Slice Spacing Research Articles

Optimizing the efficiency of high‐field multivoxel spectroscopic imaging by multiplexing in space and time

A new strategy to yield information from the maximum number of voxels, each at the optimum signal-to-noise ratio (SNR) per unit time, in MR spectroscopic imaging (MRSI) is introduced. In the past, maximum acquisition duty-cycle was obtained by multiplexing in time several single slices each repetition time (TR), while optimal SNR was achieved by encoding the entire volume of interest (VOI) each TR. We show that optimal SNR and acquisition efficiency can both be achieved simultaneously by multiplexing in space and time several slabs of several slices, each. Since coverage of common VOIs in 3D proton MRSI in the human brain typically requires eight or more slices, at 3 T or higher magnetic fields, two or more slabs can fit into the optimum TR (approximately 1.6 s). Since typically four or less slices would then fit into each slab, Hadamard encoding is favored in that direction for slice profile reasons. It is demonstrated that per fixed examination length, the new method gives, at 3 T, twice as many voxels, each of the same SNR and size, compared with current 3D chemical shift imaging techniques. It is shown that this gain will increase for more extensive spatial coverage or higher fields.

SU‐FF‐T‐336: Multi‐Slice Tomotherapy Delivery Methods Using a Novel Multileaf Collimator

Purpose: In this study, we present an initial dosimetric investigation of multi‐slice tomotherapy delivery methods using a novel multileaf collimator design. Method and Materials: A compact multileaf collimator design for multi‐slice tomotherapy is under investigation. Intensity modulation is achieved through binary actuation of adjacent pivoting leaves with multiple leaf banks employed to deliver multi‐slice tomotherapy. Pitch may be determined by the ratio of the couch travel distance for a complete gantry rotation divided by the slice width at the axis of rotation. For multi‐slice tomotherapy the concept of pitch is complicated by the use of multiple collimated slices and differing fan beam divergences. We have studied the dosimetric effect of: (a) using regular pitch, where a given collimated slice does not irradiate beyond the adjacent slice and (b) using multi‐slice pitch, where different collimated slices irradiate the same region in the patient. Other novel aspects of tomotherapy delivery with the multi‐slice collimator are presented. Results: The multi‐slice pitch delivery method allows for treatment of extended volumes greater than the spacing between slices, without the junctioning effect of the regular pitch method. A pitch less than 1 may be achieved when considering irradiation from different collimated slices and is a determined by the slice spacing, slice width and couch travel. The difference in fan beam divergence in the axial direction may be clinically advantageous. Single‐slice techniques may also benefit from non‐coplanar delivery. Conclusions: A method for multi‐slice tomotherapy delivery is investigated. Dosimetric results are presented for various methods of dose delivery including a multi‐slice pitch method for extended treatment lengths. Multi‐slice delivery will result in shorter treatment times for both linac and cobalt‐based tomotherapy systems and development of novel radiation therapy techniques. Conflict of Interest: Research was supported in part through a licensing agreement with TomoTherapy Inc.

MO‐D‐ValB‐02: OpenGL Based 2D‐3D Registration of a CT Image Dataset With OBI Images

