Rapid, high-resolution, whole-brain, susceptibility-based MRI of multiple sclerosis.

BACKGROUND: Susceptibility-based MRI offers a unique opportunity to study neurological diseases such as multiple sclerosis (MS). In this work, we assessed a three-dimensional segmented echo-planar-imaging (3D-EPI) sequence to rapidly acquire high-resolution T2 -weighted and phase contrast images of the whole brain. We also assessed if these images could depict important features of MS at clinical field strength, and we tested the effect of a gadolinium-based contrast agent (GBCA) on these images. MATERIALS AND METHODS: The 3D-EPI acquisition was performed on four healthy volunteers and 15 MS cases on a 3T scanner. The 3D sagittal images of the whole brain were acquired with a voxel size of 0.55 × 0.55 × 0.55 mm(3) in less than 4 minutes. For the MS cases, the 3D-EPI acquisition was performed before, during, and after intravenous GBCA injection. RESULTS: Both T2-weighted and phase-contrast images from the 3D-EPI acquisition were sensitive to the presence of lesions, parenchymal veins, and tissue iron. Conspicuity of the veins was enhanced when images were obtained during injection of GBCA. CONCLUSIONS: We propose this rapid imaging sequence for investigating, in a clinical setting, the spatiotemporal relationship between small parenchymal veins, iron deposition, and lesions in MS patient brains.

Hepatic MR imaging with a dynamic contrast-enhanced isotropic volumetric interpolated breath-hold examination: feasibility, reproducibility, and technical quality.

PURPOSE: To evaluate the feasibility, reproducibility, and technical quality of a dynamic contrast material-enhanced isotropic three-dimensional (3D) volumetric interpolated breath-hold hepatic magnetic resonance (MR) imaging examination. MATERIALS AND METHODS: Fifty patients underwent 3D spoiled gradient-echo imaging (4.2/1.8 [repetition time msec/echo time msec]; flip angle, 12 degrees; interpolation in three directions; intermittent fat saturation; pixel size

Water excitation MPRAGE MRI of VII and VIII cranial nerves.

OBJECTIVE: Our goal was to compare magnetization prepared rapid gradient echo--water excitation (MRPRAGE-WE) with conventional spin echo (CSE) in the evaluation of the VII and VIII cranial nerves. METHODS: One hundred three consecutive patients with symptoms referable to the VII/VIII nerves were studied with CSE T1 and MPRAGE-WE following intravenous gadolinium contrast agent. Each right and left nerve pair was independently evaluated for the presence of an enhancing mass and for visualization of the nerves. RESULTS: On the CSE images, 26 definite and 2 possible lesions were identified, whereas 28 definite and 2 possible abnormalities were seen on the MPRAGE-WE. Four cases were better identified on the MPRAGE-WE and one better seen on the CSE. This difference was not statistically significant (p = 0.19). CSE demonstrated the nerves partially in 23 instances and completely in 6; MPRAGE-WE showed the nerves partially in 35 and completely in 73. This was highly significant (p<0.001). CONCLUSION: With equivalent or slightly improved lesion detection and better visualization of the nerves, MPRAGE-WE may replace CSE in studying the VII/VIII nerves.

Improved detectability in low signal-to-noise ratio magnetic resonance images by means of a phase-corrected real reconstruction.

We show that for magnetic resonance (MR) images with signal-to-noise ratio (SNR) less than 2 it is advantageous to use a phase-corrected real reconstruction, rather than the more usual magnitude reconstruction. We discuss the results of the phase correction algorithm used to experimentally verify the result. We supplement the existing literature by presenting closed form expressions (in an MR context) for the probability distribution and first moments of the signal resulting from a magnitude reconstruction.

Regional T2 and sodium concentration estimates in the normal human brain by sodium-23 MR imaging at 1.5 T.

We have analyzed multiple spin echo Na magnetic resonance (MR) images of the normal human brain in four volunteer subjects. Utilizing the much slower T2 decay of the CSF, we obtained images that separate cortex from the surrounding CSF and measured regional T2 of cortex, white matter, CSF, vitreous humor, and superior sagittal sinus. Assuming a sodium concentration of 145 mM in the vitreous humor, we normalized the extrapolated equilibrium magnetization (M0) for each region to the M0 of the vitreous humor to estimate regional sodium concentration. We found that regional T2 measurements more consistently distinguish the high signal regions of cortex, CSF, and blood than do our regional sodium estimates, whereas regional sodium estimates adequately distinguish white matter from cortex. The T2 values of white matter and cortex, on the other hand, are nearly identical. Our work addresses the problems encountered in establishing norms for clinical application of Na MR and represents a step toward establishing those norms.

Multiple short-echo (2.5-ms) quantitation of in vivo sodium T2 relaxation.

The MR behavior of the sodium-23 nucleus in vivo is a complex problem which has generated considerable interest over the last 20 years. Early studies on excised tissue samples revealed that the sodium nucleus exhibited a two-component T2 relaxation. This biexponential T2 relaxation was characterized by a short component with a T2 = 0.7-4.8 ms, and a long component with a T2 = 7.0-26.0 ms. We have developed a 3D pulse sequence capable of performing multiple Hahn echo in vivo sodium-23 imaging at echo times as short as 2.5 ms. This sequence obtains the shorter spin echo times by presaturating the spins outside of the desired imaging region, allowing the use of nonselective rf pulses. Using this sequence we have been able to quantify the long and short T2 components of normal brain tissue, vitreous humor of the eye, and a rabbit VX-2 carcinoma. We found that gray matter and white matter of normal brain have a monoexponential T2 relaxation with T2 = 17.6 +/- 2.4 ms. The vitreous humor T2 relaxation is also monoexponential with T2 = 56.8 +/- 2.1 ms. However, we find that some of the rabbit VX2 carcinomas exhibit a biexponential T2 decay with a short component of 3.3 +/- 4.6 ms and a long component of 22.0 +/- 9.0 ms.

Pulse sequence generated oblique magnetic resonance imaging: applications to cardiac imaging.

A pulse sequence procedure for producing oblique magnetic resonance images is described. Using this procedure we present a new, accurate method to obtain true short-axis views and true long-axis views (both parallel and perpendicular to the septal plane) of the heart. The method is accurate regardless of the orientation of patient's heart. The method does not require the patient to be rotated, nor otherwise moved, and does not require any additional hardware. The method is experimentally verified with both human and phantom studies. The phantom study indicates accuracy of approximately 1 degree with a commercial scanner that reports angular measurements to a precision of 1 degree. Application of the short-axis views to measurement of left ventricular volume, and possible advantages of Gauss-Legendre integration for this measurement are discussed. Finally, multiphase oblique cardiac images are presented.