Comparison of Contrast Agents During CT Angiography
Condition: Contrast Enhancement on Cardiac CT
Study type: Interventional

Summary: 
      The purpose of this study is to compare the effects of a certain contrast agent (iodixanol)
      to two other commonly used contrast agents called Iopamidol (Isovue) and iohexol (Omnipaque),
      on heart and kidney safety in patients undergoing a cardiac CT angiogram. The investigators
      will evaluate whether iodixanol 320 (Visipaque®), an iso-osmolar agent, is better tolerated
      (flushing, injection site pain/warmth, headache, nausea) and provides equal image quality
      compared with iohexol 350 (Omnipaque®) and Isovue 370 during 64-slice multidetector computed
      tomography angiography (MDCTA). A fourth group (Visipaque 270) will be included, using low
      radiation dose technology during acquisition, to evaluate image quality, tolerability, and
      contrast enhancement compared to both Visipaque 320 and Omnipaque and Isovue. In addition to
      image quality, tolerability, and contrast enhancement, the investigators will evaluate heart
      rate, adverse events, reimaging, costs, and patient satisfaction among all four cohorts.

      The study will recruit 400 participants already undergoing CT angiography and consent and
      randomize them to one of four groups. Each of the possible contrast agents used are commonly
      used for CT angiography, so the primary risk is loss of confidentiality and being asked
      questions about tolerability. All other facets of the study (3 lead ECG, beta blockade,
      nitroglycerine use, CT angiography and contrast administration) are standard of care and
      being done for clinical uses.
    

Detailed description: 
      CTA infusion is administered using a 5 ml/sec IV iodinated contrast infusion. 50-70 ml of
      iodinated contrast is used for the scan depending on the patient's body habitus. The total
      contrast dose must not exceed 70 ml. An automated bolus tracking feature (SmartPrep, GE
      Healthcare, Milwaukee, USA) is used to judge contrast bolus arrival and optimize image
      quality. Patients will be asked to hold their breaths during scanning for up to 10 seconds. A
      Field of View (FOV) of 25 cm is adjusted to include the heart from below the carina to just
      below diaphragm. The aorta will be included in the FOV to exclude aortic pathology (ie.
      dissection, aneurysm, etc.). For patients in sinus rhythm, prospective ECG gating centered at
      75% of the R-R interval is used while those in Atrial fibrillation or HR >65 despite oral and
      IV medications, a retrospective gating is used. The following parameters are used Tube
      voltage = 100-120kV (based on body habitus), tube current = 400 mA, gantry rotation speed =
      0.35 seconds, slice thickness = 0.625 mm, rows = 64, coverage = 128-160 mm.

      Estimated radiation dose is = 2-5 mSv dependent on BMI, cardiac height and heart rate. A post
      acquisition software (Adaptive Statistical Iterative Reconstruction, GE healthcare,
      Milwaukee, USA) is used to reduce pixel noise standard deviation (noise) by 30 percent and
      allows for reduced mA in the acquisition while still yielding diagnostic images, thereby
      reducing total dose required. At the conclusion of each acquisition, technologists collect a
      survey of patient satisfaction quantifying side effects of different contrasts: flushing,
      headache, nausea, and pain at injection site as mild, moderate or severe.

      Advantage Workstation 4.6 software (GE healthcare, Milwaukee, USA) is used for post
      acquisition processing. Readers, who are blinded to the type of contrast media used, assess
      image quality by measuring contrast enhancement in aorta, LV myocardium, left main, proximal
      Left Anterior Descending artery, proximal and distal Right Coronary arteries. Subjects with
      coronary artery bypass graft and stents are excluded. Heart rate (HR) variability during the
      scan is also evaluated. A comparison of the degree of contrast enhancement of the coronary
      lumen as well as the differences for each of the four contrast agents will be measured and
      reported, stratified by 100 kVp and 120 kVp acquisition. The image quality of 17 coronary
      artery segments will be graded by two cardiologists in consensus with the use of a four-point
      scale (1= excellent, 2=good, 3=fair , 4= poor enhancement) blinded to contrast agent
      administration.

      Statistical Analysis:

      All analysis is conducted using SPSS 18.0 for window (SPSS Inc., Chicago, IL, USA).
      Comparisons between groups are performed using a Student t-test for continuous variables with
      normal distributions and the Mann-Whitney U test for continuous variables with non-normal
      distributions. Categorical variables were analyzed by means of χ2 analysis. Correlation
      between minimum HR and maximum HR was calculated with the Pearson correlation coefficient.
      The Cochran-Mantel-Haenszel test was used for analyzing the difference in visual quality
      between two groups.
    

Intervention name(s): contrast agent
Intervention type(s): Diagnostic Test
Intervention description(s): we are randomizing patients to different contrast agents.
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: randomized cohort into 4 groups - each group with a different contrast agent (omnipaque, visipaque 280, visipaque 320, isovue)
Masking: Triple (Participant, Care Provider, Investigator)
Primary purpose: Diagnostic
Keywords: cardiac CT; enhancement; contrast; safety; image quality