An array of the frequency components of the MR signal according to frequency. Nuclei with different resonant frequencies will show up as values at different corresponding frequencies in the spectrum. When resonances are relatively isolated they appear as peaks or lines in the spectrum.
A spectrum is also a graphic representation of the range over which a quantity extends.
Postoperative evaluation of lumbar spine: disk vs. scar
•
Evaluation of syrinx
•
Localized back pain with no radiculopathy (leg pain)
Contrast enhanced MRI techniques delineate infections vs. malignancies, show a syrinx cavity and support to differentiate the postoperative conditions. After surgery for disk disease, significant fibrosis can occur in the spine. This scarring can mimic residual disk herniation. Magnetic resonance myelography evaluates spinal stenosis and various intervertebral discs can be imaged with multi angle oblique techniques. Cine series can be used to show true range of motion studies of parts of the spine.
Advanced open MRI devices are developed to perform positional scans in the position of pain or symptom (e.g. Upright™ MRI formerly Stand-Up MRI).
Bruker Medical Inc. provides a wide range of instruments that incorporate MR imaging technology. The TOMIKON series includes MRI instruments for routine clinical applications, S50 (0.5T), S100 (1.0T), and S200 (2.0T).
(TOF) The time of flight angiography is used for the imaging of vessels. Usually the sequence type is a gradient echosequences with short TR, acquired with slices perpendicular to the direction of blood flow.
The source of diverse flow effects is the difference between the unsaturated and presaturated spins and creates a bright vascular image without the invasive use of contrast media. Flowing blood moves unsaturated spins from outside the slice into the imaging plane. These completely relaxed spins have full equilibriummagnetization and produce (when entering the imaging plane) a much higher signal than stationary spins if a gradient echo sequence is generated. This flow related enhancement is also referred to as entry slice phenomenon, or inflow enhancement.
Performing a presaturationslab on one side parallel to the slice can selectively destroy the MR signal from the in-flowing blood from this side of the slice. This allows the technique to be flow direction sensitive and to separate arteriograms or venograms. When the local magnetization of moving blood is selectively altered in a region, e.g. by selective excitation, it carries the altered magnetization with it when it moves, thus tagging the selected region for times on the order of the relaxation times.
For maximum flow signal, a complete new part of blood has to enter the slice every repetition (TR) period, which makes time of flight angiography sensitive to flow-velocity. The choice of TR and slice thickness should be appropriate to the expected flow-velocities because even small changes in slice thickness influences the performance of the TOF sequence.
The use of sequential 2 dimensional Fourier transformation (2DFT) slices, 3DFT slabs, or multiple 3D slabs (chunks) are depending on the coverage required and the range of flow-velocities.
3D TOF MRA is routinely used for evaluating the Circle of Willis.