3D gradient echo sequence provides better images in contrast-enhanced imaging of the pituitary gland at 3 T

With the increasing availability of 3 T MRI systems in the clinics, radiologists are getting acquainted with the different image sequences and its superiority over the images obtained by 1.5 T MRI. In comparison with 1.5 T MRI, 3 T MRI has prolonged T1 values, a higher specific absorption rate, increased susceptibility artifacts and magnetic field inhomogeneity. Therefore, it is necessary to optimize organ-specific image acquisition parameters and sequences. It is common practice to acquire postcontrast thin-slice 2D spin echo (SE) T1-weighted images (T1WI) for pituitary lesions. As mentioned by Kakite et al., owing to prolongation of T1 values for 3 T systems, postcontrast 2D-SE T1WI may not enable the correct demarcation or delineation of pituitary microadenoma from surrounding structures. Moreover, 3D gradient echo T1 sequences will have susceptible artifacts and high signal intensity from flowing blood, which may also make image interpretation difficult. The present study compared the image qualities in delineating the borders between pituitary gland and cavernous sinus, cavernous sinus and lesions, lesions and pituitary gland, and other surrounding anatomical structures. The study compared the image qualities in 33 consecutive patients with suspected sellar (pituitary fossa) lesions from May 2008 to March 2009. All patients underwent MRI by a clinical 3 T system (Signa Excite HD; GE healthcare) and postcontrast 3D fast-spoiled gradient echo (FSPGR) recalled acquisition in the steady state and 2D-SE T1WI were obtained. The following parameters were used to acquire the images: coronal 2D-SE (repetition time/echo time [TE]: 550–620/20–21 ms; flip angle [FA]: 90°; matrix: 512 × 256; one excitation; field of view: 21 cm; bandwidth: 122 Hz/pixel; slice thickness: 3 mm with 0.3 mm intersection gap); coronal 3D FSPGR T1WI (repetition time/TE: 9/2 ms; FA: 13°; matrix 512 × 256; one excitation; field of view: 21 cm; bandwidth: 122 Hz/pixel; slice thickness: 1.4 mm without intersection gap). The images of 3D FSPGR were reformatted to match SE T1WI (3 mm thickness and 0.3 mm gap). Approximately half of the patients had 3D FSPGR images obtained first and rest of the patients had 2D-SE T1WI obtained first, following intravenous administration of contrast agents. Two experienced neuroradiologists reviewed and evaluated the images independently for eight different points of interest: The border between the pituitary gland and the cavernous sinus The border between the cavernous sinus and the lesion The border between the pituitary gland and the lesion Visualization of the cranial nerves in the cavernous sinus Visualization of the optic nerve Susceptibility artifact Pulsation artefact Total image quality Except for the first point, 3D FSPGR images demonstrate a significantly higher quality and could demarcate different structures with confidence. The improved interpretations of 3D FSPGR images are due to a short TE, which reduces the pulsation artifacts, and thin-slice imaging, which reduces the partial volume effect; furthermore, FSPGR is less dependent on magnetic field inhomogeneity. However, FSPGR will have disadvantages, such as hyperintensity of the blood vessels, caused by short TE, and magnetic susceptibility effects. The study has the following limitations: optimal FA was not determined for sellar lesions, the authors used an FA that produces optimal contrast-to-noise ratio between gray and white matters; 2D-SE T1WI was acquired as a multislice sequence, which may have degraded the image quality; and 3D FSPGR acquisition was not isotropic. Reformation and multiplanar reconstruction from isotropic 3D images would provide better images, although acquisition time will increase.