Guidelines on commercial sector donations of health equipment should be clarified after concerns were raised over a two-tier NHS, an MSP has urged.
It follows the gifting of one of the world's best CT scanners to Edinburgh by the Royal Bank of Scotland.
RBS staff will have access to the machine for 25% of the time but NHS Lothian said it would not be a problem.
However, independent MSP Margo MacDonald plans to raise the question of conditional gifts at Holyrood.
The £4m equipment at Edinburgh Royal Infirmary will be helping to diagnose heart problems by the end of the year.
Professor Allyson Pollock of Edinburgh University said the move undermined the NHS principle of equal access for all.
Prof Pollock - head of the University's Centre for International Public Health Policy - called it "philanthropy with conditions".
The scanner will be shared by NHS Lothian, Edinburgh University and the bank.
The whole point is that we have equal access on the basis of need
Prof Allyson Pollock Edinburgh University
The bank said it was gifting the equipment to the NHS, which will be used for 25% of the time for its own staff.
For the rest of the time it will be used for NHS patients and research.
Prof Pollock told BBC Radio's Good Morning Scotland programme: "The whole point is that we have equal access on the basis of need.
"Introducing this system of public private partnership actually undermines that because some people are going to have better access with lesser needs than others."
She called it a "disturbing" development and questioned whether there was a commercial contract underpinning the gift.
NHS Lothian medical director Charles Swainson said there was no contract, but simply an agreement about how the scanner would be used and dismissed Prof Pollock's concerns as "nonsense".
RBS staff will have access to the scans for 25% of the time
He said: "The fact is we don't have waiting lists or waiting times for these kind of investigations and the really important point is that this new scanner is completely additional to normal NHS services."
Mr Swainson said he would welcome similar deals with other donors who wished to invest in research equipment.
"This is really good news for the NHS and for patients because after all 75% of the time it is being used for them," he added.
But Ms MacDonald, the independent MSP for the Lothians, said she would raise the issue in the Scottish Parliament.
She said: "I'm putting a motion down for the parliament, suggesting that before we stray into this territory of conditional charity or gifts to the NHS, we should debate what the ground rules are going to be.
"It's not that I think that the Royal Bank means to be anything other than charitable and look after its own staff, perhaps give something back to the community, it's just that I wish this had been talked about first of all."
Scottish Conservative health spokeswoman Mary Scanlon said: "We should be thanking RBS for this generous donation".
She added: "Everyone needs to be open-minded by supporting medical research and enhanced patient care in Scotland."
It is the first time a hospital in the UK has had such advanced technology.
It will allow our clinicians to diagnose life-threatening illnesses within a matter of minutes and will also pave the way for quicker treatment
Charles Swainson NHS Lothian
The scanner, which has taken 10 years and £250m to develop, is said to be a major change in the field of CT (computerised axial tomography) scanning technology.
The Toshiba device will provide an additional 4,000 patient scans a year to the current NHS provision.
It will also be used by Edinburgh and Queen Margaret universities to conduct research to improve the diagnosis and treatment of a range of heart and cancer illnesses.
Unlike previous scanners, it can capture entire organs such as the heart or brain in a fraction of a second.
Given the novel method of image capture, radiation exposure is reduced by approximately 80% compared with conventional CT scans.
Professor David Newby, director of the Clinical Research Imaging Centre, said: "The potential of new imaging technologies lies not only in replacing more intrusive tests but also in helping us to better understand and treat conditions such as heart disease, cancer and strokes.
The Edinburgh scanner "represents a major advance in imaging the body, and in particular provides the ability to examine the heart and the coronary arteries within one heart beat, at high resolution and with markedly reduced radiation doses," he added.
Mr Swainson added: "It is excellent news for the region as it will allow our clinicians to diagnose life-threatening illnesses within a matter of minutes and will also pave the way for quicker treatment."
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