Previous researchers have successfully demonstrated the application of temperature feedback control for thermal treatment of disease using MR thermometry. Using the temperature-dependent proton resonance frequency (PRF) shift, ultrasound heating for hyperthermia to a target organ (such as the prostate) can be tightly controlled. However, using fixed gain controllers, the response of the target to ultrasound heating varies with type, size, location, shape, stage of growth, and proximity to other vulnerable organs. To adjust for clinical variables, feedback self-tuning regulator (STR) and model reference adaptive control (MRAC) methods have been designed and implemented using real-time, online MR thermometry by adjusting the output power to an ultrasound array to quickly reach the hyperthermia target temperatures. The use of fast adaptive controllers in this application is advantageous because adaptive controllers do not require a priori knowledge of the initial tissue properties and blood perfusion and can quickly reach the steady-state target temperature in the presence of dynamic tissue properties (e.g., thermal conductivity, blood perfusion). This research was conducted to rapidly achieve and manage therapeutic temperatures from an ultrasound array using novel MRI-guided adaptive closed-loop controllers both in ex vivo and in vivo experiments. The ex vivo phantom experiments with bovine muscle (n = 5) show that within 6 ± 0.2 minutes, the tissue temperature increased by 8 ± 1.37°C. Using rabbits’ (n = 5) thigh muscle, the in vivo experiments demonstrated the target temperature reached 44.5°C ± 1.2°C in 8.0 ± 0.5 minutes. The preliminary in vivo experiment with canine prostate hyperthermia achieved 43 ± 2°C in 6.5 ± 0.5 minutes. These results demonstrate that the adaptive controllers with MR thermometry are able to effectively track the target temperature with dynamic tissue properties.

Summary

We sought to assess the feasibility of using thermosensitive chitosan/β-glycerophosphate for embolotherapy. The renal arteries in nine rabbits were embolized with chitosan/β-glycerophosphate. The animals were studied angiographically and sacrificed at one week (n = 3), four weeks (n = 3), and eight weeks (n = 3) after embolotherapy. Histology was obtained at these three time points. Delivery of chitosan/β-glycerophosphate was successful in all cases. Complete occlusion was achieved in all cases. No recanalization was observed in the follow-up angiograms. No untoward inflammatory reactions were observed in the target renal arteries and infarcted kidneys during the histological examinations. Our preliminary feasibility evaluation in rabbit renal arteries indicates that C/GP is a satisfactory embolization agent.

Quantification of the mechanical behavior of normal and cancerous tissues has important implication in the diagnosis of breast tumor. The present work extends the authors' nonlinear elastography framework to incorporate the conventional X-ray mammography, where the projection of displacement information is acquired instead of full three-dimensional (3D) vector. The elastic parameters of normal and cancerous breast tissues are identified by minimizing the difference between the measurement and the corresponding computational prediction. An adjoint method is derived to calculate the gradient of the objective function. Simulations are conducted on a 3D breast phantom consisting of the fatty tissue, glandular tissue, and cancerous tumor, whose mechanical responses are hyperelastic in nature. The material parameters are identified with consideration of measurement error. The results demonstrate that the projective displacements acquired in X-ray mammography provide sufficient constitutive information of the tumor and prove the usability and robustness of the proposed method and algorithm.

Summary

A great deal of concern has recently arisen regarding the safety of anaesthesia in infants and children. There is mounting and convincing preclinical evidence in rodents and non-human primates that anaesthetics in common clinical use are neurotoxic to the developing brain in vitro and cause long-term neurobehavioural abnormalities in vivo. An estimated 6 million children (including 1.5 million infants) undergo surgery and anaesthesia each year in the USA alone, so the clinical relevance of anaesthetic neurotoxicity is an urgent matter of public health. Clinical studies that have been conducted on the long-term neurodevelopmental effects of anaesthetic agents in infants and children are retrospective analyses of existing data. Two large-scale clinical studies are currently underway to further address this issue. The PANDA study is a large-scale, multisite, ambi-directional sibling-matched cohort study in the USA. The aim of this study is to examine the neurodevelopmental effects of exposure to general anaesthesia during inguinal hernia surgery before 36 months of age. Another large-scale study is the GAS study, which will compare the neurodevelopmental outcome between two anaesthetic techniques, general sevoflurane anaesthesia and regional anaesthesia, in infants undergoing inguinal hernia repair. These study results should contribute significant information related to anaesthetic neurotoxicity in children.

