bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐33: Evaluation of Z‐Axis Resolution for Axial and Helical Scanning Modes On MDCT
Authors: Klahr P , Yanof J
Published: April 2010

Purpose: To evaluate Z‐axis resolution for axial and low pitch helical scanning modes on a multi‐detector CT (MDCT). Axial scanning, performed in a cine mode, and helical scanning are both presently used to acquire 4D‐CT data sets. Method and Materials: The slice sensitivity profile (SSP) is considered as an indicator of Z‐axis resolution. The CT‐SSP Phantom (Model 76‐412, Fluke Biomedical) was used. The scans were performed on a Philip's Brilliance Big Bore 16 slice scanner. The phantom was scanned at incremental distances from the CT isocenter from 0mm to 200mm. The 16×1.5mm collimation mode, standard resolution and standard recon filter were used for both helical and axial modes. For helical scans, the pitch was varied between 0.04 and 0.08. The slices were reconstructed at 0.2mm increments. For axial mode, a 0.5mm increment was used. The effective slice thickness or Z‐axis resolution was calculated as the full width at half maximum (FWHM) of the SSP. Results: For helical scan modes, the measured slice thickness remained below 2mm for all points in the X/Y plane. In axial mode, the FWHM of the SSP plot was 1.5 +/−0.3mm with the phantom well centered. At 20cm from the CT isocenter, the measured Z‐axis resolution was close to 5.0mm. Conclusions: When imaging with high Z‐axis resolution is required, axial mode scanning should be utilized when the region of interest is small and the patient is well centered within CT gantry. For scans where Z‐axis resolution must be maintained over a large area, helical mode scanning would be preferred. When performing 4D‐CT using cine axial scans, the Z‐axis resolution can be compromised near the periphery of the imaging plane.
SU‐FF‐I‐35: Multi‐Slice CT Dose Evaluation Using Optically Stimulated Luminescence (OSL) System
Authors: Ruan C , Clouse W , Yukihara E , Gasparian P , Ahmad S
Published: April 2010

Purpose: To demonstrate the feasibility of OSL system for measuring full dose profile and to establish the CTDI efficiency factors as reference values for compensating the underestimation of pencil chamber based CTDI100 methodology. Materials and Methods: The OSL dose calibration was first performed using a 0.3 cm3 Semiflex Chamber. Field‐specific conversion factors were determined in the diagnostic CT energy range. The 64‐slice Multi‐Slice CT (MSCT) dose profiles were measured by irradiating OSL strips placed inside an extended FDA CT head and body dosimetry phantom with different combination of scan parameters. The exposed strips were then read out using custom‐made OSL strip reader and corrected with field‐specific conversion factors. Based on the corrected dose profile, the CTDI∞ and CTDI100 were evaluated. CTDI100 was also obtained using a 100‐mm long pencil chamber for accuracy verification. Results: The OSL detectors were found to have good sensitivity and dose response over a wide range of diagnostic CT x‐ray beam energy viz. the primary beam and the scatter tail part of the dose profile. Based on the overall OSL and MSCT physical performance, the total length of 450 mm was determined for z‐axis coverage of dose profile. The CTDI efficiency was calculated by CTDI100 /CTDI450. For the broadest collimation setting, 40 mm, the average CTDI efficiency is 56.2% and 81.7% respectively for body phantom center and periphery positions. For these positions, the OSL CTDI100 agreed well within 1.0% and 2.7% compared to CTDI100 measured by pencil chamber. Conclusions: OSL detectors can be accurate alternative devices for CT dose evaluations. The established CTDI efficiency factors for various scan parameters allow in accurately estimating CTDI∞ with the current use of 100‐mm pencil chamber. The OSL field‐specific conversion factors offer a potential solution for estimating patient organ dose.
SU‐FF‐I‐37: Precision of Exposure Measurements Obtained On Current Multi‐Slice CT Scanners
Authors: Boitnott K , Kim H , McNitt‐Gray M , Cagnon C , Zhang D , Cody D
Published: April 2010

Purpose: The stability of exposure measurements made over time on CT scanners is not well understood. To determine the stability of exposure measurements, the precision of such measurements must first be determined. Precision can be characterized by the coefficient of variation (CV) which is the standard deviation divided by the mean times 100%. The least significant change (LSC) is defined as the smallest change between two measurements that reflects a real change in the system with 95% confidence and is calculated by multiplying the CV by 2.77. Method and Materials: Exposure readings were collected on CT scanners of three makes and models using a 10‐cm pencil ionization chamber and electrometer. Three GE VCT, three GE Lightspeed 16, and three Siemens Sensation 64 scanners were used to determine the precision of scanners over time and across sibling scanners (scanners of the same make and model). Precision of the scanners was evaluated at consistent techniques using in air exposures and CTDI phantom measurements. Results: The maximum observed in air exposure CV for individual scanners over several minutes was 0.25%, over three weeks was 1.13%, and over four to six months was 3.34%. In CTDI phantoms, the maximum observed CV of the individual scanners was 3.77% in measurements taken over weeks and 3.91% in measurements taken over months. When sibling scanners were compared, the maximum observed CV was 4.33%. Conclusion: Using a maximum CV of 4 %, the LSC is 11%. Therefore, repeated exposure measurements taken on a CT scanner, during annual testing, for example, must vary by more than 11% to be considered a real change with 95% confidence.
SU‐FF‐I‐39: The Effects of Additional Scatter Media and Tube Current Modulation On MDCT Organ Doses
Authors: Fisher R , Hintenlang D
Published: April 2010

