Slot Scanning Research Articles

Assessment of the axial rotation of the pelvis with the EOS® imaging system: intra- and inter-observer reproducibility and accuracy study

A source of radiological bias occurs when the axial rotation of the pelvis is disregarded in hip and spine biomechanics analyses. The EOS imaging system (EOS Imaging, France) offers the possibility of detecting and measuring the axial rotation of bones. Reproducibility and accuracy have not been documented in the case of the pelvis. A dry pelvis has been X-rayed with the EOS system every 5° from 30° left to 30° right according to a laser line reference goniometer. Three observers have measured the rotation. One observer did it 3 times. The intra- and inter-observer reproducibility and the accuracy have been calculated using the root mean square standard deviation calculation. The relationship between the axial rotation and the offset between the left and right acetabulae on the lateral view was investigated. The 95 % CI was ±0.23° for the intra-observer and ±0.33° for the inter-observer reliability. The mean of signed differences between the software calculation and the actual axial rotation of the pelvis was -0.39° (SD 0.77°). The lateral acetabular offset was proportional to the sin of the rotation. Approximately, 30 mm offset corresponded to about 10° rotation. The 3D slot scanning imaging system demonstrated significant reproducibility and accuracy for the assessment of the axial rotation of the pelvis.

인식 슬롯 스캔 기반 능동형 RFID 태그 수집 알고리즘 개선

본 논문에서는 이전 연구에서 능동형 RFID 시스템의 태그 수집 성능 향상을 위해 제안된 인식 슬롯 스캔 기반 태그 수집 알고리즘의 단점을 개선하는 수정된 태그 수집 알고리즘을 제안한다. 기 제안된 인식 슬롯 스캔 기반 태그 수집 알고리즘은 태그 수집 과정에서 모든 태그들로부터 정해진 크기의 데이터를 수집하는 상황에 최적화 되어 있기 때문에 태그들이 다양한 크기의 데이터를 가지는 환경에 적용할 경우 제대로 된 성능 향상을 가져오지 못한다. 본 논문에서 새롭게 제안하는 개선된 태그 수집 알고리즘은 먼저 인식 슬롯 스캔 단계에서 각 태그로부터 자신이 가진 데이터를 전송하는데 필요한 슬롯 크기 정보를 획득하고 이를 활용하여 태그 수집 단계를 수행함으로써, 기 제안된 알고리즘의 문제점을 해결하고 모든 환경에서 능동형 RFID 태그 수집의 성능을 효율적으로 향상시키도록 설계되었다. 성능 평가를 위해 수행한 시뮬레이션 결과는 제안하는 개선된 태그 수집 알고리즘이 태그들이 동일한 데이터 크기를 가지는 환경에서는 기 제안된 알고리즘과 거의 동일한 성능을 보이고, 태그들이 다양한 데이터 크기를 가지는 환경에서는 기 제안된 알고리즘과 달리 ISO/IEC 18000-7 표준의 태그 수집 성능을 크게 향상시킴을 보여주었다. This paper proposes a modified tag collection algorithm that improves the drawback of the identified slot scan-based tag collection algorithm presented in a previous paper to improve the tag collection performance in active RFID systems. The previous identified slot scan-based tag collection algorithm is optimized in situations where all the tags store the fixed size of data, so it could not result in a good performance improvement with tags having the variable size of data. The improved tag collection algorithm proposed in this paper first collects the slot size information required for the data transmission from each tag via the identified slot scan phase, and then performs the tag collection phase using the information, which resolves the problem of the previous identified slot scan-based tag collection algorithm. The simulation results for performance evaluation showed that the proposed tag collection algorithm resulted in the almost same tag collection performance as the previous algorithm when all the tags have the same size of data and led a large improvement of the tag collection performance in ISO/IEC 18000-7 unlike the previous algorithm when each tag has a random size of data.

