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.
The first test, the HCV antibody test, sees if you have been exposed to the virus. The second test is the viral load test, and it detects whether you were merely exposed or if you actually have hep C. If that test is positive, then a genotype test is done to find out what kind of hep C you have.