bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐45: An Automatic Method for Reduction of Metal Artifacts Caused by Metallic Implants
Authors: Xu C , Beaulieu L , Laurendeau D , Verhaegen F
Published: April 2010

Purpose: To develop an automatic method for metal artifact reduction (MAR) from small objects such as brachytherapy (BT) seeds. Method and Materials: A phantom made of agar (water‐like) and consisting of 6 slices of 5 mm in which 75 seeds (activity at background level) were implanted for imaging purposes. The phantom was scanned on a helical CT scanner (Siemens Somatom) to produce continuous 1 mm and 3 mm slices of the full phantom. The proposed method is based on the interpolation of missing projections by directly using raw CT data (sinogram). First, an initial image was reconstructed from the raw projection data. Then, the metal objects segmented from the reconstructed image were re‐projected into the same sinogram. The Steger method was used to precisely determine the position and edges of the seed traces in raw CT data. By combining the use of Steger detection and re‐projections, the missing projections were finally detected and further replaced by interpolation of non‐missing neighbouring projections. Results: In both phantom experiment and patient studies, the missing projections have been well detected and the artifacts caused by metallic objects in the image reconstructed using the corrected sinogram have been significantly reduced. The performance of the algorithm has been also proven after a quantitative evaluation by comparing the intensity uniformity between the uncorrected and corrected phantom images. Conclusion: An efficient algorithm for MAR in seed brachytherapy was developed. The challenge of detecting and correcting artifacts from 60 to 120 tiny objects in sinogram space has been successfully demonstrated. The detected traces can be further processed to extract, from a large sample of points, the position and orientation of each seed with high precision. This should enable a more accurate use of advance brachytherapy dose calculations, such as Monte Carlo simulations.
SU‐FF‐I‐46: Accurate Image Reconstruction From Incomplete Kilovoltage Cone‐Beam CT Data in Radiation Therapy
Authors: Han X , Bian J , Cho S , Sidky E , Pearson E , Pelizzari C , Pan X
Published: April 2010

Purpose: Kilovoltage cone‐beam CT (CBCT) is becoming an increasingly important clinical tool for image‐guided radiation therapy. Current CBCT imaging procedures acquire data from hundreds of angular views, during which considerable amount of radiation dose is deposited in the patient body. This raises patient safety concerns as CBCT is often used for frequent image acquisitions. Dose reduction can be achieved in part by acquiring data collected from a considerably reduced number of views. In this work, we develop a total‐variation‐minimization‐based image reconstruction algorithm (TV algorithm) to reconstruct images for situations when only a fraction of full‐scan CBCT data is acquired in radiation therapy. Materials and methods: The TV algorithm seeks among all the image candidates satisfying a given data‐fidelity tolerance the one with minimum total variation. Projection onto convex sets (POCS) and gradient‐descent techniques were used in the algorithm to achieve this goal. To test the algorithm, we acquired 856‐view CBCT data of a home‐built phantom with the on‐board imaging (OBI) system mounted on a Trilogy linear accelerator (Varian Medical Systems, Palo Alto, CA). We then extracted 32‐, 62‐, and 96‐view data for reconstruction using TV and other analytical and iterative algorithms. Results: Among all the tested reconstruction algorithms, the reconstructed images using TV algorithm is least contaminated with artifacts caused by insufficient angular sampling, and the low‐contrast object in the phantom is most distinguishable from background in TV reconstructed images. Conclusion: The proposed TV algorithm produces more accurate reconstruction images than other algorithms in the tested cases where only a fraction of the full dataset is used. The TV algorithm may be potentially useful in reducing radiation dose in CBCT image‐guided radiation therapy.
SU‐FF‐I‐58: Pediatric CT On 64‐Slice MDCT: Radiation Dose and Cancer Risk
Authors: Law M , Ng C , Huang B , Feng S , Khong P
Published: April 2010

Purpose: To measure the radiation dose from CT scan in children and to calculate the associated cancer risk. Method and Materials: Organ absorbed doses were measured with a 5‐year‐old pediatric phantom and thermoluminescent dosimeters on a 64‐slice CT scanner (Discovery VCT, GE Healthcare) with four CT protocols (head, thorax, abdomen and pelvis). Lifetime attributable risk (LAR) of cancer incidence was estimated for 5‐year‐old children according to the National Academies' Biological Effects of Ionizing Radiation VII Report. In our study the LAR data was updated using the cancer statistics data and life tables in US, as previously reported. Results: The effective doses, expressed in mSv, from the four protocols were 0.69, 3.46, 2.92, 1.23 for boys, and 0.7, 3.5, 3.0, 1.3 for girls respectively. The corresponding LARs estimated for 5‐year‐old boys and girls were 0.015%∼0.053% and 0.034%∼0.155% respectively. In relation to the total cancer incidence (baseline cancer incidence plus LAR), LAR from radiation exposure contributed up to 0.46% and 1.57% for boys and girls respectively. The LAR of cancer incidence caused to thyroid in head CT scan was 0.015% for girls and 0.003% for boys. For thorax, the organ of highest LAR is lung for boys and breast for girls, with a LAR of 0.014% and 0.069% respectively. For abdomen, the organ of highest LAR is colon for boys and lung for girls with a LAR of 0.017% and 0.016% respectively. For pelvis, the organ of highest LAR is bladder for boys and girls with the same LAR of 0.008%. Conclusion: Our results suggest that radiation dose and cancer risk of body CT imaging to pediatric patients are not negligible. Our study provides quantitative information for pediatricians to consider the benefit‐risk arising from CT scan before referring the patients for CT imaging.
SU‐FF‐I‐59: Acceptance and Commissioning of a Novel Ionizing Radiation Emitting Isotope Hospital Detection and Notification System Suitable for Use in Radiation Counter‐Terrorism
Authors: Huq M , Kim J , Novotny J , Bednarz G , Palatine R , Reilly M , Paris P , Greenberger J
Published: April 2010

