Other Imaging Modalities

Other less frequent imaging modalities include:

Impedance plethysmography

  • Impedance plethysmography¬† is a non-invasive test that measures small changes in electrical resistance of the calf. These measurements reflect blood volume changes, and can indirectly indicate the presence or absence of venous thrombosis.
  • Insensitive for non-occluding thrombus, calf thrombus, or thrombus above the inguinal ligament


  • Approaching venography for sensitivity and specificity
  • Highly sensitive for calf thrombus, also for thrombus above the inguinal ligament when CT not practical
  • Particular benefit in pregnancy when Doppler flow characteristics change with the gravid uterus
  • Limited availability of scanners


  • Limited trials report similar results to ultrasonography
  • Effective in diagnosis of ileofemoral and more proximal thrombus
  • Problems arise with contrast reactions, radiation exposure and presence of metal implants


  • Previously the gold standard, this has now been replaced with non-invasive and less harmful techniques such as ultrasound.