Medical Phantom Research Articles

Simulating Tissues with 3D-Printed and Castable Materials.

Manufacturing technologies continue to be developed and utilized in medical prototyping, simulations, and imaging phantom production. For radiologic image-guided simulation and instruction, models should ideally have similar imaging characteristics and physical properties to the tissues they replicate. Due to the proliferation of different printing technologies and materials, there is a diverse and broad range of approaches and materials to consider before embarking on a project. Although many printed materials' biomechanical parameters have been reported, no manufacturer includes medical imaging properties that are essential for realistic phantom production. We hypothesize that there are now ample materials available to create high-fidelity imaging anthropomorphic phantoms using 3D printing and casting of common commercially available materials. A material database of radiological, physical, manufacturing, and economic properties for 29 castable and 68 printable materials was generated from samples fabricated by the authors or obtained from the manufacturer and scanned with CT at multiple tube voltages. This is the largest study assessing multiple different parameters associated with 3D printing to date. These data are being made freely available on GitHub, thus affording medical simulation experts access to a database of relevant imaging characteristics of common printable and castable materials. Full data available at: https://github.com/nmcross/Material-Imaging-Characteristics .

Additively Manufactured Patient-Specific Anthropomorphic Thorax Phantom With Realistic Radiation Attenuation Properties.

Conventional medical imaging phantoms are limited by simplified geometry and radiographic skeletal homogeneity, which confines their usability for image quality assessment and radiation dosimetry. These challenges can be addressed by additive manufacturing technology, colloquially called 3D printing, which provides accurate anatomical replication and flexibility in material manipulation. In this study, we used Computed Tomography (CT)-based modified PolyJetTM 3D printing technology to print a hollow thorax phantom simulating skeletal morphology of the patient. To achieve realistic heterogenous skeletal radiation attenuation, we developed a novel radiopaque amalgamate constituting of epoxy, polypropylene and bone meal powder in twelve different ratios. We performed CT analysis for quantification of material radiodensity (in Hounsfield Units, HU) and for identification of specific compositions corresponding to the various skeletal structures in the thorax. We filled the skeletal structures with their respective radiopaque amalgamates. The phantom and isolated 3D printed rib specimens were rescanned by CT for reproducibility tests regarding verification of radiodensity and geometry. Our results showed that structural densities in the range of 42–705HU could be achieved. The radiodensity of the reconstructed phantom was comparable to the three skeletal structures investigated in a real patient thorax CT: ribs, ventral vertebral body and dorsal vertebral body. Reproducibility tests based on physical dimensional comparison between the patient and phantom CT-based segmentation displayed 97% of overlap in the range of 0.00–4.57 mm embracing the anatomical accuracy. Thus, the additively manufactured anthropomorphic thorax phantom opens new vistas for imaging- and radiation-based patient care in precision medicine.

Measurement of mass attenuation coefficient of polyvinyl alcohol (PVAL) as breast tissue equivalent material in the photon energy range of 16.61–25.26 keV

Medical physics phantom is commonly designed to mimic physical properties of human tissue. Phantom is widely used to provide quantitative and qualitative information upon its interaction with ionizing radiation in medical imaging, radiation dosimetry and treatment planning procedures. This study was carried out to fabricate a potential medical physics phantom material for mammography using polyvinyl alcohol (PVAL). The mass attenuation coefficients (μ/ρ ) of the PVAL gel samples were calculated based on the measurement of attenuation coefficient studies with low photon energy. The gel samples were prepared at 4 concentrations (5, 10, 15 and 20 %) of PVAL solution. Single photon beam transmission in the energy range between 16.61 and 25.26 keV was used to determine the μ/ρ of the PVAL gel. The low photon energy was chosen as the effective energy used in mammography is in a range between 17.5 to 22.6 keV. This was achieved by using the X-ray fluorescent (XRF) configuration. The experimental μ/ρ were compared with theoretical values of water and breast tissue calculated by using the XCOM computer program. The measured value of μ/ρ of the PVAL gels agreed with the XCOM values of water and breast tissue. The 5% and 10% PVAL gel samples were the closest to water while the 20% PVAL was the closest to breast tissue.

