MRI in France: the French paradox.

Although France is a modern, developed country, which spends nearly 10% of the gross national product on healthcare and has a highly praised level of medicine, the number of modern imaging scanners, such as CT (595), MRI (182), and PET (5), is quite low when compared to other European countries. Politics and a long-standing tradition of centralization are prominent among reasons for such an underdevelopment. This situation has resulted in another French paradox not linked to wine consumption. The French life expectancy is very high, but the number of imaging equipment is very low.

[Marketing of MRI in the world]. / Diffusion de l'IRM dans le monde.

The authors are recalling the main tendancies of the medical imaging world market before studying MRI diffusion in the 3 great sectors, USA, Europe and Japan. MRI diffusion is highly regulated in Europe but in the 2 other areas the growth of MRI was slower than the CT growth for the same period of time for medical, technological and financial reasons. The market evolution with the uprising of the mid-field niche and industrial offers will be presented.

[The STIR sequence. Comparison with other MRI sequences and scintigraphy in detecting spinal metastases]. / La séquence STIR. Comparison avec les autres séquences IRM et la scintigraphie dans le dépistage des métastases osseuses vertébrales.

A prospective MRI study of the spine comparing short inversion-recovery sequences (STIR)-one the features of which is to potentiate the contrast of both long T1 and T2 sequences-with other spin echo and/or gradient echo MRI sequences, was conducted in 20 patients with suspected vertebral metastases. The features of the signal on STIR sequences were initially defined in 14 healthy volunteers. In the patients, the various MRI sequences were also compared to each other and to standard x-rays and bone scans. The sensitivity of detection of vertebral metastases did not appear to be significantly different between T1 sequences and the STIR sequence. However, these two sequences appeared to be significantly more sensitive than T2-weighted sequences. The STIR sequences therefore appears to be a logical complement to T1-weighted sequences in the detection of vertebral secondaries. This sequence even appears to be superior in the following situations: investigation of the cervical vertebrae, follow-up of irradiated bone, early detection of periduritis and lesions of the posterior arch.

[Post-traumatic paraosteoarthropathy of the hip. Analysis with x-ray computed tomography and 3-dimensional reconstruction. 2 cases]. / Paraostéoarthropathie de hanche post-traumatique. Analyse en TDM et reconstruction 3D. A partir de 2 observations.

Two cases of paraosteoarthropathy developed soon after hip trauma and without associated spinal disorders are described. CT perfectly discriminates ectopic bone formation from osseous fragments and calcified hematoma. These lesions display different signs and have different locations, which allows an easy differentiation. The aetiology of these traumatic osteomas (hip trauma associated with surgical repair in one case coma in the other) is compared to literature. The effectiveness of CT with 3D reconstruction is emphasized in paraosteoarthropathy and hip trauma screening.

[Cerebral MRI in the study of prognostic factors in AIDS. Hypotheses from tests on 15 patients]. / Apport de l'IRM cérébrale à l'étude des facteurs pronostiques du SIDA. Hypothèses à partir de l'examen de 15 patients.

In an attempt to determine factors of predictive value in HIV (human immuno-deficiency virus) seropositive patients, particular attention was payed to symptoms indicating early involvement of the central nervous system (CNS). A cohort of healthy carriers was thus constituted. Follow-up will be carried out every six month including clinical, biological as well as CNS imaging by NMR. Among the first 15 of them, abnormalities could be observed in 4 individuals. Lesions consisted in nodules of high signal in T2 which were localized either in the white matter or thalamic nuclei. No relationship could be demonstrated between the existence of these lesions and various criteria such as age, sex, risk factors and T4 cells count. Such lesions appeared similar to the localizations observed in multiple sclerosis or to the scars of limited vascular accidents. The nature of these lesions is not clear. They certainly indicate early involvement of CNS after primary infection by the HIV virus. They may either represent sequellae of this primary infection or early alterations announcing developing encephalopathy.

[Magnetic resonance imaging: early detection of involvement of the central nervous system in acquired immunodeficiency syndrome]. / Imagerie par résonance magnétique: dépistage précoce des atteintes du système nerveux central au cours du syndrome d'immuno-déficience acquise (SIDA).

Central Nervous System (CNS) involvement, whether primary by the Human Immunodeficiency Virus--HIV--itself, or secondary (toxoplasmosis or lymphoma) is remarkably frequent in AIDS, in 40 to 70% of cases, depending upon the author. In order to study the natural history of this illness, a cohort of 25 asymptomatic seropositive patients have been established. Every 6 months these patients undergo biological and clinical examinations, as well as Magnetic Resonance brain scans. After two examinations at a 6 month's interval, the first results are reported. Out of these 25 cases, 9 present anomalies: One patient with diffuse cerebral atrophy and 8 others with high signal intensity areas on T2 weighted sequences, like those of the Multiple Sclerosis. No relationship could be demonstrated between the existence of these lesions and various criteria such as age, sex, risk factors and T4 cells count. The nature of these lesions is not clear. They certainly indicate early involvement of the CNS after primary infection by the HIV virus. They may either represent scars of the primary infection or early alterations announcing developing encephalopathy.

[How to analyze a nuclear magnetic resonance image. Application to the study of the pelvis]. / Comment lire une image de résonance magnétique. Application á l'étude du pelvis.

Nuclear magnetic resonance (NMR) is based on the behaviour of some atomic nuclei when they are placed in a magnetic field and subjected to radiofrequency waves of a specific length. The resonance signals they emit under such conditions are collected as localized digital data which are used to construct an image. The signals vary according to multiple tissue characteristics, notably proton density, relaxation times T1 and T2 and, where applicable, blood flow direction and velocity. The relative influences exerted by these tissue factors on resonance signals can be evaluated by altering the technical parameters of the examination, that is practically the radiofrequency wave sequence. Special formulae make it possible to predict signal variations and to increase, decrease or even reverse contrast, thus obtaining as many morphological or functional images of the different media in the body. NMR semiology therefore is copious, complex and variable, but a diagrammatic description of the interplay between parameters provides a key to elementary analysis. Images of pelvic structures taken as examples illustrate the necessity to select the exploratory procedure according to the purpose of the exploration or to manipulate sequences with greater safety.