bluuebunny/crossref_metadata_2025 huggingface dataset:
Meiosis and small ubiquitin‐related modifier (SUMO)‐conjugating enzyme, Ubc9
Authors: Sakaguchi Kengo , Koshiyama Akiyo , Iwabata Kazuki
Published: July 2007

In this review, we describe the role of a small ubiquitin‐like protein modifier (SUMO)‐conjugating protein, Ubc9, in synaptonemal complex formation during meiosis in a basidiomycete, Coprinus cinereus. Because its meiotic cell cycle is long and naturally synchronous, it is suitable for molecular biological, biochemical and genetic studies of meiotic prophase events. In yeast two‐hybrid screening using the meiotic‐specific cDNA library of C. cinereus, we found that the meiotic RecA homolog CcLim15 interacted with CcUbc9, CcTopII and CcPCNA. Moreover, both TopII and PCNA homologs were known as Ubc9 interactors and the targets of sumoylation. Immunocytochemistry demonstrates that CcUbc9, CcTopII and CcPCNA localize with CcLim15 in meiotic nuclei during leptotene to zygotene when synaptonemal complex is formed and when homologous chromosomes pair. We discuss the relationships between Lim15/Dmc1 (CcLim15), TopII (CcTopII), PCNA (CcPCNA) and CcUbc9, and subsequently, the role of sumoylation in the stages. We speculate that CcLim15 and CcTopII work in cohesion between homologous chromatins initially and then, in the process of the zygotene events, CcUbc9 works with factors including CcLim15 and CcTopII as an inhibitor of ubiquitin‐mediated degradation and as a metabolic switch in the meiotic prophase cell cycle. After CcLim15–CcTopII dissociation, CcLim15 remains on the zygotene DNA and recruits CcUbc9, Rad54B, CcUbc9, Swi5‐Sfr1, CcUbc9 and then CcPCNA in rotation on the C‐terminus. Finally during zygotene, CcPCNA replaces CcLim15 on the DNA and the free‐CcLim15 is probably ubiquitinated and disappears. CcPCNA may recruit the polymerase. The idea that CcUbc9 intervenes in every step by protecting CcLim15 and by switching several factors at the C‐terminus of CcLim15 is likely. At the boundary of the zygotene and pachytene stages, CcPCNA would be sumoylated. CcUbc9 may also be involved with CcPCNA in the switch from the replicative polymerase being recruited at zygotene to the repair‐type DNA polymerases being recruited at pachytene.
Catalytic mechanism of SGAP, a double‐zinc aminopeptidase from Streptomyces griseus
Authors: Hershcovitz Yifat F. , Gilboa Rotem , Reiland Vera , Shoham Gil , Shoham Yuval
Published: July 2007

The catalytic mechanism underlying the aminopeptidase from Streptomyces griseus (SGAP) was investigated. pH‐dependent activity profiles revealed the enthalpy of ionization for the hydrolysis of leucine‐para‐nitroanilide by SGAP. The value obtained (30 ± 5 kJ·mol−1) is typical of a zinc‐bound water molecule, suggesting that the zinc‐bound water/hydroxide molecule acts as the reaction nucleophile. Fluoride was found to act as a pure noncompetitive inhibitor of SGAP at pH values of 5.9–8 with a Ki of 11.4 mm at pH 8.0, indicating that the fluoride ion interacts equally with the free enzyme as with the enzyme–substrate complex. pH‐dependent pKi experiments resulted in a pKa value of 7.0, suggesting a single deprotonation step of the catalytic water molecule to an hydroxide ion. The number of proton transfers during the catalytic pathway was determined by monitoring the solvent isotope effect on SGAP and its general acid–base mutant SGAP(E131D) at different pHs. The results indicate that a single proton transfer is involved in catalysis at pH 8.0, whereas two proton transfers are implicated at pH 6.5. The role of Glu131 in binding and catalysis was assessed by determining the catalytic constants (Km, kcat) over a temperature range of 293–329 °K for both SGAP and the E131D mutant. For the binding step, the measured and calculated thermodynamic parameters for the reaction (free energy, enthalpy and entropy) for both SGAP and the E131D mutant were similar. By contrast, the E131D point mutation resulted in a four orders of magnitude decrease in kcat, corresponding to an increase of 9 kJ·mol−1 in the activation energy for the E131D mutant, emphasizing the crucial role of Glu131 in catalysis.
Achieving Nutrient Water Quality Goals: Bringing Market‐Like Principles to Water Quality Management*1
Authors: Shabman Leonard , Stephenson Kurt
Published: July 2007

Abstract:  Market‐like trading programs for water quality management begin with enforceable limits on the amount of the pollutant allowed in a watershed. Properly designed market‐like trading programs then create incentives for dischargers to reduce nutrient control costs over time by making pollution prevention innovations. However, the structure of the Clean Water Act can be a barrier to establishing market‐like trading programs. First, we describe the general features and advantages of market‐like trading programs. Then we offer practical suggestions for bringing market‐like design concepts to nutrient trading programs within the existing legal and regulatory setting.
New angiotensin II type 1 receptor blocker olmesartan improves portal hypertension in patients with cirrhosis
Authors: Hidaka Hisashi , Kokubu Shigehiro , Nakazawa Takahide , Okuwaki Yuusuke , Ono Kouji , Watanabe Masaaki , Shibuya Akitaka , Saigenji Katsunori
Published: July 2007

Aim:  To evaluate the effect of the new oral angiotensin II type 1 receptor blocker olmesartan on portal hemodynamics in patients with cirrhosis.

