Biomedical subjects

P Lievens

Publications and source records attributed to P Lievens.

At least 19 recordsLinked to original sources

PubMed2006

Isomorphous substitution in bimetallic oxide clusters.

The geometric and electronic structure of bimetallic oxide clusters is studied as a function of their composition with gas phase vibrational spectroscopy. Infrared multiple photon dissociation spectra of titanium-vanadium oxide cluster anions are measured in the 500 to 1200 wave number range and assigned on the basis of harmonic frequencies calculated using density functional theory. Singly substituted (V(2)O(5))(n-1)(VTiO(5))(-) (n=2-4) cluster anions are shown to form polyhedral caged structures similar to those predicted for their isoelectronic counterparts, the neutral (V(2)O(5))(n) clusters. Upon systematic exchange of V by Ti atoms in V(4-n)Ti(n)O(-)(10) (n=1-4), the structure does not change. The stress induced by the isomorphous substitution results in an increased number of unpaired electrons (n-1) for the Ti-rich systems, leading to a quartet ground state for Ti(4)O(-)(10).

Journal Article↗

PubMed2006

Demonstration of tissue alterations by ultrasonography, magnetic resonance imaging and spectroscopy, and histology in breast cancer patients without lymphedema after axillary node dissection.

Estimates of the incidence of arm swelling after axillary lymph node dissection for breast cancer range from 10 to 37%. Yet the subjective sensation of edema is described in at least 54% of patients. The purpose of this research was to examine the structural changes occurring in the subcutaneous tissue that might explain these subjective complaints using multiple imaging modalities. Two female cadavers with unilateral breast amputation and axillary dissection were studied. The dermal and subcutaneous layers of both arms were visualized with high frequency ultrasonography, and magnetic resonance imaging and spectroscopy (MRS), and tissue biopsies were taken for histological evaluation. On the operated side, ultrasound imaging showed a hyperechogenic subcutis and the fat-to-water relationship in adipose cells was higher as measured by MRS. Dissection of the arms revealed structural adipose tissue changes, which were confirmed by microscopic evaluation.

Biopsy↗

PubMed2005

Size-dependent carbon monoxide adsorption on neutral gold clusters.

We report on experiments probing the reactivity of neutral Au(n) clusters, n = 9-68, with carbon monoxide. The gold clusters are produced in a pulsed laser vaporization cluster source, operated at room temperature (RT) or at liquid-nitrogen temperature (LNT), pass through a low-pressure reaction cell containing CO gas, and are subsequently laser ionized. The reaction probabilities are determined by recording mass abundance spectra with time-of-flight mass spectrometry. The main observations are a strong temperature dependence and a remarkable size dependence. Upon cooling of the cluster source to LNT, the reactivity increases substantially. At LNT, the reaction probabilities for Au(n) with the first CO molecule are about a factor 10 higher than at RT. Moreover, adsorption of two, three, and even four CO molecules is observed, in contrast to RT clusters which at most adsorb one CO molecule. This temperature dependence is related to the lifetime of the cluster-molecule complexes, being much longer for cold clusters. The observed striking size dependence is similar at both temperatures and is discussed in terms of the electronic structure effects.

Journal Article↗

PubMed2005

Modification and stability of aromatic self-assembled monolayers upon irradiation with energetic particles.

We have studied ion and electron irradiation of self-assembled monolayers (SAMs) of 2-(4'-methyl-biphenyl-4yl)-ethanethiol (BP2, CH3-C6H4C6H4CH2CH2-SH), phenyl mercaptan (PEM, C6H5CH2CH2-SH), and 4'-methyl-biphenyl-4-thiol (BP0, CH3-C6H4C6H4-SH) deposited on Au(111) substrates. Desorption of neutral particles from PEM/Au and BP2/Au was investigated using laser ionization in combination with mass spectrometry. The ion-induced damage of both BP2 and PEM SAMs is very efficient and interaction with a single ion leads to the modification of tens of molecules. This feature is the result of a desorption process caused by a chemical reaction initiated by an ion impact. Both for ions and electrons, experiments indicate that the possibility for scission of the Au-S bond strongly depends on the chemical nature of the SAM system. We attribute the possible origin of this effect to the orientation of the Au-S-C angle or adsorption sites of molecules. The analysis of electron-irradiated PEM/Au and BP2/Au, using ion-initiated laser probing, enabled measurements of the cross section for the electron-induced damage of the intact molecule or specific fragment. Analysis of electron-irradiated BP0/Au by using time-of-flight secondary ion mass spectrometry (TOF-SIMS) provides direct evidence for the quasi-polymerization process induced by electron irradiation.

Journal Article↗

PubMed2005

Quenching of the magnetic moment of a transition metal dopant in silver clusters.

Single magnetic atoms embedded in a nonmagnetic host exhibit the Kondo effect in the bulk limit, while in very small molecules the magnetic atom is hardly affected by the matrix. In a combined theoretical (density functional theory) and experimental (photofragmentation and mass spectrometry) study we consider the intermediate case of nanometer sized transition-metal-doped silver clusters. In particular, we provide experimental evidence for enhanced stability of the cobalt-doped silver cluster Ag10Co+ and show theoretically that it has a symmetric endohedral geometry with a closed 18-electron singlet electronic shell structure. This implies that the magnetic moment on the cobalt atom is quenched.

