Self-made Phantom Research Articles

Investigation of the Influence of Image Reconstruction Parameters to Improve the Ability to Depict Internal Tumor Necrosis

There are attempts to assess tumor heterogeneity by texture analysis. However, the ordered subsets-expectation maximization (OSEM) reconstruction method has problems depicting heterogeneities. The aim of this study was to identify image reconstruction parameters that improve the ability to depict internal tumor necrosis using a self-made phantom that simulates internal necrosis. Self-made phantoms were prepared using polypropylene cylinders with inner diameters of 18.0 mm and 6.0 mm. The concentration ratios of the simulated tumor : tumor interior were 4 : 0 and 4 : 1. For each reconstruction method, the iteration for OSEM and OSEM+point spread function (PSF) were 1 to 25 and the subset was 12. The β values for block sequential regularized expectation maximization (BSREM) were set between 10 and 400. We evaluated the features of the profile curve, contrast-to-noise ratio, and grey-level co-occurrence matrix (GLCM). In the phantom study, OSEM and OSEM+PSF showed a better delineation of the differences between the inside and outside of the cylinder as iteration was increased and BSREM showed a better delineation as β was decreased. The highest value for each feature, both 4 : 0 and 4 : 1, was BSREM β 10 for angular second moment (ASM) and inverse differential moment (IDM), OSEM iteration 25 for contrast and entropy. We have identified image reconstruction parameters that improve the ability to visualize internal tumor necrosis. The parameter was BRSEM β 10.

Diagnosis of Osteoporosis by Quantifying Volumetric Bone Mineral Density of Lumbar Vertebrae Using Abdominal CT Images and Two-Compartment Model

With the aging population, osteoporosis has become an important public health issue. The purpose of this study was to establish a two-compartment model (TCM) to quantify the volumetric bone mineral density (vBMD) of the lumbar spine using abdominal computed tomography (CT) images. The TCM approach uses water as the bone marrow equivalent and K2HPO4 solution as the cortical bone equivalent. A phantom study was performed to evaluate the accuracy of vBMD estimation at 100 kVp and 120 kVp. The data of 180 patients who underwent abdominal CT imaging and dual-energy X-ray absorptiometry (DXA) within one month were retrospectively collected. vBMD of L1-L4 vertebrae were calculated, and the receiver-operating characteristic curve analysis was performed to establish the diagnostic thresholds for osteoporosis and osteopenia in terms of vBMD. The average difference between the measured vBMD following TCM and the theoretical vBMD of the self-made phantom was 0.2%, and the maximum difference was 0.5%. vBMD of lumbar vertebrae obtained from TCM and aBMD obtained by DXA had a significant positive correlation (r = 0.655 to 0.723). The average diagnostic threshold for osteoporosis was 0.116 g/cm3. The sensitivity, specificity, and accuracy were 95.7%, 75.6.5%, and 80.0%, respectively. The average diagnostic threshold for osteopenia was 0.126 g/cm3. The sensitivity, specificity, and accuracy were 81.3%, 82.5%, and 82.7%, respectively. The aforementioned threshold values were used to perform the diagnostics on a test cohort, and the performance was equivalent to that in the experimental cohort. From the perspective of preventive medicine, opportunistic screening of bone mineral density using abdominal CT images and the TCM approach can facilitate early detection of osteoporosis and osteopenia and, with in-time treatment, slow down their progression.

Internal Electric Field Reconstruction and SAR Estimation of In-Body Antenna Using Inverse Equivalent Current Method

In this article, we reconstruct the internal electric field due to a dipole antenna embedded in a dielectric phantom for developing a noninvasive specific absorption rate (SAR) measurement system. The reconstruction method is based on the surface equivalent theorem and boundary conditions, which relate the external field radiated from the embedded antenna to equivalent electromagnetic surface currents on the human body. The electric field data sampled at spatial points on a surface enclosing the phantom are used in the inverse calculation. All field integrals are discretized and numerically solved to obtain the electromagnetic currents on the phantom's surface. The internal electric field distribution and SAR value in a phantom can be calculated from the reconstructed surface currents if the electric properties of the phantom are known. The validity of the method was demonstrated numerically and experimentally using a dipole antenna embedded in the lossy rectangular phantom, which has a dielectric constant close to human skin tissue at 2.5 GHz. Comparison with forward numerical simulations has shown that the surface current and electric field distribution can be predicted with great precision. Carefully performing the experiments using a self-made phantom validated our numerical demonstration and provided satisfactory reconstruction results.

