(CPMG) This type of spin echo pulse sequence consisting of a 90° radio frequency pulse followed by an echo train induced by successive 180° pulses and is useful for measuring T2 weighted images. It is a modification of the Carr-Purcell RF pulse sequence, with 90° phase shift in the rotating frame of reference between the 90° pulse and the subsequent 180° pulses in order to reduce accumulating effects of imperfections in the 180° pulses. Suppression of effects of pulse error accumulation can alternatively be achieved by switching phases of the 180° pulses by 180°.

Cervical spine MRI is a suitable tool in the assessment of all cervical spine (vertebrae C1 - C7) segments (computed tomography (CT) images may be unsatisfactory close to the thoracic spine due to shoulder artifacts). The cervical spine is particularly susceptible to degenerative problems caused by the complex anatomy and its large range of motion.
Advantages of magnetic resonance imaging MRI are the high soft tissue contrast (particularly important in diagnostics of the spinal cord), the ability to display the entire spine in sagittal views and the capacity of 3D visualization. Magnetic resonance myelography is a useful supplement to conventional MRI examinations in the investigation of cervical stenosis. Myelographic sequences result in MR images with high contrast that are similar in appearance to conventional myelograms. Additionally, open MRI studies provide the possibility of weight-bearing MRI scan to evaluate structural positional and kinetic changes of the cervical spine.
Indications of cervical spine MRI scans include the assessment of soft disc herniations, suspicion of disc hernia recurrence after operation, cervical spondylosis, osteophytes, joint arthrosis, spinal canal lesions (tumors, multiple sclerosis, etc.), bone diseases (infection, inflammation, tumoral infiltration) and paravertebral spaces.
State-of-the-art phased array spine coils and high performance MRI machines provide high image quality and short scan time. Imaging protocols for the cervical spine includes sagittal T1 weighted and T2 weighted sequences with 3-4 mm slice thickness and axial slices; usually contiguous from C2 through T1. Additionally, T2 fat suppressed and T1 post contrast images are often useful in spine imaging.

See also Lumbar Spine MRI.

Biphasic oral contrast agents may produce either high or low signal intensities depending on the pulse sequence used, for example low signal intensity on T1 weighted MR images and high signal intensity on T2 weighted images. The combination of different oral contrast agents can generate a macroscopic cancellation of negative and positive magnetic susceptibility, thereby eliminating susceptibility artifacts.
Possible combinations are e.g., ferric ammonium citrate and corn oil, or ferrous sulfate emulsified with baby formula. Paramagnetic agents combined with oil emulsion may be used in MRI as positive abdominal contrast agents. The combination of diamagnetic barium sulfate and superparamagnetic iron oxide (SPIO) in one suspension may be a useful negative contrast agent.

See also Gastrointestinal Paramagnetic Contrast Agents, Gastrointestinal Superparamagnetic Contrast Agents, Gastrointestinal Diamagnetic Contrast Agents, Gastrointestinal Imaging.

(CISS) This gradient echo sequence is a stimulated T2 echo. Two TrueFISP sequences are acquired with differing RF pulses and than combined for strong T2 Weighted high resolution 3D images.
These TrueFISP sequences are normally affected by dark phase dispersion bands, which are caused by patient induced local field inhomogeneities and made prominent by the relatively long TR used. The different excitation pulse regimes offset these bands in the 2 sequences. Combining the images results in a picture free of banding. The image combination is performed automatically after data collection, adding some time to the reconstruction process. The advantage of the 3D CISS sequence is its combination of high signal levels and extremely high spatial resolution.
Used for, e.g. inner ear, cranial nerves and cerebellum.

See also Steady State Free Precession.

Contrast agents are chemical substances introduced to the anatomical or functional region being imaged, to increase the differences between different tissues or between normal and abnormal tissue, by altering the relaxation times. MRI contrast agents are classified by the different changes in relaxation times after their injection.
The design objectives for the next generation of MR contrast agents will likely focus on prolonging intravascular retention, improving tissue targeting, and accessing new contrast mechanisms. Macromolecular paramagnetic contrast agents are being tested worldwide. Preclinical data shows that these agents demonstrate great promise for improving the quality of MR angiography, and in quantificating capillary permeability and myocardial perfusion.
Ultrasmall superparamagnetic iron oxide (USPIO) particles have been evaluated in multicenter clinical trials for lymph node MR imaging and MR angiography, with the clinical impact under discussion. In addition, a wide variety of vector and carrier molecules, including antibodies, peptides, proteins, polysaccharides, liposomes, and cells have been developed to deliver magnetic labels to specific sites. Technical advances in MR imaging will further increase the efficacy and necessity of tissue-specific MRI contrast agents.

See also Adverse Reaction and Nephrogenic Systemic Fibrosis.

See also the related poll result: 'The development of contrast agents in MRI is'