Introduction. A limiting factor in registration of a three‐dimensional (3D) computed tomography (CT) dataset with two‐dimensional (2D) x‐ray images has been the time‐consuming generation of digitally reconstructed radiographs (DRRs). This can be overcome using a commercial graphics card for DRR generation enabling fast, robust, and accurate automatic image‐based 2D‐3D registration. Methods and Materials. For the iterative registration process hundreds of DRRs are created using hardware rendering in OpenGL. Each DRR from a 512×512×100 CT volume is rendered in less than 0.1 seconds using an nVidia 7800GT graphics card. The registration is based on a publicly available implementation of Mattes Mutual Information (ITK, U.S. National Library of Medicine, Bethesda, MD). To improve speed, the registration is performed on a sub‐image. A two‐step registration strategy is adopted for robustness with the first pass using a larger margin around the sub‐image and a down‐sampled resolution. A thoracic phantom (Model 602, CIRS, Norfolk, VA) was imaged and setup according to our clinical protocol and then shifted from 0–1.5 cm along each of the major axes. Anterior‐Posterior and Lateral kV x‐ray images were acquired using a commercial patient imaging system (OBI, Varian Medical System, Palo Alto, CA). Results: The mean registration times were 8 and 16 seconds without and with rotations respectively. We observed a systematic 1.1 mm offset in the longitudinal direction that we believe results from 2.5 mm CT slice spacing and OBI calibration. With this removed the mean three‐dimensional distance of the registered positions from the phantom positions was 0.4 mm with the largest disagreement being 0.75 mm. The systems ability to calculate rotations was only tested numerically.Conclusions. The speed and accuracy of this system demonstrate that it could be a viable tool for reducing daily setup uncertainty by automating the analysis of setup images.Research sponsored by Phillips Medical Systems.

TH‐C‐ValB‐01: Prostate Contouring Uncertainty in Mega‐Voltage Computed Tomography (MVCT) Images Acquired with a Helical Tomotherapy Unit During Image‐Guided Radiation Therapy (IGRT)

Purpose: To evaluate the image guidance capabilities of helical tomotherapy‐based MVCT, this work compares the inter‐ and intra‐observer contouring uncertainty in KVCT used for radiotherapy planning with MVCT acquired with a tomotherapy unit. Methods and Materials: Five prostate cancer patients who underwent tomotherapy treatment (with daily MVCT) at our institution were selected. One planning KVCT and one randomly selected MVCT from each patient were used. Slice spacings for KVCT and MVCT were 3 mm and 6 mm, respectively. Retrograde urethrography was performed on the KVCT studies only. For inter‐observer study, seven observers contoured the prostate on the 10 CT studies. For intra‐observer study, the same seven observers repeat‐contoured one patient's KVCT and MVCT studies. Quantitative analysis of contour variations was performed using volumes and radial distances. F‐test was performed to detect statistically significant differences between KVCT and MVCT. Results: The inter‐ and intra‐observer contouring variability was larger in MVCT than KVCT. The largest variability was mainly found in the prostate apex and base regions. Up to 1 cm (SD) was found in MVCT. In the prostate apex region, interestingly, large but similar variability between KVCT and MVCT was observed. This suggest that the use of urethrography during KVCT simulation was not very helpful. For F‐test, generally, the regions with significant differences were patient‐dependent and uniformly distributed in all directions. In terms of prostate volume, observers consistenly contoured larger prostate in MVCT (by 10 %). This reflects the poorer soft‐tissue contrast in MVCT than KVCT since observers tend to over‐estimate or over‐draw target volumes under less visible conditions. Conclusions: Based on our data, the application of MVCT for estimating daily organ motion and deformation during image‐guided radiotherapy (IGRT) is somewhat discouraging. Optimization of slice thickness and dose utilization may result in better imaging performance for prostate delineation and adaptive tomotherapy.

Phased-Array Design for Biological Clutter Rejection: Simulation and Experimental Validation

