Visualisation of calcifications and thin collagen strands in human breast tumour specimens by the diffraction-enhanced imaging technique: a comparison with conventional mammography and histology

High-Resolution Phase-Contrast Tomography on Human Collagenous Tissues: A Comprehensive Review

Phase-contrast X-ray imaging is becoming increasingly considered since its first applications, which occurred almost 30 years ago. Particular emphasis was placed on studies that use this technique to investigate soft tissues, which cannot otherwise be investigated at a high resolution and in a three-dimensional manner, using conventional absorption-based settings. Indeed, its consistency and discrimination power in low absorbing samples, unified to being a not destructive analysis, are pushing interests on its utilization from researchers of different specializations, from botany, through zoology, to human physio-pathology research. In this regard, a challenging method for 3D imaging and quantitative analysis of collagenous tissues has spread in recent years: it is based on the unique characteristics of synchrotron radiation phase-contrast microTomography (PhC-microCT). In this review, the focus has been placed on the research based on the exploitation of synchrotron PhC-microCT for the investigation of collagenous tissue physio-pathologies from solely human samples. Collagen tissues' elasto-mechanic role bonds it to the morphology of the site it is extracted from, which could weaken the results coming from animal experimentations. Encouraging outcomes proved this technique to be suitable to access and quantify human collagenous tissues and persuaded different researchers to approach it. A brief mention was also dedicated to the results obtained on collagenous tissues using new and promising high-resolution phase-contrast tomographic laboratory-based setups, which will certainly represent the real step forward in the diffusion of this relatively young imaging technique.

X-ray dark-field phase-contrast imaging: Origins of the concept to practical implementation and applications

The basic idea of X-ray dark-field imaging (XDFI), first presented in 2000, was based on the concepts used in an X-ray interferometer. In this article, we review 20 years of developments in our theoretical understanding, scientific instrumentation, and experimental demonstration of XDFI and its applications to medical imaging. We first describe the concepts underlying XDFI that are responsible for imparting phase contrast information in projection X-ray images. We then review the algorithms that can convert these projection phase images into three-dimensional tomographic slices. Various implementations of computed tomography reconstructions algorithms for XDFI data are discussed. The next four sections describe and illustrate potential applications of XDFI in pathology, musculoskeletal imaging, oncologic imaging, and neuroimaging. The sample applications that are presented illustrate potential use scenarios for XDFI in histopathology and other clinical applications. Finally, the last section presents future perspectives and potential technical developments that can make XDFI an even more powerful tool.

Assessment of the additional clinical potential of X-ray dark-field imaging for breast cancer in a preclinical setup

Background:

Mammography can identify calcifications up to 50–100 μm in size as a surrogate parameter for breast cancer or ductal carcinoma in situ (DCIS). Microcalcifications measuring <50 µm are also associated with breast cancer or DCIS and are frequently not detected on mammography, although they can be detected with dark-field imaging. This study examined whether additional breast examination using X-ray dark-field imaging can increase the detection rate of calcifications. Advances in knowledge:

 (1) evaluation of additional modality of breast imaging;

 (2) specific evaluation of breast calcifications.

Implications for patient care: the addition of X-ray dark-field imaging to conventional mammography could detect additional calcifications.

Methods:

Talbot–Lau X-ray phase–contrast imaging and X-ray dark-field imaging were used to acquire images of breast specimens. The radiation dosage with the technique is comparable with conventional mammography. Three X-ray gratings with periods of 5–10 µm between the X-ray tube and the flat-panel detector provide three different images in a single sequence: the conventional attenuation image, differential phase image, and dark-field image. The images were read by radiologists. Radiological findings were marked and examined pathologically. The results were described in a descriptive manner.

Results:

A total of 81 breast specimens were investigated with the two methods; 199 significant structures were processed pathologically, consisting of 123 benign and 76 malignant lesions (DCIS or invasive breast cancer). X-ray dark-field imaging identified 15 additional histologically confirmed carcinoma lesions that were visible but not declared suspicious on digital mammography alone. Another four malignant lesions that were not visible on mammography were exclusively detected with X-ray dark-field imaging.

Conclusions:

Adding X-ray dark-field imaging to digital mammography increases the detection rate for breast cancer and DCIS associated lesions with micrometer-sized calcifications.

The use of X-ray dark-field imaging may be able to provide more accurate and detailed radiological classification of suspicious breast lesions.

Adding X-ray dark-field imaging to mammography may be able to increase the detection rate and improve preoperative planning in deciding between mastectomy or breast-conserving therapy, particularly in patients with invasive lobular breast cancer.

Discrimination analysis of breast calcifications using x-ray dark-field radiography

BACKGROUND

X-ray dark-field radiography could enhance mammography by providing more information on imaged tissue and microcalcifications. The dark field signal is a measure of small angle scattering and can thus provide additional information on the imaged materials. This information can be useful for material distinction of calcifications and the diagnosis of breast cancer by classifying benign and malign association of these calcifications.

