bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐114: Effects of Exposure Level and Anatomical Background On Detection of Simulated Microcalcifications in Digital Mammography
Authors: Lai C , You Z , Zhong Y , Shen Y , Chen L , Liu X , Han T , Ge S , Yi Y , Geiser W , Whitman G , Yang W , Shaw C
Published: April 2010

Purpose: To assess the influence of quantum and anatomic noises on the detection of simulated microcalcifications (MCs) on digital mammograms. Materials and Methods: Images of an anthropomorphic breast phantom (RMI 169) overlapping with simulated MCs ranging from 160 to 224 micron in size placed at various locations were acquired with an aSi/aSe flat panel based digital mammography system (Selenia) operated with Mo‐Mo target/filter combination at 28 kVp. These mammograms were exposed with 10, 20, 40, 80, 160, and 325 mAs. All images were displayed randomly on a review workstation and reviewed by five readers independently. The readers were asked to count the number of visible MCs. The ratio of visible MCs was computed for each different combination of MC size, reader and mAs setting. The performance differences in the ratios averaged from all readers between mAs levels was assessed by performing Student t‐test to compute the p values. Results: It was found that in the dense tissue region the visibility reached 90% at 10, 33 and 37 mAs for 200–212, 160–180 and 180–200 micron MCs, respectively; and at 10 mAs for 180–200 and 200–212 micron MCs and at 15 mAs for 160–180 micron MCs in the fatty region. The lower visibility in the dense tissue region may be due to the fact that the photon flux was lower in the dense tissue regions therefore requiring higher mAs setting to achieve sufficient image SNRs for detection of MCs. Our results also show that in the dense tissue region, the visibility of 180–200 micron MCs stayed at 90% at 80 mAs. This may indicate that the anatomical noise was limiting the detectability of 180–200 micron MCs.

This work was supported in part by grants CA104759 and CA124585 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.
SU‐FF‐I‐116: Estimation of Imaging Geometry Parameters of a Multiple Source Digital Tomosynthesis System Using a Standard Cone Beam CT Calibration Phantom
Authors: Paidi A , Bose S , Maltz J , Bani‐Hashemi A
Published: April 2010

Purpose: To describe and evaluate a calibration procedure to compute the imaging geometry parameters (IGPs) of a stationary multiple source digital tomosynthesis (DTS) system mounted on a medical linear accelerator (linac) equipped with a cone beam CT (CBCT) imaging system. DTS reconstructed image quality depends on the precise computation of IGPs. The novelty of the proposed method is that it employs the same calibration phantom used for calibrating the CBCT imaging system. This offers two major advantages as opposed to using different phantoms: 1) It ensures both the imaging systems (CBCT and DTS) reference a common machine isocenter. This is of critical importance for 3D image guidance during radiation therapy. 2) It ensures a seamless workflow while calibrating the medical linac. Owing to the unconventional nature of source‐detector configuration employed by the DTS system, the DTS projections of a conventional helical bead geometry calibration phantom are characterized by bead occlusion, distortion and missing information. Therefore calibrating the multiple source DTS system with the standard CBCT calibration phantom is a non‐trivial task Materials and methods: Projections of the calibration phantom, which contains radio‐opaque tungsten beads, are obtained using each of the individual x‐ray sources. An ideal model of the projection geometry is used to obtain reference projection images of the calibration phantom for each of the x‐ray sources. IGPs are perturbed using an optimization scheme in order to minimize the difference between acquired projection images and the model. Results: The algorithm is able to detect changes in the source and detector positions with accuracy of approximately 0.3 mm. Considerable improvements are seen in the reconstructed image quality as a result of using precise IGPs in the reconstruction algorithm. Conclusion: We have demonstrated a robust method of performing geometry calibration for both regular and irregular source geometries. Research sponsored by Siemens Healthcare
SU‐FF‐I‐117: Evaluation of Measure Discontinuity Metrics for 4‐D CT Reconstruction Data
Authors: Han D , Bayouth J , Wu X , Sonka M
Published: April 2010

Introduction Measure discontinuity plays a key role for a successful radiotherapy treatment planning in 4‐D radiotherapy therapy, which is increasingly used for lung cancer treatment. An important issue is to define a metric that can determine which breath period is well trained and the obtained image data can be used to reconstruct the 4‐D volume. We evaluate several metrics on 4‐D CT data. Our research can give some practical guidance to determine the quality of the acquired data. Method and Material Supporting s1 is above s2, the difference between the last slice in s1 and the first slice in s2 is computed (denoted as d). d should be following a distribution p. If we have no prior knowledge, Gaussian distribution is a reasonable choice that is d∼Gaussian(μ,ϐ). The parameters of the distribution can be learned from the differences sets computed from s1 and s2. The metrics are computed based on these parameters. Results (1) One of the metrics is effective which can detect about 83.3% stacks with large artifacts. By ROC analysis, the error at equal error rate (intersection with curve diagonal) is 0.833, the threshold at equal error is 0.0320 and the area under curve is 0.8747. (2) Pre‐processing is important. (3) Not all metrics work well. Conclusion Measure discontinuity is a fundamental issue in 4‐D reconstruction, which is not well addressed in the state‐of‐the‐art. The conclusions of our work are: (1) Ground truth data on large scale 4‐D CT data should be created. To our knowledge, no work is done is this field; (2) The distribution of d, should be analyzed further. May be more complicated distributions are better than Gasussian distribution.
SU‐FF‐I‐118: Assessment of the Spatial Resolution of Digital Imaging Systems Using a Star Pattern
Authors: Gingold E , Dave J
Published: April 2010

