Hepatocellular carcinoma is the most common form of primary liver cancer and ranks third among all cancers in worldwide mortality. For tumors caught at an early stage, percutaneous thermal ablation, in which a needle-like antenna delivers heat to cook the tumor away, is considered the optimal minimally invasive locoregional therapy. But the technique depends entirely on the operator’s ability to see the tumor. At most institutions, tumors between 3 and 5 centimeters are typically treated with radiation segmentectomy or with transarterial chemoembolization combined with microwave ablation. Both approaches rely on catheters threaded into the arteries feeding the tumor, and both depend on iodinated contrast to map the tumor’s blood supply. When contrast is off the table, those pathways close.

The patient in this report faced exactly that dilemma. His tumor board determined he was ineligible for transplantation, surgical resection, or stereotactic body radiotherapy because of regional lymph node metastases and compromised liver function, classified as Child-Pugh B7 cirrhosis. His stage 4 chronic kidney disease made contrast-enhanced procedures hazardous, and he refused contrast administration altogether. That ruled out radiation segmentectomy, transarterial chemoembolization, and cone-beam CT arteriography, the contrast-enhanced imaging technique that normally guides such procedures in the angiography suite. After extensive discussion, he agreed to a novel alternative: microwave ablation guided by ultrasound-placed fiducial markers and non-contrast cone-beam CT with trajectory planning software.

The technique began with the placement of six radio-opaque fiducial markers, short pushable coils measuring 2 millimeters, delivered through a 15-centimeter, 20-gauge needle under ultrasound guidance. Each coil was positioned at one of the tumor’s anatomic boundaries: cranial, caudal, medial, lateral, anterior, and posterior. Ultrasound and fluoroscopic imaging confirmed that all six markers sat satisfactorily around the lesion. The concept is elegantly simple. Because the tumor itself was poorly visible on non-contrast imaging, the team created an artificial outline of it, framing the cancer with metal beacons that any X-ray-based imaging system could detect. The coils effectively drew the tumor’s borders in a language the treatment equipment could read.

With the tumor framed, the team advanced a microwave antenna under ultrasound guidance until its tip abutted the first fiducial marker. A planning cone-beam CT confirmed the probe’s position, and the images were exported to a standalone desktop running ablation visualization software. That software calculated the maximal yet safe ablation zone for the probe’s position, predicting the volume of tissue that a given energy delivery would destroy, and computed the resulting ablation margin, the buffer of treated tissue extending beyond the tumor edge. The team targeted margins of 0.5 to 1 centimeter, the standard needed to eliminate microscopic tumor extensions that imaging cannot see.

What followed was a carefully choreographed sequence of overlapping ablations. After the first burn, a second probe trajectory was planned using the post-placement cone-beam CT, and the antenna was repositioned with the help of a planned trajectory overlaid on live fluoroscopic guidance. A repeat cone-beam CT verified the new position, the planning software extrapolated the residual tumor still to be treated, and the next trajectory was calculated accordingly. The team worked through the fiducials one by one, ultimately performing eight fiducial-targeted ablations plus two additional burns to confirm adequate margins using the cumulative ablation zones displayed by the software and verified on post-ablation imaging. Because the software mapped every zone and cone-beam CT followed each ablation, no additional immediate postoperative imaging was needed.

The technical footprint of the procedure was modest. Total fluoroscopic time was 18.5 minutes, with a cumulative radiation dose of 1405 milligray. There were no intraoperative or immediate complications. The patient experienced only mild epigastric pain for one week after the procedure and reported no complaints at one-month follow-up. Most strikingly, the initial post-procedural MRI and the most recent 26-month follow-up MRI both demonstrated complete response of the target lesion by modified RECIST criteria, the standardized imaging assessment used to judge treatment success in liver cancer trials. For a tumor larger than 3 centimeters treated without contrast, that durability is the report’s central evidence.

The authors acknowledge meaningful limitations. This is a single-patient retrospective case report, and skeptics could argue that the same outcome might have been achieved with ultrasound or conventional CT alone. But the authors counter that the tumor’s size demanded multiple probe placements and overlapping ablations, which would have been impossible to verify with ultrasound alone because the ablation planning software requires cross-sectional imaging to confirm sufficient coverage. Non-contrast conventional CT, meanwhile, would have limited the precise oblique probe trajectories needed to cover the entire lesion while protecting adjacent bowel. Out-of-plane needle placements are more accurate with the trajectory planning and real-time fluoroscopic guidance that cone-beam CT uniquely provides. The fundamental weakness of non-contrast cone-beam CT is its limited soft tissue resolution, which is precisely the problem the fiducials were designed to solve.

