Separate Slices Research Articles

Integrating spatial and temporal contexts into a factorization model for POI recommendation

ABSTRACTMatrix factorization is one of the most popular methods in recommendation systems. However, it faces two challenges related to the check-in data in point of interest (POI) recommendation: data scarcity and implicit feedback. To solve these problems, we propose a Feature-Space Separated Factorization Model (FSS-FM) in this paper. The model represents the POI feature spaces as separate slices, each of which represents a type of feature. Thus, spatial and temporal information and other contexts can be easily added to compensate for scarce data. Moreover, two commonly used objective functions for the factorization model, the weighted least squares and pairwise ranking functions, are combined to construct a hybrid optimization function. Extensive experiments are conducted on two real-life data sets: Gowalla and Foursquare, and the results are compared with those of baseline methods to evaluate the model. The results suggest that the FSS-FM performs better than state-of-the-art methods in terms of precision and recall on both data sets. The model with separate feature spaces can improve the performance of recommendation. The inclusion of spatial and temporal contexts further leverages the performance, and the spatial context is more influential than the temporal context. In addition, the capacity of hybrid optimization in improving POI recommendation is demonstrated.

Abstract P2-05-25: Predictive value of ultra-high ESR1 mRNA expression in early breast cancer

Abstract Background Quantitative determination of estrogen receptor mRNA expression in luminal breast tumors is predictive for benefit from adjuvant tamoxifen compared to placebo treatment as has been shown in the large randomized NSABP B-14 trial, while protein determination by IHC or LBA is not (Kim et al JCO 2011). Interestingly, the ultrahigh expression of ESR1 mRNA (above ER score 10 by Oncotype test) has been indicative for tamoxifen benefit. This predictive cut-off value of mRNA expression is significantly higher than the diagnostic cut-off (at ER score 6.5). Here we tested wether the ultrahigh expression of ESR1 mRNA determined by commercial MammaTyper® testing is predictive for survival after neoadjuvant chemotherapy treatment of advanced breast cancer. Materials and Methods Pretreatment core cut biopsies from n=54 patients with PBC treated within a randomized phase II trial (2) of anthracyline/taxane based NAC with available clinical follow-up information were examined. RNA was extracted from the FFPE sections and ESR1 mRNA from each section was measured by commercial assays. For technical comparison of ESR1 mRNA values by Oncotype DX versus MammaTyper® from n=113 surgical samples were analyzed by both commercial assays in a blinded fashion. Statistical analysis was performed using the SAS JMP® 9.0.0 software. Results Quantification of ESR1 mRNA expression after RNA extraction from separate slices of 113 primary breast tumors and determination by different commercial RT-qPCR assays resulted in high correlation of continuous expression results (Spearman r=0,85; p<0,0001). The rate of ESR1 mRNA negative cases by both methods by predefined diagnostic cut-offs was low in this cohort (1/113 and 6/113, respectively) resulting in high concordance for positive ER status by both methods.The median expression of ER score and ESR1 40-DDCq was high (10,2 and 39,8, respectively) and almost exactly at the predictive ER score cut-off. Hence, the Tamoxifen benefit cut-off of ER score 10 by Oncotype is comparable with a 40-DDCqvalue of 39,6 for ESR1 mRNA determination by MammaTyper®, which resembles an ESR1 mRNA expression 3fold above the diagnostic cut-off. In the independent chemotherapy cohort theoptimal discrimination for overall survival could be achieved by an elevated ESR1 mRNA expression exactly at 39,6 resulting in 100% overall survival for ultra-high expressors and 75 % overall survival for lower ESR1 mRNA expression after 5 years (p=0,006). Conclusion Previous data suggest that ultrahigh expression of ESR1 mRNA is predictive for improved overall survival and tamoxifen benefit (1). Here we show that ultrahigh expression of ESR1 mRNA is also prognostic in more advanced breast tumors after neoadjuvant chemotherapy. These findings validate the importance of quantitative determination of estrogen receptor expression and substantiate the understanding of receptor expression being a continuous determinant with indication specific cut-off values. Ultrahigh expression of ESR1 seems to identify a distinct subset of luminal breast tumors with superior prognosis and benefit from tamoxifen treatment. These findings warrant further investigation, which are currently being done in independent large breast cancer cohorts. Citation Format: Wirtz RM, Scheffen I, Marme F, Laible M, Sclombs K, Schumacher C, Schneeweiss A, Eidt S, Sinn H-P. Predictive value of ultra-high ESR1 mRNA expression in early breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-05-25.