Purpose: To demonstrate a method of measuring the modulation transfer function (MTF) of digital imaging systems using the common star pattern test tool. The goal of this research is to develop a technique that brings precise and objective evaluation of spatial resolution to routine quality control in radiography and fluoroscopy. Method and Materials: Images of a 2‐degree star pattern were obtained on a variety of digital radiographic imaging systems, spanning a range of spatial resolution performance levels. One‐dimensional profiles from concentric circles around the center of the star were obtained from each star image. The circular profiles were unwrapped to produce a series of square waves, which were analyzed to produce the square wave response function (SWRF). Droege's method was used to compute the MTF from the SWRF. The MTF determined using the star pattern method was compared to published and quality control measurements of the MTF for several digital mammography and digital radiography systems. In implementing this method, important parameters that must be considered include the radial and angular sampling rates, the method for determining the zero‐frequency normalization and correction for beam nonuniformity. Results: The MTF computed from star pattern profile measurements closely matched the MTF obtained using other methods over the range of spatial frequencies between the Nyquist frequency and 1/3 of the Nyquist frequency. The star pattern MTF, which is a system measurement and includes the effects of detector and geometric unsharpness, was within 6–8% of reference values obtained from the scientific literature for two models digital mammography equipment. Conclusion: Images of a 2‐degree star pattern can produce estimates of the two‐dimensional system MTF. This method may offer a convenient means of assessing the spatial resolution of digital imaging systems for acceptance testing and quality control.
SU‐FF‐I‐126: Varied Vasomotor Responses Among Brain Territories in Unilateral ICA Stenosis Patients Studied Using Breath‐Hold BOLD MRI
Authors: Kuan W , Chang T , Hsu Y , Lim K , Liu H
Published: April 2010

Introduction: Patients with significant internal carotid artery (ICA) stenosis increase the incidence of ischemic stroke and benefit from carotid interventions, such as carotid angioplasty with stenting (CAS). Hyperperfusion syndrome usually causes disastrous outcome if occurred after carotid interventions. In recent studies, impaired cerebral vasoreactivity (CVR) is considered as one of the predictors for hyperperfusion syndrome. Hypercapnia stresses such as breath holding result in vasodilatation in human subjects. Thus combining breath holding and BOLD MRI may be a useful method to characterize the impaired CVR in patients prone to hyperperfusion after CAS. Most recently, Leoni et. al. found different hemodynamic response among different brain territories in normal subjects during breath holding. The aim of this study was to evaluate the varied hemodynamic responses among different brain territories in unilateral ICA stenosis patients using the same MRI method. Methods: Six patients with unilateral ICA stenosis participated in this study and were asked to hold their breath for 15 sec. Three cycles of the breath holding task were performed. A single‐shot T2* gradient‐echo EPI sequence was used for BOLD measurements at a 1.5T scanner. Twenty axial slices were acquired to cover the whole brain. Echo‐planar images were spatial normalized to the MNI template and averaged BOLD signal time curves were drawn from six regions of interest, i.e. ACA, MCA and PCA on both sides. To show the extent of voxels with significant BOLD signal changes, a correlation analysis (p<0.05, corrected) was applied using the averaged signal time curve from the whole brain tissue. Results and Conclusion: In summary, our results showed the impaired CVR in patients with ICA stenosis was territory dependent (Fig. 2). Detailed analysis of the hemodynamic responses measured from breath‐holding BOLD MRI may help predict hyerperfusion syndrome after CAS.
SU‐FF‐I‐129: A Comprehensive QA Program for Radiotherapy MR Simulators
Authors: Chen L , Doss M , Richardson T , Ma C
Published: April 2010

Purpose: To our knowledge, there are no publications on the acceptance, commissioning and quality assurance (QA) procedures for MR simulators in radiotherapy. The purpose of this work is to develop a comprehensive protocol for MR simulators in radiotherapy. Materials and Method: A GE 1.5T MR scanner was installed in our department in 2006. During acceptance testing and commissioning, the MR scanner was tested according to the standards established by the American College of Radiology (ACR) MRI Accreditation Program. An ACR phantom was used for the study. Our QA protocol includes procedures for geometric accuracy, high‐contrast spatial resolution, slice thickness accuracy, slice position accuracy, image intensity uniformity, percent signal ghosting, low‐contrast object detectability, inter‐slice RF interference, fringe field survey, magnetic field homogeneity, eddy currents, coils SNR check and cryogen consumption. We also checked the patient/console intercom 2464_3 2464_4 system, table stop buttons, emergency stop button, table docking, vertical movement, alignment lights and the ventilation system. Monthly QA were developed to check the RF, transmission gain/attenuation, imaging distortion and resolutions using the ACR phantom. A phantom from GE was used for daily QA to check the SNR, RF, isocenter position and the gradients. The lasers installed in the MR room for patient setup were also checked. QA procedures were developed for MR spectroscopy. The results from monthly and daily QA were compared with the commissioning data. Results: The acceptance/commissioning test and monthly QA showed that the MR scanner met the criteria established by the ACR MRI Accreditation Program. The results from the daily QA are SNA: 29.66±0.84; Noise: 2.31±0.1, CTR Frequency: 63860229±4778; iso‐Z: 8916.33±9.26; Gradient X, Y and Z: 100.14±0.11; 100.05±0.08; and 99.8±0.10, respectively, for >2 years. The variations were within 1% of the commission data. Conclusions: A comprehensive QA protocol was developed and routinely used for our MR simulator for radiotherapy.
SU‐FF‐I‐132: Simultaneous Estimation of Perfusion and Permeability Parameters: Validation Study On Animal Model
Authors: Yu Y , Jiang Q , Bao S , Feng W , Wu W , Haccke E. Mark , Hu J
Published: April 2010

