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Paul M Meaney,
Peter A Kaufman,
Lori S Muffly,
Michael Click,
Steven P Poplack,
Wendy A Wells,
Gary N Schwartz,
Roberta M di Florio-Alexander,
Tor D Tosteson,
Zhongze Li,
Shireen D Geimer,
Margaret W Fanning,
Tian Zhou,
Neil R Epstein,
Keith D Paulsen
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ABSTRACT: INTRODUCTION: Microwave tomography recovers images of tissue dielectric properties, which appear to be specific for breast cancer, with low-cost technology that does not present an exposure risk, suggesting the modality may be a good candidate for monitoring neoadjuvant chemotherapy. METHODS: Eight patients undergoing neoadjuvant chemotherapy for locally advanced breast cancer were imaged longitudinally five to eight times during the course of treatment. At the start of therapy, regions of interest (ROIs) were identified from contrast-enhanced magnetic resonance imaging studies. During subsequent microwave examinations, subjects were positioned with their breasts pendant in a coupling fluid and surrounded by an immersed antenna array. Microwave property values were extracted from the ROIs through an automated procedure and statistical analyses were performed to assess short term (30 days) and longer term (four to six months) dielectric property changes. RESULTS: Two patient cases (one complete and one partial response) are presented in detail and demonstrate changes in microwave properties commensurate with the degree of treatment response observed pathologically. Normalized mean conductivity in ROIs from patients with complete pathological responses was significantly different from that of partial responders (P value = 0.004). In addition, the normalized conductivity measure also correlated well with complete pathological response at 30 days (P value = 0.002). CONCLUSIONS: These preliminary findings suggest that both early and late conductivity property changes correlate well with overall treatment response to neoadjuvant therapy in locally advanced breast cancer. This result is consistent with earlier clinical outcomes that lesion conductivity is specific to differentiating breast cancer from benign lesions and normal tissue.
Breast cancer research: BCR 04/2013; 15(2):R35. · 5.24 Impact Factor
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ABSTRACT: Microwave tomographic image quality can be improved significantly with prior knowledge of the breast surface geometry. The authors have developed a novel laser scanning system capable of accurately recovering surface renderings of breast-shaped phantoms immersed within a cylindrical tank of coupling fluid which resides completely external to the tank (and the aqueous environment) and overcomes the challenges associated with the optical distortions caused by refraction from the air, tank wall, and liquid bath interfaces.
The scanner utilizes two laser line generators and a small CCD camera mounted concentrically on a rotating gantry about the microwave imaging tank. Various calibration methods were considered for optimizing the accuracy of the scanner in the presence of the optical distortions including traditional ray tracing and image registration approaches. In this paper, the authors describe the construction and operation of the laser scanner, compare the efficacy of several calibration methods-including analytical ray tracing and piecewise linear, polynomial, locally weighted mean, and thin-plate-spline (TPS) image registrations-and report outcomes from preliminary phantom experiments.
The results show that errors in calibrating camera angles and position prevented analytical ray tracing from achieving submillimeter accuracy in the surface renderings obtained from our scanner configuration. Conversely, calibration by image registration reliably attained mean surface errors of less than 0.5 mm depending on the geometric complexity of the object scanned. While each of the image registration approaches outperformed the ray tracing strategy, the authors found global polynomial methods produced the best compromise between average surface error and scanner robustness.
The laser scanning system provides a fast and accurate method of three dimensional surface capture in the aqueous environment commonly found in microwave breast imaging. Optical distortions imposed by the imaging tank and coupling bath diminished the effectiveness of the ray tracing approach; however, calibration through image registration techniques reliably produced scans of submillimeter accuracy. Tests of the system with breast-shaped phantoms demonstrated the successful implementation of the scanner for the intended application.
Medical Physics 06/2012; 39(6):3102-11. · 2.83 Impact Factor
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ABSTRACT: A critical need exists for new imaging tools to more accurately characterize bone quality beyond the conventional modalities of dual energy X-ray absorptiometry (DXA), ultrasound speed of sound, and broadband attenuation measurements. In this paper we investigate the microwave dielectric properties of ex vivo trabecular bone with respect to bulk density measures. We exploit a variation in our tomographic imaging system in conjunction with a new soft prior regularization scheme that allows us to accurately recover the dielectric properties of small, regularly shaped and previously spatially defined volumes. We studied six excised porcine bone samples from which we extracted cylindrically shaped trabecular specimens from the femoral heads and carefully demarrowed each preparation. The samples were subsequently treated in an acid bath to incrementally remove volumes of hydroxyapatite, and we tested them with both the microwave measurement system and a micro-CT scanner. The measurements were performed at five density levels for each sample. The results show a strong correlation between both the permittivity and conductivity and bone volume fraction and suggest that microwave imaging may be a good candidate for evaluating overall bone health.
