Effect of templated quenched disorder on fluid phase equilibrium.

Templating offers a means to direct the structure of quenched disorder. We show here that changes in phase equilibrium due to the presence of quenched disorder can themselves be altered by templating. We calculate the phase diagram of a fluid in a collection of template-directed, quenched particles by solving a set of replica Ornstein-Zernike equations within the mean spherical approximation and show templating to enhance phase behavior, that is, shift the phase envelope upward from its location for a nontemplated system of identical available volume. This enhancement is due to an augmented number of fluid-fluid interactions.

History dependence of protein adsorption kinetics.

The behavior of proteins at biological and synthetic interfaces is often characterized by a strong history dependence caused by long relaxation times or irreversible transitions. In this work, we introduce the rate of adsorption as a means to systematically quantify the extent, and identify the underlying causes, of history dependence. We use multistep kinetic experiments in which the i'th step is an exposure of a Si(Ti)O(2) surface to a flowing fibronectin or cytochrome c solution of concentration c(i) for a time t(i) (c(i) = 0 corresponds to a rinse) and measure the protein adsorption by optical waveguide light mode spectroscopy. The rate of adsorption is sensitive to the structure of the adsorbed layer, and we observe it to greatly increase, for a given adsorbed density, when going from a first to a subsequent adsorption step. This increase is most pronounced when the duration of the initial adsorption step is long. We attribute these observations to the gradual and irreversible formation of protein clusters or locally ordered structures and use them to explain previous underestimates of kinetic data by mesoscopic model descriptions. A thorough understanding of these complex postadsorption events, and their impact on history dependence, is essential for many physiological and biotechnological processes. Optical waveguide lightmode spectroscopy is a promising technique for their macroscopic quantification.

Brain metastasis from a primary liposarcoma of the digit: case report.

Soft-tissue sarcomas of the digit are uncommon. We herein report on a patient with a de-novo subungual right thumb liposarcoma with subsequent failure in the brain. The pertinent literature and recommendations for management are presented.

Malignant gliomas: MR imaging spectrum of radiation therapy- and chemotherapy-induced necrosis of the brain after treatment.

PURPOSE: To describe both the common and less frequently encountered magnetic resonance (MR) imaging features of radiation therapy- and chemotherapy-induced brain injury, with particular emphasis on radiation necrosis. MATERIALS AND METHODS: A cohort of 148 adult patients underwent surgical resection of malignant brain (glial) tumors and were subsequently entered into a research protocol that consisted of accelerated radiation therapy with carboplatin followed by chemotherapy with procarbazine, lomustine, and vincristine. Patients typically underwent sequential MR imaging at 6-8-week intervals during the 1st year and at 3-6-month intervals during subsequent years. In all patients, histopathologic confirmation of lesion composition was performed by board-certified neuropathologists. RESULTS: The patients exhibited different types of MR imaging-detected abnormalities of the brain: pure radiation necrosis in 20 patients, a mixture of predominantly radiation necrosis with limited recurrent and/or residual tumor (less than 20% of resected tissue) in 16 patients, radiation necrosis of the cranial nerves and/or their pathways in two patients, radiation-induced enhancement of the white matter in 52 patients, and radiation-induced enhancement of the cortex in nine patients. CONCLUSION: The frequent diagnostic dilemma of recurrent neoplasm versus radiation necrosis is addressed in this study through a description of the varying spatial and temporal patterns of radiation necrosis at MR imaging.

Cranial magnetic resonance imaging examination of normal term neonates: a pilot study.

This pilot study's aim was to determine, using magnetic resonance imaging (MRI), if and to what extent asymptomatic intracranial hemorrhage occurs in normal term neonates after uncomplicated vaginal deliveries. Eight normal, term, vaginally delivered infants and three cesarean-section deliveries used as controls underwent cranial MRI. No sedation was administered. Small subdural hematomas of the falx cerebri or tentorium cerebelli were found in half of those with an uneventful vaginal delivery. Pediatric follow-up, on average 3.9 years after the MRI study was performed, demonstrated normal growth and development. It appears that more data is needed to confirm the observation that the intracranial hemorrhages described should not be considered the etiology for neurologic abnormalities present in symptomatic neonates.

Theoretical model of adsorption in a templated porous material.

We introduce a theoretical description of adsorption in a templated porous material modeled as a quenched binary mixture configuration with one component removed. Using tools from equilibrium statistical mechanics, we analyze the diagrammatic structure of and derive an approximate formula for this nonequilibrium material's porosity and Henry regime selectivity. We find that templating significantly increases the porosity as well as the selectivity for the larger component of a mixture.

