Low Attenuation Material Research Articles

Optimizing and applying high-resolution, in-line laboratory phase-contrast X-ray imaging for low-density material samples.

In-line, or propagation-based phase-contrast X-ray imaging (PBI) is an attractive alternative to the attenuation-based modality for low-density, soft samples showing low attenuation contrast. With the growing availability of micro- and nano-focus X-ray tubes, the method is increasingly applied in the laboratory. Here, we discuss the technique and demonstrate its advantages for selected low-density, low attenuation material samples using a lab-based micro- and nano-computed tomography systems Easytom XL Ultra, providing micron and sub-micron range resolution PBI images. We demonstrate a multi-step optimization of the lab-based PBI technique on our scanner that includes choosing the optimal detector-source hardware combination available in the setup, then optimizing the imaging geometry and finally the phase retrieval process through a parametric study. We point out and elaborate on the effect of noise correlation and texturing due to phase retrieval. We demonstrate the overall benefits of using the phase image and the phase retrieval for the selected samples such as improved image quality, increased contrast-to-noise ratio while only marginally influencing the spatial resolution. The improvement in image quality also enables further image processing steps for detailed structural analysis of the samples, which would be much more complicated if not impossible based on the transmissionimage.

Influence of Data Acquisition Algorithms on X-Ray Phase Contrast Imaging Computed Tomography

Abstract X-ray phase contrast imaging (XPCI) is a nondestructive evaluation technique that enables high-contrast detection of low-attenuation materials that are largely transparent in traditional radiography. Extending a grating-based Talbot-Lau XPCI system to three-dimensional imaging with computed tomography (CT) imposes two motion requirements: the analyzer grating must translate transverse to the optical axis to capture image sets for XPCI reconstruction, and the sample must rotate to capture angular data for CT reconstruction. The acquisition algorithm choice determines the order of movement and positioning of the two stages. The choice of the image acquisition algorithm for XPCI CT is instrumental to collecting high fidelity data for reconstruction. We investigate how data acquisition influences XPCI CT by comparing two simple data acquisition algorithms and determine that capturing a full phase-stepping image set for a CT projection before rotating the sample results in higher quality data.

A Comprehensive Report on Ultrasonic Attenuation of Engineering Materials, Including Metals, Ceramics, Polymers, Fiber-Reinforced Composites, Wood, and Rocks

In this paper, ultrasonic attenuation of engineering materials is evaluated comprehensively, covering metals, ceramics, polymers, fiber-reinforced composites, wood, and rocks. After verifying two reliable experimental methods, 336 measurements are conducted and their results are tabulated. Attenuation behavior is determined over broadband spectra, extending up to 15 MHz in low attenuating materials. The attenuation spectra are characterized in combination with four power law terms, with many showing linear frequency dependence, with or without Rayleigh scattering. Dislocation damping effects are re-evaluated and a new mechanism is proposed to explain some of the linear frequency dependencies. Additionally, quadratic and cubic dependencies due to Datta–Kinra scattering and Biwa scattering, respectively, are used for some materials to construct model relations. From many test results, some previously hidden behaviors emerged upon data evaluation. Effects of cold working, tempering, and annealing are complex and sometimes contradictory. Comparison to available literature was attempted for some, but most often prior data were unavailable. This collection of new attenuation data will be of value in materials selection and in designing structural health monitoring and non-destructive inspection protocols.

Development of Novel Immobilization Adapter for Head and Neck Radiotherapy with Low-attenuation Material

