Rethink Imaging

EP 45 • May 28, 2026

Are CT Scans Safe? What Most People Get Wrong About Radiation

Featured Guest

Dr. M. Mahesh, MS, PhD, FAAPM, FACR, FACMP, FSCCT, FIOMP

Chief Physicist, The Johns Hopkins Hospital; Professor of Radiology and Radiological Science • Johns Hopkins Medicine

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Day one, the headline says screening mammography saves lives. Day two, it says mammograms cause cancer. Dr. M. Mahesh, Chief Physicist at The Johns Hopkins Hospital, has spent his career pushing back on that whiplash. He tells Chris St. John what happened when a 2009 NCRP report he helped author got compressed into “radiation to the US population up 600%,” a framing that ran in every paper and triggered congressional and FDA hearings. The 2019 follow-up, which showed exposure had actually dropped about 20 percent, landed on page four. Mahesh walks through why the scariest claims about CT risk keep ignoring how much less dose modern scanners use.

The second half gets practical. Mahesh explains why AAPM and ACR came out against lead shielding for patients, and how a Facebook Live he ran with radiologist Elliot Fishman on that exact topic drew 60,000 views in 24 hours. He calls technologists the window of radiology, argues that comic strips and two-minute videos reach patients in ways journal PDFs never will, and points out that every accurate post now feeds the AI tools patients consult before they ever reach the department. His advice to clinicians: treat public communication as part of the job, start small, stay consistent, and be reachable when a scared patient needs a straight answer.

Host

Chris St. John

Host, Rethink Imaging • Imalogix

Featured Guest

Dr. M. Mahesh, MS, PhD, FAAPM, FACR, FACMP, FSCCT, FIOMP

Chief Physicist, The Johns Hopkins Hospital; Professor of Radiology and Radiological Science • Johns Hopkins Medicine

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Key Takeaways

The infamous “600% increase” in US population radiation dose came from a 2009 NCRP report Mahesh worked on, and the framing set off congressional and FDA hearings. The 2019 follow-up report showed a roughly 20 percent decrease in exposure, and it ran on page four or five. Fear travels; corrections do not.
Mahesh’s critique of the JAMA projection that current CT use will produce over 100,000 future cancers: the calculation reuses decades-old dose assumptions and ignores how much technology and protocol optimization have cut per-scan dose. AAPM and ACR issued public pushback statements within 24 hours.
Lead shielding during patient imaging is out. With digital radiography and automatic exposure control, a shield in the primary beam can raise dose and obscure anatomy, and out-of-field dose comes from internal scatter a lap shield cannot block. A Facebook Live with Elliot Fishman explaining this reached 60,000 views in 24 hours.
Technologists are the window of radiology. Patients rarely meet a radiologist and almost never a medical physicist, so equipping technologists to answer radiation questions, and giving them someone to escalate to, is the most effective safety communication a department can build.
AI tools answer with whatever the internet contains. Mahesh’s argument: every accurate post is “a pixel of value” that gets picked up alongside the misinformation, so publishing correct dose information consistently is now a patient-safety activity, not a vanity project.

Full Transcript

Rethink Imaging Podcast Transcript

Guest: Dr. M Mahesh

Host: Chris St. John

CHRIS ST. JOHN 00:00:47 Welcome back to Rethink Imaging. I am joined today by Dr. Mahesh. We’re going to be talking about a lot today, particularly diving into the role of social media in shaping public understanding of healthcare and how clinicians can step beyond academic circles to combat disinformation and connect more deeply with patients. Mahesh, it’s great to have you here today.

DR. M. MAHESH 00:02:12 Thank you, Chris. Thank you for inviting me to your podcast for this conversation. I am looking forward to this very much.

CHRIS ST. JOHN 00:02:23 Yeah, of course. I’ve been super excited to have you here. For our listeners, Mahesh and I have met a few times in the past, but recently, when we had a longer conversation preparing for this show, I felt like I got to know you, your personality, and your enthusiasm much better. I’m just excited to talk.

