Zurich symposium examines 25 years of PET/CT and its future

At one point, the international interest in PET/CT at University Hospital Zurich (USZ) became so intense that a colleague walked into the office of nuclear medicine pioneer Gustav K. von Schulthess announcing: "I'm going to quit."

The colleague was struggling to keep up with his clinical work. Visiting fellows were constantly asking questions, and he was getting home at 10 p.m. because he had not finished reading his own examinations.

Von Schulthess, now professor emeritus at the University of Zurich in Zurich, Switzerland, understood the frustration. But the department wanted to keep training visiting physicians. The solution was to organize the teaching more systematically, eventually establishing a structured fellowship program in 2007.

Now the program gives visiting physicians a hands-on learning environment, with dedicated workstations, daily lectures, and supervised case discussions. Fellows typically spend four weeks in Zurich, reviewing between 200 and 400 PET/CT and PET/MR cases during their stay. The hospital's published fellowship records include students from Asia, Europe, Africa, North and South America, and Australia. 

Twenty-five years after the installation of a pioneering clinical PET/CT scanner at USZ, some of those international connections were on-site again. Former fellows travelled back to Zurich to reunite with colleagues, meet von Schulthess and take part in the anniversary celebration on 30 October, which included a scientific symposium and a tour of the nuclear medicine department.

The anniversary symposium, organized by USZ in collaboration with GE HealthCare also brought together clinicians, researchers and industry specialists to revisit the early days of PET/CT and discuss where molecular imaging might go next.

From an experimental idea to routine clinical imaging

The first commercial PET/CT systems arrived in 2001, but the technology had already been tested in Pittsburgh. An integrated prototype developed by CTI PET Systems and researchers including Dr. David Townsend and Dr. Ronald Nutt entered clinical evaluation at the University of Pittsburgh in Pennsylvania, US, in 1998.

The idea was to bring together two complementary imaging methods. CT showed anatomical structures, while PET revealed biological activity through the distribution of radioactive tracers.

Before the modalities were integrated, physicians could identify abnormal tracer uptake on PET images but sometimes struggled to determine its exact anatomical location. Combining the examinations helped resolve that uncertainty.

Zurich became an early center for clinical PET/CT when GE's Discovery LS system was installed at USZ in 2001. Siemens introduced its Biograph PET/CT system the same year, and other manufacturers subsequently entered the market.

From early skepticism to international recognition

Von Schulthess recalled recognizing the potential of the technology as soon as he encountered the experimental approach. "This is the solution. This is going to be the solution," he remembered thinking. 

His conviction, however, did not guarantee funding. The early development of PET/CT faced skepticism over its commercial prospects and clinical value. Von Schulthess described how private philanthropic support, university contributions, and public funding had to be brought together to make the project possible.

Dr. Philipp A. Kaufmann, director of the Department of Nuclear Medicine at USZ in Zurich, Switzerland, also recalled the persistent advocacy required to convince industry of the technology's potential.

At the time, some specialists questioned whether combining the relatively slow PET examination with a much faster CT scanner would be practical. Others believed that separately acquired examinations could simply be aligned afterwards.

In 2003, a prospective Zurich study published in the New England Journal of Medicine provided evidence of the benefit. Among 49 evaluable patients with suspected or confirmed non-small-cell lung cancer, integrated PET/CT provided additional diagnostic information in 20 cases, or 41%, compared with conventional visual correlation of PET and CT. It also improved the accuracy of tumor staging.

The study helped establish the clinical value of integrated imaging, although it did not directly investigate long-term survival outcomes. PET/CT subsequently became an established part of oncological imaging, with applications extending to cardiology, neurological conditions, infections and inflammatory diseases.

Silvia Steiner, education director of the canton of Zurich, told participants that approximately 12,000 PET/CT examinations had been performed at USZ in the preceding year.

Successive generations of PET/CT technology have been evaluated and introduced in Zurich, including systems with digital detectors and extended axial fields of view. Kaufmann said the long-standing collaboration with GE HealthCare had allowed clinicians to provide engineers with direct feedback during technology development.

