Hierarchical Tomography: Mapping Human Organs at the Cellular Level

Imagine possessing a map of the world so incredibly advanced that you could view the entire expanse of a continent, and then, with a simple scroll of a mouse, zoom continuously downward to inspect a single blade of grass on a suburban lawn—all without losing an ounce of clarity or focus. For centuries, medical science has yearned for an equivalent map of the human body. Physicians and researchers have longed for a way to view a whole, intact human organ and simultaneously zoom in to observe the behavior of its individual microscopic cells. Today, this monumental ambition is no longer relegated to the realm of science fiction. Thanks to a revolutionary imaging technology known as Hierarchical Phase-Contrast Tomography (HiP-CT), we are entering a new era of anatomical discovery.

Dubbed the "Google Earth of the human body," HiP-CT represents one of the most significant breakthroughs in biomedical imaging in modern history. By harnessing the power of the world’s most advanced particle accelerator, an international coalition of scientists is mapping human organs from the macro-scale down to the cellular level without ever lifting a scalpel. The resulting database, known as the Human Organ Atlas, is fundamentally transforming our understanding of human anatomy, pathology, and the insidious ways in which diseases like COVID-19, cancer, and heart disease ravage the body.

The Century-Old Chasm in Medical Imaging

To appreciate the sheer magnitude of HiP-CT, one must first understand the severe limitations that have plagued medical imaging for over a century. Since the discovery of X-rays by Wilhelm Röntgen in 1895, the field of radiology has advanced tremendously, yielding powerful tools like Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scanners. These technologies are invaluable for clinical diagnostics, providing excellent three-dimensional overviews of human organs. However, clinical CT and MRI scans are fundamentally constrained by their resolution, which operates primarily in the millimeter range. They can reveal a tumor, a broken bone, or a major arterial blockage, but they are entirely blind to the microscopic cellular ecosystem where diseases actually originate.

On the other end of the spectrum is histology, the study of the microscopic anatomy of cells and tissues. Histology provides staggering, ultra-high-resolution views of cellular structures. However, to achieve this, pathologists must physically cut tissue into infinitesimally thin, two-dimensional slices, place them on glass slides, and view them under a microscope. This destructive process destroys the complex, three-dimensional architecture of the organ. As Dr. Claire Walsh, an imaging scientist at University College London (UCL), astutely explained, relying on histological sections to find early-stage disease is "like looking for a needle in a haystack".

For decades, this created a massive, unbridgeable chasm in biomedicine: you could either look at the whole organ with low resolution, or look at a tiny fragment of the organ with high resolution. You could never do both. You could never trace the intricate plumbing of an organ’s blood vessels from the major arteries all the way down to the microscopic capillaries that feed individual cells.

Hierarchical Phase-Contrast Tomography has permanently bridged this gap.

Harnessing the Power of a Particle Accelerator

The genesis of HiP-CT did not occur in a standard hospital ward, but rather deep within the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The ESRF is a massive, ring-shaped particle accelerator where electrons are fired at near the speed of light to produce X-rays of unfathomable brilliance. In 2020, the facility underwent a massive upgrade to become the Extremely Brilliant Source (EBS), creating the world's first high-energy, fourth-generation synchrotron.

To put the power of the ESRF-EBS into perspective, the X-rays it produces are up to 100 billion times brighter than those generated by a conventional hospital CT scanner. This staggering luminance and spatial coherence allowed scientists to develop HiP-CT, a technique that decouples the traditional trade-off between the field of view and image resolution.

The scanning process is an engineering marvel. Deceased donor organs are carefully fixed in formalin solutions, partially dehydrated in an ethanol series, and physically stabilized inside polyethylene terephthalate jars using agar-agar gel to prevent even the slightest microscopic movement during the scan. Once prepared, the intact organ is placed into the synchrotron beamline (specifically the BM05 or BM18 beamlines).

The HiP-CT process begins with a "macro" scan of the entire intact organ at an isotropic voxel size of around 20 to 25 micrometers. To contextualize this, 25 microns is thinner than a single human hair, yet this initial overview scan is already 20 to 25 times more detailed than a clinical medical CT scan. Once this whole-organ map is generated, scientists can computationally select specific Volumes of Interest (VOIs) deep within the tissue. The synchrotron beam is then adjusted to seamlessly "zoom in" on these targeted areas, scanning them at resolutions ranging from 6 microns down to 1 micron. For some organs, the technology has reached a breathtaking resolution of 0.65 micrometers—a scale significantly smaller than the thickness of a single human red blood cell.