Introduction and Purpose: Radioactive patient contamination (from dirty bomb explosions, etc.) could force shut down of hospital services for an extended time. The University of Pittsburgh Medical Center (UMPC) established testing of Thermo Fisher Scientific's Emergency Department Notification System (EDNS) at its Presbyterian Hospital. The EDNS discriminates non‐medical radioactive isotopes from medical isotopes. The EDNS at UPMC consists of large volume Sodium Iodide Detector Enclosures, System Control Unit, and networked Thermo Scientific ViewPoint™ Monitoring Software. The purpose of this study was to perform initial acceptance and commissioning of the EDNS. Methods and Materials: The following tests were performed for the initial acceptance of the EDNS: 1) evaluation of minimum detectable activity, 2) detector response distance to various source activities, 3) detector response to different speeds of a moving radioisotope and 4) ability to detect different radioisotopes passing under the detector at the same time. The radioisotopes used in the experiments were: Cs‐137, Co‐60, Ba‐133, Th‐228, Am‐241, I 125 and Sr‐90. Results: The minimum detectable activity for the system was 4.38 μCi. The minimum detector response distance for a Cs‐137 source of activity 7.28 μCi moving at an approximate speed of 1.2 m/s was found to be 2.3 m from the detector's centerline. The system easily detected a Cs‐137 source of activity 7.28 μCi moving under the detector enclosure at speeds ranging from 0 to 2.5 m/s. The system detected and identified combinations of radioisotopes when these were moved under the detector probe at an approx. speed of 1.2 m/s. Conclusions: All performed tests were within preset specifications. This novel EDNS system can effectively track movement of non‐medical/suspicious radioisotopes in a hospital environment, identify potentially dangerous radioisotopes, and report their location. Further testing and evaluation of the EDNS system is in progress.
SU‐FF‐I‐67: Converting CT Dose Length Product (DLP) to Kerma Area Product (KAP)
Authors: Ogden K , Huda W
Published: April 2010

Purpose: The amount of radiation that is incident on patients in CT is measured using the Dose Length Product (DLP mGy‐cm) which is not commensurate with the corresponding quantity currently used in radiography and fluoroscopy, namely the Kerma Area Product [KAP]. This study computed DLP to KAP conversion factors that will enable patient exposures in CT to be compared with radiography and fluoroscopy. Method and Materials: We computed the DLP and KAP values for head and abdominal CT examinations on a GE LS 16 CT scanner for the same examination. Scan DLP data were obtained using the ImPACT spreadsheet. Average CT Kerma values were obtained from the free‐in‐air intensity of the CT at the scanner isocenter and relative intensities within the fan beam plane. Average x‐ray beam areas were obtained using the focal isocenter distance (541 mm) and modeling adult patients as ellipses (heads radii of 7.38 cm/9.47; abdomens radii of 11.25 cm/15.5 cm). Values of KAP were computed per 100 mGy‐cm for head and abdominal CT scanning computed in 16 cm and 32 cm diameter acrylic cylinders, respectively. Results: In head and body CT, a DLP of 100 mGy‐cm corresponds to a KAP incident on the patient of 1.9 Gy‐cm2 and 5.4 Gy‐cm2, respectively. Conclusion: Conversion of DLP into KAP permit patient exposures in CT to be compared to exposures in radiography and fluoroscopy including head and chest radiography (∼1 Gy‐cm2), abdominal radiography (∼5 Gy‐cm2), barium studies (∼20 Gy‐cm2) and interventional procedures (∼100 Gy‐cm2).
SU‐FF‐I‐78: Effective Doses in Whole Body and Brain PET/CT Procedures of Adult Patients
Authors: Al‐Haj A , Lobriguito A , Parker R
Published: April 2010

Purpose: To determine the variation in patient effective doses for whole body and brain PET‐CT procedures and determine methods for dose optimization. Method and Materials: Demographic data (age, gender, and weight), CT exposure parameters and activity of 18F (FDG) were taken from patient records of 543 whole body and initial 54 brain PET/CT cases. PET Effective doses were estimated using the dose conversion coefficients for 18F (FDG) in ICRP Report No. 80. CT effective doses for the manufacturer's stated CTDIair were estimated using the IMPACT dose calculator. The Pearson correlation (p <0.0001) of PET effective doses with weight, age and 18F (FDG) activity was analyzed. Results: There are more male patients (55% and 61%) than females (45% and 39%) for whole body and brain procedures respectively. The mean age of patients for whole body is 47 ±18 years old and 34 ±16 years old for brain studies. The mean 18F (FDG) for whole body is 460 ± 130 MBq and 410 ± 45 Mbq for brain procedures. Pooling all ages, the mean effective doses are 8 ± 2 mSv and 10 ± 1mSv for whole body and brain respectively and dose correlate poorly with weight, age and activity. CT effective doses are in the range of 11 to 15 Msv. Conclusion: There is a wide variation in the 18F(FDG) activity which is about 30% of the mean activity. Standardization of activity can be formulated per weight or per age and a study of the setting image quality criteria and using low dose CT should be made. A dose conversion coefficient of 1.8 Msv per Gy can be used for whole body CT using 6 and 9 mGy CTDI to estimate effective dose.
SU‐FF‐I‐87: DTA‐Based Metrics for the Evaluation of Autosegmentation Algorithms in Clinical Radiotherapy Workflow
Authors: Moore KL
Published: April 2010