Secondary caries and restoration fracture remain common problems in dentistry. This study tested the hypothesis that combining nano-CaF2 and glass fillers would yield nanocomposites with high mechanical properties and F release. Novel CaF2 nanoparticles (56-nm) were synthesized via spray-drying and incorporated into resin. F release increased with increasing the nano-CaF2 content, or with decreasing pH (p < 0.05). F-release rates at 70–84 days were 1.13 µg/(cm2·day) and 0.50 µg/(cm2·day) for nanocomposites containing 30% and 20% nano-CaF2, respectively. They matched the 0.65 µg/(cm2·day) of resin-modified glass ionomer (p > 0.1). The nanocomposites had flexural strengths of 70–120 MPa, after 84-day immersion at pH 4, pH 5.5, and pH 7. These strengths were nearly three-fold that of resin-modified glass ionomer, and matched/exceeded a composite with little F release. In summary, novel CaF2 nanoparticles produced high F release at low filler levels, thereby making room in resin for reinforcement glass. This yielded nanocomposites with high F-release and stress-bearing properties, which may help reduce secondary caries and restoration fracture.

Secondary caries and restoration fracture remain common problems in dentistry. This study tested the hypothesis that combining nano-CaF2 and glass fillers would yield nanocomposites with high mechanical properties and F release. Novel CaF2 nanoparticles (56-nm) were synthesized via spray-drying and incorporated into resin. F release increased with increasing the nano-CaF2 content, or with decreasing pH (p < 0.05). F-release rates at 70-84 days were 1.13 µg/(cm2·day) and 0.50 µg/(cm2·day) for nanocomposites containing 30% and 20% nano-CaF2, respectively. They matched the 0.65 µg/(cm2·day) of resin-modified glass ionomer (p > 0.1). The nanocomposites had flexural strengths of 70-120 MPa, after 84-day immersion at pH 4, pH 5.5, and pH 7. These strengths were nearly three-fold that of resin-modified glass ionomer, and matched/exceeded a composite with little F release. In summary, novel CaF2 nanoparticles produced high F release at low filler levels, thereby making room in resin for reinforcement glass. This yielded nanocomposites with high F-release and stress-bearing properties, which may help reduce secondary caries and restoration fracture.

Morphological changes of hepatocyte death have so far only been described on cells in culture or in tissue sections. Using a high-resolution and high-magnification multiphoton microscopic system, we recorded in living mice serial changes of acetaminophen (APAP)-induced hepatocyte necrosis in relevance to metabolism of a fluorogenic bile solute. Initial changes of hepatocyte injury included basal membrane disruption and loss of mitochondrial membrane potential. An overwhelming event of rupture at adjacent apical membrane resulting in flooding of bile into these hepatocytes might ensue. Belbs formed on basal membrane and then dislodged into the sinusoid circulation. Transmission electron microscopy disclosed a necrotic hepatocyte depicting well the changes after apical membrane rupture and bile flooding. Administration of the antidote N-acetylcysteine dramatically reduced the occurrence of apical membrane rupture. The present results demonstrated a hidden but critical step of apical membrane rupture leading to irreversible APAP-induced hepatocyte injury.

