Application of projection presaturation to localized proton relaxometry

Abstract

In recent years, spatial localization techniques have been combined with pulse spectrometer techniques to measure tissue relaxation times frcm a localized volume in vivo. However, obtaining a high degree of tissue discrimination, e.g., whether a lesion is benign or malignant, by differential localized relaxometry puts a high demand on the accuracy of localization and relaxation-time measurement from the localized region of interest (ROI ). Here, we have modified our previously developed projection presaturation technique to localize a small ROI (typical size ⩽10 mm diameter) accurately by presaturating a relatively large outer volume and then applied it to measure proton relaxation times from the ROI. Results of a phantom study are presented, which show good agreement (within 8%) between the spectrometer and the localized data acquired from a ROI (in the phantom) filled with various concentrations (1–40 mM) of copper sulfate solutions chosen so as to cover a clinical range of T 1 and T 2 values. Since the technique leaves the ROI magnetization untouched during localization, it enables one to acquire multipoint relaxation data of high S N ratio (in a relatively short time) to check the multicompartmental behavior (where appropriate) of a tissue volume, even in the case of short-T 2 species. Furthermore, since the localization is performed by outer-volume suppression, any contamination of ROI data from outside caused by flow or motion, as in a common clinical situation, will automatically be suppressed.