Purpose: To demonstrate the feasibility of simultaneously obtaining permeability and perfusion parameters using one MR pulse sequence with one administration of contrast agent (CA). Method and material: A 3D dual‐echo pulse sequence was used to simultaneously acquire T1‐weighted and ‐weighted images. Data were acquired from a stroke mouse model using the pulse sequence with six pre‐contrast and eighty four post‐contrast dynamic contrast‐enhanced series. An analysis method was developed to estimate perfusion and permeability parameters. Shortening in T1 by CA enhances signal intensity, while shortening in T2* reduces signal intensity. This competitive process by T1 and T2* was taken into account in our analysis method. To minimize subjectivity and increase consistency, AIF was automatically estimated using fuzzy C‐means clustered based techniques. Result: Three‐dimensional pharmacokinetic parameter maps of volume transfer constant (Ktrans), extracellular extravascular space (Ve) and reflux rate (Kep), as well as perfusion parameter maps of the relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF) and relative mean transit time (rMTT) were successfully obtained. Conclusion: It is feasible to simultaneously estimate permeability and perfusion parameters using data acquired by one pulse sequence with only one administration of CA. This new technique should prove to be a useful tool for both animal and human DCE‐MRI studies.
SU‐FF‐I‐134: Mechanical Activation of the Brain for MR Elastography
Authors: Weaver J , Perrinez P , Lollis S , Pattison A , Perreard I , Paulsen K
Published: April 2010

MR elastography (MRE) has three essential elements: mechanical activation, MR motion estimation and shear modulus reconstruction. Mechanical activation of the brain is extremely difficult. Indeed it is much more difficult than actuation of other body parts because the skull and meninges form an excellent mechanical isolation system. Vibrations and impacts are heavily damped to protect the brain. Several methods have been used previously including whole head shaking using bite bar, a band around the head or actuators behind the head. We have found significant discomfort with all the methods we tried and that discomfort diminishes the utility dramatically because, when uncomfortable, patients do not complete examinations or introduce motion artifacts. All methods produce very small vibrations that are far below regulatory limits on vibration in the brain. We present evidence that the best way to couple shear waves to the brain is through the spinal cord. In a series of feline MRE examinations the largest shear motion occurred when the cerebellar motion was largest. The cerebellar motion was large where the spinal cord connects to the brain on every study that produced the most coherent, convergent solutions. Increased motion in the cerebellum occurred in 17 of 25 (68%) studies on seven animals. We postulate that one way to produce shear waves within the brain is through the spinal cord; i.e., that mechanical waves are transmitted along the cord and into the brain much more effectively than they are transmitted through the skull and meninges.
SU‐FF‐I‐141: Measuring Breast Density with Dual Energy Mammography: A Phantom Study
Authors: Ducote JL , Molloi S
Published: April 2010

Purpose: To investigate the feasibility of measuring breast density in phantoms with dual energy mammography. Method and Materials: Glandular and adipose equivalent phantoms of uniform thickness were used for dual energy basis decomposition calibration. The dual energy mammography system used a tungsten anode x‐ray tube with a 50 μm rhodium beam filter for low energy images and a 300 μm copper beam filter for high energy images. Three different phantom studies were used to evaluate the technique. The first study consisted of phantoms with thicknesses of 25–85 mm in 5 mm steps with a mean density of 28%. The second study consisted of step phantoms designed to more closely mimic the shape of a female breast with maximal thicknesses of 30–70 mm at a fixed density of 50%. The third study consisted of 40 mm thick phantoms of different sizes (62.5, 125, 250 cm2) at a fixed density of 50% to assess the effect of breast size on density measurement. Results: The RMS errors in breast density measurements were 0.4% for the uniform phantoms, 3.3% for the step phantoms, and 4.7% for the phantoms of different sizes. Conclusion: The results of phantom studies indicate that dual energy mammography can be used to measure breast density with an RMS error of less than 5%. Dual energy mammography can potentially be implemented with minimal changes to the standard mammography exam.
SU‐FF‐I‐149: Accuracy of Scatter and Attenuation Correction in PET Imaging
Authors: Chang T , Chang G , Clark J , Mawlawi O
Published: April 2010