This article reviews recent studies on: (1) the synthesis of novel calcium phosphate and calcium fluoride nanoparticles and their incorporation into dental resins to develop nanocomposites; (2) the effects of key microstructural parameters on Ca, PO4, and F ion release from nanocomposites, including the effects of nanofiller volume fraction, particle size, and silanization; and (3) mechanical properties of nanocomposites, including water-aging effects, flexural strength, fracture toughness, and three-body wear. This article demonstrates that a major advantage of using the new nanoparticles is that high levels of Ca, PO4, and F release can be achieved at low filler levels in the resin, because of the high surface areas of the nanoparticles. This leaves room in the resin for substantial reinforcement fillers. The combination of releasing nanofillers with stable and strong reinforcing fillers is promising to yield a nanocomposite with both stress-bearing and caries-inhibiting capabilities, a combination not yet available in current materials.

We have studied the morphology and the spatially resolved photoluminescence of rubrene thin films at the early stage of crystallization. The initial growth proceeds via the formation of a wetting layer and the nucleation of islands with an amorphous structure. Crystallization starts when the amorphous islands coalesce and needle like crystalline fibers are formed in the gap between islands. The crystalline fibers then grow on top and in between the original amorphous islands leading to an “open network” of islands. The latter acts as the basis for the growth of semi-crystalline spherulites.

This article reviews recent studies on: (1) the synthesis of novel calcium phosphate and calcium fluoride nanoparticles and their incorporation into dental resins to develop nanocomposites; (2) the effects of key microstructural parameters on Ca, PO4, and F ion release from nanocomposites, including the effects of nanofiller volume fraction, particle size, and silanization; and (3) mechanical properties of nanocomposites, including water-aging effects, flexural strength, fracture toughness, and three-body wear. This article demonstrates that a major advantage of using the new nanoparticles is that high levels of Ca, PO4, and F release can be achieved at low filler levels in the resin, because of the high surface areas of the nanoparticles. This leaves room in the resin for substantial reinforcement fillers. The combination of releasing nanofillers with stable and strong reinforcing fillers is promising to yield a nanocomposite with both stress-bearing and caries-inhibiting capabilities, a combination not yet available in current materials.

Introduction

Therapeutic strategies to treat chronic pancreatitis (CP) are very limited. Other chronic inflammatory diseases can be successfully suppressed by selective cyclooxygenase 2 (COX‐2) inhibitors. As COX‐2 is elevated in CP, we attempted to inhibit COX‐2 activity in an animal model of CP (WBN/Kob rat). We then analysed the effect of COX‐2 inhibition on macrophages, important mediators of chronic inflammation.

Methods

Male WBN/Kob rats were continuously fed the COX‐2 inhibitor rofecoxib, starting at the age of seven weeks. Animals were sacrificed 2, 5, 9, 17, 29, 41, and 47 weeks later. In some animals, treatment was discontinued after 17 weeks, and animals were observed for another 24 weeks.

Results

Compared with the spontaneous development of inflammatory injury and fibrosis in WBN/Kob control rats, animals treated with rofecoxib exhibited a significant reduction and delay (p<0.0001) in inflammation. Collagen and transforming growth factor β synthesis were significantly reduced. Similarly, prostaglandin E2 levels were markedly lower, indicating strong inhibition of COX‐2 activity (p<0.003). If treatment was discontinued at 24 weeks of age, all parameters of inflammation strongly increased comparable with that in untreated rats. The correlation of initial infiltration with subsequent fibrosis led us to determine the effect of rofecoxib on macrophage migration. In chemotaxis experiments, macrophages became insensitive to the chemoattractant fMLP in the presence of rofecoxib.

Conclusion

In the WBN/Kob rat, chronic inflammatory changes and subsequent fibrosis can be inhibited by rofecoxib. Initial events include infiltration of macrophages. Cell culture experiments indicate that migration of macrophages is COX‐2 dependent.

