bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of MTF measurement for digital mammography quality control
Authors: Carton Ann‐Katherine , Vandenbroucke Dirk , Struye Luc , Maidment Andrew D. A. , Kao Yen‐Hong , Albert Michael , Bosmans Hilde , Marchal Guy
Published: June 2005

The modulation transfer function (MTF) describes the spatial resolution properties of imaging systems. In this work, the accuracy of our implementation of the edge method for calculating the presampled MTF was examined. Synthetic edge images with known MTF were used as gold standards for determining the robustness of the edge method. These images simulated realistic data from clinical digital mammography systems, and contained intrinsic system factors that could affect the MTF accuracy, such as noise, scatter, and flat‐field nonuniformities. Our algorithm is not influenced by detector dose variations for MTF accuracy up to the sampling frequency. We investigated several methods for noise reduction, including truncating the supersampled line spread function (LSF), windowing the LSF, applying a local exponential fit to the LSF, and applying a monotonic constraint to the supersampled edge spread function. Only the monotonic constraint did not introduce a systematic error; the other methods could result in MTF underestimation. Overall, our edge method consistently computed MTFs which were in good agreement with the true MTF. The edge method was then applied to images from a commercial storage‐phosphor based digital mammography system. The calculated MTF was affected by the size (sides of 2.5, 5, or ) and the composition (lead or tungsten) of the edge device. However, the effects on the MTF were observed only with regard to the low frequency drop (LFD). Scatter nonuniformity was dependent on edge size, and could lead to slight underestimation of LFD. Nevertheless, this negative effect could be minimized by using an edge of or larger. An edge composed of lead is susceptible to L‐fluorescence, which causes overestimation of the LFD. The results of this work are intended to underline the need for clear guidelines if the MTF is to be given a more crucial role in acceptance tests and routine assessment of digital mammography systems: the MTF algorithm and edge object test tool need to be publicly validated.
The effect of overscanning on patient effective dose from multidetector helical computed tomography examinations
Authors: Tzedakis A. , Damilakis J. , Perisinakis K. , Stratakis J. , Gourtsoyiannis N.
Published: June 2005

overscanning in multidetector (MD) helical CT scanning is prerequisite for the interpolation of acquired data required during image reconstruction and refers to the exposure of tissues beyond the boundaries of the volume to be imaged. The aim of the present study was to evaluate the effect of overscanning on the patient effective dose from helical MD CT examinations. The Monte Carlo ‐particle radiation transport code was employed in the current study to simulate CT exposure. The validity of the Monte Carlo simulation was verified by (a) a comparison of calculated and measured standard computed tomography dose index (CTDI) dosimetric data, and (b) a comparison of calculated and measured dose profiles along the axis. CTDI was measured using a pencil ionization chamber and head and body CT phantoms. Dose profiles along the axis were obtained using thermoluminescence dosimeters. A commercially available mathematical anthropomorphic phantom was used for the estimation of effective doses from four standard CT examinations, i.e., head and neck, chest, abdomen and pelvis, and trunk studies. Data for both axial and helical modes of operation were obtained. In the helical mode, overscanning was taken into account. The calculated effective dose from a CT exposure was normalized to . The percentage differences in the normalized effective dose between contiguous axial and helical scans with , may reach 13.1%, 35.8%, 29.0%, and 21.5%, for head and neck, chest, abdomen and pelvis, and trunk studies, respectively. Given that the same kilovoltage and tube load per rotation were used in both axial and helical scans, the above differences may be attributed to overscanning. For helical scans with , broader beam collimation is associated with increased overscanning and consequently higher normalized effective dose value, when other scanning parameters are held constant. For a given beam collimation, the selection of a higher value of reconstructed image slice width increases the normalized effective dose. In conclusion, overscanning may significantly affect the patient effective dose from CT examinations performed on MD CT scanners. Therefore, an estimation of the patient effective dose from MD helical CT examinations should always take into consideration the effect of overscanning.
Characterization of a new MOSFET detector configuration for in vivo skin dosimetry
Authors: Scalchi Paolo , Francescon Paolo , Rajaguru Priyadarshini
Published: June 2005

The dose released to the patient skin during a radiotherapy treatment is important when the skin is an organ at risk, or on the contrary, is included in the target volume. Since most treatment planning programs do not predict dose within several millimeters of the body surface, it is important to have a method to verify the skin dose for the patient who is undergoing radiotherapy. A special type of metal oxide semiconductors field‐effect transistors (MOSFET) was developed to perform in vivo skin dosimetry for radiotherapy treatments. Water‐equivalent depth (WED), both manufacturing and sensor reproducibility, dependence on both field size and angulation of the sensor were investigated using photon beams. Patient skin dosimetries were performed during total body irradiations (TBI). The resulting WEDs ranged from 0.04 and ( on average). The reproducibility of the sensor response, for doses of , was within (maximum deviation) and improves with increasing sensitivity or dose level. As to the manufacturing reproducibility, it was found to be . No WED dependence on the field size was verified, but possible variations of this quantity with the field size could be hidden by the assessment uncertainty. The angular dependence, for both phantom‐surface and in‐air setups, when referred to the mean response, is within until 80° rotations. The results of the performed patient skin dosimetries showed that, normally, our TBI setup was suitable to give skin the prescribed dose, but, for some cases, interventions were necessary: as a consequence the TBI setup was corrected. The water‐equivalent depth is, on average, less than the thinnest thermoluminescent dosimeters (TLD). In addition, when compared with TLDs, the skin MOSFETs have significant advantages, like immediate both readout and reuse, as well as the permanent storage of dose. These sensors are also waterproof. The in vivo dosimetries performed prove the importance of verifying the dose to the skin of the patient undergoing radiotherapy.
Experimental determination of the dosimetric characteristics for the I‐Plant™ model 3600 brachytherapy source
Authors: Tries Mark A. , Mancevice Corinne G. , Munro John J.
Published: June 2005

