Composite Phantom Research Articles

Morphological characteristics of Olympic sprint canoe and kayak paddlers

Canoe and kayak paddlers (n = 50 M & 20 F) who competed in the sprint events at the 2000 Olympic Games in Sydney were measured on a battery of 38 anthropometry dimensions prior to competition. The ensuing analysis aimed to identify common physical characteristics that provide these elite paddlers with a competitive advantage. This study demonstrated that participants in Olympic sprint paddling events can be considered homogeneous in shape and physical size; male and female paddlers have SAMs of 1.1 and 1.0 respectively. Compared to other athlete groups, the variance in stature and body mass of paddlers is generally low. Whilst sprint paddlers are not athletes with extreme proportionality profiles, they do possess unique characteristics not commonly observed in the general population. These include a lean body composition (Phantom z-scores for skinfolds range from -1.5 to -2.5 for most sites) with proportionally large upper body girths (z-scores > +1.0 for arm and chest girths), and narrow hips (for males). The morphology of elite paddlers appears to have altered during the past 25 years toward a more compact, robust physique. This trend is especially noticeable for the female competitors.

Fast T2-weighted MR imaging: impact of variation in pulse sequence parameters on image quality and artifacts.

The purpose of this study was to quantitatively evaluate in a phantom model the practical impact of alteration of key imaging parameters on image quality and artifacts for the most commonly used fast T(2)-weighted MR sequences. These include fast spin-echo (FSE), single shot fast spin-echo (SSFSE), and spin-echo echo-planar imaging (EPI) pulse sequences. We developed a composite phantom with different T1 and T2 values, which was evaluated while stationary as well as during periodic motion. Experiments involved controlled variations in key parameters including effective TE, TR, echo spacing (ESP), receive bandwidth (BW), echo train length (ETL), and shot number (SN). Quantitative analysis consisted of signal-to-noise ratio (SNR), image nonuniformity, full-width-at-half-maximum (i.e., blurring or geometric distortion) and ghosting ratio. Among the fast T(2)-weighted sequences, EPI was most sensitive to alterations in imaging parameters. Among imaging parameters that we tested, effective TE, ETL, and shot number most prominently affected image quality and artifacts. Short T(2) objects were more sensitive to alterations in imaging parameters in terms of image quality and artifacts. Optimal clinical application of these fast T(2)-weighted imaging pulse sequences requires careful attention to selection of imaging parameters.

Cross-calibration of GE/Lunar pencil and fan-beam dual energy densitometers--bone mineral density and body composition studies.

In vitro and in vivo comparisons of bone mineral density (BMD) and body composition between GE/Lunar pencil (DPXL) and fan-beam (PRODIGY) absorptiometers. Comparison of BMD, bone mineral content (BMC) and area of lumbar spine (L2-L4), femoral neck and total body. Total body composition compartments tissue (TBTissue), fat (TBF), lean tissue (TBLean) and %TBF were also compared. Centre for Bone and Body Composition Research, University of Leeds. PHANTOMS/SUBJECTS: A range of spine phantoms, a variable composition phantom (VCP) and total body phantom. A total of 72 subjects were included for the in vivo study. In vitro: A small significant underestimation of BMD by the Prodigy compared to the DPXL ranging from 0.7 to 2% (p<0.05-0.001) for the spine phantoms. The Prodigy underestimated the VCP %Fat. Although the Prodigy underestimated phantom TBBMD by 1.1+/-1.0%, TBBMC and area were reduced by 8.2+/-1.4 and 7.3+/-1.0%, respectively. The Prodigy overestimated TBTissue 1508 g (2.2%), TBLean 588 g (1.2%), TBF 919 g (4.8%) and %TBF (0.8%). In vivo: BMD cross-calibration was only required in the femoral neck, DPXL(BMD)=0.08+0.906*PRODIGY(BMD). The Prodigy had higher estimates for TBTissue 1360 g (2.3%), TBLean 840 g (2.0%), TBF 519 g (3.4%), TBBMC 32.8 g (1.3%) and %TBF (0.3%). Cross-calibration equations were required for TBTissue(DPXL)=-1158+0.997*TBTissue(PRODIGY) and TBBMC(DPXL)= 89.7+0.949*TBBMC(PRODIGY). Small differences between the two absorptiometers for both BMD and body composition can be made compatible by use of cross-calibration equations and factors. The discrepancy in body composition compartments requires further research.