Elastography is developed as a quantitative approach to imaging linear elastic properties of tissues to detect suspicious tumors. In this paper a nonlinear elastography method is introduced for reconstruction of complex breast tissue properties. The elastic parameters are estimated by optimally minimizing the difference between the computed forces and experimental measures. A nonlinear adjoint method is derived to calculate the gradient of the objective function, which significantly enhances the numerical efficiency and stability. Simulations are conducted on a three-dimensional heterogeneous breast phantom extracting from real imaging including fatty tissue, glandular tissue, and tumors. An exponential-form of nonlinear material model is applied. The effect of noise is taken into account. Results demonstrate that the proposed nonlinear method opens the door toward nonlinear elastography and provides guidelines for future development and clinical application in breast cancer study.

Mechanical loading is thought to be a determinant of bone mass and geometry. Both ground reaction forces and tibial strains increase with running speed. This study investigates the hypothesis that surrogates of bone strength in male and female master sprinters, middle and long distance runners and race-walkers vary according to discipline-specific mechanical loading from sedentary controls.

Bone scans were obtained by peripheral Quantitative Computed Tomography (pQCT) from the tibia and from the radius in 106 sprinters, 52 middle distance runners, 93 long distance runners and 49 race-walkers who were competing at master championships, and who were aged between 35 and 94 years. Seventy-five age-matched, sedentary people served as control group.

Most athletes of this study had started to practice their athletic discipline after the age of 20, but the current training regime had typically been maintained for more than a decade. As hypothesised, tibia diaphyseal bone mineral content (vBMC), cortical area and polar moment of resistance were largest in sprinters, followed in descending order by middle and long distance runners, race-walkers and controls. When compared to control people, the differences in these measures were always > 13% in male and > 23% in female sprinters (p < 0.001). Similarly, the periosteal circumference in the tibia shaft was larger in male and female sprinters by 4% and 8%, respectively, compared to controls (p < 0.001). Epiphyseal group differences were predominantly found for trabecular vBMC in both male and female sprinters, who had 15% and 18% larger values, respectively, than controls (p < 0.001). In contrast, a reverse pattern was found for cortical vBMD in the tibia, and only few group differences of lower magnitude were found between athletes and control people for the radius.

In conclusion, tibial bone strength indicators seemed to be related to exercise-specific peak forces, whilst cortical density was inversely related to running distance. These results may be explained in two, non-exclusive ways. Firstly, greater skeletal size may allow larger muscle forces and power to be exerted, and thus bias towards engagement in athletics. Secondly, musculoskeletal forces related to running can induce skeletal adaptation and thus enhance bone strength.

Nano-particles of dicalcium phosphate anhydrous (DCPA) were synthesized for the first time. The objectives of this study were to incorporate DCPA nano-particles into resin for Ca-PO4 release to combat dental caries, and to investigate the filler level effects. Nano-DCPA and nano-silica-fused silicon nitride whiskers at a 1:1 ratio were used at filler mass fractions of 0–75%. The flexural strengths in MPa (mean ± SD; n = 6) of DCPA-whisker composites ranged from (106 ± 39) at 0% fillers to (114 ± 23) at 75% fillers, similar to (112 ± 22) of a non-releasing composite (TPH) (p > 0.1). The composite with 75% fillers in a NaCl solution (133 mmol/L, pH = 7.4, 37°C) yielded a Ca concentration of (0.65 ± 0.02) mmol/L and PO4 of (2.29 ± 0.07) mmol/L. Relationships were established between ion-release and DCPA volume fraction VDCPA: Ca = 4.46 VDCPA1.6, and PO4 = 66.9 VDCPA2.6. Nano-DCPA-whisker composites had high strength and released high levels of Ca-PO4 requisite for remineralization. These new nano-composites could provide the needed combination of stress-bearing and caries-inhibiting capabilities.

Background

Understanding the three-dimensional (3D) volumetric relationship between imaging and functional or histopathologic heterogeneity of tumours is a key concept in the development of image-guided radiotherapy. Our aim was to develop a methodologic framework to enable the reconstruction of resected lung specimens containing non-small-cell lung cancer (nsclc), to register the result in 3D with diagnostic imaging, and to import the reconstruction into a radiation treatment planning system.