Purpose: To establish quantitative metrics to assess the performance of autosegmentation programs in the context of clinical radiotherapy workflow. Method and Materials: One of the more time intensive and predominantly un‐automated tasks in radiation therapy treatment planning is the segmentation of the anatomical structures which are relevant for a particular intended radiotherapy treatment. We present performance metrics based on the distance‐to‐agreement (DTA) between manually‐contoured reference sets and the results of a generic autosegmentation platform. Results: To correlate to the time expended to correct erroneous auto‐contouring results we posit the slice‐by‐slice , where{xr,i} and {xt,i} are the vertices on the reference and test sets, respectively, on the ith axial CT slice. The histogram of DTAs (or simple pass/fail DTA thresholds) will assess the amount of manual correction required to bring an auto‐contoured structure into acceptable agreement with the reference set. Beyond this application, full automation of the contouring process (i.e. no manual correction) would require stricter, 3‐dimensional, and site‐specific DTA metrics, for which we propose generalized quality factors. As a test bed for these metrics, we have compared manually‐generated clinical contours to those created by CMS' Atlas‐Based Autosegmentation system and shown that, for some sites, the autosegmentation is nearly indistinguishable from the variability in our clinic's manual contouring. Conclusion: Depending on the desired use of an autosegmentation package, either slice‐by‐slice or 3D DTA metrics facilitate the assessment of clinical performance. Regardless of intended application, the DTA‐based metrics may be used as (a) a quantitative benchmark of an autosegmentation algorithm against the inherent variability in manual contouring and (b) a potential correlate to efficiency gains should the software be brought into full clinical use.
SU‐FF‐I‐113: Anatomical Power Spectrum and Detectability: An Analytical and Experimental Basis
Authors: Gang G , Tward D , Siewerdsen J
Published: April 2010

Purpose: Superposition of anatomical clutter in medical images is known to degrade detectability of underlying structures. This paper investigates background power spectrum (PS) in tomosynthesis and cone‐beam CT (CBCT) in a manner that is general to various applications (e.g., breast and chest imaging) and allows analysis of generalized noise‐equivalent quanta (GNEQ) and task‐specific detectability. Methods: An analytical basis for physical phantom design was established from principles of self‐similarity and fractal dimension. Random arrangements of equal volumes of spheres were found to present power‐law noise comparable to that of, for example, breast or chest imaging. Rectangular and cylindrical phantoms containing spheres of various diameter (3–16 mm) were configured on an experimental bench for tomosynthesis and CBCT. Background PS was analyzed as a function of orbital extent, ranging from ∼10°–360°. Results were fit to the empirical form K/f∧b and incorporated in the GNEQ to investigate detectability versus tomosynthesis arc, imaging task, and dose. Results: Clutter phantoms based on self‐similar collections of spheres provided background PS described well by power‐law noise. 3D background PS were highly asymmetric, subtending the tomosynthesis arc in the Fourier domain and scales with the number of backprojected views. Analysis of the fully 3D background PS yields K and b that vary with tomosynthesis angle in a manner consistent with expectations, is distinct from that previously analyzed in 2D slices, and highlights the effect of orbital extent on 3D detectability. Analysis of GNEQ identified total arc and dose required to achieve a given level of detectability, depending on the imaging task. Conclusions: An analytical basis drawn from fractal theory guided phantom design providing power‐law noise. Analysis of background PS, GNEQ, and detectability index over a broad range of system configurations provided a general basis pertinent to modality‐specific systems, such as breast and chest tomosynthesis and CBCT.
SU‐FF‐I‐120: Monte Carlo Simulation of Thin‐Film CdTe Detector Performance for Diagnostic Imaging Applications
Authors: Jin X , Parsai E , Shvydka D , Kang J
Published: April 2010

Purpose: As a semiconductor material of high atomic number and density, cadmium telluride (CdTe) is highly suitable for direct radiation detection, producing electronic signal in response to incoming x‐rays. Development of thin‐film CdTe deposition techniques in recent years allows for manufacturing of low cost large‐area detectors with superior imaging capabilities and outstanding radiation hardness. We investigate performance on thin‐film CdTe based detector under a range of energies relevant to diagnostic imaging applications. Method and Materials: Our analysis is based on Monte Carlo modeling of the detector performance with MCNP5 package. In order to calculate input spectra for different tungsten anode voltages (kVp) of our clinical simulator unit, we performed series of output measurements required for spectra generation with Tungsten Anode Spectral Modeling using Interpolating Polynomials (TASMIP) algorithm. In the next step these generated spectra were ran through a 20 cm water phantom, representing an imaged patient and resulting in a set of primary photon spectra used for detector characterization. Finally, x‐ray beam is set to fall normally at the detector surface through a narrow slit, following a typical setup for line spread function LSF(x) measurement. Results: We calculate frequency‐dependent pre‐sampling detective quantum efficiency DQE(f) for kVp voltages from 40 to 140 kV. Thickness of CdTe was varied from 10 to 1000 microns, covering the range of feasible thin‐film devices. Conclusion: Thin‐film CdTe based detector offers high performance and high spatial resolution due to low signal spreading inherent of direct detection design. In combination with low manufacturing cost of large‐area flat panel device, the detector is decidedly suitable for critical all the diagnostic imaging applications.
SU‐FF‐I‐123: Clinical Value of Diffusion‐Weighted MRI in White Matter in Vivo
Authors: Olariu E , Cameron I
Published: April 2010

