bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐48: Assessment of Detective Quantum Efficiency: Inter‐Comparison of IEC 62220‐1 with Representative Prior Methods
Authors: Ranger NT , Samei E , Dobbins JT , Ravin CE
Published: July 2006

Purpose: To evaluate a new international standard method for the measurement of detective quantum efficiency (DQE) of digital radiography systems in comparison with representative prior methods. Methods and Materials: Three DQE evaluation methods were considered: 1) a relatively recent international standard method published by the International Electrotechnical Commission (IEC, 62220‐1, 2003) which was evaluated in comparison with previously published methods by 2) Dobbins et al (Med Phys 22:1581–1593, 1995) and 3) Samei et al (Med Phys 30: 608–622, 2003). In addition to an overall comparison of the methods, the impact of the defining factors that comprise each method were evaluated including: beam quality, the presence of beam‐limiting devices (apertures or collimators), the NNPS analysis algorithm and processing parameters, and the MTF test device and associated analysis methodology. Results: The IEC DQE results at low/mid‐frequencies were lower than those obtained using the method of Dobbins et al and Samei et al by 3.3% and 6.5%, respectively. Averaged over 1.5–2.5 mm−1, the DQE estimate according to the IEC method was 7.1% lower and ̃12.4% higher than that of the other two methods, respectively. The overall DQE methods of Dobbins et al and Samei et al agreed well (within 2.0%) in the low‐ to mid‐frequency range but diverged by up to 10% at higher frequencies. Of the influencing factors on the DQE estimate considered, the most significant impact was seen with the MTF measurement method, followed by the beam‐limitation method. Conclusions: Comparison of DQE estimates using the new standard technique with results using prior methods demonstrated that measurement method can impact the DQE estimate by as much as 12%. Specifically, the results suggest the use of beam limitation using internal collimation (rather than external apertures) and use of a radio‐opaque edge MTF test device for more accurate estimation of the DQE.
SU‐FF‐I‐49: Normalized Absolute Average Deviation: A New Method for Computing MR Image Uniformity
Authors: Steckner M , Schaefer D , Profusz S
Published: July 2006

Purpose: To evaluate the new Normalized Absolute Average deviation (NAAD) MR image uniformity metric that is in the new IEC MRI performance standard. NAAD is SNR insensitive and applicable to volume, surface and phased array coils, unlike the current standard peak difference (PD) NEMA uniformity method (formerly called the integral uniformity measure). Method and Materials: NAAD computes the average absolute deviation of each pixel within the measurement region of interest (MROI) from the mean of the MROI, normalized with respect to the MROI average. Data collected on a Philips Infinion 1.5T scanner (Highland Heights, OH) using a body coil transmitter, a quadrature head coil and a surface coil. Both NAAD and NEMA PD method uniformity computed. The head coil data was collected over a range of slice thicknesses and receiver bandwidths to vary the image SNR significantly and demonstrate NAAD SNR robustness. NAAD is demonstrated to work with a highly non‐uniform surface coil by measuring a series of nested MROI, starting at the intense signal region near the coil and growing away to less intense signal regions. Results: By using all pixels within the MROI NAAD is less SNR sensitive than the PD NEMA method. As SNR varies within the MROI, NAAD results are essentially constant while PD results vary significantly. NAAD produces surface coil uniformity measurements that are more realistic than PD uniformity measurements. Conclusion: Our evaluation shows that NAAD is almost completely insensitive to SNR levels and can be used with all coils. This increased flexibility and robustness should be useful for the evaluating the new generation of surface coils optimized for MRI parallel imaging where coil spatial non‐uniformities are used as a spatial encoding mechanism. Conflict of Interest: This work was supported by the authors' employers.
SU‐FF‐I‐50: A Mechanical Alignment Method for Removing Moiré Pattern in Digital Radiography with a Carbon‐Interspaced Grid
Authors: Yoon J , Kim D , Kim S , Choe B , Suh T , Park Y , Lee J , Chung N , Lee H
Published: July 2006

Purpose: To remove moiré patterns of a carbon‐interspaced X‐ray anti‐scatter grid in use with a digital radiographic detector by matching a grid line frequency with a DR sampling frequency. Method and Materials: A carbon interspaced grid with a line frequency a little higher than the sampling frequency of DR was processed by a sawing machine which was controlled as micro unit. An amorphous selenium DR panel was used in imaging. A motion‐control jig was developed to change the disposition of the grid with respect to the detector pixels. An alignment process was divided into horizontal and vertical directions. The detector underneath of the X‐ray grid was translated and rotated with the resolution of 2 microns and 0.01 degrees respectively so that the pattern lines were oriented perpendicular to a horizontal axis in an image plane. A height of the grid from the detector was varied by 4 micrometers to magnify the shades of the grid lines at the detector and, hence, to exactly match with the sampling frequency of the detector. Results: A moiré frequency was proportional to a difference between the grid shade frequency and the DR sampling frequency. An angular displacement of the detector caused a frequency difference to indicate a higher frequency of moiré. The horizontal translation did not change the moiré frequency but only phases. An impact of the phase shift on image became larger at lower frequency of moiré patterns. Conclusion: A Moiré pattern in the use of a fixed type of grid can be removed by matching a grid line frequency with a DR sampling frequency. High straightness and uniformity of grid lines of carbon‐interspaced grids and micro‐controlled alignment methods enable frequency matching to remove moiré patterns without a software filtering and a moving grid.
SU‐FF‐I‐51: New Combined High‐Resolution Region‐Of‐Interest Microangiographic Detector and Large Field of View Image Intensifier System: A Contrast‐To‐Noise Comparison
Authors: Kuhls AT , Patel V , Bednarek DR , Hoffmann KR , Rudin S
Published: July 2006