Fiducial markers are not new to interventional radiology. They have previously been used to guide ablation of colorectal metastases, particularly for lesions that disappear on imaging after chemotherapy, leaving nothing visible to target. But little research exists on fiducial placement for prospective ablation guidance in hepatocellular carcinoma, and the authors argue that the effectiveness and reproducibility of this approach make it a worthy addition to the literature. They also sketch a more refined evolution of the technique: a staged workflow in which fiducials are placed first, a preoperative CT or MRI is then acquired, and that study is uploaded and overlaid on the patient in the procedure room. A single fiducial would serve as an internal control for respiration and patient positioning, allowing the ablation zone to be planned from preoperative imaging alone.

The broader significance of the report lies in what it demonstrates about adaptability in image-guided medicine. Predictive ablation software, originally developed to help operators estimate burn volumes in conventional settings, proved capable of anchoring an entire treatment plan around metal markers instead of a contrast-visible tumor. The approach preserves three advantages that are usually lost when contrast is unavailable: accurate margin assessment, safe probe trajectories through difficult anatomy, and confidence that overlapping ablations have covered the target completely. The authors are careful to note that future prospective studies are needed before the technique can be considered standard practice, and a single case cannot establish safety across diverse patients and tumor geometries. Still, for the growing population of patients with liver cancer and kidneys that cannot tolerate contrast, the report offers a concrete, technically grounded path forward, one in which six small coils and clever software stand in for the contrast dye that medicine long took for granted.

Subject of Research: Fiducial marker-assisted, contrast-free microwave ablation of hepatocellular carcinoma using cone-beam CT guidance and ablation predictive software

Article Title: Fiducial marker-assisted microwave ablation of hepatocellular carcinoma: achieving margins without contrast

Article References: Daniel, B., & Kouri, B. (2025). Fiducial marker-assisted microwave ablation of hepatocellular carcinoma: achieving margins without contrast. CVIR Oncology, 1(1), Article 16. https://doi.org/10.1007/s44343-025-00013-3

Image Credits: AI Generated

DOI: 10.1007/s44343-025-00013-3

Keywords: hepatocellular carcinoma, microwave ablation, fiducial markers, cone-beam CT, interventional radiology, ablation predictive software, contrast contraindication, liver cancer, trajectory planning, cirrhosis, mRECIST, case report

Writing in the open-access journal HardwareX, Bas Stijnen, Joseph Thompson, Ryan Paetzold, Eoghan Somers, and David McKeown present a fully open-source, camera-based trifilar pendulum system designed to measure the mass moment of inertia of CubeSat-class objects with impressive accuracy. The complete hardware and software package, from 3D-printed platform tiles to Python analysis code, is released under permissive licenses including CERN-OHL, CC-BY-4.0, and the MIT License, and the total cost ranges from roughly 55 euros for the bare pendulum platform to about 550 euros for a full setup with support frame and camera. The system has even earned open-source hardware certification under OSHWA UID IE000005, a formal stamp of reproducibility that few laboratory instruments can claim.

The trifilar pendulum itself is a beautifully simple piece of physics. A platform is hung from three equal-length wires and given a gentle twist. Because the platform’s centre of mass sits directly beneath the suspension point, it oscillates about the vertical axis with a period that depends on its rotational inertia, its mass, the suspension radius, and the length of the wires. The classical relation, derived under the assumptions of small-angle motion, rigid bodies, and negligible friction, links the measured oscillation period directly to the moment of inertia. What has traditionally made such setups expensive is not the pendulum but the instrumentation: precision rotary encoders or inertial sensors must be physically attached to the oscillating platform, adding mass, friction, and damping that corrupt the very quantity being measured.

The Dublin team’s key innovation is to remove contact entirely. Instead of sensors, they print two paper fiducial markers and tape them to the underside of the platform. These are not ordinary targets but N-fold markers, one with four-fold and one with five-fold rotational symmetry, selected using the MarkerLocator framework. The coprime symmetry orders allow the image-processing software to distinguish the two markers unambiguously and estimate rotational pose reliably from a single camera, even as the platform twists back and forth. A webcam or action camera mounted below the platform records the oscillation, and open-source Python software built on OpenCV, NumPy, and PyQt6 extracts the oscillation period, applies the trifilar equation, and reports the moment of inertia in kilogram metres squared, complete with an estimated measurement error.