The dosimetric characteristics for a new brachytherapy seed source (I‐Plant™ model 3600) were measured using LiF thermoluminescent dosimeters and appropriate phantom materials in conformance with the methodology and guidance provided by the AAPM Task Group 43. The I‐Plant™ model 3600 is the successor to the I‐Plant™ model 3500. The major difference between these sources is that the model 3600 contains a leaded‐glass core to provide radio‐opacity (while the model 3500 contains a silver core), which does not produce spectral contamination upon neutron activation. The dose rate constant for the model 3600 was determined to be (with a 6% overall relative standard deviation), compared to reported for the model 3500 in previous studies. The remaining dosimetric characteristics also are similar for both sources.
Development of a three‐dimensional freehand endorectal ultrasound system for use in rectal cancer imaging
Authors: Warmath John R. , Bao Philip , Clements Logan W. , Herline Alan J. , Galloway Robert L.
Published: June 2005

The initial study reporting the accuracy of an optically tracked endorectal ultrasound (TERUS) probe for the purpose of improving the staging of rectal cancer is presented here. In this work we describe the need for a more accurate ERUS system and why the incorporation of image guidance makes this goal feasible. A rectal phantom was constructed with five targets placed in positions where tumors normally occur. The locations of these targets were found using two different imaging modalities, CT and ultrasound, and the target registration error (TRE) between these two image sets was calculated. The average TRE of 33 image captures of the five targets using TERUS was . This is a promising outcome because the desired tumor margins for rectal cancer are on the order of centimeters. These preliminary results support the proof of concept for a TERUS system that should improve ultrasound imaging in rectal cancer.
Volume concentration and size dependence of diffuse reflectance in a fractal soft tissue model
Authors: Sharma S. K. , Banerjee Srilekha
Published: June 2005

Employing a fractal model for the particle size distribution, we examine the possibility of relating the size/volume concentration changes in the tissue to its diffuse reflectance. It is noted that for the practically interesting range of fractal dimension values , the curves depicting the variation of diffuse reflectance (the ratio of diffuse reflectance at two suitably chosen source detector separations) with at fixed volume concentration , are single valued. The same is true if is fixed and is varied. This crucial observation shows that it should be possible to identify changes in the size/volume concentration of the tissue from the diffuse reflectance measurement at two source detector separations when either or is a priori known. Similar results have been obtained for ratio of fluence measured at two suitably chosen depths within the tissue.
SU‐AA‐P‐6B‐01: Structure and Function of ASTRO Health Policy and Economics Council: Medical Physicist Implications
Authors: Beyers D
Published: June 2005

(no abstract submission)
SU‐AA‐P‐6B‐02: Process of New Technology Coverage and Current Medical Physics Reimbursement Issues
Authors: Hevezi J
Published: June 2005

The process of covering new technologies in medicine is complicated, both from the viewpoint of government agency reimbursement through the Centers for Medicare and Medicaid Services (CMS) and through the private sector carrier reimbursement entities such as Aetna, Blue Cross/Blue Shield and the like. The process is further complicated by coverage differences in the Hospital environment versus coverage in clinics and “stand‐alone” treatment centers. Coverage decisions generally begin with CMS assignment of temporary coverage codes in the Hospital environment for new procedures and technologies. These take the form of the so‐called “G” codes and are put forward for coverage by medical specialty societies when these professional organizations have agreed that the procedure or technology is “ready for prime time.” Coverage decisions include actual dollar amounts for performing the procedure under current CMS rules. The medical specialty society then must submit the procedure to rigorous review for eventual coverage in the clinic or stand‐alone center environment as the “G” code process is a time‐limited coverage process. Most carriers regard the randomized prospective clinical trial for a new procedure as the “gold standard” for coverage decisions. ASTRO and other organizations are lobbying for some surrogate to this process which will allow coverage for an effective procedure in a shorter time frame. Although other private carriers will generally follow CMS' approval process for new technology/procedures, they are not required to do so. In point of fact, private carriers can renege on a previously covered procedure if their medical advisory board decides the procedure will not be a benefit for its insurees. This has happened recently with the denial of coverage for one of the medical physics codes, CPT 77336 by one of the private carriers. Other examples of coverage denials and actions taken by the specialty societies to fight these denials will be presented.
SU‐DD‐A3‐02: Slice Based Image Guidance with Tomotherapy
Authors: Sheng K , Shaw R , Jeraj R , Mackie T , Paliwal B
Published: June 2005

