7. Special Investigations Test Advantages Disadvantages Contrast “ Gold standard” Invasive Venography Sensitivity ~ 100% Requires specialized equipment Easily interpretable Rare, but serious side effects MRI Highly accurate Expensive Safe during pregnancy Not readily available Non-invasive CT Non-invasive Limited data Can diagnose pelvic DVT Concurrently exclude PE Ultrasonography Highly accurate Not accurate for calf or pelvic DVT Non-invasive Complete study is time consuming D-Dimer Rapid laboratory study Only used to rule-out DVT Can aide in exclusion of DVT