Objectives: PET data is usually corrected for scatter and attenuation among other factors during image reconstruction. The aim of this abstract is to study the accuracy of scatter and attenuation correction using different tissue equivalent and object sizes in PET/CT imaging. Methods: A phantom containing three cylindrical inserts (Air, water and Teflon) each of 40mm diameter was scanned on a GE DRX PET/CT scanner. The inserts were used to simulate air, soft tissue, and bone at 511 keV. The activity concentration (AC) in the phantom background was set to 0.12uCi/cc to emulate background AC found in clinical studies. PET data was acquired in 3D mode for 6 minutes (2 FOVs, 3 min per FOV). The same experiment was then repeated twice while wrapping the phantom with one and two layers of saline bags to simulate patients with medium and large cross sections. Each layer of saline bags added 4cm to the phantom diameter. All PET images were reconstructed using OSEM (2 iterations 21 subsets). A 20mm diameter ROI was drawn on each of the three cylinders and background as well as ±6 slices and the mean AC was calculated. In addition, cold contrast defined as one minus the ratio of cylinder to background AC was calculated for each cylinder type and phantom size. Results: Contrast in the air cylinder was constant for all phantom sizes, but decreased for water and Teflon with increasing phantom sizes. The decrease was 17% and 15% for Teflon and water respectively between the small and large phantom sizes. The highest contrast was observed in the Teflon cylinder for all phantom sizes. Conclusion: Current scatter and attenuation correction techniques do not fully recover the true AC in tissue particularly in large objects which might impact the accuracy of quantification in PET imaging.
SU‐FF‐I‐154: The Diagnostic Accuracy of in Vivo Confocal Laser Scanning Microscopy of Basal Cell Carcinoma: A Preliminary Study in Chinese Patients
Authors: Gao M , Yin Y , Liu H
Published: April 2010

Purpose The objective of this study was to evaluate the diagnostic accuracy of in vivo CLSM compared with the golden standard diagnostic technology‐histopathology. Methods 62 patients with suspicious lesions of BCC were prospectively recruited to undergo clinical, CSLM (VivaScope 1500 Plus, Lucid Inc, Henrietta, NY) examinations, and biopsies. A diagnosis was made preoperatively with CLSM technique, and the lesion was then excised and diagnosed using histopathology. The diagnostic criteria with CLSM were presence of elongated monomorphic basaloid nuclei, polarization of these nuclei along the same axis of orientation, prominent inflammatory infiltrate, increased dermal vasculature, and pleomorphism of the overlying epidermis indicative of actinic changes, which had been reported elsewhere. Results 62 patients with 62 lesions were determined with histopathology, comprising 40 BCC, 5 Squamous cell carcinoma (SCC), 3 Actinic Keratosis and 14 others. The CLSM had a sensitivity of 95.23%, specificity of 91.30% in BCC imaging. Conclusions This is the first study in China mainland to investigate the accuracy of CLSM in BCC imaging. Non‐invasive CLSM offered a sensitive and specific tool in diagnosis of BCC, which was essential screening tool in BCC diagnosis.
SU‐FF‐I‐164: Automated Suppression of Ribs in Digital PA Chest Images by Means of Image Processing
Authors: Veldkamp W , Kroft L , Geleijns J
Published: April 2010

Purpose: Ribs in chest images have a negative effect on observer performance for detecting lung lesions. The purpose of this study was to develop a fully automated image processing technique for reducing the contrast of ribs by means of image processing and thereby to increase the sensitivity of lesion detection. Method and Materials: Digital chest radiography (ThoraScan, Delft Imaging Systems) provides sufficient large dynamic range and high bit depth to register accurately the entire range of radiation intensities in the latent PA chest image. This implies that visibility of lesions in the lungs should improve after suppression of ribs. The rib suppression technique incorporates four basic steps: lung field segmentation, global rib segmentation, rib contour detection and signal subtraction in rib regions. Ribs are suppressed using estimates of the pixel intensity in the rib structure and its adjacent background. The difference between these estimates is weighted and subtracted from the rib structure, the degree of suppression of the ribs can be adjusted by changing the weight. The result is optimized using model information of the rib. To provide a proof of concept, PA chest images of ten patients were included in a pilot study. Results: Ribs in PA digital chest radiographs of ten patients were automatically suppressed by means of image processing. The general appearance of lung tissue, vessels and lesions in the lung fields improved. Conclusion: An automated image‐processing technique for rib suppression has been developed. The impact of this technique on the sensitivity of detection of lung nodules in digital chest radiographs will be investigated in a future observer performance study.
SU‐FF‐I‐169: Endovascular Abdominal Aortic Aneurysm Repair: Patient Dose and Radiation Risks
Authors: Geleijns J , Koning O , van Bockel H
Published: April 2010

Purpose: To assess cumulative patient dose and to calculate associated radiation risks for patients undergoing abdominal endovascular aortic aneurysm repair (EVAR). Method and Materials: A traditional protocol and a reduced dose scenario for medical imaging in EVAR planning, repair and surveillance was assumed and patient dose was assessed. The excess relative radiation risk was calculated using a model for age‐, gender‐ and site‐specific solid cancer mortality. Life tables were used to calculate risk related parameters for patients that underwent EVAR at 55, 65, 75 and 85 years of age. In addition to radiation risk, mortality rates that are typical for the EVAR population were taken into account, knowingly the probability of 30‐day mortality and the mortality rate from AAA‐related causes in general during follow‐up. Results: Effective dose for EVAR planning was 18 (8) mSv; for EVAR repair 10 (10) mSv; and during the first, second and subsequent years of surveillance 87.5 (35) mSv/y, 35 (17.5) mSv/y and 17.5 (17.5) mSv/y. The number of radiation induced deaths per 1000 EVAR patients was 12 (10), 8 (6), 4 (3) and 1 (1) for patients treated at ages 55, 65, 75 and 85 years (respectively traditional protocol and between brackets reduced dose scenario). The corresponding number of abdominal aortic aneurysm (AAA) related deaths per 1000 EVAR patients was: 126, 91, 67 and 47, respectively (for both the traditional protocol and the reduced dose scenario). The average radiation induced and AAA related reduction of life expectancy will be presented. Conclusion: Radiation exposure accumulates rapidly for patients undergoing surveillance after abdominal EVAR. However, associated radiation risks are modest, even for the traditional surveillance protocol that is associated with a relatively high patient dose. Radiation risks are much smaller compared to AAA‐related risks.
SU‐FF‐J‐01: Feasibility of a Pre‐Object‐Grid to Reduce Scatter and Improve Image Quality in Cone‐Beam Computed Tomography (CBCT)
Authors: Jin J , Liu Q , Kim J , Wen N , Movsas B , Chetty I
Published: April 2010