Evaluation of a new low-dose biplanar system to assess lower-limb alignment in 3D: a phantom study

Knee coronal alignment is routinely assessed on a full-length radiograph of the lower limbs. However, poor positioning of the knee during the procedure affects the accuracy of this kind of measurement, particularly in cases combining knee rotation and flexion. The purpose of this study was to assess the value of a three-dimensional assessment of the hip-knee-ankle (HKA) angle based on a biplanar radiographic system. A biplanar slot scanning system was used to take radiographs of three lower-limb synthetic models with similar frontal deviation (5° valgus) but different flexion angulations (0°, 9°, and 18°). Biplane acquisitions were done with lower-limb axial rotations ranging from 20° of internal rotation to 20° of external rotation on each of the lower limb models. Three independent observers performed standard 2D measurements of the HKA angle from each anteroposterior (AP) image and also modeled the lower limb in 3D for each biplane acquisition with dedicated software. The HKA angle was automatically calculated from the 3D models. The results of the 2D and 3D techniques were compared. Axial rotation provoked 2D HKA measurement errors up to, respectively, 1.4°, 4.7°, and 6.8° for the lower extremities with 0°, 9°, and 18° flexion, while it never affected the 3D HKA measurement for more than 1.5°. Interobserver errors were 0.7° (SD = 0.5°) for the 2D measurements and 0.6° (SD = 0.4°) for the 3D measurements. The 3D modeling allows for a more accurate evaluation of coronal alignment compared to 2D, eliminating bias due to wrong knee positioning.

Diagnosing breast cancer: an opportunity for innovative engineering

In an ancient papyrus, dating back to 2500 BC, an Egyptian named Imhotep, thought to be the first physician and engineer in history, offers a glimpse into the earliest recorded case of breast cancer. Treatment has evolved over the years, from radical mastectomy to radiation by X-rays, and from adjuvant chemotherapy to hormonal therapy. A key challenge in fighting the 'war' on breast cancer is early diagnosis and here innovative engineers play a vital role. While full-field digital mammography has emerged in the past decade, this technique suffers from relatively high dose levels and poor sensitivity when the breasts are dense. We aimed to develop a diagnostic imaging system that exposes the patient to lower ionising radiation and improves the sensitivity and specificity for women with dense breasts. Our PantoScanner platform has been designed to implement slot scanning digital X-rays, thereby lowering the dose and increasing signal-to-noise ratio, while also accommodating automated ultrasound and digital tomosynthesis. Early results based on mammographic phantoms are encouraging while the PantoScanner is undergoing clinical testing prior to commercial release. Since breast cancer kills 500 000 people globally every year, early diagnosis by breast screening could save the lives of many women. Our fervent hope is that the PantoScanner system will significantly contribute to this effort in South Africa and around the world.

The EOS™ imaging system and its uses in daily orthopaedic practice

The EOS™ X-ray machine, based on a Nobel prize-winning invention in physics in the field of particle detection, is capable of a simultaneous capture of biplanar X-ray images by slot scanning of the whole body in an upright, physiological load-bearing position, using ultra-low radiation doses. The simultaneous capture of spatially calibrated anterioposterior and lateral images provides a three-dimensional (3D) surface reconstruction of the skeletal system using a special software. Parts of the skeletal system in X-ray images and 3D-reconstructed models appear in true 1:1scale for size and volume, thus spinal and vertebral parameters, lower limb axis lengths and angles, as well as any relevant clinical parameters in orthopaedic practice can be very precisely measured and calculated. Visualisation of 3D reconstructed models in various views by sterEOS 3D software enables presentation of top view images to help analyse rotational conditions of lower limbs, joints and spine deformities in the horizontal plane, providing revolutionary novel possibilities in orthopaedic surgery, especially in spine surgery. Our department has been extensively using the very first commercially available EOS™ imaging system worldwide for routine orthopaedic diagnostics since June 2007. During this period of about 4.5years, more than 5,700 standard examinations have been carried out, about a third of them in spine deformity cases and the rest in lower limb orthopaedic cases. In this mini-review, general principles and uses of this groundbreaking integrated orthopaedic solution is reviewed with a few highlighted examples from our own clinical practice.

