The effect of storage time and repeated measurements on the elastic properties of isolated porcine aortas using high resolution x-ray CT

A Laboratory CT scanner with a resolution of (0.1 mm)(3) was used to determine if storage up to 7 days in saline at 4 degrees C and (or) repeated measurements would alter the compliance, C, and incremental elastic modulus, E-inc, of isolated porcine aortas. All specimens were obtained fresh, made pressure-tight, and then mounted in the scanner, with humidified air used to produce adequate x-ray contrast. The specimens were imaged at pressures of 4, 8, 12, 16, 20, and 24 kPa, and vessel measurements were then obtained with a computerized technique and analyzed. Seven thoracic aortas were studied on days 0, 3, 5, and 7, with a significant change (p < 0.05) in compliance first occurring after three imaging studies (i.e., day 5). Compliance of the fresh thoracic aortas (mean +/- SD) was 0.90 +/- 0.28 mm/kPa at 14.4 kPa and 0.85 +/- 0.31 mm/kPa at 22.5 kPa. Six thoracic aortas were studied only on days 0 and 6 with no intermediate measurements. They showed no change in either compliance (0.88 +/- 0.07 mm/kPa at 14.4 kPa and 0.64 +/- 0.09 mm/kPa at 22.5 kPa) or E-inc (0.46 +/- 0.05 MPa at 14.4 kPa and 0.88 +/- 0.15 MPa at 22.5 kPa) from day 0 to day 6. Thus, number of measurements rather than time appears to be the important factor. Six abdominal aortas were studied similarly but on days 0, 3, and 6. No significant change occurred in compliance (0.15 +/- 0.06 mm/kPa at 14.4 kPa and 0.032 +/- 0.026 mm/kPa at 22.5 kPa) but E-inc showed a change, possibly due to their viscoelastic properties. We conclude that this nondestructive CT measurement method is suitable for repeated studies on porcine thoracic aortas, but not abdominal aortas, if the measurement involves two consecutive imaging sessions separated by no more than 6 days.