Articles

Determinants of Macular Pigment: The Irish Longitudinal Study on Ageing (TILDA).

J M. Nolan et al. — Tue, 20 Nov 2012 05:57:59 PST

PURPOSE. The three carotenoids lutein, zeaxanthin, and meso-zeaxanthin, are found at the macula and referred to as macular pigment (MP). This study was undertaken to investigate determinants of MP in a large randomly selected sample from the Republic of Ireland (as part of The Irish Longitudinal Study

The Impact of Macular Pigment Augmentation on Visual Performance Using Different Carotenoid formulations.

James Loughman et al. — Tue, 20 Nov 2012 05:30:11 PST

To investigate changes in macular pigment optical
density (MPOD) and visual performance following supplementation
with different macular carotenoid formulations.

Kinetic Studies of the Photo-Degradation of Poly Arylene Vinylenes

Luke O'Neill et al. — Mon, 22 Oct 2012 07:45:22 PDT

The kinetics of the degradation of a homologous series of Poly phenylene vinylenes in which the phenylene units of the PPV structure are systematically substituted by naphthyl and anthyrl units is presented. Degradation is monitored according to the decay of the long wavelength absorption maximum upon illumination with UV radiation. Compared to Toluene solution, the photo-degradation is seen to be accelerated in Chloroform solution. All decays are fitted with first order kinetics. It is found that all substitutions improve the stability of the vinylene polymers against decay. In particular the highly electro-negative naphthyl group serves to drastically increase the stability due to electron depletion across the vinyl bond. The decay rate is shown to correlate well with the variation of the electronic properties of the backbone and with the reduction of vinylene bond strength as measured using Raman spectroscopy.

Structure-Property Relationships for Electron-Vibrational Coupling in Conjugated Organic Oligomeric Systems

Luke O'Neill et al. — Mon, 22 Oct 2012 07:15:33 PDT

A series of ð-conjugated oligomers containing one to six monomer units were studied by absorption and photoluminescence spectroscopy. As is common for these systems, a linear relationship between the positioning of the lowest-energy absorption and the highest-energy photoluminescence maxima plotted versus inverse conjugation length is observed, in good agreement with a simple nearly free electron model, one of the earliest descriptions of the properties of one-dimensional organic molecules. It was observed that the Stokes shift and therefore Huang-Rhys factor also exhibit a well-defined relationship with increasing conjugation length, implying a correlation between the electron-vibrational coupling and chain length. This correlation is further examined using Raman spectroscopy, whereby the integrated relative Raman scattering is seen to behave superlinearly with chain length. The Stokes shift and the Raman activity are also well-correlated in these systems. There is a clear indication that the vibrational activity and thus nonradiative decay processes are controllable through molecular structure.

Psychophysical Impact and Optical and Morphological Characteristics of Symptomatic Non-Advanced Cataract.

S. Charalampidou et al. — Tue, 28 Aug 2012 05:52:18 PDT

Purpose To investigate whether
psychophysical, morphological, and/or optical
characteristics of symptomatic non-advanced
cataract are complementary to, or more
appropriate than, visual acuity (VA) for the
purposes of recording visual data that reflect
subjective visual difficulty in patients with
cataract that exhibit relative sparing of high
contrast acuity (0.4 logarithm of minimal angle
of resolution (logMAR) scale or better).

Macular carotenoid Supplementation in Subjects with Atypical Spatial Profiles of Macular Pigment.

A M. Chaitanya et al. — Tue, 28 Aug 2012 02:52:17 PDT

This study was designed to investigate the impact of macular carotenoid supplementation on the spatial
profile of macular pigment (MP) in subjects where the profile does not exhibit the typical central peak

Comparative Imaging Study in Ultrasound MRI, CT and DSA using a Multi-Modality Renal Artery Phantom

Deirdre King et al. — Thu, 08 Sep 2011 07:51:21 PDT

A range of anatomically-realistic multi-modality renal artery phantoms consisting of vessels with varying degrees of stenosis was developed and evaluated using four imaging techniques currently used to detect renal artery stenosis (RAS). The spatial resolution required to visualize vascular geometry and the velocity detection performance required to adequately characterize blood flow in patients suffering from RAS is currently ill-defined, with the result that no one imaging modality has emerged as a gold standard technique for screening for this disease.

