[HIRE (high intensity reduction). New cerebrospinal fluid suppressed T2-weighted imaging sequence]

The HIRE sequence utilizes the very long T2 value of CSF to suppress its high signal contribution in T2-weighted imaging by an image subtraction technique.

To assess the diagnostic potential of a new dark fluid sequence HIRE (High Intensity REduction) in the diagnostic work-up, 20 patients with histologically confirmed cerebral gliomas were examined with T2-weighted FSE, T1-weighted SE, fast FLAIR and HIRE using identical scan parameters. In patients with enhancing lesions fast FLAIR and HIRE were added to the contrast-enhanced T1-weighted SE images. Images were analyzed in a qualitative and quantitative evaluation. In the qualitative lesion analysis, lesion delineation 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.

HIRE achieved a significant reduction of the CSF signal without loosing the high gray-to-white matter contrast of T2 weighted sequences. In the quantitative analysis, the contrast ratios of the HIRE were lower compared to the FLAIR images due to a relative high background and CSF signal. After the application of contrast media HIRE images revealed a significant signal increase in enhancing lesions, which subsequently increased the contrast and contrast-to-noise ratios. In the qualitative analysis, both readers found 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 was rated superior in three patients, equal in nine patients and inferior in another three patients. Delineation of the enhancing tumor parts was possible with HIRE in all patients. HIRE images present significant less image artifacts than FLAIR images due to reduced inflow effects.

The presented T2 based HIRE sequence is an alternative to the T1 based FLAIR sequence with the advantage of a better gray to white matter contrast and shorter measurement time. Due to the subtraction technique signal intensities from tissues with T2 relaxation times in the range between white matter and CSF are also partially affected depending on their T2 values. With respect to this undesired effect, an improvement in HIRE imaging will be expected by a self-weighted subtraction algorithm.