Evaluation of vertebral bone strength with a finite element method using low dose computed tomography imaging

BackgroundFocusing on compression fractures of bone by finite elements, we evaluated bone strength based on the computed tomography-based finite element method. However, the exposure dose is an issue. We aimed to investigate the quantity of reduction of the radiation dose with respect to the reference dose by comparing the calculation results of compression fractures of the vertebral body using experimental data obtained from the spine of a pig. MethodsComputed tomography images of a self-made phantom that enclosed the lower lumbar vertebra of edible wild pigs were obtained under baseline-dose conditions using various lower tube currents. Images obtained under reference-dose conditions were reconstructed using the filtered back-projection method, whereas images obtained under low-dose conditions were reconstructed using both the filtered back-projection method and the iterative reconstruction method. Computer simulations involving the creation of finite element models using all images were implemented for the compression load calculation for vertebral body parts. Based on the calculated results, images of the low-dose and reference-dose conditions were compared. ResultsUsing pigs’ lower lumbar vertebrae, finite element model analysis of low-dose X-ray computed tomography images showed that equivalent results can be obtained with a dose of approximately 40% of the standard radiographic reference doses. As for the compression stress intensity, the same results as those under reference-dose conditions were obtained using the iterative reconstruction method in combination with computed tomography-based finite element method. ConclusionsThe combination of the iterative reconstruction method with the computed tomography-based finite element method is an effective image reconstruction method for achieving dose reduction.

Evaluation of Fat Suppression Effect and SNR Using Pixel Shift Method of Fat Suppression Images with CHESS and IDEAL in Head and Neck MR Imaging

This study aims to evaluate the fat suppression effect on images of the head and neck region using chemical shift selective (CHESS), and iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). A self-made phantom containing oil around the simulated bone marrow and muscle was scanned. The signal-to-noise ratio (SNR) was calculated using the National Electrical Manufacturers Association (NEMA) subtraction and pixel shift methods. Thereafter, the fat suppression effect and SNR were calculated in clinical images using the pixel shift method. In both phantom and clinical images, the fat suppression effect was higher using IDEAL. In addition, the SNR of the NEMA subtraction method and the pixel shift method in phantom images was higher in the simulated bone marrow than in the simulated muscle. The SNR of the vertebral body was higher than that of the tongue in the clinical images using IDEAL, and the same tendency was observed in the phantom image evaluation. However, there was a difference in SNR between the phantom and clinical images. In the head and neck region, fat-suppressed images using IDEAL showed the same higher fat-suppressing effect as that in a previous study. The SNR for the phantom and the clinical images was different. The SNR calculated using the pixel shift method for the phantom images with IDEAL and the clinical images showed the same tendency. Although there is a difference between the SNRs of phantom and clinical images calculated by the pixel shift method, it is suggested that the method can be used to compare the SNR between tissues such as the vertebral body and the tongue.

Effectiveness of a Brief Teaching Scenario in a Phantom-Based Learning Model for Students to Achieve Ultrasound-Guided Vascular Access—a Prospective Study

For students, early hands-on experience is very limited and often non-existent during study time. Thus, we aimed to evaluate the progress of inexperienced medical students in successfully establishing an ultrasound-guided vessel access. One brief, condensed single teaching lesson in a prior to post-teaching scenario was performed using an inexpensive, self-made phantom model. In this prospective study, medical students (n = 11) with no experience in ultrasound imaging performed an ultrasound-guided vessel access simulated by a gelatin-based phantom model. Success rates and time of procedures were measured. Afterwards, participants underwent dedicated supervised teaching in a single lesson (duration 30 min) with both theoretical information given and practical training skills shown. Then, every student performed the very same procedure again and results were compared with paired t test. Success rate of guide wire placement rose from 36.4 (4/11) to 100%. Mean number of attempts significantly decreased with 2.5 SD1.3 before and 1.2 SD0.4 after teaching (p < 0.05). Overall time to successful guide wire placement improved from 291 SD8 to 151 SD37 s (p < 0.05). With already limited training time and opportunities available during medical education, short and simple, but highly effective training tools are invaluable. With the help of an inexpensive, self-made gelatin-based phantom model for ultrasound-guided vascular access, medical students demonstrate significantly improved practical puncture skills after only one brief, condensed teaching lesson and thus an important progress with regard to their future clinical routine. The performance of ultrasound-guided vascular access can be highly improved for inexperienced medical students by applying one short teaching session using an inexpensive, self-made phantom model.

