Mild traumatic brain injury: Is DTI ready for the courtroom?

Important advances in neuroscience and neuroimaging have revolutionized our understanding of the human brain. Many of these advances provide new evidence regarding compensable injuries that have been used to support changes in legal policy. For example, we now know that regions of the brain involved in decision making continue to develop into the mid-20s, and this information weighs heavily in determining that execution or automatic sentence of life without the possibility of parole for someone younger than 18 years old, at the time of the crime, violates the 8th Amendment prohibition against "cruel and unusual punishment." The probative value of other testimony regarding neuroimaging, however, is less clear, particularly for mild traumatic brain injury (mTBI), also known as concussion. There is nonetheless some evidence that new imaging technologies, most notably diffusion tensor imaging (DTI), may be useful in detecting mTBI. More specifically, DTI is sensitive to detecting diffuse axonal brain injuries in white matter, the most common brain injury in mTBI. DTI is, in fact, the most promising technique available today for such injuries and it is beginning to be used clinically, although it remains largely within the purview of research. Its probative value is also not clear as it may be both prejudicial and misleading given that standardization is not yet established for use in either the clinic or the courtroom, and thus it may be premature for use in either. There are also concerns with the methods and analyses that have been used to provide quantitative evidence in legal cases. It is within this context that we provide a commentary on the use of neuroimaging in the courtroom, most particularly DTI, and the admissibility of evidence, as well as the definition and role of expert testimony. While there is a great deal of evidence demonstrating cognitive impairments in attention, processing speed, memory, and concentration from neuropsychological testing following mTBI, we focus here on the more recent introduction of DTI imaging in the courtroom. We also review definitions of mTBI followed by admissibility standards for scientific evidence in the courtroom, including Daubert criteria and two subsequent cases that comprise the so-called Daubert trilogy rulings on the admissibility of expert testimony. This is followed by a brief review of neuroimaging techniques available today, the latter with an emphasis on DTI and its application to mTBI. We then review some of the court rulings on the use of DTI. We end by highlighting the importance of neuroimaging in providing a new window on the brain, while cautioning against the premature use of new advances in imaging in the courtroom before standards are established in the clinical arena, which are informed by research. We also discuss further what is needed to reach a tipping point where such advances will provide important and meaningful data with respect to their probative value.