Purpose: To demonstrate the advantage of combining a new high‐resolution region‐of‐interest (ROI) microangiographic detector (MA) and a standard x‐ray image intensifier (II), using contrast‐to‐noise ratios (CNR) of vessel phantoms within a scattering medium. Methods and Materials: The MA was mounted onto a Toshiba Infinix 3000 C‐arm angiographic unit so that the user can switch between the MA and II during an intervention at any viewing angle. Projection images can be acquired at nearly identical geometry with either detector, allowing for accurate inter‐comparisons. CNRs were measured for vessel phantoms (50–1000μm inner‐diameter polyethylene tubing) filled with iodine‐contrast agent and placed on a uniform head‐equivalent phantom used to simulate the scatter and beam hardening effects of the head. Both detectors were operated with optimal exposure techniques (allowing the II system to choose the ‘best’ kVp and mAs settings and selecting an exposure (mAs) that provides a sufficiently high signal for the MA). The CNR provides a quantitative measure of object visibility in the image, and hence system performance. Results: Compared to the II, the MA provides consistently higher CNR for all vessel sizes, with an average improvement factor (CNRMA/CNRII) of 1.6. A clear trend is observed, with CNR improvement factors increasing with decreasing vessel diameter. Conclusion: A new MA‐II system has been developed allowing use of the high resolution MA as an alternative to a standard II and easy switching between the two during a procedure, when the imaging task demands. The MA is shown to provide increased CNR for all vessel phantoms in a uniform head‐equivalent scattering material. This combined system should lead to improved neurovascular image‐guided interventions. (Partial support from NIH Grants R01EB002873, R01NS43924, Toshiba Medical Systems Corp., and the Frank B. Silvestro Endowment Scholarship).
SU‐FF‐I‐52: Evaluation of the Contrast‐Detail Response of Digital Radiographic Systems Using the CDRAD Contrast‐Detail Phantom with the CDRAD Analyser Software
Authors: Christodoulou E , Goodsitt M , Kim J , Bailey B
Published: July 2006

Purpose: The CDRAD phantom is frequently used to subjectively evaluate the contrast‐detail response of diagnostic imaging systems. We investigated the use of this phantom in conjunction with the automated CDRAD Analyser program as a quantitative tool for the evaluation of digital radiographic systems. Method and Materials: Three DR systems (Trixell Pixium 4600, Canon CXDI‐50G, and DirectRay detectors), and one CR system (35‐cm × 43‐cm FUJI ST‐VI plates) were evaluated under two experimental conditions. For the first, the CDRAD phantom was positioned directly on the detector housing, the anti‐scatter grid was removed, and the detector was exposed with two different beam qualities. Quality A: 0.5‐mm Cu filtration, ∼75 kV, 7.1‐mm Al HVL, and Quality B: 0.5‐mm Cu filtration, ∼125 kV, 10.2‐mm Al HVL. The detectors were exposed to ∼0.4, ∼0.8, ∼1.5, ∼2.5, and ∼5.5 mR, for both beam qualities. For the second condition the phantom was sandwiched between two 10‐cm slabs of Lucite, and placed on the patient table. The exposure conditions were the defaults for the Abdomen examination for each system, and the “skin” entrance exposures employed were ∼180, ∼250 and ∼350 mR. Results were compared using the CDRAD Analyser contrast‐detail figure of merit IQFinv. Results: For the Trixell detector the IQFinv increased with exposure from 6.31 to 7.67 for beam quality A, from 5.45 to 7.43 for beam quality B, and from 2.91 to 3.91 for the Abdomen exam. Corresponding values for the Canon detector were 2.88 to 4.77, 2.50 to 4.61, and 1.56 to 2.14. Those for the DirectRay detector were 2.49 to 5.00, 1.86 to 4.93, and 1.34 to 2.15, and those for the CR system were 2.89 to 4.16, 2.82 to 4.00, and 1.89 to 2.32. Conclusion: Our results indicate the potential of the CDRAD phantom/CDRAD Analyser as a quantitative image quality analysis tool.
SU‐FF‐I‐56: Image Quality Testing Using An Oil‐Filled ACR MRI Phantom at 3 T
Authors: Wey HY , Huang JC , Hsu YY , Lim KE , Kuan WC , Chen CC , Liu HL
Published: July 2006

Purpose: Image uniformity testing at high field clinical MRI scanners is challenging using a phantom filled with aqueous solution due to the dielectric resonance effect. This study aimed to investigate the feasibility of using silicone oil‐filled ACR MRI phantom for quality control testing at 3 T. Method and Materials: Experiments were conducted on a 3.0 T GE Signa HD MRI scanner using the standard quadrature head coil. Two ACR MRI phantoms, one filled with standard aqueous materials and the other with silicone oil were used for image quality testing following the ACR guidance. Five series of images were acquired, including a sagittal image and four series of axial images, i.e. ACR T1, ACR T2, site T1 (SE, TR/TE=500 ms/ Min Full), and site T2 (FSE, TR/TE=4000/102 ms, ETL=17). Finally, the images were analyzed according to the ACR MRI Quality Control Manual (2001) and the results obtained from the two phantoms were compared. Results: The percent intensity uniformity (PIU) obtained from the oil phantom was at least 6% higher than that from the original phantom (88% vs. 82% for ACR T1 and 94% vs. 81% for ACR T2). No significant differences were found in all other measures as obtained from the two phantoms. Conclusion: Image inhomogeneity in high field MRI is directly affected by both the coil configuration and the electric properties of the object. Our results indicate that silicone oil is more suitable for use in the routine quality assurance test at high field by minimize the effect from the phantom materials. Filling the ACR MRI phantom with silicone oil permits the same testing procedures without compromising the action criteria for the image uniformity.
SU‐FF‐I‐57: MR Image Quality Testing of K‐Space‐ and Image‐Based Parallel Imaging Techniques Using the ACR Phantom
Authors: Chen CC , Wai YY , Liu HL
Published: July 2006