HUMAN MANDIBULAR BONE DENSITY DISTRIBUTION: IMAGE ANALYSIS AND BONE REMODELING SIMULATION

<h3>Background</h3> Bone density distribution affects the short-term and long-term success of dental treatments. Currently, there is no quantitative method to analyze bone density distribution in alveolar bone. <h3>Objective</h3> In this study, the bone density distribution in human mandibles was obtained from quantitative analysis on medical images and was also modeled by using biomechanics simulations. <h3>Materials and Methods</h3> Cone beam computed tomography (CBCT) images from 33 patients were obtained from dental clinics. The CBCT scanner was calibrated by using our self-made phantoms to convert gray-scale to mineral density. The CBCT images of multiple human mandibles were analyzed. Finite element models were used to simulate the effects of normal chewing and bite force on bone density distribution. A strain energy density–based bone remodeling algorithm was used in the simulations. <h3>Results</h3> For the same materials in phantoms, there was no significant difference in gray scale in different locations inside the regions of interest, despite the known drawbacks of CBCT. At the chosen effective energy level, the gray scale in CBCT images had high linearity with attenuation coefficients for all materials in the phantoms. The averaged trend in mandibular bone density distribution was obtained. It was higher near the root of the tooth and lower away from the tooth, especially near the lingual arc of the jaw. The numerical simulation results showed a similar trend in bone density distribution under chewing force. <h3>Discussion</h3> The gray scale in CBCT images from the 1 CBCT scanner used in this study had linearity and spatial consistency inside certain regions of interest. The bone density distribution obtained from image analysis had good agreement with that obtained from bone remodeling simulations based on biomechanics analysis. The results may provide detailed information on dental anatomy and can also build the foundation for future improvements in dental treatments using image-based biomechanics analysis.

Effect of table height displacement and patient center deviation on size-specific dose estimates calculated from computed tomography localizer radiographs.

The aim of this study is to evaluate the effect of table height displacement and patient center deviation along the [Formula: see text]-axis on size-specific dose estimate (SSDE) calculations based on computed tomography (CT) localizer radiographs in pediatric and adult abdominal CT examinations. CT localizer radiographs and CT axial images were acquired with table heights of - 5.0, - 2.5, 0.0 (center), 2.5, and 5.0cm using two acrylic self-made phantoms filled with water. Water-equivalent diameters ([Formula: see text]) were calculated from the CT localizer radiographs and CT axial images. Relative errors of SSDEs from the CT localizer radiographs to SSDEs from the CT axial images were calculated to evaluate the effect of table height displacement. Furthermore, patient center deviations and indices of SSDE overestimation were measured from the clinical data of 110 abdominal CT examinations. The relative errors of SSDEs in phantoms equivalent to 1-year-old and 20-year-old Japanese reference persons ranged from - 2.45% (table height of 50mm) to + 1.88% (- 50mm) and from - 4.22% (50mm) to + 3.79% (- 50mm), respectively. The largest center deviation in all patients ranged from - 43.1 to 21.5mm (median: - 14.4mm). The indices of SSDE overestimation for all patients ranged from - 16.2 to 6.9mm (median: - 2.2mm). We found that the effects of table height displacement and patient center deviation along the [Formula: see text]-axis on SSDEs calculated from CT localizer radiographs in pediatric phantoms were smaller compared to adult phantoms. In order to correct these patient center deviations, it is necessary to apply an appropriate correction technique in each section along the [Formula: see text]-axis.