Principles of the EOS™ X-ray machine and its use in daily orthopedic practice

The EOS™ X-ray machine, based on a Nobel prize-winning invention in Physics in the field of particle detection, is capable of simultaneously capturing biplanar X-ray images by slot scanning of the whole body in an upright, physiological load-bearing position, using ultra low radiation doses. The simultaneous capture of spatially calibrated anterioposterior and lateral images allows the performance of a three-dimensional (3D) surface reconstruction of the skeletal system by a special software. Parts of the skeletal system in X-ray images and 3D-reconstructed models appear in true 1:1 scale for size and volume, thus spinal and vertebral parameters, lower limb axis lengths and angles, as well as any relevant clinical parameters in orthopedic practice could be very precisely measured and calculated. Visualization of 3D reconstructed models in various views by the sterEOS 3D software enables the presentation of top view images, through which one can analyze the rotational conditions of lower limbs, joints and spine deformities in horizontal plane and this provides revolutionary novel possibilities in orthopedic surgery, especially in spine surgery.

Effects of exposure equalization on image signal‐to‐noise ratios in digital mammography: A simulation study with an anthropomorphic breast phantom

The scan equalization digital mammography (SEDM) technique combines slot scanning and exposure equalization to improve low-contrast performance of digital mammography in dense tissue areas. In this study, full-field digital mammography (FFDM) images of an anthropomorphic breast phantom acquired with an anti-scatter grid at various exposure levels were superimposed to simulate SEDM images and investigate the improvement of low-contrast performance as quantified by primary signal-to-noise ratios (PSNRs). We imaged an anthropomorphic breast phantom (Gammex 169 "Rachel," Gammex RMI, Middleton, WI) at various exposure levels using a FFDM system (Senographe 2000D, GE Medical Systems, Milwaukee, WI). The exposure equalization factors were computed based on a standard FFDM image acquired in the automatic exposure control (AEC) mode. The equalized image was simulated and constructed by superimposing a selected set of FFDM images acquired at 2, 1, 1/2, 1/4, 1/8, 1/16, and 1/32 times of exposure levels to the standard AEC timed technique (125 mAs) using the equalization factors computed for each region. Finally, the equalized image was renormalized regionally with the exposure equalization factors to result in an appearance similar to that with standard digital mammography. Two sets of FFDM images were acquired to allow for two identically, but independently, formed equalized images to be subtracted from each other to estimate the noise levels. Similarly, two identically but independently acquired standard FFDM images were subtracted to estimate the noise levels. Corrections were applied to remove the excess system noise accumulated during image superimposition in forming the equalized image. PSNRs over the compressed area of breast phantom were computed and used to quantitatively study the effects of exposure equalization on low-contrast performance in digital mammography. We found that the highest achievable PSNR improvement factor was 1.89 for the anthropomorphic breast phantom used in this study. The overall PSNRs were measured to be 79.6 for the FFDM imaging and 107.6 for the simulated SEDM imaging on average in the compressed area of breast phantom, resulting in an average improvement of PSNR by ∼35% with exposure equalization. We also found that the PSNRs appeared to be largely uniform with exposure equalization, and the standard deviations of PSNRs were estimated to be 10.3 and 7.9 for the FFDM imaging and the simulated SEDM imaging, respectively. The average glandular dose for SEDM was estimated to be 212.5 mrad, ∼34% lower than that of standard AEC-timed FFDM (323.8 mrad) as a result of exposure equalization for the entire breast phantom. Exposure equalization was found to substantially improve image PSNRs in dense tissue regions and result in more uniform image PSNRs. This improvement may lead to better low-contrast performance in detecting and visualizing soft tissue masses and micro-calcifications in dense tissue areas for breast imaging tasks.

スリット撮影を用いた長尺撮影装置における全脊椎撮影の最適化

The purpose of this study was to optimize X-ray conditions for full spine X-ray examinations in slot-scan digital radiography (SSDR). Follow-up of spinal deformities, such as scoliosis, typically involves many radiographs of the patient throughout childhood and adolescence. The Radiation doses for the full spine X-ray examination should be minimized. Recently, SSDR has been introduced for full spine as well as lower extremity examinations. This system utilizes slot scanning geometry to acquire the radiographic images. X-ray energy characteristics of direct amorphous Selenium (a-Se) digital fluoroscopy and short time X-ray tube loads of this system were investigated. Orthopedists evaluated the irradiation time for full spine radiographs in various conditions using an observer study. Patient doses were measured with radiophotoluminescence glass dosimeters, which were implanted in various tissue and organ positions within an anthropomorphic phantom. In the optimization of conditions for SSDR, patient doses are reduced by approximately 60% compared to default setting.