Introduction: Scattered radiation is a major contributor to the degradation of image quality in Cone‐beam Computed Tomography (CBCT). The purpose of this study is to demonstrate a novel technique that samples scattered radiation during imaging acquisition, and subsequently account for it during image processing, thereby significantly improving CBCT image quality. Methods and material: A grid composed of multiple, interspaced, lead strips is placed between the x‐ray source and the imaging object. The grid alternately blocks half of the entrance radiation and divides the imaging field into multiple strips of fan‐beam fields. In each projection, scatter is sampled in the shadowed strips, then interpolated and subtracted from the original imaging data in the fan‐beam fields. Half of the 3D‐CBCT images in an alternate pattern can be obtained from these projection data with one rotation. A complete set of CBCT images can be obtained by two rotations in axial mode, or one rotation in helical mode. We have tested the feasibility of the method by comparing an incomplete set of CBCT images of an enlarged Catphan phantom using the Varian Trilogy CBCT system using 3 settings: (A) without the grid; (B) with the grid, but without scatter correction; (C) with the grid including scatter correction. Results: CBCT image quality improved dramatically using setting C (grid with scatter correction). Streaking artifacts around the air and high‐density inserts, apparent in A and B, were almost completely removed in C. CT number linearity (R2) was improved from 0.880 (A) and 0.967 (B) to 0.998 (C). Contrast scales were 0.42, 0.71 and 1.47 for A, B and C respectively. The corresponding contrast‐to‐noise ratios were 4.29, 6.60 and 6.42, respectively. Conclusion: Preliminary results suggest that the proposed pre‐object‐grid method can be used to substantially reduce scatter in projection data and therefore improve image quality in CBCT.
SU‐FF‐J‐02: Impact of Cross Scatter On CNR in Fluoroscopic Images Taken with a Dual Flat Panel X‐Ray Imaging System
Authors: Giles W , Bowsher J , Roper J , Yin F
Published: April 2010

Purpose: To examine the impact of cross scatter on contrast‐to‐noise ratio (CNR) in fluoroscopic images acquired with a dual flat‐panel x‐ray imaging system. Method and Materials: An x‐ray imaging system has been developed consisting of two tube/detector pairs mounted orthogonally; each chain includes a 40×30 cm amorphous silicon flat panel detector. A timing system was developed to offset the exposures of each imaging chain relative to the detector cycle which remained synchronous for both imagers. The amount of cross scatter present is dependent on several factors: kVp, mAs, time between exposures, detector lag, and object size. Several cylindrical phantoms that incorporate areas of varying contrast were used to perform CNR measurements. CNR was taken as the relative contrast between two ROIs divided by the noise, the average of the standard deviation of the contrast measured in 15 images. Effects of cross‐scatter were determined by comparing CNR when both tubes were fired to CNR when only one tube was fired. Additionally, the dependence of CNR on kVp and the number of scrub frames was measured. Since cross scatter is non‐uniform across the imaging plane, CNR was measured using ROIs in various regions of scatter intensity across the detector. Results: Preliminary results show that contrast and CNR can be reduced by up to factors of approximately 10 when cross scatter is present. Contrast reductions are greater at lower kVp. CNR reductions are greater at higher kVp. By inserting scrub frames and time delays, contrast and CNR can be restored to near the values observed without cross scatter. Conclusion: Cross scatter can be substantial in dual x‐ray projection imaging. It's effects vary with kVp and can be alleviated by scrub frames and tube timing. Conflict of Interest: This research is supported in part by Varian collaboration.
SU‐FF‐J‐04: Improving Image Quality of Low Dose Cone Beam CT (CBCT) Imaging with Sparse Representation
Authors: Xia J , Chen Y , Samant S
Published: April 2010

Purpose: To present a methodology for reducing cone beam CT (CBCT) dose using low dose imaging protocols and sparse representation techniques to achieve similar image quality as regular or high dose imaging protocols. Method and Materials: The frequent usage of CBCT raises the concern of excessive non‐therapeutic dose delivered to patients, especially to pediatric patients. Sparse representation (SR) was applied to low dose CBCT imaging, achieved by using low mAs, to suppress image noise and streak artifacts. The denoising algorithm was applied to low dose clinical images based on the concept of sparse representation using the training dictionary, which was constructed from the regular dose clinical images to approximate the anatomical site of interest. Validation was carried out using two phantoms (a CATPHAN phantom and an anthropomorphic head & neck phantom) and clinical prostate images. Comparisons with the modified edge preserving curvature anisotropic diffusion filter (MCDF) were carried out. Results: For CATPHAN phantom images, the SR algorithm outperformed the MCDF algorithm in terms of contrast to noise ratio (CNR). CNR was improved by an average of 32% for the SR algorithm. In contrast, MCDF only improved CNR by an average of 2.4%. Visual assessments of the anthropomorphic head & neck phantom and patient images indicated the SR algorithm not only suppressed the image noise but also preserved fine details of anatomical structures and was significantly better than MCDF. Conclusion: SR can be used to reduce image noise and CBCT imaging artifacts present in low dose CBCT images. Dose reductions up to 88% were observed without loss of image quality based on visual assessment.
SU‐FF‐J‐06: Off‐Axis Variation of the Varian OBI Photon Spectrum and Impact On Cone‐Beam CT Image Quality
Authors: Zhang L , Lazos D , Zheng D , Pokhrel D , Williamson J
Published: April 2010