Reduction of Operator Exposure Radiation Dose and Evaluation of Image Quality Using Half Scan in CT Fluoroscopy

In recent years, the number of examinations and treatments using computed tomography fluoroscopy (CTF) has been increasing, and there is concern about an increase in the exposure radiation dose of the operator. Use of half scan CTF can be expected to reduce the exposure radiation dose, but there is no report. The purpose of this study was to evaluate the exposure radiation dose at the operator's position and image quality when using a half scan CTF. The left side facing the gantry was the operator's position, and the ambient dose equivalent at 160 cm, 130 cm, and 100 cm from the floor was measured using an ionization chamber survey meter. The absorbed dose at the forceps holding position of the operator was measured using a fluorescent glass dosimeter with the forceps holding position 15 cm caudal from the scan center. The imaging conditions used a tube voltage of 120 kV and a tube current of 50 mA. Half scan CTF was performed by changing the center angle of the half scan on the console every 45°. As a result, the set angles were 135°and 90°at the operator's position, and 135°at the operator's forceps holding position. In addition, we evaluated the effect of half scan CTF on image quality. CTF images were collected with a cryogenic needle used for cryotherapy punctured in a water-equivalent self-made phantom. The profile curves of the obtained images were drawn and compared using analysis software to evaluate the effects of artifacts. Then, the SD of the CT value of the region of interest with and without the artifact was measured, and the relative artifact index was calculated and evaluated. Using the same image, CT value and SD were tested to evaluate noise. Half scan CTF had no effect on the image quality due to artifacts and noise.

Low-cost Self-made Phantom Model for Ultrasound-guided Breast Intervention Practice

Low-cost Self-made Phantom Model for Ultrasound-guided Breast Intervention Practice

Accuracy of Biopsy needle in Computed Tomography Guided Biopsy Using a Self-Made Gelatin Phantom

The purpose of this study was to analyze the actual reflection of the biopsy needle when performing computed tomography (CT) guided biopsy in lung cancer. CT used in the experiment was a 128-channel dual source SOMATOM Definition flash. A 21-gauge biopsy needle was inserted into the self-made gelatin phantom at 10 mm intervals from 20 mm to 80 mm on the Y -axis of the CT scanner. At each insertion depth, the CT axial scan was performed with 0.6 mm, 1.0 mm, and 2.0 mm slice thickness. We examined 30 times for each slice thickness for a total of 270 times. These acquired images were used to compare actual and measured insertion lengths. As a result, 40 mm depth was measured as 4.00 ± 0.01 in 1.0 mm slice thickness (p > 0.05) while the remaining slice thickness was considered smaller or larger than the actual value. A 1.0 mm slice thickness was closer to the actual measurement value than the other two slice thicknesses (p < 0.05). Therefore, the accuracy of CT-guided biopsy in lung cancer is increased by positioning the lesion at the isocenter at a slice thickness of 1.0 mm.

Consideration on SNR in Synthetic MRI

Synthetic magnetic resonance imaging (MRI) can create different contrast weighted images by quantifying the T1, T2, and proton density values of the subjects from a single series of scan data. It has not been clarified how the signal to noise ratio (SNR) of the synthesized image varies depending on imaging parameters. We investigated the change of SNR in synthesized MR images by the experiment using self-made phantom. The SNR ratio of synthesized image by synthetic MRI showed the same tendency as the theoretical values due to parameter change in Ny, Nx, slice thickness, number of excitations. However, as for BW, the SNR ratio tended to be different from the theoretical values in some cases. In addition, it was suggested that the SNR of the composite image has relevance to the quantitative accuracy of the T1, T2, and proton density values. We thought that this is due to the image acquisition process by synthetic MRI.

Evaluation of Low-contrast Detectability of Iterative Reconstruction Algorithm in High-speed CT Technology for Head

The purpose of this study was to assess the feasibility of high-speed CT technology for head without deterioration of low-contrast detectability using the brain LCD (Canon Medical Systems) of iterative reconstruction. System performance (SP) function analysis, low-contrast object specific contrast-to-noise ratio (CNRLO) analysis, and visual evaluation using Scheffe's paired comparison were performed. Additionally, analysis of the correlation of CNRLO and visual scores was performed. SP was performed with the self-made phantom. CNRLO was calculated with the catphan 504 phantom (CTP 515). Visual evaluation was performed using the brain phantom which simulated such as cerebral infarction and investigated on a fivepoint scale. All images were acquired with pitch factor of 0.61 (low pitch) and 1.40 (high pitch). All images were reconstructed with filtered back projection (FBP), brain LCD standard (LCD STD) and strong (LCD STR). SP of brain LCD improved compared with FBP. CNRLO of FBP decreased in high pitch compared with low pitch. CNRLO of brain LCD images acquired by low- and high pitch were improved compared with FBP. Visual scores denoted similar trends to that of CNRLO and there was high correlation with CNRLO. It was suggested that using brain LCD can achieve the high speed CT technology for head without deterioration of low-contrast detectability.