Methods:  From January 2005 to March 2006, 18 cirrhosis patients treated with endoscopic band ligation for primary esophageal variceal bleeding were included in the present study. Hepatic venous pressure gradient (HVPG) of the patients was ≥12 mmHg at baseline measurement. The patients were given 10 mg olmesartan orally once daily for 2 weeks. Eighteen cirrhosis patients with esophageal variceal bleeding who did not receive any antihypertensive agents were included in the study as control. On day 14, HVPG, blood pressure, heart rate, and parameters of hepatic and renal function were examined after the treatment. Responders were defined as those with HVPG reduction of >20% versus baseline.

Results:  Olmesartan significantly reduced HVPG by −16.8 ± 22.0% (P = 0.031) and mean arterial pressure by −13.1 ± 10.8% (P = 0.0041). Six of 18 (33.3%) patients in the olmesartan group showed >20% reduction of HVPG from baseline values. None of the patients treated with olmesartan had any complications.

Conclusion:  Olmesartan reduces portal pressure and may be safe and highly effective in the treatment of portal hypertension.
Accuracy and feasibility of cone‐beam computed tomography for stereotactic radiosurgery setup
Authors: Chang Jenghwa , Yenice Kamil M. , Narayana Ashwatha , Gutin Philip H.
Published: July 2007

Image fusion, target localization, and setup accuracy of cone‐beam computed tomography (CBCT) for stereotactic radiosurgery (SRS) were investigated in this study. A Rando head phantom rigidly attached to a stereotactic Brown‐Roberts‐Wells (BRW) frame was utilized to study the geometric accuracy of CBCT. Measurements of distances and angular separations between selected pairs of multiple radio‐opaque targets embedded in the head phantom from a conventional simulation CT provided comparative data for geometric accuracy analysis. Localization accuracy of the CBCT scan was investigated from an analysis of BRW localization of four cylindrical objects ( in diameter and in length) independently computed from CBCT and conventional CT scans. Image fusion accuracy was quantitatively evaluated from BRW localization of multiple simulated targets from the CBCT and conventional CT scan. Finally, a CBCT setup procedure for stereotactic radiosurgery treatments was proposed and its accuracy was assessed using orthogonal target verification imaging. Our study showed that CBCT did not present any significant geometric distortions. Stereotactic coordinates of the four cylindrical objects as determined from the CBCT differed from those determined from the conventional CT on average by with a standard deviation (SD) of . The mean image registration accuracy of CBCT with conventional CT was . Setup uncertainty of our proposed CBCT setup procedure was on the same order as the conventional framed‐based stereotactic systems reported in the literature (, ). In conclusion, CBCT can be used to guide SRS treatment setup with accuracy comparable to the currently used frame‐based stereotactic radiosurgery systems provided that intra‐treatment patient motion is prevented.
Minimizing artifacts resulting from respiratory and cardiac motion by optimization of the transmission scan in cardiac PET/CT
Authors: Nye Jonathon A. , Esteves Fabio , Votaw John R.
Published: July 2007

The introduction of positron emission/computed tomography (PET/CT) systems coupled with multidetector CT arrays has greatly increased the amount of clinical information in myocardial perfusion studies. The CT acquisition serves the dual role of providing high spatial anatomical detail and attenuation correction for PET. However, the differences between the interaction of respiratory and cardiac cycles in the CT and PET acquisitions presents a challenge when using the CT to determine PET attenuation correction. Three CT attenuation correction protocols were tested for their ability to produce accurate emission images: gated, a step mode acquisition covering the diastolic heart phase; normal, a high‐pitch helical CT; and slow, a low‐pitch, low‐temporal‐resolution helical CT. The amount of cardiac tissue in the emission image that overlaid lung tissue in the transmission image was used as the measure of mismatch between acquisitions. Phantom studies simulating misalignment of the heart between the transmission and emission sequences were used to correlate the amount of mismatch with the artificial defect changes in the emission image. Consecutive patients were studied prospectively with either paired gated (diastolic phase, , , ) and slow CT (0.562:1 pitch, , Auto‐mA, ) or paired normal (0.938:1 pitch, , Auto‐mA, ) and slow CT protocols, prior to a Rb‐82 perfusion study. To determine the amount of mismatch, the transmission and emission images were converted to binary representations of attenuating tissue and cardiac tissue and overlaid using their native registration. The number of cardiac tissue pixels from the emission image present in the CT lung field yielded the magnitude of misalignment represented in terms of volume, of where a small volume indicates better registration. Acquiring a slow CT improved registration between the transmission and emission acquisitions compared to the gated and normal CT protocols. The volume of PET cardiac tissue in the CT lung field was significantly lower for the slow CT protocol in both the rest and stress emission studies. Phantom studies showed that an overlaying volume greater than would produce significant artificial defects as determined by a quantitative software package that employs a normal database. The percentage of patient studies with overlaying volume greater than was reduced from 71% with the normal CT protocol to 28% with the slow CT protocol. The remaining 28% exhibited artifacts consistent with heart drift and patient motion that could not be corrected by adjusting the CT acquisition protocol. The low pitch of the slow CT protocol provided the best match to the emission study and is recommended for attenuation correction in cardiac PET/CT studies. Further reduction in artifacts arising from cardiac drift is required and warrants an image registration solution.
PET/CT image registration: Preliminary tests for its application to clinical dosimetry in radiotherapy
Authors: Baños‐Capilla M. C. , García M. A. , Bea J. , Pla C. , Larrea L. , López E.
Published: July 2007