DR. M. MAHESH 00:02:45 You’re very kind. Thank you, Chris.

CHRIS ST. JOHN 00:02:49 You wear so many different hats: you’re a professor, a clinical leader, and a global policy contributor, but you also take the time to engage directly with the public. You post on social media and consistently try to get clear information out there. What drives you specifically to prioritize public communication in your work?

DR. M. MAHESH 00:03:11 First and foremost, as a medical physicist, you deal with many issues related directly to patient care. I feel that patients and the public often do not have the right information or do not know where to turn to find it. As a professional, I feel it is my obligation to share my knowledge and make myself available to provide comforting, accurate answers. It is fundamentally part of my profession, and that is one of the main drivers for me.

Second, in academia, we frequently publish papers and reports, but we know those only reach a very select, small audience—and even within that audience, only a fraction actually read them. On the other hand, by engaging on social media, you not only share what you are working on, but you also put helpful information out to people you don’t even know, who may find it extremely valuable. That engagement is deeply fulfilling to me as a professional.

CHRIS ST. JOHN 00:04:39 Can you tell me how your relationship to providing public information has changed with the rise of the social media landscape, especially where we are now, with so many people relying on social media and large language models for health information?

DR. M. MAHESH 00:05:00 There is still inherent resistance among some academicians and professionals regarding social media engagement. But I was curious right from the time Twitter launched back in 2009. I opened an account, started engaging, liking issues, and sharing information. Initially, I joined for two reasons: first, to share information; second, to maintain my own repository. If I like an article and post it, that post remains in my account forever. If I can’t find it on my computer later, I can quickly search my feed and retrieve it.

Over time, I expanded to other social media platforms. It serves my self-interest in staying knowledgeable about ongoing developments. In the social media environment, I am exposed to ideas outside my immediate field. For example, if you search an Amazon bookstore, you only look for the exact book you intended to buy. But if you walk into a physical bookstore, you browse aisles like travel, fiction, romance, or mystery, and accidentally stumble across fascinating material.

I see a similar dynamic on social media. I find useful articles on psychology, emotional intelligence, kindness, and history that I would never be exposed to if I stayed strictly in my own lane. It expands my learning, and bringing those insights back to medical physics has improved my communication skills.

In medical physics, we are required to communicate concepts in multiple “languages.” I don’t mean geographical languages like German or Spanish; I mean communicating tailored messages to medical physicists, radiologists, nurses, technologists, and even to a grandmother asking about radiation safety. I strongly advocate that every medical physicist develop the skill to express the same technical concept in multiple ways to suit the audience. Social media is an excellent training ground for that. It has also allowed me to build new professional contacts and global collaborations that I find immensely advantageous.

CHRIS ST. JOHN 00:08:09 I like your point about navigating different “languages” and vocabularies within public communication. When you are writing articles or posting online, what is your specific approach to language so that you reach people in a way they can easily understand?

DR. M. MAHESH 00:08:53 I’ll give you two examples. Yesterday, I read an interesting paper in Radiology: Artificial Intelligence about deepfake clinical images. The investigators created synthetic clinical images nearly indistinguishable from real ones, mixed them into actual clinical workflows, and evaluated how accurately radiologists could spot the deepfakes. It turned out to be very difficult, and many deepfakes went unrecognized.

The paper was dense, but I synthesized the key takeaways into a concise post. That is why I originally appreciated Twitter: the character limit forces you to distill complex scientific findings into brief, consumable sentences.

Because people are overwhelmed with information overload, few have time for lengthy essays online. A two- or three-sentence summary capturing the core essence, paired with a clear visual image and a link to the full publication, is far more engaging. When I post content, I cross-post the image, key takeaways, and paper link across Twitter, LinkedIn, and Instagram. For that deepfake study, the authors even provided an interactive link where readers could test their own ability to spot deepfake images versus real scans. I tested myself and scored about 50-50! Sharing that resource gives students or researchers in Southeast Asia, South America, or anywhere else immediate access to relevant science.