Comparative study of fast MR imaging: quantitative analysis on image quality and efficiency among various time frames and contrast behaviors

The purpose of this study is to quantitatively compare the image quality and efficiency provided by widely available fast MR imaging pulse sequences. A composite phantom with various T1 and T2 values and subjected to periodic motion was imaged at 1.5 T. The fast MRI sequences evaluated included fast spin-echo (FSE), single shot fast spin-echo (SSFSE), echo-planar imaging (EPI), multi-slice gradient recalled (MPGR), fast MPGR (FMPGR), and fast multi-slice spoiled gradient echo (FMPSPGR). T1-weighted (T1WI), T2-weighted (T2WI), proton-density-weighted (PDWI), and T2∗-weighted (T2∗WI) images were evaluated in breath-hold and non-breath-hold time frames. Analysis included measurement of image signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), nonuniformity, ghosting ratio, SNR per unit time and CNR per unit time. Among fast T2WI sequences, FSE with breath-hold time frame resulted in the highest image quality and in superior SNR and CNR efficiency by a factor of 5 or 6 as compared with conventional spin echo sequence. Among fast T1WI sequences, FMPGR and FMPSPGR both with non-breath-hold time frame produced the highest image quality and SNR and CNR efficiency by a factor of greater than 5 as compared with conventional spin echo. Among fast PDWI and T2∗WI sequences, FSE produced the highest SNR and CNR, and was maximally efficient with a factors of greater than 6 as compared with conventional spin echo.

Contrast-enhanced near-infrared laser mammography with a prototype breast scanner: feasibility study with tissue phantoms and preliminary results of imaging experimental tumors.

Near-infrared (NIR) optical mammography without contrast has a low specificity. The application of optical contrast medium may improve the performance. The concentration-dependent detectability of a new NIR contrast medium was determined with a prototype optical breast scanner. In vivo imaging of experimental tumors was performed. The NIR contrast agent NIR96010 is a newly synthesized, hydrophilic contrast agent for NIR mammography. A concentration-dependent contrast resolution was determined for tissue phantoms consisting of whole milk powder and gelatin. A central part of the phantoms measuring 2 x 2 cm2 without contrast was replaced with phantom material containing 1 micromol/L to 25 nmol/L NIR96010. The composite phantoms were measured with a prototype NIR breast scanner with lasers of lambda1 = 785 nm and lambda2 = 850 nm wavelength. Intensity profiles and standard deviations of the transmission signal in areas with and without contrast were determined by linear fit procedures. Signal-to-noise ratios and spatial resolution as a function of contrast concentration were determined. Near-infrared imaging of five tumor-bearing SCID mice (MX1 breast adenocarcinoma, tumor diameter 5-10 mm) was performed before and after intravenous application of 2 micromol/kg NIR96010. Spectrometry showed an absorption maximum of the contrast agent at 755 nm. No spectral shifts occurred in protein-containing solution. Signal-to-noise ratio in the transmission intensity profiles ranged from 1.1 at 25 nmol/L contrast to 28 at 1 micromol/L. At concentrations <40 nmol/L, no differentiation from the background was possible. The transitional area between the contrast-free edge of the phantom and the central contrast-containing part appeared in the profiles as a steep increase with a width of 4.2 +/- 1.8 mm. The experimental tumors were detectable in nonenhanced images as well as contrast-enhanced images, with better delineation after contrast administration. In postcontrast absorption profiles, a 44.1% +/- 11.3% greater absorption increase was seen in tumor tissue compared with normal tissue. The laser wavelength lambda1 of the prototype laser mammography device was not situated at maximum absorption of the contrast agent NIR96010 but on the descending shoulder of the absorption spectrum. This implies a 20% signal loss for contrast detection. Despite the nonideal measurement conditions, concentrations as low as 40 nmol/L were detectable in vitro. In vivo, all tumors were detectable in color-coded nonenhanced scans as well as in contrast-enhanced scans, with better delineation after contrast administration.

Evaluation of Linear and Nonlinear Tomosynthetic Reconstruction Methods in Digital Mammography

Rationale and Objectives The purpose of this study was to comparatively evaluate digital planar mammography and both linear and nonlinear tomosynthetic reconstruction methods. Materials and Methods A “disk” (ie, target) identification study was conducted to compare planar and reconstruction methods. Projective data using a composite phantom with circular disks were acquired in both planar and tomographic modes by using a full-field, digital mammographic system. Two-dimensional projections were reconstructed with both linear (ie, backprojection) and nonlinear (ie, maximization and minimization) tuned-aperture computed tomographic (TACT) methods to produce three-dimensional data sets. Four board-certified radiologists and one 4th-year radiology resident participated as observers. All images were compared by these observers in terms of the number of disks identified. Results Significant differences ( P < .05, Bonferroni adjusted) were observed between all reconstruction and planar methods. No significant difference, however, was observed between the planar methods, and only a marginally significant difference ( P < .054, Bonferroni adjusted) was observed between TACT-backprojection and TACT-minimization. Conclusion A combination of linear and nonlinear reconstruction schemes may have potential implications in terms of enhancing image visualization to provide radiologists with valuable diagnostic information.

