High Resolution Ultrasound Imaging of Melanocytic and Other Pigmented Lesions of the Skin

For two main reasons, dermatology is one of the later medical disciplines to use imaging techniques: 1) skin lesions are readily visible to the naked eye or through a magnifying glass, allowing clinical diagnosis with no invasive examination, 2) skin lesions can easily be biopsied or removed for histological study. This approach has therefore remained the basis of clinicopathological diagnosis of skin diseases for a long time. There has also been a third factor, i.e. the technical factors limiting image resolution (1-12). It is often necessary to visualise sub-centimeter lesions or even smaller, as in the case when measuring the thickness of a melanoma, and this cannot be achieved using traditional 7-10 MHz ultrasound. However, such techniques are useful in dermatology, especially in detecting lymph node spread of melanoma (6,13,14). Other techniques such as optical coherence tomography and confocal microscopy are now available, with better resolution than 20-100 MHz ultrasound. However, both are more expensive and more time-consuming than ultrasound. Moreover, in certain European countries (e.g. France and Germany) ultrasound examination of the skin is reimbursed by health insurance services. High resolution ultrasound imaging systems enable ultrasound to differentiate structures of less than 100 microns on the beam axis (axial resolution) and 200 microns on the scan axis (resolution axis). This can be achieved by the use of ultrasound frequencies above 15 MHz. Several groups have been working to extend the limits of existing machines by increasing the frequency (11,12,15,16). Working in our group, Berson et al. proposed a new ultrasound device operating at 17 MHz (1).This device was compact and had a very handy probe with an acoustic window enclosed by a thin membrane, allowing easier exploration of skin tumours on the face where they are more frequent than on other sites of the skin. We currently use a device derived from this prototype (Dermcup 2020®, Atys Medica, St