Purpose: Bow‐tie filters used in CBCT image acquisition alter photon spectra across the radiation field. Furthermore, incident spectra vary along the longitudinal direction of an X‐ray tube due to the anode‐heel effect. The goal of this study is to characterize off‐axis spectral variation of a Varian® on‐board kV imager and to investigate its impact on the quality of reconstructed images. Method and Materials: Spectra were derived by fitting the semi‐empirical Birch‐Marshall (BM) model to narrow‐beam aluminum transmission data measured with a parallel‐plate ion‐chamber at different locations along the transverse axes of the OBI field. Photon spectra with and without filtration of the full and half bow‐tie filters were measured. Simple analytical models for deriving off‐axis spectra at arbitrary detector locations from the central‐axis spectrum were developed and validated against the measured spectra. Images reconstructed from synthetic datasets with constant and spatially variant photon spectra were used to assess both bow‐tie filter and anode‐heel spectral hardening effects on image quality. Results: The derived spectra accurately reproduced the transmission measurements with mean and maximum deviations of 0.6% and 2.5%, respectively. The anode‐heel effect is insignificant at small off‐axis angles. The variation of aluminum HVLs of spectra is less than 0.5 mm within 3° off‐axis angles. Bow‐tie filters significantly alter photon off‐axis spectra. The mean photon energies at 5° off‐axis angle with the full bow‐tie and the half bow‐tie filter are 78.7 keV and 67.6 keV, respectively, compared to the centralaxis mean energy of 60.0 keV. Conclusion: Our investigation demonstrates the feasibility of using narrow‐beam transmission measurements in conjunction with the BM model to characterize relative small off‐axis spectral variations. The spectra at arbitrary off‐axis angles can be adequately characterized by hardening the central‐axis spectra. The anode‐heel effect does not significantly alter beam‐hardening artifacts in the reconstructed images.

Supported by Varian Medical Systems
SU‐FF‐J‐07: Modeling the Elekta XVI CBCT Beam in a Commercial Treatment Planning System
Authors: Alaei P , Spezi E , Downes P , Radu E , Jarvis R
Published: April 2010

Purpose: To investigate the feasibility of modeling the kilovoltage beam from a cone beam CT system in a model‐based treatment planning system. And to further investigate the accuracy of CBCT dose calculations using the planning system and inclusion of the dose in patient treatment plan. Method and Materials: The beam data from an Elekta XVI CBCT system has been entered into the Philips Pinnacle treatment planning system (TPS) and the beams for various filters are modeled in the TPS. The data was obtained from measurements and Monte Carlo simulation which were recently published1. The kilovoltage x ray generator has been modeled in Pinnacle as an added machine and both manual and auto‐modeling has been employed to match the measured data. The Pinnacle system's capabilities were previously extended to dose calculations at the kilovoltage energy range2. Similar work was recently performed for a Varian OBI kilovoltage CBCT system3. Results: The agreement between modeled and measured depth dose and cross profiles is reasonably well. The depth dose values agree to within 2% at depths beyond 1 cm. The cross profiles at three depths (1, 5, and 10 cm) and in two directions (X, Y) agree to within 2% in regions within the field, with larger discrepancies observed in the beam penumbra. The modeled beams are used to compute dose in phantom and the results are compared with TLD measurements. Conclusion: The dose from Elekta XVI kilovoltage CBCT can be accurately modeled in the Pinnacle treatment planning system. Inclusion of this dose in treatment plans can lead to more accurate dose prediction, especially when the doses to organs at risk are of importance.
SU‐FF‐J‐10: Converting Cone‐Beam CT to In‐Room Conventional CT by a Deformable Image Registration Method
Authors: Zhang Y , Yang J , Zhang L , Dong L
Published: April 2010

