| dc.description.abstract | Endovascular aneurysm repair (EVAR) has become increasingly popular over the last
few years, but is associated with complications such as endoleaks, graft fracture and
migration (Ouriel, Clair et al. 2003), which prompt urgent intervention. This has
necessitated lifelong follow up of patients with CT scans at regular intervals, which
has significant cost implications and exposes patients to a large radiation dose.
Duplex ultrasound has been proposed as an alternative (Henao, Hodge et al. 2006,
Sandford, Bown et al. 2006), but substantial variation has been reported in the
literature in terms of its sensitivity and specificity for detecting complications.
The aim of this research project was to assess the limitations of duplex ultrasound and
to establish whether its sensitivity and specificity in routine clinical imaging for the
surveillance of patients post EVAR could be improved to the same level as CT. Novel
ultrasound blood and tissue mimicking phantoms were used to assess the limits of
ultrasound, and the effects of operator experience, in detecting complications
(Ramnarine, Nassiri et al. 1998, Teirlinck, Bezemer et al. 1998, Madsen, Dong et al.
1999, Surry, Austin et al. 2004).
The study was divided into a clinical arm and a laboratory-based arm. The clinical
arm compared results from CT and Duplex ultrasound for patients post EVAR. In the
laboratory, novel tissue and blood mimicking ultrasound phantoms with known
geometry, material and blood flow parameters were used to assess the limitations of
duplex ultrasound, independent of the operator. The effect of operator experience on
the reliable detection and classification of complications was also assessed. In
12
addition, machine dependent parameters were studied to optimise the sensitivity of
duplex ultrasound in EVAR evaluations.
The results of our laboratory experiments demonstrated that endoleak detection with
duplex ultrasound proved more difficult with increasing depth of the endoleak from
the viewing position and when the endoleak was in a plane distal to the aortic flow.
Our results also demonstrated an increasing trend toward flow detection with
increasing flow rates of the endoleak. Our clinical arm corroborated the findings of
the laboratory arm with endoleaks that were missed on DUS being identified as slow
flow endoleaks located posteriorly and in direct apposition with the stent graft.
Although our results did not unequivocally demonstrate the superiority of DUS
compared to CT, there was a clear trend towards diagnosis of all endoleaks that
required intervention. Our experiments support the use of DUS for the surveillance of
patients post EVAR in a complimentary role to CT, thus reducing the substantial
radiation exposure for these patients and the associated cost burden to health
providers. | en_US |