Methods and Results

We recruited 12 patients for an investigation of radiology–pathology correlation (rpc) in nsclc. Before resection, imaging by positron emission tomography (pet) or computed tomography (ct) was obtained. Resected specimens were formalin-fixed for 1–24 hours before sectioning at 3-mm to 10-mm intervals. To try to retain the original shape, we embedded the specimens in agar before sectioning. Consecutive sections were laid out for photography and manually adjusted to maintain shape. Following embedding, the tissue blocks underwent whole-mount sectioning (4-μm sections) and staining with hematoxylin and eosin. Large histopathology slides were used to whole-mount entire sections for digitization. The correct sequence was maintained to assist in subsequent reconstruction.

Using Photoshop (Adobe Systems Incorporated, San Jose, CA, U.S.A.), contours were placed on the photographic images to represent the external borders of the section and the extent of macroscopic disease. Sections were stacked in sequence and manually oriented in Photoshop. The macroscopic tumour contours were then transferred to MATLAB (The Mathworks, Natick, MA, U.S.A.) and stacked, producing 3D surface renderings of the resected specimen and embedded gross tumour. To evaluate the microscopic extent of disease, customized “tile-based” and commercial confocal panoramic laser scanning (TISSUEscope: Biomedical Photometrics, Waterloo, ON) systems were used to generate digital images of whole-mount histopathology sections. Using the digital whole-mount images and imaging software, we contoured the gross and microscopic extent of disease.

Two methods of registering pathology and imaging were used. First, selected pet and ct images were transferred into Photoshop, where they were contoured, stacked, and reconstructed. After importing the pathology and the imaging contours to MATLAB, the contours were reconstructed, manually rotated, and rigidly registered. In the second method, MATLAB tumour renderings were exported to a software platform for manual registration with the original pet and ct images in multiple planes. Data from this software platform were then exported to the Pinnacle radiation treatment planning system in dicom (Digital Imaging and Communications in Medicine) format.

Conclusions

There is no one definitive method for 3D volumetric rpc in nsclc. An innovative approach to the 3D reconstruction of resected nsclc specimens incorporates agar embedding of the specimen and whole-mount digital histopathology. The reconstructions can be rigidly and manually registered to imaging modalities such as ct and pet and exported to a radiation treatment planning system.

Transcatheter arterial chemoembolisation (TACE) has become the standard treatment for unresectable hepatocellular carcinoma (HCC). However, this method is often unsuccessful. The p53 gene, which is present as a mutant form in many human tumours, is known to have broad spectrum antitumour effects when expressed normally. In this study, we report a 23 year old patient with recurrent HCC who was treated with the p53 gene (Gendicine) combining TACE, which resulted in a good clinical prognosis.

A simple fabrication technique was developed to produce high frequency (100 MHz) self-focused single element transducers with sputtered zinc oxide (ZnO) crystal films. This technique requires the sputtering of a ZnO film directly onto a curved backing substrate. Transducers were fabricated by sputtering an 18 μm thick ZnO layer on 2 mm diameter aluminum rods with ends shaped and polished to produce a 2 mm focus or f-number equal to one. The aluminum rod served a dual purpose as the backing layer and positive electrode for the resultant transducers. A 4 μm Parylene matching layer was deposited on the transducers after housing and interconnect. This matching layer was used to protect the substrate and condition the transfer of acoustic energy between the ZnO film and the load medium. The pulse-echo response for a representative transducer was centered at 101 MHz with a -6 dB bandwidth of 49%. The measured two way insertion loss was 44 dB. A tungsten wire phantom and an adult zebrafish eye were imaged to show the capability of these transducers.

