Transluminal attenuation-gradient coronary CT angiography on a 320-MDCT volume scanner: Effect of scan timing, coronary artery stenosis, and cardiac output using a contrast medium flow phantom

Abstract Purpose Transluminal-attenuation-gradient (TAG) may reflect patient characteristics and physiological parameters. Furthermore, TAG may be affected by factors such as the CT scanner speed, scanning method, scan timing after contrast-medium (CM) injection, and the injection methods. The purpose of our study was to investigate quantitative TAG at different scan timing points after CM injection for coronary CT angiography. Materials and methods Using a CM flow phantom and two types of connecting tube mimicking 0% and 70% coronary artery stenosis, we performed 320-detector volume scanning. The heart rate was set at 60 bpm and cardiac-output (CO) at 2.0 and 4.0 l/min, respectively. The acquisition time repeated at 0.5-s intervals for 40 and 25 s at a CO of 2.0- and 4.0 l/min. We measured the CT number on the same slice level, calculated the time-density-curve (TDC) and the TAG at each time point. Results At COs of 2.0 and 4.0 l/min at 0% stenosis, TAG exhibited smaller variations (−3.02 to +0.55 HU/cm at 2.0 l/min, −2.63 to +0.43 HU/cm at 4.0 l/min) than at 70% stenosis at each time point along the TDC. Compared with a CO at 2.0 l/min with 70% stenosis, the TAG curve for a CO at 4.0 l/min gradually changed with time (−6.64 to +1.18 HU/cm at 2.0 l/min vs. −3.46 to +2.75 HU/cm at 4.0 l/min). Conclusion The TAG value was affected by scan timing after CM injection and by CO although the size of the connecting tube with and without stenosis was identical.