Purpose: To quantify the effect of scatter media surrounding the scanned volume in CT on organ dose. This information could prove valuable in using patient specific data with Monte Carlo simulations to determine clinical organ doses. The effects of beam width and automatic tube current modulation (ATCM) on organ doses in CT were also explored, as most current Monte Carlo simulations do not account for the ATCM systems incorporated in modern clinical scanners. Method and Materials: Average organ dose measurements were taken in an adult male anthropomorphic phantom using a fiber optic coupled dosimetry system during a routine clinical chest CT exam. The amount of scatter media was increased longitudinally from a normal 33 cm scan length to include the entire 176 cm length of the phantom. Both modulated and fixed tube current scans were performed using multiple beam widths (2.4 mm and 1.2 mm) to determine the effects of these parameters on organ doses. Results: Within experimental error, the presence of additional scatter media did not cause an increase in measured doses. A 2.4 mm beam produced an 11% dose reduction as compared to a 1.2 mm beam. ATCM was found to reduce average organ doses by approximately 24%, with individual organ dose reductions ranging from 36% in the breast to 10% in the lungs compared to fixed current scans. Conclusion: Monte Carlo simulations performed on patient scan data will not significantly underestimate organ doses due to scatter contribution from outside the scan volume for an average‐sized patient. A combination of ATCM and a wider beam was found to reduce average doses by 33% during a chest CT. It was found that a comparison of the ATCM tube current per slice is an accurate predictor of individual and average organ dose savings for ATCM compared to fixed current techniques.
SU‐FF‐I‐50: Development of a 15MsP Super High Resolution Medical Liquid Crystal Display for the Digital Mammography
Authors: Hasegawa M , Ichikawa K , Tanaka Y
Published: April 2010

We developed a new medical display by utilizing our independent sub‐pixel drive (ISD) technology and anti reflection‐coated panel, which realizes resolution of 15M sub‐pixels to accept higher resolution output from modality devices. The ISD technology enables each of three sub‐pixels constituting one pixel element of monochrome displays to be driven independently, and consequently three times resolution enhancement is achieved. We evaluated its sharpness and noise characteristics quantitatively, and performed perceptual evaluations by radiologists by using clinical images for comparison with conventional displays. This new technology was considered effective for the accurate depiction of the fine anatomical structures such as micro‐calcifications of the mammography.
SU‐FF‐I‐51: Relative Dynamic Range Evaluation for Image Chain and PACS Station Displays
Authors: Mckinney D , Rutel IB
Published: April 2010

Current display performance evaluation in digital radiography use station resident digital test patterns allowing comparison with measured values. However, these techniques require the use of special tools (A photometer and vendor loaded resident patterns) which may not be consistent; can be time intensive; and give little information about the performance of the rest of the imaging chain. This study describes the construction and use of an experimental phantom designed to visually evaluate the relative dynamic range of multiple components in the imaging chain and across multiple (vendor independent) displays. The results of exposure technique testing and evaluation of the phantom as a QA component for image quality tests will be discussed.
SU‐FF‐I‐53: Comparisons of Organ and Effective Doses From ImPACT and DLP/ED Methods to MDCT‐Specific Monte Carlo Simulations
Authors: Turner A , Zankl M , Angel E , McNitt‐Gray M
Published: April 2010

Purpose: Organ and effective dose (ED) are the preferred metrics for estimating risk from CT. Common methods to obtain these values include the ImPACT CT Patient Dosimetry Calculator and DLP to ED coefficients. This study compares the reported values from these methods to doses calculated from MDCT‐specific Monte Carlo (MC) simulations. Method and Materials: Using two 64‐slice MDCT scanners, organ doses were obtained from the ImPACT calculator for a 120 kVp, helical (pitch 1) chest\abdominal scan. Analogous MC simulations were performed on two voxelized female models of different sizes. ED values (ICRP 60 and 103) were calculated using the resulting organ doses and also using the DLP method. The agreements of the ED and organ doses from ImPACT and the DLP methods to MC values were calculated for each scanner and patient. Results: The % differences between ImPACT and MC organ doses had a wide range (−76% to 465%) depending on the scanner, patient, and organ, with an absolute mean of 53%. For a given scanner and organ, the agreement level across patients varied considerably. For a given patient and organ, the agreement across scanners varied less. Agreement between ImPACT and MC ED values were within 10% (both scanners) for one patient but varied between 28% and 46% for the other. The DLP method resulted in % differences ranging from 5% to 32% depending on the patient. Conclusion: Organ dose comparisons demonstrate differences up to 400% between approaches, which could be due to different patient models (MIRD vs. voxelized phantoms of different sizes) and/or variations in scanner modeling approaches (ImPACT scanner matching vs. MC method). Agreement levels between ED values obtained from the ImPACT or DLP methods to MC results are highly dependent on the particular scanner and patient under consideration but were within 30% in all cases.
SU‐FF‐I‐55: Reconstruction of Mammography X‐Ray Spectrum Using Rayleigh and Compton Scattering Corrections
Authors: Kawaguchi S , Yamaguchi Y , Arimura H , Morishita J , Ohki M , Uno Y , Ideguchi T , Higashida Y , Toyofuku F
Published: April 2010

