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.
A positive herpes simplex culture or HSV DNA (PCR) test from a vesicle scraping indicates an active HSV-1 or HSV-2 infection. A negative culture or PCR test result indicates that the herpes simplex virus was not detected but does not definitely rule out the presence of virus. The sample may contain too few copies of the virus to be detected or does not contain actively replicating virus.