PexLoc—Parallel excitation using local encoding magnetic fields with nonlinear and nonbijective spatial profiles

With the recent proposal of using magnetic fields that are nonlinear by design for spatial encoding, new flexibility has been introduced to MR imaging. The new degrees of freedom in shaping the spatially encoding magnetic fields (SEMs) can be used to locally adapt the imaging resolution to features of the imaged object, e.g., anatomical structures, to reduce peripheral nerve stimulation during in vivo experiments or to increase the gradient switching speed by reducing the inductance of the coils producing the SEMs and thus accelerate the imaging process. In this work, the potential of nonlinear and nonbijective SEMs for spatial encoding during transmission in multidimensional spatially selective excitation is explored. Methods for multidimensional spatially selective excitation radiofrequency pulse design based on nonlinear encoding fields are introduced, and it is shown how encoding ambiguities can be resolved using parallel transmission. In simulations and phantom experiments, the feasibility of selective excitation using nonlinear, nonbijective SEMs is demonstrated, and it is shown that the spatial resolution with which the target distribution of the transverse magnetization can be realized varies locally. Thus, the resolution of the target pattern can be increased in some regions compared with conventional linear encoding. Furthermore, experimental proof of principle of accelerated two‐dimensional spatially selective excitation using nonlinear SEMs is provided in this study. Magn Reson Med 70:1220–1228, 2013. © 2012 Wiley Periodicals, Inc.     

Enhanced yield of chromosome aberrations after CT examinations in paediatric patients

Purpose: To determine whether computed tomography (CT) could enhance the chromosome aberration yields in paediatric patients.

Material and methods: Blood samples were taken before and after CT scans from 10 children for whom the medical justifications for CT examinations were accidental injuries and not diseases as investigated in earlier studies. Chromosome analysis was carried out in lymphocytes by fluorescence plus Giemsa (FPG) staining exclusively in metaphases of the first cell cycle in vitro.

Results: The mean blood dose of the 10 children was about 12.9 mGy which was determined by a newly developed dose estimation. Based on more than 20,000 analyzed cells it was found that after CT examination the frequencies of dicentrics (dic) and excess acentric fragments (ace) in lymphocytes were significantly increased. By subdividing the children into two age groups, those with an age from 0.4 years to 9 years and from 10 – 15 years, it became obvious that the observed increase in chromosome aberrations was mainly contributed by the younger age group. In this group the frequency of dicentrics was significantly increased whereas in the older group the observed increase was not significant.

Conclusion: Our results demonstrate that CT examinations enhance the dicentrics yields in peripheral lymphocytes of children aged up to 15 years. Since in particular significantly increased dicentric yields could be observed in children with an age from 0.4 – 9 years, it can be assumed that children younger than 10 years may be more radiation sensitive than older subjects.     

Gadolinium neutron capture in glioblastoma multiforme cells

Purpose: A proof of principle for cell killing by Gadolinium (Gd) neutron capture in Magnevist® preloaded Glioblastoma multiforme (GBM) cells is provided.

Materials and methods: U87cells were pre-loaded with 5 mg/ml Magnevist® (Gd containing compound) and irradiated using an enhanced neutron beam developed at NIU Institute for Neutron Therapy at Fermilab. These experiments were possible because of an enhanced fast neutron therapy assembly designed to use the fast neutron beam at Fermilab to deliver a neutron beam containing a greater fraction of thermal neutrons and because of the development of improved calculations for dose for the enhanced neutron beam. Clonogenic response was determined.

Results: U87 cell survival after γ irradiation, fast neutron irradiation and irradiation with the enhanced neutron beam in the presence or absence of Magnevist® were determined.

Conclusions: U87 cells were the least sensitive to γ radiation, and increasingly sensitive to fast neutron irradiation, irradiation with the enhanced neutron beam and finally a significant enhancement in cell killing was observed for U87 cells preloaded with Magnevist®. The sensitivity of U87 cells pre-loaded with Magnevist® and then irradiated with the enhanced neutron beam can at least in part be attributed to the Auger electrons emitted by the neutron capture event.     

Extracellular matrix deposition and cell proliferation in a model of chronic glomerulonephritis in the rat.

