Biomedical subjects

Axel Scherer

Publications and source records attributed to Axel Scherer.

29 records · Page 2Linked to original sources

PubMed2004

High quality factors and room-temperature lasing in a modified single-defect photonic crystal cavity.

We propose and analyze a new photonic crystal cavity design that supports a dipole mode with a quality factor greater than 20,000. Such a high quality factor is obtained by precise tuning of the cavity length with minimal disruption of the surrounding photonic crystal. A fabrication procedure based on dry etching of InGaAsP material in HI/H2/Ar is used to demonstrate photonic crystal lasers with smooth and straight sidewalls. These room-temperature lasers concentrate optical energy in air and are suitable for use as tunable lasers and chemical sensors.

Journal Article↗

PubMed2004

Diagnostic value of magnetic resonance imaging of the forefeet in early rheumatoid arthritis when findings on imaging of the metacarpophalangeal joints of the hands remain normal.

OBJECTIVE: To investigate the diagnostic role of magnetic resonance imaging (MRI) of the forefeet in patients with early rheumatoid arthritis (RA) in whom findings on MR images of the hands are normal and conventional radiographs of the hands and feet do not show erosions. METHODS: The study group comprised 25 patients with early RA (disease duration of <12 months) in whom erosions were not demonstrated on conventional radiographs of the hands and feet. These patients underwent MRI of the clinically dominant hand to detect signs of arthritis. If results of MRI of the hand were normal according to the Outcome Measures in Rheumatology Clinical Trials (OMERACT) RA-MRI scoring system (RAMRIS), MRI of the dominant forefoot was performed. The MRI protocol comprised coronal and sagittal T1-weighted spin-echo (before and after administration of contrast medium), coronal fat-suppressed short tau inversion recovery sequences, coronal and sagittal T2-weighted turbo spin-echo sequences, and axial fat-suppressed T1-weighted spin-echo sequences after administration of contrast medium. MRI of the forefeet was analyzed on the basis of a modified RAMRIS. RESULTS: MRI revealed pathologic findings in the hands of 15 of 25 patients (edema in 9 patients, synovitis in 12, erosions in 6, defects in 3). In 10 patients with a mean disease duration of 9.4 weeks, hand MRI scans were normal according to RAMRIS. Four of these 10 patients had tenosynovitis of the finger flexor tendons (there was no OMERACT criterion for tenosynovitis). RAMRIS analysis of the corresponding MRI scans of the forefeet of these patients revealed signs of edema in 7 patients, synovitis in all 10 patients (at the third metatarsophalangeal [MTP] joint in 7, at the fourth MTP joint in 6, at the first MTP joint in 4, and at the fifth MTP joint in 2 patients), tenosynovitis of the foot flexor tendons in 2 patients, erosions at the second and third MTP joints in 1 patient, and a single defect at the first MTP joint in 1 patient. CONCLUSION: RAMRIS analysis of MRI scans of the forefeet detected synovitis and bone edema in patients with early RA in whom MRI of the finger joints was normal. MRI of the forefeet contributes an additional tool aimed at earlier and more accurate diagnosis and thus might allow an earlier decision to start appropriate medication in patients with early RA.

Adult↗

PubMed2003

Microfabricated fountain pens for high-density DNA arrays.

We used photolithographic microfabrication techniques to create very small stainless steel fountain pens that were installed in place of conventional pens on a microarray spotter. Because of the small feature size produced by the microfabricated pens, we were able to print arrays with up to 25,000 spots/cm2, significantly higher than can be achieved by other deposition methods. This feature density is sufficiently large that a standard microscope slide can contain multiple replicates of every gene in a complex organism such as a mouse or human. We tested carryover during array printing with dye solution, labeled DNA, and hybridized DNA, and we found it to be indistinguishable from background. Hybridization also showed good sequence specificity to printed oligonucleotides. In addition to improved slide capacity, the microfabrication process offers the possibility of low-cost mass-produced pens and the flexibility to include novel pen features that cannot be machined with conventional techniques.

Electrochemistry↗

PubMed2003

Jaccoud's arthropathy in systemic lupus erythematosus: differentiation of deforming and erosive patterns by magnetic resonance imaging.

