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Biomedical subjects

S Akoka

Publications and source records attributed to S Akoka.

At least 37 records · Page 2Linked to original sources
PubMed1995

Chemical shift imaging from simultaneous acquisition of a primary and a stimulated echo.

An imaging method is presented for obtaining chemical shift images from only one acquisition. Images are acquired with the same spatial resolution as in regular spin-echo imaging. The sequence is based on the simultaneous acquisition of a spin echo and a stimulated echo in a single pass. The use of 90 degrees radiofrequency pulse flip angles results in the same proton density, T2 and T1 weighting for the two echoes. Application of this sequence to chemical shift imaging is discussed for three fat suppression techniques (chopper, CHESS, and hybrid). Imaging was performed on phatoms and volunteers. The image quality was the same as those obtained by the chopper and the hybrid methods and the acquisition time was reduced by a factor of two.

Adipose Tissue↗
PubMed1995

[Nuclear magnetic resonance spectroscopy: methodology and applications to the study of asphyxia neonatorum].

Cerebral metabolism has been extensively studied by magnetic resonance spectroscopy (MRS). MRS allows the study of neonates brain maturation as well as the onset and the evolution of brain injury. The use of phosphorous spectroscopy allows the quantification of phosphorylated metabolites. Thus, the measurement of the relative concentrations of creatine-phosphate and inorganic-phosphate is a prognostic factor of the outcome of a neonate after birth asphyxia. Absolute concentrations have more recently been studied and seem to be more significant. Proton MRS gives access to brain metabolites such as choline, lactate, N-acetyl aspartate and taurine. Its use is more recent than the phosphorous spectroscopy but first results already show its potential in neonatology.

Asphyxia Neonatorum↗
PubMed1995

Measurement of epidermal moisture content by magnetic resonance imaging: assessment of a hydration cream.

The moisture content of the epidermis was measured by magnetic resonance imaging (MRI), using transverse relaxation time. The spatial resolution was 86 microns, allowing a quantitative, accurate and localized determination of variations in epidermal hydration. The wrists of 15 volunteers were studied before and after application of a hydration cream. Results showed an increase of 15% of epidermal T2 after application of the cream. Moisture content curves varied according to different degrees of skin dryness. This study demonstrates that MRI is a useful tool in evaluation of epidermal hydration.

Administration, Cutaneous↗
PubMed1995

Magnetic resonance imaging in vivo monitoring of T2 relaxation time: quantitative assessment of primate brain maturation.

This work describes quantitative MRI assessment of primate brain maturation. Nine young baboons were followed from the age of one to 30 months. Assessment of myelination was based on the gray/white matter contrast on MR images and the evolution of T2 relaxation time respectively. The brain maturation began in the posterior fossa and progressed to the olfactory bulbs corresponding to decreasing white matter T2 values. Relaxation parameters provide new opportunities to trace the myelination process in vivo.

Aging↗
PubMed1995

T1 mapping from spin echo and stimulated echoes.

We present an imaging method to obtain a map of the spin-lattice relaxation time. Images were acquired with the same spatial resolution and in the same time as for a regular spin-echo acquisition. The sequence was based on the simultaneous acquisition of a spin echo and several stimulated echoes with the same intensity except for T1 weighting which increases with the interval between the excitation pulse and the readout pulse. T1 values obtained on phantoms were compared to those from the inversion-recovery method and show the accuracy (2%) and the precision (5%) of the method. T1 images of the brain of a healthy volunteer are presented and demonstrate the ability of the method to obtain T1 mapping in vivo in 12 min and without susceptibility artifacts. In vivo and in vitro results were compared to those obtained by a TOMROP sequence in the same acquisition time.

Biophysical Phenomena↗
PubMed1995

Experimental MR study of cerebral radiation injury: quantitative T2 changes over time and histopathologic correlation.

PURPOSE: To use the pig brain as a large-animal model to examine the effects of high-dose single-fraction irradiation on MR images, T2 relaxation time, and histologic integrity. METHODS: A total of 24 Meishan pigs were studied: 20 irradiated animals and 4 unirradiated controls. A high dose was delivered to the right hemisphere of the animals, using a 12-MeV electron beam. Ten animals received 40 Gy at the 90% isodose, and 10 animals received 60 Gy. Quantitative measurement of T2 relaxation time was compared with qualitative analysis of T2-weighted images and histologic studies. RESULTS: Quantitative analysis revealed a reproducible increase of the T2 parameter within the irradiated areas. The T2 kinetic could be analyzed in two phases, which appeared before the visualization of ventricle compression, necrosis, and edema. The first is characterized by vascular inflammation and the latter by radiation necrosis and edema. Both are dose dependent. CONCLUSION: These results underline the ability of quantitative MR for early diagnosis of brain radiation lesions in vivo.