Abstract This paper highlights recent results obtained with the Turbulent Eddy Profiler (TEP), which was developed by the University of Massachusetts. This unique 915-MHz radar has up to 64 spatially separated receiving elements, each with an independent receiver. The calibrated raw data provided by this array could be processed using sophisticated imaging algorithms to resolve the horizontal structures within each range gate. After collecting all of the closely spaced horizontal slices, the TEP radar can produce three-dimensional images of echo power, radial velocity, and spectral width. From the radial velocity measurements, it is possible to estimate the three-dimensional wind with high horizontal and vertical resolution. Given the flexibility of the TEP system, various array configurations are possible. In the present work exploitation of the flexibility of TEP is attempted to enhance the rejection of clutter from unwanted biological targets. From statistical studies, most biological clutter results from targets outside the main imaging field of view, that is, the sidelobes and grating lobes (if they exist) of the receiving beam. Because the TEP array's minimum receiver separation exceeds the spatial Nyquist sampling requirement, substantial possibilities for grating-lobe clutter exist and are observed in actual array data. When imaging over the transmit beam volume, the receiving array main lobe is scanned over a ±12.5° region. This scanning also sweeps the grating lobes over a wide angular region, virtually guaranteeing that a biological scatterer outside of the main beam will appear somewhere in the imaged volume. This paper focuses on suppressing pointlike targets in the grating-lobe regions. With a subtle change to the standard TEP array hardware configuration, it is shown via simulations and actual experimental observations (collected in June 2003) that adaptive beamforming methods can subsequently be used to significantly suppress the effects of point targets on the wind field estimates. These pointlike targets can be birds or planes with strong reflectivity. By pointlike the authors mean its appearance is a distinct point (up to the imaging resolution) in the images. The pointlike strong reflectivity signature exploits the capability of adaptive beamforming to suppress the interference using the new array configuration. It should be noted that this same array configuration does not exhibit this beneficial effect when standard Fourier beamforming is employed.

FESS control: Realization and evaluation of navigated control for functional endoscopic sinus surgery

In this paper, a new system for navigated control in functional endoscopic sinus surgery (FESS) is presented. The system allows the safe and convenient use of a shaver that can be enabled by the surgeon only within a specified working space. Preoperatively, the surgeon defines this working space in the axial slices of the CT scan. During the surgery, the positions of the shaver and patient are tracked by an optical navigation system, which calculates whether the shaver is within the working space. The navigated control electronics receives a signal from the navigation system and disables the shaver if it is outside the working space. If the shaver is inside the working space, the surgeon can set its speed freely with a foot pedal. Experimental evaluation shows that the system allows convenient and intuitive safe removal of inflamed tissue while protecting sensitive structures. The clinical applicability was proven in a clinical trial with 10 patients.

Modeling, description, and characterization of fractal pore via mathematical morphology

The aim of this paper is to provide description of fast, simple computational algorithms based upon mathematical morphology techniques to extract descriptions of pore channels—throats—and bodies and to represent them in 3D space, and to produce statistical characterization of their descriptions. Towards this goal, a model fractal binary pore is considered and is eroded recursively to generate different slices possessing decreasing degrees of porosity. By employing simple morphology-based approach, each slice of this pore space is decomposed into pore-channel, pore-throat, and pore-body, which are abstract structures that summarize the overall connectivity, orientation, and shape of the pore space. We consider the pore slices and their corresponding morphological quantities to stack them to further represent them in 3D space. We further provide a formulation essentially based on set theory to represent these three morphologic quantities to connect them appropriately across slices. The connected quantities are further fragmented to designate each fragmented portion with orders ranging from 1 toN.

Image coding of 3D volume using wavelet transform for fast retrieval of 2D images

An encoder/decoder system for 3D volumetric medical data is proposed. The system allows fast access to any 2D image by decoding only the relevant information from each subband image and thus provides minimum decoding time. This will be of immense use for the medical community because most of the computerised tomography, magnetic resonance imaging and positron emission tomography modalities produce volumetric data. As a fully fledged 3D wavelet transform is used for compression, the advantage of good compression ratio is preserved. Preprocessing is carried out prior to wavelet transform, to enable easier identification of coefficients from each subband image. Inclusion of special characters in the bit stream (markers) facilitates access to corresponding information from the encoded data. Experiments are carried out by performing Daub4 filter along x (row) and y (column) directions and Haar filter along the z (slice) direction to account for the difference between interslice and intraslice resolution. The performance of the system has been evaluated on four sets of volumetric data and the results are compared to other 3D encoding/2D decoding schemes. Results show that for slice spacing of 3–10 mm, there is substantial improvement in decoding time. The speedup is found to be 2.

