KEYWORDS: 3D displays, Radiotherapy, 3D volumetric displays, Visualization, Tumors, 3D image processing, Human-machine interfaces, Computed tomography, Cancer
We describe PerspectaRAD, the first tool for the review and modification of external-beam radiation therapy treatment
plans with a volumetric three-dimensional display (Perspecta 1.9, Actuality Medical, Bedford, MA, USA) and a dedicated software application (PerspectaRAD, Actuality Medical). We summarize
multi-institution retrospective studies that compare the system's efficacy to the incumbent 2-D display-based workflow. Contributions include: visualizing the treatment plan in a volumetric 3-D display, modifying the beam locations and performing point-and-click measurement in 3-D with a 3-D physical interface, and simultaneously viewing volumetric projections of the native CT data and isodose contours. The plans are synchronized with the hospital treatment planning system, Pinnacle3 (Philips Medical, WI, USA). In the largest of five studies, 33 plans were retrospectively randomized and replanned at three institutions, including 12 brain, 10 lung, and 11 abdomen / pelvis. The PerspectaRAD plan was as good as or better than plans created without PerspectaRAD 70% of the time. Radiation overdose regions were more likely to be obvious inside the target volume than when reviewed in the 2-D display alone. However, the planning time was longer with PerspectaRAD. The data demonstrate that PerspectaRAD facilitates the use of non-coplanar beams and has significant potential to achieve better plan quality in radiation therapy.
Planar X-ray mammography is the standard medical imaging modality for the early detection of breast cancer. Based on
advancements in digital flat-panel detector technology, dedicated x-ray computed tomography (CT) mammography is a
modality under investigation that offers the potential for improved breast tumor imaging. We have implemented a
prototype half cone-beam CT breast imaging system that utilizes an indirect flat-panel detector. This prototype can be
used to explore and evaluate the effect of varying acquisition and reconstruction parameters on image quality. This
report describes our system and characterizes the performance of the system through the analysis of Modulation Transfer
Function (MTF) and Noise Power Spectrum (NPS). All CT reconstructions were made using Feldkamp's filtered
backprojection algorithm. The 3D MTF was determined by the analysis of the plane spread function (PlSF) derived
from the surface spread function (SSF) of reconstructed 6.3mm spheres. 3D NPS characterization was performed
through the analysis of a 3D volume extracted from zero-mean CT noise of air reconstructions. The effect of varying
locations on MTF and the effect of different Butterworth filter cutoff frequencies on NPS are reported. Finally, we
present CT images of mastectomy excised breast tissue. Breast specimen images were acquired on our CTMS using an
x-ray technique similar to the one used during performance characterization. Specimen images demonstrate the inherent
CT capability to reduce the masking effect of anatomical noise. Both the quantitative system characterization and the
breast specimen images continue to reinforce the hope that dedicated flat-panel detector, x-ray cone-beam CT will
eventually provide enhanced breast cancer detection capability.
In considering a breast CT system, it is important to note that the spectral attenuation profile of a tumor is very similar to that of fibro-glandular tissue. Preliminary evidence based on imaging breast specimens suggest that the CT number of a malignant breast tumor is very similar to that of surrounding fibro-glandular tissue. Therefore, it is expected that radiologists will probably rely more on tumor morphology to distinguish a malignant tumor from fibro-glandular tissue than an increase in contrast per se. Previous studies have shown that iodinated contrast agents can increase the effective attenuation coefficient yielded by a breast tumor thereby providing increased CT tumor contrast. In order to characterize how the intravenous administration of an iodinated contrast agent can affect the performance of CT breast imaging, a computer simulation of such a system was conducted. The two primary goals of this investigation were first to determine how mean glandular dose, choice of x-ray energy spectrum, and iodine contrast agent density affect tumor detection, and second to determine what effect Compton and Rayleigh scattering have on the variability of the attenuation coefficient yielded by CT mammography. The first goal was achieved by making use of a modified version of the Bakic (Med. Phys. 2003) digital breast phantom to model the uncompressed breast, and a 0.5 cm sphere representing a breast tumor was digitally inserted into the ductal region of this phantom. Several projection sets were generated with the tumor containing various densities of iodine contrast agent, different x-ray energy spectra, and different mean glandular dosage (MGD) levels . Slices through the tumor were extracted from the reconstructions of these projections and were used in human observer studies to determine tumor detectability. The second goal was achieved by using the GATE (Geant 4 Application for Tomographic Emission) Monte-Carlo software package to compute the scattering incident on the flat panel detector for an x-ray projection, then using the aforementioned Bakic phantom, a 0.5 cm sphere representing a breast tumor attenuation and a 3.0 mg/ml of Iodinated contrast agent were inserted at various locations with varying attenuation for 100 projection sets with scatter, and 100 projections without scatter. Histograms of the resulting effective attenuation coefficients yielded by Feldkamp filtered backprojection were plotted and compared.