The dosimetric error due to immobilization devices has been highlighted by the AAPM Task Group 176. We developed a novel low-radiation-absorbent immobilization adaptor (HMA), which can be used with a Styrofoam headrest for head and neck region in radiotherapy. The purpose of this study was to investigate the impact of the HMA on the dose distribution and compare with a commercially released plastic adapter. Computed tomography (CT) simulation and dose calculation on a treatment planning system (TPS) were performed by the use of HMA and the plastic adapter with a cylindrical phantom. Both the adapters were placed on the phantom upside and the attenuation rate was measured. Gantry angles were changed at every 1°interval from 0°to 50°for measurements. The measured dose was normalized by the value of 90°. The treatment equipment was TrueBeam (Varian medical systems); X-ray energies were set on 4, 6 and 10 MV, respectively. The measured attenuation rates were also compared with calculation results of TPS. The highest differences on attenuation rate of both the adapters were observed at a gantry angle of 32.0°; the differences were 3.0% at 4 MV, 2.7% at 6 MV and 3.0% at 10 MV, respectively, and lower absorption was HMA. TPS calculation results of monitor unit for the HMA were within 1.0% in each energy. The HMA was able to provide absorption dose and calculation errors lower than a commercially released adapter. It can also provide more accurate dose delivery for radiotherapy in head and neck because of the low absorption characteristics.

Evaluation of sample holders designed for long-lasting X-ray micro-tomographic scans of ex-vivo soft tissue samples

X-ray microradiography and microtomography are imaging techniques with increasing applicability in the field of biomedical and preclinical research. Application of hybrid pixel detector Timepix enables to obtain very high contrast of low attenuating materials such as soft biological tissue. However X-ray imaging of ex-vivo soft tissue samples is a difficult task due to its structural instability. Ex-vivo biological tissue is prone to fast drying-out which is connected with undesired changes of sample size and shape producing later on artefacts within the tomographic reconstruction. In this work we present the optimization of our Timepix equipped micro-CT system aiming to maintain soft tissue sample in stable condition. Thanks to the suggested approach higher contrast of tomographic reconstructions can be achieved while also large samples that require detector scanning can be easily measured.

High resolution micro-CT of low attenuating organic materials using large area photon-counting detector

To overcome certain limitations of contemporary materials used for bone tissue engineering, such as inflammatory response after implantation, a whole new class of materials based on polysaccharide compounds is being developed. Here, nanoparticulate bioactive glass reinforced gelan-gum (GG-BAG) has recently been proposed for the production of bone scaffolds. This material offers promising biocompatibility properties, including bioactivity and biodegradability, with the possibility of producing scaffolds with directly controlled microgeometry. However, to utilize such a scaffold with application-optimized properties, large sets of complex numerical simulations using the real microgeometry of the material have to be carried out during the development process. Because the GG-BAG is a material with intrinsically very low attenuation to X-rays, its radiographical imaging, including tomographical scanning and reconstructions, with resolution required by numerical simulations might be a very challenging task. In this paper, we present a study on X-ray imaging of GG-BAG samples. High-resolution volumetric images of investigated specimens were generated on the basis of micro-CT measurements using a large area flat-panel detector and a large area photon-counting detector. The photon-counting detector was composed of a 010× 1 matrix of Timepix edgeless silicon pixelated detectors with tiling based on overlaying rows (i.e. assembled so that no gap is present between individual rows of detectors). We compare the results from both detectors with the scanning electron microscopy on selected slices in transversal plane. It has been shown that the photon counting detector can provide approx. 3× better resolution of the details in low-attenuating materials than the integrating flat panel detectors. We demonstrate that employment of a large area photon counting detector is a good choice for imaging of low attenuating materials with the resolution sufficient for numerical simulations.

Suspected Pulmonary Thromboembolism and Deep Venous Thrombosis: A Comprehensive 64-slice Multidetector Computed Tomography Diagnosis in Gynecologic Patients.

Suspected Pulmonary Thromboembolism and Deep Venous Thrombosis: A Comprehensive 64-slice Multidetector Computed Tomography Diagnosis in Gynecologic Patients.

TH-C-17A-04: Shining Light On the Implementation of Cherenkov Emission in Radiation Therapy

