Advances in ultra-high field MRI for the clinical management of patients with brain tumors
Department of Radiology and Biomedical Imaging, University of California, San Francisco, California 94158-2330, USA. Current opinion in neurology
(Impact Factor: 5.31).
10/2011; 24(6):605-15. DOI: 10.1097/WCO.0b013e32834cd495
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.
Available from: Josa M Frischer
- "It is tempting to speculate that the administration of contrast enhancement at 7 T might further increase the detection rate of associated venous malformations since the resolution at 7 T is improved. However, preliminary data in brain tumours have shown that gadolinium contrast enhancement was similar between field strengths (Lupo et al., 2011; Moenninghoff et al., 2010). "
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ABSTRACT: Background and aim
In the diagnosis of cerebral cavernous malformations (CCMs) magnetic resonance imaging is established as the gold standard. Conventional MRI techniques have their drawbacks in the diagnosis of CCMs and associated venous malformations (DVAs). The aim of our study was to evaluate susceptibility weighted imaging SWI for the detection of CCM and associated DVAs at 7 T in comparison with 3 T.
Patients and methods
24 patients (14 female, 10 male; median age: 38.3 y (21.1 y–69.1 y) were included in the study. Patients enrolled in the study received a 3 T and a 7 T MRI on the same day. The following sequences were applied on both field strengths: a T1 weighted 3D GRE sequence (MP-RAGE) and a SWI sequence. After obtaining the study MRIs, eleven patients underwent surgery and 13 patients were followed conservatively or were treated radio-surgically.
Patients initially presented with haemorrhage (n = 4, 16.7%), seizures (n = 2, 8.3%) or other neurology (n = 18, 75.0%). For surgical resected lesions histopathological findings verified the diagnosis of CCMs. A significantly higher number of CCMs was diagnosed at 7 T SWI sequences compared with 3 T SWI (p < 0.05). Additionally diagnosed lesions on 7 T MRI were significantly smaller compared to the initial lesions on 3 T MRIs (p < 0.001). Further, more associated DVAs were diagnosed at 7 T MRI compared to 3 T MRI.
SWI sequences at ultra-high-field MRI improve the diagnosis of CCMs and associated DVAs and therefore add important pre-operative information.
Available from: Jan Sobesky
- "For a few years, ultrahigh-field (UHF) MRI at 7 T has been available for imaging in humans. Recent reports demonstrated the use of UHF MRI at 7 T for brain imaging and showed relevant diagnostic benefits for brain tumors , cerebral malformations , Parkinsons's disease  and multiple sclerosis . The sensitivity gain inherent to UHF MRI at 7 T allows for enhanced spatial resolution versus 3 T MRI and holds the promise of new diagnostic approaches for brain pathologies . "
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ABSTRACT: Magnetic resonance imaging (MRI) using field strengths up to 3 Tesla (T) has proven to be a powerful tool for stroke diagnosis. Recently, ultrahigh-field (UHF) MRI at 7 T has shown relevant diagnostic benefits in imaging of neurological diseases, but its value for stroke imaging has not been investigated yet. We present the first evaluation of a clinically feasible stroke imaging protocol at 7 T. For comparison an established stroke imaging protocol was applied at 3 T.
In a prospective imaging study seven patients with subacute and chronic stroke were included. Imaging at 3 T was immediately followed by 7 T imaging. Both protocols included T1-weighted 3D Magnetization-Prepared Rapid-Acquired Gradient-Echo (3D-MPRAGE), T2-weighted 2D Fluid Attenuated Inversion Recovery (2D-FLAIR), T2-weighted 2D Fluid Attenuated Inversion Recovery (2D-T2-TSE), T2* weighted 2D Fast Low Angle Shot Gradient Echo (2D-HemoFLASH) and 3D Time-of-Flight angiography (3D-TOF).
The diagnostic information relevant for clinical stroke imaging obtained at 3 T was equally available at 7 T. Higher spatial resolution at 7 T revealed more anatomical details precisely depicting ischemic lesions and periinfarct alterations. A clear benefit in anatomical resolution was also demonstrated for vessel imaging at 7 T. RF power deposition constraints induced scan time prolongation and reduced brain coverage for 2D-FLAIR, 2D-T2-TSE and 3D-TOF at 7 T versus 3 T.
The potential of 7 T MRI for human stroke imaging is shown. Our pilot study encourages a further evaluation of the diagnostic benefit of stroke imaging at 7 T in a larger study.
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To improve the radiofrequency (RF) field strength and uniformity in a local imaging region, individual RF transmitting phases were controlled in surface coil elements in a 7T transceive array coil; the RF field distribution was compared with the conventional in-phase approach at 7 T.
Optimal RF transmitting phases in the individual coil elements in a four-channel transceive array coil were numerically calculated using the electromagnetic (EM) field solver to obtain uniform RF field in a local imaging region. In 7 T phantom experiments, the RF field uniformity and mean SNR were evaluated on gradient echo images. In addition, a flip angle map was obtained by the double angle method.
Experimental results clearly show that the EM calculation yielded an improved RF field strength and uniformity in the specific imaging region along the center of the coil array when the RF transmitting phase offset was 180° between the left and right rows of surface coil elements. In a 7 T experiment, B1 field uniformity and mean SNR with this phase offset were better than the other cases and the FA map showed a more focused and symmetric distribution as compared to other cases.
Even though the RF field distribution in the transceive array coil is still strongly affected by dielectric properties at 7 T, the 180° phase offset between the left and right rows of the coil elements gave the highest magnetic flux density in the specific imaging.
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