A new hand-held device that uses lasers and sound waves may change the way doctors treat and diagnose the deadly skin cancer melanoma, says new research.

The instrument can be used directly on a patient and accurately measure how deep a melanoma tumour extends into the skin, providing valuable information for treatment, diagnosis or prognosis.

The technique relies on the photoacoustic effect in which light is converted into vibrations.

In the case of the new device, a laser beam shines into the skin at the site of a tumour.

Melanin, the skin pigment that's also in tumours, absorbs the light whose energy is transferred into high-frequency acoustic waves.

Unlike light, acoustic waves do not scatter as much when traveling through skin.

Tumour cells will produce more melanin than the surrounding healthy skin cells, and as a result, the acoustic waves can be used to map the entire tumour with high resolution.

The device has a detector that can then turn the acoustic signal into a three-dimensional image on a screen.

"Being able to measure the depth of the tumour in vivo enables doctors to determine prognoses more accurately a" potentially at the time of initial evaluation a" and plan treatments and surgeries accordingly," said dermatologist Lynn Cornelius from Washington University in St Louis.

The latest version is not only hand-held but it also delivers light around and below the tumour, which generates a bright image of the tumour's bottom and an accurate measurement of its depth, researchers added.

The paper was published in the journal Optics Letters.