The quality of dosimetry in radiotherapy treatment requires the accurate delimitation of the gross tumor volume. This can be achieved by complementing the anatomical detail provided by CT images through fusion with other imaging modalities that provide additional metabolic and physiological information. Therefore, use of multiple imaging modalities for radiotherapy treatment planning requires an accurate image registration method. This work describes tests carried out on a Discovery LS positron emission/computed tomography (PET/CT) system by General Electric Medical Systems (GEMS), for its later use to obtain images to delimit the target in radiotherapy treatment. Several phantoms have been used to verify image correlation, in combination with fiducial markers, which were used as a system of external landmarks. We analyzed the geometrical accuracy of two different fusion methods with the images obtained with these phantoms. We first studied the fusion method used by the PET/CT system by GEMS (hardware fusion) on the basis that there is satisfactory coincidence between the reconstruction centers in CT and PET systems; and secondly the fiducial fusion, a registration method, by means of least‐squares fitting algorithm of a landmark points system. The study concluded with the verification of the centroid position of some phantom components in both imaging modalities. Centroids were estimated through a calculation similar to center‐of‐mass, weighted by the value of the CT number and the uptake intensity in PET. The mean deviations found for the hardware fusion method were: and . These values were substantially improved upon applying fiducial fusion based on external landmark points: and . We also noted that differences found for each of the fusion methods were similar for both the axial and helical CT image acquisition protocols.
Design of respiration averaged CT for attenuation correction of the PET data from PET/CT
Authors: Chi Pai‐Chun Melinda , Mawlawi Osama , Nehmeh Sadek A. , Erdi Yusuf E. , Balter Peter A. , Luo Dershan , Mohan Radhe , Pan Tinsu
Published: July 2007

Our previous patient studies have shown that the use of respiration averaged computed tomography (ACT) for attenuation correction of the positron emission tomography (PET) data from PET/CT reduces the potential misalignment in the thorax region by matching the temporal resolution of the CT to that of the PET. In the present work, we investigated other approaches of acquiring ACT in order to reduce the CT dose and to improve the ease of clinical implementation. Four‐dimensional CT (4DCT) data sets for ten patients (17 lung/esophageal tumors) were acquired in the thoracic region immediately after the routine PET/CT scan. For each patient, multiple sets of ACTs were generated based on both phase image averaging (phase approach) and fixed cine duration image averaging (cine approach). In the phase approach, the ACTs were calculated from CT images corresponding to the significant phases of the respiratory cycle: from end‐inspiration (0%) and end‐expiration (50%), from mid‐inspiration (20%) and mid‐expiration (70%), from 0%, 20%, 50% and 70%, and from all ten phases, which was the original approach. In the cine approach, which does not require 4DCT, the ACTs were calculated based on the cine images from cine durations of at increments. PET emission data for each patient were attenuation corrected with each of the above mentioned ACTs and the tumor maximum standard uptake value , average SUV , and tumor volume measurements were compared. Percent differences were calculated between PET data corrected with various ACTs and that corrected with . In the phase approach, the can be approximated by the to within a mean percent difference of 2% in SUV and tumor volume measurements. In cine approach, can be approximated to within a mean percent difference of 3% by ACTs computed from cine durations . Acquiring CT images only at the four significant phases for the ACT can reduce radiation dose to of the current 4DCT dose; however, the implementation of this approach requires additional hardware that is not standard equipment on PET/CT scanners. In the cine approach, we recommend a duration of in order to include variations of respiratory patterns in a larger population. This approach can be easily implemented because cine acquisition mode is available on all GE PET/CT scanners. The CT dose in the cine approach can be reduced to approximately by using the lowest mA setting , while still maintaining good quality CT data for PET attenuation correction. In our scanning protocol, the ACT is only acquired if respiration‐induced misregistration is observed (determined before the PET scan is completed), and therefore patients do not receive unnecessary CT radiation dose.
Secondary range shifting with range compensator for reduction of beam data library in heavy‐ion radiotherapy
Authors: Kanematsu Nobuyuki , Torikoshi Masami , Mizota Manabu , Kanai Tatsuaki
Published: July 2007