Keeping posts brief forces me to read efficiently, capture the core message, and archive the paper for future reference.

CHRIS ST. JOHN 00:12:32 Your point about character limits and concise messaging makes me think about online behavior. On platforms like Reddit, someone might post a slightly sensationalized variation of a news headline, and the entire comment section reacts exclusively to the headline without reading the study. When you actually read the paper, the comments rarely reflect the actual findings. How do you view short snippets being misconstrued, leading low-attention-span readers to take misleading headlines as absolute truth?

DR. M. MAHESH 00:13:41 That happens frequently. A high-impact study published in JAMA Internal Medicine or The New England Journal of Medicine might be covered in a 30-second local television news segment using an eye-catching headline, which does a massive disservice to the science.

Take screening mammography as an example. We know it saves lives. However, if a study comes out discussing theoretical risks, local media headlines might proclaim, “Screening mammograms cause cancer.” Sitting at home, a patient sees “Mammograms save lives” on Day 1, and “Mammograms cause cancer” on Day 2, causing immense confusion.

I strongly advise against spending time reading negative online comment sections. You can easily spiral down a rabbit hole of false information, often posted by anonymous accounts or bots. Most of my posts receive constructive engagement because I avoid feeding into online outrage. Misinformation surrounding CT radiation is particularly widespread, which is why professionals in our field have an obligation to put accurate data out into the public domain.

CHRIS ST. JOHN 00:16:20 When a headline like “Mammograms cause cancer” generates ten times the views and engagement of nuanced scientific facts, even official statements from respected breast cancer organizations struggle to gain equal traction. How can our community effectively counter the clickbait nature of fear-based messaging?

DR. M. MAHESH 00:17:02 There is no simple answer, but consistency is key. In 2009, I served on an NCRP committee that published a comprehensive report detailing radiation exposure to the US population—the first major update since 1982. The findings showed that medical radiation exposure had increased significantly, primarily due to the rise in CT imaging, resulting in a headline stating US population radiation dose increased by 600%. Every major media outlet picked up that dramatic figure. It led to congressional hearings, FDA inquiries, and widespread public alarm.

Ten years later, in 2019, NCRP published an updated report evaluating population exposure over the preceding decade. We demonstrated a roughly 20% decrease in overall medical radiation exposure due to optimized protocols and improved technology. Where did that headline end up? Page four or five.

That is the reality of media coverage. However, we cannot let that discourage us or retreat to our laboratories. Professional societies like the AAPM and ACR must consistently engage news outlets, podcasts, and digital channels to push back with sound science. If our efforts clarify facts for even one patient who was previously terrified of getting a necessary CT scan, that work is entirely worth it.

CHRIS ST. JOHN 00:19:47 There also seems to be a broader societal erosion of trust in medical institutions and scientific authorities. That cultural backdrop must make public education even more challenging.

DR. M. MAHESH 00:20:24 It certainly does. At a recent conference, speaker data illustrated a geographic trust survey of the US population. The highest levels of public distrust centered around government institutions and academic universities. As academics, we spent decades isolated in an “ivory tower” mentality without adequate public outreach. As Carl Sagan warned back in the 1980s, if scientists fail to communicate clearly with the public, public trust will inevitably erode.

However, when an individual or family member faces an urgent medical decision involving radiation, they still want accurate answers from a trusted expert. We must ensure we are accessible when they seek that guidance. Building that trust is a long-term commitment.

Collaborating with patient advocacy groups is exceptionally impactful. For instance, at the Journal of the American College of Radiology (JACR), where I serve as an associate editor, we brought a patient advocate onto our editorial board. Her team translates complex clinical Appropriateness Criteria into accessible, one-page patient summaries published alongside the scientific papers. These advocacy groups become powerful spokespeople for radiology. We must proactively build those bridges rather than dismissing public communication as outside our scope.