METHODS

For this study, institutional review board approval was obtained. We present the evaluation of images acquired with interferometric grating-based x-ray imaging of 323 microcalcifications (166 malign and 157 benign associated) in freshly dissected breast tissue and compare the results to the information extracted in follow-up pathological evaluation. The number of imaged calcifications is sufficiently higher than in similar previous studies. Fourteen calcification properties were extracted from the digital images and used as predictors in three different models common in discrimination analysis namely a simple threshold model, a naive Bayes model and a linear regression model, which classify the calcifications as associated with a benign or suspicious finding. Three of these fourteen predictors have been newly defined in this work and are independent from the tissue background surrounding the microcalcifications. Using these predictors no background correction is needed, as in previous works in this field. The new predictors are the length of the first and second principle component of the absorption and dark-field data, as well as the angle between the first principle component and the dark-field axis. We called these predictors data length, data width, and data orientation.

RESULTS

In fourfold cross-validation malignancy of the imaged tissue was predicted. Models that take only classical absorption predictors into account reached a sensitivity of 53.3% at a specificity of 81.1%. For a combination of predictors that also include dark field information, a sensitivity of 63.2% and specificity of 80.8% were obtained. The included dark field information consisted of the newly introduced parameters, data orientation and data width.

CONCLUSIONS

While remaining at a similar specificity, the sensitivity, with which a trained model was able to distinguish malign from benign associated calcifications, was increased by 10% on including dark-field information. This suggests grating-based x-ray imaging as a promising clinical imaging method in the field of mammography.

Assessment of intraductal carcinoma in situ (DCIS) using grating-based X-ray phase-contrast CT at conventional X-ray sources: An experimental ex-vivo study

BACKGROUND

The extent of intraductal carcinoma in situ (DCIS) is commonly underestimated due to the discontinuous growth and lack of microcalcifications. Specimen radiography has been established to reduce the rate of re-excision. However, the predictive value for margin assessment with conventional specimen radiography for DCIS is low. In this study we assessed the potential of grating-based phase-contrast computed tomography (GBPC-CT) at conventional X-ray sources for specimen tomography of DCIS containing samples.

MATERIALS AND METHODS

GBPC-CT was performed on four ex-vivo breast specimens containing DCIS and invasive carcinoma of non-specific type. Phase-contrast and absorption-based datasets were manually matched with corresponding histological slices as the standard of reference.

RESULTS

Matching of CT images and histology was successful. GBPC-CT showed an improved soft tissue contrast compared to absorption-based images revealing more histological details in the same sections. Non-calcifying DCIS exceeding the invasive tumor could be correlated to areas of dilated bright ducts around the tumor.

CONCLUSIONS

GBPC-CT imaging at conventional X-ray sources offers improved depiction quality for the imaging of breast tissue samples compared to absorption-based imaging, allows the identification of diagnostically relevant tissue details, and provides full three-dimensional assessment of sample margins.

Phase-contrast imaging with a compact x-ray light source: system design

X-ray phase-contrast imaging (XPCI) overcomes the problem of low contrast between different soft tissues achieved in conventional x-ray imaging by introducing x-ray phase as an additional contrast mechanism. This work describes a compact x-ray light source (CXLS) and compares, via simulations, the high quality XPCI results that can be produced from this source to those produced using a microfocus x-ray source. The simulation framework is first validated using an image acquired with a microfocus-source, propagation-based XPCI (PB-XPCI) system. The phase contrast for a water sphere simulating a simple cyst submersed in muscle is evaluated and the evolution of PB-XPCI signal as the object to detector distance is increased is demonstrated. The proposed design of a PB-XPCI system using the CXLS is described and simulated images of a coronary artery compared between CXLS and microfocus source PB-XPCI systems. To generate images with similar noise levels, a microfocus source would require a 3000 times longer exposure than would the CXLS. We conclude that CXLS technology has the potential to provide high-quality XPCI in a medical environment using extremely short exposure times relative to microfocus source approaches.

Non-invasive classification of breast microcalcifications using x-ray coherent scatter computed tomography

We investigate the use of energy dispersive x-ray coherent scatter computed tomography (ED-CSCT) as a non-invasive diagnostic method to differentiate between type I and type II breast calcifications. This approach is sensitive to the differences of composition and internal crystal structure of different types of microcalcifications. The study is carried out by simulating a CSCT system with a scanning pencil beam, considering a polychromatic x-ray source and an energy-resolving photon counting detector. In a first step, the multidimensional angle and energy distributed CSCT data is reduced to the projection-space distributions of only a few components, corresponding to the expected target composition: adipose, glandular tissue, weddellite (calcium oxalate) for type I calcifications, and hydroxyapatite for type II calcifications. The maximum-likelihood estimation of scatter components algorithm used, operating in the projection space, takes into account the polychromatic source, the detector response function and the energy dependent attenuation. In the second step, component images are reconstructed from the corresponding estimated component projections using filtered backprojection. In a preliminary step the coherent scatter differential cross sections for hydroxyapatite and weddellite minerals were determined experimentally. The classification of type I or II calcifications is done using the relative contrasts of their components as the criterion. Simulation tests were carried out for different doses and energy resolutions for multiple realizations. The results were analyzed using relative/receiver operating characteristic methodology and show good discrimination ability at medium and higher doses. The noninvasive CSCT technique shows potential to further improve the breast diagnostic accuracy and reduce the number of breast biopsies.

