The tesla (symbol T) is the International System of Units (SI) derived unit of magnetic field strength or magnetic flux density, commonly denoted as B. One tesla is equal to one weber per square metre, and it was named in 1960.
see 3 Tesla
With recent developments in MR acquisition at 7T, smaller brainstem structures such as the red nuclei, substantia nigra and subthalamic nuclei can be imaged with good contrast and resolution.
7 Tesla MRI allows identification of a large number of metabolites at higher spatial resolutions than currently possible at lower field strengths. However, several challenges complicate in vivo localization and artifact suppression in MRS at high spatial resolution within a clinically feasible scan time at 7 tesla. Published MRS sequences at 7 tesla suffer from long echo times, inherent signal-to-noise ratio (SNR) loss, large chemical shift displacement artifacts or long repetition times because of excessive radiofrequency (RF) power deposition. In a study a pulse-acquire sequence was used that does not suffer from these high field drawbacks. A slice selective excitation combined with high resolution chemical shift imaging for in-plane localization was used to limit chemical shift displacement artifacts. The pulse-acquire approach resulted in a very short echo time of 1.4 ms. A cost function guided shimming algorithm was developed to constrain frequency offsets in the excited slice, therefore adiabatic frequency selective suppression could be employed to minimize artifacts from high intensity lipids and water signals in the excited slice. The high sensitivity at a TR of 1 s was demonstrated both on a supraventricular slice as well as in an area very close to the skull in the frontal cortex at a nominal spatial resolution of 0.25 cc within a feasible scan time 5).
Conventional saturation pulses cannot be used for 7 Tesla ultra-high-resolution time-of-flight magnetic resonance angiography (TOF MRA) due to specific absorption rate (SAR) limitations. The use of novel low flip angle VERSE algorithm pulses for saturation of venous vessels can overcome SAR limitations in 7 Tesla ultra-high-resolution TOF MRA. The protocol is suitable for clinical application with excellent image quality for delineation of various intracranial vascular pathologies 6).
Unruptured intracranial aneurysm wall and its variation in thickness can be visualized with 7.0-T MRI. Aneurysm wall thickness variation can now be further studied as a risk factor for rupture in prospective studies 7).
Different studies already demonstrated the benefits of 7T for precontrast time of flight magnetic resonance angiography in the visualization of intracranial small vessels.
High-resolution postcontrast TOF-MRA at 7T was able to visualize multiple intracranial perforators branching off from various parts of the circle of Willis and proximal intracranial arteries. Although confirmation in a larger study is needed, the administration of a contrast agent for high-resolution TOF-MRA at 7T seems to enable a better visualization of the distal segment of certain intracranial perforators 8).