Effect of DRR Resolution on Assessment of Patient Position for Head and Neck IMRT

Purpose/Objective: To evaluate the effect of CT slice thickness and spacing on the spatial resolution of digitally reconstructed radiographs (DRRs) and on the ability to accurately assess patient positioning errors for IMRT treatment of head and neck cancers. For IMRT head and neck treatments, patient set-up accuracy is typically assessed by comparison of megavoltage treatment portals to DRRs. With the replacement of radiographic portal films by electronic portal imaging devices (EPIDs) and the introduction of multislice CT scanners capable of enhanced resolution images and DRRs for radiotherapy, there is the potential to visualize finer anatomic details, which may lead to more accurate assessment of shifts and rotations in patient position.

The littlest Higgs in anti-de Sitter space

We implement the SU(5)/SO(5) littlest Higgs theory in a slice of 5D Anti-de Sitter space bounded by a UV brane and an IR brane. In this model, there is a bulk SU(5) gauge symmetry that is broken to SO(5) on the IR brane, and the Higgs boson is contained in the Goldstones from this breaking. All of the interactions on the IR brane preserve the global symmetries that protect the Higgs mass, but a radiative potential is generated through loops that stretch to the UV brane where there are explicit SU(5) violating boundary conditions. Like the original littlest Higgs, this model exhibits collective breaking in that two interactions must be turned on in order to generate a Higgs potential. In AdS space, however, collective breaking does not appear in coupling constants directly but rather in the choice of UV brane boundary conditions. We match this AdS construction to the known low energy structure of the littlest Higgs and comment on some of the tensions inherent in the AdS construction. We calculate the 5D Coleman-Weinberg effective potential for the Higgs and find that collective breaking is manifest. In a simplified model with only the SU(2) gauge structure and the top quark, the physical Higgs mass can be of order 200 GeV with no considerable fine tuning (25%). We sketch a more realistic model involving the entire gauge and fermion structure that also implements T-parity, and we comment on the tension between T-parity and flavor structure.

Relative equilibria in systems with configuration space isotropy

We present a framework for studying Lagrangian and Hamiltonian systems with symmetries, near points with configuration space isotropy. We use twisted parametrisations corresponding to phase space slices based at zero points of (co-)tangent fibres. Given a hyperregular Lagrangian, we find a Legendre transform in the twisted coordinates. For simple mechanical systems, we state necessary and sufficient conditions for the existence of relative equilibria in terms of an augmented-amended potential.

SU-FF-T-393: An Anthropomorphic Phantom for Respiratory Motion Research in Dynamic SRS

Purpose: The purpose of our experiment is to study the use of a respiratory anthropomorphic phantom evaluating the respiratory motion tracking capabilities in dynamic stereotactic radiosurgery (SRS). Method and Materials: An anthropomorphic phantom was scanned with 1.25 mm slice spacing on a 4-slice GE Lightspeed CT. A Harvard lung pump was attached to the lung bellows of the phantom and set to 15 breath/min, 40% expiration. The abdominal cavity was filled with humid sponges to resemble lung tissue density. A mini-ballcube containing a pair of orthogonal GaF-chromic films was attached to the diaphragm. The spherical target was treated to 3000cGy at 100% isodose line using both a static SRS and dynamic SRS (Synchrony) treatment. The films were analyzed using a Vidar VXR-16 scanner and the Accuray film analysis tool. Results: CT numbers measured in the phantom range from 42–162 for the sponges, 1111–1193 for the silicone tissue, and 1412 – 1512 for the embedded plastic skeleton. The total targeting error for the diaphragm treatment was 0.77 mm in the static and 0.91 in the dynamic case. The eccentricity for the spherical target was 1.27 mm in the axial plane for both treatments, and 1.34 mm for the static and 1.41 mm for the dynamic treatment in the coronal plane. The respiratory pattern was very similar to patterns observed in Synchrony patients. The extent of diaphragmatic motion was 8–10 mm in the superior/inferior direction. Conclusion: The respiratory anthropomorphic phantom is a promising tool for evaluating the respiratory motion tracking capabilities of dynamic SRS in a patient-like environment. The accessible abdominal cavity allows for different target positions. It can easily be filled with different materials (sponges, saline solution, organic material, gels) to simulate different environments in the body. The electron densities (CT numbers) of the phantom material are very close to human tissue.

