Intraoperative Imaging Changes Management in Orbital Fracture Repair.

PURPOSE: Intraoperative imaging is gaining widespread use in the management of facial fracture repair. The aim of this study was to determine whether intraoperative imaging changes the management of orbital fracture repair. MATERIALS AND METHODS: A retrospective case series was performed of all cases of orbital fracture repair from 2008 to 2015 in which the intraoperative O-arm was used at Regions Hospital (St Paul, MN), a level I trauma center. The primary outcome variable was a change in management, ranging from orbital plate repositioning to proceeding with orbital floor exploration. RESULTS: The study sample was composed of 101 patients with a mean age of 40 ± 15 years. Approximately 75% (76 of 101) of patients were male and 25% (25 of 101) were female. All cases were secondary to assault, motor vehicle accident, fall, or gunshot wounds. Use of the O-arm resulted in a change in management in 44% (44 of 101) of cases. In 48% (21 of 44) of these cases in which intraoperative imaging resulted in a change in management, the orbital plate was repositioned to optimize repair. In 16% (7 of 44) of these cases, the orbital plate was exchanged for a different size or type of plate. In 7% (3 of 44) of these cases, the orbital plate was reshaped by bending to improve contour for the repair. In another 7% (3 of 44) of these cases, the orbital plate was reshaped by trimming the plate to optimize the length or width of the plate for repair. In 7% of these cases, the orbital floor required exploration based on intraoperative imaging. In 5% of these cases, the orbital floor was found to be adequately reduced after zygoma reduction based on intraoperative imaging and did not require exploration. CONCLUSIONS: Use of intraoperative imaging allows the surgeon to make real-time changes in operative management ranging from orbital plate repositioning to deciding whether to proceed with orbital floor exploration. This not only allows for immediate optimization of repair but also could decrease the need for revision procedures, thus decreasing patient morbidity and improving patient outcomes.

Generalized Objective Performance Assessment of a New High-Sensitivity Microangiographic Fluoroscopic (HSMAF) Imaging System.

The objective performance evaluation metrics, termed Generalized Modulation Transfer Function (GMTF), Generalized Noise Power Spectrum (GNPS), Generalized Noise Equivalent Quanta (GNEQ), and Generalized Detective Quantum Efficiency (GDQE), have been developed to assess total imaging-system performance by including the effects of geometric unsharpness due to the finite size of the focal spot and scattered radiation in addition to the detector properties. These metrics were used to evaluate the performance of the HSMAF, a custom-built, high-resolution, real-time-acquisition detector with 35-mum pixels, in simulated neurovascular angiographic conditions using a uniform head-equivalent phantom. The HSMAF consists of a 300-mum-thick CsI(Tl) scintillator coupled to a 4 cm diameter, variable-gain, Gen2 light image intensifier with dual-stage microchannel plate, followed by direct fiber-optic coupling to a 30-fps CCD camera, and is capable of both fluoroscopy and angiography. Effects of focal-spot size, geometric magnification, irradiation field-of-view, and air-gap between the phantom and the detector were evaluated. The resulting plots of GMTF and GDQE showed that geometric blurring is the more dominant image degradation factor at high spatial frequencies, whereas scatter dominates at low spatial frequencies. For the standard image-geometry and scatter conditions used here, the HSMAF maintains substantial system imaging capabilities (GDQE>5%) at frequencies above 4 cycles/mm where conventional detectors cannot operate. The loss in image SNR due to scatter or focal-spot unsharpness could be compensated by increasing the exposure by a factor of 2 to 3. This generalized evaluation method may be used to more realistically evaluate and compare total system performance leading to improved system designs.

New light-amplifier-based detector designs for high spatial resolution and high sensitivity CBCT mammography and fluoroscopy.

New cone-beam computed tomographic (CBCT) mammography system designs are presented where the detectors provide high spatial resolution, high sensitivity, low noise, wide dynamic range, negligible lag and high frame rates similar to features required for high performance fluoroscopy detectors. The x-ray detectors consist of a phosphor coupled by a fiber-optic taper to either a high gain image light amplifier (LA) then CCD camera or to an electron multiplying CCD. When a square-array of such detectors is used, a field-of-view (FOV) to 20 × 20 cm can be obtained where the images have pixel-resolution of 100 µm or better. To achieve practical CBCT mammography scan-times, 30 fps may be acquired with quantum limited (noise free) performance below 0.2 µR detector exposure per frame. Because of the flexible voltage controlled gain of the LA's and EMCCDs, large detector dynamic range is also achievable. Features of such detector systems with arrays of either generation 2 (Gen 2) or 3 (Gen 3) LAs optically coupled to CCD cameras or arrays of EMCCDs coupled directly are compared. Quantum accounting analysis is done for a variety of such designs where either the lowest number of information carriers off the LA photo-cathode or electrons released in the EMCCDs per x-ray absorbed in the phosphor are large enough to imply no quantum sink for the design. These new LA- or EMCCD-based systems could lead to vastly improved CBCT mammography, ROI-CT, or fluoroscopy performance compared to systems using flat panels.

Generalized Performance Evaluation of X-ray Image Intensifier compared with a Microangiographic System.

Standard objective parameters such as MTF, NPS, NEQ and DQE do not reflect complete system performance, because they do not account for geometric unsharpness due to finite focal spot size and scatter due to the patient. The inclusion of these factors led to the generalization of the objective quantities, termed GMTF, GNNPS, GNEQ and GDQE defined at the object plane. In this study, a commercial x-ray image intensifier (II) is evaluated under this generalized approach and compared with a high-resolution, ROI microangiographic system previously developed and evaluated by our group. The study was performed using clinically relevant spectra and simulated conditions for neurovascular angiography specific for each system. A head-equivalent phantom was used, and images were acquired from 60 to 100 kVp. A source to image distance of 100 cm (75 cm for the microangiographic system) and a focal spot of 0.6 mm were used. Effects of varying the irradiation field-size, the air-gaps, and the magnifications (1.1 to 1.3) were compared. A detailed comparison of all of the generalized parameters is presented for the two systems. The detector MTF for the microangiographic system is in general better than that for the II system. For the total x-ray imaging system, the GMTF and GDQE for the II are better at low spatial frequencies, whereas the microangiographic system performs substantially better at higher spatial frequencies. This generalized approach can be used to more realistically evaluate and compare total system performance leading to improved system designs tailored to the imaging task.