OBJECTIVE: To evaluate alterations of the soft tissues, tendons, and bones as detected by magnetic resonance imaging (MRI) in patients with systemic lupus erythematosus (SLE)-associated arthritis of the finger joints. METHODS: Both hands of 14 patients with SLE of various activities and durations and with arthritis and/or deformities of the finger joints were examined by MRI and conventional radiography. Coronal T1-weighted spin-echo (with and without gadolinium contrast), axial T2-weighted turbo spin-echo, coronal fat-suppressed short tau inversion recovery, and 3-dimensional double-echo steady-state sequences were acquired and analyzed, and the findings were compared with those from conventional radiographs. RESULTS: MRI detected periarticular capsular swelling in all 14 patients, joint effusion in 7, edematous tenosynovitis in 6, proliferative tenosynovitis (flexor and/or extensor tendons) in 4, and intraarticular signs of synovial membrane hypertrophy in 10 patients, 9 of whom showed enhancement after administration of contrast medium. Bony erosions were identified in 8 patients by MRI; conventional radiography missed these erosions in 2 of the 8 patients. Four of the 14 patients were designated as Jaccoud's arthropathy index-positive, and all 4 showed severe edematous tenosynovitis and capsular swelling, but no signs of bony erosions despite longstanding disease (mean 21.5 years). Four of the 10 patients with mild deformity exhibited prominent soft tissue pathology, with minimal destruction of bone; the other 6 patients had bony alterations that resembled rheumatoid arthritis. CONCLUSION: In SLE patients with arthritis of the finger joints, MRI detects characteristic signs of soft tissue pathology (e.g., capsular swelling, edematous and proliferative tenosynovitis, synovial hypertrophy) and bony alterations (e.g., erosions, some of which are missed by conventional radiography). MRI thus helps to distinguish different types of lupus arthritis/Jaccoud's arthropathy, which allows more differentiated treatment strategies and monitoring.

Adult↗

PubMed2003

Efficient excitation of self-collimated beams and single Bloch modes in planar photonic crystals.

Using finite-difference time-domain calculations, we investigate out-of-plane coupling between a square-lattice planar photonic crystal and a conventional waveguide located above the photonic crystal. We couple a waveguide oriented in the gamma(chi) direction to a photonic crystal mode in the second band and show that anticrossing takes place. In this way, a self-collimated beam is launched in the planar photonic crystal, with full power transfer. Furthermore, we investigate the coupling between a waveguide oriented in the gamma(mu) direction and a photonic crystal and show that single photonic crystal modes can be selectively excited.

Journal Article↗

PubMed2003

Photonic crystal waveguide-mode orthogonality conditions and computation of intrinsic waveguide losses.

We simulate the propagation of light in a W1 planar photonic crystal waveguide with the three-dimensional finite-difference time-domain method and apply an inner product against previously calculated mode profiles to the simulated field cross sections. We show that this inner product satisfies mode orthogonality for both photonic crystal waveguides and segmented waveguides and use the obtained data to evaluate waveguide losses.

Journal Article↗

PubMed2002

Diffusion-weighted MR imaging in the brain in children: findings in the normal brain and in the brain with white matter diseases.

PURPOSE: To establish quantitative standards for age-related changes in diffusion restriction of cerebral white matter in healthy children and to compare data with results in children with white matter diseases. MATERIALS AND METHODS: Diffusion-weighted magnetic resonance (MR) imaging was performed in 44 children (age range, 7 days to 7.5 years) without brain abnormalities and in 13 children with proved leukodystrophy. Apparent diffusion coefficient (ADC) and apparent anisotropy (AA) were measured in 11 regions of interest within white matter. Age-related changes were analyzed with regression analysis. RESULTS: During normal brain myelination, ADCs in different anatomic regions were high at birth (range, 1.04 x 10(-9) m(2)/sec +/- 0.05 [SD] to 1.64 x 10(-9) m(2)/sec +/- 0.09) and low after brain maturation (range, 0.75 x 10(-9) m(2)/sec +/- 0.02 to 0.92 x 10(-9) m(2)/sec +/- 0.02). AA was low at birth (range, 0.05 +/- 0.01 to 0.52 +/- 0.04) and high after brain maturation (range, 0.25 +/- 0.02 to 0.85 +/- 0.03). Age relationship could be expressed with monoexponential functions for all anatomic regions. Anisotropy preceded the myelination-related changes at MR imaging. ADC and AA in four children with Pelizaeus-Merzbacher disease were identical with results in healthy newborn children and showed no age dependency. In peroxisomal disorders, Krabbe disease, and mitochondriopathy, demyelination on T1- and T2-weighted MR images led to expected findings at diffusion-weighted MR imaging, with high ADC and low AA, whereas in Canavan disease and metachromatic leukodystrophy, the opposite findings were revealed, with low ADC within the demyelinated white matter. CONCLUSION: During early brain myelination, diffusion restriction in normal white matter increases. Anisotropy precedes myelination changes that are visible at MR imaging. Compared with T1- and T2-weighted MR imaging, diffusion-weighted MR imaging in white matter diseases reveals additional information.