Methods: The phantoms, which contained a range of stenosis values (0, 30, 50, 70 and 85%), were designed for use with ultrasound, magnetic resonance imaging, X-ray computed tomography and X-ray digital subtraction angiography. The construction materials used were optimized with respect to their ultrasonic speed of sound and attenuation coefficient, MR relaxometry (T₁, T₂) properties, and Hounsfield number / X-ray attenuation coefficient, with a design capable of tolerating high-pressure pulsatile flow. Fiducial targets, incorporated into the phantoms to allow for registration of images among modalities, were chosen to minimize geometric distortions.

Results: High quality distortion-free images of the phantoms with good contrast between vessel lumen, fiducial markers and background tissue to visualize all stenoses were obtained with each modality. Quantitative assessments of the grade of stenosis revealed significant discrepancies between modalities, with each underestimating the stenosis severity for the higher-stenosed phantoms (70% and 85%) by up to 14%, with the greatest discrepancy attributable to DSA.

Conclusions: The design and construction of a range of anatomically-realistic renal artery phantoms containing varying degrees of stenosis is described. Images obtained using the main four diagnostic techniques used to detect RAS were free from artifacts and exhibited adequate contrast to allow for quantitative measurements of the degree of stenosis in each phantom. Such multi-modality phantoms may prove useful in evaluating current and emerging US, MRI, CT and DSA technology.

Development of a Vessel Mimicking Material for use in Anatomically Realistic Doppler Flow Phantoms

Deirdre King et al. — Thu, 08 Sep 2011 07:49:58 PDT

Polyvinyl alcohol cryogel, (PVA-C) is presented as a vessel mimicking material for use in anatomically realistic Doppler flow phantoms. Three different batches of 10 % wt PVA-C containing (i) PVA-C alone, (ii) PVA-C with anti-bacterial agent and (iii) PVA-C with silicon carbide particles were produced, each with 1 to 6 freeze-thaw cycles. The resulting PVA-C samples were characterized acoustically (over a range 2.65 - 10.5 MHz) and mechanically in order to determine the optimum mixture and preparation for mimicking the properties of healthy and diseased arteries found in vivo. This optimum mix was reached with the PVA-C with anti-bacterial agent sample, prepared after 2 freeze/thaw cycles, which achieved a speed of sound of 1538 ± 5 m s^-1 and a Young's elastic modulus of 79 ± 1lkPa. This material was used to make a range of anatomically-realistic flow phantoms with varying degrees of stenoses, and subsequent flow experiments revealed that higher degrees of stenoses and higher velocities could be achieved without phantom rupturing compared to a phantom containing conventional wall-less vessels

Development of a Range of Anatomically Realistic Renal Artery Flow Phantoms

Deirdre King et al. — Wed, 26 Jan 2011 04:10:41 PST

Computer-aided modelling techniques were used to generate a range of anatomically realistic phantoms of the renal artery from medical images of a 64-slice CT data set acquired from a healthy volunteer. From these data, models of a normal healthy renal artery and diseased renal arteries with 30%, 50%, 70% and 85% stenoses were generated. Investment casting techniques and a low melting point alloy were used to create the vessels with varying degrees of stenosis. The use of novel inserts significantly reduced the time, materials and cost required in the fabrication of these anatomically realistic phantoms. To prevent residual metal remaining in the final phantom lumens a technique employing clingfilm was used to remove all molten metal from the lumen. These novel flow phantoms developed using efficient methods for producing vessels with various degrees of stenosis can provide a means of evaluation of current and emerging ultrasound technology. (E-mail: king.deirdre@mayo.edu)

Studies of Chemical Fixation Effects in Human Cell Lines Using Raman Microspectroscopy