The excellent soft tissue contrast of diffusion‐weighted magnetic resonance imaging, DW‐MRI has made it an invaluable technique especially in oncological assessment bringing hope in distinguishing between brain abscesses and necrotic and cystic neoplasms. However, a clear characterization of brain tumors and the associated pathologic structures is still a challenge. In this study, a tissue model is proposed to interpret the water diffusion behaviour in white matter based on the measured apparent diffusivities and their volume fractions.

Measurements were performed on a 1.5T clinical scanner (Siemens). The protocol included: DTI measurements (b=0 and 500s/mm2), DW images (96 b‐values ranging from 0 to 10,000s/mm2 with diffusion gradient rotated in the x‐z plane, NEX=6, TE=200ms) and 96‐echoes, non‐linearly sampled using T2‐sequence.

All decay curves measured in the splenium agreed well with the assumed bi‐exponential function: .

The fast water pool, ADCfast had a long apparent T2 relaxation rate while the slow water pool, ADCslow had a shorter T2 constant. The volume fraction fslow correlate with the volume fraction directly estimated from the T2 spectrum. Markedly anisotropy was observed in ADCfast and fslow and more subtle in ADCslow.

Evaluation of water diffusion in normal appearing corpus callosum is clearly assisting the peculiar properties of water in biological system, invoking long‐range hydration structures modulated by the concentration of lipid‐protein complexes in the membranes, cellular size and tissue architecture. ADCslow originate from the water in the hydration layers, as ADCfast the rest of the tissue bulk water. The membrane and associated hydration layers form a barrier to water diffusion perpendicular to them since diffusion within the hydration layers is anisotropic.

This model is very sensitive to cellularity and further to a brain tumor grade; cell swelling and increased density of membranes enlarge fslow resulting in a decreased ADCs linked to cell proliferation.
SU‐FF‐I‐128: Effects of Slice Orientation and Parallel Acquisition On EPI‐Based PASL Perfusion Imaging in Areas with Susceptibility Artifact
Authors: Cheng S , Kuan W , Hsu Y , Lim K , Liu H
Published: April 2010

Purpose GE EPI is commonly applied for acquiring perfusion MRI with arterial spin labeling (ASL). A key problem is the long echo train that causes problems in image quality due to the susceptibility artifact. This study aimed to focus on the orbitofrontal cortex (OFC) region and evaluate the effects of slice angle combined with parallel imaging technique on ASL image quality. Methods FAIR combined with a single‐shot GE EPI was applied with TI = 1400 ms, TR/TE/FA = 3000 ms /20 ms /90°, 5mm slice thickness, 7 slices, NEX = 15, FOV = 220 mm and matrix = 64. The slice tilt was set from −45°, 0 to +40° relative to the AC‐PC direction. Images were obtained both with and without applying the SENSE (factor = 2). Signal‐to‐noise ratio (SNR) and contrast was calculated from the nonselective (MNS) and the selective inversion image (MNS). Results The SNR became more stable when the parallel imaging was used (Fig.1). On the contrary, the susceptibility gradient caused a greater effect on the SNR without parallel acquisition with a maximum at −15° slice tilt. At two of the slice orientations the resulted images exhibited greater SNR in the OFC region due to reduced susceptibility artifact. The changes of SNR can be appreciated from the spatially normalized images showed in Fig. 2. Figure 3 demonstrated slight varied contrast at different slice orientation measured with parallel imaging. The highest value is about 1.8% at −15° slice tilt. Conclusion For the purpose of reducing signal losses in OFC, this study found the optimal slice tile without parallel imaging. However, parallel imaging may be preferable because it was less subject to slice orientation. Further studies with more subjects and anatomical areas are required to better understand the changes in inflow contrast as the slice tilt.
SU‐FF‐I‐130: Effects of Inter‐Frame Motion in Pharmacokinetic Modeling Using Simulated Heterogeneous Phantoms
Authors: Song C , Fain S
Published: April 2010

Purpose: Motion induced errors in parametric measures using DCE‐MRI are reduced after image co‐registration, but no prior studies considered heterogeneity of lesions for assessment of uncertainties from inter‐frame motion. It is necessary to investigate heterogeneity dependence of motion effects, since tumors are known to be heterogeneous for many characteristics. In this study, we investigated motion effects in kinetic modeling using the simulated phantoms generated at various levels of heterogeneity in vascular permeability. Method and Materials: We created 3D ellipsoidal phantoms. Time series images were generated for three different tumor types using the Tofts model. To simulate heterogeneity, a sinusoidal pattern was generated in a Ktrans map. The kinetic parameters were generated from multivariate normal distributions, and pixel values at 16 time points were filled using the Tofts model. All the images were randomly transformed based on the in vivo measurements with fiducial markers. Image co‐registration was performed. Pharmacokinetic analysis was done on a voxel‐by‐voxel basis with and without motion correction (MC). Results: Motion correction improved accuracy for all lesions, but the degree of improvement depended on malignancy. Coefficient of variation of Ktrans was much larger in benign lesions than in malignant lesions. Mean Ktrans was overestimated for all lesions even after MC. Largest overestimation of 55% in mean Ktrans was observed for heterogeneous benign tumors. Large variation in mean Ktrans due to heterogeneity was seen for benign tumors leading to poor separation between benign and malignant lesions. Conclusion: Results showed that small scale motion leads to large errors in quantitative measures of kinetic modeling especially for benign lesions. After MC, the accuracy was improved but mean Ktrans was overestimated for all lesions. Large overestimation of mean Ktrans for benign lesions makes it difficult to distinguish benign from malignant lesions. The results will be validated with an increased number of realizations.
SU‐FF‐I‐135: Breast Density Measurement with Cone‐Beam CT and MRI: A Post Mortem Study
Authors: Ducote JL , Molloi S
Published: April 2010