Cystlike white matter lesions in tuberous sclerosis.

PURPOSE: To investigate the presence of small cystlike structures in the cerebral hemispheric white matter on MR images of patients with tuberous sclerosis. METHODS: The MR images of 18 consecutive patients with tuberous sclerosis were reviewed retrospectively. RESULTS: Eight of the 18 patients were found to have cystlike structures in the cerebral white matter. The signal intensity of these lesions was isointense with cerebrospinal fluid on T1-, proton density-, and T2-weighted images. Four patients were imaged with a fluid-attenuated inversion recovery sequence, which in each case also showed fluid-type signal in these areas. Three of the patients had CT for correlation, and these scans supported the diagnosis of cystic lesions. Cysts ranged in number from one to 12 per patient and were usually smaller than 1 cm. The most common location was adjacent to the occipital horn or trigone of the lateral ventricle (six of eight patients). Less frequent sites were near the frontal horns, in the corpus callosum, and in the deep white matter near the body of the lateral ventricle. Cysts in five patients were either immediately adjacent to a cortical tuber or in the center of a white matter dysplastic lesion. A cyst in one patient had septa, and none of the cysts enhanced. CONCLUSIONS: Cystlike structures in the cerebral hemispheric white matter were seen on the MR images of 44% of 18 patients with tuberous sclerosis. Whether these findings represent cystic degeneration of dysplastic tissue or are unrelated to the disease process of tuberous sclerosis is unknown. More than one pathogenesis may exist.

MR of nasolabial cysts.

We report the MR imaging findings in two cases of nasolabial cysts. Demonstration of their extraosseous location with cross-sectional imaging should prevent confusion with maxillary cysts and obviate unwarranted dental or maxillary surgery.

Progressive venous occlusion in a neonate with Sturge-Weber syndrome: demonstration with MR venography.

Progressive cerebral sinovenous occlusion in a neonate with Sturge-Weber syndrome was documented by using two-dimensional time-of-flight MR venography. There was no evidence of intraluminal thrombus on routine spin-echo images obtained either before or after the onset of seizures, despite MR venographic evidence in both studies of venous abnormalities.

Nonneoplastic intracranial cysts and cystic lesions.

This article reviews the gamut of cystic lesions, unrelated to neoplastic disease, that are found in the brain, subarachnoid space, and ventricles. The utility of MRI in diagnosing these entities is shown.

MR of toxic effects of accelerated fractionation radiation therapy and carboplatin chemotherapy for malignant gliomas.

PURPOSE: To present MR findings of parenchymal brain injury after accelerated fractionation radiation therapy combined with carboplatin chemotherapy in the treatment of malignant brain gliomas. METHODS: Eighty-one evaluable subjects in an ongoing treatment protocol for malignant gliomas form the patient base for this report. After surgical resection of tumors, patients underwent a course of accelerated fractionation radiation therapy to a total dose of 60 Gy. Carboplatin was infused intravenously before each radiation treatment. Precontrast and postcontrast MR scans were obtained before treatment and at 4-week intervals afterward and were analyzed retrospectively. RESULTS: Posttreatment MR imaging in 20 of the 81 patients showed development of unusual parenchymal lesions or enlarging masses needing debulking, and these patients underwent second operations. Two groups emerged: those with tumor and necrotic brain (n = 11) and those with necrosis and reactive gliosis but no definitive tumor (n = 9). Enhancing lesions in the tumor-negative group appeared later than those in the tumor-positive group, were often multiple, and were usually located several centimeters away from the tumor resection site or even contralaterally. Common locations were the corpus callosum and corticomedullary junctions. Lesions in the tumor-positive group were more often solitary and located immediately adjacent to the surgical site. Positive and negative results of positron emission tomography with fludeoxyglucose F 18 were obtained in both groups. The incidence of brain necrosis without associated tumor was 11%. CONCLUSIONS: A pattern of unusual enhancing parenchymal brain lesions was seen on MR imaging after accelerated fractionation radiation therapy and concomitant carboplatin chemotherapy. The abnormalities seem more extensive than focal necrotic lesions on enhanced CT or MR imaging after conventional radiation therapy, and they may mimic recurrent tumor.

Normal and variant anatomy of the dural venous sinuses.

