Uma Numburi MS, Presenter: Nothing to Disclose

Sandra Simon Halliburton PhD, Abstract Co-Author: Research grant, Siemens AG

Among the most dramatic changes in MDCT impacting coronary imaging is the decreased scan time now ranging from less than 1 to 6 sec. Contrast injection protocols have largely been adjusted through trial and error. Our objective was to provide an empirical model for determining patient-specific contrast injection protocols for 2, 4, and 6 sec coronary scans.

Test bolus data from 25 patients was obtained using MDCT. Each patient received an injection of 20 mL of contrast (Ultravist 370) at 4.5 mL/sec followed by saline and the resulting test enhancement curve was measured in the ascending aorta. Using a previously validated transfer-function model, each patient was considered a linear, time-invariant system such that the contrast injection profile (system input) was related to the enhancement curve (system output) by a patient-specific transfer function computed using the test injection and enhancement. This function was then used to predict the contrast injection profiles required for each patient to achieve and maintain 300 HU in the heart for 2, 4 and 6 sec. Multiple regression analysis was also performed to empirically correlate patient-specific injections (volumes and flow rates) with patient and test enhancement curve characteristics and was validated by comparison to results from the transfer-function model.

Individual transfer-functions were obtained in all patients and successfully used to predict contrast injection profiles. Injection parameters from regression equations were similar to values from the transfer function model. On average, these were biphasic injections requiring reduced total contrast volumes and flow rates with longer phase1 and shorter phase 2 durations as scan time decreased. Average values for a 6 sec scan were phase1: 23 mL at 4.9 mL/sec, phase2: 41 mL at 3.5 mL/sec; 4 sec, phase1: 29 mL at 4.6 mL/sec, phase2: 26 mL at 3.3 mL/sec; 2 sec, phase1: 34 mL at 4.3 mL/sec, phase2: 14 mL at 2.6 mL/sec.

Biphasic injections requiring average total contrast volumes of 49, 55 and 64 mL may be appropriate for 2, 4 and 6 sec coronary imaging, respectively. Patient-specific protocols can be determined using empirical equations.

Latest scanners enable short acquisition times for coronary imaging and require optimization of contrast protocols to allow use of decreased contrast volumes and ensure optimal enhancement.

Numburi, U, Halliburton, S, Modeling of Contrast Injection for Coronary MDCT with Short Scan Times.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8011049.html