Evaluation of a New Body Composition Phantom for Quality Control and Cross-Calibration of DXA Devices.

Evaluation of a New Body Composition Phantom for Quality Control and Cross-Calibration of DXA Devices.

Comparison of tomosynthesis methods used with digital mammography

The authors performed this study to investigate the potential applicability of tomosynthesis to digital mammography. Four methods of tomosynthesis-tuned aperture computed tomography (TACT)-backprojection, TACT-iterative restoration, iterative reconstruction with expectation maximization, and Bayesian smoothing-were compared to planar mammography and analyzed in terms of their contrast-detail characteristics. Specific comparisons between the tomosynthesis methods were not attempted in this study. A full-field, amorphous, silicon-based, flat-panel digital mammographic system was used to obtain planar and tomosynthesis projection images. A composite tomosynthesis phantom with a centrally located contrast-detail insert was used as the object of interest. The total exposure for multiple views with tomosynthesis was always equal to or less than that for the planar technique. Algorithms were used to reconstruct the object from the acquired projections. Threshold contrast characteristics with all tomosynthesis reconstruction methods were significantly better than those with planar mammography, even when planar mammography was performed at more than twice the exposure level. Reduction of out-of-plane structural components was observed in all the tomosynthesis methods analyzed. The contrast-detail trends of all the tomosynthesis methods analyzed in this study were better than those of planar mammography. Further optimization of the algorithms could lead to better image reconstruction, which would improve visualization of valuable diagnostic information.

Lung compensator design using an electronic portal imaging device

Using a liquid filled electronic portal imaging device (EPID) installed on a linear accelerator and a composite chest phantom, exit dose measurements were carried out to establish an empirical relationship between the pixel values of the imaging detector and the corresponding equivalent thickness of the overlying phantom material. Results for 6 and 10 MV photons show that the relationship depends on the so-called input/output characteristics of the imaging device for a particular photon energy. For a chest irradiation, an EPID image obtained under treatment geometry provides the pixel value information that is used to calculate the tissue deficit over the lung region. The compensators are made of lead whose thickness is calculated from the established empirical relationship to replace the tissue deficit over lungs. The effectiveness of the method is demonstrated with thermoluminescent dosimetry (TLD) for 6 and 10 MV beams. With compensators in place, the dose uniformity was found to be within +/− 5%.

X-ray characterization of breast phantom materials

A pulse-height spectroscopic technique is used to measure the linear attenuation coefficients of commercially available composite phantom materials designed to simulate the attenuation characteristics of breast fat and breast glandular tissue. The manufacturers have specified the composition of these materials with the goal of matching the linear attenuation coefficients of breast tissues, calculated using the mixture rule. Over the energy range 18 to 100 keV, measurements from these materials are in close agreement with manufacturers' predictions and with previously measured linear attenuation coefficients of breast tissue samples.

Determination of Photon Backscatter from Several Calibration Phantoms

The photon backscatter factor for several irradiation phantoms was determined by calculational and experimental methods and compared with a phantom constructed of International Commission on Radiation Units and Measurements (ICRU) four-element tissue. Calculations of the photon backscatter factor over the energy range from 10 to 2000 keV were performed using the MCNP 4A code for each of the phantoms. Measurements of the backscatter factor were carried out using a thin-walled ionisation chamber that was exposed to X-ray beams with narrow energy spectra. The calculations and measurements agreed to within uncertainties and demonstrated that the backscatter factors over this energy range for a water-filled phantom recommended by the International Organization for Standardization (ISO) and a phantom constructed of tissue-equivalent (RS-I) plastic are nearly the same as that of the ICRU tissue reference phantom. However, the backscatter from a polymethylmethacrylate (PMMA) phantom was up to about 8% higher. In addition, it was found that a composite phantom of polytetrafluoroethylene (PTFE) and PMMA also produced a backscatter factor quite similar to that of the ICRU tissue reference phantom.

Effective atomic numbers of composite materials for total and partial interaction processes for photons, electrons, and protons.

