Results: CT Clinical Practice: Data acquisition protocols

Coronary CT Angiography

1. Can we get away without betablocker with any new software? Could it be gold standard?

Answer: Coronary artery CTA has come a long way, and will continue to evolve rapidly over the next 2-3 years. I worked with Tony Cook, of SMS, yesterday, and here are some keys for you to be successful:

  • (1) You need a heart rate around 60 bpm, so beta blocking is mandatory
  • (2) You need to make sure the techs know how to use the gating software and the optimization of segments on the reconstructions
  • (3) You need to know how to use InSpace and vessel view, to do the post processing
  • (4) Saline chase works best for good right coronary artery visualization.
  • (5) A 23 to 25 second delay and a 4 cc/second bolus are needed.
  • (6) Post processing is critical.
  • (7) There is a learning curve, so spend time early.

2. We are currently experimenting with our protocol for CT angiography bypass grafts. We are using a Siemens Somatom Sensation 16. We would value your input on what protocol you and your staff have found works best for you.

Answer: The protocol we use is:

  • 23 to 25 second delay
  • 100-120 cc bolus of contrast at 4 cc/sec followed by a flush of 25 cc saline.
  • .75 -1 mm thick slices
  • Reconstruct at 10% intervals thru the heart cycle for 4D display w/InSpace 4D
  • We scan from the tracheal bifurcation thru the base of the heart.
  • It is key to have a heart rate of 60-70 (max) BPM, so beta blockers are used routinely.
  • For more good tips- check with Tony Cook of Siemens.

3. We have recently installed a GE LS16 for cardiac imaging and preliminarily we are doing some coronary angiograms but very often the cardiologists challenge our findings. We find we have quite a high false-positive rate, but they do feel the threat of emerging non-invasive cardiac imaging. One interesting point is they ask whether 16 slide could do or have any role in myocardial perfusion study, just like that done by MRI. Have you ever heard about this before?

Answer: As for your false positives, I have a few questions.

  • (1) What heart rate patients are you studying? If beta blockers are not used, this could be a factor
  • (2) What is your post processing data workflow? This is critical to success
  • (3) There are other factors as well, including scan protocols? What protocol are you using?
  • (4) I asked your question to GE, and they provided the following response to the question:
    - If the heart rate is controlled properly, and if the appropriate scan protocol is used (Burst or Burst + for high HR's), we have seen 95%+ success rates with few false positives. Factors that can influence success include how well they gated the study, what software they used for the visualization and analysis, and how well trained they are in those techniques. I agree with the answer you provided--the post processing is critical. We recommend that they read from axial and MIP and NOT from volume rendered for their primary diagnosis. Also, in heavily-calcified and/or tortuous arteries, it is useful sometimes to "spin around" the vessel with MPR or MIP images to ensure that you've seen it all. After you get answers to the questions you asked, we can hopefully shed some more light on this.-Sholom M. Ackelsberg, General Manager, Global CT Research and Advanced Applications, GE Medical Systems.

4. In what percentage of cases of coronary CT do you achieve non-equivocal visualization of the circumflex, the two largest obtuse marginals, posterolaterals, diagonals PDA and acute marginals? What's you coronary equivocation rate and what are your recommended study protocol factors to minimize it? Can non equivocal visualization of the main secondary branches (forget the tertiary branches for now) be accomplished routinely in > 95% of patients with any of the main vendors if one is willing to go the extra mile in protocol design? What does one need in equipment, in study design and photon deliver to get a stand-alone coronary CTA in > 95% of patients including the large sized patient?

Answer: Coronary CTA is new, with little published results and a study where progress is being made daily. If you want a system that is exactly equal to catheter angio at this point in 100% of cases, you will be disappointed. I believe you will need a 64 slice scanner to approach these numbers. With current technology, the key is technique and protocol:

  • (1) 100 to 120 cc Visipaque followed by saline flush w/dual head injector
  • (2) Routine use of beta blockers to get heart rate in the 60s
  • (3) Good post processing software for vessel analysis and quantification
  • (4) Reconstruction of multiple phases of the cardiac cycle to get the best view of each vessel (i.e. 60% best for LAD)
  • (5) Fast rotation time like with the new Siemens Straton tube, which also has higher mAs for bigger patients.
  • (6) In our practice we are getting better every day, so experience for the techs and the radiologists is critical

5. I am interested in cardio-radiology. I would like to know the protocol of 16 slice MDCT coronary angiography (including the amount of contrast medium/saline flush administered and the flow rate).

Answer: We will post detailed protocols soon, but briefly we use:

  • Delay 23 to 25 seconds
  • Inject 4 cc/sec of 100 ml Visipaque 320
  • Inject 25 cc saline bolus to follow at 4 cc/sec
  • We use 1 mm thick sections off .75 mm detectors
  • We do MIP and VRT 3D post processing.

References


Schoepf UJ, Becker CR, Ohnesorge BM, Yucel EK. CT of coronary artery disease. Radiology 2004; 232 (1): 18-37.

  • Summary: This recent review covers MDCT acquisition protocols for coronary artery calcification and coronary artery angiography, as well as radiation dose. For angiography, image display (2D and 3D) and clinical applications are discussed and demonstrated.

Schoenhagen P, Halliburton SS, Stillman AE et al. Noninvasive imaging of coronary arteries: Current and future role of multi-detector row CT. Radiology 2004; 232(1): 7-17.

  • Summary: This review article addresses the clinical utility of MDCT angiography of the coronary arteries. Calcium scoring and assessment of plaque morphology are discussed as well.

Choi HS, Choi BW, Choe KO et al. Pitfalls, artifacts and remedies in multi-detector row CT coronary angiography. Radiographics 2004; 24: 787-800.

  • Summary: This article emphasizes the importance of recognizing artifacts encountered during coronary CT angiography, including artifacts due to motion, beam-hardening, adjacent structures and technical errors. The authors make recommendations to minimize artifacts during data acquisition and post-processing.

Pannu HK, Florh TG, Corl FM and Fishman EK. Imaging of the coronary artery: Current concepts in multi-detector row CT evaluation of the coronary arteries: principles, techniques and anatomy. Radiographics 2003; 23: S111-S125.

  • Summary: This review of multislice coronary CTA includes a discussion of acquisition parameters (heart rate, scan time, spatial resolution, temporal resolution, motion artifact and dose). Acquisition protocols are described with slice thickness specified for 4, 8 and 16 slice CT. An overview of coronary artery anatomy is provided with numerous images. This article provides CME credit.