Purpose: Poor image quality in Cone‐beam CT (CBCT) usually poses a challenge for soft tissue based target localization or accurate dose calculation for adaptive radiotherapy. The purpose of this study is to develop an effective post‐processing method to drastically improve CBCT image quality without losing anatomical and geometric information it provides. Method and Materials: We used an image‐based deformable registration algorithm to establish dense correspondence among voxels of the daily CBCT and the planning CT images. Once the voxel‐by‐voxel correspondence is obtained, conventional CT numbers from the planning CT can be mapped to the geometrically aligned voxel locations of the daily CBCT. The converted CBCT (Mapped‐CBCT) maintains the geometrical information of the daily CBCT while retaining the more accurate electron density information from the original planning CT. A previously validated, in‐house developed “demons” algorithm was used in combination with an intensity pre‐processing method. Results: Soft tissue contrast is greatly enhanced in each of the prostate, lung, and head & neck cases we tested. In addition, various CBCT imaging artifacts, caused by beam hardening, detector response lag, scatter, and organ motion during CBCT acquisition etc., were all disappeared. Histogram distribution of voxel intensities in the soft tissue region showed a better tissue/fat separation in the mapped CBCT than the original CBCT. For a prostate case, we observed a 41% reduction in entropy, which further demonstrates improved soft‐tissue discrimination. Correspondence ambiguity in some anatomical objects is one limitation for this method. For example, the daily variation of rectal gas will not be presented if the rectum is empty in the planning CT. Conclusion: We demonstrated an effective voxel mapping procedure to match the CBCT image to the quality of a conventional CT, which should improve online image evaluation or provide a more accurate CT data set for adaptive replanning or dose accumulation.
SU‐FF‐J‐12: HU and Dosimetric Comparison of Six Cone‐Beam CT Acquisition Techniques for Radiation Therapy Planning
Authors: Leeper S , Yoo S , Yin FF
Published: April 2010

Purpose: It has been shown that cone‐beam computed tomography (CBCT) can be used in dose calculation for treatment planning. This study investigates the HU and dosimetric properties of six CBCT techniques in comparison with conventional CT to determine which techniques are proper for planning. Method and Materials: HU of material disks in Catphan and HU profiles for homogeneous and inhomogeneous phantoms for six different CBCT techniques (Low‐Dose Head, Standard‐Dose Head, High Quality Head, Pelvis Spotlight, Pelvis, and Low‐Dose Thorax) were compared to CT images. Plans with a single photon beam based on CBCT techniques and conventional CT of phantoms were compared using dose values at the isocenter, isodose distributions, and dose volume histograms. Results: HU values of all the CBCT techniques are very close to those of CT in Catphan and in homogeneous phantoms except for Low‐Dose Thorax (LDTH) technique, which overestimates HU by 85. However, the LDTH CBCT showed the HU profile in the lung area matched well with the CT compared to the other five techniques. The dose distribution based on all CBCT techniques in the homogeneous phantoms matched well with the CT except for LDTH, which underestimated the dose. For the lung area, the LDTH dose distribution matched well with CT and the other CBCT techniques did not. For the spine area, the dose distribution of the Pelvis technique matched best with CT, but the other techniques matched relatively well with CT too except for LDTH. Conclusion: This study illustrates HU values and dose calculation based on six different CBCT techniques compared to conventional CT for the purpose of radiation therapy treatment planning. The dose calculation accuracy depends on combination of CBCT acquisition technique and treatment site. A CBCT technique should be properly selected for a treatment site if CBCT‐based dose calculation is to be performed.
SU‐FF‐J‐19: V‐Q SPECT to Individualize Adaptive Radiation Plan in Patients with Non‐Small Cell Lung Cancer (NSCLC)
Authors: Kong F , Yuan S , Moran J , Tatro D , Lochart C , Ten Haken R
Published: April 2010

Purposes: This study aimed to assess the changes of lung ventilation (V) and perfusion (Q) function by single photon emission tomography (V/Q SPECT) at 45 Gy during radiation therapy (RT), and determine if V/Q SPECT during‐RT can be used to decrease dose to the functioning lung. Methods: V/Q SPECT‐CT and FDG‐PET‐CT were performed prior and during‐RT (@45Gy) for patients enrolled in prospective clinical trials for stage I–III NSCLC. The V and Q functions were assessed using a semi‐quantitative system. An adaptive plan was generated after RT of 45 Gy to the target based on the during‐RT FDG‐PET‐CT. The during‐RT SPECT was used to optimize the plan to minimize dose to the functioning lung. Results: Of 45 patients analyzed, 100% had lung functional defects at or around the primary tumor and the majority of them have defects in the remaining lung. The V/Q defects were mismatched in 40% and 50% patients for pre‐ and during‐RT SPECT, respectively. After 45 Gy, the global and local lung function improved in one third patients. Specifically, there was a significant improvement in V scores in ipsilateral lung (P=0.002), while there was no significant changes in V scores of the contralateral lung and Q scores of the ipsilateral lung at or around the tumor at 45 Gy during‐RT. Using V/Q SPECT at 45 Gy for voxel based optimization, the mean dose to the functioning lung decreased remarkably while maintaining the physical dose to the target and the physical dose based lung normal tissue complication probability. Conclusion: V/Q SPECT‐CT acquired during the course of treatment has a potential to escalate the tumor dose and or decrease the dose to the functioning lung. Clinical trials are ongoing to assess if the therapeutic ratio (long‐term survival over lung toxicity) will improve in patients with NSCLC.
SU‐FF‐J‐26: Multimodal Sono‐Contrast NIR Spectroscopy System for Breast Cancer Diagnosis
Authors: Yan K , Podder T , Huang K , Hu Y , Li J , Liao L , Yu Y
Published: April 2010

