Nagarajan Rajakumar PhD, Presenter: Nothing to Disclose

Saadallah Ramadan PhD, Abstract Co-Author: Nothing to Disclose

Gaurav Verma MS, Abstract Co-Author: Nothing to Disclose

Michael Albert Thomas PhD, Abstract Co-Author: Nothing to Disclose

Using water suppressed 1H MR Spectroscopy (MRS) in vivo, detection of aliphatic, selected amide and aromatic proton resonances of many brain metabolites (N-acetyl aspartate (NAA), creatine (Cr), choline (Ch), glutamine (Gln), glutamate (Glu), etc.) was demonstrated. Although most of the amide and selected amine protons of nucleotide/nucleoside have slower exchange rates (<100 s-1) and are detectable, these signals are heavily attenuated while using presaturation techniques such as WET. A goal of this work was to investigate the reproducibility of detecting the J-coupled cross peaks between the amide and methine protons of NAA, the most concentrated metabolite in human brain, while using WET-based water presaturation 2D L-COSY.

10 healthy subjects (mean age 31.5 yo) were scanned after informed consent on a 3T MRI/MRS scanner equipped with a four channel Nova “receive” coil and a quadrature body “transmit” coil. 2D L-COSY parameters were: TR/TE =2s/30 ms, 100 Δt1 increments (Δt1), 8 averages per Δt1, and total acquisition time of 25 minutes. The 2D raw matrix consisted of 512 complex points along the first dimension and 100 points along the second dimension. Matrices were zero filled to 1024 x 256, and processed by Felix.

In the 2D L-COSY spectrum recorded in a healthy human brain, the diagonal and cross peaks can be clearly seen (NAA, Cr, Ch, phosphoethanolamine (PE), phosphocholine (PCh), glutathione (GSH), myo-inositol (mI), lactate (Lac)/threonine (Thr), aspartate (Asp), Glu/Gln(Glx), GABA and macromolecules (MM)). The J-coupled network of NAA displaying the J-coupling between amide-methine (F2=4.3ppm, F1=7.8ppm), and methine-methylene protons (F2=4.3ppm, F1=2.5ppm). Mean volumes ± standard deviation (SD) of the cross peaks between the amide and methine protons were 0.049±0.016 and 0.026±0.011, in the prefrontal white (n=4) and occipital gray (n=6) matter regions, respectively.

This pilot work demonstrates that the cross peaks between the amide and methine protons of NAA can be reliably recorded while using WET presaturation. Without WET presaturation, we expect that water suppression before detection may enhance other amide cross peaks due to Glu, Gln and GSH.

Detection of amide protons will improve the understanding of various biochemicals and minimize the surgical resection of human brain tumors.

Rajakumar, N, Ramadan, S, Verma, G, Thomas, M, Detection of J-Coupled Cross Peaks between Amide and Aliphatic Protons of N-Acetylaspartate in Human Brain Using Localized Correlated Spectroscopy.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8013417.html