How PET/CT changed treatment decisions

Kaufmann did not originally intend to build a career in nuclear medicine.

"I was a cardiologist. I had no intention to do nuclear medicine," he recalled. 

He joined the Zurich department in 1995 to investigate cardiac PET and myocardial blood flow, attracted by the research infrastructure and expertise already established under von Schulthess. Over time, his work contributed to the development of hybrid cardiac imaging, combining anatomical information about coronary arteries with measurements of myocardial perfusion.

Kaufmann illustrated its clinical value with a patient who had coronary abnormalities and an area of reduced blood flow during stress. The challenge was identifying which coronary lesion was responsible for the ischemia and where an intervention should be performed.

By combining coronary anatomy with functional imaging, the team could better relate the impaired blood flow to a particular lesion and guide the placement of a stent.

The role of PET/CT in infectious diseases and lymphoma

"That's how high precision diagnosis allows high precision treatment," Kaufmann said. 

Kaufmann also described the importance of PET/CT in infectious diseases. In one example, imaging helped distinguish an infection involving bone from one confined to adjacent tissue, a distinction that could determine whether surgery or antibiotic treatment was appropriate.

Dr. Patrick Veit-Haibach of the University of Toronto and University Health Network in Toronto, Canada, identified lymphoma as one of the strongest examples of its impact.

PET/CT is used for staging and treatment response assessment in many fluorodeoxyglucose (FDG)-avid lymphomas, including Hodgkin lymphoma and diffuse large B-cell lymphoma. In these settings, findings can influence treatment decisions and the interpretation of residual disease.

The 2025 European Society for Medical Oncology clinical practice guideline recommends PET/CT for baseline and response assessment in diffuse large B-cell lymphoma, although routine surveillance imaging after complete metabolic remission is generally not recommended.

Veit-Haibach also highlighted prostate-specific membrane antigen (PSMA) imaging, which has substantially changed the assessment of selected patients with prostate cancer.

Finding more than we need to treat

During the panel discussion, moderator Dr. Mathias Goyen, chief medical officer for imaging at GE HealthCare, asked whether examinations are sometimes performed because the technology makes them possible, rather than because sufficient evidence shows that they will change patient management.

Veit-Haibach suggested that practice varies between healthcare systems, partly according to reimbursement. He cautioned that changes in tracer uptake can influence treatment decisions even when their prognostic significance is uncertain.

An imaging signal may increase or decrease after treatment, but that does not necessarily establish whether a patient is benefiting in a clinically meaningful way, particularly when new therapies are being assessed.

Dr. David M. Kersting of University Hospital Essen in Essen, Germany, made a similar point about quantitative imaging.

Modern PET technology can detect increasingly small changes in tracer uptake, but a change in standardized uptake value (SUV) does not necessarily indicate a meaningful treatment response. Measurements can also be affected by acquisition protocols, reconstruction methods and biological variability. 

A different perspective came from Dr. Frank Urbaniok honorary professor at the University of Konstanz in Germany, and his background in forensic psychiatry. He cautioned against assuming that increasingly detailed scientific information always translates directly into useful conclusions.

In his field, findings concerning the brain may be interesting without providing reliable evidence about a person's behavior. 

Veit-Haibach predicted that future applications could include surveillance of people with high-risk conditions who do not yet have clinically apparent disease. Greater scanner sensitivity and lower administered radiation activities may make some of these approaches more feasible.

The next breakthroughs may come from radiotracers

Despite the continuing improvements in scanners, Dr. Roger Schibli professor of radiopharmaceutical chemistry at ETH Zurich in Zurich, Switzerland, and laboratory head at the Paul Scherrer Institute in Villigen, Switzerland, suggested that the next major advances may come from the radiopharmaceuticals themselves.

He invoked a familiar prediction that the future of imaging belongs to the tracers, while stressing the specific contribution of nuclear medicine.

Radiotracers make it possible to visualize biological processes by targeting particular molecules or pathways. Their usefulness depends on identifying a suitable biological target and developing a labelled compound that can reveal clinically relevant information.

Schibli pointed to fibroblast activation protein (FAP) as another promising target and anticipated that additional radiopharmaceuticals could open up new applications. 

