A dual modality, DCE-MRI and x-ray, physical phantom for quantitative evaluation of breast imaging protocols

The current clinical standard for breast cancer screening is mammography. However, this technique has a low sensitivity which results in missed cancers. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has recently emerged as a promising technique for breast cancer diagnosis and has been reported as being superior to mammography for screening of high-risk women and evaluation of extent of disease. At the same time, low and variable specificity has been documented in the literature as well as a rising number of mastectomies possibly due to the increasing use of DCE-MRI. In this study, we developed and characterized a dual-modality, x-ray and DCE-MRI, anthropomorphic breast phantom for the quantitative assessment of breast imaging protocols. X-ray properties of the phantom were quantitatively compared with patient data, including attenuation coefficients, which matched human values to within the measurement error, and tissue structure using spatial covariance matrices of image data, which were found to be similar in size to patient data. Simulations of the phantom scatter-to-primary ratio (SPR) were produced and experimentally validated then compared with published SPR predictions for homogeneous phantoms. SPR values were as high as 85% in some areas and were heavily influenced by the heterogeneous tissue structure. MRI properties of the phantom, T1 and T2 relaxation values and tissue structure, were also quantitatively compared with patient data and found to match within two error bars. Finally, a dynamic lesion that mimics lesion border shape and washout curve shape was included in the phantom. High spatial and temporal resolution x-ray measurements of the washout curve shape were performed to determine the true contrast agent concentration as a function of time. DCE-MRI phantom measurements using a clinical imaging protocol were compared against the x-ray truth measurements. MRI signal intensity curves were shown to be less specific to lesion type than the x-ray derived contrast agent concentration curves. This phantom allows, for the first time, for quantitative evaluation of and direct comparisons between x-ray and MRI breast imaging modalities in the context of lesion detection and characterization

Real-time quantitative sonoelastography in an ultrasound research system

Quantitative Sono-Elastographie ist eine neue Technologie für die Ultraschall Bildgebung, die Radiologen maligne Tumoren ohne Risiko der strahlungsinduzierten Krebs (d.h. Mammographie) zu erfassen können. Aufgrund gefunden Rechenkomplexität in der aktuellen Algorithmen, Implementierung von Echtzeit-Anwendungen, die Prüfungsverfahren profitieren wurde jedoch noch nicht berichtet. Zusätzlich, aktuelle Schätzer für die Darstellung eine Elastizität Bilder vorhanden Artefakte der hohen Schätzung Varianz, die die Techniker in die Gegenwart steifer Massen irreführen könnten und zwar, falsch-positive Diagnose zu erzeugen. In dieser Arbeit wird eine GPU-basierte Elastographie-System entwickelt und an einem Forschungsultraschallgeräten implementiert. Quantitative Elastizität in Echtzeit bei 2 FPS mit einer Verbesserung Rechenzeitfaktor aus 26 wird gezeigt. Validierung der Systemgenauigkeit Anzeige wurde, auf Gelatinebasis Gewebe Phantome durchgeführt., waren niedrige Vorspannung der Elastizitätswerte berichtet wurde (4,7 %) bei geringe Anregungsfrequenzen nachahmt. Ausserdem wird eine neue Elastizität Schätzer auf quantitative Sono-Elastographie basiert eingeführt. Ein lineares Problem wurde entlang der seitlichen Abmessung modelliert und eine Regularisierung Methode wurde implementieren. Elastizität Bilder mit niedriger Vorspannung wurde darstellen (1,48 %) sowie seine Leistung in einer Brust kalibrierte Phantom mit verbesserter CNR (47,3 dB) im Vergleich mit anderen Schätzer ausgewertet sowie die Verringerung Seiten Artefakte bereits erwähnt in der Literatur (PD: 22,7 dB, 1DH 28,7 dB) gefunden. Diese zwei Beitrag profitieren, die Umsetzung und Entwicklung weiterer Elastographie Techniken, die eine verbesserte Qualität der Elastizität Bilder liefern könnten und somit eine verbesserte Genauigkeit der Diagnose.Quantitative sonoelastography is an alternative technology for ultrasound imaging that helps radiologist to diagnose malignant tumors with no risk of radiation-induced cancer (i.e. mammography). However, due to the high computational complexity found in the current algorithms, implementation of real-time systems that could benefit examination procedures has not been yet reported. Additionally, elasticity maps depicted from current estimators feature artifacts of high estimation variance that could mislead the technician into the presence of stiffer masses, generating false positive diagnosis. In this thesis, a GPU-based elastography system was designed and implemented on a research ultrasound equipment, displaying quantitative elasticity in real-time at 2 FPS with an improvement computational time factor of 26. Validation of the system accuracy was conducted on gelatin-based tissue mimicking phantoms, where low bias of elasticity values were reported (4.7%) at low excitation frequencies. Additionally, a new elasticity estimator based on quantitative sonoelastography was developed. A linear problem was modeled from the acquired sonolastography data along the lateral dimension and a regularization method was implemented. The resulting elasticity images presented low bias (1.48%), enhanced CNR and reduced lateral artifacts when evaluating the algorithm’s performance in a breast calibrated phantom and comparing it with other estimators found in the literature. These two contribution benefit the implementation and development of further elastography techniques that could provide enhanced quality of elasticity images and thus, improved accuracy of diagnosis.Tesi

