Surgeons are cautious with brain tumours as removing the surrounding tissue could lead to disability.
Brain tumour researchers say the technique used to analyse the chemistry of the tissue could be an "exciting development in brain tumour research".
Balancing act of removing a tumour
Study lead Dr Daniel Orringer said: "Neurosurgery is plagued by a problem, it's very difficult to see when a brain tumour ends and normal tissue begins.
"If you're removing a colon cancer you can take 2cm either side with no damage, but in the brain it could disable a patient. SRS microscopy allows us to see the margins on an microscopic scale."
Removing a brain tumour is a balancing act - take too little and the cancer could return, take too much and it seriously affects a patient's quality of life.
But the team at the University of Michigan Medical School and Harvard University have come up with a new way of analysing the tissue, called SRS microscopy, while it is still in the brain.
Exciting development in visualising tumour tissue
A laser is fired at the tissue. However, the beam of light's properties are changed depending on what it hits. The differing chemistry of a cancerous cell and normal brain tissue mean the laser can show a surgeon the outside edge of a tumour.
The method has been tested in mice and on human brain samples, but actual trials in patients are still needed.
Dr Colin Watts, a Cancer Research UK brain tumour expert at the University of Cambridge, said: "It needs to be tested in a clinical trial, but this technique could be an exciting development in visualising tumour tissue, which is the first step in enhancing removal of disease.
"This technique is particularly exciting because it has the potential for helping us to remove tissue at the tumour/brain interface from where recurrent disease can emerge. It will also be interesting to determine if SRS microscopy can be used in tumours that recur after treatment."