Three-dimensional MP-RAGE--an alternative to conventional three-dimensional FLASH sequences for the diagnosis of viscerocranial tumours?

Abstract

Imaging with three-dimensional (3D) sequences is a frequently used magnetic resonance (MR) technique in the assessment of ear, nose and throat (ENT) tumours near the skull base. Few reports on the contrast behaviour of 3D magnetization prepared rapid gradient echo (MP-RAGE) sequences and their application in ENT tumours exist in the published literature. This paper discusses whether 3D MP-RAGE is an alternative to conventional 3D gradient echo (3D GE) sequences for the diagnostic evaluation of the visceral cranum. Measurements were performed with a Magnetom SP 63 MR system (Siemens) at 1.5 T. 10 healthy volunteers were examined using 3D FLASH sequences with varied flip angles (90 degrees, 70 degrees, 40 degrees, 20 degrees, 10 degrees) and using 3D MP-RAGE to optimize the signal-to-noise ratio (SNR) of muscle, fat and gland tissue. After this optimization 25 patients with ENT tumours near the skull base were examined with 3D FLASH 40 degrees, 3D MP-RAGE 10 degrees (both before and after application of contrast medium) and with 3D FISP 70 degrees (without contrast medium). SNR and contrast-to-noise ratio (CNR) of tumour, inflammatory disease, brain (white and grey matter), compact bone, fat and muscle were calculated. The advantages of 3D MP-RAGE over 3D FLASH 40 degrees include decreased imaging time with decreased motion artifacts and a relatively high contrast between tumour and surrounding tissues. The tissue contrast yielded by the T1/T2* weighted 3D gradient echo sequence FISP with a flip angle of 70 degrees was not as good as that yielded by 3D MP-RAGE with and without contrast together. In conclusion a combination of contrast enhanced and unenhanced 3D MP-RAGE sequences is the technique of choice for the examination of ENT tumours near the base of the skull.