Let me preface this by saying I work with both the IAC and Radiology 
standards and my own lab scans from thigh to ankle.  Medical staff, not 
administrators (or anyone with a stop watch), should determine how medical 
testing gets performed. 

But not everyone who scans to the knee (and not below it) is jeopardizing 
patients or even doing a bad job.

BTW, the AIUM-ACR standard DOES recommend scanning below the knee 
when the study does not explain the patient's symptoms, e.g. calf pain with a 
negative femoropopliteal study.
"Symptomatic areas such as the calf generally require additional evaluation 
and additional images if the cause of the symptoms is not readily elucidated 
by the standard examination." 
"The patient presentation, clinical indication, or clinical management pathways 
may require protocol adjustments such as more detailed evaluation of the 
superficial venous system, evaluation of the deep calf veins, or a bilateral 
study." 

While it is true that many DVT are totally or in part below the knee, there are 
reasonable people who think scanning below the knee is NOT necessary for all 
patients. 

Many centers, especially Europeans and North American internal medicine 
groups, use 2 thigh to knee ultrasounds a week apart. This requires two scans 
for moderate to high risk groups and no further scanning for low risk groups 
or those with negative d-dimer (I recognize how few patients get good 
evaluation before coming to a lab and this is one reason while I personally 
support the complete examination). This approach is well researched and is 
safe. 

The current anticoagulation guidelines from the Chest Physicians support this. 
The chapters are hundreds of pages long and have a VERY long chapter on 
diagnosing DVT. The guidelines do not recommend treating everyone with calf 
DVT and support tailoring imaging to diagnose treatable conditions rather than 
all DVT (i.e. calf DVT)

How did they come to this conclusion. 
1) Very few people evaluated have DVT, they have something else.
2) The minority of patients with calf DVT will propagate to above the knee 
(about 20%).
3) Larger veins are more likely to cause symptomatic PE, calf veins not at all 
or only rarely.
4) There is weak evidence that treating calf DVT affects the rate of chronic 
venous insufficiency or recurrent DVT. (Obviously more work needs to be done 
since it makes some sense that treating a disease earlier should help).
5) The risks of anticoagulation are real and the risks of overtreating 
insignificant calf DVT may outweigh the benefit of treating calf DVTs which 
have a more aggressive natural history.

1.	Guyatt GH, Akl EA, Crowther M, Gutterman DD, Schuunemann HJ, for 
the American College of Chest Physicians Antithrombotic Therapy and 
Prevention of Thrombosis Panel. Executive Summary: Antithrombotic Therapy 
and Prevention of Thrombosis, 9th ed: American College of Chest Physicians 
Evidence-Based Clinical Practice Guidelines. Chest. 2012Feb.6;141(2 
suppl):7S–47S. 
2.	Bates SM, Jaeschke R, Stevens SM, Goodacre S, Wells PS, Stevenson 
MD, et al. Diagnosis of DVT: Antithrombotic Therapy and Prevention of 
Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based 
Clinical Practice Guidelines. Chest. 2012Feb.6;141(2 suppl):e351S–e418S. 

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