Signs analysis and clinical assessment: phase-contrast computed tomography of human breast tumours

Purpose

To analyse the diagnostic signs present in slices of human breast tumour specimens using synchrotron radiation phase-contrast imaging computed tomography (PCI-CT) for the first time and assess the feasibility of this technique for clinical applications.

Materials and Methods

The ethics committee of our university and relevant clinical hospital approved this prospective study, and written informed consent was obtained from all patients. PCI-CT of human breast tumour specimens with synchrotron radiation was performed at the Shanghai Synchrotron Radiation Facility (SSRF). A total of 14 specimens of early-stage carcinomas and 8 specimens of adenomas were enrolled. Based on raw data reconstruction, the diagnostic signs present in the slices were analysed and correlated with histopathology. We proposed a criterion for clinical diagnosis according to the evaluated signs and the Breast Imaging Reporting and Data System (BI-RADS) for reference. The criterion was then assessed by clinicians in a double-blind method. Finally, descriptive statistics were evaluated, depending on the assessment results.

Results

The 14 carcinoma specimens and 8 adenoma specimens were diagnosed as malignant and benign tumours, respectively. The total coincidence rate was 100%.

Conclusion

Our study results demonstrate that the X-ray diagnostic signs observed in the specimen slices and the criterion used for clinical diagnosis were accurate and reliable. The criterion based on signs analysis can be used to differentiate early-stage benign or malignant tumours. As a promising imaging method, PCI-CT can serve as a possible and feasible supplement to BI-RADS in the future.

[Phase contrast imaging of the breast. Basic principles and steps towards clinical implementation]

CLINICAL/METHODICAL ISSUE

Breast cancer is the most common cancer and the leading cause of cancer deaths in women worldwide.

STANDARD RADIOLOGICAL METHODS

Mammography is the only imaging technique approved for nationwide breast cancer screening. Digital full field mammography has improved mammographic image quality. Nevertheless, mammography has a low positive predictive value and a low sensitivity especially in mammographically dense breasts. One of the major limitations is the inherently low contrast between healthy breast parenchyma and breast cancer.

METHODICAL INNOVATIONS

Phase contrast imaging is based on the phase shift that occurs when X-rays encounter a change in refractive index between different materials.

PERFORMANCE

The improved soft tissue contrast makes the technology particularly promising for breast diagnostics.

ACHIEVEMENTS

The studies presented here suggest that phase contrast imaging provides additional diagnostic information both using phase contrast mammography and phase contrast computed tomography (CT).

PRACTICAL RECOMMENDATIONS

This paper provides an overview of the basic principles of the phase contrast imaging and describes recent developments towards in vivo and ex vivo phase contrast imaging of the breast.

A study on mastectomy samples to evaluate breast imaging quality and potential clinical relevance of differential phase contrast mammography

OBJECTIVES

Differential phase contrast and scattering-based x-ray mammography has the potential to provide additional and complementary clinically relevant information compared with absorption-based mammography. The purpose of our study was to provide a first statistical evaluation of the imaging capabilities of the new technique compared with digital absorption mammography.

MATERIALS AND METHODS

We investigated non-fixed mastectomy samples of 33 patients with invasive breast cancer, using grating-based differential phase contrast mammography (mammoDPC) with a conventional, low-brilliance x-ray tube. We simultaneously recorded absorption, differential phase contrast, and small-angle scattering signals that were combined into novel high-frequency-enhanced images with a dedicated image fusion algorithm. Six international, expert breast radiologists evaluated clinical digital and experimental mammograms in a 2-part blinded, prospective independent reader study. The results were statistically analyzed in terms of image quality and clinical relevance.

RESULTS

The results of the comparison of mammoDPC with clinical digital mammography revealed the general quality of the images to be significantly superior (P < 0.001); sharpness, lesion delineation, as well as the general visibility of calcifications to be significantly more assessable (P < 0.001); and delineation of anatomic components of the specimens (surface structures) to be significantly sharper (P < 0.001). Spiculations were significantly better identified, and the overall clinically relevant information provided by mammoDPC was judged to be superior (P < 0.001).

CONCLUSIONS

Our results demonstrate that complementary information provided by phase and scattering enhanced mammograms obtained with the mammoDPC approach deliver images of generally superior quality. This technique has the potential to improve radiological breast diagnostics.

