Characteristic Signal Pattern Research Articles

In situ monitoring of thermal transitions in thin polymeric films via optical interferometry

A novel, low-cost, rapid, accurate, non-invasive and high throughput method based on the principles of Optical Interferometry (OPTI method) has been developed and applied for the in situ monitoring in one simple run of first (melting) and second (glass transition) order transitions as well as of the thermally induced decomposition of various thin polymeric films spin coated on flat reflective substrates (untreated silicon wafers). The new method has been applied successfully for measuring the glass transition, melting and decomposition temperatures of six commercially available polymers [poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate), (PHEMA), poly(vinyl acetate- co-crotonic acid), (PVACA), poly(vinyl pyrrolidone) (PVP), poly(vinyl chloride- co-vinyl acetate) (PVCVA) and crystalline poly(vinylidene fluoride- co-hexafluoropropylene) (PVFHP)] of known T gs or T ms. The recorded interferometric signals were identified and characteristic signal patterns were qualitatively correlated to specific transitions. The monitoring of first and second order transitions in thin polymeric films is based on detectable differentiations of the total energy of a fixed wavelength laser beam incident almost vertically (angle of incidence <5°) onto a thin polymeric film spin coated on a flat reflective substrate. These differentiations are caused by film thickness and/or refractive index changes of the polymeric film both resulted from the significant change of the polymer's free volume taking place on the transitions. For film thicknesses over approx. 200–250 nm, the T g or T m of the polymeric films measured with the OPTI method were in excellent agreement with the corresponding values of the polymer, measured by DSC. An investigation on the trends of the T g of PHEMA and PMMA films in a wide thickness range (30–1735 nm) was also carried out. Ultra-thin (∼30 nm) films of PMMA and PHEMA showed significant increase in their T g values by approx. 30 °C upon comparing to their corresponding bulk T gs. This behavior was attributed to an enhanced polymer–surface interaction through hydrogen bonding and/or to changes in the tacticity of the polymer.

Hemorrhagic cavernoma or ruptured dermoid of the orbit: Diagnosis with MRI

MRI is a useful tool to study space-occupying lesions of the orbit. We present two cases of intraorbital lesions that were found to be a hemorrhagic cavernous hemangioma and a ruptured dermoid, respectively. The difficulties in arriving at the diagnosis of these rare entities with MRI are discussed. In general, dermoids are characterized by a peripheral, extra-conal location in the immediate vicinity of an orbital suture, while cavernous hemangiomas tend to be intraconal. Secondary complications of both entities, such as hemorrhage or rupture, may alter the characteristic MRI signal patterns found in uncomplicated lesions. Inflammatory reactions may be observed. The signal of the fatty dermoid and the hemorrhagic part of a cavernoma are both of high intensity on the T1-weighted images, and this may lead to diagnostic difficulties.

Analytical characterization of natural waxes employing pyrolysis–gas chromatography–mass spectrometry

Three natural waxes (bleached beeswax, lanolin, yellow carnauba wax) were investigated by means of pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Pyrograms were obtained showing very characteristic signal patterns. Mass spectrometric detection enabled the structural identification of the pyrolytically formed fragments. For a more detailed investigation of the thermal degradation behaviour of waxy materials, relevant model compounds were selected. Hexadecylpalmitate, cholesterylstearate, heptadecanoic acid and 1-hexacosanol were examined under identical Py–GC–MS conditions. From the resulting product distribution general statements were able to be derived according to the thermal degradation pathways of typical wax constituents. The findings obtained from the model compounds were then applied to the interpretation of the real wax pyrograms. As a result, conclusions according to their origin from corresponding wax constituents were drawn for the majority of pyrolysis products. Thus, the extended potential of the method for the compositional analysis of natural waxes is demonstrated.

Al 2O 3 particle fluxes from the ECS 2 apogee maneuver—Witnessed by the LDEF interplanetary dust experiment

The Long Duration Exposure Facility (LDEF) Interplanetary Dust Experiment (IDE) witnessed a highly dynamic microparticle environment during its active measurement period (April 1984, through March 1985). Certain characteristic impact signal patterns were identified during the analyses of the data set. One particular impact pattern, the socalled Multiple Orbit Event Sequences (MOES), triggered the investigation presented here. After a brief overview of an apogee insertion maneuver (APM) and the IDE experiment, the orbits of Al 2O 3 particles exhausted by a Solid Rocket Motor (SRM) propelled transfer systems are discussed. An attempt is made to correlate particle stream generated by the insertion of the ECS 2 satellite on August 6, 1984, with IDE data.

Color Doppler flow as an indicator of nodal metastasis in solid breast masses.

Tumor metastases are dependent on angiogenesis. This prospective study evaluates the role of color Doppler sonographic signals in (1) detecting blood flow in solid breast masses, (2) differentiating between benign and malignant breast tumors, and (3) identifying women at risk for axillary lymph node metastasis. Ultrasonographically proved solid breast masses from 95 women were evaluated with color Doppler imaging for the presence of blood flow. A characteristic curvilinear or branching signal pattern, labeled the "rim sign," was noted to be either present or absent at the periphery of the mass in all cases. The color Doppler sonographic signals in 86 patients with pathologic results were correlated with the occurrence of malignancy and axillary lymph node metastasis. Fifty-three of the 86 patients (62%) had benign breast disease and 33 patients (38%) had malignant tumors. Sixteen (30%) of the benign tumors and 20 (61%) of the malignant cancers demonstrated a positive rim sign. A positive rim sign has a 61% sensitivity and a 70% specificity for the prediction of breast malignancy. In the malignant masses, nodal involvement occurred in 50% of patients with a positive rim sign and 10% of patients with a negative rim sign. A negative rim sign has a negative predictive value of 90% for nodal metastasis. Color Doppler imaging can detect blood flow in both malignant and benign solid breast masses. A positive rim sign is a poor prognostic factor whereas a negative rim sign is a good prognostic indicator for axillary nodal metastases.