The platform itself is assembled from nine triangular 3D-printed PLA tiles joined with brass threaded inserts and M4 screws, forming an equilateral triangular footprint roughly 407 millimetres on a side. The validated configuration handles test articles up to approximately two kilograms, a limit set not by the suspension hardware but by the stiffness of the printed platform, which can flex under concentrated loads and alter the effective suspension geometry. An optional support frame built from aluminium extrusion holds the pendulum and mounts the camera, making the system portable enough for ISO 8 CubeSat assembly cleanrooms, though the team found that suspending the platform directly from a rigid ceiling generally yields better results.

Validation was thorough and revealing. Using calibration masses with analytically known inertias, the researchers tested nine different moment of inertia values spanning from 0.15 to 6.1 times ten to the minus three kilogram metres squared, repeating every measurement five times. The results fell into three clear regimes. For inertias above three times ten to the minus three kilogram metres squared, errors stayed below five percent regardless of camera choice. In the intermediate range, errors ranged between five and fifteen percent, still acceptable for CubeSat characterisation. Below ten to the minus three, accuracy degraded sharply, sometimes exceeding forty percent with the support frame, because the inertia of the object becomes small compared with that of the platform itself, and the final answer emerges from subtracting two large, similar numbers.

Two practical findings stand out for anyone planning to build the system. First, the suspension material matters more than one might expect. Replacing steel cables with braided Dyneema fishing line, chosen for its negligible mass and bending stiffness, cut measurement errors dramatically, bringing even the lowest-inertia test case down to about 6.6 percent error. Second, camera quality matters mainly at the low end: a GoPro Hero 7 Black at fifty frames per second outperformed a basic Logitech C270 webcam by roughly ten percent for small inertias, thanks to better tracking resolution, while the two cameras performed nearly identically for larger objects. Camera distance, between fifteen and thirty centimetres below the platform, proved almost irrelevant, though the GoPro’s wide-angle fish-eye distortion introduced slight errors when markers drifted toward the frame edges.

The software also tackles a common experimental headache: imperfect centring. The trifilar equation assumes the test object’s centre of mass sits exactly over the platform centre, but real satellites are rarely so cooperative. The team implemented an optional correction based on the parallel axis theorem, subtracting the term mass times offset squared from the measured value. Verification tests with calibration masses displaced by five to twenty millimetres showed the software’s corrections matched theoretical predictions to within one part in a million of a kilogram metre squared. A free-decay experiment further confirmed that damping is negligible: the logarithmic decrement of 0.0162 corresponds to a damping ratio of just 0.00257, and the oscillation period shifted by only 0.38 percent over fifty seconds of decay.

The most convincing demonstration came with a representative CubeSat mock-up, an aluminium frame carrying four PCB-based solar panel simulators and integrated calibration masses. The pendulum measured a moment of inertia of 6.738 times ten to the minus three kilogram metres squared, within 3.7 percent of the CAD prediction of 6.996. The small discrepancy was attributed to exactly the kinds of details that make experimental measurement valuable in the first place: tape, fasteners, T-slot hardware, and assembly tolerances that no model captures perfectly. For university CubeSat programmes and small research groups, the message is clear. With a desktop 3D printer, a webcam, a kitchen scale, and freely downloadable design files and software, laboratory-grade mass property measurement is now within reach of virtually any team, and the era of guessing a satellite’s inertia may finally be drawing to a close.

Subject of Research: An open-source camera-based trifilar pendulum for measuring the mass moment of inertia of small satellites

Article Title: An open-source camera-based trifilar pendulum setup for measuring mass moment of inertia of small satellites

Article References: Stijnen, B., Thompson, J., Paetzold, R., Somers, E., & McKeown, D. (2026). An open-source camera-based trifilar pendulum setup for measuring mass moment of inertia of small satellites. HardwareX, Article e00821. https://doi.org/10.1016/j.ohx.2026.e00821

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00821

Keywords: mass moment of inertia, trifilar pendulum, CubeSats, open-source hardware, fiducial markers, optical tracking, 3D printing, attitude control, small satellites, PocketQubes, HardwareX, low-cost instrumentation