Nonunion is a major complication of spinalinterbody fusion. Currently X-ray and computed tomography(CT) are used for evaluating the spinal fusion process.However, both imaging modalities have limitations injudgment of the early stages of this fusion process, as theyonly visualize mineralized bone. Magnetic resonanceimaging (MRI) could be of great value as it is able to discriminatebetween different types of tissue. A feasibilitystudy was performed in nine animals from a goat spinalfusion study, to evaluate the detection capacity of differenttissues with micro-MRI. In this study bioresorbable polylacticacid cages were used. Six- and 12-months follow-upspecimens were scanned in a 6.3 T micro-MRI scanner.After scanning, the specimens were processed for histology.Different types of tissue as well as the degradable cagematerial were identified in the fusion zone and designated asregions of interest (ROIs). Subsequently, the location ofthese ROIs was determined on the corresponding micro-MRI image, and average signal intensities of every individualROI were measured. An excellent match was seenbetween the histological sections and micro-MRI images.The micro-MRI images showed quantifiable differences insignal intensity between bone with adipose marrow, bonewith hematopoietic marrow, fibrocartilage, fibrous tissue,and degradable implant material. In time the signal intensityof bone with adipose marrow, bone with hematopoietic redmarrow, and of fibrous tissue remained relatively constant.On the other hand, the signal intensity of the degradableimplant material and the fibrocartilage changed significantlyin time, indicating change of structure andcomposition. In conclusion, in our model using bioresorbablecages the MRI provides us with detailed informationabout the early fusion process and may therefore, allowearly diagnosis of non-union.