Iniciación a la estandarización del estudio imaginológico mediante resonancia magnética de la anatomía y los procesos patológicos de la extremidad equina

Résumé

Despite the numerous existing publications related to this topic, the full application of MRI for the exploration and diagnosis of pathological processes in the equine limb, to this date, is lacking sufficient standardised criteria in order to obtain, describe and analyse these types of images adequately. The equipment utilized in this research study was comprised of a 0,2 T, low magnetic field MRI. From a group of 553 horses that presented to the Department of Imaging and Diagnostic Service of the Faculty of Veterinary Medicine at the University of Leon, from 1990 to 2008, 3 live animals and 28 deceased were selected. From these, a total of 1266 images were obtained, which were grouped in 77 studies originating from 47 different limbs. Within the selected animals, there were newborn foals, foals of few months of age and adults whose ages varied between 5 and 25 years old, both healthy and ill. The pathological processes assessed in this study were: edema due to decubitus, traumatic skin inflammation, pressure ulcers, skin scars and laminitis. The serial of images were obtained by sequences of pulses of the spin echo kind (SE) with the T1 (T1 SE), proton density (PD) (PD SE) and T2 weighted images, for the main spatial planes (sagital, transversal and coronal), from which skin and surrounding air, periople, perioplic corium and coronary corium were analysed . As the main contribution of this study, a standardised system to describe the anatomy and lesions was proposed and evaluated, with the goal of making observations more objective. For this purpose the following parameters: grey scale tone, heterogeneity, texture and grain diameter were given a numeric value based on international scales when possible, and a value assigned by a numeric scale following observational criteria when it was not. Finally, for the remainder, there were set up qualitative categories. All these values were combined with the median signal intensity of the voxel obtained from the MR equipment, which is the most objective parameter available. The results highlight the fact that the weighted images and its variants used in this project were a solid method to standardize the acquisition of appropriate studies as a means to explore and diagnose the equine limb. It was also observed 1124 Summary that the parameters used in this study, with the purpose of decreasing the subjectivity of the MR images description, fulfil the objective. As a result there is a significant increase of the precision and confidence of the descriptions both of the anatomy and of the pathological processes that were analysed. We can conclude that the use of T1 SE combined with the T2 FSTIR provides more complementary and less overlapping information for the same slice, compared to the rest of the possible combinations of different weighted images and its variants, taking into account the fact that giving up on any of them always means renouncing to a certain part of information. The DP SE-weighted images, provide good identification of the structures, but are more difficult to interpret in its varieties of signal intensity compared to the rest of weighted types and their variants. Other observations made were that in general, MR images with less matrix and smaller field of view proved to be less useful for clinical assessment. MRI of the new born and young foal limbs showed a better quality than those of adults, although intensity signal relations within the structures between these 2 groups are different. The system that was implemented to standardize the collection, description and analysis of the MR Images of the equine limb, has allowed us to appreciate notable differences between animal groups and also within weighted images and their variants. In the subcutaneous edema cases, from these differences we established the predominance or balance of the inflammatory component compared to the osmotic component itself. The analysis of the periople and perioplic corium has revealed that horses that have sub-acute or chronic laminitis turn to develop alterations related to certain histochemical changes and show an increase in retention of water. In evaluating the coronary corium of the horses who suffered from sub-acute or chronic laminitis, we can state that the changes detected show variations of the signal intensity compatible with the existence of an inflammatory processes with an increment of water content within the tissue. Due to these findings, we consider the periople, perioplic corium and coronary corium to be part of those structures affected by the disease process Summary 1125 called laminitis. And it is our opinion that in order to achieve a better diagnosis and follow up of the disease when using MRI; all three structures should be evaluated.