Biomedical subjects

A Sotgiu

Publications and source records attributed to A Sotgiu.

At least 19 recordsLinked to original sources

PubMed2005

HLA-DR,DQ and APOE genotypes and gender influence in Sardinian primary progressive MS.

The authors examined the influence of APOE and human leukocyte antigen-DRB1-DQB1 polymorphisms on the course of multiple sclerosis in 871 patients, 773 with relapsing and 98 with primary progressive disease, and 348 control subjects. The risk of the primary progressive course was increased (odds ratio = 6.81, p = 0.002) in women carrying the APOE4 but not the DRB1-DQB1 predisposing genotype, suggesting in this subgroup of patients a reciprocal influence between these genes and gender in modulating clinical variability of the disease.

Apolipoprotein E4↗

PubMed2004

Versatile coil design and positioning of transverse-field RF surface coils for clinical 1.5-T MRI applications.

Clinical MRI/MRS applications require radio frequency (RF) surface coils positioned at an arbitrary angle alpha with respect to B(0). In these experimental conditions the standard circular loop (CL) coil, producing an axial RF field, shows a large signal loss in the central region of interest (ROI). We demonstrate that transverse-field figure-of-eight (FO8) RF surface coils design are not subject to the same amount of signal loss in the central ROI as loop coils when their orientations are changed. The 1.5-T CL and FO8 prototypes (diameter = 10 cm) were built on Plexiglas using copper strips (width = 4 mm, thickness = 100 mum). The two linear elements of the FO8 coil were 1 cm apart. Axial spoiled gradient echo (SPGR) images of a phantom containing doped water were acquired with the coil plane at alpha=0 degrees , 45 degrees , and 90 degrees . As alpha increases, the CL images show, in the central ROI, a signal that decreases from a maximum value to zero. Whereas the FO8 images show, in the same ROI, a signal that varies little from the maximum value (20%). Optimized FO8 coils can be oriented with the coil plane positioned along any direction with respect to B(0) without significant signal loss. Transverse RF coil design should be useful for clinical MRS studies and also for parallel imaging techniques where versatile RF coils disposed along arbitrary directions are required.

Computer Simulation↗

PubMed2002

Serum uric acid and multiple sclerosis.

Several studies indicate that patients with multiple sclerosis (MS) have low serum levels of the endogenous antioxidant uric acid (UA), although it has not been established whether UA is primarily deficient or secondarily reduced due to its peroxynitrite scavenging activity. We measured serum urate levels in 124 MS patients and 124 age- and sex-matched controls with other neurological diseases. In addition, we compared UA levels when MS patients were stratified according to disease activity (by means of clinical examination and MRI), duration, disability and course. MS patients had significantly lower serum urate levels than controls (p= 0.001). However, UA levels did not significantly correlate with disease activity, duration, disability or course. Our study favors the view that reduced UA in MS is a primary, constitutive loss of protection against oxidative agents, which deserves further pathogenetic elucidation aimed at future therapeutic strategies.

Adolescent↗

PubMed2002

Multiple sclerosis complexity in selected populations: the challenge of Sardinia, insular Italy.

Several lines of evidence indicate a genetic contribution to multiple sclerosis (MS) both in terms of predisposition to the disease and of immunological mechanisms which are known to play crucial roles in MS pathogenesis. The presence of high- and low-risk areas for MS in neighbouring regions supports the theory that MS predisposition is influenced by a complex interaction of genetic and environmental factors. Therefore, the use of genetically homogeneous and geographically isolated populations becomes an increasing requirement to reduce biasing biological variables. Sardinians fulfil these conditions well because of their different phylogeny from Europeans and the unique selective pressures which shaped their genome. Sardinians display amongst the highest MS prevalence rates world-wide and increasing MS incidence rates over time. Also, MS in Sardinia is linked to distinct human leucocyte antigen (HLA) alleles and associated to different patterns of cytokine production from lymphoid cells of different HLA subtypes. In this context, recent findings and future perspectives on the peculiarities of Sardinian MS concerning genetic, immunological and epidemiological aspects are presented. So far, our results indicate that variations at the level of territorial distribution and HLA-association are present which render MS heterogeneous even in this ethnically homogeneous population.

Humans↗

PubMed2001

New experimental apparatus for multimodal resonance imaging: initial EPRI and NMRI experimental results.