Adolescent↗

PubMed2002

Virtual arterial endoscopy as a diagnostic aid in a patient with basilar artery fenestration and thromboembolic pontine infarct.

Focal signal intensity loss of the basilar artery on MR angiograms obtained in a 69-year-old man was considered to be caused by an embolus, and thrombolytic therapy was initiated. On the follow-up MR angiograms, the same oval signal intensity loss of the basilar artery was observed. On the basis of a virtual endoscopic look into the basilar artery, the diagnosis of a rare vascular anomaly--a fenestration of the basilar artery--was confirmed and the presence of a thrombus at the site of the signal intensity loss was excluded.

Aged↗

PubMed2001

Design of photonic crystal microcavities for cavity QED.

We discuss the optimization of optical microcavity designs based on two-dimensional photonic crystals for the purpose of strong coupling between the cavity field and a single neutral atom trapped within a hole. We present numerical predictions for the quality factors and mode volumes of localized defect modes as a function of geometric parameters, and discuss some experimental challenges related to the coupling of a defect cavity to gas-phase atoms.

Journal Article↗

PubMedDate not supplied

Correlation of bone marrow response with hematological, biochemical, and visceral responses to enzyme replacement therapy of nonneuronopathic (type 1) Gaucher disease in 30 adult patients.

PURPOSE: This investigation correlates the marrow response with the degree of increase in hemoglobin (Hb) and platelet count (Plt); decrease in concentrations of plasma tartrate-resistant acid phosphatase, serum angiotensin-converting enzyme (ACE), serum ferritin, and plasma chitotriosidase; and decrease in liver and spleen size, measured by ultrasonography. METHODS: Thirty adult patients with nonneuronopathic (type 1) Gaucher disease (23% splenectomized) were followed for mean periods of 12 and 36 months. RESULTS: The series achieved highly significant mean responses in all hematological, biochemical, and visceral parameters over both observation periods; over a mean 36 months, 19 (63%) had a marrow response, 11 (37%) did not. Six of 7 splenectomized patients attained a marrow response. There were no significant differences between the marrow responders and nonresponders in age, sex, spleen status, Gaucher genotype distribution, mean baseline hematological or biochemical values or liver size, or mean follow-up. At a mean follow-up of 12 months, no significant differences yet were evident between marrow responders and nonresponders in seven of eight response parameters, but marrow responders had a significantly greater reduction in plasma chitotriosidase and a trend toward significantly greater reduction in serum ACE. At a mean follow-up of 36 months, marrow responders had a significantly greater mean increase in Plt and mean decrease in serum ferritin concentration and liver size than did marrow nonresponders; the trend toward greater ACE reduction in marrow responders deepened. However, chitotriosidase response now was equivalent in both subgroups. Marrow nonresponders had a significantly greater mean diminution in spleen size than did marrow responders, but the marrow nonresponders had significantly larger mean spleen size at baseline. Marrow nonresponders also had a greater mean increase in Hb than did marrow responders, but the difference was not significant. The two subgroups had equivalent mean reductions of plasma TRAP. CONCLUSIONS: The clinical relevance of qualitative MRI of the bone marrow in monitoring patients receiving ERT for nonneuronopathic Gaucher disease show that marrow nonresponders can derive considerable benefit from ERT across a variety of other response parameters and suggest an influence of spleen size on marrow response to ERT.

Adult↗

PubMedDate not supplied

A tumour masquerade.

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Abdominal Neoplasms↗