The normal and variant anatomy of the cerebral veins and dural venous sinuses is poorly understood by many radiologists. Beginning with a discussion of cerebral venous anatomy, this review illustrates clinically pertinent anatomy of the cerebral sinovenous system. Various methods of imaging cerebral veins and dural venous sinuses are described. Techniques and pitfalls of MR venography are emphasized.

Congenital and acquired abnormalities of the dural venous sinuses.

The imaging features of a variety of dural venous sinus (DVS) abnormalities are reviewed. Congenital and heritable diseases affecting the DVS, tumor-related sinus compression, and traumatic injuries of the DVS are discussed. The causes, clinical manifestations, and imaging findings in cerebral sinovenous thrombosis are described, and pertinent imaging techniques and pitfalls are illustrated. Etiologic theories about the formation of dural arteriovenous malformations are discussed and their imaging features are demonstrated.

MRI features of intracranial sarcoidosis mimicking meningiomas.

We present three young African-American patients in whom magnetic resonance imaging (MRI) showed dural based masses that were initially thought to represent meningiomas. Two patients underwent surgery and the diagnosis of sarcoidosis was made. The third patient underwent a trial of steroids with considerable improvement of her symptoms. We suggest that sarcoidosis should always be considered in the differential diagnosis of dural-based masses which have MRI characteristics similar to those of meningiomas. The possibility of sarcoidosis should lead to appropriate laboratory tests and therapy.

Magnetic resonance imaging of spinal infections.

The manifestations of infectious disease of the spine are numerous. Viruses commonly affect the spinal cord and meninges, while tuberculosis and various bacterial and fungal organisms may involve the vertebrae, intervertebral disks, epidural and paraspinal regions, the leptomeninges, and, rarely, the cord itself. Magnetic resonance imaging, with its multiplanar capability and superb contrast resolution, is definitely the modality of choice in evaluating the patient with suspected infection of the spinal column or spinal cord and its coverings. The addition of postcontrast images is often helpful in the differential diagnosis.

Zeolite adsorption site location and shape shown by simulated isodensity surfaces.

The graphics software package Ribbons is used to display isodensity surfaces of Xe atoms adsorbed in the alpha cage of zeolite NaA. The location, size, and shape of the adsorption sites are highly dependent on the loading and the crystal cation content. When the zeolite has a high number of cations, ellipsoidal sites arrange in a cuboctahedron. When the zeolite has fewer cations, cone-shaped sites arrange in an octahedron at low loading, but at high loading the sites become ellipsoidal and new sites form at cuboctahedral positions. The effect of the nature of the adsorption site on the development of a universal adsorption model is discussed.

Leptomeningeal toxoplasmosis after allogeneic marrow transplantation. Case report and review of the literature.

A 37-year-old woman with chronic myelogenous leukemia underwent allogeneic bone marrow transplantation with CD8-depleted marrow from an HLA-identical sister. On day 43 post-transplant, the patient developed a headache and became lethargic and tremulous. Magnetic resonance imaging (MRI) of the brain showed abnormal meningeal and superficial parenchymal enhancement anteriorly. The spinal fluid had an elevated protein level with normal glucose and a neutrophilic pleocytosis. At autopsy, Toxoplasma meningoencephalitis was seen. On review of the literature, headache and confusion at 1-2 months post-transplant are common presenting signs of central nervous system toxoplasmosis. The predominance of neutrophils in the spinal fluid in this patient probably reflects the meningeal component of the infection and is an unusual finding. The presentation of toxoplasmosis in marrow transplant recipients is quite pleomorphic, and a definite diagnosis is difficult to obtain antemortem. Empiric therapy with pyrimethamine and sulfadiazine should be considered for marrow transplant recipients with neurologic deficits for which there is no other apparent etiology.

Diagnostic imaging advances in neurooncology.

As we move into the 1990s, the field of diagnostic imaging displays greater usefulness as a result of continued technical improvements in existing modalities and the discovery of new techniques. Magnetic resonance (MR) imaging is now, without question, the imaging modality of choice for evaluation of tumors of the brain and spine. The general availability of the MR imaging contrast agent, gadolinium diethylenetriamine penta-acetic acid (Gd-DTPA), for the last three years has greatly expanded the role of MR imaging. Progress in metabolic imaging and MR spectroscopy may offer yet greater understanding of the physiology of brain tumors and has application for the diagnosis and posttreatment follow-up of these patients. These topics will be addressed in this review, which spans the years 1989 and 1990.