Journal Article↗

PubMed2005

Measurement of the spin and magnetic moment of 31Mg: evidence for a strongly deformed intruder ground state.

Unambiguous values of the spin and magnetic moment of 31Mg are obtained by combining the results of a hyperfine-structure measurement and a beta-NMR measurement, both performed with an optically polarized ion beam. With a measured nuclear g factor and spin I=1/2, the magnetic moment mu(31Mg)=-0.88355(15)mu(N) is deduced. A revised level scheme of 31Mg (Z=12, N=19) with ground state spin/parity I(pi)=1/2(+) is presented, revealing the coexistence of 1p-1h and 2p-2h intruder states below 500 keV. Advanced shell-model calculations and the Nilsson model suggest that the I(pi)=1/2(+) ground state is a strongly prolate deformed intruder state. This result plays a key role for the understanding of nuclear structure changes due to the disappearance of the N=20 shell gap in neutron-rich nuclei.

Journal Article↗

PubMed2005

Drainage pattern of the upper medial quadrant of the breast in young healthy women after subdermal injection: a lymphscintigraphic study.

This study examines the lymphatic drainage after injection of a radiotracer in the upper medial quadrant of the right breast in young healthy female subjects. Most studies concerning lymphatic drainage pathways have focused on the upper lateral quadrant of the breast because of the high incidence of carcinoma in this quadrant while the drainage pattern of the medial quadrant has been less studied. We injected radiotracer (Human Serum Albumin labeled with 99 technetium) subdermally into the upper medial quadrant of the right breast tissue of 33 young healthy female volunteers and obtained static images with a scintillation camera briefly after injection and approximately one hour after injection. We identified lymphatic pathways in 82.8% of our subjects, lymph nodes in 79.3% and in 3.4%, a sentinel lymph node was found in the internal mammary chain. In early images, lymph nodes were visualized in 65.5% of subjects while in 17.2% of subjects, lymphatic vessels only appeared on later images.

Adult↗

PubMed2004

Extremely stable metal-encapsulated AlPb10+ and AlPb12+ clusters: mass-spectrometric discovery and density functional theory study.

We report the experimental discovery of extremely stable metal-encapsulated superatom clusters of a group IVA element: AlPb+10 and AlPb+12. Ab initio density functional geometry optimizations at the B3LYP/LANL2DZ level result in a perfect icosahedron with an exceptionally large HOMO-LUMO gap of 3.1 eV for AlPb+12, and a related structure with D(4d) symmetry for AlPb+10, with a HOMO-LUMO gap of 2.6 eV. Their high stability is attributed to the reinforcing influence of the most favorable closed-packed structure and optimally filled electron shells.

Journal Article↗

PubMed2004

Lymphedema development following breast cancer surgery with full axillary resection.

Several studies have investigated the influence of disease related, treatment related, and patient related risk factors on the development of postmastectomy edema (PME). The aim of the present study was to determine which factors present a higher risk of developing PME after breast surgery with full axillary resection (level I, II and III). To accomplish this aim, we investigated 245 women who underwent unilateral breast cancer surgery in the Academic Hospital of the Vrije Universiteit, Brussels. Information concerning treatment and disease related factors were collected from the patient's medical records and factors related to clinical condition were obtained by a personal interview. Arm circumference was taken at 15 cm proximal and 10 cm distal to the olecranon. PME was defined as 2.5 cm difference between the arms. Height and weight of the patient were also measured. Statistical analysis was performed by calculating the Odds Ratio and the 95% Confidence Interval. We found the following factors posed an increased risk of developing PME: axillary/supraclavicular radiotherapy, pathological status of the lymph nodes, overweight (BMI > 25 kg/m2), trauma to the arm, menopause and surgery on the dominant side.

Adult↗

PubMed2003

Element- and size-dependent electron delocalization in AuNX+ clusters (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni).

We investigated the stability of gold clusters doped with open 3d-shell atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni). Steps, peaks, and odd-even staggering in mass abundance spectra upon photofragmentation provide evidence for enhanced stability for specific cluster sizes. The observed magic numbers are explained in terms of size- and dopant-dependent modifications of the effective mean-field potential within a phenomenological shell-model approach. Element-dependent 3d electron delocalization and odd-even staggering amplitudes are related to the dopant-atom structure.

Journal Article↗

PubMed2002

Lymphatic pathways of the upper medial quadrant of the breast in healthy women: radiotracer study of the sentinel lymph node.

