Quantitative coronary angiography: impact of imaging parameters on accuracy and confidence interval

The impact of patient size, image intensifier (II) dose, focal spot size, and matrix size on accuracy and the confidence interval of a quantitative coronary analysis (QCA) system has been investigated using calibrated tube phantoms in combination with a varying amount of water representing the patient's size. We found good accuracy for the whole range of patients' sizes (15-30 cm H2O) except that a 0.5-mm vessel diameter (phi) can no longer be measured at > or = 25 cm H2O. Moreover, at 1-mm vessel phi gives no reliable confidence interval for > or = 30 cm H2O. A small focus (F = 0.4 mm) is favorable for small objects (< or = 15 cm H2O) only. For larger patient sizes the lack of contrast due to higher kilovoltage compensates the improved resolution. Low digital "cine dose" (e.g., 0.1 microGy/f at 17 cm II) is acceptable except for 0.5 mm vessel phi. Better contrast compensates for the increased noise. There is a small improvement in accuracy and confidence interval for vessels < or = 1.0 mm phi using the matrix 1024(2). The HICOR system allows one to stay within the DICOM card standard (matrix 512(2) using the mode "acquisition zoom" while providing high resolution in a limited field size.