Scanning synthetic radiation pattern antennas

It is proposed conception of development of new type transmitting-receiving scanning antennas, which are called antennas with synthetic radiation pattern. It is based on application of movement of radiating (receiving) element together with synthesizing of radiation pattern (RP) by means of SAR for processing of recorded information about radiated and received signals. Physical radiator movement can be real or virtual (switching of radiation phase center) due to switching in turns of radiators of one-dimension antenna array (AA) to single-channel transmitter-receiver. There are represented two applications of this approach realization, such as spiral-waveguide slot and tape-slot scanning synthetic RP antennas for registration of radio images and radiofilms in 8-mm wavelength band.

Curved crystal x‐ray optics for monochromatic imaging with a clinical source

Monochromatic x-ray imaging has been shown to increase contrast and reduce dose relative to conventional broadband imaging. However, clinical sources with very narrow energy bandwidth tend to have limited intensity and field of view. In this study, focused fan beam monochromatic radiation was obtained using doubly curved monochromator crystals. While these optics have been in use for microanalysis at synchrotron facilities for some time, this work is the first investigation of the potential application of curved crystal optics to clinical sources for medical imaging. The optics could be used with a variety of clinical sources for monochromatic slot scan imaging. The intensity was assessed and the resolution of the focused beam was measured using a knife-edge technique. A simulation model was developed and comparisons to the measured resolution were performed to verify the accuracy of the simulation to predict resolution for different conventional sources. A simple geometrical calculation was also developed. The measured, simulated, and calculated resolutions agreed well. Adequate resolution and intensity for mammography were predicted for appropriate source/optic combinations.

MO-D-332-03: Scatter Rejection Properties and Low-Contrast Performance of a Scan Equalization Digital Radiography (SEDR) System: Initial Experience with Chest Phantom Images

Purpose: To investigate scatter rejection properties and low-contrast performance of a flat-panel based SEDR system for chest imaging. Method and Materials: A prototype SEDR system was developed to improve the image quality especially in heavily attenuated regions. Slot scan imaging geometry was used to reduce x-ray scatter without attenuating primary x-rays. Regional beam width modulation was used to equalize the x-ray exposures at the detector input for more uniform image signal-to-noise ratios. A low-dose chest phantom (pre-scan) image was acquired with the slot-scan technique to determine the equalization factors for SEDR imaging. A steel bar was placed in front of the chest phantom to measure the scatter component and scatter-to-primary ratios (SPRs) across the phantom image. Two images acquired with the same techniques were subtracted from each other for measuring the noise levels. SPRs, SNRs, and contrast-to-noise ratios (CNRs) of the SEDR images were measured and compared with those of the slot-scan images and full-field images acquired with and without anti-scatter grid. Results: The SEDR technique resulted in lower SPRs in heavily attenuated regions like retrocardum and mediastinum than the slot-scan and full-field techniques. They resulted in similar SPRs in lungs as the slot-scan technique. Both the SEDR and slot-scan methods produced better SNRs than the anti-scatter grid method in full-field imaging. The SEDR technique resulted in the best CNRs, followed in order by the slot-scan and anti-scatter grid techniques. The improvement of CNR was more pronounced in heavily attenuated regions. Conclusion: The SEDR technique can effectively reject scatter without having to attenuate the primary x-rays. Furthermore, it can improve image SNRs and CNRs by regionally compensating for x-ray attenuation by patient's anatomy. Acknowledgement: This work was supported in part by grants CA104759 and CA124585 from NIH-NCI, a grant EB00117 from NIH-NIBIB, and a subcontract from NIST-ATP.