X-ray phase-contrast imaging of the breast--advances towards clinical implementation

Breast cancer constitutes about one-quarter of all cancers and is the leading cause of cancer death in women. To reduce breast cancer mortality, mammographic screening programmes have been implemented in many Western countries. However, these programmes remain controversial because of the associated radiation exposure and the need for improvement in terms of diagnostic accuracy. Phase-contrast imaging is a new X-ray-based technology that has been shown to provide enhanced soft-tissue contrast and improved visualization of cancerous structures. Furthermore, there is some indication that these improvements of image quality can be maintained at reduced radiation doses. Thus, X-ray phase-contrast mammography may significantly contribute to advancements in early breast cancer diagnosis. Feasibility studies of X-ray phase-contrast breast CT have provided images that allow resolution of the fine structure of tissue that can otherwise only be obtained by histology. This implies that X-ray phase-contrast imaging may also lead to the development of entirely new (micro-) radiological applications. This review provides a brief overview of the physical characteristics of this new technology and describes recent developments towards clinical implementation of X-ray phase-contrast imaging of the breast.

A new conversation between radiology and pathology-identifying microvascular architecture in stages of cirrhosis via diffraction enhanced imaging in vitro

Background/Aim

Diffraction enhanced imaging (DEI) is a synchrotron radiation X-ray phase-contrast imaging technique that can better reveal the microstructure of biological soft tissues than conventional X-rays. The aim of this study is to investigate the angio-architectural changes of the liver during fibrosis, cirrhosis and its subsequent regression by applying synchrotron radiation based DEI.

Methods

DEI experiments were performed at the 4W1A station of Beijing Synchrotron Radiation Facility. Twenty-four Sprague-Dawley rats were induced with liver fibrosis by carbon tetrachloride (CCl₄) for up to 10 weeks, after which spontaneous regression started and continued until week 30. Quantitative analysis of the DEI images yielded the mean vascular density and intercapillary distance, which was then re-confirmed by immunohistochemical analysis of CD34.

Results

Based on the DEI results, the mean vascular density was 1.4-fold higher in fibrotic rats (at week 6) and 2-fold higher in cirrhotic rats (at week 10) compared with the control (p<0.05). Accordingly, the intercapillary distance decreased to 563.89±243.35 µm in fibrotic rats and 392.90±92.68 µm in cirrhotic rats compared with 673.85±214.16µm in the control (p<0.05). During fibrosis regression at week 30, vascular density was 0.7-fold lower and intercapillary distance increased to 548.60±210.94 µm as compared with cirrhotic rats (p<0.05).In parallel to the DEI results, immunohistochemical analysis of CD34 showed similar changes.

Conclusion

Synchrotron-based DEI can conduct radiological as well as pathological analysis. Our results are consistent with previous reports indicating that angiogenesis is directly proportional to fibrosis progression. Furthermore, by clarifying the vascular characteristics of liver diseases, DEI reveals that cirrhosis cannot fully reverse during fibrosis regression.

Optimization of analyzer-based imaging systems for minimal surface absorbed dose

Analyzer-based imaging has improved tissue X-ray imaging beyond what conventional radiography was able to achieve. The extent of the improvement is dependent on the crystal reflection used in the monochromator and analyzer combination, the imaging photon energy, the geometry of the sample and the imaging detector. These many factors determine the ability of the system to distinguish between various bone tissues or soft tissues with a specified statistical certainty between pixels in a counting detector before any image processing. The following discussion will detail changes in the required number of imaging photons and the resulting surface absorbed dose when the imaging variables are altered. The process whereby the optimal imaging parameters to deliver the minimum surface absorbed dose to a sample while obtaining a desired statistical certainty between sample materials for an arbitrary analyzer-based imaging system will be described. Two-component samples consisting of bone and soft tissue are discussed as an imaging test case. The two-component approach will then be generalized for a multiple-component sample.

On a dark-field signal generated by micrometer-sized calcifications in phase-contrast mammography

We show that a distribution of micrometer-sized calcifications in the human breast which are not visible in clinical x-ray mammography at diagnostic dose levels can produce a significant dark-field signal in a grating-based x-ray phase-contrast imaging setup with a tungsten anode x-ray tube operated at 40 kVp. A breast specimen with invasive ductal carcinoma was investigated immediately after surgery by Talbot-Lau x-ray interferometry with a design energy of 25 keV. The sample contained two tumors which were visible in ultrasound and contrast-agent enhanced MRI but invisible in clinical x-ray mammography, in specimen radiography and in the attenuation images obtained with the Talbot-Lau interferometer. One of the tumors produced significant dark-field contrast with an exposure of 0.85 mGy air-kerma. Staining of histological slices revealed sparsely distributed grains of calcium phosphate with sizes varying between 1 and 40 μm in the region of this tumor. By combining the histological investigations with an x-ray wave-field simulation we demonstrate that a corresponding distribution of grains of calcium phosphate in the form of hydroxylapatite has the ability to produce a dark-field signal which would-to a substantial degree-explain the measured dark-field image. Thus we have found the appearance of new information (compared to attenuation and differential phase images) in the dark-field image. The second tumor in the same sample did not contain a significant fraction of these very fine calcification grains and was invisible in the dark-field image. We conclude that some tumors which are invisible in x-ray absorption mammography might be detected in the x-ray dark-field image at tolerable dose levels.