Professor Peter Lee, a leading materials scientist and HiP-CT project lead at UCL’s Department of Mechanical Engineering, noted that the resulting organ scans contain "one million times the information" of standard clinical CT scans. Because the process is entirely non-destructive, the tissue remains perfectly intact, allowing researchers to explore the multi-scale hierarchy of the body in its true three-dimensional state.

The Catalyst: Decoding the Devastation of COVID-19

While the ESRF-EBS upgrade provided the technological foundation for HiP-CT, it was a global tragedy that served as the catalyst for its accelerated development. In the early, dark days of the COVID-19 pandemic, the medical community was utterly baffled by the erratic, catastrophic damage the SARS-CoV-2 virus was inflicting on human lungs. Traditional hospital scans showed opaque, cloudy regions known as "ground-glass opacities," but they lacked the resolution to explain why patients' blood oxygen levels were plummeting so dramatically even when their lungs appeared partially clear.

A multidisciplinary team, led by researchers at UCL and the ESRF, alongside clinicians from Hannover and Mainz in Germany, quickly pivoted the synchrotron's focus to scan the intact lungs of deceased COVID-19 victims. What they uncovered was a revelation that changed the course of clinical treatment.

Using HiP-CT, the researchers essentially flew through the respiratory tracts of the victims, zooming from the major bronchioles down into the finest micro-vasculature of the alveoli. They discovered that the virus was not merely causing standard pneumonia; it was fundamentally destroying the intricate vascular networks of the lung. The ultra-high-resolution imaging revealed massive remodeling of the finest blood vessels, with a diameter of less than five micrometers.

Most shockingly, the HiP-CT scans exposed a phenomenon known as arteriovenous shunting—where normally separate blood systems were connecting with each other abnormally, creating microscopic "short circuits". Furthermore, the imaging revealed severe micro-ischemia (restricted blood flow), extensive subpleural hot spots of fibrotic remodeling, and widespread intussusceptive angiogenesis (a bizarre form of blood vessel splitting and generation). The detailed imaging of irregular vascular lumens plagued by numerous micro-thromboses (tiny blood clots) provided visual, irrefutable evidence that severe COVID-19 was heavily vascular in nature. This unprecedented insight supported the crucial clinical decision to administer anticoagulant (blood-thinning) drugs to severe COVID-19 patients during a time of great global uncertainty.

The Human Organ Atlas: Democratizing Anatomy

Realizing the profound implications of this technology, the team—supported by a $2.75 million grant from the Chan Zuckerberg Initiative (CZI)—expanded their scope far beyond the lungs. If HiP-CT could map the devastation of a novel coronavirus, what could it reveal about heart disease, Alzheimer's, cancer, and healthy human aging?

Thus, the Human Organ Atlas (HOA) was born. The HOA is a globally accessible, open-data repository designed to share these massive, hierarchical 3D image datasets with researchers, clinicians, educators, and the general public worldwide. As of early 2026, the atlas has grown into a colossal library, providing access to over 300 full 3D datasets extracted from 56 organs across 25 to 32 human donors. The repository includes meticulously detailed scans of the brain, heart, lungs, kidneys, liver, spleen, colon, eyes, placenta, uterus, prostate, and testes.

Following the FAIR principles (Findable, Accessible, Interoperable, and Re-usable), the data is distributed under a permissive open license. "From the beginning, we wanted these data to be accessible to everyone and build an open, shared scientific infrastructure at a global scale," emphasized Paul Tafforeau, the lead beamline scientist at the ESRF. Through a standard web browser, without the need for specialized supercomputers, anyone in the world can virtually "fly through" these organs.

A Virtual Voyage: Exploring the Organs

The application of HiP-CT across different biological systems is yielding a treasure trove of anatomical discoveries, rewriting medical textbooks along the way.

The Heart: A Google Earth for Cardiology

Cardiovascular disease remains the leading cause of death globally. Until recently, imaging the heart meant sacrificing either the view of the entire cardiac pump or the microscopic details of its muscle fibers. Utilizing the ESRF's BM18 beamline, researchers imaged two whole adult human hearts—one from a healthy 63-year-old donor and another from an 87-year-old donor with a history of ischemic heart disease, hypertension, and atrial fibrillation.

The resulting 3D cinematic renderings allow cardiologists to strip away epicardial fat digitally and trace the major coronary arteries down to the finest penetrating arterioles that feed the myocardium (muscle cells). The scans clearly visualize the heart's valves and, crucially, the cardiac conduction system—the complex electrical wiring that triggers heart contractions. "The first time you see the heart with HiP-CT, it is quite surprising, as it clearly shows soft tissue not typically visible with conventional X-ray imaging," noted Joseph Brunet, a researcher at UCL. By comparing the healthy and diseased hearts, experts can observe how diseased muscle fibers wither and how tissue thickness varies, offering unprecedented insights into the onset of cardiac rhythm abnormalities and the potential efficacy of surgical ablation strategies. (It is important to note that because the synchrotron radiation dosage required is exceedingly high, this imaging is strictly limited to deceased donor organs; it cannot currently be performed on living patients).