Aidan Meade et al. — Mon, 10 Jan 2011 08:38:49 PST

The in vitro study of cellular species using Raman spectroscopy has proven a powerful non-invasive modality for the analysis of cell constituents and processes. This work uses micro-Raman spectroscopy to study the chemical fixation mechanism in three human cell lines (normal skin, normal bronchial epithelium, and lung adenocarcinoma) employing fixatives that preferentially preserve proteins (formalin), and nucleic acids (Carnoy’s fixative and methanol–acetic acid). Spectral differences between the mean live cell spectra and fixed cell spectra together with principal components analysis (PCA), and clustering techniques were used to analyse and interpret the spectral changes. The results indicate that fixation in formalin produces spectral content that is closest to that in the live cell and by extension, best preserves the cellular integrity. Nucleic acid degradation, protein denaturation, and lipid leaching were observed with all fixatives and for all cell lines, but to varying degrees. The results presented here suggest that the mechanism of fixation for short fixation times is complex and dependent on both the cell line and fixative employed. Moreover, important spectral changes occur with all fixatives that have consequences for the interpretation of biochemical processes within fixed cells. The study further demonstrates the potential of vibrational spectroscopy in the characterization of complex biochemical processes in cells at a molecular level. Figure Chemical preservation of cells for Raman microspectroscopy is shown to be strongly dependent on the cell type and the fixative used, in a variety of cell lines, with formalin fixation show to result in spectral content most comparable to that in the live cell

Spectroscopic and Chemometric Approaches to Radiobiological Analyses

Aidan Meade et al. — Mon, 10 Jan 2011 08:18:04 PST

Functional and Pathological Analysis of Biological Systems Using Vibrational Spectroscopy with Chemometric and Heuristic Approaches

Aidan Meade et al. — Mon, 10 Jan 2011 08:04:57 PST

Vibrational spectroscopy (Raman and FTIR microspectroscopy) is an attractive modality for the analysis of biological samples since it provides a complete non-invasive acquisition of the biochemical fingerprint of the sample. Studies in our laboratory have applied vibrational spectroscopy to the analysis of biological function in response to external agents (chemotherapeutic drugs, ionising radiation, nanoparticles), together with studies of the pathology of tissue (skin and cervix) in health and disease. Genetic algorithms have been used to optimize spectral treatments in tandem with the analysis of the data (using generalized regression neural networks (GRNN), artificial neural networks (ANN), partial least squares modelling (PlS) and support vector machines (SVM), to optimize the complete analytical scheme and maximise the predictive capacity of the spectroscopic data. In addition we utilise variable selection techniques to focus on spectral features that provide maximal classification or regress ion of the spectroscopic data against analytical targets. This approach has yielded interesting insights into the variation of biochemical features of the biological system with its state, and has provided the means to develop further the analytical and predictive capabilities of vibrational spectroscopy in biological analysis.

Validation of a Sensitivity Performance Index Test Protocol and Evaluation of Colour Doppler Sensitivity for a Range of Ultrasound Scanners