International Journal of Biomedical Imaging 01/2012; 2012:649612.
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ABSTRACT: Microwave imaging techniques are prone to signal corruption from unwanted multipath signals. Near-field systems are especially vulnerable because signals can scatter and reflect from structural objects within or on the boundary of the imaging zone. These issues are further exacerbated when surface waves are generated with the potential of propagating along the transmitting and receiving antenna feed lines and other low-loss paths. In this paper, we analyze the contributions of multi-path signals arising from surface wave effects. Specifically, experiments were conducted with a near-field microwave imaging array positioned at variable heights from the floor of a coupling fluid tank. Antenna arrays with different feed line lengths in the fluid were also evaluated. The results show that surface waves corrupt the received signals over the longest transmission distances across the measurement array. However, the surface wave effects can be eliminated provided the feed line lengths are sufficiently long independently of the distance of the transmitting/receiving antenna tips from the imaging tank floor. Theoretical predictions confirm the experimental observations.
International Journal of Biomedical Imaging 01/2012; 2012:697253.
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ABSTRACT: Microwave Tomography (MT) can determine the permittivity and conductivity of a volume of interest; it has been shown that a contrast exists between these electrical properties in healthy and malignant tissues, and MT can be used to discern the dielectric contrast image of these tissues by recovering their electrical property values. Simulation and phantom experiments of objects with known spatial locations have shown that using boundary information derived from internal structures in the imaged volume greatly increases the accuracy of the recovered property values. In practice this spatial information, which will be used for reconstructing the tissue's electrical property images, must be determined with high enough resolution to segment boundary regions and internal structures of interest. This experiment investigates the use of Magnetic Resonant Imaging (MRI) in obtaining the desired spatial information used in mesh generation for image reconstruction and provides microwave image results comparing electrical properties recovered with and without this prior spatial information.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2011; 2011:5738-41.
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ABSTRACT: Microwave imaging is based on the electrical property (permittivity and conductivity) differences in materials. Microwave imaging for biomedical applications is particularly interesting, mainly due to the fact that available range of dielectric properties for different tissues can provide important functional information about their health. Under the assumption that a 3D scattering problem can be reasonably represented as a simplified 2D model, one can take advantage of the simplicity and lower computational cost of 2D models to characterize such 3D phenomenon. Nonetheless, by eliminating excessive model simplifications, 3D microwave imaging provides potentially more valuable information over 2D techniques, and as a result, more accurate dielectric property maps may be obtained. In this paper, we present some advances we have made in three-dimensional image reconstruction, and show the results from a 3D breast phantom experiment using our clinical microwave imaging system at Dartmouth Hitchcock Medical Center (DHMC), NH.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2011; 2011:5730-3.
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ABSTRACT: Microwave imaging for medical applications is attractive because the range of dielectric properties of different soft tissues can be substantial. Breast cancer detection and monitoring of treatment response are areas where this technology could be important because of the contrast between normal and malignant tissue. Unfortunately, the technique is unable to achieve the high spatial resolution at depth in tissue which is available from other conventional modalities such as x-ray computed tomography (CT) or magnetic resonance imaging (MRI). We have incorporated a soft-prior regularization strategy within our microwave reconstruction algorithm and compared it with the images obtained with traditional no-prior (Levenberg-Marquardt) regularization. Initial simulation and phantom results show a significant improvement of the recovered electrical properties. Specifically, errors in the microwave property estimates were improved by as much as 95%. The effects of a false-inclusion region were also evaluated and the results show that a small residual property bias of 6% in permittivity and 15% in conductivity can occur that does not otherwise degrade the property recovery accuracy of inclusions that actually exist. The work sets the stage for integrating microwave imaging with MR for improved resolution and functional imaging of the breast in the future.
Journal of Medical Physics 07/2011; 36(3):159-70.