Tissue mimicking materials for imaging and therapy phantoms: a review

Tissue mimicking materials (TMMs), typically contained within phantoms, have been used for many decades in both imaging and therapeutic applications. This review investigates the specifications that are typically being used in development of the latest TMMs. The imaging modalities that have been investigated focus around CT, mammography, SPECT, PET, MRI and ultrasound. Therapeutic applications discussed within the review include radiotherapy, thermal therapy and surgical applications. A number of modalities were not reviewed including optical spectroscopy, optical imaging and planar x-rays. The emergence of image guided interventions and multimodality imaging have placed an increasing demand on the number of specifications on the latest TMMs. Material specification standards are available in some imaging areas such as ultrasound. It is recommended that this should be replicated for other imaging and therapeutic modalities. Materials used within phantoms have been reviewed for a series of imaging and therapeutic applications with the potential to become a testbed for cross-fertilization of materials across modalities. Deformation, texture, multimodality imaging and perfusion are common themes that are currently under development

It is hard to see a needle in a haystack: Modeling contrast masking effect in a numerical observer

Within the framework of a virtual clinical trial for breast imaging, we aim to develop numerical observers that follow the same detection performance trends as those of a typical human observer. In our prior work, we showed that by including spatiotemporal contrast sensitivity function (stCSF) of human visual system (HVS) in a multi-slice channelized Hotelling observer (msCHO), we can correctly predict trends of a typical human observer performance with the viewing parameters of browsing speed, viewing distance and contrast. In this work we further improve our numerical observer by modeling contrast masking. After stCSF, contrast masking is the second most prominent property of HVS and it refers to the fact that the presence of one signal affects the visibility threshold for another signal. Our results indicate that the improved numerical observer better predicts changes in detection performance with background complexity

Acoustical structured illumination for super-resolution ultrasound imaging.

Structured illumination microscopy is an optical method to increase the spatial resolution of wide-field fluorescence imaging beyond the diffraction limit by applying a spatially structured illumination light. Here, we extend this concept to facilitate super-resolution ultrasound imaging by manipulating the transmitted sound field to encode the high spatial frequencies into the observed image through aliasing. Post processing is applied to precisely shift the spectral components to their proper positions in k-space and effectively double the spatial resolution of the reconstructed image compared to one-way focusing. The method has broad application, including the detection of small lesions for early cancer diagnosis, improving the detection of the borders of organs and tumors, and enhancing visualization of vascular features. The method can be implemented with conventional ultrasound systems, without the need for additional components. The resulting image enhancement is demonstrated with both test objects and ex vivo rat metacarpals and phalanges