Our study demonstrated that the detection of pars fractures using a single sagittal UTE MR sequence is superior in performance and confidence to conventional and optimized MR protocols at 3 T, whereas matching those from CT evaluation. Furthermore, we demonstrated the feasibility of in vivo application of the UTE sequence in subjects with and without spondylolysis.
Human lumbar spine is composed of multiple tissue components that serve to provide structural stability and proper nutrition. Conventional magnetic resonance (MR) imaging techniques have been useful for evaluation of IVD, but inadequate at imaging the discovertebral junction and ligamentous tissues due primarily to their short T2 nature. Ultrashort time to echo (UTE) MR techniques acquire sufficient MR signal from these short T2 tissues, thereby allowing direct and quantitative evaluation. This article discusses the anatomy of the lumbar spine, MR techniques available for morphologic and quantitative MR evaluation of long and short T2 tissues of the lumbar spine, considerations for T2 relaxation modeling and fitting, and existing and new techniques for spine image post-processing, focusing on segmentation. This article will be of interest to radiologic and orthopaedic researchers performing lumbar spine imaging.
OBJECTIVES:In human menisci, investigate whether calcium pyrophosphate crystal deposition (CPPD) affects biomechanical and quantitative MR properties, and their zonal distribution.
MATERIALS AND METHODS:From nine cadaveric knees, sectioned triangular meniscus pieces were harvested. Samples were classified into "Normal" or "CPPD" groups based upon visual inspection. Micro-CT scan verified CPPD. Using MRI, ultrashort echo time (UTE) T2* and spin echo (SE) T2, quantitative values in three zones (red, red-white and white) were determined. Using biomechanical test, indentation forces (g) in the same zones were determined. Effects of CPPD and meniscal zone on indentation force and quantitative MR values were compared.
RESULTS:On UTE MR images, CPPD-affected menisci exhibited punctate dark regions, found mostly (92%) in avascular white and red-white zones. Indentation forces were significantly higher for CPPD samples in the red-white (all p<0.02) and white (all p<0.004) zones but not in the vascular red zone (all p>0.2). Similarly, UTE T2* red zone values were similar between both groups (~6.6 ms, p=0.8) while in the red-white and white zones, CPPD samples had significantly lower values (~5.1 ms, p=0.005 to 0.007). In contrast, SE T2 values showed no difference with CPPD (p=0.12 to 0.16). UTE T2*, but not SE T2, correlated significantly with indentation force (R=−0.29, p=0.009).
CONCLUSIONS:Dark CPP deposits were detectable on UTE images featuring high signal intensity from surrounding meniscal tissue. Preliminary results indicate that CPP deposits were almost exclusively found in the avascular zones. Compared to normal, CPPD menisci featured higher indentation stiffness and lower UTE T2* values in the affected zones.
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