Purpose: To compare breast density measurements from cone‐beam CT and breast MRI. Methods and Materials: Three pairs of postmortem breasts were scanned with MRI and cone‐beam CT. The cone‐beam CT system was built in our lab using a standard x‐ray tube, a rotation stage, and a flat panel detector. The imaging technique was 80 kVp, 0.16 mAs and 921 frames spanning 360 degrees. Each scan used a total of 147 mAs. MR images were acquired with an Aurora 1.5T dedicated Breast MRI system. A T1‐weighted gradient echo technique was used to maximize the contrast between the adipose and glandular tissues. Image processing procedures were implemented to segment the glandular tissue from adipose tissue. Specifically, median filters and isodata thresholding were used to identify tissue types. Percentage glandular tissue was compared between the two imaging modalities. Results: Breast densities computed from CT (DCT) were related to densities computed from MRI (DMRI) as DCT = 0.851 DMRI + 0.012 (r2 = 0.973, SE = 0.012). The average error between DCT and DMRI was 9.75%. Conclusion: The breast density measurements using Cone‐beam CT and breast MRI were highly correlated. However, it is anticipated that more sophisticated segmentation techniques can further improve the results.
SU‐FF‐I‐137: Scatter Correction in Quantitative Dual Energy Mammography
Authors: Ducote JL , Molloi S
Published: April 2010

Purpose: To investigate the performance of a new algorithm designed to correct x‐ray scatter and estimate the primary intensity in mammography. Method and Materials: The algorithm is based on image convolution and implements a spatially variant scatter point spread function which is energy and thickness dependent. The scatter kernel was characterized in terms of its scattering fraction and radial extent on uniform PMMA phantoms with thicknesses of 0.8 – 8.0 cm. The algorithm operates on a pixel by pixel basis by grouping pixels of similar thicknesses into a series of mask images that are then individually deconvolved using Fourier image analysis with a distinct kernel for each image. The algorithm was tested with four experimental phantoms, three step phantoms made of PMMA and one anthropomorphic breast phantom on a full field digital mammography system at energies of 24, 28, 31, and 49 kVp. The true primary signal was measured with a multi hole collimator. Results: For all 16 studies, the average mean percentage error in estimating the true primary signal was found to be −2.13% and the average rms percentage error was 2.60%. Conclusion: The new algorithm allows improved accuracy in estimating primary image intensity. It is also expected to improve the accuracy of quantitative dual energy mammography.
SU‐FF‐I‐138: Computer‐Aided Image Texture Analysis as An Indicator of Image Quality: A Feasibility Study in FFDM
Authors: Berger R , Kontos D , Carton A , Maidment A
Published: April 2010

Purpose: Image quality is often quantified using signal‐to‐noise‐ratio (SNR). We hypothesize that clinical image texture features are also reflective of image quality. To test feasibility, we investigated the relationship between quantitative image texture features and SNR as a function of acquisition parameters for a full‐field digital mammography (FFDM) system. Method and Materials: An anthropomorphic breast phantom (Model 169, Gammex RMI, Madison, WI) was imaged with a Senographe 2000D (General Electric Medical Systems, Chalfont St. Giles, UK). Images were acquired with various target/filter, kV (25 – 32 kV) and mAs combinations. The mAs was varied from 10 to 300% of that required for a standard phototimed exposure yielding an average glandular dose (AGD) of 1.8 mGy. SNR was computed in a 2.5cm2 retroareolar region of interest (ROI) segmented from linear images after flat‐field and offset correction. Signal intensity was computed as the average pixel value in the ROI. Noise was computed as the RMS difference of two images acquired using the same acquisition parameters. Image texture features of skewness, coarseness, contrast, energy, homogeneity, and fractal dimension were computed in the corresponding ROI from the Premium View™ processed FFDM images. Results: Homogeneity decreases continuously as a function of mAs. Skewness, coarseness, and fractal dimension increase, while contrast and energy decrease, until all reach a threshold. The threshold occurs between 40–100% of the phototimed AGD, beyond which no further change is seen. Linear regressions with mAs were strong after logrithmic transformation, having R2 ⩾ 0.84, p < 0.001 for coarseness, energy, and homogeneity. Conclusions: Clinical texture features are indicative of image quality. While homogeneity correlates closely with SNR, other texture features reach a threshold, seeming to indicate optimal dose settings. Further work is underway to fully investigate the potential use of image texture as an indicator of clinically acceptable FFDM image quality.
SU‐FF‐I‐139: Low Dose Breast CT with Photon Counting Detectors: A Phantom Study
Authors: Le H , Ducote J , Klopfer M , Molloi S
Published: April 2010

