Analytical tools for magnetic resonance imaging

The response of different magnetic resonance (MR) techniques to tissue parameters - T1, T2, and N(H) - is a determinant of clinical efficacy. The large possible number of imaging techniques and range of variable parameters for each make it difficult to perform exhaustive evaluations in a single patient or even in animal models. In addition, changes in operating magnetic field strength change the relaxation times sufficiently so that the efficacy of a technique at a given field does not imply similar results at another field value. Tools are demonstrated that permit the evaluation of the efficacy of any model of response to tissue parameters, and also allow the investigation of the effects of changing magnetic field. Global maps of signal difference between tissues as well as calculated images are obtainable from a minimally sufficient data set. These tools serve as an important adjunct to experimental work.     

Phantom pain: A sensitivity analysis

Purpose: To analyse how decisions to dichotomise the frequency and impediment of phantom pain into absent and present influence the outcome of studies by performing a sensitivity analysis on an existing database.

Method: Five hundred and thirty-six subjects were recruited from the database of an orthopaedic workshop and filled out a questionnaire in which the following items were assessed: demographics, side, date, level and reason of amputation, presence and frequency of phantom sensations, phantom pain and stump pain, and impediment due to phantom pain.

Results: The prevalence of phantom pain ranged from 7 - 72% when different cut off points for the frequency of phantom pain were applied. The significance of the various risk factors for the prevalence of phantom pain changed when different cut off points were applied. Only stump pain and phantom sensations were significant risk factors for all cut off points. Risk factors for the impediment of phantom pain changed when different cut off points were applied and these risk factors were different from those for the prevalence of phantom pain.

Conclusion: The choice of cut off points influences the outcome of phantom pain studies considerably. This study provides some insight into the differences in prevalence and risk factors found in literature.