Magnetic prestressing for a d32-mode single crystal ultrasonic transducer

This work describes a 35.9 kHz ultrasonic transducer that incorporates a magnetic arrangement to apply a static-compressive prestress to a d₃₂-mode relaxor ferroelectric single crystal drive-element. The magnetic arrangement produces a 22.5 N static-compressive force, inducing a static compression of ∼630 nm on the drive-element. Operating in air with a continuous-wave 10 V peak drive at ∼35.9 kHz, the measured resonant peak displacement of the transducers head-mass was 127 nm. This is well within the predicted static compression, thus, the drive-element is protected from damaging tensile stress. Under the same drive conditions and at an axial distance of 10 mm from the face of the head-mass, the measured acoustic pressure was ∼12 Pa. Analytical and finite element model predictions and the measured behaviour of a prototype device are presented and show good correlation, demonstrating that magnetic prestressing of the drive-element can be a viable alternative to the traditional bolt-clamp.

Simultaneous Large Optical and Piezoelectric Effects Induced by Domain Reconfiguration Related to Ferroelectric Phase Transitions

Electrical switching of ferroelectric domains and subsequent domain wall motion promotes strong piezoelectric activity, however, light scatters at refractive index discontinuities such as those found at domain wall boundaries. Thus, simultaneously achieving large piezoelectric effect and high optical transmissivity is generally deemed infeasible. Here, it is demonstrated that the ferroelectric domains in perovskite Pb(In_1/2 Nb_1/2 )O₃ -Pb(Mg_1/3 Nb_2/3 )O₃ -PbTiO₃ domain-engineered crystals can be manipulated by electrical field and mechanical stress to reversibly and repeatably, with small hysteresis, transform the opaque polydomain structure into a highly transparent monodomain state. This control of optical properties can be achieved at very low electric fields (less than 1.5 kV cm^-1 ) and is accompanied by a large (>10 000 pm V^-1 ) piezoelectric coefficient that is superior to linear state-of-the-art materials by a factor of three or more. The coexistence of tunable optical transmissivity and high piezoelectricity paves the way for a new class of photonic devices.

Giant room temperature compression and bending in ferroelectric oxide pillars

Plastic deformation in ceramic materials is normally only observed in nanometre-sized samples. However, we have observed high levels of plasticity (>50% plastic strain) and excellent elasticity (6% elastic strain) in perovskite oxide Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3, under compression along <100>pc pillars up to 2.1 μm in diameter. The extent of this deformation is much higher than has previously been reported for ceramic materials, and the sample size at which plasticity is observed is almost an order of magnitude larger. Bending tests also revealed over 8% flexural strain. Plastic deformation occurred by slip along {110} <1[Formula: see text]0 > . Calculations indicate that the resulting strain gradients will give rise to giant flexoelectric polarization. First principles models predict that a high concentration of oxygen vacancies weaken the covalent/ionic bonds, giving rise to the unexpected plasticity. Mechanical testing on oxygen vacancies-rich Mn-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 confirmed this prediction. These findings will facilitate the design of plastic ceramic materials and the development of flexoelectric-based nano-electromechanical systems.

Functional brain mapping using positron emission tomography scanning in preoperative neurosurgical planning for pediatric brain tumors

OBJECT

The purpose of this report is to demonstrate the value of functional brain mapping using the positron emission tomography (PET) method for preoperative neurosurgical planning in children with brain tumors. Brain maps were used to characterize the relationship between potentially resectable tumors and functionally eloquent brain areas.

METHODS

Five children, ranging in age from 3 to 13 years, with hemispheric brain tumors adjacent to eloquent cortex were studied. Magnetic resonance (MR) imaging was used to identify the brain tumors; PET imaging after injection of [18F] fluorodeoxyglucose (FDG), [11C]L-methionine (CMET), or a combination of the two was performed to grade the tumors; and a [15O] H2O uptake study was used to characterize the anatomical relationships of the tumors to functional cortex. The cortical activation maps were obtained during control periods and during behavioral tasks and were used to document motor, visual, and speech and language organizational areas. Wada tests were performed in two patients. Language and speech activation was concordant with the results of Wada testing.

CONCLUSIONS

Functional brain mapping using PET scans and coregistered MR images provided the neurosurgeon with precise definitions of structural and functional cortical areas; this altered surgical management in some cases and/or was used to predict outcome. The combination of PET imaging with FDG and/or CMET and measurements of [15O] water uptake was useful in characterizing and grading tumors and instrumental in achieving effective neurosurgical planning. Postoperative results in the five cases suggest that preoperative functional brain mapping has the potential to improve outcome by defining a surgical plan to maximize resection and minimize the risk of neurological sequelae.

