Current Clinical Concerns in CT: Results : Protocols
DVT
1. What protocol is recommended for DVT on a GE 4 multislice? Also- what predelay would be used if the access to the vein is in the lower extremity? What predelay would you use if you have an AC 18 gauge line?
Answer: Most centers are no longer doing lower extremity studies for pulmonary embolism. However, if you want to, I would use a 3-4 minute delay and scan 5 mm sections every 10 - 15 mm from the renal hilum through the mid calf. |
2. What protocol do you use for CT venogram post pulmonary angiography when you are looking for DVT's?
Answer: Using a 3-4 minute delay (from the start of injection) most people scan from the renal hilum through the mid calves at 10-15 mm intervals. |
3. What protocol would you suggest for combined CT venography and Pulmonary angiography in suspicion of PE? To my limited experience to start scanning veins of abdomen, pelvic and legs in recommended 3-4 minutes after start of injection (150 cc) is not providing sufficient highlighting of vein lumens. Would you prefer to scan veins from diaphragm to calf or opposite? How would you rely on examining calf veins with CTV?
Answer: Using a 3-4 minute delay (from the start of injection) most people scan from the renal hilum through the mid calves at 10-15 mm intervals. |
4. A website says that there are hospitals that are scanning through the lower extremities looking for a DVT post-PE study. Are there places that still do this, and if so, what protocol would you suggest? We did this a few years ago and found that it had very low yield.
Answer: Some sites do indeed do the pelvis/legs as part of the PE protocol. The published results in the literature have shown CT to be better than ultrasound, but many are concerned with the increased radiation dose. If you do this protocol, you need a scan delay of 3 minutes or so, so scan from the renal hilum through the popliteal fossa. You can scan with lower dose scans at 5 mm intervals. |
References
Katz DS, Loud PA, Bruce D et al. Combined CT venography and pulmonary angiography: A comprehensive review. Radiographics 2002; 22: S3-S24.
- Summary: This article includes a review of the literature, description of CT findings in the setting of DVT, results from the authors' experience with 957 patients, and recommendations for a protocol to perform CT venography after CT pulmonary angiography. The authors reviewed 957 CTVPA examinations and found an incidence of 10.5% (100 patients), of which 58% had associated pulmonary embolism. The distribution was nearly equal among the common femoral, superficial femoral, popliteal and deep calf veins. The protocol recommended is as follows: after infusing 150 cc of 300 mgI/ml intravenous contrast, scanning is initiated following a 3 to 3.5 minute delay from the onset of the infusion. They acquire 5 or 10 mm axial venographic images at 4-cm intervals, extending from the diaphragm to the ankles.