Purpose: Using ACR MRI phantom testing to evaluate the change of image quality caused by k‐space‐ and image‐based parallel imaging techniques in a 3‐Tesla MRI scanner. Method and Materials: All phantom images are acquired from a 3 Tesla Siemens Tim‐Trio MRI scanner. Four sequences, namely ACR T1, ACR T2, Site T1 IR‐TSE, TR/TE/TI=2200 ms/11 ms/900 ms, ETL=5 and Site T2 TSE, TR/TE=4280 ms/88 ms, ETL=15, are scanned with each of the conventional, GRAPPA (iPAT=2) and modified SENSE (mSENSE, iPAT=2) modes. Images are analyzed according to standard ACR MRI QC procedures on a PC‐based workstation. Results: The results derived from the phantom images indicating that both of the tested parallel imaging techniques make no significant changes in the degree of the geometric distortion, the high contrast spatial resolution, the measured slice thickness and position accuracy, and the percent image uniformity. The signal‐to‐noise ratios (SNRs) obtained from all scans are lower while using parallel imaging techniques (SNR_conventional / SNR_GRAPPA = 1.18 +/− 0.08, SNR_conventional / SNR_mSENSE = 1.11 +/− 0.19). The averaged scores of low contrast object detecting test in conventional, GRAPPA, and mSENSE group are 39.3 +/− 0.5, 35.0 +/− 4.4, and 34.3 +/− 3.9, respectively. The percent signal ghosting (PSG) of GRAPPA and mSENSE images are 1.57 +/− 0.72 and 2.26 +/− 1.47 times of that measured in the conventional images. In addition, there is an obvious aliasing artifact observed in the mSENSE groups that cannot be demonstrated by the above data analysis. Conclusion: The ACR QC test is able to detect the lower SNR, lower contrast detectability, and higher PSG caused by both k‐space‐ and image‐based parallel imaging techniques. More accurate measurement of SNR reduction and improved artifact detection require repeated phantom imaging and additional image analysis.
SU‐FF‐I‐59: Relative SNR Benefits of Dynamic Arterial Spin Labeling at 3T as Determined by Simulation and Comparison with Imaging at 1.5T
Authors: Maleki N , Stainsby J , Roberts T
Published: July 2006

Purpose: To demonstrate the benefits of brain perfusion imaging at high magnetic field MR scanner using Dynamic Flow‐sensitive alternating Inversion Recovery (FAIR) spin labeling technique as compared to standard FAIR at lower field. Method and Materials: FAIR signal behavior as a function of the inflow time (TI) at 1.5T and 3T were simulated for both dynamic and standard FAIR methods. Simulations were performed considering initial inversion of the magnetization, it's subsequent T1 recovery, in‐flow of blood into the slice and signal reduction due to repetitive RF excitations (Look‐Locker sampling) in dynamic FAIR. Experimental brain perfusion imaging of healthy volunteers (n=3) was performed on GE scanners. Results: The results showed overall signal behavior in dynamic FAIR is almost independent of readout rate. This means the temporal resolution of imaging can be increased to any desired amount as far as the scanner hardware permits. On the other hand multiple small readout flip angles will induce smaller perturbations than larger flip angles however for a given magnetic field dynamic FAIR with small flip angles lead to lower SNR as compared to standard FAIR. But given the same noise level a low flip angle dynamic FAIR would lead to higher SNR as compared to standard FAIR at 1.5T. For flip angle=20 the relative SNR of dynamic FAIR at 3T to standard FAIR at 1.5 for TI=500, 1200 would be 1.42 and 1.60 respectively. Conclusions: Significant increase in temporal resolution and SNR in FAIR arterial spin labeling technique can be achieved by performing multiple (dynamic) readouts after FAIR preparation. By implementing dynamic FAIR at higher field strength the quality of FAIR images in terms of SNR would be even much higher than standard FAIR imaging at lower field strength. This improvement can be further enhanced by repeating the dynamic FAIR more and averaging the results.
SU‐FF‐I‐62: Hemodynamic Response Without Large Vein Signals: BOLD Imaging Using Diffusion‐Weighted Spin‐Echo EPI
Authors: Kuan W , Liu H , Chu T , Wan Y , Wai Y , Wang J
Published: July 2006