Animals↗
PubMed1994

Concurrent changes in intracranial pressure, cerebral blood flow velocity, and brain energy metabolism in rabbits with acute intracranial hypertension.

The relationship between intracranial pressure or cerebral perfusion pressure (CPP), cerebral blood flow, and brain energy failure is unpredictable throughout the development of acute intracranial hypertension. The purpose of the present study was to correlate intracranial pressure with cerebral blood flow velocities and brain energy metabolism in adult rabbits. The acute intracranial hypertension was achieved by pressure transmission. Transcranial Doppler wave-forms were obtained from the basilar artery for monitoring cerebral blood flow velocities. 31P-Magnetic resonance spectroscopy was used to assess brain energy metabolism. The diastolic blood flow velocity began to decrease significantly (34.5%) when the intracranial pressure was equal to half the diastolic arterial pressure for a CPP of 36 +/- 18 mmHg. Circulatory cerebral resistances increased significantly (55%) for the same value of CPP. Diastolic frequency was near zero when intracranial pressure approached diastolic arterial pressure (51 +/- 12 mmHg), corresponding to a CPP of 30 +/- 15 mmHg. At the same time, only a tendency for brain energy metabolism to decrease was observed. Consequently, transcranial Doppler sonography could be proposed for the follow-up of intracranial hypertension. Magnetic resonance spectroscopy could help to monitor these patients and could be especially proposed in case of high intracranial pressure (near diastolic arterial pressure). The joint use of these two methods would help in making appropriate therapeutic decision in humans.

Animals↗
PubMed1994

Acquisition of spin echo and stimulated echo by a single sequence: application to MRI of diffusion.

A new method is described to measure the restricted diffusion coefficient with magnetic resonance imaging. The two images necessary to calculate the diffusion image are obtained with a simultaneous acquisition of a spin-echo and a stimulated echo, and so, in half the time needed by usual spin-echo or stimulated echo method. A different diffusion contrast is created on each echo. A map of an estimate of the diffusion coefficient and an estimation of T1 value are obtained with only one experiment. The accuracy of the method has been evaluated on phantom and results are in agreement with values found in previous papers and with measurements performed with a usual spin-echo method. Furthermore, in vivo measurements have shown that this method can be used without electrocardiogram triggering.

Brain↗
PubMed1993

Radiofrequency map of an NMR coil by imaging.

We propose a new imaging method to obtain a map of the radiofrequency (RF) field amplitude over a sample. The sequence contains three RF pulses (alpha, 2 alpha, and alpha) and produces two images by a classical spin echo and a stimulated echo. A third image is computed and gives the distribution of the flip angle alpha, and so the RF amplitude, over the sample. The accuracy of the flip angle determination is verified on an homogeneous sample and results show a good correlation between experimental and theoretical flip angles in the range of 50 degrees to 130 degrees. Experiments with a surface coil and a resonator show the method is available in an inhomogeneous RF field. Images obtained on the calf of a volunteer confirms the independence of the computed RF distribution from proton density, T1, or T2 contrast.

Humans↗
PubMed1993

Evaluation of a fast pseudo-cinematic method for magnetic resonance imaging of the temporomandibular joint.

A pseudo-cinematic magnetic resonance imaging study of the temporomandibular joint (TMJ) was undertaken with the aim of reconciling image quality with the shortest possible examination time. Two receivers were compared, a surface coil and a circularly polarized head coil, and the latter was found to be superior. Using a gradient echo sequence, repetition time and flip angle were optimized by visual assessment of the images and by measuring the contrast-to-noise ratio. A mechanical device was used to control opening and closing. The technique has been used on a series of 75 subjects, 60 of whom had TMJ dysfunction. Total acquisition time was 7 min. The results confirmed that it is possible to obtain pseudo-cinematic TMJ images suitable for clinical diagnosis by optimizing the choice of receiver and capture parameters.

Evaluation Studies as Topic↗
PubMed1993

1H nuclear magnetic resonance studies of seminal plasma from fertile and infertile men.

Glycerylphosphorylcholine (GPC), glycerylphosphorylethanolamine (GPE), citrate, and lactate content of human seminal plasma was analysed by measuring the peak area of 1H nuclear magnetic resonance (NMR) spectra in samples from four groups of patients: 21 spermatogenic failure subjects; 14 obstructive azoospermic subjects (vasectomized); seven patients presenting very severe oligoasthenozoospermia (OAT) and 18 normozoospermic subjects (control). The peak areas for GPC, citrate and lactate in seminal plasma were significantly smaller for patients with azoospermia than for the control group: 16.79, 8.18 and 2.28 versus 23.38, 10.58 and 4.30, respectively (P < 0.01). The peak area ratios for citrate:lactate and GPC:lactate were significantly different (P < 0.01) between the control group and the spermatogenic failure or obstructive azoospermia groups. A significant difference was also found in GPE:GPC peak intensity ratio between spermatogenic failure and obstructive azoospermia subjects (P < 0.001). These results provide some quantitative markers which may be used for examining infertility by using 1H NMR of seminal plasma samples.