Jacinta Browne et al. — Tue, 06 Jul 2010 08:56:41 PDT

The ability to detect flow is the most crucial aspect of an ultrasound (US) system because, if flow cannot be detected, no other aspect of performance matters. The objectives of this study were to validate a Doppler “sensitivity performance index,” a figure of merit, and to determine if it could be used to differentiate colour Doppler sensitivity performance in scanners of varying complexity. The sensitivity performance index was developed to give a combined measure of related aspects of sensitivity, such as the lowest detectable velocity, the vessel size and the penetration depth. The colour Doppler sensitivity was evaluated objectively as the lowest detectable velocity signal from the deepest achievable point within the Doppler sensitivity phantom free from extraneous noise in a small diameter vessel (3.2 mm inner diameter). The effect of vessel size and mean velocity on the sensitivity performance index were investigated and it was found that the index was not proportional to vessel size, but this may be accounted for by considering the effect of the acoustic properties of the vessel material, the clutter filter and beam shape. The results obtained using flow phantoms with vessel sizes different from those used in this study are, therefore, not directly comparable to the results found in this study; however, a similar trend should be found in the results for the effect of control settings and a similar range of US scanners. It was found that the Doppler sensitivity performance index was a robust challenging test because none of the US scanners evaluated was capable of achieving the highest sensitivity performance index score, which would be limited by the lowest pump velocity and the deepest point of the vessel within the flow phantom. Therefore, this suggests that this method of determining Doppler sensitivity performance is valuable in the absence of other suitable methods, despite the fact that the relationship between the sensitivity performance index and vessel size is not proportional. Furthermore, use of the Doppler sensitivity performance index for the evaluation of a range of scanners demonstrated that curvilinear transducers have higher sensitivity performance indices than higher-frequency linear transducers, due to the higher achievable penetration depth. The effect of instrument settings was assessed for two transducers, the 4C3 curvilinear general-purpose transducer (Aspen) and the PVM375AT curvilinear general-purpose transducer (Nemio). The colour Doppler sensitivity performance was found to be significantly dependent on the clutter filter setting and the output power setting for both transducers tested. Users need to be aware of the effect of these settings on the colour Doppler sensitivity performance of their US scanner when interpreting the clinical significance of the colour Doppler information.

Assessment of the Acoustic Properties of Common Tissue-mimicking Test Phantoms

Jacinta Browne et al. — Mon, 27 Jul 2009 07:05:03 PDT

Ultrasound (US) test phantoms incorporating tissue-mimicking materials (TMMs) play an important role in the quality control (QC) and performance testing of US equipment. Three commercially available TMMs (ZerdineTM from CIRS Inc.; condensed-milk-based gel from Gammex RMI; urethane-rubber-based from ATS Labs) and a noncommercial agar-based TMM, were investigated. Acoustic properties were measured over the frequency range 2.25 to 15 MHz at a range of ambient temperatures (10 to 35°C). The acoustic velocity of the TMMs remained relatively constant with increasing frequency. Only the agar-based TMM had a linear increase of attenuation with frequency, with the other materials exhibiting nonlinear responses to varying degrees (f1.08 to f1.83). The acoustic velocity and attenuation coefficient of all the TMMs varied with temperature, with the urethane-rubber TMM showing the greatest variation of ± 1.2% for acoustic velocity and ± 12% for attenuation coefficient. The data obtained in this study highlight the importance of greater knowledge of the acoustic behavior of TMMs to variations in both frequency and temperature, to ensure that accurate and precise measurements are obtained during QC and performance testing.

Colour Doppler Spatial Resolution Performance Testing

Jacinta Browne et al. — Mon, 27 Jul 2009 06:50:36 PDT

No abstract available

Investigation of the Effect of Subcutaneous Fat on Image Quality Performance of 2D Conventional Imaging and Tissue Harmonic Imaging

Jacinta Browne et al. — Mon, 27 Jul 2009 06:50:34 PDT

Tissue harmonic imaging (THI) has been reported to improve contrast resolution, tissue differentiation and overall image quality in clinical examinations. However, a study carried out previously by the authors (Browne et al. 2004) found improvements only in spatial resolution and not in contrast resolution or anechoic target detection. This result may have been due to the homogeneity of the phantom. Biologic tissues are generally inhomogeneous and THI has been reported to improve image quality in the presence of large amounts of subcutaneous fat. The aims of the study were to simulate the distortion caused by subcutaneous fat to image quality and thus investigate further the improvements reported in anechoic target detection and contrast resolution performance with THI compared with 2D conventional imaging. In addition, the effect of three different types of fat-mimicking layer on image quality was examined. The abdominal transducer of two ultrasound scanners with 2D conventional imaging and THI were tested, the 4C1 (Aspen-Acuson, Siemens Co., CA, USA) and the C5–2 (ATL HDI 5000, ATL/Philips, Amsterdam, The Netherlands). An ex vivo subcutaneous pig fat layer was used to replicate beam distortion and phase aberration seen clinically in the presence of subcutaneous fat. Three different types of fat-mimicking layers (olive oil, lard and lard with fish oil capsules) were evaluated. The subcutaneous pig fat layer demonstrated an improvement in anechoic target detection with THI compared with 2D conventional imaging, but no improvement was demonstrated in contrast resolution performance; a similar result was found in a previous study conducted by this research group (Browne et al. 2004) while using this tissue-mimicking phantom without a fat layer. Similarly, while using the layers of olive oil, lard and lard with fish oil capsules, improvements due to THI were found in anechoic target detection but, again, no improvements were found for contrast resolution for any of the layer combinations. Therefore, it was felt that the lack of improvement in contrast resolution performance may be due to the test phantom design and not to whether a layer was present that caused beam distortion and phase aberrations.