Purpose: This study aimed to evaluate the temporal characteristic and variability of hemodynamic responses measured by the diffusion‐weighted spin‐echo (DWSE) BOLD‐fMRI and compare with spin‐echo (SE) and gradient‐echo (GE) results. Method and Materials: Six volunteers participated in this study and using 1.5T scanner. The paradigm consisted of 40 repeated trials for DWSE and 30 for GE and SE, with each trial consisting of 1‐s visual stimulation followed by 13‐s fixation. The GE images were acquired by a single‐shot GE EPI, with TR/TE/FA=1000ms/60ms/75°. SE EPI were used to measure DWSE and SE BOLD signals with TR/TE=1000ms/80ms. Bipolar diffusion gradients were incorporated into SE EPI with b values of 50(DWSE50) and 200 s/mm2(DWSE200). Activated voxels were detected by correlating with a gamma variate function. The time series of selected ROI within the visual cortex were extracted for each pixel and averaged randomly across repeated single trials. Results: Statistically earlier onset times and remarkably smaller variance at the same CNR level (controlled by averaging different number of trials) were observed with the DWSE than the GE data, with SE performed in between. No significant difference was found between DWSE50 and DWSE200. Conclusions: Since DWSE technique is able to null the intravascular signal and more sensitive extravascular signal around small vessels, we suggest DWSE could more accurately detect onset time. Further, the curve profiles in GE and SE showed a good correlation with exponential decay and in DWSE50 and DWSE200 correlated well with linear decay. In other words, at higher CNR the onset time variance may approach constant for GE and SE but continue decreasing for DWSE. The curves of DWSE50 and DWSE200 overlapped, which suggests b value of 50 s/mm2 may be sufficient to eliminate the large vessels' contamination on the determination of the onset of BOLD fMRI responses.
SU‐FF‐I‐63: Evaluation of the Turn Variation of Spiral RF Surface Coils for MR Microscopic Imaging and Spectroscopy
Authors: Woo D , Choe B , Ha S
Published: July 2006

Purpose: The purpose of this study was to enhance the technical improvement which can develop the advanced sensitive RF surface coil to investigate the sensitivities of the multi‐spiral surface coils and eventually achieve the high resolution of microscopic MR images and MR spectra. Method and Materials: The simulation of a coil's magnetic field was processed in MATLAB. Biot‐Savart law provides information about the relation between the amplitude and the position. The experiment was processed in the Oxford magnet (1.5T), Copley gradient (25mT/m) coil and Analogic RF amplitude system. The diameter of a coil was fixed at 4cm, and the turn of a coil was increased with a spiral turning method. Results: 1. Simulation of magnetic field. The magnetic field strength was increased close to the wire because of a ring‐shape wire coil. This simulation was performed assuming no obstruction in the current and domain. Thus, the shape and the field distribution of a RF surface coil were able to be visually analyzed. 2. Coils' performance. The ROI with approximately 3cm was identified by a water phantom in 1.5T. The three and five turned spiral coils were developed and their Q‐factor and bandwidth were estimated. Conclusion: The present study showed that the sensitivity of RF surface coil was improved by the increasing the number of a spiral coil's turn, and also the SNR of RF surface coil was dependent upon the number of a spiral coil's turn. However, the sensitivity was not proportional to the number of a spiral RF coil's turn. There is an optimal vale in a spiral RF coil turn and sensitivity. In order to obtain a high sensitivity as varying the spiral RF coil's performance, it is important to find the optimal number of turn. This study provides an efficient approach to designing high‐field RF coils.
SU‐FF‐I‐66: MRI Relaxometry BMD Measurements Using Conventional Phase Symmetrized Rapid Increased Flip Spin Echo and Standard Gradient Echo and Its Correlation with DXA
Authors: Bakhtiary M , Riyahi‐Alami N , Oghabian M , Ghasemzadeh A , Ghanaati H , Sarkar S
Published: July 2006

Purpose: Recently, several special MRI protocols have been developed for BMD measurements for deriving R2(=1/T2), R2*(=1/T2*) and R2′(=R2*‐R2) applied in several cross sectional studies. But, due to high slew rate gradients with high amplitudes in small periods, such protocols can be used only in system with high slew rate (22 mT/m.s or greater). However, our main aim in this study was to develop optimized versions of standard GE and conventional SE protocols using in existing MRI systems for BMD measurements, as most systems do not support such newly high slew rate protocols. Method and Materials: This study was performed by 1.5T‐MRI system(Picker Vista‐Q800, slew rate=13mT/m.s), SNR phantom (1.25g/l , T2=200ms) for calibration, a body RF‐Coil, cross sectional study with 12 normal, 12 osteopenia, 12 osteoporosis volunteers done with a Lunar DXA system‐(DPX‐MD). To determine R2* and R2, simple standard‐GE and conventional phase‐symmetrized‐rapid‐increased‐flip‐SE(PRISE) protocols with different TE/TR were applied. Then in coronal section of femoral‐neck, relaxation rates were compared with BMD from DXA. The optimized conditions of the protocols for R2* measurement standard‐GE protocol with TE=13.42/18/26.8ms, TR=800ms and ST=8mm(CV(R2*)=2.96%) and for R2 measurement PRISE protocol with TE=36/54/63/72ms, TR=800ms and ST=8mm(CV(R2)=3%), receiver bandwidth of 21.2 kHz for PRISE, 31.75kHz for GE, Matrix=190×256, FOV=45cm leading to good SNR. Results: The overall Pearson's correlation coefficient of R2*, R2′ and R2 vs. BMD were calculated as 0.62(p<0.003), 0.62(p<0.003) and 0.03(p<0.9), respectively. Based on the R2* and R2′ parameters, significant difference between normal and abnormal groups (osteopenia and osteoporosis) were found. However, there was no significant difference between osteopenia and osteoporosis groups using the relaxation parameters. Conclusion: R2* and R2′ showed a significant positive correlation with BMD. Therefore, in accordance with DXA values, the results showed standard‐GE and conventional‐SE(PRISE) could be proper protocols for BMD‐measurements in femoral‐neck even in low slew rates systems.
SU‐FF‐I‐69: The Impact of Sparse Data Sets On the Quality of MR Images
Authors: Sobol W , Bankston J
Published: July 2006

Purpose: To evaluate the impact of reduction in acquired data size on the final appearance of MR images and to assess the synergetic impact of image interpolation, used in softcopy viewing, on the perception of image quality. Method and Materials: A rapid progress in signal quality of the MRI data acquired with modern MRI hardware, coupled with a desire to speed up the acquisition times as much as possible, promotes a practice where drastic reductions in the size of acquired data are implemented by the MRI system operator. Routinely, the physician viewing the MR images is presented with incomplete and confusing information about the true size of the acquired data. Most physicians are oblivious to the potential impact of complex acquisition algorithms on the quality of images. The situation is further confounded by various image interpolation techniques used by softcopy display systems.

