Protocol modifications for CT perfusion (CTp) examinations of abdomen-pelvic tumors: Impact on radiation dose and data processing time

To evaluate the effect of CT perfusion (CTp) protocol modifications on quantitative perfusion parameters, radiation dose and data processing time. CTp datasets of 30 patients (21M:9F) with rectal (n = 24) or retroperitoneal (n = 6) tumours were studied. Standard CTp protocol included 50 sec cine-phase (0.5 sec/rotation) and delayed-phase after 70 ml contrast bolus at 5-7 ml/sec. CTp-data was sub-sampled to generate modified datasets (n = 105) with cine-phase(n = 15) alone, varying cine-phase duration (20-40 sec, n = 45) and varying temporal sampling-interval (1-3 sec, n = 45). The estimated CTp parameters (BF,BV,MTT&PS) and radiation dose of standard CTp served as reference for comparison. CTp with 50 sec cine-phase showed moderate to high correlation with standard CTp for BF&MTT (r = 0.96&0.85) and low correlation for BV (0.75, p = 0.04). Limiting cine-phase duration to 30 sec demonstrated comparable results for BF&MTT, while considerable variation in CTp values existed at 20 sec. There was moderate-to-high correlation of CTp parameters with sampling interval of 1&2 sec (r = 0.83-0.97, p > 0.05), while at 3 sec only BF showed high correlation (r = 0.96, p = 0.05). Increasing sampling interval (47-60%) and reducing cine-phase duration substantially reduced dose(30.8-65%) which paralleled reduced data processing time (3-10 min). Limiting CTp cine-phase to 30 sec results in comparable BF&MTT values and increasing cine-phase sampling interval to 2 sec provides good correlation for all CTp parameters with substantial dose reduction and improved computational efficiency.