Purpose: To improve the temporal resolution of image guided radiation therapy with slice based CT images from treatment beams of tomotherapy. In slice based image guidance (SBIG), the patient position would be monitored nearly concurrently at the time treatment. Method and Materials: The experiment was performed on a benchtop tomotherapy (BT) and on a regular TomoTherapy Hi.Art 2.0 (TH2). BT consists of a 6MV source, a kV source, a standard CT detector and an actuator. A Rando phantom was scanned by BT with two different dose levels of 1 cGy and 0.1 cGy and a ROI was contoured on the lower dose image. The treatment beams that delivered conformal dose to the ROI were used to filter the sinogram of the higher dose scan. Based on multi‐resolution analysis, the incomplete filtered sinogram was locally reconstructed to obtain ROI, which was fused back to lower dose image. A similar process was repeated with lung phantom on the TH2 with MLC modulation. The number of projections for BT is 600/rotation and for TH2 is 51/rotation. Results: Images reconstructed from the conformal beams on BT shows that without additional beams, the ROI can be reconstructed with good quality. Fine structures with width of 2–4 mm are clear. The MLC reproducibility is higher than 99.97% but the ROI image from TH2 was degraded by severe artifacts. Conclusion: The fusion image from BT suggests that a positioning accuracy of 2mm is achievable. The SBIG image from TH2 shows substantial artifacts, which mainly because that the number of projections are too few and the scatters from the multi‐leaf collimator. The first problem can be solved by using pulses instead of the 51 angles from optimization. The second problem would require a modified optimization by adding conformal beams without MLC modulation.
SU‐DD‐A4‐04: Registration of Prostate MRI/MRSI and CT Studies Using the Narrow Band Approach
Authors: Levy D , Schreibmann E , Thorndyke B , Li T , Yang Y , Boyer A , Xing L
Published: June 2005

Purpose: High‐field MR techniques makes possible to obtain high quality MRI metabolic images of the prostate to accurately identify the intra‐prostatic lesion(s). However, the use of rigid endorectal probe deforms the shape of the prostate gland and the images so obtained are not directly usable in radiation therapy planning. This work applies a narrow band deformable registration model to faithfully map the MRI information onto treatment planning CT images. Method and Materials: The narrow band is a hybrid method combining the advantages of pixel‐based and distance‐based registration techniques, since the calculation is restricted to those points contained in a region around user‐delineated structures. The narrow band method is inherently efficient because of the use of a priori information of the meaningful contour data. The deformable mapping is described by the B‐spline model. The limited memory algorithm (L‐BFGS) was implemented to optimize a normalized cross correlation metric function. It's convergence behavior was studied by comparing final metrics obtained in 100 registrations self‐registering an MR image starting from 100 randomly initiated positions. The spatial performance of the algorithm was assessed by intentionally distorting an MRI image and an attempt was then made to register the distorted image with the original one. The MRI‐CT mapping was carried out for two clinical cases. Results: The convergence analysis showed absence of local minima. The technique can restore an MR image from the intentionally introduced deformations with an accuracy of ∼2 mm. On clinical cases the method was capable of producing clinically sensible mapping. The whole registration procedure for a complete 3D study took less than 15 minutes on a standard PC. Conclusion: Both hypothetical tests and patient studies have indicated that narrow‐band based registration is reliable and provides a valuable tool to integrate the ER‐based MRI/MRSI information to guide prostate radiation therapy treatment.
SU‐DD‐A1‐06: Synchronized Delivery for DMLC IMRT for Stationary and Moving Targets
Authors: Rangaraj D , Papiez L
Published: June 2005

Purpose: To eliminate tongue and groove (TG) underdosage effects during DMLC IMRT delivery for stationary and moving targets by synchronizing leaf pair trajectories using a non iterative algorithm. Method and Materials: Optimal leaf trajectories to deliver the desired intensities are calculated independently for all leaf pairs. The mid‐time trajectories for all leaf pairs are also determined. From the mid‐time trajectories of all leaf pairs one common synchronized mid‐time (MT) trajectory is determined. Trajectories for all leaf pairs are reconstructed from this synchronized mid‐time trajectory. Properties of the mid‐time trajectory guarantee that no violation of velocity constraints occurs. The same procedure works for both moving and stationary targets. Results: The intensity delivered in the overlapped region without leaf synchronization, and with leaf synchronization, is examined using two examples. One example shows the leaf synchronization of five leaf pairs to deliver clinical intensity for stationary target and other shows ten leaf pair synchronization to deliver clinical intensity for moving target. The no collision property between the leading and following leaves of neighboring leaf pairs for MT‐synchronized trajectories is assured. This property is illustrated in snapshots of the MLC leaves at different times of irradiation for moving targets. Conclusion: The mid time synchronization based solutions remove TG underdosage in DMLC IMRT delivery for stationary and moving targets. The delivery based on these solutions (i) removes TG underdosage in overlapped region in the sense that the intensity in the region is guaranteed to be equal to the lower intensity delivered by any one of two pairs of neighboring leaves (ii) facilitates simultaneous multiple leaf correlation and thus avoids iterative algorithms (iii) minimizes the time of delivery provided all constraints imposed on leaf motions are satisfied (iv) assures that no collisions between leading and following leaves of neighboring leaf pairs occur.
SU‐EE‐A3‐03: Incorporate the Imager's Performance Characteristics Into the Design of Prostate IMRT Dose Painting Protocols
Authors: Zhang P , Liu T , Osterman K , Li X , Schiff P , Kutcher G
Published: June 2005