We report our experience with extended usage of range compensators in heavy‐ion radiotherapy with broad beams to lighten the management task of the beam data library, which is a collection of the standard beams to be referenced in treatment planning. Partly due to interference between lateral spreading and range shifting, as many as hundreds of beam entries may be necessary to cover all the possible clinical situations. We have introduced downstream secondary range shifting with a range compensator to reduce the interference and consequently to simplify the library. In our case, 30% reduction in beam entries is achieved without significantly degrading the beam quality nor increasing the material consumption by more than 3%, which is experimentally verified with carbon‐ion beams or statistically estimated from the clinical records.
Calculation of x‐ray spectra emerging from an x‐ray tube. Part II. X‐ray production and filtration in x‐ray targets
Authors: Poludniowski Gavin G.
Published: July 2007

A new approach to the calculation of the x‐ray spectrum emerging from an x‐ray tube is proposed. Theoretical results for the bremsstrahlung cross section appearing in the literature are summarized. Four different treatments of electron penetration, based on the work presented in Part I, are then used to generate bremsstrahlung spectra. These spectra are compared to experimental data at 50, 80 and tube potentials. The most sophisticated treatment of electron penetration was required to obtain good agreement. With this treatment both the National Institute of Standards and Technology bremsstrahlung cross sections, based on accurate partial wave calculations, and the Bethe‐Heitler cross section [H. A. Bethe and W. Heitler, Proc R. Soc. London, Ser. A. 146, 83–112 (1934)] corrected by a modified Elwert factor [G. Elwert, Ann. Phys. (Leipzig) 426, 178–208 (1939)], provided good agreement to measured data. An approximate treatment of the characteristic spectrum is suggested. The dependencies of the bremsstrahlung and characteristic outputs of an x‐ray tube on tube potential are compared to experimentally derived data for 70– potentials. Agreement is to within a few percent of the total output over the entire range. The spectral predictions of the semiempirical models of Birch and Marshall [R. Birch and M. Marshall, Phys. Med. Biol. 24, 505–513 (1979)] (IPEM Report 78) and of Tucker et al. [D. M. Tucker, G. T. Barnes, and D. P. Chakraborty, Med. Phys. 18, 211–218 (1991).] are also assessed. The predictions of Tucker et al. are very close to the model developed here. The predictions of IPEM Report 78 are similar, but consistently harder for the range of tube potentials examined ). Unlike the semiempirical models, the model proposed here requires the introduction of no empirical and unphysical parameters in the differential bremsstrahlung cross section, bar an overall normalization factor which is close to unity.
Verification of the plan dosimetry for high dose rate brachytherapy using metal–oxide–semiconductor field effect transistor detectors
Authors: Qi Zhen‐Yu , Deng Xiao‐Wu , Huang Shao‐Min , Lu Jie , Lerch Michael , Cutajar Dean , Rosenfeld Anatoly
Published: July 2007

The feasibility of a recently designed metal–oxide–semiconductor field effect transistor (MOSFET) dosimetry system for dose verification of high dose rate (HDR) brachytherapy treatment planning was investigated. MOSFET detectors were calibrated with a NE‐2571 Farmer‐type ionization chamber in water. Key characteristics of the MOSFET detectors, such as the energy dependence, that will affect phantom measurements with HDR sources were measured. The MOSFET detector was then applied to verify the dosimetric accuracy of HDR brachytherapy treatments in a custom‐made water phantom. Three MOSFET detectors were calibrated independently, with the calibration factors ranging from . A distance dependent energy response was observed, significant within from the source. The new MOSFET detector has a good reproducibility , small angular effect , and good dose linearity . It was observed that the MOSFET detectors had a linear response to dose until the threshold voltage reached approximately for source measurements. Further comparison of phantom measurements using MOSFET detectors with dose calculations by a commercial treatment planning system for computed tomography‐based brachytherapy treatment plans showed that the mean relative deviation was for dose points away from the source and for dose points located away. The percentage deviations between the measured doses and the planned doses were below 5% for all the measurements. The MOSFET detector, with its advantages of small physical size and ease of use, is a reliable tool for quality assurance of HDR brachytherapy. The phantom verification method described here is universal and can be applied to other HDR brachytherapy treatments.
Novel image registration quality evaluator (RQE) with an implementation for automated patient positioning in cranial radiation therapy
Authors: Wu Jian , Samant Sanjiv S.
Published: July 2007

In external beam radiation therapy, digitally reconstructed radiographs (DRRs) and portal images are used to verify patient setup based either on a visual comparison or, less frequently, with automated registration algorithms. A registration algorithm can be trapped in local optima due to irregularity of patient anatomy, image noise and artifacts, and/ or out‐of‐plane shifts, resulting in an incorrect solution. Thus, human observation, which is subjective, is still required to check the registration result. We propose to use a novel image registration quality evaluator (RQE) to automatically identify misregistrations as part of an algorithm‐based decision‐making process for verification of patient positioning. A RQE, based on an adaptive pattern classifier, is generated from a pair of reference and target images to determine the acceptability of a registration solution given an optimization process. Here we applied our RQE to patient positioning for cranial radiation therapy. We constructed two RQEs—one for the evaluation of intramodal registrations (i.e., portal‐portal); the other for intermodal registrations (i.e., portal‐DRR). Mutual information, because of its high discriminatory ability compared with other measures (i.e., correlation coefficient and partitioned intensity uniformity), was chosen as the test function for both RQEs. We adopted translation and 1° rotation as the maximal acceptable registration errors, reflecting desirable clinical setup tolerances for cranial radiation therapy. Receiver operating characteristic analysis was used to evaluate the performance of the RQE, including computations of sensitivity and specificity. The RQEs showed very good performance for both intramodal and intermodal registrations using simulated and phantom data. The sensitivity and the specificity were 0.973 and 0.936, respectively, for the intramodal RQE using phantom data. Whereas the sensitivity and the specificity were 0.961 and 0.758, respectively, for the intermodal RQE using phantom data. Phantom experiments also indicated our RQEs detected out‐of‐plane deviations exceeding and 2.5°. A preliminary retrospective clinical study of the RQE on cranial portal imaging also yielded good sensitivity and specificity . Clinical implementation of a RQE could potentially reduce the involvement of the human observer for routine patient positioning verification, while increasing setup accuracy and reducing setup verification time.
Design, development, and implementation of the Radiological Physics Center's pelvis and thorax anthropomorphic quality assurance phantoms
Authors: Followill David S. , Evans DeeAnn Radford , Cherry Christopher , Molineu Andrea , Fisher Gary , Hanson William F. , Ibbott Geoffrey S.
Published: July 2007

