HIRE (high intensity reduction) - a new CSF suppressed T2-weighted MR imaging sequence

Purpose. The HIRE sequence utilizes the very long T2 value of CSF to suppre ss its high signal contribution in T2-weighted imaging by an image subtract ion technique. Methods. To assess the diagnostic potential of a new dark fluid sequence HI RE (High Intensity REduction) in the diagnostic workup, 20 patients with hi stologically confirmed cerebral gliomas were examined with T2-weighted FSE, T1-weighted SE, fast FLAIR and HIRE using identical scan parameters. In pa tients with enhancing lesions fast FLAIR and HIRE were added to the contras t-enhanced T1-weighted SE images. Images were analyzed in a qualitative and quantitative evaluation. In the qualitative lesion analysis, lesion deline ation and differentiation between enhancing and non enhancing tumor tissue were by two readers. For the quantitative analysis lesion-to-background and lesion-to-CSF contrast and contrast to noise ratios were determined in an region of interest analysis. Results. HIRE achieved a significant reduction of the CSF signal without lo osing the high gray-to-white matter contrast of T2 weighted sequences. In t he quantitative analysis, the contrast ratios of the HIRE were lower compar ed to the FLAIR images due to a relative high background and CSF signal. Af ter the application of contrast media HIRE images revealed a significant si gnal increase in enhancing lesions,which subsequently increased the contras t and contrast-to-noise ratios. In the qualitative analysis, both readers f ound all tumors clearly delineated on HIRE imaging. Compared to T2-weighted FSE the tumor delineation with HIRE was better in nine patients, equal in four patients and less in one patient. Compared to the FLAIR images HIRE wa s rated superior in three patients, equal in nine patients and inferior in another three patients. Delineation of the enhancing tumor parts was possib le with HIRE in all patients. HIRE images present significant less image ar tifacts than FLAIR images due to reduced inflow effects. Conclusions. The presented T-2 based HIRE sequence is an alternative to the T-1 based FLAIR sequence with the advantage of a better gray to white matt er contrast and shorter measurement time. Due to the subtraction technique signal intensities from tissues with T2 relaxation times in the range betwe en white matter and CSF are also partially affected depending on their T-2 values. With respect to this undesired effect, an improvement in HIRE imagi ng will be expected by a self-weighted subtraction algorithm.