Evaluation of phase-contrast CT of breast tissue at conventional X-ray sources - presentation of selected findings

BACKGROUND

Grating-based phase contrast computed tomography (PC-CT) at synchrotron radiation sources has been shown to provide improved visualization of breast tumors. However, broad clinical application of phase-contrast imaging will likely depend on transferring the technology to standard polychromatic X-ray sources. On the basis of selected findings, we demonstrate the potential of grating-based PC-CT using a conventional X-ray source.

MATERIALS AND METHODS

Grating-based PC-CT of two ex-vivo formalin fixed breast specimens containing lobular carcinoma was conducted using a Talbot Lau interferometer run at a polychromatic X-ray source of 40kVp. Phase-contrast and absorption-based 3D-datasets of both specimens were simultaneously recorded. Radiological images were manually matched with corresponding histological sections. The visualization of selected histological findings in phase contrast was compared to absorption contrast.

RESULTS

Grating-based PC-CT was able to depict the 3-dimensional structure of dilated ducts and high phase contrast was found as a correlate to thickened fibrous ductal walls. Differences in contrast between fibrous and less fibrous breast tissue were observed in phase- but not in absorption-contrast images. Furthermore, regions of low phase contrast correlated with the extension of compact tumor components.

CONCLUSIONS

On the basis of selected findings, we show that grating-based PC-CT at a polychromatic X-ray source provides complementary information to conventional absorption contrast; albeit at lower spatial resolution than synchrotron-based imaging.

Ideal-observer detectability in photon-counting differential phase-contrast imaging using a linear-systems approach

PURPOSE

To provide a cascaded-systems framework based on the noise-power spectrum (NPS), modulation transfer function (MTF), and noise-equivalent number of quanta (NEQ) for quantitative evaluation of differential phase-contrast imaging (Talbot interferometry) in relation to conventional absorption contrast under equal-dose, equal-geometry, and, to some extent, equal-photon-economy constraints. The focus is a geometry for photon-counting mammography.

METHODS

Phase-contrast imaging is a promising technology that may emerge as an alternative or adjunct to conventional absorption contrast. In particular, phase contrast may increase the signal-difference-to-noise ratio compared to absorption contrast because the difference in phase shift between soft-tissue structures is often substantially larger than the absorption difference. We have developed a comprehensive cascaded-systems framework to investigate Talbot interferometry, which is a technique for differential phase-contrast imaging. Analytical expressions for the MTF and NPS were derived to calculate the NEQ and a task-specific ideal-observer detectability index under assumptions of linearity and shift invariance. Talbot interferometry was compared to absorption contrast at equal dose, and using either a plane wave or a spherical wave in a conceivable mammography geometry. The impact of source size and spectrum bandwidth was included in the framework, and the trade-off with photon economy was investigated in some detail. Wave-propagation simulations were used to verify the analytical expressions and to generate example images.

RESULTS

Talbot interferometry inherently detects the differential of the phase, which led to a maximum in NEQ at high spatial frequencies, whereas the absorption-contrast NEQ decreased monotonically with frequency. Further, phase contrast detects differences in density rather than atomic number, and the optimal imaging energy was found to be a factor of 1.7 higher than for absorption contrast. Talbot interferometry with a plane wave increased detectability for 0.1-mm tumor and glandular structures by a factor of 3-4 at equal dose, whereas absorption contrast was the preferred method for structures larger than ∼0.5 mm. Microcalcifications are small, but differ from soft tissue in atomic number more than density, which is favored by absorption contrast, and Talbot interferometry was barely beneficial at all within the resolution limit of the system. Further, Talbot interferometry favored detection of "sharp" as opposed to "smooth" structures, and discrimination tasks by about 50% compared to detection tasks. The technique was relatively insensitive to spectrum bandwidth, whereas the projected source size was more important. If equal photon economy was added as a restriction, phase-contrast efficiency was reduced so that the benefit for detection tasks almost vanished compared to absorption contrast, but discrimination tasks were still improved close to a factor of 2 at the resolution limit.

CONCLUSIONS

Cascaded-systems analysis enables comprehensive and intuitive evaluation of phase-contrast efficiency in relation to absorption contrast under requirements of equal dose, equal geometry, and equal photon economy. The benefit of Talbot interferometry was highly dependent on task, in particular detection versus discrimination tasks, and target size, shape, and material. Requiring equal photon economy weakened the benefit of Talbot interferometry in mammography.

