had straight or kyphotic cervical spines or segments preoperatively but not in those who had lordotic cervical spines or segments preoperatively. A more vigorous surgical correction of the segmental kyphosis than achieved in this study might have caused the kyphotic segments to behave like the lordotic segments. Paraspinal muscles and ligaments may play a role in determining the segmental angle as graft settling in patients with lordotic spines or segments is not linearly correlated with angular change

Changes in the range of motion of the cervical spine and adjacent segments at ≥ 24 months after uninstrumented corpectomy for cervical spondylotic myelopathy

Background: Few clinical studies have described the changes in the range of motion (ROM) of the cervical spine and adjacent segments following central corpectomy. We aimed to quantify the changes in range of motion (ROM) of the cervical spine and the adjacent segments at ≥24 months following uninstrumented central corpectomy (CC) for cervical spondylotic myelopathy (CSM) and to determine the contribution of the adjacent segments to the compensation for loss of motion of the cervical spine following CC. Methods: Preoperative and follow-up lateral cervical spine radiographs of 36 patients who underwent CC for CSM between 2001 and 2007 were compared for the ROM of the subaxial cervical spine, superior and inferior adjacent segment. Anterior osteophytes as seen on the radiographs were classified according to Nathan's grading system. Results: The mean duration of follow-up was 48.5 months. At follow-up, the total cervical spine ROM decreased by 18.3° ± 2.2° (p < 0.001), the superior adjacent segment ROM increased by 2.3° ± 0.9° (p = 0.01) and the inferior adjacent segment ROM, measured in 20 cases, increased by 6.2° ± 1.7° (p = 0.01). The superior adjacent segment showed a 70% increase, whereas the inferior adjacent segment showed a 110% increase in mobility. Nathan's grade at the superior or inferior adjacent segment increased in 12 cases. Conclusions: CC significantly reduces the motion of the cervical spine and increases the adjacent segment mobility at intermediate follow-up. The inferior adjacent segment shows greater compensation of motion as compared to the superior adjacent segment in our series. Adjacent segment degeneration as estimated by Nathan's grade was seen in one-third of the cases