Microstructural evolution in multiseeded YBCO bulk samples grown by the TSMG process

Superconducting single-grain YBCO bulk samples with the ability to trap high magnetic fields can be grown using the top-seeded melt-growth process. Multiseeding techniques have the potential to enable larger diameter bulks to be grown, but the performance of these materials is not yet comparable to the single-seeded bulks. Here we carry out detailed three-dimensional microstructural characterisation on a multiseeded sample grown with the seeds aligned in the 0°–0° geometry using high resolution microanalysis techniques. Chemical and structural variations have been correlated with the trapped field distribution in three separate slices of the sample. The top slice of the sample shows four peaks in trapped field, indicating that the current flows in four separate loops rather than in one large loop within the sample. This has been explained by the build-up in insulating Y-211 particles where the growth fronts from the two seeds meet, forming a barrier to current flow, as well as the low Y-211 content (and hence low Jc) of the large c-axis growth sector.

High Femoral Anteversion Is Related to Femoral Trochlea Dysplasia

To investigate the possible relation between femoral anteversion (AV) and trochlear morphology. Among 560 available lower-limb computed tomography (CT) scans, those with previous fracture, arthroplasty, or osteotomy were excluded and 40 cases were randomly selected. The following 4 lines were determined from the CT scans: 1 through the center of the femoral head and neck; 1 through the lesser trochanter and the center of the femoral shaft; 1 as a tangent to the dorsal part of the distal femur, just above the gastrocnemius insertion; and 1 as a tangent to the posterior condyles. Between the respective lines, the following parameters of femoral AV were determined: (1) total AV, (2) proximal AV, (3) diaphyseal AV, and (4) distal AV. Trochlea parameters were determined from 2 separate axial CT slices (proximal trochlea and 5mm farther distally): trochlea height (medial, central, lateral), transverse trochlea shift, trochlea depth, sulcus angle, lateral trochlea slope, and Dejour trochlea type. To prove or disprove our study hypothesis, a correlation analysis was performed between the variables of AV and trochlear morphology. The total AV was significantly correlated with the trochlea parameters trochlea depth (P= .032), sulcus angle (P= .05), and lateral trochlea slope (P= .001). The diaphyseal AV was significantly correlated with the sulcus angle (P= .009). The distal AV showed significant correlations with medial, central, and lateral trochlea height (.005 <P < .032) and with Dejour trochlea type (P= .043). The morphology of the trochlea is significantly related to femoral AV. Increased AV is associated with a flatter, more dysplastic trochlea. This was particularly true for AV located at the distal femur. Level III, diagnostic study of nonconsecutive patients.

Trace element composition of rutile and Zr-in-rutile thermometry in meta-ophiolitic rocks from the Kazdağ Massif, NW Turkey

In northwest Turkey, ophiolitic meta-gabbros are exposed on the Kazdag Massif located in the southern part of the Biga Peninsula. Trace element composition of rutile and Zr-in-rutile temperatures were determined for meta-gabbros from the Kazdag Massif. The Zr content of all rutiles range from 176 to 428 ppm and rutile grains usually have a homogeneous Zr distribution. The rutile grains from studied samples in the Kazdag Massif are dominated by subchondritic Nb/Ta (11–19) and Zr/Hf ratios (20–33). Nb/Ta and Zr/Hf show positive correlation, which is probably produced by silicate fractionation. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents. The core of rutile grains are generally characterized by low Nb/Ta ratios of 17–18 whereas the rims exhibit relatively high Nb/Ta ratios of 19–23. Trace element analyses in rutile suggest that these rutile grains were grown from metamorphic fluids. The P-T conditions of meta-gabbros were estimated by both Fe–Mg exchange and Zr-in-rutile thermometers, as well as by the Grt-Hb-Plg-Q geothermobarometer. The temperature range of 639 to 662 °C calculated at 9 kbar using the Zr-in-rutile thermometer is comparable with temperature estimates of the Fe-Mg exchange thermometer, which records amphibolite-facies metamorphism of intermediate P-T conditions. The P-T conditions of meta-ophiolitic rocks suggest that they occur as a different separate higher-pressure tectonic slice in the Kazdag metamorphic sequence. Amphibolite-facies metamorphism resulted from northward subduction of the Izmir-Ankara branch of the Neo-Tethyan Ocean under the Sakarya Zone. Metamorphism was followed by internal imbrication of the Kazdag metamorphic sequence resulting from southerly directed compression during the collision.

