Anthropomorphic liver phantom with flow for multimodal image-guided liver therapy research and training

Lipid Microparticle-Based Phantoms Modeling Hepatic Steatosis for the Validation of Quantitative Imaging Techniques

Metabolic dysfunction-associated steatotic liver disease (MASLD) typically presents as "macrovesicular steatosis", where each hepatocyte contains a large fat vacuole (30-50 µm), indicating a more indolent form. In about 20% of cases, "microvesicular steatosis" occurs, with smaller vacuoles (1-15 µm) linked to steatohepatitis, cirrhosis progression, and increased risk of liver cancer. Emerging quantitative ultrasound (QUS) liver fat quantification (QUS-LFQ) tools measure various acoustic properties, but few methods compare techniques and imaging modalities, and the impact of fat vacuole size remains unclear. This study introduces a methodology to create ultrasound (US) phantoms that replicate fat vesicle size in MASLD. While imaging phantoms validate quantitative tools, no model currently links QUS-LFQ measurements to steatosis severity. Existing homogeneous phantoms assessing properties like attenuation, backscatter, and speed of sound overlook the microstructure of steatosis, despite the known effect of particle size on acoustic interactions. Here, agar-based phantoms simulate fat accumulation in steatotic hepatocytes using stable peanut oil droplets as analogs for lipid vacuoles. Microscopy and sizing confirm stability at 4 °C, 23 °C, and 50 °C. Both microscopy and US imaging confirm uniform distribution, with QUS-LFQ measurements reflecting fat content. These phantoms hold promise for validating quantitative imaging methods, particularly for US-based MASLD screening tools.

Phantoms for Quantitative Body MRI: a review and discussion of the phantom value

In this paper, we review the value of phantoms for body MRI in the context of their uses for quantitative MRI methods research, clinical trials, and clinical imaging. Certain uses of phantoms are common throughout the body MRI community, including measuring bias, assessing reproducibility, and training. In addition to these uses, phantoms in body MRI methods research are used for novel methods development and the design of motion compensation and mitigation techniques. For clinical trials, phantoms are an essential part of quality management strategies, facilitating the conduct of ethically sound, reliable, and regulatorily compliant clinical research of both novel MRI methods and therapeutic agents. In the clinic, phantoms are used for development of protocols, mitigation of cost, quality control, and radiotherapy. We briefly review phantoms developed for quantitative body MRI, and finally, we review open questions regarding the most effective use of a phantom for body MRI.

Liver Phantoms Cast in 3D-Printed Mold for Image-Guided Procedures

INTRODUCTION

Image-guided invasive procedures on the liver require a steep learning curve to acquire the necessary skills. The best and safest way to achieve these skills is through hands-on courses that include simulations and phantoms of different complications, without any risks for patients. There are many liver phantoms on the market made of various materials; however, there are few multimodal liver phantoms, and only two are cast in a 3D-printed mold.

METHODS

We created a virtual liver and 3D-printed mold by segmenting a CT scan. The InVesalius and Autodesk Fusion 360 software packages were used for segmentation and 3D modeling. Using this modular mold, we cast and tested silicone- and gelatin-based liver phantoms with tumor and vascular formations inside. We tested the gelatin liver phantoms for several procedures, including ultrasound diagnosis, elastography, fibroscan, ultrasound-guided biopsy, ultrasound-guided drainage, ultrasound-guided radio-frequency ablation, CT scan diagnosis, CT-ultrasound fusion, CT-guided biopsy, and MRI diagnosis. The phantoms were also used in hands-on ultrasound courses at four international congresses.

RESULTS

We evaluated the feedback of 33 doctors regarding their experiences in using and learning on liver phantoms to validate our model for training in ultrasound procedures.

CONCLUSIONS

We validated our liver phantom solution, demonstrating its positive impact on the education of young doctors who can safely learn new procedures thus improving the outcomes of patients with different liver pathologies.