This study examined the lymphatic drainage after injection of a radiotracer into the upper medial quadrant of the breast in healthy women. Most studies of lymphatic pathways of the breast have been performed in patients with breast cancer and concentrate on the upper lateral quadrant of the breast because of the high incidence of carcinoma at this site. The lymphatic drainage pathways of the medial half of the breast, however, has been less studied. A radiotracer (Tc-99m human serum albumin nanocolloid or HSA) was injected intradermally into the upper medial quadrant of the right breast in 12 healthy women. Dermal markers were placed at the middle of the clavicle, the axilla and at the jugular incisura. Three minutes after injection a static image of the injection site was made with a scintillation camera (Multispect 2 Gamma Camera System) over 20 seconds. After nine minutes, local soft massage was instituted at the injection site for 6 minutes. Fifteen minutes after injection, a graphic scintigraphic image was made of both breasts and axillae over 22 minutes. After this interval, three or four static images were made for a few seconds to locate the sentinel lymph node as related to the injection site. A sentinel lymph node (lymphatic pathway) in the axilla was visualized in 11 subjects (91.9%) and was undetected in one subject (8.3%). The radiotracer migrated in all patients (100% ) towards the ipsilateral axilla. In 9 subjects, the sentinel lymph node was visualized 15 minutes after injection, whereas in 2 subjects it appeared within an hour.

Adult↗

PubMed2001

A key to understanding postoperative lymphoedema: a study on the evolution and consistency of oedema of the arm using ultrasound imaging.

Post-mastectomy oedema is a very serious complication that, in the course of time, will transform into fibrotic tissue. The aim of our study is to evaluate when and in which layer liquid oedema transforms into fibrotic tissue. To do so, ultrasonographic images were taken of 22 patients and 9 control women at the shoulder and 10 cm proximal and distal from the olecranon, with the images then being scanned and imported into a computer program to determine echogenicity of the dermis, subcutis, subcutis on dermal side and subcutis on fascial side. Statistical analyses were performed by means of the Wilcoxon test and a Student's t-test. No significant differences (P< or =0.05) were found for the different parameters in the control group. In the experimental group: significant differences in perimeter, skinfold, thickness of dermis and subcutis were found. Although not significant, subcutaneous tissue was more echogenic on the oedematous side, with significant hyperechogenicity at the fascial subcutaneous layer. This indicates that fibrotic tissue develops distally in the forearm.

Journal Article↗

PubMed2000

Electromagnetic diathermia: a lymphoscintigraphic and light reflection rheographic study of leg lymphatic and venous dynamics in healthy subjects.

Because electromagnetic diathermia (ED) has been reported to reduce lymphedema, we opted to examine the effects of ED on leg venous and lymph dynamics in healthy subjects. To examine lymph flow, we performed lymphangioscintigraphy (LAS) in 10 subjects without leg edema and used static images at the injection site and at the inguinal region for "control data." Later, we applied ED (2450 MHz, 200W) and then repeated the LAS using the same dosage and volume. Differences between the first and second sessions were examined using two way ANOVA and the differences between the scores with or without ED were analyzed by a Student's t-test. To examine venous flow, we first tested the left lower leg of 15 healthy subjects on two occasions using light reflection rheography (LRR). Venous refill time was recorded after each individual performed 10 dorsiflexions with the left foot on three occasions with an interval of 3 minutes between each recording. Thereafter, 20 minutes ED (2450 MHz, 200 W) was applied and using the same protocol venous refill time was recorded and repeated after an interval of one week. The 20% level and the declination angle of the refill time was determined and differences between the experimental and control groups analyzed by ANOVA. The results between the first and second sessions were consistent and reproducible with or without the electromagnetic application, with no change of radiotracer transport from the injection site or arrival at the inguinal nodes. There was also a high correlation between the scores for the 50% level and declination angle (r = 0.97) after LRR. Thus, after ED there was an accelerated venous refill time. In conclusion, after ED there was no increase in lymph flow but there was accelerated venous return.

Adult↗

PubMed1998

NF-Y organizes the gamma-globin CCAAT boxes region.

The CCAAT-binding activator NF-Y is formed by three evolutionary conserved subunits, two of which contain putative histone-like domains. We investigated NF-Y binding to all CCAAT boxes of globin promoters in direct binding, competition, and supershift electrophoretic mobility shift assay; we found that the alpha, zeta, and proximal gamma CCAAT boxes of human and the prosimian Galago bind avidly, and distal gamma CCAAT boxes have intermediate affinity, whereas the epsilon and beta sequences bind NF-Y very poorly. We developed an efficient in vitro transcription system from erythroid K562 cells and established that both the distal and the proximal CCAAT boxes are important for optimal gamma-globin promoter activity. Surprisingly, NF-Y binding to a mutated distal CCAAT box (a C to T at position -114) is remarkably increased upon occupancy of the high affinity proximal element, located 27 base pairs away. Shortening the distance between the two CCAAT boxes progressively prevents simultaneous CCAAT binding, indicating that NF-Y interacts in a mutually exclusive way with CCAAT boxes closer than 24 base pairs apart. A combination of circular permutation and phasing analysis proved that (i) NF-Y-induced angles of the two gamma-globin CCAAT boxes have similar amplitudes; (ii) occupancy of the two CCAAT boxes leads to compensatory distortions; (iii) the two NF-Y bends are spatially oriented with combined twisting angles of about 100 degrees. Interestingly, such distortions are reminiscent of core histone-DNA interactions. We conclude that NF-Y binding imposes a high level of functionally important coordinate organization to the gamma-globin promoter.

Base Sequence↗

PubMed1997