Fiducial Marker and Hybrid Alignment Methods for Single- and Double-axis Tomography
Accurate alignment of projection images is an important step in obtaining a high-quality tomographic reconstruction. Ideally, all images should be aligned so that each represents a projection of the same 3D object at a known projection angle. Inadequate image alignment will result in blurring or smearing of features in the reconstruction. The problem is made more difficult because exposure to the electron beam during the acquisition of a tilt series induces geometric changes in many samples (primarily plastic-embedded material). For any sample, but particularly for ones that are not rigid during imaging, a powerful method of image alignment uses the measured coordinates of fiducial markers through the series of images; these can be fit to equations that describe the image projection. Alternative methods are based on cross-correlation of images. The fiducial marker method has the advantage that it guarantees a consistent alignment among the images from the full range of tilt angles. It is also more easily adapted to correct for changes in the sample that occur during imaging.
KeywordsTilt Angle Gold Particle Local Alignment Projection Image Fiducial Marker
Unable to display preview. Download preview PDF.
- Frank, J. and McEwen, B. F. (1992). Alignment by cross-correlation. In Electron Tomography (J. Frank, ed.). Plenum Press, New York, pp. 205–213.Google Scholar
- Koval, J. J. (1997). Variable metric function minimization. Appl. Stat. 46:515–540.Google Scholar
- Lawrence, M.C. (1992). Least-squares method of alignment using markers. In Electron Tomography (J. Frank, ed.). Plenum Press, New York, pp. 197–204.Google Scholar
- Radermacher, M. (1992). Weighted back-projection methods. In Electron Tomography (J. Frank, ed.). Plenum Press, New York, pp. 91–115.Google Scholar
- Ress, D., Harlow, M. L., Schwarz, M., Marshall, R. M. and McMahan, U. J. (1999). Automatic acquisition of fiducial markers and alignment of images in tilt series for electron tomography. J Electron Microsc. (Tokyo) 48:277–287.Google Scholar