CHRIS ST. JOHN 00:25:22 I’d like to touch specifically on common imaging misinformation, such as fears surrounding CT radiation or MRI contrast agents. What specific health claims or myths do you encounter most frequently that feel particularly persistent or challenging to address?

DR. M. MAHESH 00:26:02 Last December, I delivered a presentation at an IAEA conference titled “Dealing with Mis- and Disinformation.” Radiation myths remain widespread. A simple example is the belief that radiation lingers in an X-ray room after the exam is complete. I explain that diagnostic X-rays function like a light bulb: once the switch is turned off, no radiation remains in the room. (Nuclear medicine procedures involve radiopharmaceuticals, which operate differently.)

Another major challenge is that the public cannot easily distinguish between a 1 mSv dose and a 10,000 mSv dose—the term “radiation” immediately conjures images of atomic bombs, Chernobyl, or fictional comic book origins like the Incredible Hulk. Because radiation is invisible and intangible, fear of the unknown takes over.

Last year, a published paper used statistical modeling to claim that current CT utilization would result in 100,000 future cancer cases. The headline generated significant alarm. Working through the AAPM and ACR, we issued public statements within 24 hours to address the paper’s methodological limitations. The study relied on historical linear risk models that failed to account for modern CT technology, where dose-reduction features and protocol optimization deliver significantly lower radiation doses than exams performed 20 or 30 years ago.

I also joined podcasts with Diagnostic Imaging alongside radiologists to provide balanced context. Publishing accurate content online serves a vital secondary purpose today: artificial intelligence. Large language models scrape public web data to synthesize health answers for users. The more evidence-based, high-quality data we publish online, the higher the likelihood that AI algorithms will ingest and output accurate medical information to patients.

CHRIS ST. JOHN 00:31:38 That is a crucial insight regarding AI ingestion. While patients should always consult their physicians, LLMs are increasingly used for preliminary health questions. Recently, when my partner experienced an unexpected neurological issue in the ER, an LLM correctly identified the underlying condition based on symptoms long before our diagnostic imaging results returned.

DR. M. MAHESH 00:32:33 Physicians encounter this daily now; patients arrive for appointments with detailed printouts or AI searches. Next month, I am presenting a webinar on effective clinical communication in the AI era. When patients bring AI-generated health information into the clinic, we should view it as an opportunity for open discussion rather than dismissing it. If the information is correct, it reinforces their knowledge; if it is flawed, we can gently explain the nuances.

CHRIS ST. JOHN 00:34:00 In hospital settings, radiologic technologists usually have the most direct, face-to-face contact with patients during imaging procedures. What role can technologists play in improving public understanding of imaging safety?

DR. M. MAHESH 00:34:31 Technologists are truly the frontline ambassadors for radiology. Patients naturally feel comfortable asking them questions during an exam. Because medical physicists cannot be present for every procedure, partnering with professional organizations like the ASRT to equip technologists with clear communication tools is vital.

When new CT scanners are installed, clinical application specialists train technologists on machine operations. Whenever I perform acceptance testing on new equipment, I encourage application specialists to explain the physical rationale behind dosage settings so technologists understand the underlying science, not just which buttons to press.

Furthermore, technologists should have direct escalation pathways to consult medical physicists when complex patient questions arise. At Johns Hopkins, my radiology colleagues routinely connect me with patients who have detailed questions regarding radiation risks. Speaking directly with patients provides tremendous reassurance, and those informed patients often share that clarity with their families. Technologists play a pivotal role, and we must empower them with resources.

CHRIS ST. JOHN 00:37:00 Before I entered the medical imaging industry, I wouldn’t have known to ask for a medical physicist if I had technical questions during a scan. I didn’t even realize the discipline existed.

DR. M. MAHESH 00:37:19 Raising professional awareness remains an ongoing priority. Last year during our AAPM annual meeting in Washington, DC, we hosted our first congressional Advocacy Day. Our members met directly with representatives and senators to explain the role of medical physicists in patient safety, healthcare infrastructure, and research. The ACR conducts similar advocacy annually, ensuring policymakers understand our field when drafting regulations. I am working to expand these advocacy frameworks globally through the International Organization for Medical Physics (IOMP).

