Limitations of ultrasonography in surveillance of small abdominal aortic aneurysms.

The repeatability, observer bias and instrument bias of aortic diameter measurement by ultrasonography, were investigated in ten patients with small (3-6 cm by computed tomography) infrarenal abdominal aortic aneurysm. The repeatability of maximum aortic diameter measurement by ultrasonography was much better for anterior-posterior than transverse diameter, with coefficients of repeatability 3.0-7.5 mm and 10-15 mm respectively. The repeatability of suprarenal aortic diameter measurement was poor. Surprisingly, maximum diameter using ultrasonography was larger than that using computed tomography, the difference being least for anterior-posterior measurements. At best a single, experienced observer, using the same instrument may provide aortic diameters using ultrasonography accurate to within 5 mm, but more commonly such aortic diameter is only accurate to within 8 mm.