KEYWORDS: Signal to noise ratio, Sensors, Breast, X-rays, X-ray detectors, Imaging systems, Modulation transfer functions, Mammography, Image quality, Systems modeling
The detection of lesions in conventional mammography is a difficult task, predominantly due to the masking effect of
superimposed parenchymal breast patterns. Breast tomosynthesis is a technique that has been proposed to reduce this
masking effect, by providing the radiologist with tomographic image slices through the breast. The goal of this research
was to investigate the impact of varying x-ray spectra on image quality of breast tomosynthesis using an indirect CsI
based detector. The ideal observer SNR was used as a figure-of-merit, under the assumption that the imaging system is
linear and shift-invariant. Computations of the ideal observer SNR used a serial cascade model to predict signal and
noise propagation through the detector, as well as a model of the lesion detection task in breast imaging. An indirect
detector breast tomosynthesis prototype system was modeled which acquires 11 projection views by rotating the x-ray
tube over a 50° angular range, with the breast and detector remaining stationary. Specific attention was focused on the
impact of electronic noise for indirect detector breast tomosynthesis. Three different target/filters were studied including
Mo/Mo, Mo/Rh, and W/Rh. Spectra were scaled to give a total of 2.4 mGy average glandular dose to the breast. It was
observed that theW/Rh target/filter exhibited the best performance. In addition, electronic noise was observed to have a
moderate effect on the SNR with more impact for thicker breasts and lower kVp settings.
Although conventional mammography is currently the best modality to detect early breast cancer, it is limited in that the recorded image represents the superposition of a 3D object onto a 2D plane. As an alternative, cone-beam CT breast imaging with a CsI based flat-panel imager (CTBI) has been proposed with the ability to provide 3D visualization of breast tissue. To investigate possible improvements in lesion detection accuracy using CTBI over digital mammography (DM), a computer simulation study was conducted using simulated lesions embedded into a structured 3D breast model. The computer simulation realistically modeled x-ray transport through a breast model, as well as the signal and noise propagation through the flat-panel imager. Polyenergetic x-ray spectra of W/Al 50 kVp for CTBI and Mo/Mo 28 kVp for DM were modeled. For the CTBI simulation, the intensity of the x-ray spectra for each projection view was determined so as to provide a total mean glandular dose (MGD) of 4 mGy, which is approximately equivalent to that given in a conventional two-view screening mammography study. Since only one DM view was investigated here, the intensity of the DM x-ray spectra was defined to give 2 mGy MGD. Irregular lesions were simulated by using a stochastic growth algorithm providing lesions with an effective diameter of 5 mm. Breast tissue was simulated by generating an ensemble of backgrounds with a power law spectrum. To evaluate lesion detection accuracy, a receiver operating characteristic (ROC) study was performed with 4 observers reading an ensemble of images for each case. The average area under the ROC curves (Az) was 0.94 for CTBI, and 0.81 for DM. Results indicate that a 5 mm lesion embedded in a structured breast phantom can be detected by CT breast imaging with statistically significant higher confidence than with digital mammography.
