bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐57: Comparison of CT Head Dose Estimates Using DLP vs. Monte‐Carlo Simulations
Authors: Cook T , Couch G , Couch TJ , Boonn W , Kim W
Published: November 2011

Purpose: Imaging centers are increasingly seeking means to track radiation dose from computed tomography (CT). Many of these methods are based on the dose‐length product (DLP) reported on image‐based dose sheets, such as RADIANCE, an open‐source dose extraction software. We compare dose estimates from RADIANCE to those computed by eXposure, a commercial product which computes organ doses using Monte‐Carlo simulations. Methods: We review dose estimates for 1936 single‐phase, unenhanced head CT examinations performed in 2010 at our institution. The estimated whole‐body effective dose (ED) is derived from the total study DLP by multiplying the ICRP 60‐based k factor of 0.0021. For the same set of studies, ED is derived from the organ doses computed via Monte‐Carlo simulations using MIRD Adult and Age 15 phantom, average scanner model and ICRP 60 tissue weighting factors. ED estimates from both methods are compared. Results: The average ED derived from total DLP is 1.84 +/− 0.44 mSv, while the average ED derived from the organ doses is 2.01 +/− 0.3 mSv. ED estimates derived from the organ doses were 1.91 +/− 0.28 mSv for male patients and 2.11 +/− 0.29 mSv for female patients. According to the literature, adult female heads are 10% smaller on average than adult male heads. We hypothesize that the 11% higher ED estimate in the female patients reflects this head size differential between genders. A common adult head phantom is used for head CT acquisitions, and higher dose estimates in adult females may reflect a longer‐than‐necessary scan length. Conclusions: Estimating whole‐body effective dose using DLP is practical in the current clinical setting. For head CT exams, DLP‐based ED estimates appear concordant with organ dose‐based estimates. The data additionally suggests that dose savings may be achieved by optimizing scan length and mA for female patients.
SU‐E‐I‐79: Patient Doses Reduction in Simple Radiographic Examinations in Busy Radiology Departments
Authors: Khosravi H R , Gholamalizadeh Z , Zadeh M R Hanteh , Lahroodi K Asnaashari , Rastkhah N , Deevband M R
Published: November 2011

Purpose: To reduce entrance surface air Kerma (ESAK) of routine radiological examinations in some heavy loaded radiology departments using proper equipments and training.Methods: ESAK for 12 routine radiographic examinations has been measured in 10 high loaded radiology departments belonging to country main health insurance organization after quality control for x_ray units and proper training for all radiographers of each departments to use proper technical charts for each room, mainly according to EUR 16260 and optimized exposure factors. The ESAK were measured according to X‐ray tube output, optimized exposure parameters including tube potential(kVp), tube current (mA), focus to skin distance (FSD) for each technique. Results: .The mean reduced ESAK values after optimization of exposure parameters for abdomen, AP and lateral cervical spine, PA and lateral chest, AP and lateral lumbar spine, pelvis, PA and lateral skull, AP and lateral thoracic spine 4.61, 1.19,1.20, 0.26, 0.59 4.63, 6.56, 4.23, 2.90, 2.55, 3.89 and 4.94 mGy, respectively. There were very significant reduction in ESAK by a factor of 36% for abdomen,28% and 35% for AP and lateral cervical spine,62% and 60% for PA and lateral chest, 41% and 53% for AP and lateral lumbar spine, 35% for pelvis, 27% and 22% for AP and lateral skull, 47% and 53% for AP and lateral thoracic spine. Mean, median, first and third quartile of values of ESAK are reported. Conclusion: Significant dose reduction was achieved with proper and simple training and without considerable change in repeat and reject analysis. This reasonable outcome will lead us to establish optimized National Diagnostic Reference Levels (NDRLs).
SU‐E‐I‐81: Radiation Dose for a 320 Slice Cone Beam CT: Methods and Analysis
Authors: Nickoloff E , Lu Z , Dutta A , So J
Published: November 2011

Purpose: The new 320 slice CT scanners can irradiate x‐ray beam widths from 2.0 mm to 160 mm length in one rotation, and they present challenges for the measurement and analysis of radiation doses. Various methods to perform and analyze the radiation dose data were examined. Methods: These CT scanners have various modes of operation such as: 320 detector axial volume mode, 64 detector axial and helical scan, and scan mode with 4 narrow axial slices ranging from 4*0.5 mm to 4*8 mm. There are many selectable scan parameters such as: four kVp settings (80, 100, 120 and 135), three x‐ray beam filters, 50 to 550 mA, several scan time settings of 0.35 to 3.0 seconds, various pitch values and automatic mA modulation. These options complicate the radiation dose measurement and analysis procedures. Longer CT dose phantoms were evaluated. Several ionization chambers (100 mm pencil chamber and 0.6 cc thimble) and OSL dosimeters were utilized to perform the measurements and evaluated. Results: The radiation dose profiles were measured, and the narrowest beam width resulted in the largest radiation doses. In the 320 slice volume mode, the utilization of 3 radiation dose phantoms stacked together only changes the measured radiation dose by less than 10%. The large amount of data was reduced to a few simple equations and graphs that could be used to estimate the CT radiation dose for any of the clinical procedures. Both thimble ionization and OSL radiation detectors provide useful contributions in CT dosimetry. Conclusions: Limitations and approaches to CT radiation dosimetry for large cone beam CT scanners are reviewed and guidance is provided. Current dosimetry methods can be employed without significant errors.
SU‐E‐I‐96: Evaluation of Intraoral Dental X‐Ray Imaging Equipment via Mail
Authors: Gray J
Published: November 2011

