7-T MR--from research to clinical applications?

Centre for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
NMR in Biomedicine (Impact Factor: 3.45). 11/2011; 25(5):695-716. DOI: 10.1002/nbm.1794
Source: PubMed

ABSTRACT Over 20,000 MR systems are currently installed worldwide and, although the majority operate at magnetic fields of 1.5 T and below (i.e. about 70%), experience with 3-T (in high-field clinical diagnostic imaging and research) and 7-T (research only) human MR scanners points to a future in functional and metabolic MR diagnostics. Complementary to previous studies, this review attempts to provide an overview of ultrahigh-field MR research with special emphasis on emerging clinical applications at 7 T. We provide a short summary of the technical development and the current status of installed MR systems. The advantages and challenges of ultrahigh-field MRI and MRS are discussed with special emphasis on radiofrequency inhomogeneity, relaxation times, signal-to-noise improvements, susceptibility effects, chemical shifts, specific absorption rate and other safety issues. In terms of applications, we focus on the topics most likely to gain significantly from 7-T MR, i.e. brain imaging and spectroscopy and musculoskeletal imaging, but also body imaging, which is particularly challenging. Examples are given to demonstrate the advantages of susceptibility-weighted imaging, time-of-flight MR angiography, high-resolution functional MRI, (1)H and (31)P MRSI in the human brain, sodium and functional imaging of cartilage and the first results (and artefacts) using an eight-channel body array, suggesting future areas of research that should be intensified in order to fully explore the potential of 7-T MR systems for use in clinical diagnosis.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Purpose This paper presents a novel inductive decoupling technique for form-fitting coil arrays of monolithic transmission line resonators (TLR), which target biomedical applications requiring high SNR over a large FOV to image anatomical structures varying in size and shape from patient to patient. Methods Individual TLR elements are mutually decoupled employing magnetic flux sharing by overlapping annexes. This decoupling technique was evaluated by electromagnetic simulations and bench measurements for two- and four-element arrays, comparing single- and double-gap TLR designs, combined either with a basic capacitive matching scheme or inductive pick up loop matching. The best performing array was used in 7T MRI experiments demonstrating its form-fitting ability and parallel imaging potential. Results The inductively matched double-gap TLR array provided the best decoupling efficiency in simulations and bench measurements (< 15 dB). The decoupling and parallel imaging performance proved robust against mechanical deformation of the array. Conclusion The presented decoupling technique combines the robustness of conventional overlap decoupling regarding coil loading and operating frequency with the extended FOV of non-overlapped coils. While demonstrated on four-element arrays, it can be easily expanded in order to fabricate readily decoupled form-fitting 2D arrays with an arbitrary number of elements in a single etching process.
    Magnetic Resonance in Medicine 04/2014; early view. · 3.27 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Automated morphometric approaches are used to detect epileptogenic structural abnormalities in 3D MR images in adults, using the variance of a control population to obtain z-score maps in an individual patient. Due to the substantial changes the developing human brain undergoes, performing such analyses in children is challenging. This study investigated six features derived from high-resolution T1 datasets in four groups: normal children (1.5T or 3T data), normal clinical scans (3T data), and patients with structural brain lesions (3T data), with each n = 10. Normative control data were obtained from the NIH study on normal brain development (n = 401). We show that control group size substantially influences the captured variance, directly impacting the patient's z-scores. Interestingly, matching on gender does not seem to be beneficial, which was unexpected. Using data obtained at higher field scanners produces slightly different base rates of suprathreshold voxels, as does using clinically derived normal studies, suggesting a subtle but systematic effect of both factors. Two approaches for controlling suprathreshold voxels in a multidimensional approach (combining features and requiring a minimum cluster size) were shown to be substantial and effective in reducing this number. Finally, specific strengths and limitations of such an approach could be demonstrated in individual cases.
    Human Brain Mapping 07/2014; 35(7):3199-215. · 6.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Since the introduction of 4 Tesla human systems in three academic laboratories circa 1990, rapid progress in imaging and spectroscopy studies in humans at 4 Tesla and animal model systems at 9.4 Tesla have led to the introduction of 7 Tesla and higher magnetic fields for human investigation at about the turn of the century. Work conducted on these platforms has demonstrated the existence of significant advantages in signal-to-noise ratio and biological information content at these ultrahigh fields, as well as the presence of numerous challenges. Primary difference from lower fields is the deviation from the near field regime; at the frequencies corresponding to hydrogen resonance conditions at ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image non-uniformities for a given sample-coil configuration because of interferences. These non-uniformities were considered detrimental to progress of imaging at high field strengths. However, they are advantageous for parallel imaging for signal reception and parallel transmission, two critical technologies that account, to a large extend, for the success of ultrahigh fields. With these technologies, and improvements in instrumentation and imaging methods, today ultrahigh fields have provided unprecedented gains in imaging of brain function and anatomy, and started to make inroads into investigation of the human torso and extremities. As extensive as they are, these gains still constitute a prelude to what is to come given the increasingly larger effort committed to ultrahigh field research and development of ever better instrumentation and techniques.
    IEEE transactions on bio-medical engineering 03/2014; · 2.15 Impact Factor


Available from
May 20, 2014