Scalp immersion proxigraphy (SIP): an improved imaging technique for phototrichogram analysis*

Abstract

In recent years we have developed the concept of using automated computer assisted image analysis (ACAIA) for hair growth evaluation. The success of this sophisticated technology depends on the quality of the original images that are fed into the mainframe of the image analyzer. Application of immersion oil onto the scalp site to be photographed appears to improve contrast between hair and scalp and has been named ‘Scalp Immersion Proxigraphy’ (SIP) in contrast to crude proxigraphy, that is close-up photography without application of immersion oil, commonly used for phototrichogram analysis (PT). In this paper, we report evidence indicating that besides the qualitative improvement of the image, SIP also contributes to generate more accurate quantitative data. Such a conclusion was reached after hair growth variables were compared as a function of the photographic method (SIP vs. PT: 16 scalp sites; 5 balding subjects with clinical features consistent with androgen dependent alopecia). Each site was photographed with both techniques immediately after clipping and 48 h later. After image recording, we manually re-processed the original pictures on transparencies. The original pictures and the transparencies were analyzed with ACAIA. There was a significant difference between methods in terms of evaluation of linear hair growth rate (LHGR; mm/day, n= 1332 bairs; Scheffe F-test, P < 0.05). LHGR recorded with re-processed SIP pictures (0.317 mm/day) was very close to that measured in our laboratory with micrometric methods. Distorted figures were generated by PT, leading to an underestimation of this parameter by 30% on average (0.224 mm/day). From previous studies, we knew that hair diameter correlates with linear hair growth rate: the thinner the hair fiber, the slower the growth rate. Both variables may be considered as additive in terms of severity of the alopecia. In this comparative trial of two phototrichogram techniques, we showed that linear hair growth rates can only be accurately estimated with SIP. Therefore, SIP should be used instead of crude proxigraphy when a global assessment of hair growth is to be monitored during clinical trials.