Tissue imaging is a promising technique that allows scientists to follow the distribution patterns derived from drug treatment (precursor drug and metabolites) in specific tissues or their distribution within a whole rat. Although there have been major advances in the quality of tissue imaging, the challenge of background noise remains, making the identification of the analyte of interest among all the other signals present extremely difficult.
Matrix-assisted laser desorption ionization (MALDI) coupled to a linear ion trap mass spectrometry is emerging as a competent technique for fast and accurate tissue imaging that surpasses the more traditional time-of-flight (TOF) method. The MALDI linear ion trap mass spectrometer used in the study highlighted in this article consists of a set of quadrupoles that guide the ions into the linear ion trap and two detectors. When coupled with specialized imaging visualization software, this technique enables the precise visualization of the spatial distribution of a particular analyte within sections of tissue samples, regardless of the chemical noise.
Tissue Imaging Techniques
Although TOF has long been the mass spectrometry technique of choice for tissue imaging, this method is only capable of performing MS or MS2 detection. Through the application of MALDI and linear ion trap mass spectrometry, the effective isolation and detection of analytes of interest from tissue is made possible.
With conventional methods of tissue analysis, the sample is homogenized before the metabolites or analytes of interest are extracted. However, this process can cause analyte localization within the tissue to be lost. With direct tissue MALDI MS analysis, the identification of a specific analyte in the sample is possible and a 2-D image of the tissue can be generated, showing the precise location of the analyte. Using mass spectrometry for tissue imaging distinguishes between and provides distribution of both parent drug and metabolites, a result not possible with the most commonly used technique of whole body quantitative autoradiography.