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ABSTRACT: Microwave image reconstruction is typically based on a regularized least-square minimization of either the complex-valued field difference between recorded and modeled data or the logarithmic transformation of these field differences. Prior work has shown anecdotally that the latter outperforms the former in limited surveys of simulated and experimental phantom results. In this paper, we provide a theoretical explanation of these empirical findings by developing closed form solutions for the field and the inverted electromagnetic property parameters in one dimension which reveal the dependency of the estimated permittivity and conductivity on the absolute (unwrapped) phase of the measured signal at the receivers relative to the source transmission. The analysis predicts the poor performance of complex-valued field minimization as target size and/or frequency and electromagnetic contrast increase. Such poor performance is avoided by logarithmic transformation and preservation of absolute measured signal phase. Two-dimensional experiments based on both synthetic and clinical data are used to confirm these findings. Robustness of the logarithmic transformation to variation in the initial guess of the reconstructed target properties is also shown. The results are generalizable to three dimensions and indicate that the minimization form with logarithmic transformation offers image reconstruction performance characteristics that are much more desirable for medial microwave imaging applications relative to minimizing differences in complex-valued field quantities.
Biomedical Optics Express 01/2011; 2(2):315-30. · 2.33 Impact Factor
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Proceedings of the 8th IEEE International Symposium on Biomedical Imaging: From Nano to Macro, ISBI 2011, March 30 - April 2, 2011, Chicago, Illinois, USA; 01/2011
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ABSTRACT: We are developing a microwave tomographic system for assessment of overall bone health. We hypothesize that as the mineralization of bone decreases due to the normal aging process and for more extreme situations such as osteoporosis, the dielectric property signature will also vary accordingly. To determine the merits of this approach, we have begun by performing initial exams of the heel to assess the level of image quality achievable. Early experience from our pilot study is encouraging and indicates that multiple planes of 2D images produce good representations of the 3D structural features within the heel.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:1218-21.
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ABSTRACT: The notion of applying microwave imaging to breast cancer imaging has been studied at various levels by numerous scientists. The earliest appeal of this concept related to the presumably high property contrast between benign and malignant tissue that was unique to the breast. Subsequent published studies have shown that this assumption was overly simplistic and that the tissue property heterogeneity is considerable within the breast. As we have expanded the clinical use of our microwave tomographic system, we are now using this approach to monitor tumor progressions during neoadjuvant chemotherapy. In these cases, while we can still characterize and track the tumor progression, we have observed a new phenomenon. Very often these cancer patients exhibit skin thickening near the tumor site. Our images have reconstructed elevated dielectric properties along the breast surface associated with the accompanying edema. These observations further add to the complex nature of breast dielectric properties and the challenges for imaging them using microwave interrogation.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:3398-401.
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ABSTRACT: Magnetic resonance (MR) technique was used to detect small displacements induced by localized absorption of pulsed 434 MHz microwave power as a potential method for tumor detection.
Phase contrast subtraction was used to separate the phase change due to motion from thermoelastic expansion from other contributions to phase variation such as the bulk temperature rise of the medium and phase offsets from the MR scanner itself. A simple set of experiments was performed where the motion was constrained to be one dimensional which provided controls on the data acquisition and motion extraction procedures. Specifically, the MR-detected motion signal was isolated by altering the direction of the microwave-induced motion and sampling the response with motion encoding gradients in all three directions when the microwave power was turned on and turned off.
Successful signal detection, as evidenced by the recording of a systematic alternating (zigzag) phase pattern, occurred only when the motion encoding was in parallel with either the vertical or horizontal direction of the microwave-induced motion on both 10 and 4 mm spatial scales.
These results demonstrate, for the first time, that motion associated with thermoelastic expansion from the absorption of pulsed microwave power can be detected with MR.
Medical Physics 11/2009; 36(11):5190-7. · 2.83 Impact Factor
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Ryan J Halter,
Tian Zhou, Paul M Meaney,
Alex Hartov,
Richard J Barth,
Kari M Rosenkranz,
Wendy A Wells,
Christine A Kogel,
Andrea Borsic,
Elizabeth J Rizzo,
Keith D Paulsen
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ABSTRACT: Electromagnetic (EM) breast imaging provides low-cost, safe and potentially a more specific modality for cancer detection than conventional imaging systems. A primary difficulty in validating these EM imaging modalities is that the true dielectric property values of the particular breast being imaged are not readily available on an individual subject basis. Here, we describe our initial experience in seeking to correlate tomographic EM imaging studies with discrete point spectroscopy measurements of the dielectric properties of breast tissue. The protocol we have developed involves measurement of in vivo tissue properties during partial and full mastectomy procedures in the operating room (OR) followed by ex vivo tissue property recordings in the same locations in the excised tissue specimens in the pathology laboratory immediately after resection. We have successfully applied all of the elements of this validation protocol in a series of six women with cancer diagnoses. Conductivity and permittivity gauged from ex vivo samples over the frequency range 100 Hz-8.5 GHz are found to be similar to those reported in the literature. A decrease in both conductivity and permittivity is observed when these properties are gauged from ex vivo samples instead of in vivo. We present these results in addition to a case study demonstrating how discrete point spectroscopy measurements of the tissue can be correlated and used to validate EM imaging studies.
