Ultrashort Echo Time and Fast Field Echo Imaging for Spine Bone Imaging with Application in Spondylolysis Evaluation

Isthmic spondylolysis is characterized by a stress injury to the pars interarticularis bones of the lumbar spines, often missed by conventional magnetic resonance imaging (MRI) necessitating a computed tomography (CT) for accurate diagnosis. We compare MRI techniques suitable for producing CT-like images. Lumbar spines of asymptomatic and low back pain (LBP) subjects were imaged at 3-Tesla with multi-echo ultrashort echo time (UTE) and field echo (FE) sequences followed by simple post-processing of averaging and inverting to depict spinal bone with CT-like appearance. Contrast-to-noise ratio (CNR) for bone was determined to compare UTE vs. FE and single-echo vs. multi-echo images. Visually, both sequences depicted cortical bone with good contrast; UTE-processed provided a flatter contrast for soft tissues that made it easy to distinguish from bone, while FE-processed images had better resolution and bone-muscle contrast, important for fracture detection. Additionally, multiecho images provided significantly (p=0.03) greater CNR compared single-echo. Using these techniques, a progressive spondylolysis was detected in a LBP subject. This study has demonstrated the feasibility of spine bone MRI to yield CT-like contrast. Through the employment of multiecho UTE and FE sequences combined with simple processing, we have observed enhancements in image quality and contrast, sufficient to detect pars fracture.