Eur Radiol (2011) 21:1390–1396 Fig. 6 Medtronic Hall mechan- ical PHV in mitral position 1395 be compromised by motion artefacts and rhythm irregu- larities. The current study was undertaken to systemati- cally examine the clinical performance of CT, and, to our knowledge, is the largest series of PHVs assessed by CT described to date. In addition to the 5 PHVs tested in vitro, we currently evaluated 9 additional PHV types covering a whole range of mechanical and biological PHV. For the mechanical PHV, our findings reflected the in vitro experience: we found that the Medtronic Hall valve had a significantly better image quality than Björk-Shiley and Sorin tilting disc valves. Furthermore, the Carbomedics and ON-X valves had a better image quality than the St Jude and Medtronic Hall valves (Table 1). However, this finding was not significant. This discrepancy in image quality can be related to the differences in PHV design. The assessment of the Fig. 7 PHV dysfunction on MDCT. A St Jude PHV in the mitral position with paravalvular leakage (arrowhead) Björk-Shiley and the Sorin monoleaflet tilting disc valves resulted in non-diagnostic image quality of all scoring regions due to severe artefacts. These artefacts are the result of the presence of cobalt in the valve housing and strut mechanism. In clinical practice, these cobalt containing PHVs are not suitable for evaluation with MDCT [3, 4, 6]. All currently implanted mechanical PHVs can be assessed by MDCT because they are all manufactured of titanium and carbon. The biological PHVs show a good image quality except for valvular detail. We scored diastolic images and found that the leaflets of several bioprostheses could not be identified properly. We postulate that the limitations in spatial and temporal resolution of the CT may preclude good image quality in bioprostheses with thin leaflets (porcine aortic valve leaflets). Our results were less promising than a recent report from Chenot et al. [7] that demonstrated the feasibility of planimetric measurement of the orifice area of biological prostheses. The primary cause for this disparity may well be that our series was purely retrospective and that not all scans were specifically made for imaging of the bioprosthesis. Six of the 21 (29%) biological PHVs were examined using a CT protocol for aortic imaging that uses a lower mAs setting which may have hampered the visualisation of the valve leaflets. The differences in contrast and imaging protocols may have resulted in a superior image quality in Chenot’s series. Furthermore, Chenot et al. [7] identified several modes of biological PHV dysfunction such as leaflet thickening, calcification and possible thrombus. Leaflet thickening is likely to make the leaflets more easily discernable on CT. However, the retrospectively ECG- gated scans that allow for dynamic assessment of PHV are associated with a relative high radiation dose. Lower dose PHV CT protocols are currently being explored [8]. Continued efforts for large scale prospective studies are required to further determine (1) normal MDCT character- istics of commonly implanted PHV types, (2) the exact