The Radiological Physics Center (RPC) developed two heterogeneous anthropomorphic quality assurance phantoms for use in verifying the accuracy of radiation delivery: one for intensity‐modulated radiation therapy (IMRT) to the pelvis and the other for stereotactic body radiation therapy (SBRT) to the thorax. The purpose of this study was to describe the design and development of these two phantoms and to demonstrate the reproducibility of measurements generated with them. The phantoms were built to simulate actual patient anatomy. They are lightweight and water‐fillable, and they contain imageable targets and organs at risk of radiation exposure that are of similar densities to their human counterparts. Dosimetry inserts accommodate radiochromic film for relative dosimetry and thermoluminesent dosimetry capsules for absolute dosimetry. As a part of the commissioning process, each phantom was imaged, treatment plans were developed, and radiation was delivered at least three times. Under these controlled irradiation conditions, the reproducibility of dose delivery to the target TLD in the pelvis and thorax phantoms was 3% and 0.5%, respectively. The reproducibility of radiation‐field localization was less than for both phantoms. Using these anthropomorphic phantoms, pelvic IMRT and thoracic SBRT radiation treatments can be verified with a high level of precision. These phantoms can be used to effectively credential institutions for participation in specific NCI‐sponsored clinical trials
Computer modeling of the spatial resolution properties of a dedicated breast CT system
Authors: Yang Kai , Kwan Alexander L. C. , Boone John M.
Published: July 2007

Computer simulation methods were used to evaluate the spatial resolution properties of a dedicated cone‐beam breast CT system. x‐ray projection data of a nickel‐chromium wire were simulated. The modulation transfer function (MTF) was calculated from the reconstructed axial images at different radial positions from the isocenter to study the spatial dependency of the spatial resolution of the breast CT scanner. The MTF was also calculated in both the radial and azimuthal directions. Subcomponents of the cone beam CT system that affect the MTF were modeled in the computer simulation in a serial manner, including the x‐ray focal spot distribution, gantry rotation under the condition of continuous fluoroscopy, detector lag, and detector spatial resolution. Comparison between the computer simulated and physically measured MTF values demonstrates reasonable accuracy in the simulation process, with a small systematic difference ( difference, due to unavoidable uncertainties from physical measurement and system calibration). The intrinsic resolution in the radial direction determined by simulation was about uniformly through the field of view. The intrinsic resolution in the azimuthal direction degrades from at the isocenter to at the periphery with from the isocenter. The results elucidate the intrinsic spatial resolution properties of the prototype breast CT system, and suggest ways in which spatial resolution can be improved with system modification.
SU‐DD‐A4‐01: Nonrigid Registration of Mesorectal Region for PET Signal Follow‐Up During Radiation Therapy
Authors: Slagmolen P , Roels S , Loeckx D , Maes F , Haustermans K
Published: July 2007

Purpose: We wish to achieve maximum registration performance in the region around the tumor for patients with rectal cancer to assess the changes in PET signal due to radiotherapy. Method and Materials: A nonrigid registration was performed on nine PET‐CT images of three patients with rectal cancer. We use a B‐spline transformation model with mutual information as similarity criterion. The registration is performed in a multiresolution framework. To exclude the influence of differences in bladder filling, registration was limited to the mesorectum, delineated at planning time, by only calculating the similarity criterion for the control points inside the mesorectum. In the last multiresolution stages of the registration, a small, local volume constraint was used to regularize the deformation field inside the tumor region. Validation was performed by comparing volume overlap (Dice Similarity Coefficient or DSC), centroid distance and volume change of the manually delineated rectum contour for all slices where tumor was actually seen on the FDG‐PET. Results: When using the region of interest, volume overlap increases while centroid distance decreases for all registrations. The mean DSC when using the entire image for registrations was 0.68 compared to 0.79 when only registering inside the mesorectum. The mean centroid distance decreased from 4.40mm to 3.30mm. The mean volume difference decreased from 28.11% to 14.09%. Conclusion: Results show that by limiting the registration to the mesorectum, a much higher volume overlap for the rectum can be seen. Also, by regularizing the deformation field around the tumor in the last stages of the registration, a slight increase in rectum correspondence is found. The results of these registrations can be used to evaluate the PET signal around the tumor over time.
SU‐FF‐I‐81: 3.0T FMRI Implementation for Surgical Planning In a Clinical Health Care Center
Authors: Liu Yu
Published: July 2007