Biomarkers↗
PubMed1993

[Investigation of seminal plasma. Value of nuclear magnetic resonance].

The purpose of this study was to investigate whether the measurement by NMR of some biochemical markers such as glycerylphosphorylcholine (GPC), glycerylphosphorylethanolamine (GPE), citrate, and lactate in human seminal plasma may be able to differentiate spermatogenic failure from obstructive azoospermia. The peak area ratios citrate/lactate, between normozoospermic and spermatogenic failure or obstructive azoospermia groups were significantly different. We have also found significant differences in GPE/GPC peak intensity ratio between spermatogenic failure men and obstructive azoospermia patients (P < 0.001). This ratio appears to be a very important parameter to differentiate spermatogenic failure from obstructive azoospermia. These results demonstrate the potential use of 1H NMR on human seminal plasma in male infertility evaluation and such analysis may be used to elucidate the molecular basis of the human pathologic seminal plasma disturbances.

Anticoagulants↗
PubMed1993

Parasagittal magnetic resonance imaging of the lateral pterygoid muscle: a preliminary study.

Ten anatomic territories, including both lateral pterygoid muscle and temporomandibular joint heads, were explored with magnetic resonance imaging in subjects with no dysfunctional disorders. The sequence used was one of inversion-recovery, supplemented with image contrast reversal for better visualization. The muscles were observed in the resting position and in dynamic relation. Slice plane definition provided information on the anatomic variations of the superior head and on the muscle-articular junction, in particular on the fascicular aspect of the superior lateral pterygoid muscle and on the differentiation between condyle insertions under effort. The choice of technique and the results are discussed. Avenues are opened for the exploration of muscles utilizing magnetic resonance imaging.

Adult↗
PubMed1991

Biochemical events occurring during the respiratory burst of macrophages: A 31P and 13C NMR study.

In a previous study, 31P NMR revealed that an intracellular acidification occurred during the respiratory burst of P388 D1 macrophages, but this NMR technique could not provide information about the localization of this event in cells. However, using a fluorescent pH-dependent probe, it was confirmed that this transient pH decrease does not occur in the cytosol but more probably occurs in relation to the function of endocytic vesicles. A 31P NMR study allowed us to evidence a transient increase in ADP phosphorylation at the beginning of the respiratory burst, possibly in connection with the initiation of the oxidase complex involved in superoxide anion production. A 13C NMR study of perchloric acid extracts from in vivo primed cells revealed an increase in glucose consumption due to Con A triggering. Sugar phosphates, which must be considered markers of the hexose monophosphate shunt involved in the respiratory burst, were also observed upon this activation process.

Adenosine Diphosphate↗
PubMed1989

Calcium and spermine interaction with phospholipid bilayers: a 15N NMR study.

The binding of Ca2+ to membrane models composed of diplamitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE) 15N-labeled in the polar head group was investigated at pH 8.5 and pH 9.4 by 15N-NMR spectroscopy. Both phospholipids exhibit a decrease in the chemical shift anisotropy, indicating changes of the order parameter of the C-N bond and decrease in half-height width. Binding of Ca2+ induces a chemical shift change for the DPPE signal which indicates a decrease in the pKa of the amino group. The binding of spermine was also investigated for mixed phase (DPPC/DPPE) at pH 8 and pH 9.4; a decrease in the DPPE pKa was also noted. The signals of both phospholipids are broadened and the line shapes are more complex because of the lower mobility and the higher steric bulk of this molecule. The results show the value of 15N-NMR in the study of mixed liposomes and indicate that the deprotonation of membrane surface could constitute a necessary step for fusion processes.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

Gd-25 DTPA-MAb, a potential NMR contrast agent for MRI in the xenografted nude mouse: preliminary studies.

Monoclonal antibodies (MAbs) 19-9 and 73-3 specific for human colon adenocarcinoma were labelled with a high number of gadolinium atoms. Twenty five DTPA were chelated per MAb, with only slight loss of immunoreactivity. The NMR contrast agent Gd-25 DTPA-MAb 19-9 or 73-3 ([Gd] 17 mumole/kg, [MAb] 60 microM) was injected into nude mice bearing human colon adenocarcinoma (SW948). Tumours were removed 24 hr after injection and T1 was measured in vitro. T1 relaxation time varied according to MAb specificity against tumour targets; T1 decreased 20% for MAb 19-9 and MAb 73-3 with SW948 tumour. Imaging was performed with this model. Very good contrast was obtained 24 hr after Gd-25 DTPA-MAb injection.

Animals↗