Spinal cord-midbrain functional connectivity is related to perceived pain intensity: a combined spino-cortical FMRI study.

The dynamic interaction between ascending spinocortical nociceptive signaling and the descending control of the dorsal horn (DH) by brain regions such as the periaqueductal gray matter (PAG) plays a critical role in acute and chronic pain. To noninvasively investigate the processing of nociceptive stimuli in humans, previous fMRI studies either focused exclusively on the brain or, more recently, on the spinal cord. However, to relate neuronal responses in the brain to responses in the spinal cord and to assess the functional interplay between both sites in normal and aberrant conditions, fMRI of both regions within one experiment is necessary. Employing a new MRI acquisition protocol with two separate slice stacks, individually adapted resolutions and parameter settings that are dynamically updated to the optimized settings for the respective region we assessed neuronal activity in the spinal cord and in the brain within one measurement at 3 T. Using a parametric pain paradigm with thermal stimulation to the left radial forearm, we observed BOLD responses in the ipsilateral DH of the spinal segment C6 and corresponding neuronal responses in typical pain-processing brain regions. Based on correlations of adjusted time series, we are able to reveal functional connectivity between the spinal C6-DH and the thalamus, primary somatosensory cortex, bilateral insula, bilateral striatum, and key structures of the descending pain-modulatory system such as the PAG, the hypothalamus, and the amygdala. Importantly, the individual strength of the spinal-PAG coupling predicted individual pain ratings highlighting the functional relevance of this system during physiological pain signaling.

Alteration of Airway Reactivity and Reduction of Ryanodine Receptor Expression by Cigarette Smoke in Mice.

Small airways are a major site of airflow limitation in chronic obstructive pulmonary disease (COPD). Despite the detrimental effects of long-term smoking in COPD, the effects of acute cigarette smoke (CS) exposure on small airway reactivity have not been fully elucidated. Balb/C mice were exposed to room air (sham) or CS for 4 days to cause airway inflammation. Changes in small airway lumen area in response to contractile agents were measured in lung slices in situ using phase-contrast microscopy. Separate slices were pharmacologically maintained at constant intracellular Ca(2+) using caffeine/ryanodine before contractile measurements. Gene and protein analysis of contractile signaling pathways were performed on separate lungs. Monophasic contraction to serotonin became biphasic after CS exposure, whereas contraction to methacholine was unaltered. This altered pattern of contraction was normalized by caffeine/ryanodine. Expression of contractile agonist-specific receptors was unaltered; however, all isoforms of the ryanodine receptor were down-regulated. This is the first study to show that acute CS exposure selectively alters small airway contraction to serotonin and down-regulates ryanodine receptors involved in maintaining Ca(2+) oscillations in airway smooth muscle. Understanding the contribution of ryanodine receptors to altered airway reactivity may inform the development of novel treatment strategies for COPD.