Purpose: There has been lot of progress during past decade in blood oxygenation level dependent (BOLD) functional MRI (fMRI) and Diffusion Tensor Imaging (DTI). However their clinical use has not been available to many tertiary care centers because of lack of support in paradigm generation, presentation and post processing. Recently, technical advances in 3.0 T clinical MRI scanners, paradigm presentation/post processing, and available medical physics support have made fMRI achievable for clinical MRI settings. The purpose of this study is to utilize 3.0T fMRI study for clinical neurological surgical planning in a tertiary care setting. Method and Materials: All clinical fMRI are done on a 3.0 T GE Signa scanner using an 8 channel head coil. IFIS/Brainvoyager (MRI Devices) is used for paradigm development/presentations and analysis. Visual, verb generating, left/right motor, passive listening, rhyming, semantic paradigms/protocols are developed for clinical fMRI. Post processing of BOLD fMRI data on the scanner console (Brainwave) communicates with paradigm generating PC directly. Real‐time BOLD fMRI post processing is done with Brainwave (GE Medical Systems). Additional post processing, including 3D rendering of functional activation mapping of the brain, are done on the scanner console using Brainwave, or Brainvoyager on a standalone workstation. DTI is acquired and post processed using Functool MR tractography (GE Medical Systems) for fiber tracking. Results: 15 clinical patients have been scanned using both BOLD fMRI and DTI for neurological surgical planning. Diagnostic results from 3.0T fMRI scan had significant impact on the planning of neurological procedures. Conclusion: Clinical fMRI at 3.0 T has been successfully implemented in a tertiary care center for neurological surgical planning. With the technical advances in clinical 3.0T scanner, paradigm software/hardware options, and medical physics support, fMRI is becoming robust and increasingly available for routine clinical use.
SU‐FF‐I‐89: Effects of EPI Slice Angle, Slice Thickness and Phase Encoding Direction On FMRI Sensitivity in Areas with Susceptibility Artifact
Authors: Cheng SY , Kuan WC , Wan YL , Wai YY , Liu HL
Published: July 2007

Purpose: A key problem of using EPI for BOLD fMRI is the field inhomogeneities near air/tissue interfaces, or the susceptibility artifact. Therefore, fMRI studies in brain areas such as orbitofrontal cortex (OFC) and temporal lobes (TL) may suffer from signal dropouts and spatial distortions. This study aimed to determine the optimal EPI slice angle, slice thickness and phase‐encoding (PE) direction for the reduction of BOLD sensitivity (BS) losses in TL and OFC. Methods: The study was performed on five healthy volunteers using a 1.5‐T MRI scanner. A single‐shot GE EPI sequence was applied with TR/TE/FA = 3000ms/60ms/900, FOV = 220mm and matrix = 64. The slice tilt was set from −45° to +30° (in 6 steps of 15°) relative to the AC‐PC direction, 35 or 24 slices for the slice thickness of 3 or 6 mm, respectively, and the PE direction either left‐right or anterior‐posterior, which resulted in 24 parameter combinations. BS maps were calculated with corresponding phase maps for each combination and normalized to a brain template using SPM2 for comparison. Results: Significant BS gain (>15%) were observed in several parameter combinations, when comparing to the baseline BS (no slice tilt, slice thickness= 6mm, PE= anterior‐posterior). The optimal parameters that introduced most voxels with such BS gain were +30° slice tile, slice thickness= 3mm and PE = anterior‐posterior in the OFC, and −45° slice tile, slice thickness= 6mm and PE = left‐right in the TL. Conclusion: For the purpose of reducing BS losses in OFC and TL, this study provided the optimal EPI parameters that can be easily adopted in a clinical 1.5T MR scanner. For the PE direction, however, it is better to be kept in the anterior‐posterior direction to avoid peripheral nerve stimulation. Similar studies at 3T are currently under investigation.
SU‐FF‐I‐91: Diagnostic Medical Physics Characterization of a High Field MR Scanner Using a State of the Art MR Head Coil
Authors: Hussain I , Jain J , Kaufman R
Published: July 2007

Purpose: To discuss design characteristics of state of the art “multi‐element” coil technology and performance testing of 3.0T MR imager. Method and Materials: All tests were conducted on a Siemens Trio 3.0T imager using a 12 element head coil. ACR accreditation phantom and manufacturer provided phantoms were used. With the development of new imaging techniques such as parallel imaging, manufacturers have developed multi‐element coils for advanced imaging capabilities. These receive only coils can be applied independently or subsets of elements can be used for a particular exam. The signals are combined by a hardware called Mode‐Matrix. Multi‐element coils, however, have associated problems such as drop in signal uniformity across the image. Further image distortion can be more significant with high performance gradients. Various processing filters are available to address these issues.

Our tests included:

a. Operational characterization of MR scanner at the coil element level.

b. Effect of image quality filters available.