P015] Contrast of dual energy CT in carotid artery analysis, a phantom study

Purpose Dual Energy Computed Tomography (DECT) has high tissue characterization properties compared to traditional computed tomography (CT). In CT angiography (CTA), this property is important for analyzing the stage of atherosclerosis. The goal of this project was to study the significance of DECT technology in CTA especially for atherosclerosis diagnosis. Methods A self-made phantom was designed to model the neck area and carotid arteries. Main organs in the neck area were built by using various materials. Agar was used to mimic soft tissue, cattle bone to spine, empty plastic bottle to trachea, oil to lipid, and two small plastic tubes to mimic left and right carotid arteries. A human tooth was placed in the phantom to study the artefacts. The artery tubes contained water and diluted iodine as contrast agent. A 300 mg/ml iodine concentration was diluted to 6 mg/ml to meet the image contrast obtained in arteries of the patients using SECT CTA procedure. The phantom was then scanned with CTA SECT and DECT protocols. Images were analyzed using image processing tool. Results Image resulted from DECT show changes in material contrast compared to SECT. The contrast agent, bone, air and tooth have lower HU when scanned with DECT, while water, oil and agar show increased HU values. Improvement in oil contrast is highly visible on DECT image. The artefact from beam hardening effect caused by tooth and bone was reduced significantly by the DECT technology. Conclusions DECT seems to produce better image quality for studying carotid arteries than SECT. DECT images have higher material contrast and lower artefact from beam hardening effect. Both properties are important in atherosclerosis analysis.

Measurement Accuracy of Fat and Iron Deposits in the Liver Using 1H-MRS (HISTO)

1H-MRS, which is a method of measuring fat and iron deposits in the liver, has a single voxel spectroscopy imaging method called high-speed T2-corrected multiecho (HISTO) based on the STEAM method. If HISTO measurement accuracy is high, it will be one of the biomarkers, so the measurement accuracy was examined. We imaged a self-made phantom simulating a known amount of fat and iron deposition in the liver. A regression analysis of HISTO-measured values for hepatic fat phantom was performed. In addition, regression analysis was performed on the hepatic iron phantom for the R2 values obtained from the T2 values measurement and the actually measured value of the HISTO. From the regression analysis, the correlation coefficients were 0.999, 0.992 and 0.977, respectively. The measurement accuracy of HISTO is high, and the reliability of the obtained fat and iron deposit value is high.

The Effect of Metal Artifact Reduction at Different Rotation Time in Computed Tomography

The purpose of the study was to examine the metal artifact-reducing effects of single energy metal artifact reduction (SEMAR) at different rotation time. Helical and volume scans were employed to photograph a self-made phantom at various rotation time. Metal artifacts were examined using artifact index (AI) values and visual scores. At rotation times of 0.35, 0.4, 0.5, 0.6, 0.75, and 1.0 s/rotation on the helical scans (SEMAR-ON), AI values were 66.6, 64.3, 39.7, 39.7, 40.8, and 15.4, respectively, and visual scores were 3.2, 3.4, 3.0, 3.1, 3.0, and 2.8, respectively. Similar results were obtained on the volume scans. Specifically, the AI values reduced with a decreasing rotation time, although the visual scores did not significantly differ with a rotation time changes. The metal artifact-reducing effects of SEMAR are not altered by the rotation time.

