Dedicated cone-beam CT system for extremity imaging.

PURPOSE: To provide initial assessment of image quality and dose for a cone-beam computed tomographic (CT) scanner dedicated to extremity imaging. MATERIALS AND METHODS: A prototype cone-beam CT scanner has been developed for imaging the extremities, including the weight-bearing lower extremities. Initial technical assessment included evaluation of radiation dose measured as a function of kilovolt peak and tube output (in milliampere seconds), contrast resolution assessed in terms of the signal difference-to-noise ratio (SDNR), spatial resolution semiquantitatively assessed by using a line-pair module from a phantom, and qualitative evaluation of cadaver images for potential diagnostic value and image artifacts by an expert CT observer (musculoskeletal radiologist). RESULTS: The dose for a nominal scan protocol (80 kVp, 108 mAs) was 9 mGy (absolute dose measured at the center of a CT dose index phantom). SDNR was maximized with the 80-kVp scan technique, and contrast resolution was sufficient for visualization of muscle, fat, ligaments and/or tendons, cartilage joint space, and bone. Spatial resolution in the axial plane exceeded 15 line pairs per centimeter. Streaks associated with x-ray scatter (in thicker regions of the patient--eg, the knee), beam hardening (about cortical bone--eg, the femoral shaft), and cone-beam artifacts (at joint space surfaces oriented along the scanning plane--eg, the interphalangeal joints) presented a slight impediment to visualization. Cadaver images (elbow, hand, knee, and foot) demonstrated excellent visibility of bone detail and good soft-tissue visibility suitable to a broad spectrum of musculoskeletal indications. CONCLUSION: A dedicated extremity cone-beam CT scanner capable of imaging upper and lower extremities (including weight-bearing examinations) provides sufficient image quality and favorable dose characteristics to warrant further evaluation for clinical use.

Model-based super-resolution for MRI.

Conventional 1.5 T magnetic resonance imaging (MRI) systems suffer from poor out-of-plane resolution (slice dimension), usually with in-plane resolution being several times higher than the former. Post-acquisition, super-resolution (SR) filtering is a viable alternative and a less expensive, off-line image processing approach that is employed to improve tissue resolution and contrast on acquired three-dimensional (3D) MR images. We introduce an SR framework that models a true acquired volume information by taking into account slice thickness and spacing between slices. Previous SR schemes have not considered this type of acquisition information or they have required specialized MR acquisition techniques. Evaluations based on synthetic data and clinical knee MRI data show superior performance of this method over an existing averaging method.