Purpose: We hypothesize that Cherenkov emission (CE) by radiotherapy beams is correlated with radiation dose, CE detection can be maximized by a spectral shift towards the near-infrared (NIR) window of biological tissue, and in certain tissue types (ex. breast/oropharynx), it could prove superior to mega-voltage (MV) imaging. Therefore, we compare CE imaging to onboard MV imaging. Methods: Dose-CE correlation was investigated via simulation and experiment. A Monte Carlo (MC) CE simulator was designed using Geant4. Experimental phantoms include: water; tissuesimulating phantom composed of water, fat emulsion, and beef blood; plastic phantom with solid water insert. The optical spectrometry system consisted of a multi-mode optical fiber and diffraction-grating spectrometer incorporating a front/back-illuminated charge-coupled device (CCD). CdSe/ZnS quantum dots (QDs), emitting at (650±10) nm, were used to achieve NIR shift of the CE signal. CE and MV images were acquired with a complementary metal-oxide-semiconductor (CMOS) camera and an electronic portal imaging device (EPID), respectively. Results: MC and experimental studies indicate a strong linear correlation between radiation dose and CE (Pearson coefficient > 0.99). CE by an 18 MeV beam was effectively shifted towards the NIR in water and in a tissue-simulating phantom, exhibiting a 50% increase at 650 nm for QD depths of ∼3 mm. CE images exhibited relative contrast superior to EPID images by a factor of 30. Conclusion: Our work supports the potential for application of CE in radiotherapy online imaging for patient setup and treatment verification, since CE is intrinsic to the beam and non-ionizing, and QDs can be used to improve CE detectability, yielding image quality superior to MV imaging for the case of low density variability, low optical attenuation materials, such as breast or oropharyngeal cavities. Ongoing work involves microenvironment functionalization of QDs and application of multichannel spectrometry for simultaneous acquisition of dosimetric and tumor oxygenation signals. Funding received from the following organizations: Natural Sciences and Engineering Research Council of Canada, McGill University. YZ acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290).

Temporal behavior of laser induced elastic plate resonances

This paper investigates the dependence on Poisson’s ratio of local plate resonances in low attenuating materials. In our experiments, these resonances are generated by a pulse laser source and detected with a heterodyne interferometer measuring surface displacement normal to the plate. The laser impact induces a set of resonances that are dominated by Zero Group Velocity (ZGV) Lamb modes. For some Poisson’s ratio, thickness-shear resonances are also detected. These experiments confirm that the temporal decay of ZGV modes follows a t−0.5 law and show that the temporal decay of the thickness resonances is much faster. Similar decays are obtained by numerical simulations achieved with a finite difference code. A simple model is proposed to describe the thickness resonances. It predicts that a thickness mode decays as t−1.5 for large times and that the resonance amplitude is proportional to D−1.5 where D is the curvature of the dispersion curve ω(k) at k=0. This curvature depends on the order of the mode and on the Poisson’s ratio, and it explains why some thickness resonances are well detected while others are not.

20: Targeted Gold Nanoparticles as Vascular Disrupting Agents during Radiotherapy

towards the near-infrared (NIR) window of biological tissue, and in tissues of low density variability and low optical attenuation, such as breast or oropharyngeal cavities, it can provide contrast superior to MV imaging. Materials/Methods: Dose-CE correlation was investigated via both simulation and experiment. A Monte Carlo (MC) CE simulator was designed using Geant4. Experimental phantoms include: a water tank; a tissue-simulating phantom composed of water, a fat emulsion, and beef blood; and a Poly(methyl methacrylate) (PMMA) phantom with a solid insertion radiologically equivalent to water. The optical spectrometry system consists of a multi-mode optical fiber, connected to a diffraction grating spectrometer incorporating a frontor back-illuminated chargecoupled device (CCD). CdSe/ZnS core-shell quantum dots (QDs), emitting at (650 10) nm, were used to achieve a NIR shift of the CE signal. CE and MV images were acquired with a complementary metal-oxide-semiconductor (CMOS) camera and an amorphous silicon electronic portal imaging device (EPID), respectively. Results: MC analyses indicate a strong linear correlation between radiation dose and CE (Pearson coefficient r > 0.99). Dose-CE correlation was investigated experimentally via water tank ion chamber and optical fiber scans. The effective points of measurement of dose by our optical system for 18, 12, and 6 MeV clinical electron beams were at 1.7, 0.8, and 0.1 cm, respectively, downstream from the fiber axis (r > 0.99). CE by an 18 MeV beam was effectively shifted toward 650 nm in a water tank, confirming its capacity to stimulate CdSe/ZnS photoluminescence, and in a tissuesimulating phantom, exhibiting a 30% increase at QD depths of w3 mm. CE images exhibited 30x better relative contrast than EPID images. Conclusions: Our work validates the potential for application of CE in RT online imaging for patient setup and treatment verification, since CE is intrinsic to the beam and non-ionizing and QDs can be used to improve CE detectability, yielding image quality superior to MV imaging for the case of a low density variability and low optical attenuation material, which is the case for breast or oropharyngeal cavities. Future work involves modification of QDs to capture microenvironment parameters and the use of a multi-channel spectrometer for simultaneous acquisition of dosimetric and tumor oxygenations signals. Author Disclosure: Y. Zlateva: None. N. Quitoriano: None. S. Davis: None. I. El Naqa: None.