Purpose: There is much interest in using biological and functional imaging to provide guidance in IMRT dose painting. Yet, it is important to incorporate the performance characteristics of these modalities. In this study an example of Ultrasound Tissue Typing (UTT) was utilized to investigate the implications of the imager's performance on the design of a population based prostate dose painting protocol. Method and Materials: The performance of an imaging modality can be evaluated via the receiver operating characteristic curve, which is a plot of the imaging modality's sensitivity versus false‐positive ratio (1‐specificity). As sensitivity increases, more tumors are detected, although specificity worsens, causing more false negatives. The UTT tumor map obtained with a specific sensitivity and specificity setup is fused with the patient's CT image to guide IMRT planning. The optimal escalation dose to the tumor positive region identified by UTT, as well as the safe dose to the identified tumor negative background was obtained by maximizing uncomplicated control, which is a combination of tumor control probability (TCP), and weighted normal tissue complication probability (NTCP). Results: A practical dose escalation protocol requires a high specificity imager setup to reduce complications. For tumors at the high‐risk stage, with sensitivity at 0.6 and specificity at 0.9, optimal dose to the positive and negative regions are 88.2Gy and 83.6Gy respectively, which resulted in a 25% NTCP reduction compared to that the whole prostate is dose escalated to the same TCP. If the imager becomes more accurate, i.e., sensitivity improves to 0.9 when specificity remains at 0.9, the optimal plan would have a further 10% NTCP decrease with a 2% TCP increase. Conclusion: Performance characteristics of an imager as described by sensitivity and specificity has important implications in prostate dose painting, and should be considered in the future design of dose painting protocols.
SU‐EE‐A3‐06: An Efficient Algorithm for Image‐Based Dose Deformation and Accumulation
Authors: Kaus M , Pekar V , McNutt T , Bzdusek K
Published: June 2005

Purpose: Construction of the accumulated dose distribution for fractionated radiation delivery in deforming organs based on automated image segmentation and deformable registration of primary and secondary CT datasets. Method and Materials: Femur heads, bladder, rectum and prostate were automatically segmented in CT image pairs with 3D deformable triangular surface models. A displacement vector was estimated for each voxel using deformable point‐based registration. The vertices of corresponding adapted surface meshes provided corresponding anatomical landmarks, and the deformation between the surfaces was interpolated to every voxel according to a physics‐based deformation model. The deformation vector field was applied to warp the primary to the secondary CT, and to warp the dose distributions of the simulated treatments to the original treatment plan. The performance of the registration algorithm to match surfaces was evaluated by warping the bladder and the rectum from one patient to a second patient and measuring surface distances between the warped and target structures. The performance for dose warping was assessed by visually comparing the planned dose in the secondary image to the dose warped from the primary to the secondary image. Results: The surface difference between the warped and target bladder (rectum) was 0.65±0.12 mm (1.80±0.97 mm) in 26 patients. The quality of the dose distribution and the variation of dose volume histograms between warped and un‐warped plans appeared reasonable on visual inspection. Efficient image resampling techniques enable visual evaluation of the warping result at interactive speed on standard hardware. The surface warp took 2 seconds, plus 5 seconds for warping the 79×60×35 dose grid. Conclusion: The work indicates the potential for efficient dose re‐planning based on secondary CT imaging during treatment and automated image‐processing. Validation work is necessary to assess the effect of different volumetric deformation models on the resulting dose distribution.
SU‐EE‐A1‐06: Investigation of MR Image Distortion for Radiotherapy Treatment Planning of Prostate Cancer
Authors: Chen Z , Ma C , Yang J , Paskalev K , Li J , Fan J , Richardson T , Palacio L , Chen L
Published: June 2005