Image quality in parallel imaging. Results: ACR tests passed without the application of image quality filters except for uniformity, for which pre‐scan normalize was used. Raw filter reduced truncation artifact with loss of spatial resolution. No major impact on SNR or distortion correction when using Elliptical and LargeFOV filters, respectively. With GRAPPA based parallel imaging, low contrast detectibility decreased along with slight reduction in maximum uniformity (around 99%, 98% and 96%) for acceleration factors of 2, 3 and 4, respectively. Number of spokes visible varied as 8, 5, and 0, for acceleration factors of 2, 3 and 4, respectively, in slice number 11 (ACR recommended phantom and slice prescription). Spatial resolution remained unchanged at 0.9 mm. Uncombined images showed individual coil elements with different SNR values while noise remained approximately constant.

Conclusion: System design and application‐based testing of magnetic resonance imagers provide valuable insight into scanner capabilities.
SU‐FF‐I‐93: Use of Novel Gradient Directions to Synthesize Complex Diffusion Geometries: When A Hot Dog Is a Pancake
Authors: Yanasak N , Zhao Q , Allison J , Hu T
Published: July 2007

Purpose: The goal of this project is to demonstrate that usage of different gradient directions during the acquisition and reconstruction phases of a DTI scan can produce images exhibiting complex diffusion characteristics. In this manner, a simple anisotropic phantom (e.g., “hot dog” geometry) could be employed to infer the quality of data for more clinically‐realistic tissue structures (e.g., oblate, or “pancake” structures, and two prolate structures that intersect). Method and Materials: A water‐filled phantom containing glass capillary arrays was constructed. Three DTI series of images from a 3.0T GE HDx scanner were acquired by specifying sets of acquisition directions to produce synthetic oblate diffusion distributions and two diffusion distributions where prolate distributions intersect, using standard gradient directions for reconstruction. Acquisition directions were calculated so that diffusion was most restricted in the y‐direction. The three desired diffusion distributions were first simulated using MATLAB, and acquisition directions appropriate for each were computed. Eigenvalues, eigenvectors, and fractional anisotropy of the oblate tensor were calculated within an ROI. RMS differences between generated and measured ADCs were determined. Results: The simulated oblate data produced a tensor with reasonable symmetry in the x‐z plane, restricted in the y direction. Eigenvalue magnitudes were consistent with those measured for the capillary array, albeit with the values associated with different eigenvectors. ADC distributions for intersecting prolate distributions qualitatively resemble the simulated distributions, and quantitatively match the simulated distributions more closely than a spherical distribution. Conclusion: This work suggests that one could use simple phantoms to monitor scanner performance for measuring diffusion distributions with more similarity to tissue. Gradient duty cycle is similar to an ordinary diffusion protocol; the effect of noise, originating from sources other than the gradients, on complicated diffusion distributions could be characterized empirically.
SU‐FF‐I‐96: Towards a Modality‐Independent Image Processing Workstation for Digital Mammography
Authors: Seibert J , Kennedy R , Cavanaugh B , Barnett C
Published: July 2007

Purpose: To measure the characteristic curve response of the raw, “for processing” digitized screen‐film and digital detectors to variations in incident exposure for mammography applications. Conversion and transformation of digital data to values directly proportional to exposure normalizes the output independent of the detector response to allow a “universal” workstation to render DICOM “for presentation” images of similar appearance. Method and Materials: Screen‐film response was measured by varying tube current under tight collimation with a 4.5 cm plastic attenuator in a scatter‐free geometry. Multiple exposures on a film were achieved by repositioning the cassette under the collimated area and recording the incident exposure with a calibrated radiation dosimeter, which ranged from ∼1 mR to ∼40 mR over 11 exposures. Film processing and digitization provided DICOM images. Region of interest analysis on the exposed film areas yielded average value as a function of exposure. A look up table (LUT) was constructed by fitting the curve with a third‐order polynomial, and scaling the output to a range of 4000. Application of the digital number to exposure LUT on the digitized films produced “exposure normalized” images. A similar technique was used with a prototype CR mammography system to discern the digital number to exposure relationship, using an exponential fit for the LUT transform to provide exposure normalized CR images. Results: Transformation of digitized screen‐film calibration images was achieved with good fidelity; likewise, CR conversion was achieved with excellent linearity. Subsequent processing enhancement of normalized images yielded good appearance matching compared to the original “for presentation” film and CR images. Conclusion: Digitized mammography films and CR mammography images transformed to a linear exposure response can yield similar DICOM “for presentation” appearance with independent image processing, important for longitudinal comparisons by the radiologist. Conflict of Interest: Research sponsored partially by Pacsgear, Inc.
SU‐FF‐I‐102: Signal Dependence On Frequency in Magnetic Particle Imaging
Authors: Weaver J , Rauwerdink A , Sullivan C , Baker I
Published: July 2007

Purpose: To evaluate the frequency dependence of signal detection in magnetic particle imaging (MPI) using heterodyne mixing of the odd harmonics down to DC for detection. Method and Materials: Magnetic particle imaging detects the odd numbered harmonics generated when a sinusoidal driving field saturates the nanoparticles. A solenoidal coil was used to generate the driving field of approximately 10 mT in a 3.2 cm inner diameter tube. Smaller diameter loops were connected to a phase‐lock amplifier to detect the harmonics. The difference in the third harmonic with and without a 1 ml sample of 300 microgram/ml, 40 nanometer, nanoparticles was measured over a one minute acquisition. The contrast to noise ratio (CNR) was calculated for frequencies between 500 Hz and 20 kHz. Results: The CNR increased linearly with frequency; the linear correlation coefficient was 0.993 (p‐value 10−7). Further, the CNR per cycle was essentially constant (p‐value 10−6) over the entire range of frequencies. The sensitivity allowed detection of nanoparticles down to 20 microgram/ml concentrations.

