The 1H NMR water signal from spectroscopic voxels localized in gray matter contains contributions from tissue and cerebral spinal fluid (CSF). A typically weak CSF signal at short echo times makes separating the tissue and CSF spin-lattice relaxation times (T1) difficult, often yielding poor precision in a bi-exponential relaxation model. Simulations show that reducing the variables in the T, model by using known signal intensity values significantly improves the precision of the T1 measurement. The method was validated on studies on eight healthy subjects (four males and four females, mean age 21 ± 2 years) through a total of twenty-four spectroscopic relaxation studies. Each study included both T1 and spin-spin relaxation (T2) experiments. All volumes were localized along the Sylvian fissure using a stimulated echo localization technique with a mixing time of 10 ms. The T2 experiment consisted of 16 stimulated echo acquisitions ranging from a minimum echo time (TE) of 20 ms to a maximum of 1000 ms, with a repetition time of 12 s. All T1 experiments consisted of 16 stimulated echo acquisition, using a homospoil saturation recovery technique with a minimum recovery time of 50 ms and a maximum 12 s. The results of the T2 measurements provided the signal intensity values used in the bi-exponential T1 model. The mean T1 values when the signal intensities were constrained by the T2 results were 1055.4 ms ± 7.4% for tissue and 5393.5 ms ± 59% for CSF. When the signal intensities remained free variables in the model, the mean T1 values were 1085 ms ± 19.4% and 5038.8 ms ± 113.0% for tissue and CSF, respectively. The resulting improvement in precision allows the water tissue T1 value to be included in the spectroscopic characterization of brain tissue.
All Science Journal Classification (ASJC) codes
- Biomedical Engineering
- Radiology Nuclear Medicine and imaging