School of Human Development, Academic Division of Reproductive Medicine, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK E-mail: nick.fenning{at}nottingham.ac.uk
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Introduction |
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The article by Hsien-An Pan and colleagues on the application of 3D power Doppler ultrasonography in the diagnosis of polycystic ovarian syndrome (PCOS) (Pan et al., 2002) contains several areas that require further explanation and clarification before valuable conclusions can be made.
3D power Doppler ultrasonography or angiography (3D-PDA) is a relatively new technique. The work is original in terms of the application of 3D-PDA in patients with PCOS, but not in terms of the assessment of stromal blood flow in this group of patients. This has repeatedly been shown to be increased with pulsed-wave Doppler ultrasound (Zaidi et al., 1995; Aleem and Predanic, 1996
; Agrawal et al., 1998
). A comparison of these two techniques would have been more valuable and a prospective study testing their individual diagnostic capabilities is needed.
The authors refer to Pairleitner and colleagues' work on the application of a histogram to semi-quantify the power Doppler signal (Pairleitner et al., 1999). However, their description of the vascularization flow index is incorrect. This index actually represents the ratio of weighted colour voxels to total voxels rather than a simple multiplication of the flow index and vascularization index, which would produce a totally different result. The vascularization index simply reflects the ratio of colour voxels to total voxels whilst the flow index assesses the colour signals only, which are weighted and compared with the total number of colour voxels.
The other key issue in 3D-PDA is that of reproducibility. The authors conducted a limited reliability assessment looking at two consecutive measurements by a single observer of the study patients and a further 10 post-menopausal women. Only a single scan was obtained from each patient and there was no mention as to the number of observers in terms of data acquisition. This is an extremely important issue as 3D-PDA is a difficult technique to reproduce; volume acquisition is relatively slow, allowing for increased movement artefact as a result of either patient or observer movement (Raine-Fenning et al., 2002a). If the technique is to have a role in the clinical setting then the inter-observer reliability must be established.
Virtual Organ Computer-aided Analysis (VOCALTM, Kretztechnik, Zipf, Austria) was used to measure ovarian volume and semi-quantify the blood supply, but there was no description of the actual measurement technique in terms of rotation step or plane used; these significantly affect the results (Raine-Fenning et al., 2002b). The authors quite rightly maintained the Doppler settings throughout the study and provide these values with the exception of the two main parameters that significantly affect the calculation of the vascular indices, namely the actual power and pulse repetition frequency (Fenning et al., 2001
). Whilst this does not affect this individual study, it is important that these parameters are stipulated in detail to facilitate comparison with future studies from different institutions.
Another potential criticism of 3D-PDA is the problem of attenuation of the ultrasound signal with increasing distance from the transducer. Whilst transvaginal ultrasound reduces this by approximating the object of interest and the ultrasound probe, attenuation remains a significant problem that can only be addressed by comparing like-subjects or the change in an individual (Deane, 2001; Welsh et al., 2001
), rather than comparing different groups as in this study.
The authors state that 3D power Doppler ultrasonography is, `More accurate than other methods to measure blood flow changes', but the study did not compare it with pulsed-wave Doppler. The authors may be right in that 3D-PDA is probably more representative of total ovarian blood supply and it may well be more reproducible, but they cannot claim it is more accurate as we do not know what the true blood supply is or indeed what these new indices of vascularity represent. They also conclude that the results, `Support the notion that PCOS is a primary disorder of the ovary' and that 3D power Doppler ultrasonography, `May provide substantial assistance to the management of PCOS'. Clearly neither of these conclusions are supported by this study and the true predictive power of 3D power Doppler ultrasonography in the diagnosis of PCOS remains undetermined.
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References |
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Zaidi, J., Campbell, S., Pittrof, R., Kyei-Mensah, A., Shaker, A., Jacobs, H.S. et al. (1995) Ovarian stromal blood flow in women with polycystic ovariesa possible new marker for diagnosis? Hum. Reprod., 10, 19921996.[Abstract]