Feasibility of single-voxel MRS measurement of apparent diffusion coefficient of water in breast tumors

We report initial results with single voxel spectroscopy (SVS) using diffusion weighting and localization by adiabatic selective refocusing (LASER) in breast tumors to measure the apparent diffusion coefficient of water (ADCw). This is a quick (30 s) and relatively easy method to implement compared with image-based diffusion measurements, and is insensitive to lipid signal contamination. The ADCw and concentration of total choline containing compounds [tCho] were evaluated for associations with each other and final pathologic diagnosis in 25 subjects. The average (+/- SD) ADCw in benign and malignant lesions was 1.96 +/- 0.47 mm(2)/s and 1.26 +/- 0.29 x 10(-3) mm(2)/s, respectively, P< 0.001. Receiver operating characteristic curve analysis showed an area under the curve of 0.92. Analysis of the single voxel (SV) ADCw and [tCho] showed significant correlation with a R(2) of 0.56, P< 0.001. Compared with more commonly used image-based methods of measuring water ADC, SV-ADCw is faster, more robust, insensitive to fat, and potentially easier to implement on standard clinical systems.

Spatially varying steady state longitudinal magnetization in distant dipolar field-based sequences

Sequences based on the distant dipolar field (DDF) have shown great promise for novel spectroscopy and imaging. Unless spatial variation in the longitudinal magnetization, Mz(s), is eliminated by relaxation, diffusion, or spoiling techniques by the end of a single repetition, unexpected results can be obtained due to spatial harmonics in the steady state MzSS(s) profile. This is true even in a homogeneous single-component sample. We have developed an analytical expression for the MzSS(s) profile that occurs in DDF sequences when smearing by diffusion is negligible in the TR period. The expression has been verified by directly imaging the MzSS(s) profile after establishing the steady state.