Purpose: To implement MRI based treatment planning clinically for prostate cancer, the machine generated geometrical distortions on MR images must be investigated to ensure the accuracy of dose calculation and treatment delivery. Method and Materials: The MR system used for this study was a 0.23 Tesla open scanner (Philips Medical System, Cleveland, OH) operating clinically as an MR simulator. Based on the fact that there was no observable patient induced MR image artifact with 0.2 T low magnetic fields, the patient induced geometrical distortions were negligible for our MR unit and the machine induced geometrical distortions could be detected, studied and corrected accurately. A distortion evaluation phantom (F18) was employed to measure the distortions after a gradient distortion correction (GDC) software was installed to post‐process the images and a point‐by‐point correction method was then developed to remove the residual distortion based on precise measurements. Results: With our routine clinical 3‐dimensinal fast spin echo sequences, our work shows that there are no patient induced distortions detected and the machine specific geometrical distortions can be quantified and corrected first by the GDC post‐processing software and then by the point by point correction technique. The residual distortions after the corrections are reduced from the original > 2 cm to < 3 mm in the external contour determination for patients with large lateral dimensions. An effective FOV has been established, which can be used clinically to set up patient selection criteria for MR based treatment planning. Conclusion: MR geometrical distortions on MR scanners can be corrected and, with the GDC post‐processing and our point by point correction technique, 2% to 5% improvement in dose accuracy can be expected in the treatment planning for prostate cancer.
SU‐FF‐E‐01: A Streamlined Syllabus for Training of Radiation Therapy Professionals On Linac Operations
Authors: Free B , Martin J , Thompson G , Avadhani J , de Boer S , Malhotra H , Podgorsak M
Published: June 2005

Purpose: To define a syllabus for the education and periodic re‐training of radiation therapists and other professionals operating a linear accelerator (linac) on issues related to safety, routine operations, and emergency procedures. Method and Materials: An extensive review of manufacturer recommendations and published literature regarding linac safety and operational issues has enabled the compilation of a streamlined syllabus. The course material is geared toward rapid and effective training of radiation therapists and other individuals charged with operating a linear accelerator either during treatment delivery or while performing commissioning or periodic quality assurance measurements. The training material is meant to be delivered on a rotating schedule such that re‐training of personnel is accomplished. The course material itself is designed to be delivered by a Chief Therapist, Linac Engineer, and/or Medical Physics staff. Results: A syllabus including course material to be delivered monthly, semi‐annually, and annually has been developed. The target audience includes radiation therapists, service engineers, and physicists/dosimetrists involved in the operation of a linac. The course material includes separate components catered to the interest and knowledge requirement for different trainees. For example, concise protocols to be followed for morning warm‐up are presented semi‐annually to the therapists in charge of opening the department. All treating therapists are exposed to pertinent safety procedures during monthly inservices developed such that a complete cadre of safety related issues is covered twice per year. More extensive annual refresher courses are also defined, along with measurable indicators that can be used to document understanding of the procedures. Conclusion: Quality assurance requirements mandated by most jurisdictions dictate frequent training of appropriate personnel pertaining to linac safety including coverage of routine operations and emergency procedures. This work standardizes a syllabus that can be used to satisfy these training requirements. Monthly, semi‐annual, and annual training programs are included.
SU‐FF‐E‐02: Modern Digital Seminar/Teaching/ Conference Room
Authors: Venkataramanan N , Ortiz Orlando
Published: June 2005

Purpose: Digital Teaching/Seminar/Conference Room for the modern era. Method and Materials: Learn about and become familiar with the resources available to set up a digital teaching/seminar/conference room Results: 1. Assess the technologic innovations in hardware, software and network design and the impact to the conference room. 2. Understand ways to optimize your images for visual display with respect to luminance, gray scale imaging, contrast and distortion. 3. Review the technologies available for the storage, projection, and display of a presentation. Conclusion: Reviewed how the teaching/seminar / conference room has evolved in parallel with the changes from an analog to a digital environment.
SU‐FF‐E‐03: RadSim, a Program to Simulate Individual Radiation Interactions for Teaching Purposes
Authors: Palefsky S , DeBlois F , Verhaegen F
Published: June 2005

Purpose: To develop a computer program to simulate individual particle interactions in a visual way, as a teaching aid in radiotherapy physics. Method and Materials: A program, RadSim, was developed using the RealBasic software development environment. A Graphical User Interface allows users to select individual interactions to be simulated for photons, electrons and positrons in the energy range encompassing radiation oncology (1 keV — several hundred MeV). The program is designed to operate in two modes. In the Manual mode a single interaction is performed. In the Simulated mode the user can run a short Monte Carlo simulation for a small number of particles. In the latter mode statistics on the interaction variables are displayed graphically. The program is made available in versions for the Windows, Linux and Mac operating systems, via free download from a website. Results: The user can simulate the following types of interactions: for photons: Compton scatter, photoelectric effect with characteristic x‐rays, Rayleigh scattering and pair‐production, for electrons: inelastic nuclear scattering with Bremsstrahlung production, electron‐electron scattering, for positrons: Bhabha scattering and annihilation. The Manual mode allows visual evaluation of kinematic equations. The user can initialize any combination of a minimally required set of interaction variables and the program evaluates the remaining variables, and displays the interaction visually showing incoming and outgoing particles. In the Simulated mode, the user can only change the kinetic variables of the initial particle. The final state of all particles involved is generated from a Monte Carlo simulation. The user defines the number of particles used in the simulation and frequency distributions are displayed during the simulation so that the user can watch the distributions grow. Conclusion: The program RadSim enables virtual radiation experiments in the classroom and for self‐learning and is found to be a useful addition to textbook teaching.
SU‐FF‐I‐01: A New Nipple Detection Algorithm Based On Curvature
Authors: Sun Y
Published: June 2005