The main challenges facing composite restorations are secondary caries and bulk fracture. The objective of this study was to develop nano DCPA (dicalcium phosphate anhydrous)-whisker composites with high strength and Ca and PO4 ion release to combat caries. Flexural strength for the nano DCPA-whisker composites at a nano DCPA:whisker mass ratio of 1:2 ranged from (148 ± 9) MPa to (167 ± 23) MPa, significantly higher than the (103 ± 32) MPa of an inlay/onlay commercial control composite without Ca-PO4 release. The nano DCPA-whisker composite released PO4 to a concentration of (1.95 ± 0.13) mmol/L and Ca of (0.68 ± 0.05) mmol/L. Compared with previous conventional Ca- and PO4-releasing composites, the nano DCPA-whisker composites had strengths two-fold higher, and released comparable or higher levels of Ca and PO4. In conclusion, combining nano-DCPA with whiskers yielded novel composites that released high levels of Ca and PO4 requisite for remineralization. These high-strength composites may provide a unique combination of stress-bearing and caries-inhibiting capabilities.

Transforming growth factor beta (TGFβ) can modulate the activity of various MAP kinases. However, how this pathway may mediate TGFβ-induced malignant phenotypes remains elusive. We investigated the role of autocrine TGFβ signaling through MAP kinases in the regulation of cell survival in breast carcinoma MCF-7 cells and untransformed human mammary epithelial cells (HMECs). Our results show that abrogation of autocrine TGFβ signaling with the expression of a dominant negative type II TGFβ receptor (DNRII) or the treatment with a TGFβ type I receptor inhibitor significantly increased apoptosis in MCF-7 cell, but not in HMEC. The expression of DNRII markedly decreased activated/phosphorylated Erk, whereas increased activated/phosphorylated p38 in MCF-7 cells. In contrast, there was no or little change of phosphorylated Erk and p38 in HMECs after the expression of DNRII. Inhibition of Erk activity in MCF-7 control cell induced apoptosis whereas restoration of Erk activity in MCF-7 DNRII cell reduced apoptosis. Similarly, inhibition of p38 activity also inhibited apoptosis in MCF-7 DNRII cell. Thus, autocrine TGFβ signaling can enhance the survival of MCF-7 cells by maintaining the level of active Erk high and the level of active p38 low. Furthermore, the survival properties of TGFβ pathway appear related to transformation supporting the notion that it may be a potential target for cancer therapy.

To investigate the prevalence of, and risk factors for, cervical infection with human papillomavirus (HPV) in the rural province of Shanxi, People's Republic of China, which has relatively high cervical cancer mortality rates, we interviewed and obtained cervical cell samples from 662 women aged 15–59 years. A total of 24 different HPV types were identified using a GP5+/6+-based PCR assay able to detect 44 different HPV types. Human papillomavirus prevalence was 14.8% overall and 9.6% among women without cervical abnormalities (14.2 and 8.9%, respectively, age standardised to the world standard population). Multiple-type infections accounted for 30.6% of all infections. By far the most commonly found type was HPV16 (5.7% of all women and 38.8% of HPV-positive women), followed by HPV 58, 52, 33 and 18. Unlike most previous studies published, HPV prevalence was lower among women younger than 35 years (8.7%) than those older than 35 years (17.8%). High-risk HPV types predominated in all age groups. Although low-risk HPV types were rare in young women, they became more common with increasing age. 92.3% of women with cervical intraepithelial neoplasia grade 3 were infected with high-risk HPV types, but none with low-risk types only. No significant difference in HPV positivity was observed by educational level, sexual habits, reproductive history or use of contraceptive methods in this rural low-income Chinese population.