Pulmonary Parenchymal Consolidation on Thoracic CT

Consolidation is defined pathologically as an exudate, or other disease product, that replaces alveolar air and renders the pulmonary parenchyma airless. The chest radiographic appearance of consolidation is usually relatively nonspecific and may be the result of a wide variety of disorders, including infection, neoplasm, hemorrhage, and rare infiltrative diseases. Similarly, the appearance of consolidation on thoracic computed tomography (CT) is rarely specific enough to suggest a single diagnosis. Occasionally, however, the attenuation characteristics of consolidation on thoracic CT may provide a specific etiology for pulmonary parenchymal infiltration; such is the case when low attenuation material, representing fat, is seen in patients with lipoid pneumonia on thoracic CT. Often the diagnosis of lipoid pneumonia is difficult to establish clinically, and abnormalities detected on thoracic CT may first suggest this condition. Once thoracic CT indicates the presence of lipoid pneumonia, directed history often discloses the offending agent. Bronchoscopy with bronchioloalveolar lavage may disclose lipid-laden macrophages within the lung parenchyma in selected patients. Therapy may then be directed at discontinuation of the offending lipid and treatment of any coexistent bacterial superinfection. Patients with acute lipoid pneumonia often improve clinically and radiographically with appropriate therapy, whereas patients with chronic lipoid pneumonia may show relatively little improvement despite appropriate treatment.

Human Chorionic Gonadotropin (HCG) Secreting Hepatocellular Carcinoma

Purpose: To describe an unusual case of a Human Chorionic Gonadotropin (HCG) secreting hepatocellular carcinoma. Case: 47 year old woman with co-morbidities including end-stage liver disease secondary to hepatitis C and hepatocellular carcinoma presented with fatigue and nausea. She denied any fever, chills, dyspnea, chest pain, abdominal pain, diarrhea or dysuria. On physical exam she had scleral icterus, ascites and jaundiced skin. Laboratory tests revealed a platelet count of 96,000 th/ul, albumin of 1.9 g/dl, total bilirubin of 10.5 mg/dl, AST of 104 u/l and ALT of 34 u/l. Surprisingly, a urine HCG done as part of standard screening prior to imaging tests was positive so a quantitative measure was done which showed an HCG of 113 mIU/ml. A pelvic ultrasound showed a non gravid uterus. A computed tomography (CAT) scan was then done which showed a 2.4 x 2.0 cm hypodense lesion in the caudate lobe of the liver, cirrhotic morphology of the liver, enlargement of the spleen, ascites, cholelithiasis and low attenuation material in a dilated main portal vein extending into the right and left portal veins concerning for portal vein thrombosis. She underwent a liver transplantation and splenectomy. Pathology showed a dominant tumor nodule in the caudate lobe and diffuse small multifocal cirrhosis-like hepatocellular carcinoma nodules involving about 25% of the liver. The tumor nodules showed variable differentiation from moderate to poor with giant cells. Staining of the tumor was positive for HCG. The spleen showed passive venous congestion and the distal pancreas showed hemorrhage, focal pancreatitis and fat necrosis. There was also an unsuspected organizing thrombus with tumor embolization seen in the portal vein. The HCG level measured two weeks after transplant normalized to < 1.0 mIU/ml and remained normal during follow up. Discussion: Hepatocellular carcinoma is an aggressive tumor that often occurs in the setting of chronic liver disease and cirrhosis. It commonly secretes alpha-fetoprotein and in case reports has been shown to secrete parathyroid hormone and other hormones. This case is novel in that HCG has not been reported before in this setting. The utility of this marker in terms of treatment prognosis remains to be determined. We report a case of an HCG secreting tumor in which the level of HCG normalized after transplantation.