Proton beam radiotherapy versus fractionated stereotactic radiotherapy for uveal melanomas: A comparative study

A comparative treatment planning study was undertaken between proton and photon therapy in uveal melanoma to assess the potential benefits and limitations of these treatment modalities. A fixed proton horizontal beam (OPTIS) and intensity-modulated spot-scanning proton therapy (IMPT), with multiple noncoplanar beam arrangements, was compared with linear accelerator-based stereotactic radiotherapy (SRT), using a static and a dynamic micromultileaf collimator and intensity-modulated RT (IMRS). A planning CT scan was performed on a brain metastasis patient, with a 3-mm acquisition slice spacing and the patient looking at a luminous spot with the eyes in three different positions (neutral and 25 degrees right and left). Four different gross tumor volumes were defined for each treatment technique. These target scenarios represented different locations (involving vs. not involving the macula and temporal vs. nasal) and volumes (10 x 6 mm vs. 16 x 10 mm) to challenge the proton and photon treatment techniques. The planning target volume was defined as the gross tumor volume plus 2 mm laterally and 3 mm craniocaudally for both modalities. A dose homogeneity of 95-99% of the planning target volume was used as the "goal" for all techniques. The dose constraint (maximum) for the organs at risk (OARs) for both the proton and the SRT photon plans was 27.5, 22.5, 20, and 9 CGE-Gy for the optic apparatus, retina, lacrimal gland, and lens, respectively. The dose to the planning target volume was 50 CGE-Gy in 10 CGE-Gy daily fractions. The plans for proton and photon therapy were computed using the Paul Scherrer Institute and BrainSCAN, version 5.2 (BrainLAB, Heimstetten, Germany) treatment planning systems, respectively. Tumor and OARs dose-volume histograms were calculated. The results were analyzed using the dose-volume histogram parameters, conformity index (CI(95%)), and inhomogeneity coefficient. Target coverage of all simulated uveal melanomas was equally conformal with the photon and proton modalities. The median CI(95%) value was 1.74, 1.86, and 1.83 for the static, dynamic, and IMSRT plans, respectively. With proton planning, the median CI(95%) was 1.88 for OPTIS and substantially improved with IMPT in some tumor cases (median CI(95%), 1.29). The tumor dose homogeneity in the proton plans was, however, always better than with SRT photon planning (median inhomogeneity coefficient 0.1 and 0.15 vs. 0.46, 0.41, and 0.23 for the OPTIS and IMPT vs. the static, dynamic, and IMSRT plans, respectively). Compared with the photon plans, the use of protons did not lead to a substantial reduction in the homolateral OAR total integral dose in the low- to high-dose level, except for the lacrimal gland. The median maximal dose and dose at the 10% volume with the static, dynamic, and IMSRT plans was 33-30.8, 31.8-28, and 35.8-49 Gy, respectively, for the lacrimal gland, a critical organ. For protons, only the OPTIS plans were better, with a median maximal dose and dose at the 10% volume using OPTIS and IMPT of 19.2 and 8.8 and 25.6 and 23.6 CGE, respectively. The contralateral OARs were completely spared with the proton plans, but the median dose delivered to these structures was 1.2 Gy (range, 0-6.3 Gy) with the SRT photon plans. These results suggest that the use of SRT photon techniques, compared with protons, can result in similar levels of dose conformation. IMPT did not increase the degree of conformality for this small tumor. Tumor dose inhomogeneity was, however, always increased with photon planning. Except for the lacrimal gland, the use of protons, with or without intensity modulation, did not increase homolateral OAR dose sparing. The dose to all the contralateral OARs was, however, completely eliminated with proton planning.