A Rate-Distortion Optimized Coding Method for Region of Interest in Scalable Video Coding

The support for region of interest (ROI) browsing, which allows dropping background part of video bitstreams, is a desirable feature for video applications. With the help of the slice group technique provided by H.264/SVC, rectangular ROI areas can be encoded into separate ROI slices. Additionally, by imposing certain constraints on motion estimation, ROI part of the bitstream can be decoded without background slices of the same layer. However, due to the additional spatial and temporal constraints applied to the encoder, overall coding efficiency would be significantly decreased. In this paper, a rate-distortion optimized (RDO) encoding scheme is proposed to improve the coding efficiency of ROI slices. When background slices are discarded, the proposed method uses base layer information to generate the prediction signal of the enhancement layer. Thus, the temporal constraints can be loosened during the encoding process. To do it in this way, the possible mismatch between generated reference frames and original ones is also considered during rate-distortion optimization so that a reasonable trade-off between coding efficiency and decoding drift can be made. Besides, a new Lagrange multiplier derivation method is developed for further coding performance improvement. Experimental results demonstrate that the proposed method achieves significant bitrate saving compared to existing methods.

Ultrashort x-ray pulse generation by electron beam slicing in storage rings

We propose a new method to generate ultrashort x-ray pulses using focused short low energy ($\ensuremath{\sim}20\text{ }\mathrm{MeV}$) electron bunches to create short slices of electrons from the circulating electron bunches in a synchrotron radiation storage ring. When a low energy electron bunch crosses from the top of a high energy storage ring electron bunch, its Coulomb force will kick a short slice from the core of the storage ring electron bunch. The separated slices, when passing through an undulator, will radiate ultrashort x-ray pulses at about 160 fs. We discuss the advantages, challenges, and provide data which confirm the feasibility of this new method.

Accelerated human cardiac diffusion tensor imaging using simultaneous multislice imaging

To demonstrate the feasibility of accelerating measurements of cardiac fiber structure using simultaneous multislice (SMS) imaging. SMS excitation with a blipped controlled aliasing (CAIPI) readout was incorporated into a diffusion-encoded stimulated echo pulse sequence to obtain diffusion measurements in three separate slices of the heart (8-mm thickness, 12-mm gap). A novel image entropy-based method for removing image ghosts in blipped CAIPI acquisitions is also introduced that enables SMS imaging of closely spaced slices in the heart. The average retained signal-to-noise ratio (SNR) using this acquisition scheme is 70% ± 5%, higher than the standard 1/3 = 57% SNR penalty with three-fold acceleration. No significant difference was observed in the apparent diffusion coefficient and helix angle diffusion parameters between a time-equivalent conventional single-slice scan and the three-fold accelerated SMS acquisition. A 10% mean bias was observed in fractional anisotropy between single-slice and SMS acquisitions. The new sequence was used to obtain high-quality diffusion measurements in three closely spaced cardiac slices in a clinically feasible nine breath-hold examination. The accelerated multiband sequence is anticipated to improve quantitative measurements of cardiac microstructure by reducing the number of breath-holds required for the scan, making it practical to incorporate diffusion tensor measurements within a comprehensive clinical examination.

Abstract T P28: Brain MRI FLAIR Signal Intensity Ratio Is Correlated With Matrix Metalloproteinase-9 Level In Acute Ischemic Stroke

Introduction: Increased Matrix Metalloproteinase-9 (MMP9) level is associated with symptomatic hemorrhagic transformation (HT) after stroke. Higher risk of HT has also been reported in patients with early FLAIR hyperintensity on brain MRI. Hypothesis: We assessed whether FLAIR hyperintensity is associated with MMP9 levels. Methods: We retrospectively analyzed a cohort of acute stroke subjects who had acute brain MRI images and blood samples within the first 12 hours after onset of stroke. FLAIR hyperintensity was quantitatively assessed using FLAIR signal intensity ratio between the stroke lesion and corresponding normal contralateral hemispheres. For each subject, the FLAIR ratio was generated from the average of 6 regions of interest: 2 white matter and 2 gray matter regions each on 2 separate slices. MMP9 was measured using standard ELISA technique. Univariate and multivariate analyses were used to evaluate the relationship between FR and MMP9 and clinical covariates. Results: 180 subjects had brain MRI and MMP9 available for analysis. MRI occurred within 6 ±3 hours and blood samples were drawn within 7 ± 4 hours from last seen well time. The mean MMP9 level was 238 ± 242 ng/mL and the mean FLAIR ratio was 1.40± 0.23. In univariate analysis, FLAIR ratio was associated with time to MRI (r= 0.18, p=0.01) and MMP9 (r=0.29, p&lt;0.001). In multivariate analysis both FLAIR ratio (p&lt;0.001) and time to MRI (p=0.003) remained associated with MMP9. Conclusions: There is a significant association between FLAIR ratio and MMP9 in acute stroke subjects. This raises the possibility that FLAIR hyperintensity reflects blood brain barrier changes during ischemia. Future studies to validate the prognostic value of FLAIR ratio in predicting symptomatic hemorrhagic transformation are warranted.

