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.
Herpes simplex virus testing is performed to identify an acute herpes infection or to detect herpes antibodies, an indication of a previous exposure to herpes. One of the most common viral infections, herpes simplex virus (HSV) exists as two main types, HSV-1 and HSV-2.SV testing detects the virus itself, its viral DNA, or antibodies to the virus. During an acute primary infection or reactivation, the virus may be detected by: 1  Herpes culture. 2  A sample of fluid is collected via swab from an open sore and inoculated into cells that allow the virus to grow.