Purpose: To describe a system to evaluate image quality, patient dose, and half‐value layer of intraoral x‐ray systems via the mail.Methods: A system has been developed to evaluate intraoral x‐ray equipment via the mail for state radiation protection agencies. The state agencies provide a list of facility names, addresses, etc. A kit including an “Analyzer” is mailed to the facility along with a Userˈs Guide and Data Form. The Analyzer consists of a flat cardboard device which unfolds into a box holding a dosimeter, test objects, and a packet of dental film containing both D‐speed and E‐F‐speed dental film (this can also be used with digital dental imaging systems). The exposed dental film is processed by the facility and the film images, or digial images, are returned along with the Analyzer. The film images are digitized and the digitized images (including digital dental images) are evaluated for seven image quality characteristics including image sharpness, contrast, density, base‐plus‐fog, effective speed, film processor quality, and residual fixer (as appropriate). The patient dose and half‐value layer (HVL) are determined from the dosimeter. A summary report is sent to the state radiation protection agency. (Patent # 7503694 applies to the Analyzer and process.)Results: Several studies relative to the accuracy and precision of the measurements indicate that the dose and HVL can be determined to about 10%. Experience with measurements of over 4,500 intraoral x‐ray units indicates issues that must be addressed through education of dental facility staff. These issues include about 25% of the facilities exceeding reasonable patient dose levels; about 80% of facilities still using the low speed D‐speed film; and that photographic processing is a major issue Conclusions: Evaluation of intraoral dental equipment via the mail is a viable and effective approach for image quality and radiation protection purposes.
SU‐E‐I‐98: Neurovascular Device Localization Accuracy Dependence on Exposure, Temporal Filtering, and Motion Blur for Real Time Imaging with the Microangiographic Fluoroscope
Authors: Panse A , Jain A , Bednarek D , Rudin S
Published: November 2011

Purpose: To study the accuracy of localization during fluoroscopy for static and moving objects and its dependence on quantum noise determined by exposure and temporal filtering and on motion blur determined by speed of object movement. Methods: A stainless steel stent (90 micron struts) used as object of interest was mounted on a stepper motor controlled linear stage with effective step size of 1.7 micron. The new high resolution 35‐ micron‐ pixel Microangiographic Fluoroscope (MAF) was used for imaging the stent as it was moved forward 7500 steps and brought back to the original position for different speeds. Fluoroscopy was performed at 4 different exposures. The object detection algorithm available in LabVIEW IMAQ Vision software was used to localize the stent using different temporal filtering weights. Results: (a) For fixed exposure, stationary object localization accuracy is improved by a factor of 5 for higher temporal filtering compared to no temporal filtering; however, for moving objects the error in localization increased 50 percent due to motion blurring when the filter weight was increased from 4 to 8. (b) For fixed temporal filtering, localization accuracy improved with higher exposure. Doubling the exposure improved accuracy 3 times for stationary and 1.5 times for the moving object. (c) Localization accuracy for stationary objects at a given dose and temporal filtering is similar to that at twice the dose and half the temporal filtering weight, whereas that for moving objects was found to be slightly better for the latter case. (d) Localization accuracy was observed to decrease proportionally with increased object speed due to increased motion blur. Conclusions: Localization accuracy in high quantum noise situations can be improved by increasing the temporal filtering. There is a need to implement variable weight temporal filtering depending on the amount of motion detected.

Support: NIH Grants R01‐EB008425, R01‐EB002873
SU‐E‐I‐106: Differential Diagnosis of Mild Cognitive Impairment and Alzheimerˈs Disease with VOI Based Diffusion Tensor Analysis
Authors: Juh R , Suh T , Kim S
Published: November 2011

Purpose: The investigation of gray matter (GM) structural changes in MCI the integrity of white matter (WM) has been assessed by diffusion tensor imaging (DTI) which is focused on fractional anisotropy (FA) or mean diffusivity indexes (MD). The purpose of this study was to evaluate the FA values of WM tracts using region of interest (ROI) with the aim of differentiating a control from MCI or AD.Methods: Sixty individuals (20 controls, 20 MCI and 20 AD) with age‐matched underwent DTI and three‐ dimensional (3D) were included. FA and ADC measurements were obtained for the whole brain and specific areas using ROIs. 3D MRI was helpful in validating ROIs in the proper anatomic regions. WM tract‐based analysis of MD and FA was performed by manual placement of ROIs on the color‐ coded FA maps and measured for hippocampal formations, superior longitudinal fascicles, and posterior cingulate gyri, splenium of the corpus callosum, and inferior longitudinal, superior longitudinal, uncinate fasciculus.Results: Relative to AD patients showed significant FA decreases and MD increases (Control/MCI/AD=mean FA:0.48 SD: 0.02/FA:0.46 SD: 0.03/ FA:0.45 SD: 0.03, on whole brain). In the left uncinate fasciculus was clearly compromised as they were left inferior fronto‐occipital. The FA values in the splenium of the corpus callosum (Control/MCI/AD=mean FA:0.73/FA:0.66/FA:0.66), bilateral posterior cingulated gyri (Control/MCI/AD=mean FA:0.67/FA:0.61/FA:0.59), and bilateral superior longitudinal fascicles (Control/MCI/AD=mean FA:0.65/FA:0.57/FA:0.55), of patients with MCI and AD were significantly lower than those of controls Conclusions: We found compromise of the uncinate fasciculus among AD but not in MCI patients and DTI is a good for the evaluation of patients with probable from MCI to AD. The limitations of this study cannot exclude some degree of partial volume effect on the measurements, although the ROIs were carefully positioned, magnetic field heterogeneity and susceptibility artifacts might have impaired study.
SU‐E‐I‐117: Quantifying Search and Classification Performance in Lesion Localization Tasks
Authors: Chakraborty D
Published: November 2011