Nitric oxide‐dependent long‐term depression but not endocannabinoid‐mediated long‐term potentiation is crucial for visual recognition memory

Synaptic plasticity in perirhinal cortex is essential for recognition memory. Nitric oxide and endocannabinoids (eCBs), which are produced in the postsynaptic cell and act on the presynaptic terminal, are implicated in mechanisms of long-term potentiation (LTP) and long-term depression (LTD) in other brain regions. In this study, we examine these two retrograde signalling cascades in perirhinal cortex synaptic plasticity and in visual recognition memory in the rat. We show that inhibition of NO-dependent signalling prevented both carbachol- and activity (5 Hz)-dependent LTD but not activity (100 Hz theta burst)-dependent LTP in the rat perirhinal cortex in vitro. In contrast, inhibition of the eCB-dependent signalling prevented LTP but not the two forms of LTD in vitro. Local administration into perirhinal cortex of the nitric oxide synthase inhibitor NPA (2 μm) disrupted acquisition of long-term visual recognition memory. In contrast, AM251 (10 μm), a cannabinoid receptor 1 antagonist, did not impair visual recognition memory. The results of this study demonstrate dissociation between putative retrograde signalling mechanisms in LTD and LTP in perirhinal cortex. Thus, LTP relies on cannabinoid but not NO signalling, whilst LTD relies on NO- but not eCB-dependent signalling. Critically, these results also establish, for the first time, that NO- but not eCB-dependent signalling is important in perirhinal cortex-dependent visual recognition memory.

Simulation and analysis of nonlinear self-focusing phenomenon based on ray-tracing

The simulation of nonlinear self-focusing phenomenon using ray-tracing method can macroscopically provide an intuitive picture of the propagation of light in a self-focusing material, without adopting paraxial approximation or self-similar hypothesis. In this paper, propagation of light is sampled by discrete slices along a certain direction. Thus nonlinear propagation is turned into the combination of optical modulation of the refractive index on separate slices and linear propagation between each two adjacent slices. On each slice, after calculating the flux, we use a novel algorithm to suppress the quantized errors. For the linear propagating process, Adams method is adopted to solve the ray equations, which solve the problem that the widely used Runge-Kutta method cannot be used in simulation of light in nonlinear materials. The simulation results reveal that there are several foci along the propagating axis and the location of the first focus becomes closer to the incident plane as the power of light goes up. Furthermore, because the program traces real rays, it is possible to reach the non-paraxial region and reveal the phenomenon of ring-structure flux distributions caused by self-focusing. This is significant for the safety of high-power laser systems. Some commercial optical design and simulation software are also based on ray-tracing methods. Thus the systems including both nonlinear and linear materials are possible to simulate, which can guide people to set up the corresponding experimental systems.

Allochthonous Mesozoic marine sequences of northeastern Asia and western North America: Correlation of the stratigraphic levels and geodynamic depositional settings