SU‐GG‐I‐30: Magnitude of Scattered Radiation and Dose Efficiency in Volume‐Of‐Interest (VOI) Cone Beam CT

The magnitude of scattered radiation and dose efficiency inside and outside the VOI was investigated for VOI cone beam computed tomography (CBCT) technique. For experiments, a bench‐top CBCT system with a flat‐panel digital detector was constructed. Two cylindrical polycarbonate phantoms (11 cm and 15 cm in diameter) were used to simulate breasts. To implement the VOI scanning technique, a lead filter with a rectangular opening was placed between the x‐ray source and the phantoms. The x‐ray tube voltage setting was 80 kVp. The phantoms were imaged without and with the VOI filter for the open filed and the VOI field, respectively. Slot scanning technique with varying slot width was used to measure SPR values at the detector plane. Dose measurement was performed using TLD dosimeters at five different locations for the 11‐cm phantom and six locations for the 15 cm phantom. The results showed that the SPR value inside the VOI were about 0.37 and 0.039 for the open field and the VOI field, respectively, for the 11 cm phantom. This indicates that the SPR can be reduced by a factor of 9 inside the VOI. The results also showed that dose increases from the center toward to the edge for the open field, but decreases for the VOI field. The dose can be reduced by a factor of 3 or more outside the VOI and by a factor of 1.6 at the center of the phantom for the 11 cm phantom (this work was supported in part by a grant CA104759 from the NCI and a research grant EB00117 from the NIBIB).

Comparison of slot scanning digital mammography system with full‐field digital mammography system

The purpose of this study was to evaluate and compare microcalcification detectability of two commercial full-field digital mammography (DM) systems. The first unit was a flat panel based DM system (FFDM) which employed an anti-scatter grid method to reject scatter, and the second unit was a charge-coupled device-based DM system (SSDM) which used scanning slot imaging geometry to reduce scatter radiation. Both systems have comparable scatter-to-primary ratios. In this study, 125-160 and 200-250 microm calcium carbonate grains were used to simulate microcalcifications and imaged by both DM systems. The calcium carbonate grains were overlapped with a 5-cm-thick 50% adipose/50% glandular simulated breast tissue slab and an anthropomorphic breast phantom (RMI 165, Gammex) for imaging at two different mean glandular dose levels: 0.87 and 1.74 mGy. A reading study was conducted with seven board certified mammographers with images displayed on review workstations. A five-point confidence level rating was used to score each detection task. Receiver operating characteristic (ROC) analysis was performed and the area under the ROC curve (A(z)) was used to quantify and compare the performances of these two systems. The results showed that with the simulated breast tissue slab (uniform background), the SSDM system resulted in higher A(z)'s than the FFDM system at both MGD levels with the difference statistically significant at 0.87 mGy only. With the anthropomorphic breast phantom (tissue structure background), the SSDM system performed better than the FFDM system at 0.87 mGy but worse at 1.74 mGy. However, the differences were not found to be statistically significant.

Dependence of the electrical properties of stabilized a-Se on the preparation conditions and the development of a double layer X-ray detector structure

Abstract Stabilized a-Se films deposited at sufficiently low substrate temperatures are n-like in which electrons can drift but holes are deeply trapped. Such layers can be conveniently incorporated in a multilayer a-Se detector structure to block the injection of holes from the positive electrode. We have shown that a simple double-layer detector structure based on a cold deposited n-layer (which is then annealed) on which an i-like layer is grown can have dark current densities lower than 10−10 A cm−2 at a field of 10 V/μm. The dark current depends on the thickness of the n-like layer. An a-Se X-ray detector for slot scanning was fabricated by having the i–n a-Se photoconductor structure coated onto a CCD chip. The latter detector was shown to have excellent resolution with a modulation transfer function remaining above 0.5 up to a spatial frequency of 11–14 lp mm−1.

SU‐FF‐I‐76: Slot Scan Imaging Versus Anti‐Scatter Grid Method in Digital Chest Imaging‐ a 4‐AFC Study

