Most would agree that the father of medical imaging is Wilhelm Röntgen who in 1895 made 2 interesting discoveries. The 1st were x-rays themselves and the 2nd was their ability to discern anatomic features such as bones. X-rays occupy the part of the electromagnetic spectrum between 0.01 and 10.0 nm. They fall between the lower energy ultraviolet rays and the higher energy gamma rays. X-ray imaging can be used for a number of purposes such as identifying broken bones (fractures), dislocations of bones, air fluid levels in the gut, abnormal fluid in the lung suggesting possibly pulmonary edema versus pneumonia, and many other useful screenings. Almost everybody who has visited an emergency room has at least seen large portable x-ray machines lumbering up and down the hallways or possibly needed imaging themselves. Any medical television show will feature 1 or more discussions about imaging results. So how do we evaluate the risk-benefit ratio of medical imaging?
At one level, we have partial answers (at least regarding risks between modalities of imaging). Medical imaging with ultrasound is not thought to have much risk. The energy transfer to living tissue is small and based on pressure waves, not electromagnetic waves. The former is not thought to damage tissue generally or DNA specifically while electromagnetic waves might. MRIs (magnetic resonance imaging) are also thought to be quite safe because magnetic radiation, similar to ultrasound, is not thought to damage tissue or DNA. Some caution is reasonable with MRIs, e.g. patients having ferromagnetic materials in them (e.g., pacemakers) should not undergo this imaging. Also, the contrast used for MRI studies, gadolinium, if given injudiciously can itself be troublesome. In contrast, potential troublemakers are standard “plain films” (single image radiographs), mammograms, CAT scans, and so-called radionuclide scans. These generate x-ray or gamma rays. These can damage DNA beyond a given cell’s ability to repair. This can lead to cell death or carcinogenesis. The risk of damage is proportional to the total time of exposure x the intensity of the exposure.
Of special note are images generated by gamma rays (which are more powerful than x-rays). PET (positron emission tomography) scans generate positrons which are the antimatter counterpart to electrons. When positrons and electron counterparts meet, each annihilates the other and releases energy in the form of gamma rays. Where there are a lot of gamma rays produced on an image, this area is called “hot” and where there is a paucity, the area is called “cold”. One type of PET scan is useful for detecting blood flow to the heart muscle. Cardiologists are becoming more and more fond of this test. If there is a significant arterial blockage to that part of the heart, the tissue surfaced will appear relatively “cold” (dark) on the PET scan compared to normally vascularized heart tissue. As noted, gamma rays are more “energetic” than x-rays.
All imaging (or indeed any exposure to radiation) should be evaluated on a risk/benefit ratio continuum. However, what surprises this author is the apparent lack of any authoritative guidelines for how “safe” any exposure is. Up until the 1960s, for example, using external beam radiation for facial acne vulgaris was a frequent treatment. This led to a measurable increase in thyroid and skin cancers later. Mammograms can both save lives by finding cancerous lesions early but also take lives because the imaging radiation can itself cause cancer. Generally, mammography is considered quite safe and worthwhile but some fundamental questions are still unaddressed.
One aspect of the problem is the increasing use of the imaging studies which ionize tissue per patient per year (which risks cellular death or generation of cancer). An example, once again, is the use of PET scans. According to Statista 2025, the number of PET scans in 2010 was 875,000 and in 2019 was 2,220,000, a 250% increase. Other higher dose x-ray examinations are also increasing, e.g. CAT scans.
Another aspect of the problem on the newer combination studies such as combined same day PET/CAT scans. The PET scan produces gamma rays and the CAT scan produces x-rays. What are the consequences (if any) of applying 2 types of radiation in the same general temporal window? Which, if either, should be done first? Should the tested be done a certain number of hours apart? Are there any “basic science” studies in peer-reviewed magazines regarding these issues? Are there any clinical follow-up studies to follow these individuals years after the testing? One would have to imagine that the companies making these products would be indifferent to paying for these studies.
A final question to be asked, then, is who follows a patient’s lifetime exposure to ionizing radiation. The answer is, for the most part, nobody. With the potential exception of radiation oncologists who treat amenable cancers with radiation, there is no recording of how much cumulative radiation has been absorbed by our tissues. Dental x-rays, chest x-rays, bone x-rays, CAT scans, PET scans and many other frequently ordered tests are things that many of us have undergone and will continue to need. However, in spite of this being critical metric of one’s medical history, nobody is recording how many sieverts (the term for radiation absorbed by tissue) we have received and when. If the option were there, what should be done?
The answer will bring us full circle back to the August 15, 2024 article in this magazine regarding computerized medical records. In that article, we discussed recording all medical information such as progress notes, EKGs, laboratory results, medical images and so on for each of us centrally at one location. As noted before, critical challenges would have to be addressed for this to work (security of information, speed, accuracy, redundancy, backups, cost efficiency, and so on). Each of us would have one medical file with all of our information. The benefits for that are huge. In terms of this article, the central storage of all this information would allow us to accumulate all the medical imaging studies and related radiation dose. Every time we had a CAT scan, not only would the image be transmitted but the calculated millisieverts this generated be recorded and accumulated. Lower intensity imaging like dental x-rays and chest x-rays would be recorded. Higher dose images like combination CAT/PET scans would also be. With everything recorded, studies could be done which could calculate the risk of subsequent “excess” cancers in those who undergo CAT/PET scans compared to those who do not.
Another benefit of centrally storing records would be to find out who would be outliers for ordering expensive and to some extent risky imaging tests. One mantra of some physicians is, to paraphrase, the next best thing to knowing what’s actually going on is to get more data. Colleagues who are metaphorically hidden in the tall grass of daily practice could be guided about better, more cost-effective practices for our patients. Not every patient who presents to the emergency room with belly pain needs an abdominal and pelvic CAT scan. A good medical history (which takes time and focus) and a practiced examination can reduce the need for temporizing imaging. If/when global capitation is put in place, the feedback generated by the centralized medical record and statistical regressions should allow for fewer tests with better patient outcomes. This should be done as soon as possible.
Editor’s note: It was previously announced that OMRUM would be in “hiatus”. However, kind feedback has led to the updated decision to publish one article per month while a book based on the magazine is being developed. Your ongoing support has been (and no doubt will continue to be) greatly appreciated. Thank you!