An Acoustic Tracking Approach for Medical Ultrasound Image Simulator

Ultrasound examinations are a standard procedure in the clinical diagnosis of many diseases. However, the efficacy of an ultrasound examination is highly dependent on the skill and experience of the operator, which has prompted proposals for ultrasound simulation systems to facilitate training and education in hospitals and medical schools. The key technology of the medical ultrasound simulation system is the probe tracking method that is used to determine the position and inclination angle of the sham probe, since this information is used to display the ultrasound images in real time. This study investigated a novel acoustic tracking approach for an ultrasound simulation system that exhibits high sensitivity and is cost-effective. Five air-coupled ultrasound elements are arranged as a 1D array in front of a sham probe for transmitting the acoustic signals, and a 5 × 5 2D array of receiving elements is used to receive the acoustic signals from the moving transmitting elements. Since the patterns of the received signals can differ for different positions and angles of the moving probe, the probe can be tracked precisely by the acoustic tracking approach. After the probe position has been determined by the system, the corresponding ultrasound image is immediately displayed on the screen. The system performance was verified by scanning three different subjects as image databases: a simple commercial phantom, a complicated self-made phantom, and a porcine heart. The experimental results indicated that the tracking and angle accuracies of the presented acoustic tracking approach were 0.7 mm and 0.5°, respectively. The performance of the acoustic tracking approach is compared with those of other tracking technologies.

Comprehensive Curriculum for Phantom-Based Training of Ultrasound-Guided Intercostal Nerve and Stellate Ganglion Blocks

Ultrasound (US)-guided pain procedures become increasingly important due to their numerous advantages. Solid proficiency is necessary, however, to minimize complications and guarantee adequate performance. To enable beginners to learn the relevant skills in the technique of US-guided stellate ganglion (SGB) and intercostal nerve block (ICB), a training curriculum was developed and tested using self-made phantoms. The curriculum comprised an introduction to the didactics of US, SGB, and ICB, a demonstration of the techniques by an expert user, as well as hands-on training of needle guidance using a gel pad and two phantoms. Three groups of participants with different levels of expertise with US-guided procedures took part in the curriculum: 12 medical students with no prior experience, 12 anesthesiologists with some experience, and five senior anesthesiologists who already applied these techniques on a regular basis. Participants evaluated the curriculum via questionnaire, and their performance of time until adequate puncture, attempts required for adequate puncture, number of corrections, and unintentional punctures was assessed. The medical students significantly increased their speed during both nerve blocks and reduced the number of attempts and corrections necessary to perform adequate ICB. The anesthesiologists with some experience also increased their speed in both blocks. The participants rated the curriculum as good to very good. The combination of theoretical teaching, expert demonstration, and hands-on training on phantoms proved useful in acquiring skills needed for US-guided procedures such as SGB and ICB, and can potentially improve graduate and post-graduate medical education.

Low cost anatomically realistic renal biopsy phantoms for interventional radiology trainees

This paper describes manufacturing of economically affordable renal biopsy phantoms for radiology residents and practicing radiologists. We reconstructed a realistic 3-dimensional patient-specific kidney model from CT data, manufactured an organ mould and casted the kidney phantoms. Using gelatin gel materials with calibrated parameters allowed making phantoms with realistic mechanical, ultrasound and CT properties including various pathologies. The organ phantoms with cysts included were further casted into gelatin gel medium. They were validated by radiology residents in biopsy training and compared against self-made phantoms traditionally used in the curriculum of interventional radiology. The realism, durability, price and suitability for training were evaluated. The results showed that our phantoms are more realistic and easier to use than the traditional ones. Our proposed technology allows creating a low-cost (50$/kg) alternative to the pricy commercial training phantoms available today.

Qualitätsvergleich digitaler 3D-fähiger Röntgenanlagen bei HNO-Fragestellungen am Schläfenbein und den Nasennebenhöhlen

Comparison of dosage and spatial resolution of digital X-Ray devices with 3D-capability in head and neck imaging. Three on-site X-Ray devices, a general purpose multi-slice CT (CT), a dedicated cone-beam CT (CBCT) and the CT-mode of a device for digital angiography (DSA) of the same generation were compared using paranasal sinus (PNS) and temporal bone imaging protocols. The radiation exposure was measured with a puncture measuring chamber on a CTDI head phantom as well as with chip-strate-dosimeters on an Alderson head phantom in the regions of the eyes and thyroid gland. By using the Alderson head phantom, the specific dosage of the X-Ray device with regard to different protocols was read out. For the assessment of the high-contrast resolution of the devices, images of a self-made phantom were qualitatively analysed by six observers. The three devices showed marked variations in the dosage and spatial resolution depending on the protocol and/or modus. In both parameters, CBCT was superior to CT and DSA using standard protocols, with the difference being less obvious for the investigation with PNS. For high-contrast investigations CBCT CT is a remarkable option in head and neck radiology.