*7.1. T1*

As discussed, accurate DBS implantation requires careful trajectory planning and identification of vasculature to limit the risk of hemorrhagic complications. Visualization of larger venous architecture is most commonly achieved with an anatomical T1w scan with added gadolinium [119,120]. In its most basic form, T1w can be viewed as an anatomical scan that approximates the appearance of macroscopic tissues. T1w will visualize white matter as hyperintense; fluid, e.g., cerebral spinal fluid (CSF) as hypointense; and grey matter at intermediate intensity. A T1w contrast is achieved with a short echo time (TE) and repetition time (TR) and is a function of the longitudinal relaxation time, referring to the time it takes excited protons to return to their equilibrium subsequent to the application of an RF pulse. T1 is more sensitive to fat and fluid and therefore provides excellent di fferentiation between grey and white matter. Additional intravenous contrast agents will cause the recovery of the longitudinal magnetization of blood to quicken and therefore increase further contrast between veins and white matter [121–123]. For visualization of venous architecture, some centers may use any or a combination of T1w structural imaging, or they may use post-processing techniques such as susceptibility weighted imaging (SWI) and venography, which can be created from GRE-based sequences with flow compensation, or time-of-flight angiography. These types of sequences apply multiple RF pulses with short TRs to over-saturate static tissues and therefore suppress their signal, causing moving components such as blood to appear more hyperintense [124–126]. T1w MRI can also be used to rule out co-morbidities such as oedema, tumors, or other brain pathologies. See Figure 2 for an example of di fferent contrasts.