Are lateral electronic portal images adequate for accurate on-line daily targeting of the prostate? Results of a prospective study

Are lateral electronic portal images adequate for accurate on-line daily targeting of the prostate? Results of a prospective study

Dosimetric uncertainties of three‐dimensional dose reconstruction from two‐dimensional data in a multi‐institutional study

Inconsistencies in the treatment planning process leading to dosimetric uncertainties may affect conclusions drawn from interinstitutional radiation oncology clinical trials. The purpose of this study was to assess the dosimetric uncertainties resulting from the process of reconstructing three‐dimensional dose distributions from two‐dimensional treatment plan information provided by participating institutions in a randomized clinical trial. This study was based on American College of Radiology Protocol #427, Locally Advanced Multi‐Modality Protocol; a multi‐institutional phase II randomized study involving radiation therapy for patients with inoperable non‐small cell lung cancer. Several sources of dosimetric uncertainty were identified and analyzed, including image quality of hard‐copy computed tomography (CT) images, slice spacing of CT scans, treatment position, interpretations of target volumes by radiation oncologists, the contouring of normal anatomic structures, and the use of common beam models for all dose calculations. Each source of uncertainty was investigated using a set of plans, with the ideal characteristics of digital images with 3‐mm axial slice spacing and a flat couch, consisting of eight cases from Vanderbilt University Medical Center with electronically transferred CT data. The target volume DVH values were dependent on the additional uncertainty introduced by differences in delineation of the target volumes by the participating radiation oncologists. The DVH values for the lungs and heart were dependent on image quality and treatment position. Esophagus DVH values were not dependent on any of the sources of uncertainty. None of the structure DVH values were dependent on slice thickness or variations in the contouring of normal anatomic structures. Reconstruction of three‐dimensional dose distributions from two‐dimensional treatment plan information may be useful in cases for which digital CT data is not available or for historical data review. However, dosimetric accuracy will depend on image quality of the treatment planning CT data and consistency in the delineation of tumor volumes.PACS number: 87.53.‐j

Lung tumor motion measured using retrospective 4D CT and correlated with tumor location and attachment

To measure lung tumor motion using retrospective 4D CT and correlate the motion with tumor position and attachment. Lung patients were scanned using retrospective 4D CT to account for respiratory motion of the tumor. For 4D CT, multiple images are acquired at each slice location and then sorted according to the phase of the respiratory cycle in which the image was acquired. In order to acquire the 4D CT, each patient was positioned on the CT couch with his/her arms in a wingboard and feet tied together. While acquiring a scout CT and a helical CT (not yet the 4D CT), the patient’s breathing cycle is observed using the “RPM computer” (Varian Medical Systems). The respiratory cycle is observed using a marker block taped to the patient’s abdomen about 5 cm below the xiphoid. The motion of the marker block is relayed to the RPM computer by an infrared camera. An audible breathing coach is programmed with the patient’s breathing cycle time and started. The patient is asked if the rhythm is comfortable and if not, slight adjustments are made to the time until a comfortable rhythm is achieved. The CT slice spacing is set to 2.5 mm so that motions as small as 2.5 mm in the superior-inferior (S-I) direction can be observed. The volume to be scanned is determined from the scout image. The number of images is limited to 1500. The user programs the scanner to remain at each slice location acquiring multiple images for at least one full breathing cycle of the patient. All of these images are synchronized with the breathing cycle and sorted according to the breathing phase at which they were acquired. A 3D image is created for each breathing phase. The location of the tumor was identified by the lung lobe in which the tumor resided. Any attachment observed superiorly, inferiorly, anteriorly, posteriorly, medially, or laterally was recorded even if the attachment was only via a distinguishable vessel. Tumor displacement was measured by locating each edge of the tumor on the phases representing its most superior and most inferior positions. If the Medial-Lateral (M-L) displacement and the Anterior-Posterior (A-P) displacements were less than 3 mm, the superior and the inferior edges of the tumor were recorded on the phases representing its most superior and most inferior positions. The average displacement of the inferior and superior edges was identified as the tumor displacement. Tumors with A-P or M-L displacements of more than 3 mm were contoured before identifying their displacements. To contour the tumors, the 3D images representing its most superior and most inferior positions were exported to the planning computer (Eclipse, Varian Medical Systems). The tumor was contoured on both 3D images. The planning computer was then used to identify the center of the tumor on each phase using a built in center of mass calculation. These centers at the superior and inferior positions were recorded and their S-I difference represents the S-I displacement of the tumor. Lung tumor motion has been measured in 10 patients and associated with tumor position and attachment. Tumors located in the superior and inferior lobes of the lungs have been observed. Superior, inferior, anterior, posterior, lateral, and medial attachments have all been observed. The tumors that moved more than 3 mm were all located in the inferior lobes. Of these tumors, those attached posteriorly were observed to move the most. Tumors with extensive attachment moved the least. Tumor S-I motions from 0 to 13.8 mm were observed.