Purpose: Search involves identifying the locations of potential lesions. Classification involves determining if an identified region is a lesion. The area (AUC) under the ROC curve is affected by both search and classification performance. The purpose of this work is to suggest a method for quantifying the two distinct contributions. Methods: The search model for free‐response data involves sampling from noise and signal site unit variance normal distributions. It predicts ROC curves that extend from (0,0) to (x,y), where (x,y) is to the lower left of (1,1). The quantity (y‐x) is proposed as a measure of search performance. It equals the perpendicular distance from (x,y) to the chance diagonal multiplied by the square root of 2. The probability that a sample from the signal distribution is greater than a sample from the noise distribution is proposed as a measure of classification performance. AUC performance is the probability that the highest sample from an abnormal image is greater than the highest sample from a normal image. Search, classification and AUC performance were calculated for mammographer data from a FROC study in which 5 radiologists interpreted 96 normal and 89 disease‐present cases in breast tomosynthesis (BT) and digital mammography (DM) modalities. Results: Search performance ranged from zero to 0.65, classification performance ranged from 0.64 to 0.98 and AUC performance ranged from 0.68 to 0.88. AUC correlated positively with search performance while classification performance was inversely correlated with search performance. All three measures were greater for the BT modality. Conclusions: The method, which is applicable to FROC or ROC data, allows separation of physically distinct contributions to AUC, and consequent identification of the weak link. The preliminary results suggest that search is generally the weak link but that radiologists may learn to compensate for poor search performance with better classification performance.

This work was supported by grants from the Department of Health and Human Services, National Institutes of Health, R01‐EB005243 and R01‐ EB008688.
SU‐E‐I‐129: Determining the Cramer‐Rao Lower Bound in Magnetic Resonance Imaging
Authors: MacDonald Matthew Ethan , Lauzon M Louis , Nielsen John , Frayne Richard
Published: November 2011

Purpose: Maximizing the signal‐to‐noise ratio (SNR) and/or contrast‐to‐ noise ratio (CNR) is very frequently the primary goal when designing new imaging protocols or when choosing from among several magnetic resonance (MR) imaging methods that give similar physiological measurements. In both cases, minimization of the noise inherent in the reconstructed image becomes the key goal. By optimizing with the Cramer‐ Rao Lower Bound (CRLB), a best achievable case of variance can be found in the unbiased estimator sense and, ranges can be found were biased estimators improve upon the CRLB. Methods: We perform derivations of the MR image channel in order to find the best case of the CRLB. Simulations with a digital brain phantom, using ideal parameters, are then performed and matched with the derivation. In addition, simulations with distortions from the B0 field, B1 field, gradient field and receiver coil sensitivity profiles were also performed to define the CRLB in the presence of machine imperfections. Results: From the derivation and simulation, we showed an increase in data variance of greater then 1000× when distortions from common machine imperfections are present. Using the derived CRLB value is not a suitable benchmark to compare biased estimators as the value is much lower then what is achieved practically. Conclusions: We have demonstrated in this work that improving upon the best case CRLB is not a reasonable goal, rather we should be focused upon achieving estimates that are 1000× times greater then the derived CRLB. This work allows us to find the bound where we may choose to switch from conventional FFT reconstruction to alternative methods, resulting in lower data variance.
SU‐E‐I‐133: Novel Methods of Magnetic Resonance Imaging Near Metals
Authors: Hoff M , Xiang Q
Published: November 2011

Purpose: This study demonstrates two novel MRI techniques for imaging near metals, and compares their artifact correction abilities, ease of use, acquisition time, and SNR. Future directions for imaging near metals are derived from this comparison. Methods: A water phantom containing an ASTM F75 Cobalt‐Chromium‐Molybdenum alloy hip prosthesis encased in a Lego structure was imaged using a 1.5T Siemens Avanto MRI scanner. For the 3D‐PLACE technique, two 3D turbo spin echo (TSE) complex datasets were acquired with 12×5mm slices, TR=300ms, TE=11ms, and variable frequency encoding gradients. Differing gradients allowed computation of a displacement field from the complex image phase difference for mapping pixels to their undistorted locations. Further post‐processing addressed fractional pixel shift. For the GS‐bSSFP technique, four 3D balanced steady state free precession (bSSFP) complex datasets were acquired with 52×3mm slices, flip angle=41 degrees, TR=4.2ms, TE=2.1ms, and phase cycling = 0, 90, 180, and 270 degrees respectively. For each pixel, the four phase cycled image values were plotted in the complex plane to locate the demodulated solution at the intersection of lines connecting alternating phase cycles. SNR was improved through a second pass solution. Comparisons were made through observations and parameter calculations. Results: Relative to 3D‐PLACE, GS‐bSSFP yielded ∼60% of the signal void, reduced signal pile‐up, and almost as accurate distortion correction. Strikingly, GS‐bSSFP achieved more than twice the SNR in 28% of the scan time of 3D‐PLACE, with no pulse sequence programming requirements. Conclusions: This study indicates that GS‐bSSFP shows potential for expeditious high signal clinical imaging near metals. Currently the technique is being revised to use less than four acquisitions; combined with limitations on the number of slices and subsampling techniques, this technique should become fast enough to be employed intraoperatively. Remnant distortion artifacts in GS‐SSFP images can be eliminated by combining the technique with 3D‐PLACE.
SU‐E‐I‐134: Integration of Multiparametric and Multimodality Whole Body Radiological Imaging (MRI/PET/CT)
Authors: Jacobs MA , Akbardeh A.
Published: November 2011