On the nature of shear horizontal wave propagation in elastic plates coated with viscoelastic materials

The possibility of using long–range ultrasonic guided–wave non–destructive testing for the inspection of metallic structures coated with attenuative layers is extremely attractive. However, the material damping may cause severe attenuation of the acoustic signal, resulting in reduction of the test range. This paper addresses the dispersion of shear horizontal waves propagating in metallic plates coated with viscoelastic layers. It is shown that the bilayer modes can be viewed as an interaction between the free elastic plate modes and the modes of the viscoelastic layer if it were clamped on its lower surface. For low–attenuation materials the interaction is strong and the trajectories of the bilayer dispersion curves jump between the two families as the frequency increases. However, as the material damping increases the interaction becomes weak and most of the energy is confined in either the metallic plate or in the attenuative layer, and modes no longer jump. The guided–wave attenuation is related to the strain energy in the viscoelastic layer per unit in–plane power flow by means of an energy–balance argument. The guided–wave attenuation of the modes whose energy travels primarily in the elastic plate exhibits periodic peaks in the frequency domain, which occur at roughly equally spaced critical frequencies. These frequencies are close to the through–thickness resonance frequencies of the clamped–free viscoelastic layer if it is considered to be elastic. Minima of the guided–wave attenuation occur around the Love transition frequencies.

Small bowel obstruction due to intestinal migration of an inferior vena cava polytetrafluoroethylene graft

Surgery 2002;131:465-7.

Optimum index profile of the perfluorinated polymer-based GI polymer optical fiber and its dispersion properties

The significant advantages in bandwidth and low material dispersion of perfluorinated (PF) polymer-based graded-index polymer optical fiber (GI POF) are theoretically and experimentally reported for the first time. It is confirmed that the low attenuation and low material dispersion of the PF polymer enables 1 Gb/s km and 10 Gb/s km transmission at 0.85-/spl mu/m and 1.3-/spl mu/m wavelengths, respectively. The PF polymer-based CI POF has very low material dispersion (0.0055 ns/nm/spl middot/km at 0.85 /spl mu/m), compared with those of the conventional PMMA-based POF and of multimode silica fiber (0.0084 ns/nm km at 0.85 /spl mu/m). Since the PF polymer-based GI POF has low attenuation from the visible to near infrared region, not only the 0.65-/spl mu/m wavelength which is in the low attenuation window of the PMMA-based GI POF, but other wavelengths such as 0.85-/spl mu/m or 1.3-/spl mu/m etc. can be adopted for the transmission wavelength. It is clarified in this paper that the wavelength dependence of the optimum index profile shape of the PF polymer-based GI POF is very small, compared to the optimum index profile shape of the silica-based multimode fiber. As a result, the PF polymer-based GI POF has greater tolerance in index profile variation for higher speed transmission than multimode silica fiber. The impulse response function of the PF polymer-based GI POF was accurately analyzed from the measured refractive index profile using a Wentzel, Kramers, Brillouin (WKB) numerical computation method. By considering all dispersion factors involving the profile dispersion, predicted bandwidth characteristic of the PF polymer-based GI POF agreed well with that experimentally measured.

