Advances in ultra-high field MRI for the clinical management of patients with brain tumors.
ABSTRACT The last 5 years have seen the number of ultra-high field (UHF; 7 T and beyond) MRI scanners nearly double. Benefits include improved specificity, better sensitivity for signal-starved compounds, and the ability to detect, quantify, and monitor tumor activity and treatment effects. This is especially important in the current climate in which new treatments alter established markers of tumor and the surrounding environment, confounding traditional response criteria.
Intra-tumoral heterogeneity and dramatic improvement in spatial localization have been observed with 7 and 8 T high-resolution T2-weighted and T2*-weighted imaging. This depiction of lesions that were not readily detected at lower field improved the classification of glioma. Sub-millimeter visualization of microvasculature has facilitated the detection of microbleeds associated with long-term effects of radiation. New metabolic markers seen at UHF may also assist in distinguishing tumor progression from treatment effect.
Although progress has been limited by technical challenges, initial experience has demonstrated the promise of 7-T MRI in advancing existing paradigms for diagnosing, monitoring, and managing patients with brain tumors. The success of these systems will depend upon what new information can be gained by UHF, rather than simply improving the quality of the current lower field standard.
- SourceAvailable from: Guadalupe Soria[Show abstract] [Hide abstract]
ABSTRACT: Different strategies have been used to study fiber tract anatomy of the human brain in vivo and ex vivo. Nevertheless, the ideal method to study white matter anatomy is yet to be determined, since it should integrate information obtained from multiple sources. We developed an anatomical method in cadaveric specimens to study the central core of the cerebrum combining the "traditional" white matter dissection with high-resolution 7 Tesla (T) magnetic resonance imaging (MRI) of the same specimen coregistered using a neuronavigation system. Ten cerebral hemispheres were prepared using traditional Klingler's technique. Before dissection, a structural ultra-high magnetic field 7T MRI study was performed on each hemisphere specifically prepared with surface fiducials for neuronavigation. The dissection was then performed from the medial hemispheric surface using the classic white fiber dissection technique. During each step of the dissection, the correlation between the anatomical findings and the 7T MRI was evaluated with the neuronavigation system. The anatomic study was divided in two stages. The diencephalic stage included epithalamic, thalamic, hypothalamic, and subthalamic components. The limbic stage consisted of extending the dissection to complete the Papez circuit. The detailed information given by the combination of both methods permitted us to identify and validate the position of fibers that may be difficult to appreciate and dissect, i.e. the medial forebrain bundle. The correlation of high-definition 7T MRI and the white matter dissection technique with neuronavigation significantly improves the understanding of the structural connections in complex areas of the human cerebrum.Neurosurgery 12/2013; · 3.03 Impact Factor
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ABSTRACT: The adiabatic Shinnar Le-Roux (SLR) algorithm for radiofrequency (RF) pulse design enables systematic control of pulse parameters such as bandwidth, RF energy distribution and duration. Some applications, such as diffusion weighted imaging (DWI) at high magnetic fields, would benefit from RF pulses that can provide greater B1-insensitivity while adhering to echo time and specific absorption rate (SAR) limits. In this study, the adiabatic SLR algorithm was employed to generate 6-ms and 4-ms 180° semi-adiabatic RF pulses which were used to replace the refocusing pulses in a twice refocused spin echo (TRSE) diffusion weighted echo planar imaging (DW-EPI) sequence to create two versions of a twice refocused adiabatic spin echo (TRASE) sequence. The two versions were designed for different trade offs between adiabaticity and echo time. Since a pair of identical refocusing pulses are applied, the quadratic phase imposed by the first is unwound by the second, preserving the linear phase created by the excitation pulse. In vivo images of the human brain obtained at 7 T demonstrate that both versions of the TRASE sequence developed in this study achieve more homogeneous signal in the diffusion weighted images than the conventional TRSE sequence. Semi-adiabatic SLR pulses offer a more B1-insensitive solution for diffusion preparation at 7 T, while operating within SAR constraints. This method may be coupled with any EPI readout trajectory and parallel imaging scheme to provide more uniform coverage for DTI at 7 T as well as 3 T.Magnetic Resonance Imaging 09/2014; · 2.02 Impact Factor
Article: Ultra-High-Field MR Neuroimaging.[Show abstract] [Hide abstract]
ABSTRACT: At ultra-high magnetic fields, such as 7T, MR imaging can noninvasively visualize the brain in unprecedented detail and through enhanced contrast mechanisms. The increased SNR and enhanced contrast available at 7T enable higher resolution anatomic and vascular imaging. Greater spectral separation improves detection and characterization of metabolites in spectroscopic imaging. Enhanced blood oxygen level-dependent contrast affords higher resolution functional MR imaging. Ultra-high-field MR imaging also facilitates imaging of nonproton nuclei such as sodium and phosphorus. These improved imaging methods may be applied to detect subtle anatomic, functional, and metabolic abnormalities associated with a wide range of neurologic disorders, including epilepsy, brain tumors, multiple sclerosis, Alzheimer disease, and psychiatric conditions. At 7T, however, physical and hardware limitations cause conventional MR imaging pulse sequences to generate artifacts, requiring specialized pulse sequences and new hardware solutions to maximize the high-field gain in signal and contrast. Practical considerations for ultra-high-field MR imaging include cost, siting, and patient experience. © 2015 American Society of Neuroradiology.American Journal of Neuroradiology 12/2014; · 3.68 Impact Factor