Purpose: An analysis of the x‐ray spectrum is important for quality assurance (QA) and quality control (QC) of a radiographic system. In the case of mammography, the direct measurement of the primary x‐ray spectra under clinical conditions is very difficult and time‐consuming. The method of obtaining the primary x‐ray spectrum by the Compton scattering correction has been established for relatively high x‐ray tube voltages. However, the influence of Rayleigh scattering can not be neglected for mammography. We have developed a new method of reconstructing the primary x‐ray spectrum from the scattered x‐ray spectrum taking into account both Rayleigh and Compton scattering. Method and Materials: The primary x‐ray beam from a 28 kV mammography x‐ray unit was incident on a PMMA (polymethyl methacrylate) sphere scatterer with a diameter of 6 mm. The 90‐degree scattered x‐ray spectrum was measured by using a CdTe semiconductor detector. The measured x‐ray spectrum was separated into three energy regions, and the characteristic x‐ray peaks and bremsstrahlung x‐rays were fitted by Gaussian and quadratic functions. The energy shift corrections of the Compton and Rayleigh components were made at each photon energy channel by splitting the number of photons at each channel into the two scattering components according to the corresponding cross sections. The Monte Carlo simulation of the 90‐degree scattered x‐ray spectra were also performed using the EGS5 code. Results: The reconstructed spectrum agreed fairly well with a directly measured primary x‐ray spectrum. In the Monte Carlo simulation, the scattered x‐ray spectrum calculated for the incidence of the reconstructed x‐ray spectrum showed a very good agreement to the measured scattered x‐ray spectrum. Conclusions: The Rayleigh and Compton scattering correction method could be suitable for measuring the mammography x‐ray spectra under clinical conditions and useful for QA and QC of the mammography x‐ray units.
SU‐FF‐I‐61: Gypsum Barrier Shielding Estimates for Two Cone‐Beam CT Systems Dedicated to Head Imaging
Authors: Larson S , Goodsitt M , Christodoulou E
Published: April 2010

Purpose: Cone‐beam CT is becoming increasingly popular for bone imaging of the head. Shielding practices for CT defined in NCRP Report No. 147 do not directly apply to a cone‐beam system, but standard methods for radiographic systems are also inadequate for the highly filtered x‐ray beams in cone‐beam CT systems. This study evaluates the use of published 120kVp CT transmission curves for gypsum [Simpkin 1990] to estimate required shielding for two cone‐beam CT systems at different energies in comparison to measured transmission data. Method and Materials: The head CTDI phantom was used with an E‐Woo Technologies Master3DS dental CT at 90kVp and a Xoran Technologies MiniCAT at 120kVp to produce scattered radiation. Transmission of scattered radiation through two 3‐foot by 3‐foot sheets of standard 5/8‐inch (16mm) gypsum wallboard was measured with an 1800 cc ionization chamber. Results: For the Master3DS, transmission through 2 layers (32mm) of gypsum wallboard was 0.30. The estimated shielding from the 120kVp transmission curves for a 1968 mAs/week workload and 2 mR/week permitted exposure at 2.09m distance was 32mm gypsum. The corresponding exposure determined with the measured transmission was 1.3 mR/week, indicating a calculated shielding over‐estimate of 22mm of gypsum. For the MiniCAT, transmission through 32mm of gypsum wallboard was 0.51. The estimated shielding from the 120kVp transmission curves for a 960 mAs/week workload and 2 mR/week permitted exposure at 1.46m distance was 32mm gypsum. The corresponding exposure determined with the measured transmission was 2.2 mR/week, indicating a calculated shielding under‐estimate of 4 mm gypsum. Conclusion: The transmission curve data for gypsum at 120kVp overestimates the shielding requirement for this 90kVp cone‐beam system, but slightly underestimates the shielding requirement for the 120kVp system. However, since lead is more likely to be necessary to shield the 120kVp system, a minor underestimate for gypsum may be insignificant.
SU‐FF‐I‐62: Radiation Risks to Patients with Suspected PE Undergoing Chest CT and V/Q Scans
Authors: Huda W , Bisdas S , Ravenel J , Gordon L
Published: April 2010

Purpose. To compare the risks of radiation induced cancer to patients with a suspected pulmonary embolism (PE) undergoing chest CT scans with those of ventilation/perfusion (V/Q) nuclear medicine scans. Method. We determined absorbed doses to eight radiosensitive organs in adult male and female patients with ages that ranged from 20 to 80. Organ doses for a chest CT scan were determined for a Sensation 64 scanner operated at 120 kV (DLP 190 mGy‐cm) using the ImPACT spreadsheet. Corresponding doses were obtained for ventilation study (110 MBq 99mTc labeled DTPA aerosol) and a perfusion study (370 MBq 99mTc labeled MAA) using ICRP organ dose per unit administered conversion coefficients. Organ doses were converted into lifetime attributable risk factors provided by BEIR VII. Results. In 40 year old patients, cancer incidence rates in CT were 26 and 53 per 100,000 for males and females respectively. Corresponding cancer incidence rates in ventilation studies were 7 per 100,000 (males) and 9 per 100,000 (females), and in perfusion studies were 33 per 100,000 (males) and 68 per 100,000 (females). When averaged over all ages and sexes, the average cancer mortality rate was 67%. Reducing the patient age to 20 years increased the patient risk by an average of 51%, whereas increasing patient age to 80 reduced the cancer risk by an average 69%. For CT and perfusion studies, the highest risks were for the lung whereas for ventilation studies, the highest risk from irradiation of the bladder. Conclusion. Cancer radiation risks depend much more on patient demographics than on the choice of imaging modality (i.e., CT vs V/Q).
SU‐FF‐I‐66: Calculation of Broad Beam Transmission Factor for 511 KeV Photons Using Energy Spectra Measured in the Presence of Scatter
Authors: Brinkley B , Yester M , White S
Published: April 2010