Physiological Measurement 07/2009; 30(6):S121-36. · 1.68 Impact Factor
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ABSTRACT: Microwave tomographic imaging of the breast for cancer detection is a topic of considerable interest because of the potential to exploit the apparent high-dielectric property contrast between normal and malignant tissue. An important component in the realization of an imaging system is the antenna array to be used for signal transmission/detection. The monopole antenna has proven to be useful in our implementation because it can be easily and accurately modeled and can be positioned in close proximity to the imaging target with high-element density when configured in an imaging array. Its frequency response is broadened considerably when radiating in the liquid medium that is used to couple the signals into the breast making it suitable for broadband spectral imaging. However, at higher frequencies, the beam patterns steer further away from the desired horizontal plane and can cause unwanted multipath contributions when located in close proximity to the liquid/air interface. In this paper, we have studied the behavior of these antennas and devised strategies for their effective use at higher frequencies, especially when positioned near the surface of the coupling fluid which is used. The results show that frequencies in excess of 2 GHz can be used when the antenna centers are located as close as 2 cm from the liquid surface.
International Journal of Antennas and Propagation 01/2008; 2008:580782. · 0.47 Impact Factor
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ABSTRACT: We have developed a simple approach for mechanically scanning a focused bowl ultrasound (US) transducer for either hyperthermia or tissue ablation therapies called the 3-point support (3PS) mechanical steering technique. The scanning involves translation of the required 3D motion of the ultrasound transducer to the more manageable linear movement of three support rods. It is a cost-effective alternative, especially compared with electronic scanning and other previous implementations of mechanically scanned systems. The 3PS approach is particularly well suited for integration with our microwave breast imaging technique--the combination of which could be an effective, low-cost thermal therapy/monitoring approach. The results show that the US focus can be moved laterally in a spiral pattern 3 cm below the surface in a gel phantom and that similar patterns can be moved to multiple locations within the phantom volume in succession. The feasibility of simultaneously acquiring microwave thermal images is also demonstrated.
Physics in Medicine and Biology 07/2007; 52(11):3045-56. · 2.83 Impact Factor
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ABSTRACT: Microwave tomographic imaging falls under a broad category of nonlinear parameter estimation methods when a Gauss-Newton iterative reconstruction technique is used. A fundamental requirement in using these approaches is evaluating the appropriateness of the regression model. While there have been numerous investigations of regularization techniques to improve overall image quality, few, if any, studies have explored the underlying statistical properties of the model itself. The ordinary least squares (OLS) approach is used most often, but there are other options such as the weighted least squares (WLS), maximum likelihood (ML), and maximum a posteriori (MAP) that may be more appropriate. In addition, a number of variance stabilizing transformations can be applied to make the inversion intrinsically more linear. In this paper, a statistical analysis is performed of the properties of the residual errors from the reconstructed images utilizing actual measured data and it is demonstrated that the OLS algorithm with a log transformation (OLSlog) is clearly advantageous relative to the more commonly used OLS approach by itself. In addition, several high contrast imaging experiments are performed, which demonstrate that different subsets of data are emphasized in each method and may contribute to the overall image quality differences.
Medical Physics 07/2007; 34(6):2014-23. · 2.83 Impact Factor
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ABSTRACT: To prospectively assess quantitatively the inherent contrast of electromagnetic (EM) properties that can be imaged by using available technology in women with abnormal findings at conventional breast imaging who underwent subsequent biopsy.