An Investigation of the Relationship Between In-vitro and In-vivo Ultrasound Image Quality Parameters

Jacinta Browne et al. — Mon, 27 Jul 2009 06:50:32 PDT

The aim of this paper is to investigate the relationship between Bmode and colour Doppler technical test methods with the clinical perception of Bmode and Doppler invivo test parameters. It was found that technical and clinical comparisons between the Bmode test parameters: lateral resolution versus clinical resolution; anechoic target detection versus clinical noise; and penetration depth versus clinically useful penetration depth, demonstrated moderate correlations, (r= 0.69, p

Objective Measurements of Image Quality

Jacinta Browne et al. — Mon, 27 Jul 2009 06:50:30 PDT

Tissue harmonic imaging (THI) and compound imaging have been reported clinically to improve contrast resolution, tissue differentiation and overall image quality. However, there have been limited studies to date to quantify objectively the improvements in image quality achieved with these new imaging techniques. The aim of this study was to quantify differences in image quality that exist between conventional B-mode imaging, harmonic imaging, compound imaging and harmonic compound imaging. An ATL HDI 5000 scanner with three probes (C5-2, L7-4 and L12-5) was tested with two different types of test object, the Gammex-RMI model 404 GS LE and the Gammex-RMI 403 GS LE. The measurement limitations associated with subjective analysis methods were not present in this study because an automated image analysis program was used to determine the image quality parameters. Therefore, subtle differences between the four imaging modes could be detected. Significant improvements in lateral resolution and slice thickness as a function of depth were found with THI. Contrast resolution and anechoic target detection improved with compound imaging, and harmonic compound imaging improved lateral resolution, slice thickness as a function of depth and contrast resolution.

Thickness Variation of Self-processing Acrylamide-based Photopolymer and Reflection Holography

F. T. O'Neill et al. — Wed, 13 May 2009 09:38:28 PDT

There are many types of holographic recording material. The acrylamide-based recording material examined here has one significant advantage: it is self-processing. This simplifies the recording process and enables holographic interferometry to be carried out without the need for complex realignment procedures. However, the effect that the polymerization process has on the grating thickness must be examined. This question is fundamental to the material's use in holographic optical elements, as thickness variations affect the replay conditions of the produced elements. This paper presents a study of this thickness variation and reports for the first time the production of reflection holographic gratings in this material.

Modernization of the Hilger and Watts Guage-block Interferometer

Michael O'Hora et al. — Tue, 12 May 2009 08:54:23 PDT

The Hilger & Watts gauge-block interferometer was designed and manufactured commercially in the 1950s. The instrument uses isotope lamps as wavelength standards to perform absolute length calibration of gauge blocks (slip gauges) up to 100 mm in length, to an accuracy of approximately 1 ppm. It is entirely manually operated. In order to make the instrument more suitable for the modern laboratory, new hardware has been added, and a customized software package developed to automate the measurement process. This paper shows how interferograms may be imaged successfully at each of the eight available wavelengths, and the critical fringe fraction measurement automated, ensuring an accuracy better than ±0.05 fringe. To demonstrate the validity of the new system, representative data are presented alongside data obtained using the traditional method and from an external accredited laboratory.