DTI applies the diffusion-sensitizing gradients in many (at least 6) different directions in order to generate a second-order tensor that characterizes directionality of water molecule diffusion. This can be visualized as a diffusion ellipsoid, where the long axis represents axial diffusivity, and the short axes represent radial diffusivity. An important summary measure of the degree of asymmetry between the long and short axes is fractional anisotropy. Fractional anisotropy is higher in white matter than gray matter or CSF because of its microstructure (fiber-tract architecture); therefore, fractional anisotropy has been studied extensively as a potential marker of axonal integrity, especially in the setting of persistently symptomatic mild TBI [18]. Multiple studies have shown regions of decreased fractional anisotropy and increased mean diffusivity in patients with mild, moderate, and severe TBI, as compared with healthy controls [53]. Other DTI studies performed in the early subacute phase have shown paradoxically increased fractional anisotropy, which has been attributed to cytotoxic edema or to postinjury repair [54,55]. Overall, there is significant heterogeneity in fractional anisotropy measurements among both TBI and healthy subjects, with published data based primarily upon group-level analyses. Despite continuing improvements in scanner gradients and diffusion techniques (eg, intravoxel resolution Head Trauma of crossing fibers), there is insufficient evidence to support the routine clinical use of DTI at the individual patient level [45]. Radiography Skull There is no relevant literature to support the use of radiographs in the initial imaging evaluation of subacute or chronic head trauma with unexplained cognitive or neurologic deficit(s). Variant 8: Head trauma with suspected intracranial arterial injury due to clinical risk factors or positive findings on prior imaging.
Head Trauma PCAs. DTI applies the diffusion-sensitizing gradients in many (at least 6) different directions in order to generate a second-order tensor that characterizes directionality of water molecule diffusion. This can be visualized as a diffusion ellipsoid, where the long axis represents axial diffusivity, and the short axes represent radial diffusivity. An important summary measure of the degree of asymmetry between the long and short axes is fractional anisotropy. Fractional anisotropy is higher in white matter than gray matter or CSF because of its microstructure (fiber-tract architecture); therefore, fractional anisotropy has been studied extensively as a potential marker of axonal integrity, especially in the setting of persistently symptomatic mild TBI [18]. Multiple studies have shown regions of decreased fractional anisotropy and increased mean diffusivity in patients with mild, moderate, and severe TBI, as compared with healthy controls [53]. Other DTI studies performed in the early subacute phase have shown paradoxically increased fractional anisotropy, which has been attributed to cytotoxic edema or to postinjury repair [54,55]. Overall, there is significant heterogeneity in fractional anisotropy measurements among both TBI and healthy subjects, with published data based primarily upon group-level analyses. Despite continuing improvements in scanner gradients and diffusion techniques (eg, intravoxel resolution Head Trauma of crossing fibers), there is insufficient evidence to support the routine clinical use of DTI at the individual patient level [45]. Radiography Skull There is no relevant literature to support the use of radiographs in the initial imaging evaluation of subacute or chronic head trauma with unexplained cognitive or neurologic deficit(s). Variant 8: Head trauma with suspected intracranial arterial injury due to clinical risk factors or positive findings on prior imaging.