Effect of scan time on perfusion and flow extraction product (K-trans) measurements in lung cancer using low-dose volume perfusion CT (VPCT).

Rationale And Objectives: To assess the effect of measurement time on blood flow (BF), blood volume (BV), and k-trans-values (flow extraction product) in patients undergoing volume perfusion computed tomography (VPCT) for lung cancer.

Materials And Methods: This prospective study was approved by our local Research Ethics Committee and informed consent was obtained in all patients. Between December 2009 and December 2010, 75 VPCT scans were obtained in 54 consecutive patients (15 women, 39 men) with histologically confirmed lung cancer. A 64-second VPCT of the tumor (80 kV, 60 mAs) using 128 × 0.6-mm collimation, 6.9-cm z-axis coverage and a total of 26 volume measurements, was performed. BF, BV, and K(trans) were determined. Data evaluation was performed for different measurement times (64 seconds, 45 seconds, 39 seconds, and 36 seconds) by removing the last two, four, and five scans and repeating the analysis. A one-way repeated-measures analysis of variance was used to test for effects of measurement time on BF, BV, and k-trans and unpaired/paired Student t-tests were applied for comparisons within/between groups, respectively.

Results: No effect of measurement time on BF values was noted (P > .05), whereas a significant decrease of BV values (at 39 seconds: 71% ± 2% of 64-second values) and a significant increase of k-trans-values (at 39 seconds: 146% ± 8% of 64-second values) were observed with progressively shortened measurement time (P < .05, respectively). Additionally, with reduced measurement time, the increase in k-trans-values was significantly more pronounced in those patient groups with higher BV (at 39 seconds: 171% ± 15% versus 120% ± 3% of 64-second measurements), and those with lower k-trans (at 39 seconds: 167% ± 16% versus 126% ± 4% of 64-second measurements) (P < .05, respectively).

Conclusion: Whereas estimation of BF in lung cancer was independent from VPCT measurement time within the chosen ranges, approximation of both BV and k-trans was affected by measurement duration. A fixed measurement time of 40 seconds is recommended.