Electron paramagnetic resonance imaging (EPRI) is a recently developed imaging technique employed in the study of free radicals in living systems. A full understanding of many physiological and pathological processes involving free radicals has not yet been attempted. The reason for this is that whilst nuclear magnetic resonance imaging (NMRI) is able to generate very accurate images of soft tissues and organs, EPRI does not have this capability because of its sensitivity limitations and the large linewidths of paramagnetic probes. This work describes the development and optimization of a multimodal apparatus capable of performing both pulsed EPRI and NMRI experiments on the same sample. The instrument combines the possibilities offered by both techniques: the functional and biochemical information achieved with EPRI, and the high-resolution anatomical images generated by NMRI. At present, these experiments are performed by moving the sample from an EPRI spectrometer to an NMRI apparatus. Consequently, the acquisition times are very long and several problems arise in image reconstruction. On the other hand, a unique apparatus operating in the two modalities greatly reduces the acquisition times and makes it possible to relate accurately the observed distribution of electron spin density with the anatomical description of individual organs. The experiments are performed at 357 Gauss, corresponding to a resonance frequency of 1.52 MHz for NMR and 1 GHz for EPR. In the present work, a detailed description of the apparatus is reported, including the main magnet, the gradient assembly, the multimodal cavity and the transmitter and receiver systems. The preliminary experimental results obtained by this apparatus are presented.

Electron Spin Resonance Spectroscopy↗

PubMed2001

Chlamydia pneumoniae in the cerebrospinal fluid of patients with multiple sclerosis and neurological controls.

Chlamydia pneumoniae infection is a common event in neurological patients and recovery of C. pneumoniae DNA in the cerebrospinal fluids (CSF) of multiple sclerosis (MS) patients could represent an epiphenomenon. We assessed the relevance of C. pneumoniae infection in 62 CSF samples from 32 MS patients and 30 neurological controls by means of PCR, immunofluorescence microscopy, enzyme-linked fluorescence and antibody detection. Multiple sclerosis (9.3%) and neurological controls (13.3) had similar percentage of anti-C. pneumoniae antibodies. However, C. pneumoniae DNA was only detectable in MS patients' CSF (9.3%). Our data support the hypothesis that C. pneumoniae persistence in some MS patients may be the result of an impaired clearance within the central nervous system.

Adult↗

PubMed2000

Omega-space adaptive acquisition technique for magnetic resonance imaging from projections.

An omega-space adaptive acquisition technique for MRI from projections is presented. It is based on the evaluation of the information content of a set composed of four initial projections, measured at angles 0 degrees, 45 degrees, 90 degrees, and 135 degrees, followed by the selection of new angles where the information content is maximum. An entropy function is defined on the power spectrum of the projections that is useful for evaluating the information content of each projection. The method makes it possible to reduce the total acquisition time with little degradation of the reconstructed image and it adapts to the arbitrary shape of the sample. For this reason, it can be particularly useful in those applications where acquisition from projections is strongly recommended to save acquisition time, such as functional MRI, imaging of species having very short T(2), or angiography. The method has been tested both on simulated data and on experimental data collected by a commercial MRI apparatus. The method has also been compared to the regular acquisition method, that is, the standard acquisition method in MRI from projections.

Image Processing, Computer-Assisted↗

PubMed2000

EPR imaging from projections: errors due to misalignment of projection centres and their rectification by a novel acquisition modality.

Continuous wave and pulsed wave electron paramagnetic resonance imaging (EPRI) makes use of classical methods of acquisition of projections. Acquisition/reconstruction techniques, such as spin-echo, gradient-echo, etc, cannot be applied to EPRI because they would require very short switching times for the gradient coils. Due to the use of the polar acquisition technique, it is necessary to define a centre of rotation about which the measured projections are rotated during the reconstruction process. This centre represents the point at which the field gradient coils must produce zero magnetic field. Due to the presence of a magnetic field control system that serves to compensate for field variations, principally due to heating, some interference can occur in the control system between the main magnetic field and the magnetic field produced by the gradient coils. The effect changes as the orientation changes. This results in a shift of the centres of the projections as a function of the variation of magnetic field produced by the gradient coils on the control Hall probe. If this condition is present, some artefacts can appear on the reconstructed image. This effect is irrelevant when EPR is used for imaging of paramagnetic probes whose linewidths are of the order of 10(-4) T, while it can be significant in the case of linewidths of the order of 10(-5) T or lower or when EPR is used in microimaging applications (i.e. for high values of magnetic field gradient). We describe the effects that misalignments of the projections have on the reconstructed images. We present a useful method for estimating the real position of the centre and correcting the measured projections before the application of the reconstruction algorithm. Moreover, we demonstrate the functioning of our technique by presenting some examples of EPR reconstruction collected by an X-band EPR imaging apparatus.

Algorithms↗

PubMed1999

Optimization of axial RF field distribution in low-frequency EPR loop-gap resonators.

A novel coupling method that optimizes the axial RF distribution of low-frequency EPR loop-gap resonators is presented. It consists of a resonant coupling loop positioned at the centre of a two-section loop-gap resonator. This arrangement ensures a symmetrical distribution of the radio frequency field along the axis of the resonator. The design of a central coupling system suitable for EPR resonators operating at about 220 MHz is described. Experimental results show that with the central coupling system the RF field is symmetrical and has a very good axial homogeneity (100% of the resonator length).

Biophysical Phenomena↗

PubMed1999

Pulsed EPR imaging: image reconstruction using selective acquisition sequences.

Pulsed nuclear magnetic resonance imaging (NMRI) apparatus has developed very quickly. On the other hand, the development of apparatus for pulsed electron paramagnetic resonance imaging (EPRI) has been very slow. This fact is due to the extremely reduced relaxation times of the paramagnetic probes. EPR linewidths are larger than typical NMR linewidths. These large linewidths are also responsible for a substantial worsening of spatial resolution. Due to the brevity of the electronic relaxation times, not all the acquisition/reconstruction techniques currently used in NMRI (such as spin-echo, gradient-echo, etc) can be applied in pulsed EPRI. In fact, the usable sequences in pulsed EPRI are only acquisitions from projections, where it is possible to use stationary magnetic field gradients. Moreover, the use of high fixed magnetic field gradients induces a short decay time constant T2*. The low T2* value can make it impossible for the analogue to digital conversion system (ADC) to reproduce signal variations during the whole acquisition interval and the resolution can worsen. A new pulsed EPRI acquisition sequence from projections, based on selective reception, is presented that is particularly useful in solving the problems of worsening of spatial resolution associated with the use of an ADC. In order to demonstrate the capabilities of our acquisition method, simulated numerical tests will also be reported.

Electron Spin Resonance Spectroscopy↗

PubMed1998

A Radiofrequency (220-MHz) Fourier Transform EPR Spectrometer

Radiofrequency continuous wave EPR spectrometers for detecting and localizing free radicals in vivo in samples of 50-100 g have been developed. The main limitation of these EPR instruments is the slow acquisition time, and a sensible improvement is expected by the adoption of pulsed EPR techniques. We present here a Fourier transform EPR spectrometer operating at 220 MHz suitable for large volume samples (up to 50 ml). A detailed description of the transmitter and receiver sections, including the EPR resonator, is given. Representative free induction decay data obtained from a sample with a relaxation time of about 900 ns are reported. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

Fourier reconstruction as a valid alternative to filtered back projection in iterative applications: implementation of Fourier spectral spatial EPR imaging.

The qualitative equivalence between the Fourier reconstruction (FR) algorithm and the filtered back projection (FBP) algorithm is demonstrated when all the different phase errors that can occur in FR are eliminated. The causes of phase errors are underlined and methods to eliminate them are presented. The practical comparison between FR and FBP has been evaluated on a numerical test image and the results are reported, demonstrating the qualitative equivalence. FR has the advantage of being very computationally efficient. In fact, the time spent to obtain the FR image was 1/20 of that used to obtain the FBP image. Because of the computational efficiency of FR and the good quality of the results obtained, an iterative version of FR has been used to implement the spectral-spatial imaging (SSI) algorithm in the field of electron paramagnetic resonance imaging (EPRI). An experimental example, demonstrating its good performance, is reported.

Electron Spin Resonance Spectroscopy↗

PubMed1998

Two-dimensional 220 MHz Fourier transform EPR imaging.

In the last decade radiofrequency continuous-wave EPR spectrometers have been developed to detect and localize free radicals in vivo. Only recently, pulsed radiofrequency EPR spectrometers have been described for imaging applications with small samples. In the present work, we show the first two-dimensional image obtained at 220 MHz on a large phantom (40 ml) that simulates typical conditions of in vivo EPR imaging. This pulsed EPR apparatus has the potential to make the time required for three-dimensional imaging compatible with the biological half-life of normally used paramagnetic probes.

Animals↗

PubMed1998

pH-sensitive imaging by low-frequency EPR: a model study for biological applications.

The use of pH-sensitive nitroxides, in conjunction with low-frequency EPR, offers a unique opportunity for non-invasive assessment of pH values (in the range 0 to 14) in living animals. In the present study, we have investigated the potential use of pH-sensitive nitroxide free radicals in conjunction with EPR imaging techniques at low and very low frequencies (280 MHz-2.1 GHz). In particular, we have measured the hyperfine splitting (hfs) of a pH-sensitive probe at three different EPR frequencies: 280 MHz, 1.1 GHz and 2.1 GHz. We have also developed EPR imaging experiments with phantoms simulating in vivo conditions, using pH-sensitive probes at 280 MHz (spatial-spatial) and 1.1 GHz (spectral-spatial). Finally, we discuss the actual sensitivity/resolution limits of the EPR imaging techniques at low frequencies. Practical applications of this method in the biomedical field are suggested for the continuous and non-invasive localization of pH in vivo.

Animals↗

PubMed1998

Multipolar laminated electromagnet for low-field magnetic resonance imaging and electron paramagnetic resonance imaging.

A cylindrical 16-pole electromagnet (EM) for electron paramagnetic resonance imaging (EPRI) and low-field magnetic resonance imaging (MRI) has been designed by means of two-dimensional and three-dimensional (3-D) finite element analysis (FEA). The use of an automatic procedure that combines FEA with a minimization routine allowed the optimization of the design, in order to improve the homogeneity along the axis of the EM. A prototype has been built by using electrical steel sheets that were cut by laser; this solution reduced significantly the manufacturing cost. The EM operates with a maximum flux density, in the bore, of 0.08 T and has a homogeneity along the axis of about 40 parts per million (ppm) in a spherical region 10 cm in diameter. It generates the main field and two of the three field gradients required in the 3-D image reconstruction. Good agreement was found between the results of simulation and the measured values.

Electromagnetic Phenomena↗

PubMed1997

Water soluble free radicals as biologically responsive agents in electron paramagnetic resonance imaging.

Electron paramagnetic resonance imaging (EPRI) is currently being developed at frequencies between 200 MHz and 2 GHz. EPRI can map the in vivo distribution of paramagnetic species, such as water soluble free radicals; nitroxide free radicals are commonly used. EPR images reflect the complexity of metabolic actions on the exogenous delivered nitroxides. Their reduction rate in vivo is affected by parameters such as oxygen concentration, pH and biodistribution. This paper illustrates the main features of low frequency EPRI and reconstruction techniques. Examples of EPR imaging, such as two-dimensional (2D) spatial mapping of the distribution of a nitroxide free radical in phantoms and in whole rat, are given.

Animals↗

PubMed1996

Present status of electron paramagnetic resonance (EPR) spectroscopy/imaging for free radical detection.

Our group and others have been working on the development of EPR imaging to obtain "in vivo" free radical images. Using a 280 MHz apparatus a pyrrolidine nitroxide free radical was localized in the rat abdomen and thorax during its kinetic in whole body. We investigated the role of different experimental and instrumental parameters on the resolution of the images. The conclusion of these studies is that the instrumentation presents the advantage to perform EPR measurements on whole body rats with limited sensitivity (50 microM). The present resolution (8 mm) allows to get images in which it is not possible to resolve all the organs; instead L-band instruments provide images of single organs (up to 25 mm in size) with a higher resolution.

Animals↗

PubMed1994

In vivo electron paramagnetic resonance spectroscopy-imaging in experimental oncology: the hope and the reality.

PURPOSE: Low frequency (280 MHz) electron paramagnetic resonance imaging is a new magnetic resonance technique, still being developed, that can map the in vivo spatial distribution of paramagnetic species such as nitroxide free radicals. The reduction rate of these molecules is affected by oxygen concentration. This paper gives some examples of the use of electron paramagnetic resonance imaging methodology in whole rats in the framework of its possible use in experimental oncology. METHODS AND MATERIALS: The 280 MHz apparatus based on a cylindrical 16 pole magnet was developed and designed specifically for 50-200 g laboratory animals. It generates the main field and the three field gradients required for three-dimensional (3-D) projections. A pyrrolidine nitroxyl (2,2,5,5,-tetramethylpyrrolidine-1-oxyl-3-carboxylic acid) was injected intravenously in rats to provide an electron paramagnetic resonance signal for in vivo measurements. Electron paramagnetic resonance X-band spectrometer was used to monitor pyrrolidine nitroxyl decay in an external blood circuit during normoxia and moderate hypoxia (15% O2). RESULTS AND CONCLUSION: One-dimensional (1-D) transversal and longitudinal mapping of this nitroxide free radical distribution in rat whole body was obtained 7-9 min after injection. In circulating blood, nitroxide half-life decreased significantly during hypoxia. The present sensitivity (10(-4)-10(-5) M), spatial resolution (3-10 mm) and collection time (3-5 min) could be drastically improved by narrow linewidth paramagnetic probes and pulsed techniques.

Animals↗