Purpose: To investigate and compare the anti‐scatter grid and slot scanning methods for their effects on the observers' performance in digital chest imaging. Materials and Methods: Anthropomorphic chest phantom was imaged with an a‐Si/a‐Se flat‐panel based digital radiography system. The system was operated in both the slot scanning and full‐field modes. An anti‐scatter grid was used. Imaging technique was 120 kVp and 0.15 to 16 mAs for both modes. After that, the grid was removed and same imaging technique was applied to acquire phantom images for both modes. 1‐cm diameter computer‐simulated nodule with a nominal peak contrast ratio of 5% was used to generate simulated nodules at hilum and sub‐diaphragm locations by applying SPR values for all images. 4‐AFC experiment was conducted to measure the ratio of correct observations as a function of the exposure level for various imaging conditions and locations. 24 sets of four‐512×512 images were generated for each exposure level, resulting in generating 192 sets for each imaging condition and location. These images were displayed randomly on a review workstation. The ratios of correct observations versus exposure levels were computed for various imaging conditions and locations. Result: With low exposure, the observers' performance improved with the exposure level but reached the maximum at ∼4 mAs for all techniques. At the hilum location, slot scan imaging without grid performed the best, followed by full‐field imaging without grid. The use of an anti‐scatter grid in both full‐field and slot scan modes seemed to degrade the performance significantly. Conclusion: Improvement with the exposure level has been observed for all imaging techniques. However, the observers' performance reached the maximum at different rates depending on the nodule location and techniques.(This work was supported in part by a research grant EB000117 from the NIH‐NIBIB and a research grant CA104759 from the NIH‐NCI).

MO‐SAMS‐L100J‐01: Digital Mammography Update: Design and Characteristics of Current Systems

Mammography still remains the best screening tool for early detection of breast cancer, and the recent ACRIN DMIST results draw attention to the fact that digital mammography is better at detecting cancers in dense breasts. Digital mammography equipment has continued to develop and improve and more vendors and models have entered the marketplace with FDA approval. The technology used in these systems generally falls into four main categories: direct capture detectors, indirect capture detectors, slot scanning, and cassette‐based storage phosphors (computed radiography). Additionally, a photon counting system is being developed. Each of these technologies has its advantages and disadvantages. A review of the systems currently available is presented, including the detector technology utilized. Features of these systems are also presented. This is a Self Assessment Module (SAM) to help fulfill the requirements of the Maintenance of Certification (MOC) process as defined by the American Board of Radiology (ABR). As such, audience participation through interactive questions will be provided during the course of the lecture.Educational Objectives:1. Become familiar with the detector technologies currently used in digital mammography systems.2. Become familiar with the digital mammography systems available from each manufacturer.3. Become familiar with the unique elements of each system.

MO‐E‐L100J‐06: Slot Scan Imaging with a High Frame Rate Flat Panel Detector‐Measurement and Correction for In‐Slot Scatter

Purpose: To report on the use of a new scatter measurement technique to characterize the scatter rejection properties and to further correct for the in‐slot scatter in slot scan imaging with a high frame rate flat panel detector. Method and Materials: A new slot scan imaging technique was developed with a high frame rate (7.5 fps) flat panel detector. 300 images were acquired as an x‐ray fan beam, defined by a slot collimator placed in front of the tube, was scanned across an anthropomorphic chest phantom. Time‐intensity curves were formed from the image sequence for all pixels. They were integrated over the fan beam passing frames to form the scatter rejected image signals and over all frames to form the open field image signals. By assuming the primary component to be constant during the fan beam exposure, the scatter components were extracted from the time‐intensity curves to estimate the in‐slot scatter using an iterative background estimation algorithm. The results were used to measure the scatter signals and to correct for in‐slot scatter. Results: Slot scan images of an anthropomorphic chest phantom were acquired and formed for various projected fan beam widths. 2D maps of scatter‐to‐primary ratios and contrast‐to‐noise ratio (CNR) improvement factors were generated and plotted for the slot‐scan images and compared with those for the full field, non‐grided images . In the lungs, CNR was improved by 30 to 50%, and in the mediastinum, CNR was improved by 60 to 150%. Conclusion: We have described and demonstrated the use of a new scatter measurement technique to estimate and correct for the in‐slot scatter on a pixel‐by‐pixel basis in slot scan imaging with a high frame rate flat panel detector.This work was supported in part by research grants EB00117 from the NIH‐NIBIB and CA51248 and CA104759 from the NIH‐NCI.

