Sensitivity to change of cartilage morphometry using coronal FLASH, sagittal DESS, and coronal MPR DESS protocols--comparative data from the Osteoarthritis Initiative (OAI)

Abstract

Objective: The Osteoarthritis Initiative (OAI) is targeted at identifying sensitive biomarkers and risk factors of symptomatic knee osteoarthritis (OA) onset and progression. Quantitative cartilage imaging in the OAI relies on validated fast low angle shot (FLASH) sequences that suffer from relatively long acquisition times, and on a near-isotropic double echo steady-state (DESS) sequence. We therefore directly compared the sensitivity to cartilage thickness changes and the correlation of these protocols longitudinally.

Methods: Baseline (BL) and 12 month follow-up data of 80 knees were acquired using 1.5 mm coronal FLASH and 0.7 mm sagittal DESS (sagDESS) sequences. In these and in 1.5 mm coronal multi-planar reconstructions (MPR) of the DESS the medial femorotibial cartilage was segmented with blinding to acquisition order. In the weight-bearing femoral condyle, a 60% (distance between the trochlear notch and the posterior femur) and a 75% region of interest (ROI) were studied.

Results: The standardized response mean (SRM = mean change/standard deviation of change) in central medial femorotibial (cMFTC) cartilage thickness was -0.34 for coronal FLASH, -0.37 for coronal MPR DESS, -0.36 for sagDESS with the 60% ROI, and -0.38 for the 75% ROI. Using every second 0.7 mm sagittal slice (DESS) yielded similar SRMs in cMFTC for the 60% and 75% ROI from odd (-0.35/-0.36) and even slice numbers (-0.36/-0.39), respectively. BL cartilage thickness displayed high correlations (r > or = 0.94) between the three protocols; the correlations of longitudinal changes were > or = 0.79 (Pearson) and > or = 0.45 (Spearman).

Conclusions: Cartilage morphometry with FLASH and DESS displays similar longitudinal sensitivity to change. Analysis of every second slice of the 0.7 mm DESS provides adequate sensitivity to change.

Figure 1

Bland-Altman plots showing the differences (errors in mm) between the baseline cartilage thickness values of the different imaging protocols in the medial femorotibial compartment (MFTC) in relation to the mean value of the baseline cartilage thickness in the MFTC. The plot shows the relation between A) the coronal (cor) FLASH and the cor multiplanar reconstruction (MPR) of the DESS, B) the cor FLASH and the sagittal (sag) DESS (selecting a 60% region of interest of the femoral condyle), and C) for the cor MPR DESS and the sag DESS. The mean difference is indicated by the continous line, the limits of agreement (± 1.96 times the standard deviation of the difference) are indicated by dotted lines.

Figure 2

Correlation between the longitudinal changes of cartilage thickness in the medial femorotibial compartment (MFTC). The correlation of the change in cartilage thickness (ThC.tAB in mm) between baseline and year 1 followup is shown for A) the coronal (cor) FLASH and the cor multiplanar reconstruction (MPR) of the DESS, B) the cor FLASH and the sagittal (sag) DESS (60% region of interest of the femoral condyle), and C) for the cor MPR DESS and the sag DESS. The continous lines show the smallest detectable difference (SDD) for each imaging protocol based on previously published test-retest precision errors for paired readings.