CHRIS ST. JOHN 00:38:00 Given your extensive international experience, how does the US landscape regarding medical disinformation compare to other regions globally?

DR. M. MAHESH 00:38:26 Two key differences stand out. First, global imaging utilization varies. In 2008, the US accounted for 30% to 40% of all CT scans performed worldwide. According to recent UNSCEAR data, while the US now performs nearly 100 million CT scans annually, that volume represents roughly 18% of the global total, reflecting massive expansion of healthcare imaging worldwide.

Second, cultural dynamics around medical authority differ. In many countries outside the US and Western Europe, patients rarely question prescribed medical imaging or express anxiety regarding radiation doses. In Europe, medical radiation awareness is higher, and European colleagues historically emphasized dose optimization compared to US practice patterns. In rapidly expanding systems like China, patient questioning is gradually increasing. However, because US media outlets amplify health news so intensely, American headlines often shape global perceptions.

CHRIS ST. JOHN 00:40:04 You have previously advocated for creating short, digestible summaries of complex medical physics papers for public consumption. What does your ideal format for public science communication look like—whether through YouTube, short-form podcasts, or newsletters?

DR. M. MAHESH 00:40:23 I have experimented with several formats. I contributed to RadiologyInfo.org—a public-facing patient portal jointly managed by the ACR and RSNA—where we created patient-friendly radiation safety tables comparing medical procedures to natural background radiation. I also produced two-minute educational videos explaining CT dose concepts for Johns Hopkins platforms and recorded technical videocasts for radiology residents on CTisus.com.

A great example of public communication involved routine patient shielding. A few years ago, the AAPM issued a formal position statement—co-signed by the ACR, RSNA, and other authorities—recommending against routine gonadal and fetal lead shielding during diagnostic X-ray exams. Shielding had been an established practice for decades, but modern digital X-ray systems utilize automatic exposure control (AEC). If a lead shield inadvertently covers the AEC sensor, the system automatically increases exposure, paradoxically increasing overall radiation dose or obscuring critical diagnostic details. Furthermore, radiation to tissues outside the primary target area results from internal scatter, which external lead shields cannot prevent.

When the statement was released, significant public and clinical confusion ensued. The New York Times covered the story. That same day, Dr. Elliot Fishman and I hosted a Facebook Live session to explain the scientific reasoning behind ending routine shielding. That video generated over 60,000 views globally within 24 hours. We later published a paper in JACR analyzing how live social media broadcasts can rapidly disseminate updated scientific consensus worldwide.

To further clarify the issue, I worked with a graduate student in the Medical and Biological Illustration master’s program at Johns Hopkins to create a five-minute animated video depicting a dialogue between two technologists discussing shielding policy. We evaluated technologist understanding before and after viewing the video and published the findings in JACR. Concise animations, graphic media, and short video formats are highly effective tools for translating complex clinical guidelines without sacrificing technical accuracy.

CHRIS ST. JOHN 00:45:22 We will include links to those JACR papers and educational videos in our show notes so listeners can explore them directly. Using illustrative media and comics to explain dense clinical concepts is a brilliant approach.

DR. M. MAHESH 00:45:37 Visual storytelling is exceptionally effective. High-impact journals like the Archives of Internal Medicine have published illustrative comic formats to explain complex subjects like institutional review board (IRB) approvals and informed consent processes.

While traditional academia sometimes views illustrated formats as juvenile, visual storytelling bridges the gap between complex science and public comprehension. I recently watched a Japanese television drama series on Netflix called Radiation House, which follows the daily life of a diagnostic radiologic technologist. Each episode highlights diagnostic problem-solving across modalities like mammography and cardiac catheterization in an engaging narrative format. Finding creative ways to communicate scientific concepts broadens our reach and ensures reliable information is available to both human audiences and AI platforms.

