Comparison of distortion correction preprocessing pipelines for DTI in the upper limb.

PURPOSE: DTI characterizes tissue microstructure and provides proxy measures of nerve health. Echo-planar imaging is a popular method of acquiring DTI but is susceptible to various artifacts (e.g., susceptibility, motion, and eddy currents), which may be ameliorated via preprocessing. There are many pipelines available but limited data comparing their performance, which provides the rationale for this study. METHODS: DTI was acquired from the upper limb of heathy volunteers at 3T in blip-up and blip-down directions. Data were independently corrected using (i) FSL's TOPUP & eddy, (ii) FSL's TOPUP, (iii) DSI Studio, and (iv) TORTOISE. DTI metrics were extracted from the median, radial, and ulnar nerves and compared (between pipelines) using mixed-effects linear regression. The geometric similarity of corrected b = 0 images and the slice matched T1-weighted (T1w) images were computed using the Sörenson-Dice coefficient. RESULTS: Without preprocessing, the similarity coefficient of the blip-up and blip-down datasets to the T1w was 0·80 and 0·79, respectively. Preprocessing improved the geometric similarity by 1% with no difference between pipelines. Compared to TOPUP & eddy, DSI Studio and TORTOISE generated 2% and 6% lower estimates of fractional anisotropy, and 6% and 13% higher estimates of radial diffusivity, respectively. Estimates of anisotropy from TOPUP & eddy versus TOPUP were not different but TOPUP reduced radial diffusivity by 3%. The agreement of DTI metrics between pipelines was poor. CONCLUSIONS: Preprocessing DTI from the upper limb improves geometric similarity but the choice of the pipeline introduces clinically important variability in diffusion parameter estimates from peripheral nerves.

Incidental findings associated with magnetic resonance imaging of the brachial plexus.

OBJECTIVE: The identification and management of incidental findings is becoming increasingly problematic, particularly in relation to brachial plexus imaging because the prevalence is unknown. Therefore, we aimed to estimate the prevalence of incidental findings in symptomatic patients undergoing MRI of the brachial plexus. METHODS: This retrospective cohort study included all children and adults who underwent MRI over a 12-year period, in a tertiary care centre in the UK. An incidental finding was any abnormality which was not a direct injury to or disease-process of the brachial plexus. An "incidentaloma" was defined by the need for further investigation or treatment. Multivariable logistic regression was used to estimate the odds ratio (OR) of an "incidentaloma". To estimate which factors were associated with the incident rate ratio (IRR) of incidental findings, multivariable Poisson regression was used. RESULTS: Overall, 502 scans (72%) reported incidental anomalies. Although the number of MRIs performed per annum increased by 23%, the prevalence of "incidentalomas" remained static (p = 0.766). Musculoskeletal incidental findings were the most prevalent (63%) and when identified, there were a median of 3 incidental anomalies per patient. Overall, 125 (18%) anomalies were "incidentalomas" which required further investigation or treatment. The odds of having further investigation or treatment was strongly related to the frequency of incidental findings [adjusted OR 1.16 (95% CI 1.08, 1.24)] and when a tumour was identified [adjusted OR 2.86 (95% CI 1.81, 4.53)]. The number of incidental findings recorded per scan increased when trainees co-reported with consultants [adjusted IRR 0.36 (95% CI 0.05, 0.67)] and in the presence of a tumour [adjusted IRR 0.39 (95% CI 0.28, 0.49)]. CONCLUSIONS: The prevalence of clinically important incidental findings on brachial plexus MRI is lower than organ-specific imaging, but still 18% of scans identified an 'incidentaloma' which required further investigation or treatment. ADVANCES IN KNOWLEDGE: This cohort study shows that approximately 1 in 5 symptomatic patients undergoing a brachial plexus MRI had a clinically important incidental findings, which required further investigation or treatment. This information can be used to inform patients consenting to clinical or research imaging.