The protocol was HIPAA compliant and approved by the institutional review board. All participants provided informed consent. Fifty-three women with normal (Breast Imaging Reporting and Data System [BI-RADS] category 1) and ninety-seven women with abnormal (BI-RADS category 4 or 5) screening mammograms were imaged with three EM imaging methods: electrical impedance spectroscopy (EIS), microwave imaging spectroscopy (MIS), and near-infrared spectral tomography (NIR). A region-of-interest (ROI) analysis was used to assess the EM image properties for comparison of findings with conventional image findings and correlation with specific pathologic parameters for women with abnormal findings. Statistical analyses were conducted.
One hundred fifty participants (age range, 35-81 years) were included. EM image property contrast ratios of 150%-200% were found in breast abnormality ROIs relative to the ipsilateral breast background. Analysis of variance demonstrated significant differences in ROI image summaries of mammographically normal versus abnormal breasts for EIS, across diagnostic groups for NIR, and for MIS (analysis restricted to lesions larger than 1 cm(3)). Receiver operating curve (ROC) analysis of the EM properties for cancers among subjects with BI-RADS category 4 or 5, compared with the EM properties for the subjects with normal breasts (BI-RADS category 1), yielded areas under the ROC curve ranging from 0.67 to 0.81. Pathologic correlations with mean vessel density, mean vessel area, and epithelium-to-stroma ratio suggest a biological origin of the EM image properties associated with disease.
Results from EM breast examinations provide statistical evidence of a mean increase in image contrast of 150%-200% between abnormal (benign and malignant) and normal breast tissue.
Radiology 05/2007; 243(2):350-9. · 5.73 Impact Factor
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ABSTRACT: We have developed a microwave tomography system for experimental breast imaging.
In this article, we illustrate a strategy for optimizing the coupling liquid for the antenna array based on in vivo measurement data. We present representative phantom experiments to illustrate the imaging system's ability to recover accurate property distributions over the range of dielectric properties expected to be encountered clinically. To demonstrate clinical feasibility and assess the microwave properties of the normal breast in vivo, we summarize our initial experience with microwave breast exams of 43 women with negative mammography according to the Breast Imaging Reporting and Data System (BI-RADS 1).
The clinical results show a high degree of bilateral symmetry in the whole breast average microwave properties. Focal assessments of microwave properties are associated with breast tissue composition evaluated through radiographic density categorization verified through magnetic resonance image correlation in selected cases. Specifically, both whole-breast average and local microwave properties increase with increasing radiographic density, in which the latter exhibits a more substantial rise.
These findings support our hypothesis that water content variations in the breast play an influential role in dictating the overall dielectric property distributions and indicate that the microwave properties in the breast are more heterogeneous than previously believed based on ex vivo property measurements reported in the literature.
Academic Radiology 03/2007; 14(2):207-18. · 1.69 Impact Factor
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ABSTRACT: We have developed a clinical microwave imaging system for breast imaging applications including cancer detection and monitoring of neoadjuvant chemotherapy. For the latter, key features of any montoring system must include the ability to image a target in a repeatable fashion while being noninvasive and relatively inexpensive. Our microwave imaging system is particularly useful in this setting because we have overcome challenges such as the use of a priori information with the combination of our unique imaging configuration and software. The hardware incorporates monopole antennas which present isotropically radiated fields within which complex nulls (and accompanying non-unique signal phase distributions) are generally not generated until the electromagnetic wave has propagated beyond the illumination zone and associated receiver antennas. This is particularly useful for our variance stabilizing transformation algorithm which can recover accurate dielectric property maps without a priori information or converging to local minima as long as the unwrapped phase distribution remains unique. The associated unwrapping of the measurement data can be readily performed through the use of multi-frequency data and standard unwrapping algorithms.
Antennas and Propagation, 2006. EuCAP 2006. First European Conference on; 12/2006
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ABSTRACT: Spatial unwrapping of the phase component of time varying electromagnetic fields has important implications in a range of disciplines including synthetic aperture radar (SAR) interferometry, MRI, optical confocal microscopy, and microwave tomography. This paper presents a fundamental framework based on the phase unwrapping integral, especially in the complex case where phase singularities are enclosed within the closed path integral. With respect to the phase unwrapping required when utilized in Gauss-Newton iterative microwave image reconstruction, the concept of dynamic phase unwrapping is introduced where the singularity location varies as a function of the iteratively modified property distributions. Strategies for dynamic phase unwrapping in the microwave problem were developed and successfully tested in simulations and clinical experiments utilizing large, high contrast targets to validate the approach.
IEEE Transactions on Image Processing 12/2006; 15(11):3311-24. · 3.04 Impact Factor