Purpose: To investigate the use of non linear dimensionality reduction (NLDR) techniques for integration, segmentation and quantification of multiparametric whole body (WB) radiological imaging methods. Methods: Twenty subjects were prospectively scanned with WB‐MRI and PET/CT, ten patients(age:61±12) and ten normal subjects(age:48± 11). WB‐MRI of T2WI, T1‐STIR and DWI were acquired at 3T. PET/CT using 18FDG or other advanced radiotracers, 11C‐acetate, 11C‐choline and Na18F was obtained on patients. If present, metastatic disease was confirmed by clinical standards. Whole body trace ADC maps, T1 and T2 were constructed for quantitative analysis and ROIs were drawn in regions of normal and abnormal appearing signal intensity. WB‐MRI and PET/CT data were co‐registered before application of the NDLR methods using a non‐rigid model. NLDR methods used were Isomap, locally linear embedding(LLE) and Diffusion‐Maps. The embedded image was constructed by projecting the feature spaces (image intensities) associated with each of the radiological modalities into a one dimensional embedding space (manifold). Dice similarity(DS) indices were calculated and statistical analysis was performed on them. Results: Integration of multiparametric WB‐MRI and PET/CT is feasible. WB‐DWI was able to distinguish potential metastatic regions in 7 patients, none were found in the other three with colocalization on WB‐MRI and 11C‐choline PET, but not in the NAF. These regions had decreased ADC values compared to normal tissue. The ADC values were significantly different(p=0.01) between patients and normal subjects. The segmented regions were congruent with a mean DS of (90.4+/−2.6)%. The computational load varied with the LLE as the having lowest compared to Isomap and Diffusion‐Maps. Conclusions: The integration of different WB modalities will provide a method to identify “global” tumor burdens and monitor treatment. There were significant differences in the ADC values in areas of metastatic disease compared to normal subjects. Our data suggest the potential of multimodality WB methods for characterization of metastatic disease.
SU‐E‐I‐138: EPI Stability Testing on 3T MRI Scanners with Clinical and 32‐ Channel Head Coils
Authors: Chu W.C. , Chen C.C. , Wan Y.L. , Liu H.L.
Published: November 2011

Purpose: Detectibility of brain activation with functional MRI (fMRI) strongly depends on signal stability and noise of the echo‐planar imaging (EPI), the most commonly applied pulse sequence. This study aimed to test the EPI stability using Weisskoff s method for clinical and 32‐channel head coils, with and without parallel imaging, at two 3T MRI scanners. Materials and Methods: Experiments were performed on two 3T MR systems, the MAGNATOM Trio (Siemens) and the Signa MR750 (GE). The same head phantom filled with silicone oils (GE Model No. 2359877) was scanned using a clinical (12‐channel) and a 32‐channel head coils on the Siemens, and a clinical (8‐channel) and a 32‐channel head coils on the GE system. Single‐shot gradient‐echo EPI sequences were applied in all experiments with TR/TE/FA = 2 s/30 ms/90‐degrees, FOV = 256 mm, matrix size = 64 × 64, number of dynamics = 300. Thirty contiguous axial slices with thickness = 3 mm and gap = 1 mm were acquired. For scans with parallel imaging, an acceleration factor of 2 was applied. Signal‐to‐noise ratio (SNR0) and the relative fluctuation (as a function of ROI size) were determined following Weisskoff s method. Results: The results from the Siemens system showed lower relative fluctuations with the 32‐channel coil as compared to the 12‐ channel coil. For both coils, parallel imaging improved the stability for larger ROIs. The results from the GE system showed greater instability with the 32‐channel coil when parallel imaging was applied. The other three conditions demonstrated similar instability. Conclusion: EPI stability was found varied between imaging methods, coils and systems. It might as well differ between two installations of scanners with the same manufacture/model. Further study will be conducted to compare images from different sites with the same imaging hardware and method.
SU‐E‐I‐141: Repeat Rates and Their Effect on Dose in Transitioning from Screen/Film to Full‐Field Digital Mammography
Authors: Ripley E , Otto P , Hatab M
Published: November 2011

