[Show abstract][Hide abstract] ABSTRACT: Cortical lesions have recently been a focus of multiple sclerosis (MS) MR research. In this study, we present a white matter signal attenuating sequence optimized for cortical lesion detection at 7 T. The feasibility of white matter attenuation (WHAT) for cortical lesion detection was determined by scanning eight patients (four relapsing/remitting MS, four secondary progressive MS) at 7 T. WHAT showed excellent gray matter-white matter contrast, and cortical lesions were hyperintense to the surrounding cortical gray matter, The sequence was then optimized for cortical lesion detection by determining the set of sequence parameters that produced the best gray matter-cortical lesion contrast in a 10-min scan. Despite the B1 inhomogeneities common at ultra-high field strengths, WHAT with an adiabatic inversion pulse showed good cortical lesion detection and would be a valuable component of clinical MS imaging protocols.
Full-text · Article · May 2012 · Magnetic Resonance Imaging
[Show abstract][Hide abstract] ABSTRACT: Magnetic resonance imaging of cortical lesions due to multiple sclerosis (MS) has been hampered by the lesions' small size and low contrast to adjacent, normal-appearing tissue. Knowing cortical lesion T1 and proton density (PD) would be highly beneficial for the process of developing and optimizing dedicated magnetic resonance (MR) sequences through computer modeling of MR tissue responses. Eight patients and seven healthy control subjects were scanned at 7 T using a series of inversion recovery turbo field echo scans with varying inversion times. Regions of interest were drawn in white matter, gray matter, cortical lesions, white matter lesions and cerebrospinal fluid. White matter and gray matter T1s were significantly higher in MS patients than in controls. Cortical and white matter lesion T1 and PD are also presented for the first time. The advantages of ultrahigh field MR imaging will be important for future investigations in MS research and sequence optimization for the detection of cortical lesions.
Full-text · Article · Sep 2011 · Magnetic Resonance Imaging
[Show abstract][Hide abstract] ABSTRACT: To develop a protocol which optimizes contrast, resolution and scan time for three-dimensional (3D) imaging of the human eye in vivo using a 7 Tesla (T) scanner and custom radio frequency (RF) coil.
Initial testing was conducted to reduce motion and susceptibility artifacts. Three-dimensional FFE and IR-TFE images were obtained with variable flip angles and TI times. T(1) measurements were made and numerical simulations were performed to determine the ideal contrast of certain ocular structures. Studies were performed to optimize resolution and signal-to-noise ratio (SNR) with scan times from 20 s to 5 min.
Motion and susceptibility artifacts were reduced through careful subject preparation. T(1) values of the ocular structures are in line with previous work at 1.5T. A voxel size of 0.15 x 0.25 x 1.0 mm(3) was obtained with a scan time of approximately 35 s for both 3D FFE and IR-TFE sequences. Multiple images were registered in 3D to produce final SNRs over 40.
Optimization of pulse sequences and avoidance of susceptibility and motion artifacts led to high quality images with spatial resolution and SNR exceeding prior work. Ocular imaging at 7T with a dedicated coil improves the ability to make measurements of the fine structures of the eye.
Full-text · Article · Nov 2009 · Journal of Magnetic Resonance Imaging
[Show abstract][Hide abstract] ABSTRACT: PURPOSE
To identify and characterize cortical lesions in patients with multiple sclerosis using 7T ultrahigh resolution Susceptibility Weighted Images (SWI) and White Matter Attenuation (WHAT) imaging.
METHOD AND MATERIALS
Five patients were scanned using a 7T scanner (Philips Achieva, Cleveland, OH). Optimized WHAT and SWI sequences were acquired with voxel sizes 0.4x1.0x1.4 mm3 for the WHAT sequence, and 0.23x0.32x1.4 mm3 for the SWI sequence. The SWI images were post-processed to give magnitude and phase. In addition, pre- and post-contrast T1-weighted IR-TFE images were acquired with 0.50x0.55x1.4 mm3 for two patients.
The WHAT sequence provided excellent contrast between gray and white matter. White matter lesions were readily identifiable due to different intrinsic T1. Cortical lesions had lower contrast to gray matter, but nevertheless were identified in the WHAT images. In the corresponding SWI magnitude and phase images, the cortical lesions could also be identified. A greater amount of structural detail was visible in the SWI, compared to the WHAT image. In some cases, small veins draining cortical lesion were seen enhanced on post-contrast T1.
Both WHAT and SWI sequences provided valuable information in identifying and characterizing cortical lesions. Cortical lesions were more readily seen in the WHAT images, whereas the structure was more evident in the SWI phase images. In our ongoing study comparing histopathology with MRI, lesion structure seen on SWI was demonstrated to correlate with the presence of iron-loaded microglia.
Recent studies indicate that cortical lesion load may correlate better with clinical outcome than white matter lesion burden, thus tools for better depiction of cortical lesions are needed.