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A teaching and information resource on ventilation/perfusion imaging in Nuclear Medicine, primarily for the differential diagnosis

of Pulmonary Thrombo-Embolism (PTE/PE), especially where the images are complicated by the presence of other diseases

such as pneumonia and chronic obstructive airways disease (COPD/COAD).

The Diagnostic Difficulty of Pulmonary Embolism

A function of this site is to help increase the knowledge about diagnostic options for General Practitioners and other Doctors who are frequently faced with the diagnostic dilemma that is Pulmonary Embolism.
Whilst the easiest action is to ‘go with the flow’, which in recent times has meant to refer your patient for a ‘Computed Tomography Pulmonary Angiogram’ (CTPA) at the nearest hospital or Radiology clinic, there are now solid grounds for reviewing such decisions in the light of a less hazardous diagnostic alternative of at least equal efficacy.
PE demands a quick and accurate diagnosis, as the consequences of missing it- either way – can be catastrophic. And this understandable fear has led to a discounting of the radiation dose to which your patients will be exposed in CTPA on the very reasonable grounds that a downstream ‘possible’ risk of radiation-induced cancer pales to insignificance beside the risk of a fatal PE. Then equally, you have to consider that on average only about 20% of referrals for PE actually turn out to be positive. Thus minimising the radiation exposure for those 80% demands serious consideration.
But if a Nuclear Medicine clinic exists within your referral range, it is time to consider referring potential PE patients for a Ventilation/Perfusion (V/Q) study because:
  1. Peer reviewed literature clearly shows V/Q to be AT LEAST equally efficacious to CTPA
  2. V/Q delivers a much lower radiation dose to your patient, especially in females where the breast dose is about 7% of that delivered by CTPA. To put it all in perspective, a CTPA for PE can deliver up to 23 times the breast dose of a mammogram.
  3. The test can be modified for pregnant women to reduce foetal dose even further.
  4. No patient need be excluded, whereas up to one in five patients are either barred from being injected with contrast media, or are unable to breath-hold at all.
Pulmonary Embolism (PE) is currently listed as the third highest cause of death in hospitalised patients in the USA.  A national survey published back in 1975, as summarised in the diagram below adapted from that survey, is still being quoted in support of the need to take care in ensuring the correct diagnosis is made.
It is generally agreed that a clinical differential diagnosis is only accurate in about 60+% of cases, underlining the critical importance of a high quality, rapid, safe and easily performed screening test.
This webpage, written by experts in the field, is designed to analyze in detail the various options for screening patients for PE, and puts the case for choosing ventilation/perfusion (V/Q) SPECT diagnostic imaging, specifically using the Australian-invented ventilation agent, Technegas as the best possible test for your patients.   Although this technique did not exist at the time of the survey, and no doubt the safety of anti-coagulation therapy will have improved over the years, a careful study of the diagram that highlights the consequences of a wrong diagnosis is still very meaningful today.