Purpose: To present a multimodal imaging system that combines three modalities, optical spectroscopy, ultrasonography and acoustic radiation force (ARF) for improved diagnosis of breast cancer based on noninvasive interrogation of vasculature. Method and Materials: The scanhead incorporates two 1MHz focused transducers aligned orthogonally to deliver ARF in a 2.4cm region. A commercial ultrasound probe is positioned to image the focal plane. The ultrasound probe and focused transducers have two degrees‐of‐freedom, so that the focal zone can be scanned in tissue depth‐wise and laterally. Three force sensors are mounted on the breast compression plate to ensure consistent, slight compression. A fiber array (6 sources and 12 detectors) connects to the concave bottom plate of the scanhead. Sources are illuminated by two laser diodes (680 and 830nm) through a multi‐channel optical switch. Diffuse reflectance signals are collected by 12 detectors, amplified by avalanche photodiodes, and transmitted through a multi‐channel data acquisition card for analysis. The scanhead is mounted on a 360° ring gantry, which can rotate around the breast and move towards or away from the patient. A software system was implemented in Visual C++ to perform real‐time tasks, including acquisition of optical and force signals, control of optical switch and function generator, and data display. Results: The maximum exposure to laser was controlled within 0.2W⋅cm−2 (ANSI Z136.1). The ARF fields were maintained below FDA diagnostic limits (0.72W⋅cm−2) for manipulating blood flow and oxyhemoglobin concentrations at the time and location of detection, causing measurable differences in the dynamic behavior of tissue blood supply as reported by optical spectroscopy. This technique was demonstrated to be highly diagnostic in a murine tumor model. Conclusions: A multimodal system incorporating ARF, optical spectroscopy and ultrasonography has been developed to characterize breast cancers. Pilot clinical study is being carried out.

Acknowledgement: Work supported by NCI Grant CA107860.
SU‐FF‐J‐36: Efficient 4D Treatment Planning Using CT Datasets Synthesized Via Deformable Image Registration
Authors: Zhong H , Fragoso M , Chetty I
Published: April 2010

Purpose: 4D treatment planning is often a time‐intensive process, requiring a series of procedures on multiple (up to 10) CT‐datasets. We hypothesize that more efficient strategies exist for lung cancer, 4D planning, and that dosimetrically, these methods are equivalent to plans based on the typical 4D process. Method and Materials: Three strategies were tested: (a) Exhale and Inhale CT‐datasets were registered using deformable image registration (ITK “demons”) and the resulting displacement vector field (DVF) was used to “synthesize” 8 additional CT datasets, at equally spaced phases between inhale and exhale. A single dataset, based on average CT‐number of the 10 datasets was then generated for planning purposes, CTAVE_SYN. (b) Ten CT‐datasets were retrospectively reconstructed during a patient 4D scan, and an average dataset was generated for planning purposes, CTAVE_4D. (c) Dose is computed on each of the ten datasets independently, dose accumulation is performed (trilinear interpolation), to yield a “warped” 4D, benchmark dataset, CTWARPED_4D. A step‐and‐shoot IMRT plan was developed and applied to the CTAVE_SYN, CTAVE_4D, and CTWARPED_4D datasets. Dose calculations were performed using Monte Carlo (BEAMnrc/DOSXYZnrc) integrated with Pinnacle. Doses were mapped to the reference image dataset (end‐exhale) for dosimetric comparison. Results: PTV and ITV mean doses generated using the CTAVE_SYN and CTAVE_4D datasets agreed within 0.5% of each other. Mean doses generated using CTWARPED_4D agreed with the CTAVE_SYN and CTAVE_4D datasets within 1% and 1.5% for the ITV and PTV, respectively. Biological dose indices, including EUD (ITV and PTV), and NTCP and mean lung dose (normal lung tissue) were within 1% agreement for treatment plans using all 3 datasets. Conclusion: Results are suggestive that 2 CT‐datasets used to synthesize an average 4D dataset (via a DVF and CT‐number averaging) may be a feasible approach, offering the potential for improved efficiency in the lung cancer 4D planning process.

Acknowledgement_NIH‐R01CA106770
SU‐FF‐J‐39: The Impact of Improving Techniques for Phase Reassignment in 4D CT Reconstruction
Authors: Park H , Yoon J , Jung W , Song J , Suh T
Published: April 2010

Purpose: To develop the respiratory signal analysis program for a phase‐based retrospective 4D CT using RPM, spirometer, stereo‐camera and removed the irregular peaks of respiratory signals for accurate phase assignment in 4D CT. Methods: In this study, an in‐house respiratory signal analysis program was developed for the phase reassignment and the analysis of the irregular respiratory signals. Various irregular respiratory patterns were obtained from clinical experimental volunteers. After then, the in‐house program analyzed the factors affecting to phase assignment which is directly related to irradiate sector. The algorithms for separating individual respiratory signals are presented, which made use of baseline signals of input signal to identify the nodes between baseline signals and input signal. Therefore, we could achieve irregular peak reduction and noise elimination in phase assignment. Subsequently, accuracy of phase assignment was improved with removal of irregular signals by self‐developed algorithm. Furthermore, this program also has a function to detect period and amplitude automatically. Result: The standard deviation (SD) of breathing period representing the baseline method was shown stable compare with gradient method, but the difference was not statistically significant. Gradient method shows inaccurate phase assignment when all irregular peaks were detected and assigned. On the other hand, baseline method which was self‐developed algorithm confirmed accurate phase assignment with removal of error peak detection due to tussis. It was also verified superior peak detection with the suggested baseline method at respiratory signals which contained irregular period changes and drifts of amplitude. Conclusion: This study is considered to be useful for not only image reconstruction and elevation of irradiating accuracy through phase assignment of RPM system but also analysis of respiratory signals. Moreover, this respiratory analysis program can be applied to the 4D CT reconstruction using various respiratory sensors for the reduction of motion artifact.