Strategies for improving the detection of fMRI activation in trigeminal pathways with cardiac gating
Section snippets
Introduction and background
Functional imaging of the trigeminal system in humans is important to increase our understanding of its physiological and pathological role in diseases such as migraine and neuropathic pain. It is however more difficult to achieve than imaging of the cortex because of the presence of numerous potential artifacts. Only a few functional studies have examined the trigeminal system, either during headache using positron emission tomography (PET) (Hsieh et al., 1999, Matharu et al., 2004) or during
Materials and methods
Ten right-handed healthy subjects (age: 31.9 ± 5.6 years, mean ± SD; 6 females) were enrolled and gave informed written consent. None of the subjects reported a history of or was suffering from acute or chronic trigeminal or cervical pain. The study protocol was approved by the Institutional Review Board of our institution.
All MRI scans were performed on a Siemens 3-T Trio MR scanner (Siemens Medical Systems, Erlangen, Germany) with an 8-channel head array coil. Each subject was wired to a
Results
The ratios of subjects who showed activation in the ipsilateral principle sensory trigeminal nucleus (PSTN) and ventroposterior medial nucleus (VPM) in the contralateral thalamus are summarized in Table 2. Four out of 10 (40%) ungated time series showed activation in PSTN. The detection rate increased to 70% for the gated single echo (TR = 3 HBs) and to 67% for the second echo (TE2) of dual-echo EPI time series. The detection rate of T2* time series calculated from dual-echo images was 89%, the
Discussion
The present study systematically compared different cardiac gating methods to conventional ungated fMRI in their ability to detect activation in the trigeminal pathway. Brainstem studies clearly require novel approaches: unlike primary sensory fMRI activation, where discussions focus around how to best quantify the robust activation present in nearly every subject, simply finding any activation in these small regions of the moving brain is considered an accomplishment, hence, the strong
Acknowledgments
This work was supported by PHS grants 5P01 NS35611-07, National Center for Research Resources General Clinical Resource Centers Program (M01-RR-01066), NCRR Center for Functional Neuroimaging Technologies (5P41RR014075), Mental Illness and Neuroscience Discovery (MIND) Institute, and Federazione Italiana Sclerosi Multipla (FISM) 2003/B/8. We also want to thank Dr. Nouchine Hadjikhani, Dr. Vitaly Napadow and Dr. Kathleen Hui for the constructive discussions.
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