TU‐FF‐A4‐04: Intensity Modulation Patterns for Regional Exposure Control with Multiple Angle Slot Scan Imaging: Simulated Annealing Optimization Technique Approach

Purpose: To study the feasibility of using simulated annealing algorithm to determine the intensity modulation patterns for regional exposure control with multiple angle slot scan imaging. Method and Materials: We acquired a digital image from the chest radiography and then processed with a 2‐D Gaussian filter as an exposure equalization mask. Slot scanning exposures at evenly spaced angle between 0 and 180 degrees were used to achieve the ideal exposure distribution. An optimization technique, simulated annealing, was used to search the best intensity modulation patterns. This method is based on the theory of statistical physics and uses Boltzmann probability distribution to locate the minimum energy state. An objective function was mathematically constructed and Metropolis scheme was incorporated into the numerical computation. Various tuning parameters such as the control temperature setting for the annealing schedule were explored and the best combination was empirically chosen. We also calculated the percent root mean square error to quantify the results. Results: A wide range of scanning angles was tested in the study. For 8 projection angles, it took 10 minutes to complete the intensity modulation patterns search in a single processor computer and the percent root mean square error was 12.0%. The percent root mean square error can be further reduced by adding the number of scanning angles. Conclusion: Our study indicated that simulated annealing technique has the potential to determine the optimized intensity modulation patterns. Current work is focused on the reduction of both the computing time and percent root mean square error. Other optimization techniques such as the conjugate gradient method and the applications of parallel computing methods to accelerate the search algorithms are to be investigated.Supported in part by a research grant EB00117 by the National Institute of Biomedical Imaging and Bioengineering.

TU‐C‐330D‐01: Advances in Breast Imaging

Despite development and advances of new modalities, x‐ray mammography remains the main screening tool for early detection of breast cancers. It also continues to play an important role in the diagnosis and management of breast cancers. X‐ray mammography has relied on the use of high resolution screen/film combinations. Such techniques, although improved over the years, have the drawbacks of all the inconveniences and inflexibility associated with the use of film for image acquisition, storage and display. Motivated by search for better image quality and a general move towards filmless radiology, various digital mammography techniques have been developed, investigated and commercialized. These techniques can be largely divided into four types: amorphous silicon and selenium flat panel detector, amorphous silicon and cesium iodide flat panel detector, CCD and cesium iodide based slot scanning system, and storage phosphor imaging technique with dual‐side image read out. Each of these systems has its unique advantages and disadvantages and achieves various degrees of clinical implementation. Typical of all digital mammography techniques is the potential compatibility with digital image archival, retrieval and distribution systems. Furthermore, the acquisition of breast images in digital format has begun to facilitate the development and investigation of many advanced imaging techniques. Among them, dual‐energy mammography techniques have been developed to quantify breast tissue composition or to separate calcifications from the overlying tissue structures. Stereo‐mammography has been developed to use two projection views to provide a 3‐D perspective of the breast tissue structures, thus reducing the problem of overlapping structures. Tomosynthesis imaging pushes the idea of 3‐D imaging further by acquiring 10–25 projection views and use them to synthesize images to depict the breast structures as a number of thick layers. More recently, cone beam breast CT has been developed and investigated to scan the breast in a dedicated manner and provide true 3‐D images of the breast. Along a different direction, the development and investigation of various contrast mammography techniques have allowed x‐ray imaging to be used to image and study breast vasculatures as possible indication of breast cancer.In this presentation, we will try to achieve the following educational objectives:1. Review the development and investigation of major digital mammography techniques.2. Review the development and investigation of various advanced breast x‐ray imaging techniques.Research sponsored by the National Cancer Institute and the National Institute of Biomedical Imaging and Bioengineering.

Automatic exposure control for a slot scanning full field digital mammography system

Automatic exposure control (AEC) is an important feature in mammography. It enables consistently optimal image exposure despite variations in tissue density and thickness, and user skill level. Full field digital mammography systems cannot employ conventional AEC methods because digital receptors fully absorb the x-ray beam. In this paper we describe an AEC procedure for slot scanning mammography. With slot scanning detectors, our approach uses a fast low-resolution and low-exposure prescan to acquire an image of the breast. Tube potential depends on breast thickness, and the prescan histogram provides the necessary information to calculate the required tube current. We validate our approach with simulated prescan images and phantom measurements. We achieve accurate exposure tracking with thickness and density, and expect this method of AEC to reduce retakes and improve workflow.