The problem of correlating the isolated outcrops of allochthonous Middle Mesozoic deposits developed in northeastern Asia and western North America includes several aspects: (1) the stratigraphic subdivision of the sequences using the radiolarian assemblages and taking into account the complex nappe-thrust structure of the region; (2) the analysis of their facies composition with reconstructing the geodynamic depositional settings; (3) the search for features in common (with respect to the previous two aspects) in all these localities. The first widely applied radiolarian analysis revealed that the Middle Mesozoic marine rocks from separate nappes and slices of tectono-stratigraphic sections in East Asia enclose 20 different-age (Norian to Hauterivian) radiolarian assemblages. The correlation of these assemblages revealed the wide lateral distribution of their host Middle Mesozoic marine sequences in the regions under consideration. The significance of the presented materials is determined by the following facts: (1) using the radiolarian analysis, the Middle Mesozoic marine sequences of northeastern Asia are first subdivided into stage and substage units with defining their analogs in western North America; (2) despite the discrete distribution of Mesozoic allochthons, it is shown that the defined stratigraphic units are widespread in northeastern Asia; (3) it is established that these allochthons consist of rocks formed in different geodynamic depositional settings: ocean floor, island arc, fore-arc, and marginal-sea domains. This spectrum of heterogeneous rocks is traceable practically through the entire northeastern Asia region.

Jadeitite from Guatemala: new observations and distinctions among multiple occurrences

In Guatemala, jadeitite occurs as blocks in serpentinite melange in distinct settings on opposite sides of the Motagua fault. Jadeitites north of the Motagua fault are associated with eclogites, blueschists, and garnet amphibolites and distributed over a 200km E-W area. Omphacitite, omphacite - taramite metabasite, albitite, and phengite rock are found with jadeitite. The assemblages indicate formation at 6-12kbar and 300-400°C, however jadeite - omphacite pairs yield T from ~200 to gt;500oC for jadeite crystallization. Jadeitites south of the Motagua fault are sourced from three separate fault slices of serpentinite in Jalapa and Zacapa departments and are distinctive: 1) Jadeitite near Carrizal Grande is found in serpentinite with lawsonite eclogites, variably altered to blueschist, and rarely in schists. A large jadeite – omphacite gap and lawsonite suggests T=300-400°C, but at high P as indicated by the presence of quartz: Pgt;12-20kbar. Lawsonite eclogites (P=20-25kbar, T=350-450°C) occur with these jadeitites. 2) At La Ceiba, jadeitites coexist with omphacite blueschists and contain late-stage veins of quartz, diopside, cymrite, actinolite, titanite and vesuvianite. A large jadeite – omphacite gap suggests 300-400°C, but at lower P as indicated by quartz + albite: P=10-14kbar. 3) At La Ensenada jade i tites occur with lawsonite-glaucophane blueschists and chloritite. It is a fine-grained jadeite-pumpellyite rock, intensely deformed and veined with grossular, omphacite, albite and titanite, but no quartz. A large jadeite–omphacite gap and pumpellyite suggest ~200-~300°C at lower P consistent with primary albite: P=6-9kbar. The silicates contain little iron

A dual-slice k-t approach for highly accelerated flow MRI

We propose the combination of k-t undersampling with a dual slice excitation approach. The dual slice excitation and reconstruction principle is incorporated into the k-t SENSE reconstruction framework, allowing a doubling of the net acceleration factor when acquiring two slices as compared to acquiring two separate undersampled slices.

Dynamic visualizations of language change

This paper uses diachronic corpus data to visualize language change in a dynamic fashion. Bivariate and multivariate data sets form the input for so-called motion charts, i.e. series of diachronically ordered scatterplots that can be viewed in sequence. Based on data from COHA (Davies 2010), two case studies illustrate recent changes in American English. The first study visualizes change in a diachronic analysis of ambicategorical nouns and verbs such as hope or drink; the second study shows structural change in the behavior of complement-taking predicates such as expect or remember. Whereas motion charts are typically used to represent bivariate data sets, it is argued here that they are also useful for the analysis of multivariate data over time. The present paper submits multivariate diachronic data to a multi-dimensional scaling analysis. Viewing the resulting data points in separate time slices offers a holistic and intuitive representation of complex linguistic change.