A standard spin echo imaging sequence (270/10, FOV 30 cm, slice thickness 5 mm, gap 5 mm, 11 slices, 1 NEX, BW=2*15.63 kHz) was used to generate a baseline image with 256*256 acquisition matrix. This was followed by an acquisition of a 512*512 image that served as a “golden reference standard”, given the fact that the standard MR displays use 512*512 image size as a default. The baseline protocol was then repeated by varying options and parameters that affected the sizes of the acquisition matrix, processing matrix, or display matrix. Results: Images other than the golden reference standard exhibit artifacts whose strength strongly depends on the resampling algorithm applied. The extent and severity of observed artifacts increases with the number of options used to generate the image. Conclusion: The image acquisition parameters and display resampling algorithms need to be carefully accounted for when evaluating image artifacts in MR images.
SU‐FF‐I‐73: Comparison of the Effects of Viewing Conditions and Viewing Angle On Object Dectectability for Different AMLCD Displays
Authors: Thomas J , Chakrabarti K , Kaczmarek R , Mitchell C , Romanyukha A , Nemmers S , Loscocc M
Published: July 2006

Purpose: The ability to interpret images displayed on active matrix liquid crystal displays (AMLCD) can be influenced by factors such as display luminance, surrounding background, room illuminance and viewing angle. We have been investigating how these parameters influence reader scores with images featuring both small objects and low contrast as typically seen in mammography. We are in a position to make some comparisons between the results obtained with displays from two different manufacturers. Method and Materials: Reader studies were conducted using a computer generated contrast detail phantom alternately presented against a display background of selected luminance levels. Luminance was also measured at different viewing angles and at four selected room illuminance levels. Image scoring was performed at each combination of background level, viewing angle and room illuminance level. Results: Image scoring performance was interpreted using k values, which reflect the contrast and diameter of the objects detected in the images. The best image scoring results were obtained when viewing angles were kept small, and also when room illuminance was at the level of 5 – 10 lux. Better scoring results were also obtained when the image background luminance was adjusted to 5 – 20 % of maximum. These results differ from what had previously been found when evaluating displays from a different manufacturer. In this case the best scoring results were obtained at zero background and the room illuminance did not seem to have a significant effect on the results obtained when kept in the range of 0 – 20 lux. Conclusion: The results support the view that while it is advisable to keep the viewing angle to a minimum, it may be advisable also to adjust the room illuminance and monitor background luminance to specific levels which may be best suited for a particular AMLCD display.
SU‐FF‐I‐74: Comparison of Image Quality in Contact and Magnification Modes in Digital Mammography
Authors: Liu B
Published: July 2006

Purpose: To compare image quality in contact and magnification modes in digital mammography. Method and Materials: Images of three anthropomorphic breast phantoms were acquired using a Hologic FFDM system. First, images were acquired in contact mode with grid. The exposure parameters were determined by AEC. Second, images were acquired in 1.5x magnification mode without grid. The exposure parameters were selected such that the detector entrance exposures were the same as those in the first experiment. The third, images were acquired in contact mode with grid and with the same patient doses in magnification mode. Image quality was analyzed using MIPAV software. Results: 9lp/mm and 6lp/mm were resolved in the magnification mode and in the contact mode respectively. However, the smallest specks group in the phantoms (0.13 mm) could be detected in all modes. For masses and fibers, more features were detected in the magnification mode when the detector entrance exposures were fixed at those determined in the contact mode. More masses and fibers were detected in contact mode when the breast skin entrance exposures were the same as those in the magnification mode. Conclusion: At the same patient dose, the contact mode provides better detectability of masses and fibers. The detectability of microcalcification above 0.13 mm is not improved by using the magnification mode. The detectability of smaller microcalcifications (<0.13 mm) needs further investigation.
SU‐FF‐I‐76: Observed Inter‐Camera Variability of Clinically Relevant Performance Characteristics for SIEMENS Symbia® Gamma Cameras
Authors: Kappadath S C , Erwin W D , Wendt R E
Published: July 2006