Effective atomic numbers for total and dominant partial interaction processes of photons (1-50 MeV), electrons (1-50 MeV), and protons (1-200 MeV) for the composite materials bone (cortical), muscle (striated), water, polystyrene, Perspex, and Nylon-6 are derived. For photons, the effective atomic number from pair production in the nuclear field is greater than it is from the incoherent scattering. For electrons the effective atomic number from the radiative losses is greater than it is from the collision losses. In both of these cases however, the effective atomic numbers from partial interaction processes remain more or less the same, whereas the number from the total interaction increases with increasing energy. But in the energy regions from 1 to 5 MeV for photons and from 1 to 10 MeV for electrons, the number from the total interaction remains approximately the same for each of these composite materials. For all these materials, in these energy regions the interaction is predominantly with atomic electrons and the contributions from the pair production for photons and radiative losses for electrons are small. In the case of protons the number from total interaction remains more or less the same in the energy region considered. In this energy region collisions with atomic electrons dominate, and the contribution to the total stopping power is mainly from this process only. Hence the derived effective atomic number is basically from the partial process involving the interactions with atomic electrons. Thus, for photons from 1 to 5 MeV for electrons from 1 to 10 MeV and for protons from 1 to 200 MeV, the dosimetric data collected with composite tissue equivalent phantoms, designed on the basis of interaction with atomic electrons for treatment planning, will have less uncertainty.

Artifacts and thresholding in X-ray CT of a cortical bone and titanium composite.

X-Ray CT has the potential to provide precise and accurate data from which the mechanical properties of bone can be calculated. Such data would be useful in understanding the response of bone tissue to implants. Various artifacts can, however, degrade accuracy of the data. The aim of this study was to measure the artifactual errors produced in CT of a simulated femoral bone-titanium composite and to propose a method to correct for them. A composite phantom that simulates cortical bone and a titanium implant was designed and constructed. The phantom was scanned and the image data were analyzed over a range of thresholds with image analysis software developed for this study. The outer (OD) and inner (ID) diameter and the CT number of the cortical bone, with and without titanium, were measured over a range of cortical thicknesses. While ID can be accurately measured by choosing the proper threshold (800 HU), OD, even at optimal threshold, will be underestimated by approximately 2%. If a proper threshold is selected, CT number can also be accurately determined. Errors of up to 5%, however, are produced by titanium unless corrected by proper threshold selection. Intramedullary titanium is not a deterrent to obtaining accurate measurements of cortical bone dimensions and properties. Proper choice of thresholds for image analysis of CT scan data can yield accuracy and precision of < or = 2%.

Lung compensation in total body irradiation: A radiographic method

Using megavoltage radiography and a composite chest phantom, exit dose measurements were carried out to establish an empirical relationship between the optical film density and the corresponding equivalent thickness of overlying phantom material. Results for Co-60, 4-MV, and 10-MV photons show that the relationship depends on the sensitometric properties of the radiographic film and the photon beam quality. For an actual patient undergoing total body irradiation (TBI), a chest radiograph in treatment geometry provides the optical density information that is used to calculate the tissue deficit in the lung region. The compensators are made of lead whose thickness is chosen to replace the tissue deficit over the lung region. The validity of the method is established both by comparing its results to that obtained from multiple-slice computed tomography (CT) data for 4- and 10-MV photons, and by in-phantom thermoluminescent dosimetry (TLD) for Co-60, 4-MV and 10-MV beams.

Personal Dosemeter Intercomparisons as Indices of Performance - A Quality Assurance Procedure

This Centre participated in four intercomparisons for personal dosemeters conducted independently by IAEA/RCA, Japan and Australian Radiation Laboratory (ARL), Victoria using CaSO4:Dy Teflon disc-based personal monitoring TLD badges. The irradiations were performed by the organisers free-in-air as well as on the surface of water and PMMA equivalent composite phantoms. The performance of our personal dosemeters in these intercomparisons was analysed using ANSI-N13-11-1983 criteria testing the performance of personal dosimetry. The tolerance level, L, was lower than the limiting value of 0.5 for all the intercomparisons. The results were also analysed using trumpet curve analysis which incorporates the accuracy requirements of ICRP-35 and ICRP-60. The dosemeter quotients (measured dose/conventional true dose) for all irradiated dosemeters fall within the limits of the trumpet curves. These results indicated satisfactory performance of our personal dosemeters in these intercomparisons.

Experimental study of a real-time corona discharge imaging system as a future biomedical imaging device.

