This technical approach can be employed to study cerebral white and gray matter lesions in MS patients with greater detail at 7.0 Tesla. The main advantage is that we can examine brain changes with greater detail at 7.0 Tesla compared to lower magnetic field strengths. The enhanced spatial resolution is made possible by the increased signal-to-noise ratio and by the sensitivity gain at 7.0 Tesla.
Disseminating these methods will be significant as they should provide the foundation for other researchers that are starting MS studies at 7.0 Tesla, and that's the main goal is to gain further insight into the MS pathology. Demonstrating the procedure will be Antje Els, a radiographer and study nurse from our facility. When the subject is ready, accompany them to the 7T MR scanner room and ask the subject to lie on the scanning table using pillows, blade cushions, and blankets to make the subject as comfortable as possible.
Connect an MRI safe pulse oximeter to the subject and provide ear plugs and a handheld squeeze ball to be used during the examination in the case of emergency. Ask the subject to move closer to the radio frequency head coil and have the subject close their eyes while the table is moved very slowly until the laser positioning is in full alignment with the marker cross on top of the coil. After saving this position, move the subject table very slowly to the ISO center of the MR scanner while explaining to the subject that any side effects should resolve as soon as the table comes to a halt.
After leaving the scanner room, use the intercom to confirm audible communication with the subject within the scanner. Before acquiring the scanning data, enter the required subject details, including the subject ID, date of birth, sex, age, and weight, as well as the study details such as the study name, institution, and individual performing the MR investigation. Select localizer and mark the sequence.
Select options and adjustments and select go under the frequency tab. Under the transmitter tab, set the voltage as appropriate for the radio frequency coil and amplifier being used and click apply. Under a 3D shim, select measure.
When the B0 map is generated, select calculate to acquire the shim values. When the shim values are consistent with the previous value, make sure that the basic frequency is re-centered and select apply and close. Then using at least three slices per orientation, make sure that all of the channels have been selected and press apply to run the localizer sequence in the sagittal, transversal, and coronal orientations.
To acquire a 3D MPRAGE sequence, use the zoom and panning tool to zoom in and move the field of view on the localizer images and the adjustment volume. Make sure that all of the channels are selected and click apply to acquire the sequence in the sagittal orientation in alignment with the interhemispheric fissure. To run a FLAIR sequence, copy the geometry of the field of view in the same sagittal orientation and adjustment volume as for the MPRAGE scan, taking care of that the phase encoding is in the anterior to posterior direction and that all of the channels are selected and press apply to start the scan.
To run a FLASH-ME, adjust the field of view according to the anatomy of the subject using the 3D MPRAGE and localizer images to plan the geometry and using the zoom and panning tool to manually adjust the field of view such that the entire head is in the middle. Tilt the head such that the lower boundary of the field of view is in line with the lower corpus callosum line before adjusting the uppermost layer end with the skull callate. Modify the adjustment volume if it's no longer aligned with the geometry volume and rerun the manual 3D shimming and frequency adjustments before clicking apply to run the sequence.
For susceptibility-weighted imaging, rearrange the field of views such that the slice slab is shifted in the cranial direction and the uppermost border is aligned with the skull callate. Displace the slab in the ventral or dorsal direction so that the brain is completely in the middle of field of view. Modify the adjustment volume if it is no longer aligned with the geometry volume and rerun the manual 3D shimming and frequency adjustments before clicking apply to start the scan.
For quantitative susceptibility mapping, move the slice stack cranially so that the top layer is aligned with the skull callate and rerun the manual 3D shimming and frequency adjustments to make sure that all of the channels are selected. Then click apply to run the sequence. For diffusion-weighted imaging, select a 2D echo planar imaging sequence and use the localizer images to plan the geometry in the transversal orientation without introducing any angulation.
Move the field of view such that the upper line of the layer block is aligned with the skull callate. When the brain is exactly in the middle of the field of view, make sure that the phase encoding is in the anterior to posterior direction, that 64 different diffusion encoding directions are selected, and that the B values are set to 0 and 1, 000 seconds per square millimeter before clicking apply to run the sequence. To cancel any distortion artifacts, acquire the same echo planar imaging sequence, but using the reverse polarity of the phase encoding direction using the version of the echo planar imaging sequence with the phase encoding in the posterior to anterior direction.
Set the direction to 180 degrees if necessary and confirm that 64 different diffusion encoding directions are selected, but only one B value at zero seconds per square millimeter, which will significantly reduce the scan time, but will be sufficient to correct any distortion artifacts during post-processing. Then click apply to run the sequence. As soon as the last sequence has finished and been reconstructed, the MRI examination will be ready.
When all of the images have been completely acquired, move the subject table slowly away from the ISO center of the scanner and check in with the subject regarding any side effects from during or after the measurements. In this analysis, a 26-year-old woman diagnosed with relapsing remitting MS was examined at 7.0 Tesla as demonstrated. Some distortions in the B1 plus profile can be observed in the MR images, which is anticipated when moving to higher resonance frequencies as shorter wavelengths increase the destructive and constructive interferences.
As observed, sagittal and transversal views provide different contrasts in the brain images. Although the MS diagnosis was subsequently challenged due to an increase in T2 lesions and multiple clinical relapses with incomplete remission, 7T MRI supported the MS diagnosis by revealing the central vein sign in the majority of paraventricular and juxtacortical lesions. The MS diagnosis was further corroborated by cortical pathology and hypointense rim structures surrounding a subset of T2 hyperintense lesions.
These techniques are derived from strong collaborations between MR physics, imaging sciences, neurology specialists and neuro radiology experts and provide new MS-specific neuroimaging markers, such as a central vein sign and hypointense rim structures on T2 style weighted images.