Purpose: To evaluate the inter‐camera variability of clinically relevant performance characteristics for Symbia® gamma cameras (Siemens Medical Solutions, USA). Materials and Methods: Evaluation of the inter‐camera variability was based on measurements made with nine separate systems. Performance characteristics measurements were based on NEMA standards and AAPM Reports (#22 and #52). All of the measurements were performed using Tc‐99m (except Co‐57 for extrinsic resolution) and low‐energy high‐resolution collimation. Of the nine cameras, 4 have 3/8″ and 5 have 5/8″ crystals. Energy resolution, intrinsic and extrinsic spatial resolution, intrinsic integral and differential flood uniformity over the useful field‐of‐view, pixel size, deadtime, sensitivity, SPECT resolution, and SPECT integral uniformity were evaluated. The mean, standard deviation, and coefficient of variability (CV) of each metric were computed for each crystal thickness. Results: The mean (standard deviation) of the measured metrics for the 3/8″ and 5/8″ crystal systems, respectively, were as follows: energy resolution [FWHM‐%] of 9.5 (0.2) and 9.5 (0.3); intrinsic resolution [FWHM‐mm] of 3.46 (0.08) mm and 3.87 (0.09) mm; extrinsic resolution [FWHM‐mm] of 4.39 (0.09) mm and 4.70 (0.10) mm; integral uniformity [%] of 4.5 (0.4) and 4.7 (0.7); differential uniformity [%] of 2.6 (0.3) and 2.7 (0.2); pixel size [mm] of 0.601 (0.001) and 0.602 (0.001); maximum count rate [kcps] with 20% deadtime loss of 125 (18) and 130 (13); sensitivity [cpm/ Ci] of 203 (5) and 217 (8); SPECT resolution [FWHM‐mm] of 13.2 (0.1) and 13.4 (0.1); and SPECT integral uniformity [%] of 0.14 (0.02) and 0.13 (0.01). The mean and maximum CV were determined to be ∼6% and ∼17%, respectively, with the intrinsic uniformity, deadtime, and SPECT uniformity displaying the greatest CV amongst the different systems. Conclusions: All of the tested gamma cameras exhibited performance characteristics within specifications and the inter‐camera variability was observed to be low.
SU‐FF‐I‐77: Photon and Electron Specific Absorbed Fractions From the UF Pediatric Tomographic Phantoms
Authors: Lee C , Lee C , Bolch W
Published: July 2006

Purpose: To calculate photon and electron specific absorbed fractions (SAF) by utilizing series of realistic tomographic phantoms of pediatric patients. Method and Material: The series of UF tomographic phantoms, 9‐month male, 4‐year female, 8‐year female, 11‐year male, and 14‐year male, developed at University of Florida, were imported into the EGSnrc Monte Carlo code for this study. Monoenergetic photons and electrons were simulated as homogeneously distributed in various source organs. All possible source‐target organ pairs were considered to calculate absorbed fractions at the target organs from both internal electron and photon emitters localized in source organs. Results: The new sets of photon and electron SAFs were tabulated for the particle energies from 0.01 MeV to 4 MeV. The photon SAFs were compared with those from the ORNL phantoms. It was shown that ORNL phantoms failed to correctly represent the proximities of certain organ pairs and caused significant discrepancies from the UF phantom in terms of photon SAF values. The electron self‐absorbed fractions calculated from the UF phantoms were compared to that given in the ICRP Publication 30 assumptions. For higher electron energies, the assumption of 100% self‐absorption in the ICRP schema was shown to be incorrect, especially for the smaller phantoms and smaller organs with large surface‐to‐volume ratios. For example, the thyroid self absorption was only 21% for 4 MeV electrons in the UF 9‐month phantom. Conclusion: Photon and electron SAFs were calculated for various ages of pediatric patients by utilizing realistic tomographic computational phantoms. It was shown that the tomographic phantoms accurately represent the shapes of various internal organs and their proximities to surrounding organs. The explicit consideration of electron transport demonstrates that the traditional assumption of full energy deposition by energetic beta‐particles can be in error, especially for the younger and smaller patients of this age series.
SU‐FF‐I‐79: Java‐Based Plugin for Tomographic Reconstruction for SPECT Data
Authors: Andrade M , Costa M , Marques da Silva A
Published: July 2006

Purpose: To implement a plugin for the software ImageJ, a public domain and open source software, written in JAVA, used for image processing and analysis, able to perform the filtered backprojection (FBP) algorithm for tomographic reconstruction of SPECT data. Method and Materials: New classes were added to the software ImageJ in order to implement the plugin. The following classes have been developed: (1) the backprojection process, in which data from projections or filtered projection are smeared back into the image matrix; (2) the tomographic reconstruction ramp filter with other windowing possibilities using loss‐pass filters such as Butterworth, Shepp‐Logan and Hamming; (3) the one‐dimensional Fourier transform to perform the projection filtering; (4) and the user interface of the plugin. The plugin was tested with Monte Carlo simulated projection data of Zubal brain phantom, NCAT phantom and patient data. Results: The plugin is able to reconstruct sinograms of 8, 16 and 32‐bits. Users can choose filter/window combinations. After the user sets the parameters needed for each combination (cutoff frequency and/or order), the filter curve can be visualized. When no filtering is choosen, simple backprojection is performed. The final reconstructed image is displayed and can be visualized or analyzed using segmentation and processing tools available in ImageJ. Conclusion: The outcome of this work consists of a plugin for the software ImageJ to reconstruct images from SPECT data as sinograms using filtered backprojection or simple backprojection. The plugin is plataform independent and runs either in Windows or Linux, freely downloadable and accessible, and based on open source code. Further implementations will allow this plugin to work with DICOM images and offer iterative methods of tomographic reconstruction.