Assessment of grating-based X-ray phase-contrast CT for differentiation of invasive ductal carcinoma and ductal carcinoma in situ in an experimental ex vivo set-up

OBJECTIVE

Limited contrast between healthy and tumour tissue is a limiting factor in mammography and CT of the breast. Phase-contrast computed tomography (PC-CT) provides improved soft-tissue contrast compared with absorption-based techniques. In this study, we assessed the technical feasibility of grating-based PC-CT imaging of the breast for characterisation of ductal carcinoma in situ (DCIS).

METHODS

Grating-based PC-CT was performed on one breast specimen containing an invasive ductal carcinoma and DCIS using monochromatic radiation of 23 keV. Phase-contrast and absorption-based images were compared qualitatively and quantitatively with histopathology in a blinded fashion.

RESULTS

Grating-based PC-CT showed improved differentiation of soft-tissue components. Circular structures of high phase-shift contrast corresponding to the walls of the dilated ductuli of the DCIS were visualised with a contrast-to-noise ratio (CNR) of 9.6 using PC-CT but were not detectable on absorption-based images (CNR = 0.27). The high phase-shift structures of the dilated ductuli were identifiable in the PC-CT volume data set allowing for 3D characterisation of DCIS.

CONCLUSIONS

Our results indicate that unlike conventional CT, grating-based PC-CT may allow the differentiation between invasive carcinoma and intraductal carcinoma and healthy breast tissue and provide 3D visualisation of DCIS.

Synchrotron-radiation phase-contrast imaging of human stomach and gastric cancer: in vitro studies

The electron density resolution of synchrotron-radiation phase-contrast imaging (SR-PCI) is 1000 times higher than that of conventional X-ray absorption imaging in light elements, through which high-resolution X-ray imaging of biological soft tissue can be achieved. For biological soft tissue, SR-PCI can give better imaging contrast than conventional X-ray absorption imaging. In this study, human resected stomach and gastric cancer were investigated using in-line holography and diffraction enhanced imaging at beamline 4W1A of the Beijing Synchrotron Radiation Facility. It was possible to depict gastric pits, measuring 50-70 µm, gastric grooves and tiny blood vessels in the submucosa layer by SR-PCI. The fine structure of a cancerous ulcer was displayed clearly on imaging the mucosa. The delamination of the gastric wall and infiltration of cancer in the submucosa layer were also demonstrated on cross-sectional imaging. In conclusion, SR-PCI can demonstrate the subtle structures of stomach and gastric cancer that cannot be detected by conventional X-ray absorption imaging, which prompt the X-ray diagnosis of gastric disease to the level of the gastric pit, and has the potential to provide new methods for the imageology of gastric cancer.

Visualization of microvascular proliferation as a tumor infiltration structure in rat glioma specimens using the diffraction-enhanced imaging in-plane CT technique

In order to study potent microenvironments of malignant gliomas with a high- resolution x-ray imaging technique, an injection orthotopic glioma model was made using the Sprague-Dawley rat. Total brain tissue, taken out as an ex vivo model, was examined with diffraction-enhanced imaging (DEI) computed tomography (CT) acquired with a 35 keV monochromatic x-ray. In the convolution-reconstructed 2D/3D images with a spatial resolution of 12.5 × 12.5 × 25 µm, distinction among necrosis, typical ring-shaped viable tumors, edemas and healthy tissues was clearly observed near the frontal lobe in front of the rat's caudate nucleus. Multiple microvascular proliferations (MVPs) were observed surrounding peritumoral edemas as a tumor infiltration structure. Typical dimensions of tubular MVPs were 130 (diameter) ×250 (length) µm with a partial sprout structure revealed in the 3D reconstructed image. Hyperplasia of cells around vessel walls was revealed with tumor cell infiltration along the perivascular space in microscopic observations of mild MVP during histological analysis. In conclusion, DEI-CT is capable of imaging potent tumor-infiltrating MVP structures surrounding high-grade gliomas.

Comparison of in vitro breast cancer visibility in analyser-based computed tomography with histopathology, mammography, computed tomography and magnetic resonance imaging

High-resolution analyser-based X-ray imaging computed tomography (HR ABI-CT) findings on in vitro human breast cancer are compared with histopathology, mammography, computed tomography (CT) and magnetic resonance imaging. The HR ABI-CT images provided significantly better low-contrast visibility compared with the standard radiological images. Fine cancer structures indistinguishable and superimposed in mammograms were seen, and could be matched with the histopathological results. The mean glandular dose was less than 1 mGy in mammography and 12-13 mGy in CT and ABI-CT. The excellent visibility of in vitro breast cancer suggests that HR ABI-CT may have a valuable role in the future as an adjunct or even alternative to current breast diagnostics, when radiation dose is further decreased, and compact synchrotron radiation sources become available.