Purpose: To investigate any change in the number of extra views acquired for screening mammography in transitioning from screen/film (SFM) to full field digital mammography (FFDM) and the resulting effect this had on total dose. Methods and Materials: This was a retrospective study of screening mammograms performed at our institution over a four year period. A total of almost 50,000 screening exams were performed during the last two years of SFM use and the first two years of FFDM implementation with a 24 × 29 cm detector. The picture archiving and communications system was used to view and record the number of images taken per screening procedure for all digital exams, whereas the radiology information system was the source for repeat analysis for the SF period. Results: Of the 23,516 patients who received screening mammograms on FFDM equipment, 36.5% had more than the standard four‐views (craniocaudal and mediolateral oblique views of each breast). There were 15.5% who had a total of 5 images, 12.1% had 6 images, 3.3% had 7 images, and 5.6% had 8 or more images. The total repeat rate averaged over all patients was 14.1%. In contrast, preliminary results show that the repeat rate for patients undergoing SFM screening for an equivalent 2 year period was close to 5.5%. As for dose, there was, on average, an 18% decrease in mean glandular dose per view in going from SFM to FFDM imaging. This dose saving is decreased considerably when the number of extra views is taken into consideration. Conclusions: A notable increase in the total repeat rate for screening mammograms was observed once the switch from SFM to FFDM occurred. These extra views had the undesired effect of offsetting some of the dose savings afforded by the digital equipment.
SU‐E‐I‐146: An X‐Ray Scatter Technique for Extracting Differential Linear Scattering Coefficients
Authors: Tang R , LeClair R
Published: November 2011

Purpose: To devise a scatter technique for extracting differential linear scattering coefficients of breast biopsies.Methods: An energy dispersive x‐ ray system is used to measure the scattered number of photons Ns(E) as a function of energy (E) from a 5 mm diameter 3 mm thick polycarbonate (lexan) biopsy at 6 degree, 12 degree, and 18 degree. A 50 kV 2.3 mA polychromatic pencil beam irradiates an area of 2.62 mm diameter on the sample for 3 minutes (X = 0.18 C/kg). A 25 mm̂2 by 1 mm thick CdTe detector is positioned 43 cm from the target with a 4.2 mm diameter aperture defining its active volume. Ns(E) spectra coupled with a semianalytic model are used to determine the differential linear scatter coefficients MUs(x) of biopsies, where x=E/(hc) sin(theta/2) is the momentum transfer argument. The Ns(E) spectrum for a biopsy of water was measured and was used with the model in reverse fashion to estimate the incident number of photons No. Water is chosen because diffraction data for water is considered the gold standard.Results: The MUs values were calculated using a bin size x = 0.06 nm̂−1 and E ranging from 7 to 40 keV. The values of MUs for lexan obtained at 6 degree using an No estimated from a 6 degree water scatter measurement were in good agreement with literature provided that a background subtraction correction is applied. At x=0.96 nm̂−1 the peak height is MUs=30.7 m̂−1 sr̂−1, a 2% overshoot. The MUs for lexan obtained from the 12 degree scatter measurement but with No estimated using the 18 degree scatter water measurement also resulted in good agreement with a 9% overshoot at the peak Conclusions: This work demonstrates a scatter technique with great potential for measuring the scatter signals of breast biopsies.
SU‐E‐I‐147: New Digital Mammography Equipment: Physical Characterization and Image Quality Evaluation
Authors: Oberhofer N
Published: November 2011

Purpose: Recently several new digital mammography equipments with different innovative features have been proposed on the market. This work compares 7 different systems with respect to physical characteristics, phantom image quality and dose. Methods: The studied units are: Fujifilm Amulet (innovative photoconductive switching read‐out), GE Senographe DS, Hologic Selenia (old and new target/filter materials), Hologic Dimensions (new filter, new tomosynthesis modality), Sectra Microdose, Siemens Mammomat Inspiration (new active matrix flat panel imager). All system detectors have been characterized in terms of MTF, NNPS and DQE according to IEC 62220‐1‐2. Image quality has been assessed by means of contrast detail evaluation with the phantom CDMAM ver. 3.4 and the software CDMAM Analyser for automated image analysis using the Inverse Image Quality Figure IQFinv. Dose was expressed as average glandular dose (AGD). Performances have been evaluated in clinical setup using automatic exposure control modality (AEC) and in optimized setup. Optimization was based on contrast to noise ratio (CNR) measurements.Results: DQE of all systems ranked between 55% and 80%, being higher in systems applying direct conversion technology. Generally a higher DQE reflected in a higher IQFinv score. Target/filter combinations producing spectra of higher mean energy confirmed better performances than conventional Mo/Mo ones. Photoconductive switching readout exhibited a potential average 20% dose saving; also scanning acquisition showed improved image quality at equal dose compared to standard flat panel detectors. The tomosynthesis modality allowed acquisitions with less AGD than a standard 2‐view screening examination for every breast thickness. Conclusions: Generally, technological innovations allow better image quality with lower AGD.
SU‐E‐I‐157: A Calibration Phantom for Dual‐Modality Mechanical Alignment: Numerical Simulation
Authors: Ji C
Published: November 2011

