This work presents a new method for localized T1 measurements, based upon the OSIRIS scheme. It relies on the use of a non-selective 180 degrees pulse applied before the OSIRIS preparation cycle. The accuracy of the method has been verified with test tubes and in vivo for two nuclei, 1H and 19F. The accuracy of the T1 values is discussed, as well as possible applications of the inversion-recovery method to non-invasive in vivo pO2 measurements.

Animals↗

PubMedDate not supplied

Susceptibility-based MRI contrast of the CSF by intravascular superparamagnetic nanoparticles.

Endorem, a suspension of superparamagnetic iron oxide dextran nanoparticles (NP), have been injected intravenously to healthy anesthetized rats for the purpose of contrast enhancement of brain in gradient-echo imaging at 200 MHz. Not only gray and white matter but also particular regions of the cerebrospinal fluid (CSF) were contrasted in sagittal and transverse images, although samples of this fluid did not contain NP. The selected contrast in the CSF would result form the ability of dense vascular beds containing highly magnetized particles to induce a remote susceptibility effect far beyond the vascular walls into a large fraction of extravascular water.

Animals↗

PubMedDate not supplied

TO5 as a magnetization transfer contrast test object: characterization of the gels and determination of the real magnetization transfer.

Following the work of the European concerted action, "Tissue characterization by magnetic resonance spectroscopy and imaging," sets of five test objects (TO) were designed, produced, and distributed among European laboratories. The TO were designed to control the image quality of clincial magnetic resonance imaging in an independent and uniform mode. The fifth test object (TO5) was devoted to relaxation measurements and composed of 18 agarose tubes, inserted in an holder filled with a CuSO4 solution. These gels are subject to magnetization transfer (MT). The purpose of this paper is to characterize their MT parameters. An individual study of each gel was performed in a spectrometer, and an individual fit, as well as a global fit, was done on the two-pool model. The MT parameters found in each case are in agreement with the known properties of the agarose gels and given below. The real MT (transfer of magnetization from water to macromolecules) was computed, taking into account the "bleeding over" (direct saturation of the water magnetization). The maximum real MT ranges from 15 to 35% and can be obtained with almost the same saturation pulse conditions for all the gels. However, the saturating field required to reach the maximum MT is very high (46 microT) and unserviceable on a clinical device.

Biometry↗

PubMedDate not supplied

Filtered backprojection and spectral width of MR signal.

Reconstructed images obtained by filtered backprojection are altered when the projections are distorted by an attenuation of the high frequency components of the demodulated magnetic resonance (MR) signal. This attenuation occurs if the spectral width of the MR signal is reduced by the bandwidth of the receiver radiofrequency coil as well as by the use of imperfect refocusing pulses. This signal spectrum has to be wide when the sampling bandwidth is wide, because the sampling time is very short, for instance in the case of very short interpulse delay such as 6 ms. A short interpulse delay is needed when many images are required, to enable the transverse magnetization decay of each pixel to be recorded accurately. This paper presents an analysis of backprojection reconstruction for such a case and demonstrates a contamination of each pixel by surrounding pixels. The consequence on the results of T2 measurement and biexponential decomposition of transverse magnetization decay curves are discussed. A method for correction of such artifacts is described.

Image Enhancement↗

PubMedDate not supplied

Evaluation of RARE-MR urography in the assessment of ureterohydronephrosis.

OBJECTIVE: The goal of this prospective study was to evaluate the value of the fast imaging sequence called RARE-MR urography (RMU) for the diagnosis of ureterohydronephrosis. MATERIALS AND METHODS: Sixty-nine patients underwent this procedure. The results were compared with those obtained by intravenous urography (IVU) and ultrasonography (US). RESULTS: The accuracy of RMU in the detection of urinary tract dilatation and the localization of the level of obstruction was excellent (100%). The determination of the type of obstruction, intrinsic versus extrinsic, was 80% by IVU and 60% for RMU. The RMU sequence alone could not specify the nature of the obstruction. Functional information about the obstructed collecting system could not be obtained. CONCLUSION: The RMU technique may be considered in the following circumstances: contraindications to IVU (allergy to contrast medium, severe renal failure), impairment of renal excretion, and failure to locate the level of obstruction by US. The absence of ionizing radiations favors the promotion of this procedure to study ureterohydronephrosis during pregnancy.

Adult↗

PubMedDate not supplied

Technique for MRI of ocular motility.

Our goal was to improve existing MR methods used in the assessment of ocular motility in the horizontal gaze direction, by using high resolution 20 s images and an experimental setup that prevents physiologically induced head motion in patients and eye convergence to the fixation point, thus improving the analysis of the relationships between the eyeball and the right muscle bellies in horizontal gaze exploration. The method has potential clinical applications for the diagnosis and/or follow-up of complex strabismus.

Eye Movements↗

PubMedDate not supplied

Changes in serum testosterone levels after myocardial infarction.

To evaluate the effect of a severe non-endocrine disease on testosterone levels we determined the total testosterone (T), free testosterone (fT), myoglobin and myosin plasmatic levels in 18 men at the time of hospitalization for acute myocardial infarction (AMI), and 1, 3, 7 and 21 days later. Five different methods for determining fT were applied and compared; 1) radioimmunoassay after ultrafiltration, 2) direct analogue based radioimmunoassay (RIA), 3) calculation from total T, sex-hormone-binding globulin (SHBG) and albumin concentrations, 4) calculation from total T, SHBG concentrations with albuminemia fixed at 40 g/L, and 5) evaluation by the (total T)/(SHBG) ratio (fT index). After AMI the total T and fT decreased rapidly (minimum at day 1) and then increased until day 21. While a lower sensitivity in detecting small changes was noted for the direct analogue based fT RIA and for the calculation using a fixed albuminemia, the evolving pattern of the 5 different fT determinations was similar despite different absolute values. However, there was a wide scattering in the results from the different methods used to determine fT. Compared to ultrafiltration, the fT values were lower by direct analogue based assay and higher by calculation. There was a trend of correlation between changes in total T and the maximum myosin concentration (r = 0.557, p = 0.02), showing a relationship between the hormonal changes and the severity of the myocardial infarction.

Adult↗

PubMedDate not supplied

[Diagnostic elements of a right papyraceous ventricle. The value of nuclear magnetic resonance].

We are reporting the case of a young man presenting repeated syncopes linked to episodes of ventricular tachycardia. The rhythm disorders were due to the existence of a papyraceous right ventricle with concomitant involvement of the left ventricle disclosed during the etiological work-up. We are reporting, at this time, the usual diagnostic elements of this disease, but mostly original data provided by the nuclear magnetic resonance, as the clinical examination and the EKG are often less revealing except for late potentials always found in the arrhythmic form. The right, ventricular dysplasia and the papyraceous right ventricle represent two very close entities. Particular characteristics enable to differentiate them and also the differential diagnosis with other diseases are discussed by stressing the advantage of magnetic resonance imaging, a new method, non invasive, which lends itself well to the analysis of cardiac morphology.

Adult↗