Bright ultrashort echo time SWIFT MRI signal at the osteochondral junction is not located in the calcified cartilage

Abstract

In this study, we aimed to precisely localize the hyperintense signal that is generated at the osteochondral junction when using ultrashort echo time magnetic resonance imaging (MRI) and to investigate the osteochondral junction using sweep imaging with Fourier transformation (SWIFT) MRI. Furthermore, we seek to evaluate what compositional properties of the osteochondral junction are the sources of this signal. In the study, we obtained eight samples from a tibial plateau dissected from a 68‐year‐old male donor, and one additional osteochondral sample of bovine origin. The samples were imaged using high‐resolution ultrashort echo time SWIFT MRI and microcomputed tomography (μCT) scans. Localization of the bright signal in the osteochondral junction was performed using coregistered data sets. Potential sources of the signal feature were examined by imaging the bovine specimen with variable receiver bandwidths and by performing variable flip angle T1 relaxation time mapping. The results of the study showed that the hyperintense signal was found to be located entirely in the deep noncalcified articular cartilage. The intensity of this signal at the interface varied between the specimens. Further tests with bovine specimens indicated that the imaging bandwidth and T1 relaxation affect the properties of the signal. Based on the present results, the calcified cartilage has low signal intensity even in SWIFT imaging. Concomitantly, it appears that the bright signal seen in ultrashort echo time imaging resides within the noncalcified cartilage. Furthermore, the most likely sources of this signal are the rapid T1 relaxation of the deep cartilage and the susceptibility‐induced effects arising from the calcified tissues.

Knee osteochondral junction imaging using a fast 3D T1-weighted ultrashort echo time cones sequence at 3T

“…This can be caused by signal contribution from the deep layer, which also has a short T 1 , short T 2 blurring, and partial volume effect (using a relatively thick slice of 2 mm in this study). A most recent study also demonstrated that the bight signals were mainly located at the deep layer cartilage [30]. In general, the qualitative method is more likely to be of clinical utility, given that assessment is rapid and intuitive.…”

Feasibility of an Inversion Recovery-Prepared Fat-Saturated Zero Echo Time Sequence for High Contrast Imaging of the Osteochondral Junction

“…Therefore, the IR-FS-ZTE sequence's TE of 12 µs should be able to directly detect signals from these tissue regions. However, a recent study by Nykanen et al found that the bright signal line seen in UTE sweep imaging with Fourier transformation (SWIFT) imaging of cartilage samples resided within the deep radial noncalcified cartilage (44). This is likely due to the low proton densities of the calcified cartilage and subchondral bone, as well as their extremely short T 2 *s, which together result in a very low signal intensity in SWIFT imaging.…”

Ultrashort echo time magnetic resonance imaging of the osteochondral junction

“…The SNR in the subchondral plate with SWIFT (0.91) was more than four times higher than with conventional FSE (0.12) and GRE (0.19) MR images 76 . The same group carefully coregistered the SWIFT MRI, μCT, and histology images for the OCJ samples 65 . They found that the bright SWIFT MRI signal at the OCJ region is not located in the calcified cartilage but in the deep layers of the radial zone in cartilage.…”