Purpose: Accurate hardware alignment is important for dual modality medical imaging devices, such as PET/CT. We propose an automated retrospective dual‐modality mechanical alignment to improve mechanical accuracy for combined medical imaging devices. We design and validate, by numerical simulation, a calibration phantom for fast dual‐modality hardware alignment. Method and Materials:We design a calibration phantom with a curve marker, which can be fabricated from a segment of flexible thin tube containing a mixture of contrast and radio‐activity. The spatial transformation of two modalities is then estimated from reconstructed volumes of each modality. To do this, the curve marker at each slice can be extracted by calculating thresholded center of mass. The spatial transformation is estimated using Iterative Closest Point (ICP) algorithm. Results: We simulated and compared different winding scheme (including normal helical, variable pitch helical, helical with straight ends and two‐way helical) of curve marker. A two‐way helical curve marker formulates a better conditioned estimation problem, which results in higher accuracy and faster convergence speed. In addition, simulation results show that the curve marker we proposed is robust to handle practical cases with added noise and discontinuity caused by air bubble. Conclusions: We can use a calibration phantom with a two‐way helical curve marker to efficiently and accurately determine the spatial transformation for dual‐modality mechanical alignment. The shape of curved marker can be in either 2D or 3D.
SU‐E‐I‐174: Monte‐Carlo‐Based Scatter Analysis for Improving Image Reconstruction of PET/CT Systems
Authors: Huang Z , Tung C , Hu Z , Wu Y , Zhu M , Brown R , Mayr N , Yuh W , Lo S
Published: November 2011

Purpose: Scatter analysis plays an important role in image reconstruction system. In Philips GEMINI TF system, the image reconstruction system is idle, waiting for scatter information from all five bed positions. To reduce the time used for image reconstruction, this study was to investigate whether three bed positions might be enough for image reconstruction by exploring the distribution of scatters using Monte Carlo simulations. Methods: A Geant4‐based Monte Carlo tool—GATE is used to generate detected event lists and spectra, and to simulate the Philips Allegro PET/GEMINI systems. To mimic clinically realistic conditions, two 70‐cm‐long phantoms with a uniform activity in the FOV and different activity distributions outside the FOV are required to perform scatter proportion and scatter distribution measurements. The outside of the FOV (OFOV) is divided into two components: the proximal OFOV (POFOV), describing the two bed positions on either side of the FOV under consideration, and the distal OFOV (DOFOV), describing the two bed positions on either side of the POFOV. Including the FOV, all five bed positions are currently required for single scatter simulation (SSS). It is possible to use what we learn from an analysis based on uniform activity to apply scaling factors when we analyze POFOV data corresponding to real patient activity. To test this hypothesis, we compare two (uniform and non‐uniform) activity distributions outside the FOV in our Monte Carlo simulations. Results: Most (at the 80± 5% level, depending on the scanner) of the scattered coincidences are from the activity in the FOV, POFOV contributes at the 20± 5% level), and the activity in the DOFOV makes a negligible contribution (1%) to scatter events. Conclusions: Based on our preliminary results, we showed that only three bed positions are necessary for image reconstructions, thereby speeding up the image reconstruction systems, while the image quality remains unchanged.
SU‐E‐I‐175: Evaluation of Quantitative Direct PET/CT Imaging of Y‐90 Microspheres Using the Jaszczak Phantom
Authors: Pasciak A , Owen R
Published: November 2011

Purpose: Selective internal radiation therapy (SIRT) of liver metastases and hepatocellular carcinoma with radiolabeled microspheres has become a viable treatment modality in recent years. This technique uses the high‐ energy, pure beta‐emitting radioisotope of yttrium‐90 (Y‐90) embedded in a glass or resin microsphere which is infused into the liver via the hepatic artery. However, direct imaging the post‐infusion distribution of Y‐90 SIRT has been a long standing problem due to the lack of any gamma emission. Recently, however, a low‐yield branch of Y‐90 decaying by internal pair‐ production was used to perform direct PET/CT coincidence imaging. With only a few publications summarizing preliminary clinical results, we have designed a quantitative phantom analysis allowing for a detailed and portable image quality and quantitation evaluation of this new imaging technique. Methods: Owing to its wide availability, the Jaszczak PET imaging phantom is an ideal choice for Y‐90 PET/CT imaging evaluation with a few minor modifications. As the Jaszczak phantom is water filled, a major difficulty is the fast settling of the microspheres, which stay in uniform suspension for less than one minute. An aqueous linear polymer (CH2CHCONH2) can be used to produce a uniform suspension of Y‐90 microspheres which lasts for several days. Additionally, a 0.4mm inner‐ diameter capillary tube was also filled with Y‐90 and placed in the Jaszczak phantom, with no modification, to provide a quantitative resolution evaluation . Results: The modified Jaszczak phantom was scanned on a prototype Siemens molecular CT through a research agreement with Siemens medical. Results gave a good indication of the accuracy in quantitation expected as well as image quality improvement over post‐ infusion bremsstrahlung SPECT that we may see when we begin Y‐90 post‐ infusion PET/CT patient imaging. Conclusion: The proposed modifications to the Jaszczak phantom allow for accurate, portable evaluation of a PET/CT system for quantitative Y‐90 imaging.
SU‐E‐I‐176: Impact of Residual Activity and Clock Synchronization on Quantitative Treatment Response Assessment
Authors: Jallow N , Scully P , Vanderhoek M , Perlman S , Liu G , Jeraj R
Published: November 2011

