The first patients have used a scanner that can diagnose cancer in five minutes rather than 30.
The £8 million positron emission tomography (PET) scanner has been installed at the Royal Free Hospital.
The state-of-the-art technology is 11 times more sensitive than standard machines, exposing patients to half the radiation and scanning at least twice as quickly.
The new scanner, named the long axial field of view (LAFOV) and also known as a Total Body PET scanner, allows patients to begin life-saving treatment sooner.
Michael O’Sullivan, 84, from High Barnet was one of the first to use the scanner as part of his prostate cancer care.
He said: "I was really pleased to be one the first patients and that my appointment went very smoothly.
"I felt very relaxed and the staff were all lovely and put me at ease."
PET scans create three-dimensional pictures of body parts.
This allows doctors to learn more about the functioning of tumours they are examining.
Greater understanding of tumour function helps doctors deliver more effective treatments to cancer patients.
The LAFOV PET scanner will reduce scanning time from 20 to five minutes, providing capacity to see more patients sooner after referral.
Thomas Wagner, a nuclear medicine consultant, said: "This is an extremely exciting development for us.
"The lower dose of radiation is a great benefit to patients, especially for younger patients who need to come for repeat scans.
"And because we can complete the scans much more quickly, we can see more patients every day."
The LAFOV PET scanner is funded by the Royal Free Charity.
Peter Landstrom, chief executive of the Royal Free London, said: "I’m delighted that the first patients are now receiving their scans.
"Huge thanks should go to Royal Free Charity and its generous donors for making this possible."
The Royal Free London is one of the busiest cancer services in the NHS, receiving almost 50,000 referrals each year.
The Total Body PET scanner widens possibilities of research and effective new treatments.
The scanner's high sensitivity and lower radiation offers opportunities for research trials involving healthy volunteers.
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