Magnetic nanoparticle imaging by means of minimum norm estimates from remanence measurements.

In magnetic nanoparticle imaging, magnetic nanoparticles are coated and functionalized to bind to specific targets. After measuring their magnetic relaxation or remanence, their distribution can be determined by means of inverse methods. The reconstruction algorithm presented in this paper includes first a dipole fit using a Levenberg-Marquardt optimizer to determine the reconstruction plane. Secondly, a minimum norm estimate is obtained on a regular grid placed in that plane. Computer simulations involving different parameter sets and conditions show that the used approach allows for the reconstruction of distributed sources, although the reconstructed shapes are distorted by blurring effects. The reconstruction quality depends on the signal-to-noise ratio of the measurements and decreases with larger sensor-source distances and higher grid spacings. In phantom measurements, the magnetic remanence of nanoparticle columns with clinical relevant sizes is determined with two common measurement systems. The reconstructions from these measurements indicate that the approach is applicable for clinical measurements. Our results provide parameter sets for successful application of minimum norm approaches to Magnetic Nanoparticle Imaging.

Isoflurane is associated with a similar incidence of emergence agitation/delirium as sevoflurane in young children--a randomized controlled study.

BACKGROUND: Children may be agitated or even delirious especially when recovering from general anesthesia using volatile anesthetics. Many trials have focused on the newer agents sevoflurane and desflurane but for the widely used isoflurane little is known about its potential to generate agitation. We investigated the emergence characteristics of small children after sevoflurane or isoflurane with caudal anesthesia for postoperative pain control. METHODS: After institutional approval and parental consent, anesthesia was randomly performed with sevoflurane (n = 30) or isoflurane (n = 29) in children at the age of 3.8 +/- 1.8 years during surgical interventions on the lower part of the body. After induction, all children received caudal anesthesia with bupivacaine (0.25%, 0.8 ml x kg(-1)). Postoperatively, the incidences of emergence agitation (EA) and emergence delirium (ED) were measured by a blinded observer using a ten point scale (TPS; EA = TPS > 5 ED = TPS > 7) as well as vigilance, nausea/vomiting and shivering. RESULTS: The two groups were comparable with respect to demographic data, duration of surgery and duration of anesthesia. There were also no differences in the period of time from the end of surgery until extubation, duration of stay in the PACU, postoperative vigilance and vegetative parameters. Incidence of EA was 30% (9/30) for sevoflurane and 34% (10/29) for isoflurane during the first 60 min in the PACU (P = 0.785). Likewise, the incidence of ED was not different between the groups (20% and 24%, respectively). CONCLUSIONS: In our randomized controlled study, we found no difference in the incidence of EA or ED between sevoflurane and isoflurane. Therefore, the decision to use one or the other should not be based upon the incidence of EA or ED.