Cell membranes are semi-permeable. Just like your private dinner party, only certain molecules can cross the cell membrane. This allows the cell some control over what enters and leaves. Water, small molecules, and molecules without a charge can pass freely.
Magnetic Resonance Angiography (MRA) and Magnetic Resonance Venography (MRV) Aetna considers magnetic resonance angiography (MRA) medically necessary according to the selection criteria outlined below. MRA is considered appropriate when it can replace a more invasive test (e.g., contrast angiography) and reduce risk for members. While MRA is a rapidly evolving technology, its clinical safety and effectiveness for all anatomical regions have not been established by the peer- reviewed medical literature.
What is an MRCP? </>An MRCP test is a specialized MRI exam that evaluates the hepatiobiliary and pancreatic systems, including the liver, gallbladder, bile ducts, pancreas and pancreatic duct. An MRCP test can also be ordered to find the cause of pancreatitis or diagnose unexplained abdominal pain. Additionally, MRCP is a less invasive alternative to ERCP, a procedure that uses an endoscope combined with an IV injection of x-ray contrast dye and fluoroscopy (x-ray images).