Purpose: To investigate image quality improvement of breast computed tomography (CT) using a photon counting detector as compared to an energy integrating flat panel detector. Method and Materials: A cone‐beam CT system was built that utilized a CsI‐based flat panel detector. The system consisted of a standard tungsten target x‐ray tube and a CsI indirect flat panel detector (Paxscan 4030CB) mounted on an optical bench. The photon counting CT system was built with the same setup, but with the flat panel detector replaced by a row of cadmium. (CZT) detector (eV2500, eV Products). The CZT detector consisted of 64 pixels with a pitch of 0.8 mm and five energy bins for spectral separation. A Lucite phantom (2.5 cm in diameter) was constructed with iodine and calcium contrast materials. Tomographic data were acquired with both systems and the contrast‐to‐noise ratio was compared. The data from CZT was energy weighted before analysis. Results: Image quality improved when comparing the CZT energy weighted images to flat panel images. The CNR improvements were 24% and 19% for calcium and iodine, respectively. Conclusions: Phantom results showed significant improvement in CNR for breast CT using an energy resolving photon counting detector as compared with an energy integrating flat panel detector.
SU‐FF‐I‐142: Quantifying the 4D PET/CT Volumetric Distortions: A 4D Dynamic Phantom Study Based On Pre‐Recorded Patient Data
Authors: Ionascu D , Park S , Mamede‐Lewer M , Gerbaudo V , Killoran J , Berbeco R
Published: April 2010

Introduction 4DPET/CT imaging is a powerful technique to assist clinicians in accurate definition of gross‐tumor‐volumes (GTV) in the lung and abdomen. We present the results of phantom studies designed to evaluate the accuracy of 4DPET/CT at reconstructing the true GTV when tumor motion and abdominal motion are reproduced based on pre‐recorded data from real patients. Methods Measurements were conducted using a 4D dynamic phantom control system capable of reproducing a time‐dependent 3D motion (GTV) and a synchronous, decoupled 1D motion (abdominal surface). The tumor and the abdominal motion trajectories programmed into the phantom are based on pre‐recorded patient data (tumor and abdominal motion). A 4ml spherical vial of FDG, representing the tumor, was used within a water‐FDG mixture adjusted to produce a target‐to‐background activity‐ratio of 8:1. The image reconstruction was done using 10 phase bins over the respiratory cycle. The patient selection was based on the amplitude of the internal marker motion (> 1cm). Results and Discussion Based on a 3DPET scan with no target motion, two methodologies were used to determine the activity threshold that recovers the active volume of the target (4ml) relative to: (1) the maximum intensity voxel; (2) the average intensity obtained from the five highest intensity voxels;. The percentage difference between the true and calculated volume was determined for each phase bin of the 4D studies. Errors as large as 45% were observed for specific patients and phases with a statistical bias towards overestimation of the target volume. However, the activity threshold based on the average intensity has shown to reduce the inter‐phase volumetric distortions. Conclusion Our results have quantified volumetric distortions that occur during 4D PET/CT imaging based on previously recorded internal target and abdominal motions in patients. These results are relevant to the accurate application of 4D PET/CT to radiotherapy target definition.
SU‐FF‐I‐147: Monte Carlo Based Evaluation of 3D PET Quantification Inaccuracy for the Lung
Authors: Kang H , Schmidtlein CR , Mitev K , Gerganov G , Madzhunkov Y , Humm JL , Amols HI , Kirov AS
Published: April 2010

Purpose: Our goal is to investigate the effect on PET accuracy of the various physical and instrumental phenomena using realistic Monte Carlo (MC) models of patient activity distributions and PET scanners. Methods and materials: Data from a lung PET/CT scan is used to create numerical voxelized phantom for realistic MC simulations using the GATE MC code. We compared the activity reconstructed from the simulations to the input (“true”) values. We investigated the effects of random coincidences, photon scatter and positional shift between transmission and emission scans on the degradation of 3D PET quantification accuracy. Results: When exact attenuation, scatter and random corrections are applied, the activity from the simulated scans deviated from the input by more than 50% for 25% of the voxels. Inaccuracy of the random and scatter corrections of 20% will add additional quantification errors of about 20% and 40% respectively. The attenuation correction (AC) adds random and scatter events to the high tissue density regions. AC based on misaligned transmission data causes pronounced changes in the activity distribution in regions that have a high density gradient such as at junctions between soft tissue, bone and lung. AC misalignment causes errors of the activity levels, which may exceed a factor of five around the ribs for 1.5 cm shift between the PET data and the AC image. Conclusions: MC methods are a useful tool in investigating PET scanner response to realistic distributions of the activity and the attenuation properties and in establishing the uncertainty in PET quantification in patient studies. The potential quantification errors due to possible misregistration and inaccurate scatter and random corrections have been determined as indicated above for the lung.