Positron emission tomography using [18F] fluorodeoxyglucose and [11C] l-methionine to metabolically characterize dysembryoplastic neuroepithelial tumors

Dysembryoplastic neuroepithelial tumors are unique and benign congenital tumors occurring frequently in children and adolescents. Differentiation from other low-grade tumors is important for management. Five patients with confirmed dysembryoplastic neuroepithelial tumors were studied with positron emission tomography using glucose and protein metabolic uptake in an attempt to categorize these tumors metabolically. Functional brain mapping also was obtained to aid in operative management. Results of the study conclude that dysembryoplastic neuroepithelial tumors, although having similar neuroimgaing characteristics to other low-grade tumors, are distinguished by a unique metabolic profile. They are inactive tumors with no significant glucose or protein metabolic activity. The combination of preoperative positron emission tomographic metabolic studies with functional brain mapping allowed for prediction of tumor type, defined eloquent areas of cortical function, and improved approach and resection of the tumors with minimal risk of neurologic impairment.

Controlled external lumbar drain as treatment for therapy resistant intracranial hypertension--case report

We report the case of an eleven year old male with a history of severe head injury who had manifested high intracranial pressure refractory to aggressive medical therapy, including ventriculostomy, controlled hyperventilation, mannitol and barbiturate application. The insertion of an external lumbar drain in this patient resulted in rapid permanent control of the intracranial hypertension. No transtentorial or tonsillar herniation occurred.

Nonsurgical, nonorthotic treatment of occipital plagiocephaly: what is the natural history of the misshapen neonatal head?

Management of neonates with nonsynostotic occipital plagiocephaly has been controversial, and there has been a lack of uniformity concerning its treatment. Patients with nonsynostotic occipital plagiocephaly have been treated surgically or with cranial remodeling orthotic devices and have shown improvement in asymmetry. The cost of orthotic treatment has risen, and its validity has been contested by many third-party insurance payers. The effectiveness of orthotic treatment has not been adequately compared to the natural history of nonsynostotic occipital plagiocephaly. A nonsurgical, nonorthotic treatment study was initiated in June 1995 at Phoenix Children's Hospital. All new patients referred with a diagnosis of nonsynostotic occipital plagiocephaly were categorized into two groups: those with mild-to-moderate asymmetry and those with moderate-to-severe asymmetry. Categories were determined by cephalic measurements. The patients with moderate-to-severe asymmetry were offered orthotic treatment with a cranial remodeling band. Those patients with mild-to-moderate asymmetry were treated with physiotherapy, repositioning of the head, and repeated notation of cephalic measurements without orthotic devices or surgery. Seventy-two neonates, seen consecutively, with mild-to-moderate, nonsynostotic occipital plagiocephaly were evaluated by noting cephalic measurements. The parents of six of these patients elected treatment with a cranial remodeling band and results in these patients were excluded from our data. The remaining 66, treated without orthotic devices, showed improvement in average cranial vault asymmetry (CVA) from 9.2 to 4.7 mm over an average treatment period of 4.5 months that commenced when the average age of the patient was 6.4 months. A comparison of the present data with data published in 1994 for neonates treated with a headband indicates that neonates with mild-to-moderate asymmetry who are treated aggressively with physiotherapy and repositioning have similar improvement in CVA.

Use of positron emission tomography for presurgical localization of eloquent brain areas in children with seizures

