Hi Jacob, I see you're still in the crystallography business.
While you have an interesting idea, I doubt refining structures against entire images would be of any use in obtaining higher quality macromolecular structures. Much of what you see on the screen is a function of parameters completely unrelated or irrelevant to the structure being studied. Diffuse scattering can come from the cryo liquid surrounding the crystal as well as the fibers of the mounting loop itself. Background scattering is related to beam collimation. Spot size/shape is a function of crystal morphology among other things. In addition, every detector has its own peculiarities that make the intensities observed apart from diffraction spots particular to that detector. Also, you would have to take into account other physical properties such as ambient temperature, detector dark current fluctuations, variations in air absorption, etc. So, you could conceivably fit all of these various parameters to the images on hand, but none of them give you any actual information about your structure. As always, if you want more information about your structure, get higher resolution data. Nonetheless, I do think some thought could be put in to exactly how data are reduced. Perhaps the impending era of real time detector readout will help us rethink about spot profiles and intensity integration in a more sophisticated way. We may see a return to thinking about ccd readouts like an area detector which makes the process of analyzing images moot. --Paul --- On Wed, 1/20/10, Jacob Keller <[email protected]> wrote: > From: Jacob Keller <[email protected]> > Subject: [ccp4bb] Refining against images instead of only reflections > To: [email protected] > Date: Wednesday, January 20, 2010, 12:47 PM > Dear Crystallographers, > > One can see from many posts on this listserve that in any > given x-ray diffraction experiment, there are more data than > merely the diffraction spots. Given that we now have vastly > increased computational power and data storage capability, > does it make sense to think about changing the paradigm for > model refinements? Do we need to "reduce" data anymore? One > could imagine applying various functions to model the > intensity observed at every single pixel on the detector. > This might be unneccesary in many cases, but in some cases, > in which there is a lot of diffuse scattering or other > phenomena, perhaps modelling all of the pixels would really > be more true to the underlying phenomena? Further, it might > be that the gap in R values between high- and low-resolution > structures would be narrowed significantly, because we would > be able to model the data, i.e., reproduce the images from > the models, equally well for all cases. More information > about the nature of the underlying macromolecules might > really be gleaned this way. Has this been discussed yet? > > Regards, > > Jacob Keller > > ******************************************* > Jacob Pearson Keller > Northwestern University > Medical Scientist Training Program > Dallos Laboratory > F. Searle 1-240 > 2240 Campus Drive > Evanston IL 60208 > lab: 847.491.2438 > cel: 773.608.9185 > email: [email protected] > ******************************************* >
