Purpose or Case Report: Though first line evaluation of bone lesions is projection radiography (XR), this is often supplemented by both computed tomography (CT), with attendant ionizing radiation, and MRI for associated marrow and soft-tissue assessment. However, if bone can be evaluated on MRI as well, then a CT may be obviated. Thus, we aim to assess an isotropic Zero Echo Time (ZTE) MRI sequence.
Methods & Materials: A ZTE MR sequence utilized immediate signal acquisition after RF pulse, radial k-space filling to acquire images with near zero echo time. Inverting the display window yields a “CT-like” appearance. Ray-summation image processing on the inverted ZTE image using 3D software (TeraRecon) then produced “x-ray-like” images. With IRB approval and informed consent/assent, 32 consecutive pediatric patients with concurrent XR (mean age 10yr, range 6mo-18yr) referred for extremity exams at 3T (MR750, GE Healthcare) were recruited (May–October 2019) to undergo ZTE imaging. Image quality for native/raysum-ZTE was assessed from 1 (non-diagnostic) to 5 (outstanding). Visualization between raysum-ZTE and XR was assessed (from -2 = XR more delineated to +2 = ZTE more delineated, 0 = same) for bone cortex and intramedullary cavity. Cortical thickness was compared using Wilcoxon sign-rank test. 10 cases with concurrent CT and 23 pathology cases with concurrent XR were also compared visually with ZTE.
Results: For the consecutive case cohort, comparative visualization between raysum-ZTE and XR cortex/IMC was assessed as -2/XR best delineation 0/47%, -1/XR preferred 22/31%, 0/same 63/22%, +1/raysum-ZTE 15/0%. Image quality showed native/raysum ZTE with 84%/40% scoring good or outstanding for cortex and 13%/0% for IMC. Raysum-ZTE and XR showed no difference between measured cortical thickness (p=0.72). Visual comparison of Native-ZTE/CT cortex/intramedullary cavity/pathology -1/CT preferred 20/80/20%, 0/same 60/20/60%, +1/native-ZTE preferred 20/0/20%. Lastly, pathology raysum-ZTE and XR cohort visual comparison showed -1/XR preferred 17%, 0/same 57%, +1/ZTE preferred 13% and +2/ZTE best delineation 13%.
Conclusions: ZTE has comparable cortical visualization to XR and CT. ZTE has limited intramedullary cavity visualization and anatomy delineation, though this is better evaluated on conventional MR sequences. Pathology visualization was similar to slightly improved with ZTE, especially in cases with small lesions and radiographically occult fractures.