New scans from old: digital reformatting knee MRI

Purpose: To determine the accuracy of cartilage volume and bone areas measured from a 3D knee MRI sequence reformatted in different planes. Methods: MRI of 16 adult subjects (9 females, 7 males, age range 45–68 years) were acquired in the sagittal plane using a 3D T1-weighted fat suppressed spoiled gradient echo sequence. Medial and lateral tibial cartilage volumes were determined by processing images acquired in the sagittal plane and from the same image data reformatted in the coronal plane. Tibial plateau areas were determined by processing images acquired in the sagittal plane and reformatted in the axial plane. Results: Cartilage volumes calculated from the original sagittal acquisition and data reformatted into the coronal plane were similar. The average over- or under-estimation of the lateral and medial cartilage volume from the reformatted coronal scans compared to the sagittal sequences was 4.6% and 9.8% respectively. Similar medial and lateral tibial plateau areas were obtained when the sagittal data was reformatted in the axial plane. The average over- and under-estimate of lateral and medial tibial plateau areas from the reformatted axial scans compared to the originally acquired sagittal sequences was 6.5% and 6.8% respectively. Conclusion: Knee data acquired via MRI in one plane can be reformatted into different planes, providing comparable cartilage volumes and bone areas. As different planes through the knee may provide better visualization of different joint structures, this method may be useful clinically and as a research tool, while avoiding the cost associated with the prolonged scanning times associated with acquiring multiple planes.