Gelatin-Based Liver Phantoms for Training Purposes: A Cookbook Approach

Background: Patients with liver pathology benefit from image-guided interventions. Training for interventional procedures is recommended to be performed on liver phantoms until a basic proficiency is reached. In the last 40 years, several attempts have been made to develop materials to mimic the imaging characteristics of the human liver in order to create liver phantoms. There is still a lack of accessible, reproducible and cost-effective soft liver phantoms for image-guided procedure training. Methods: Starting from a CT-scan DICOM file, we created a 3D-printed liver mold using InVesalius (Centro de Tecnologia da informação Renato Archer CTI, InVesalius 3 open-source software, Campinas, Brazil) for segmentation, Autodesk Fusion 360 with Netfabb (Autodesk software company, Fusion 360 2.0.19426 with Autodesk Netfabb Premium 2023.0 64-Bit Edition, San Francisco, CA, USA) for 3D modeling and Stratasys Fortus 380 mc 3D printer (Stratasys 3D printing company, Fortus 380 mc 3D printer, Minneapolis, MN, USA). Using the 3D-printed mold, we created 14 gelatin-based liver phantoms with 14 different recipes, using water, cast sugar and dehydrated gelatin, 32% fat bovine milk cream with intravenous lipid solution and technical alcohol in different amounts. We tested all these phantoms as well as ex vivo pig liver and human normal, fatty and cirrhotic liver by measuring the elasticity, shear wave speed, ultrasound attenuation, CT-scan density, MRI signal intensity and fracture force. We assessed the results of the testing performed, as well as the optical appearance on ultrasound, CT and MRI, in order to find the best recipe for gelatin-based phantoms for image-guided procedure training. Results: After the assessment of all phantom recipes, we selected as the best recipe for transparent phantoms one with 14 g of gelatin/100 mL water and for opaque phantom, the recipes with 25% cream. Conclusions: These liver gelatin-based phantom recipes are an inexpensive, reproducible and accessible alternative for training in image-guided and diagnostic procedures and will meet most requirements for valuable training.

Mechanical properties of human hepatic tissues to develop liver-mimicking phantoms for medical applications

Using liver phantoms for mimicking human tissue in clinical training, disease diagnosis, and treatment planning is a common practice. The fabrication material of the liver phantom should exhibit mechanical properties similar to those of the real liver organ in the human body. This tissue-equivalent material is essential for qualitative and quantitative investigation of the liver mechanisms in producing nutrients, excretion of waste metabolites, and tissue deformity at mechanical stimulus. This paper reviews the mechanical properties of human hepatic tissues to develop liver-mimicking phantoms. These properties include viscosity, elasticity, acoustic impedance, sound speed, and attenuation. The advantages and disadvantages of the most common fabrication materials for developing liver tissue-mimicking phantoms are also highlighted. Such phantoms will give a better insight into the real tissue damage during the disease progression and preservation for transplantation. The liver tissue-mimicking phantom will raise the quality assurance of patient diagnostic and treatment precision and offer a definitive clinical trial data collection.

A Review of Low-Cost Ultrasound Compatible Phantoms

Ultrasound-compatible phantoms are used to develop novel US-based systems and train simulated medical interventions. The price difference between lab-made and commercially available ultrasound-compatible phantoms lead to the publication of many papers categorized as low-cost in the literature. The aim of this review was to improve the phantom selection process by summarizing the pertinent literature. We compiled papers on US-compatible spine, prostate, vascular, breast, kidney, and li ver phantoms. We reviewed papers for cost and accessibility, providing an overview of the materials, construction time, shelf life, needle insertion limits, and manufacturing and evaluation methods. This information was summarized by anatomy. The clinical application associated with each phantom was also reported for those interested in a particular intervention. Techniques and common practices for building low-cost phantoms were provided. Overall, this article aims to summarize a breadth of ultrasound-compatible phantom research to enable informed phantom methods selection.

