Use of single voxel intermediate echo time magnetic resonance spectroscopy at 3 Tesla in dogs with meningoencephalitis of unknown origin
Introduction Magnetic resonance spectroscopy (MRS) is a magnetic resonance imaging (MRI) sequence that identifies and quantifies metabolites within brain tissue by identifying the degree and amplitude of the chemical shift. MRS is rarely used in veterinary medicine due to a lack of published research and familiarity with scanning techniques and interpretation. By evaluating relative changes to metabolite concentration within brain tissue, this sequence can identify pathologic processes. This study evaluated the use of a single voxel, intermediate echo time MRS sequence at 3T in dogs with non-infectious meningoencephalitis of unknown origin (MUO) to determine the feasibility and utility of this scan as an additional diagnostic tool for this disease. Methods MRS was incorporated into MRI scans of client-owned dogs presenting to the University of Missouri Veterinary Health Center (MU VHC). Dogs with MUO were diagnosed antemortem based on history, imaging findings, cerebrospinal fluid analysis, and/or response to therapy. Dogs with structurally normal brains on MRI were used as a control group. Dogs aged 1-10 years were included in the study, identifying 18 normal dogs and 4 dogs with MUO. Patient signalment, clinical information, and clinical history details were recorded and compared. Metabolite height, area, and ratios were compared between groups. A secondary evaluation of dogs with seizures was performed to identify if a time-dependent association with MRI changes or metabolite area existed. Results This study found a statistically significant increase in choline peak height (p = 0.001) and area (p = 0.003) within the patients within the MUO cohort compared to dogs in the normal group. The height of the creatine peak was also significantly higher in the MUO group (p = 0.04), though the overall concentration indicated by peak area was not. Other trends, including a decreased NAA/creatine ratio and an increased NAA height and area, lactate height, and choline/creatine ratio, were identified in the MUO group. All MUO patients and all but one normal dog had a measurable lactate peak, indicating that a small amount of lactate concentration may be incidental in the dog brain at 3T. The presence of postictal changes in dogs with seizures was found not to be related to days since the last seizure. The NAA/Cr ratio had a time-dependent positive correlation to days since the last seizure. Lastly, a dog with a genetic neurodegenerative disease was identified during the acquisition of this study, and this dog's MRS spectra may be the first described in dogs with this disease. Discussion This study found several significant differences between groups, some of which were expected (increased choline in the MUO group) and some unexpected (increased NAA in dogs with MUO). This investigation showed that this MRS method is feasible, creates good quality spectral data, and could have diagnostic benefit in dogs with MUO. Further validation of this pilot study, notably with baseline correction and reevaluation of NAA concentration, is needed before adopting this sequence into the standard diagnostic workup for dogs with MUO.