The traveling heads: multicenter brain imaging at 7 Tesla

Objective

This study evaluates the inter-site and intra-site reproducibility of 7 Tesla brain imaging and compares it to literature values for other field strengths.

Materials and methods

The same two subjects were imaged at eight different 7 T sites. MP2RAGE, TSE, TOF, SWI, EPI as well as B1 and B0 field maps were analyzed quantitatively to assess inter-site reproducibility. Intra-site reproducibility was measured with rescans at three sites.

Results

Quantitative measures of MP2RAGE scans showed high agreement. Inter-site and intra-site reproducibility errors were comparable to 1.5 and 3 T. Other sequences also showed high reproducibility between the sites, but differences were also revealed. The different RF coils used were the main source for systematic differences between the sites.

Conclusion

Our results show for the first time that multi-center brain imaging studies of the supratentorial brain can be performed at 7 T with high reproducibility and similar reliability as at 3T. This study develops the basis for future large-scale 7 T multi-site studies.

     

7 Tesla quantitative hip MRI: a comparison between TESS and CPMG for T2 mapping

Objectives

We aimed to evaluate the feasibility of triple-echo steady state (TESS) T2 mapping as an alternative to conventional multi-echo-spin-echo (CPMG) T2 mapping for the quantitative assessment of hip joint cartilage at 7 T.

Materials and methods

A total of eight healthy volunteers and three patients were included. Reproducibility of both techniques was evaluated in five volunteers in five scans each. T2 relaxation times were measured by manually drawing regions of interest in multiple regions of the hip joint. Data from both methods were compared using Pearson correlation coefficient, intra-class correlation coefficient, and coefficient of repeatability. The overall image quality and presence of artifacts was assessed.

Results

Cartilage transplant and surrounding fluid were well depicted by both methods. Compared to CPMG, TESS provided systematically reduced T2 values (43.3 ± 7.3 vs. 19.2 ± 5.5 ms for acetabular cartilage, and 41.4 ± 5.6 vs. 21.7 ± 5.2 ms for femoral cartilage), in line with previously reported values. No correlation between both methods was found. TESS yielded a slightly better reproducibility than CPMG, while CPMG showed pronounced sensitivity to B1 inhomogeneities.

Conclusion

TESS seems to be an attractive alternative to CPMG for improvements in quantitative hip joint imaging at 7 T, allowing shortening of the total acquisition time paired with insensitivity to B1, while rendering comparable image quality with good repeatability.

     

Cranial fixation plates in cerebral magnetic resonance imaging: a 3 and 7 Tesla in vivo image quality study

Objective

This study assesses and quantifies impairment of postoperative magnetic resonance imaging (MRI) at 7 Tesla (T) after implantation of titanium cranial fixation plates (CFPs) for neurosurgical bone flap fixation.

Materials and methods

The study group comprised five patients who were intra-individually examined with 3 and 7 T MRI preoperatively and postoperatively (within 72 h/3 months) after implantation of CFPs. Acquired sequences included T₁-weighted magnetization-prepared rapid-acquisition gradient-echo (MPRAGE), T₂-weighted turbo-spin-echo (TSE) imaging, and susceptibility-weighted imaging (SWI). Two experienced neurosurgeons and a neuroradiologist rated image quality and the presence of artifacts in consensus reading.

Results

Minor artifacts occurred around the CFPs in MPRAGE and T₂ TSE at both field strengths, with no significant differences between 3 and 7 T. In SWI, artifacts were accentuated in the early postoperative scans at both field strengths due to intracranial air and hemorrhagic remnants. After resorption, the brain tissue directly adjacent to skull bone could still be assessed. Image quality after 3 months was equal to the preoperative examinations at 3 and 7 T.

Conclusion

Image quality after CFP implantation was not significantly impaired in 7 T MRI, and artifacts were comparable to those in 3 T MRI.

     

To TOF or not to TOF: strategies for non-contrast-enhanced intracranial MRA at 7 T

Object The purpose of this study was to optimize and to evaluate 3D time-of-flight (TOF)-like non-contrast enhanced MR-angiography (MRA) techniques for display of the intracranial vessels on a 7 T whole-body scanner. Materials and methods Three different gradient echo sequences (TOF, VIBE, MPRAGE) were compared in 12 healthy volunteers and 13 patients. Two blinded senior radiologists independently rated the presence or absence of artefacts and the conspicuity of ten different vessel segments in source and maximum-intensity-projection (MIP) images. Results In source images, MPRAGE achieved the best results; even the fine vessels and the vessels near the air-containing mastoid were depicted very well. Intraluminal signal loss, which was a problem in the greater vessels in TOF and VIBE imaging, was less pronounced in MPRAGE images. In the MIP images, TOF performed best. Both VIBE and MPRAGE can generate TOF-like contrast and cover the whole brain in less than 15 min, whereas TOF covered only a subvolume of the brain. Conclusion MPRAGE performed especially well in this 7 T imaging study. The accuracy of the sequence deserves further evaluation in patients with vessel stenoses and aneurysms. For inclusion of the special issue on High Field MR as new concepts paper.     

