The technological future of 7 T MRI hardware

Spinal cord MRI at 7T

Magnetic resonance imaging (MRI) of the human spinal cord at 7T has been demonstrated by a handful of research sites worldwide, and the spinal cord remains one of the areas in which higher fields and resolution could have high impact. The small diameter of the cord (∼1 cm) necessitates high spatial resolution to minimize partial volume effects between gray and white matter, and so MRI of the cord can greatly benefit from increased signal-to-noise ratio and contrasts at ultra-high field (UHF). Herein we review the current state of UHF spinal cord imaging. Technical challenges to successful UHF spinal cord MRI include radiofrequency (B1) nonuniformities and a general lack of optimized radiofrequency coils, amplified physiological noise, and an absence of methods for robust B0 shimming along the cord to mitigate image distortions and signal losses. Numerous solutions to address these challenges have been and are continuing to be explored, and include novel approaches for signal excitation and acquisition, dynamic shimming and specialized shim coils, and acquisitions with increased coverage or optimal slice angulations.

MRI in the Study of Animal Models of Neurodegenerative Diseases

Magnetic Resonance Imaging (MRI) is an important tool to study various animal models of degenerative diseases. This chapter describes routine protocols of T ₁-, T ₂-, and T ₂*-weighted and diffusion-weighted MRI for rodent brain and spinal cord. These protocols can be used to measure atrophy, axonal and myelin injury and changes in white matter connectivity.

Open Source 3D Multipurpose Measurement System with Submillimetre Fidelity and First Application in Magnetic Resonance

Magnetic resonance imaging (MRI) is the mainstay of diagnostic imaging, a versatile instrument for clinical science and the subject of intense research interest. Advancing clinical science, research and technology of MRI requires high fidelity measurements in quantity, location and time of the given physical property. To meet this goal a broad spectrum of commercial measurement systems has been made available. These instruments frequently share in common that they are costly and typically employ closed proprietary hardware and software. This shortcoming makes any adjustment for a specified application difficult if not prohibitive. Recognizing this limitation this work presents COSI Measure, an automated open source measurement system that provides submillimetre resolution, robust configuration and a large working volume to support a versatile range of applications. The submillimetre fidelity and reproducibility/backlash performance were evaluated experimentally. Magnetic field mapping of a single ring Halbach magnet, a 3.0 T and a 7.0 T MR scanner as well as temperature mapping of a radio frequency coil were successfully conducted. Due to its open source nature and versatile construction, the system can be easily modified for other applications. In a resource limited research setting, COSI Measure makes efficient use of laboratory space, financial resources and collaborative efforts.

Clinical value of MRI-detected extramural venous invasion in rectal cancer

Extramural venous invasion (EMVI) is associated with a poor prognosis and a poor overall survival rate in rectal cancer. It can independently predict local and distant tumor recurrences. Preoperative EMVI detection in rectal cancer is useful for determining the treatment strategy. EMVI status is beneficial for the post-treatment evaluation and analysis of rectal cancer. Magnetic resonance imaging (MRI) is a non-invasive diagnostic modality with no radiation effects. High-resolution MRI can detect EMVI with high accuracy. In addition, MRI results are equal to or even better than pathological results in the detection of medium to large EMVI in rectal cancer. MRI-detected EMVI (mrEMVI) can be used as a potential biomarker that facilitates treatment methods. This review highlights the importance of MRI before and after rectal cancer treatment. In addition, we analyze the prognostic correlation between mrEMVI and circulating tumor cells (CTC) in rectal cancer. This article may help shed light on the significance of mrEMVI.

Integrated parallel reception, excitation, and shimming (iPRES) with multiple shim loops per radio-frequency coil element for improved B0 shimming

PURPOSE

Integrated parallel reception, excitation, and shimming (iPRES) coil arrays allow radio-frequency currents and direct currents to flow in the same coils, which enables excitation/reception and localized B₀ shimming with a single coil array. The purpose of this work was to improve their shimming performance by adding the capability to shim higher-order local B₀ inhomogeneities that are smaller than the radio-frequency coil elements.

METHODS

A novel design was proposed in which each radio-frequency/shim coil element is divided into multiple direct current loops, each using an independent direct current current, to increase the number of magnetic fields available for shimming while maintaining the signal-to-noise ratio of the coil. This new design is termed iPRES(N), where N represents the number of direct current loops per radio-frequency coil element. Proof-of-concept phantom and human experiments were performed with an 8-channel body coil array to demonstrate its advantages over the original iPRES(1) design.

RESULTS

The average B₀ homogeneity in various organs before shimming and after shimming with the iPRES(1) or iPRES(3) coil arrays was 0.24, 0.11, and 0.05 ppm, respectively. iPRES(3) thus reduced the B₀ inhomogeneity by 53% and further reduced distortions in echo-planar images of the abdomen when compared with iPRES(1).

CONCLUSION

iPRES(N) can correct for localized B₀ inhomogeneities more effectively than iPRES(1) with no signal-to-noise ratio loss, resulting in a significant improvement in image quality. Magn Reson Med 77:2077-2086, 2017. © 2016 International Society for Magnetic Resonance in Medicine.