The Brain: Unraveling the Neural Labyrinth

The human brain is arguably the most complex structure in the known universe. Current whole-brain MRI scans max out at roughly 100-micron resolution, while detailed histological studies are limited to 2D slices at 20 microns or finer. HiP-CT perfectly fills this critical gap, capturing entire post-mortem human brains at isotropic resolutions of around 7.7 microns per voxel. This allows neuroscientists to track the intricate, 3D spatial orientation of white matter tracts and resolve localized cellular features without slicing the delicate cerebral tissue. The potential applications for neurodegenerative diseases like Alzheimer's and Parkinson's are profound, as researchers can now look for microscopic plaques and structural degradation within the context of the intact brain network.

The Kidneys, Liver, and Beyond

In the kidneys, HiP-CT has been utilized for the precise quantification and 3D morphometry of glomeruli—the millions of tiny vascular tufts responsible for filtering blood. In reproductive health, the technology has successfully visualized and reconstructed the complete microvasculature of a human uterus affected by adenomyosis, a painful condition where endometrial tissue grows into the muscular wall of the uterus. In oncology, the ability to scan massive volumes of tissue at sub-micron resolutions allows pathologists to detect elusive micrometastases—tiny clusters of cancer cells that easily evade traditional clinical imaging and are often missed in random biopsy slices.

Transforming Medical Education and Artificial Intelligence

Beyond immediate clinical and pathological research, the Human Organ Atlas is poised to revolutionize two entirely different spheres: medical education and Artificial Intelligence (AI).

For centuries, medical students have learned anatomy by poring over static, two-dimensional diagrams in textbooks, or through the gross dissection of cadavers. The HOA shifts the paradigm from static memorization to interactive, guided discovery. Students can dynamically scroll through anatomical sections, rotate organs in three-dimensional space, and zoom seamlessly from the macroscopic surface of the liver down into its microscopic lobules. "It creates an immersive exploratory alternative to classic anatomy diagrams, helping learners build a clearer spatial understanding of complex structures," researchers noted, a shift that promises to produce a generation of physicians with a vastly superior spatial comprehension of the human body.

Simultaneously, the HOA is providing the ultimate training ground for Artificial Intelligence. Developing robust machine-learning algorithms for healthcare requires massive, high-quality, accurately labeled datasets. The hierarchical nature of HiP-CT data is a goldmine for computer vision models. AI researchers are using these multiscale scans to train algorithms in automatic tissue segmentation, super-resolution analysis, and early disease detection. By analyzing the shapes, volumes, and microscopic deformations caused by diseases like severe COVID-19, AI can help clinicians establish highly accurate prognostic biomarkers, ultimately predicting patient outcomes with greater precision.

The Horizon: Mapping the Entire Human Body

As astonishing as the current capabilities of Hierarchical Phase-Contrast Tomography are, the international team of over 80 scientists and clinicians behind the Human Organ Atlas views this as only the beginning. "After 6 years of efforts, we are still only at the beginning," said Paul Tafforeau.

Currently, the BM18 beamline at the ESRF is the only place in the world where complete human organs can be imaged with such a high level of contrast, and the team is still pushing the limits of the facility's capabilities. The primary bottleneck is no longer the physical imaging, but rather the immense computational power required to process, store, and navigate the petabytes of data generated by these multiscale scans.

Yet, the project's ambition remains boundless. The Human Organ Atlas team has set its sights on an even more audacious goal: transitioning from scanning isolated, individual organs to mapping the entirety of an intact human body. In the coming years, researchers expect to scale the technique to image complete, whole human bodies with a localized resolution reaching potentially 2 micron voxels—10 to 20 times higher than what is physically possible today.

Achieving this "Whole-Body Google Earth" will allow medical science to fully map multisystemic diseases. For conditions like hypertension, diabetes, and long-COVID, physicians will no longer have to guess how a microscopic failure in the kidney's blood vessels correlates with structural changes in the heart or brain. They will be able to trace the biological domino effect across the entire human ecosystem, in three dimensions, at the cellular level.

We are witnessing the dawn of a new era in biomedical imaging. Hierarchical Phase-Contrast Tomography is not simply a new camera; it is an entirely new lens through which we are decoding the physical blueprint of human life. By peeling back the opaque layers of our biology, the Human Organ Atlas is granting us a profound, unprecedented window into the inner architecture of ourselves—a map of the human microcosm that will guide medical science for generations to come.