Comparison of the Relationships Between Body Size and Cardiorespiratory Fitness With High Frequency Head‐Motion Contamination in fMRI

ABSTRACT

Functional MRI (fMRI) is widely used to assess brain function, but neural‐derived fMRI signals are susceptible to contamination from in‐scanner head motion. Preprocessing pipelines often regress out and censor head motion artifacts using six rigid‐body motion parameters. However, recent research suggests these head‐motion estimates are susceptible to contamination from other sources of noise, such as respiratory rate, body size, and estimated cardiorespiratory fitness (eCRF), that correspond to apparent head motion at higher frequencies (HF‐motion; > 0.1 Hz). Thus, these health variables are thought to be linked to the artifactual inflation of head motion estimates, introducing additional challenges to appropriate modeling and preprocessing procedures that reduce noise. Whether this artifactual relationship extends to changes in body size, midline abdominal fat (i.e., body composition), CRF measured with gold‐standard methods, and respiratory rate measured during scanning remains unclear. The Brain EXTEND Trial acquired multiple health variables before and after an exercise intervention that changed CRF, offering a means to test the relationship between these health variables and HF‐motion in a longitudinal design. Subjects (55–80 years of age) completed a 6‐month chronic exercise intervention at two intensities. We analyzed baseline and longitudinal (EXTEND, baseline n  = 122; longitudinal n  = 84) relationships between HF‐motion and health variables that included body mass index (BMI), waist circumference (WC), CRF measured with a maximal exercise test (VO ₂ max), and resting respiratory rate. HF‐motion was examined in each head‐motion parameter as the proportion of HF‐motion above > 0.1 Hz—the typical upper bound of fMRI signals at rest. At baseline, HF‐motion for all translational axes was positively associated with body size (BMI, WC) while CRF was negatively associated with only the roll y‐rotation. Additionally, longitudinally, decreased BMI related to reduced HF‐motion in the z‐translation. Results indicate health changes related to body size associate with the presentation of high‐frequency MRI head‐motion artifacts. We caution researchers against ignoring the presence of HF‐motion in their analyses as their use of contaminated motion traces will negatively affect their modeling of fMRI measures. Results have implications for a wide range of investigations in health neuroscience involving body size, respiratory function, and cardiorespiratory fitness.