Purpose: Nipple is an important anatomical feature for mammogram registration and bilateral asymmetry analysis. We will investigate a new nipple detection algorithm based on curvature analysis. Method and Materials: Nipple extends outward and changes the curvature on the breast skin‐line. Curvature analysis will be proposed to locate the nipple in this study. The breast skin‐line is first estimated by using a dependency approach. The skin‐line is then smoothed by average‐smoothing. Curvature is calculated along the skin‐line boundary. The intersection point between the nipple and the skin‐line is characterized by a large negative curvature. The nipple is thus located between two positions having the largest negative curvature values. The final nipple position is computed as the average of these two positions. We have tested our algorithm on 26 mammograms with the extended nipple from the MIAS database. Results: The proposed curvature‐based algorithm correctly detects the nipple position in each image. Conclusion: Our proposed nipple detection method is based on curvature analysis and performs well on mammograms with the outward nipples. The further work will be quantitative evaluation of the algorithm.
SU‐FF‐I‐03: Evaluation of Computer Aided Diagnosis On Thin‐Slice Pulmonary CT Images
Authors: Wang P , Fuller D , O'Dell W
Published: June 2005

Purpose: Pulmonary stereotactic radiation therapy achieves a >90% local control rate for small tumors (<30mm); motivating early detection of small lung nodules. With the increasing image resolution afforded by multi‐slice CT scanners, radiologists can discern more easily these very small lung nodules. However, to overcome the challenge of image overload, assistance from lung CAD systems becomes a necessity. The purpose of this work is to evaluate the performance of our lung CAD algorithm on low‐dose, thin‐slice CT images from the Early Lung Cancer Action Program (ELCAP) database. Method and Materials: Our CAD algorithm models lung nodules as spheres (a modification of the 3D template‐matching method presented in AAPM'03) and searched for structures similar to the templates throughout the whole lung volume. This approach eliminates the need for segmentation of blood vessel‐nodule complex and is insensitive to noise and low‐contrast of some nodules. In the extraction of lung volume, a watershed transform was applied to separate left and right lungs when necessary. A 3D spherical structure element was used to smooth out the surface of both lungs in order to incorporate pleural nodules. An improved padding scheme was adapted on the templates to make the detection capacity of templates more isotropic. A test dataset was used, consisting of 55 central contiguous slices (voxel size: 0.57×0.57×1.25mm3) from a particularly challenging subject in the ELCAP database. 41 nodules were identified by an experienced radiologist from our institution. Results: 37 out of 41 nodules were detected by our CAD algorithm, a sensitivity of 90.2%. Among them, 28 out of 32 nodules with diameter <3mm were detected. The smallest detected nodule had a diameter of only ∼3 pixels (1.7mm) and a volume of ∼17 voxels. Conclusion: Our CAD method is capable of detecting with high sensitivity very small lung nodules in low‐dose thin‐slice chest CT.
SU‐FF‐I‐04: A Comparison of Two Genetic Algorithms for Feature Selection in the Detection of Breast Cancers
Authors: Sun Y , Babbs C , Delp E
Published: June 2005

Purpose: Features are usually extracted for separating breast cancers from normal areas in computer‐aided detection (CAD) on screening mammograms. Feature selection is an important step to select a best subset for achieving the best detection of breast cancers. Method and Materials: The study is to evaluate two genetic algorithms for feature selection for breast cancer detection. Normal regions of 512×512 pixels were extracted from normal mammograms, and abnormal regions of 512×512 pixels depicting breast cancers were extracted from cancer cases. A total of 86 features were extracted from each region, including 18 features from curvilinear structure analysis, 16 from texture analysis, 32 from Gabor filtering, and 20 from wavelet decomposition. Two genetic algorithms (GA), simple GA (SGA) and CHC, were used to select a subset of features. A linear discriminant analysis (LDA) was used to classify cancer regions from normal regions with the selected feature subset. The performance was evaluated by using the Receiver Operating Characteristic (ROC) analysis. We have tested these two feature selection methods on a dataset of 296 normal regions and 164 cancer regions (including 53 masses, 56 spiculated lesions and 55 microcalcifications) extracted from mammograms selected from DDSM database. Results: The overall ROC performance of SGA and LDA is Az=0.90, with comparison to Az=0.93 of CHC and LDA. Conclusion: We compared two genetic algorithms for feature selection. CHC performed better than SGA for the detection of breast cancers in the current study.
SU‐FF‐I‐08: What Is the Best Way of Measuring An Image Quality Index From CT Data?
Authors: Ogden K , Huda W , Scalzetti E , Roskopf M , Ogden D
Published: June 2005

