A normal proton brain spectrum is seen in this figure. Notice that the zero frequency is on the right-hand side of the spectrum and it is usual to read the spectrum from right to left.
The metabolites have a unique pattern of peaks at specific chemical shifts and the presence and concentration of these chemicals can be found by detecting peaks at the appropriate ppm.
Four of the most important peaks are demonstrated by this figure:
• 2.0 ppm: N-Acetyl Aspartate (NAA) is regarded as a marker of neuronal integrity and will be reduced if neurons are being destroyed by a disease process.
• 3.0 ppm: Creatine (Cr) is the total peak from phosphocreatine and creatine and is often taken as a reference level, as it is relatively constant throughout the brain and it tends not to change significantly in disease process. However, there is evidence that it can change particularly in malignant tumours.
• 3.2 ppm: Choline (Cho) is considered to be an indicator of membrane activity since phosphocholines are released during myelin breakdown and it is often elevated if malignant processes are present.
• 3.6 ppm: myo-Inositol (mI) is a sugar alcohol which is thought to be a product of myelin breakdown and its peak is often higher in conditions such as Alzheimer’s disease and malignant tumours.
Lactate (Lac) at 1.3 ppm (on in vivo spectra it’s often hard to distinguish lipid from lactate) and Glutamine & Glutamate complex (Glx) at 2.1-2.5 ppm are the other two most important peaks on proton brain MR Spectroscopy.