Vocal pain expression augmentation for a robopatient

Abdominal palpation is one of the basic but important physical examination methods used by physicians. Visual, auditory, and haptic feedback from the patients are known to be the main sources of feedback they use in the diagnosis. However, learning to interpret this feedback and making accurate diagnosis require several years of training. Many abdominal palpation training simulators have been proposed to date, but very limited attempts have been reported in integrating vocal pain expressions into physical abdominal palpation simulators. Here, we present a vocal pain expression augmentation for a robopatient. The proposed robopatient is capable of providing real-time facial and vocal pain expressions based on the exerted palpation force and position on the abdominal phantom of the robopatient. A pilot study is conducted to test the proposed system, and we show the potential of integrating vocal pain expressions to the robopatient. The platform has also been tested by two clinical experts with prior experience in abdominal palpation. Their evaluations on functionality and suggestions for improvements are presented. We highlight the advantages of the proposed robopatient with real-time vocal and facial pain expressions as a controllable simulator platform for abdominal palpation training studies. Finally, we discuss the limitations of the proposed approach and suggest several future directions for improvements.

Motion-robust, blood-suppressed, reduced-distortion diffusion MRI of the liver

PURPOSE

To evaluate feasibility and reproducibility of liver diffusion-weighted (DW) MRI using cardiac-motion-robust, blood-suppressed, reduced-distortion techniques.

METHODS

DW-MRI data were acquired at 3T in an anatomically accurate liver phantom including controlled pulsatile motion, in eight healthy volunteers and four patients with known or suspected liver metastases. Standard monopolar and motion-robust (M1-nulled, and M1-optimized) DW gradient waveforms were each acquired with single-shot echo-planar imaging (ssEPI) and multishot EPI (msEPI). In the motion phantom, apparent diffusion coefficient (ADC) was measured in the motion-affected volume. In healthy volunteers, ADC was measured in the left and right liver lobes separately to evaluate ADC reproducibility between the two lobes. Image distortions were quantified using the normalized cross-correlation coefficient, with an undistorted T2-weighted reference.

RESULTS

In the motion phantom, ADC mean and SD in motion-affected volumes substantially increased with increasing motion for monopolar waveforms. ADC remained stable in the presence of increasing motion when using motion-robust waveforms. M1-optimized waveforms suppressed slow flow signal present with M1-nulled waveforms. In healthy volunteers, monopolar waveforms generated significantly different ADC measurements between left and right liver lobes ( p = 0 . 0078 $$ p=0.0078 $$ , reproducibility coefficients (RPC) =  470 × 1 0 - 6 $$ 470\times 1{0}^{-6} $$ mm 2 $$ {}^2 $$ /s for monopolar-msEPI), while M1-optimized waveforms showed more reproducible ADC values ( p = 0 . 29 $$ p=0.29 $$ , RPC = 220 × 1 0 - 6 $$ \mathrm{RPC}=220\times 1{0}^{-6} $$ mm 2 $$ {}^2 $$ /s for M1-optimized-msEPI). In phantom and healthy volunteer studies, motion-robust acquisitions with msEPI showed significantly reduced image distortion ( p < 0 . 001 $$ p<0.001 $$ ) compared to ssEPI. Patient scans showed reduction of wormhole artifacts when combining M1-optimized waveforms with msEPI.

CONCLUSION

Synergistic effects of combined M1-optimized diffusion waveforms and msEPI acquisitions enable reproducible liver DWI with motion robustness, blood signal suppression, and reduced distortion.

Synthesis and characterisation of a cancerous liver for presurgical planning and training applications

OBJECTIVES

Oncology surgeons use animals and cadavers in training because of a lack of alternatives. The aim of this work was to develop a design methodology to create synthetic liver models familiar to surgeons, and to help plan, teach and rehearse patient-specific cancerous liver resection surgery.

