Items tagged “needs review”
7 results found
Article
MRI
MRI (an abbreviation of magnetic resonance imaging) is an imaging modality that uses non-ionizing radiation to create useful diagnostic images.
In simple terms, an MRI scanner consists of a large, powerful magnet in which the patient lies. A radio wave antenna is used to send signals to the bod...
Article
Gradient echo sequences
Gradient echo sequences (GRE) are an alternative technique to spin-echo sequences, differing from it in two principal points:
utilization of gradient fields to generate transverse magnetization
flip angles of less than 90°
Compared to the spin-echo and inversion recovery sequences, gradient e...
Article
Gastrointestinal MRI contrast agents
Gastrointestinal MRI contrast agents may be helpful in certain clinical scenarios in distinguishing bowel from intra-abdominal masses and normal organs. The contrast agents can be divided into positive agents (appearing bright on MRI) or negative agents (appearing dark on MRI).
Positive contras...
Article
Intravascular (blood pool) MRI contrast agents
Intravascular MRI contrast agents normally remain confined to the intravascular space, compared to Gd-DTPA which distributes throughout the extracellular fluid space. This is a result of intravascular agents having a molecular weight of approximately 70,000 and above, compared to a molecular wei...
Article
Reticuloendothelial MRI contrast agents
Reticuloendothelial MRI contrast agents can best be discussed in terms of those used for liver and spleen imaging and those for lymph node imaging.
Liver and spleen
The use of Gd-DTPA with routine imaging sequences of the liver is unsatisfactory. Particulate contrast agents targeted to the ret...
Article
Tumor specific MRI contrast agents
Tumor specific MRI contrast agents are pharmaceuticals that are targeted to tumors, either specifically or nonspecifically. Monoclonal antibodies are targeted to specific tumors such as adenocarcinoma of the colon. Metalloporphyrins exhibit affinity for many tumor types including carcinoma, sarc...
Article
Phase contrast imaging
Phase contrast imaging is an MRI technique that can be used to visualize moving fluid.
Basic principle
Spins that are moving in the same direction as a magnetic field gradient develop a phase shift that is proportional to the velocity of the spins. This is the basis of phase-contrast angiograp...