Characterizing Protein Concentration in Cerebrospinal Fluid with T2 Component Analysis.

Purpose: T₂ values are hypothesized to be reduced where protein accumulates in the cerebrospinal fluid (CSF). We aimed to verify the accuracy of Carr-Purcell-Meiboom-Gil (CPMG) pulses and non-negative least squares (NNLS) analysis in visualizing protein concentrations by mapping the T₂ values.

Methods: We first dissolved 1.2g of bovine serum albumin powder in 4 mL of artificial CSF to purify an albumin solution with a concentration of 4.5 mM. Artificial CSF was added thereto, and eight types of albumin solutions, with concentrations of 0.002-4.5 mM, were purified. We acquired this albumin solution with CPMG pulses and NNLS, decomposed the T₂ values per pixel, and derived 25 T₂ component values of 60-2000 ms. We assessed the change of T₂ values by the difference in albumin concentration of a single voxel. Finally, we used the method to assess T₂ values from two patients, one with a subdural hematoma and one with a suprasellar cystic tumor. T₂ component values were plotted graphically, presented individually, and created in color maps.

Results: T₂ component values for albumin concentrations ranging from 0.056 to 4.55 mM showed different T₂ peaks, whereas, for concentrations 0.002 to 0.019 mM, the peaks were similar heights and overlapped. Peak width was similar for all concentrations. The color maps successfully reflected the changes in T₂ values across both RGB color patterns. T₂ components for albumin samples with 2.5 mM and 6.1 mM concentrations within a single voxel were represented separately and reflected the ratio of the two samples in nine different regions of interest within one slice. In the clinical cases, the T₂ component map imaged differences in albumin concentrations, similar to those observed in the albumin samples.

Conclusion: The present method with CPMG sequences and NNLS provide adequate images to differentiate accumulating protein concentrations in the CSF, even at the level of a single pixel.