Resolution limitations for tailored picture-generating freeform surfaces.

Picture-generating freeform surfaces are able to generate a picture in a defined plane by incoherent beam shaping comparable to illumination purposes. No classical imaging is performed. Therefore the classical Rayleigh criterion of the diffraction limit cannot be applied. In this paper, we investigate the physical light formation of picture-generating freeform surfaces using Fresnel-Huygens-based simulations. A criterion for the diffraction limit was found. The resolution of such surfaces is significantly inferior to the resolution of classical imaging systems. However, in many cases, such systems are limited by the geometrical resolution. The influence of those two limitations were examined and a maximum of resolution, being limited by diffraction and by geometrical parameters can be found.

Fully automated intrinsic respiratory and cardiac gating for small animal CT.

A fully automated, intrinsic gating algorithm for small animal cone-beam CT is described and evaluated. A parameter representing the organ motion, derived from the raw projection images, is used for both cardiac and respiratory gating. The proposed algorithm makes it possible to reconstruct motion-corrected still images as well as to generate four-dimensional (4D) datasets representing the cardiac and pulmonary anatomy of free-breathing animals without the use of electrocardiogram (ECG) or respiratory sensors. Variation analysis of projections from several rotations is used to place a region of interest (ROI) on the diaphragm. The ROI is cranially extended to include the heart. The centre of mass (COM) variation within this ROI, the filtered frequency response and the local maxima are used to derive a binary motion-gating parameter for phase-sensitive gated reconstruction. This algorithm was implemented on a flat-panel-based cone-beam CT scanner and evaluated using a moving phantom and animal scans (seven rats and eight mice). Volumes were determined using a semiautomatic segmentation. In all cases robust gating signals could be obtained. The maximum volume error in phantom studies was less than 6%. By utilizing extrinsic gating via externally placed cardiac and respiratory sensors, the functional parameters (e.g. cardiac ejection fraction) and image quality were equivalent to this current gold standard. This algorithm obviates the necessity of both gating hardware and user interaction. The simplicity of the proposed algorithm enables adoption in a wide range of small animal cone-beam CT scanners.

Safety and efficacy of early postoperative solid food consumption after cesarean section.

Traditionally patients have received a physician-dictated regimen of gradual expansion of their diets following cesarean section. This has been based upon concern about the possibility of ileus from expanding the diet too rapidly. Given the economic necessity of earlier postoperative discharge following abdominal delivery, many patients have solid food reintroduced in their diets around the time they leave the hospital. This prospective, randomized, controlled study compared a traditional, gradual dietary expansion scheme with patient-determined reintroduction of solid food, which was offered within eight hours of surgery. The hypotheses were that women would eat more rapidly after cesarean section when given the opportunity and that early solid food consumption would reduce the need for analgesia. The results indicated that both hypotheses were correct. Given the opportunity, women will eat solid food very soon after cesarean section (mean +/- SD 10.2 +/- 5.2 hours from surgery to onset of solid food consumption) as compared to women on a traditional dietary expansion regimen (mean +/- SD 41.5 +/- 16.0 hours, P < .001). Women offered food within hours of cesarean section required less patient-requested injectable narcotic postoperatively than did women on gradual dietary expansion (median, 75 mg versus 225 mg meperidine, P < .05). There was no evidence of compromise of safety or comfort from introducing solid food early and allowing the patient to decide when to eat postoperatively. The conclusion from these data is that early postoperative feeding after cesarean section is a safe and effective alternative for most women, who now face early hospital discharge.