Successful surgical management of a neoplastic or nonneoplastic seizure focus in close proximity to or within eloquent brain areas relies on precise delineation of the relationship between the lesion and functional brain areas. The aim of this series was to validate the usefulness and test the efficacy of noninvasive presurgical PET mapping of eloquent brain areas to predict surgical morbidity and outcome in children with seizures. To identify eloquent brain areas in 15 children (6 female and 9 male; mean age 11 years) with epileptogenic lesions PET images of regional cerebral blood flow were performed following the administration of [(15)O]water during motor, visual, articulation, and receptive language tasks. These images with coregistered magnetic resonance (MR) images were then used to delineate the anatomic relationship of a seizure focus to eloquent brain areas. Additional PET images using [18F]fluoro-2-deoxy-D-glucose (FDG) and [11C]methionine (CMET) were acquired to help localize the seizure focus, as well as characterize the lesion. Patient surgical management decisions were based on PET mapping in combination with coregistered MR images, PET-FDG findings, and the anatomic characteristics of the lesion. At follow-up 1-26 months after surgery, all patients that underwent temporal lobectomy (9 patients) and extratemporal resection (4 patients) for a neoplastic or nonneoplastic seizure focus are seizure-free with minimal postoperative morbidity. Of prime importance, no child sustained a postoperative speech or language deficit. PET imaging was also well tolerated without procedural complications. Based on PET mapping, a nonoperative approach was used for 2 children and a biopsy only was used in one child. When cortical injury involved prenatally determined eloquent cortex, PET demonstrated reorganization of language areas to new adjacent areas or even to the contralateral hemisphere. Integration of anatomical and functional data enhanced the surgical safety, defined optimal surgical approach, delineated the seizure focus from eloquent brain areas, facilitated maximum resection and optimized the timing of surgery, thereby minimizing surgical morbidity while maximizing surgical goals. PET measurements of FDG and CMET uptake were also helpful in localizing the seizure focus and grading the tumors. PET used for brain mapping in children provides the surgeon with strategic preoperative information not readily attainable with traditional invasive Wada testing or intraoperative cortical stimulation. PET mapping may also improve the outcome of extratemporal resections by allowing aggressive seizure focus resection. In addition, serial brain maps may optimize timing for surgical intervention by demonstrating reorganization of eloquent cortex often seen in younger children after cortical injury. Our results suggest that noninvasive presurgical brain mapping has the potential to reduce risk and improve neurologic outcome.

Nonsurgical, nonorthotic treatment of occipital plagiocephaly: what is the natural history of the misshapen neonatal head?

Plagiocephaly has recently received increased attention in pediatric neurosurgical circles and its treatment has been controversial. Lack of uniformity persists in the treatment of neonates with occipital plagiocephaly. Plagiocephaly resulting from synostosis is rare. Many patients with nonsynostotic plagiocephaly have been treated surgically. Cranial remodeling orthotic devices (such as headbands and helmets) have also been reported to correct nonsynostotic plagiocephaly. The cost of orthotic treatment has risen and its validity has been contested by many third-party insurance payers. The effectiveness of orthotic treatment has not been adequately compared to the natural history of nonsynostotic plagiocephaly. The first phase of a natural history study was initiated in June 1995 at Phoenix Children's Hospital. All new patients referred with a diagnosis of plagiocephaly were categorized into two groups: those with mild-to-moderate asymmetry and those with moderate-to-severe asymmetry. Categories were determined by cephalic measurements. The patients with moderate-to-severe asymmetry were offered orthotic treatment with a cranial remodeling band. Those patients with mild-to-moderate asymmetry were observed with repeated measurements. Data in patients left untreated and followed for natural history were compared to our data published in 1994 for those treated with external cranial orthosis. Our published data in 47 patients treated with a headband during the period from 1988 to 1993 indicated that cranial vault asymmetry improved from a mean of 8.9 mm to 4 mm over an average treatment period of 4.3 months beginning when the average age of the patient was 5.9 months. Seventy-two neonates treated with neck stretching exercises and repositioning of the head without surgery or orthotic devices showed improvement in cranial vault asymmetry from 10.6 mm to 5.5 mm over an average treatment period of 4.5 months beginning when the average age of the patient was 4.5 months. This study indicates that neonates with mild-to-m oderate asymmetry who are less than 6 months of age and who are treated with physiotherapy and repositioning have similar improvement in cranial vault asymmetry as those treated with orthotic devices. The second phase of our study deals with neonates who have moderate-to-severe plagiocephaly.

Controlled lumbar drainage in pediatric head injury

A retrospective study of external lumbar subarachnoid drainage in 16 pediatric patients with severe head injuries is presented. All patients had Glasgow Coma Scale scores of 8 or lower at 6 hours postinjury and were initially treated with ventriculostomy. Five patients required surgical evacuation of focal mass lesions. All patients manifested high intracranial pressures (ICPs) refractory to aggressive therapy, including hyperventilation, furosemide, mannitol, and in some cases, artificially induced barbiturate coma. After lumbar drainage was instituted, 14 patients had an abrupt and lasting decrease in ICP, obviating the need for continued medical management of ICP. In no patient did transtentorial or cerebellar herniation occur as a result of lumbar drainage. It was also noted retrospectively that the patients in this study had discernible basilar cisterns on computerized tomography scans. Fourteen patients survived; eight made good recoveries, three are functional with disability, and three have severe disabilities. Two patients died, most likely from uncontrolled ICP before the lumbar drain was placed. It is concluded that controlled external lumbar subarachnoid drainage is a useful treatment for pediatric patients with severe head injury when aggressive medical therapy and ventricular cerebrospinal fluid evacuation have failed to control high ICP. Selected patients with elevated ICP, which may be a function of posttraumatic cerebrospinal fluid circulation disruption and/or white matter cerebral edema, can be treated with this modality, which accesses the cisternal spaces untapped by ventriculostomy.