Supported in part by NCI grant CA‐059017 and performed in part on the Physon cluster, funded by Bulgarian NSF contract DO‐1‐872.
SU‐FF‐I‐153: First Experience of High Resolution 3D Optical‐CT Scanning of An Anthropomorphic, Leuco‐Dye Doped, Radiochromic Plastic Dosimeter
Authors: Sakhalkar H , Thomas A , McMahon R , Washington A , Adamovics J , Oldham M
Published: April 2010

Purpose: To investigate feasibility of high‐resolution three dimensional (3D) optical‐CT scanning of an anthropomorphic leuco‐dye doped radiochromic plastic dosimeter. Method and Materials: An anthropomorphic head phantom made out of PRESAGE™ (a leuco‐dye‐doped radiochromic plastic) was from Heuris Pharma. Co‐planar alignment marks (visible on x‐ray CT and optical‐CT) were placed on the surface. These were used to setup the phantom for x‐ray CT and treatment and for registration of measured dose from optical‐CT with the eclipse treatment planning system calculations. A RapidArc™ treatment for brain tumor was delivered and radiochromic response was scanned using optical‐CT. Optical‐CT (pre‐irradiation and post‐irradiation) was with a commercial laser beam scanner called OCTOPUS‐5X™ (MGS Research Inc). The following imaging parameters were used: Image matrix of 418×418, pixel size of 0.5 mm, 1200 projections at 0.3 degree angular increments and inter‐slice spacing of 2.5 mm. The relationship between post‐irradiation radiochromic response and dose was established by irradiation of 1 cm path‐length cuvettes to a known dose and measuring the corresponding optical density change. Results: Pre‐irradiation and post‐irradiation optical‐CT scans of the head‐phantom were promising with artefacts generally confined to the edge because of refractive index mismatch between scanning fluid and phantom material. Even with a refractive index mismatch, challenging surfaces like the nose and ears were reconstructed with clarity. A profile through the center of the reconstructed central slice was flat suggesting uniform optical density. Further improvements to optical‐CT images are possible by satisfying the Nyquist sampling‐sufficiency criteria and with precise refractive index matching. Cuvette irradiations confirmed that the relationship between delivered dose and radiochromic response was linear with a slope of 0.0144 OD change per Gray. Conclusion: Results suggest that anthropomorphic dosimetry phantoms could be used for patient specific 3D quality‐assurance in the near future, which represents a major advance in the field of 3D dosimetry.
SU‐FF‐I‐159: Conditions for Practical Measurement of X‐Ray Spectra for Clinical Radiography of the Chest
Authors: Dougall T , Erwin W , Willis C
Published: April 2010

Purpose: To establish conditions necessary for measuring x‐ray spectra in simulated clinical chest radiography examinations. Method and Materials: X‐ray spectra were obtained for simulated chest examinations of the CDRH LucAl Chest phantom for 12 cases: 141, 125, and 109 kilovolt peak; with/without 0.2 mm Cu pre‐patient filtration; and with/without a scatter reduction grid. X‐ray spectra were acquired using an Amptek XR‐100T‐CdTe semiconductor detector and PX4 digital pulse processor behind the phantom. Acquired spectra were corrected for characteristic CdTe x‐ray escape events using Amptek XRF‐XP software, and for the energy‐dependent absorption of Cd and Te. Channel‐to‐energy calibration was verified with Gd‐153, Co‐57, and Ba‐133. Spectra were acquired with 8mm Pb shielding of off‐axis radiation. Validity of acquired spectra was tested by three methods: comparison with simulated x‐ray spectra; comparison of the measured half‐value layer (HVL) to HVL calculated from spectra acquired without attenuation; and comparison of measured exposure to exposure calculated from acquired spectra. Results: Collimating the beam results in narrow beam geometry that does not represent broad beam clinical geometry. However, when off‐axis radiation is excluded from the detector, acquired spectra agree with simulated spectra and measured HVL. The calculation of exposure from the spectra depends strongly on actual collimator orifice diameter, but results suggest approximately 80% measurement efficiency. Off‐axis radiation may be over‐represented in spectra collected without extensive forward shielding for broad beam exposure conditions. The digital pulse processor allows acquisition at higher incident flux than the older PX2T analog version. Conclusion: Using improved electronics and appropriate methods to limit flux and off‐axis radiation, it is possible to collect accurate spectra under simulated clinical conditions. These methods could be used to study optimization of radiographic technique for clinical examinations.
SU‐FF‐I‐161: Non‐Destructive Grid Ratio Measurement
Authors: Pasciak A , Jones A
Published: April 2010

Purpose: The anti‐scatter grid is often neglected during acceptance testing or is only examined for damage, non‐uniformities, and centering. Other important performance parameters are being overlooked, including grid ratio. The grid ratio is an important parameter that determines the ability of a grid to improve contrast, and should be verified during acceptance. Materials and methods: We developed an analytical method for calculating the grid ratio from simple measurements. An image of the grid is acquired at an SID not equal to the focal distance, and mean pixel values are measured in three regions of interest in the resulting image — at the center and equal distances to either side of the center. These data, along with the known focal distance of the grid and the SID used to acquire the image, are used to calculate the grid ratio for each half of the grid. Grid ratios were measured for four DR systems — three identical systems and one from a different manufacturer. Results: Measured ratios were in some cases substantially less than nominal ratios. In several cases, different ratios were measured for each side of a grid. Our results identified one of the three grids from the identical systems as having a higher ratio than the others. Measurements made at distances greater than the focus distance yielded more reproducible results than ones made at distances less than the focus distance. Two stand‐alone grids were measured, then disassembled to measure the actual grid ratio for comparison. Conclusions: This method can be used to measure ratios for both DR and CR systems and other grids. The method can be extended to use screen‐film as the receptor. Our results indicate that the actual grid ratios for many grids in use at our institution are less than the stated ratio, resulting in reduced image quality.
SU‐FF‐I‐163: Study of Dosimetric Characteristics of MAGIC Polymer Gel with Formaldehyde for Electrons Beams Using PENELOPE Code
Authors: Pianoschi T , Marques T , Baffa O , Nicolucci P
Published: April 2010

