Our brain is the most important and complex organ in our entire body. It makes us a human and who we are. The brain as the centre of the nervous system is a communication structure to control and coordinate all actions and reactions in our body. The brain is involved in many functions including movement, touch sensing, vision, hearing, smelling and also it enables us to have a great number of abilities such as learning, memory, concentration, planning, problem-solving, recognition, parts of speech, judgment and many more. However, the mechanism for most of these brain functions is still unclear. The brain has a complex composition and is mainly composed of water (77 to 78 %), fatty substances called lipids (10 to 12 %), proteins (8%), sugars called carbohydrates (1%), inorganic salts (1%) and other organic substances (2%). Therefore, 50-60% of the brain’s dry weight is made of lipid compounds. In fact, the brain is the second fattiest organ after the liver in the body. Therefore, change in the brain composition of these fats can have a big effect on its function in the body. If we aim to investigate the possible changes in the chemistry of the brain caused by some diseases, drugs or diets, the study of lipid compositions and their distributions in the brain would be critical. Lipids are important naturally occurring molecules in all living cellular organisms. They structurally have a polar head group with non-polar hydrocarbon chains allowing them to have both hydrophilic and hydrophobic properties, which aid in forming the cellular bilayer membrane that surrounds all cells. In fact, they are the main component of the cell membrane and play key roles in many cell functions. In order to analyze the lipid compositions of the brain sample, I used a mass spectrometry imaging (MSI) technique that provides great advantages for biological studies. The MSI technique is a label-free method that is able to detect several hundred different biomolecule species and to illustrate their distribution map at the different regions of brain tissue with the micrometer resolution. This is like taking a high-resolution chemical photograph. In the MSI technique, a beam of charged molecules is used to hit the surface of the sample and knock off chemical compounds from a very small area at the surface called a pixel. The ionized chemicals are then transferred to another instrument called a mass analyzer where they are sorted by their size and counted. This results in a mass spectrum that allows identification of the substances detected. The analyzing beam is used to scan an entire sample to make an image or chemical photograph. In this thesis, I developed new ways to use this imaging method, new ways to prepare samples for imaging, and used the methods to measure the lipid compositions and their localization in brain tissue samples. This enabled me to better understand the effects of diet on the chemical composition of the brain. We are indeed what we eat. This chemical imaging method can be also used to study the mechanism of brain functions and diseases.