DESIGN

Synthetic gels were selected and processed to recreate accurate anthropomorphic qualities. Organic and synthetic materials were mechanically tested with the same equipment and standards to determine physical properties like hardness, elastic modulus and viscoelasticity. Collected data were compared with published data on the human liver. Patient-specific CT data were segmented and reconstructed and additive manufactured models were made of the liver vasculature, parenchyma and lesion. Using toolmaking and dissolvable scaffolds, models were transformed into tactile duplicates that could mimic liver tissue behaviour.

RESULTS

Porcine liver tissue hardness was found to be 23 H00 (±0.1) and synthetic liver was 10 H00 (±2.3), while human parenchyma was reported as 15.06 H00 (±2.64). Average elastic Young's modulus of human liver was reported as 0.012 MPa, and synthetic liver was 0.012 MPa, but warmed porcine parenchyma was 0.28 MPa. The final liver model demonstrated a time-dependant viscoelastic response to cyclic loading.

CONCLUSION

Synthetic liver was better than porcine liver at recreating the mechanical properties of living human liver. Warmed porcine liver was more brittle, less extensible and stiffer than both human and synthetic tissues. Qualitative surgical assessment of the model by a consultant liver surgeon showed vasculature was explorable and that bimanual palpation, organ delivery, transposition and organ slumping were analogous to human liver behaviour.

3D Printing of Physical Organ Models: Recent Developments and Challenges

Physical organ models are the objects that replicate the patient-specific anatomy and have played important roles in modern medical diagnosis and disease treatment. 3D printing, as a powerful multi-function manufacturing technology, breaks the limitations of traditional methods and provides a great potential for manufacturing organ models. However, the clinical application of organ model is still in small scale, facing the challenges including high cost, poor mimicking performance and insufficient accuracy. In this review, the mainstream 3D printing technologies are introduced, and the existing manufacturing methods are divided into "directly printing" and "indirectly printing", with an emphasis on choosing suitable techniques and materials. This review also summarizes the ideas to address these challenges and focuses on three points: 1) what are the characteristics and requirements of organ models in different application scenarios, 2) how to choose the suitable 3D printing methods and materials according to different application categories, and 3) how to reduce the cost of organ models and make the process simple and convenient. Moreover, the state-of-the-art in organ models are summarized and the contribution of 3D printed organ models to various surgical procedures is highlighted. Finally, current limitations, evaluation criteria and future perspectives for this emerging area are discussed.

Dynamic Hepatocellular Carcinoma Model Within a Liver Phantom for Multimodality Imaging

Introduction

Hepatocellular carcinoma (HCC) is one of the most common cancer in the world, and the effectiveness of its treatment lies in its detection in its early stages. The aim of this study is to mimic HCC dynamically through a liver phantom and apply it in multimodality medical imaging techniques including magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound.

Methods and materials

The phantom is fabricated with two main parts, liver parenchyma and HCC inserts. The liver parenchyma was fabricated by adding 2.5 wt% of agarose powder combined with 2.6 wt% of wax powder while the basic material for the HCC samples was made from polyurethane solution combined with 5 wt% glycerol. Three HCC samples were inserted into the parenchyma by using three cylinders implanted inside the liver parenchyma. An automatic injector is attached to the input side of the cylinders and a suction device connected to the output side of the cylinders. After the phantom was prepared, the contrast materials were injected into the phantom and imaged using MRI, CT, and ultrasound.

Results

Both HCC samples and liver parenchyma were clearly distinguished using the three imaging modalities: MRI, CT, and ultrasound. Doppler ultrasound was also applied through the HCC samples and the flow pattern was observed through the samples.

Conclusion

A multimodal dynamic liver phantom, with HCC tumor models have been fabricated. This phantom helps to improve and develop different methods for detecting HCC in its early stages.