Quantification of uncertainties involved in the conformational study of polymers by light scattering

Gel permeation chromatography (GPC) combined with a multi-angle light scattering (MALS) is a very powerful characterization technique because it provides both absolute molecular weight ( M w) and the radius of gyration ( R g) throughout the separated slices obtained by GPC. This combination of M w and R g, can be used to obtain information about the conformation of polymer chains in solutions and the branching of molecules. Due to the interesting properties obtained for polymers, it is essential to quantify the effect of different error sources in light scattering measurements as well as in the data treatment that highly affect the accuracy of obtained molar mass and radius of gyration. Usually, the results obtained for M w and R g in this analysis are dispersed for determined ranges of retention time and to have both reliable R g and M w for calculation, only high confidence data points have to be chosen. This range is arbitrarily chosen by the user for the data observation. In this work a new method of calculation to obtain R g and M w by means of GPC–MALS technique has been developed. As a first point, a data analysis procedure was set in order to describe both R g and M w vs. retention time and to determine the range where experimental data are confident. Several aspects in the data analysis have been studied. The polynomial fit function, the influence of the concentration of the sample, the reproducibility of the experiments and the conformational scaling law have been investigated by statistic technique in order to quantify the uncertainties involved.

Design, manufacture, and evaluation of an anthropomorphic pelvic phantom purpose-built for radiotherapy dosimetric intercomparison

An anthropomorphic pelvic phantom was designed and constructed to meet specific criteria for multicenter radiotherapy dosimetric intercomparison. Three dimensional external and organ outlines were generated from a computed tomography image set of a male pelvis, forming the basis of design for an anatomically realistic phantom. Clinically relevant points of interest were selected throughout the dataset where point-dose values could be measured with thermoluminescence dosimeters and a small-volume ionization chamber. Following testing, three materials were selected and the phantom was manufactured using modern prototyping techniques into five separate coronal slices. Time lines and resource requirements for the phantom design and manufacture were recorded. The ability of the phantom to mimic the entire treatment chain was tested. The phantom CT images indicated that organ densities and geometries were comparable to those of the original patient. The phantom proved simple to load for dosimetry and rapid to assemble. Due to heat release during manufacture, small air gaps and density heterogeneities were present throughout the phantom. The overall cost for production of the prototype phantom was comparable to other commercial anthropomorphic phantoms. The phantom was shown to be suitable for use as a "patient" to mimic the entire treatment chain for typical external beam radiotherapy for prostate and rectal cancer. The phantom constructed for the present study incorporates all characteristics necessary for accurate Level III intercomparison studies. Following use in an extensive Level III dosimetric comparison over a large time scale and geographic area, the phantom retained mechanical stability and did not show signs of radiation-induced degradation.

Inverse-direction scanning improves the image quality of whole carotid CT angiography with 64-MDCT

The purpose of this prospective study was to clarify whether reducing the incidence of perivenous artifacts through craniocaudal scanning improves the quality of 64-multidetecter computed tomography (MDCT) angiography images of the whole carotid artery. Forty patients underwent MDCT angiography in the caudocranial (n=20) or craniocaudal (n=20) direction in 2007. All patients were injected with 75 ml of contrast media followed by a 35-ml saline chaser bolus at 4.0 ml/s in the right antecubital vein. Maximum intensity projection (MIP) images were scored according to image quality on a scale of 1-5. Bilateral arterial and venous attenuation was measured on 10 separated slices. We compared the mean image quality score of the two groups (i.e. those scanned caudocranially and those scanned craniocaudally). We analyzed the correlation between vascular attenuation and mean image quality. Compared with the caudocranial group, the craniocaudal group had higher image quality scores (median, 3.70 vs. 3.40; 95% CI, 3.50-3.96 vs. 3.06-3.60; p<0.05), higher arterial attenuation (median, 550 HU vs. 489 HU; range, 270-686 vs. 302-574; p<0.05), and lower maximum venous attenuation (median, 436 vs. 1452 HU; range, 250-617 vs. 377-2044; p<0.01). Multiple regression analysis revealed that the most significant correlation factor with image quality was minimum arterial attenuation (R2=0.42, p<0.001) measured near the brachiocephalic artery. In the caudocranial group only, there was a negative correlation between right brachiocephalic venous attenuation and minimum arterial attenuation. Compared with conventional caudocranial scanning, craniocaudal scanning improves the image quality of 64-MDCT angiography images of the whole carotid artery.