Evaluation of 2D and 3D navigation for iliosacral screw fixation.

PURPOSE: Image guidance is essential in some orthopedic surgical procedures, especially iliosacral screw fixation. Currently, there is no consensus regarding the best image guidance technique. An ex-vivo study was performed to compare conventional, 2-dimensional (2D), and 3D imaging techniques and determine the optimal image guidance technique for pelvic surgery. METHODS: Plastic (n = 9) and donated cadaver pelvises (n = 8) were evaluated in the laboratory. The pelvises were positioned on radiolucent operation tables in a prone position. Transiliosacral screws were inserted without or with 2D- and 3D-navigational support. A digital mobile X-ray unit with flat-panel fluoroscopy and navigation software was used to measure precision, radiation exposure, and time requirements. RESULTS: 2D-navigation resulted in 40% incorrect screw positioning for the cadavers, 6% for the plastic phantoms, and 21% overall. The highest accuracy was accomplished with 3D-navigation (plastic: 100%; cadavers: 83%; p < 0.05). The dose-area product showed that both 2D- and 3D-navigation required increased exposure compared to the conventional technique (p < 0.01). For both plastic and cadaver specimens, navigated techniques required significantly longer times for screw insertion than the conventional technique (p < 0.01). CONCLUSION: 3D image guidance for transiliosacral screw fixation enabled more accurate screw placement in S1 and S2 vertebrae. However, radiation exposure in 3D-navigation was excessive; thus, we recommend avoiding 3D-navigation in young patients. A primary advantage of 3D-navigation was that the operating team could leave the room during the scan; thus, it reduced their radiation exposure. Moreover, the time required for screw insertion with 3D-navigation was similar to that required in the conventional technique; thus, 3D-navigation is recommended for older patients.

A high-resolution scanning microprobe matrix-assisted laser desorption/ionization ion source for imaging analysis on an ion trap/Fourier transform ion cyclotron resonance mass spectrometer.

A new scanning microprobe matrix-assisted laser desorption/ionization (SMALDI) ion source for high spatial resolution has been developed for linear ion trap and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The source is fully compatible with commercial ion trap flanges (such as the LTQ series, Thermo Fisher Scientific). The source is designed for atmospheric pressure (AP) operation but is also suitable for mid-pressure operation. The AP mode is especially useful for investigating volatile compounds. The source can be interchanged with other ion sources within a minute when operated in the AP mode. Combining high-lateral resolution MALDI imaging with high mass resolution and high mass accuracy mass spectrometry, available in the FT-ICR mode, provides a new quality of analytical information, e.g. from biological samples. First results obtained with the new ion source demonstrate a maximum lateral resolution of 0.6 by 0.5 microm. Depending on the limit of detection of the chosen mass analyzer, however, the size of the focus had to be enlarged to a diameter of up to 8 microm in the FT-ICR mode, in order to create enough ions for detection. Mass spectra acquired for analytical imaging were obtained from single laser pulses per pixel in all the experiments. This mode allows us to investigate biological thin sections with desorption focus diameters in the micrometer range, known to cause complete evaporation of material under the laser focus with a very limited number of laser pulses. As a first example, peptide samples deposited in microstructures were investigated with the new setup. A high quality and validity of the acquired images were obtained in the ion trap mode due to the low limit of detection. High mass resolution and accuracy but poorer image quality were obtained in the ICR mode due to the lower detection sensitivity of the ICR detector.