The original work found that the best SNR was obtained using a swept low frequency excitation. However, filters were used to isolate the driving field from the harmonics. In contrast, the phase‐lock amplifier heterodyne mixes the harmonic frequencies to DC before filtering so the filtering is much more effective. The difference in detection is probably responsible for the different results. The harmonic signal is generated from the edges in the magnetization occurring when the nanoparticles saturate so the harmonics should increase linearly with the number of edges which would result in a linear increase with frequency. Conclusions: The CNR increases linearly with frequency. The constant CNR per cycle over all frequencies implies that distortion of the hysteresis curve that can reduce the harmonics for higher driving frequencies is not significant below 20 kHz for these nanoparticles.
SU‐FF‐I‐105: Dosimetric Comparison of Planar and 3‐Dimensional Methods of Anatomic Localization for Breast Lymphoscintigraphy
Authors: Dickinson R , Stevens D , Williams C , Wendt R
Published: July 2007

Purpose: To estimate the absorbed dose for a range of settings of CT topograms and scans to determine the best technique for node localization in breast lymphoscintigraphy while minimizing the dose to the patient. Method and Materials: This study was performed with an anthropomorphic thorax phantom on a Symbia‐T6® SPECT/CT to produce mechanically registered datasets [Siemens Medical Solutions USA, Hoffman Estates IL]. The data included a SPECT, anterior and lateral topograms, a CT, and static anterior and lateral emission scintigrams. CT topograms and scans were acquired at 80, 110, and 130 kVp with varied mAs settings to compare the quality of the images and dose estimates for lower dose settings. Scintigram and SPECT scans were fused to each topogram and CT, respectively, to allow for qualitative comparison of localization. Exposure measurements for topograms were acquired using an ion chamber at isocenter, and entrance skin doses were estimated for the CT topograms. A CTDI body phantom was used to acquire data for estimation of effective dose for the CT scans. Results: The skin dose for a CT topogram ranges from 0.089 mGy to 0.235 mGy, and the effective dose for the CT scan ranges from 0.308 mSv (lowest dose settings) to 5.265 mSv (clinical scan setting). Qualitative comparison showed the 80 kVp, 20 mA topogram and 110 kVp, 10 mAs CT to be sufficient for localization. The skin dose is 0.089 uSv and the effective dose is 0.392 uSv for these techniques, respectively. Conclusion: The absorbed dose to the patient can be substantially reduced for CT topograms and CTs that are to be used for localization. These do not have to be of diagnostic quality in order to provide enough anatomical information to localize the sentinel nodes in breast lymphoscintigraphy. Conflict of Interest: Research sponsored by Siemens Medical Solutions USA.
SU‐FF‐I‐109: Image Deconvolution in Autoradiography: A Preliminary Study
Authors: Zhang M , Chen Q , Li X , O'Donoghue J , Ruan S , Zanzonico P , Ling C , Humm J
Published: July 2007

Purpose: To improve the image contrast and resolution of phosphor imaging plate based digital autoradiography (DAR) through a deconvolution algorithm. Method and Materials: The study was conducted with Fuji BAS‐MS2325 phosphor imaging plates. Series of small radioactive sources, typically 100–200 microns in diameter, were constructed on a hydrophobic surface of glass micro slides for different radioactive iodines. The DAR images of these test sources are analyzed using the Richardson‐Lucy (R‐L) deconvolution algorithm to derive the point spread function (PSF) of the radionuclides on the imaging plate. DAR image recovery is performed with the R‐L algorithm using measured PSF. The performance of this methodology is evaluated with a sham DAR image, and demonstrated on actual tumor sections containing radiotracers. Results: The measured PSF shows satisfactory reproducibility for each radionuclide, and can be represented by the sum of three 2‐D Gaussian peaks. Simulations suggest that within a wide range of signal noise ratio (SNR), the deconvolution algorithm can closely recover the radioactivity distributions on tissue sections. In addition, there exists optimal R‐L iteration numbers for different SNR levels in terms of the correlation of radioactivity distribution and restored image intensity. In the reconstructed images of tumor sections, the contrast and details are remarkably improved. Conclusion: Deconvolution improves image contrast and detail but amplifies noise. The usefulness of image deconvolution lies in the removal of false‐positive pixels and achieving a better defined map of the radioactivity distribution within the tissue section, allowing for quantitative analysis of marker distribution at the loco‐regional level. Our method does not require sophisticated instrument, and can be conveniently conducted in laboratory equipped with ordinary DAR and microscopy devices.