Schibli also emphasized personalized dosimetry, estimating the radiation absorbed by tumors and healthy organs in an individual patient, rather than relying exclusively on fixed administered activities.

The approach offers opportunities to tailor radionuclide therapy more closely to a patient's disease and normal-tissue exposure, although such individualization is not yet routine across all treatments and centers.

Kersting predicted that molecular imaging could increasingly help select patients for other targeted treatments as well, including certain antibody-based cancer therapies.

Looking ahead a decade, Schibli expected radioligand therapies to move earlier in oncology treatment pathways, potentially in combination with chemotherapy or immunotherapy.

The cost of a better scanner

Long-axial-field-of-view PET systems can detect a larger proportion of the radiation emitted from administered tracers. Their improved sensitivity creates opportunities for faster examinations, lower injected activities and more detailed quantitative imaging.

Dr. Floris Jansen, a former chief scientist for molecular imaging at GE HealthCare and now a strategic adviser at Zenta, argued that one of the most consequential advances would be a new detector material capable of providing high performance at a substantially lower cost.

Scintillator materials, which detect the radiation used to produce PET images, account for an important part of the expense of modern systems.

Jansen acknowledged that although long-axial-field-of-view scanners have attracted considerable interest, relatively few institutions worldwide can afford the largest configurations.

He described how researchers had spent years investigating alternative detector materials, only to encounter problems when promising laboratory results had to be reproduced at the scale required for a clinical scanner.

Jansen also questioned whether producing increasingly detailed images would necessarily be the most important route to improving care. New radiotracers, he suggested, might provide greater clinical value than further incremental gains in scanner performance.

Innovation looks different outside Zurich

Dr. Mike Sathekge, head of nuclear medicine at the University of Pretoria in Pretoria, South Africa, described the uneven development of molecular imaging services in his country.

South Africa has advanced nuclear medicine centers, but other regions have limited access to the necessary infrastructure. Hospitals also need reliable access to radiopharmaceuticals, trained staff, appropriate facilities, regulatory approval and financing.

Sathekge argued that the value of nuclear medicine must be demonstrated to governments and healthcare decision-makers through clinical and economic evidence. He also raised financial toxicity as an important concern.

Schibli described several medical cyclotrons operating in the Zurich area that are used to produce radioisotopes for diagnostic imaging. Schibli suggested that generator-based production systems and longer-lived isotopes could help address some of the geographical constraints.

He also distinguished diagnostic tracer production from the supply challenges associated with therapeutic radionuclides, where growing clinical demand could require substantial new manufacturing capacity.

The contrast was not confined to differences between Europe and Africa. Kersting pointed out that access to advanced molecular imaging varies between European countries and even between hospitals within the same country.

For new techniques to become widely useful, they must be feasible outside the highly specialized centers where they are first developed.

Clinical trials beyond wealthy healthcare systems

As molecular imaging becomes more closely linked with targeted treatment, Sathekge called for trials that include a wider range of countries, patient population,  and healthcare settings.

Differences in infrastructure, disease patterns, patient populations, and access to subsequent treatment can affect how a technology performs in routine clinical practice.

Behind the radiopharmaceuticals

Behind the advances in PET/CT, Kaufmann reminded the audience, are the radiopharmacy teams who start work as early as 2 a.m., producing radioactive compounds, performing quality checks, and preparing deliveries to hospitals.

He described how the work has changed over the decades, with increased automation reducing the need for manual handling of radioactive materials and thanked his colleagues for their work over the years, describing the reliable supply of radiopharmaceuticals as an achievement in itself.

Another 25 years

Dr. Beatrice Beck-Schimmer, vice president of medicine at the University of Zurich in Zurich, Switzerland, had opened the symposium by reflecting on the conditions needed to turn an invention into medical practice: an idea, an environment in which it can be developed, and people prepared to take it forward.

The installation of a pioneering clinical scanner in 2001 was followed by decades of research, collaboration with industry and international training. The physicians who once came to Zurich to learn hybrid imaging are now part of a wider community practicing and developing the technology across the world.