Patrick Le Roux

Very selective suppression pulses for clinical MRSI studies of brain and prostate cancer

Focal three‐dimensional magnetic resonance spectroscopic imaging (3D MRSI) methods based on conventional point resolved spectroscopy (PRESS) localization are compromised by the geometric restrictions in volume prescription and by chemical shift registration errors. Outer volume saturation (OVS) pulses have been applied to address the geometric limits, but conventional OVS pulses do little to overcome chemical shift registration error, are not particularly selective, and often leave substantial signals that can degrade the spectra of interest. In this paper, an optimized sequence of quadratic phase pulses is introduced to provide very selective spatial suppression with improved B1 and T1 insensitivity. This method was then validated in volunteer studies and in clinical 3D MRSI exams of brain tumors and prostate cancer. Magn Reson Med 43:23–33, 2000.

Simplified model and stabilization of SSFP sequences

Abstract Steady-state free precession (SSFP) is used today in a form similar to other rapid sequences like fast spin echo (FSE) where a large longitudinal magnetization is present at the beginning of the train of excitations. This results in a transient behavior which impedes any measurement before the steady state is established. Several solutions have been proposed to stabilize the signals more quickly. Starting from a simplified model of signal generation, and by a suitable change of reference frame, this paper justifies theoretically the linear ramp-up proposed by Nishimura and Vasanawala (p. 301, 8th Annual Proceedings of ISMRM, 2000, Denver). This linear ramp-up can be generalized into a one giving less oscillatory residues. The solution is efficient in the sense that it does not require nutation angles larger than the one used during the stabilized period. Also, this solution is robust because it scales up or down nicely and is thus insensitive to B 1 variations.

High temporal resolution functional MRI using parallel echo volumar imaging

To combine parallel imaging with 3D single‐shot acquisition (echo volumar imaging, EVI) in order to acquire high temporal resolution volumar functional MRI (fMRI) data.

Diffusion tensor imaging of the human optic nerve using a non-CPMG fast spin echo sequence

To investigate the diffusion tensor properties of the human optic nerve in vivo using a non‐Carr‐Purcell‐Meiboom‐Gill (CPMG) fast spin echo (FSE) sequence.

On the application of a non-CPMG single-shot fast spin-echo sequence to diffusion tensor MRI of the human brain

The strong sensitivity of Carr‐Purcell‐Meiboom‐Gill (CPMG) fast spin‐echo (FSE) sequences, such as rapid acquisition with relaxation enhancement (RARE), to the phase of the prepared transverse magnetization means that artifact‐free single‐shot diffusion‐weighted images can currently only be obtained with a 30–50% reduction in the signal‐to‐noise ratio (SNR). However, this phase sensitivity and signal loss can be addressed in FSE sequences that use quadratic phase modulation of the radiofrequency (RF) refocusing pulses to generate a sustained train of stable echoes. Here the first application of such a non‐CPMG single‐shot FSE (ssFSE) sequence to diffusion tensor MR imaging (DT‐MRI) of the human brain is described. This approach provides high SNR diffusion‐weighted images that have little or no susceptibility to poor B0 magnetic field homogeneity and the strong eddy currents typically present in DT‐MRI experiments. Magn Reson Med 48:6–14, 2002.

Rapidly reversible myocardial edema in patients with acromegaly: assessment with ultrafast T2 mapping in a single-breath-hold MRI sequence.

OBJECTIVE The purpose of this study was to use a single-breath-hold T2-mapping MRI sequence to evaluate the reversibility of myocardial edema in patients treated for acromegaly. SUBJECTS AND METHODS Before and after treatment, 15 patients with acromegaly underwent myocardial T2 mapping with an experimental single-breath-hold black-blood fast spin-echo sequence. Myocardial T2 mapping with both a multiple-breath-hold fast spinecho sequence and the experimental sequence also was performed on 14 volunteers. T2 relaxation times were calculated with a standard linear least-squares fit applied to myocardial signal intensity. The T2 relaxation times of patients were compared with those of volunteers and correlated with levels of serum growth hormone and insulinlike growth factor 1. Left ventricular function and mass index were determined with cine MRI. RESULTS T2 values before treatment were higher in patients (71 +/- 12 milliseconds) than in volunteers (55.9 +/- 3.6 milliseconds) (p = 0.0003). These T2 values in patients decreased soon after treatment (57.6 +/- 6.6 milliseconds, p = 0.0007). This reduction correlates with successful reduction of levels of serum growth hormone and insulinlike growth factor 1. In volunteers, myocardial T2 values did not vary significantly between the single-breath-hold sequence and the multiple-breath-hold fast spin-echo sequence. In patients, myocardial mass and left ventricular function did not differ significantly before and after treatment. CONCLUSION Patients with acromegaly have increased myocardial T2 values, which decrease soon after treatment, reflecting reversible myocardial edema. T2 value is more sensitive than left ventricular mass index in the detection of early reversal of acromegalic cardiomyopathy. These results highlight the potential role of MRI in direct assessment of the tissular effects of growth hormone and insulinlike growth factor 1 and in evaluation of the efficacy of treatment.

Use of fast spin echo for phase shift magnetic resonance thermometry.

To propose a modified fast spin echo (FSE) magnetic resonance imaging sequence for MR thermometry, employing the proton resonance frequency (PRF) shift by means of MR phase maps. Despite their obvious advantages of speed and high signal‐to‐noise ratio (SNR), FSE sequences have not until now been used for this purpose due to the restraints imposed by the Carr‐Purcell‐Meiboom‐Gill (CPMG) conditions.

Reproducibility of left ventricular mass measurement using a half‐Fourier black‐blood single‐shot fast spin‐echo sequence within a single breath hold: Comparison with a conventional multiple breath‐hold segmented gradient echo technique in patients

To compare the reproducibility of left ventricular (LV) mass measurements using a black‐blood half‐Fourier single‐shot fast spin‐echo (SSFSE) and a segmented gradient echo magnetic resonance (MR) pulse sequence.

Feasibility study of non Carr Purcell Meiboom Gill single shot fast spin echo in spinal cord diffusion imaging

The fast spin echo (FPE) sequence is sensitive to the phase of the magnetization, hindering its use in procedures such as diffusion imaging. The current solutions to this problem reduce the available signal by one half. We present the first volunteer study of a sequence which does not suffer from this loss of signal while measuring diffusion coefficients.

Slice profile effects on nCPMG SS-FSE: nCPMG Slice Profile Considerations

To determine the effects of the RF refocusing pulse profile on the magnitude of the transverse signal smoothness throughout the echo train in non‐Carr‐Purcell‐Meiboom‐Gill (nCPMG) single‐shot fast spin echo (SS‐FSE) imaging and to design an RF refocusing pulse that provides improved signal stability.