Purpose: To investigate how tissue contrast and noise correlate with the size of patients undergoing chest CT examinations. Method and Materials: We used 572 chest CT examinations obtained with a standard protocol for subjects participating in a lung cancer‐screening project. Measurements were made of the mean CT number (HU), and corresponding noise level (standard deviation), in liver and blood in the descending aorta. Data on patient size included the patient weight (kg), body dimensions (Anterior‐Posterior [AP] and lateral [L]), as well as the body mass index (BMI) obtained as the ratio of the body weight (kg) divided by the square of the patient height (m). Results: Visual inspection of the CT images shows the expected increase in image noise with increasing patient size. Mean CT numbers for liver showed a modest decrease with increasing patient weight (r2 = 0.18), whereas blood showed no correlation with patient size (r2 < 0.01). There was good correlation between noise and patient mass for the liver (r2 = 0.65) and for blood (r2 = 0.54). Compared to noise alone, contrast to noise ratios for both tissues showed a reduced correlation with patient mass. The correlation between noise and patient size was similar for body weight and three measures of patient size (i.e., (AP + L), (AP × L)0.5, and (ln[AP × L]0.5), but was significantly poorer with BMI. Conclusion: The most suitable image quality metric from CT data is noise, with no useful benefit obtained from consideration of tissue contrast. Weight and patient dimensions are equally satisfactory for predicting how noise varies with patient size, and are superior to the use of BMI.
SU‐FF‐I‐09: Comparison of Radiation Dose Indexes For CT Scanners: Measured Verses Automated Scanner Calculations
Authors: Nickoloff E , Lu Z , So J , Dutta A
Published: June 2005

Purpose: Modern CT scanners provide radiation dose indexes such as CTDI and DLP for every patient based upon the selected scan parameters. Our goal is to study the potential sources of errors for these automated calculations. Method and Materials: The measured and automated radiation dose indexes were compared on five different CT models from two manufacturers. Acrylic cylindrical phantoms with diameters ranging from 6 – 32 cm were utilized for the study. Measurements were made at all available kVp's and typical scan techniques in both axial and helical modes. The measured CTDI and DLP values were compared with the displayed automated values. Results: The automated displayed CTDI and DLP values are derived from system calibration using fixed size phantoms representing a typical adult head (16 cm) and adult body (32 cm). They vary with parameters such as kVp, mAs, pitch, x‐ray beam collimation and selected protocols. For typical adult head, our measured CTDI and DLP values agreed with the automated values to an average of 7.8% discrepancy. Similarly, an average of 14% discrepancy was observed for typical adult body. However, the discrepancies widened significantly for those measured on other sizes. For pediatric body scans using a 16 cm diameter phantom on table top, the measured CTDI values are more than doubled compared to the displayed automated values. Conclusion: It is important to realize that the automated radiation dose indexes by CT scanners only represent estimates based upon standardized adult body and head sizes. No considerations are given to patient age, size, weight and tissue composition. Especially, the values for pediatric scans are not represented correctly by the automated CTDIs. Future calculated radiation dose assessments needs to be incorporated with more patient factors.
SU‐FF‐I‐16: Calibration of TLD Chips to Maximize Accuracy in Radiographic Phantom Dosimetry
Authors: Ogden K , Lavallee R , Huda W , Roskopf M , Scalzetti E
Published: June 2005

Purpose: To develop an efficient annealing/readout protocol for TLD dosimetry that will maximize the accuracy and precision in radiographic dosimetry measurements. Method and Materials: 500 TLD chips were grouped in batches of 100 and subjected to varying annealing protocols and then irradiated to varying exposure levels. Three different annealing/readout protocols were tested. In protocol ♯1, the chips were annealed at 400 C for 1 hour followed by 2 hours at 100 C. The chips were exposed, and then allowed to rest for 24 hours before reading. In protocol ♯2, the anneal cycle was 400 C for 1 hour followed with a 30 minute cool‐down, followed by 20 hours at 80 C. Immediately after exposure, the TLD's were heated to 120 C for 10 minutes, then read. In protocol ♯3, the anneal cycle was 400 C for 1 hour followed by a 30 minute cool‐down, then 100 C for 2 hours. After exposure, the TLDs were pre‐heated and read as in protocol ♯2. Results: For protocol ♯1, the inter‐exposure uncertainty in the response (nC/mR) was approximately 4.2%. Using protocol ♯2, the intra‐batch uncertainty was reduced to 4.0%, and for protocol ♯3 the uncertainty was reduced to ∼3.7%. By using individual chip calibrations, the intra‐batch uncertainty for estimating consecutive exposures was reduced to 3.5%, 1.8%, and 1.7% for protocols ♯1, 2, and 3, respectively. By binning TLD signals over groups of 3 chips, the uncertainty in estimating exposures was reduced to ∼1.1% for protocol ♯3. Conclusion: With careful calibration and binning of results, an accuracy approaching 1% is readily obtained. The anneal/readout protocol that yielded the highest accuracy also required the least time for a complete cycle, with a batch of 100 chips being processed in <1 working day using a single furnace for annealing and a single‐chip reader.
SU‐FF‐I‐22: An Inward Mammilla Detection Algorithm for Analysis of Skin‐Line Retraction
Authors: Sun Y , Suri J , Rangayyan R
Published: June 2005