Purpose: Conformational techniques require an accurate control of doses and dose distributions. A dosimeter with high spatial resolution and high sensitivity is essential while 3D features would be a plus. Polymer gel dosimeters have appropriate spatial and dose resolutions for quality control in conformational radiotherapy with photon beams, but the study for their use in electron beams is still a gap. This work analyzes the dosimetric equivalence between MAGIC polymer gel with formaldehyde and water for therapy electron beams using PENELOPE Monte Carlo code. Method and Materials: In this study, the gel‐water dosimetric equivalence was studied for electron beams in an energy range of 5 to 22 MeV, with 15 × 15 cm2 field size at 100 cm source‐surface distance. The phantoms of homogeneous MAGIC polymer gel[1] and water had dimensions of 20 × 20 × 20 cm3. The spatial resolution set in the simulations was 2 mm from the central‐axis depth‐dose distribution. The percentage depth‐dose (PDD) curves and 3D dose distributions in the phantoms were determined by PENELOPE code. Results: The PDP curves showed that the MAGIC gel has a higher attenuation coefficient than water for all energies evaluated. For therapeutic range the smallest difference found was 0.4 cm for the 5 MeV and the highest difference was 1.6 cm for the 22 MeV beam showing that as higher the electrons energy as higher the difference in attenuation in comparison with water. Conclusion: The comparison between the PDP curves for the gel and water showed the greatest attenuation coefficient of the gel, due to its higher effective atomic number. Future studies with MAGIC gel will evaluate the feasibility and applicability of this dosimeter in conformal radiotherapy with electron beams.
SU‐FF‐I‐165: Ultrasound Transducer Performance Evaluation Summary for a Large Multi‐Specialty Clinic
Authors: Kruger R
Published: April 2010

Purpose: The objective of this study was to evaluate and identify the type of element failures found in ultrasound transducers used in our clinical practice.

Method and Materials: Assessing transducer functional performance was accomplished using the Sonora FirstCall Test System, Sonora Medical Systems Inc. (Longmont, CO, USA). This system is an ultrasound transducer tester, which can test all essential transducer parameters according to FDA regulation 21CFR 820. The system was used to evaluate 199 transducers at 7 clinical sites from September 2007 to December 2008. All transducers were of the same manufacturer and may have been tested up to three times. The test system is connected to the transducer but not the ultrasound scanner. Each transducer element is tested and evaluated. The test is performed in water, where the elements are activated one by one using a metal target plate to reflect the ultrasound pulse emitted by each activated element. The returning pulse is analyzed by means of the peak‐to‐peak amplitude, center frequency, pulse width, bandwidth, and the pulse waveform. Additionally, the accumulated capacitance of every element is evaluated and element electrical integrity is tested identifying electrical failures. Results: This investigation found that 35 transducers (17.6%) failed our acceptance criteria. The 199 transducers evaluated during this study consisted of 5,168 total elements. An evaluation of the 35 transducers that failed our acceptance criteria resulted in a total of 291 elements that had one of the following defects: dead elements, lens delamination, wire cuts, capacitance short. Conclusion: Ultrasound Quality Assurance measurements using a commercial phantom are subjective and can require a considerable investment. Our survey indicates an urgent need for increased quantitative testing of the transducers in clinical departments, such testing should augment the current QA program to insure the highest quality performance of clinical ultrasound systems.
SU‐FF‐I‐166: Prostate Volume Contouring: Delineation Variations Using CT Versus Combined CT + US for Image‐Guided Radiotherapy
Authors: Fiandra C , Ragona R , Ricardi U , Munoz F , Guarneri A , Franco P
Published: April 2010

Purpose: To verify if 3D‐US may be helpful in the definition of prostate for external beam radiotherapy Method and Materials: The clinical study involved ten patients with localized prostate cancer receiving conformal radiation between January and April 2009. Patients underwent a planning CT scan and a pelvic MR scan Prior to each scan (and subsequently before each fraction of radiotherapy) patients were asked to evacuate their bowels, and to have a comfortably full bladder. Immediately after the CT scan for planning is done, a trans‐abdominal 3D‐US image (Clarity, Resonant Medical, Toronto, CA) is acquired with the patient in the exact same position. With the help of a ceiling‐mounted tracking camera and 3D‐ultrasound (3D‐US) probe with active infrared sensors in the planning room, is possible to obtain an accurate spatial reconstruction of the ultrasound pixels in relation to the room's global coordinate system making feasible a simple superimposition between CT and US images . The MR scan was performed soon after the CT (1/2 hour) and the patient underwent CT and MRI in the planned treatment position with an indexed shaped knee rest and indexed ankle support A routine T2‐weighted prostate pulse sequence with a TE of 90 ms and a slice thickness of 4 mm was used. Results: No significative variations among observers considering together all the modalities imaging are registered (p=0.629). Significative variations between the three modalities considering together all the observers are reported (p=0.038). No significative variations of dosimetric predictors were found (p=0.965). Conclusion: 3D‐US have been shown to correlate well with MR in reducing volume respect to the TC. Dose to OAR is not significatively reduced even if MRI imaging is considered. However 3D‐US may be confirmed as a very good technique of imaging for prostate and thus for IGRT of prostate cancer.