Magnetic resonance imaging findings in pulmonary Kaposi's sarcoma: a series of 10 cases.

Since chest X-ray and CT scan features of Kaposi's sarcoma (KS) are nonspecific, we wanted to test the hypothesis that the histological components of this tumour and/or the associated haemorrhagic component, may result in a characteristic signal pattern on magnetic resonance imaging (MRI). Thoracic MRI was performed in a prospective manner in ten patients with acquired immune deficiency syndrome (AIDS) and pulmonary KS. MRI examinations (1.5 Tesla) included Spin-echo T1 (SE-T1), before and after gadolinium injection, as well as T2-weighted sequences (SE-T2). For each sequence the signal intensity of lesions was measured and compared with each other as well as with the signal intensity of muscle. Results were compared to the hemosiderin content of macrophages in the bronchoalveolar lavage (BAL) in all patients and with histological findings in three. The results were compared to values obtained in a control group of seven patients with pneumocystis carinii pneumonia. SE-T1 showed focally increased signal intensity in the pulmonary parenchyma (n = 5). Signal enhancement in parenchymal lesions (n = 10) and along peribronchovascular trees (n = 5) was observed after gadolinium injection. The second echo of SE-T2 showed a markedly reduced signal intensity in pathologic areas (n = 10). This last finding was not observed in the control group. In conclusion, we have identified a pattern of MRI signal abnormalities suggestive of Kaposi's sarcoma. The MRI signal intensity of KS lesions may be related to the angiomatous and fibrous components of the tumour.(ABSTRACT TRUNCATED AT 250 WORDS)

Cortical atrophy and other brain magnetic resonance imaging (MRI) changes after extremely high-altitude climbs without oxygen.

The purpose of the present study is to detect by means of MRI any structural changes in the brain and their correlation with the clinical history of climbers who have ascended to extremely high altitudes without supplementary oxygen. Clinical history, neurological examinations and brain MRI were obtained from a group of 26 climbers who ascended to over 7000 m without supplementary oxygen, and the results were compared with a control group (n = 21) of healthy subjects. All the MRI studies were carried out between 26 days and 36 months after return to sea level. Significant neuropsychological disorders were experienced by all climbers during the ascent with residual neurobehavioural impairment after returning to sea level in 58% of them. The neurological examination was normal in all subjects. Almost half of the climbers showed MRI abnormalities (46%). Characteristic signal patterns of cortical atrophy were detected in five subjects. Periventricular hyperintensity lesions in the T2-weighted images were observed in other five climbers. Both types of lesions were found in two subjects. These pathological findings did not correlate with age, sex, clinical symptoms, maximal altitude reached, or length of exposure to extreme altitude. The exact long-term pathological significance of these MRI abnormalities is as yet unknown.

Intrakranielle MR-Flußsignalveränderungen bei extrakraniellen Verschlüssen der A. carotis interna

Spin-echo sequences allow an identification of the basal brain vessels because of their typical signal void. The increasing use of MRI also in clarification of cerebrovascular disease requires a good knowledge of intracranial flow alterations. We saw characteristic signal pattern in the carotid siphon in 22 prospective examined patients with occlusion of the internal carotid artery confirmed by ultrasound. The lower siphon showed a loss of flow void and a brain isointense signal. The signal in the upper siphon was identical or showed a flow void with significant calibre reduction, probably because of collateral filling. This diagnostic potential of MRI is a remarkable advantage in comparison to CT and should be routinely considered in patients with cerebrovascular disease.

Normal perivascular spaces mimicking lacunar infarction: MR imaging.

Perivascular (Virchow-Robin) spaces normally surround perforating arteries that enter the medial temporal lobes, corpus striatum, and thalamus. The high soft-tissue sensitivity of magnetic resonance (MR) imaging allows for the frequent detection of such cerebrospinal fluid (CSF)-filled spaces. Especially on axial images, these CSF-filled perivascular spaces may be confused with pathologic lesions, such a lacunar infarcts. Postmortem brain specimens demonstrate the anatomy of perivascular spaces around perforating arteries. Orthogonal images in the living patient help confirm this anatomic relationship. The characteristic CSF signal patterns from these foci are further evidence of their anatomic identification and true benign nature.

Magnetic resonance imaging in evaluating focal liver lesions.

We report the results of magnetic resonance imaging (MRI) of the liver in 46 patients with various previously confirmed focal lesions. A characteristic signal pattern was found in hemangiomas (n = 11), with marked signal hyperintensity on T2 and proton weighted images as compared to normal liver tissue. Cysts (n = 7) also showed marked hyperintensity on T2 images, but could easily be differentiated by a lesser intensity on proton weighted images and signal hypointensity on T1 weighted images. Primary liver tumors (n = 4), metastatic liver disease (n = 18), focal nodular hyperplasia (n = 5), and liver adenoma (n = 1) revealed a weak signal hyperintensity on T2 images, with varying signals in T1 and proton weighted modalities. These data combined with other recent communications in the literature indicate that MRI is a promising diagnostic technique in the detection of focal liver lesions and that it may offer a high degree of specificity in the diagnosis of hepatic hemangiomas and benign cysts.