Research sponsored by FRIDA Program/LACNIC and CNPq.
SU‐FF‐I‐82: Variability and Accuracy of Standardized Uptake Values in FDG PET Scans
Authors: Halama J , Sadjak R , Wagner R
Published: July 2006

Purpose: The standard uptake value (SUV) in FDG PET images is used in defining tumor volumes. In lung tumors, an SUV greater than 2.5 may be assumed as tumor. This investigation sought to (1) establish a threshold SUV above which there is significant FDG uptake, and (2) determine other variables leading to inaccuracies in SUV. Method and Materials: Phantoms (SUV calibration, SPECT, and anthropomorphic with heart and lung inserts) with known activity 18F‐FDG concentrations were placed end‐to‐end to simulate a patient torso of 70 cm. A PET system with GSO detectors and Cs‐137 transmission source was evaluated. The activities used, scan and transmission imaging protocols simulated those used clinically. The SUV phantom served as reference and had a SUV = 1.0. Ten ml phantom aliquots were counted separately to determine true activity concentrations. Results: Three times the noise level of the SUV phantom images determined the threshold for significant SUV. Regions in the SUV phantom yielded a SUV of 0.96 +− 7.7%, and a 1.18 SUV threshold. For activity used clinically, the noise was 12%. The average SUV was the highest at the phantom centers with a range of inaccuracy of at most 20%, attributed to errors in the image reconstruction scatter correction algorithm. Additional errors include incorrect activity and scanner calibrations, and patient weight measurements. These errors can be reduced to very low levels with careful protocol control. Conclusion: This study yielded a threshold of significant SUV of 1.2, but depends on starting activity. Inaccuracies in the reconstruction lead to further variability in the SUV and was 20% in this study. If This inaccuracy level implies that a threshold of 3.0 should be used instead of 2.5. Similar measurements should be carried out on other PET scanners to determine the limits of SUV delectability and accuracy.
SU‐FF‐I‐83: Derivation of Diagnostic X‐Ray Spectra Using An Interpolation Program with Calculated and Measured Input Parameters
Authors: Waggener R , Terry J , Manciu M
Published: July 2006

Purpose: To determine diagnostic x‐ray photon spectra using simple transmission measurements. Method and Materials: A database of measured and calculated x‐ray photon spectra values from the Catalogue of Spectral Data for Diagnostic X‐rays, R. Birch, M. Marshall and G.M. Ardran, Diagnostic Topic Group of the Hospital Physicists' Association, England, 1979 was collected and used to form a multidimensional interpolation matrix. These researchers measured x‐ray spectra using a Ge(Li) detector for various x‐ray systems in the diagnostic energy range and derived a calculation method to calculate x‐ray spectra which agreed closely with measured spectra for different conditions. X‐ray spectra for tungsten targets and different inherent filtration in Al and Cu were coded in relative number of photons per mm2 per keV for kVps ranging from 30 to 140 kVp at 10 kVp intervals. Other parameters were given such as mean photon energy in keV, photon flux at 0.75 m in photons‐mA−1‐s−1‐mm−2, output in micro Gy‐mA−1‐s−1 and exposure in mR‐mA−1‐s−1 and 1st, 2nd, and 3rd half‐value layer (HVL) in mm Al. Most spectra were derived for constant potential units but some with ripple were also derived. Target angles included 10, 17, 20 and 22 degrees. Results: From this input, interpolation curves were derived which enables one to interpolate between the 10 kVp intervals and to derive the inherent filtration for a particular unit in Al equivalent from simple transmission measurements in Al and mR/mAs at a particular distance. The kVp of the unit was also derived from the transmission measurements by comparison with the calculated curves. Conclusion: With some additional data, this method could be used to derive the x‐ray spectra for any unit in this energy range, 30 to 140 kVp for different parameters.
SU‐FF‐I‐84: Comparison of LINACs Either Equipped with On‐Board Imaging/cone‐Beam CT Or CT‐On‐Rails for IGRT
Authors: Shiu A , Wang C , Chang E , Wang H
Published: July 2006

Introduction: The purpose of this study is to investigate the advantages and limitations of LINAC equipped with either OBI/CBCT or CT‐on‐rails with a 6D robotic couch‐top for IGRT. Method and Materials: An optimal IGRT delivery system should be capable of handling the auto setup of the updated isocenter with 6D corrections, the adaptive radiotherapy, and treating multiple lesions simultaneously. The CT image quality should be suitable for designing a treatment plan. The planning CT and the daily CT are acquired in the treatment setup condition, minimizing systematic errors coiled into the image‐data. A 60‐cm diameter of maximum field‐of‐view (FOV) is crucial to scan almost all the patients. The scanning‐range in superior‐inferior direction should cover the maximum treatment‐field available on the delivery system. It should have KVp and MV portal‐imaging capabilities for setup verification. Monitor the target‐isocenter shift due to couch rotation. A thoracic phantom was used to evaluate the IGRT setup accuracy using either OBI/CBCT or LINAC/CT‐on‐rails. Results: the current CT image quality of CBCT is suitable only for image registration. However, the relative large intra‐ and inter‐variation of CT numbers for the same tissue inhibits the use of CBCT for treatment planning and adaptive radiotherapy. The single scanning‐range of CBCT is limited to 14 cm. Both scanners need to increase the FOV to 60‐cm diameter. The phantom study indicated that both units could setup the daily isocenter correctly based on the image registration. One of the findings suggests that the rotation corrections are essential for the crucial treatment to avoid treating the critical structures. It should be corrected either through a 6D robotic couch‐top or software. Conclusions: Based on the image registration, LINACs equipped with either OBI/CBCT or CT‐on‐rails perform the IGRT treatment nicely. Conflict of interest: Supported in parts by SRA grants from Varian Medical Systems, Inc.
SU‐FF‐I‐85: Optimization of Image Quality and Minimization of Radiation Dose for Chest Computed Radiography
Authors: Kong X , Liu H , Rong X , Sweet C , Yang Z , Edwards S , Thai T , Thomas J
Published: July 2006

Purpose: To investigate the effects of x‐ray exposure parameters and added beam filtration on patient dose and image quality for optimization of chest computed radiography (CR). Method and Materials: A chest x‐ray phantom (CardinalHealth Model 76‐211) was used to simulate a patient of standard size. To achieve a small or a large patient size, one sheet of 25‐mm acrylic was removed or added, respectively. Pre‐ and post‐patient x‐ray spectra were measured using a CdTe x‐ray spectrometer at various exposure conditions and added filters. kVp stations of 80, 100, and 120 were selected. An Al plate of 0, 1.0, 2.0, 3.0 mm or a Cu plate of 0, 0.1, 0.3, 0.5 mm was placed at the tube exit window for each exposure setting. Patient entrance exposure was measured using a Radcal ion chamber under automatic exposure control at each exposure condition. Corresponding CR images were acquired at above conditions using a contrast‐detail phantom (CDRAD) placed between acrylic plates of the chest phantom for evaluating image quality. The same protocol for processing of CR image plate was used throughout. Both printed films and digital images were archived. Reading sessions were conducted to interpret the 72 CR images. Results: CDRAD images were ranked based on image quality. Corresponding patient dose and x‐ray spectrum were analyzed. Beam effective energy and spectrum information were evaluated. Optimal imaging condition was determined. In general, with increased beam filtration and effective energy, image quality decreased with dose saving as expected. However, at certain conditions of patient size, filtration, and kVp, image quality actually appeared improved with reduced or comparable patient dose. Conclusion: Proper use of pre‐patient filtration can improve CR chest image quality while maintaining or reducing patient dose at carefully selected kVp setting for a patient. Optional filters should be made available for digital chest radiography.
SU‐FF‐I‐86: Commissioning and Evaluation of An Amorphous Silicon Flat‐Panel Digital Imaging System (XRD 1640, Perkin Elmer) for Its Application in Proton Beam Therapy
Authors: Nookala P , Cho J , Ghebremedhin A , Patyal B
Published: July 2006

Purpose: Accurate, patient‐specific anatomical information is a prerequisite for successful radiation therapy planning and delivery to the tumor, while minimizing dose to surrounding tissues. A new FPDI system (XRD 1640, Perkin Elmer) was installed and commissioned replacing a CCD and mirror‐based digital imager (DI, Optivus). The details of the tests performed during the commissioning will be presented. Methods and Materials: Rando phantom is used for testing patient orientation in the imager. A RMI magnification plate and a radio‐opaque ruler are used to measure the magnification factor of the imaging system. A black‐hole phantom along with a line‐pair phantom, aluminum and copper plates are used to measure the image quality. To test the alignment of two sources (x‐ray and proton), the x‐rays and proton beam double‐exposure (one x‐ray and one proton) was done on two cross‐wires (one in the aperture and one in front of FPDI) at four cardinal angles. To test the drift of the nozzle, the same test (with two double‐exposures) was done for nozzle at fully extended and fully retracted positions and at different gantry angles. Results: FPDI requires low x‐ray energy settings (90 kVp, 20–40 mAs) for collecting images of similar quality when compared to the previous imager (105 kVp, 250 mAs). The acceptance test showed the maximum high‐contrast spatial visibility (resolution) of 0.8 line pairs per mm and the maximum low‐contrast visibility (resolution) of 0.5 mm diameter circular objects. The images obtained from double‐exposure as well as two double‐exposures showed the coincidence within 1 mm. The FPDI images obtained from Rando phantom depicted differences to the images of exported DRRs, which enabled the correct adjustment of the phantom alignment and orientation. Conclusion: When compared to the previous imager, FPDI provides a sharper image for locating the landmarks for patient alignment with less exposure to the patient.
SU‐FF‐I‐91: Computational Representation of In‐Vivo Acquired Stenotic Renal Artery Geometries Using Turbulence Modeling
Authors: Kagadis G , Skouras E , Bourantas G , Katsanos K , Diamantopoulos A , Karnabatidis D , Paraskeva C , Mihailidis D , Liatsikos E , Siablis D , Nikiforidis G
Published: July 2006

Purpose: To report on the in‐vivo simulation of arterial blood flow hemodynamics using anatomically realistic CFD models constructed through non‐invasive CT imaging, in order to facilitate therapeutic decision‐making. The methodology is pivotally applied in a case of severe RAS. Method and Materials: The highly accurate SST turbulence model is introduced in the simulation of blood flow in the severely constricted region at the ostium of a human renal artery, obtained from CT scans. This work also proposes a systematic creation and examination of simulated cases of the particular arterial segment after endovascular stent deployment. Results: The significance of specific factors relevant to the arterial geometry and their impact on blood flow across the arterial segment are investigated. The increased resistance to flow due to the presence of the atheromatic plaque is quantified. The presence of a stent at the blood inlet of the artery leads to predictable higher velocity profiles at the outlet. The internal differential pressure profiles, the WSS, and the net forces acting on the plaque at peak pulse in the RAS case are found to be considerably higher than the non‐obstructed one. Each of these hemodynamic factors is shown to retain sufficient high contrast between stenosed and unimpeded cases in view of their consideration as potential indicators of clinically significant RAS. Conclusion: The proposed methodology provides insight on a RAS development, with estimates of a healthy situation and after a potential stent implementation, using modern CT and CFD methods. It allows interventionalists to quantitatively evaluate the hemodynamic significance of RAS both non‐invasively and within reasonable time. It provides diagnostic indicators for the selection of angioplasty and/or stenting, ideally even before the patient becomes symptomatic.