Christoph G. Rose-Petruck

Christoph G. Rose-Petruck
Professor of Chemistry 

Research Areas:
Ultrafast x-ray science, ultrafast spectroscopy of chemical reactions, medical x-ray and ultrasound imaging, x-ray microscopy

Contact Information:
Office: GeoChem 245
Phone: 401-863-1533
Email   
Research@Brown Profile 
Research Statement:

Ultrafast chemical dynamics: 
A fundamental goal of chemical research has always been to understand the reaction mechanisms leading to specific reaction products. Reaction mechanisms, in turn, are a consequence of the structural dynamics of molecules participating in the chemical process with atomic motions occurring on the ultrafast timescale of femtoseconds (10^-15 s) and picoseconds (10^-12 s). Since these ultrafast motions are the essence of every chemical process, detailed knowledge about their nature is of fundamental importance. Consequently, theoretical modeling and experimental measurement of these ultrafast structural dynamics is of fundamental importance to chemistry and it is our primary area of research. 
We use ultrafast x-ray absorption fine structure (UXAFS) measurements of the atomic motions of solvated organometallic complexes during photo-induced ligand substitution reactions. These measurements are accompanied by ultrafast UV transient absorption (UVTA) experiments that measure the reactions times of various reaction paths suggested by our theoretical studies. The UXAFS experiments are carried out in my laboratory using a laser-driven plasma x-ray source as well as at ID7-C at the Advanced Photon Source (Argonne National Laboratory) and at BL6.0.1.2 at the Advance Light Source (Lawrence Berkeley National Laboratory). The UVTA experiments are carried out in my laboratory. 

Ultrafast physical dynamics: 
The laser-driven plasma x-ray source is used additionally for ultrafast x-ray holographic imaging of picosecond ultrasonic wave packets propagating in the bulk of optically opaque materials. The imaging method relies on x-ray phase contrast imaging, introduced in the next section, and not on x-ray diffraction. The sample material's crystal structure is irrelevant for the imaging process and in the future, materials not accessible to x-ray diffraction will be the major application area. 

Bio-medical imaging: 
A phase-sensitive x-ray imaging method is applied to biological tissues. This phase-contrast x-ray imaging is fundamentally different from conventional x-ray radiography because the mechanism of image formation does not rely on differential absorption by tissues. Instead, x-ray beams undergo differential phase shifts in passing through an organ and subsequently interfere constructively or destructively at the x-ray camera or film. Hence, tissues are distinguished by their different indices of refraction rather than their absorptive properties. This imaging method is more than a thousand times more sensitive to density variations of tissues than conventional absorption methods and enables imaging of soft tissues with high contrast without the use of contrast agents. We currently apply this modality to the imaging of the micro vascularization of healthy and cancerous murine livers. 

Furthermore, our research focuses on the development of an x-ray imaging modality that combines ultrasound-induced motions in tissue with the detection of such motions by phase contrast x-ray imaging. The goal of the research is to lay the foundation for providing, in a single high resolution, high contrast x-ray image, a delineation of differences in tissue elastic properties. The method combines tissue specificity typically exploited in palpation, elastography, and ultrasound imaging, with the high contrast and high resolution of x-ray phase contrast imaging. As a consequence, the modality not just encodes tissue density but also tissue elasticity into the same high-resolution x-ray image, yielding remote palpation with high spatial resolution. The combined information in the x-ray image should greatly aid the detection and characterization of suspicious lesions even in complicated imaging situations such as radiologically dense breast tissue. The image size is only dependent on the size of the x-ray image detector and therefore can be as large as with conventional film systems. Much of this work is carried out in collaboration with Prof. G. Diebold, Dept. of Chemistry, and Prof. J. R. Wands, Alpert Medical School. 

Education: 

Dr. rer. nat., Ludwid-Maximilians University Muchen, Germany (1993)
Diplom, Physics, Technical University Hannover, Germany (1988)
Vordiplom, Georg-August University at Gottingen, Germany (1984) 


Selected Publications: