Biomedical subjects

J Rosell

Publications and source records attributed to J Rosell.

At least 19 recordsLinked to original sources

PubMed2001

Sensitivity maps and system requirements for magnetic induction tomography using a planar gradiometer.

We evaluated analytically and experimentally the performance of a planar gradiometer as a sensing element in a system for magnetic induction tomography. A system using an excitation coil and a planar gradiometer was compared against a system with two coils. We constructed one excitation coil, two different sensing elements and a high-resolution phase detector. The first sensor was a PCB square spiral coil with seven turns. The second sensor was a PCB planar gradiometer with two opposite square spirals of seven turns, with a distance between centres of 8 cm. Theoretical sensitivity maps were derived from basic equations and compared with experimental data obtained at 150 kHz. The experimental sensitivity maps were obtained measuring the perturbation produced by a brass sphere of 12 mm in empty space. The advantage of using a gradiometer is that it can be adjusted to give a minimum signal for homogeneous objects, while increasing the sensitivity to local perturbations of the conductivity. Results show that a system using a planar gradiometer as detector has less demanding requirements for the electronic system than a system using simple coils.

Electric Impedance↗

PubMed2001

Magnetic induction tomography: hardware for multi-frequency measurements in biological tissues.

Magnetic induction tomography (MIT) is a contactless method for mapping the electrical conductivity of tissue. MIT is based on the perturbation of an alternating magnetic field by a conducting object. The perturbation is detected by a voltage change in a receivercoil. At physiologically interesting frequencies (10 kHz-10 MHz) and conductivities (< 2 S m(-1)) the lower limit for the relative voltage change (signal/carrier ratio = SCR) to be resolved is 10(-7)-10(-10). A new MIT hardware has been developed consisting of a coil system with planar gradiometers and a high-resolution phase detector (PD). The gradiometer together with the PD resolves an SCR of 2.5 x 10(-5) (SNR = 20 dB at 150 kHz, acquisition speed: 100 ms). The system operates between 20 and 370 kHz with the possibility of extending the range up to 1 MHz. The feasibility of measuring conductivity spectra in the beta-dispersion range of biological tissues is experimentally demonstrated. An improvement of the resolution towards SCR = 10(-7) with an SNR of > or = 20 dB at frequencies > 100 kHz is possible. On-line spectroscopy of tissue conductivity with low spatial resolution appears feasible, thus enabling applications such as non-invasive monitoring of brain oedema.

Brain Edema↗

PubMed2000

Algorithms for parametric images in MEIT systems.

In this work we show the algorithms developed to extract the Cole parameters from multi-frequency EIT. With these parameters it is possible to obtain information about various different tissues and their pathologies. The algorithms developed obtain the Cole-model parameters from the real and imaginary parts of impedance, or using only the real part, without problems of convergence. A study of the influence of noise is performed with simulations. We find a correct solution in all cases with signal to noise ratio in the data higher than 40 dB. Finally, we show parametric images of the human abdomen obtained with these algorithms.

Abdomen↗

PubMed2000

Percutaneous electrocatheter technique for on-line detection of healed transmural myocardial infarction.

Healed myocardial infarction has been recognized by its particular tissue electrical impedance spectrum measured with intramural needle electrodes in animal models. The aim of this study was to develop a percutaneous approach for in vivo recognition of areas of healed myocardial infarction by measuring myocardial electrical impedance with an intracavitary contact electrocatheter. Electrical impedance (resistance and phase angle) of normal myocardium and of a 2-month-old anterior transmural infarction were measured in nine chloralose anesthetized pigs by applying alternating currents from 1 kHz to 1 MHZ between a bipolar intracavitary catheter and a reference electrode placed on the epicardium (group I, n = 4) or on the precordium (group II, n = 5). Resistance of the infarcted myocardium was lower than that of healthy tissue at all current frequencies (ANOVA, P < 0.001) (i.e., at 1 kHz: 15 +/- 4 omega vs 50 +/- 19 omega in group I, and 64 +/- 13 omega vs 76 +/- 13 omega in group II). Phase angle at 316 kHz best differentiated transmural infarction from normal tissue (group I: -2.5 +/- 1.9 degrees vs -14.8 +/- 4.6 degrees, P < 0.001; group II: +0.7 +/- 1.0 degrees vs -2.7 +/- 1.4 degrees, P < 0.001). This study shows that analysis of myocardial impedance spectrum using a percutaneous intracavitary contact catheter approach permits on-line recognition of areas of healed transmural myocardial infarction. This technique may be useful to optimize clinical application of energy sources (i.e., radiofrequency ablation, laser myocardial revascularization).

Analysis of Variance↗

PubMed1999

In vivo and in situ ischemic tissue characterization using electrical impedance spectroscopy.

The investigation of processes of ischemia in different organ tissues is very important for the development of methods of protection and preservation during surgical procedures. Electrical impedance spectroscopy was used to distinguish between different tissues and their degree of ischemia. We describe mathematical methods used to adjust experimental data to Cole-Cole models for one-circle and two-circle impedance loci and a study of the main parameters for representing the behavior of ischemia in time. In vivo and in situ postmortem measurements of different tissues from pigs are shown in the 100 Hz to 1 MHz range. The Cole parameters that best characterize the ischemia are R0 and fc.

Animals↗

PubMed1998

A clinical variant of neurofibromatosis type 1: familial spinal neurofibromatosis with a frameshift mutation in the NF1 gene.

Spinal neurofibromatosis (SNF) has been considered to be an alternative form of neurofibromatosis in which spinal cord tumors are the main clinical characteristic. Familial SNF has been reported, elsewhere, in three families-two linked to markers within the gene for neurofibromatosis type 1 (NF1) and the other not linked to NF1-but no molecular alterations have been described in these families. We describe a three-generation family that includes five members affected by SNF. All the affected members presented multiple spinal neurofibromas and café au lait spots, one member had cutaneous neurofibromas, and some members had other signs of NF1. Genetic analysis, performed with markers within and flanking the NF1 gene, showed segregation with the NF1 locus. Mutation analysis, performed with the protein-truncation test and SSCP/heteroduplex analysis of the whole coding region of the NF1 gene, identified a frameshift mutation (8042insA) in exon 46, which should result in a truncated NF1 protein. The 8042insA mutation was detected in all five family members with the SNF/NF1 phenotype. To our knowledge, this is the first time that a mutation in the NF1 gene has been associated with SNF. The clinical homogeneity in the severity of the disease among the affected members of the family, which is unusual in NF1, suggests that a particular property of the NF1 mutation described here, a gene closely linked to NF1, or posttranscriptional events are involved in this severe neurological phenotype.

Adult↗

PubMed1998

Molecular, cytogenetic, and clinical characterisation of six XX males including one prenatal diagnosis.

Cytogenetic analysis, fluorescent in situ hybridisation (FISH), and molecular amplification have been used to characterise the transfer of Yp fragments to Xp22.3 in six XX males. PCR amplification of the genes SRY, RPS4Y, ZFY, AMELY, KALY, and DAZ and of several other markers along the Y chromosome short and long arms indicated the presence of two different breakpoints in the Y fragment. However, the clinical features were very similar in five of the cases, showing a male phenotype with small testes, testicular atrophy, and azoospermia. All these patients have normal intelligence and a stature within the normal male range. In the remaining case, the diagnosis was made prenatally in a fetus with male genitalia detected by ultrasound and a 46,XX karyotype in amniocytes and fetal blood. Molecular analysis of fetal DNA showed the presence of the SRY gene. FISH techniques also showed Y chromosomal DNA on Xp22.3 in metaphases of placental cells. To our knowledge, this is the second molecular prenatal diagnosis reported of an XX male.

DNA-Binding Proteins↗

PubMed1997

MRI of a family with focal abnormalities of gyration.

Focal abnormalities of gyration (FAG) are developmental disorders that may occur in isolated patients or, as in the case being reported, as part of a familial disorder. Analysis of individuals in a family spanning three generations was carried out using MRI. Abnormalities, present in all members of generations II and III, included focal cortical dysplasia (three patients), focal cortical infolding (two patients) and schizencephaly (one patient); associated minor anomalies, such as white matter abnormalities, were seen in the remaining three members of generations II and III. MRI recognition of FAG in the family being reported proved useful in defining their phenotypical expression and providing proper counselling for individual family members.

Adult↗

PubMed1996

A parallel broadband real-time system for electrical impedance tomography.

This paper deals with the design, implementation and performance of TIE-4sys, an electrical impedance tomograph. This instrument is a parallel broad-band real-time system. It measures impedance using an array of 16 electrodes and reconstructs the images using a weighted back-projection technique. The objective of this development is to enable multifrequency EIT clinical studies to be undertaken. The system is capable of acquiring 25 frames/s and makes multifrequency cardiac-gated images. The frequency range is from 10 kHz to 250 kHz and the signal to noise ratio for the real component is better than 60 dB.

Electric Impedance↗

PubMed1996

Broadband quasi-differential multifrequency electrical impedance imaging system.

Dynamic and multifrequency imaging methods have been demonstrated both theoretically and experimentally. Multifrequency methods are able to produce images of static structures inside the measured object. Data collection systems, however, are affected by errors due to their non-ideal frequency behaviour. If the frequencies used in the measurement were close enough, the system would behave in almost the same way. In this case, however, the impedance change displayed by biological tissues is small, so the situation is similar to dynamic imaging. We call this method the quasi-differential imaging method. We have designed and built an instrument able to apply signals from 1 kHz to 1 MHz, with frequency increments of 10 Hz. Patient interface circuits and demodulators were designed to display a flat response in the full frequency range of operation. Signals are digitized with 16 bit resolution and sent to the host computer using a high-speed serial interface. This allows a maximum measurement speed of about 8 images/s. All the system parts were full characterized out of the system and the results of these measurements are given as an indication of the limits of its use as a quasi-static imaging or quasi-differential imaging data collection system.

Electric Impedance↗

PubMed1996

Electrical impedance tomography of the eye: in vitro measurements of the cornea and the lens.

This study was designed to perform multifrequency impedance measurements on the pig's eye. On one hand, impedance of the ocular tissues was measured from 10 kHz to 10 MHz. The aqueous and vitreous humours and the cornea showed no relaxation in this range of frequencies, whereas the lens and its parts (the cortex and the nucleus) did. On the other hand, multifrequency EIT and dynamic imaging were performed on the lens and on the whole eye. Data and images obtained after thermal and chemical injuries are presented and discussed.

Animals↗

PubMed1996

Homozygous myotonic dystrophy: clinical and molecular studies of three unrelated cases.

We report the clinical and molecular study of three unrelated homozygous myotonic dystrophy patients. In the first family, the homozygous patient shows the classical form of the disease with two DM alleles of very different expansion sizes (1000 and 60 repeats). In the second family, the homozygous patient is mildly affected and carries a minimally expanded allele (64 repeats) and a "normal" allele (38 repeats) that increases in size when transmitted. Such an intergenerational expansion of an allele in this range of repeats has not been reported to date. The third homozygous case has late onset bilateral cataracts as the only symptom. She has two minimally expanded alleles (51 and 120 repeats) that showed different intergenerational enlargement during transmission to the next generation.

Adult↗

PubMed1995

Acute otitis media in childhood: a study of 20,532 cases.

We present a study of acute otitis media among 20,532 Spanish children during a 6-month period from January through June 1991. The study was done by distributing a questionnaire to all Spanish pediatricians. Of the patients 51.7% were girls and 48.3% boys; 68.7% of all children were younger than 5 years. The most frequent symptoms were otalgia or irritability, 92.7%; fever, 63.5%; otorrhea, 24.9%; vomiting, 21.4%; and another concomitant upper respiratory tract infection, 65.5%. Otitis was bilateral in 45.6% of the cases. The most frequently used antibiotic was cefixime (38%), followed by amoxicillin-clavulanate (22.2%), amoxicillin (15.3%), 2nd-generation cephalosporins (13.5%) and macrolides (8.8%). In 11.8% of the patients, a change in the initial antibiotic therapy was required due to adverse effects. Resolution of symptoms occurred in 77.8% of the patients.

Acute Disease↗

PubMed1995

Multi-frequency static imaging in electrical impedance tomography: Part 1. Instrumentation requirements.

Static images of the human body using electrical impedance tomography techniques can be obtained by measuring at two or more different frequencies. The frequencies used depend on the application, and their selection depends on the frequency behaviour of the impedance for the target tissue. An analysis using available data and theoretical models for tissue impedance yields the expected impedance and boundary voltage changes, therefore setting the measurement instrument specifications. The instrument errors produced by different sources are analysed, and, from this analysis it is possible to determine the feasibility of building the instrument, the limit values for some parameters (or components) and indications on the most suitable design of critical parts. This analysis also shows what kinds of error can be expected in the reconstructed images. It is concluded that it is possible to build an instrument with limited errors, allowing static images to be obtained. An instrument has been built that meets some of the design requirements and fails in others because of technological problems. In vivo images obtained with this instrument will be presented in Part 2 of this work.

Electric Impedance↗

PubMed1995

Errors in prolonged electrical impedance measurements due to electrode repositioning and postural changes.

Long-term electrical impedance measurements are affected by specific errors. Electrode failure, changes in its impedance due to aging, and postural changes are among the most important. We analyse errors due to electrode replacement and body postural changes. Electrode replacement errors can cause impedance changes up to 5% of basal value. This is one of the most important factors in data reproducibility. Body postural changes also contribute to impedance variations. We have proposed the use of a reference position to carry out impedance measurements as the one that shows the smallest impedance sensitivity to postural changes. In general, we observed that this is achieved with arms and legs slightly separated from the body. We propose the use of a ratio of impedance at two different frequencies to discern the origin of impedance changes, whether from physiological phenomena or postural errors.

Adult↗

PubMed1995

A multifrequency multichannel electrical impedance data acquisition system for body fluid shift monitoring.

This paper discusses some important issues for the design of electrical impedance measurement systems intended for body fluid shift monitoring, in particular during dialysis treatments. We have studied two common signal generation systems: digital synthesis and carrier recovery. We have found that in prolonged measurement applications, digital synthesis yields the best performance. On the demodulation side, we balance the demodulator errors between the real and imaginary parts by rotating the demodulation axes. We use segmental multifrequency impedance measurements to estimate the values of intracellular and extracellular impedance by adjusting the parameters of a Cole-Cole model for each segment measured. We stress the need to perform segmental measurements in order to accurately measure the segments of interest, in particular the trunk during dialysis treatments. Our results show that there is a sharp disequilibrium between the intracellular and extracellular compartments in the very first dialysis period. This fact generates the need to continuously measure segmental impedance instead of comparing initial and final values.

Body Fluid Compartments↗

PubMed1995

Signal-to-motion artifact ratio versus frequency for impedance pneumography.

We measured transthoracic impedance between 12.5 and 185 kHz in nine adults. We used a system with two impedance channels, both simultaneously detecting the real part of impedance at two different frequencies. We used only two electrodes in the midaxillary line, connecting both channels in parallel. The amplitude relation between the two channels was measured for different maneuvers and frequencies. Results show for normal breathing an increase of the signal of 20% and a decrease in motion artifacts from 12.5 to 185 kHz. We conclude that, for the maneuvers studied, it is better to work at higher frequencies than the ones commonly used. Also, we suggest a method to further increase the signal-to-motion artifact ratio based on measurement at two frequencies.

Adult↗

PubMed1995

Reduction of motion artifacts using a two-frequency impedance plethysmograph and adaptive filtering.

We measured transthoracic impedance in nine presumed healthy adult subjects with a two-frequency plethysmograph at 57 kHz and 185 kHz. The measurement protocol included periods of normal breathing without motion and periods of motion without breathing. We analyzed the cross-correlation and the ratio between the signals at both frequencies for all the different maneuvers. The correlation coefficient was between 0.97 and 1 for breathing, the minimal cross-correlation (0.81) was for simulated obstructive apnea. We found that the amplitude ratio between the two-frequency signals was different for normal breathing and for motion. Based on these results, we designed and tested an adaptive filter to increase the signal-to-artifact ratio (SAR). The increase in SAR (mean +/- standard deviation) compared with the signal at 57 kHz was: 183% +/- 117% for arm movement, 133% +/- 93% for leg movement, and 34% +/- 62% for simulated obstructive apnea.

Adult↗