KEYWORDS: Signal to noise ratio, Breast, Sensors, X-rays, Imaging systems, Mammography, Breast imaging, X-ray detectors, Computed tomography, Systems modeling
In recent years, there has been interest in exploring the feasibility of CT breast imaging using flat-panel digital detectors in a truncated cone-beam geometry. Preliminary results are promising and it appears as if 3D tomographic imaging of the breast has great potential for reducing the masking effect of superimposed parenchymal structure typically observed with conventional mammography. In this study, a mathematical framework used for determining optimal design and acquisition parameters for such a CT breast imaging system is described. The ideal observer SNR is used as a figure-of-merit, under the assumptions that the imaging system is linear and shift-invariant. Computation of the ideal observer SNR used a parallel-cascade model to predict signal and noise propagation through the detector, as well as a realistic model of the lesion detection task in breast imaging. For all optimizations discussed here, the total mean glandular dose for a CT breast imaging study is constrained to be approximately equivalent to that of a two-view conventional mammography study. The framework presented is used to explore the affect of the specific task on the optimal exposure technique of flat-panel CT breast imaging. In particular, it is observed that modeling the normal mammographic structure in the projection images can sometimes impact the optimal kVp settings.
Purpose: To study the frequency and severity of artifacts in optical Coherence tomography images and to develop a new algorithm for improved retinal thickness detection.
Methods: We propose a new method to measure the retinal thickness in OCT scans. We compared our modified edge detection (MED) method to the Markov method and the conventional OCT algorithm (cOCT) in 226 OCT macular scans.
Results: We defined errors as a difference in detected interface location of less than 100 µm offset for less than 10 A-scans, otherwise it was an artifact. The frequency of errors was reduced from 32% (cOCT) to less than 2% with the MED method, while the Markov method had a frequency of 5%. Artifacts were reduced from 9.3% (cOCT) to 0.9% (MED) while the Markov method had a frequency of 11.5%.
Conclusion: The results show the MED method of detecting retinal thickness is superior to the other two methods, since the OCT method is prone to both errors and artifacts and the Markov method is robust only to healthy retina. Our MED method is robust for detection of normal retinas and effective even in eyes with pathological conditions. Use of improved retinal thickness detection algorithm should significantly improve clinical utility of the optical coherence tomograph.
The purpose of this study is to investigate the detectability of microcalcification clusters (MCCs) using CT mammography with a flat-panel detector. Compared with conventional mammography, CT mammography can provide improved discrimination between malignant and benign cases as it can provide the radiologist with more accurate morphological information on MCCs. In this study, two aspects of MCC detection with flat-panel CT mammography were examined: (1) the minimal size of MCCs detectable with mean glandular dose (MGD) used in conventional mammography; (2) the effect of different detector pixel size on the detectability of MCCs. A realistic computer simulation modeling x-ray transport through the breast, as well as both signal and noise propagation through the flat-panel imager, was developed to investigate these questions. Microcalcifications were simulated as calcium carbonate spheres with diameters set at the levels of 125, 150 and 175 μm. Each cluster consisted of 10 spheres spread randomly in a 6×6 mm2 region of interest (ROI) and the detector pixel size was set to 100×100, 200×200, or 300×300μm2. After reconstructing 100 projection sets for each case (half with signal present) with the cone-beam Feldkamp (FDK) algorithm, a localization receiver operating characteristic (LROC) study was conducted to evaluate the detectability of MCCs. Five observers chose the locations of cluster centers with correspondent confidence ratings. The average area under the LROC curve suggested that the 175 μm MCCs can be detected at a high level of confidence. Results also indicate that flat-panel detectors with pixel size of 200×200 μm2 are appropriate for detecting small targets, such as MCCs.
KEYWORDS: Sensors, X-rays, Mammography, Signal attenuation, Imaging systems, Breast, Signal to noise ratio, X-ray detectors, Monte Carlo methods, Scintillators
Software has been developed to simulate a cone-beam CT mammography imaging system that consists of an x-ray tube and a flat-panel detector that rotate simultaneously around the pendant breast. The simulation uses an analytical expression or ray-tracing to generate projection sets of breast phantoms at 1 keV intervals dictated by the input x-ray energy spectra. The x-ray focal spot was modeled as having a Gaussian distribution. The detector was modeled as an amorphous silicon (aSi:H) flat-panel imager that uses a structured CsI scintillator. Noise propagation through the detector was simulated by modeling statistical variations of the projection images at each energy interval as a scaled Poisson process. Scintillator blurring was simulated by using an empirically determined modulation transfer function. After introducing noise and detector blur, projection sets simulated at each energy were then combined and reconstructed using Feldkamp's cone-beam reconstruction algorithm. Using this framework, the effects of a number of acquisition and reconstruction parameters can be investigated. Some examples are shown including the impact of the kVp setting and the number of projection angles on the reconstructed image.
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