Chemical Characteristics, Motivation and Strategies in choice of Materials used as Liver Phantom: A Literature Review

Liver phantoms have been developed as an alternative to human tissue and have been used for different purposes. In this article, the items used for liver phantoms fabrication are mentioned same as in the previous literature reviews. Summary and characteristics of these materials are presented. The main factors that need to be available in the materials used for fabrication in computed tomography, ultrasound, magnetic resonance imaging, and nuclear medicine were analyzed. Finally, the discussion focuses on some purposes and aims of the liver phantom fabrication for use in several areas such as training, diagnoses of different diseases, and treatment planning for therapeutic strategies – for example, in selective internal radiation therapy, stereotactic body radiation therapy, laser-induced thermotherapy, radiofrequency ablation, and microwave coagulation therapy. It was found that different liver substitutes can be developed to fulfill the different requirements.

A Multimodal Pancreas Phantom for Computer-Assisted Surgery Training

Training of surgical residents and the establishment of innovative surgical techniques require training phantoms that realistically mimic human anatomy. Because animal models have their limitations due to ethical aspects, costs, and the required efforts to set up such training, artificial phantoms are a promising alternative. In the field of image-guided surgery, the challenge lies in developing phantoms that are accurate both anatomically and in terms of imaging properties, while taking the cost factor into account. With respect to the pancreas, animal models are less suitable because their anatomy differs significantly from human anatomy and tissue properties rapidly degrade in the case of ex vivo models. Nevertheless, progress with artificial phantoms has been sparse, although the need for innovative, minimally invasive therapies that require adequate training is steadily increasing. Methods: In the course of this project, an artificial pancreas phantom that is compatible with basic electrosurgical techniques was developed with realistic anatomic and haptic properties, computed tomography, and ultrasound imaging capabilities. This article contains step-by-step instructions for the fabrication of a low-cost pancreatic phantom. The molds are also available for download in a 3D file format. Results: The phantom was successfully validated with regard to its computed tomography and ultrasound properties. As a result, the phantom could be used in combination with a state-of-the-art computer-assisted navigation system. The resection capabilities were positively evaluated in a preclinical study evaluating endoscopic resections using the navigation system. Finally, the durability of the phantom material was tested in a study with multiple needle insertions. Conclusion: The developed phantom represents an open-access and low-cost durable alternative to conventional animal models in the continuous process of surgical training and development of new techniques.

Designing and validating a PVA liver phantom with respiratory motion for needle-based interventions

Purpose

The purpose is to design and validate an anthropomorphic polyvinyl alcohol (PVA) liver phantom with respiratory motion to simulate needle-based interventions. Such a system can, for example, be used as a validation tool for novel needles.

Methods

Image segmentations of CT scans of four patients during inspiration and expiration were used to measure liver and rib displacement. An anthropomorphic liver mold based on a CT scan was 3D printed and filled with 5% w/w PVA-to-water, undergoing two freeze–thaw cycles, in addition to a 3D-printed compliant rib cage. They were both held in place by a PVA abdominal phantom. A sinusoidal motion vector, based on the measured liver displacement, was applied to the liver phantom by means of a motion stage. Liver, rib cage and needle deflection were tracked by placing electromagnetic sensors on the phantom. Liver and rib cage phantom motion was validated by comparison with the CT images of the patients, whereas needle deflection was compared with the literature.

Results

CT analysis showed that from the state of expiration to inspiration, the livers moved predominantly toward the right (mean: 2 mm, range: − 11 to 11 mm), anterior (mean: 15 mm, range: 9–21 mm) and caudal (mean: 16 mm, range: 6–24 mm) direction. The mechatronic design of the liver phantom gives the freedom to set direction and amplitude of the motion and was able to mimic the direction of liver motion of one patient. Needle deflection inside the phantom increased from 1.6 to 3.8 mm from the initial expiration state to inspiration.

Conclusions

The developed liver phantom allows for applying different motion patterns and shapes/sizes and thus allows for patient-specific simulation of needle-based interventions. Moreover, it is able to mimic appropriate respiratory motion and needle deflection as observed in patients.

Electronic supplementary material

The online version of this article (10.1007/s11548-019-02029-6) contains supplementary material, which is available to authorized users.