Purpose: The accuracy of quantitative PET is influenced by many factors whose uncertainties need to be characterized for its reliable use in treatment response assessment. Among the factors are residual activity and lack of synchronization between PET‐scanner and dose‐calibrator clocks which are frequently overlooked. Therefore, we characterized their effects on PET‐ based treatment response assessment. Methods: Fifteen patients receiving targeted molecular therapy underwent whole body [18F]FLT PET/CT scans at multiple time points. Response was calculated as the change in SUV between subsequent scans. Residual‐activity left in syringe after injection effects were assessed by comparing response measures when SUV values were corrected for residual activity (range: 0.07mCi‐0.61mCi) to when they were not. Uncertainty in response was also compared between scans where the synchronization of the PET‐scanner and dose‐calibrator clocks were randomly offset (range: 1min‐60mins) to when they were synchronized. The effect of both factors on PERCIST classification of treatment response was assessed. Results: Residual‐activity and lack of clock synchronization had significant effects on treatment response (p=0.05). 3% change in clock offsets between subsequent scans resulted in 2.5% absolute difference in response. The mean difference in responses due to desynchronized clocks was 18% (maximum=35%). 3% change in residual activity resulted in 0.1% absolute difference in response. Not accounting for residual‐activity caused mean difference of 1% (maximum=6%) in the response. Changes in clock synchronization and not accounting for residual activity resulted in reclassification of the PERCIST response status of over 30% of the patients. Conclusions: Lack of synchronization between PET‐scanner and dose‐ calibrator clocks and not accounting for residual activity caused a difference in response. Administration procedures that minimize residual activity (e.g. flushing syringe with saline) have to be implemented. Also, all clocks used with dose‐calibrator have to be synchronized with PET‐scanner clock periodically. Otherwise patients can be wrongly classified as partial, stable, or progressive disease.
SU‐E‐I‐177: Electric Field and Ionization Signal Simulation in Liquid Xenon Detectors for PET
Authors: Zhu H , Bryman D , Clements C , Glister J , Kurchaninov L , Miceli A , Retiere F. , Sossi V
Published: November 2011

Purpose: A liquid xenon (LXe) detector prototype was developed to assess the performance of LXe for use in positron emission tomography. In this prototype, the measurement of ionization signals was achieved by using a time projection chamber (TPC), and scintillation light was measured by large area avalanche photodiodes. This work is aimed to simulate the electric field and readout signals in the LXe TPC.Methods: The electric field inside a single sector of the prototype detector was calculated through the finite element method using the software of Opera‐3d, with focus given to determining the uniformity of the field. The simulation model consists of a cathode, an anode, and field cage strips, which were immersed in a liquid xenon volume. With the electric field map obtained by Opera‐3d, the signals simulation were implemented in the Garfield package. The detector responses, including the primary ionization, generation of electron clouds, electron drift, diffusion, induced current signals on induction wires, and collection signals on anodes, were simulated. Comparison of simulation signals and measurement signals was made.Results: Three‐dimensional simulation results for the prototype detector showed that the field was nearly uniform in the center, with electron drifts deviating by less than 1 mm between the cathode and anode. The region of dead space constitutes 2.9% of the total volume in this sector. The simulation signals were in a good agreement with measurements. Conclusions: The good uniformity inside the chamber guaranteed 3‐D sub‐millimeter position resolution across the entire field of view. Based on the 3D electric field map, we can assign correction factors to correct the non‐uniformity in the whole sector. We also correctly simulated the signals of the TPC.
SU‐E‐J‐48: Measurement of Radiation Induced Pulmonary Function Change from 4DCT
Authors: Ding K , Du K , Cao K , Reinhardt J , Christensen G , Benedict S , Buatti J , Bayouth J
Published: November 2011

Purpose: 4DCT can be used to measure pulmonary function change following radiation therapy for adaptive treatment planning. The purpose of this study is to analyze the effects of the measurement variation and compare the planned radiation dose and pulmonary function change due to radiation not measurement variation. Methods: Two 4DCT data sets before RT scanned with thirty minutes break and one 4DCT data set acquired 5 months after RT from one patient were used in this study. Tissue volume and vesselness preserving image registration algorithm was applied to register the maximum inhalation image to the maximum exhalation image for the calculation of local lung expansion as a measurement of regional pulmonary function (PF). The pulmonary function changes (PFC) before RT and after RT were calculated via the PF ratio between two 4DCT scans. The radiation induced pulmonary function change (RI‐PFC) is calculated from PFC after RT by filtering measurement variation calculated in PFC before RT. We compared the RI‐PFC with planned radiation dose at the contralteral/ipsilateral lung, and the upper/lower lobes of the ipsilateral lung. Results: Significant measurement difference is found between lobes in the same ipsilateral lung. For the contralateral lung in the RI‐PFC region, the average radiation dose is 2.5 Gy and the average PFC value is 1.10. For the ipsilateral lung in the RI‐PFC region, left upper lobe shows the average ration dose as 59.1 Gy with average PFC value 0.9, and the left lower lobe shows the average ration dose as with 2.5 Gy the average PFC value 1.14. Conclusions: We described a technique that uses 4DCT, image registration and biomechanical analysis to measure regional pulmonary function change. We compared the radiation induced pulmonary function change to the planned radiation dose distribution and examined the differences in different lungs, and at the lobar level.

