Human breast lesions: characterization with proton MR spectroscopy.

PURPOSE: To assess the clinical usefulness of spatially localized hydrogen-1 magnetic resonance (MR) spectroscopy in distinguishing benign from malignant lesions on the basis of total choline levels. MATERIALS AND METHODS: These studies were performed at 1.5 T with a four-channel multicoil that compresses the breast sagittally. Contrast material-enhanced MR imaging and single-voxel H-1 MR spectroscopy were performed in 17 patients (age range, 25-68 years) who had nonspecific mammographic findings. Histopathologic correlations were made from biopsy or surgical specimens. Ten patients had various malignant breast lesions 1-4 cm in diameter, and seven patients had benign processes. RESULTS: Most studies were performed with nominal voxel sizes (< 2 cm3). Spectra obtained with an echo time of 31 msec showed resonances from water and mobile fatty acids and, in some cases, the N-trimethyl resonance of choline-containing compounds (Cho) at 3.2 ppm. The absolute concentration of Cho in each lesion was determined with a phantom containing 1 mmol/L Cho as an external reference. On the basis of reference measurements, the least detectable level of Cho was 0.2 mmol/L. With this threshold, seven of 10 malignant lesions showed detectable levels of Cho. In contrast, Cho was seen in only one patient with an extremely rare benign process, a tubular adenoma. The remaining six patients with benign processes demonstrated no detectable Cho levels. CONCLUSION: Spatially localized H-1 MR spectroscopy can provide sufficient sensitivity and spectral resolution at 1.5 T to demonstrate Cho in human breast lesions with a spectroscopic protocol that provides up to 1-cm3 resolution. Determining the presence of Cho may provide a useful test for malignancy.

Segmentation of MRS signals using ASPECT (analysis of SPectra using Eigenvector Decomposition of Targets).

Efforts to minimize the effects of partial volume contamination (PVC) in in vivo magnetic resonance spectroscopy (MRS) have focused upon improving the sensitivity and efficiency of spatially localized MRS measurements. Such improvements may improve spatial resolution and reduce the time required to acquire multiple spectra, however, PVC can affect in vivo spectra at any resolution. In this paper, a model for segmenting in vivo MRS signals compromised by PVC in selected applications is introduced. The segmentation algorithm used is linear and is based on filters originally developed for image processing applications. The model is developed from first principles and evaluated using computer simulations. It is suited for segmenting multivoxel or chemical shift imaging data, and can be used with spectra acquired at any spatial resolution. It is used to estimate the size of the partial volumes contributing to a voxel compromised by PVC and the spatially selective signal components that would be expected to arise from these partial volumes if they could be measured directly. Several spectral perturbants present in in vivo MRS measurements violate the linearity assumptions underlying the model and produce systematic errors that must be accounted for. A number of perturbants are discussed, and the potential in vivo applications of the model are illustrated using solvent-suppressed 1H-CSI spectra from the normal human brain.

Correction of phase effects produced by eddy currents in solvent suppressed 1H-CSI.

Accurate phasing of MRS spectra is often difficult unless time varying phase effects produced by gradient-induced eddy currents that persist during data acquisition are eliminated. This effect is particularly problematic in 1H-CSI spectra where frequency shifts produced by static field inhomogeneity and phase shifts produced by eddy currents combine. In this paper we present a method that corrects both shifts and eliminates manual phasing of individual CSI spectra typically required to recover a pure absorption line shape. The method uses a time domain phase correction derived from the ambient water signal acquired under identical conditions (i.e., acquisition parameters, gradient sequence) as the solvent-suppressed CSI data. Results from CSI experiments on phantoms and in vivo solvent suppressed 1H-CSI spectra from normal human brain are presented demonstrating the capabilities of the technique.

Predominantly extraaxial astroblastoma: imaging and proton MR spectroscopy features.

The CT, angiographic, MR, and proton MR spectroscopy findings in a case of astroblastoma, a rare neoplasm of glial cell origin, are presented. Of particular interest is the predominantly extraaxial location of the tumor. CT and MR demonstrated a complex mass consisting of a solid nodule and a peripheral septated cystic component. The extraaxial nature of the mass was suggested on MR.

A fast and accurate algorithm for volume determination in MRI.

The determination of volumes in clinical MRI studies are prohibitive because of the time required to compute an accurate volume. Techniques that speed up the calculation are prone to large errors which make most impractical for an accurate diagnosis. A linear filter, called the eigenimage filter, has been developed that separates a desired feature from other features which interfere with its observation in an image. Using the images produced by this technique (eigenimages), the amount of operator interaction required to calculate volumes are significantly reduced. The technique also has the ability to correct for partial volume averaging effects and as a result a more accurate volume can be determined. The technique was applied to a computer simulation and two phantom studies. The time required to calculate the volume was less than 1 min per slice and the errors in accuracy and reproducibility were less than 2% for all studies.