Comparison of Three Magnetic Resonance Imaging Sequences for Measuring Cartilage Thickness in the Canine Stifle

Abstract

Magnetic Resonance Imaging (MRI) using 3 sequences; Proton Density Spin Echo (PDSE), 3 Dimensional Spoiled Gradient with Fat Suppression (3D SPGR-FS) and Steady State Free Precision (SSFP) in the sagittal plane was carried out on 11 normal cadaver stifles. The stifles were imaged within 24hrs postmortem. Three readers obtained cartilage thickness measurements from the images of all sequences. These measurements were compared to those obtained from histological prepared specimens in the sagittal plane. Histology specimens were prepared from the location where MRI images had been obtained. The values for mean cartilage thickness from MRI and histology were compared using regression, correlation, and student’s t test. Pearson’s Correlation was used to assess correlation of cartilage thickness values obtained from magnetic resonance images and histology as well as to assess correlation among readers. There was no significant difference between MRI and histology measurements in 20.2% of the images combined for all sequences. Of these, the Balanced Steady State Free Precision (BSSFP) sequence had the highest number of images that were not significantly different from the histologic measurements (24%). MRI measurements generally overestimated cartilage thickness when compared to histology. There was moderate correlation between histology measurements and MRI images for all readers (R values: 0.25 to 0.77). Correlation between readers for all sequences varied from moderate to poor (R values: 0.25 to 0.77). There was poor coefficient of variations for all image types when compared to histology. All sequences had sufficient contrast resolution to identify the articular cartilage of the femoral condyles. Further investigation of these sequences using a higher field strength magnet may allow more accurate evaluation of cartilage thickness by allowing further manipulation of the matrix size and field of view to more accurately represent cartilage thickness in the canine stifle.