In the paper, a preliminary real-time corona discharge imaging system is introduced, and the effects of the imaging parameters, such as electric field intensities and their frequencies, on the resulting images are investigated. From experiments using metal phantoms and plant leaves, it is found that no insulators can be captured by the corona discharge, and the effect of imaging parameters on the image quality is clearly demonstrated. For the future application of this real-time corona discharge imaging system, a composite phantom made of four different metal substances is investigated, along with the various combinations of imaging parameters, and the corona discharge images of a fresh plant leaf are captured as a test version of biomedical objects. The ionisation current, which is important in biomedical applications, is measured in each imaging procedure and estimated by curve-fitting the measured values to the previously known theory of ionisation.

Proton MR chemical shift imaging using double and triple phase contrast acquisition methods.

Conventional chemical shift magnetic resonance (MR) imaging with the phase contrast technique has a number of limitations with respect to quantitative accuracy. The hypothesis of this study is that the accuracy of phase contrast chemical shift MR may be improved by increasing the number of basis images from two to three. Water and fat images were obtained from phantoms and volunteers with a 1.5 T MR system using double and triple acquisition phase contrast chemical shift methods. Longitudinal relaxation time and relative water and fat content were calculated from these basis images. The T1 relaxation times of the aqueous component of composite phantoms were determined more accurately using the triple acquisition method than with the double acquisition method. In vivo studies demonstrate that the triple acquisition method separated fat and water signals more accurately and showed less field inhomogeneity dependence than the modified double acquisition method. The new method also provided a map of static field magnetic inhomogeneity and tissue magnetic susceptibility. The triple acquisition phase contrast chemical shift imaging technique should improve the prospect for quantitative tissue characterization in clinical MR.

Hyperthermia by magnetic induction: I. Physical characteristics of the technique

Several electromagnetic techniques are currently used in hyperthermia therapy for cancer. This report discusses the magnetic induction technique, in which application of an alternating magnetic field to a conductor results in induction of eddy current flow and power deposition via ohmic losses. The power density in tissues depends upon the heterogeneous tissue conductivities and dielectric constants, magnetic field intensity and distribution, and eddy current radius. Using a newly developed magnetic field probe, the magnetic fields produced at 13.56 MHz by electrodes of a commercial magnetic induction device have been accurately mapped and used to calculate power densities in static phantoms. Calculated and observed temperature elevations in a cylindrically symmetric phantom agree well, confirming the simple formula in this case relating power density to magnetic field strength. The efficiencies of three commercially available electrodes have been accurately measured using calorimetric techniques and phantom loads modeling human anatomy and electrical conductivity. The effect of eccentric positioning of the load has been studied using magnetic field mapping techniques. Power densities in a very simplified model of human anatomy that retains cylindrical symmetry were calculated. Effects of inhomogeneities in conductivity have been investigated qualitatively using composite static phantoms modeling human cross-sectional anatomy and thermographic camera recordings of surface temperature distributions. The advantages and disadvantages of this heating technique are discussed from the point of view of the power density distributions in heterogeneous materials. Evaluation of power density distributions is essential for optimizing this heating technique using various electrode arrangements and/or load modifications, for providing part of the information needed for solution of the bioheat transfer equation in living subjects, and for predicting the ability of the technique to heat specific tumors.

A preliminary investigation of radiation dose reduction on an EMI CT5005 whole body scanner using a copper wedge.

The effects of the existing filtration system upon a narrow, parallel beam of X rays were considered. The profile of a Cu filter to be placed on the tube-side A1 wedge was calculated on the basis that the total energy incident on the detector box would remain unchanged when the other A1 wedge was removed. A Cu wedge was machined according to this profile. The effects of this modification on surface radiation dose delivered to a 25 cm EMI water phantom were both predicted and measured for horizontal traverses, and were in broad agreement. The reduction in integral radiation dose to the 25 cm water phantom was predicted as 39%. Dose reductions measured at several points on the surface and within an Alderson Rando anthropomorphic phantom head averaged 53% and 20% respectively. The modified system was evaluated in terms of imaging ability, and although some degradation was seen, images of the EMI composite phantom remained "diagnostic" in quality, despite non-ideal responses of some photomultiplier tubes at intermediate and extreme positions of the traverse periphery.

Physical measurements with a high-energy proton beam using liquid and solid tissue substitutes

The measurement of the physical parameters of a high-energy proton beam, using a range of liquid and solid tissue substitutes, is described. The system, the detectors used and the experimental verification of the tissue equivalence of the new tissue substitutes is presented. The measurements with the scattered but uncollimated proton beam in muscle- and brain-equivalent liquids and in water are compared to similar data obtained from the scattered but collimated beam. The effect of lung, fat and bone on the dose distributions in composite phantoms is also investigated and the necessary corrections established. A simulated patient treatment indicated that the Bragg peak can be positioned with an error not exceeding +or-0.5 mm.