Abdominal aortic stent graft planning with automatically extracted vessel centerlines/cross-sections in multislice CT

The abdominal aorta is the most common site for an aneurysm, which may lead to hemorrhage and death, to develop. The aim of this study was to develop a fully automated method to delineate the blood flow, suppress bones and subsequently detect the centerline of contrast enhanced blood vessels to make measurements necessary for stent design from computed tomograms. We developed a combination of methods to suppress bones while tracking the aortic vessel tree using series of image processing, such as spatial correlation measures to filter vessel like structures, fast marching method to delineate the blood flow, morphological and distance transforms methods to extract centerlines. Twenty patients were scanned with contrast on Mx8000 CT scanner (Philips Medical Systems), with a 1.3 mm thickness, 1.0–2.0 mm slice spacing and 400 to 900 slices per volume. The automated image processing took approximately 30 to 90 s to compute the centerline and borders of the aortic vessel tree. We compared our results and found that vessel tree perfectly extracted in 11 of 20 cases. With additional four or less clicks, vessel trees in four more cases were accomplished. The remaining cases, although the dominant aortic vessel is picked, requiring five or more additional clicks, were considered as poor.

How to achieve fast, accurate, and robust rigid registration between fluoroscopic X-ray and CT images

This paper presents algorithmic refinements to our method for rigid registration between preoperative CT and intraoperative X-rays and studies the influence of various setups and factors on the methods' performance. Experimental results on five different anatomical structures show that the new three-phase algorithm achieves a mean accuracy of 0.7 mm (max=1.1 mm) 95% of the time with an initial pose offset of up to 60 mm in 80 s average with three X-ray images and CT slice spacing of 2.4 mm and handles image clutter well.

Web caching in broadcast mobile wireless environments

Effectively exploiting available communication bandwidth and client resources is vital in wireless mobile environments. One technique for doing so is client-side data caching, which helps reduce latency and conserve network resources. The SliCache generic self-tunable cache-replacement policy addresses these issues by using intelligent slicing of the cache space and novel methods for selecting which objects to purge. Performance evaluations show that SliCache improves mobile clients' access to Web objects compared to other common policies.

A new method for real radiation at next-to-next-to-leading order

We propose a new method of computing real emission contributions to hard QCD processes. Our approach uses sector decomposition of the exclusive final-state phase space to enable extraction of all singularities of the real emission matrix elements before integration over any kinematic variable. The exact kinematics of the real emission process are preserved in all regions of phase space. Traditional approaches to extracting singularities from real emission matrix elements, such as phase space slicing and dipole subtraction, require both the determination of counterterms for double real emission amplitudes in singular kinematic limits and the integration of these contributions analytically to cancel the resulting singularities against virtual corrections. Our method addresses both of these issues. The implementation of constraints on the final-state phase space, including various jet algorithms, is simple using our approach. We illustrate our method using ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}$ jets at $O({\ensuremath{\alpha}}_{S}^{2})$ as an example.