A new mayfly species, Heptagenia whitingi Webb & McCafferty n.sp. is described from larvae, a male subimago, a female adult, and eggs collected from large rivers in the west-central portion of North America. Larvae are differentiated from other North American Heptagenia Walsh by a pair of large, rectangular pale markings on abdominal tergum 4, and the combination of having the posterior margin of the abdominal terga with bluntly pointed spines less than half the length of the fine setae, small blunt spines on the posterior margin of the caudal filaments, and numerous rows of setae laterally on the ventral surface of the labrum. A 630 bp partial sequence of the mitochondrial gene cytochrome oxidase 1 (COI) from three specimens of H. whitingi n.sp. was compared with those of 12 specimens representing eight other North American species of Heptagenia. Intraspecific sequence divergences based on Kimura-2-parameter (K2P) distance ranged from 0–1.1%. Interspecific sequence divergence based on K2P distance ranged from 8.9–20.0%. Heptagenia whitingi n.sp. differed from its sister taxon H. flavescens (Walsh) by 11.7%. Heptagenia diabasia Burks and H. elegantula (Eaton) differed from each other by only 1.1%; these two alleged species show a clinal pattern in larval abdominal coloration and there are no structural differences between the semaphorants. On this basis, H. diabasia is placed as a junior subjective synonym of H. elegantula, n.syn.

A new imaging modality framework, called elasto-mammography, is proposed to generate the elastograms of breast tissues based on conventional X-ray mammography. The displacement information is extracted from mammography projections before and after breast compression. Incorporating the displacement measurement, an elastography reconstruction algorithm is specifically developed to estimate the elastic moduli of heterogeneous breast tissues. Case studies with numerical breast phantoms are conducted to demonstrate the capability of the proposed elasto-mammography. Effects of noise with measurement, geometric mismatch, and elastic contrast ratio are evaluated in the numerical simulations. It is shown that the proposed methodology is stable and robust for characterization of the elastic moduli of breast tissues from the projective displacement measurement.

Major heart diseases such as ischemia and hypertrophic myocardiopathy are accompanied with significant changes in the passive mechanical properties and active contractility of myocardium. Identification of these changes helps diagnose heart diseases, monitor therapy, and design surgery. A dynamic cardiac elastography (DCE) framework is developed to assess the anisotropic viscoelastic passive properties and active contractility of myocardial tissues, based on the chamber pressure and dynamic displacement measured with cardiac imaging techniques. A dynamic adjoint method is derived to enhance the numerical efficiency and stability of DCE. Model-based simulations are conducted using a numerical left ventricle (LV) phantom with an ischemic region. The passive material parameters of normal and ischemic tissues are identified during LV rapid/reduced filling and artery contraction, and those of active contractility are quantified during isovolumetric contraction and rapid/reduced ejection. It is found that quasistatic simplification in the previous cardiac elastography studies may yield inaccurate material parameters.

The crystal structure of the RNA octamer duplex r(CCCIUGGG)2has been elucidated at 2.5 A resolution. The crystals belong to the space group P21and have unit cell constants a = 33.44 A, b = 43.41 A, c = 49.39 A and beta = 104.7 degrees with three independent duplexes (duplexes 1-3) in the asymmetric unit. The structure was solved by the molecular replacement method and refined to an Rwork/Rfree of 0.185/0.243 using 3765 reflections between 8.0 and 2.5 A. This is the first report of an RNA crystal structure incorporating I.U wobbles and three molecules in the asymmetric unit. Duplex 1 displays a kink of 24 degrees between the mismatch sites, while duplexes 2 and 3 have two kinks each of 19 degrees and 27 degrees, and 24 degrees and 29 degrees, respectively, on either side of the tandem mismatches. At the I.U/U.I mismatch steps, duplex 1 has a twist angle of 33.9 degrees, close to the average for all base pair steps, but duplexes 2 and 3 are underwound, with twist angles of 24.4 degrees and 26.5 degrees, respectively. The tandem I.U wobbles show intrastrand purine-pyrimidine stacking but exhibit interstrand purine-purine stacking with the flanking C.G pairs. The three independent duplexes are stacked non-coaxially in a head-to-tail fashion to form infinite pseudo-continuous helical columns which form intercolumn hydrogen bonding interactions through the 2'-hydroxyl groups where the minor grooves come together.