Gadolinium-enhanced MR imaging of normal renal transplants. An evaluation of a T1-weighted dynamic echo-planar sequence.

PURPOSE: To evaluate the potential usefulness of dynamic MR with echoplanar imaging (EPI) in assessing the renal function in patients with renal allografts. MATERIAL AND METHODS: Using a T1-weighted sequence, EPI was performed after injection of a Gd-chelate in 17 patients with normally functioning renal allografts. Time-intensity curves were plotted from the signal intensity (SI) measurements of the cortex and the medulla. RESULTS: The pattern of corticomedullar differentiation (CMD) observed after contrast enhancement was divided into four phases using the T1-EPI. After a rapid decrease in the SI of cortical structures, and a subsequent return to precontrast levels, a gradual fall in the SI of the medulla was observed. The average time between the two periods of signal loss was 60 s. CONCLUSION: This study illustrated the potential use of dynamic T1-EPI to demonstrate contrast-induced CMD in renal allografts.

Cinematic study of temporomandibular joint motion using ultra-fast magnetic resonance imaging.

Magnetic Resonance Images (MRI) of the temporomandibular joint (TMJ) are usually performed to study the opening/closing movements of the mandible and have up to now been pseudodynamic step-by-step images simulating condylar motion by post-processing reconstruction. The aim of this study was: 1. to optimize a TMJ cine-imaging method to give a better clinical result than the step-by-step methods; 2. to develop an ultra-fast MRI Gradient Echo (GE) sequence for this purpose; and 3. to analyze condylar movements in the sagittal, coronal and para-axial planes during border mandibular displacements and chewing. Both TM joints were studied in six asymptomatic volunteers. The method involved a compromise between in-plane resolution, slice thickness, signal-to-noise ratio and time resolution. Routine clinical use was found to be a GE pulse sequence providing three images per second with an isometric voxel resolution of approximately two millimeters in ridge. This did not allow visualization of the disk. Using this sequence enabled real and simultaneous condylar displacement observation in the three planes of space and therefore contributed to a better functional diagnosis of pathologic TMJ motions.

Polylysine-Gd-DTPAn and polylysine-Gd-DOTAn coupled to anti-CEA F(ab')2 fragments as potential immunocontrast agents. Relaxometry, biodistribution, and magnetic resonance imaging in nude mice grafted with human colorectal carcinoma.

RATIONALE AND OBJECTIVES: Immunocontrast agents used for magnetic resonance imaging require antibodies that preserve the immunoreactivity while containing a high number of chelated paramagnetic ions. METHODS: Anti-CEA F(ab')2 fragments were coupled to polylysine-Gd-DOTA and polylysine-Gd-DTPA. A paramagnetic load as high as n = 24 to 28 metal ions per antibody was reached. RESULTS: The immunoreactivity of the gadolinium (Gd)-labeled anti-CEA F(ab')2 immunoconjugates was 80% to 85%. Compared with that of commercial chelates, the relaxivity (R1) increase is as follows: Gd-DTPA < Gd-DOTA < Gd-H2O < PL-Gd-DTPA24-28 < PL-Gd-DTPA24-28 F(ab')2 < PL-Gd-DOTA24-28 < PL-Gd-DOTA24-28 F(ab')2. 1H nuclear magnetic relaxation dispersion data of immunoconjugates showed that the high relaxivity enhancement was the result of a reduction of the molecular tumbling rate. Twenty-four hours after intravenous injection of 50 micrograms (1 mumol Gd/kg) of Gd-labeled immunoconjugates to nude mice grafted with human colorectal carcinoma LS 174T, the tumor uptake was 10% to 15%, resulting in an increase of R1 of up to 15% to 20% versus noninjected mice. No difference was found between PL-Gd-DTPA24-28 F(ab')2 and PL-Gd-DOTA24-28 F(ab')2 immunoconjugates for tumor, liver, and kidney uptake. A high signal intensity of tumor was observed in 50% of the tested mice.

[The evaluation of 3DFT time-of-flight MR-angiography versus angiography in the study of carotid atheromatous lesions with a review of the literature]. / Evaluation de l'angio-MR 3DFT temps-de-vol versus angiographie dans l'exploration de lésions athéromateuses carotidiennes avec revue de la littérature

In 37 patients suspected of having a stroke 71 carotid bifurcations were explored by MR-angiography and by digital angiography the reference technique. A 3D sequence was acquired with the time-of-flight technique, using a transmitter-receiver cranial coil, followed by a strictly receiver Helmoltz coil on a 1 Tesla magnet. Two examiners evaluated the carotid bifurcations and measured the degree of stenosis in terms of diameters, according to the north american symptomatic carotid endarterectomy trial (NASCET). Five classes were established: class 1: normal; class 2: 1 to 29%; class 3: 30 to 69%; class 4: 70 to 99% and class 5: thrombosis. The results obtained in the determination of classes were identical with both coils: the coefficient of correlation with straight angiography were 0.973 with the cranial coil and 0.966 with the Helmoltz coil. Five stenoses were overestimated and classified as Class 3 instead of Class 2. The five stenoses greater than 70% (Class 4) showed a signal-void area at their level, due to severe dephasing induced by turbulences. Finally, there was a false-negative image of occlusion: the high-intensity signal of the thrombus was mistaken for one of flow. The data of our study were in accordance with the excellent results obtained by several authors in the literature, which makes it possible for us to propose this type of examination as a novel mean of investigating bifurcations of carotid arteries. Provided a strict technique is applied, and in addition to carotid bifurcation the Willis' circle and the cerebral parenchyma are explored, MR-angiography can complete the results of Doppler-echo. Standard arteriography could then be reserved to surgical patients and to those with discordant results of MR-arteriography and Doppler echo systems.

Contribution of MR-angiography to the diagnosis and the therapeutic indication and follow-up of intracranial aneurysms.

The purpose of this study was to evaluate MR-Angiography (MRA) in comparison with digital angiography in the diagnosis, therapeutic indication and therapeutic follow-up of cerebral aneurysms. Out of 27 patients explored by angiography and MRA, 17 had aneurysm, 5 had an aneurysm excluded by a detachable balloon, and 5 without aneurysm were used as controls. MRA, performed by the paradoxical enhancement technique, required a 3 DFT acquisition with short TR and TE (40-8 ms) in gradient echo, with a 15 degrees flip angle. Analysis of angiograms and partitions was compared with that of angiography. Sixteen of the 17 aneurysms were found by a study of both angiograms and partitions. The result was doubtful in 1 patient. No false-negative result was recorded. Spasm was always detected, but the neck of the aneurysm was never sufficiently well defined. The quality of angiogram depends on the type of balloon used in the patients treated: only the balloon without metallic index did not induce an artefact. Thus, MRA seems to be useful in the detection of cerebral aneurysms, and the absence of artefact induced by detachable balloons without metallic index could allow a therapeutic follow-up. But for the moment, arteriography remains the reference for pretherapeutic evaluation.