Scientists have developed a way to measure the severity of a patient's multiple sclerosis and gauge how well drugs are working.
MS can be debilitating
The researchers at New York University hope it will improve both diagnosis and treatment of the disease.
The technique measures the amount of a key chemical that is found in lower quantity than usual in the brain cells of MS patients.
Details were revealed at a Radiological Society of North America meeting.
The researchers have dubbed the new technique whole brain N-acetylaspartate (WBNAA).
Lead researcher Professor Oded Gonen said: "WBNAA measures the amount of a chemical in the brain called N-acetylaspartate (NAA) that is exclusive to brain cells
"MS is a progressive brain disorder that leads to having less and less of the chemical in the brain.
"The deficit is proportional to the severity of the disease - as is the rate of the loss of the chemical."
The new procedure is performed at the same time the patient undergoes a standard scan.
MS attacks the central nervous system, resulting in a loss of myelin, the protective layer around nerve fibres.
This damages the nerves' ability to conduct electrical impulses to and from the brain, resulting in various symptoms that can include memory loss, depression, fatigue, pain or numbness, dizziness, and difficulty in walking or maintaining balance.
Variation in symptoms
Symptoms vary widely in severity among individuals. Therefore, it is imperative to closely tailor therapy to an individual's needs.
Early diagnosis and proper treatment are key to minimizing the symptoms and damaging effects of MS.
Dr Gonen said: "We're trying to customize the type of treatment and dose to the severity of the disease."
The researchers studied 42 patients with the relapsing-remitting form MS, which is characterized by flare-ups of symptoms followed by partial or complete recovery periods lasting months to years.
Currently, doctors look for signs of brain wasting, or atrophy when trying to determine the progression of the disease.
But the results from the New York team suggested that measuring NAA levels was a more sensitive measure as it seems levels of the chemical start to dip before signs of atrophy become apparent.
They suggest that the new technique should be used alongside more traditional diagnostic methods.
Chris Jones, chief executive of the MS Trust, said: "MS is a very unpredictable condition.
"No two people experience the same symptoms to the same degree and it is difficult to predict the course of the condition in individuals.
"Precise and early diagnosis will enable physicians to adapt therapy to suit the individual and possibly slow down the progression of the MS.
"The insight the study offers into the disease process is valuable and the results certainly important.
"We look forward to hearing more when the technique is in regular clinical use "
Mike O'Donovan, chief executive of the MS Society, said: "This is an encouraging addition to the growing range of magnetic resonance measuring techniques which are helping to develop and monitor new treatments for this dreadful disease."