In vivo assessment of spinal cord elasticity using shear wave ultrasound in dogs

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Evaluation of living tissue elasticity has wide applications in disease characterization and prognosis prediction. Few previous ex vivo attempts have been made to characterize spinal cord elasticity (SCE). Recently, tissue elasticity assessment has been clinically feasible using ultrasound shear wave elastography (SWE). The current study aims to characterize SCE in healthy dogs, in vivo, utilizing SWE, and to address SCE changes during compression.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>Ten Greyhound dogs (mean age 14 months; mean weight 14.3 kg) were anesthetized and tracheally intubated, with hemodynamic and neurological monitoring. A 3-level, midcervical laminectomy was performed. SCE was assessed at baseline. Next, 8- and 13-mm balloon compressions were sequentially applied ventral to the spinal cord.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>The mean SCE was 18.5 ± 7 kPa. Elasticity of the central canal, pia mater, and dura mater were 21.7 ± 9.6 kPa, 26.1 ± 14.8 kPa, and 63.2 ± 11.5 kPa, respectively. As expected, the spinal cord demonstrated less elasticity than the dura mater (p &lt; 0.0001) and pia mater (trend toward significance p = 0.08). Notably, the 13-mm balloon compression resulted in a stiffer spinal cord than at baseline (233 ± 73 kPa versus 18.5 ± 7 kPa, p &lt; 0.0001) and 8-mm balloon compression (233 ± 73 kPa versus 185 ± 68 kPa, p &lt; 0.048).</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>In vivo SCE evaluation using SWE is feasible and comparable to earlier reports, as demonstrated by physical sectioning of the spinal cord. The compressed spinal cord is stiffer than a free spinal cord, with a linear increase in SCE with increasing mechanical compression. Knowledge of the biomechanical properties of the spinal cord including SCE has potential implications for disease management and prognosis.</jats:p></jats:sec>

A New Framework for Investigating the Biological Basis of Degenerative Cervical Myelopathy [AO Spine RECODE-DCM Research Priority Number 5]: Mechanical Stress, Vulnerability and Time

“…In DCM, the mechanical stress experienced will be complicated by how these forces interact, 84 for example, in a finite-element model of static compression of the spinal cord, elasticity measured using ultrasound reduced when the spinal cord was compressed. 113 These forces too, will have been exhibited in combination, within the existing pre-clinical models that underpin our current investigations of DCM. 17 , 114 Mechanical stress will also be influenced by the different mechanical properties and tolerance of microstructures within the spinal cord, for example, the white vs gray matter, or relative myelin content of spinal cord pathways 115 which are also subject to change, for example, with age and evolution of injury.…”

Stiffness-matched biomaterial implants for cell delivery: clinical, intraoperative ultrasound elastography provides a ‘target’ stiffness for hydrogel synthesis in spinal cord injury

“…A value of 18.5 ± 7 kPa was reported for uninjured in vivo cervical cord when measured by USE in experimental dogs, although these measures were not calibrated. 26 The elasticity of spinal cord in anaesthetised experimental puppies and cats 22 , 23 was reported as 265 kPa when measured using mechanical methods (tensile extension at loads of 5–10 g). As with our findings, this was higher than measures of canine cadaver spinal cord under the same conditions (11.9–16.8 kPa).…”

“…It has been successfully used in people for ancillary diagnosis of mammary neoplasia 24 and staging of liver fibrosis, 25 and has been applied to the spinal cord of experimental dogs where large areas of the spinal cord were exposed. 26 Acoustic radiation force impulse USE detects the speed of displacement of target tissue (shear wave velocity) in response to an acoustic impulse generated from the ultrasound transducer. This speed varies with the stiffness of the tissue 27 and can be mathematically converted to modulus of elasticity 28,29 allowing quantitative comparisons; materials with a higher elastic modulus will be stiffer and deform less for a given stress.…”

Quantifying tethered spinal cord tension: Ultrasound elastography results from computational, cadaveric, and intraoperative first-in-human studies

“…While SWV has been modeled in soft tissue materials with varying fiber alignments and strain, its utility in spinal cord tension quantification has yet to be investigated [40][41][42] . Recent shear wave elastography studies have successfully quantified compression in the spinal cord 43,44 . Although this approach supplements clinical insights, deformation from a spinal cord injury is often visualizable with conventional imaging (e.g., MRI, computed tomography, or B-mode ultrasound imaging) 45 .…”