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Neuroradiology (2006) 48:881885 DOI 10.1007/s00234-006-0145-5
DIAGNOSTIC NEURORADIOLOGY
Utility of fat-suppressed FLAIR and subtraction imaging in detecting meningeal abnormalities
Alexander McKinney & Chris Palmer & James Short &
Leandro Lucato & Charles Truwit
Received: 8 June 2006 / Accepted: 16 July 2006 / Published online: 13 September 2006 # Springer-Verlag 2006
Abstract We describe the use of a combination of fat-suppression SPIR (spectral inversion recovery) and subtraction FLAIR imaging to aid in detection of abnormal meningeal enhancement.
Keywords Subtraction . FLAIR . SPIR . Gadolinium . Meningitis
Introduction
FLAIR images have an inherent component of T1-weighting [1] that enables visualization of contrast enhancement, and FLAIR has been shown to be particularly sensitive in detecting leptomeningeal contrast enhancement [24], related to the T1-shortening effect of gadolinium, slow-flowing superficial vessels, and probably even magnetization transfer effects [2]. SPIR imaging can be used in conjunction with FLAIR for fat suppression of signal within the skull base, scalp, cavernous sinus, and orbits [5, 6], and may result in more homogeneous fat suppression than that typically obtained with conventional T1-weighted (T1-W) images, since the inversion time selected relates to the null point (T1 recovery time) of fat, rather than the precessional frequency [7]. Additionally, subtraction techniques, which involve subtracting the precontrast from the
postcontrast image, have been proposed to detect abnormal contrast enhancement on T1-W images underlying hyper-intense hemorrhage [8]. A similar concept could be applied to FLAIR sequences, where fat-suppressed SPIR/FLAIR techniques could help delineate abnormal meningeal enhancement, and the subtraction technique could aid in detection of meningeal enhancement in the midst of underlying sulcal hyperintensities present on noncontrast FLAIR.
Technique and representative cases
A group of 15 patients with a high clinical suspicion for meningitis were studied by 22 MR examinations. Sequences included pre- and postcontrast T1-W gradient echo (flip angle 8090-), and fat-suppressed SPIR/turboFLAIR imaging. Sequences were obtained with 1.5 and 3.0-T magnets, with turboFLAIR sequence parameters: TR/TE/TI 6,500/105/2,000 ms, NEX 2, turbo factor 18, slice thickness 5 mm, gap 1 mm, matrix 256[notdef]256. The patients were not moved between the pre- and postcontrast imaging, facilitated by long intravenous tubing, with a 12 min delay between pre- and postcontrast imaging. SPIR fat suppression added 510 s to the prescan phase, but no additional time during image acquisition. Subtraction...