BACKGROUND: Resident glomerular cell proliferation, matrix deposition and secretion of matrix metalloproteinases play a major role in the progression of chronic glomerular disease. These features were studied in a novel approach in a rat model of chronic glomerulonephritis induced by four injections of an anti-Thy 1.1 antiserum at weekly intervals. METHODS: Chronic immune mediated mesangial injury was induced in male Sprague-Dawley rats by repeated intravenous injection of an anti-Thy 1.1 antiserum. One week after the first and fourth injection of the antiserum proteinuria was evaluated and the kidneys were removed. Immunohistology was performed for proliferating cells, monocytes and collagen type IV. Furthermore, mRNA expression of collagen type IV, TGF-beta and the matrix degrading enzyme MMP-2 as well as MMP-2 protein expression were studied. RESULTS: Urinary protein excretion was dramatically increased after one antiserum injection and stayed elevated at a lower level after the fourth antiserum injection. After the initial induction of nephritis, 7 days following antiserum, resident glomerular cell proliferation was increased whereas with repeated injections of the antiserum cell numbers were not different from controls, as measured 1 week after the fourth injection. In contrast, extracellular matrix accumulation (collagen type IV) increased after the first antiserum injection and further increased after the fourth antiserum injection. The mRNA expression for collagen type IV increased after the first antiserum injection and showed further increase after the fourth antiserum injection. Induction of nephritis also stimulated glomerular mRNA expression of MMP-2 and TGF-beta, both of which remained at a high level after the fourth antiserum injection. Glomerular protein levels of MMP-2 also increased after the first antiserum injection and showed a further slight increase after the fourth injection. CONCLUSION: Increased cellular proliferation is involved in an early stage of this disease, while enhanced expression of glomerular matrix and augmented mRNA and protein expression of the matrix degrading enzyme MMP-2 continue into the chronic phase, and contribute to the extensive structural remodeling process that accompanies this form of glomerular injury.     

Successful implantation of Schwann cells in acellular muscles

Acellular muscle grafts can support axonal regeneration over short gaps. Due to the lack of viable Schwann cells in the grafts, failure of regeneration is evident with increasing gap lengths. To create a biological nerve conduit, Schwann cells were implanted into acellular muscle. The grafts were then incubated in vitro and assessed histologically and morphometrically. For cultivation of the Schwann cells, rat sciatic nerves were allowed to predegenerate to obtain a high cell yield. Rat gracilis muscles were harvested and made acellular by a liquid nitrogen treatment. After Schwann cell implantation, the muscles were incubated in vitro for 2, 5, and 7 days. S100-immunostaining, NGF, and N-cadherin, characterized the Schwann cells within the muscle. Viability was assessed by fluoresceine-fluorescence staining. Proliferation was determined by BrdU-DNA incorporation. Cell implantation did not to affect Schwann cell viability. Cells were seen throughout the entire length of the muscle basal lamina. They aligned and formed a cell column. Immunostained for S-100, implanted cells showed 100 percent staining. N-cadherin and NGF were expressed by all of the S-100 positive cells. Predegeneration is considered to be a highly efficacious method, if a high yield of activated Schwann cells is required. The successful implantation of the cells into an acellular muscle provides the possibility of a biologic conduit, offering the advantage of large basal lamina tubes serving as a pathway for regenerating axons. It also provides the beneficial effects of viable Schwann cells that produce neurotrophic and neurotropic factors to support axonal regeneration. Functional outcomes require evaluation in further in vivo studies.     

Visibility of Sutures of the Orbit and Periorbital Region Using Multidetector Computed Tomography

Objective

Knowledge of cranial suture morphology is crucial in emergency medicine, forensic medicine, and maxillofacial reconstructive surgery. This study assessed the visibility of sutures of the orbit and periorbital region on multidetector computed tomography.

Materials and Methods

Multidetector computed tomography scans of 200 patients (127 males, 73 females; mean age 51.3 years; range, 6-92 years) were evaluated retrospectively. The slice thicknesses varied from 0.5 to 1 mm, and the tube current from 25 to 370 mAs, depending on the CT indication. The visibility of sutures was estimated according to a 4-point scale from "not visible" to "well visible". The chi-squared test was used to test the association of the visibility of sutures with the slice thickness, tube current, and age of patients. Statistical significance was assumed at p < 0.05.

Results

Overall, best visibility was found for the sutura frontozygomatica (98%), sutura frontonasalis (88.5%), and sutura sphenozygomatica (71.5%), followed by the sutura zygomaticomaxillaris (65.8%), sutura temporozygomatica (41.8%), sutura frontomaxillaris (44.5%), and sutura sphenofrontalis (31%). Poor visibility was found for the sutura frontolacrimalis (16.8%) and sutura frontoethmoidalis (1.3%). The sutura ethmoidomaxillaris, sutura lacrimomaxillaris, and sutura ethmoidolacrimalis were not visible.

Conclusion

Although the sutures of the superior, lateral, and inferior orbit are well visible, those of the medial orbit are poorly visible on CT scans.     