In vivo x-ray phase contrast analyzer-based imaging for longitudinal osteoarthritis studies in guinea pigs

Over the last two decades phase contrast x-ray imaging techniques have been extensively studied for applications in the biomedical field. Published results demonstrate the high capability of these imaging modalities of improving the image contrast of biological samples with respect to standard absorption-based radiography and routinely used clinical imaging techniques. A clear depiction of the anatomic structures and a more accurate disease diagnosis may be provided by using radiation doses comparable to or lower than those used in current clinical methods. In the literature many works show images of phantoms and excised biological samples proving the high sensitivity of the phase contrast imaging methods for in vitro investigations. In this scenario, the applications of the so-called analyzer-based x-ray imaging (ABI) phase contrast technique are particularly noteworthy. The objective of this work is to demonstrate the feasibility of in vivo x-ray ABI phase contrast imaging for biomedical applications and in particular with respect to joint anatomic depiction and osteoarthritis detection. ABI in planar and tomographic modes was performed in vivo on articular joints of guinea pigs in order to investigate the animals with respect to osteoarthritis by using highly monochromatic x-rays of 52 keV and a low noise detector with a pixel size of 47 × 47 µm(2). Images give strong evidence of the ability of ABI in depicting both anatomic structures in complex systems as living organisms and all known signs of osteoarthritis with high contrast, high spatial resolution and with an acceptable radiation dose. This paper presents the first proof of principle study of in vivo application of ABI. The technical challenges encountered when imaging an animal in vivo are discussed. This experimental study is an important step toward the study of clinical applications of phase contrast x-ray imaging techniques.

Noninvasive visualization of microvessels using diffraction enhanced imaging

The architecture of the vascular network is crucial because almost every disease alters the morphology of the blood vessel. Although existing imaging technique can provide vessel images, microvessels will not be discerned without the use of contrast agents. Furthermore, conventional imaging technique can only provide the outline of the vessels due to the restriction of spatial resolution. In this study, a novel imaging technique, diffraction enhanced imaging (DEI), is applied to the observation of microvessels in mouse hepatic fibrosis samples. With high spatial resolution and contrast of biological soft tissues, DEI is a non-invasive synchrotron-based imaging technique and does not require contrast agents. Particularly, this article highlights the exploration of the objects inside microvessels. A segment of blood vessel, which is obstructed by a blood clot, is under quantitative assessment and the result provides a precise description of vessel stenosis. Additionally, as one of the application of the diffraction enhanced imaging, blood stream simulation is carried out on the three-dimensional model of the vessel. It proves that this imaging technique has great value in evaluating hemodynamics and histopathology of microvascular diseases.

Radiologist evaluation of an X-ray tube-based diffraction-enhanced imaging prototype using full-thickness breast specimens

RATIONALE AND OBJECTIVES

Conventional mammographic image contrast is derived from x-ray absorption, resulting in breast structure visualization due to density gradients that attenuate radiation without distinction between transmitted, scattered, or refracted x-rays. Diffraction-enhanced imaging (DEI) allows for increased contrast with decreased radiation dose compared to conventional mammographic imaging because of monochromatic x-rays, its unique refraction-based contrast mechanism, and excellent scatter rejection. However, a lingering drawback to the clinical translation of DEI has been the requirement for synchrotron radiation.

MATERIALS AND METHODS

The authors' laboratory developed a DEI prototype (DEI-PR) using a readily available tungsten x-ray tube source and traditional DEI crystal optics, providing soft tissue images at 60 keV. Images of full-thickness human breast tissue specimens were acquired on synchrotron-based DEI (DEI-SR), DEI-PR, and digital mammographic systems. A panel of expert radiologists evaluated lesion feature visibility and correlation with pathology after receiving training on the interpretation of refraction contrast mammographic images.

RESULTS

For mammographic features (mass, calcification), no significant differences were detected between the DEI-SR and DEI-PR systems. Benign lesions were perceived as better seen by radiologists using the DEI-SR system than the DEI-PR system at the [111] reflectivity, with generalizations limited by small sample size. No significant differences between DEI-SR and DEI-PR were detected for any other lesion type (atypical, cancer) at either crystal reflectivity.

CONCLUSIONS

Thus, except for benign lesion characterizations, the DEI-PR system's performance was roughly equivalent to that of the traditional DEI system, demonstrating a significant step toward clinical translation of this modality for breast cancer applications.

Design and implementation of a compact low-dose diffraction enhanced medical imaging system

RATIONALE AND OBJECTIVES

Diffraction-enhanced imaging (DEI) is a new x-ray imaging modality that differs from conventional radiography in its use of three physical mechanisms to generate contrast. DEI is able to generate contrast from x-ray absorption, refraction, and ultra-small-angle scatter rejection (extinction) to produce high-contrast images with a much lower radiation dose compared to conventional radiography.

MATERIALS AND METHODS

A prototype DEI system was constructed using a 1-kW tungsten x-ray tube and a single silicon monochromator and analyzer crystal. The monochromator crystal was aligned to reflect the combined Kalpha1 (59.32 keV) and Kalpha2 (57.98 keV) characteristic emission lines of tungsten using a tube voltage of 160 kV. System performance and demonstration of contrast were evaluated using a nylon monofilament refraction phantom, full-thickness breast specimens, a human thumb, and a live mouse.