Development of a Medical Phantom to Evaluate the Function of Low Dose 3D MDCT

Background/Objectives: Low dose radiation-based CT imaging is a technology that dramatically improves the information on borders between similar substances but with difference in density. The findings will serve as basic data in developing a CT phantom dedicated for X-ray phase differential imaging.Method/Statistical Analysis: To evaluate the benefits of a phantom for low dose 3D MDCT, SOMATOM Definition AS? (Siemens, Germany) CT scanner that produces 128 slices of images with one rotation was used. The auto-exposure condition (AEC) was applied as it is frequently used in clinical settings for high dose CT. After the image was acquired, a qualitative analysis was conducted to verify the practical use in a clinical setting.Findings: In order to evaluate the images acquired from the in-house produced medical phantom and the resolution in the image space, the phantom must be made of substances that have a similar actual atomic number as water. It is practical to produce the phantom for 3D CT by mixing a pure liquid and powder. The absorption, dispersion and phase differential images acquired through the low dose X-ray device were analyzed on a 5 point Likert scale. The absorption image scored 4.3 points for liquid form and 3.50 points for powder form. Both the dispersion image and the phase differential image scored 3.00 points for the liquid form and 4.50 points for the powder form, indicating that the liquid form produces better quality images in the absorption image, while the powder form produces better images in dispersion or phase differential images. The differences were statistically significant (p<0.05).Improvements/Applications: The findings show that for dispersion and phase differential images, compared to the absorption images, substances in powder form rather than liquid form are conducive to better images. These findings are expected to be of use in the field of medical imaging to produce images with high diagnostic value using low dose radiation.

Artificial beating blood vessel model for medical phantom

In this paper, an artificial beating blood vessel model was constructed in order to reproduce the cardiovascular system with beating and to be embedded it in a medical phantom. The torque generated by the motor is proportional to the driving current, so the current was controlled to generate artificial beating blood flow. The constructed vascular model exhibited a first-order lag system in pulse pressure response corresponding to a step-like input current. Based on this result, a drive waveform that combined with function waveforms was created by a function generator, and the motor was driven through a current driver to generate blood flow due to artificial beating. The pulse response was obtained as a pressure change that occurs according to the flow of blood flow due to the generated artificial beating. The completed artificial beating vascular model showed the characteristics of the first-order lag system with the time constant 1.3s.

Artificial pulsatile blood vessel model for medical phantom

Artificial pulsatile blood vessel model for medical phantom

Construction of an Affordable Lumbar Neuraxial Block Model Using 3D Printed Materials.

Access to affordable 3D printing technology has resulted in increased interest in the creation of medical phantom task trainers. Recent research has validated the use of these trainers in simulation education. However, task trainers remain expensive, limiting their availability to medical training programs. We describe the construction of a low-cost task trainer using fused filament fabrication (FFF) printed spinal vertebrae placed in a synthetic gelatin matrix. Additionally, our model contains a realistic simulated ligamentum flavum, a removable silicone skin, as well as spinal fluid reservoir that provides a positive endpoint for intrathecal blocks. The total cost of this model was less than $400 USD. The time to 3D print the bony anatomic parts was approximately 26 hours. While we have not formally validated our model, initial impressions of tactile feel and realism were deemed positive by experienced anesthesia providers. Future work will focus on continued refinement of the model features and construction.

Evaluation of Usability on Mobile Detector X-ray Absorption, Scattering, and Phased Image Phantom

Existing X-ray medical imaging acquired the image data of X-ray absorption difference using the differencein density of the subject tissue. X-ray scattering and phase contrast imaging technology is a technologythat dramatically increases boundary information between homogeneous materials of similar density usingscattering and phase contrast information. To acquire and evaluate absorption, scattering, and phase contrastimages, using the phantom made of polyethylene, on a round rod with a diameter of 3?1cm, a hole with adiameter of 0.5cm was drilled on 5 round rods, and the medical phantom was produced by sealing withsodium chloride, neon, calcium, phosphorus, and selenium powder. At a distance of 40cm from the focus,the distribution of absorbed doses have shown 1,277 ± 0.31?Gy in the center area. The measurement dosein the anode side direction was 110.1 ± 0.35?Gy and the cathode side direction was 117.7 ± 0.77?Gy. It hasshown dose inequality that depends on the geometry of the target. It has shown similar tendency in 60cm and80cm Compared with absorption images in graphite materials, it was confirmed that scattering and phasecontrast images were showing relatively high image information. These results are expected to be utilizedas an important basic data for reducing medical exposure dose and acquiring, evaluating and utilizing X-rayabsorption, scattering and phase contrast images.

X-ray cone-beam computed tomography geometric artefact reduction based on a data-driven strategy.

