A 12-channel flexible receiver coil for accelerated tongue imaging

A flexible 16-channel custom coil array for accelerated imaging of upper and infraglottic airway at 3 T

PURPOSE

To develop a custom coil and evaluate its utility for accelerated upper and infraglottic airway MRI at 3 T.

METHODS

A 16-channel flexible and anatomy-conforming coil was developed to provide localized sensitivity over upper and infraglottic airway regions of interest. Parallel-imaging capabilities were compared against existing head and head-neck coils. SENSE geometry factor losses were quantified for retrospectively accelerating 3D MRI. Blinded image-quality ratings from two experts were performed. Spiral GRAPPA reconstructions were evaluated for a speaking task at a time resolution of 40 ms. Contrast-to-noise ratios between air and tissue at key landmarks along the vocal tract were compared. SENSE imaging with the custom coil in the lateral recumbent posture was evaluated. Multislice imaging was performed to image swallowing at 17 ms/frame via constrained reconstruction.

RESULTS

The custom coil showed improved SENSE imaging up to 3-fold acceleration when accelerated along either the anterior-posterior or the superior-inferior direction and a net 4-fold acceleration when accelerated along both directions. Spiral GRAPPA reconstructions with the custom coil showed higher contrast-to-noise ratio when compared with existing coils. In the lateral posture, robust SENSE imaging was achieved at up to 2-fold and 3-fold acceleration levels in the superior-inferior and anterior-posterior directions, respectively. Key events of swallowing in the multislice dynamic images were identified by an otolaryngologist.

CONCLUSION

The coil provided improved parallel imaging of upper and infraglottic airway in both supine and lateral recumbent postures. It enabled efficient accelerated dynamic imaging of speaking and swallowing.

RF Coil Setup for 31P MRSI in Tongue Cancer in vivo at 7 T

Surgery for tongue cancer often results in a major loss in quality of life. While MRI may be used to minimise the volume of excised tissue, often the full tumour extent is missed. This tumour extent may be detected with metabolic imaging. One of the main reasons for the lack of metabolic information on tongue cancer would be the absence of an x-nuclear coil with the tongue as a focus target. Metabolic MRI through ³¹P MRSI is known as a powerful tool to non-invasively study elevated cell proliferation and disturbed energy metabolism in tumours. Severe magnetic field non-uniformities are inherently caused by the substantial difference in magnetic susceptibilities of tissue and air in the mouth and its environs. Despite this, the wide chemical shift dispersion of ³¹P could still facilitate precise detection of the cell proliferation biomarkers, phospomonoesters and diesters, as well as energy metabolites ATP, inorganic phosphate, and phosphocreatine potentially mapped over the tongue or tumour in vivo. In this study, we present the first ³¹P MRSI data of the human tongue in vivo from healthy volunteers and a patient with a tongue tumour at 7 T MRI using a ¹H 8-channel transceiver setup placed inside a body ³¹P transmitter, which is able to get a uniform excitation from the tongue while providing comfortable access to the patient. In addition, a user-friendly external ³¹P receiver array is used to provide high sensitivity (80%) comparable to an uncomfortable inner mouth loop coil positioned on the tongue. The primary aim is the demonstration of ³¹P metabolite profiles in the tongue and the differences between healthy and malignant tissue. Indeed, clear elevated cell proliferation expressed as enhanced phosphomonoesters is observed in the tumour vs. the healthy part of the tongue. This can be performed within a total scan duration of 30 min, comparable to clinical scans, with a spatial resolution of 1.5 cm for the 10-min ³¹P MRSI scan.

Dynamic MRI of swallowing: real-time volumetric imaging at 12 frames per second at 3 T

Objective

Dysphagia or difficulty in swallowing is a potentially hazardous clinical problem that needs regular monitoring. Real-time 2D MRI of swallowing is a promising radiation-free alternative to the current clinical standard: videofluoroscopy. However, aspiration may be missed if it occurs outside this single imaged slice. We therefore aimed to image swallowing in 3D real time at 12 frames per second (fps).

Materials and methods

At 3 T, three 3D real-time MRI acquisition approaches were compared to the 2D acquisition: an aligned stack-of-stars (SOS), and a rotated SOS with a golden-angle increment and with a tiny golden-angle increment. The optimal 3D acquisition was determined by computer simulations and phantom scans. Subsequently, five healthy volunteers were scanned and swallowing parameters were measured.

Results

Although the rotated SOS approaches resulted in better image quality in simulations, in practice, the aligned SOS performed best due to the limited number of slices. The four swallowing phases could be distinguished in 3D real-time MRI, even though the spatial blurring was stronger than in 2D. The swallowing parameters were similar between 2 and 3D.

Conclusion

At a spatial resolution of 2-by-2-by-6 mm with seven slices, swallowing can be imaged in 3D real time at a frame rate of 12 fps.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10334-021-00973-6.

Magnetic resonance neurography of the head and neck: state of the art, anatomy, pathology and future perspectives

Magnetic resonance neurography allows for the selective visualization of peripheral nerves and is increasingly being investigated. Whereas in the past, the imaging of the extracranial cranial and occipital nerve branches was inadequate, more and more techniques are now available that do allow nerve imaging. This basic review provides an overview of the literature with current state of the art, anatomical landmarks and future perspectives. Furthermore, we illustrate the possibilities of the three-dimensional CRAnial Nerve Imaging (3D CRANI) MR-sequence by means of a few case studies.