Abstract
PurposeTo present an improved three‐dimensional (3D) interleaved phase sensitive inversion recovery (PSIR) sequence including a concomitantly acquired new contrast, null point imaging (NPI), to help detect and classify abnormalities in cortical gray matter.MethodsThe 3D gradient echo PSIR images were acquired at 0.6 mm isotropic resolution on 11 multiple sclerosis (MS) patients and 9 controls subjects using a 7 Tesla (T) MRI scanner, and 2 MS patients at 3T. Cortical abnormalities were delineated on the NPI/PSIR data and later classified according to position in the cortex.ResultsThe NPI helped detect cortical lesions within the cortical ribbon with increased, positive contrast compared with the PSIR. It also provided improved intrinsic delineation of the ribbon, increasing confidence in classifying the lesions' locations.ConclusionThe proposed PSIR facilitates the classification of cortical lesions by providing two T1‐weighted 3D datasets with isotropic resolution, including the NPI showing cortical lesions with clear delineation of the gray/white matter boundary and minimal partial volume effects. Magn Reson Med 76:1512–1516, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Highlights
Cortical lesions, for instance in multiple sclerosis (MS), and other cortical abnormalities are difficult to distinguish with MRI, due to the need to provide threedimensional (3D) coverage of the whole cortex with isotropic high spatial resolution, and to provide high contrast between gray matter (GM) and white matter (WM) as well as within the cortex
The phase sensitive inversion recovery (PSIR) sequence is an inversion recovery sequence which acquires an image in which GM and WM have equal and opposite signals [i.e., equal signals in the unsigned magnitude image, or null point image (NPI] (3), and the resulting PSIR image is reconstructed by phase correcting the null point imaging (NPI) to give a signed dataset with double the dynamic range
Mixed GM/WM (Figure 3 green arrows) and juxta cortical WM lesions (Figure 3, blue arrows) were more detected on PSIR than NPI due to the dark appearance of the lesions within WM, and GM involvement in mixed GM/WM lesions was easy to detect on NPI images (Figs. 3i,j,l)
Summary
For instance in multiple sclerosis (MS), and other cortical abnormalities are difficult to distinguish with MRI, due to the need to provide threedimensional (3D) coverage of the whole cortex with isotropic high spatial resolution, and to provide high contrast between gray matter (GM) and white matter (WM) as well as within the cortex. This study presents a combination of the T1 weighted phase sensitive inversion recovery (PSIR) sequence (1,2) and MP2RAGE (two inversion-contrast magnetization-prepared rapid gradient echo sequence) sequence, aimed at improving detection of GM abnormalities. PSIR (4) has been shown to improve classification of cortical lesions (1,2) by increasing the T1-weighting in the images. At two different inversion times, and was introduced to provide T1-weighted images of the brain with increased contrast-to-noise ratio (CNR). We combined these approaches by using MP2RAGE to acquire two images, the NPI and a fully recovered image (Fig. 1), to produce a PSIR with 3D isotropic coverage and simplified phase correction and bias field correction. We describe a series of simple but significant modifications to PSIR to increase its value in detecting and classifying cortical abnormalities, including making use of the NPI
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