Cone-beam computed tomography (CBCT) enables three-dimensional imaging of the internal structure of objects in a non-invasive way with high accuracy. Practical misalignment of the CBCT system causes geometric artefacts in reconstructed images, which seriously degrades image quality in ways such as detail loss and decreased spatial resolution. This leads to inaccurate distinction of defects in detection, especially in precise industrial fields like aerospace and instrument manufacturing. This paper presents a method to reduce the geometric artefacts based on a data-driven strategy, which is an end-to-end modified fully convolutional neural network (M-FCNN). The designed M-FCCN contains five convolution layers and five deconvolution layers for feature extraction and output image rebuilding, respectively. In addition, the pooling layer is not used in the designed M-FCNN, considering the preservation of details in the reconstructed image. In this M-FCCN, artefact images with different features have been trained separately. After training, the M-FCNN can be applied to directly reduce geometric artefacts in the reconstructed image. The designed M-FCNN has been demonstrated with different types of synthetic data and has achieved accurate results. It is also validated with practical data, including carbon composite and medical oral phantoms with comparable quality to phantom-based methods, proving that it is an effective way to reduce geometric artefacts in the image domain by means of a data-driven strategy.

Development and Characterization of Medical Phantoms for Ultrasound Imaging Based on Customizable and Mouldable Polyvinyl Alcohol Cryogel–Based Materials and 3-D Printing: Application to High-Frequency Cranial Ultrasonography in Infants

This work presents an affordable and easily customizable methodology for phantom manufacturing, which can be used to mimic different anatomic organs and structures. This methodology is based on the use of polyvinyl alcohol–based cryogels as a physical substitute for biologic soft tissues and of 3-D printed polymers for hard tissues, moulding and supporting elements. Thin and durable soft-tissue mimicking layers and multilayer arrangements can be obtained using these materials. Special attention was paid to the acoustic properties (sound speed, attenuation coefficient and mechanical impedance) of the materials developed to simulate soft tissues. These properties were characterized as a function of the additives concentration (propylene-glycol and alumina particles). The polyvinyl alcohol formulation proposed in this work is stable over several freeze-thaw cycles, allowing the manufacturing of multilayer materials with controlled properties. The manufacturing methodology presented was applied to the development of a phantom for high-frequency cranial ultrasonography in infants. This phantom was able to reproduce the main characteristics of the ultrasound images obtained in neonates through the anterior fontanel, down to 8-mm depth.

Evaluation of Usability on Mobile Detector X-ray Absorption, scattering, and Phased Image Phantom

Existing X-ray medical imaging acquired the image data of X-ray absorption difference using the difference in density of the subject tissue. X-ray scattering and phase contrast imaging technology is a technology that dramatically increases boundary information between homogeneous materials of similar density using scattering and phase contrast information. To acquire and evaluate absorption, scattering, and phase contrast images, using the phantom made of polyethylene, on a round rod with a diameter of 3×1cm, a hole with a diameter of 0.5cm was drilled on 5 round rods, and the medical phantom was produced by sealing with sodium chloride, neon, calcium, phosphorus, and selenium powder. At a distance of 40cm from the focus, the distribution of absorbed doses have shown 1, 277 ± 0.31μGy in the center area. The measurement dose in the anode side direction was 110.1 ± 0.35μGy and the cathode side direction was 117.7 ± 0.77μGy. It has shown dose inequality that depends on the geometry of the target. It has shown similar tendency in 60cm and 80cm Compared with absorption images in graphite materials, it was confirmed that scattering and phase contrast images were showing relatively high image information. These results are expected to be utilized as an important basic data for reducing medical exposure dose and acquiring, evaluating and utilizing X-ray absorption, scattering and phase contrast images.

Numerical simulation of aberrated medical ultrasound signals

Abstract Transcranial ultrasound examination is hampered by the skull which acts as an irregular aberrator of the ultrasound signal. Numerical recovery of the ultrasound field can help in elimination of aberrations induced by the skull. In this paper, we address the simulation of medical phantom scanning through silicon aberrators with wave notching. The numerical model is based on the 2D acoustic equations which are solved by the wavefront construction raytracing method. Numerical B-scan images are compared with experimental B-scan images.

An efficient statistical approach to design 3D-printed metamaterials for mimicking mechanical properties of soft biological tissues

Using 3D printed, patient-specific medical phantoms has become increasingly popular for use in biomedical applications including medical device testing, medical education, and surgical planning, etc. To overcome the inherent differences in mechanical properties between biological tissues and printable polymers, metamaterials are being introduced to mimic the mechanical response of the biological tissues. However, the existing trial-and-error approaches for finding the geometric parameters of the metamaterial result in time-consuming trials, which cannot meet the urgent needs for medical applications. We addressed this issue by proposing an optimization-based statistical approach with an easy-to-evaluate surrogate model to guide the design process and reduce the design time. In this paper, several validation tests were reported, including a biomedical application of mimicking the mechanical response of human articular cartilage. The proposed approach achieves excellent accuracy both visually and quantitatively. In addition, we provide an analysis of mimicking different stress-strain curves using different metamaterials. This data-driven approach demonstrates efficacy and flexibility in building the surrogate model even when no obvious physical trends can be extracted. With the proposed statistical approach, we can efficiently design the metamaterial and 3D-print mechanically accurate phantoms for sophisticated engineering applications.