Subjective acceptance of 7 Tesla MRI for human imaging

Objective One prerequisite for transferring ultra-high-field magnetic resonance imaging (MRI) (>3T) into clinical diagnostic workup is a low rate of side effects. To our knowledge, publications of subjective acceptance and willingness to undergo examinations at >3T are rare. We present first results from our research site. Materials and methods Exposure to 7T whole-body MRI of head, extremities, or breast was assessed in 102 subjects. They judged sources of discomfort (examination duration, room temperature) and physiological sensations (vertigo, light flashes) on a 10-point scale, differentiating between examination phases: table stationary or moving. For comparison, the same questionnaire was completed by 43 of these subjects after undergoing a 1.5T examination. Vertigo was the most pronounced sensation at 7T with 5% rating it as very unpleasant (none at 1.5T). This should be compared with the fact that the lengthy exam duration was regarded as even more uncomfortable. Compared to 1.5T, average study duration at 7T was roughly doubled, and 7T elicited a wider range of complaints. Conclusion Although the number of side effects is increased at 7T compared to 1.5T, 7T was well tolerated by the majority of subjects. Further data collection is necessary for better understanding of these effects.     

The physical face of slums: a structural comparison of slums in Mumbai,India, based on remotely sensed data

The term “slum” is difficult to define, but if we see one, we know it. Definitions for slums are qualitative such as “areas of people lacking, for example, durable housing or easy access to safe water”. This study aims at identifying characteristic physical features of the built environment that allows defining slum areas based on quantitative and measurable parameters. In general, spatial data on slums are generalized, outdated, or even nonexistent. The bird’s eye view of remotely sensed data is capable to provide an independent, area-wide spatial overview, to capture the complex morphological pattern and at the same time capture the large-scale individual objects typical for slums. Using high-resolution optical satellite data, parameters such as building density, building heights, and sizes are used to differentiate between slums and formal settlements. From it, the physical features are used to analyze structural homogeneity and heterogeneities within and across slums and to suggest characteristic physical features for spatial slum delineation at three study sites in Mumbai, India.     

Optimized spectrally selective steady-state free precession sequences for cartilage imaging at ultra-high fields

Object Fat suppressed 3D steady-state free precession (SSFP) sequences are of special interest in cartilage imaging due to their short repetition time in combination with high signal-to-noise ratio. At low-to-high fields (1.5–3.0 T), spectral spatial (spsp) radio frequency (RF) pulses perform superiorly over conventional saturation of the fat signal (FATSAT pulses). However, ultra-high fields (7.0 T and more) may offer alternative fat suppression techniques as a result of the increased chemical shift. Materials and methods Application of a single, frequency selective, RF pulse is compared to spsp excitation for water (or fat) selective imaging at 7.0 T. Results For SSFP, application of a single frequency selective RF pulse for selective water or fat excitation performs beneficially over the commonly applied spsp RF pulses. In addition to the overall improved fat suppression, the application of single RF pulses leads to decreased power depositions, still representing one of the major restrictions in the design and application of many pulse sequences at ultra-high fields. Conclusion The ease of applicability and implementation of single frequency selective RF pulses at ultra-high-fields might be of great benefit for a vast number of applications where fat suppression is desirable or fat–water separation is needed for quantification purposes. Submitted to MAGMA for inclusion in the Special Issue on High Field MR as New Concepts paper.     

Development and evaluation of a numerical simulation approach to predict metal artifacts from passive implants in MRI

Objective

This study presents the development and evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment that can be applied to improve the testing procedure for MR image artifacts in medical implants according to ASTM F2119.

Methods

The numerical approach is validated by comparing simulations and measurements of two metallic test objects made of titanium and stainless steel at three different field strengths (1.5T, 3T and 7T). The difference in artifact size and shape between the simulated and measured artifacts were evaluated. A trend analysis of the artifact sizes in relation to the field strength was performed.

Results

The numerical simulation approach shows high similarity (between 75% and 84%) of simulated and measured artifact sizes of metallic implants. Simulated and measured artifact sizes in relation to the field strength resulted in a calculation guideline to determine and predict the artifact size at one field strength (e.g., 3T or 7T) based on a measurement that was obtained at another field strength only (e.g. 1.5T).

Conclusion

This work presents a novel tool to improve the MR image artifact testing procedure of passive medical implants. With the help of this tool detailed artifact investigations can be performed, which would otherwise only be possible with substantial measurement effort on different MRI systems and field strengths.

     

Integrated watershed management in Michigan: Challenges and proposed solutions

Michigan's current water management system is highly decentralized and based more on jurisdictional than watershed boundaries. There is both environmental and economic justification to examine alternate water resource management approaches given the current system's potential for inefficiency and redundancy. Our research addresses a central question: How might an integrated watershed governance system be applied in Michigan, where jurisdictional authority and political will are fragmented both horizontally across agencies and vertically across scales? We identify the key challenges facing Michigan's current approach to managing water resources and then describe two alternatives, referred to as Integrated Watershed Commissions (IWCs), which would coordinate water resource management and decision making on a watershed basis. The first alternative represents a relatively radical departure from the state's current structure, an “unconstrained” vision for comprehensive watershed management, which is not bound by the state's present political and management limitations. The second alternative, a more conservative or “constrained” vision for watershed coordination, operates primarily within Michigan's existing governance structures, and therefore includes mostly incremental change. For each alternative, we propose watershed boundaries and management structures, and discuss possible benefits and caveats. We also identify plausible next steps that can be taken in the near future, short of IWC implementation, that may catalyze water management reform and enhance coordination and collaboration in managing water resources in Michigan.