Purpose: To obtain the energy spectra from patients after administration of F‐18 FDG and measure the broad beam attenuation of lead under clinical conditions. Method and Materials: A sodium iodide detector was used to measure the spectrum of photon energies emitted from patients after being injected with FDG. Spectra were taken through an unshielded wall, and through a wall shielded with 15.9 mm of lead as the patient was seated in the uptake room. Exposure rate readings were also made using an ionization chamber survey meter. The spectra were corrected for detector efficiency, summed over all energies, and the results converted to exposure rates. The spectra of energies emitted from a point source of FDG were also measured, through various thicknesses of lead. Results: Both the spectra data and the ionization chamber results are compared to transmission factors for lead at 511 keV given in “AAPM Task Group 108: PET and PET/CT Shielding Requirements”. Conclusion: Due to scatter in the patient, the fraction of lower energies is significant compared to 511 keV photons and can influence the effective attenuation of lead in clinical PET facilities.
SU‐FF‐I‐68: Survey of MSCT and SSCT Scanners in Taiwan: Technical Factors, CTDIs, and Effective Doses
Authors: Liao YL , Tsai HY , Lin JH , Chen CP
Published: April 2010

Purpose: To assess the current level of radiation dose from computed tomography scanning in Taiwan. Method and Materials: The dose characteristics of CT scanners were investigated on the basis of questionnaires in Taiwan. The information included scanner model and manufacturer, the scanning parameters of the most frequent five adult standard CT examinations. Radiation doses were estimated in terms of computerized tomography dose index (CTDI), dose length product (DLP), and effective dose (E) using the software from the ImPACT website and the Monte Carlo simulation data from National Radiation Protection Board's SR 250 report. Results: Responses were received from 231 of 409 questionnaires (56%). They included 49 % MSCT and 51 % SSCT. The mean CTDIw, DLP, and effective dose for the head and body region ranged from 16±9 to 52±21 mGy, 418±301 to 746±427 mGy cm and 1.6±0.9 to 10.8±9.6 mSv, respectively. On average, the CTDIw and DLP are lower than the values recommended by European Commission. The tube current is the most variable parameter. The tube current for MSCT (229∼309 mA) are higher than those for SSCT (176∼191 mA). The DLP and effective dose for MSCT are 19∼68 % and 28∼67 % greater than those for SSCT. Comparing with other countries' survey results during the past ten years, the doses in Taiwan are lower than those in the U.S., but roughly higher than those in U.K. and Germany. Conclusion: This national CT dose survey provided a wealth and updated data. The results revealed the MSCT scanners have great possibility to become the majority in Taiwan, and the dose contributions from MSCT at the same scanning procedure are higher than those from SSCT.
SU‐FF‐I‐69: Monte‐Carlo Evaluation of the Backscattering Shielding of Two EPIDs
Authors: Wang S , Gordon J , Gardner J , Siebers J
Published: April 2010

Purpose: To evaluate two possible designs to shield the imaging panel from radiation backscattered from objects downstream of the imager. Method and Materials: Two EPID panel variants, panel 1 and panel 2, are prototyped with an in‐house EGSnrc Monte Carlo code module. These panels differ from commercial panels via the addition of composite materials within the detector panel, designed to shield the detection screen from radiation backscattered. No, medium, and strong backscattering materials are simulated via the addition of 10 cm vacuum, water and lead respectively beneath the imager geometry. Poly‐energetic energy deposition kernels for 6 and 18 MV photon beams are calculated using Monte Carlo simulation. The integrated energy is used to evaluate the signal enhancement due to the backscattering. Each kernel is convolved with 5×5, 10×10, 15×15, and 25×25 cm2 fluence profiles to determine the maximum backscatter signal deviation attributable to the added materials as a function of field size. Results: The largest signal enhancements for poly‐energetic irradiations are 2.87% and 3.07% for panel 1 and panel 2 respectively, which occur with the 18 MV incident energy and the lead backscatter. For water, the maximum enhancement is 0.74% and 1.08%. The back‐scatter signal induced deviation decreases with field size. Conclusions: Both prototype imaging panels will reduce the maximum backscatter signal enhancement to <3.1%. For typical clinical field sizes and backscattering materials, the signal enhancement should be <1%. Use of these panels could reduce the backscattering induced uncertainties and improve the reliability of measurements.

Conflict of Interest: This work was funded in part by Varian Medical Systems.
SU‐FF‐I‐71: Study of a Well‐Type Ionization Chamber by Monte Carlo Simulation
Authors: Santos M , Takeda F , Pianoschi T , Nicolucci P
Published: April 2010

Purpose: Study the linearity of response of a well‐type ionization chamber for different activities and radioisotopes used in Nuclear Medicine by means of experimental procedures and Monte Carlo simulation. Method and Materials: The well‐type ionization chamber being developed has a multi‐layer brass electrode configuration with stainless steel walls (0.5mm‐thickness inner wall). High pure argon at 0.3MPa is used in the sensitive volume. PENELOPE simulation package was used to study the linearity of response with activity for and . In the simulations the sources were assumed to be volumetric and an specific glass vial used in Nuclear Medicine services was simulated. The ionization current per photon emission was simulated for the three previously cited nuclides. Results: For the linearity study, the comparison between simulated and experimental results showed agreement better than 98% for , 95% for and 96% for . For the radionuclides and range of activities used both the simulated and the experimental results showed a linear (better than R=0.995) behavior with activity. The experimental relative sensitivity is 0.245, 0.155 and 3.45 nA/mC for and , respectively. Using the normalized response for these radionuclides, a maximum difference in sensitivity between simulation and experimental data was 6% for . Conclusion: The agreement between simulated and experimental results obtained in this work suggests the feasibility of using PENELOPE Monte Carlo package to study the construction features of well‐type ionization chambers.
SU‐FF‐I‐74: The Use of a Simple Contrast to Noise Ratio (CNR) Metric to Predict Low Contrast Resolution Performance in CT
Authors: Brown M , Zhang D , Branham T , Cody D , Kofler J , McCollough C , Pfeiffer D , Strauss K , Yu L , McNitt‐Gray M
Published: April 2010

Purpose: To investigate the use of a simple contrast to noise metric and its ability to predict low contrast resolution in CT scans. Method and Materials: The ACR low contrast phantom was scanned with 120 kVp and various exposure levels ranging from 50 to 1600 effective mAs. Each scan was reconstructed with 5 mm thickness and 8 different reconstruction filters, ranging from very smooth (B10) through very sharp (B80). Each image was windowed and leveled to the same settings, anonymized to reduce reader bias and put in random order. The images were sent to 9 independent readers, experienced in evaluating the ACR phantom for low contrast resolution. Each reader scored the smallest size set of rods visible in each image. Separately, a simple contrast to noise ratio (CNR) was obtained for each image, calculated as (A‐B)/σ where A is the mean of an ROI placed over the 25mm rod, B is an ROI of samesize placed in the background next to the 25mm rod, and σ is the standard deviation of the background. Results: For many of the lower exposure and filter combinations, the largest 25mm rod was not visible and no measurement of CNR could be made. For those images in which it was visible, the CNR ranged from 0.15 for 300mAs and filter B70, to 6.4 for 1600mAs and filter B10. The measured CNR does correlate well with observer performance within a reconstruction filter setting, though there is wide variability in observer performance. However, CNR did not correlate well with observer performance across reconstruction filters. Conclusion: The correlation between CNR and observer performance suggests it may be possible to use this metric to predict low contrast performance for cases with a fixed reconstruction filter and might be useful if a limited range of filters are used.
SU‐FF‐I‐80: Evaluation of Dose Rate of Occupational Exposure in Nuclear Medicine Service
Authors: Schwarcke M , Marques T , Nicolucci P , Cardoso D , Ferreira N
Published: April 2010

Purpose: Characterize the value of dose rate received by the nuclear medicine professionals during the examination procedure and handling of radiopharmaceuticals, permiting the realization of more specific pratices of radioprotection in nuclear medicine. Method and Materials: For this work was monitoring two professional in two separate nuclear medicine services, totaling four profissionals monitoring during two moths. Their routine was not modified. The measuring of the rate dose was made with an ionization chamber model Babyline 81 at a distance of 1.0 m from the source. The measurements were made during the eluation of radioisotope, preparation the radiopharmaceuticals, in the administration and during the exam realization. The value of the rate dose was associated the procedure realized, for this way to caracterize the level of exposure that the professional it was sudmitted during your daily work. Results: It was observed for the test of renal scintigraphy with DTPA an average of 2.55 μGy/h and an average value of 1.20 μGy/h to DMSA. For examinations of bone scintigraphy with MDP was observed an average of 2.63 μGy/h for the protocol of time and 3.09 μGy/h for the protocol of counting, the difference in protocol is due to different interpretation medical. The bone flow scintigraphy the average rate dose was 5.17 μGy/h. The values of the background radiation measured over the handling of radiopharmaceuticals shows a maximum increase of up to six times the background radiation before manipulation and this value influence the measurements performed by measuring activity. Conclusion: The evaluation of the values of dose rate may help in taking action directed to optimizing the radioprotection and minimize the sum of errors during a correct administered radiopharmaceutical to the patient, minimizing the dose in the pacient and in the professional.
SU‐FF‐I‐81: Lead Apparel Management Program at a Large Medical Center
Authors: Schultz C , Emerson S , Feng W , Robertson S
Published: April 2010

Purpose: To determine whether our new lead apparel management program was effective at minimizing radiation doses to waist badges worn underneath lead apparel, improving compliance with lead apparel integrity testing, and detecting lead apparel defects. Method and Materials: From 1999–2008, 14,343 items of lead apparel were tested for integrity (including both visual and fluoroscopy testing). Of these, 723 failed (5.0%) and were removed from service. In 2006, number of items tested decreased by 20% compared to 2005, and failed items decreased to 1.2%, which prompted the new lead apparel program. To minimize radiation dose to waist badges, lead apparel below 85% in lead equivalence above 100 kVp, was not allowed to be purchased. The basis for this was kVp recorded for 14,644 scenes in our 4 busiest cardiac catheterization labs over a 3 month period. From 14.4 to 33.9% of scenes were taken at 100 – 120 kVp; and from 1 – 4% of scenes were taken at > 120 kVp. To improve inventory and tracking, each piece of lead apparel was required to be embroidered with a unique code sewn to the inside cover. Training and skills validation were instituted for integrity testing personnel. Results: The average annual waist and collar doses to 17 interventional cardiology fellows were 0.72 (+1.1) mSv and 8.2 (+10.6), respectively, in 2008, and the estimated lead apparel effectiveness was 90%. Twenty‐five technical personnel were trained to perform the integrity testing which included skills validation by an experienced medical physicist. The number of items tested increased significantly to 1,951 in 2008 (vs. 1,444 in 2006), the highest in 10 years. In 2008, failure rate increased significantly to 8.3% (162 defective items). Conclusions: Our lead apparel management program is effective at minimizing waist doses, tracking and testing lead apparel, and identifying defects.
SU‐FF‐I‐82: Simulation of X‐Ray Phantom Performances
Authors: Penchev P , Fiebich M
Published: April 2010

Purpose: For quality assurance x‐ray phantoms are commonly used. To design or test the performance of the phantom, simulations studies using Monte Carlo simulations could be helpful. A problem in quality assurance occurred, due to different phantoms from different vendors which yield different results. A simulation was performed to verify the reason for those diiferences. Material and methods: The EGSnrc package was used for the Monte Carlo simulations. The phantoms with their slightly different designs were modeled, used in the simulations and compared to the measurement results. All main features, except resolution test were reproduced in the mathematical phantom, the x‐ray spectra was simulated using BEAMnrc. Results: The Monte Carlo simulations yield excellent results and reproduced the differences seen in the measurements. The contrast differences correspond to the different design of the phantoms. Conclusion: Monte Carlo simulations can predict the performance of x‐ray phantoms used in quality assurance. They can be used to digitally design phantoms and predict their performance with a very good accuracy. Simulations can reduce costs and development time in the design of x‐ray phantoms.
SU‐FF‐I‐85: Effects of Automatic Dose Rate Control On Patient Dose in a Digital Flat‐Panel Detector System
Authors: Lai PL , Tsai HY , Li YY , Tyan YS , Tung CJ
Published: April 2010

Purpose: The purpose of this study is to demonstrate how automatic dose control logics, which control dose rate depending on the body thickness, affect radiation doses of patients undergoing therapeutic and diagnostic liver interventional angiography using a modern angiographic unit with a digital flat‐panel system. Method and Materials: Seventy procedures of transarterial embolization (therapy) and hepatic angiography (diagnosis) were considered in this study. All procedures were performed on a digital flat‐panel angiographic system (Siemens Axiom dBA Twin system software version VB31). Dose‐area products (DAP) were measured by build‐in transmission ion chambers. The DAPs, fluoroscopy time and skin doses (total calculated skin dose of acquisitions in one plane) for each examination were recorded. The organ doses and effective doses were calculated by WinODS (v1.0a; Rados Technology Oy, Turku, Finland). Moreover, the relationship between dose rates, weight, height and body mass index (BMI) were analyzed. Results: The median DAP values were 105.5 and 117.2 Gy cm2 for therapeutic and diagnostic liver interventional angiography, respectively. The dose rates were highly correlated with body thickness (R2=0.888 and 0.866 for DSA and fluoroscopy, respectively) and BMI (R2=0.773 and 0.840 for DSA and fluoroscopy, respectively) in one complete procedure. The dose rates were nearly the same for the patients with similar heights, weights, or BMIs. For patients with equal abdomen thickness, the dose rate increases with the BMI. Conclusion: The results of this study indicated the dose varies according to patient sizes. It should be further investigated whether patient doses could be reduced without degradation of the diagnostic and therapeutic liver interventional angiography outcome.
SU‐FF‐I‐88: A Method to Derive a Probabilistic Estimate of “truth” for the Validation of Tumor Segmentation Techniques
Authors: Yu H , Caldwell C , Mah K
Published: April 2010

Purpose: To develop a robust technique that can combine biased segmentations from observers or multiple imaging modalities to estimate a “true” reference for evaluating tumor segmentation techniques. Method and Materials: A probabilistic “truth” was estimated from a group of observers' segmentations via the analysis of a maximum likelihood (ML) using simulated annealing (SA) and Expectation Maximum (EM) optimization algorithms. A loose condition, qualitative ranking of performance level of segmentations, was introduced to steer the SA based method to find an optimal solution when the relative qualities of input contours are known. The SA based method was compared with a previously published “truth” estimation method “STAPLE”, firstly, using digital phantoms, then, using clinical data ‐ the gross tumor volumes (GTVs) of 12 head and neck cancer patients contoured by three experienced radiation oncologists using CT alone and subsequently, using PET /CT. Results: The SA based method accurately determined the “truth” in digital phantom studies. In comparison, STAPLE was not correctly estimate the “truth”. In the study of the 12 head and neck patients, with a defined probabilistic “true” reference, the mean and range of sensitivity of the SA method were 0.90(0.70–0.98) compared to STAPLE 0.75 (0.45–0.94); the mean and range of volume ratio between the SA method and the reference were 0.964 (0.790–1.048), and between STAPLE and the reference were 0.762 (0.464–1.005). The reference volumes produced by the SA method were reliable and reasonable in all cases. Conclusions: This work suggests that the SA method can accurately estimate a “truth” to validate segmentation methods which could potentially improve accuracy of radiation therapy or surgical target localization. The technique provides a reliable and convenient tool that could be used to optimally combine localization information from different sources to delineate clinical targets.
SU‐FF‐I‐89: A Comparison of Perfusion Parameters From the Kinetic Modeling of Head and Neck Cancers in DCE CT
Authors: La Fontaine M , Nyflot M , Song C , Gentry L , Jeraj R
Published: April 2010

Purpose: While various kinetic models are used for estimating perfusion parameters from contrast‐enhanced CT scans, the difference amongst the model results are not well researched. The aim of this study was to determine the discrepancy between two of the most commonly used kinetic models: maximum‐slope and deconvolution. Methods: Seven patients with head and neck tumors underwent dynamic CT scans with an injected contrast agent. Contrast enhancement curves were obtained by segmenting arteries, veins, and tumor ROIs from the CT scans. The maximum‐slope model was used to calculate the blood flow, while the Patlak analysis interpolated the blood volume ratio and the permeability. The central volume theorem determined the mean transit time. These parameters were also generated via a deconvolution method implemented in the GE's Advantage Perfusion 4 software. Results: The mean population values of all parameters ‐ blood flow (BF), blood volume (BV), permeability (P) and mean transient time MTT) ‐ were similar between the maximum slope and deconvolution methods (BV: 116 vs 107 ml/100g/min, BV: 6.9 vs 7.9 ml/100g, P: 29 vs 20 ml/100g/min, MTT: 4.9 vs 7.3 s). However, on the individual patient level the difference were significant (BF difference: 70% ±60 %, BV difference: 35% ± 30%, P difference: 75% ± 60%. and MTT difference: 35% ± 25%. Conclusion: No significant differences were found amongst the mean population perfusion parameters. However, on the individual patient level, the differences were significant between the maximum slope and deconvolution‐based CT perfusion methods.
SU‐FF‐I‐92: Partial Volume Correction in PET Images: A Single Correction Method Applied for Multiple Source to Background Ratios
Authors: Piper J , Shen G , Nelson AD , Nelson AS
Published: April 2010

Purpose: With the growing importance of PET for determining prognosis and assessing response to therapy, methods are needed to generate quantitative statistics that accurately reflect true activity levels. Difficulties can arise in implementing partial volume correction (PVC) methods due to inaccurate tumor volumes and the wide range of tumor to background ratios that occur clinically. We have created a PVC method based on homogeneous activity in spheres, using our gradient‐based PET segmentation technique for size approximation, which will equal or underestimate SUV in the clinical situation. Methods & Materials: PET scans were acquired for spherical phantoms with fillable spheres emulating clinical conditions of activity levels, acquisition and reconstruction. Phantom studies were acquired with C‐11 background and F‐18 in the spheres to obtain contrast levels ranging from 5:1 to 70:1. The spheres, radii 5mm, 6.5mm, 8.5mm, 11mm, 14mm and 18.5mm, were segmented using the gradient algorithm. A single exponential curve was fit to the maximum activities to produce a correction factor based on gradient‐based segmentation radius with the maximum value in the largest phantom serving as ground truth. Results: The uncorrected SUV percent error was very consistent for different contrast levels ranging from −32.0% (28.3%), Mean (SD), for 5:1 to −33.1% (29.0%) for 70:1. The uncorrected errors for the 5, 6.5, 8.5, 11, and 14mm phantoms were −70.8 (2.6%), −54.3 (4.5%), −31.5% (3.7%), −10.0% (6.0%), −2.1% (2.3%), respectively. After correction, they were reduced to −13.6% (17.7%), 8.0% (10.8%), 1.0% (10.0%), −2.0% (7.3%), −1.5% (2.5%), which was statistically significant for each phantom size at p<0.01 using a paired t‐test. Conclusions: The PVC method provides a means for more closely reflecting the true activity levels of tumors resulting in more accurate quantitative assessments. Monte Carlo simulations will help to determine accuracy for different tumor shapes and activity distributions. Research sponsored by MIMvista Corp.
SU‐FF‐I‐103: A Segmentation‐Based Deformable Registration Algorithm for Cone Beam CT and Helical CT Images
Authors: Li X , Li T , Yang Y , Heron D , Huq M
Published: April 2010

Purpose: Optical flow‐based deformable registration algorithm, which assumes that the image intensity does not change during the deformation, is not suitable for cone beam CT (CBCT) and Helical CT (HCT) image registration because CBCT image possesses a intensity inhomogeneity due to Compton scatter effect. The objective of this study is to develop a new deformable registration algorithm for CBCT and HCT image registration. Method and Materials: The proposed deformable registration algorithm for CBCT and HCT image registration is divided into two steps. First, a maximum a posteriori probability (MAP) based adaptive segmentation method is utilized to accurately segment the voxels of CBCT images and HCT images into four tissue types: air, fat, muscle and bone, even in the presence of severe image intensity inhomogeneity due to Compton scatter. The intensities of the segmented images represent the probability of each voxel belonging to different tissue types and are globally uniform. Thus, the image intensity inhomogeneity effect can be eliminated. Second, an optical flow based deformable registration algorithm is applied to the segmented images, instead of original CBCT and HCT image, to determine the deformation between CBCT and HCT images. Thus, the CBCT image can be deformed to match the HCT images. Results: The performance of the proposed deformable registration algorithm was tested using both digital phantoms and clinical CBCT images. Our studies showed that the conventional optical flow‐based method failed to converge to expected solution due to intensity inhomogeneity effect, and its registration results showed a severe mismatch on many detailed structures between CBCT and HCT images. In contrary, the proposed method matched CBCT and HCT image very well. Conclusion: The proposed segmentation‐based deformable registration algorithm is capable of CBCT and HCT image registration.
SU‐FF‐I‐107: Study of An Adaptive Planning in the Proton Therapy
Authors: Cheong M , Yoon M , Kim J , Shin D , Park S , Lee S , Kim D , Lim Y , Ahn S
Published: April 2010

We evaluated the feasibility of automated depth determination‐based adaptive proton therapy to minimize the effect of inter‐fractional movements of the prostate. Based on the center of mass method, using three fiducial gold markers in the prostate target volume, we determined the differences in prostate target location between the planning and treatment stages. Thirty‐eight images from 10 patients were used to assess the automated depth determination method, which was also compared with manually determined depth values. The mean differences in prostate target location for the left to right (LR) and superior to inferior (SI) directions were 0.9 mm and 2.3 mm, respectively, while the maximum discrepancies in location in individual patients were 3.3 mm and 7.2 mm, respectively. In the bilateral beam configuration, the difference in the LR direction represents the target depth changes, which was found to range from 0.7 mm to 3.3 mm in our study. We found that 42.1%, 26.3% and 2.6% of thirty‐eight inspections showed greater than 1 mm, 2 mm and 3 mm depth differences, respectively, between the planning and treatment stages. Adaptive planning based on automated depth determination may be a solution for inter‐fractional movements of the prostate in proton therapy since small depth changes of the target can significantly reduce target dose during proton treatment of prostate cancer patients.
SU‐FF‐I‐109: Quantitative Breast Tomosynthesis: Development of An Estimation Performance Metric and Optimization Framework
Authors: Richard S , Samei E
Published: April 2010

Purpose: To develop performance metrics for estimation tasks and employ the framework to optimize breast tomosynthesis systems for quantitative imaging purposes. Method and Materials: A maximum likelihood (ML) estimator was derived in terms of the noise power spectrum (NPS), which yielded a figure of merit for quantitative imaging performance denoted the ML mean error (sML). The sML was computed for the estimation of lesion diameter, volume, and attenuation. Volumetric tomosynthesis reconstructions of a breast phantom, which incorporated electronic, quantum, and anatomical noise (1/fb) with embedded spherical lesions were simulated at tomosynthesis acquisition angles (tomo‐angle) varying from 4o to 200o and at constant total acquisition dose (1.5 mGy). The estimation task results were further compared with a more conventional lesion detection task. Results: Results reveals tradeoffs between electronic, quantum, and anatomical noise. For a 1.25 mm radius spherical lesion, the mean error (sML) as a function of tomo‐angle varied from 0.06 to 0.5 mm for the 2D disk radius estimation task and from 0.2 to 0.9 mm for the 3D sphere radius estimation task. Furthermore, for a given sML, the 3D size estimation task required a larger tomo‐angle than for the 2D size estimation task, highlighting the need for larger acquisition angles in 3D imaging tasks (i.e., volume estimation). Overall, size estimation performance was maximized at a tomo‐angle of ∼90o. Results also suggested that size estimation tasks generally required a larger tomo‐angle than conventional detection task. Conclusions: Analysis of quantitative imaging performance using Fourier metrics highlights the difference between 2D and 3D estimation tasks in breast tomosynthesis and provides a meaningful framework for optimizing the performance of volumetric imaging systems for quantitative imaging tasks.
SU‐FF‐I‐111: Exploration of the Scatter Distribution in Cone‐Beam CT Using Monte Carlo Techniques
Authors: Bootsma G , Verhaegen F , Jaffray D
Published: April 2010

Purpose: To validate our current Monte Carlo (MC) model and explore the scatter distribution in cone‐beam CT (CBCT) projection images. The MC data will be used to garner a better understanding of the relationship between imaging parameters and the resulting scatter distribution. Method and Materials: Measured images to validate the CBCT MC model where collected using a flexible bench‐top CBCT system. The x‐ray tube was modeled using the BEAMnrc MC code system and the imaging geometries using a modified DOSXYZnrc program that differentiates primary from scattered particles. Two objects were investigated, a 16.4 and 30.6 cm diameter water cylinder. Projections were simulated for three different cone angles (1.4°, 5.7°, and 11.3°), three different source‐to‐axis distances (SAD: 50, 75, and 100 cm), and four different axis‐to‐detector distances (ADD: 9, 18, 30, and 56 cm). All simulations and measurements were done with an energy of 100 kVp. In order to validate the simulated scatter distributions experiments were conducted using beam‐blocking techniques to estimate the scatter for a 16.4 cm and 30.6 cm water cylinder for a single geometry (SAD=100, ADD=56 cm). Results: The simulated projections had a mean local absolute difference of 3.7 +/− 2.1% and 8.7 +/− 3.8% with the measured projections for the 16.4 and 30.6 cm diameter water cylinder respectively. Scatter simulations had a mean local absolute difference of 9.6 +/− 4.1% and 5.4 +/− 3.3% with the scatter measurements for the 16.4 cm and 30.6 cm diameter water cylinders respectively. Conclusion: The results support the use of MC to gain a further understanding of scatter and develop new techniques to correct for scatter induced image quality artifacts in CBCT. The scatter database created will be a valuable tool in exploring the relationships between imaging geometry parameters and the scatter distribution.