This work was supported in part by NIH grant HL079406 and EB004126.
SU‐E‐J‐51: Automatic Detection of Markers Based on Threshold Clustering in 3D CT Images for Image‐Guided Radiation Therapy
Authors: Jia J , Huang S , Li J , Pei X , Cao R
Published: November 2011

Purpose: Marker‐based registration, needed especially when there is no sufficient bony anatomy for adequate match, plays an important role in the image guided radiation therapy (IGRT) systems, of which the accuracy of registration greatly depends on that of the location of the markers embed. Since the manual marker detection has many limits for its time consuming and labor intensive, it is essential to enable an automatic detection of makers to help to cut down the human error in registration as well as to get a speedup of the registration process, making IGRT systems more efficient. Methods: In this study, we present a simple and efficient clustering method based on the k‐means clustering algorithm, which we call threshold‐based clustering. This method is established in three procedures. First, we got a set of segmented 3D CT images using binary thresholding method since the value of the markers is far different from that of the CT images. Second, the calculation was done by comparing the spacial distance between every two possible marker candidates to make marker points with similar intensity clustered. Finally, the centers of markers can be obtained after a given number of iteration time which can be changed according to the prior estimated number of markers. Results: This method has been tested on 46 CT slices with a size of 512*512. Markers were successfully identified in at least 99.00%. It took less than a second to detect three markers with the average location accuracy of 0.56mm compared to 1.50mm for the conventional manual technique. Conclusions: It has been testified that the method proposed can accurately detect the location of the markers within 3D CT images. Our results demonstrate the subvoxel accuracy can be achieved completely automatically which makes the method well suited for clinical applications.

Supported by the National Natural Science Foundation under grant No.30900386 and the Anhui Provincial Natural Science Foundation under grant No. 090413095 and 11040606Q55
SU‐E‐J‐67: Dual Resolution CT‐Based Phantoms for Monte Carlo Simulation Against Small‐Field Irradiations in Tiny/heterogeneous Tissues
Authors: Chao T , Hsieh Y , Lee C , Tu S , Cheng H , Tung C
Published: November 2011

Purpose: Dose over/underestimation is a common problem for highly irregular fields or around tiny and heterogeneous tissues such as the mucosa/epidermis near teeth/false teeth, skin, bone marrow, vestibulocochlear nerve, and pituitary glands, leading to unexpected normal tissue complications or tumour recurrence. Owing to the limitation of computer efficiency and RAM capacity, it is impossible at present to construct a very high‐resolution phantom for calculating tumour/organ dose together with realistic and accurate dose estimation for tiny and heterogeneous tissues in one simulation. This study aimed to develop dull resolution CT‐based phantoms for Monte Carlo simulation against small‐field irradiation in tiny/heterogeneous tissues. Methods: A homemade VC++ 6.0 code was developed to translate DICOM CT images to dual resolution CT‐based phantoms in the format of an egs‐phantom used in DOSXYZnrc. This code uses regular spatial resolution to define the tumour/organ, but enhances the resolution around the region of interest. This dual resolution phantom can be used for patient treatment evaluation and dose distribution around tiny and heterogeneous tissues in one simulation. Results: A dual resolution pure water phantom will not impact the outcome of MC simulation under large uniform field irradiation. However, the results of this pure water phantom under small field irradiation showed dose underestimation of more than 30% owing to the partial volume effect of not using enhanced resolution. Another dual resolution heterogeneous phantom was used to investigate the interface dose distribution near the boundary of different materials. Finally, a dual‐resolution CT‐based phantom, BigMouse, was created to study the dose distribution around teeth. Isodose curves and PDD/profile comparisons showed that enhanced resolution doses were higher when irradiation fields or phantoms were not uniform. Conclusions: Dose underestimation due to over‐sized voxels can cause severe damage to mucosa in the oral cavity.

This work was supported by NSC99‐2314‐B‐182‐040‐MY2 from the National Science Council, Taiwan and CMRPD180162 from the Chang Gung Memorial Hospital
SU‐E‐J‐71: Uncertainty Representation in a Composite Radiation Dose Using Fuzzy Logic
Authors: Park S B , Monroe J I , Machtay M , Sohn J W
Published: November 2011

Purpose: To present dose uncertainty in composite radiation plans generated through Deformable Image Registration (DIR). We introduce a Fuzzy Composite Dose (FCD) with fuzzified deformation vectors. We compared the Fuzzy method to the statistical approach. Methods: The accuracy of the DIR is generally verified through visual checks, including confirmation of matching corresponding anatomies. However, most of the soft tissues have few significant image features and therefore greater uncertainty in registration. We fuzzified the deformation vectors and derived a FCD. We utilized a Gaussian function for uncertainty allocation. A Gaussian variance (two standard deviation; 2sigma) between 2mm to 10mm was assigned, which is based on previous publications analyzing the difference between various DIR methods. The least uncertainty (2sigma=2mm) was assigned to the areas having significant image features. The most uncertainty (2sigma=10mm) was assigned to the areas with few features or a lot of noise. A Fuzzy union operator was utilized to derive the FCD from the Fuzzy deformation vector. The Alpha‐cut method was employed to present the uncertainty range of FCD. A patient example is presented. After radiation treatment to the right lung, they returned to the hospital later to have another radiation treatment to the right rib cage near the liver. B‐Spline DIR was utilized to create the composite dose. Results: In the liver, the statistical analysis shows the uncertainty up to 2sigma=17Gy. With the fuzzy approach, the alpha‐cut showed the uncertainty range up to 35Gy. The dose uncertainty range using the alpha‐cut is shown to be asymmetric, a representation not possible using the standard statistical approach. Conclusions: FCD showed the better presentation including the range and direction of uncertainty in the composite dose. This will enable the clinician to deliver effective dose to a recurrent tumor or new tumor near the previously treated site while minimizing complications.