RESULTS

Images acquired using this system successfully demonstrated all three DEI contrast mechanisms. Flux measurements acquired using this 1-kW prototype system demonstrated that this design can be scaled to use a more powerful 60-kW x-ray tube to generate similar images with an image time of approximately 30 seconds. This single-crystal pair design can be further modified to allow for an array of crystals to reduce clinical image times to <3 seconds.

CONCLUSIONS

This paper describes the design, construction, and performance of a new DEI system using a commercially available tungsten anode x-ray tube and includes the first high-quality low-dose diffraction-enhanced images of full-thickness human tissue specimens.

Generalized subtraction methods in digital mammography

Digital mammography can greatly facilitate new applications, with the potential of further improving early diagnosis of breast cancer. Indeed, early manifestations of breast cancer are often very subtle and are displayed on the variable pattern of normal anatomy that may either obscure or simulate disease. This is particularly important in dense breasts, because of the complexity of overlying fibroglandular structures. The requirement of improved lesion conspicuity has brought to the application of a number of subtraction methods such as the tomographic technique to exploit depth-dependent information or the digital angiography where subtraction in the temporal domain is applied in conjuction with administration of contrast medium. Since there are various parameters that might be used for subtraction, such techniques have to be intended in generalized form. Generalized subtraction methods in mammography are here presented and compared.

Analyzer-based imaging technique in tomography of cartilage and metal implants: a study at the ESRF

Monitoring the progression of osteoarthritis (OA) and the effects of therapy during clinical trials is still a challenge for present clinical imaging techniques since they present intrinsic limitations and can be sensitive only in case of advanced OA stages. In very severe cases, partial or complete joint replacement surgery is the only solution for reducing pain and restoring the joint functions. Poor imaging quality in practically all medical imaging technologies with respect to joint surfaces and to metal implant imaging calls for the development of new techniques that are sensitive to stages preceding the point of irreversible damage of the cartilage tissue. In this scenario, X-ray phase contrast modalities could play an important role since they can provide improved contrast compared to conventional absorption radiography, with a similar or even reduced tissue radiation dose. In this study, the analyzer-based imaging (ABI), a technique sensitive to the X-ray refraction and permitting a high scatter rejection, has been successfully applied in vitro on excised human synovial joints and sheep implants. Pathological and healthy joints as well as metal implants have been imaged in projection and computed tomography ABI mode at high resolution and clinically compatible doses (<10 mGy). Volume rendering and segmentation permitted visualization of the cartilage from volumetric CT-scans. The results demonstrate that ABI can provide an unequivocal non-invasive diagnosis of the state of disease of the joint and be considered a new tool in orthopaedic research.

Application of x-ray phase contrast imaging to microscopic identification of Chinese medicines

In the last decade, x-ray phase contrast imaging (XPCI) has received considerable attention as a novel imaging technique, which has proved to be suitable for weakly absorbing materials such as biomedical samples and polymers. In this paper, the microstructures of traditional Chinese medicines (TCMs), which are used as judging criteria in the identification of TCMs, were investigated by XPCI based on a nano-focus x-ray tube. The results demonstrated that XPCI is a promising new method for the identification of TCMs, with advantages such as nondestructivity, no special sample preparation and suitability for thick samples.

Human breast cancerin vitro: matching histo-pathology with small-angle x-ray scattering and diffraction enhanced x-ray imaging

Twenty-eight human breast tumour specimens were studied with small-angle x-ray scattering (SAXS), and 10 of those were imaged by the diffraction enhanced x-ray imaging (DEI) technique. The sample diameter was 20 mm and the thickness 1 mm. Two examples of ductal carcinoma are illustrated by histology images, DEI, and maps of the collagen d-spacing and scattered intensity in the Porod regime, which characterize the SAXS patterns from collagen-rich regions of the samples. Histo-pathology reveals the cancer-invaded regions, and the maps of the SAXS parameters show that in these regions the scattering signal differs significantly from scattering by the surrounding tissue, indicating a degradation of the collagen structure in the invaded regions. The DEI images show the borders between collagen and adipose tissue and provide a co-ordinate system for tissue mapping by SAXS. In addition, degradation of the collagen structure in an invaded region is revealed by fading contrast of the DEI refraction image. The 28 samples include fresh, defrosted tissue and formalin-fixed tissue. The d-values with their standard deviations are given. In the fresh samples there is a systematic 0.76% increase of the d-value in the invaded regions, averaged over 11 samples. Only intra-sample comparisons are made for the formalin-fixed samples, and with a long fixation time, the difference in the d-value stabilizes at about 0.7%. The correspondence between the DEI images, the SAXS maps and the histo-pathology suggests that definitive information on tumour growth and malignancy is obtained by combining these x-ray methods.