Transplanted demineralized bone graft in cranial reconstructive surgery

Surgical reconstruction of cranial deformities and synostosis is occasionally accompanied by incomplete bone growth to cover all areas of cranial vault that have been exposed in the correction. The restrictive nature of some forms of synostosis require more bone in the repair than is available using the child's natural skull for autogenous bone cranioplasty. Rib and iliac crest autografts have been used with success. These grafts must be harvested form a remote site with increased morbidity. A split-thickness skull autograft is the cranioplasty material of choice but children under the age of 6 years may lack the skull thickness needed to use this technique. Perforated demineralized bone matrix has been transplanted in 46 operations in 42 patients from 1990 to 1995 for repair of residual skull defects in children having previously undergone craniofacial repairs, for primary reconstruction of the cranial vault for patients with synostosis and for repair of skull defects resulting from trauma and skull tumor excisions. The vast majority of grafts have resulted in complete closure of the defect, providing a matrix for new bone formation. These patients are presented. Surgical techniques of cranial defect repair with perforated demineralized bone matrix are discussed.

Treatment of positional plagiocephaly with dynamic orthotic cranioplasty

Dynamic orthotic cranioplasty (DOC) was developed to treat asymmetrical head shape of a nonsynostotic origin, which is defined by the term positional plagiocephaly. These positional deformations have been found to correlate with a number of environmental factors. Infants with positional plagiocephaly may exhibit complex multistructural asymmetry affecting the cranial vault, face, and skull base, or expression may be local in nature. Between 1988 and 1993, we performed DOC on 124 infants with positional plagiocephaly. Through clinical, anthropometric, radiographic, and statistical evaluation, we found that DOC corrects positional deformation of the cranial vault, skull base, and upper face, with no evident relapse following treatment. The design and the global approach to deformation address a wide spectrum of abnormal head shapes. The procedure is dynamic and customized, and it does not rely on passive growth alone for improvement.

Magnetic field guided endoscopic dissection through a burr hole may avoid more invasive craniotomies. A preliminary report

The neuroendoscope, coupled with radiofrequency or laser dissecting tools, can effectively resect obstructing membranes, biopsy and debulk tumor, and evacuate hematomas when the pathology is within the ventricular system. This less invasive approach through a burr hole usually avoids craniotomies. When the abnormal condition is within parenchyma or in the presence of opacifying bloody fluid, landmarks are not recognizable and the neurosurgeon quickly becomes disoriented. A more extensive craniotomy or a stereotaxic-guided procedure is then necessary. We describe our preliminary experience with a geographic intracranial navigation system using realtime measurement of electromagnetic field strength in multiple planes to precisely indicate the position of the tip of the endoscope. A transmitting antenna is positioned beneath the patient's head. A 1.5 centimeter cubic antenna receiver is mounted upon a lenscope with instrument channel. The scope is guided into the surgical field after insertion through a burr hole. A square wave pulsed electromagnetic field measurement is made 140 times per second with correction for the earth's magnetic field once per second. Intracranial position data for the dissecting tip in regard to X, Y, Z, pitch, roll and yaw are output to a digitized computer map of the patient's MRI or CT scan. Also displayed on the computer screen is the video image from the endoscope. The neurosurgeon thus has simultaneous realtime geographic and near-field localization as he dissects. Electromagnetic field guided accuracy is within 2.0 mm inside the allowable 24 inch working sphere about the patient's head. Coupled with near-field video precision, accuracy is within 1 mm of recognizable dissection planes.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrauterine growing skull fracture

Growing skull fractures with development of leptomeningeal cysts are rare complications of head injuries and have not been described in the perinatal period. The case history of a newborn with bilateral parietal fractures and the formation of a leptomeningeal cyst on one side detected at birth is presented. The importance of radiographic evaluation, including skull films, computered tomography, and magnetic resonance imaging, as well as the associated subarachnoid cyst and the age of presentation are discussed.