Tissue-equivalence of 3D-printed plastics for medical phantoms in radiology

The paper describes measurement of the linear attenuation coefficients for 59.5 keV, 122.0 keV and 344.5 keV photons and Hounsfield units for 80 kVp and 120 kVp computed tomography imaging of a large set of commercially 3D-printed test samples of different plastic materials aiming to provide a basis for a selection of a suitable and available material for 3D printing of medical phantoms used in radiology, and specifically for imaging in targeted radionuclide therapy. The results were compared to ICRU44 skeletal muscle and adipose tissues. The results also showed large differences between photon attenuation properties of the same type of plastic material printed by different companies on different printers using filaments from different manufacturers. As a result, it is highly recommended to print a medical phantom on the same printer, with the same settings, and with the same filament as the test sample.

Parallel implementation for 3D medical volume fuzzy segmentation

In the past, 2D models were the main models for medical image processing applications, whereas the wide adoption of 3D models has appeared only in recent years. The 2D Fuzzy C-Means (FCM) algorithm has been extensively used for segmenting medical images due to its effectiveness. Various extensions of it were proposed throughout the years. In this work, we propose a modified version of FCM for segmenting 3D medical volumes, which has been rarely implemented for 3D medical image segmentation. We present a parallel implementation of the proposed algorithm using Graphics Processing Unit (GPU). Researchers state that efficiency is one of the main problems of using FCM for medical imaging when dealing with 3D models. Thus, a hybrid parallel implementation of FCM for extracting volume objects from medical files is proposed. The proposed algorithm has been validated using real medical data and simulated phantom data. Segmentation accuracy of predefined datasets and real patient datasets were the key factors for the system validation. The processing times of both the sequential and the parallel implementations are measured to illustrate the efficiency of each implementation. The acquired results conclude that the parallel implementation is 5X faster than the sequential version of the same operation.

Low-cost three-dimensional printed phantom for neuraxial anesthesia training: Development and comparison to a commercial model.

Neuraxial anesthesia (spinal and epidural anesthesia) procedures have significant learning curves and have been traditionally taught at the bed side, exposing patients to the increased risk associated with procedures done by novices. Simulation based medical education allows trainees to repeatedly practice and hone their skills prior to patient interaction. Wide-spread adoption of simulation-based medical education for procedural teaching has been slow due to the expense and limited variety of commercially available phantoms. Free/Libre/open-source (FLOS) software and desktop 3D printing technologies has enabled the fabrication of low-cost, patient-specific medical phantoms. However, few studies have evaluated the performance of these devices compared to commercially available phantoms. This paper describes the fabrication of a low-cost 3D printed neuraxial phantom based on computed tomorography (CT) scan data, and expert validation data comparing this phantom to a commercially available model.MethodsAnonymized CT DICOM data was segmented to create a 3D model of the lumbar spine. The 3D model was modified, placed inside a digitally designed housing unit and fabricated on a desktop 3D printer using polylactic acid (PLA) filament. The model was filled with an echogenic solution of gelatin with psyllium fiber. Twenty-two staff anesthesiologists performed a spinal and epidural on the 3D printed simulator and a commercially available Simulab phantom. Participants evaluated the tactile and ultrasound imaging fidelity of both phantoms via Likert-scale questionnaire.ResultsThe 3D printed neuraxial phantom cost $13 to print and required 25 hours of non-supervised printing and 2 hours of assembly time. The 3D printed phantom was found to be less realistic to surface palpation than the Simulab phantom due to fragility of the silicone but had significantly better fidelity for loss of resistance, dural puncture and ultrasound imaging than the Simulab phantom.ConclusionLow-cost neuraxial phantoms with fidelity comparable to commercial models can be produced using CT data and low-cost infrastructure consisting of FLOS software and desktop 3D printers.

