The main goal of this study is to determine if brain lithium-concentrations predict clinical lithium treatment-response. Secondary, to study correlations between intracerebral distribution-patterns of lithium with clinical treatment outcome.

Brain lithium concentrations will be measured using ultra-high field (7 Tesla) lithium magnetic resonance (MR) imaging, which has recently been introduced. Determining lithium-concentrations in the brain has been difficult so far due to lithium's relatively low concentration (compared to protons, which are targeted in conventional MRI). 7T lithium MR imaging has the potential to produce much more detailed MR images compared with previous studies, for the first time. The BLISS study is expected to yield new insights, helping to better understand why clinical lithium response varies between individuals.

Introduction Lithium treatment is considered the first-line pharmacological treatment for bipolar disorder. However, individual responses vary greatly, which undermines the ability to achieve rapid stabilization in many patients with bipolar disorder. The neurobiological mechanisms underlying lithium's action are still largely unknown, which hampers the development of clinically applicable predictors for individual treatment response. The recent introduction of ultra-high-field lithium magnetic resonance imaging offers a promising avenue to better link brain measures with clinical responses to lithium treatment.

Methods and Analysis This is a longitudinal observational study involving 80 adults with bipolar disorder who are initiating lithium as part of their regular treatment regimen. Ultra-high-field lithium magnetic resonance imaging of the brain will be performed within four weeks of reaching stable therapeutic serum lithium concentrations. The primary outcome is clinical response to lithium treatment at one-year follow-up, as measured using a validated questionnaire. Linear regression analysis will be used to establish correlations between brain lithium concentrations-including whole brain, voxel-wise, parcellation, mean, and region-of-interest approaches-and clinical lithium response.

Inclusion Criteria:

1. age 18 years or above,
2. a clinical diagnosis of bipolar disorder type I or type II ,
3. having reached stable therapeutic serum lithium concentrations (reference values 0.6-1.0 mM in age to 65 years; 0.4-0.8 in age 65 years and above) within four weeks prior to study participation, and
4. provided written informed consent.

Exclusion Criteria:

1. insufficient comprehension of the Dutch language,
2. unable to provide informed consent,
3. drug or alcohol abuse over a period of two weeks prior to study participation, and
4. meeting any exclusion criterium for MR imaging.

Subjects with bipolar disorder type I or II who start with lithium treatment as part of standard care.

Lithium MR imaging data.

Study protocol - currently submitted for OA publication CSR - after termination of the BLISS study Analytic code - after termination of the BLISS study IPD - after termination of the BLISS study

Study protocol - open access CSR and analytic code - open access

IPD: lithium imaging data will be made available upon request with the study chair, and no sooner then after study termination.