Radiation-induced meningiomas in pediatric patients

Radiation-induced meningiomas rarely have latency periods short enough from the time of irradiation to the clinical presentation of the tumor to present in the pediatric patient. Three cases of radiation-induced intracranial meningiomas in pediatric patients are presented. The first involved a meningioma of the right frontal region in a 10-year-old boy 6 years after the resection and irradiation of a 4th ventricular medulloblastoma. Review of our pediatric tumor cases produced a second case of a left temporal fossa meningioma presenting in a 15-year-old boy with a history of irradiation for retinoblastoma at age 3 years and a third case of a right frontoparietal meningioma in a 15-year-old girl after irradiation for acute lymphoblastic leukemia. Only three cases of meningiomas presenting in the pediatric age group after radiation therapy to the head were detected in our review of the literature.

Pediatric cerebral abscess

Fifty-four consecutive cases of children with cerebral abscess from 1958 to 1987 are reviewed. Their average age was 6.6 years, ranging from 3 days to 19 years. A wide range of organisms and underlying diseases was encountered. The predominant mode of surgical therapy was craniotomy with resection of the abscess. Aspiration and craniotomy with drainage-evacuation were also employed in our series. No underlying disease was found in 10 (19%) of the children. Cyanotic heart disease (CHD) was present in 13 (24%) of the children. Four children had dental abscesses and 1 had otitis media. Seven (13%) children had abscesses secondary to hydrocephalus/shunt infections. Sinusitis and otitis accounted for 5 cases (9%). Four children (7%) had tuberculomas. One abscess was associated with a nasal dermal sinus and one was congenital. Fourteen (26%) patients had negative cultures. Fourteen (26%) abscesses contained streptococci of various types. Staphylococci were found in only 5 (9%) of the abscesses. The congenital abscess was caused by salmonella. Two abscesses (7%) were fungal. Both of these patients died. Six children (11%) were treated without surgical intervention. Three of them died. Forty-eight children had surgical intervention; 12 underwent aspiration, 14 underwent open evacuation of the abscess, and 22 had abscesses resected. Mortality in the aspiration group was twice that of the evacuation or resection group (17, 7 and 9%), respectively). The factor which correlated best with mortality was the patient's clinical status on admission. The advent of CT scan at our facility improved mortality by facilitating accurate diagnosis and surgical intervention. Overall mortality rates decreased from 31 to 5.7% and surgical mortality fell from 21 to 2.9%.

Congenital supratentorial and infratentorial peripheral neurogenic tumor: a clinical, ultrastructural, and immunohistochemical study

Congenital neoplasms of the central nervous system are extremely rare, although they have been well documented since the earliest reports from the mid-19th century. Medulloblastoma, other primitive neuroectodermal tumors, and various types of gliomas have comprised the majority of cases. This report describes a highly unusual infratentorial and supratentorial tumor presenting as a scalp mass in a neonate who experienced in utero distress. The supratentorial mass extended through a defect in the skull to the parietooccipital lobe, and the infratentorial aspect involved the 9th and 10th cranial nerves in the region of the cerebellopontine angle. A complex spindle cell neoplasm incorporating peripheral nerve sheath and vascular characteristics was further characterized by electron microscopy and immunohistochemistry. Based upon these studies, the tumor was interpreted as a congenital schwannoma with divergent vascular differentiation. The child has been tumor-free for approximately 2 years after the initial operative procedure.

In vivo continuous monitoring of K+ in animals using ISFET probes

Potassium ion sensitive field effect transistor probes have been developed and tested in various clinical applications involving continuous monitoring of serum and interstitial fluid potassium levels. Initial results are presented that demonstrate the importance of continuous monitoring of serum and/or IF K+. Probe construction, calibration, and in vivo placement techniques are described. Use of continuous monitoring that ChemFET probes provide offers the potential for much improved management of patients recovering from many types of clinical disease states that may involve electrolyte abnormalities. Further studies are in progress that will provide additional insight into electrolyte dynamics among the various fluid compartments of the body in response to various physiological stresses.

A microelectronic pH sensor

This paper presents preliminary data on a new integrated circuit microelectronic pH sensor. The device is extremely miniaturized by the use of integrated circuit technology, and uses the intrinsic hydrogen ion selective properties of the gate insulator material. In order to make the device compatible with aqueous solution monitoring, the silicon dioxide-silicon nitride gate insulator structure is used. The integrated circuit chip was designed, processed, and packaged by a variety of techniques which protect all metal parts from the aqueous solution. Test data are reported on leakage current, sensitivity, reproducibility, linearity, stability, response time, and life. The results indicate that this type of pH sensor may have many significant advantages for biomedical research and application.