Measurement of Percentage Depth Dose and Half Value Layer of the Rhizophora spp. Particleboard Bonded by Eremurus spp. to 60, 80 and 100 kVp Diagnostic X-rays

Some researchers formerly provided the mechanical, physical, and attenuation properties of the fabricated Eremurus–Rhizophora spp. particleboard phantom. In this study, the percentage depth dose (PDD) and the half value layer (HVL) of fabricated Eremurus–Rhizophora spp. particleboard phantom were determined and compared with those of Perspex and water phantoms, with the same standard phantom size (30 cm × 30 cm × 30 cm) in the diagnostic energy range using TLD 100H. In addition, the energy range of X-ray was in diagnostic range of energy. The results indicated that the PDD and HVL of the fabricated Eremurus–Rhizophora spp. particleboard phantom were close to those of the Perspex phantom. Likewise, the PDD and HVL of the fabricated Eremurus–Rhizophora spp. particleboard phantom were found in good agreement with those of water phantom. According to the results of this study, the fabricated Eremurus–Rhizophora spp. particleboard phantom can be used as medical phantoms.

Analysis and Validation of medical Application through Electrical Impedance based System

This paper discussed the Design and implementation of the electrical impedance-based system, which covers both techniques (Impedance Plethysmography (IPG) and Electrical Impedance Tomography (EIT)). The electrical impedance distribution image of the cross section of a phantom based on current excitation and voltage measurement using electrodes pair is reconstructs image according to the electrical property of the medical phantom. The electrical impedance based image provides the significant morphological information. Image quality depends upon many other iterative process and image processing algorithms in addition to. The hardware designing of the system is a most important part for all impedance-based techniques. In measurement section, the current source of the electrical impedance-based system should supply multi-frequency signal for measurement because it provides more useful information about the phantom. Therefore, a signal source that provides accurate excitation and a reference signal for measurement are more useful. Matlab is used for image reconstruction and processing of the impedance data.

First approach to ionizing radiation based 3D printing: fabrication of free standing dose gels using high energy gamma photons

3D printing technique is used for the fabrication of differently shaped objects for industrial, research, medical and societal applications. The technique explores scanning laser beam which interacts with a printing material according to the printing algorithm thus fabricating the required 3D object. In medical field 3D printing is successfully used for fabrication of anatomic bone structures, the first attempts are made to print out artificial skin however there are some limits due to the non-equivalency of printing materials to soft tissue. 3D printing concept might have a big potential in radiotherapy for fabrication of tumor imitators – phantoms for quality control of individual patient treatment.Well known radiation induced polymerization of near tissue equivalent dose gels that are used for dose assessment in radiotherapy is a key issue for the development of the ionizing radiation based 3D printing. However it is to point out, that according to irradiation scenario differently shaped polymerized gel parts usually are being produced inside the gel matrix and cannot be removed from the gel.The aim of this work was to develop high energy photon irradiation based 3D printing method for fabrication of nearly tissue equivalent free-standing 3D dose gel shapes. The first approach for method’s application was fabrication of tumor imitators for brachytherapy treatment.Free standing dose gel shapes that are produced using radiotherapy equipment might serve as medical phantoms (tumour imitators) having the size and shape of a real irradiated volume with dose distribution assessment option within this volume. Concept of this method was firstly proposed in our previous publication (Adlienė et al., 2015).Special dose gels were used as “3D printing material” for the processing of free standing dose gel shapes. Varying dose gel content and adjusting high energy photon irradiation parameters with a pre-planned cancer patient treatment procedure, 3D polymerized gel shapes as the separate free-standing objects were fabricated (3D printing). Comparison of the size and shape of produced 3D objects with the irradiation volumes pre-planned by using standard treatment dose planning system of radiotherapy was performed and the obtained results were analyzed and discussed.

Development and characterization of a synthetic PVC/DEHP myocardial tissue analogue material for CT imaging applications

A simple myocardial analogue material has great potential to help researchers in the creation of medical CT Imaging phantoms. This work aims to outline a Bis(2-ethylhexyl) phthalate (DEHP) plasticizer/PVC material to achieve this. DEHP-PVC was manufactured in three ratios, 75, 80, and 85% DEHP by heating at 110 °C for 10 min to promote DEHP-PVC binding followed by heating at 150 °C to melt the blend. The material was then tested utilizing FTIR, tensile testing, dynamic mechanical analysis and imaged with computed tomography. The FTIR testing finds the presence of C-CL and carbonyl bonds that demonstrate the binding required in this plasticized material. The tensile testing finds a modulus of 180–20 kPa that increases with the proportion of plasticizer. The dynamic mechanical analysis finds a linear increase in viscoelastic properties with a storage/loss modulus of 6/.5–120/18 kPa. Finally, the CT number of the material increases with higher PVC content from 55 to 144HU. The 80% DEHP-PVC ratio meets the mechanical and CT properties necessary to function as a myocardial tissue analogue.