DR. M. MAHESH 00:47:33 I’ll share one more story demonstrating the real-world impact of public communication. A few years ago, national news outlets reported alarming stories regarding radiation contamination at a funeral home following a case report published in JAMA.

A patient who had received radioactive seed implants (brachytherapy) for prostate cancer discharged himself from one hospital and later passed away at another facility. When the body was brought to a crematorium, residual radiation from the implanted seeds triggered facility radiation monitors, leading to sensationalized headlines on major television networks about radioactive hazards in funeral homes.

To address public alarm, our team hosted an immediate Facebook Live session to explain Nuclear Regulatory Commission (NRC) safety guidelines, clarify radiation decay principles, and explain why public health risks in such circumstances were negligible.

The issue had tangible consequences: in Canada, a family was initially refused funeral services for their deceased father because local funeral directors feared radiation contamination from cancer treatments he had received years earlier. Media coverage referencing our explanatory broadcast helped clarify the actual safety protocols, allowing the family to proceed with funeral arrangements. The National Association of Funeral Directors even invited me to address their national conference. It underscored how accessible expert communication directly resolves real-world confusion.

CHRIS ST. JOHN 00:51:52 What advice would you offer to healthcare professionals—whether radiologists, technologists, or physicists—who want to start engaging publicly on social media but feel hesitant or unsure where to begin?

DR. M. MAHESH 00:52:19 View public communication as a professional obligation to your community. You don’t need to launch a massive campaign immediately; start small by following reputable sources, liking informative posts, and sharing insightful articles.

Some professionals maintain strictly technical social media profiles, whereas I mix professional updates with personal interests, such as cooking, travel, or lighthearted commentary. Sharing human moments helps break down the intimidating “ivory tower” perception.

For early-career professionals and students, sharing your work on social media exposes your research to global collaborators. My email signature includes the line “Be curious.” Curiosity drives continuous learning. For example, I recently discovered a thought-provoking paper on AI governance in The New England Journal of Medicine co-authored by an anthropologist and a psychologist—an interdisciplinary insight I would have missed had I not been active on social media. Public engagement refines your communication skills and provides profound professional satisfaction.

CHRIS ST. JOHN 00:55:12 Dr. Mahesh is a renowned medical physicist, professor of radiology at Johns Hopkins, and chair of the Radiation Control Committee for the Johns Hopkins Health System. Dr. Mahesh, where can listeners connect with you and follow your work online?

DR. M. MAHESH 00:55:31 I am active across major platforms, including LinkedIn, Instagram, X (formerly Twitter), and BlueSky. LinkedIn has become particularly active for scientific discussion. I will share my handles for inclusion in the show notes. I welcome connecting with colleagues and listeners, and I truly appreciate this conversation, Chris. Thank you for having me.

CHRIS ST. JOHN 00:56:33 Thank you so much for joining us, Dr. Mahesh. We look forward to having you back on Rethink Imaging soon.

Questions from This Episode

Did radiation exposure to the US population really increase 600%?
That number came from comparing a 2009 NCRP report (about 3 mSv from medical imaging) against a 1982 baseline of 0.56 mSv, and headlines ran with the ratio without context. The follow-up report in 2019 found overall exposure had dropped about 20 percent, but that finding got buried while the scary version stuck.
Why did experts stop recommending lead shielding for patients?
With modern digital equipment, a shield that drifts into the primary beam can trip automatic exposure control and raise the dose, or hide anatomy the radiologist needs. Dose outside the imaged area comes mostly from scatter inside the body, which an external shield cannot stop. AAPM’s position statement, co-signed by ACR and others, applies to patients only; staff working around radiation still shield.
Should patients worry about headlines predicting 100,000 future cancers from CT scans?
Mahesh’s answer is that these are statistical projections built on outdated dose assumptions from the same group that has published against CT for years. Today’s scanners use far less radiation per exam than 20 or 30 years ago, and professional societies have pushed vendors and sites to optimize protocols. A CT ordered for a clinical reason answers a question that matters now; the projection math does not account for that benefit.