Value of monoenergetic low-kV dual energy CT datasets for improved image quality of CT pulmonary angiography

Purpose

High vessel attenuation and high contrast-to-noise ratio (CNR) are prerequisites for high diagnostic confidence in CT pulmonary angiography (CTPA). This study evaluated the impact of calculated monoenergetic dual-energy (DE) CTPA datasets on vessel attenuation and CNR.

Materials and methods

50 Patients (24 men, mean age 68 ± 14 years) who underwent DE-CTPA were retrospectively included in this study. The 80 and 140-kV DE polyenergetic image data were used to calculate virtual monoenergetic image datasets in 10 kiloelectron volt (keV) increments from 40 to 120 keV. Vessel and soft tissue attenuation and image noise were measured in various regions of interest and the CNR was subsequently calculated. Differences in vessel attenuation and CNR were compared between the different monoenergetic datasets. The best monoenergetic dataset was then compared to the standard 120-kV polyenergetic dataset.

Results

Vessel attenuation and CNR of 70-keV CTPA datasets were superior to all other monoenergetic image datasets (all p < 0.05). 70-keV monoenergetic datasets provided a statistically significant 12% increase in mean vessel attenuation compared to standard 120-kV polyenergetic datasets (384 ± 117 HU vs. 342 ± 106 HU, respectively; p < 0.0001) and a statistically significant 18% increase in mean CNR (29 ± 13 vs. 24± 11 respectively; p < 0.0001).

Conclusion

Virtual 70-keV monoenergetic CTPA image datasets significantly increase vessel attenuation and CNR of DE-CTPA studies, suggesting that clinical application of low-keV monoenergetic reconstructions may allow a decrease in the amount of iodinated contrast required for adequate image quality in DE-CTPA examinations.     

Substance use among elite adolescent athletes: Findings from the GOAL Study

Elite athletes often find themselves in a dilemma between maintaining optimal health to be successful and accepting health risks by pushing their physical limits. For elite adolescent athletes, this dilemma becomes a trilemma as they are also confronted with developmental challenges typical for adolescence. As many adolescents encounter different substances during this critical period of development, we analyzed prevalence of substance use to identify determinants related to these behaviors and to compare the prevalences with nonelite athletes. Our main data were drawn from the German Young Olympic Athletes’ Lifestyle and Health Management Study (GOAL Study) including 1138 elite adolescent athletes (14–18 years). For comparisons, the data were combined with data from the German Health Interview and Examination Survey for Children and Adolescents (KiGGS). Beside uni‐ and bivariate analyses, we conducted (conditional) logistic regression analyses. Eighty‐six percent had consumed alcohol at least once. Binge drinking was performed by 24% during the last month. Alcohol consumption was positively associated with age, education, technical sports, lower squads, and attending boarding schools. Binge drinking was higher in males, older adolescents, and in technical sports. Smoking (3%) and marijuana use (3%) were less prevalent. Compared with nonelite athletes, they showed less risky behavior except for binge drinking. As we could identify risk groups, prevention and health promotion programs could be developed for this specific target group.     

Laparoscopic vs open repair of gastric perforation and abdominal lavage of associated peritonitis in pigs

Background: Laparoscopy is increasingly used in conditions complicated by peritonitis, e.g., peptic ulcer perforation. Of some theoretical concern is the capnoperitoneum, which may aggravate peritonitis and induce septic shock due to increased intraabdominal pressure and distension of the peritoneum. This animal study was devised to analyze the effectiveness of laparoscopic versus traditional open repair of gastric perforation and abdominal lavage for associated peritonitis. Methods: To simulate gastric perforation, female Duroc pigs were subjects to standardized gastrotomy. Either 6 or 12 h after gastric perforation, the animals underwent either traditional open or laparoscopic repair of the gastric defect and peritoneal lavage. The subjects were divided into the following four groups: peritonitis for 6 h and open surgery (group I) or laparoscopic surgery (group II); peritonitis for 12 h and open surgery (group III) or laparoscopic surgery (group IV). After an observation period of 6 days, the surviving animals were killed. The main outcome criteria were survival, perioperative changes of hemodynamics suggestive for septic shock, bacteremia, and endotoxemia. Results: There were no significant differences between group I and II. Mortality was 22% in group III, as compared to 78% in group IV (p= 0.045). In group IV, the incidence of perioperative bacteremia and plasma endotoxin concentrations were significantly higher than in group III. Concomitantly, decreased mean arterial pressure and systemic vascular resistance, and increased cardiac output suggested a higher incidence of septic shock in group IV. Conclusion: Critical appraisal of laparoscopic surgery is warranted in conditions associated with severe, longstanding peritonitis. Received: 28 February 1997/Accepted: 1 July 1997