Purpose: A specific algorithm is designed for the detection of the mammilla to locate the inward mammilla position along the breast skin‐line in mammograms. The position of the inward mammilla can assist in the analysis of focal retraction near the nipple. Method and Materials: Between the breast skin‐line and the fibro‐glandular tissue is a zone of fatty peripheral tissue, which appears with low gray‐levels on mammograms. Due to the mammary glands connecting to the mammilla, the gray‐level in the fatty zone near the mammilla will be higher. We define a fatty peripheral zone (Zf) of 40 pixels width (8mm) parallel to the skin‐line on mammograms. A disk mask of diameter 40 pixels, KP, tangential to the skin‐line boundary point P and rolling in the zone Zf, is used to obtain a mammilla index value for P. A mammilla index (IP) for P is defined as the average gray‐level of the pixels in both Zf and the current mask Kp. Then, three highest values, It1 (highest), It2 (second highest), and It3 (third highest), corresponding to position indexes Pt1, Pt2, and Pt3 on the skin‐line, are found on the curve of IP. If the differences between Pt1 and Pt2, as well as between Pt1 and Pt3, are larger than a threshold T1, and the difference between Pt2 and Pt3 is less than another threshold T2, the mammilla position is defined as the average of Pt2 and Pt3; otherwise the mammilla position is defined as Pt1. Empirically, we selected T1=90 and T2=36. Results: We have tested our algorithm on 40 mammograms from the MiniMIAS database with inward nipples, and our method achieved accurate detection of the mammilla position on each image. Conclusion: The proposed algorithm for the detection of the inward mammilla position gave accurate results on the mammograms tested.
SU‐FF‐I‐23: An Iterative Method for Flat‐Field Correction of Digital Radiography with Arbitrary Detector Position
Authors: Kim D , Kim S , Youn J , Choe B , Suh T , Lee H
Published: June 2005

Purpose: To investigated the effect of X‐ray tube positions with respect to detector on the non‐uniformity correction, and propose a method to reduce the effect using a new algorithm with computer simulation. Method and Materials: Gain images that represented the reference image used to execute the flat field correction were taken in two SIDs (Source to Image‐receptor Distance). Pixel values at second SID was calculated using the pixel values at first SID, the assumed gain coefficient, and the formula based on the solid angle of each detector pixel facing to the x‐ray source. Gain coefficient was adjusted using the difference between calculated and real pixel values at second SID. Calculation was repeated with new gain coefficient until the gain coefficient was converged into prescribed range. Flat field correction could be performed using acquired gain image. Non‐uniformity of blank x‐ray images taken with the detector tilted by 0 to 45 degrees was corrected and five ROIs across the image were defined and analyzed. Results: With a blank image obtained with the detector tilting angle of 45 degrees the lowest ROI mean value was 53% less than the highest ROI mean value when usual non‐uniformity correction was performed. When the proposed was used for the flat field correction, however, the lowest ROI mean value was only 7% less than the highest ROI mean value, and standard deviations of pixel values in the ROIs were reduce to 10% of the cases of usual flat field correction. Conclusion: Because of the characteristic of usual flat field correction, non‐uniformity in detector that was not aligned to the X‐ray source considerably increased. We also calculated the gain coefficient and performed the flat field correction with the iterative method in the tilted or arbitrary detector position. The proposed algorithm gave a satisfactory uniformity.
SU‐FF‐I‐24: Band‐Pass Filtering vs. Multiscale Dyadic Wavelet Transform for Contrast Enhancement of Digital Mammograms
Authors: Ye Z , Mantri A , Suri J , Laine A , Jin Y
Published: June 2005

Purpose: This paper discusses two methods for contrast enhancement of digital mammograms. One method is based on the Gaussian band‐pass filter and the other is based on the dyadic wavelet transform and multiscale non‐linear enhancement. Method and Materials: Band‐pass filter: A logarithmic tone mapping operator with adaptive base is applied to an image to elevate the lower intensities which lie mainly in the skin‐line zone. The mammogram is then filtered using a Gaussian band‐pass filter to enhance the structure of breast while suppressing noise and the slowly varying high density structure. Dyadic wavelet enhancement: Dyadic wavelet transform is applied to an image to decompose the image into horizontal detail and vertical detail subband images at different scales. Then, a non‐linear weighting function is used to modify the wavelet coefficients of each subband image followed by synthesis to yield the final enhanced image. The final enhanced image is obtained by synthesis of the modified subband images. Results: We compared the enhancement performance between these two approaches. Band‐pass filter does a better job of elevating the skin‐line zone to the intensity level of the interior of the breast and also enhancing the contrast. However, there are some ringing artifacts which lead to saturation in a few regions near the top and the bottom part of the image. The local contrast can be improved to emphasize both salient and subtle features of mammograms. However, the contrast of the skin‐line zone can not be enhanced well by the dyadic wavelet enhancement. Conclusion: Band‐pass filter is fast and can obtain a good result on skin‐line zone except for some ringing artifacts. Dyadic wavelet transform can enhance the unseen and barely seen features but is weak on skin‐line. We tested the above methods on MIAS and Fischer Imaging databases.