Seismic attenuation tomography of the Tonga‐Fiji region using phase pair methods

The anelastic structure of the region surrounding the Tonga slab and Lau back arc spreading center in the southwest Pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs. Two differential attenuation methods determine δt* over the frequency band 0.1 to 3.5 Hz for earthquakes in the Tonga slab. The S‐P method measures the difference in spectral decay between P and S waves arriving at the same station. The P‐P method measures the difference in spectral decay for P waves with different paths through the upper mantle. Eight hundred sixty phase pairs are used to invert for two‐dimensional 1/Qα structure using a nonnegative least squares algorithm. A grid search method determines the Qα/Qβ ratio most compatible with both the S‐P and P‐P differential measurements. The highest attenuation (Qα = 90) is found within the upper 100 km beneath the active portions of the Lau Basin extending westward to the Lau Ridge. These regions probably delineate the source region for the back arc spreading center magmas, expected to be within the upper 100 km based on petrological considerations. The high attenuation regions also correlate well with zones of low P wave velocity determined by regional velocity tomography. Somewhat lower attenuation is found beneath the Fiji Plateau than beneath the Lau Basin. The entire back arc is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km. The slab is imaged as a region of low attenuation (Qα &gt; 900) material. A Qα/Qβ ratio of 1.75 provides the best fit between the S‐P and P‐P data sets upon inversion. Spectral stacking shows no frequency dependence within the frequency band analyzed.

The potential for dose reduction in diagnostic radiology using low attenuation materials in table tops.

It is important to be able to assign priorities to the purchase of radiological equipment. The ability to incorporate potential dose savings into a ranking procedure involving costs is therefore of interest. In this paper we have considered the question of the dose saving made available by the selection of low attenuation table tops and have described how to generate a factor which can be used in a ranking procedure such as cost effectiveness analysis. We describe how data on the expected dose saving can be obtained from measurements of the aluminium equivalent thickness in air used in conjunction with theoretical spectral data. The magnitude of the overestimate when in air measurements alone are used is presented, as is a ready reckoner for determining the true dose saving when changes in table top are considered. Unless the table to be replaced is of some age, the expected dose saving will vary between 6% and 1%.

Optimization of patient radiation dose through development of specifications for purchase of X-ray equipment.

X-ray equipment characteristics and performance have an important influence on radiation doses to patients. In order that these factors can be taken into consideration when X-ray equipment is purchased, dose related requirements need to be included in specifications and additional dose information requested from manufacturers. Dose factors include techniques that directly reduce exposure; use of low attenuation materials; provision of flexibility in choice of exposure parameters; and availability of data for dose assessment. If a standard format can be developed, this should enable manufacturers to supply this information. Specifications for different types of X-ray equipment and lists of dose information to be requested from manufacturers have been prepared by the Scottish Radiation Protection Advisers' Group for use in hospitals throughout Scotland. It is hoped that this will allow patient dose to be taken into account when X-ray equipment is purchased.

Low-attenuation periportal collar in transplanted liver is not reliable CT evidence of acute allograft rejection.

Recent reports indicate that the presence or absence of a periportal low-attenuation rim ("periportal collar" sign) on CT scans is of variable reliability in predicting rejection after liver transplantation. To study this matter further, we reviewed 178 CT scans in 68 patients (74 allografts) after hepatic transplantation. One hundred twenty-one scans were obtained within 7 days of liver biopsy. The presence or absence of a central or peripheral periportal collar on these scans was correlated with the presence or absence of acute rejection found at biopsy. A central periportal collar was defined as an abnormally large amount of low-attenuation material surrounding the main portal vein, the right portal vein, or the left portal vein. A peripheral periportal collar was defined as a low-attenuation area surrounding a portal vein branch distal to the left or right portal veins. A weak, but statistically significant correlation between the presence of a peripheral periportal collar and acute allograft rejection was shown in patients in whom CT scans were obtained within 3 days of biopsy. However, the sensitivity, specificity, accuracy, and positive predictive value of the presence of a peripheral collar in this group were 60%, 67%, 64%, and 63%, respectively. The sensitivity, specificity, accuracy, and positive predictive value of the presence of a central collar in patients scanned within 3 days of biopsy were 74%, 35%, 54%, and 52%, respectively. Negative predictive values of peripheral and central collars were 65% and 59%, respectively. Our study shows that a periportal collar is seen more commonly in patients with recently transplanted allografts (mean interval after transplantation, 46 days for peripheral collars and 57 days for central collars) and in patients with ascites. The presence of a central or peripheral periportal collar on CT is not sufficiently sensitive, specific, or accurate to reliably diagnose or exclude acute allograft rejection.

Low-attenuation materials and rare-earth screens in radiodiagnosis.Statement by the British Institute of Radiology

Low-attenuation materials and rare-earth screens in radiodiagnosis.<i>Statement by the British Institute of Radiology</i>