Developing 3-D Imaging Mass Spectrometry
Anna C. Crecelius, D. Shannon Cornett, Betsy Williams, Bobby Bodenheimer, Benoit Dawant, and Richard M. Caprioli
Imaging MALDI mass spectrometry has been successfully used to obtain
the distribution of proteins in thin tissue slices . The goal of
the present study is to expand this technique by adding a third
dimension allowing the 3-D mapping of proteins in specific regions of
the mouse brain by imaging serial sections. The 3-D distribution of
targeted proteins can be an important tool for the diagnosis, early
detection and understanding of disease, such as Parkinson disease, and
The animal model we have chosen to study is the mouse brain. The
methodology required for 3-D imaging mass spectrometry is developed in
a first approach with printed images of mouse brain slices on paper to
establish stacking parameters. Nine serial images spanning the full
corpus callosum of a male C57Bl/6J mouse brain are downloaded from a
PhotoShop the downloaded images are converted to a series of model
sections by color coding the section periphery and the corpus callosum
of each image blue and red, respectively. The colored regions are
extracted from the original image and printed at a 1:1 scale on
paper. A digital camera is used to record an optical image from each
of the model slices before MS ion images of the dyes are acquired
using a Voyager DE-STR MALDI TOF mass spectrometer (Applied
Biosystems, Framingham, MA) at a spatial resolution of 50 Ám. The data
acquisition is performed using software developed in-house [2-3].
Each ink color in the printed images of the mouse brain slices on
paper produces specific ions from which MS ion images can be
constructed, as shown in Figure 1. The blue ink used for the brain
outline produces two characteristic ion signals at m/z 584 and m/z
1166, and the red ink used for the corpus callosum produces one strong
ion signal at m/z 342. This mimics the expression of different
proteins in real tissue slices. The integration of the acquired MS ion
images to the optical images requires a registration step to link the
images together. This is achieved by placing four black ink dots
around the printed images of the mouse brain slices. The four black
ink dots are used as landmarks, since they are visible in the optical
image and yield unique MS signals below m/z 300. Therefore, they can
be identified during the imaging process. To align both images a
computer algorithm  is used to identify the x,y coordinates of the
centers of the dots in both the optical and MS ion images. The next
step in the registration procedure is the alignment of a series of
optical images. The external contours of the corpus callosum and the
whole mouse brain are extracted and registered to one another,
according to their position in the mouse brain, using novel image
processing techniques . The final stage is the 3-D reconstruction
of the corpus callosum. The surfaces (3-D shape) of both the corpus
callosum and the whole mouse brain are constructed from the extracted
contours as described in . Subsequently, the MS data of the red dye
are extracted out of the registered MS ion images for each individual
paper slice. Finally, the 3-D shape of the corpus callosum, the mouse
brain and the extracted m/z points are combined and rendered using a
commercial renderer . The resulting 3-D model is presented in
This study shows the successful development of stacking parameter
tools for 3-D imaging mass spectrometry. The next stage is the
construction of 3-D warping parameters using real mouse brain tissue
in order to advance this technique for the 3-D mapping of marker
proteins in the mouse brain.
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A poster presentation is here.
Last modified: Wed Jun 25 14:16:18 CDT 2003