IMPORTANCE OF CALIBRATION FOR DIAMETER AND AREA DETERMINATION BY INTRAVASCULAR ULTRASOUND

Background: Intravascular ultrasound (IVUS) permits quantitative asses sment of the lumen diameter and area of coronary arteries. The experim ental study was performed to evaluate the accuracy of diameter and are a measurements. Methods and results: Lumen quantitation (lumen diamete r D and cross-sectional area A) in lucite tubes (lumen diameter 2.5 to 5.7 mm, Plexiglas(TM)) was performed using a mechanical IVUS system ( HP console, 3.5F catheter, Boston Scientific, 30 MHz). The influence o f fluid type (blood, water and saline solution), fluid temperature (20 degrees C/37 degrees C), catheter to catheter variation, gain setting and ultrasound frequency (12, 20 and 30 MHz) was determined. In blood at 20 degrees C there was a constant deviation of the measured diamet er from the true luminal diameter of -0.29 +/- -0.04 mm (p<0.06). In w ater and saline solution at 20 degrees C the mean deviation from true diameter was -0.21 +/- -0.06 mm (p<0.06). At 37 degrees C, the deviati on in blood was greater than at 20 degrees (-0.34 +/- -0.02 mm) which is >10% in a 3mm tube (p<0.06). Three of the ten catheters tested in w ater at 20 degrees C underestimated true diameter by more than -0.3 mm . The deviation from true diameter (5mm tube) with varying gain settin gs was -0.14 mm to -0.23 mm compared to -0.19 mm at standard settings (p>0.288). At 12 MHz diameter measured was overestimated. The error in absolute area estimation increased with increasing diameter tested in blood at 37 degrees C (-1.21 to -2,72mm(2)), whereas the relative err or ([Measured Area-True Area]/True Area x 100 [%]) was more striking a t smaller diameters (up to -25% in the 2.5 mm tube). Conclusion: Lumin al diameters and areas are underestimated by this particular IVUS syst em. When IVUS imaging and measurements are made during coronary interv entions this error should be taken into account with regard to appropr iate sizing of the device and the assessment of the postprocedure resu lt. Because systematic errors might also occur in other IVUS systems ( not tested in this study), it is advisable to ensure that each system is validated prior to clinical use, especially when exact measurements are required.